Combined time and code division scheduling for enhanced uplink packet access in WCDMA

This paper contains an evaluation of three different time and code division schedulers, for data transmission on enhanced dedicated channel (E-DCH) in WCDMA uplink. Time scheduling on E-DCH is possible thanks to fast node B scheduling operation on a transmission time interval (TTI) basis. Time scheduling allows for allocating users for transmission with instantaneously high data rates, and possibly when they experience favourable channel conditions. The system capacity can therefore be increased, also because interference generated to other cells is reduced. We apply a combined time and code division scheduling strategy in three different cases: a "blind fair throughput" scheduler (BFT), a "maximise transmit power efficiency" scheduler (MTPE) and a "channel-state aware fair throughput" scheduler (CSAFT). The two latter schedulers utilise an appositely defined uplink channel quality indicator (UCQI) to exploit channel-state information in the packet scheduling procedure. While the MTPE scheduler maximises cell throughput at the cost of at low degree of fairness between users, the CSAFT algorithm is shown to offer an appealing trade-off between users\´ fairness and throughput maximisation. Under a specific outage constraint for the packet call throughput, the capacity gain of the CSAFT scheduler over a node B code division scheduler is 17% and 30% for vehicular A and pedestrian A channel profile at 3 km/h, respectively. The estimated capacity increase compared to a reference RNC-based scheduler is estimated between 50% and 80%, also depending on the propagation scenario.