Capacity and spectrum efficiency analysis of an asymmetric PMR system with DAB downlink

Abstract

Different trunked Private Mobile Radio (PMR) systems have been designed over the last several decades, all of which have symmetric downlink and uplink channel capacities. Due to this symmetry, those systems may not be spectrally efficient in case of different types of services which are only supported by PMR systems, such as group (acknowledged or unacknowledged) and broadcast calls, either voice or data. In this thesis, a new asymmetric trunked PMR system comprising an OFDM based broadband, wide-area downlink and a narrowband cellular uplink, is proposed to achieve a higher capacity and higher spectral efficiency than current digital trunked PMR systems have. This thesis concentrates on the system capacity analysis of the proposed system associated only with the downlink part for voice communications, as well as the spectrum efficiency comparison of the proposed system with the Terrestrial Trunked Radio (TETRA) system, which is accepted as the spectrally most efficient PMR system. In this study, we study the performance and capacity of the proposed system using Digital Audio Broadcasting (DAB) downlink. In particular, we study the capacity of such a system for voice calls using voice activity detection and statistical multiplexing. Moreover, we show that, the capacity of the system can significantly increase, if the incoming calls, which cannot find an available channel, are allowed to wait a certain amount of time before occupying a channel. The system is shown to have high trunking efficiency since all users are assumed to use the pool of channels available in the wideband downlink. Spectral efficiency of the proposed system and a standard TETRA system are compared using numerical case studies against different traffic loads, cell sizes and number of clusters. The optimum point, with respect to number of clusters, up to which the proposed system is more efficient, is determined. It is shown that for a realistic PMR scenario the proposed system is more efficient up to 5 clusters, i.e. 35 cells, and therefore it can be concluded that the proposed system can be used efficiently in realistic situations.