Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last Five Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last five years (2010-2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input-single-output (SISO), multiple-input-multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorise the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions.Comment: submitted for journal publicatio

Joint Doppler frequency shift compensation and data detection method using 2-D unitary ESPRIT algorithm for SIMO-OFDM railway communication systems

In this paper, we present a joint Doppler frequency shift compensation and data detection method using 2-D unitary ESPRIT algorithm for SIMO-OFDM railway communication systems over fast time-varying sparse multipath channels. By creating the spatio-temporal array data matrix utilizing the ISI-free part of the CP (cyclic prefix), we first propose a novel algorithm for obtaining auto-paired joint DOA and Doppler frequency shift estimates of all paths via 2-D unitary ESPRIT algorithm. Thereafter, based on the obtained estimates, a joint Doppler frequency shift compensation and data detection method is developed. This method consists of three parts: (a) the received signal is spatially filtered to get the signal corresponding to each path, and the signal corresponding to each path is compensated for the Doppler frequency shift in time domain, (b) the Doppler frequency shift-compensated signals of all paths are summed together, and (c) the desired information is detected by performing FFT on the summed signal after excluding the CP. Moreover, we prove that the channel matrix becomes time-invariant after Doppler frequency shift compensation and the ICI is effectively avoided. Finally, simulation results are presented to demonstrate the performance of the proposed method and compare it with the conventional method.Comment: 25 pages, 5 figure

Simple sampling clock synchronisation scheme for reduced-guard-interval coherent optical OFDM systems

A simple data-aided scheme for sampling clock synchronisation in reduced-guard-interval coherent optical orthogonal frequency division multiplexing (RGI-CO-OFDM) systems is proposed. In the proposed scheme, the sampling clock offset (SCO) is estimated by using the training symbols reserved for channel estimation, thus avoiding extra training overhead. The SCO is then compensated by resampling, using a time-domain interpolation filter. The feasibility of the proposed scheme is demonstrated by means of numerical simulations in a 32-Gbaud 16-QAM dual-polarisation RGI-CO-OFDM system.Comment: 2 pages, 5 figures, Journa

Phase Noise Compensation for OFDM Systems

We describe a low complexity method for time domain compensation of phase noise in OFDM systems. We extend existing methods in several respects. First we suggest using the Karhunen-Lo\'{e}ve representation of the phase noise process to estimate the phase noise. We then derive an improved datadirected choice of basis elements for LS phase noise estimation and present its total least square counterpart problem. The proposed method helps overcome one of the major weaknesses of OFDM systems. We also generalize the time domain phase noise compensation to the multiuser MIMO context. Finally we present simulation results using both simulated and measured phased noise. We quantify the tracking performance in the presence of residual carrier offset.Comment: This paper was accepted for publication in IEEE Transactions on Signal Processin

A Method for RFO Estimation Using Phase Analysis of Pilot Symbols in OFDM Systems

In this paper, a method for CFO/RFO estimation based on proportional coefficients extraction in OFDM system is proposed, which may be applied to any pilot symbol pattern.Comment: 11 pages, 9 figure

Phase Noise Influence in Coherent Optical OFDM Systems with RF Pilot Tone: Digital IFFT Multiplexing and FFT Demodulation

We present a comparative study of the influence of dispersion induced phase noise for CO-OFDM systems using Tx channel multiplexing and Rx matched filter (analogue hardware based); and FFT multiplexing/IFFT demultiplexing techniques (software based). An RF carrier pilot tone is used to mitigate the phase noise influence. From the analysis, it appears that the phase noise influence for the two OFDM implementations is very similar. The software based system provides a method for a rigorous evaluation of the phase noise variance caused by Common Phase Error (CPE) and Inter-Carrier Interference (ICI) and this, in turns, leads to a BER specification. Numerical results focus on a CO-OFDM system with 1GS/s QPSK channel modulation. Worst case BER results are evaluated and compared to the BER of a QPSK system with the same capacity as the OFDM implementation. Results are evaluated as a function of transmission distance, and for the QPSK system the influence of equalization enhanced phase noise (EEPN) is included. For both types of systems, the phase noise variance increases significantly with increasing transmission distance. An important and novel observation is that the two types of systems have very closely the same BER as a function of transmission distance for the same capacity. For the high capacity QPSK implementation, the increase in BER is due to EEPN, whereas for the OFDM approach it is due to the dispersion caused walk-off of the RF pilot tone relative to the OFDM signal channels. For a total capacity of 400 Gb/s, the transmission distance to have the BER < 10-4 is less than 277 km.Comment: 10 page

Spectrum Monitoring Using Energy Ratio Algorithm For OFDM-Based Cognitive Radio Networks

This paper presents a spectrum monitoring algorithm for Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radios by which the primary user reappearance can be detected during the secondary user transmission. The proposed technique reduces the frequency with which spectrum sensing must be performed and greatly decreases the elapsed time between the start of a primary transmission and its detection by the secondary network. This is done by sensing the change in signal strength over a number of reserved OFDM sub-carriers so that the reappearance of the primary user is quickly detected. Moreover, the OFDM impairments such as power leakage, Narrow Band Interference (NBI), and Inter-Carrier Interference (ICI) are investigated and their impact on the proposed technique is studied. Both analysis and simulation show that the \emph{energy ratio} algorithm can effectively and accurately detect the appearance of the primary user. Furthermore, our method achieves high immunity to frequency-selective fading channels for both single and multiple receive antenna systems, with a complexity that is approximately twice that of a conventional energy detector

Power Penalty Due to First-order PMD in Optical OFDM/QAM and FBMC/OQAM Transmission System

Polarization mode dispersion (PMD) is a challenge for high-data-rate optical-communication systems. More researches are desirable for impairments that is induced by PMD in high-speed optical orthogonal frequency division multiplexing (OFDM) transmission system. In this paper, an approximately analytical method for evaluating the power penalty due to first-order PMD in optical OFDM with quadrature amplitude modulation (OFDM/QAM) and filter bank based multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) transmission system is presented. The simulation results show that, compared with the single carrier with quadrature phase shift keying(SC-QPSK), both the OFDM/QAM and the FBMC/OQAM can decrease the power penalty caused by PMD by half. Furthermore, the FBMC/OQAM shows better power penalty immunity than the OFDM/QAM under the influence of first order PMD.Comment: 10 pages, 7 figure

DBSCAN for nonlinear equalization in high-capacity multi-carrier optical communications

Coherent optical multi-carrier communications have recently dominated metro-regional and long-haul optical communications. However, the major obstacle of networks involving coherent multi-carrier signals such as coherent optical orthogonal frequency-division multiplexing (CO-OFDM) is the fiber-induced nonlinearity and the parametric noise amplification from cascaded optical amplifiers which results in significant nonlinear distortion among subcarriers. Here, we present the first nonlinear equalizer in optical communications using the traditional Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm and a novel modified version of DBSCAN which combines K-means clustering on the noisy un-clustered symbols. For a 24.72 Gbit/sec differential quaternary phase-shift keying (DQPSK) CO-OFDM system, the modified DBSCAN can increase the signal quality-factor by up to 2.158 dB compared to linear equalization at 500 km of transmission. The modified DBSCAN slightly outperforms the traditional DBSCAN, fuzzy-logic C-means, hierarchical and conventional K-means clustering at high launched optical powers.Comment: This work will be presented at the 3rd International Conference & Expo on Laser, Optics & Photonics (Laser and Optics 2019) that will be held at London, UK on June 14-15, 201

Implementation of Physical-layer Network Coding

This paper presents the first implementation of a two-way relay network based on the principle of physical-layer network coding. To date, only a simplified version of physical-layer network coding (PNC) method, called analog network coding (ANC), has been successfully implemented. The advantage of ANC is that it is simple to implement; the disadvantage, on the other hand, is that the relay amplifies the noise along with the signal before forwarding the signal. PNC systems in which the relay performs XOR or other denoising PNC mappings of the received signal have the potential for significantly better performance. However, the implementation of such PNC systems poses many challenges. For example, the relay must be able to deal with symbol and carrier-phase asynchronies of the simultaneous signals received from the two end nodes, and the relay must perform channel estimation before detecting the signals. We investigate a PNC implementation in the frequency domain, referred to as FPNC, to tackle these challenges. FPNC is based on OFDM. In FPNC, XOR mapping is performed on the OFDM samples in each subcarrier rather than on the samples in the time domain. We implement FPNC on the universal soft radio peripheral (USRP) platform. Our implementation requires only moderate modifications of the packet preamble design of 802.11a/g OFDM PHY. With the help of the cyclic prefix (CP) in OFDM, symbol asynchrony and the multi-path fading effects can be dealt with in a similar fashion. Our experimental results show that symbol-synchronous and symbol-asynchronous FPNC have essentially the same BER performance, for both channel-coded and unchannel-coded FPNC