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Wireless Conference 2006 - Enabling Technologies for Wireless Multimedia Communications (European Wireless), 12th European

Date 2-5 April 2006

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Displaying Results 1 - 25 of 112
  • Fixed Point Channel Estimation for 802.11a Wireless Receivers

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1075 KB)  

    We consider a wireless network system based on the IEEE 802.11a standard and propose a fixed point algorithm that has low computational complexity and is statistically optimal in a white Gaussian noise environment (Minimum Variance Unbiased Estimator). Simulation results in an exponentially decaying Rayleigh multipath fading channel, show that 10 bit precision is sufficient for the channel estimation algorithm, in order to get practically the same performance (Packet Error Rate) as the corresponding floating point algorithm. This is achieved using a frequency domain window resulting in a complexity reduction of about 70% w.r.t. straight matrix-vector estimation approach. View full abstract»

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  • Channel Estimation Optimisation In Wideband DS¿CDMA Rake Receivers

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1233 KB)  

    It is well established that the quality of the channel estimate plays a crucial role in the performance of a rake receiver. This paper addresses the problem of optimising the channel estimate for a wideband DS¿CDMA rake receiver equipped with a sliding¿window adaptive channel estimator. The mean squared error of the channel estimate is analytically extracted providing the means to optimise the window size in a minimum¿MSE sense. Unfortunately, the BER at the output of the rake receiver is only partially analytically tractable, but minimum¿BER optimisation of the window size is experimentally shown to outperform the MMSE criterion. View full abstract»

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  • New Channel Interpolation Method for OFDM Systems by Nearest Pilot Padding

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1312 KB)  

    Orthogonal Frequency Division Multiplexing scheme has many attractive characteristics that make it a useful scheme to combat multi-path environments and to be able to transmit at high data rates. If the data symbol is not transmitted differentially, coherent detection is obliged and the channel estimation process is indispensable. In this proposal, different methods for channel interpolation are investigated for estimating the channel state information when a rectangular pilot pattern is used. A new and simple method named NPI (Nearest Padding Interpolation) for channel sample interpolation is proposed and its performance is analysed. The main concluded result show that it can be considered as a good alternative comparing with a variety of actual channel estimation methods in terms of the Mean Square Error (MSE), the Mean Phase Error (MPE) and the computational cost. View full abstract»

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  • Unified Approach to the Analytical Assessment of Multi-user Diversity with Imperfect Channel State Information

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    In this paper, we explore the combined use of spatial and multi-user diversity in a cellular system where the channel state information (CSI) available at the base station (BS) is subject to imperfections. To do that, we consider a general statistical approach to describe the degree of CSI imperfection. By doing so, performance assessment is conducted for the generalized case in terms of ergodic system capacity, for which closed-form expressions are derived. In order to gain some insight, practical examples are presented and spatial vs. multi-user diversity trade-offs are analytically assessed. View full abstract»

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  • Broadcasting Traffic Information over Bursty Channels

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1181 KB)  

    Telematics services, particularly road traffic information, are normally of interest to many drivers in a geographically large area. Therefore, digital broadcast networks, such as Digital Audio Broadcasting (DAB) are well suited for distributing such traffic information services. In this paper, DAB channel measurements have been performed under typical driving conditions in a hilly terrain with quite challenging propagation conditions. The results show that errors occur in bursts of varying length and frequency, interrupting long intervals of completely error free reception. Based on these measurements, different data transmission methods on ISO-OSI Layer III have been evaluated by simulations and optimized with respect to minimizing overhead and maximizing the probability of successful reception of data. The goal was finding a suitable tradeoff between the two contradicting objectives. Simulation results showed that only relatively small data objects, up to 500 Bytes, can be broadcast en bloc. For longer data objects, segmentation is essential. We therefore recommend the use of the Multimedia Object Transfer (MOT) protocol, which provides such a segmentation functionality. The additional overhead caused by the MOT protocol layer is by far compensated by its gains, i.e. increased reliability and reduced latency. View full abstract»

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  • Comparison of MIMO Transceiver Techniques with Practical Considerations

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    Recently, multiple-input multipleoutput (MIMO) techniques have received a lot of attention because of their high spectral efficiency. Recent studies have been focused on the practical implementation of these MIMO techniques. In this paper, a comparison of MIMO transceiver techniques such as Tomlinson-Harashima precoding (THP), zero forcing dirty paper coding (ZF-DPC) and vertical Bell Laboratories Layered Space-Time (V-BLAST) is performed. We consider the effect of practical impairments such as imperfect CSI (channel state information) and a transmit power constraint. If the total power is restricted at the transmitter for fairness, ZF-DPC performs worst among those techniques although it does not suffer modulo loss and error propagation. Due to the presubtraction of the spatial interference, precoding techniques like ZF-DPC and THP are more sensitive to the effect of imperfect CSI than V-BLAST. View full abstract»

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  • Prediction of antenna patterns for hotspots in WCDMA Networks

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1567 KB)  

    This paper proposes a new method of balancing traffic load in mobile cellular networks and predicting the change of radio coverage to prevent congestion in advance. Case-Based Reasoning (CBR) is used to learn traffic patterns at periods of congestion and to apply the most suitable antenna patterns when a similar traffic pattern reappears. Unlike previous work, this scheme does not require calculating the optimum patterns each time, hence the computational complexity is greatly reduced. In addition, CBR also provides the capability of congestion prediction. Simulations have been performed to evaluate the system performance for different traffic scenarios, and the results are presented. View full abstract»

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  • Ordered Parallel Detection for Multiple Antenna Wireless Systems

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1047 KB)  

    The parallel detection (PD) is considered as a simple yet effective detector for multiple antenna wireless systems. PD is advantageous since it is faster than sequential detection, it does not require power ordering at the receiver and it reduces the system latency. However, the performance of PD is unsatisfied because of the error propagation which is strongly related to the accuracy of interference from the estimate of other layers. In this paper, we propose two ordered parallel detection (OPD) algorithms for multiple antenna wireless systems. Unlike classical parallel detection, to detect the desired signal for each layer, we only subtract the signals which have the higher SNR than the desired signal from the received signal, so we can get more accurate detected signals than classical PD. Also the proposed algorithms allow for concurrent detection of all the symbols and thus reduce the system delay. The proposed OPD algorithms show marked improvement in performance over the classical PD. View full abstract»

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  • A Printed ESPAR Antenna for Mobile Computing Applications

    Page(s): 1 - 4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1100 KB)  

    Electronically Steerable Passive Array Radiator (ESPAR) antennas have been shown to be a significant adjunct in modern wireless communications. However, their size and 3- dimentional geometry has restrained them from being widely used in mobile terminals. In this paper a printed three-element ESPAR antenna system is presented operating in the 2.4 GHz ISM band. The antenna elements used are low-profile Koch monopoles printed on a PCMCIA card. The structure¿s performance was evaluated through extensive simulations when inserted in the PCMCIA slot of a notebook computer. The proposed structure shows attractive characteristics in terms of reduced size, high bandwidth, beamsteering and null steering capabilities. View full abstract»

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  • Space Diversity for Multi-antenna Multi-relay Channels

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (611 KB)  

    In this paper we analyze the performance of multiple relay channels when multiple antennas are deployed only at relays. We apply two antenna diversity techniques at relays, namely maximum ratio combining (MRC) on receive and transmit beamforming (TB). We show that with K relays the network can be decomposed into K diversity channels each with a different channel gain, and that the signals can be effectively combined at the destination. We assume that the total number of antennas at all relays is fixed at N. If the total transmit power for all relays are the same as for the source and equally distributed among all the relays, the network capacity will be lower bounded by that of N relay channels each with single antenna, and upper bounded by that of single relay channels with N antennas. View full abstract»

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  • A Modified EVM SNR Estimation Method for QAM OFDM Systems in AWGN Channel

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1573 KB)  

    Signal-to-Noise Ratio (SNR) is an important parameter in many receivers to improve their performance. In this paper, we develop a modified Error Vector Magnitude (mEVM) SNR estimation algorithm for Orthogonal Frequency Division Multiplexed (OFDM) systems in Additive White Gaussian Noise (AWGN) channels. At first mEVM is introduced for QPSK modulation. We also generalize the idea to 16- and 64-QAM modulation using two groups of selected data: data representing a specific single constellation point and data belonging to a group (up to 4) of neighboring constellation points. Criteria used to measure its performance are the SNR estimation accuracy compared to the actual SNR, the variance of the estimation and the mean square error (MSE). Computer simulations show that the proposed estimator for both types of data selection at SNR values of practical interest for each modulation type is highly accurate and reliable for OFDM systems, outperforming previously published generic QPSK SNR estimators. Finally the impact of the channel estimation method used to improve signal¿s reception, on the SNR estimation accuracy is examined. View full abstract»

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  • Improved Performance of Quasi-orthogonal Space-time Block Code over Time-selective Channels

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (934 KB)  

    -Quasi-orthogonal space-time block code (QO-STBC) can provide full rate transmission and partial diversity under low decoding complexity. Previous work on QO-STBC assumes that channel is flat or remains static over the length of the codeword. However, time-selective channels do exist, and in this case, the detector proposed in H. Jafarkhani, ¿A quasi-orthogonal space-time block code¿ can not be used to achieve a proper error performance. In order to mitigate the severe performance degradation, the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer are employed in this paper. Meanwhile we also propose a zero forcing interference cancellation decision feedback equalizer (ZF-IC-DFE) and a minimum meansquare error interference cancellation decision feedback equalizer (MMSE-IC-DFE) via Cholesky factorization of Gram matrix of the channel after performing interference cancellation. By feeding back past decisions on already detected symbols, DFE schemes can achieve an additional performance gain compared to their corresponding linear equalizers. View full abstract»

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  • Improved Channel Estimation for Complexity-Reduced MIMO-OFDM Receiver by Estimation of Channel Impulse Response Length

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1071 KB)  

    Using a priori knowledge of maximum channel impulse response (CIR) length, time domain OFDM channel estimation systems outperforms frequency domain channel estimation. Because CIR length is an unknown quantity at the receiver side, a suitable estimation method is necessary. In this paper, we propose a novel algorithm named FCLI-Frequency Domain Channel Length Indicator, which estimates CIR length in order to minimize MSE. The FCLI algorithm works in OFDM systems with null-subcarriers, like the spectrum mask defined in IEEE802.11a/g and does not require to average indicators over more than one OFDM symbol. Furthermore, FCLI is designed to work in both SISO and MIMO-OFDM. The simulation results show that channel estimation performance by the FCLI algorithm can approach or outperform the performance with perfect knowledge of channel length in low or high SNR. View full abstract»

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  • Higher Order Modulation IR-UWB Signals For Short-Range Communications

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1713 KB)  

    High data-rate applications can be foreseen for future ultra-wideband systems in the areas of internet access, multimedia services, wireless interfaces and location-aware services. Since it is particularly important to design low cost and low power devices, a growing attention will be devoted to the UWB systems with high spectral efficiency. In this paper, higher order modulation schemes are derived for Impulse Radio (IR) systems. The original signalling schemes provide a higher spectral efficiency and permit higher datarate applications: though the IR systems are based on the use of baseband signals, the introduction of a proper orthogonal basis permits to derive higher order constellations as a linear combination of the elements of the basis with no additional bandwidth. Therefore, the increase of the spectral efficiency also permits to have a higher system throughput. View full abstract»

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  • HPA Pre-Distortion Based on An Improved LUT Technique

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1211 KB)  

    In this paper, we focus on the Look-up Table (LUT) technique for compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with the conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8dB gain in out-of-band spectrum re-growth suppression and about 0.3dB BER performance gain than the conventional LUT technique under the same simulation conditions. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitte. View full abstract»

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  • Impact of Fountain Codes on GPRS channels

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1090 KB)  

    The rateless and information additive properties of fountain codes make them attractive for use in broadcast/multicast applications, especially in radio environments where channel characteristics vary with time and bandwidth is expensive. Conventional schemes using a combination of ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) suffer from serious drawbacks such as feedback implosion at the transmitter, the need to know the channel characteristics apriori so that the FEC scheme is designed to be effective and the fact that a reverse channel is needed to request retransmissions if the FEC fails. This paper considers the assessment of fountain codes over radio channels. The performance of fountain codes, in terms of the associated overheads, over radio channels of the type experienced in GPRS (General Packet Radio Service) is presented. The work is then extended to assessing the performance of Fountain codes in combination with the GPRS channel coding schemes in a radio environment. View full abstract»

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  • Channel Quality Estimation Index (CQEI): An Improved Performance Criterion for Wireless Communications Systems Over Fading Channels

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    We introduce the Channel Quality Estimation Index (CQEI) as an alternative improved performance criterion of wireless communications systems operating over fading channels, directly related to the system's average error rate. CQEI is simple to evaluate, since it depends on the channel statistics, which vary much more slowly than the channel state itself, and thus can be obtained at the initialization state using a long training sequence and continuously improved during the whole communication period. As an application, we use CQEI to find the optimum number of branches in equal gain combining (EGC) receivers, operating over non-identical fading channels. Numerical and simulations results show that CQEI represents an efficient and easy to evaluate criterion to assess the performance of wireless systems. View full abstract»

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  • Are IEEE 802 Wireless Technologies Suited for Fire Fighters?

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (827 KB)  

    Ad hoc networks are considered to provide flexible and robust communication in emergency scenarios like fire fighting. However, for the time being, it is not clear how existing digital wireless communication technologies perform in environments with fire, smoke and vapour. To investigate this issue, we carried out several experiments at the training facilities of the Paris fire brigade. Our goal was to evaluate the performance of standard wireless communication systems in a real fire fighting scenario. The main result is that wireless communication is not affected much by fire and smoke but is indeed affected by vapour. Technologies operating in the 2.4 GHz frequency achieve a higher communication range than those with 5 GHz in our setup. View full abstract»

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  • A Polar Transmitter for Multi-mode Wireless Applications

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1147 KB)  

    In this paper, a transmitter including a linearassisted switch-mode envelope amplifier (LASEA) and a two-point Sigma - Delta controlled fractional-N phase modulator (TPSDM) is proposed and simulated. The LASEA can amplify wideband envelope signals efficiently and linearly, and its time delay is minimized. The TPSDM can up-convert wideband phase signals to the RF band, and its time response is much more agile than conventional PLL-based phase up-converter. These two modules make it possible to restore the RF signal at the final power amplifier stage with high precision. Simulation results verify these ideas. For EDGE signal, the LASEA has a neglectable impact to the EVM and spectral performance. The TPSDM degrades the EVM to 3.7% and the spectrum is degraded less than 10dB, much lower than the specification mask. View full abstract»

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  • Distributed Organization of Cooperative Antenna Systems

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1347 KB)  

    Cooperative antenna systems have become a hot research topic and promise significant performance gains w.r.t. throughput and capacity. For cellular mobile radio systems the so called service area concept (SA) ¿ a multi user MIMO (MU-MIMO) approach - is very promising. Several adjacent base stations (BS) are tightly coupled over the backbone network. A joint transmission/joint detection (JT/JD) algorithm located in a central unit (CU) calculates a common weighting matrix for all BS of an SA allowing to serve several mobile stations (MS) simultaneously. This results in a real frequency reuse equal to 1 or near to 1. Normally it is assumed that the backbone provides the fast interconnection of the BS and the CU for calculation of the weighting matrix. The drawback of this solution is that this results in a hierarchical network structure which ¿ while available in today¿s 2G or 3G networks with the radio network controller (RNC) ¿ is something network planer want to get rid off for future enhancements like 3GPP UTRA long term evolution (LTE). Here instead of a hierarchical higher CU a de-centrally over the air organized distributed cooperative radio system is proposed, minimizing the requirements to the backbone network. View full abstract»

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  • The effect of imperfect feedback on broadcast opportunistic beamforming schemes

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1238 KB)  

    In multiantenna systems the optimization of linear spatial precoding is severely hampered by the amount of feedback. An efficient solution consists in the opportunistic beamforming (OB), which randomly generates the precoding and schedules the users according to the corresponding signal-to-noise ratio. Performance of OB can be enhanced by matching the generation of the beamforming to the users spatial covariance as in the recently proposed Cluster-eigenbeamforming (Cluster-EB). In this paper we show that the benefits of Cluster-EB further improve in practical systems when the transmitter has imperfect knowledge of the instantaneous feedback. Cluster-EB capitalizes on the knowledge of the spatial covariance to reduce the sensitivity with respect to the feedback degradation, thus preserving the systems performance. Analytical derivations and simulation results validate the analysis. View full abstract»

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  • Implementation of Linearly Precoded MIMO Communication Systems with BSS Techniques

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1153 KB)  

    One of the problems of implementing precoded Multiple Input Multiple Output (MIMO) communication systems is that Channel Status Information (CSI) has to be available at the transmitting side. In practical applications, CSI can be sent through a feedback channel that is severely limited in data rate. In this paper we explore how to use Adaptive Blind Source Separation (ABSS) algorithms to detect strong channel time-variations and considerably reduce the feedback channel overhead. Moreover, ABSS algorithms also provide adequate matrices to implement the decoding process. Simulation results show that degradation in performance due to the utilization of ABSS decoding matrices and imperfect CSI is acceptable. View full abstract»

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  • Channel assignment in multi-antenna OFDM systems

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (593 KB)  

    This paper considers channel (subchannel, subcarrier) assignment problems that arise multi-carrier multi-antenna wireless systems. In particular, we propose channel-aware assignment of subcarriers to different antennas so that we improve performance while reducing the peak-to-average ratio in the antenna-specific power amplifiers. Moreover, simplifications to the proposed optimization models are proposed in order to reduce the computational complexity of the assignment problem. Simulation results demonstrate the applicability of the proposed techniques in frequency-selective channels. View full abstract»

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  • Experimental Multipath Component Results from MIMO Measurements in a Microcell Urban Environment

    Page(s): 1 - 6
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    This paper presents results on the parameters of multipath components extracted from wideband measured MIMO channel matrices. Experimental data were collected with wideband channel sounding measurements at 5.2 GHz in a microcell urban environment, under line of sight propagation conditions. The double directional and propagation delay parameter values of the dominant multipaths were estimated using the multidimensional parameter estimation algorithm. The results presented provide information in the context of parametric MIMO channel characterization and refer to the number of identified waves, and focus on the path weights characteristics. Additionally, the extracted multipath estimates are used to synthesize MIMO matrices that are compared to the directly measured data. View full abstract»

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  • A practical implementation of GUP architecture and its migration path to IMS

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1065 KB)  

    This paper describes the basic concepts of the 3GPP Generic User Profile (GUP) architecture and provides an overview of a practical implementation of the GUP concepts (FlexiNET), identifying at the same time potential improvements to the current GUP architecture by providing a step-by-step comparison of the GUP functionalities with FlexiNET. Finally, it presents how this practical implementation is currently being integrated in existing UMTS and WLAN network infrastructures and paves the way for the embodiment of GUP in the IP Multimedia Subsystem (IMS). View full abstract»

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