Overview

This chapter looks at the characteristics and use of a DDCA strategy.

In the previous chapter, spectral partitioning for a HCS formed of two layers of cells was analyzed and simulated. The partitioning was done in terms of the pdf of the speed of users and in terms of the expected blocking probability in each layer. This meant that each layer was also given a fixed bandwidth. However, this spectrum partitioning technique has no flexibility for readjusting the actual partitioning or for sharing resources between layers when one of the parameters used to obtain the partitioning suddenly changes (e.g., velocity of users).

The spectrum partitioning technique described in Chapter 5 creates an initial and long-term division of resources between layers and is used as such in cellular systems. So, given a pdf describing the speed of the users, the spectrum partitioning is performed once every day, week, and month, for example, and is updated by the system planning engineers as often as is needed or as often as possible. Hence, this technique cannot adapt itself to sudden changes in the pdf of speed of users and hot spots, for example.

To cope with sudden changes of traffic load in each layer, after spectrum partitioning is been performed initially, a way of sharing resources is needed that continues to do this automatically, not only between cells of the same layer but also between cells of different layers of the hierarchy. Due to their unique characteristics, DCA strategies provide the flexibility...