Blind Estimation Of The Carrier Frequency Offset In OFDM Systems

We present a novel approach for carrier frequency offset estimation in OFDM systems. Before they enter the OFDM system, the information bearing symbols are segmented into blocks so that each even indexed block shares one common symbol with the previous block. This redundancy allows for the frequency offset estimation at the receiver, without the need of pilot symbols. The offset is obtained based on cross-correlations of successive received blocks, and is decoupled from the channel estimate. With the proposed approach, offset estimation is achieved with very small reduction of rate of the OFDM system, as opposed to higher reduction caused by other existing approaches

MIMO System Estimation Based on Second-Order Spectra Correlations Applied to Estimation of Sparse Channels

We consider blind estimation of a MIMO system with a sparse impulse response, excited with cyclostationary inputs with known statistics. Such systems appear in cellular communications, HDTV, and underwater acoustic communications. We employ the blind system estimation method of [1], which yields each impulse response sample as the minimum of a function constructed based on frequency domain correlations of the system output. We propose a modification that exploits the sparseness of the channel. 1

On Blind Identifiability of FIR-MIMO Systems with Cyclostationary Inputs Using Second Order Statistics

We consider a general nn MIMO system excited by unobservable inputs that are spatially independent, cyclostationary with unknown statistics. Such a MIMO scenario appears in many applications, such as multi-user communications and separation of competing speakers in speech processing. A special case of this problem, i.e., a 22 system case, was recently addressed in [1] using frequency-domain correlations of the system output. In this paper we provide a set of conditions under which a general n n system is uniquely identifiable based on the second-order frequency-domain correlations of the system output. We provide a constructive proof for the uniqueness of the system solution, which could also serve as a basis for a practical algorithm for system identification

Blind Equalization Of Multiuser CDMA Channels: A Frequency-Domain Approach

We address the problem of blind equalization of mixing channels, resulting from frequency selective fading and multipath in a multi-user CDMA system. We present a novel frequency-domain approach that employs second order spectral statistics of the observations and the users signatures. Unlike other methods, which are based on time-domain analysis, no particular assumptions are made about the support of the mixing channels, except that they have finite length. Since signatures correlations, rather that signatures themselves, are used, the proposed estimation is independent of users delays. Although performance does depend on the users signatures, signatures orthogonality is not required. 1. INTRODUCTION Code Division Multiple Access (CDMA) communication systems have attracted a lot of attention recently due to their efficient utilization of the available bandwidth and their flexibility in accommodating variable traffic patterns. In CDMA each user is assigned a unique code sequence, whi..

Blind MIMO FIR Channel Identification Based on Second-Order Spectra Correlations

We consider a problem of identifying a Multiple-Input Multiple-Output (MIMO) finite impulse response system excited by colored inputs with known statistics. We propose a new, nonlinear optimization based method that involves the power spectra and cross-spectra of the system output. The proposed algorithm is tested for the case of cyclostationary inputs (CDMA scenario) and stationary inputs (SDMA scenario). Simulation results indicate that the proposed scheme works well, even for large order systems, and is robust to noise and channel length mismatch