Spatial multiplexing gain for a distributed cooperative communications system using randomized coding
Multiple cooperative relays operate in a highly mobile environment and form a virtual antenna array. Multiple independent streams of data can be simultaneously, transmitted in parallel to the destination receiver. Thus a higher spatial multiplexing gain can be obtained. Each relay device that receives the information without errors splits it into multiple streams. For example, if the relay devices receive B symbols and the number of streams is K, each stream contains B/K symbols. Each relay device then generates a random linear combination of all the streams and transmits this output simultaneously with the other relay devices.
1. A method for transmitting data from a source wireless device to a destination wireless device, the method comprising:
a) receiving, with each of a plurality of relay wireless devices, a transmission of the data from the source wireless device;
b) splitting, with each of the plurality of relay wireless devices, the received transmission into K streams;
c) encoding, with each of the plurality of relay wireless devices, each of the K streams;
d) applying, with each of the plurality of relay wireless devices, multiple-input-multiple-output (MIMO) encoding to the K encoded streams to generate K parallel streams;
e) independently generating, with each of the plurality of relay wireless devices, a random vector of length K;
f) linearly combining, with each of the plurality of relay wireless devices, the K parallel streams using the random vector to obtain an output signal; and
g) transmitting, with each of the plurality of relay wireless devices, the output signal to the destination device.
2. The method of claim 1 wherein the act of transmitting, with each of the plurality of relay wireless devices, the output signal to the destination device is done in synchronization with, and in parallel with, the transmissions by each of the other of the plurality of relay wireless devices.
3. The method of claim 1 wherein the act of encoding, with each of the plurality of relay wireless devices, each of the K streams, is performed with a channel encoder.
4. The method of claim 1 wherein the plurality of relay wireless devices consists of M relay wireless devices, and wherein the value of K is less than the value of M.
5. The method of claim 1 wherein the act of independently generating, with each of the plurality of relay wireless devices, a random vector of length K, uses a complex Gaussian variable generator.
6. The method of claim 5 wherein the complex Gaussian variable generator has a zero mean.
7. The method of claim 5 wherein the complex Gaussian variable generator has a variance of 1/K or less.
8. The method of claim 1 wherein the act of transmitting, with each of the plurality of relay wireless devices, the output signal to the destination device is performed a fixed time interval after the act of receiving, with the each of the plurality of relay wireless devices, the transmission of data from the source wireless device.
9. The method of claim 1 wherein each of the plurality of relay wireless devices is locked to a reference carrier signal.
10. A method comprising:
a) receiving, with one of a plurality of relay wireless devices, a transmission of data from a source wireless device;
b) splitting, with the one relay wireless device, the received transmission into K streams;
c) encoding, with the one relay wireless device, each of the K streams;
d) applying, with the one relay wireless device, multiple-input-multiple-output (MIMO) encoding to the K encoded streams to generate K parallel streams;
e) independently generating, with the one relay wireless device, a random vector of length K;
f) linearly combining, with the one relay wireless device, the K parallel streams using the random vector to obtain an output signal; and
g) transmitting, with the one relay wireless device, the output signal to a destination device.
11. The method of claim 10 wherein the act of transmitting, with the one relay wireless device, the output signal to the destination device is done in synchronization with, and in parallel with, the transmissions by other of the plurality of relay wireless devices.
12. The method of claim 10 wherein the act of encoding, with the one relay wireless device, each of the K streams, is performed with a channel encoder.
13. The method of claim 10 wherein the plurality of relay wireless devices consists of M relay wireless devices, and wherein the value of K is less than the value of M.
14. The method of claim 10 wherein the act of independently generating, with the one relay wireless device, a random vector of length K, uses a complex Gaussian variable generator.
15. The method of claim 14 wherein the complex Gaussian variable generator has a zero mean.
16. The method of claim 14 wherein the complex Gaussian variable generator has a variance of 1/K.
17. The method of claim 10 wherein the complex Gaussian variable generator has a variance of less than 1/K.
18. The method of claim 10 wherein the act of transmitting, with the one relay wireless device, the output signal to the destination device is performed a fixed time interval after the act of receiving, with the one of relay wireless devices, the transmission of data from the source wireless device.
19. The method of claim 10 wherein each of the plurality of relay wireless devices is locked to a reference carrier signal.
20. A wireless apparatus comprising:
a) a receiver configured to receive a transmission of data from a source wireless device;
b) a converter configured to split the received transmission into K streams;
c) channel encoders configured to encode each of the K streams;
d) a multiple-input-multiple-output (MIMO) encoder configured to apply multiple-input-multiple-output (MIMO) encoding to the K encoded streams to generate K parallel streams;
e) a randomizing processor configured to independently generate a random vector of length K;
f) a combiner configured to linearly combine the K parallel streams using the random vector to obtain an output signal; and
g) a transmitter configured to transmit the output signal to a destination device.