Overview

As mentioned in Chapter 4, TD/CDMA has been selected as one of the MAS to be used for UTRA. In this chapter, an extended DDRA strategy for a HCS based on the strategy HDCA-II presented in the previous chapter is derived and evaluated. The evaluation environment used in this chapter is rather more complex than those used before, and multiple services are considered simultaneously.

In this new version of the DDRA, resources are shared not only between cells of the same hierarchy but between layers of the HCS. In HDCA-II this was not possible. In fact, slow-moving users were only able to use macrocell channels when they were overflowed to the macrocell layer. The DDRA presented here allows one to use macrocell channels in the microcell layer.

This proposed DDRA strategy is evaluated using the hybrid TD/CDMA-FDD proposal made in the Frames Project Mode 1 (FMAl) as a case study. A mixed environment is suggested for the evaluation of the DDRA, which consists of Manhattan-like microcells covered by hexagonal-shaped umbrella cells (macrocells). As in the previous case, users are classified according to their speed as slow-moving users and fast-moving users and are attended by the most suitable layer of the hierarchy according to their speeds. Two types of real time circuit-switched services are considered in the evaluation: speech and data at different rates. The DDRA is compared with the FRA strategy with overflow and with FRA allowing overflow, hand-down, and channel reallocations (FRAHR) (FRA and FRAHR strategies were presented...