Traffic models impact on OFDMA scheduling design
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Traffic models impact on OFDMA scheduling design Pablo Ameigeiras1, Yuanye Wang2, Jorge Navarro-Ortiz1, Preben E Mogensen2,3 and Juan M Lopez-Soler1*
Abstract This article studies the impact on the design of scheduling algorithms for Orthogonal Frequency Division Multiple Access (OFDMA) systems of two traffic models described in the evaluation methodology proposals from standardization bodies: the full buffer and the finite buffer traffic models. The analysis concentrates on utility-based scheduling with an a-fair utility function for Non-Real Time (NRT) services. The results show that a gradient scheduling algorithm is able to maximize the aggregate utility over all the users when the less realistic full buffer model is adopted; but not when the finite buffer model is applied. The results also show that with the full buffer model a gradient scheduler exhibits a trade-off between average user throughput and the user throughput at 5% outage, but it does not when the more realistic finite buffer is used. Therefore, it is concluded that designs of scheduling algorithms for NRT services for OFDMA systems carried out under the full buffer model assumption may fail to provide the desired performance benefits in realistic scenarios. Based on the results presented, a recommendation on scheduling design is provided. Keywords: finite buffer traffic model, full buffer traffic model, OFDMA, packet scheduling, α-fair function, fairness.
1. Introduction Orthogonal Frequency Division Multiple Access (OFDMA) has become an essential technology in broadband wireless communications. Systems such as the 3GPP Long-Term Evolution (LTE) [1], IEEE 802.16d (i.e. fixed WiMAX) [2], IEEE 802.16e (i.e. mobile WiMAX) [3], LTE-Advanced [4] and IEEE 802.16m [5] have adopted OFDMA as their multiple access technique for either downlink or both uplink and downlink air interfaces. In the design of the mentioned wireless access systems, the evaluation methods and models play a key role. There exist publications in the literature that have already indicated that the performance results of algorithms [6] or enhancing features [7] in OFDMA systems significantly depends on the considered traffic model. In this respect, the Next Generation Mobile Networks (NGMN) Alliance and the Institute of Electrical and Electronic Engineers (IEEE) have proposed evaluation methodologies for next generation wireless access * Correspondence: [email protected] 1 Department of Signal Theory, Telematics and Communications, University of Granada, Granada, Spain Full list of author information is available at the end of the article
networks in [8,9], respectively. In addition, evaluation models from the 3rd Generation Partnership Project (3GPP) can be found, for example, in [10]. In these documents, two types of simplified traffic models can be identified for Non-Real Time (NRT) services: (i) Full buffer model [8-10]: it is a simplified version of the traffic received/transmitted by a user in a data session. It is characterized by two facts: the number of
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