COMM-10.1

A New Approach for Symbol Frame Synchronization and Carrier Frequency Estimation in OFDM Communications
Jacob H Gunther (Brigham Young University), Hui Liu (University of Washington), Lee Swindlehurst (Brigham Young University)

This work considers the problem of jointly estimating symbol frame boundaries and carrier frequency offsets for orthogonal frequency division multiplexed (OFDM) communications in frequency selective fading environments. Orthogonality between the modulated and virtual carriers over an interference free window of the received signal is used to develop an algorithm for estimating the carrier frequency offset and detecting the beginning of a symbol frame. By using a cyclic prefix to remove interference from neighboring frames, the the method is applicable in the presence of dispersive channels. The main contribution of this work is the joint estimation of the frequency offset and the frame boundary.

COMM-10.2

Transmitter Optimization for Single Carrier and Multicarrier Transceivers on Crosstalk-Impaired ISI Channels
Naofal Al-Dhahir (GE Corporate R & D Center)

Transmitter optimization techniques for maximizing the throughput of linear ISI channels impaired by additive-Gaussian noise and crosstalk are presented. Transmitter ends of both single carrier and multicarrier transceiver structures are optimized subject to a fixed average input energy constraint. The effect of transmitter optimization on channel throughput is quantified by comparison with scenarios where both the desired user and the crosstalker use a flat energy distribution across the transmission bandwidth.

COMM-10.3

Joint Channel Estimation and Equalization in Multicarrier Modulation System Using Cyclic Prefix
Xiaowen Wang, K. J. Ray Liu (University of Maryland)

Multicarrier modulation (MCM) is a promising technique for high rate data transmission. A one-tap equalizer is an essential part of the MCM system and the channel estimation is needed to get the coefficient of the equalizer. Lack of correct channel estimation may cause significant performance degradation. We propose to use the cyclic prefix to estimate the channel for the MCM system. We found that the cyclic prefix originally used solely to guarantee the optimality of modulation using discrete Fourier transform (DFT) can be viewed as a source of channel information. Based on this observation, we propose a joint channel estimation and equalization algorithm using the cyclic prefix. Our simulations show that the algorithm can adaptively track the variation of a moderately time varying channel and has about 1-2dB gain over the system using the channel estimation obtained by the conventional training schemes.

COMM-10.4

Phase Noise in Sampling and its importance to Wideband Multicarrier Base Station Receivers
Patrik Eriksson, Hannu Tenhunen (Electronic System Design Lab, Royal Institute of Technology, Stockholm, Sweden)

Future base stations for the narrowband cellular standards, e.g GSM and D-AMPS, will deploy wideband multicarrier receivers. In these receivers the phase noise of the sampling stage is crucial in order to meet the blocking performance specified in the standards. In this paper an expression relating the single sideband phase noise power density to carrier ratio of a sampled signal to that of the sampling clock is derived. The implications of the theory for the clock local oscillator (LO) and clock drive amplifier for a GSM-1900 receiver are shown.

COMM-10.5

Mutually Orthogonal Transceivers for Blind Uplink CDMA Irrespective of Multipath Channel Nulls
Georgios B Giannakis, Zhengdao Wang (Dept. of Electrical Engr., Univ. of Virginia, Charlottesville, VA 22903-2442, USA), Anna Scaglione, Sergio Barbarossa (Infocom Dept., Univ. of Rome ``La Sapienza'', Roma, ITALY)

Suppression of multiuser interference (MUI) and mitigation of multipath effects constitute major challenges in the design of third-generation wireless mobile systems. Most wideband and multicarrier uplink CDMA schemes suppress MUI statistically in the presence of unknown multipath. For fading resistance, they all rely on transmit- or receive-diversity and multichannel equalization based on training or bandwidth-efficient blind techniques. Either way, they impose restrictive and difficult to check conditions on the FIR channel nulls. Relying on symbol blocking, we design A Mutually-Orthogonal Usercode-Receiver (AMOUR) system for quasi-synchronous blind uplink CDMA that eliminates MUI deterministically and mitigates fading irrespective of the unknown multipath. Analytic evaluation and preliminary simulations reveal the generality, flexibility, and superior performance of AMOUR over competing alternatives.

COMM-10.6

Blind and semi-blind channel identification methods using second order statistics for OFDM systems
Bertrand Muquet, Marc de Courville (Centre de Recherche Motorola)

In this paper two new blind channel identification methods suited to multicarrier system (OFDM) exploiting the redundancy introduced by the adjunction of a cyclic prefix at the emitter and relying on the evaluation of the received signal autocorrelation matrix are presented. The proposed algorithms are able to identify any channel without any constraint on their zeroes location (including non-minimum phase channels) and are robust to the addition of white noise. Moreover a further enhancement of the estimation accuracy can easily be achieved by taking advantage of already present training symbols in current systems operating in a semi-blind context. Furthermore one of the two identification strategies has a very low arithmetical complexity which makes it particularly attractive in practice. Notice that these methods are not restricted to classical DFT-type modulators and still apply with any perfect reconstruction modulator.

COMM-10.7

BLIND ESTIMATION OF SYMBOL TIMING AND CARRIER FREQUENCY OFFSET IN PULSE SHAPING OFDM SYSTEMS
Helmut Bolcskei (Institute of Communications and Radio-Frequency Engineering, Vienna University of Technology)

We introduce a blind algorithm for the joint estimation of symbol timing and carrier frequency offset in pulse shaping OFDM systems. The proposed estimator exploits the cyclostationarity of the received OFDM signal and can be seen as an extension of the Gini-Giannakis estimator [1] for single-carrier systems. An important feature of our method is the capability to perform a carrier frequency acquisition over the entire bandwidth of the OFDM signal. Furthermore, our estimator can be applied even if no cyclic prefix is used. We provide simulation results demonstrating the performance of the new estimator.

COMM-10.8

FAST ALGORITHM FOR FINITE-LENGTH MMSE EQUALIZERS WITH APPLICATION TO DISCRETE MULTITONE SYSTEMS
Navid Lashkarian (Oregon State University), Sayfe Kiaei (Motorola)

This paper presents a new, fast algorithm for finite-length minimum mean square error (MMSE) equalizers. The research exploits asymptotic equivalence of Toeplitz and circulant matrices to estimate Hessian matrix of a quadratic form. Research shows that the Hessian matrix exhibits a specific structure. As a result, when combined with the Rayleigh minimization algorithm, it provides an efficient method to obtain the global minimum of constrained optimization problem. A salient feature of this algorithm is that extreme eigenvector of the Hessian matrix can be obtaind without direct computation of the matrix. In comparison to the previous methods, the algorithm is more computationally efficient and highly parallelizable, which makes the algorithm more attractive for real time applications. The algorithm is applied for equalization of discrete multitone (DMT) systems for asynchronous digital subscriber line (ADSL) applications.

< COMM-9

Last Update: February 4, 1999 Ingo Höntsch