Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink

In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.

I. Introduction

Orthogonal frequency-division multiplexing (OFDM) [1] has been selected as the physical-layer technology for a number of wireless applications, such as digital audio broadcasting (DAB) [2] and terrestrial digital video broadcasting (DVB) [3]. It has also been adopted by IEEE 802.11a [4] and HIPERLAN/2 [5] for high-data-rate wireless packet transmissions. In OFDM, a set of equally spaced subcarriers is used for parallel data transmission. To increase the frequency efficiency, these subcarriers are overlapping in the frequency domain, but orthogonal to each other such that there is no intercarrier interference (ICI). The most important feature of OFDM is the capability of mitigating frequency-dependent distortion across the channel band and simplifying the equalization in a multipath fading environment.