Impact of the change of the propagation coefficient at the break point on fixed channel assignment for GSM networks

The fixed channel assignment problem in GSM networks has been commonly modelled as a constraint satisfaction problem with binary channel separation constraints (graph-colouring model). However, it has been observed that heuristics using direct estimations of carrier-to-interference ratio (CIR) have several advantages over those using binary constraints, being the economisation of spectrum the most important one. This is due to the fact that CIR constraints provide the possibility of taking more accurately into account different propagation phenomena that directly impact the channel assignment plans. In this paper, we present further improvement to an existing CIR-constraint heuristic algorithm for fixed channel assignment. We demonstrate that accounting for the change of the propagation coefficient at the break point in line-of-sight conditions (commonly seen in urban environments with rectangular grid street plans) might further economise spectrum. Results of practical examples are included.