Abstract—This paper deals with the capacity behavior of wireless Orthogonal Frequency Division Multiplexing (OFDM)-based spatial multiplexing systems in broadband fading environments for the case where the channel is unknown at the transmitter and perfectly known at the receiver. Intro-ducing a physically motivated multiple-input multiple-output (MIMO) broadband fading channel model, we study the influence of physical parameters such as the amount of delay spread, cluster angle spread, and total angle spread, and system parameters such as the number of antennas and antenna spacing on ergodic capacity and outage capacity. We find that in the MIMO case, unlike the single-input single-output (SISO) case, delay spread channels may provide advantage over flat fading channels not only in terms of outage capacity but also in terms of ergodic capacity. Therefore, MIMO delay spread channels will in general provide both higher diversity gain and higher multiplexing gain than MIMO flat-fading channels.

Abstract – A new approach to low-complexity channel estimation in orthogonal-frequency division multiplexing (OFDM) systems is proposed. A lowrank approximation is applied to a linear minimum mean-squared error (LMMSE) estimator that uses the frequency correlation of the channel. By using the singular-value decomposition (SVD) an optimal low-rank estimator is derived, where performance is essentially preserved – even for low computational complexities. A fixed estimator, with nominal values for channel correlation and signalto-noise ratio (SNR), is analysed. Analytical meansquared error (MSE) and symbol-error rates (SER) are presented for a 16-QAM OFDM system. I.

This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10 04 . Keywords---Adaptive modulation, adaptive orthogonal frequency -division multiplexing (AOFDM), applications of OFDM, blind modem mode detection in OFDM, broadcasting using OFDM, channel quality estimation in OFDM, coded OFDM (COFDM), coherent and noncoherent detection of OFDM, crest factor in OFDM, frequency and timing errors in OFDM, HIPERLAN, mode signaling in OFDM, multicarrier modulation, OFDM, peak-to-mean envelope fluctuation in OFDM, phase noise in OFDM, preequalization, synchronization in OFDM, throughput of adaptive OFDM, wireless asynchronous transfer mode (WATM) using OFDM, wireless local-area networks (WLAN's) using OFDM. I. INTRODUCTION High-data-rate communications are limited not only by noise but---especially with increasing symbol rates---oft

Abstract: The video performance of the Median wireless asynchronous transfer mode (WATM) system is evaluated for a range of application scenarios using the H.263 video codec and a novel packetisation and acknowledgement scheme. The video resolutions and system parameters used are summarised in Tables 1 and 2. The required channel signal-to-noise ratio for near-unimpaired video quality is about 16dB over the dispersive worst-case channel used. 1 System Overview The proposed wireless LAN system's schematic is shown in Figure 1, which supports videophone calls. The video signal is compressed using the H.263 video compression standard [1]. The H.263 standard achieves very high compression ratio, however the resulting bitstream is extremely sensitive tochannel errors. This sensitivity tochannel errors is not a serious problem over benign wireline-based Gaussian channels, but it is an impediment, when used over wireless networks. There have been several solutions suggested in the literature for overcoming this using Automatic Repeat Request (ARQ) [2], dual-level coding [3] and the use of a feedback channel [4]. A range of further robust video schemes were proposed in [5]-citecherriman96-journal.

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Abstract—Wireless systems employing multiple antennas at the transmitter and the receiver have recently been shown to have the potential of achieving extraordinary bit rates. Orthogonal frequency division multiplexing (OFDM) significantly reduces receiver complexity in multiantenna broadband systems. In this paper, we introduce an algorithm for blind channel identification and equalization in OFDM-based multiantenna systems. Our approach uses second-order cyclostationary statistics, employs antenna precoding, and yields unique channel estimates (up to a phase rotation for each transmit antenna). Furthermore, it requires only an upper bound on the channel order, it does not impose restrictions on channel zeros, and it exhibits low sensitivity to stationary noise. We present simulation results demonstrating the channel estimator and the corresponding multichannel equalizer performance. Index Terms—Blind equalization, cyclostationarity, MIMO, multiantenna systems, OFDM.

This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also

Abstract—We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. In our scenario, we assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal’s power spectral density as a priori information. Using frequency invariant design it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, also show that without perfect a priori information this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal to noise ratio and symbol error rate degradation. Index Terms—Digital subscriber lines (DSL), discrete multitone (DMT), industrial–scientific–medical (ISM) band, orthogonal frequency-division multiplexing (OFDM), radio frequency interference (RFI), wireless local area network (WLAN). I.

Abstract. Digital signal processing has played a key role in the development of telecommunication systems over the last two decades. In recent years digital filter banks have been occupying an increasingly important role in both wireless and wireline communication systems. In this paper we review some of these applications of filter banks with special emphasis on discrete multitone modulation which has had an impact on high speed data communication over the twisted pair telephone line. We also review filter bank precoders which have been shown to be important for channel equalization applications. 1 1.

To ease equalization in a multicarrier system, a cyclic prefix (CP) is typically inserted between successive symbols. When the channel order exceeds the CP length, equalization can be accomplished via a time-domain equalizer (TEQ), which is a finite impulse response (FIR) filter. The TEQ is placed in cascade with the channel to produce an effective shortened impulse response. Alternatively, a bank of equalizers can be used to remove the interference tone-by-tone. This paper presents a unified treatment of equalizer designs for multicarrier receivers, with an emphasis on discrete multitone (DMT) systems.