A Robust Carrier Frequency Offset Estimation Algorithm in Burst Mode Multicarrier CDMA based Ad Hoc Networks

The future wireless communication systems demand very high data rates, anti-jamming ability and multiuser support. People want large amount of data to be continuously accessible in their personal devices. Direct Sequence (DS) spread spectrum based techniques such as Code Division Multiple Access (CDMA) fulfil these requirements but, at the same time, suffer from the Intersymbol Interference (ISI). Multicarrier CDMA (MC-CDMA) is an emerging technology to be used in mobile devices operating in an ad hoc setting due to its immunity towards ISI and having all the advantages of spread spectrum communication. One of the major problems with MC-CDMA is the high sensitivity towards carrier frequency offsets caused due to the inherent inaccuracy of crystal oscillators. This carrier frequency offset destroys the orthogonality of the subcarriers resulting in Intercarrier Interference (ICI). In this paper, we propose a computationally efficient algorithm based on Fast Fourier Transform (FFT) and biquadratic Lagrange interpolation. The FFT is based on the use of overlapping windows for each frame of the data instead of non-overlapping windows. This gives a coarse estimate of the frequency offset which is refined by the successive application of Lagrange quadratic interpolation to the samples in the vicinity of FFT peak. The proposed algorithm has been applied to the multiuser ad hoc network and simulated in Stanford University Interim (SUI) channels. It has been shown by simulations that the proposed algorithm provides better performance of almost 1~2 dB as compared to the well-known algorithms

Information theoretic approach to synchronization: the OFDM carrier frequency offset example

International audienceIn practical mobile communication systems, data-aided synchronization is performed before actual data exchanges, and synchronization methods are tailored to the pilot sequence. In this paper, we propose a framework for initial synchronization that works independently of the pilot sequence. We show that classical data-aided and blind techniques are particular cases of this general framework. We thoroughly study the specific problem of OFDM data-aided carrier frequency offset estimation. For the latter, we provide theoretical expressions of performance upper-bounds. Also, a practical thin CFO estimator for OFDM is provided under the form of a novel algorithm which is shown by simulations to perform better than classical pilot based methods

Synchronization and Parameter Estimation in Wireless Communications

This dissertation is devoted to the design and analysis of synchronization and channel parameter estimation schemes in wireless communications. Intrigued by the observation that the information is conveyed through wireless channels by uniformly spaced pulses that are some kind of "distorted" convolution of data symbols and a shaping pulse, we try to set up a framework to study synchronization and channel parameter estimation problems in the frequency domain. The dissertation consists of four major parts. Many issues in digital communications and signal processing involve the analysis of the inverse of Toeplitz matrices. In the first part, the convergence of the inverse of Toeplitz matrices and its application are presented. Under the condition that the $z$-transform of the sequence with which the Toeplitz matrices are associated has no zero on the unit circle, we show that the inverse converges to a circular matrix in the weak sense. Furthermore, for the finite boundary quadratic form, a sufficient condition under which the convergence can be strengthened into the strong sense and an upper bound of the approximation residue error are derived. It is well known that a circular matrix can be eigendecomposed by the discrete Fourier transform (DFT) which provides the desired frequency domain approach. In practical systems, synchronization parameters such as timing and carrier phase offsets, and channel response in fading channels are acquired with the help of a training sequence (TS) that is known to the receiver, which is called the data-aided (DA) estimation. In the second part, the performance limit that is the Cramer-Rao lower Bound (CRB) for the DA joint carrier phase and timing offsets estimation with an arbitrary TS is derived using the properties of Toeplitz matrices. Unlike the CRB derived in the literature, the bound derived in this dissertation reveals the close relation between a TS and its resultant performance limit, therefore it provides a quantitative approach to design TS for the acquisition of synchronization parameters. Following the estimation theorem, we derive a maximum likelihood (ML) slow frequency-selective fading channel estimator using the frequency domain approach introduced by the properties of Toeplitz matrices in the third part. In the fourth part, a carrier frequency offset estimator and a joint carrier phase and timing offset estimators with moderate complexities are proposed. Their systolic VLSI implementations are also presented. The performance of the proposed estimators approaches their corresponding performance limits. <p

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 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 5 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 categorize 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

Data-Aided ML Parameter Estimators of PSK Burst Modems and Their Systolic VLSI Implementations

A high performance Universal Modem ASIC that supports several modulation types and burst mode frame formats is under development. Powerful and generic data-aided (DA) parameter estimators are necessary to accommodate many modes. In this paper we present an approximated maximum likelihood (ML) carrier frequency offset estimator, ML joint carrier phase and timing offsets estimator and their systolic VLSI implementations for PSK burst modems. The performances are close to the Cramer-Rao lower bounds (CRLB) at low SNRs. Compared with theoretical solutions, the estimators proposed here are much simpler and easier to implement by the current VLSI technology. The CRLB for DA estimations is discussed in some depth, some issues on training sequence design is also addressed in this work.Globecomm99</i

VLSI Implemented Data-Aided ML Parameter Estimators of PSK Burst Modems

A high performance Universal Modem ASIC that supports several modulation types and burst mode frame formats is under development. The ASIC is designed to work under stringent conditions such as large carrier frequency offset (up to 13 percent symbol rate) and low signal-to-noise ratio (SNR). Powerful and generic data-aided (DA) parameter estimators are necessary to accommodate many modes. In this paper we present an approximated maximum likelihood (ML) carrier frequency offset estimator, ML joint carrier phase and timing offsets estimator and their systolic VLSI implementations for PSK burst modems. The performances are close to the Cramer-Rao lower bounds (CRLB) at low SNRs. Compared with theoretical solutions the estimators proposed here are much simpler and easier to implement by the current VLSI technology.VTC'99</i

On the Impact of Phase Noise in Communication Systems –- Performance Analysis and Algorithms

The mobile industry is preparing to scale up the network capacity by a factor of 1000x in order to cope with the staggering growth in mobile traffic. As a consequence, there is a tremendous pressure on the network infrastructure, where more cost-effective, flexible, high speed connectivity solutions are being sought for. In this regard, massive multiple-input multiple-output (MIMO) systems, and millimeter-wave communication systems are new physical layer technologies, which promise to facilitate the 1000 fold increase in network capacity. However, these technologies are extremely prone to hardware impairments like phase noise caused by noisy oscillators. Furthermore, wireless backhaul networks are an effective solution to transport data by using high-order signal constellations, which are also susceptible to phase noise impairments. Analyzing the performance of wireless communication systems impaired by oscillator phase noise, and designing systems to operate efficiently in strong phase noise conditions are critical problems in communication theory. The criticality of these problems is accentuated with the growing interest in new physical layer technologies, and the deployment of wireless backhaul networks. This forms the main motivation for this thesis where we analyze the impact of phase noise on the system performance, and we also design algorithms in order to mitigate phase noise and its effects. First, we address the problem of maximum a posteriori (MAP) detection of data in the presence of strong phase noise in single-antenna systems. This is achieved by designing a low-complexity joint phase-estimator data-detector. We show that the proposed method outperforms existing detectors, especially when high order signal constellations are used. Then, in order to further improve system performance, we consider the problem of optimizing signal constellations for transmission over channels impaired by phase noise. Specifically, we design signal constellations such that the error rate performance of the system is minimized, and the information rate of the system is maximized. We observe that these optimized constellations significantly improve the system performance, when compared to conventional constellations, and those proposed in the literature. Next, we derive the MAP symbol detector for a MIMO system where each antenna at the transceiver has its own oscillator. We propose three suboptimal, low-complexity algorithms for approximately implementing the MAP symbol detector, which involve joint phase noise estimation and data detection. We observe that the proposed techniques significantly outperform the other algorithms in prior works. Finally, we study the impact of phase noise on the performance of a massive MIMO system, where we analyze both uplink and downlink performances. Based on rigorous analyses of the achievable rates, we provide interesting insights for the following question: how should oscillators be connected to the antennas at a base station, which employs a large number of antennas