Fast timing estimation for CDMA waveforms in a near-far environment

A new algorithm is proposed for extracting timing information for all users in a CDMA system operating in a near-far environment without a-priori knowledge of individual user´s power. With unique design of the training sequences, the algorithm is capable of rejecting multiuser interference and thus is not near-far limited. It is shown that the total acquisition time for all system users is considerably reduced compared to previously studied CDMA timing acquisition algorithms without increasing the computation complexity. In fact, the computation complexity of the proposed algorithm is also reduced to MN_b ²+(Mlog M)N_b, where M is the number of users in the system and N_b is the number of samples taken per bit interval. The most significant advantage of this algorithm is that the estimation can be obtained with high accuracy even at a very low signal to noise ratio (SNR). For instance, with M=20 and N_b=254, the probability of acquisition error for a user with SNR at -15 dB is on the order of 10^-5