Optimal FIR transmit filters for multiuser wireline communications

In the near future, very high data rates will be available over wirelines. The need to distribute these high rates among several users will arise. In this paper 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. We show that an optimized FIR transmit filter, maximizing the channel throughput, outperforms both the flat FIR and the popular raised-cosine FIR transmit filters. We derive the throughput function for the fractionally sampled filter and show that more throughput maximization is achieved compared to the symbol-spaced sampled filter. We extend the optimization for multi-dimensional signaling to accommodate multiple users using two possible techniques. For the first option, we derive the multi-user throughput function, and optimize the multi-dimensional filter to maximize this throughput. This will outperform the time multiplexing technique. For the second option, we generate orthogonal signals incrementally. This offers flexibility in accommodating more users and relaxes the receiver equalization process.