Pan Liu, NJIT
Date : November 10, 2006 (Friday)
Time : 10:00 AM
Location : ECE 202, NJIT

Abstract

Multiple input multiple output (MIMO)-based orthogonal frequency division multiplexing system (OFDM) is a promising block transmission system for future 4G and other broadband applications by achieving high spectral efficiency and increasing system throughput. However, similar to OFDM, MIMO-OFDM suffers from significant performance degradation due to the presence of phase noise, which causes common phase error and intercarrier interference among subcarriers.

Although various phase noise analysis and mitigation schemes were presented for OFDM in the past, issues related to the impact of phase noise on MIMO-OFDM systems are not comprehensively addressed in current literature. Moreover, most papers are concerned with phase noise generated at receiver only, which is inappropriate for the increasing demand of the uplink high data rate transmission, where transmitter employs relatively low cost local oscillators.

In this research, by proving certain relation between phase noise at both sides of the channel, and at the receiver side only, we first present closed-forms of the bit error rate (BER) in OFDM systems, which exhibit the severe impact of phase noise on the system performance. Then we propose a traditional maximum likelihood (ML)-based phase noise estimation approach, which can be considered as a general method for the algorithms already existed in the literature for MIMO-OFDM systems. Next, in order to improve the overall performance, a new subcarrier-based phase noise mitigation method is proposed and analyzed in terms of computational complexity and minimum mean-square error (MMSE), which has been used in the selection of the optimum number of pilots. From a practical point of view, however, this academic scheme has a relatively high complexity and cannot be implemented in a spatially correlated channel. Hence we finally propose a simplified estimation algorithm for the correlated channel with low complexity and practical implementation. Simulation results validate our demonstration of equivalence and show the effectiveness of the proposed schemes.

Another block transmission system, somewhat equivalent to OFDM, is single carrier frequency domain equalization (SC-FDE), which is also an important block transmission candidate for the future communication system in multipath fading channels. Unlike in OFDM systems, the effect of phase noise and carrier frequency offset (CFO) turns out to be a controversial problem in SC-FDE. By carefully examining the assumptions and limitations of the existing analysis on this topic, we solve the controversy and conclude that SC-FDE systems are also vulnerable to phase noise and CFO in AWGN channels.

Finally, we extend our conclusions to multipath fading channels. Under fair assumptions, we first compare the capacity of the two candidates without phase noise to show the similarity between them. Then by analyzing the MMSE and capacity in the presence of phase noise with a common MMSE filter bank, we conclude that SC-FDE also suffers from phase noise which may cause significant performance degradation. Therefore, a simple and effective least squares (LS) based phase noise compensation scheme is proposed. Simulation results show that the performance is unacceptable without phase noise compensation and our scheme exhibits excellent performance with only a few pilots.

Advisor:

Dr. Yeheskel Bar-Ness, Distinguished Professor, ECE Dept., NJIT.

Committee Members:

Dr. Ali Abdi, Assistant Professor, ECE Dept., NJIT

Dr. Alexander M. Haimovich, Professor, ECE Dept., NJIT

Dr. Hongya Ge, Associate Professor, ECE Dept., NJIT

Dr. Ravi Narasimhan, Assistant Professor, ECE Dept., University of California, Santa Cruz