1. Field of the Invention
The present invention relates to a method for transmitting data in a communication system, and more specifically, a process and circuits for transmitting information by mapping antennas in a communication system.
2. Description of the Related Art
A typical cellular radio system includes a number of fixed base stations and a number of mobile stations. Each base station covers an geographical area, which is defined as a cell.
Typically, a non-line-of-sight (NLOS) radio propagation path exists between a base station and a mobile station due to natural and man-made objects disposed between the base station and the mobile station. As a consequence, radio waves propagate while experiencing reflections, diffractions and scattering. The radio wave which arrives at the antenna of the mobile station in a downlink direction, or at the antenna of the base station in an uplink direction, experiences constructive and destructive additions because of different phases of individual waves generated due to the reflections, diffractions, scattering and out-of-phase recombination. This is due to the fact that, at high carrier frequencies typically used in a contemporary cellular wireless communication, small changes in differential propagation delays introduces large changes in the phases of the individual waves. If the mobile station is moving or there are changes in the scattering environment, then the spatial variations in the amplitude and phase of the composite received signal will manifest themselves as the time variations known as Rayleigh fading or fast fading attributable to multipath reception. The time-varying nature of the wireless channel require very high signal-to-noise ratio (SNR) in order to provide desired bit error or packet error reliability.
The scheme of diversity is widely used to combat the effect of fast fading by providing a receiver with multiple faded replicas of the same information-bearing signal.
The schemes of diversity in general fall into the following categories: space, angle, polarization, field, frequency, time and multipath diversity. Space diversity can be achieved by using multiple transmit or receive antennas. The spatial separation between the multiple antennas is chosen so that the diversity branches, i.e., the signals transmitted from the multiple antennas, experience fading with little or no correlation. Transmit diversity, which is one type of space diversity, uses multiple transmission antennas to provide the receiver with multiple uncorrelated replicas of the same signal. Transmission diversity schemes can further be divided into open loop transmit diversity and closed-loop transmission diversity schemes. In the open loop transmit diversity approach no feedback is required from the receiver. In one type of closed loop transmit diversity, a receiver knows an arrangement of transmission antennas, computes a phase and amplitude adjustment that should be applied at the transmitter antennas in order to maximize a power of the signal received at the receiver. In another arrangement of closed loop transmit diversity referred to as selection transmit diversity (STD), the receiver provides feedback information to the transmitter regarding which antenna(s) to be used for transmission.
An example of open-loop transmission diversity scheme is the Alamouti 2×1 space-time diversity scheme. The Alamouti 2×1 space-time diversity scheme contemplates transmitting a Alamouti 2×2 block code using two transmission antennas using either two time slots (i.e., Space Time Block Code (STBC) transmit diversity) or two frequency subcarriers (i.e., Space Frequency Block Code (SFBC) transmit diversity).
One limitation of Alamouti 2×1 space-time diversity scheme is that this scheme can only be applied to two transmission antennas. In order to transmit data using four transmission antennas, a Frequency Switched Transmit Diversity (FSTD) or a Time Switched Transmit Diversity (TSTD) is combined with block codes.
The problem with combined SFBC+FSTD scheme and STBC+TSTD schemes is that only a fraction of the total transmission antennas and hence power amplifier capability is used for transmission in a given frequency or time resource. This is indicated by ‘0’ elements in the SFBC+FSTD and STBC+TSTD matrix given above. When the transmit power on the non-zero elements in the matrix is increased, bursty interference is generated to the neighboring cells degrading system performance. Generally, bursty interference manifests itself when certain phases of a frequency hopping pattern incur more interference than other phases.
In the Third Generation Partnership Project Long Term Evolution (3GPP LTE) system, the downlink reference signals mapping for four transmission antennas determines that a transmission density on the third antenna port and the fourth antenna port is half of the density on the first antenna port and the second antenna port. This leads to weaker channel estimates on the third and the fourth antenna ports.
Moreover, the antenna correlation depends upon, among other factors, angular spread and antennas spacing. In general, for a given angle spread, the larger the antenna spacing the smaller the correlation among the antennas. In a four transmission antenna 3GPP LTE system, the four antennas are usually aligned sequentially with equal spacing between two immediate antennas. Therefore, the correlation between the first antenna and the second antenna is larger than the correlation between the first antenna and the third antenna. Similarly, the correlation between the third antenna and the fourth antenna is larger than the correlation between the second antenna and the fourth antenna. Because smaller correlation among antennas means higher achievable diversity, this kind of antenna arrangement may result in degraded transmit diversity performance for the symbols transmitted via the first and the second antennas, and for the symbols transmitted via the third and the fourth antennas.
It is therefore an object of the present invention to provide an improve method and an improved apparatus for transmitting information.
It is another object to provide an improve method and an improved apparatus for transmitting information in order to improve the transmission performance and increase the system throughput.
It is another object to provide an improve method and an improved apparatus for transmitting information in order to improve the transmission diversity performance.
According to on aspect of the present invention, a method and an apparatus may be provided to include demultiplexing information to be transmitted into a plurality of stream blocks; inserting a respective cyclic redundancy check to each of the stream blocks; encoding each of the stream blocks according to a corresponding coding scheme; modulating each of the stream blocks according to a corresponding modulation scheme; demultiplexing the stream blocks to generate a plurality of sets of symbols, with each stream block being demultiplexed into a set of symbols; and transmitting the plurality of symbols via a plurality of antenna ports, with each set of symbols being transmitted via a subset of the plurality of antenna ports, and the antenna ports having weaker channel estimates being equally distributed among the plurality of subsets of antenna ports.
When four symbols are transmitted via four antenna ports according to a transmission matrix where a first symbol and a second symbol are generated from a first stream block, a third symbol and a fourth symbol are generated from a second stream block, and the first and second antenna ports have higher channel estimates than the third and the fourth antenna ports, the transmission matrix may be expressed as:
where Tij represents symbol transmitted on the ith antenna port and the jth subcarrier or jth time slot, S1, S2, S3, and S4 represent the first through the fourth symbols respectively.
According to another aspect of the present invention, a method and an apparatus may be provided to include generating four reference signals for four antenna ports, with each reference signal corresponding to an antenna port; mapping the four antenna ports to four physical antennas in accordance with a selected antenna port mapping scheme, with each antenna port corresponding to a physical antenna, with the four physical antennas being aligned sequentially with equal spacing between two immediately adjacent physical antennas, and the channel estimates of the third and the fourth antenna ports are weaker than the channel estimates of the first and the second antenna ports; demultiplexing information to be transmitted into two stream blocks including a first stream block and a second stream block; inserting a respective cyclic redundancy check to each of the two stream blocks; encoding each of the two stream blocks according to a corresponding coding scheme; modulating each of the two stream blocks according to a corresponding modulation scheme; demultiplexing a first stream block into a first symbol and a second symbol and demultiplexing a second stream block into a third symbol and a fourth symbol; and transmitting the four symbols via the four antenna ports according to a selected transmission matrix.
The selected antenna port mapping scheme may be established such that a first antenna port is mapped to a first physical antenna, a second antenna port is mapped to a third physical antenna, a third antenna port is mapped to a second physical antenna, and a fourth antenna port is mapped to a fourth physical antenna. In this case, the transmission matrix may be established as:
where Tij represents the symbol transmitted on the ith antenna port and the jth subcarrier or jth time slot, S1, S2, S3, and S4 represent the first through the fourth symbols respectively.
Alternatively, the selected antenna port mapping scheme may be established such that a first antenna port is mapped to a first physical antenna, a second antenna port is mapped to a second physical antenna, a third antenna port is mapped to a third physical antenna, and a fourth antenna port is mapped to a fourth physical antenna. In this case, the transmission matrix may be established as:
where Tij represents the symbol transmitted on the ith antenna port and the jth subcarrier or jth time slot, S1, S2, S3, and S4 represent the first through the fourth symbols respectively.
According to yet another aspect of the present invention, a method and an apparatus may be provided to include generating a plurality of reference signals for a plurality of antenna ports, with each reference signal corresponding to an antenna port; mapping the plurality of antenna ports to a plurality of physical antennas in accordance with a selected antenna port mapping scheme, with each antenna port corresponding to a physical antenna, and the plurality of physical antennas being aligned sequentially with equal spacing between two immediately adjacent physical antennas; demultiplexing information to be transmitted into a plurality of stream blocks; inserting a respective cyclic redundancy check to each of the stream blocks; encoding each of the stream blocks according to a corresponding coding scheme; modulating each of the stream blocks according to a corresponding modulation scheme; demultiplexing the stream blocks to generate a plurality of sets of symbols, with each stream block being demultiplexed into a set of symbols; mapping the plurality of sets of symbols into the plurality of antenna ports in accordance with a selected symbol mapping scheme; and transmitting the plurality of sets of symbols via the corresponding antenna ports, with each set of symbols being transmitted via a subset of antenna ports, with, within each subset of antenna ports, the distance between the physical antennas of the corresponding antenna ports being larger than the average distance among the plurality of physical antennas.
When two stream blocks are transmitted via four antenna ports, the selected antenna port mapping scheme may be established such that a first antenna port is mapped to a first physical antenna, a second antenna port is mapped to a third physical antenna, a third antenna port is mapped to a second physical antenna, and a fourth antenna port is mapped to a fourth physical antenna. In this case, the selected symbol mapping scheme may be established such that a first stream block is mapped to the first and the second antenna ports, and a second stream block is mapped to the third and the fourth antenna ports.
Alternatively, when two stream blocks are transmitted via four antenna ports, the selected antenna port mapping scheme may be established such that a first antenna port is mapped to a first physical antenna, a second antenna port is mapped to a second physical antenna, a third antenna port is mapped to a third physical antenna, and a fourth antenna port is mapped to a fourth physical antenna. In this case, the selected symbol mapping scheme may be established such that a first stream block is mapped to the first and the third antenna ports, and a second stream block is mapped to the second and the fourth antenna ports, such that the third and the fourth antenna ports having weaker channel estimates are equally distributed between the first and the second stream blocks.
According to still another aspect of the present invention, a method and an apparatus may be provided to include demultiplexing information to be transmitted into a plurality of stream blocks; inserting a respective cyclic redundancy check to each of the stream 1I blocks; encoding each of the stream blocks according to a corresponding coding scheme; modulating each of the stream blocks according to a corresponding modulation scheme to generate a plurality of modulated symbols; dividing the plurality of modulated symbols into a plurality of groups of modulated symbols; selecting a subset of matrices from among six permuted versions of a selected Space Frequency Block Code matrix; repeatedly applying the selected set of matrices to the plurality of groups of modulated symbols to generate a plurality of transmit matrices, with each matrix corresponding to a group of modulated symbols and each matrix being applied to each pair of modulated symbols in the corresponding group of modulated symbols; and transmitting the plurality of transmit matrices via four transmission antennas using a plurality of subcarriers, with each transmit matrix using two subcarriers.
The selected Space Frequency Block Code diversity matrix may be a Space Frequency Block Code Cyclic Delay Diversity (SFBC-CDD) matrix, and the six permutated versions may be expressed as:
where S1 and S2 are two modulated symbols, g=[k/2] is the group index of two subcarriers, k is the subcarrier index, and functions b1(g) and b2(g) are two pseudo-random phase shift vectors that are functions of the subcarrier group index g.
Alternatively, the selected Space Frequency Block Code diversity matrix may be a Space Frequency Block Code Phase Switched Diversity (SFBC-PSD) matrix, and the six permutated versions may be expressed as:
where S1 and S2 are two modulated symbols, k is the subcarrier index, and θ1 and θ2 are two fixed phase angles.
According to a further aspect of the present invention, a method and an apparatus may be provided to include demultiplexing information to be transmitted into a plurality of stream blocks; inserting a respective cyclic redundancy check to each of the stream blocks; encoding each of the stream blocks according to a corresponding coding scheme; modulating each of the stream blocks according to a corresponding modulation scheme to generate a pair of modulated symbols; selecting a subset of matrices from among six permuted versions of a selected Space Frequency Block Code matrix; repeatedly transmitting the pair of symbols by applying the selected set of matrices to the pairs of modulated symbols, with each matrix being transmitted at a time slot.
A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying. drawings in which like reference symbols indicate the same or similar components, wherein:
The total bandwidth in an OFDM system is divided into narrowband frequency units called subcarriers. The number of subcarriers is equal to the FFT/IFFT size N used in the system. In general, the number of subcarriers used for data is less than N because some subcarriers at the edge of the frequency spectrum are reserved as guard subcarriers. In general, no information is transmitted on guard subcarriers.
The scheme of diversity is widely used to combat the effect of fast fading by providing a receiver with multiple faded replicas of the same information-bearing signal.
An example of open-loop transmission diversity scheme is the Alamouti 2×1 space-time block code (STBC) transmission diversity scheme as illustrated in
The 2×1 Alamouti scheme can also be implemented in a space-frequency block code (SFBC) transmission diversity scheme as illustrated in
The received signal at the receiver on subcarrier having frequency f1 is r1, and the received signal at the receiver on subcarrier having frequency f2 is r2. r1 and r2 can be written as:
r
1
=h
1
s
1
+h
2
s
2
+n
1
r
2
=−h
1
s*
2
+h
2
s*
1
+n
2, (2)
where h1 and h2 are channel gains from ANT 1 and ANT 2 respectively. We also assume that the channel from a given antennas does not change between subcarrier having frequency f1 and subcarrier having frequency f2. The receiver performs equalization on the received signals and combines the two received signals (r1 and r2) to recover the symbols S1 and S2. The recovered symbols Ŝ1 and Ŝ2 can be written as:
It can be seen that both of the transmitted symbols Ŝ1 and Ŝ2 achieve full spatial diversity, that is, the each of the transmitted symbols Ŝ1 and Ŝ2 completely removes the interference from the other one.
For the case of four transmission antennas, orthogonal full-diversity block codes are not available. An example of quasi-orthogonal block code also known as ABBA code is given below:
where Tij represents the symbol transmitted on the ith antenna and the jth subcarrier or jth time slot (i=1,2,3,4, j=1,2,3,4) for the case of four transmission antennas. A and B are block codes given as below.
The problem with quasi-orthogonal block codes is that the loss of orthogonality may result in inter-symbol interference and hence degrades system performance and throughput.
Another example of orthogonal block code for four transmission antennas is SFBC with balanced Frequency Switched Transmit Diversity (FSTD). The code structure can be expressed as:
Other proposals found in the art for four transmission antennas transmit diversity combines Frequency Switched Transmit Diversity (FSTD) or Time Switched Transmit Diversity (TSTD) with block codes. In case of combined SFBC+FSTD scheme or STBC+TSTD scheme, the matrix of the transmitted symbols from the four transmission antennas are given as:
The receiver algorithms for detecting the signal S1, S2, S3, and S4 can be expressed as:
where h1, h2, h3, h4 are channel gains from ANT 1, ANT 2, ANT 3 and ANT 4, respectively; r1, r2, r3, and r4 are the received signal for sub-carrier 1, 2, 3, and 4, respectively. r1, r2, r3, and r4 can be expressed as follow.
r
1
=h
1
s
1
+h
2
s
2
−h
3
s
3
−h
4
s
4 (12)
r
2
=h
2
s*
1
−h
1
s*
2
−h
4
s*
3
+h
3
s*
4 (13)
r
3
=h
1
s*
1
+h
1
s*
2
+h
3
s*
3
+h
4
s*
4 (14)
r
4
=h
2
s*
1
−h
1
s*
2
+h
4
s*
3
−h
3
s*
4 (15)
The problem with combined SFBC+FSTD scheme and STBC+TSTD schemes is that only a fraction of the total transmission antennas and hence power amplifier (PA) capability is used for transmission in a given frequency or time resource. This is indicated by ‘0’ elements in the SFBC+FSTD and STBC+TSTD matrix given above. When the transmit power on the non-zero elements in the matrix is increased, bursty interference is generated to the neighboring cells degrading system performance.
The downlink reference signals mapping for four transmission antennas in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) system is shown in
In case of combined SFBC+FSTD scheme or STBC+TSTD scheme for four transmission antennas, the symbols S1 and S2 are transmitted from antenna ports 0 and 1, while symbols S3 and S4 are transmitted from antenna ports 2 and 3. The received symbol estimates are given as:
where h1, h2, h3, h4 denote channel gains from antenna port 0, 1, 2 and 3 respectively; r1, r2, r3, and r4 are the received signal for sub-carriers 1, 2, 3, and 4 in the case of SFBC+FSTD respectively, or for time slots 1, 2, 3, and 4 in the case of STBC+TSTD, respectively. It can be seen that symbols S1 and S2 transmitted from antennas ports 0 and 1 benefit from more reliable channel estimates than symbols S3 and S4 transmitted from antenna ports 2 and 3. This is because the reference signal density is twice as high on antenna ports 0 and 1 relative to antenna ports 2 and 3, as shown in
The antenna correlation depends upon, among other factors, angular spread and antennas spacing. In general, for a given angle spread, the larger the antenna spacing the smaller the correlation among the antennas. An example of antenna spacing for the case of four transmission antennas is shown in
Assume that symbols from the combined SFBC+FSTD scheme or STBC+TSTD scheme are transmitted via the antennas shown in
where Tij represents the symbol transmitted on the ith antenna and the jth subcarrier or jth time slot, and i=1,2,3,4, j=1,2,3,4 for the case of four transmission antennas. Accordingly, symbols S1 and S2 are transmitted via ANTP0 and ANTP1, while symbols S3 and S4 are transmitted via ANPT2 and ANTP3. This results in degraded transmit diversity performance for symbols S1 and S2 because the correlation between ANTP0 and ANTP1 is higher compared to the correlation between ANTP0 and ANTP2, or the correlation between ANTP1 and ANTP3. Similarly, symbols S3 and S4 may also experience a degraded transmit diversity performance because ANTP2 and ANTP3 have higher correlation compared to the correlation between ANTP0 and ANTP2, or the correlation between ANTP1 and ANTP3.
Another approach of transmit diversity scheme for four transmission antennas is called SFBC-Phase Switched Diversity (SFBC-PSD), where the transmit space-frequency code structure is given by:
where g=[k/2] is the group index of two subcarriers, and k is the subcarrier index. Functions b1(g) and b2(g) are two pseudo-random phase shift vectors that are functions of the subcarrier group index g, and they are known at Node-B (i.e., the base station) and all User Equipments (UEs).
Another approach of transmit diversity scheme for four transmission antennas is called SFBC-Cyclic Delay Diversity (SFBC-CDD), where the transmit space-frequency code structure is given by:
where k is the subcarrier index, and b1 and b2 are two fixed phase angles. Note that in this case, a simple orthogonal detection algorithm does not exist, and either Maximum Likelihood (ML) receivers, or Minimum Mean Square Error (MMSE) receivers, or other advanced receivers are needed to capture diversity.
Multiple Input Multiple Output (MIMO) schemes use multiple transmission antennas and multiple receive antennas to improve the capacity and reliability of a wireless communication channel. A MIMO system promises linear increase in capacity with K where K is the minimum of number of transmit (M) and receive antennas (N), i.e. K=min(M,N). A simplified example of a 4×4 MIMO system is shown in
The MIMO channel estimation consists of estimating the channel gain and phase information for links from each of the transmission antennas to each of the receive antennas. Therefore, the channel for M×N MIMO system consists of an N×M matrix:
where hij represents the channel gain from transmission antenna j to receive antenna i. In order to enable the estimations of the elements of the MIMO channel matrix, separate pilots are transmitted from each of the transmission antennas.
An example of single-code word MIMO scheme is given in
In case of multiple codeword MIMO transmission, shown in
Similarly, codeword-1 (CW1) mapped to ANTP0 and ANTP1 experience less diversity because of higher correlation between ANTP0 and ANTP1. Similarly, codeword-2 (CW2) mapped to ANTP2 and ANTP3 experience less diversity because of higher correlation between ANTP2 and ANTP3.
In a first embodiment according to the principles of the present invention, we describe an open-loop transmit diversity scheme where symbols S1 and S2 are transmitted via antennas ports ANTP0 and ANTP2 as shown in
where Tij represents symbol transmitted on the ith antenna port and the jth subcarrier or jth time slot, and i=1,2,3,4, j=1,2,3,4 for the case of four transmission antennas.
The received symbol estimates are given as:
where h1, h2, h3, h4 denote channel gains from antenna ports 0, 1, 2 and 3 respectively; n1, n2, n3, and n4 represents noise for sub-carriers 1, 2, 3, and 4 in the case of SFBC respectively, or for time slots 1, 2, 3, and 4 in the case of STBC, respectively. It can be seen that symbols S1 and S2 transmitted from antennas ports 0 and 2 experience a good channel estimate h1 and a weak channel estimate h3. Similarly, symbols S3 and S4 transmitted from antenna ports 1 and 3 experience a good channel estimate h2 and a weak channel estimate h4. This way the effect of weaker channel estimates is distributed across all the four symbols, S1, S2, S3, and S4.
The Multi-code word MIMO scheme according to the principles of the current invention is shown in
In a second embodiment according to the principles of the present invention, reference symbols for the four transmission antennas are mapped as shown in
Now we assume the symbols in the combined SFBC+FSTD scheme or STBC+TSTD scheme are transmitted via the antenna ports shown in
where Tij represents symbol transmitted on the (i−1)th antenna port and the jth subcarrier or jth time slot, and i=1,2,3,4, j=1,2,3,4 for the case of four transmission antennas. That is, symbols T11, T12, T13, and T14 are transmitted via antenna port ANTP0 which corresponds to the physical antenna 1, symbols T21, T22, T23, and T24 are transmitted via antenna port ANTP1 which corresponds to the physical antenna 3, symbols T31, T32, T33, and T34 are transmitted via antenna port ANTP2 which corresponds to the physical antenna 2, and symbols T41, T42, T43, and T44 are transmitted via antenna port ANTP3 which corresponds to the physical antenna 4.
The received symbol estimates are given as:
where h1, h2, h3, h4 denote channel gains from antenna ports 0, 1, 2 and 3 respectively; n1, n2, n3, and n4 represents noise for sub-carriers 1, 2, 3, and 4 in the case of SFBC respectively, or for time slots 1, 2, 3, and 4 in the case of STBC, respectively. It can be seen that symbols S1 and S2 experience higher diversity due to larger spacing between antenna port 0 and antenna port 1. Similarly, symbols S3 and S4 experience higher diversity due to larger spacing between antenna port 2 and antenna port 3 according to antenna ports to physical antennas mapping shown in
In a third embodiment according to the principles of the present invention shown in
In a fourth embodiment according to the principles of the present invention, reference symbols for the four transmission antennas are mapped as shown in
where Tij represents symbol transmitted on the (i−1)th antenna port and the jth subcarrier or jth time slot, and i=1,2,3,4, j=1,2,3,4 for the case of four transmission antennas. The received symbol estimates are given as:
where h1, h2, h3, h4 denote channel gains from antenna ports 0, 1, 2 and 3 respectively; n1, n2, n3, and n4 represents noise for sub-carriers 1, 2, 3, and 4 in the case of SFBC respectively, or for time slots 1, 2, 3, and 4 in the case of STBC, respectively. It can be seen that with the mapping of antenna ports to physical antennas shown in
In a fifth embodiment according to the principles of the present invention, as shown in
In a sixth embodiment according to the principles of the present invention, we derive the six permuted version of SFBC-PSD matrices:
where i=1, . . . , N, and N is the number of the symbols. While the transmitter maps the modulated symbols to the physical time-frequency OFDM resource, it select a subset of K (1≦K≦6) permuted matrices from the six permuted SFBC-PSD matrices. Afterward, the transmitter divides up the modulated signal into K parts, each of the K parts contains 2M symbols, where M is an positive integer and M≧1. Each of the K parts uses a different permuted matrix from the subset of K matrices. One example is to let K=3, and let the three permuted matrices be PA,PB,PC. And we also assume there are 30 modulated symbols S1, S2, . . . , S30. The 30 modulated symbols are divided into 3 parts: the first part contains symbols S1, S2, S7, S8, S13, S14, S19, S20, S25, S26; the second part contains symbols S3, S4, S9, S10, S15, S16, S21, S22, S27, S28; and the third part contains symbols S5, S6, S11, S12, S17, S18, S23, S24, S29, S20. In this example, these three matrices PA,PB,PC will be applied along the frequency dimension, in a pattern that repeats every 6 sub-carriers. That is, PA is assigned to each pair of modulated symbols in the first part of modulated symbols, PB is assigned to each pair of modulated symbols in the second part of modulated symbols, and PC is assigned to each pair of modulated symbols in the third part of modulated symbols.
In a seventh embodiment according to the principles of the present invention, the Node-B, i.e., the base station, selects a subset of K (1≦K≦6) permuted SFBC-PSD matrices for the purpose of Hybrid Automatic Repeat-reQuest (HARQ) transmission. Furthermore, the Node-B applies different SFBC-PSD matrices within this subset of K permuted SFBC-PSD matrices on different retransmissions of the packet. Noteworthy, this approach of applying permuted SFBC-PSD matrices on retransmissions apply to both Chase Combining and incremental redundancy.
In an eighth embodiment according to the principles of the present invention, we derive the six permuted version of SFBC-CDD matrices:
where k is the subcarrier index, and θ1 and θ2 are two fixed phase angles, i=1, . . . N, and N is the number of the symbols. While the transmitter maps the modulated symbols to the physical time-frequency OFDM resource, it select a subset of K (1≦K≦6) permuted matrices from the six permuted SFBC-CDD matrices. Afterward, the transmitter divides up the modulated signal into K parts, each uses a different permuted matrix from the subset of K matrices. One example is to let K=3, and let the three permuted matrices be CA,CB,CC. In this example, these three matrices will be applied along the frequency dimension, in a pattern that repeats every 6 sub-carriers.
In a ninth embodiment according to the principles of the present invention, the Node-B select a subset of K (1≦K≦6) permuted SFBC-CDD matrices for the purpose of HARQ. Furthermore, the Node-B applies different SFBC-CDD matrices within this subset on different retransmissions of the packet. Noteworthy, this approach of applying permuted SFBC-CDD matrices on retransmissions apply to both Chase Combining and incremental redundancy.
Note that the present invention does not limit the number of the antennas. That is, a communication system may have more than four transmission antennas. For example, two code words, CW1 and CW2 are transmitted via ten transmission antennas. Then CW1 can be map to even numbered antenna ports, i.e., ANTP0, ANTP2, ANTP4, ANTP6 and ANTP8, while CW2 can be map to odd numbered antenna ports, i.e., ANTP1, ANTP3, ANTP5, ANTP7 and ANTP9. For the case of SFBC-FSTD, we can create five pairs of symbols S1 and S2, S3 and S4, S5 and S6, S7 and S8, S9 and S10. We can then map each pair to antennas to maximize transmit diversity gain. For example, the first pair S1 and S2 can be mapped to antenna ports 0 and 5, the second pair S3 and S4 can be mapped to antenna ports 1 and 6, and the last pair S9 and S10 to ports 4 and 9.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from a provisional application earlier filed in the U.S. Patent & Trademark Office on 4 May 2007 and there duly assigned Ser. No. 60/924,222.
Number | Date | Country | |
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60924222 | May 2007 | US |