Multiple access over digital subscriber loops using optimal FIR transmit filter bank

With the emerging high bit rate wireline channels, multiple access is inevitable. We explain a technique which allows several users to use the same communication medium while at the same time allowing their transmissions to be separated at the receiver. The problem is defined as FIR filter bank design over two steps. First, the 1-D FIR filter is designed by optimizing the bit-rate over a given channel and this optimization is extended for an oversampled filter. It is shown that the optimum 1-D filter outperforms both the flat FIR and the popular raised-cosine FIR transmit filters. Second, a multi-dimensional filter bank is designed by jointly optimizing a set of filters. The overall bit rate for the multi-dimensional filter bank exceeds that of the 1-D FIR, thus outperforming time multiplexing technique for multiple access. The new filter bank has attractive features for multiple access applications over wireline channels. Simulations are carried out to confirm the functionality of the transmit filter bank for the popular digital subscriber loop channel