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In practice only imperfect channel state information (CSI) is available at the transmitter due to noisy and time-varying channel. In this paper, we consider optimal bit loading for orthogonal frequency division multiplexing (OFDM) with imperfect CSI subject to channel estimation. The frame length comes in as an important control parameter, while soft channel estimation and the Cramer-Rao bound are...
This paper deals with the case of a high speed mobile receiver operating in an orthogonal-frequency-division-multiplexing (OFDM) communication system. Assuming the knowledge of delay-related information, we propose an iterative algorithm for joint multi-path Rayleigh channel complex gains and data recovery in fast fading environments. Each complex gain time-variation, within one OFDM symbol, is approximated...
In this paper we revisit the carrier frequency offset (CFO) estimation and removal for broadband orthogonal frequency division multiplexing (OFDM) systems. We propose an algorithm that explores the time-domain (TD) properties of transmitted symbols carrying pilots and data. A careful examination of the components that constitute the TD received symbols leads to the definition of a simple, yet effective,...
Main goal of this work is to give insight on the possible performance improvement arising in the wireless local ad-hoc access from the synergic cooperation of two emerging paradigms, multi-antenna and cognitive radios. The target is the competitive maximization of each access rate in presence of multiple-access interference (MAI) induced by the other accessing terminals. Being the radios cognitive,...
The on-line Bayesian Cramer-Rao (BCRB) lower bound for the dynamic estimation of a time-varying multi-path Rayleigh channel in 4-QAM OFDM system is considered. In case of negligible channel variation within one symbol and delay related information, true BCRB for data-aided (DA) context, and two closed-form expressions for non-data aided (NDA) context are derived.
We propose a new technique to estimate the signal-to-noise ratio (SNR) over flat fading time-varying single-input multiple-output (SIMO) channels, for quadrature amplitude modulation (QAM) signals in complex additive white Gaussian noise (AWGN). This technique relies on the use of periodically transmitted pilot symbols in the estimation process. It is a decision directed (DD) procedure since detected...
This paper proposes a two-step noise suppression method in the frequency and time domains for frequency domain channel estimation in single-carrier (SC)-FDMA radio access using a variable transmission bandwidth. In the proposed method, a weighted coherent averaging filter suppresses the noise component of the estimated channel gain in the frequency domain and then, after conversion of the channel...
This paper deals with transform domain channel estimation (TD-CE) in the MIMO-OFDM system when null carriers are placed at the edges of the spectrum in order to assure band isolation from interfering signals that occupy neighboring frequency bands. Indeed, the presence of these null carriers leads to a degradation of channel estimation because of a ??border effect?? phenomenon when using a discrete...
The Expectation-Maximization (EM) algorithm is studied to perform channel estimation in a low cost and high data rate impulse radio UWB receiver. The system under consideration uses a pulse position modulation with a simple analog energy detector. In order to overcome the problems inherent to high data rates, such as inter-symbol interferences, a probabilistic equalizer is used. The EM algorithm and...
In this paper an Improved RLS Based Adaptive MMSE Decision Directed MC-CDMA Receiver With Frequency Domain Interpolation (ImRLS-P) for Rayleigh Fading Channels is developed. The technique adopted by the ImRLS-P, is to reduce the noise components in the RLS-estimated channel frequency response before applying it to the MMSE adaptive detector and to reduce the computational rate as well. This is done...
We have recently introduced in the literature a new access control protocol for next generation wireless cellular networks, which showed superior performance in comparison to other (TDMA and WCDMA-based) protocols when integrating various types of multimedia traffic. In this Extended Abstract, we show that the use of stack protocols to resolve contention among contending multimedia terminals is not...
Recently, a new impulse postfix OFDM (IP-OFDM) system, which performs channel estimation in time-domain by exploiting the impulse postfix instead of pilot tones, was proposed . The proposed IP-OFDM system exploits the impulse postfix, which consists of a high power impulse sample and several zero samples at the end of a OFDM symbol block, to estimate channel impulse response. As shown in , , the IP-OFDM...
In this paper system level performance evaluation of channel aware schedulers that apply previously presented multiple input-multiple output (MIMO) link adaptation algorithms is given. The analyzed schedulers operate in single-user (SU) and in multi-user (MU) mode, and adapt either only modulation and coding scheme, or MIMO scheme in addition. The performance evaluation is done by comparative analysis...
This work presents a simple method to estimate IEEE 802.11 distributed coordination function (DCF) service time. This is the total amount of time needed to transmit a given frame, which is defined as the duration from the instant a node starts the transmission, until the instant when the transmission task effectively finishes. We are motivated by the fact that IEEE 802.11 DCF does not provide time-bounded...
Cellular radio systems are often limited due to the presence of cochannel interference. Basically, radio systems may be operated by utilizing asynchronous or synchronous downlink transmission from all base stations in the system, where synchronization between terminals and their serving base station is mandatory in both concepts. We provide a comparison between the theoretical achievable spectral...
We propose a method for concurrent OFDM fine time synchronization to different stations with propagation delay differences, and a receiver based delay difference compensation method for MMSE channel estimation, which are needed to enable cooperative MIMO-OFDM transmission. Cyclic prefix removal is done dynamically with respect to the closest station, which allows for intersymbol interference free...
The context of this paper is interception, thus nothing is known on emission. This paper addresses the problem of time-varying multiple input multiple output channel estimation and tracking with Kalman filter for Alamouti scheme. Generally, Kalman filter must be initialized by training sequences, but in interception systems, such sequences don??t exist. So, we propose in this paper to use blind source...
This contribution deals with the Turbo-like noncoherent data-aided (e.g., no blind) synchronization of Ultra-Wideband Impulse-Radio (UWB-IR) terminals operating over broadband channels affected by multipath fading with ??a priori?? unknown number of paths. The synchronizer we develop achieves the data-aided joint estimate of the number of paths and their arrival times without requiring any a priori...
Time reversal (TR) is a transmission technique that relies on pre-processing the signal at the transmitter (TX) by filtering it through a filter, the impulse response of which is a time reversed and phase conjugated version of the channel impulse response (CIR) to the target receiver (RX). TR is known to have remarkable temporal and spatial focusing properties. Specifically temporal focusing indicates...
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