Method and apparatus for optimizing transmission diversity
A method and apparatus are provided for transmission in a communication system. The system includes a transmitter having at least one first and second antenna and a receiver, which includes at least one receiving antenna. The method includes determining a transmit diversity scheme for at least one group of symbols from among a plurality of modulated symbols. This step includes at least one step of obtaining a phase shift of at least one symbol of the at least one group of symbols. The phase shift is based on: at least one phase shift parameter N; and responses (h k1 , h k2 ), respectively, between the at least one first antenna and the at least one receiving antenna and between the at least one second antenna and the at least one receiving antenna. The method further includes a step of phase shifting, allowing rotation of said symbol at a multiple of a π/N value.
1. A method for transmitting in a communication system, said system comprising a transmitter, which comprises at least one first antenna and at least one second antenna and a receiver which comprises at least one receiving antenna, said method comprising:
a step of determining a transmit diversity scheme for at least one group of symbols from among a plurality of modulated symbols, comprising at least one step of choosing a phase shift value of at least one symbol of said at least one group of symbols, said phase shift value being chosen based on:
at least one phase shift parameter N, N being an integer, and
N calculated quantities which are functions of responses (h k1 , h k2 ), respectively, between said at least one first transmitting antenna and said at least one receiving antenna and between said at least one second transmitting antenna and said at least one receiving antenna, at an emitting time k; and
a step of phase shifting, which rotates said symbol of said phase shift value at a multiple of a π/N value, wherein said step of phase shifting comprise a step of choosing a highest quantity H n , among a plurality of quantities H k (n) where 0≦n≦N−1 and wherein said highest quantity H n determines a phase shift factor that is used to calculate said phase shift value.
2. The method as claimed in claim 1 , wherein said step of determining comprises:
a step of processing the plurality of quantities H k (n), where 0≦n≦N−1 which are a function of:
said responses of the two antennas (h k1 , h k2 ) at time k; and
a quantity calculation parameter n, where 0≦n≦N−1;
a step of selecting the phase shift value based on said plurality of quantities H k (n) where 0≦n≦N−1 previously processed.
3. The method as claimed in claim 2 , wherein, when said transmitter comprises one first and one second antenna and said receiver comprises one receiving antenna, said quantity H k (n) is calculated with the following formula:
H k ( n )=| h k1 +e jnπ/2 h k2 |.
4. The method as claimed in claim 2 , wherein said value of said phase shift is e jnπ/2 , where 0≦n≦N−1.
5. The method as claimed in claim 2 , wherein, when said transmitter comprises one first and one second antenna and said receiver comprises one first and one second antenna, said quantity H(n) is calculated with the following formula:
H k ( n )=| h k1 +e jnπ/2 h k2 | 2 +|h k3 +e jnπ/2 h k4 | 2
where:
h k1 is the response of the channel between first transmitting antenna and first receiving antenna at time k;
h k2 is the response of the channel between second transmitting antenna and first receiving antenna at time k;
h k3 is the response of the channel between first receiving antenna at and second receiving antenna time k; and
h k4 is the response of the channel between second transmitting antenna and second receiving antenna at time k.
6. The method, according to claim 3 , wherein at time k, a first signal x k1 is transmitted from the first antenna with the value
x
k
1
=
s
k
2
and wherein a second signal x k2 is transmitted from the second antenna with the value
x
k
2
=
ⅇ
j
n
π
/
2
s
k
2
,
where S k corresponds to a symbol at time k.
7. The method according to claim 1 , wherein in an OFDM based system, said method is used on a carrier-by-carrier basis, allowing calculating a phase shift for at least some of a plurality of carriers.
8. An apparatus transmitting in a communication system, said system comprising a transmitter, which comprises at least one first and at least one second antenna, and a receiver, which comprises at least one receiving antenna, said apparatus comprising:
means for determining a transmit diversity scheme for at least one group of symbols from among a plurality of modulated symbols, comprising means for choosing a phase shift value of at least one symbol of said at least one group of symbols, said phase shift value being chosen based on:
at least one phase shift parameter N, N being an integer, and
N calculated quantities which are functions of responses (h k1 , h k2 ) respectively between said at least one first antenna and said at least one receiving antenna and between said at least one second antenna and said at least one receiving antenna, at an emitting time k,
means for phase shifting, which rotates said symbol of said phase shift value at a multiple of a π/N value, wherein phase shifting comprises a step of choosing a highest quantity H n , among a plurality of quantities H k (n) where 0≦n≦N−1 and wherein said highest quantity H n determines a phase shift factor that is used to calculate said phase shift value.
9. A computer program product stored on a non-transitory computer readable medium, wherein the product includes instructions of program code for implementing a method of transmitting in a communication system, which includes a transmitter which comprises at least one first antenna and at least one second antenna and a receiver which comprises at least one receiving antenna, when run on a computer, wherein the method comprises:
a step of determining a transmit diversity scheme for at least one group of symbols from among a plurality of modulated symbols, comprising at least one step of choosing a phase shift value of at least one symbol of said at least one group of symbols, said phase shift value being chosen based on:
at least one phase shift parameter N, N being an integer, and
N calculated quantities which are functions of responses (h k1 , h k2 ), respectively, between said at least one first transmitting antenna and said at least one receiving antenna and between said at least one second transmitting antenna and said at least one receiving antenna, at an emitting time k; and
a step of phase shifting, which rotates said symbol of said phase shift value at a multiple of a π/N value, wherein said step of phase shifting comprise a step of choosing a highest quantity H n , among a plurality of quantities H k (n) where 0≦n≦N−1 and wherein said highest quantity H n determines a phase shift factor that is used to calculate said phase shift value.