Low-Complexity Joint Time Synchronization and Channel Estimation for OFDM-Based PLC Systems

Abstract

Orthogonal frequency division multiplexing (OFDM) plays an important role in powerline communications (PLC), due to its robustness to frequency-selective channels. Nevertheless, it also presents some persistent drawbacks over the years, some of them related to the synchronization and channel estimation and equalization, whose features are a key aspect in the global performance of the medium access technique. This work presents a novel timing synchronization and channel estimation method for OFDM under PLC conditions. Typical joint fine synchronization and channel estimation techniques for OFDM make use of the cross correlation from a transmitted pilot symbol with suitable correlation properties. However, these proposals often present the drawback of having a high computational load, sometimes reducing the feasibility of later practical implementations. Our proposal takes advantage of the properties of complementary pairs of sequences, as they provide good correlation properties, as well as efficient algorithms for generation and correlation. Furthermore, some practical thresholds for synchronization are derived, which adapt the system to the current signal-to-noise ratio and channel conditions. Finally, all the theoretical proposals have been validated by simulation, including an analysis of the performance achieved. INDEX TERMS Channel estimation, complementary pair of sequences, orthogonal frequency division multiplexing (OFDM), power-line communications (PLC).

Efficient Low-Complexity Optimized Channel Estimating Methods for OFDM-Based Low-Voltage Broadband Power Line Communication Systems

“…As can be seen in Fig. 11, our proposed schemes IPSO-based LS and LMMSE estimators outperform the schemes in [2]and [25]. For instance, at a lower 20 dB SNR, the proposed IPSO-based LMMSE and LS algorithms attained nearly 8.3849×10 −12 and 6.0157×10 −9 MSE values, compared to, 9.35×10 −8 and 7.854×10 −7 MSE values for the matched filter and DPTE-PTS algorithms, respectively.…”

“…However, the schemes in [2] and [25] show superior performance over the proposed PSO-inspired LS developed in [7] to combat impulsive noise in the PLC system. The authors show that the proposed blind PSO approach improved system performance but deteriorates at higher SNRs.…”

“…A Turbo Equalizer for the PLC system was proposed in [27] which showed marginal performance in terms of MSE reduction for all SNR values and greatly reduced the computational complexity. A matched filter for an OFDM-based PLC system was investigated in [2] for guaranteed low computational complexity and MSE reduction capability, but such a filter is impracticable. In [25], Dynamic Peak-Based Threshold Estimation is combined with Partial Transmit Sequence (DPTE-PTS) technique to suppress impulsive noise in the PLC system.…”

“…However, due to the diversity of practical power network configurations and fluctuations of various loads connected to the termination points of the networks, PLC channels experience time-varying and multipath propagation frequency-selective fading, signal attenuation, reflection, and strong noise interference effects, which can significantly degrade system performance. To provide robust immunity against the frequency-selective multipath fading effects, multi-carrier OFDM-based on single-carrier Quadrature Amplitude Modulation (QAM) formats have become the preferred solution over the last decade [2]. In this case, the OFDM modulation technique transforms the frequencyselective fading effects into flat-fading effects and also supports higher data rates in PLC systems.…”

“…For this reason, a plethora of channel estimation methods have been published in the literature for OFDM-based PLC channels which can generally be put into two main categories: 1) pilot-aided [4] [5], e.g., Least Square (LS) [6], Particle Swarm Optimization (PSO) [6], Maximum-Likelihood (ML) [8] complementary sequences [2], Linear Minimum Mean Square Error (LMMSE) [9],…”