U.S. patent application number 11/493273 was filed with the patent office on 2007-01-11 for communication decoder employing single trellis to support multiple code rates and/or multiple modulations.
This patent application is currently assigned to Broadcom Corporation, a California Corporation. Invention is credited to Kelly Brian Cameron, Ba-Zhong Shen, Hau Thien Tran.
Application Number | 20070011595 11/493273 |
Document ID | / |
Family ID | 36974670 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070011595 |
Kind Code |
A1 |
Cameron; Kelly Brian ; et
al. |
January 11, 2007 |
Communication decoder employing single trellis to support multiple
code rates and/or multiple modulations
Abstract
Communication decoder employing single trellis to support
multiple code rates and/or multiple modulations. A single trellis
is employed by the decoder to decode a plurality of encoded
symbols. Each of the plurality of encoded symbols is governed by a
rate control. A rate control sequence, having a period, is used to
decode the plurality of encoded symbols that may be arranged within
a frame. Various parameters of the plurality of encoded symbols may
vary on a symbol by symbol basis; these parameters may include
modulation, constellation, mapping, and/or bandwidth efficiency.
For example, various symbols may be encoded differently, yet they
may all be decoded using the same trellis. The functionality of
this decoder may be implemented within a variety of different
decoder embodiments including a trellis code modulation (TCM)
decoder, a turbo trellis code modulation (TTCM) decoder, and/or a
parallel concatenated turbo code modulation (PC-TCM) decoder.
Inventors: |
Cameron; Kelly Brian;
(Irvine, CA) ; Shen; Ba-Zhong; (Irvine, CA)
; Tran; Hau Thien; (Irvine, CA) |
Correspondence
Address: |
GARLICK HARRISON & MARKISON
P.O. BOX 160727
AUSTIN
TX
78716-0727
US
|
Assignee: |
Broadcom Corporation, a California
Corporation
Irvine
CA
|
Family ID: |
36974670 |
Appl. No.: |
11/493273 |
Filed: |
July 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10338377 |
Jan 8, 2003 |
7111226 |
|
|
11493273 |
Jul 26, 2006 |
|
|
|
60384698 |
May 31, 2002 |
|
|
|
Current U.S.
Class: |
714/796 |
Current CPC
Class: |
H03M 13/6516 20130101;
H03M 13/3905 20130101; H03M 13/6362 20130101; H03M 13/256 20130101;
H03M 13/3988 20130101; H03M 13/258 20130101; H03M 13/2957
20130101 |
Class at
Publication: |
714/796 |
International
Class: |
H03M 13/03 20060101
H03M013/03 |
Claims
1. An apparatus, comprising: an input that is operable to receive a
signal from a communication channel, wherein: the signal includes a
first symbol, that includes a first plurality of bits, that has
been symbol mapped to a first modulation; and the signal includes a
second symbol, that includes a second plurality of bits, that has
been symbol mapped to a second modulation; a metric generator that
is operable to: for the first symbol, calculate a first plurality
of metrics that is indexed by a first symbol mapping of
constellation points within the first modulation; for the second
symbol, calculate a second plurality of metrics that is indexed by
a second symbol mapping of constellation points within the second
modulation; transform the first plurality of metrics to a first
plurality of trellis metrics, wherein the first plurality of
trellis metrics is a first subset of a total plurality of trellis
metrics that corresponds to a plurality of possible branch
transitions within a trellis; and transform the second plurality of
metrics to a second plurality of trellis metrics, wherein the
second plurality of trellis metrics is a second subset of the total
plurality of trellis metrics; and a decoder that is operable to:
employ the first plurality of trellis metrics during decoding
processing to make a first best estimate of the first plurality of
bits within the first symbol; and employ the second plurality of
trellis metrics during decoding processing to make a second best
estimate of the second plurality of bits within the second
symbol.
2. The apparatus of claim 1, wherein: the first symbol also
includes an uncoded bit.
3. The apparatus of claim 1, wherein: the second plurality of
trellis metrics is also a subset of the first plurality of trellis
metrics.
4. The apparatus of claim 1, wherein: at least two metrics within
the first plurality of metrics or the second plurality of trellis
metrics are assigned to a single trellis metric value within the
total plurality of trellis metrics.
5. The apparatus of claim 1, further comprising: a first memory,
having a first size, that is operable to store the total plurality
of trellis metrics; and wherein: a second memory being operable to
store the first plurality of trellis metrics would require at least
a second size; a third memory being operable to store the second
plurality of trellis metrics would require at least a third size;
and because at least one trellis metric of the trellis metrics
within the total plurality of trellis metrics is included within
each of the first plurality of trellis metrics and the second first
plurality of trellis metrics, the first size of the first memory
within the apparatus is relatively less than a combined size of the
second size of the second memory and the third size of the third
memory.
6. The apparatus of claim 1, wherein: the first modulation and the
second modulation each include a same number of constellation
points; constellation points within the first modulation are symbol
mapped according to a first symbol mapping; and constellation
points within the second modulation are symbol mapped according to
a second symbol mapping.
7. The apparatus of claim 1, wherein: the first modulation includes
a first plurality of constellation points; the second modulation
includes a second plurality of constellation points; constellation
points within the first modulation are symbol mapped according to a
first symbol mapping; and constellation points within the second
modulation are symbol mapped according to a second symbol
mapping.
8. The apparatus of claim 1, wherein: the first modulation includes
a first plurality of constellation points; the second modulation
includes a second plurality of constellation points; and the second
plurality of constellation points is a subset of the first
plurality of constellation points.
9. The apparatus of claim 1, further comprising: a rate control
sequencer that provides a rate control sequence to the metric
generator and to the decoder, wherein the rate control sequence
includes a first rate control and a second rate control; and
wherein: for the first symbol, the first rate control indicates the
first modulation and which trellis metrics of the total plurality
of trellis metrics compose the first plurality of trellis metrics
to the metric generator and to the decoder; and for the second
symbol, the second rate control indicates the second modulation and
which trellis metrics of the total plurality of trellis metrics
compose the second plurality of trellis metrics to the metric
generator and to the decoder.
10. The apparatus of claim 1, further comprising: a rate control
sequencer that is operable to provide a rate control sequence to
the metric generator and to the decoder, wherein the rate control
sequence includes a first rate control and a second rate control;
and wherein: the first symbol has been encoded using a first code
rate; the second symbol has been encoded using a second code rate;
the first rate control indicates the first code rate of the first
symbol to the metric generator and to the decoder; and the second
rate control indicates the second code rate of the second symbol to
the metric generator and to the decoder.
11. The apparatus of claim 1, wherein: at least one trellis metric
of the first plurality of trellis metrics is set to a predetermined
maximum value or a predetermined minimum value when one bit within
the first plurality of bits is estimated to be either a value of 0
or 1.
12. An apparatus, comprising: an input that is operable to receive
a signal from a communication channel, wherein: the signal includes
a first symbol, that includes a first plurality of bits, that has
been symbol mapped to a first modulation, wherein the first symbol
has been encoded using a first code rate; and the signal includes a
second symbol, that includes a second plurality of bits, that has
been symbol mapped to a second modulation, wherein the second
symbol has been encoded using a second code rate; and a decoder
that is operable to: employ the first plurality of trellis metrics
during decoding processing to make a first best estimate of the
first plurality of bits within the first symbol, wherein the first
plurality of trellis metrics is a first subset of a total plurality
of trellis metrics that corresponds to a plurality of possible
branch transitions within a trellis; and employ the second
plurality of trellis metrics during decoding processing to make a
second best estimate of the second plurality of bits within the
second symbol, wherein the second plurality of trellis metrics is a
second subset of the total plurality of trellis metrics.
13. The apparatus of claim 12, further comprising: a metric
generator that is operable to: for the first symbol, calculate a
first plurality of metrics that is indexed by a first symbol
mapping of constellation points within the first modulation; for
the second symbol, calculate a second plurality of metrics that is
indexed by a second symbol mapping of constellation points within
the second modulation; transform the first plurality of metrics to
the first plurality of trellis metrics; and transform the second
plurality of metrics to the second plurality of trellis
metrics.
14. The apparatus of claim 12, further comprising: a rate control
sequencer that provides a rate control sequence to the metric
generator and to the decoder, wherein the rate control sequence
includes a first rate control and a second rate control; and
wherein: for the first symbol, the first rate control indicates the
first modulation, which trellis metrics of the total plurality of
trellis metrics compose the first plurality of trellis metrics, and
the first code rate to the metric generator and to the decoder; and
for the second symbol, the second rate control indicates the second
modulation, which trellis metrics of the total plurality of trellis
metrics compose the second plurality of trellis metrics, and the
second code rate to the metric generator and to the decoder.
15. The apparatus of claim 12, wherein: the second plurality of
trellis metrics is also a subset of the first plurality of trellis
metrics.
16. The apparatus of claim 12, further comprising: a first memory,
having a first size, that is operable to store the total plurality
of trellis metrics; and wherein: a second memory being operable to
store the first plurality of trellis metrics would require at least
a second size; a third memory being operable to store the second
plurality of trellis metrics would require at least a third size;
and because at least one trellis metric of the trellis metrics
within the total plurality of trellis metrics is included within
each of the first plurality of trellis metrics and the second first
plurality of trellis metrics, the first size of the first memory
within the apparatus is relatively less than a combined size of the
second size of the second memory and the third size of the third
memory.
17. The apparatus of claim 12, wherein: the first modulation and
the second modulation each include a same number of constellation
points; constellation points within the first modulation are symbol
mapped according to a first symbol mapping; and constellation
points within the second modulation are symbol mapped according to
a second symbol mapping.
18. The apparatus of claim 12, wherein: the first modulation
includes a first plurality of constellation points; the second
modulation includes a second plurality of constellation points;
constellation points within the first modulation are symbol mapped
according to a first symbol mapping; and constellation points
within the second modulation are symbol mapped according to a
second symbol mapping.
19. The apparatus of claim 12, wherein: the first modulation
includes a first plurality of constellation points; the second
modulation includes a second plurality of constellation points; and
the second plurality of constellation points is a subset of the
first plurality of constellation points.
20. A method, comprising: receiving a signal from a communication
channel, wherein: the signal includes a first symbol, that includes
a first plurality of bits, that has been symbol mapped to a first
modulation, wherein the first symbol has been encoded using a first
code rate; and the signal includes a second symbol, that includes a
second plurality of bits, that has been symbol mapped to a second
modulation, wherein the second symbol has been encoded using a
second code rate; and employing the first plurality of trellis
metrics during decoding processing to make a first best estimate of
the first plurality of bits within the first symbol, wherein the
first plurality of trellis metrics is a first subset of a total
plurality of trellis metrics that corresponds to a plurality of
possible branch transitions within a trellis; and employing the
second plurality of trellis metrics during decoding processing to
make a second best estimate of the second plurality of bits within
the second symbol, wherein the second plurality of trellis metrics
is a second subset of the total plurality of trellis metrics.
21. The method of claim 20, further comprising: for the first
symbol, calculating a first plurality of metrics that is indexed by
a first symbol mapping of constellation points within the first
modulation; for the second symbol, calculating a second plurality
of metrics that is indexed by a second symbol mapping of
constellation points within the second modulation; transforming the
first plurality of metrics to the first plurality of trellis
metrics; and transforming the second plurality of metrics to the
second plurality of trellis metrics.
22. The method of claim 20, wherein: the first modulation and the
second modulation each include a same number of constellation
points; constellation points within the first modulation are symbol
mapped according to a first symbol mapping; and constellation
points within the second modulation are symbol mapped according to
a second symbol mapping.
23. The method of claim 20, wherein: the first modulation includes
a first plurality of constellation points; the second modulation
includes a second plurality of constellation points; constellation
points within the first modulation are symbol mapped according to a
first symbol mapping; and constellation points within the second
modulation are symbol mapped according to a second symbol
mapping.
24. The method of claim 20, wherein: the first modulation includes
a first plurality of constellation points; the second modulation
includes a second plurality of constellation points; and the second
plurality of constellation points is a subset of the first
plurality of constellation points.
Description
CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS
Continuation Priority Claim, 35 U.S.C. .sctn.120
[0001] The present U.S. Utility patent application claims priority
pursuant to 35 U.S.C. .sctn.120, as a continuation, to the
following U.S. Utility patent application which is hereby
incorporated herein by reference in its entirety and made part of
the present U.S. Utility patent application for all purposes:
[0002] 1. U.S. Utility application Ser. No. 10/338,377, entitled
"Communication decoder employing single trellis to support multiple
code rates and/or multiple modulations," (Attorney Docket No.
BP2333.2), filed Jan. 8, 2003, pending, which claims priority
pursuant to 35 U.S.C. .sctn.119(e) to the following U.S.
Provisional Patent Application which is hereby incorporated herein
by reference in its entirety and made part of the present U.S.
Utility patent application for all purposes:
[0003] 1. U.S. Provisional Patent Application Ser. No. 60/384,698,
entitled "Variable code rate and signal constellation turbo trellis
coded modulation codec," (Attorney Docket No. BP2333), filed May
31, 2002.
Incorporation by Reference
[0004] The following U.S. Utility patent applications are hereby
incorporated herein by reference in their entirety and made part of
the present U.S. Utility patent application for all purposes:
[0005] 1. U.S. Utility application Ser. No. 10/264,486, entitled
"Variable code rate and signal constellation turbo trellis coded
modulation codec," (Attorney Docket No. BP2333), filed Oct. 4,
2002, pending.
[0006] 2. U.S. Utility patent application Ser. No. 10/338,571,
entitled "Parallel concatenated turbo code modulation encoder,"
(Attorney Docket No. BP2333.1), filed Jan. 8, 2003, pending.
[0007] 3. U.S. Utility patent application Ser. No. 10/338,185,
entitled "Symbol by symbol variable code rate capable communication
device," (Attorney Docket No. BP2333.3), filed Jan. 8, 2003,
pending.
[0008] 4. U.S. Utility patent application Ser. No. 10/338,376,
entitled "Symbol by symbol variable constellation type and/or
mapping capable communication device," (Attorney Docket No.
BP2333.4), filed Jan. 8, 2003, pending.
[0009] 5. U.S. Utility patent application Ser. No. 10/338,432,
entitled "Determination of variable code rates for a rate control
sequence," (Attorney Docket No. BP2333.5), filed Jan. 8, 2003,
pending.
BACKGROUND OF THE INVENTION
[0010] 1. Technical Field of the Invention
[0011] The invention relates generally to communication systems;
and, more particularly, it relates to devices that decode
information within such communication systems.
[0012] 2. Description of Related Art
[0013] Turbo code and variants thereof have been the focus of a
great deal of interest in the recent years. A primary directive in
this area of development has been to try continually to lower the
error floor within a communication system. The ideal goal has been
to try reach Shannon's limit in a communication channel. Shannon's
limit may be viewed as being the data rate that is used in a
communication channel, having a particular signal to noise ratio
(SNR), that will achieve error free transmission through the
channel. In other words, the Shannon limit is the theoretical bound
for channel capacity for a given modulation and code rate. The code
rate is the ratio of information bits over the total number of bits
transmitted within the communication system. In the turbo code
context, it is common to refer to code rate of n/m, where n is the
number of information bits and m is the total number of bits, and
where m>n. The difference between m and n typically being
referred to as the number of redundant bits. Turbo codes typically
introduce a degree of redundancy to at least a portion of data
prior to transmission through a communication channel. This is
generally referred to as forward error correction (FEC) coding.
[0014] Although there has been much development within the context
of turbo code and related coding applications with increased
interest recently, this focus has been primarily towards achieving
very low bit error rates (BERs) across relatively noisy
communication channels. As such, these prior art turbo codes
largely operate at relatively low rates across the noisy
communication channels. The area of turbo code and variants thereof
is still an area of relative immaturity in the technological
development sense. While there has no doubt been a great amount of
progress achieved this far, there still remains a great deal of
development and improvement that can be done. This is a technology
area where industry-wide consensus has certainly not yet been
achieved, and there are many competing viewpoint within the
industry as to which direction effort should be directed.
[0015] The use of turbo codes providing such low error, while
operating at relatively low rates, has largely been in the context
of communication systems having a large degree of noise within the
communication channel and where substantially error free
communication is held at the highest premium. Some of the earliest
application arenas for turbo coding were space related where
accurate (ideally error free) communication is often deemed an
essential design criterion. The direction of development then moved
towards developing terrestrial-applicable and consumer-related
applications. Still, the focus of effort here has continued to be
achieving low error floors, and not specifically towards reaching
higher throughput.
[0016] As such, there exists a need in the art to develop turbo
code related coding that is operable to support higher amounts of
throughput while still preserving the relatively low error floors
offered within the turbo code context. Whereas the development of
turbo code related technology has primarily been directed towards
relatively low rates across noisy communication channels, there
exists a need to overcome the many hurdles that prevent the
application of turbo code to higher data rate applications. In
doing so, these higher data rate applications may benefit from the
low BERs offered by turbo codes.
BRIEF SUMMARY OF THE INVENTION
[0017] The present invention is directed to apparatus and methods
of operation that are further described in the following Brief
Description of the Several Views of the Drawings, the Detailed
Description of the Invention, and the claims. Other features and
advantages of the present invention will become apparent from the
following detailed description of the invention made with reference
to the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0018] FIG. 1 is a system diagram illustrating an embodiment of a
satellite communication system that is built according to the
invention.
[0019] FIG. 2 is a system diagram illustrating an embodiment of a
HDTV communication system that is built according to the
invention.
[0020] FIG. 3 is a system diagram illustrating an embodiment of a
cellular communication system that is built according to the
invention.
[0021] FIG. 4 is a system diagram illustrating another embodiment
of a cellular communication system that is built according to the
invention.
[0022] FIG. 5 is a system diagram illustrating an embodiment of a
microwave communication system that is built according to the
invention.
[0023] FIG. 6 is a system diagram illustrating an embodiment of a
point-to-point communication system that is built according to the
invention.
[0024] FIG. 7 is a system diagram illustrating an embodiment of a
uni-directional TTCM communication system that is built according
to the invention.
[0025] FIG. 8 is a system diagram illustrating an embodiment of a
bi-directional TTCM communication system that is built according to
the invention.
[0026] FIG. 9 is a system diagram illustrating an embodiment of a
one to many TTCM communication system that is built according to
the invention.
[0027] FIG. 10 is a system diagram illustrating an embodiment of a
satellite receiver set-top box system that is built according to
the invention.
[0028] FIG. 11 is a system diagram illustrating an embodiment of a
TTCM communication system that is built according to the
invention.
[0029] FIG. 12 is a diagram illustrating a single interleaver
embodiment of the turbo encoder of the FIG. 11.
[0030] FIG. 13 is a diagram illustrating a dual interleaver
embodiment of the turbo encoder of the FIG. 11.
[0031] FIG. 14 is a diagram illustrating an embodiment of a
systematic encoder that is built according to the invention.
[0032] FIG. 15 is a diagram illustrating an embodiment of a
non-systematic encoder that is built according to the
invention.
[0033] FIG. 16 is a diagram illustrating an embodiment of a
non-systematic encoder using puncturing and rate control sequencer
to support multiple encoders according to the invention.
[0034] FIG. 17 is a diagram illustrating an embodiment of periodic
sequencing of a non-systematic encoder using puncturing and rate
control sequencer according to the invention.
[0035] FIG. 18 is a diagram illustrating a generic embodiment of
variable puncturing, constellation, and mapping using a single
encoder according to the invention.
[0036] FIG. 19 is a diagram illustrating an embodiment of a rate
1/2 recursive convolutional encoder with non-systematic output that
is built according to the invention.
[0037] FIG. 20 is a diagram illustrating an embodiment of a rate
2/5 prototype encoder that is built according to the invention.
[0038] FIG. 21 is a block diagram of a rate 2/5 systematic
prototype encoder that is built according to the invention.
[0039] FIG. 22 is a block diagram of the rate 2/5 non-systematic
prototype encoder of the FIG. 20.
[0040] FIG. 23 is a trellis diagram of a trellis employed by the
rate 2/5 non-systematic prototype encoder of the FIG. 20.
[0041] FIG. 24 is a diagram illustrating the functional operation
the non-systematic rate 2/5 encoder of the FIG. 20 using puncturing
and rate control sequencer to support multiple encoders performing
various rate controls according to the invention.
[0042] FIG. 25 shows additional rate controls supported by the
non-systematic rate 2/5 encoder of the FIG. 20.
[0043] FIG. 26 shows yet additional rate controls supported by the
non-systematic rate 2/5 encoder of the FIG. 20.
[0044] FIGS. 27, 28, 29, and 30 are diagrams illustrating
embodiments of periodic sequencing of the non-systematic rate 2/5
encoder of the FIG. 20 using puncturing and rate control sequencer
according to the invention.
[0045] FIG. 31 is a constellation diagram illustrating an
embodiment of rate control governed mapping to 8 PSK constellations
according to the invention.
[0046] FIGS. 32, 33, and 34 are constellation diagrams illustrating
embodiments of rate control governed mapping to QPSK constellations
according to the invention.
[0047] FIG. 35 is a constellation diagram illustrating an
embodiment of rate control governed mapping to a 16 QAM
constellation according to the invention.
[0048] FIG. 36 is a constellation diagram illustrating an
embodiment of rate control governed mapping to 16 APSK
constellations according to the invention.
[0049] FIG. 37 is a diagram illustrating an embodiment of variable
puncturing, modulation, and mapping using the single non-systematic
rate 2/5 encoder of the FIG. 20 according to the invention.
[0050] FIG. 38 is a system diagram illustrating an embodiment of a
TTCM decoder system that is built according to the invention.
[0051] FIG. 39 is a system diagram illustrating an embodiment of an
alternative TTCM decoder system that recycles a single SISO
according to the invention.
[0052] FIG. 40 is a diagram illustrating an embodiment of I,Q
extraction that is performed according to the invention.
[0053] FIG. 41 is a diagram illustrating an embodiment of received
I,Q mapping performed based on rate control according to the
invention.
[0054] FIG. 42 is a diagram illustrating an embodiment of metric
calculation performed by one of the metric generators shown in the
FIG. 38 and the FIG. 39.
[0055] FIG. 43 is a functional block diagram illustrating an
embodiment of metric mapping functionality that is performed
according to the invention.
[0056] FIG. 44 is a diagram illustrating an embodiment of SISO
calculations and operations that are performed according to the
invention.
[0057] FIG. 45 is a diagram illustrating an embodiment of alpha,
beta, and extrinsic calculation, based on the trellis of the FIG.
23 of the rate 2/5 non-systematic prototype encoder of the FIG. 20
according to the invention.
[0058] FIG. 46 is a diagram illustrating an embodiment of final
output of decoding that is performed according to the
invention.
[0059] FIG. 47 is a diagram illustrating an embodiment of a
variable code rate codec (encoder/decoder) servicing channels of
various SNRs according to the invention.
[0060] FIG. 48 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate coding method that is
performed according to the invention.
[0061] FIG. 49 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate encoding method that is
performed according to the invention.
[0062] FIG. 50 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate decoding method that is
performed according to the invention.
[0063] FIG. 51 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate encoding method that is
performed according to the invention.
[0064] FIG. 52 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate decoding method that is
performed according to the invention.
[0065] FIG. 53 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method that is
performed according to the invention.
[0066] FIG. 54 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method that is
performed according to the invention.
[0067] FIG. 55 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method that is
performed according to the invention.
[0068] FIG. 56 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate encoding method that is
performed according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0069] The variable code rate functionality of the invention may
properly be described as being within the context of turbo trellis
code modulation (TTCM) communication systems. TTCM coding may also
be viewed as a hybrid combination of turbo coding and trellis code
modulation (TCM). Some of the particular embodiments of the
invention are performed within communication systems that may more
properly be categorized as being parallel concatenated turbo code
modulation (PC-TCM) communication systems.
[0070] FIGS. 1-9 illustrate a number of communication systems
context embodiments where certain aspects of the invention may be
implemented.
[0071] FIG. 1 is a system diagram illustrating an embodiment of a
satellite communication system 100 that is built according to the
invention. A satellite transmitter 110 includes a TTCM encoder 112.
The TTCM encoder 112 is one of several possible embodiments that
are described herein. The TTCM encoder 112 is operable to encode
data that is to be transmitted by the satellite transmitter 110.
The satellite transmitter 110 is communicatively coupled to a
satellite dish 115 that is operable to communicate with a satellite
150. The satellite transmitter 110 may also be communicatively
coupled to a wired network. This wired network may include any
number of networks including the Internet, proprietary networks,
and other wired networks. The satellite transmitter 110 employs the
satellite dish 115 to communicate to the satellite 150 via a
wireless communication channel. The satellite 150 is able to
communicate with one or more satellite receivers, shown as a
satellite receiver 120 (having a satellite dish 125), . . . , and a
satellite receiver 130 (having a satellite dish 135). Each of the
satellite receiver 120 and the satellite receiver 130 includes a
TTCM decoder; specifically, the satellite receiver 120 includes a
TTCM decoder 122, and the satellite receiver 130 includes a TTCM
decoder 132. Each of the satellite receiver 120 and the satellite
receiver 130 may also be communicatively coupled to a display.
Again, specifically, the satellite receiver 120 may be
communicatively coupled to a display 127, and the satellite
receiver 130 may be communicatively coupled to a display 137.
Various and further details will be provided below regarding the
various embodiments in which the TTCM encoder 112, and the TTCM
decoders 122 and 132 may be implemented.
[0072] Here, the communication to and from the satellite 150 may
cooperatively be viewed as being a wireless communication channel,
or each of the communication to and from the satellite 150 may be
viewed as being two distinct wireless communication channels.
[0073] For example, the wireless communication "channel" may be
viewed as not including multiple wireless hops in one embodiment.
In other embodiments, the satellite 150 receives a signal received
from the satellite transmitter 110 (via its satellite dish 115),
amplifies it, and relays it to satellite receiver 120 (via its
satellite dish 125); the satellite receiver 120 may also be
implemented using terrestrial receivers such as satellite
receivers, satellite based telephones, and satellite based Internet
receivers, among other receiver types. In the case where the
satellite 150 receives a signal received from the satellite
transmitter 110 (via its satellite dish 115), amplifies it, and
relays it, the satellite 150 may be viewed as being a
"transponder." In addition, other satellites may exist that perform
both receiver and transmitter operations in cooperation with the
satellite 150. In this case, each leg of an up-down transmission
via the wireless communication channel would be considered
separately.
[0074] In whichever embodiment, the satellite 150 communicates with
the satellite receiver 120. The satellite receiver 120 may be
viewed as being a mobile unit in certain embodiments (employing a
local antenna); alternatively, the satellite receiver 120 may be
viewed as being a satellite earth station that may be
communicatively coupled to a wired network in a similar manner in
which the satellite transmitter 110 may also be communicatively
coupled to a wired network. In both situations, the satellite
receiver 110 and the satellite receiver 120 are each operable to
support the TTCM encoder 112 and the TTCM decoder 122 contained
therein. The FIG. 1 shows one of the many embodiments where TTCM
coding (TTCM encoding and TTCM decoding) may be performed according
to any one or more of the various embodiments of the invention.
[0075] FIG. 2 is a system diagram illustrating an embodiment of a
HDTV communication system 200 that is built according to the
invention. An HDTV transmitter 220 is communicatively coupled to a
tower 221. The HDTV transmitter 220, using its tower 221, transmits
a signal to a local tower dish 212 via a wireless communication
channel. The local tower dish 212 communicatively couples to an
HDTV set top box receiver 210 via a coaxial cable. The HDTV set top
box receiver 210 includes the functionality to receive the wireless
transmitted signal that has been received by the local tower dish
212; this may include any transformation and/or down-converting as
well to accommodate any up-converting that may have been performed
before and during transmission of the signal from the HDTV
transmitter 220 and its tower 221.
[0076] The HDTV set top box receiver 210 is also communicatively
coupled to an HDTV display 230 that is able to display the
demodulated and decoded wireless transmitted signals received by
the HDTV set top box receiver 210 and its local tower dish 212. The
HDTV transmitter 220 (via its tower 221) transmits a signal
directly to the local tower dish 412 via the wireless communication
channel in this embodiment. In alternative embodiments, the HDTV
transmitter 220 may first receive a signal from a satellite 250,
using a satellite earth station 222 that is communicatively coupled
to the HDTV transmitter 220, and then transmit this received signal
to the to the local tower dish 212 via the wireless communication
channel. In this situation, the HDTV transmitter 220 operates as a
relaying element to transfer a signal originally provided by the
satellite 250 that is destined for the HDTV set top box receiver
210. For example, another satellite earth station may first
transmit a signal to the satellite 250 from another location, and
the satellite 250 may relay this signal to the satellite earth
station 222 that is communicatively coupled to the HDTV transmitter
220. The HDTV transmitter 220 performs receiver functionality and
then transmits its received signal to the local tower dish 212.
[0077] In even other embodiments, the HDTV transmitter 220 employs
the satellite earth station 222 to communicate to the satellite 250
via a wireless communication channel. The satellite 250 is able to
communicate with a local satellite dish 213; the local satellite
dish 213 communicatively couples to the HDTV set top box receiver
210 via a coaxial cable. This path of transmission shows yet
another communication path where the HDTV set top box receiver 210
may communicate with the HDTV transmitter 220.
[0078] In whichever embodiment and whichever signal path the HDTV
transmitter 220 employs to communicate with the HDTV set top box
receiver 210, the HDTV set top box receiver 210 is operable to
receive communication transmissions from the HDTV transmitter
220.
[0079] The HDTV transmitter 220 includes an embodiment of the TTCM
encoder 112 described above. Similarly, the HDTV set top box
receiver 210 includes an embodiment of the TTCM decoder 122
described above. Cooperatively, the TTCM encoder 112 and the TTCM
decoder 122 form a TTCM codec according to the invention. The FIG.
2 shows yet another of the many embodiments where TTCM coding (TTCM
encoding and TTCM decoding) may be performed according to any one
or more of the various embodiments of the invention.
[0080] FIG. 3 is a system diagram illustrating an embodiment of a
cellular communication system 300 that is built according to the
invention. A mobile transmitter 310 includes a local antenna 315
communicatively coupled thereto. The mobile transmitter 310 may be
any number of types of transmitters including a cellular telephone,
a wireless pager unit, a mobile computer having transmit
functionality, or any other type of mobile transmitter. The mobile
transmitter 310 transmits a signal, using its local antenna 315, to
a receiving tower 345 via a wireless communication channel. The
receiving tower 345 is communicatively coupled to a base station
receiver 340; the receiving tower 345 is operable to receive data
transmission from the local antenna 315 of the mobile transmitter
310 that have been communicated via the wireless communication
channel. The receiving tower 345 communicatively couples the
received signal to the base station receiver 340.
[0081] The mobile transmitter 310 includes an embodiment of the
TTCM encoder 112 described above. Similarly, the base station
receiver 340 includes an embodiment of the TTCM decoder 122
described above. Cooperatively, the TTCM encoder 112 and the TTCM
decoder 122 form a TTCM codec according to the invention. The FIG.
3 shows yet another of the many embodiments where TTCM coding (TTCM
encoding and TTCM decoding) may be performed according to any one
or more of the various embodiments of the invention.
[0082] FIG. 4 is a system diagram illustrating another embodiment
of a cellular communication system 400 that is built according to
the invention. From certain perspectives, the cellular
communication system 400 of the FIG. 4 may be viewed as being the
reverse transmission operation of the cellular communication system
300 of the FIG. 3. A base station transmitter 420 is
communicatively coupled to a transmitting tower 425. The base
station transmitter 420, using its transmitting tower 425,
transmits a signal to a local antenna 435 via a wireless
communication channel. A mobile receiver 430 includes the local
antenna 435 communicatively coupled thereto. The local antenna 435
is communicatively coupled to a mobile receiver 430 so that the
mobile receiver 430 may receive transmission from the transmitting
tower 435 of the base station transmitter 420 that have been
communicated via the wireless communication channel. The local
antenna 435 communicatively couples the received signal to the
mobile receiver 430. It is noted that the mobile receiver 430 may
be any number of types of receivers including a cellular telephone,
a wireless pager unit, a mobile computer having receive
functionality, or any other type of mobile receiver.
[0083] The base station transmitter 420 includes an embodiment of
the TTCM encoder 112 described above. Similarly, the mobile
receiver 430 includes an embodiment of the TTCM decoder 122
described above. Cooperatively, the TTCM encoder 112 and the TTCM
decoder 122 form a TTCM codec according to the invention. The FIG.
4 shows yet another of the many embodiments where TTCM coding (TTCM
encoding and TTCM decoding) may be performed according to any one
or more of the various embodiments of the invention.
[0084] FIG. 5 is a system diagram illustrating an embodiment of a
microwave communication system 500 that is built according to the
invention. A transmitter 510 is communicatively coupled to a
microwave tower 515. The transmitter 510, using its microwave tower
515, transmits a signal to a microwave tower 525 via a wireless
communication channel. A receiver 520 is communicatively coupled to
the microwave tower 525. The microwave tower 525 is able to receive
transmissions from the microwave tower 515 that have been
communicated via the wireless communication channel.
[0085] The transmitter 510 includes an embodiment of the TTCM
encoder 112 described above. Similarly, the receiver 520 includes
an embodiment of the TTCM decoder 122 described above.
Cooperatively, the TTCM encoder 112 and the TTCM decoder 122 form a
TTCM codec according to a uni-directional communication
implementation of the invention.
[0086] However, in a bi-directional communication implementation of
the invention, the transmitter 510 also includes an embodiment of a
TTCM decoder 522; the embodiment of the TTCM decoder 522 may be
viewed as being duplicative of the TTCM decoder 122 within the
receiver 520. The TTCM encoder 112 and the TTCM decoder 522
together form a TTCM codec 511 within the transmitter 510. The
receiver 520 also includes an embodiment of a TTCM encoder 512; the
embodiment of the TTCM encoder 512 may be viewed as being
duplicative of the TTCM encoder 112 within the transmitter 510. The
TTCM decoder 122 and the TTCM encoder 512 together form a TTCM
codec 521 within the receiver 520.
[0087] The embodiment of the invention described within the FIG. 5
shows an embodiment where a TTCM codec, built according to the
invention, may be viewed as within a single device (such as the
TTCM codec 511 within the transmitter 510 or the TTCM codec 521
within the receiver 520) or as being distributed across two
separate devices, namely, the transmitter 510 and the receiver
520.
[0088] The FIG. 5 shows yet another of the many embodiments where
TTCM coding (TTCM encoding and TTCM decoding) may be performed
according to any one or more of the various embodiments of the
invention.
[0089] FIG. 6 is a system diagram illustrating an embodiment of a
point-to-point communication system 600 that is built according to
the invention. A mobile unit 610 includes a local antenna 615
communicatively coupled thereto. The mobile unit 610, using its
local antenna 615, transmits a signal to a local antenna 625 via a
wireless communication channel. A mobile unit 620 includes the
local antenna 625 communicatively coupled thereto. The mobile unit
620 may receive transmissions from the mobile unit 610 that have
been communicated via the wireless communication channel.
[0090] The mobile unit 610 includes an embodiment of the TTCM
encoder 112 described above. Similarly, the mobile unit 620
includes an embodiment of the TTCM decoder 122 described above.
Cooperatively, the TTCM encoder 112 and the TTCM decoder 122 form a
TTCM codec according to a uni-directional communication
implementation of the invention.
[0091] However, in a bi-directional communication implementation of
the invention, the mobile unit 610 also includes an embodiment of a
TTCM decoder 622; the embodiment of the TTCM decoder 622 may be
viewed as being duplicative of the TTCM decoder 122 within the
mobile unit 620. The TTCM encoder 112 and the TTCM decoder 622
together form a TTCM codec 611 within the mobile unit 610. The
mobile unit 620 also includes an embodiment of a TTCM encoder 612;
the embodiment of the TTCM encoder 612 may be viewed as being
duplicative of the TTCM encoder 112 within the mobile unit 610. The
TTCM decoder 122 and the TTCM encoder 612 together form a TTCM
codec 621 within the mobile unit 620.
[0092] The embodiment of the invention described within the FIG. 6
shows an embodiment where a TTCM codec, built according to the
invention, may be viewed as within a single device (such as the
TTCM codec 611 within the mobile unit 610 or the TTCM codec 621
within the mobile unit 610) or as being distributed across two
separate devices, namely, the mobile unit 610 and the mobile unit
620.
[0093] The FIG. 6 shows yet another of the many embodiments where
TTCM coding (TTCM encoding and TTCM decoding) may be performed
according to any one or more of the various embodiments of the
invention.
[0094] FIG. 7 is a system diagram illustrating an embodiment of a
uni-directional TTCM communication system 700 that is built
according to the invention. A transmitter 710 communicates with a
receiver 720 via a uni-directional communication channel 799. The
uni-directional communication channel 799 may be a wireline (or
wired) communication channel or a wireless communication channel
without departing from the scope and spirit of the invention. The
wired media by which the uni-directional communication channel 799
may be implemented are varied, including coaxial cable, fiber-optic
cabling, and copper cabling, among other types of "wiring."
Similarly, the wireless manners in which the uni-directional
communication channel 799 may be implemented are varied, including
satellite communication, cellular communication, microwave
communication, and radio communication, among other types of
wireless communication.
[0095] The transmitter 710 includes an embodiment of the TTCM
encoder 112. Similarly, the receiver 720 includes an embodiment of
the TTCM decoder 122. Cooperatively, the TTCM encoder 112 and the
TTCM decoder 122 form a TTCM codec according to the invention. The
FIG. 7 shows yet another of the many embodiments where TTCM coding
(TTCM encoding and TTCM decoding) may be performed according to any
one or more of the various embodiments of the invention.
[0096] FIG. 8 is a system diagram illustrating an embodiment of a
bi-directional TTCM communication system 800 that is built
according to the invention. A transceiver 841 and a transceiver 842
are able to communicate with one another via a bi-directional
communication channel 899. The bi-directional communication channel
899 may be a wireline (or wired) communication channel or a
wireless communication channel without departing from the scope and
spirit of the invention. The wired media by which the
bi-directional communication channel 899 may be implemented are
varied, including coaxial cable, fiber-optic cabling, and copper
cabling, among other types of "wiring." Similarly, the wireless
manners in which the bi-directional communication channel 899 may
be implemented are varied, including satellite communication,
cellular communication, microwave communication, and radio
communication, among other types of wireless communication.
[0097] The transceiver 841 includes a TTCM codec 811 that includes
a TTCM encoder 112 and a TTCM decoder 822. Similarly, transceiver
842 includes a TTCM codec 821 that includes a TTCM decoder 122 and
a TTCM encoder 812. The TTCM codec 811 and the TTCM codec 821 may
be viewed as being duplicative of one another within the
transceivers 841 and 842.
[0098] The FIG. 8 shows yet another of the many embodiments where
TTCM coding (TTCM encoding and TTCM decoding) may be performed
according to any one or more of the various embodiments of the
invention.
[0099] FIG. 9 is a system diagram illustrating an embodiment of a
one to many TTCM communication system 900 that is built according
to the invention. A transmitter 910 is able to communicate, via
broadcast in certain embodiments, with a number of receivers, shown
as receivers 910, 920, . . . , and 940 via a uni-directional
communication channel 999. The uni-directional communication
channel 999 may be a wireline (or wired) communication channel or a
wireless communication channel without departing from the scope and
spirit of the invention. The wired media by which the
bi-directional communication channel 999 may be implemented are
varied, including coaxial cable, fiber-optic cabling, and copper
cabling, among other types of "wiring." Similarly, the wireless
manners in which the bi-directional communication channel 999 may
be implemented are varied, including satellite communication,
cellular communication, microwave communication, and radio
communication, among other types of wireless communication.
[0100] A distribution point 950 is employed within the one to many
TTCM communication system 900 to provide the appropriate
communication to the receivers 910, 920, . . . , and 940. In
certain embodiments, the receivers 910, 920, . . . , and 940 each
receive the same communication and individually discern which
portion of the total communication is intended for themselves.
[0101] The transmitter 910 includes an embodiment of the TTCM
encoder 112. Similarly, each of the receivers 910, 920, . . . , and
940 includes an embodiment of the TTCM decoder; specifically, the
receiver 920 includes an embodiment of the TTCM decoder 122; the
receiver 930 includes an embodiment of the TTCM decoder 932; and
the receiver 940 includes an embodiment of the TTCM decoder 942.
Cooperatively, the TTCM encoder 112 and each of the TTCM decoders
122, 932, . . . , and 942 form TTCM codecs according to the
invention. The FIG. 9 shows yet another of the many embodiments
where TTCM coding (TTCM encoding and TTCM decoding) may be
performed according to any one or more of the various embodiments
of the invention.
[0102] FIG. 10 is a system diagram illustrating an embodiment of a
satellite receiver set-top box system 1000 that is built according
to the invention. The satellite receiver set-top box system 1000
includes an advanced modulation satellite receiver 1010 that is
implemented in an all digital architecture. The satellite receiver
set-top box system 1000 includes a satellite tuner 1002 that
receives a signal via the L-band. The satellite tuner 1002 extracts
I,Q (in-phase and quadrature) components from a signal received
from the L-band and provides them to the advanced modulation
satellite receiver 1010. The advanced modulation satellite receiver
1010 includes an embodiment of the TTCM decoder 112. The advanced
modulation satellite receiver 1010 communicatively couples to an
HDTV MPEG-2 (Motion Picture Expert Group) transport de-mux,
audio/video decoder and display engine 1020. Both the advanced
modulation satellite receiver 1010 and the HDTV MPEG-2 transport
de-mux, audio/video decoder and display engine 1020 communicatively
couple to a host central processing unit (CPU) 1030. The HDTV
MPEG-2 transport de-mux, audio/video decoder and display engine
1020 also communicatively couples to a memory module 1032 and a
conditional access functional block 1034. The HDTV MPEG-2 transport
de-mux, audio/video decoder and display engine 1020 provides HD
video and audio output that may be provided to an HDTV display.
[0103] The advanced modulation satellite receiver 1010 is a
single-chip digital satellite receiver supporting the TTCM decoder
122 and variable code rate operation. Several of the many
embodiments of the variable code rate operation are described in
even more detail below. Multiple modulations (constellations and
mappings) are supported with iteratively (turbo) decoded error
correction coding within the TTCM decoder 122. The advanced
modulation satellite receiver 1010 is operable to receive
communication provided to it from a transmitter device that
includes a TTCM encoder according to the invention.
[0104] It is noted that each of the various embodiments described
above in which TTCM coding (TTCM encoding and/or TTCM decoding) is
performed is operable to support variable code rate coding
according to the invention. As will be described in the various
embodiments below, this variable code rate functionality may
include rotating through a number of various modulations (of
different constellations) and mapping for those various
modulations.
[0105] FIG. 11 is a system diagram illustrating an embodiment of a
TTCM communication system 1100 that is built according to the
invention. The TTCM communication system 1100 includes a
transmitter 1110 and a receiver 1120 that are communicatively
coupled to one another via a communication channel that introduces
Additive White Gaussian Noise (AWGN) to the signal. The
communication channel may be wireline or wireless according to the
invention. The AWGN communication channel may be viewed as being a
relatively noisy communication channel.
[0106] The transmitter 1110 includes a TTCM encoder 112 that
encodes one or more information symbols and then modulates those
encoded symbols according to a constellation and a mapping. The
transmitter 1110 then prepares this signal for transmission across
the communication channel. At the other end of the communication
channel, the receiver 1120 includes a TTCM decoder 122 that
receives and estimates the encoded symbols that have been
transmitted across the communication channel. Further details of
the operation of the various functional blocks contained within the
TTCM encoder 112 and the TTCM decoder 122 are described in more
detail below.
[0107] In addition, a rate control sequencer 1150 provides one or
more rate controls to the turbo encoder 1111 and the symbol mapper
1121 of the TTCM encoder 112 and to the TTCM decoder 122. This rate
control sequencer 1150 provides rate control sequences (which may
include as few as one rate control (RC) and as many as several
RCs). Each RC includes one or more modulations (constellations and
mappings). Each modulation provides a bandwidth efficiency that may
be viewed as being a total number of information bits per symbol
that is encoded; a number of redundancy bits may also be contained
therein. Each of the TTCM encoder 112 and the TTCM decoder 122 is
operable to cycle through the rate control sequence at their
respective locations when performing encoding and decoding of
symbols, respectively.
[0108] Generally speaking within the TTCM encoder 112, the turbo
encoder 1111 performs the symbol encoding and the symbol mapper
1121 maps those encoded symbols to the appropriate modulation
according to the rate control sequence provided by the rate control
sequencer 1150. Similarly, generally speaking within the TTCM
decoder 122, the TTCM decoder 122 performs calculations that are
employed to perform decoding of the received symbols according to
the rate control sequence provided by the rate control sequencer
1150. There are a whole host of various embodiments in which
various modulations (having various modulations and various
mappings), and various periodic sequencing of rate control sequence
may be used to perform the encoding and decoding of data using the
TTCM techniques described herein. In some embodiments, the rate
control sequence is adaptively changed during operation to provide
for improved performance. In other embodiments, predetermined rate
control sequences are employed.
[0109] In adaptive embodiments, certain operating conditions may be
employed, such as a measurement of the communication channel's SNR,
to direct the changing of the rate control sequence or rate control
sequences to be used by both the TTCM encoder 112 and the TTCM
decoder 122. It is understood that either one or both of the TTCM
encoder 112 and the TTCM decoder 122 may perform the measurement of
such operating conditions and direct the TTCM communication system
1100 to change rate control sequences. In some embodiments, such as
a uni-directional communication system embodiment, it may make more
sense for the transmitter to perform such measurement and
direction, whereas within bi-directional communication system
embodiments, either of the transceivers may provide such
functionality. The particular implementation may be left to one who
implements the invention in a particular application. There exist
several options that may be employed to adaptively/dynamically
change the rate control sequence.
[0110] For example, one embodiment operates such that the
transmitter is a master to the receiver (which operates as a
slave). The transmitter determines some operational parameter, such
as the Signal to Noise Ratio (SNR) of the AWGN communication
channel (or some other parameter including, but not limited to, an
operating condition of the communication system, the system's
configuration, and/or the available resources of the communication
system), and then the transmitter directs the rate control
sequencer 1150 so that both the transmitter and the receiver change
to a new rate control sequence synchronously.
[0111] In another embodiment, the transmitter is a slave to the
receiver (which operates as a master). The receiver determines some
operational parameter, such as the Signal to Noise Ratio (SNR) of
the AWGN communication channel (or some other parameter including,
but not limited to, an operating condition of the communication
system, the system's configuration, and/or the available resources
of the communication system), and then the receiver directs the
rate control sequencer 1150 so that both the transmitter and the
receiver change to a new rate control sequence synchronously.
[0112] In even other embodiments, the transmitter and the receiver
operate cooperatively to perform any changing to a new rate control
sequence.
[0113] It is also understood that a variety of means of modulation,
transmission, receipt, and demodulation may be performed to
generate the analog signals to be transmitted across the
communication channel without departing from the scope and spirit
thereof. Each and any such means may be practiced according to the
invention while performing the TTCM encoding/decoding described
herein.
[0114] FIG. 12 is a diagram illustrating a single interleaver
embodiment of the turbo encoder 1111 of the FIG. 11. The variable
code rate functionality described herein may be performed within
this single interleaver embodiment of the turbo encoder 1111. Input
bits are provided simultaneously to a top path and a bottom path.
The top path includes a top constituent trellis encoder, and the
bottom path includes a bottom interleaver communicatively coupled
to a bottom constituent trellis encode. A variety of interleaves
may be performed as selected for the particular application within
the bottom interleaver. The outputs from the top and bottom paths
are provided to a multiplexor (MUX) whose selection is provided by
a clock signal that is clocked at 1/2 the rate at which the input
bits are provided to the top and bottom paths. This way, the output
of the MUX will alternatively select the outputs from the top and
bottom paths.
[0115] These output bits are then output to a puncturing functional
block. In certain embodiments, no puncturing is performed on the
bits output from the MUX; they are all simply passed as output from
the puncturing functional block. However, in other embodiments,
puncturing is performed according to the rate control sequence
provided by the rate control sequencer 1150. A variety of encoded
symbols may then be then generated according to the outputs from
the top and bottom paths; the bottom path being an interleaved
path. These encoded symbols are then passed to the symbol mapper
according to the invention where the symbols are mapped according
to the appropriate modulation (constellation and mapping) as
governed by the rate control sequence provided by the rate control
sequencer 1150. The single interleaver embodiment of the turbo
encoder 1111 shows just one of the many embodiments in which TTCM
encoding may be performed. Other turbo encoding embodiments are
also envisioned within the scope and spirit of the invention to
support the variable code rate functionality described herein.
[0116] It is noted that the interleaver within the FIG. 12 may be
implemented such that it operates to correspond the order of the
input bits with the order in which the encoded symbols are output
from this embodiment of the turbo encoder. That is to say, the
first output, encoded symbol corresponds to the first group of
input bits (or first input symbol); the second output, encoded
symbol corresponds to the second group of input bits (or second
input symbol). Alternatively, the interleaver may be implemented
such that corresponding the order of the input bits (or symbols)
need not necessarily correspond to the output order of the encoded
symbols to the input order of the groups of input bits (or input
symbols).
[0117] FIG. 13 is a diagram illustrating a dual interleaver
embodiment of the turbo encoder 1111 of the FIG. 11. Similar to the
embodiment of the FIG. 12, the variable code rate functionality
described herein may be performed within this dual interleaver
embodiment of the turbo encoder 1111. Input bits are provided
simultaneously to a top path and a bottom path. The top path
includes a top interleaver communicatively coupled to a top
constituent trellis encoder, and the bottom path includes a bottom
interleaver communicatively coupled to a bottom constituent trellis
encoder.
[0118] It is also noted here (similar to FIG. 12) that the
interleavers within the FIG. 13 may be implemented such that they
operate to correspond the order of the input bits with the order in
which the encoded symbols are output from this embodiment of the
turbo encoder. That is to say, the first output, encoded symbol
corresponds to the first group of input bits (or first input
symbol); the second output, encoded symbol corresponds to the
second group of input bits (or second input symbol). Alternatively,
the interleaver may be implemented such that corresponding the
order of the input bits (or symbols) need not necessarily
correspond to the output order of the encoded symbols to the input
order of the groups of input bits (or input symbols).
[0119] The outputs from the top and bottom paths are provided to a
multiplexor (MUX) whose selection is provided by a clock signal
that is clocked at 1/2 the rate at which the input bits are
provided to the top and bottom paths. This way, the output of the
MUX will alternatively select the outputs from the top and bottom
paths.
[0120] As with the embodiment described above in the FIG. 12 for
the interleaving performed by the bottom interleaver, a variety of
interleaves may be performed as selected for the particular
application. The following example shows one embodiment of how the
interleaving may be performed for the top interleaver and the
bottom interleaver.
[0121] For each of the top interleaver and the bottom interleaver,
we let .pi..sub.0 and .pi..sub.1 be the interleaves for each bit
within the two bit input symbol, i.sub.0i.sub.1. According to the
FIG. 13, we employ the following modified interleavers (Top
interleaver and Bottom interleaver) within the encoding process;
these modified interleavers are each variants of the interleaver,
.pi..sub.l, as defined below. There are, in effect, two interleaves
that are functionally performed within the Top interleaver, and two
interleaves are functionally performed within the Bottom
interleaver. A total of four interleaves are performed by the Top
interleaver and Bottom interleaver in this embodiment. These
interleaves are performed independently for each bit within the two
bit input symbol, i.sub.0i.sub.1. The decoding process, described
in more detail below, may employ the modified
interleaving/de-interleaving shown here during initialization;
however, when performing actual decoding of a received symbol's
bits, it only employs the non-modified interleave .pi..sub.l, and
the de-interleaver, .pi..sub.l.sup.-1. Within this dual interleaver
embodiment of the turbo encoder 1111, the modified interleaving is
performed as follows:
[0122] Top interleaver=i for i mod 2=0 (for even positions)
[0123] Top interleaver=.pi..sub.l.sup.-1(i) for i mod 2=1 (for odd
positions)
[0124] Bottom interleaver=.pi..sub.l (i) for i mod 2=0
[0125] Bottom interleaver=i for i mod 2=1
[0126] Where, l=0,1 for two bit input symbol, i.sub.0i.sub.1.
[0127] This modified interleaving is performed to ensure the
following: when we input a symbol sequence,
S.sub.1S.sub.2S.sub.3S.sub.4, then we want encoded corresponding
output from those symbols to be in the same order, namely, the
encoded output for S.sub.1, followed by the encoded output for
S.sub.2, followed by the encoded output for S.sub.3, and finally
followed by the encoded output for S.sub.4. The output encoded
symbol sequence, shown as BTBT, will maintain this sequential order
(based on the order of the input symbols) because of the modified
interleaving performed herein.
[0128] In other words, the input symbols (or input bits) come into
the encoder according to a particular sequence, and the encoded
symbols that are output from the TTCM encoder leave according to
that same sequence.
[0129] Again, this interleaving shows just one example of how
interleaving may be performed according to the invention. Other
interleaves may also be designed for a particular application. This
particular interleaving is used to illustrate the functionality of
the invention in several embodiments of the invention in the
various Figures and written description.
[0130] These output bits, after having undergone interleaving and
encoding, are then output to a puncturing functional block. In
certain embodiments, no puncturing is performed on the bits output
from the MUX. However, in other embodiments, puncturing is
performed according to the rate control sequence provided by the
rate control sequencer 1150. A variety of encoded symbols may then
be generated according to the outputs from the top and bottom
paths. These encoded symbols are then passed to the symbol mapper
according to the invention where the symbols are mapped according
to the appropriate modulation (constellation and mapping) as
governed by the rate control sequence provided by the rate control
sequencer 1150. The dual interleaver embodiment of the turbo
encoder 1111 shows yet another of the many embodiments in which
TTCM encoding may be performed. It is noted that other turbo
encoding embodiments are also envisioned within the scope and
spirit of the invention to support the variable code rate
functionality described herein.
[0131] FIG. 14 is a diagram illustrating an embodiment of a
systematic encoder 1400 that is built according to the invention.
In general terms, the systematic encoder 1400 shows an encoder that
encodes "a" input bits (shown as i.sub.0, i.sub.1, . . . , and
i.sub.(a-1)). The systematic encoder 1400 is a rate a/b encoder
where "a" input bits are provided and "b" output bits are output.
The "b" output bits include "x" number of redundancy bits (shown as
c.sub.x, c.sub.(x-1), . . . , and c.sub.0) that are coded as a
function of one or more of the "a" input bits as well as each of
the "a" input bits themselves. A systematic encoder may be viewed
as being an encoder where the input bits are explicitly represented
and available in the output of the encoder. In addition, one or
more uncoded bits u may be provided as output of the encoder
without having undergone any encoding at all. It is noted that sum
of the total number of coded bits "x" and the "a" input bits is
equal to the number of output bits "b" in this rate a/b
encoder.
[0132] It is also noted that one or both of the top constituent
trellis encoder and the bottom constituent trellis encoder in the
FIG. 12 or 13 may be implemented using the systematic encoder 1400
of the FIG. 14.
[0133] FIG. 15 is a diagram illustrating an embodiment of a
non-systematic encoder 1500 that is built according to the
invention. In general terms, the non-systematic encoder 1500 shows
an encoder that encodes "a" input bits (shown as i.sub.0, i.sub.1,
. . . , and i.sub.(a-1)) to provide "b" output bits (shown as
c.sub.(b-1), c.sub.(b-2), . . . , and c.sub.0). A non-systematic
encoder may be viewed as being an encoder where the input bits are
not explicitly represented and available in the output of the
encoder. In addition, one or more uncoded bits u may be provided as
output of the encoder without having undergone any encoding at all.
While the invention envisions employing either systematic or
non-systematic encoding, a non-systematic encoder is employed to
illustrate the invention's variable code rate functionality in many
of the various Figures and description. It will be understood that
systematic encoding may also be employed to perform the various
aspects of the invention as well.
[0134] It is also noted that one or both of the top constituent
trellis encoder and the bottom constituent trellis encoder in the
FIG. 12 or 13 may be implemented using the non-systematic encoder
1500 of the FIG. 15.
[0135] FIG. 16 is a diagram illustrating an embodiment of a
non-systematic encoder using puncturing and rate control sequencer
to support multiple encoders 1600 according to the invention. Here,
a single non-systematic encoder is implemented to perform the
functionality of multiple encoders. A single hardware
implementation may be used to support the functionality of each of
a number of encoders. We illustrate the non-systematic encoder as
being a rate a/b non-systematic encoder that that encodes "a" input
bits (shown as i.sub.0, i.sub.1, . . . , and i.sub.(a-1)) to
provide "b" output bits (shown as c.sub.(b-1), c.sub.(b-2), . . . ,
and c.sub.0). As mentioned above, one or more uncoded bits may also
be used. Each of the rate control sequences provided by the rate
control sequencer 1150 may select none, some, or all of the "a"
input bits and generate none, some, or all of the "b" output bits
as well as selecting none, some, or all of a number of available
uncoded bits. Puncturing is performed on the output bits of the
encoder to generate the various options of encoded symbols that
include encoded bits and/or uncoded bits.
[0136] To show the generic applicability of the variable code rate
functionality of the invention, the rate a/b non-systematic encoder
cycles through a number of rate controls (that constitute a rate
control sequence--shown as a RC A1, a RC A2, . . . , and a RC Az).
Each of the RCs has a particular bandwidth efficiency.
Cooperatively, the bandwidth efficiencies of the individual RCs (RC
A1, RC A2, . . . , and RC Az) define the rate control sequence
provide an average bandwidth efficiency across the entire rate
control sequence. These RCs are shown generically to illustrate the
wide applicability of the variable code rate functionality of the
invention.
[0137] The rate control sequencer 1150 may cycle through a
predetermined rate control sequence; it may adaptively select one
or more new rate control sequences based on operating conditions
such as a communication channel's SNR, bandwidth requirements based
on various user applications, or according to some other
consideration as well.
[0138] The rate control sequence as illustrated within the example
embodiment shown in the FIG. 16 may be described as follows:
[0139] Within the encoder as implemented according to RC A1, two
information bits (i.sub.0 and i.sub.1) and one uncoded bit u are
input to the encoder. The output of the encoder punctures all of
the coded bits except for c.sub.2 and c.sub.1, and the uncoded bit
u; these remaining bits are then used to generate a 3 bit symbol
that will be mapped according to a 3 bit symbol modulation
(constellation and mapping) as defined by RC A1.
[0140] Within the encoder as implemented according to RC A2 one
information bits (i.sub.1) is input to the encoder. The output of
the encoder punctures all of the coded bits except for c.sub.4,
c.sub.3, . . . c.sub.0; these remaining bits are then used to
generate a 5 bit symbol that will be mapped according to a 5 bit
symbol modulation (constellation and mapping) as defined by RC
A2.
[0141] Within the encoder as implemented according to RC Az, four
information bits (i.sub.0, i.sub.1, i.sub.2, i.sub.3) and one
uncoded bit u are input to the encoder. The output of the encoder
punctures all of the coded bits except for c.sub.3, c.sub.2,
c.sub.1, c.sub.0, and the uncoded bit u; these remaining bits and
the uncoded bit are then used to generate a 5 bit symbol that will
be mapped according to a 5 bit symbol modulation (constellation and
mapping) as defined by RC Az. While the RC A2 and RC Az both employ
5 bit symbols, they may nevertheless employ different modulations
(different constellations and different mappings) without departing
from the scope and spirit of the invention.
[0142] The rate a/b non-systematic encoder may then cycle through
the rate control sequence defined by the (RC A1, RC A2, . . . , and
RC Az) a predetermined number of times within a data frame.
Alternatively, the rate a/b non-systematic encoder may adaptively
select a new rate control sequence based on operating conditions of
the communication system in which the rate a/b non-systematic
encoder is implemented. Each of the individual RCs may be viewed as
being functionality supported by distinct encoders.
[0143] FIG. 17 is a diagram illustrating an embodiment of periodic
sequencing of a non-systematic encoder using puncturing and rate
control sequencer 1700 according to the invention. In this example
to show the periodic sequencing, a rate 4/6 non-systematic encoder
is employed. The rate control sequence in this embodiment includes
the RCs (RC A1, RC A2 RC A2 RC A1, and RC Az) having a period of 5
RCs.
[0144] The available input of this exemplary rate 4/6
non-systematic encoder is (i.sub.o, i.sub.1, i.sub.2, i.sub.3) and
the uncoded bit, and the available output is (c.sub.5, c.sub.4,
c.sub.3, c.sub.2, c.sub.1, c.sub.o) as well as the uncoded bit.
Puncturing is performed to select a predetermined sub-set of all of
the available input and output bits of the rate 4/6 non-systematic
encoder. The input cycles through the period of 5 RCs described
above. The inputs bits cycle through the following sequence
according to this particular period:
[0145] RC A1: ui.sub.0i.sub.1
[0146] RC A1: ui.sub.0i.sub.1
[0147] RC A2: 0i.sub.1
[0148] RC A2: 0i.sub.1
[0149] RC Az: ui.sub.0i.sub.1i.sub.2i.sub.3
[0150] The output bits of this period of RCs is as follows:
[0151] RC A1: uc.sub.2c.sub.1
[0152] RC A1: uc.sub.2c.sub.1
[0153] RC A2: c.sub.4c.sub.3c.sub.2c.sub.1c.sub.o
[0154] RC A2: c.sub.4c.sub.3c.sub.2c.sub.1c.sub.o
[0155] RC Az: uc.sub.3c.sub.2c.sub.1c.sub.o
[0156] Clearly, additional rate control sequences that include
different RCs may also be employed to perform and support the
functionality described herein. The generic embodiment of FIG. 17
shows how different constellations (3 bit symbols and 5 bit symbols
in this example) may be used within a single rate control sequence.
This means that various modulations, each having different numbers
of total constellation points, may be used in a single rate control
sequence.
[0157] In another embodiment of the invention, the encoder of the
FIG. 17 is implemented such that the remaining bits, output from
the encoder, may be groups to support multiple modulations. For
example, for one of the groups of output bits for one of the RCs,
the remaining output bits c.sub.4c.sub.3 are used for one
modulation (such as a QPSK or APSK type constellation and mapping
that employs 2 bits), and the other bits are c.sub.2c.sub.1c.sub.o
are used for another modulation (such as an 8 PSK type
constellation and mapping that employs 3 bits). Other variations
may also be employed as well, such as those that operate using 6
available encoded bits. In such a possible embodiment, 4 of the
bits may be used for one modulation (such as a 16 QAM or 16 APSK
type constellation and mapping that employs 4 bits), and the other
2 bits may be used for another modulation (such as a QPSK or APSK
type constellation and mapping that employs 2 bits).
[0158] FIG. 18 is a diagram illustrating a generic embodiment of
variable puncturing, constellations, and mapping using a single
encoder 1800 according to the invention. The FIG. 18 particularly
shows how encoder output bits are punctured, and how the remaining
bits are associated with one or more particular constellations and
how each of those constellations may have a unique mapping. The
control of the puncturing, the constellation, and the mapping are
all governed by the rate control sequencer 1150. Again, the rate
control sequencer 1150 may cycle through a predetermined rate
control sequence; it may adaptively select one or more new rate
control sequence based on operating conditions such as a
communication channel's SNR, bandwidth requirements based on
various user applications, or according to some other consideration
as well.
[0159] The available encoder output bits are provided to a
functional block that may employ one or more of a number of
multiple puncturing options. These puncturing options are shown
generically as puncturing #1, puncturing #2, . . . , and puncturing
#w. Each of these puncturing options is associated with one or more
constellations (shown as constellation #1, constellation #2, . . .
, and constellation #x). For example, the output bits remaining
after having performed the puncturing #1 are then associated with
the constellation #1. The output bits remaining after having
performed the puncturing #2 may then be associated with either the
constellation #1 or the constellation #x. The output bits remaining
after having performed the puncturing #w are then associated with
the constellation #2.
[0160] Each constellation is associated with one or more mappings,
shown as mapping #1, mapping #2, . . . mapping #y. As an example,
the constellation #1 is associated with more than one mapping,
namely, mapping #1, mapping #2, and mapping #y. The other
constellations may also be associated with various mappings as
well. The encoding process includes performing encoding,
puncturing, selection of a modulation (constellation and
mapping).
[0161] As mentioned above, a number of types of encoders may be
employed according to the invention, and the following examples of
encoders show just some of the possible encoder types that may be
used.
[0162] FIG. 19 is a diagram illustrating an embodiment of a rate
1/2 recursive convolutional encoder with non-systematic output 1900
that is built according to the invention. The rate is 1/2 as there
is one input information bit and two output encoded bits. The
encoder receives a single input bit and generates two encoded bits
(c.sub.1, c.sub.o). The recursive operation of the encoder in the
FIG. 19 may be viewed as follows. The input bit is selectively
summed with delayed versions of itself to generate the two encoded
bits.
[0163] This encoder circuit represents one way to encode an input
bit to generate two encoded bits. Clearly, the invention envisions
other embodiments and types of encoders as well. This particular
example of the rate 1/2 recursive convolutional encoder with
non-systematic output 1900 is used to illustrate the scalability
and extendibility of the invention across a number of encoding
schemes. This rate 1/2 recursive convolutional encoder with
non-systematic output 1900 will be used as one building block to
generate a rate 2/5 encoder as will be described below in FIG.
20.
[0164] FIG. 20 is a diagram illustrating an embodiment of a rate
2/5 prototype encoder 2000 that is built according to the
invention. Two bits are provided at a time as an input symbol
(having input bits i.sub.1i.sub.o) to the rate 2/5 prototype
encoder 2000. These two bits may be provided to the rate 2/5
prototype encoder 2000 serially, or alternatively, in a parallel
manner. The input of the rate 2/5 prototype encoder 2000 includes
both of these input bits. One of the bits of the input symbol is
provided as output of the encoder, i.sub.o, but because both input
bits i.sub.1i.sub.o are not available in the form in which they are
provided, the encoder may be viewed as a non-systematic encoder. In
certain situations as will be seen below, an uncoded bit may also
be employed during the encoding.
[0165] The two binary consecutive inputs that are provided to the
encoder may be viewed as (i.sub.0,i.sub.1). These two binary
consecutive inputs are provided to the rate 1/2 encoder of the FIG.
19 above. Two consecutive cycles are employed, by providing inputs
i.sub.o (first) and then i.sub.1 (second), to generate the
following outputs of the rate 1/2 encoder ((c.sub.0,1, c.sub.1,0)
and (c.sub.1,1, c.sub.1,0)). Three of these values are selected and
are set to be the coded bits (c.sub.1,1=c.sub.2, c.sub.1,0=c.sub.1,
c.sub.0,1=c.sub.0). The coded output bit c.sub.3 is taken as the
sum of the two binary consecutive inputs, namely i.sub.o and
i.sub.1. The final output coded bit c.sub.4 is taken as the second
of the two binary consecutive inputs, namely i.sub.o. This
particular encoder is used to perform illustration of one example
of the invention's operation within many of the embodiments
described below.
[0166] The encoding/decoding of bits put into the rate 2/5
prototype encoder 2000 may be described mathematically as follows.
We begin by establishing the following notation.
[0167] 1. S.sup.n(m, i.sub.0, i.sub.1): the next state after
inputting the symbol, i.sub.0, i.sub.1, to the rate 2/5 prototype
encoder 2000 with the current state m.
[0168] 2. S.sup.p(m, i.sub.0, i.sub.1): the previous state after
inputting the symbol, i.sub.0, i.sub.1, to the rate 2/5 prototype
encoder 2000 with the current state m.
[0169] 3. C.sup.n(m, i.sub.0, i.sub.1): the output of a selected
trellis used to perform the encoding/decoding by inputting the
symbol, i.sub.0,i.sub.1, to the rate 2/5 prototype encoder 2000
with the current state m.
[0170] 4. c.sup.p(m, i.sub.0, i.sub.1): the output of a selected
trellis used to perform the encoding/decoding by inputting the
symbol, i.sub.0,i.sub.1, to the rate 2/5 prototype encoder 2000
with the previous state m.
[0171] 5. app denotes using "a priori" probability. For example,
app.sub.0,50(1) is the app of i.sub.0=1 for the 50.sup.th symbol in
a frame of data.
[0172] 6. met denotes using metric of the index provided within the
parentheses.
[0173] It is noted that any selected trellis may be employed to do
this encoding. One particular embodiment of a trellis is described
in detail below in the FIG. 23, yet other trellises could similarly
be used without departing from the scope and spirit of the
invention.
[0174] Within many of the following notations, the use of Greek
letter and English equivalent is understood as being the same
element. For example, alpha=.alpha.; alpha.sub.--0=.alpha..sub.0;
beta=.beta.; beta.sub.--0=.beta..sub.0; and so on.
[0175] The decoding process employs forward metrics (alphas) and
backward metrics (betas), and extrinsic values according to the
trellis employed. Each of these alphas, beta, and extrinsics are
calculated as shown in the generic manner described below.
.alpha..sub.k(s)=min*.sub.(i.sub.0.sub.i.sub.1.sub.)=0, . . . ,
3[.alpha..sub.k-1(S.sup.p(s, i.sub.0,
i.sub.1))+app.sub.0,k-1(i.sub.0)+app.sub.1,k-1(i.sub.1)+met.sub.t,k-1(c.s-
up.p(s, i.sub.0, i.sub.1))]
.beta..sub.k(s)=min*.sub.(i.sub.0.sub.i.sub.1.sub.)=0, . . . ,
3[.beta..sub.k+1(S.sup.n(s, i.sub.0,
i.sub.1))+app.sub.0,k+1(i.sub.0)+app.sub.1,k+1(i.sub.1)+met.sub.t,k-1(c.s-
up.n(s, i.sub.0, i.sub.1))]
[0176] It is noted that the variable "s" identifies the trellis
state that varies from 0=000, 1=001, . . . , to 7=111.
[0177] We then calculate the following intermediate variables,
E.sub.m(s,i) and E.sub.l(s,i), before calculating the extrinsic
values (ext) that will be used to perform the final decoding.
E.sub.0(s,i)=min*.sub.j=0,1(met.sub.t,k(c.sup.n(s,i,j))+.beta..sub.k(S.su-
p.n(s,i,j))+app.sub.l,k(j)) ext.sub.0,k(i)=min*.sub.s=0, . . . ,
7{.alpha..sub.k(s)+E.sub.0(s,i)}
[0178] We also calculate the following ext.
E.sub.l(s,i)=min*.sub.j=0,1(met.sub.t,k(c.sup.n(s,j,i))+.beta..sub.k(S.su-
p.n(s,j,i))+app.sub.0,k(j)) ext.sub.l,k(i)=min*.sub.s=0, . . . ,
7{.alpha..sub.k(s)+E.sub.l(s,i)}
[0179] It is noted that the value of i (i=0 or i=1) is the possible
value for the denoted decoded bit. After performing these above
calculations, we then use the following comparisons to make
estimates of the input bits (i.sub.k,m, i.sub.k,l). .sub.0,k=0, if
we find that
ext.sub.0,k(1)+app.sub.0,k(1)>ext.sub.0,k(0)+app.sub.0,k(0)
.sub.0,k=1, if we find that
ext.sub.0,k(1)+app.sub.0,k(1)<ext.sub.0,k(0)+app.sub.0,k(0)
.sub.l,k=0, if we find that
ext.sub.l,k(1)+app.sub.l,k(1)>ext.sub.l,k(0)+app.sub.l,k(0)
.sub.l,k=1, if we find that
ext.sub.l,k(1)+app.sub.l,k(1)<ext.sub.l,k(0)+app.sub.l,k(0)
[0180] These equations show the generic applicability of how to
perform decoding of encoded bits according to one embodiment of the
invention. Specific examples are also shown below of how the
encoding/decoding may be performed according to the invention while
supporting variable code rate functionality in accordance with the
invention. It is also noted, however, that other encoders may also
be employed (besides the rate 2/5 prototype encoder 2000) without
departing from the scope and spirit of the invention.
[0181] FIG. 21 is a block diagram of a rate 2/5 systematic
prototype encoder 2100 that is built according to the invention. In
general terms, the rate 2/5 systematic prototype encoder 2100
encodes "2" input bits (shown as i.sub.0 and i.sub.1) and generates
"3" redundancy output bits (shown as c.sub.2, c.sub.1, c.sub.0) as
well as explicitly providing the input bits (i.sub.0 and i.sub.1).
In addition, one or more uncoded bits u may be provided as output
of the encoder without having undergone any encoding at all. The
rate 2/5 systematic prototype encoder 2100 may be viewed as being
just one of many possible embodiments of the rate a/b systematic
prototype encoder 1400 of the FIG. 14. It is also noted that the
total rate of the rate 2/5 systematic prototype encoder 2100 may be
modified when employing an uncoded bit; a rate of 3/6 may be
achieved when employing both input bits (i.sub.0 and i.sub.1) and
the uncoded bit as input and when performing no puncturing of any
bits at all.
[0182] FIG. 22 is a block diagram of the rate 2/5 non-systematic
prototype encoder 2000 of the FIG. 20 that is built according to
the invention. In general terms, the rate 2/5 non-systematic
prototype encoder 2000 encodes "2" input bits (shown as i.sub.0 and
i.sub.1) and generates "5" coded output bits (shown as c.sub.4,
c.sub.3, c.sub.2, c.sub.1, c.sub.0). In addition, one or more
uncoded bits u may be provided as output of the encoder without
having undergone any encoding at all. This illustration may be
viewed as being a prototype encoder from which many various types
of encoding may be performed. The rate 2/5 non-systematic prototype
encoder 2000 may be viewed as being just one of many possible
embodiments of the rate a/b non-systematic prototype encoder 1500
of the FIG. 15. It is also noted that the total rate of the rate
2/5 non-systematic prototype encoder 2200 may be modified when
employing an uncoded bit; a rate of 3/6 may be achieved when
employing the "2" input bits (shown as i.sub.0 and i.sub.1) and the
uncoded bit and when performing no puncturing of any bits at
all.
[0183] FIG. 23 is a trellis diagram of a trellis 2300 employed by
the rate 2/5 non-systematic prototype encoder 2000 of the FIG. 20
that is built according to the invention. It is noted that the
trellis 2300 is selected offline and employed for all of the
encoding/decoding in this particular embodiment. The trellis 2300
is an 8 state (3 register) trellis whose input/output trellis
transfer function is shown within the FIG. 23. Each of the inputs
is shown in symbol form of the 4 possible inputs: 0 is for
i.sub.0i.sub.1=00, 1 is for i.sub.0i.sub.1=01, 2 is for
i.sub.0i.sub.1=10, and 3 is for i.sub.0i.sub.1=11. The outputs are
shown in octal; however, only the first 5 bits are employed in this
embodiment. Again, the rate 2/5 non-systematic prototype encoder
2000 of the FIG. 20 employs the trellis 2300, so only five coded
output bits are available. It is noted that all of the metrics
according to the trellis 2300 may be represented by 16 unique
metrics. Although there are 5 available bits as the output of the
rate 2/5 non-systematic prototype encoder 2000, when considering
the number of options as being 2.sup.5=32, it is seen that this
particular trellis design may be represented with 16 distinct
metrics. Moreover, an efficient hardware implementation allows
these 16 distinct metrics to be represented with 8 distinct metric
values.
[0184] The 6.sup.th bit is simply not existent in the rate 2/5
encoder described here; the outputs may be viewed, in octal form,
as being xc.sub.4c.sub.3c.sub.2c.sub.1c.sub.0, where x represents
the unused bit. It is noted, however, that some other embodiments
(say, in a rate 2/6 encoder) may employ all 6 output bits when
performing a rate 2/6 encoder.
[0185] For example, following the operation and function of the
trellis, starting from the state of 0=000, the following
transitions may be achieved:
[0186] When the encoder is in the state 0=000, and when the input
i.sub.0i.sub.1=00=0, then the state of the encoder will transition
to state 0=000, and the output will be
xc.sub.4c.sub.3c.sub.2c.sub.1c.sub.0=x00000=0. When the encoder is
in the state 0=000, and when the input i.sub.0i.sub.1=01=1, then
the state of the encoder will transition to state 2=010, and the
output will be xc.sub.4c.sub.3c.sub.2c.sub.1c.sub.0=x01100=14. When
the encoder is in the state 0=000, and when the input
i.sub.0i.sub.1=10=2, then the state of the encoder will transition
to state 4=100, and the output will be
xc.sub.4c.sub.3c.sub.2c.sub.1c.sub.0=x11001=31. When the encoder is
in the state 0=000, and when the input i.sub.0i.sub.1=11=3, then
the state of the encoder will transition to state 6=110, and the
output will be xc.sub.4c.sub.3c.sub.2c.sub.1c.sub.0=x10101=25.
[0187] The transitions from other initial states may similarly be
followed according to the trellis 2300. It is here noted that the
trellis 2300 represents one such trellis that may be employed to
perform TTCM encoding. Other trellises may similarly be employed
without departing from the scope and spirit of the invention. The
encoding employs this trellis when performing each of the various
rate control sequences provided by the rate control sequencer 1150
to the rate 2/5 non-systematic prototype encoder 2000. As will be
seen below as well, this same trellis 2300 is also employed to
performing decoding of data for each of the various rate control
sequences provided by the rate control sequencer 1150.
[0188] FIG. 24 is a diagram illustrating the functional operation
of the non-systematic rate 2/5 encoder 2000 using puncturing and
rate control sequencer 1150 to support multiple encoders performing
various rate controls according to the invention. Here, the
non-systematic rate 2/5 encoder 2000 is implemented to perform the
functionality of multiple encoders. Puncturing is performed on the
output bits of the encoder to generate the various options of
encoded symbols that include encoded bits and/or uncoded bits. The
variable code rate functionality of the invention, shown in the
context of the non-systematic rate 2/5 encoder 2000 cycles through
a number of rate controls (that constitute a rate control
sequence--shown as a RC 0, a RC 9, and RC 1) in the FIG. 24. Each
of these RCs has a particular bandwidth efficiency. Cooperatively,
the bandwidth efficiencies of the individual RCs (RC 0, a RC 9, and
RC 1) define the rate control sequence provide an average bandwidth
efficiency across this entire rate control sequence.
[0189] The rate control sequencer 1150 may cycle through a
predetermined rate control sequence; it may adaptively select one
or more new rate control sequences based on operating conditions
such as a communication channel's SNR, bandwidth requirements based
on various user applications, or according to some other
consideration as well.
[0190] The rate control sequence as illustrated within the example
embodiment shown in the FIG. 24 may be described as follows:
[0191] Within the non-systematic rate 2/5 encoder 2000 as
implemented according to RC 0, a rate 2/3 encoder is achieved. Two
information bits (i.sub.0 and i.sub.1) are input to the
non-systematic rate 2/5 encoder 2000. The output of encoding
punctures all of the coded bits except for c.sub.3c.sub.2c.sub.1;
these remaining bits are then used to generate a 3 bit symbol that
will be mapped according to a 3 bit symbol modulation
(constellation and mapping) as defined by RC 0.
[0192] Within the encoder as implemented according to RC 9, a rate
1/3 encoder is achieved. One information bits (i.sub.1) is input to
the encoder. The output of the encoder punctures all of the coded
bits except for c.sub.2c.sub.1c.sub.0; these remaining bits are
then used to generate a 3 bit symbol that will be mapped according
to a 3 bit symbol modulation (constellation and mapping) as defined
by RC 9.
[0193] Within the encoder as implemented according to RC 1, a rate
3/3 encoder is achieved. Two information bits (i.sub.0 and i.sub.1)
and one uncoded bit u are input to the encoder. The output of the
encoder punctures all of the coded bits except for c.sub.4c.sub.3
and the uncoded bit u; these remaining bits and the uncoded bit
(uc.sub.4c.sub.3) are then used to generate a 3 bit symbol that
will be mapped according to a 3 bit symbol modulation
(constellation and mapping) as defined by RC A1.
[0194] The non-systematic rate 2/5 encoder 2000 may then cycle
through the rate control sequence defined by the (RC 0, a RC 9, and
RC 1) a predetermined number of times within a data frame.
Alternatively, the non-systematic rate 2/5 encoder 2000 may
adaptively select a new rate control sequence based on operating
conditions of the communication system in which the non-systematic
rate 2/5 encoder 2000 is implemented. Each of the individual RCs
may be viewed as being functionality supported by distinct
encoders, yet a single device is operable to support all of these
encoders according to the variable code rate functionality
described herein. The above-referenced comments are also applicable
to the cases presented below in the FIGS. 25 and 26.
[0195] FIG. 25 shows additional rate controls supported by the
non-systematic rate 2/5 encoder 2000 of the FIG. 20. Within the
non-systematic rate 2/5 encoder 2000 as implemented according to
RCs 7,A&D, a rate 1/2 encoder is achieved. One information bit
(i.sub.1) is input to the non-systematic rate 2/5 encoder 2000. The
output of encoding punctures all of the coded bits except for
c.sub.2c.sub.1; these remaining bits are then used to generate a 2
bit symbol that will be mapped according to the appropriate 2 bit
symbol modulation (constellation and mapping) as defined by one of
the RCs 7,A&D.
[0196] Within the encoder as implemented according to RC 8, a rate
0/2 encoder is achieved. No information bits are input to the
encoder. The output of the encoder punctures all of the coded bits
except for c.sub.2c.sub.0; these remaining bits are then used to
generate a 2 bit symbol that will be mapped according to a 2 bit
symbol modulation (constellation and mapping) as defined by RC
8.
[0197] Within the encoder as implemented according to RCs
2,3,6,C,E&F, a rate 2/2 encoder is achieved. Two information
bits (i.sub.0 and i.sub.1) are input to the encoder. The output of
the encoder punctures all of the coded bits except for
c.sub.4c.sub.3; these remaining bits (c.sub.4c.sub.3) are then used
to generate a 2 bit symbol that will be mapped according to the
appropriate 2 bit symbol modulation (constellation and mapping) as
defined by one of the RCs 2,3,6,C,E&F.
[0198] FIG. 26 shows yet additional rate controls supported by the
non-systematic rate 2/5 encoder 2000 of the FIG. 20. Within the
non-systematic rate 2/5 encoder 2000 as implemented according to
RCs 4&B, a rate 3/4 encoder is achieved. Two information bits
(i.sub.0 and i.sub.1) and one uncoded bit u are input to the
non-systematic rate 2/5 encoder 2000. The output of encoding
punctures all of the coded bits except for c.sub.3c.sub.2c.sub.1
and the uncoded bit u, leaving uc.sub.3c.sub.2c.sub.1; these
remaining bits are then used to generate a 4 bit symbol that will
be mapped according to the appropriate 4 bit symbol modulation
(constellation and mapping) as defined one of the RCs 4&B.
[0199] Within the non-systematic rate 2/5 encoder 2000 as
implemented according to RC G, a rate 2/4 encoder is achieved. Two
information bits (i.sub.0 and i.sub.1) are input to the
non-systematic rate 2/5 encoder 2000. The output of encoding
punctures all of the coded bits except for
c.sub.3c.sub.2c.sub.1c.sub.0; these remaining bits are then used to
generate a 4 bit symbol that will be mapped according to a 4 bit
symbol modulation (constellation and mapping) as defined by RC
G.
[0200] Within the non-systematic rate 2/5 encoder 2000 as
implemented according to RC 5, a rate 2/4 encoder is achieved. One
information bit (i.sub.1) and one uncoded bit u are input to the
non-systematic rate 2/5 encoder 2000. The output of encoding
punctures all of the coded bits except for c.sub.2c.sub.1c.sub.0
and the uncoded bit u, leaving uc.sub.2c.sub.1c.sub.0; these
remaining bits are then used to generate a 4 bit symbol that will
be mapped according to a 4 bit symbol modulation (constellation and
mapping) as defined by RC 5.
[0201] FIG. 27 is a diagram illustrating an embodiment of periodic
sequencing of a non-systematic rate 2/5 encoder 2000 using
puncturing and rate control sequencer 1150 according to the
invention. The rate control sequence in this embodiment includes
the RCs (RC 0, RC 9, and RC 9) having a period of 3 RCs.
[0202] The available input of this non-systematic rate 2/5 encoder
2000 is (i.sub.oi.sub.1) as well as the uncoded bit, and the
available output is (c.sub.4c.sub.3c.sub.2c.sub.1c.sub.o) as well
as the uncoded bit u, leaving the possible output to be
uc.sub.4c.sub.3c.sub.2c.sub.1c.sub.o. Puncturing is performed to
select a predetermined sub-set of all of the available input and
output bits of this non-systematic rate 2/5 encoder 2000. The input
cycles through the period of 3 RCs described above. The inputs bits
cycle through the following sequence according to this particular
period:
[0203] RC 0: i.sub.0i.sub.1;
[0204] RC 9: 0i.sub.1;
[0205] RC 9: 0i.sub.1;
[0206] The output bits of this period of RCs is as follows:
[0207] RC 0: c.sub.3c.sub.2c.sub.1;
[0208] RC 9: c.sub.2c.sub.1c.sub.0;
[0209] RC 9: c.sub.2c.sub.1c.sub.0.
[0210] Clearly, additional rate control sequences that include
different RCs may also be employed to perform and support the
functionality described herein.
[0211] FIG. 28 shows additional periodic sequencing of rate
controls supported by the non-systematic rate 2/5 encoder 2000 of
the FIG. 20. The rate control sequence in this embodiment includes
the RCs (RC D, RC 8, RC D, RC D, RC D, and RC 8) having a period of
6 RCs. Within the FIG. 28, the inputs bits cycle through the
following sequence according to this particular period:
[0212] RC D: 0i.sub.1
[0213] RC 8: 00
[0214] RC D: 0i.sub.1
[0215] RC D: 0i.sub.1
[0216] RC D: 0i.sub.1
[0217] RC 8: 00
[0218] The output bits of this period of RCs is as follows:
[0219] RC D: c.sub.2c.sub.1
[0220] RC 8: c.sub.2c.sub.0
[0221] RC D: c.sub.2c.sub.1
[0222] RC D: c.sub.2c.sub.1
[0223] RC D: c.sub.2c.sub.1
[0224] RC 8: c.sub.2c.sub.0
[0225] FIG. 29 shows yet additional periodic sequencing of rate
controls supported by the non-systematic rate 2/5 encoder 2000 of
the FIG. 20. The rate control sequence in this embodiment includes
the RCs (RC B, RC 5, RC B, RC 5, and RC 5) having a period of 5
RCs. Within the FIG. 29, the inputs bits cycle through the
following sequence according to this particular period:
[0226] RC B: ui.sub.0i.sub.1
[0227] RC 5: u0i.sub.1
[0228] RC B: ui.sub.0i.sub.1
[0229] RC 5: u0i.sub.1
[0230] RC 5: u0i.sub.1
[0231] The output bits of this period of RCs is as follows:
[0232] RC B: uc.sub.3c.sub.2c.sub.1
[0233] RC 5: uc.sub.2c.sub.1c.sub.0
[0234] RC B: uc.sub.3c.sub.2c.sub.1
[0235] RC 5: uc.sub.2c.sub.1c.sub.0
[0236] RC 5: uc.sub.2c.sub.1c.sub.0
[0237] FIG. 30 shows yet additional periodic sequencing of rate
controls supported by the non-systematic rate 2/5 encoder 2000 of
the FIG. 20. The rate control sequence in this embodiment includes
the RCs (RC B, RC 4, RC 4, RC 4, RC B, RC B, and RC 4) having a
period of 7 RCs. Within the FIG. 30, the inputs bits cycle through
the following sequence according to this particular period:
[0238] RC B: ui.sub.0i.sub.1
[0239] RC 4: ui.sub.0i.sub.1
[0240] RC 4: ui.sub.0i.sub.1
[0241] RC 4: ui.sub.0i.sub.1
[0242] RC B: ui.sub.0i.sub.1
[0243] RC B: ui.sub.0i.sub.1
[0244] RC 4: ui.sub.0i.sub.1
[0245] The output bits of this period of RCs is as follows:
[0246]
[0247] RC B: uc.sub.3c.sub.2c.sub.1
[0248] RC 4: uc.sub.3c.sub.2c.sub.1
[0249] RC 4: uc.sub.3c.sub.2c.sub.1
[0250] RC 4: uc.sub.3c.sub.2c.sub.1
[0251] RC B: uc.sub.3c.sub.2c.sub.1
[0252] RC B: uc.sub.3c.sub.2c.sub.1
[0253] RC 4: uc.sub.3c.sub.2c.sub.1
[0254] The FIG. 30 shows one of the many possible examples of where
different modulations are employed within the same rate control
sequence. This particular example shows the mixing of 16 APSK and
16 QAM modulations. Each of the modulations of these two RCs 4 and
B employs different constellations altogether. It is understood
that other modulations may also be mixed together within a rate
control sequence without departing from the scope and spirit of the
invention.
[0255] The FIGS. 31, 32, 33, 34, 35 and 36 are examples of some of
the possible modulations (constellations and mappings) that may be
employed in accordance with the invention. It is noted that any
number and types of modulations may be used (provided there are
sufficient bits available in the encoding). Some examples of
modulations include BPSK (Binary Phase Shift Keying), QPSK
(Quadrature Phase Shift Keying), QAM (Quadrature Amplitude
Modulation), APSK (Amplitude Phase Shift Keying), and variants
thereof including 8 PSK, and higher orders of PSK, 16 QAM, and
other higher orders of QAM (such as 64 QAM, 256 QAM, 1024 QAM),
among other types of modulation.
[0256] FIG. 31 is a constellation diagram illustrating an
embodiment of rate control governed mapping to 8 PSK constellations
according to the invention. The FIG. 31 shows modulations
(constellations and mappings) that may be performed according to
the 3 bit symbols generated during encoding and puncturing.
Depending on the RCs employed within a rate control sequence, when
an 8 PSK modulation is selected, then one of these appropriate
mappings may be selected. In one embodiment, these three
modulations and their respective mappings are used to perform the
final symbol mapping. The non-systematic rate 2/5 encoder 2000
employs these modulations (constellations and their mappings) when
employing the RCs (RC 0, RC 9, and RC 1). It is noted that these
RCs are exemplary and that other 3 bit symbol modulations and
different mappings of those 3 bit symbols modulations may also be
employed without departing from the scope and spirit of the
invention.
[0257] FIGS. 32, 33, and 34 are constellation diagrams illustrating
embodiments of rate control governed mapping to QPSK constellations
according to the invention. These FIGS. 32, 33, and 34 show
modulations (constellations and mappings) that may be performed
according to the 2 bit symbols generated during encoding and
puncturing. It is noted that a variety of QPSK modulations may be
employed. The RCs 3,2,A within the FIG. 33 show modulations whose
constellations points are titled with respect to the I,Q axes. The
RCs C,F,&7 within the FIG. 34 show modulations whose
constellations points have different distances from the origin of
the I,Q plane. A variety of modulations may performed according to
QPSK, including embodiments where the constellation points align
along the I,Q axes themselves and those whose constellation points
are not equidistantly spaces with respect to the origin of the I,Q
plane. These statements are also true for the other modulations
employed as well. The invention envisions any number of modulations
without departing from the scope and spirit of the invention.
[0258] FIG. 35 is a constellation diagram illustrating an
embodiment of rate control governed mapping to a 16 QAM
constellation according to the invention. The FIG. 35 shows the
modulation for RC 4 that corresponds to a 16 QAM constellation
having a particular mapping.
[0259] FIG. 36 is a constellation diagram illustrating an
embodiment of rate control governed mapping to 16 APSK
constellations according to the invention. The FIG. 36 shows the
modulations for RCs G,5&B that corresponds to a 16 APSK
constellation having a particular mapping.
[0260] The following table shows some examples of different rate
control sequences that may be supported by the non-systematic rate
2/5 encoder 2000 and the rate control sequencer 1150. These are
exemplary, and variations thereof may be implemented without
departing from the scope and spirit of the invention. For example,
other rate control sequence may also be determined to operate
within a given bandwidth of a communication channel. In addition,
it is also noted that the particular order of the RCs within the
following table may also be permutated without departing from the
scope and spirit of the invention. However, this permutation of the
RCs within a rate control sequence may affect performance in some
cases.
[0261] This table shows embodiments of how to generate various rate
control sequences, according to various bandwidth efficiencies and
periods, using the RCs described within the FIGS. 31, 32, 33, 34,
35 and 36. TABLE-US-00001 Bandwidth efficiency Constellation
(bits/second/Hz) Rate control sequence period 8 PSK 1.3333 (4/3)
099 3 1.5 (3/2) 09 2 1.6 (8/5) 00909 5 1.6667 (5/3) 009 3 1.7143
(12/7) 0009009 7 1.75 (7/4) 0009 4 2 0 1 2.1 (21/10) 0000000001 10
2.2 (11/5) 00001 5 2.25 (9/4) 0001 4 2.3 (23/10) 0001001001 10 2.4
(12/5) 00101 5 2.5 (5/2) 01 2 QPSK 0.6667 (2/3) D8DDD8 6 1 D 1
1.3333 (4/3) DDE 3 1.5 (3/2) DDEE 4 1.6 (8/5) DEE DEE DEE D 10
1.6667 (5/3) DEEEED 6 1.7143 (12/7) DDEEEDDEEEEEEEEEDDEEE 21 1.75
(7/4) DDEEEEEE 8 1.7778 (16/9) DDEEEEEEE 9 1.8 (9/5) EEDEE 5 1.8182
(20/11) EEEEEDEEEED 11 1.8333 (11/6) EEDEEEEEEDEE 12 1.8462 (24/13)
DEEDEEEEEEEEE 13 1.8571 (13/7) EDDEEEEEEEEEEDEEEEEEE 21 16 QAM 3 4
1 16 APSK 3 B 1 2.8 (14/5) BBBB5 5 2.7 (27/10) BBB5BB5BB5 10 2.6
(13/5) BB5B5 5 2.5 (5/2) B5 2 2.4 (12/5) B5B55 5 2.3 (23/10)
B555B55B55 10 2.25 (9/4) B555 4 2.2 (11/5) B5555 5 2.1 (21/10)
B555555555 10 2 5 1
[0262] FIG. 37 is a diagram illustrating an embodiment of variable
puncturing, constellations, and mapping using the single
non-systematic rate 2/5 encoder 2000 according to the invention.
The FIG. 37 particularly shows how encoder output bits are
punctured, and how the remaining bits are associated with one or
more particular constellations and how each of those constellations
may have a unique mapping. The control of the puncturing, the
constellations, and the mapping are all governed by the rate
control sequencer 1150. The rate control sequencer 1150 may cycle
through a predetermined rate control sequence; it may adaptively
select one or more new rate control sequence based on operating
conditions such as a communication channel's SNR, bandwidth
requirements based on various user applications, or according to
some other consideration as well.
[0263] The available encoder output bits are provided to a
functional block that may employ one or more of a number of
multiple puncturing options. In this embodiment, these puncturing
options are shown as puncturing for the following RCs:
0,9,1,8,2,3,6,C,E,F,7,A,D,4,B,5&G. Each of these puncturing
options is associated with one or more constellations (the
constellations being of the form of 8 PSK, QPSK, 16 QAM, and 16
APSK).
[0264] In this embodiment, the output bits remaining after having
performed the puncturing for RCs 0, 9, and 1 are then associated
with the 8 PSK constellation. The output bits remaining after
having performed the puncturing for RCs 8,2,3,6,C,E,F,7,A&D are
then associated with the QPSK constellation. The output bits
remaining after having performed the puncturing for RC 4 are then
associated with the 16 QAM modulation. The output bits remaining
after having performed the puncturing for RCs 4,B,5&G are then
associated with the 16 APSK constellation.
[0265] The RC for each particular puncturing is not only associated
with a constellation, but also with a mapping for that
constellation. For example, even though each of the RCs 0, 9, and 1
is associated with the 8 PSK constellation, each of them has a
unique mapping. Similarly, even though each of the
8,2,3,6,C,E,F,7,A&D is associated with the QPSK modulation,
each of them has a unique mapping. Similarly, even though each of
the RCs B,5,&G is associated with the 16 APSK modulation, each
of them has a unique mapping.
[0266] FIG. 38 is a system diagram illustrating an embodiment of a
TTCM decoder system 3800 that is built according to the invention.
A received signal is provided to an I,Q extraction functional block
that extracts the I,Q (in-phase and quadrature) components from the
received signal that are mapped according to a RC as determined by
the rate control sequencer 1150. This may be viewed as being
receiver pre-processing. The I,Q is then mapped according to the
modulation's appropriate constellation and mapping. Then, the
mapped I,Q is passed to a metric generator 3733 that also receives
the RC input from the rate control sequencer 1150. The metric
generator 3733 generates the appropriate metrics that are measured
from the received I,Q to the constellation points within the
modulation's appropriate constellation and mapping; the metrics are
indexed by the mapping of the constellation points within the
modulation; these metrics may be viewed as being the scaled
Euclidian distances from the location of the actual received symbol
to the expected constellation point locations within the
modulation.
[0267] We then compare the metric associated with uncoded bit (u=0)
with the metric associated with uncoded bit (u=1), and we select
the smaller metric value. The smaller metric value is deemed a
higher likelihood than the larger metric value according to this
embodiment's convention. We also select value of u based on which
metric has the smaller value. We select the possible value of the
uncoded bit u to be 1 or 0 as determined by which of the associated
metrics has the smaller value (metric associated with uncoded bit
(u=0) or the metric associated with uncoded bit (u=1)). In certain
embodiments, we may perform a min* operation that includes a
logarithmic correction in selecting the smaller metric.
Alternatively, we may perform a max* operation that includes a
logarithmic correction in selecting the smaller metric. It is noted
that the various embodiments of the invention may be implemented
using the max* operations in lieu of the min* operation when
preferred in a given implementation.
[0268] The min* calculation may be expressed as follows: min*(A,
B)=min(A, B)-ln(1+e.sup.-|A-B|) The max* calculation may be
expressed as follows: max*(A, B)=max(A, B)+ln(1+e.sup.-|A-B|)
[0269] As an example of this operation, let us assume that we are
using RC 5, whose punctured encoder output is in the form of
uc.sub.2c.sub.1c.sub.0. We then set u=1 and then u=0 for every
combination (looking at c.sub.2c.sub.1c.sub.0=111 as an example),
so we deal with the two possible values for
uc.sub.2c.sub.1c.sub.0=0111 and uc.sub.2c.sub.1c.sub.0=1111. We
then compare the location of the received symbol, as mapped within
the constellation, to the two constellation points indexed by 0111
and 1111. We then select from these two constellation points
indexed by 0111 and 1111 based on which one has the smaller valued
metric. So, in the RC 5 example used here, we reduce the total
number of 16 metrics down to 8. We then store these 8 metric values
and 8 possible uncoded bit values (indexed by the metrics indices
for each symbol in a received frame), for subsequent use in
decoding the uncoded bit after we have decoded the input bits,
i.sub.0i.sub.1. After we perform decoding of the input bits,
i.sub.0i.sub.1, then we will know with certainty what the bits
c.sub.2c.sub.1c.sub.0 are, and then we may directly determine the
uncoded bit value u based on these 8 possible uncoded bit values
that we have stored.
[0270] Continuing on with the decoding process and functionality,
the metrics that are calculated by the metric generator 3733 are
then provided to a top (even) SISO 3711 and simultaneously to a
bottom (odd) SISO 3712. Each of these SISOs 3711 and 3712
calculates forward metrics (alphas) and backward metrics (betas),
and extrinsic values according to the trellis employed (such as the
trellis 2300). The calculation of exactly how to calculate these
alphas, betas, and extrinsics according to the trellis is performed
within the TTCM decoder 122. These alphas, betas, and extrinsics
are all calculated for each symbol within a frame that is to be
decoded. These calculations of alphas, betas, and extrinsics are
all based on the trellis and according to the RC provided by the RC
input from the rate control sequencer 1150. Starting with the top
SISO 3711, after the extrinsic values have been calculated, they
are passed to an interleaver 3721 after which it is passed to the
bottom SISO 3712 as "a priori probability" (app) information.
Similarly, after extrinsic values have been calculated within the
bottom SISO 3712, they are passed to an interleaver 3722 after
which it is passed to the top SISO 3711 as "a priori probability"
(app) information. It is noted that a single decoding iteration,
within the iterative decoding process of the TTCM decoder system
3800 consists of performing two SISO operations; that is to say,
the iterative decoding process must pass through both the top
(even) SISO 3711 and through the bottom (odd) SISO 3712.
[0271] After a significant level of confidence has been achieved
and a solution is being converged upon, or after a predetermined
number of decoding iterations have been performed, then the output
from the bottom (odd) SISO 3712 is passed as output to an output
processor 3730. The operation of the SISOs 3711 and 3712 may
generally be referred to as calculating soft symbol decisions of
the symbol contained within the received symbol. These soft symbol
decisions may be performed on a true bit level in certain
embodiments. The output processor 3730 uses these soft symbol
decisions to generate hard symbol decisions for the input bits
i.sub.0i.sub.1 of the input symbol and to provide decoded output
data.
[0272] Moreover, in the situation where we have uncoded bits u that
result from the coding of the input bits, i.sub.0i.sub.1, we then
also need to use as many as 8 possible uncoded bit values (indexed
by the metrics indices), so that we can directly determine the
value of the uncoded bit. Even greater detail is provided below in
the discussion associated with FIG. 43 that continues on with the
example embodiment of RC 5.
[0273] It is also noted that the app sequence for the top (even)
SISO 3711 must be initialized before beginning the iterative
decoding. The notation for the app sequence app[i][j][k] is as
follows:
[0274] 1. i represents the possible binary value of the estimated
bit
[0275] 2. The positions of the estimated bit are denoted as
follows: (j=0 refers the first bit into the encoder and j=1 refers
the second bit into the encoder)
[0276] 3. k is the index of the symbol's location within the data
block (or frame).
[0277] More specifically, k represents the symbol index of the
symbols in a frame of data,j is the bit index (j=0 for bit i.sub.1
and j=1 for bit i.sub.0), and i is the bit value (i=0 or 1). For
example, app[1][0][50] represents the app for bit i.sub.1 of the
50.sup.th symbol being a value of 1.
[0278] At least two ways to initialize app[i][j][k] are described
below:
[0279] 1. app[i][j][k]=0.0, i,j,.epsilon.{0,1}, k .epsilon.{0, . .
. , N-1}. Each and every TTCM coding, using any of the possible
combination of RCs for a rate control sequence may use this
initialization.
[0280] 2. The TTCM coding with RC sequence 8 can have different
initialization defined as follows. [0281] app[0][1][k]=0.0 [0282]
app[1][1][k]=MAX, for all possible k. [0283] app[0][0][k]=0.0
[0284] For the sequence app[0][0][k], we may first define the
sequence based on the rate control sequence using the intermediate
variable pP and pP* (which denotes the interleaved version of pP).
[0285] pP[1][0][k]=MAX for RC 8 [0286] pP[1][0][k]=0.0
otherwise
[0287] Then, we interleave this sequence with de-interleave
.pi..sup.-1 is employed to generate the sequence pP*[1][0][k].
Finally, we define the initial app[1][0][k] as follows: [0288]
app[1][0][k]=pP[1][0][k] if k mod2=0 [0289]
app[1][0][k]=pP*[1][0][k] if k mod2=1
[0290] Moreover, by using the interleaving .pi., we can directly
define the app[1][0][k] as follows: [0291] app[1][1][k]=MAX if RC
[{circumflex over (.pi.)}(k)]=8 [0292] app[1][0][k]=0.0
otherwise
[0293] Further detail of the TTCM decoding functionality and
operation is provided within several of the following Figures.
[0294] FIG. 39 is a system diagram illustrating an embodiment of an
alternative TTCM decoder system 3900 that recycles a single SISO
according to the invention. The alternative TTCM decoder system
3900 receives as input the I,Q from a received signal. Similar to
the embodiment of the FIG. 34, an I,Q extraction functional block
may also be employed to extract these I,Q inputs within the FIG. 39
as well when performing receiver pre-processing. A ping pong
buffer, employing two input buffers, is employed for efficient
buffering of the I,Q inputs. The I,Q inputs are then passed to the
metric generator 3733. The functionality of the metric generator
3733 may be similar in both the FIG. 38 and the FIG. 39.
[0295] The output of the metric generator 3733 is passed to the
single SISO; the information necessary to perform decoding of any
possible uncoded bits will be passed to the output processor 3730.
The SISO calculates forward metrics (alphas), backward metrics
(betas), and extrinsic values (exts) according to the trellis
employed (such as the trellis 2300) and provides them to a
functional block that is operable to perform both interleaving and
de-interleaving (depending upon which SISO operation is being
performed). The output of the interleaver/de-interleaver functional
block is passed back to the SISO as app.
[0296] Similar to the embodiment of FIG. 38, it is noted that a
single decoding iteration, within the iterative decoding process of
the alternative TTCM decoder system 3900 consists of performing two
SISO operations; that is to say, the iterative decoding process
must pass through both the SISO once (when the SISO performs the
top SISO functionality) and through the SISO again (when the SISO
performs the bottom SISO functionality).
[0297] After a significant level of confidence for the soft symbol
decisions within the SISO have been achieved and a solution is
being converged upon, or after a predetermined number of decoding
iterations have been performed, then the output from the SISO is
passed as output to the output processor 3730. These soft symbol
decisions may also be performed on a true bit level in certain
embodiments. The output processor 3730 uses these soft symbol
decisions to generate hard symbol decisions and to provide decoded
output data. It is also noted that a similar app initialization of
the FIG. 38 may be used within the FIG. 39.
[0298] FIG. 40 is a diagram illustrating an embodiment of I,Q
extraction that is performed according to the invention. A received
symbol, having a magnitude and phase is provided to an I,Q
extraction block. This symbol (or signal) is mapped in a two
dimensional space such that an in-phase and a quadrature component.
This in-phase measurement and the quadrature component are provided
as output from the I,Q extraction functional block.
[0299] FIG. 41 is a diagram illustrating an embodiment of received
I,Q mapping performed based on RC according to the invention. After
the I,Qs are provided, then according to the RC provided by the
rate control sequencer 1150, the received I,Q are mapped according
to one of the modulation's constellations corresponding to the RC.
Then, after the appropriate constellation has been selected, and
the mapping has been determined based on the RC of the rate control
sequence, the I,Q is mapped to a symbol in the appropriate
modulation (with its particular constellation and mapping).
Afterwards, a mapped symbol is provided as output from the FIG.
40.
[0300] FIG. 42 is a diagram illustrating an embodiment of metric
calculation performed by a metric generator 3733 according to the
invention. A specific example is provided in the FIG. 42 using the
RC 9, and it will then be understood how the metric calculation is
performed for the other various modulations (constellations and
mappings). The metric calculation may be performed in a similar
manner in the other rate control sequences with their respective
RCs.
[0301] The received symbol is mapped within this modulation
(constellation and mapping). Then, the metric (scaled Euclidian
distance) to each of the constellation points, from the received
symbol, is calculated and indexed according to the mapping of the
respective constellation points. This distance corresponds to the
calculation in the metric generator that may be performed as
follows: Metric(Ux2x1x0)=1/(2sigma
.sup.2)*[(Rx.sub.--I-I_Coef).sup.2+(Rx.sub.--Q-Q_Coef).sup.2]
[0302] Here, the scaling of the distance by [1/(2sigma .sup.2)]
(where sigma is the standard deviation of the normalized noise of
the received symbol) accommodates for the normalized noise of the
received symbol in determining this distance. The I_Coef and the
Q_Coef are the expected locations (in terms of I,Q) at which the
received symbol is expected to be mapped (constellation point
location), and Rx_I and Rx_Q are the actual locations at which the
received symbol is mapped.
[0303] For example, the metric corresponds to the distance from the
received symbol to the constellation point associated with the
symbol 1=(001 in binary) is shown as M(1); . . . ; and the metric
corresponding to the distance from the received symbol to the
constellation point associated with the symbol 3=(011 in binary) is
shown as M(3). These metrics are output from the metric generator
3733.
[0304] FIG. 43 is a functional block diagram illustrating an
embodiment of metric mapping functionality that is performed
according to the invention. The received symbol metrics (received
metric=M.sub.r), indexed according to the modulation (constellation
and mapping) according to the RC (as provided by the rate control
sequencer 1150), are then passed to a functional block that
transforms these received metrics to trellis metrics (trellis
metric=M.sub.t). These trellis metrics are then used to calculate
the alphas, betas, and extrinsics within the SISO. These alphas,
betas, and extrinsics may be calculated using a min* approach
according to the invention. Again, a max* approach may
alternatively be used.
[0305] From the received I,Q values, a 2-bit metric for QPSK, a
3-bit metric M.sub.r(x.sub.2x.sub.1x.sub.0) for 8-PSK, and a 4-bit
metric M.sub.r(x.sub.3x.sub.2x.sub.1x.sub.0) for 16-QAM and 16-APSK
can be computed. With either of these metrics, we may form a 3-bit
metric M.sub.t that is to be sent to the SISO decoder with possible
uncoded bit information. However, metric used in the SISO decoder
depends on the trellis output that is a 5-bit symbol in general
(using the rate 2/5 prototype encoder 2000). Some additional
intelligence must be employed for proper assigning of these metrics
to the trellis.
[0306] In order to have a universal decoder for all the RC number,
some transforms from the received metric
M.sub.r(x.sub.3x.sub.2x.sub.1x.sub.0) to
M.sub.s(x.sub.2x.sub.1x.sub.0) and from the trellis metric
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0) to M.sub.s(abc) need
to be introduced.
[0307] As an example, the transformation of the follow RCs are
shown below.
[0308] For RC 0: the received metric M.sub.r(x.sub.2x.sub.1x.sub.0)
is mapped to an intermediate metric M.sub.s(c.sub.3c.sub.2c.sub.1).
This intermediate metric M.sub.s(c.sub.3c.sub.2c.sub.1) is mapped
to the trellis metric M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0).
The last three bits of the intermediate metric
M.sub.s(c.sub.3c.sub.2c.sub.1) are mapped to the four possible
trellis metrics M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0) where
the bits and may be treated as don't care. For example, the four
metrics M.sub.t(0c.sub.3c.sub.2c.sub.10),
M.sub.t(0c.sub.3c.sub.2c.sub.11), M.sub.t(1c.sub.3c.sub.2c.sub.10),
and M.sub.t(1c.sub.3c.sub.2c.sub.11) are all mapped to have the
very same value for the metrics within the trellis 2300.
[0309] These operations may be described below as follows:
M.sub.s(x.sub.2x.sub.1x.sub.0)=M.sub.r(x.sub.2x.sub.1x.sub.0)
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.3c.sub.2c.sub.-
1)
[0310] For RC 1: the received metric M.sub.r(ux.sub.1x.sub.0) that
includes an uncoded bit is initially mapped using a min* operation
to generate the following intermediate received metric {overscore
(M)}.sub.r(x.sub.1x.sub.0)=min*{M.sub.r(0x.sub.1x.sub.0),M.sub.r(1x.sub.1-
x.sub.0)}. The uncoded bit is dealt with via the min* operation to
deal with the both of the possible values by which u may take.
[0311] These operations may be described below as follows:
{overscore
(M)}.sub.r(x.sub.1x.sub.0)=min*{M.sub.r(0x.sub.1x.sub.0),M.sub.r(1x.sub.1-
x.sub.0)}
M.sub.s(x.sub.2x.sub.10)=M.sub.s(x.sub.2x.sub.11)={overscore
(M)}.sub.r(x.sub.2x.sub.1)
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.4c.sub.3c.sub.-
2)
[0312] Now, each of the following metrics would all be assigned the
same value according to the trellis.
M.sub.t(c.sub.4c.sub.3c.sub.200)=M.sub.t(c.sub.4c.sub.3c.sub.201)=M.sub.t-
(c.sub.4c.sub.3c.sub.210)=M.sub.t(c.sub.4c.sub.3c.sub.211)
[0313] The possible value of the uncoded bit indexed by
(x.sub.1x.sub.0) will be 0 if
M.sub.r(0x.sub.1x.sub.0)<M.sub.r(1x.sub.1x.sub.0), otherwise the
possible value of the uncoded bit indexed by (x.sub.1x.sub.0) will
be 1 if
M.sub.r(0x.sub.1x.sub.0).gtoreq.M.sub.r(1x.sub.1x.sub.0).
[0314] For RCs 2,3,6,C&E: for the received metric
M.sub.r(x.sub.2x.sub.1), the following transformations are
performed.
M.sub.s(x.sub.2x.sub.10)=M.sub.s(x.sub.2x.sub.11)=M.sub.r(x.sub.2x.sub.1)
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.4c.sub.3c.sub-
.2)
[0315] Now, each of the following metrics would all be assigned the
same value according to the trellis.
M.sub.t(c.sub.4c.sub.3c.sub.200)=M.sub.t(c.sub.4c.sub.3c.sub.201)=M.sub.t-
(c.sub.4c.sub.3c.sub.210)=M.sub.t(c.sub.4c.sub.3c.sub.211)
[0316] For RCs 4&B: for the received metric
M.sub.r(ux.sub.2x.sub.1x.sub.0) that includes an uncoded bit, the
min* operation is again employed. The following transformations are
performed.
M.sub.s(x.sub.2x.sub.1x.sub.0)=min*{M.sub.r(0x.sub.2x.sub.1x.sub.0),M.su-
b.r(1x.sub.2x.sub.1x.sub.0)}
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.3c.sub.2c.sub.-
1)
[0317] Now, each of the following metrics would all be assigned the
same value according to the trellis.
M.sub.t(0c.sub.3c.sub.2c.sub.10),=M.sub.t(0c.sub.3c.sub.2c.sub.11)=M.sub.-
t(1c.sub.3c.sub.2c.sub.10)=M.sub.t(1c.sub.3c.sub.2c.sub.11)
[0318] The possible value of the uncoded bit indexed by
(x.sub.2x.sub.1x.sub.0) will be 0 if
M.sub.r(0x.sub.2x.sub.1x.sub.0)<M.sub.r(1x.sub.2x.sub.1x.sub.0),
otherwise the possible value of the uncoded bit indexed by
(x.sub.2x.sub.1x.sub.0) will be 1 if
M.sub.r(0x.sub.2x.sub.1x.sub.0).gtoreq.M.sub.r(1x.sub.2x.sub.1x.sub.0).
[0319] For RCs 7,A&D: for the received metric
M.sub.r(x.sub.1x.sub.0), the following transformations are
performed. M.sub.s(x.sub.2x.sub.1x.sub.0)=M.sub.r(x.sub.1x.sub.0),
when x.sub.2=0
[0320] M.sub.s(.sub.2x.sub.1x.sub.0)=MAX, when x.sub.2=1. MAX is
the maximum metric that is employed in the decoding system.
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.4c.sub.2c.sub.-
1)
[0321] Now, each of the following metrics would all be assigned the
same value according to the trellis.
M.sub.t(c.sub.40c.sub.2c.sub.10)=M.sub.t(c.sub.40c.sub.2c.sub.11)=M.sub.t-
(c.sub.41c.sub.2c.sub.10)=M.sub.t(c.sub.41c.sub.2c.sub.11)
[0322] For RC 9: for the received metric
M.sub.r(x.sub.2x.sub.1x.sub.0), the following transformations are
performed.
M.sub.s(x.sub.2x.sub.1x.sub.0)=M.sub.r(x.sub.2x.sub.1x.sub.0)
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.2c.sub.1c.sub.-
0), when c.sub.4=0.
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=MAX, when
c.sub.4=1.
[0323] For RC 5: for the received metric
M.sub.r(ux.sub.2x.sub.1x.sub.0) that includes an uncoded bit, the
min* operation is again employed. The following transformations are
performed.
M.sub.s(x.sub.2x.sub.1x.sub.0)=min*{M.sub.r(0x.sub.2x.sub.1x.sub.0),M.sub-
.r(1x.sub.2x.sub.1x.sub.0)}
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.2c.sub.1c.sub.-
0), when c.sub.4=0.
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=MAX, when
c.sub.4-1.
[0324] The possible value of the uncoded bit indexed by
(x.sub.2x.sub.1x.sub.0) will be 0 if
M.sub.r(0x.sub.2x.sub.1x.sub.0)<M.sub.r(1x.sub.2x.sub.1x.sub.0),
otherwise the possible value of the uncoded bit indexed by
(x.sub.2x.sub.1x.sub.0) will be 1 if
M.sub.r(0x.sub.2x.sub.1x.sub.0).gtoreq.M.sub.r(1x.sub.2x.sub.1x.sub.0).
[0325] For RC 8: for the received metric M.sub.r(x.sub.1x.sub.0),
the following transformations are performed.
M.sub.s(x.sub.2x.sub.1x.sub.0)=M.sub.r(x.sub.1x.sub.0), when
x.sub.2=0
[0326] M.sub.s(x.sub.2x.sub.1x.sub.0)=MAX, when x.sub.2=1. MAX is
the maximum metric that is employed in the decoding system.
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=M.sub.s(c.sub.3c.sub.2c.sub.-
0), when c.sub.4=0.
M.sub.t(c.sub.4c.sub.3c.sub.2c.sub.1c.sub.0)=MAX, when
c.sub.4=1.
[0327] For even greater understanding of the mapping of these
metric functions to the trellis 2300 employed by the rate 2/5
prototype encoder 2000, we will walk through the following example.
We use the outputs of the trellis 2300 to perform this assigning of
the metrics. The following table is used to show how this mapping
to the trellis is performed according to RC 8. TABLE-US-00002 state
output output output output 0 = 000 0 14 31 25 x00000 octal x01100
octal x11001 octal x10101 octal Met(0) Met(6) Met(5) Met(7) MAX: as
x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2
= c.sub.4 = 1 1 = 001 31 25 0 14 x11001 octal x10101 octal x00000
octal x01100 octal Met(5) Met(7) Met(0) Met(6) MAX: as x.sub.2 =
c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4
= 1 2 = 010 12 6 23 37 x01010 octal x00110 octal x10011 octal
x11111 octal Met(4) Met(2) Met(5) Met(7) MAX: as x.sub.2 = c.sub.4
= 1 MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 3 =
011 23 37 12 6 x10011 octal x11111 octal x01010 octal x00110 octal
Met(5) Met(7) Met(4) Met(2) MAX: as x.sub.2 = c.sub.4 = 1 MAX: as
x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 4 -100 24 30 15
1 x10100 octal x11000 octal x01101 octal x00001 octal Met(6) Met(4)
Met(7) Met(1) MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 =
c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 5 = 101 15 1 24 30 x01101
octal x00001 octal x10100 octal x11000 octal Met(7) Met(1) Met(6)
Met(4) MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1
MAX: as x.sub.2 = c.sub.4 = 1 6 = 110 36 22 7 13 x11110 octal
x10010 octal x00111 octal x01011 octal Met(6) Met(4) Met(3) Met(5)
MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 MAX: as
x.sub.2 = c.sub.4 = 1 7 = 111 7 13 36 22 x00111 octal x01011 octal
x11110 octal x10010 octal Met(3) Met(5) Met(6) Met(4) MAX: as
x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2 = c.sub.4 = 1 MAX: as x.sub.2
= c.sub.4 = 1
[0328] It is seen in this example that there are only 4 distinct
valued metrics that need to be provided from the metric generator
to a SISO in the RC 8. MAX (the maximum metric value) is used to
define the "least likelihood probability." A great deal of memory
may be saved by passing only a flag bit (for those metrics who will
use the MAX value) that indicates such information to the SISO.
[0329] It is also noted that for the states 0=000 and 1=001, the
metrics are all the same values only swapped. This is the case also
for the state groupings {2=010, 3=011}, {4=100, 5=101}, and {6=110,
7=111}. Such efficiency may be similarly achieved with respect to
each of the RCs, and efficient hardware implementations may
capitalize thereon to provide for savings.
[0330] FIG. 44 is a diagram illustrating an embodiment of SISO
calculations and operations that are performed according to the
invention. For each stage (or each symbol) within a frame of
received symbols (or sequence of received symbols), the forward
metrics (alphas), the backward metrics (betas), and the extrinsics
are calculated. The extrinsics value of a stage is a function of
the alphas, betas, metrics, and apps ("a priori" probabilities) of
that stage. The metrics (that have been mapped according to the
trellis and according to the rate control sequence from the metric
generator 3733 and as also described in greater detail above within
the discussion of the FIG. 43) are provided to the SISO within the
FIG. 44. The SISO employs these metrics to calculate the alphas,
and the betas. Then, the alphas, betas, and metrics are used to
calculate the extrinsics that are provided back to the other SISO
through the other interleaver/de-interleaver as appropriate in the
particular situation. It is noted that the values of metrics,
alphas, betas, and extrinsics are all used to perform the TTCM
decoding of the information bits that have been encoded by the TTCM
encoder.
[0331] For even greater understanding of the calculation of these
variables according to the trellis 2300 that is employed by the
rate 2/5 prototype encoder 2000, we show the following steps of
calculations. It is noted that this is one particular example of
how these variables may be calculated, and other means are also
envisioned within the scope and spirit of the invention that
supports the variable code rate functionality described herein.
[0332] As mentioned above, the trellis 2300 may be represented
using 8 distinct metric values in an efficient implementation.
Therefore, for each stage (or symbol) of a received frame of
symbols (I,Qs), we will have 8 different metrics, 8 different
alphas, and 8 different betas. As also mentioned above, some
savings may be achieved when more than one of the metrics has the
same value according to the coding and the trellis 2300. Similar
savings may also be achieved within other trellises that inherently
support such redundancy.
[0333] We use the trellis to calculate the values for alpha. In
this particular embodiment, a value of 0 is associated with a high
likelihood and a value of N is associated with a value of less
likelihood. However, if desired in a particular embodiment, the
association may be reversed without departing from the scope and
spirit of the invention.
[0334] When calculating the 8 alphas for the first symbol of the
trellis 2300, we initially set the values to be as follows:
[0335] .alpha..sub.0(0)=0; the value of 0 is assigned to be a high
likelihood, and we set the other alphas to be the value of N,
associated with the less likelihood.
.alpha..sub.2(0)=.alpha..sub.3(0)=.alpha..sub.4(0)=.alpha..sub.5(0)=.alph-
a..sub.6(0)=.alpha..sub.7(0)=N
[0336] We will show the manner in which we calculate the alphas for
a first received symbol within a frame.
[0337] The alpha associated with the state 0 may be calculated as
follows: .alpha..sub.n(0)=min*{A.sub.0, A.sub.1, A.sub.2,
A.sub.3}
[0338] where,
A.sub.0=.alpha..sub.n-1(0)+Met(0)+app(i.sub.1=0)+app(i.sub.0=0),
input 0=00, output=0=x00000
A.sub.1=.alpha..sub.n-1(1)+Met(14)+app(i.sub.1=0)+app(i.sub.0=1),
input 1=01, output=14=x01100
A.sub.2=.alpha..sub.n-1(2)+Met(31)+app(i.sub.1=1)+app(i.sub.0=0),
input 2=10, output=31=x11001
A.sub.3=.alpha..sub.n-1(3)+Met(25)+app(i.sub.1=1)+app(i.sub.0=1),
input 3=11, output=25=x10101
[0339] Similarly, the alpha associated with the state 1 may be
calculated as follows: .alpha..sub.n(1)=min*{AA.sub.0, AA.sub.1,
AA.sub.2, AA.sub.3}
[0340] where,
AA.sub.0=.alpha..sub.n-1(2)+Met(31)+app(i.sub.1=1)+app(i.sub.0=0),
input 2=10, output=31=x11001
AA.sub.1=.alpha..sub.n-1(3)+Met(25)+app(i.sub.1=1)+app(i.sub.0=1),
input 3=11, output=25=x10101
AA.sub.2=.alpha..sub.n-1(0)+Met(0)+app(i.sub.1=0)+app(i.sub.0=0),
input 0=00, output=00=x00000
AA.sub.3=.alpha..sub.n-1(1)+Met(14)+app(i.sub.1=0)+app(i.sub.0=1),
input 1=01, output=14=x01100
[0341] This process will continue until all of the alphas are
calculated for the symbol. The beta values are calculated in the
backwards direction in a similar manner according to the same
trellis. The same min* design, replicated many times in hardware,
may be employed to perform simultaneous calculation of both the
alphas and the betas. However, in slower data rate applications
where throughput is not such a high priority, the same min*
hardware element may be used to perform the alpha and beta
calculations sequentially.
[0342] Once that the alphas and betas have been calculated at any
stage, we can proceed to calculate for the extrinsic values so that
we may decode the input bits of the input symbol, namely the two
input bits (i.sub.0i.sub.1), for that stage.
[0343] The following table may be used to illustrate how we
calculate these values according to the trellis 2300 that is
employed by the rate 2/5 prototype encoder 2000. In this
embodiment, since we have two input bits (i.sub.0i.sub.1), we need
to calculate the extrinsic values for the possibility that each of
the bits within the symbol may be 0 or may be 1. We will do this by
calculating the following extrinsic values: ext(00), ext(01),
ext(10), and ext(11).
[0344] The following table is used to show the 4 extrinsics that we
need to calculate to perform proper decoding of the input symbol
having the two input bits (i.sub.0i.sub.1). TABLE-US-00003 possible
two input Extrinsic value bit of concern bits [symbol =
(i.sub.0i.sub.1)] ext(00) = ext(i.sub.0 = 0) bit i.sub.0 = 0 0 = 00
or 2 = 10 ext(10) = ext(i.sub.i = 1) bit i.sub.0 = 1 1 = 01 or 3 =
11 ext(01) = ext(i.sub.1 = 0) bit i.sub.1 = 0 0 = 00 or 1 = 01
ext(11) = ext(i.sub.1 = 1) bit i.sub.1 = 1 2 = 10 or 3 = 11
[0345] In this embodiment, we perform a min* calculation to
calculate our four extrinsic values. It is noted, however, that
other embodiments may perform a min only calculation, a max only
calculation, or a max* calculation without departing from the scope
and spirit of the invention. The variable code rate functionality
of using multiple modulations (constellations and mappings), and
cycling through rate control sequences thereof may still be
performed when using other such functions to calculate the
extrinsic values within the SISO functional blocks.
[0346] We perform the min* operation on a host of values to
calculate these various extrinsic values.
[0347] First, we look at all branches within the trellis where
(i.sub.0=0), and we find that we get 16 branches. We do a min*
operation across those branches to calculate this the extrinsic
value. TABLE-US-00004 ext(00)=ext(i.sub.0=0)=min*{
[beta_0+alpha_0+a [beta_0+alpha_1+a priori(01)+met(0)];
priori(11)+met(31)]; [beta_1+alpha_6+a [beta_1+alpha_7+a
priori(11)+met(36)]; priori(01)+met(7)]; [beta_2+alpha_4+a
[beta_2+alpha_5+a priori(11)+met(30)]; priori(11)+met(1)];
[beta_3+alpha_2+a [beta_3+alpha_3+a priori(01)+met(6)];
priori(01)+met(37)]; [beta_4+alpha_0+a [beta_4+alpha_1+a
priori(11)+met(31)]; priori(11)+met(0)]; [beta_5+alpha_6+a
[beta_5+alpha_7+a priori(01)+met(7)]; priori(01)+met(36)];
[beta_6+alpha_4+a [beta_6+alpha_5+a priori(01)+met(1)];
priori(11)+met(30)]; [beta_7+alpha_2+a [beta_7+alpha_3+a
priori(11)+met(37)]; priori(01)+met(6)]}
[0348] Second, we now look at all branches within the trellis where
(i.sub.0=1), and we find that we also get 16 branches. We do a min*
operation across those branches to calculate this the extrinsic
value. TABLE-US-00005 ext(10)=ext(i.sub.0=1)=min*{
[beta_0+alpha_4+a [beta_0+alpha_5+a priori(11)+met(24)];
priori(01)+met(15)]; [beta_1+alpha_2+a [beta_1+alpha_3+a
priori(01)+met(12)]; priori(11)+met(23)]; [beta_2+alpha_0+a
[beta_2+alpha_1+a priori(01)+met(14)]; priori(01)+met(25)];
[beta_3+alpha_6+a [beta_3+alpha_7+a priori(11)+met(22)];
priori(01)+met(13)]; [beta_4+alpha_4+a [beta_4+alpha_5+a
priori(01)+met(15)]; priori(11)+met(24)]; [beta_5+alpha_2+a
[beta_5+alpha_3+a priori(11)+met(23)]; priori(01)+met(12)];
[beta_6+alpha_0+a [beta_6+alpha_1+a priori(11)+met(25)];
priori(01)+met(14)]; [beta_7+alpha_6+a [beta_7+alpha_7+a
priori(01)+met(13)]; priori(11)+met(22)]}
[0349] We may use these two extrinsic values calculated above to
decode for the first bit of the input symbol that was encoded,
namely i.sub.0. We use the following equation to do the final
decode for i.sub.0.
i.sub.0=sgn{-[ext(i.sub.0=0)+app(i.sub.0=0)]+[ext(i.sub.0=1)+app(i=1)]}
[0350] Functionally, we select the smaller one of
[ext(i.sub.0=0)+app(i.sub.0=0)] and [ext(i.sub.0=1)+app(i.sub.0=1)]
in the above equation, and we select the bit value associated with
the smaller sum. For example, if
[ext(i.sub.0=0)+app(i.sub.0=0)]<[ext(i.sub.0=1)+app(i.sub.0=1)],
then we make i.sub.0=0.
[0351] We perform similar operations to calculate for the bit value
for i.sub.1 within the input symbol.
[0352] Third, we look at all branches within the trellis where
(i.sub.1=0), and we find that we get 16 branches. We do a min*
operation across those branches to calculate this the extrinsic
value. TABLE-US-00006 ext(01)=ext(i.sub.1=0)=min*{
[beta_0+alpha_0+a [beta_0+alpha_5+a priori(00)+met(0)];
priori(10)+met(15)]; [beta_1+alpha_2+a [beta_1+alpha_7+a
priori(10)+met(12)]; priori(00)+met(7)]; [beta_2+alpha_0+a
[beta_2+alpha_5+a priori(10)+met(14)]; priori(00)+met(1)];
[beta_3+alpha_2+a [beta_3+alpha_7+a priori(00)+met(6)];
priori(10)+met(13)]; [beta_4+alpha_1+a [beta_4+alpha_4+a
priori(00)+met(0)]; priori(10)+met(15)]; [beta_5+alpha_3+a
[beta_5+alpha_6+a priori(10)+met(12)]; priori(00)+met(7)];
[beta_6+alpha_1+a [beta_6+alpha_4+a priori(10)+met(15)];
priori(00)+met(1)]; [beta_7+alpha_3+a [beta_7+alpha_6+a
priori(00)+met(6)]; priori(10)+met(13)]}
[0353] Fourth, we now look at all branches within the trellis where
(i.sub.1=1), and we find that we also get 16 branches. We do a min*
operation across those branches to calculate this the extrinsic
value. TABLE-US-00007 ext(11)=ext(i.sub.1=1)=min*{
[beta_0+alpha_1+a [beta_0+alpha_4+a priori(00)+met(31)];
priori(10)+met(24)]; [beta_1+alpha_3+a [beta_1+alpha_6+a
priori(10)+met(23)]; priori(00)+met(36)]; [beta_2+alpha_1+a
[beta_2+alpha_4+a priori(10)+met(25)]; priori(00)+met(30)];
[beta_3+alpha_3+a [beta_3+alpha_6+a priori(00)+met(37)];
priori(10)+met(22)]; [beta_4+alpha_0+a [beta_4+alpha_5+a
priori(00)+met(31)]; priori(10)+met(24)]; [beta_5+alpha_2+a
[beta_5+alpha_7+a priori(10)+met(23)]; priori(00)+met(36)];
[beta_6+alpha_0+a [beta_6+alpha_5+a priori(10)+met(25)];
priori(00)+met(30)]; [beta_7+alpha_2+a [beta_7+alpha_7+a
priori(00)+met(37)]; priori(10)+met(22)]}
[0354] We may use these two extrinsic values calculated above to
decode for the first bit of the input symbol that was encoded,
namely i.sub.0. We use the following equation to do the final
decode for i.sub.0.
i.sub.1=sgn{[ext(i.sub.1=1)+app(i.sub.1=1)]-[ext(i.sub.1=0)+app(i.sub.1=0-
)]}
[0355] Functionally, we select the smaller one of
[ext(i.sub.1=0)+app(i.sub.1=0)] and [ext(i.sub.1=1)+app(i.sub.1=1)]
in the above equation, and we select the bit value associated with
the smaller sum. For example, if
[ext(i.sub.1=0)+app(i.sub.1=0)]<[ext(i.sub.1=1)+app(i.sub.1=1)],
then we make i.sub.1=0.
[0356] Now we have decoder the individual bits for the input
symbol, (i.sub.0i.sub.1), as being one of either 0=01, 1=01, 2=10,
or 3=11.
[0357] In addition, we need to perform a little additional
computation in the situation where we have a RC that includes an
uncoded bit.
[0358] We continue on to use the RC 5 to illustrate this situation.
The other RCs would undergo analogous calculations to determine the
final value of the uncoded bit. The puncturing for the RC 5 may be
seen in the FIG. 26, and its mapping may be seen in the FIG. 36. We
use the earlier extrinsic calculated information to decode the
uncoded bit for RC 5, whose punctured output takes the form of
uc.sub.2c.sub.1c.sub.0. We can narrow our input selection somewhat
to have the form of only one of two input symbols, 0 and 1, or
0=(i.sub.0i.sub.1=00) and 1=(i.sub.0i.sub.1=01), because we know
that this RC 5 always provides the bit i.sub.0 as value 0.
Therefore, we need only to decode the other input bit i.sub.1
within this RC 5. The following table is employed to generate the
indexing of the uncoded bit so that, after we have decoded the
input bits, i.sub.0i.sub.1, we will be able to decode the uncoded
bit u properly. TABLE-US-00008 Trellis output input
c.sub.4c.sub.3c.sub.2c.sub.1c.sub.o min* operation symbol (octal)
c.sub.2c.sub.1c.sub.o (metric indexed by c.sub.2c.sub.1c.sub.o) 0 0
0 min*{[alpha_0 + beta_0 + met(0)]; (i.sub.0i.sub.1 = 00) [alpha_1
+ beta_4 + met(0)]} 0 1 1 min*{[alpha_4 + beta_6 + met(1)];
(i.sub.0i.sub.1 = 00) [alpha_5 + beta_2 + met(1)]} 0 6 6
min*{[alpha_2 + beta_3 + met(6)]; (i.sub.0i.sub.1 = 00) [alpha_3 +
beta_7 + met(6)]} 0 7 7 min*{[alpha_6 + beta_5 + met(7)];
(i.sub.0i.sub.1 = 00) [alpha_7 + beta_1 + met(7)]} 1 12 2
min*{[alpha_2 + beta_1 + met(2)]; (i.sub.0i.sub.1 = 01) [alpha_3 +
beta_5 + met(2)]} 1 13 3 min*{[alpha_6 + beta_7 + met(3)];
(i.sub.1i.sub.1 = 01) [alpha_7 + beta_3 + met(3)]} 1 14 4
min*{[alpha_0 + beta_2 + met(4)]; (i.sub.0i.sub.1 = 01) [alpha_1 +
beta_6 + met(4)]} 1 15 5 min*{[alpha_4 + beta_4 + met(5)];
(i.sub.0i.sub.1 = 01) [alpha_5 + beta_0 + met(5)]}
[0359] From the decoder input, such as input bit symbol 0,
(i.sub.0i.sub.1=00), we then determine which one of the four min*
results above is the smallest. This is then the index that we use
to select the one of the possible 8 values for the uncoded bit. As
an example, if the min* of the metric for 6 {the min* calculation
associated with met(6)} is the smallest, then we will use this
index to select the value of the uncoded bit u from the previously
stored values.
[0360] FIG. 45 is a diagram illustrating an embodiment of alpha,
beta, and extrinsic calculation, based on a trellis 2300 of a rate
2/5 non-systematic prototype encoder 2000, that is performed
according to the invention. The FIG. 45 shows how the trellis 2300
may be effectively overlaid at each symbol location within a frame
of received symbols and how this particular trellis 2300 inherently
provides an efficiency, in that, regardless of the RC that is being
employed in a given instance, the received metrics associated with
that RC may be mapped into the same trellis 2300 and reduced to a
maximum of 8 trellis metrics in certain embodiments as opposed to
storing all 16 metric values for each of the possible branches of
the trellis 2300. This is performed using normalization and
saturation in order to reduce the total number of trellis metrics
that need to be stored; by reducing the required memory storage
from 16 down to 8, a memory savings of a factor of 2 is achieved.
Similarly, normalization and saturation is performed in order to
reduce the total number of extrinsic values that need to be stored
for each input bit that is encoded. In prior art systems, there
would be a need for 4 extrinsic values per information bit thereby
requiring 8 extrinsic values for this embodiment which has 2 input
bits (4 extrinsic values each for the 2 bits). However, the
invention is able to reduce the total number of extrinsic values
that need to be stored to only 2 per bit thereby achieving a memory
savings by a factor of 2. The received metrics are calculated for
each symbol, these metrics are transformed into trellis metrics,
and the alphas, betas, and extrinsics are all calculated for each
symbol according to the invention. Again, it is noted that the
trellis 2300 shows one embodiment of how the invention may be
implemented. The invention envisions other trellises that also may
be implemented to support the variable code rate functionality as
well.
[0361] FIG. 46 is a diagram illustrating an embodiment of final
output of decoding that is performed according to the invention. In
the situation where there may be only one SISO, then the odd symbol
should be taken before de-interleave and the even symbol should be
taken after de-interleave.
[0362] In a similar manner to the ordering in which the encoding
may be performed (as described within the embodiment of the FIG.
13, for example), the order of the input symbols should be
preserved upon decoding. The final output of decoding ensures the
following: when we input a symbol sequence,
S.sub.1S.sub.2S.sub.3S.sub.4, to the encoder, and then when the
following encoded symbols
(S.sub.1-encS.sub.2-encS.sub.3-encS.sub.4-enc) are received by the
decoder, then the decoded estimates of these received symbols will
maintain this sequential order. A MUX whose selection is provided
by a clock signal that is clocked at 1/2 the rate will
alternatively select the outputs from the output and input of the
de-interleaver that is communicatively coupled to the lower SISO.
This MUX in the FIG. 46 may be viewed as being within the output
processor 3730 within either of the FIG. 38 or 39. The FIG. 46
shows an embodiment of how this may be performed in the final
decoding step.
[0363] FIG. 47 is a diagram illustrating an embodiment of a
variable code rate codec (encoder/decoder) servicing channels of
various SNRs according to the invention. A variable code rate
encoder is operable to transit/broadcast simultaneously to multiple
variable code rate decoders. When the communication channel that
communicatively couples to one of the variable code rate decoders
is of a low SNR, then the lower code rates may be employed when
coding data for use by the variable code rate decoder. Analogously,
when the communication channel that communicatively couples to one
of the variable code rate decoders is of a high SNR, then the
higher code rates may be employed when coding data for use by the
variable code rate decoder. In addition, either one or both of the
encoder and the decoder employed may adaptively change the rate
control sequence, in real-time, based on the operating conditions
of the communication channel; after there has been a change to a
new rate control sequence, then both the encoder and the decoder
will now operate at that new rate control sequence.
[0364] The rate control sequence to be employed when encoding and
subsequently decoding information may be selected based on the
given bandwidth of a communication channel. The rate control
sequence is then selected, based on the bandwidth of the
communication channel, as including the RCs that provide for the
best performance (such as the grouping of RCs that provides for the
lowest Bit Error Rate (BER)). This selection of which rate control
sequence to employ may also be performed based on the application
that is being used. For example, in some data applications, a
slight latency in the delivery of information may sometimes be
tolerated. However, in other applications, such as video or Voice
over Internet Protocol (VOIP) applications, the latency will
degrade the performance significantly. The inclusion of such
parameters may be employed when selecting which RCs to be employed
within a given rate control sequence.
[0365] Generally speaking, as the noise of the channel increases,
the coding may select a new code rate as provided by a new rate
control sequence. This new code rate (when channel noise increases)
may employ employs RCs with constellations of lower order (having a
fewer number of constellation points) and/or operate at lower
bandwidth efficiencies (fewer information bits per symbol).
Similarly, as the noise of the channel decreases, the coding may
select a new rate control sequence. This new code rate (when
channel noise decreases) may employ employs RCs with constellations
of higher order (having a larger number of constellation points)
and/or operate at higher bandwidth efficiencies (more information
bits per symbol).
[0366] This variable code rate functionality, including the
adaptive functionality thereof, may be implemented in a variety of
contexts to provide for overall improvement in the communication
system. One embodiment may include varying the rates to accommodate
the different SNR regions within wireless transmission from a
satellite to subscribers on the earth. A direct path from the
satellite may be viewed as generating a beam spot that would likely
have a SNR that is higher than the evanescent regions of the
wireless transmission where the field will fall off. The variable
code rate functionality, according to the invention, may be used to
support different rates to these various regions. In such an
implementation, a maximal throughput may be achieved by tailoring
the code rate to the communication to a particular receiver based
on the highest SNR that the channel to that receiver may
support.
[0367] Moreover, the invention envisions modifying the code rate
based on changes to the SNR of the channel as well; the device at
either end of the communication channel may perform the measurement
of the communication system's operating conditions including the
SNR of various portions of the channel. This is also described
above wherein either one or both of the transmitter and the
receiver may be employed to monitor such parameters and to change
the rate control sequence to be employed based on these parameters.
Both the encoder and decoder then will move to the new rate control
sequence synchronously to ensure proper communication of
information.
[0368] FIG. 48 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate coding method 4800 that is
performed according to the invention. As shown in a block 4810, a
RC is selected. This selection may be based on a communication
system's operating conditions as shown in the optional block 4812.
Moreover, the selection of the RC may specifically be made based on
the communication channel's SNR, as shown in an optional block
4814.
[0369] Afterwards, once one or more RCs has/have been selected,
then the information bits are encoded using a single TTCM encoder
as shown in a block 4820. These information bits are implemented as
symbols within the non-systematic rate 2/5 2000 that is used
throughout this document as an exemplary embodiment; however, in
other embodiments, a single bit may also be encoded using the
single TTCM encoder shown in the block 4820. These encoded symbols
(or bit) are provided for decoding.
[0370] In a block 4840, the received symbols are decoded using the
same single TTCM decoder according to the same RC in which the
information bits were encoded. A single TTCM encoder and a single
TTCM decoder that perform the method of the FIG. 48 will both
employ the same trellis when performing the coding/decoding
according to the RC.
[0371] In alternative embodiments, it is noted that the method may
cycle through a predetermined rate control sequence consisting of
various RCs, as shown in an optional block 4850. Each RC within the
rate control sequence may be viewed as having a unique
constellation (block 4852); each RC may have an individual
bandwidth efficiency (block 4854); multiple RCs may operate
cooperatively to provide for an average bandwidth efficiency (block
4856); and a predetermined rate control sequence may have a
particular period (block 4858) that may be repeated several times
within a data frame. This cycling through the predetermined rate
control sequence as shown in the optional block 4850 is performed
after the decoding in the block 4840 and before subsequently
repeating encoding in the block 4820 according to the appropriate
RC as defined by the rate control sequence.
[0372] It is also noted that the method may employ adaptive
selection of a new RC based on the communication system's operating
conditions as shown in an optional block 4860. Moreover, the
selection of the new RC may specifically be made based on the
communication channel's SNR, as shown in an optional block
4864.
[0373] FIG. 49 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate encoding method 4900 that
is performed according to the invention. In a block 4910, a RC is
selected. Thereafter, information bits (that may be viewed as a
symbol) are encoded using a single encoder as shown in a block
4920. None, one, or more of the encoded bits are then punctured as
shown in a block 4930; this puncturing is performed according to
the selected RC.
[0374] Based on the RC, a constellation is selected in a block
4940. Now, the remaining bits, after the puncturing is performed,
are mapped to a symbol for the selected constellation as shown in a
block 4950. This symbol is then modulated, according to the
selected modulation (having a constellation and mapping) as
determined by the RC as shown in a block 4960.
[0375] FIG. 50 is an operational flow diagram illustrating an
embodiment of a TTCM variable code rate decoding method 5000 that
is performed according to the invention. In a block 5010, a RC is
selected. The symbol is received in a block 5020. Metrics are then
calculated according to the invention for the received symbol as
shown in a block 5030. This symbol is then decoded according to the
appropriate modulation (constellation and mapping) using a single
decoder as shown in a block 5040.
[0376] FIG. 51 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate encoding method 5100 that
is performed according to the invention. In a block 5112,
information bits are provided to a first interleaver and to a first
constituent trellis encoder (CTE). Simultaneously, those same
information bits are provided to a second interleaver and to a
second CTE. After these information bits have been encoded and
interleaved using the first interleaver and CTE and the second
interleaver and the second CTE, the output from each of these
blocks 5112 and 5114 are alternatively selected as shown in a block
5120. A RC is determined as shown in a block 5130.
[0377] Thereafter, based on the RC, none, one or more selected bits
are punctured from the now combined output of the first interleaver
and CTE and the second interleaver and the second CTE as shown in a
block 5140. These remaining bits then form a symbol, and this
symbol is mapped into a particular modulation's constellation and
mapping (as governed by the RC) as shown in a block 5150. This
encoding may be performed multiple times to generate a number
symbols corresponding to one or more RCs. These symbols are then
sent out according to a rate control sequence that is made of one
or more RCs as shown in a block 5160.
[0378] FIG. 52 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate decoding method 5200 that
is performed according to the invention. As shown in a block 5210,
the I,Q portions of a received signal are received. A RC is
determined in a block 5220. Output metric are calculated based on
the I,Q of the received symbol and its mapping as shown in a block
5240.
[0379] Afterwards, soft symbol decisions are generated using these
output metrics (within a SISO) according to the RC as shown in a
block 5250. After these soft decisions have been made, then hard
symbol decisions are made based on the soft symbol decisions
according to the RC as shown in a block 5260.
[0380] FIG. 53 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method 5300 that is
performed according to the invention. A first frame is encoded
using a first rate control sequence (RC Seq 1) as shown in a block
5310. A second frame is encoded using a second rate control
sequence (RC Sequence 2) as shown in a block 5320. The operations
within the blocks 5310 and 5320 may be performed within a single
encoder in certain embodiments.
[0381] The first frame is decoded using the RC Seq 1 in a block
5340. The second frame is decoded using the RC Seq 2 in a block
5350. Each of the operations within the blocks 5340 and 5350 may be
performed within separate decoders (a decoder #1 and a decoder #2)
in certain embodiments or they may be performed within a single
decoder in other embodiments.
[0382] It is also noted that the encoding within the blocks 5310
and 5320 and the decoding within the blocks 5340 and 5350 all
employ the same trellis according to TTCM encoding/decoding.
[0383] FIG. 54 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method 5400 that is
performed according to the invention. A frame is encoded using
first rate control sequence (RC Seq 1) as shown in a block 5410.
The same frame is also encoded using a second rate control sequence
(RC Seq 1) as shown in a block 5420. The operations within the
blocks 5410 and 5420 may be performed within a single encoder in
certain embodiments.
[0384] The resultant frame that was encoded using the RC Seq 1 is
then decoded using the RC Seq 1 in a block 5440. The resultant
frame that was encoded using the RC Seq 2 is decoded using the RC
Seq 2 in a block 5450. Each of the operations within the blocks
5440 and 5450 may be performed within separate decoders (a decoder
#1 and a decoder #2) in certain embodiments or they may be
performed within a single decoder in other embodiments.
[0385] It is also noted that the encoding within the blocks 5410
and 5420 and the decoding within the blocks 5440 and 5450 all
employ the same trellis according to TTCM encoding/decoding.
[0386] FIG. 55 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate coding method 5500 that is
performed according to the invention. An individual symbol is
encoded using a first rate control (RC 1) as shown in a block 5510.
A second individual symbol is then encoded using a second rate
control (RC 2) as shown in a block 5520. The operations within the
blocks 5510 and 5420 may be performed within a single encoder in
certain embodiments.
[0387] These resultant encoded symbols, that were encoded using the
RC 1 and the RC 2 as shown in the blocks 5510 and 5520, are then
decoded using the RC 1 and the RC 2 as shown in blocks 5530 and
5540, respectively. Each of the operations within the blocks 5540
and 5550 may be performed within a single decoder in certain
embodiments. Alternatively, these operations within the blocks 5540
and 5550 may be performed within separate decoder in other
embodiments.
[0388] It is also noted that the encoding within the blocks 5510
and 5520 and the decoding within the blocks 5540 and 5550 all
employ the same trellis according to TTCM encoding/decoding.
[0389] It is noted here that the RCs (RC 1 and RC 2) that are
employed to perform the encoding of the symbols govern the code
rate and modulation (constellation and mapping) that correspond to
these symbols. That is to say, the code rate may vary on a symbol
by symbol basis. In addition, the modulation (either one or both of
the constellation and mapping) may also vary on a symbol by symbol
basis.
[0390] FIG. 56 is an operational flow diagram illustrating another
embodiment of a TTCM variable code rate encoding method 5600 that
is performed according to the invention. As shown in a block 5610,
input information is encoded thereby generating a number of encoded
bits. This encoding may also include puncturing that is performed
according to the invention. Afterwards, as shown in a block 5620,
these encoded bits are then grouped into two or more sub-groups
(shown here as a sub-group 1 and a sub-group 2).
[0391] As shown in a block 5630, the bits of one of the sub-groups
(sub-group 1) are used as a first encoded symbol (encoded symbol
1). This encoded symbol 1 is then mapped using a modulation 1
having its unique constellation and mapping. Similarly, as shown in
a block 5640, the bits of another of the sub-groups (sub-group 1)
are used as a second encoded symbol (encoded symbol 2). This
encoded symbol 2 is then mapped using a modulation 2 having its
unique constellation and mapping.
[0392] In alternative embodiment, as shown in a block 5645, the
bits of the sub-group 1 are used as a second encoded symbol
(encoded symbol 2). Then, this encoded symbol 2 is then mapped
using the same modulation 1, having its unique constellation and
mapping, as is used for the encoded symbol 1. This embodiment
corresponds to the situation where the number of bits for the
sub-group 1 and the sub-group 2 have the same number of bits.
[0393] Many benefits are provided by the various aspects of the
invention. It will now be understood that the variable code rate
functionality of the invention described herein will provide for
significantly extending the art of coding to higher order
constellations and achieving higher rates of communication thereby
enabling much greater throughput than has yet been achieved within
turbo coding systems.
[0394] In addition, it is also noted that the various aspects of
the invention are extendible to any Trellis Coded Modulation (TCM)
communication systems, and not only those that employ Turbo Trellis
Coded Modulation. For example, other trellis types of coded may
also benefit from the invention to achieve the many benefits
described herein, including variable code rate.
[0395] In view of the above detailed description of the invention
and associated drawings, other modifications and variations will
now become apparent. It should also be apparent that such other
modifications and variations may be effected without departing from
the spirit and scope of the invention.
* * * * *