Channel estimation for multirate/multicode DS/CDMA systems with long spreading codes

In this paper, we consider the problem of channel estimation in a multirate/multicode DS/CDMA system employing long spreading codes. The problem is of interest since the most part of the previously derived adaptive techniques for channel estimation relies on the short-code assumption and cannot be adopted in future wireless networks. The proposed procedure requires the transmission of known training bits and is based on a least-squares approach. It does not require timing synchronization, has a computational complexity which is quadratic in the processing gain, and may be adopted both in the uplink and in the downlink. Simulation results confirm that it may achieve satisfactory performance levels, as well as that in a multicode scenario the high-rate users propagation channels may be acquired faster than low-rate users ones.