Adaptive transmission timing control using reservation packet in reverse link for broadband DS-CDMA wireless access

This paper proposes the Adaptive Transmission Timing Control (ATTC) method utilizing reservation packets for broadband Variable Spreading Factor (VSF)-CDMA wireless access in the reverse link, in order to increase the link capacity while maintaining advantages such as one-cell frequency reuse in a cellular system in a multi-cell configuration. In the proposed method, the difference in the received reservation packet timing due to the propagation delay time is measured by utilizing the reservation packets that contain small amounts of information such as the data types, i.e., real-time or non-real time, and the size of the traffic bits in the packet data channel. The transmission timings of the successive packet data channels are controlled so that the received timings of the highest signal power path of the packet data channels of simultaneously accessing users are aligned. The simulation results elucidate that by applying ATTC using reservation packets, the required average received signal energy per bit-to-background noise power spectrum density ratio (E-b/N-0) at the average packet error rate of 10(-1) is decreased by approximately 6 (1) dB compared to the case without ATTC and the loss in the required average received E-b/N-0 from the ideal received timing alignment is 1 (0.5) dB, for six (four)-user environment associated with the spreading factor of SF = 8 and in a three-path Rayleigh fading channel, because the dominant multiple access interference caused by the highest signal power path for each user is suppressed.