Inter-Cell Interference Statistics in OFDMA Cellular Networks: The Truth

With the advent of Turbo/LDPC codes and MIMO techniques, there is widespread consensus in industry and academia that we are now very close to achieving the theoretical limit promised by Shannon in the physical layer. However, most, if not all of the currently available results are based on the assumption that the aggregate interference as observed by the receiver is Gaussian or at least very close to Gaussian. This Gaussian assumption based on the renowned Central Limit Theorem (CLT) has played a pivotal role in the analysis and design of most modern communication systems, including cellular/ad-hoc networks based on Orthogonal Frequency Division Modulation (OFDM) and Direct-Sequence Spread-Spectrum (DSSS) modulation. In this talk, we assert that the claim that we are now very close to channel capacity is, in fact, only partially true and that in many cases, we may actually be far from achieving the actual channel capacity. The basis of our claim is that unlike networks based on DSSS modulation where the Guassian assumption of the interference statistic may be quite accurate, the statistics of the inter-cell interference in networks such as those based on OFDM may not resemble the Gaussian distribution at all. Our results show that using accurate statistical models for the inter-cell interference in cellular OFDMA networks is essential not only in evaluating the performance of cellular OFDMA networks but also in designing effective receiver algorithms. We also show that with the accurate ICI model, the trade-offs between different modulation schedules (QAM vs. MFSK) could be quite different from what we would expect.

Dr. Kyungwhoon Cheun received his B.S. degree in Electronics Engineering from Seoul National University in 1985. He earned his M.S. and Ph.D. degrees from the University of Michigan, Ann Arbor in 1987 and 1989, respectively. He was an assistant professor at University of Delaware from 1989 to 1991 and joined the Pohang University of Science and Technology (POSTECH) in 1991 where he is currently a professor. At POSTECH, he heads the ITRC national center for Broadband OFDM Multiple Access (BrOMA), an 8 year research program supported by the Korean Ministry of Knowledge and Economy, involving 13 nationwide prominent university research laboratories and 5 industry sponsors. Dr. Cheun has also served as an engineering consultant to numerous industries and was on leave at Witechs, San Diego in 2001 where he developed efficient modem algorithms for the IEEE802.11 based WLAN. Aside from his academic duties, he is currently the Chief Technical Officer (CTO) for Pulsus Technologies Inc. where he is in charge of developing audio processing algorithms and sigma-delta modulation based full digital audio amplifier SoCs. Dr. Cheun’s current area of research includes modeling of OFDMA networks, ECC design for wireless networks, hardware efficient design of MIMO detector and audio enhancement algorithms.