Abstract
Synchronization of the carrier frequency offset (CFO) in the uplink of OFDMA systems is a complex task because each user presents a different CFO. It is performed in two stages: estimation and compensation. Although a few existing schemes already achieve good performance in terms of bit error rate (BER), all of them perform huge amounts of operations, specially during estimation, thus leading to very costly, if not impractical, hardware implementations. In addition, if estimation is performed in the time domain, a preamble is required. Since the IEEE 802.16e standard for OFDMA has no preamble at the beginning of the uplink frame, optional midambles must be used at the cost of reducing the system throughput. This article proposes a combined CFO estimation and compensation technique that uses the pilot subcarriers of the 802.16e frame. It achieves similar BER performance than previous approaches without any throughput penalty, while reducing the number of required computations by several orders of magnitude. This reduction is the result of a simpler estimation algorithm and two techniques that improve its accuracy: an iterative process integrated with the compensation stage and the delayed correction of the phase shifts.
Highlights
The increasing demand for multimedia communications with variable data rates and different quality of service requirements has recently led to a strong interest in Orthogonal frequency division multiple access (OFDMA)
Proposed synchronization scheme This study proposes a frequency synchronization scheme that, like pilotaided tile structure-based frequency synchronization system (PATS), implements an iterative approach during estimation supported by a feedback loop from the compensation stage to the estimation stage
Three specific techniques have been used in the design: a low-cost OFDM estimation method adapted to OFDMA, and two optimizing techniques aimed at improving its accuracy
Summary
The goal is to design a complete frequency synchronization scheme (i.e., including estimation and compensation) that, achieves good BER performance, and has reduced resource requirements and no throughput losses These new proposals should be evaluated with uplink 802.16e frames, since this is currently the main standard using OFDMA. Estimation technique At the receiver, after applying FFTs on two time-domain blocks (ym and ym+M), the frequency domain kth subcarrier from Equation (5) becomes As it can be observed, the difference between both expressions is in the factors i,m and i,m+M that multiply the data signal, assuming that the CFO and the channel remain nearly constant over the M OFDM symbols. The iterative algorithm can be described in terms of the following steps
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
