U.S. patent application number 09/999287 was filed with the patent office on 2002-08-15 for simple block space time transmit diversity using multiple spreading codes.
Invention is credited to Kim, Younglok, Zeira, Ariela.
Application Number | 20020110108 09/999287 |
Document ID | / |
Family ID | 22962586 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110108 |
Kind Code |
A1 |
Kim, Younglok ; et
al. |
August 15, 2002 |
Simple block space time transmit diversity using multiple spreading
codes
Abstract
The present invention is a system and method for use in a CDMA
communication system including a plurality of base stations and a
user equipment (UE), each for communicating with each other. The
base station has a transmitter which includes a first and second
antenna for transmitting a data field of symbols. The first
spreading device spreads the first data field using a first
channelization code and the second spreading device spreads the
second data field using a second channelization code, each
channelization code being uniquely associated with one of the first
and second antennas. The UE has a receiver for receiving a signal
including the first and second spread data fields. The UE includes
a joint detection device for detecting the symbols of the first and
second data fields using the first and second channelization codes
and a decoder for decoding the detected data fields to generate a
single data field of symbols.
Inventors: |
Kim, Younglok; (Fort Lee,
NJ) ; Zeira, Ariela; (Huntington, NY) |
Correspondence
Address: |
VOLPE AND KOENIG, PC
DEPT ICC
SUITE 400, ONE PENN CENTER
1617 JOHN F. KENNEDY BOULEVARD
PHILADELPHIA
PA
19103
US
|
Family ID: |
22962586 |
Appl. No.: |
09/999287 |
Filed: |
November 15, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60254013 |
Dec 7, 2000 |
|
|
|
Current U.S.
Class: |
370/342 ;
370/441 |
Current CPC
Class: |
H04L 25/03866 20130101;
H04L 1/0631 20130101; H04B 1/707 20130101; H04B 7/0697 20130101;
H04L 25/0202 20130101; H04L 1/0618 20130101 |
Class at
Publication: |
370/342 ;
370/441 |
International
Class: |
H04B 007/216 |
Claims
What is claimed is:
1. A method for transmitting a data field of symbols in a CDMA
communication system including a plurality of base stations and a
user equipment (UE), wherein each of said base stations include a
transmitter and said UE includes a receiver, the method comprising
the steps of: generating a first data field of symbols; encoding
said first data field producing a second data field having complex
conjugates of the symbols of said data field; spreading said first
and second data fields, wherein said first data field is spread
using a first channelization code and said second data field is
spread using a second channelization code, each channelization code
being uniquely associated with one of a first and second antennas;
transmitting an RF signal including said first and second spread
data fields over a first and second antenna of said transmitter;
detecting the symbols of said first and second data fields using
said first and second channelization codes; and decoding said
detected data fields to generate a single data field of
symbols.
2. The method of claim 1 further comprising the step of scrambling
said first and second spread data fields by a scrambling code
associated with said transmitter.
3. The method of claim 2 wherein the symbols of said first data
field of symbols are grouped into a first and second sub-data
field.
4. The method of claim 3, wherein the symbols of said second data
field of symbols are grouped into a third and fourth sub-data
field, wherein said third sub-data field is the negative complex
conjugate of said second sub-data field and said fourth sub-data
field is the complex conjugate of said first sub-data field.
5. The method of claim 4 wherein said base station further includes
said receiver; and said UE further includes said transmitter.
6. A transmitter for transmitting a data field of symbols in a CDMA
communications system including a plurality of base stations and a
user equipment (UE), said base stations including said transmitter
and said UE including a receiver for communicating with each other,
the transmitter comprising: a first and second antenna for
transmitting said data field of symbols; an encoder for encoding
said data field producing a second data field having complex
conjugates of the symbols of said data field; and a first and
second spreading device for spreading said first and second data
fields, wherein said first spreading device spreads said first data
field using a first channelization code and said second spreading
device spreads said second data field using a second channelization
code, each channelization code being uniquely associated with one
of said first and second antennas.
7. The transmitter of claim 6 further comprising a first and second
scrambling device for scrambling said first and second spread data
fields by a single scrambling code associated with said
transmitter.
8. The transmitter of claim 7 wherein said receiver for receiving a
signal including said first and second spread data field,
comprises: a joint detection device for detecting the symbols of
said first and second data fields using said first and second
channelization codes; and a decoder for decoding said detected data
fields to generate a single data field of symbols.
9. The transmitter of claim 8 wherein the symbols of said first
data field of symbols are grouped into a first and second sub-data
field.
10. The transmitter of claim 9, wherein the symbols of said second
data field of symbols are grouped into a third and fourth sub-data
field, said third sub-data field being the negative complex
conjugate of said second sub-data field and said fourth sub-data
field being the complex conjugate of said first sub-data field.
11. A CDMA communication system including a plurality of base
stations and a user equipment (UE), each for communicating with
each other, said plurality of base stations having a transmitter
including: a first and second means for transmitting a data field
of symbols including a first data field; a means for encoding said
data field producing a second data field having complex conjugates
of the symbols of said data field; and a first and second spreading
means for spreading said first and second data fields, wherein said
first spreading means spreads said first data field using a first
channelization code and said second spreading means spreads said
second data field using a second channelization code, each
channelization code being uniquely associated with one of said
first and second transmitting means; said UE having a means for
receiving a signal including said first and second spread data
fields, comprising: a means for detecting the symbols of said first
and second data fields using said first and second channelization
codes; and a means for decoding said detected data fields to
generate a single data field of symbols.
12. The system of claim 11 further comprising a means for
scrambling said first and second spread data fields by a scrambling
code associated with said transmitting means.
13. The system of claim 12 wherein the symbols of said first data
field of symbols are grouped into a first and second sub-data
field.
14. The system of claim 13, wherein the symbols of said second data
field of symbols are grouped into a third and fourth sub-data
field, wherein said third sub-data field is the negative complex
conjugate of said second sub-data field and said fourth sub-data
field is the complex conjugate of said first sub-data field.
15. The system of claim 14 wherein said base station further
includes said means for receiving and said UE further includes said
transmitting means.
16. A method for transmitting a data field of symbols in a CDMA
communication system including a plurality of base stations and a
user equipment (UE), wherein each of said base stations include a
transmitter and said UE includes a receiver, the method comprising
the steps of: generating a data field of symbols; spreading said
first data field using a first channelization code producing a
first spread data field; spreading said first data field using a
second channelization code producing a second spread data field,
each channelization code being uniquely associated with one of a
first and second antennas; transmitting an RF signal including said
first and second spread data fields over a first and second
antenna; detecting the symbols of said data field using said first
and second channelization codes; and decoding said detected data
field to generate a single data field of symbols.
17. The method of claim 16 further comprising the steps of
scrambling said first and second spread data fields by a scrambling
code associated with said transmitter.
18. The method of claim 17 wherein said base station further
includes said receiver and said UE further includes said
transmitter.
19. A transmitter for transmitting a data field of symbols in a
CDMA communications system including a plurality of base stations
and a user equipment (UE), said base stations including said
transmitter and said UE including a receiver for communicating with
each other, the transmitter comprising: a first and second antenna
for transmitting said data field of symbols; and a first and second
spreading device for spreading said data field, wherein said first
spreading device spreads said data field using a first
channelization code, producing a first spread data field, and said
second spreading device spreads said data field using a second
channelization code, producing a second spread data field, each
channelization code being uniquely associated with one of said
first and second antennas.
20. The transmitter of claim 19 further comprising a first and
second scrambling device for scrambling said first and second
spread data fields by a single scrambling code associated with said
transmitter.
21. The transmitter of claim 20 wherein said receiver for receiving
a signal including said first and second spread data fields
comprises: a joint detection device for detecting the symbols of
said data fields using said first and second channelization codes;
and a decoder for decoding said detected data fields to generate a
single data field of symbols.
22. A CDMA communication system including a plurality of base
stations and a user equipment (UE), each for communicating with
each other, said plurality of base stations having a transmitter
including: a first and second means for transmitting a data field
of symbols; a first and second spreading means for spreading said
data field, wherein said first spreading means spreads said data
field using a first channelization code producing a first spread
data field and said second spreading means spreads said second data
field using a second channelization code producing a second spread
data field, each channelization code being uniquely associated with
one of said first and second transmitting means; said UE having a
means for receiving a signal including said first and second spread
data fields, comprising: a means for detecting the symbols of said
first and second spread data fields using said first and second
channelization codes; and a means for decoding said detected data
fields to generate a single data field of symbols.
23. The system of claim 22 further comprising a means for
scrambling said first and second spread data fields by a scrambling
code associated with said transmitting means.
Description
BACKGROUND
[0001] The present invention relates to communications systems
imploring code division multiple access (CDMA) techniques. More
particularly, the present invention relates to a transmission
diversity scheme which can be applied to a CDMA communication
system.
[0002] Spacial diversity has been proposed for support of very high
data rate users within third generation wide band code division
multiple access systems such as CDMA. Using multiple antennas, the
systems achieve better gains and link quality, which results in
increased system capacity. Classically, diversity has been
exploited through the use of either beam steering or through
diversity combining.
[0003] More recently, it has been realized that coordinated use of
diversity can be achieved through the use of space-time codes. Such
systems can theoretically increase capacity by up to a factor
equaling the number of transmit and receive antennas in the array.
Space-time block codes operate on a block of input symbols
producing a matrix output over antennas and time.
[0004] In the past, space-time transmit diversity systems have
transmitted consecutive symbols simultaneously with their complex
conjugates. This type of system, though may result in symbol
overlap at the receiving end, with the amount of overlap being
dependent on the length of the impulse response of the propagation
channel. In time division duplex (TDD) mode, this symbol overlap
will have to be accounted for in the joint detection receiver. The
joint detector will have to estimate the transmitted symbols and
their conjugates, resulting in an increase in complexity of the
joint detection.
[0005] In order to alleviate this increase in joint detection,
systems have been created which transmit two similar but different
data fields. The first data field, having a first portion, D.sub.1,
and a second portion, D.sub.2, is transmitted by the first antenna.
A second data field is produced by modifying the first data field.
The negation of the conjugate of D.sub.2, -D.sub.2*, is the first
portion of the second data field and the conjugate of D.sub.1,
D.sub.1*, is the second portion. The second data field is
simultaneously transmitted by the second antenna. This type of
system results in the joint detection implemented at the receiver
needing only to estimate the same amount of symbols as in the case
of a single transmit antenna. A block diagram of this system is
illustrated in FIG. 1.
[0006] Although the above system reduces the complexity of joint
detection for a single data block, joint detection requires the use
of two joint detectors at the receiver in a system employing two
transmit diversity antennas. Each joint detection device estimates
the data from one of the antennas. The estimated data is combined
to produce the original data. Therefore, the receiver in such a
system has a high complexity resulting in higher receiver
expense.
[0007] Accordingly, there exists a need for a transmit diversity
system requiring less complexity and receiver expense.
SUMMARY
[0008] The present invention is a system and method for use in a
CDMA communication system including a plurality of base stations
and a user equipment (UE), each for communicating with each other.
The base station has a transmitter which includes a first and
second antenna for transmitting a data field of symbols. The first
spreading device spreads the first data field using a first
channelization code and the second spreading device spreads the
second data field using a second channelization code, each
channelization code being uniquely associated with one of the first
and second antennas. The UE has a receiver for receiving a signal
including the first and second spread data fields. The UE includes
a joint detection device for detecting the symbols of the first and
second data fields using the first and second channelization codes
and a decoder for decoding the detected data fields to generate a
single data field of symbols.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a block diagram of a prior art communication
system employing space-time transmit diversity.
[0010] FIG. 2 is a block diagram of a transmitter and receiver in a
communication system in accordance with the preferred embodiment of
the present invention.
[0011] FIG. 3 is a flow diagram of the transmit diversity system of
the present invention.
[0012] FIG. 4 is a graph of the performance of the transmit
diversity system of the present invention.
[0013] FIG. 5 is a block diagram of a transmitter and receiver in a
communication system in accordance with an alternative embodiment
of the present invention.
[0014] FIG. 6 is a flow diagram of an alternative transmit
diversity system of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] FIG. 2 is a block diagram of a transmitter 10, preferably
located at a base station, and a receiver 20, preferably located at
a user equipment (UE), in a CDMA communication system in accordance
with the preferred embodiment of the present invention. Although it
is preferable to have the transmitter located at a base station and
the receiver located at the UE, the receiver and transmitter may
switch locations and the present invention operate on an uplink
communication. The transmitter 10 comprises a block encoder 11, a
plurality of channelization devices 8, 9, a plurality of spreading
sequence insertion devices 12, 13, and a plurality of antennas 15,
16. Although FIG. 1 illustrates a transmitter comprising two (2)
antennas, it should be apparent to those having skill in the art
that more than two (2) antennas may be used, such as N
antennas.
[0016] A typical communication burst has two data fields separated
by a midamble sequence. Preferably, the same encoding procedure, as
discussed in the following, for one data field is also performed on
the other data field. Data to be transmitted by the transmitter is
produced by a data generator (not shown). The resulting data
symbols (S.sub.1, S.sub.2, . . . S.sub.N/2), (S.sub.N/2+1,
S.sub.N/2+2, . . . , S.sub.N) of the first data field, which can be
represented by sub-data fields D.sub.1 and D.sub.2, are input into
the block encoder 11, preferably a block space-time transmit
diversity (BSTTD) encoder. The block encoder 11 encodes the input
symbols and generates the complex conjugate of D.sub.1 and the
negation of the conjugate of D.sub.2: D.sub.1*, -D.sub.2*. The
encoder 11 also changes the order of the symbols so that -D.sub.2*
is ahead of D.sub.1*. Preferably, an analogous encoding of the
second data field is also performed.
[0017] In accordance with the preferred embodiment of the present
invention, the data fields, D.sub.1, D.sub.2 and -D.sub.2*,
D.sub.1* are forwarded to a first and second channelization device
8, 9, respectively. The first channelization device 8 spreads the
data blocks D.sub.1, D.sub.2 by a first channelization code, and
-D.sub.2*, D.sub.1* by the second channelization device 9 using a
second different channelization code. Each of the spread data
blocks from the first and second channelization devices 8, 9 are
then scrambled by the scrambling code associated with the
transmitter 10.
[0018] Once the symbols D.sub.1, D.sub.2, -D.sub.2*, D.sub.1* have
been scrambled, they are mixed with a first and second midamble
through training sequence insertion devices 12, 13, producing two
communication bursts 17, 18. The two bursts 17, 18 are modulated
and simultaneously transmitted to the receiver 20 over antenna 15
and diversity antenna 16, respectively.
[0019] The receiver 20 comprises a joint detection device (JD) 24,
a BSTTD decoder 22, a channel estimation device 23 and an antenna
26. The antenna 26 of the UE receives various RF signals including
the communication bursts 17, 18 from the transmitter 10. The RF
signals are then demodulated to produce a baseband signal.
[0020] The baseband signal is then forwarded to the joint detection
device 24 and the channel estimation device 23. As those skilled in
the art know, the channel estimation device 23 provides channel
information, such as channel impulse responses, to the joint
detection device 24.
[0021] The joint detection device 24, coupled to the channel
estimation device 23 and BSTTD decoder 22, utilizes the channel
information and the channelization codes to detect the soft data
symbols d.sub.1, d.sub.2, -d.sub.2*, d.sub.1* in the received
signal. The channel impulse response for each burst is determined
using that burst's midamble sequence. Since each burst was
transmitted using a different spreading code, the joint detection
device 24 treats each burst as being transmitted by a different
user. As a result, any joint detection device which can recover
data from different transmitter sites may be used. Such joint
detection devices include zero forcing block linear equalizers,
detection devices using Cholesky or approximate Cholesky
decomposition, as well as many others. The joint detection device
24 estimates the data symbols of each of the bursts 17, 18 output
by the transmitter antennas 15, 16 and forwards the estimates to
the BSTTD decoder 22.
[0022] The BSTTD decoder 22, coupled to the joint detection device
24, receives the estimated soft data symbols d.sub.1, d.sub.2 and
-d.sub.2*, d.sub.1* corresponding to the antennas 15, 16 and
decodes the symbols to yield a single data field's soft symbols,
d.sub.STTD.
[0023] The flow diagram of the present invention is illustrated in
FIG. 3. A data generator generates data to be transmitted to the
receiver 20 (step 301). Each data field is separated into two
sub-data fields D.sub.1, D.sub.2 (step 302). The sub-data fields
D.sub.1, D.sub.2 are forwarded to the block encoder 11 and the
first channelization device 8 (step 303). The sub-data fields
forwarded to the block encoder 11 are encoded (step 304) and
forwarded to the second channelization device 9 (step 305). Each
channelization device 8, 9 spreads their respective data input
using a separate channelization code associated with a respective
antenna 15, 16 (step 306). The two spread signals are then
scrambled, using the scrambling code associated with the base
station (step 307) and transmitted to the receiver 20 over
diversity antennas 15, 16 (step 308).
[0024] The receiver 20 receives a RF communication signal including
the two spread signals from the diversity antennas 15, 16 (step
309), demodulates the signal and forwards the demodulated signal to
the channel estimation device 23 and joint detection device 24
(step 310). The received signal is processed by the channel
estimation device 23 (step 311) and the channel information applied
by the joint detection device 24 along with the channelization
codes, to estimate the transmit symbols from the diversity antennas
15, 16 (step 312). The detected sub-data fields, corresponding to
each diversity antenna 15, 16, are forwarded to the BSTTD decoder
(step 313), which decodes the soft symbol sub-fields to yield a
single data field's soft symbols, d.sub.STTD (step 314).
[0025] Similar to the preferred embodiment disclosed above, FIG. 5
is a block diagram of an alternative transmitter 40, preferably
located at a base station, and a receiver 50, preferably located a
user equipment (UE) in a communication system. The transmitter 40
comprises a plurality of channelization devices 48, 49, a plurality
of spreading sequence insertion devices 42, 43, and a plurality of
antennas 45, 46.
[0026] Data to be transmitted by the transmitter 40 is produced by
a data generator (not shown). The resulting data symbols (S.sub.1,
S.sub.2, . . . S.sub.N/2), (S.sub.N/2+1, S.sub.N/2+2, . . . ,
S.sub.N) of the first data field, which can be represented by
sub-data fields D.sub.1 and D.sub.2, are input to a first and
second channelization device 48, 49, respectively. The first
channelization device 8 spreads the data blocks D.sub.1, D.sub.2 by
a first channelization code, and the second channelization device
49 spreads the data blocks D.sub.1, D.sub.2 by a second different
channelization code. Each of the spread data blocks from the first
and second channelization devices 48, 49 are scrambled by the
scrambling code associated with the transmitter 40.
[0027] Once the symbols have been scrambled, they are mixed with a
first and second midamble through training sequence insertion
devices 42,43, producing two communication bursts 44, 45. The two
bursts 44, 45 are modulated and simultaneously transmitted to the
receiver 50 over antenna 46 and diversity antenna 47,
respectively.
[0028] The receiver 50 comprises a joint detection device (JD) 54,
a decoder 22, a channel estimation device 53 and an antenna 51. The
antenna 51 of the UE receives various RF signals including the
communication bursts 44, 45 from the transmitter 40. The RF signals
are then demodulated to produce a baseband signal.
[0029] The baseband signal is then forwarded to the joint detection
device 54 and the channel estimation device 53. The joint detection
device 54, coupled to the channel estimation device 53 and decoder
52, utilizes the channel information and the channelization codes
to detect the soft data symbols d.sub.1, d.sub.2, in the received
signal. The channel impulse response for each burst is determined
using that burst's midamble sequence. Since each burst was
transmitted using a different spreading code, the joint detection
device 54 treats each burst as being transmitted by a different
user. The joint detection device 54 estimates the data symbols of
each of the signals 44, 45 output by the transmitter antennas 46,
47 and forwards the estimates to the decoder 52.
[0030] The decoder 52, coupled to the joint detection device 54,
receives the estimated soft data symbols d.sub.1, d.sub.2
corresponding to the antennas 46, 47 and decodes the symbols to
yield a single data field's soft symbols, d.
[0031] The flow diagram of the alternative embodiment is
illustrated in FIG. 6. A data generator generates data to be
transmitted to the receiver 40 (step 601). Each data field is
separated into two sub-data fields D.sub.1, D.sub.2 (step 602). The
sub-data fields D.sub.1, D.sub.2 are forwarded to the first
channelization device 48 and to the second channelization device 49
(step 603). Each channelization device 48, 49 spreads their
respective data input using a separate channelization code
associated with each antenna 46,47 (step 604). The two spread
signals are then scrambled, using the scrambling code associated
with the base station (step 605) and transmitted to the receiver 50
over diversity antennas 46, 47 (step 606).
[0032] The receiver 50 receives a RF communication signal including
the two spread signals from the diversity antennas 46, 47 (step
607), demodulates the signal and forwards the demodulated signal to
the channel estimation device 53 and joint detection device 54
(step 608). The received signal is processed by the channel
estimation device 53 (step 609) and the channel information applied
by the joint detection device 54 along with the channelization
codes, to estimate the transmit symbols from the diversity antennas
46, 47 (step 610). The detected sub-data fields, corresponding to
each diversity antenna 46,47, are forwarded to the decoder 52 (step
611), which decodes the soft symbol sub-fields to yield a single
data field's soft symbols, d.sub.STTD (step 612).
[0033] By using additional channelization codes, the above
approaches can be applied to an antenna array having any number of
antennas. Each antenna has its own associated channelization code
and midamble. If a block encoder is used, the data field
transmitted by each of the antennas has a unique encoding, allowing
the use of a single joint detector at the receiver.
[0034] The B STTD transmitter with two channelization codes of the
present invention allows for the use of a cheaper and simpler
method of transmit diversity. The use of different channelization
codes per transmit antenna requires only one joint detection device
at the receiver resulting in a less complex receiver system than
those of the prior art. FIG. 4 is a graph showing the raw BER of
various block STTD decoders. The model is based on all the
receivers using a block linear equalizer (BLE) based approach to
JD. NTD means the single antenna case, i.e., no transmit diversity.
STTD with 1 code is the traditional block STTD JD. STTD with 2 code
is the disclosed block STTD transmitter. Simple STTD with 2 code is
the transmission system disclosed in the alternative embodiment. As
illustrated, the benefit of 2 codes for STTD can be summarized as
follows: 1) there is up to a 0.5 dB gain at 0.01 raw Bit error rate
over 1 code STTD; and 2) by eliminating the encoding block in
simple STTD with 2 code, the performance degradation is only 0.2 dB
at 0.1 raw BER and no degradation at 0.01 raw BER. The performance
improvement over NTD is still 1.0 dB and 2.7 dB at 0.1 and 0.01 raw
BER.
* * * * *