U.S. patent application number 13/454194 was filed with the patent office on 2012-08-16 for adaptive puncturing technique for multicarrier systems.
Invention is credited to Alexei V. Davydov, Alexander A. Maltsev, Ali S. Sadri.
Application Number | 20120207242 13/454194 |
Document ID | / |
Family ID | 34749310 |
Filed Date | 2012-08-16 |
United States Patent
Application |
20120207242 |
Kind Code |
A1 |
Maltsev; Alexander A. ; et
al. |
August 16, 2012 |
ADAPTIVE PUNCTURING TECHNIQUE FOR MULTICARRIER SYSTEMS
Abstract
Various embodiments are described for adaptive puncturing
techniques.
Inventors: |
Maltsev; Alexander A.;
(Nizhny Novgorod, RU) ; Sadri; Ali S.; (San Diego,
CA) ; Davydov; Alexei V.; (Nizhny Novgorod,
RU) |
Family ID: |
34749310 |
Appl. No.: |
13/454194 |
Filed: |
April 24, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12346387 |
Dec 30, 2008 |
8184524 |
|
|
13454194 |
|
|
|
|
10749853 |
Dec 30, 2003 |
7489621 |
|
|
12346387 |
|
|
|
|
Current U.S.
Class: |
375/295 |
Current CPC
Class: |
H04L 1/0009 20130101;
H04L 27/2608 20130101; H04L 1/0003 20130101 |
Class at
Publication: |
375/295 |
International
Class: |
H04L 27/28 20060101
H04L027/28 |
Claims
1. An apparatus comprising: an adaptive bit loading block to
receive channel state information for a plurality of subcarriers
and to select a modulation scheme and a puncturing pattern for each
of the plurality of subcarriers or for each of a plurality of
subbands based on the channel state information; a puncturing block
to puncture a coded bit stream for each of a plurality of
subcarriers or subbands in accordance with the selected puncturing
pattern; a mapping block to map a coded and punctured bit stream
output from the puncturing block to one or more subcarrier symbols
for each of the plurality of subcarriers or subbands.
2. The apparatus of claim 1 and further comprising an encoder
coupled to the puncturing block to produce the encoded bit
stream.
3. The apparatus of claim 2 wherein the encoder comprises a
convolutional encoder.
4. The apparatus of claim 1 wherein each of the subbands comprises
a plurality of subcarriers.
5. The apparatus of claim 1 wherein the mapping block comprises a
mapping block to map a coded and punctured bit stream output from
the puncturing block to one or more OFDM subcarrier symbols for
each of a plurality of OFDM subcarriers or OFDM subcarrier
subbands, where the OFDM subcarrier subbands comprises a plurality
of OFDM subcarriers.
6. The apparatus of claim 1 and further comprising an OFDM
modulator to modulate a selected subcarrier symbol onto a OFDM
subcarrier for each of a plurality of OFDM subcarriers.
7. The apparatus of claim 1 wherein the puncturing pattern and/or
modulation scheme for a subcarrier are selected such that the
number of bits in the subcarrier symbol or subband are the same or
a multiple of a number of output coded bits in a puncturing
pattern.
8. The apparatus of claim 1 wherein a puncturing pattern and/or
modulation scheme are selected such that one or more sets of output
coded bits in a puncturing pattern may map onto one subcarrier or
one subband.
9. The apparatus of claim 1 wherein a puncturing pattern and/or
modulation scheme are selected such that one or more sets of output
coded bits in a puncturing pattern may map onto one subcarrier if
adaptive bit loading per subcarrier is performed, or map onto one
subband if adaptive bit loading per subband is performed.
10. An apparatus comprising an adaptive bit loading block to select
a modulation scheme an/or a puncturing pattern for an OFDM
subcarrier or an OFDM subcarrier subband based on subcarrier
channel state information.
11. The apparatus of claim 10 wherein the modulation scheme and the
puncturing pattern are selected such that a number of bits in an
OFDM subcarrier symbol or in an OFDM subcarrier subband to be the
same or a multiple of the number of output coded bits in the
puncturing pattern.
12. An apparatus comprising an adaptive bit loading block to select
a modulation scheme and a puncturing pattern for each of a
plurality of OFDM subcarriers or OFDM subcarrier subbands based on
subcarrier channel state information, a subcarrier subband
comprising a plurality of OFDM subcarriers.
13. The apparatus of claim 12 and further comprising a puncturing
block to puncture a coded bit stream for each of a plurality of the
subcarrier subbands according to the puncturing pattern selected
for the subcarrier subband.
14. The apparatus of claim 13 and further comprising a mapping
block to map coded and punctured bits into OFDM subcarrier symbols
according to the selected modulation scheme for each of the
subcarrier subbands.
15. A method comprising: receiving channel state information for
each of a plurality of subcarriers; and selecting a modulation
scheme and a puncturing pattern for each of a plurality of
subcarriers or subcarrier subbands based on the subcarrier channel
state information.
16. The method of claim 15 and further comprising: coding data bits
to produce a coded bit stream; puncturing the coded bit stream for
each of a plurality of subcarriers according to the selected
puncturing pattern for each subcarrier; and mapping bits from the
coded and punctured bit stream to subcarrier symbols according to
the selected modulation schemes for each subcarrier or subband.
17. The method of claim 15 wherein the selecting comprises
selecting a modulation scheme and a puncturing pattern for each of
a plurality of subcarriers or subcarrier subbands such that a
number of bits in an OFDM subcarrier symbol or OFDM subcarrier
subband is the same or a multiple of the number of output coded
bits in a puncturing pattern.
18. A method comprising: receiving channel state information for
each of a plurality of subcarriers; and selecting a modulation
scheme and a puncturing pattern for each of a plurality of
subcarrier subbands based on the subcarrier channel state
information, each subband comprising a plurality of OFDM
subcarriers.
Description
BACKGROUND INFORMATION
[0001] Multicarrier communications may be described as a
communications technique in which multiple carriers or subcarriers
are used to communicate information. As an example of multicarrier
communications, Orthogonal Frequency Division Multiplexing (OFDM)
may be described as a communications technique that divides a
communications channel into a number of spaced frequency bands. In
OFDM, a subcarrier carrying a portion of the user information may
be transmitted in each band. In OFDM, each subcarrier may be
orthogonal, differentiating OFDM from the commonly used frequency
division multiplexing (FDM). An OFDM symbol may include, for
example, a symbol transmitted simultaneously on each of the OFDM
subcarriers during the OFDM symbol period. These individual symbols
may be referred to as subcarrier symbols.
[0002] Some communication systems may include features that may
adapt to some types of changing conditions. For example, some
systems allow a data transmission rate to be adjusted based upon a
detected transmission condition. However, some types of adaptive
systems can be complex or expensive. A need exists for an improved
adaptive system
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a diagram illustrating an example of a wireless
communication system in accordance with one embodiment of the
invention.
[0004] FIG. 2 is a block diagram of a wireless transceiver
according to an example embodiment.
[0005] FIG. 3 is a diagram illustrating a number of puncturing
patterns according to an example embodiment.
DETAILED DESCRIPTION
[0006] In the detailed description, numerous specific details are
set forth in order to provide a thorough understanding of the
embodiments of the invention. It will be understood by those
skilled in the art, however, that embodiments of the invention may
be practiced without these specific details. In other instances,
well-known methods, procedures and techniques have not been
described in detail so as not to obscure the foregoing
embodiments.
[0007] Some portions of the detailed description that follows are
presented in terms of algorithms and symbolic representations of
operations on data bits or binary digital signals within a computer
memory. These algorithmic descriptions and representations may be
the techniques used by those skilled in the data processing arts to
convey the substance of their work to others skilled in the
art.
[0008] An algorithm is here, and generally, considered to be a
self-consistent sequence of acts or operations leading to a desired
result. These include physical manipulations of physical
quantities. Usually, though not necessarily, these quantities take
the form of electrical or magnetic signals capable of being stored,
transferred, combined, compared, and otherwise manipulated. It has
proven convenient at times, principally for reasons of common
usage, to refer to these signals as bits, values, elements,
symbols, characters, terms, numbers or the like. It should be
understood, however, that all of these and similar terms are to be
associated with the appropriate physical quantities and are merely
convenient labels applied to these quantities.
[0009] Unless specifically stated otherwise, as apparent from the
following discussions, it is appreciated that throughout the
specification discussions utilizing terms such as processing,
computing, calculating, determining, or the like, refer to the
action or processes of a computer or computing system, or similar
electronic computing device, that manipulate or transform data
represented as physical, such as electronic, quantities within the
registers or memories of the computing system into other data
similarly represented as physical quantities within the memories,
registers or other such information storage, transmission or
display devices of the computing system.
[0010] Embodiments of the present invention may include apparatuses
for performing the operations herein. This apparatus may be
specially constructed for the desired purposes, or it may comprise
a general purpose computing device selectively activated or
reconfigured by a program stored in the device. Such a program may
be stored on a storage medium, such as, but is not limited to, any
type of disk including floppy disks, optical disks, CD-ROMs,
magnetic-optical disks, read-only memories (ROMs), random access
memories (RAMs), electrically programmable read-only memories
(EPROMs), electrically erasable and programmable read only memories
(EEPROMs), flash memory, magnetic or optical cards, or any other
type of media suitable for storing electronic instructions, and
capable of being coupled to a system bus for a computing
device.
[0011] The processes and displays presented herein are not
inherently related to any particular computing device or other
apparatus. Various general purpose systems may be used with
programs in accordance with the teachings herein, or it may prove
convenient to construct a more specialized apparatus to perform the
desired method. The desired structure for a variety of these
systems will appear from the description below. In addition,
embodiments of the present invention are not described with
reference to any particular programming language. It will be
appreciated that a variety of programming languages may be used to
implement the teachings of the invention as described herein.
[0012] In the following description and claims, the terms coupled
and connected, along with their derivatives, may be used. In
particular embodiments, connected may be used to indicate that two
or more elements are in direct physical or electrical contact with
each other. Coupled may mean that two or more elements are in
direct physical or electrical contact. However, coupled may also
mean that two or more elements may not be in direct contact with
each other, but yet may still cooperate or interact with each
other.
[0013] It is worthy to note that any reference in the specification
to "one embodiment" or "an embodiment" means in this context that a
particular feature, structure, or characteristic described in
connection with the embodiment may be included in at least one
embodiment of the invention. The appearances of the phrase "in one
embodiment" or "an embodiment" in various places in the
specification do not necessarily refer to the same embodiment, but
may be referring to different embodiments.
[0014] It should be understood that embodiments of the present
invention may be used in a variety of applications. Although the
present invention is not limited in this respect, the circuits
disclosed herein may be used in many apparatuses such as in the
transmitters and receivers of a radio system. Radio systems
intended to be included within the scope of the present invention
include, by way of example only, wireless local area networks
(WLAN) devices and wireless wide area network (WWAN) devices
including wireless network interface devices and network interface
cards (NICs), base stations, access points (APs), gateways,
bridges, hubs, cellular radiotelephone communication systems,
satellite communication systems, two-way radio communication
systems, one-way pagers, two-way pagers, personal communication
systems (PCS), personal computers (PCs), personal digital
assistants (PDAs), and the like, although the scope of the
invention is not limited in this respect.
[0015] As used herein, the term packet may include a unit of data
that may be routed or transmitted between nodes or stations or
across a network. As used herein, the term packet may include
frames, protocol data units or other units of data. A packet may
include a group of bits, which may include one or more address
fields, control fields and data, for example. A data block may be
any unit of data or information bits.
[0016] Referring to the Figures in which like numerals indicate
like elements, FIG. 1 is a diagram illustrating an example of a
wireless communication system in accordance with one embodiment of
the invention. In the communications system 100 shown in FIG. 1, a
user wireless system 116 may include a wireless transceiver 110
coupled to an antenna 117 and to a processor 112. Processor 112 in
one embodiment may comprise a single processor, or alternatively
may comprise a baseband processor and an applications processor,
although the scope of the invention is not limited in this respect.
According to one embodiment, processor 112 may include a baseband
processor and Medium Access Control (MAC).
[0017] Processor 112 may couple to a memory 114 which may include
volatile memory such as DRAM, non-volatile memory such as flash
memory, or alternatively may include other types of storage such as
a hard disk drive, although the scope of the invention is not
limited in this respect. Some portion or all of memory 114 may be
included on the same integrated circuit as processor 112, or
alternatively some portion or all of memory 114 may be disposed on
an integrated circuit or other medium, for example a hard disk
drive, that is external to the integrated circuit of processor 112,
although the scope of the invention is not limited in this respect.
According to one embodiment, software may be provided in memory 114
to be executed by processor 112 to allow wireless system 116 to
perform a variety of tasks, some of which may be described
herein.
[0018] Wireless system 116 may communicate with an access point
(AP) 128 (or other wireless system) via wireless communication link
134, where access point 128 may include at least one antenna 118.
Antennas 117 and 118 may each be, for example, a directional
antenna or an omni directional antenna, although the invention is
not limited thereto. Although not shown in FIG. 1, AP 128 may, for
example, include a structure that is similar to wireless system
116, including a wireless transceiver, a processor, a memory, and
software provided in memory to allow AP 128 to perform a variety of
functions. In an example embodiment, wireless system 116 and AP 128
may be considered to be stations in a wireless communication
system, such as a WLAN system.
[0019] Access point 128 may be coupled to network 130 so that
wireless system 116 may communicate with network 130, including
devices coupled to network 130, by communicating with access point
128 via wireless communication link 134. Network 130 may include a
public network such as a telephone network or the Internet, or
alternatively network 130 may include a private network such as an
intranet, or a combination of a public and a private network,
although the scope of the invention is not limited in this
respect.
[0020] Communication between wireless system 116 and access point
128 may be implemented via a wireless local area network (WLAN),
for example a network which may be compliant with an Institute of
Electrical and Electronics Engineers (IEEE) standard such as IEEE
802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n, IEEE 802.15,
IEEE 802.16 and so on, although the scope of the invention is not
limited in this respect.
[0021] In another embodiment, communication between wireless system
116 and access point 128 may be implemented via a cellular
communication network compliant with a 3GPP standard, although the
scope of the invention is not limited in this respect.
[0022] One or more aspects of the invention may be applied to
single carrier systems where information may be transmitted over a
single carrier. Alternatively, one or more aspects of the invention
may be applied to multicarrier systems, such as an OFDM (Orthogonal
Frequency Division Multiplexing) system for example, where
information may be transmitted over multiple carriers or
subcarriers, although the invention is not limited in this
regard.
[0023] FIG. 2 is a block diagram of a wireless transceiver
according to an example embodiment. Referring to FIG. 2,
transceiver 200 may include a transmitter 201 to transmit
information and a receiver 231 to receive information. Transceiver
200 may include an adaptive bit loading block 205 that may receive
channel state information 203. Channel state information 203 may
include a signal-to-noise ratio (SNR), a bit error rate (BER), a
packet error rate, a channel estimate or channel transfer function,
etc., or other information that may describe a channel transmission
condition.
[0024] Adaptive bit loading block 205 may adaptively select a
modulation scheme 206 and a puncturing pattern 207 to be used by at
least transmitter 201 based upon the channel state information 203.
According to an example embodiment, puncturing block 215 may
discard some of the coded bits in accordance with the puncturing
pattern 207. Therefore, puncturing may increase the code rate since
according to an example embodiment, a code rate may be considered
to be a ratio of data bits/code bits.
[0025] Instead of selecting a puncturing pattern, adaptive bit
loading block 205 may alternatively first select a desired code
rate based on the channel state information, and then select a
puncturing pattern to achieve the selected code rate given the
mother code rate provided by coder 210. In this example embodiment,
adaptive bit loading block 205 may also select a modulation scheme
based on the channel state information.
[0026] According to an example embodiment, channel state
information 203 may be provided for each of a plurality of OFDM
subcarriers. Adaptive bit loading block 205 may select a modulation
scheme 206 and a code rate and/or puncturing pattern 207 for each
OFDM subcarrier based upon the channel state information of the
corresponding subcarrier.
[0027] According to an example embodiment, the modulation scheme
206 and the puncturing pattern 207 may be varied for each OFDM
subcarrier (on a per subcarrier basis). In another embodiment, the
OFDM subcarriers may be split into blocks of two or more adjacent
subcarriers, referred to as subbands. The same modulation scheme
and same puncturing pattern (or desired code rate) may be selected
for each subband (e.g., same modulation scheme and same puncturing
pattern for all subcarriers of a subband), although the invention
is not limited thereto.
[0028] In selecting a modulation scheme and puncturing pattern for
a subband, channel state information for one or more subcarriers in
the subband may be used to select these parameters for the subband.
For example, the lowest SNR may be used (e.g., the lowest SNR for
the subcarriers in the subband), the average SNR for all
subcarriers in the subband may be used, or other technique. These
are some examples, and the invention is not limited thereto.
[0029] A variety of different modulation schemes may be used. For
example the following modulation schemes may be used: binary
phase-shift keying (BPSK), quadrature phase shift keying (QPSK),
Quadrature Amplitude Modulation (QAM) such as 16-QAM (16 different
symbols), 64-QAM (64 different symbols), 256 QAM, etc., although
the invention is not limited thereto. Other modulation schemes may
be used.
[0030] Coding may involve coding data bits using a coding technique
(such as convolutional coding, etc.) to produce coded bits or code
bits. Puncturing may include, for example, dropping or discarding
or not transmitting certain coded bits to increase the code rate.
Puncturing may be used, for example, where an existing encoder uses
a particular code rate, and it may be desirable to increase the
code rate by dropping or not transmitting one or more code bits. At
the receiving node, the receiver or demodulator may insert one or
more dummy bits in place of the omitted (punctured) bits, and then
decode the message.
[0031] According to an example embodiment, higher modulation
schemes and higher code rates (e.g., through more puncturing) may
correspond to higher SNRs (or better channel transmission
conditions generally). According to an example embodiment, if the
channel state information, such as SNR for a subcarrier corresponds
to a first SNR range, a first modulation scheme and a first
puncturing pattern may be selected for that subcarrier or subband
for the transmission of data. If the SNR corresponds to a second
SNR range, then a second modulation type and a second puncturing
pattern may be selected for transmission of data. These are just
some examples and the invention is not limited thereto.
[0032] The selected modulation scheme 206 and puncturing pattern
207 may also be provided to receiver 231 to select these parameters
for demapping and de-puncturing of received information, although
these parameters may alternatively be selected by a remote
transmitter for a receiver 231.
[0033] Transmitter 201 will now be described. An input bit stream
208 is input at an encoder 210, which may be a convolutional
encoder for example, although the invention is not limited thereto.
Other types of coding may be used. Encoder 210 may, for example,
convolutionally encode the input bit stream 208 using a mother code
rate of %, although the invention is not limited thereto. Other
mother code rates may be used. Encoder 210 may output a coded bit
stream 212.
[0034] The coded bit stream 212 may be input to a puncturing block
215. Puncturing block 215 may puncture the coded bit stream by
dropping or discarding one or more coded bits according to a
puncturing pattern 207 specified by adaptive bit loading block 205
to produce a coded and punctured data stream 217. Due to such
puncturing, the (punctured) code rate for the punctured data stream
217 may be higher than the mother code rate of the bit stream 212
output from encoder 210. Thus, each OFDM subcarrier or subcarriers
in each subband may be coded with a selected code rate (based on
the puncturing pattern that is selected on a per subcarrier or per
subband basis).
[0035] Mapping block 220 may then extract a number of bits from bit
stream 217 and maps the bits to a corresponding symbol of a
selected modulation scheme. In an example embodiment, mapping block
may extract or select a number of bits in punctured bit stream 217
and maps the bits to a corresponding subcarrier symbol of the
selected modulation scheme for each (or at least some) of the
subcarriers of the OFDM symbol. This mapping may be repeated for a
plurality of OFDM symbols. Modulation block 225 may then perform
OFDM modulation to generate modulated data output 226 for
transmission.
[0036] Receiver 231 in FIG. 2 will now be described. Modulated data
229 is received and OFDM demodulated by demodulation block 230 to
output mapped (demodulated) data 232. Demapping block 235 demaps
OFDM subcarrier symbols to demapped data bits 237. According to an
example embodiment, depuncturing block 240 depunctures the demapped
data by inserting dummy bits at the appropriate locations based on
the puncturing pattern 207 to output bit inserted (depunctured)
data 242. This recovers the mother code. Decoder 245 may then
decode the depunctured data 242 to generate an output bit stream
247. According to an example embodiment, if a convolutional encoder
is used to encode the data at the transmit end, a Viterbi decoder
may be used for example as the decoder 245, although the invention
is not limited thereto.
[0037] FIG. 3 is a diagram illustrating a number of puncturing
patterns according to an example embodiment, although the invention
is not limited to this format or type of puncturing patterns. In
this example, convolutional codes with a rate of (n-1)/n may be
formed from puncturing a mother code having a code rate=1/2
convolutional code, although the invention is not limited thereto.
Other codes or code rates may be used. In an example embodiment,
the mother code may be generated with a code constraint length of
7, and using generator polynomials of G.sub.1=133.sub.8 and
G.sub.2=171.sub.8, as examples. However, the invention is not
limited thereto.
[0038] Several example puncturing patterns are shown in FIG. 3. As
shown in FIG. 3, at 305, the mother code is shown, with one data
bit being coded as two code bits, producing a mother code rate 1/2.
No puncturing is performed for pattern 305.
[0039] At 310, two data bits are encoded as four code bits (mother
code rate=1/2). The four bits may be referred to as input coded
bits for the puncturing pattern. The puncturing pattern 310 shows
that one of the four input coded bits is discarded, resulting in a
code rate of 2/3 (two data bits being encoded as three code bits).
The grayed out bit 312 in the puncturing pattern 310 is discarded
(punctured). The three white (non-discarded) bits may be referred
to as the output coded bits of the puncturing pattern.
[0040] At 315, three data bits are encoded as six code bits (mother
code rate=1/2). A code rate of 3/4 is achieved by discarding two of
the six code bits (three data bits encoded as four code bits), as
shown by the puncturing pattern 315. Therefore, there are four
output coded bits in this puncturing pattern in 315.
[0041] At 320, five data bits are encoded as 10 code bits (mother
code rate=1/2). Four of the 10 input coded bits are discarded as
shown by the puncturing pattern 320, resulting in a code rate of
(five data bits encoded as 6 code bits). There are six output coded
bits for this puncturing pattern.
[0042] At 325, seven data bits are encoded as 14 code bits or input
coded bits (mother code rate=1/2). Six of the 14 input coded bits
are discarded as shown by the puncturing pattern 320, resulting in
a code rate of 7/8 (seven data bits encoded as eight code bits).
Therefore, there are eight output coded bits for this puncturing
pattern.
[0043] Table 1 below illustrates some parameters that may be used
for an adaptive puncturing scheme according to an example
embodiment. A number of parameters are shown in the columns of
Table 1, including the modulation type, number of bits per OFDM
subcarrier (modulation) symbol, resulting code rate (after
puncturing), the number of data bits per subcarrier symbol (after
puncturing) for both single carrier bit loading and subband bit
loading (2 subcarriers per subband in this example), and the data
rate in Mbits/s for an example 20 MHZ channel having 48 OFDM
subcarriers, although the invention is not limited thereto. Other
data rates, channel sizes, and other parameters may be used.
TABLE-US-00001 TABLE 1 Example 20 MHz channel adaptive puncturing
scheme parameters Modulation and Coding parameters Puncturing Two
Data Output Single Subcarriers Rate Length carrier Subband Mbits/s
(number of BL BL 20 Mhz Number output Number of Number of 48 Data
Of coded bits data bits data bits subcarriers Bits per Code in per
per (802.11a timing- Modulation Modulation Rate puncturing
modulation modulation related Type symbol (R) pattern) symbol
symbol parameters) BPSK 1 1/2 2 -- 0.5 6 QPSK 2 1/2 2 1 1 12 QPSK 2
3/4 4 -- 1.5 18 16 QAM 4 1/2 2 2 2 24 16 QAM 4 3/4 4 3 3 36 16 QAM
4 7/8 8 -- 3.5 42 64 QAM 6 2/3 3 4 4 48 64 QAM 6 3/4 4 -- 4.5 54 64
QAM 6 6 5 5 60 256 QAM 8 3/4 4 6 6 72 256 QAM 8 7/8 8 7 7 84
[0044] According to an example embodiment, it may be desirable in
some cases to have the number of modulation bits in a single OFDM
subcarrier symbol (if adaptive bit loading per subcarrier is
performed) or in the subcarrier symbols of a single subcarrier
subband (if adaptive bit loading per subband is performed) to be
the same or a multiple (e.g., 2.times., 3.times., . . . ) of the
number of output coded bits in a puncturing pattern that is used.
For example, a puncturing processing may be performed on a set of
input coded bits (see, e.g., FIG. 3). For example, as shown in FIG.
3, a code rate R=3/4 puncturing pattern may need 6 input coded bits
from the mother code (R=1/2). Puncturing block 215 discards 2 bits
from this set of input coded bits, e.g., in positions as indicated
by the puncturing pattern. In this example, the number of output
coded bits in the puncturing pattern is equal to 4 (this is a
number of "white squares" in puncturing pattern, shown in FIG.
3).
[0045] In an example embodiment, it may be desirable to map a set
of output coded bits from the puncturing pattern (or a multiple of
the output coded bits of the puncturing pattern) to a subcarrier
symbol in one OFDM subcarrier (e.g., if adaptive bit loading is
used for individual subcarriers) or to the subcarrier symbols in
one subband (e.g., if adaptive bit loading is used for subcarrier
subbands), because an adjacent OFDM subcarrier or subband of
subcarriers may have another code rate (e.g., use a different
puncturing pattern). Therefore, in one example embodiment, to allow
the output coded bits from a puncturing pattern to be mapped or
modulated onto a single subcarrier or a single subband, it may be
advantageous for the number of bits in one OFDM subcarrier symbol
(e.g., if adaptive bit loading per subcarrier is performed) or the
number of bits in subcarrier symbols in one subband (e.g., if
adaptive bit loading per subband is performed) to be the same or a
multiple (e.g., 2.times., 3.times., . . . ) of the number of output
coded bits of the puncturing pattern that is used.
[0046] As an additional example, referring to Table 1, a 16 QAM
modulation scheme uses four bits per subcarrier symbol. If a code
rate (after puncturing) 3/4 is used, this results in four output
coded bits in the puncturing pattern, which is the same as the
number of bits (4) per subcarrier symbol for 16 QAM. This also
transmits an integer number of data bits per OFDM subcarrier
symbol. In this example, there will be 4 code bits per subcarrier
symbol, and 3 data bits per subcarrier symbol (due to 3/4 code rate
and 16 QAM modulation for this subcarrier).
[0047] Likewise, if 16 QAM modulation scheme is used, but with a
code rate=7/8, this results in 8 output coded bits in the
puncturing pattern. The 16 QAM modulation uses 4 bits per
subcarrier symbol. Therefore, a subband of two 16 QAM subcarriers
(8 bits total across two subcarrier symbols in the subband) can
accommodate (is the same number of bits as) the 8 output coded bits
from the puncturing pattern. Thus, a two subcarrier subband works
well for this 16 QAM, R=7/8 example. These are just examples and
the invention is not limited thereto.
[0048] Note that for adaptive bit loading for single subcarrier,
adaptive puncturing allows use of data bits per subcarrier symbol
in the range 1 to 7, but does not (according to this example
embodiment) allow use of the most robust BPSK modulation, as shown
in Table 1, although the invention is not limited thereto. In this
example, using 2 subcarrier subband adaptive bit loading allows use
of data bits per subcarrier in the range 0.5 to 7 (also in finer
granularity, e.g., steps of 0.5 data bits) as well as use of BPSK,
as shown in Table 1. Therefore, in some cases, subcarrier subband
adaptive bit loading may have advantages over single subcarrier
adaptive bit loading. These are just some examples and the
invention is not limited thereto.
[0049] It may also be advantageous to select a modulation scheme
and a puncturing pattern (or code rate) where an integer number of
data bits will be mapped onto a single subcarrier symbol (for
single subcarrier adaptive bit loading). Examples where this occurs
in Table 1 include a QPSK modulation scheme with a code rate of
1/2, resulting in 1 data bit per subcarrier symbol, and 16QAM with
a code rate of 3/4, resulting in 3 data bits per subcarrier symbol.
Note, in table 1, a dash in the column entitled "number of data
bits per [subcarrier] modulation symbol" indicates where an integer
number of data bits does not map to a subcarrier symbol for those
parameters.
[0050] Note that each of the combinations of modulation types and
code rates shown in Table 1 may allow an integer number of data
bits to be encoded on a 2 subcarrier subband. For example, 16QAM
modulation with a code rate=7/8 provides 3.5 data bits per
subcarrier symbol, and therefore 7 data bits per subband (two
subcarriers per subband). These are just additional examples and
the invention is not limited thereto.
[0051] While certain features of the embodiments of the invention
have been illustrated as described herein, many modifications,
substitutions, changes and equivalents will now occur to those
skilled in the art. It is, therefore, to be understood that the
appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the embodiments of the
invention.
* * * * *