Multi-layer realistic voice capacity evaluation in LTE Rel. 9 and performance comparison with PMR and GSM

This paper proposes a multi-layer realistic voice capacity evaluation method for long term evolution (LTE) Release 9 downlink transmission, from a private mobile radio (PMR) perspective. The obtained voice spectral efficiency is also compared with existent PMR networks and global system for mobile communications (GSM). The realistic system model considers both transmission protocols overhead, including internet protocol (IP) and robust header compression (ROHC), and air frame overhead. As LTE is not designed for low bit rate voice communications, we propose to optimize the layer one transmission parameters. We modify the standard algorithm by calculating the minima normalized values for both coding rate and transport block size, considering radio allocation possibilities. The newly computed values are optima for PMR voice transmission. The LTE voice communications capacity is given for the realistic and ideal values of the protocol stack overhead. The realistic results are compared to GSM and PMR voice spectral efficiencies, with the appropriate voice coders. LTE Release 9 seems promising for future data transfers, but is not yet favourable to voice services. Even though the air frame is highly configurable, the protocol stack overhead and the standard resource allocation constraints are not designed for real-time voice packets transmission. The ROHC compressed protocol overhead remains large for voice frames and demands important air resources. On the other hand, resource allocation is not foreseen for small packets transmission. Considering the proposed allocation algorithm, results show that the voice capacity may double if the protocol overhead only were reduced to ideal values.