U.S. patent application number 09/234754 was filed with the patent office on 2001-12-13 for high data rate cdma wireless communication system.
Invention is credited to JOU, YU-CHEUN, ODENWALDER, JOSEPH P., TIEDEMANN, EDWARD G. JR..
Application Number | 20010050906 09/234754 |
Document ID | / |
Family ID | 24624882 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050906 |
Kind Code |
A1 |
ODENWALDER, JOSEPH P. ; et
al. |
December 13, 2001 |
HIGH DATA RATE CDMA WIRELESS COMMUNICATION SYSTEM
Abstract
High rate CDMA wireless communication is obtained by forming a
set of individually gain adjusted subscriber channels. Each channel
has a set of orthogonal subchannel codes having a small number of
PN spreading chips per orthogonal waveform period. Preferably, the
set of sub-channel codes are comprised of four Walsh codes, each
orthogonal to the remaining set and four chips in duration. It is
also preferred that pilot data be transmitted via a first transmit
channel and power control data transmitted via a second transmit
channel. The remaining two transmit channels are used for
transmitting non-specified digital data including user data or
signaling data, or both. One of the two non-specified transmit
channels may be configured for BPSK modulation and the other for
QPSK modulation.
Inventors: |
ODENWALDER, JOSEPH P.; (DEL
MAR, CA) ; JOU, YU-CHEUN; (SAN DIEGO, CA) ;
TIEDEMANN, EDWARD G. JR.; (SAN DIEGO, CA) |
Correspondence
Address: |
Qualcomm Incorporated
Patents Department
5775 Morehouse Drive
San Diego
CA
92121-1714
US
|
Family ID: |
24624882 |
Appl. No.: |
09/234754 |
Filed: |
January 21, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09234754 |
Jan 21, 1999 |
|
|
|
08654443 |
May 28, 1996 |
|
|
|
Current U.S.
Class: |
370/329 ;
370/208 |
Current CPC
Class: |
H04L 1/0071 20130101;
H04L 1/08 20130101; H04B 2201/70701 20130101; H04B 7/264 20130101;
H04L 1/0059 20130101; H04B 1/707 20130101; H04J 13/18 20130101;
H04J 13/0022 20130101; H04L 1/0045 20130101; H04J 13/0048
20130101 |
Class at
Publication: |
370/329 ;
370/208 |
International
Class: |
H04B 007/216 |
Claims
We claim:
1. A wireless communication system comprising: a first subscriber
unit constructed for transmitting a first reverse link signal that
includes a first set of orthogonal subchannels including a first
pilot channel and first traffic channel; a second subscriber unit
constructed for transmitting a second reverse link signal that
includes a second set of orthogonal subchannels including a second
pilot channel and second traffic channel; and a base station for
receiving said first reverse link signal and said second reverse
link signal.
2. The system as set forth in claim 1, wherein the orthogonal
subchannels are Walsh subchannels.
3. The system as set forth in claim 1 wherein said first set of
orthogonal subchannels is comprised of: a pilot subchannel; and a
traffic subchannel.
4. The system as set forth in claim 3, wherein the orthogonal
subchannels are Walsh subchannels.
5. The system as set forth in claim 1 wherein said first set of
orthogonal subchannels is formed by a set of orthogonal codes of 16
bits or less.
6. The system as set forth in claim 5, wherein the orthogonal
subchannels are Walsh subchannels and wherein the orthogonal codes
are Walsh codes.
7. A method for transmitting a frame of data comprising the steps
of: generating multiple symbols for each bit of data via
convolutional coding to create a symbol sequence; repeating said
symbol sequence a sufficient number of times to generate a set of
symbols containing a predetermined number of symbols; modulating
each symbol from said set of symbols with a first orthogonal code
having fewer than sixteen chips to generate first orthogonal code
modulated data; combining said first orthogonal code modulated data
with pilot data to produce combined data; and transmitted said
combined data.
8. The method as set forth in claim 7 wherein the orthogonal code
is a Walsh code.
Description
[0001] This application is a divisional application of application
Ser. No. 08/654,443 entitled "HIGH DATA RATE CDMA WIRELESS
COMMUNICATION SYSTEM" filed May 28, 1996 and assigned to the
assignee of the present invention.
BACKGROUND OF THE INVENTION
[0002] I. Field of the Invention
[0003] The present invention relates to communications. More
particularly, the present invention relates to a novel and improved
method and apparatus for high data rate CDMA wireless
communication.
[0004] II. Description of the Related Art
[0005] Wireless communication systems including cellular, satellite
and point to point communication systems use a wireless link
comprised of a modulated radio frequency (RF) signal to transmit
data between two systems. The use of a wireless link is desirable
for a variety of reasons including increased mobility and reduced
infrastructure requirements when compared to wire line
communication systems. One drawback of using a wireless link is the
limited amount of communication capacity that results from the
limited amount of available RF bandwidth. This limited
communication capacity is in contrast to wire based communication
systems where additional capacity can be added by installing
additional wire line connections.
[0006] Recognizing the limited nature of RF bandwidth, various
signal processing techniques have been developed for increasing the
efficiency with which wireless communication systems utilize the
available RF bandwidth. One widely accepted example of such a
bandwidth efficient signal processing technique is the IS-95 over
the air interface standard and its derivatives such as IS-95-A
(referred to hereafter collectively as the IS-95 standard)
promulgated by the telecommunication industry association (TIA) and
used primarily within cellular telecommunications systems. The
IS-95 standard incorporates code division multiple access (CDMA)
signal modulation techniques to conduct multiple communications
simultaneously over the same RF bandwidth. When combined with
comprehensive power control, conducting multiple communications
over the same bandwidth increases the total number of calls and
other communications that can be conducted in a wireless
communication system by, among other things, increasing the
frequency reuse in comparison to other wireless telecommunication
technologies. The use of CDMA techniques in a multiple access
communication system is disclosed in U.S. Pat. No. 4,901,307,
entitled "SPREAD SPECTRUM COMMUNICATION SYSTEM USING SATELLITE OR
TERRESTRIAL REPEATERS", and U.S. Pat. No. 5,103,459, entitled
"SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA
CELLULAR TELEPHONE SYSTEM", both of which are assigned to the
assignee of the present invention and incorporated by reference
herein.
[0007] FIG. 1 provides a highly simplified illustration of a
cellular telephone system configured in accordance with the use of
the IS-95 standard. During operation, a set of subscriber units
10a-d conduct wireless communication by establishing one or more RF
interfaces with one or more base stations 12a-d using CDMA
modulated RF signals. Each RF interface between a base station 12
and a subscriber unit 10 is comprised of a forward link signal
transmitted from the base station 12, and a reverse link signal
transmitted from the subscriber unit. Using these RF interfaces, a
communication with another user is generally conducted by way of
mobile telephone switching office (MTSO) 14 and public switch
telephone network (PSTN) 16. The links between base stations 12,
MTSO 14 and PSTN 16 are usually formed via wire line connections,
although the use of additional RF or microwave links is also
known.
[0008] In accordance with the IS-95 standard each subscriber unit
10 transmits user data via a single channel, non-coherent, reverse
link signal at a maximum data rate of 9.6 or 14.4 kbits/sec
depending on which rate set from a set of rate sets is selected. A
non-coherent link is one in which phase information is not utilized
by the received system. A coherent link is one in which the
receiver exploits knowledge of the carrier signals phase during
processing. The phase information typically takes the form of a
pilot signal, but can also be estimated from the data transmitted.
The IS-95 standard calls for a set of sixty four Walsh codes, each
comprised of sixty four chips, to be used for the forward link.
[0009] The use of a single channel, non-coherent, reverse link
signal having a maximum data rate of 9.6 of 14.4 kbits/sec as
specified by IS-95 is well suited for a wireless cellular telephone
system in which the typical communication involves the transmission
of digitized voice or lower rate digital data such a facsimile. A
non-coherent reverse link was selected because, in a system in
which up to 80 subscriber units 10 may communicate with a base
station 12 for each 1.2288 MHz of bandwidth allocated, providing
the necessary pilot data in the transmission from each subscriber
unit 10 would substantially increase the degree to which a set of
subscriber units 10 interfere with one another. Also, at data rates
of 9.6 or 14.4 kbits/sec, the ratio of the transmit power of any
pilot data to the user data would be significant, and therefore
also increase inter-subscriber unit interference. The use of a
single channel reverse link signal was chosen because engaging in
only one type of communication at a time is consistent with the use
of wireline telephones, the paradigm on which current wireless
cellular communications is based. Also, the complexity of
processing a single channel is less than that associated with
processing multiple channels.
[0010] As digital communications progress, the demand for wireless
transmission of data for applications such as interactive file
browsing and video teleconferencing is anticipated to increase
substantially. This increase will transform the way in which
wireless communications systems are used, and the conditions under
which the associated RF interfaces are conducted. In particular,
data will be transmitted at higher maximum rates and with a greater
variety of possible rates. Also, more reliable transmission may
become necessary as errors in the transmission of data are less
tolerable than errors in the transmission of audio information.
Additionally, the increased number of data types will create a need
to transmit multiple types of data simultaneously. For example, it
may be necessary to exchange a data file while maintaining an audio
or video interface. Also, as the rate of transmission from a
subscriber unit increases the number of subscriber units 10
communicating with a base station 12 per amount of RF bandwidth
will decrease, as the higher data transmission rates will cause the
data processing capacity of the base station to be reached with
fewer subscriber units 10. In some instances, the current IS95
reverse link may not be ideally suited for all these changes.
Therefore, the present invention is related to providing a higher
data rate, bandwidth efficient, CDMA interface over which multiple
types of communication can be performed.
SUMMARY OF THE INVENTION
[0011] A novel and improved method and apparatus for high rate CDMA
wireless communication is described. In accordance with one
embodiment of the invention, a set of individually gain adjusted
subscriber channels are formed via the use of a set of orthogonal
subchannel codes having a small number of PN spreading chips per
orthogonal waveform period. Data to be transmitted via one of the
transmit channels is low code rate error correction encoded and
sequence repeated before being modulated with one of the subchannel
codes, gain adjusted, and summed with data modulated using the
other subchannel codes. The resulting summed data is modulated
using a user long code and a pseudorandom spreading code (PN code)
and upconverted for transmission. The use of the short orthogonal
codes provides interference suppression while still allowing
extensive error correction coding and repetition for time diversity
to overcome the Raleigh fading commonly experienced in terrestrial
wireless systems. In the exemplary embodiment of the invention
provided, the set of sub-channel codes are comprised of four Walsh
codes, each orthogonal to the remaining set and four chips in
duration. The use of four sub-channels is preferred as it allows
shorter orthogonal codes to be used, however, the use of a greater
number of channels and therefore longer codes is consistent with
the invention.
[0012] In a preferred exemplary embodiment of the invention, pilot
data is transmitted via a first one of the transmit channels and
power control data transmitted via a second transmit channel. The
remaining two transmit channels are used for transmitting
non-specified digital data including user data or signaling data,
or both. In the exemplary embodiment, one of the two non-specified
transmit channels is configured for BPSK modulation and the other
for QPSK modulation. This is done to illustrate the versatility of
the system. Both channels could be BPSK modulated or QPSK modulated
in alternative embodiments of the invention. Before modulation, the
non-specified data is encoded where that encoding includes cyclic
redundancy check (CRC) generation, convolutional encoding,
interleaving, selective sequence repeating and BPSK or QPSK
mapping. By varying the amount of repeating performed, and not
restricting the amount of repeating to an integer number of symbol
sequences, a wide variety of transmission rates including high data
rates can be achieved. Furthermore, higher data rates can also be
achieved by transmitting data simultaneously over both
non-specified transmit channels. Also, by frequently updating the
gain adjust performed on each transmit channel, the total transmit
power used by the transmit system may be kept to a minimum such
that the interference generated between multiple transmit systems
is minimized, thereby increasing the overall system capacity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The features, objects, and advantages of the present
invention will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings in
which like reference characters identify correspondingly throughout
and wherein:
[0014] FIG. 1 is a block diagram of cellular telephone system;
[0015] FIG. 2 is a block diagram of a subscriber unit and base
station configured in accordance with the exemplary embodiment of
the invention;
[0016] FIG. 3 is a block diagram of a BPSK channel encoder and a
QPSK channel encoder configured in accordance with the exemplary
embodiment of the invention;
[0017] FIG. 4 is a block diagram of a transmit signal processing
system configured in accordance with the exemplary embodiment of
the invention;
[0018] FIG. 5 is a block diagram of a receive processing system
configured in accordance with the exemplary embodiment of the
invention;
[0019] FIG. 6 is a block diagram of a finger processing system
configured in accordance with one embodiment of the invention;
and
[0020] FIG. 7 is a block diagram of a BPSK channel decoder and a
QPSK channel decoder configured in accordance with the exemplary
embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] A novel and improved method and apparatus for high rate CDMA
wireless communication is described in the context of the reverse
link transmission portion of a cellular telecommunications system.
While the invention is particularly adapted for use within the
multipoint-to-point reverse link transmission of a cellular
telephone system, the present invention is equally applicable to
forward link transmissions. In addition, many other wireless
communication systems will benefit by incorporation of the
invention, including satellite based wireless communication
systems, point to point wireless communication systems, and systems
transmitting radio frequency signals via the use of co-axial or
other broadband cables.
[0022] FIG. 2 is a block diagram of receive and transmit systems
configured as a subscriber unit 100 and a base station 120 in
accordance with one embodiment of the invention. A first set of
data (BPSK data) is received by BPSK channel encoder 103, which
generates a code symbol stream configured for performing BPSK
modulation that is received by modulator 104. A second set of data
(QPSK data) is received by QPSK channel encoder 102, which
generates a code symbol stream configured for performing QPSK
modulation that is also received by modulator 104. Modulator 104
also receives power control data and pilot data, which are
modulated along with the BPSK and QPSK encoded data in accordance
with code division multiple access (CDMA) techniques to generate a
set of modulation symbols received by RF processing system 106. RF
processing system 106 filters and upconverts the set of modulation
symbols to a carrier frequency for transmission to the base station
120 using antenna 108. While only one subscriber unit 100 is shown,
multiple subscriber units communicate with base station 120 in the
preferred embodiment.
[0023] Within base station 120, RF processing system 122 receives
the transmitted RF signals by way of antenna 121 and performs
bandpass filtering, downconversion to baseband, and digitization.
Demodulator 124 receives the digitized signals and performs
demodulation in accordance with CDMA techniques to produce power
control, BPSK, and QPSK soft decision data. BPSK channel decoder
128 decodes the BPSK soft decision data received from demodulator
124 to yield a best estimate of the BPSK data, and QPSK channel
decoder 126 decodes the QPSK soft decision data received by
demodulator 124 to produce a best estimate of the QPSK data. The
best estimate of first and second set of data is then available for
further processing or forwarding to a next destination, and the
received power control data used either directly, or after
decoding, to adjust the transmit power of the forward link channel
used to transmit data to subscriber unit 100.
[0024] FIG. 3 is a block diagram of BPSK channel encoder 103 and
QPSK channel encoder 102 when configured in accordance with the
exemplary embodiment of the invention. Within BPSK channel encoder
103 the BPSK data is received by CRC check sum generator 130 which
generates a check sum for each 20 ms frame of the first set of
data. The frame of data along with the CRC check sum is received by
tail bit generator 132 which appends tail bits comprised of eight
logic zeros at the end of each frame to provide a known state at
the end of the decoding process. The frame including the code tail
bits and CRC check sum is then received by convolutional encoder
134 which performs, constraint length (K) 9, rate (R) 1/4
convolutional encoding thereby generating code symbols at a rate
four times the encoder input rate (E.sub.R). In the alternative
embodiment of the invention, other encoding rates are performed
including rate 1/2, but the use of rate 1/4 is preferred due to its
optimal complexity-performance characteristics. Block interleaver
136 performs bit interleaving on the code symbols to provide time
diversity for more reliable transmission in fast fading
environments. The resulting interleaved symbols are received by
variable starting point repeater 138, which repeats the interleaved
symbol sequence a sufficient number of times N.sub.R to provide a
constant rate symbol stream, which corresponds to outputting frames
having a constant number of symbols. Repeating the symbol sequence
also increases the time diversity of the data to overcome fading.
In the exemplary embodiment, the constant number of symbols is
equal to 6,144 symbols for each frame making the symbol rate 307.2
kilosymbols per second (ksps). Also, repeater 138 uses a different
starting point to begin the repetition for each symbol sequence.
When the value of N.sub.R necessary to generate 6,144 symbols per
frame is not an integer, the final repetition is only performed for
a portion of the symbol sequence. The resulting set of repeated
symbols are received by BPSK mapper 139 which generates a BPSK code
symbol stream (BPSK) of +1 and -1 values for performing BPSK
modulation. In an alternative embodiment of the invention repeater
138 is placed before block interleaver 136 so that block
interleaver 136 receives the same number of symbols for each
frame.
[0025] Within QPSK channel encoder 102 the QPSK data is received by
CRC check sum generator 140 which generates a check sum for each 20
ms frame. The frame including the CRC check sum is received by code
tail bits generator 142 which appends a set of eight tail bits of
logic zeros at the end of the frame. The frame, now including the
code tail bits and CRC check sum, is received by convolutional
encoder 144 which performs K=9, R=1/4 convolutional encoding
thereby generating symbols at a rate four times the encoder input
rate (E.sub.R). Block interleaver 146 performs bit interleaving on
the symbols and the resulting interleaved symbols are received by
variable starting point repeater 148. Variable starting point
repeater 148 repeats the interleaved symbol sequence a sufficient
number of times N.sub.R using a different starting point within the
symbol sequence for each repetition to generate 12,288 symbols for
each frame making the code symbol rate 614.4 kilosymbols per second
(ksps). When N.sub.R is not an integer, the final repetition is
performed for only a portion of the symbol sequence. The resulting
repeated symbols are received by QPSK mapper 149 which generates a
QPSK code symbol stream configured for performing QPSK modulation
comprised of an in-phase QPSK code symbol stream of +1 and -1
values (QPSK.sub.I), and a quadrature-phase QPSK code symbol stream
of +1 and -1 values (QPSK.sub.Q). In an alternative embodiment of
the invention repeater 148 is placed before block interleaver 146
so that block interleaver 146 receives the same number of symbols
for each frame.
[0026] FIG. 4 is a block diagram of modulator 104 of FIG. 2
configured in accordance with the exemplary embodiment of the
invention. The BPSK symbols from BPSK channel encoder 103 are each
modulated by Walsh code W.sub.2 using a multiplier 150b, and the
QPSK.sub.I and QPSK.sub.Q symbols from QPSK channel encoder 102 are
each modulated with Walsh code W.sub.3 using multipliers 150c and
154d. The power control data (PC) is modulated by Walsh code
W.sub.1 using multiplier 150a. Gain adjust 152 receives pilot data
(PILOT), which in the preferred embodiment of the invention is
comprised of the logic level associated with positive voltage, and
adjusts the amplitude according to a gain adjust factor A.sub.0.
The PILOT signal provides no user data but rather provides phase
and amplitude information to the base station so that it can
coherently demodulate the data carried on the remaining
sub-channels, and scale the soft-decision output values for
combining. Gain adjust 154 adjusts the amplitude of the Walsh code
W.sub.1 modulated power control data according to gain adjust
factor A.sub.1, and gain adjust 156 adjusts the amplitude of the
Walsh code W.sub.2 modulated BPSK channel data according
amplification variable A.sub.2. Gain adjusts 158a and b adjust the
amplitude of the in-phase and quadrature-phase Walsh code W.sub.3
modulated QPSK symbols respectively according to gain adjust factor
A.sub.3. The four Walsh codes used in the preferred embodiment of
the invention are shown in Table I.
1 TABLE I Modulation Walsh Code Symbols W.sub.0 + + + + W.sub.1 + -
+ - W.sub.2 + + - - W.sub.3 + - - +
[0027] It will be apparent to one skilled in the art that the
W.sub.0 code is effectively no modulation at all, which is
consistent with processing of the pilot data shown. The power
control data is modulated with the W.sub.1 code, the BPSK data with
the W.sub.2 code, and the QPSK data with the W.sub.3 code. Once
modulated with the appropriate Walsh code, the pilot, power control
data, and BPSK data are transmitted in accordance with BPSK
techniques, and the QPSK data (QPSK.sub.I and QPSK.sub.Q) in
accordance with QPSK techniques as described below. It should also
be understood that it is not necessary that every orthogonal
channel be used, and that the use of only three of the four Walsh
codes where only one user channel is provided is employed in an
alternative embodiment of the invention.
[0028] The use of short orthogonal codes generates fewer chips per
symbol, and therefore allows for more extensive coding and
repetition when compared to systems incorporating the use of longer
Walsh codes. This more extensive coding and repetition provides
protection against Raleigh fading which is a major source of error
in terrestrial communication systems. The use of other numbers of
codes and code lengths is consistent with the present invention,
however, the use of a larger set of longer Walsh codes reduces this
enhanced protection against fading. The use of four chip codes is
considered optimal because four channels provides substantial
flexibility for the transmission of various types of data as
illustrated below while also maintaining short code length.
[0029] Summer 160 sums the resulting amplitude adjusted modulation
symbols from gain adjusts 152, 154, 156 and 158a to generate summed
modulation symbols 161. PN spreading codes PN.sub.I and PN.sub.Q
are spread via multiplication with long code 180 using multipliers
162a and b. The resulting pseudorandom code provided by multipliers
162a and 162b are used to modulate the summed modulation symbols
161, and gain adjusted quadrature-phase symbols QPSK.sub.Q 163, via
complex multiplication using multipliers 164a-d and summers 166a
and b. The resulting in-phase term X.sub.I and quadrature-phase
term X.sub.Q are then filtered (filtering not shown), and
upconverted to the carrier frequency within RF processing system
106 shown in a highly simplified form using multipliers 168 and an
in-phase and a quadrature-phase sinusoid. An offset QPSK
upconversion could also be used in an alternative embodiment of the
invention. The resulting in-phase and quadrature-phase upconverted
signals are summed using summer 170 and amplified by master
amplifier 172 according to master gain adjust A.sub.M to generate
signal s(t) which is transmitted to base station 120. In the
preferred embodiment of the invention, the signal is spread and
filtered to a 1.2288 MHz bandwidth to remain compatible with the
bandwidth of existing CDMA channels.
[0030] By providing multiple orthogonal channels over which data
may be transmitted, as well as by using variable rate repeaters
that reduce the amount of repeating N.sub.R performed in response
to high input data rates, the above described method and system of
transmit signal processing allows a single subscriber unit or other
transmit system to transmit data at a variety of data rates. In
particular, by decreasing the rate of repetition N.sub.R performed
by variable starting point repeaters 138 or 148 of FIG. 3, an
increasingly higher encoder input rate E.sub.R can be sustained. In
an alternative embodiment of the invention rate 1/2 convolution
encoding is performed with the rate of repetition N.sub.R increased
by two. A set of exemplary encoder rates E.sub.R supported by
various rates of repetition N.sub.R and encoding rates R equal to
1/4 and 1/2 for the BPSK channel and the QPSK channel are shown in
Tables II and III respectively.
2TABLE II BPSK Channel Encoder Out N.sub.R,R=1/4 Encoder
N.sub.R,R=1/2 E.sub.R,BPSK R = 1/4 (Repetition Out R = 1/2
(Repetition Label (bps) (bits/frame) Rate, R = 1/4) (bits/frame)
Rate, R = 1/2) High Rate-72 76,800 6,144 1 3,072 2 High Rate-64
70,400 5,632 1 1/11 2,816 2 2/11 51,200 4,096 1 1/2 2,048 3 High
Rate-32 38,400 3,072 2 1,536 4 25,600 2,048 3 1,024 6 RS2-Full Rate
14,400 1,152 5 1/3 576 10 2/3 RS1-Full Rate 9,600 768 8 384 16 NULL
850 68 90 6/17 34 180 12/17
[0031]
3TABLE III QPSK Channel Encoder Out N.sub.R,R=1/4 Encoder
N.sub.R,R=1/2 E.sub.R,QPSK R = 1/4 (Repetition Out R = 1/2
(Repetition Label (bps) (bits/frame) Rate, R = 1/4) (bits/frame)
Rate, R = 1/2) 153,600 12,288 1 6,144 2 High Rate-72 76,800 6,144 2
3,072 4 High Rate-64 70,400 5,632 2 2/11 2,816 4 4/11 51,200 4,096
3 2,048 6 High Rate-32 38,400 3,072 4 1,536 8 25,600 2,048 6 1,024
12 RS2-Full Rate 14,400 1,152 10 2/3 576 21 1/3 RS1-Full Rate 9,600
768 16 384 32 NULL 850 68 180 12/17 34 361 7/17
[0032] Tables II and III show that by adjusting the number of
sequence repetitions N.sub.R, a wide variety of data rates can be
supported including high data rates, as the encoder input rate
E.sub.R corresponds to the data transmission rate minus a constant
necessary for the transmission of CRC, code tail bits and any other
overhead information. As also shown by tables II and III, QPSK
modulation may also be used to increase the data transmission rate.
Rates expected to be used commonly are provided labels such as
"High Rate-72" and "High Rate-32." Those rates noted as High
Rate-72, High Rate-64, and High Rate-32 have traffic rates of 72,
64 and 32 kbps respectively, plus multiplexed in signaling and
other control data with rates of 3.6, 5.2, and 5.2 kbps
respectively, in the exemplary embodiment of the invention. Rates
RS1-Full Rate and RS2-Full Rate correspond to rates used in IS-95
compliant communication systems, and therefore are also expected to
receive substantial use for purposes of compatibility. The null
rate is the transmission of a single bit and is used to indicate a
frame erasure, which is also part of the IS-95 standard.
[0033] The data transmission rate may also be increased by
simultaneously transmitting data over two or more of the multiple
orthogonal channels performed either in addition to, or instead of,
increasing the transmission rate via reduction of the repetition
rate N.sub.R. For example, a multiplexer (not shown) could split a
single data source into a multiple data sources to be transmitted
over multiple data sub-channels. Thus, the total transmit rate can
be increased via either transmission over a particular channel at
higher rates, or multiple transmission performed simultaneously
over multiple channels, or both, until the signal processing
capability of the receive system is exceeded and the error rate
becomes unacceptable, or the maximum transmit power of the of the
transmit system power is reached.
[0034] Providing multiple channels also enhances flexibility in the
transmission of different types of data. For example, the BPSK
channel may be designated for voice information and the QPSK
channel designated for transmission of digital data. This
embodiment could be more generalized by designating one channel for
transmission of time sensitive data such as voice at a lower data
rate, and designating the other channel for transmission of less
time sensitive data such as digital files. In this embodiment
interleaving could be performed in larger blocks for the less time
sensitive data to further increase time diversity. In another
embodiment of the invention, the BPSK channel performs the primary
transmission of data, and the QPSK channel performs overflow
transmission. The use of orthogonal Walsh codes eliminates or
substantially reduces any interference among the set of channels
transmitted from a subscriber unit, and thus minimizes the transmit
energy necessary for their successful reception at the base
station.
[0035] To increase the processing capability at the receive system,
and therefore increase the extent to which the higher transmission
capability of the subscriber unit may be utilized, pilot data is
also transmitted via one of the orthogonal channels. Using the
pilot data, coherent processing can be performed at the receive
system by determining and removing the phase offset of the reverse
link signal. Also, the pilot data can be used to optimally weigh
multipath signals received with different time delays before being
combined in a rake receiver. Once the phase offset is removed, and
the multipath signals properly weighted, the multipath signals can
be combined decreasing the power at which the reverse link signal
must be received for proper processing. This decrease in the
required receive power allows greater transmissions rates to be
processed successfully, or conversely, the interference between a
set of reverse link signals to be decreased. While some additional
transmit power is necessary for the transmission of the pilot
signal, in the context of higher transmission rates the ratio of
pilot channel power to the total reverse link signal power is
substantially lower than that associated with lower data rate
digital voice data transmission cellular systems. Thus, within a
high data rate CDMA system the E.sub.b/N.sub.0 gains achieved by
the use of a coherent reverse link outweigh the additional power
necessary to transmit pilot data from each subscriber unit.
[0036] The use of gain adjusts 152-158 as well as master amplifier
172 further increases the degree to which the high transmission
capability of the above described system can be utilized by
allowing the transmit system to adapt to various radio channel
conditions, transmission rates, and data types. In particular, the
transmit power of a channel that is necessary for proper reception
may change over time, and with changing conditions, in a manner
that is independent of the other orthogonal channels. For example,
during the initial acquisition of the reverse link signal the power
of the pilot channel may need to be increased to facilitate
detection and synchronization at the base station. Once the reverse
link signal is acquired, however, the necessary transmit power of
the pilot channel would substantially decrease, and would vary
depending on various factors including the subscriber units rate of
movement. Accordingly, the value of the gain adjust factor A.sub.0
would be increased during signal acquisition, and then reduced
during an ongoing communication. In another example, when
information more tolerable of error is being transmitted via the
forward link, or the environment in which the forward link
transmission is taking place is not prone to fade conditions, the
gain adjust factor A.sub.1 may be reduced as the need to transmit
power control data with a low error rate decreases. In one
embodiment of the invention, whenever power control adjustment is
not necessary the gain adjust factor A.sub.1 is reduced to
zero.
[0037] In another embodiment of the invention, the ability to gain
adjust each orthogonal channel or the entire reverse link signal is
further exploited by allowing the base station 120 or other receive
system to alter the gain adjust of a channel, or of the entire
reverse link signal, via the use of power control commands
transmitted via the forward link signal. In particular, the base
station may transmit power control information requesting the
transmit power of a particular channel or the entire reverse link
signal be adjusted. This is advantageous in many instances
including when two types of data having different sensitivity to
error, such as digitized voice and digital data, are being
transmitted via the BPSK and QPSK channels. In this case, the base
station 120 would establish different target error rates for the
two associated channels. If the actual error rate of a channel
exceeded the target error rate, the base station would instruct the
subscriber unit to reduce the gain adjust of that channel until the
actual error rate reached the target error rate. This would
eventually lead to the gain adjust factor of one channel being
increased relative to the other. That is, the gain adjust factor
associated with the more error sensitive data would be increased
relative to the gain adjust factor associated with the less
sensitive data. In other instances, the transmit power of the
entire reverse link may require adjustment due to fade conditions
or movement of the subscriber unit 100. In these instances, the
base station 120 can do so via transmission of a single power
control command.
[0038] Thus, by allowing the gain of the four orthogonal channels
to be adjusted independently, as well as in conjunction with one
another, the total transmit power of the reverse link signal can be
kept at the minimum necessary for successful transmission of each
data type, whether it is pilot data, power control data, signaling
data, or different types of user data. Furthermore, successful
transmission can be defined differently for each data type.
Transmitting with the minimum amount of power necessary allows the
greatest amount of data to be transmitted to the base station given
the finite transmit power capability of a subscriber unit, and also
reduces the interfere between subscriber units. This reduction in
interference increases the total communication capacity of the
entire CDMA wireless cellular system.
[0039] The power control channel used in the reverse link signal
allows the subscriber unit to transmit power control information to
the base station at a variety of rates including a rate of 800
power control bits per second. In the preferred embodiment of the
invention, a power control bit instructs the base station to
increase or decrease the transmit power of the forward link traffic
channel being used to transmit information to the subscriber unit.
While it is generally useful to have rapid power control within a
CDMA system, it is especially useful in the context of higher data
rate communications involving data transmission, because digital
data is more sensitive to errors, and the high transmission causes
substantial amounts of data to be lost during even brief fade
conditions. Given that a high speed reverse link transmission is
likely to be accompanied by a high speed forward link transmission,
providing for the rapid transmission of power control over the
reverse link further facilitates high speed communications within
CDMA wireless telecommunications systems.
[0040] In an alternative exemplary embodiment of the invention a
set of encoder input rates E.sub.R defined by the particular
N.sub.R are used to transmit a particular type of data. That is,
data may be tranmitted at a maximum encoder input rate E.sub.R or
at a set of lower encoder input rates E.sub.R, with the associated
N.sub.R adjusted accordingly. In the preferred implementation of
this embodiment, the maximum rates corresponds to the maximum rates
used in IS-95 compliant wireless communication system, referred to
above with respect to Tables II and III as RS1-Full Rate and
RS2-Full Rate, and each lower rate is approximately one half the
next higher rate, creating a set of rates comprised of a full rate,
a half rate, a quarter rate, and an eighth rate. The lower data
rates are preferable generated by increasing the symbol repetition
rate N.sub.R with value of N.sub.R for rate set one and rate set
two in a BPSK channel provided in Table IV.
4TABLE IV RS1 and RS2 Rate Sets in BPSK Channel Encoder Out
N.sub.R,R=1/4 Encoder N.sub.R,R=1/2 E.sub.R,QPSK R = 1/4
(Repetition Out R = 1/2 (Repetition Label (bps) (bits/frame) Rate,
R = 1/4) (bits/frame) Rate, R = 1/2) RS2-Full Rate 14,400 1,152 5
1/3 576 10 2/3 RS2-HaIf Rate 7,200 576 10 2/3 288 21 1/3 RS2-Quater
Rate 3,600 288 21 1/3 144 42 2/3 RS2-Eigth Rate 1,900 152 40 8/19
76 80 16/19 RS1-Full Rate 9,600 768 8 384 16 RS1-Half Rate 4,800
384 16 192 32 RS1-Quater Rate 2,800 224 27 3/7 112 54 6/7 RS1-Eigth
Rate 1,600 128 48 64 96 NULL 850 68 90 6/17 34 180 12/17
[0041] The repetition rates for a QPSK channel is twice that for
the BPSK channel.
[0042] In accordance with the exemplary embodiment of the
invention, when the data rate of a frame changes with respect to
the previous frame the transmit power of the frame is adjusted
according to the change in transmission rate. That is, when a lower
rate frame is transmitted after a higher rate frame, the transmit
power of the transmit channel over which the frame is being
transmitted is reduced for the lower rate frame in proportion to
the reduction in rate, and vice versa. For example, if the transmit
power of a channel during the transmission of a full rate frame is
transmit power T, the transmit power during the subsequent
transmission of a half rate frame is transmit power T/2. The
reduction is transmit power is preferably performed by reducing the
transmit power for the entire duration of the frame, but may also
be performed by reducing the transmit duty cycle such that some
redundant information is "blanked out." In either case, the
transmit power adjustment takes place in combination with a closed
loop power control mechanism whereby the transmit power is further
adjusted in response to power control data transmitted from the
base station.
[0043] FIG. 5 is a block diagram of RF processing system 122 and
demodulator 124 of FIG. 2 configured in accordance with the
exemplary embodiment of the invention. Multipliers 180a and 180b
dowconvert the signals received from antenna 121 with an in-phase
sinusoid and a quadrature phase sinusoid producing in-phase receive
samples R.sub.I and quadrature-phase receive samples R.sub.Q
receptively. It should be understood that RF processing system 122
is shown in a highly simplified form, and that the signals are also
match filtered and digitized (not shown) in accordance with widely
known techniques. Receive samples R.sub.I and R.sub.Q are then
applied to finger demodulators 182 within demodulator 124. Each
finger demodulator 182 processes an instance of the reverse link
signal transmitted by subscriber unit 100, if such an instance is
available, where each instance of the reverse link signal is
generated via multipath phenomenon. While three finger demodulators
are shown, the use of alternative numbers of finger processors are
consistent with the invention including the use of a single finger
demodulator 182. Each finger demodulator 182 produces a set of soft
decision data comprised of power control data, BPSK data, and
QPSK.sub.I data and QPSK.sub.Q data. Each set of soft decision data
is also time adjusted within the corresponding finger demodulator
182, although time adjustment could be performed within combiner
184 in an alternative embodiment of the invention. Combiner 184
then sums the sets of soft decision data received from finger
demodulators 182 to yield a single instance of power control, BPSK,
QPSK.sub.I and QPSK.sub.Q soft decision data.
[0044] FIG. 6 is block diagram a finger demodulator 182 of FIG. 5
configured in accordance with the exemplary embodiment of the
invention. The R.sub.I and R.sub.Q receive samples are first time
adjusted using time adjust 190 in accordance with the amount of
delay introduced by the transmission path of the particular
instance of the reverse link signal being processed. Long code 200
is mixed with pseudorandom spreading codes PN.sub.I and PN.sub.Q
using multipliers 201, and the complex conjugate of the resulting
long code modulated PN.sub.I and PN.sub.Q spreading codes are
complex multiplied with the time adjusted R.sub.I and R.sub.Q
receive samples using multipliers 202 and summers 204 yielding
terms X.sub.I and X.sub.Q. Three separate instances of the X.sub.I
and X.sub.Q terms are then demodulated using the Walsh codes
W.sub.1, W.sub.2 and W.sub.3 respectively, and the resulting Walsh
demodulated data is summed over four demodulation chips using 4 to
1 summers 212. A fourth instance of the X.sub.I and X.sub.Q data is
summed over four demodulation chips using summers 208, and then
filtered using pilot filters 214. In the preferred embodiment of
the invention pilot filter 214 performs averaging over a series of
summations performed by summers 208, but other filtering techniques
will be apparent to one skilled in the art. The filtered in-phase
and quadrature-phase pilot signals are used to phase rotate and
scale the W.sub.1, and W.sub.2 Walsh code demodulated data in
accordance with BPSK modulated data via complex conjugate
multiplication using multipliers 216 and adders 217 yielding soft
decision power control and BPSK data. The W.sub.3 Walsh code
modulated data is phase rotated using the in-phase and
quadrature-phase filtered pilot signals in accordance with QPSK
modulated data using multipliers 218 and adders 220, yielding soft
decision QPSK data. The soft decision power control data is summed
over 384 modulation symbols by 384 to 1 summer 222 yielding power
control soft decision data. The phase rotated W.sub.2 Walsh code
modulated data, the W.sub.3 Walsh code modulated data, and the
power control soft decision data are then made available for
combining. In an alternative embodiment of the invention, encoding
and decoding is performed on the power control data as well.
[0045] In addition to providing phase information the pilot may
also be used within the receive system to facilitate time tracking.
Time tracking is performed by also processing the received data at
one sample time before (early), and one sample time after (late),
the present receive sample being processed. To determine the time
that most closely matches the actual arrival time, the amplitude of
the pilot channel at the early and late sample time can be compared
with the amplitude at the present sample time to determine that
which is greatest. If the signal at one of the adjacent sample
times is greater than that at the present sample time, the timing
can be adjusted so that the best demodulation results are
obtained.
[0046] FIG. 7 is a block diagram of BPSK channel decoder 128 and
QPSK channel decoder 126 (FIG. 2) configured in accordance with the
exemplary embodiment of the invention. BPSK soft decision data from
combiner 184 (FIG. 5) is received by accumulator 240 which stores
the first sequence of 6,144/N.sub.R demodulation symbols in the
received frame where N.sub.R depends on the transmission rate of
the BPSK soft decision data as described above, and adds each
subsequent set of 6,144/N.sub.R demodulated symbols contained in
the frame with the corresponding stored accumulated symbols. Block
deinterleaver 242 deinterleaves the accumulated soft decision data
from variable starting point summer 240, and Viterbi decoder 244
decodes the deinterleaved soft decision data to produce hard
decision data as well as CRC check sum results. Within QPSK decoder
126 QPSK.sub.I and QPSK.sub.Q soft decision data from combiner 184
(FIG. 5) are demultiplexed into a single soft decision data stream
by demux 246 and the single soft decision data stream is received
by accumulator 248 which accumulates every 6,144/NR demodulation
symbols where N.sub.R depends on the transmission rate of the QPSK
data. Block deinterleaver 250 deinterleaves the soft decision data
from variable starting point summer 248, and Viterbi decoder 252
decodes the deinterleaved modulation symbols to produce hard
decision data as well as CRC check sum results. In the alternative
exemplary embodiment described above with respect to FIG. 3 in
which symbol repetition is performed before interleaving,
accumulators 240 and 248 are placed after block deinterleavers 242
and 250. In the embodiment of the invention incorporating the use
of rate sets, and therefore in which the rate of particular frame
is not known, multiple decoders are employed, each operating at a
different transmission rate, and then the frame associated with the
transmission rate most likely to have been used is selected based
on the CRC checksum results. The use of other error checking
methods is consistent with the practice of the present
invention.
[0047] Thus, a multi-channel, high rate, CDMA wireless
communication system has been described. The description is
provided to enable any person skilled in the art to make or use the
present invention. The various modifications to these embodiments
will be readily apparent to those skilled in the art, and the
generic principles defined herein may be applied to other
embodiments without the use of the inventive faculty. Thus, the
present invention is not intended to be limited to the embodiments
shown herein but is to be accorded the widest scope consistent with
the principles and novel features disclosed herein.
* * * * *