Precoding Techniques for Optimized Channel Capacity in MIMO Systems

Abstract

A method of deriving a precoding matrix for a MIMO signal operates by maximising a function of channel capacity over values of precoding matrices so as to maximise the minimum channel capacity for the set of channel realisations. In this way, the least worst channel capacity may be achieved in broadcast arrangements in which the actual channel may be unknown.

1 . A method of deriving a precoding matrix for a MIMO signal of the type having multiple transmitters arranged in pairs, each pair arranged to transmit a signal derived from common source, comprising:
 maximising a function of the channel capacity over values of precoding matrices and a set of channel realisations so as to obtain optimum precoding matrices; wherein the precoding matrices are constrained to be unitary.   
     
     
         2 . A method of deriving a precoding matrix for a MIMO signal of the type having multiple transmitters arranged in pairs, each pair arranged to transmit a signal derived from common source, comprising:
 deriving a measure of channel capacity based on a standard MIMO channel capacity formula;   determining the value of a complex channel measure which maps to a set of channel realisations yielding the lowest channel capacity for a given precoding matrix pair (G, M) from a set of candidate matrices (G,M);   determining, for the set of candidate matrices (G,M), the value of the minimum channel capacity as a function of the complex channel measure; and   selecting the precoding matrices (G,M) that maximimise the minimum channel capacity;   
       wherein the precoding matrices are constrained to be unitary. 
     
     
         3 . A method of deriving a precoding matrix for a MIMO signal of the type having multiple transmitters arranged in pairs, each pair arranged to transmit a signal derived from common source, comprising:
 deriving a measure of channel capacity based on standard MIMO channel capacity formula;   selecting a set of values of a complex channel measure from a probability distribution;   determining the average of the channel capacity over the selected set of values of complex channel measure; and   selecting the precoding matrices that maximimise the mean channel capacity; wherein the precoding matrices are constrained to be unitary.   
     
     
         4 . A method of deriving a precoding matrix for a MIMO signal of the type having multiple transmitters arranged in pairs, each pair arranged to transmit a signal derived from common source, comprising:
 cascading two full (partially correlated) channel models a the matrix pair G,M, then summing the output and maximising the average capacity over multiple realisations of the channel models.   
     
     
         5 . A method of deriving a precoding matrix for a MIMO signal as defined in equation (1). 
     
     
         6 . A method of transmitting a MIMO signal, comprising using a precoding matrix pair as derived according to  claim 1 . 
     
     
         7 . A method of transmitting a MIMO signal according to  claim 6 , wherein the MIMO signal is of the type having fewer data streams than output antennas. 
     
     
         8 . A method of transmitting a MIMO signal according to  claim 7 , wherein the MIMO signal uses two separate pre-coding matrices, one to be applied to source data for one pair of antennas, and the other to be applied to the same source data for a second pair of antennas. 
     
     
         9 . A method of transmitting a MIMO signal according to  claim 6 , wherein the MIMO signal is to be applied to an antenna arrangement using linear and/or circular polarisations. 
     
     
         10 . A method of transmitting a MIMO signal according to  claim 6 , wherein the MIMO signal is for an arrangement having a 4-transmit 2-receive (4×2) MIMO structure where two pairs of transmit antennas are fed with the same source data, but distinctly pre-coded by a matrix pair (G,M). 
     
     
         11 . A method of transmitting a MIMO signal, comprising using a matrix pair as defined in equations (2) and (3). 
     
     
         12 . A transmitter or receiver configured to operate the method of  claim 6 . 
     
     
         13 . A system comprising a transmitter and receiver configured to operate the method of  claim 6 . 
     
     
         14 . A method of processing an OFDM MIMO signal in a system having at least two transmitters arranged to transmit signal pairs, comprising operating a series of transformations including:
 a first carrier index dependent complex rotation of one of the transmit signal pairs using a first complex rotation angle;   a real 2×2 rotation matrix acting across a MIMO pair; and   a second carrier index dependent complex rotation of the one of the transmit signal pairs, using a second complex rotation angle, wherein the second complex rotation angle is different from the first complex rotation angle.   
     
     
         15 . A method of processing an OFDM MIMO signal according to  claim 14 , further comprising applying precoding matrices (G, M), one to be applied to source data for one pair of antennas, and the other to be applied to the same source data for a second pair of antennas. 
     
     
         16 . A method of processing an OFDM MIMO signal according to  claim 14 , further comprising applying cyclic diversity delay as a function of carrier index. 
     
     
         17 . A method of transmitting a MIMO signal, comprising using the method of processing of  claim 14 . 
     
     
         18 . A method of transmitting a MIMO signal according to  claim 17 , wherein the MIMO signal is of the type having fewer data streams than output antennas. 
     
     
         19 . A method of transmitting a MIMO signal according to  claim 18 , wherein the MIMO signal uses two separate pre-coding matrices, one to be applied to source data for one pair of antennas, and the other to be applied to the same source data for a second pair of antennas. 
     
     
         20 . A method of transmitting a MIMO signal according to  claim 17 , wherein the MIMO signal is to be applied to an antenna arrangement using linear and/or circular polarisations. 
     
     
         21 . A method of transmitting a MIMO signal according to  claim 17 , wherein the MIMO signal is for an arrangement having a 4-transmit 2-receive (4×2) MIMO structure where two pairs of transmit antennas are fed with the same source data, but distinctly pre-coded by a matrix pair (G,M). 
     
     
         22 . A method of transmitting a MIMO signal according to  claim 17 , comprising using a matrix pair as defined in equations (2) and (3). 
     
     
         23 . A transmitter configured to operate the method of  claim 14 . 
     
     
         24 . A receiver configured to receive the signal of  claim 14 . 
     
     
         25 . A system comprising a transmitter and receiver configured to operate the method of  claim 14 .