Cross-layer aware enhancement of VoIP mapping in wireless OFDMA systems

This work addresses the problem of efficient broadcasting of resource allocations descriptors for VoIP traffic in mobile OFDMA-based wireless systems. We show that the mapping overhead is substantially reduced by using semi-persistent allocations and that by taking advantage of the periodicity of VoIP frames, generated by a multi-phase vocoder. To handle the impact of mobility on the characteristics of the wireless channel we utilize a cross-layer decision approach to track the channel conditions and predict the expected mobile user behavior such that the system may under-react to channel changes in some cases. We present mapping algorithms that implement these decisions and show by extensive simulations, that with these mapping algorithms the allocation overhead can be substantially reduced in OFDMA-based systems such as WiMAX and LTE, while retaining a low computational complexity (O(n²)).