PACKET CDMA VERSUS DYNAMIC TDMA FOR MULTIPLE-ACCESS IN AN INTEGRATED VOICE DATA PCN

This paper presents a comparative evaluation of dynamic TDMA and sprea d-spectrum packet CDMA approaches to multiple access in an integrated voice/data PCN environment. After briefly outlining a cellular packet- switching architecture for voice/data PCN systems, dynamic TDMA and pa cket CDMA protocols appropriate for such traffic scenarios are describ ed. Simulation-based network models which have been developed for perf ormance evaluation of these competing access techniques are then outli ned. These models are exercised with example integrated voice/data tra ffic models to obtain comparative system performance measures such as channel utilization, voice blocking probability, and data delay. Opera ting points based on typical performance constraints such as voice blo cking probability less-than-or-equal-to 0.01 (for TDMA), voice packet loss rate less-than-or-equal-to 10(-3) (for CDMA), and data delay less -than-or-equal-to 250 ms are obtained. The results demonstrate the net operating bandwidth efficiencies in the range of 0.1 bits/Hz/cell ach ieved by conventional TDMA (with a fixed reuse factor of 7 and no powe r control); corresponding values for direct-sequence CDMA (with perfec t power control) are in the region of 0.2-0.4 bits/s/Hz/cell for chann el propagation constant (gamma) varying between 2.5 and 4.0. Overall, it is shown that while CDMA typically does provide a 2:1 or greater ca pacity advantage over TDMA, the gains are sensitive to the assumed pro pagation model and are generally associated with higher data delay for long messages generated by file transfer and multimedia applications.