Device and method for precoding vectors in a communication system

• US 8,320,432 B1
• Filed: 04/27/2009
• Issued: 11/27/2012
• Est. Priority Date: 04/27/2009
• Status: Expired due to Fees

• Current Assignee: Indian Institute of Science
• Original Assignee: Indian Institute of Science
• Inventors: Chockalingam, Ananthanarayanan, Rajan, Balaji Sundar, Mohammed, Saif Khan
• Primary Examiner(s): Lee, Siu
• Application Number:
  US12/430,635
• Time in Patent Office: 1,310 Days
• Field of Search: 375/227, 375/316, 375/260, 375/261, 375/259
• US Class Current: 375/219
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A device and method for precoding vectors in a communication system is provided. A transmitter may precode a data vector using information regarding a communication channel prior to transmitting the data vector. The transmitter may precode the data vector in a manner that reduces an energy value of a resulting transmit data vector so as to minimize interference in a received signal at a receiver. The transmitter may perturb entries of the data vector one-by-one in an iterative fashion until a minimum in an energy value of the transmit data vector is obtained.

Claims

1. A method of precoding vectors in a communication system, the method comprising:

receiving an information symbol vector u and a channel matrix H;

calculating a transmit vector x using the information symbol vector u and the channel matrix H;

perturbing an entry of the information symbol vector u;

determining an energy value of the transmit vector, wherein if the energy value of the transmit vector x decreased, perturbing another entry of the information symbol vector u, and if the energy value of the transmit vector x did not decrease, transmitting the transmit vector x,

wherein the method comprises perturbing one entry of the information symbol vector u at a time.

2. The method of claim 1, further comprising calculating a precoder matrix G from the channel matrix H using the following equation, G=H^T(HH^T)⁻

1, and wherein the transmit vector x is calculated according to the equation, x=Gu, where G is an (N_t×

N_u) precoding matrix, and where N_t is a number of transmit antennas, and N_u is a number of users.

3. The method of claim 2, wherein perturbing an entry of the information symbol vector u comprises perturbing the entry so as to minimize an energy value of Gu.

4. The method of claim 1, wherein perturbing an entry of the information symbol vector u comprises adding to the information symbol vector u a vector τ

p, in which τ

is a positive real number determined based on a modulation scheme and the vector p has only one non-zero entry that corresponds to an entry of the information symbol vector u that is being perturbed.

5. The method of claim 1, wherein perturbing an entry of the information symbol vector u comprises perturbing the information symbol vector u in such a way that a transformed vector ũ

is another point in a lattice of a constellation of symbols used by the information symbol vector u such that;

ũ

=u+τ

p

where p is a perturbation vector and τ

is a positive real number.

6. The method of claim 5, wherein τ

is a constellation constant value and is given by;

τ

=2|c_max|+δ

where |c_max| is a maximum value of either a real or imaginary component of constellation symbols used by the information symbol vector u, and δ

is a spacing between the constellation symbols.

7. The method of claim 5, wherein perturbing an entry of the information symbol vector u comprises changing a value of the entry of the information symbol vector u by an amount between −

τ and

+τ

.

8. The method of claim 1, wherein perturbing an entry of the information symbol vector u results in a perturbed vector ũ

, and the determining step further comprises;

determining a first energy value of a transmit vector x using the information symbol vector u and the channel matrix H;

determining a second energy value of a transmit vector x using the perturbed vector and the channel matrix H; and

comparing the first energy value and the second energy value.

9. The method of claim 1, wherein the energy value of the transmit vector x is a squared magnitude of a precoder matrix multiplied by the information symbol vector u.

10. The method of claim 9, wherein the precoder matrix is given by G=H^T(HH^T)⁻

1.

11. The method of claim 1, wherein the method iteratively sequentially perturbs entries of the information symbol vector u until the energy value of the transmit vector x is at a minimum.

12. The method of claim 1, wherein the method iteratively sequentially perturbs entries of the information symbol vector u until no decrease in the energy value of the transmit vector x occurs.

13. The method of claim 1, wherein a bit-error rate (BER) of a received signal decreases for an increase in a number of base station antennas (N_t) and users (N_u).

14. The method of claim 1, wherein a received signal-to-noise ratio (SNR) increases with an increase in a number of base station antennas (N_t) and users (N_u).

15. The method of claim 1, further comprising perturbing more than one entry of the information symbol vector u.

16. A non-transitory computer-readable medium containing a set of instructions for causing a computing device to perform the functions of:

receiving an information symbol vector u and a channel matrix H;

calculating a transmit vector x using the information symbol vector u and the channel matrix H;

perturbing an entry of the information symbol vector u;

if an energy value of the transmit vector x decreased, perturbing another entry of the information symbol vector u; and

if the energy value of the transmit vector x did not decrease, transmitting the transmit vector x,

wherein the functions comprise perturbing one entry of the information symbol vector u at a time.

17. The non-transitory computer-readable medium of claim 16, wherein perturbing an entry of the information symbol vector u results in a perturbed vector ũ

, and the instructions further cause the computing device to perform the functions of;

determining a first energy value of a transmit vector x using the information symbol vector u and the channel matrix H;

determining a second energy value of a transmit vector x using the perturbed vector ũ and

the channel matrix H; and

comparing the first energy value and the second energy value.

18. The non-transitory computer-readable medium of claim 16, wherein perturbing an entry of the information symbol vector u comprises perturbing the entry so as to minimize an energy value of the transmit vector x.

19. The non-transitory computer-readable medium of claim 16, wherein the instructions cause the computing device to iteratively perturb entries of the information symbol vector u until the energy value of the transmit vector x is at a minimum.

20. A precoder comprising:

a vector perturbation unit for receiving an information symbol vector u and perturbing an entry of the information symbol vector u to generate a perturbed information symbol vector ũ

; and

a processing unit for receiving a channel matrix H and calculating a transmit vector x using the information symbol vector u and the channel matrix H, and if an energy value of the transmit vector x is smaller when using the perturbed information symbol vector ũ

as compared to when using the information symbol vector u, instructing the vector perturbation unit to perturb another entry of the information symbol vector u.

21. The precoder of claim 20, wherein if the energy value of the transmit vector x is not smaller when using the perturbed information symbol vector ũ

as compared to when using the information symbol vector u, the processing unit transmits the transmit vector x as calculated using the information symbol vector u.

22. The precoder of claim 20, wherein the vector perturbation unit perturbs the information symbol u so as to minimize the energy value of the transmit vector x.

23. The precoder of claim 20, wherein the vector perturbation unit iteratively perturbs entries of the information symbol vector u until the energy value of the transmit vector x is at a minimum.