Downlink capacity and interference statistics of wideband code division multiple access microcells for trains in long tunnels

Abstract

The wideband code division multiple access downlink interference statistics and the capacity of equally spaced tunnel cigar-shaped microcells, used to serve users travelling in trains or metros, are analysed. The hybrid propagation model, with two defined modes, is used in the analysis. Fast fading because of multipath interference is superimposed with the main value of the loss and the slow fading up to a certain distance beyond which it can be neglected. To calculate the interference statistics and the capacity, a scenario with ten cigar-shaped microcells has been considered. The downlink capacity is then derived for different sector radii, train lengths, break point distances and propagation parameters. It is found that increasing the sector range up to 1250 m increases the sector downlink capacity. It is noticed that the maximum downlink capacity can be obtained for a sector radius of 1250–1750 m. It is also found that the increment of the propagation parameter γ reduces the sector downlink capacity. It is also noticed that increasing the train length increases the downlink capacity. It is also found that the bend loss increases the downlink capacity and reduces the maximum sector range.