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AN EFFICIENT CROSS-LAYER AWARE MAPPING OF VOIP CALLS IN WIRELESS OFDMA SYSTEMS Part I. Problem description and channel tracking

Purpose: This work addresses the problem of efficient broadcasting of resource allocations descriptors for VoIP traffic in mobile OFDMA-based wireless systems. Methods: We present the problem of mapping overhead and show that it can be substantially reduced by using semi-persistent allocations and 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 that tracks the channel quality and predicts the expected mobile user behavior such that the system may under-react to channel changes in some cases. Results: We explicitly show how the variability of the wireless channel can be tracked by using a Markovian model with a set of discrete states. By estimating both state- and transition probabilities of the multi-state Markovian model, we underline the foundations for a cross-layer decision algorithm that is able to overlook short transitions in channel states, without changing the modulation and/or the coding schemes. The main advantage of this approach is the ability to support multiple codecs, or a single codec with different operational modes, both result in different packet sizes and different periods. Practical relevance: The proposed channel tracking mechanism is simple enough to be implemented in the base station of any practical OFDMA-based system using the WiMAX or LTE technology

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ИНФОРМАЦИОННЫЕ КАНАЛЫ И СРЕДЫ UDC 654.165 doi:10.15217/issn1684-8853.2015.2.90 AN EFFICIENT CROSS-LAYER AWARE MAPPING OF VOIP CALLS IN WIRELESS OFDMA SYSTEMS Part I. Problem description and channel tracking I. Kitroser a, PhD, Electrical Engineering, kitroser@bgu.ac.il aBen-Gurion University of the Negev, POB 653, 1, Ben Gurion St., Beer Sheva, 74105, Israel Y. Ben-Shimola, PhD, Electrical Engineering, Professor, benshimo@bgu.ac.il Purpose: This work addresses the problem of efficient broadcasting of resource allocations descriptors for VoIP traffic in mobile OFDMA-based wireless systems. <...> Methods: We present the problem of mapping overhead and show that it can be substantially reduced by using semi-persistent allocations and 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 that tracks the channel quality and predicts the expected mobile user behavior such that the system may under-react to channel changes in some cases. <...> Results: We explicitly show how the variability of the wireless channel can be tracked by using a Markovian model with a set of discrete states. <...> By estimating both state- and transition probabilities of the multi-state Markovian model, we underline the foundations for a cross-layer decision algorithm that is able to overlook short transitions in channel states, without changing the modulation and/or the coding schemes. <...> Practical relevance: The proposed channel tracking mechanism is simple enough to be implemented in the base station of any practical OFDMA-based system using the WiMAX or LTE technology. <...> Keywords — Cross-Layer Design and Optimization, Resource Allocation and Interference Management, Mobile Multimedia Technology, 3.5G and 4G Technologies . <...> This suggests that with a naive resource allocation scheme the uplink map (UL-MAP) includes allocation descriptors (or information elements — IEs) for VoIP streams, thus generating overheads at a constant rate. <...> This suggests that the total amount of overhead for each VoIP call is usually very large. <...> The problem of system overhead for CBR-like applications has been examined for the emerging beyond 3G technologies such as WiMAX (IEEE 802.16) [1], IEEE 802.16m-2011 [2], 3GPP long-term evolution (LTE) [3] and 3GPP2 ultra mobile broadband (UMB) [4]. <...> This extreme overhead <...>
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