Timing and Frequency Synchronization for the Uplink of an OFDMA System

Abstract

This paper deals with timing and frequency recovery for the uplink of an orthogonal frequency-division multiple access (OFDMA) system. The frequency estimator is derived from ad hoc reasoning, whereas the timing estimator is based on the maximum-likelihood criterion. Both schemes rely on the repetition of a fixed pilot symbol. Their main feature is that they provide feedforward estimates and allow synchronization in only two OFDM blocks. In contrast to other existing methods, they do not require that the subcarriers of a given user occupy adjacent positions in the signal bandwidth. This makes it possible to interleave subcarriers of different users so as to optimally exploit the frequency diversity of the channel. Theoretical analysis and computer simulations are used to assess the performance of the proposed synchronizers. It is found that the degradations due to residual frequency and timing errors are negligible at signal-to-noise ratios of practical interest

Timing and frequency synchronization for OFDM based cooperative systems

“…A multiple parameter estimation task is performed at the destination node. As discussed in [5], accurate timing and frequency compensation cannot be accomplished at the destination node, as the correction of one relay node's offsets would misalign the other relay nodes. To overcome this problem, the destination node may feed back the estimated offsets to the relay nodes.…”

“…Thus, synchronization algorithms for uplink OFDMA (see e.g. [5,6] and references therein) may in principle be applied to our problem. However, most of these algorithms need to perform a complicated iterative search to estimate the timing and frequency offsets.…”

Channel estimation in OFDM systems operating under high mobility using Wiener filter combined basis expansion model

“…If we want to compensate this effect, we are dealing with the problem of fine-frequency adjustment. One effect of carrier frequency offset is the detrimental effect of a rotation of the subcarriers [23,24]. This effect will be recognized by a channel estimator, which does not distinguish between phase offsets caused by the channel and those caused by a frequency offset.…”

Robust estimation of carrier-frequency offset and timing offset for OFDMA uplink systems over multi-path fading channels

“…As different users' signals are mixed together at the receiver, the carrier-frequency offset and timing offset will cause inter-carrier interference both from the user itself and from all the other users. Recently, several synchronization algorithms for OFDMA uplink systems have been proposed [1]- [3]. The algorithm proposed in [1] estimates the offset by assuming that all users are already synchronized in time and frequency except for one new user.…”

“…Recently, several synchronization algorithms for OFDMA uplink systems have been proposed [1]- [3]. The algorithm proposed in [1] estimates the offset by assuming that all users are already synchronized in time and frequency except for one new user. However, this assumption may not hold in practice.…”