Capacity enhancing strategies based on fast packet scheduling

In order to support the expected traffic offered by the new coming packet services, an evolution of the UMTS system as described in 3GPP/Release 99 is necessary. However, due to the asymmetrical nature of the traffic, most of the efforts are concentrated in the downlink, in the so-called HSDPA within 3GPP. Very little attention has been given to the investigation of packet scheduling techniques and other capacity enhancing strategies for packet access in the uplink. This project proposes and investigates several schemes that aim at increasing the data rates for packet services and could potentially be included in the uplink evolution of the packet access in UMTS. Most of the investigated strategies are mainly based on moving part of the RNC functionality to the Node B, in order to circumvent the bottleneck caused by the signalling delay through the Iub interface. These strategies consist on the use of Hybrid ARQ (HARQ), Node B scheduling based on BRD and on time division multiplexing, and uplink synchronisation. The study methodology comprises theoretical analysis as well as computer simulations at system level. Some of these techniques can also be combined in order to obtain a higher gain. The use of HARQ has proven to increase the capacity in Vehicular A environments, where it has been shown that increasing the BLER target translates into a much smaller required Eb/No. Although this does not happen with a Pedestrian A PDP, the use of HARQ provides a higher capacity gain by solving coverage limitations. Two different scheduling concepts have been proposed based on moving part of the RNC functionality to the Node B. The first of them is based on blind data rate detection, and the simulations results have shown a 31.0% and 37.8% capacity gain in Vehicular A and Pedestrian A channels, respectively, when combined with HARQ. In the second one the WCDMA spectrum is divided in the time domain, which means that only a few UEs are allowed to transmit at every time interval, set to 2 ms. As previously mentioned, some of the proposed techniques can be combined. Compared to the reference packet scheduler located at the RNC, our time-rate packet scheduling algorithm with HARQ and uplink synchronisation provides a 108.0% capacity gain in a Pedestrian A PDP. (José Outes, Preben E. Mogensen, Troels B. Sørensen; Klaus I. Pedersen, Nokia)