Joint Beamforming and Viterbi Equalizer in Wireless Communications.pdf

Joint Beamforming and Viterbi Equalizer in Wireless Communications Miguel A. Lagunas, Ana I. Perez-Neira, Josep Vidal Campus Nord UPC, Mod D5 e/ Gran Capita s/n 08034 BARCELONA SPAIN Abstract The presence of a sequence detector in the baseline architecture for base stations for mobile communications has become a standard. Also the use of coding allows the baseband detector to work at very low signal to noise ratios. When spatial diversity is included in the front-end, the joint design of the beamformer, matched filter and the desired impulse response DIR of the Viterbi equalizer VE is mandatory. This work describes the joint design of these stages when the matched DIR response has priority in the maximization of the signal to noise plus interferences ratio at the input of the VE. Note that in the figure the matched filter is considered a separate and single block at the output of the beamformer; this is the case when there are full coherence between the sensors signal. A more general approach is to consider a broadband beamformer where every channel has a different matched filter, i.e. the matched filter is included in a FIR filter on every array sensor. As it is shown this is under the scope of the design procedure describe hereafter. Also in Section IV it is shown how to derive the single matched filter from the broadband beamformer design as well as the parameter to measure the goodness of the approximation. Introduction Taking as the baseline architecture the single channel receiver formed by a matched filter followed by a synibol sampler and the VE, depicted in Figure 1, Figure 1. Baseline detector with DIR equal to h, and matched filter response bn the maximum length of the matched filter response hm is four and the DIR of the VE ho is usually between four and six in order to bound the complexity and delay of the VE. When including spatial diversity, several antennas are set together with the corresponding radio-frequen