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In this paper, we investigate a cross-layer design for the packet scheduling and the resource allocation in UWB systems. This design considers the combination of queuing and channel state information (CSI) which provides QoS support for multimedia applications in UWB. For the physical layer, the use of a linear precoded orthogonal division multiplexing (LP-OFDM) waveform is proposed because of its...
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...
In this paper we investigate statistical properties of IP optimal subcarrier assignments in the down-link of an OFDMA cell. Essentially, we show that such subcarrier assignments do have ??hidden?? statistical properties which can be exploited to design an extremely simple assignment strategy. We investigate such statistical properties and the corresponding performance of the simple assignment rules...
In this paper, the peak-to-average power ratio (PAPR) metric and other metrics reflecting nonlinear distortions caused by a nonlinear element are presented. To avoid the drawbacks and ambiguity of some well-known frequently quoted metrics an attempt to reveal the influence of nonlinear elements on the transmitted signal is made, what leads to more reliable assessment of the phenomena of the occurrence...
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 consider the evaluation of nonlinear distortion effects on the downlink transmission of systems employing OFDMA (orthogonal frequency division multiple access) signals. Our results allow an analytical spectral characterization of the transmitted signals, as well as the computation of nonlinear interference levels on the received signals. It is shown that the set of subcarriers allocated...
Intercarrier Interference (ICI) is an impairment well known to degrade performance of Orthogonal Frequency Division Multiplexing (OFDM) transmissions. It arises from carrier frequency offsets (CFO), from the Doppler spread due to channel time-variation, and, to a lesser extent, from sampling frequency offsets (SFO). The literature reports several models of ICI due to each kind of impairment. Some...
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,...
The emerging evolved UTRA radio system is generally envisioned to support a large number of VoIP users. This is basically enabled by efficient frequency domain packet scheduling together with accurate channel quality feedback information. In this paper, we investigate the performance of VoIP on EUTRA downlink assuming that only limited channel quality feedback information is available. System level...
In this paper we consider a decision-directed Carrier Frequency Offset (CFO) estimation technique employed in joint equalization and synchronization schemes for broadband wireless systems using single carrier (SC) modulations combined with frequency domain equalization (FDE). We build a model for the estimates, explain the reason for their biased behavior and validate the theoretical results through...
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.
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...
Body-coupled communications (BCC), in which the human body is used as a communications channel, has been shown to be a promising solution for wireless body-area networks (WBANs). For successful deployment of these BCC-based WBANs, it is necessary to develop a clear understanding of the channel behavior. Therefore, this paper presents the key characteristics of the capacitively-coupled on-body channel...
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...
Peak to average power ratio (PAPR) is one of the serious problems in any wireless communication system using multicarrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, we suggest a new scheme based on μ-law compander where the optimum value of μ is calculated. With the newly proposed scheme, the simulation results show that, the PAPR...
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...
A frequency offset estimation algorithm based on relativity of time-domain PN sequence is proposed in this paper. The form of this algorithm under multi-path fading channel is also given. The performance of the algorithm using different parameters is studied through theoretical analysis and simulation. The high performance of this algorithm using under both AWGN channel and multi-path fading channel...
Standardization work is nearly complete on long term evolution (LTE) of the UMTS Terrestrial Radio Access and Radio Access Network which is aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration...
In order to detect the presence of the primary user signal, spectrum sensing is a fundamental requirement to achieve the goal of cognitive radio (CR). This ensures the efficient utilization of the spectrum. Cyclostationary detection is the preferred technique to detect the primary users receiving data within the communication range of a CR user at very low SNR. In this work, we investigate the performance...
The increasing development of mobile applications has changed the traditional demands of computer networks, which must now provide ubiquitous broadband wireless communication. In this context, IEEE 802.16 standardizes the physical and medium access control layers of the technology, aiming to allow network access in both nomadic and mobile scenarios. In this work we analyze the impact caused by overhead...
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