Space-time transmit diversity systems and methods for ofdm applications
View Patent ↗Embodiments of the invention provide orthogonal Frequency Division Multiplexing-Space-time Block Codes (OFDMSTBC) mappings for code rate 1, 2 and 4 codes for 4 Transmit Antennas. To overcome the innate weakness of known codes, a new class of STBC codes is provided which is particularly suited for OFDM applications, although other applications are also contemplated. Codes for STBC mappings in the time direction, the frequency direction and a combined time frequency mapping for multiple antennas are provided. In OFDM applications, these codes exploit the properties of OFDM and FEC codes to substantially maintain the advantages of Alamouti codes. Furthermore, while the detailed examples given herein focus on four antenna applications, they can be easily extended to systems with more than four antennas.
1. A method for mapping a rate one space-time block code for a 2n antenna transmitter where n=2, the method comprising transmitting 2n transmission symbols in each of a plurality of transmission periods by:
for a first set of sub-carriers, mapping a first set of 2n transmission symbols to a first set of the 2n antennas and mapping a null assignment to a second set of the 2n antennas using a first antenna hopping pattern for a first transmission period of the plurality of transmission periods, the first transmission period comprising a first set of n pairs of consecutive transmission intervals;
for a second set of sub-carriers, mapping a second set of 2n transmission symbols to a third set of the 2n antennas and mapping the null assignment to a fourth set of the 2n antennas using a second antenna hopping pattern for a second transmission period of the plurality of transmission periods;
wherein the first set of the 2n antennas and the fourth set of 2n antennas share a first antenna such that at least a portion of the second set of 2n transmission symbols are transmitted by the first antenna of the first set of the 2n antennas,
wherein the second set of the 2n antennas and the third set of the 2n antennas share a second antenna such that the null assignment is transmitted on the second antenna during both the first transmission period and the second transmission period,
the second transmission period comprising a second set of n pairs of consecutive transmission intervals, wherein the first antenna hopping pattern is different from the second antenna hopping pattern.
2. The method of claim 1 wherein the mapping achieves a diversity order 2 per transmission symbol, the method further comprising performing FEC coding before the mapping such that between the FEC coding and the mapping a full diversity is provided.
3. The method of claim 1 applied in an OFDM transmitter on a per-OFDM sub-carrier basis.
4. The method of claim 1 , wherein the first antenna hopping pattern is one of:
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
s 2
s 1 *
0
0
Antenna 3
0
0
s 3
−s 4 *
Antenna 4
0
0
s 4
s 3 *,
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
s 2
s 1 *
0
0
Antenna 4
0
0
s 4
s 3 *
or
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
0
0
s 4
s 3 *
Antenna 4
s 2
s 1 *
0
0.
5. The method of claim 3 , wherein power balancing is achieved by mapping Alamouti blocks to sub-carriers such that during a given transmission interval, each antenna has a substantially similar number of active sub-carriers.
6. The method of claim 5 , wherein the first antenna hopping pattern is one of:
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
s 2
s 1 *
0
0
Antenna 3
0
0
s 3
−s 4 *
Antenna 4
0
0
s 4
s 3 *,
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
s 2
s 1 *
0
0
Antenna 4
0
0
s 4
s 3 *
or
Time
Time
Time
Time t
(t + T)
(t + 2T)
(t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
0
0
s 4
s 3 *
Antenna 4
s 2
s 1 *
0
0.
7. The method of claim 5 , wherein the first set of sub-carriers are odd sub-carriers or even sub-carriers and the second set of sub-carriers are the remaining sub-carriers.
8. The method of claim 3 , wherein the active antennas of a given sub-carrier alternate every pair of consecutive transmission intervals.
9. A base station, comprising:
a processor configured to map a rate one space-time block code for a 2n antenna transmitter where n=2, wherein the processor transmits 2n transmission symbols in each of a plurality of transmission periods by:
a mapper, for a first set of sub-carriers, mapping a first set of 2n transmission symbols to a first set of the 2n antennas and mapping a null assignment to a second set of the 2n antennas using a first antenna hopping pattern for a first transmission period of the plurality of transmission periods, the first transmission period comprising a first set of n pairs of consecutive transmission intervals;
the mapper, for a second set of sub-carriers, mapping a second set of 2n transmission symbols to a third set of the 2n antennas and mapping the null assignment to a fourth set of the 2n antennas using a second antenna hopping pattern for a second transmission period of the plurality of transmission periods;
wherein the first set of the 2n antennas and the fourth set of 2n antennas share a first antenna such that at least a portion of the second set of 2n transmission symbols are transmitted by the first antenna of the first set of the 2n antennas,
wherein the second set of the 2n antennas and the third set of the 2n antennas share a second antenna such that the null assignment is transmitted on the second antenna during both the first transmission period and the second transmission period, the second transmission period comprising a second set of n pairs of consecutive transmission intervals, wherein the first antenna hopping pattern is different from the second antenna hopping pattern.
10. The base station of claim 9 , wherein the mapping achieves a diversity order 2 per transmission symbol, the method further comprising performing FEC coding before the mapping such that between the FEC coding and the mapping a full diversity is provided.
11. The base station of claim 9 , wherein the 2n transmission symbols are applied on a per-OFDM sub-carrier basis.
12. The base station of claim 9 , wherein the first antenna hopping pattern is one of:
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
s 2
s 1 *
0
0
Antenna 3
0
0
s 3
−s 4 *
Antenna 4
0
0
s 4
s 3 *,
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
s 2
s 1 *
0
0
Antenna 4
0
0
s 4
s 3 *
or
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
0
0
s 4
s 3 *
Antenna 4
s 2
s 1 *
0
0.
13. The base station of claim 11 , wherein power balancing is achieved by mapping Alamouti blocks to sub-carriers such that during a given transmission interval, each antenna has a substantially similar number of active sub-carriers.
14. The base station of claim 13 , wherein the first antenna hopping pattern is one of:
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
s 2
s 1 *
0
0
Antenna 3
0
0
s 3
−s 4 *
Antenna 4
0
0
s 4
s 3 *,
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
s 2
s 1 *
0
0
Antenna 4
0
0
s 4
s 3 *
or
Time t
Time (t + T)
Time (t + 2T)
Time (t + 3T)
Antenna 1
s 1
−s 2 *
0
0
Antenna 2
0
0
s 3
−s 4 *
Antenna 3
0
0
s 4
s 3 *
Antenna 4
s 2
s 1 *
0
0.
15. The base station of claim 13 , wherein the first set of sub-carriers are odd sub-carriers or even sub-carriers and the second set of sub-carriers are the remaining sub-carriers.
16. The base station of claim 11 , wherein active antennas of a given sub-carrier alternate every pair of consecutive transmission intervals.