Orthogonal re-spread for uplink WCDMA beamforming
Robert J. Piechocki, Nishan C. Canagarajah, Joe P. McGeehan, George V. Tsoulos · 2002
This paper presents a new extraction method for the spatial correlation matrix of interference and noise only based on orthogonal re-spreading. The method uses one of the remaining orthogonal variable spreading factor (OVSF) code that is orthogonal to all traffic and control channels to spread energy form the desired user while attempting to maintain the same level of co-channel interference. De-spreading with the assigned OVSF codes that is performed in parallel provides the usual noisy correlation matrix. With those two matrices at hand optimal beamforming using maximal signal-to-interference ratio (MSIR) criterion is readily performed. Although the matrix extracted by the orthogonal re-spread is not a statistically consistent estimate, remarkable potentials in practical situations are demonstrated.