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Mobile Future, 2006 and the Symposium on Trends in Communications. SympoTIC '06. Joint IST Workshop on

Date 24-27 June 2006

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Displaying Results 1 - 25 of 44
  • Measurement and modeling of wireless propagation channels for MIMO

    Page(s): i
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (85 KB)  

    Summary form only given. The ultimate performance limits, as well as the performance of practical systems, of any wireless system is limited by the radio propagation channels that the system is operating in. It is thus critical that we understand the channel properties that are relevant for MIMO systems: directional and delay properties of the multipath components. Any such understanding must be based both on the understanding of the physical propagation processes and actual measurements; furthermore, it is very helpful to have good channel models that can be used to test the performance of algorithms and systems. These aspects are treated in the tutorial. We start out with an introduction of spatial sounding techniques that form the basis for spatial channel measurements and spatial channel characterization. We present new measurement results of the directional channel properties as seen from the base station and from the mobile terminal jointly (double-directional propagation characteristics). Both indoor and outdoor scenarios are treated. We explain how these measurement results can be utilized and included in spatial channel models, which are required for the design and development of adaptive antenna and MIMO systems. A classification of MIMO models, including their "why?" and "for what?" are given. Then, the various methods to model the MIMO channel are discussed. The relative merits and shortcomings of measurement-based stochastic models, relying on parameter estimation techniques; of geometry-based parametric models, approximating a radio environment by geometry, but adding stochastic processes; and of deterministic models (ray-tracing or measured) are highlighted. Finally, a review on standardized MIMO channel modeling are given. It includes the models of 3GPP/3GPP2 for outdoor environments, the IEEE 802.11n models for indoor environments, and the COST 273 model, which is valid for all environments View full abstract»

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  • The sandbridge SB3011 SDR platform

    Page(s): ii - v
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (242 KB) |  | HTML iconHTML  

    This paper describes the Sandbridge Sandblaster real-time software defined radio platform. Specifically we describe the SB301I system on a chip multiprocessor. We describe the software development system that enables real-time execution of communications and multimedia applications. We provide results for a number of interesting communications and multimedia systems including UMTS, DVB-H, WiMAX, WiFi, and NTSC video decoding. All results presented are from completely implemented systems from RF through baseband View full abstract»

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  • Improved spectral efficiency through iterative concatenated convolutional reed-solomon software decoding

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    In this paper we describe on iterative algorithm for concatenated convolutional Reed-Solomon decoders that improve the spectral efficiency of the communication system by increasing the error correction capabilities and as a consequence lowering the retransmission rate. In our method, the decoding process starts assuming the received code word has at most t errors, where 2t+1 is the Reed-Solomon code's minimum distance. If, after the decoding process, all the syndromes are zero the decoding is successful; otherwise there were more than t errors encountered. At this point, the decoder assumes s erasure positions based on the erasure information coming from the convolutional decoder. If the error locator polynomial has degree equal to r = (2t-s)/2, then most likely the error positions are in the current Galois-field and a second decoding algorithm is performed. Otherwise, s = s+2 erasures are assumed and again the degree of the error locator polynomial is checked. This continues until the maximum number of erasures, 2t, is reached. The Reed-Solomon decoder is executed entirely in software on the Sandbridge processor, which features special instructions for single instruction multiple data (SIMD) Galois field (GF) multiplication and other SIMD operations. Multiple decoder algorithms with different degrees of complexity are stored in external memory, such that for a particular RS data packet the one with less computational complexity can be employed, depending on the error/erasure information. By using our method, the packet retransmission rate is decreased, resulting in improved spectral efficiency. The improved spectral efficiency is reflected by a total link budget improvement of up to one dB View full abstract»

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  • DSP implementation of Cholesky decomposition

    Page(s): 6 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (138 KB) |  | HTML iconHTML  

    Both the matrix inversion and solving a set of linear equations can be computed with the aid of the Cholesky decomposition. In this paper, the Cholesky decomposition is mapped to the typical resources of digital signal processors (DSP) and our implementation applies a novel way of computing the fixed-point inverse square root function. The presented principles result in savings in the number of clock cycles. As a result, the Cholesky decomposition can be incorporated in applications such as 3G channel estimator where short execution time is crucial View full abstract»

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  • Simplified max-log-MAP decoder structure

    Page(s): 10 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    Area efficient turbo decoder structures are needed in 3G receivers. Typically, max-log-MAP decoders are used as component decoders. In this paper, it is shown that all the computations of the max-log-MAP algorithm can be carried out with slightly modified add compare select (ACS) units. All the required computations of the max-log-MAP algorithm are analyzed and they are mapped to the proposed ACS units (ACSU). A set of four ACSUs is multiplexed to carry out the computations. With the presented method, the structure of the max-log-MAP decoder is simplified and the computing resources are shared economically View full abstract»

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  • High efficient two dimensional multi-level discrete wavelet transform algorithm for DM642 signal processor

    Page(s): 14 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB) |  | HTML iconHTML  

    At the present time two dimensional multilevel discrete wavelet transforms are widely used in the image and video compression area. Compression algorithms are frequently implemented on digital signal processors, because such an implementation is most flexible. The first step for wavelet-based image compression is the multilevel discrete wavelet transform and it should be done fast and efficient. The proposed high speed algorithm intended for embedded video compression systems is based on Texas Instruments DM642 digital signal processor. An algorithm is developed for 2D DWT computation under low high-speed memory condition View full abstract»

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  • Simple iterative decoding for bit-interleaved coded orthogonal modulation

    Page(s): 16 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    This paper considers bit-interleaved coded modulation with iterative decoding (BICM-ID) using M-ary orthogonal signaling. Simplified algorithms for hard-decision feedback iterative decoding for coherent and noncoherent M-FSK are studied, resulting in low complexity implementation. A performance comparison between BICM-ID systems employing M-FSK modulation in AWGN and Rayleigh flat fading channels is presented, using the proposed iterative decoder View full abstract»

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  • Low complexity BCM for wireless applications with different codeword lengths

    Page(s): 20 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    The aim of this paper is to present BCM (block-coded modulation) schemes suitable for simple wireless communication systems, using codewords with different lengths for different coding levels. The main purpose of this schemes is to allow for more flexibility on the choice of good asymptotic gain, low complexity and coding rate. The concept proof presented is a BCM/QPSK performance in the Gaussian and Rayleigh channels, obtained by Monte Carlo simulation. The results show that the performance of the arrays with different length codewords are better than an equivalent, equal length codeword array, using the same sub-optimum decoding algorithm. Furthermore, the serial operations number to decode the array is less, in the proposed coding scheme, compared with the conventional coding scheme View full abstract»

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  • Distributed source coding using T-direct codes

    Page(s): 24 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (123 KB) |  | HTML iconHTML  

    Distributed source coding is a general framework that applies to sensor networks. Recently, considerable research on the distributed source coding of correlated sources have rekindled research scientists and engineers because of its possible application to video compression. In the sequel, distributed source coding methods like DISCUS (distributed source coding using syndromes), PRISM (power efficient, robust, high compression, syndrome-based multimedia coding) are developed which aim at compression of sequence of images. This paper gives a construction to a class of T-direct codes with constituent codes are derived from the class of rank distance codes and presents yet another approach to distributed source coding of two correlated sources X, Y isin Fn using a class of multi-user codes, namely T-direct codes, where T les n and F being an arbitrary field View full abstract»

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  • Frame descriptor tables for minimized signaling overhead in beyond 3G MAC protocols

    Page(s): 28 - 31
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (261 KB) |  | HTML iconHTML  

    In this paper we assess the performance of the frame descriptor tables (FDT) concept applied in combination with a highly dynamic resource allocation scheme. Beyond 3G (B3G) medium access control protocols (MAC) have to meet challenging requirements. In order to support the need for quality of service (QoS) and considering the scarce availability of radio resources, B3G MAC protocols must implement an intelligent resource allocation strategy with minimum signaling overhead guaranteeing high spectral efficiency. In this context the FDT concept seems to be a promising candidate. By eliminating redundant description of frame contents across frames the concept helps to reduce signaling overhead in a frame based reservation scheme. To keep as much flexibility as needed it seems reasonable to apply the FDT concept in combination with a highly dynamic resource allocation scheme. Simulations done in the course of this work prove the high quality of this combined approach View full abstract»

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  • SIP for wireless positioning: System and architecture

    Page(s): 32 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    The recent boom in wireless communications has led to a wide range of new applications. Wireless positioning is an emerging technology which can provide accurate locations for indoor environments when satellite based positioning systems are not available. In this paper, a session initiation protocol (SIP) based system architecture for wireless positioning is described and an overview of how this can be used in overall system architecture has been provided. The proposed system architecture has shown that SIP is competent as a network signaling protocol for wireless positioning View full abstract»

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  • Bandwidth optimization in SLA negotiation process

    Page(s): 36 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (373 KB) |  | HTML iconHTML  

    In this paper we propose an efficient resource management technique for MPLS-based DiffServ networks. The service provider (SP) can predict sufficient link bandwidth resources for traffic caused by contracting of SLAs (service level agreement). It could be an important part of admission control in the SLA negotiation process (SLA-creation). Such bandwidth expansion and bandwidth sharing technique can be an important part of TEQUILA architecture based on autonomic computing. The problem is seen as an expansion problem of link capacities (bandwidth) that can be done dynamically from NP (network provider). Also, it helps to avoid the creation of bottleneck links on the path and maintains high network resource utilization efficiency View full abstract»

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  • Design of modified UCHT sequences

    Page(s): 40 - 43
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    In this paper, we consider the design of a class of unified complex Hadamard transform (UCHT) sequences. An efficient modification is imposed to those sequences to better suit applications in asynchronous code-division multiple-access (CDMA) systems. These modified UCHT sequences preserve the orthogonality of the original UCHT sequences and offer increased design options due to an increased number of parameters. The design of UCHT, modified UCHT, and Oppermann sequences is then formulated with reference to optimizing the maximum nontrivial aperiodic correlation value. These optimization problems can then be solved efficiently using a genetic algorithm with the maximum nontrivial aperiodic correlation value serving in the definition of a fitness function. Numerical examples illustrate the benefits of modified UCHT sequences over the original UCHT sequences View full abstract»

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  • A high peak-to-average power ratio reduction in OFDM systems by ideal N/2-shift aperiodic auto-correlation property

    Page(s): 44 - 47
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    This paper presents a new method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplex (OFDM) BPSK systems based on the auto-correlation property of the data symbol sequence. Herein it is demonstrated that a significant PAPR reduction of 6 dB, independent of the number of subcarriers, can be achieved by assuring the appropriate auto-correlation property of transmitted data symbol sequences. Since the approach relies on redundant symbols, meeting the condition of a rate R = 0.75 complementary parity code, some degree of error correction is also achieved View full abstract»

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  • Two-dimensional evaluation of the queueing network equilibrium based on clustering and self-organizing map

    Page(s): 48 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A new approach to two-dimensional evaluation of the queueing network equilibrium, based on calculations of the steady-state probability vector with use of neural modeling and clustering, is considered in this paper. The equilibrium of queueing networks is a mean for performance evaluation of real communication systems presented as Markov chains. The experimental results were obtained with use of clustering analysis and self-organizing map, and the proposed method was compared with direct techniques on the base of obtained results View full abstract»

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  • An integrated security framework for assisting in the defence of computer networks

    Page(s): 52 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    A distributed security assistance framework is proposed that unifies security mechanisms to provide enterprise-wide security defence to computer network systems. The proposed security framework offers capabilities for distributed threat detection, integrated analysis and coordinated response via security spaces. It also offers extension mechanisms to coordinate human countermeasures in protecting networks. The framework is underpinned on a new security paradigm - sensor, analysis and response View full abstract»

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  • Optimization of ANN applied to non-linear system identification based in UWB

    Page(s): 56 - 59
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (195 KB) |  | HTML iconHTML  

    In this work we propose a hybrid technique for artificial neural network optimization based in UWB system. This technique is a combination of real-coded genetic (GA) and back propagation (BP) algorithms simulating an ultra wideband (UWB) system. The main idea is to apply the back propagation over the five more adapted individuals of each generation produced by the real coded GA, in order to allow the evolution of these individuals before the crossover operation. The combined algorithms are used in non-linear system identification. Some solutions are presented to solve common problems arising from the application of genetic algorithm View full abstract»

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  • Joint blind channel estimation and interference suppression for single carrier systems

    Page(s): 60 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB) |  | HTML iconHTML  

    Block transmission with zero padding (ZP) and cyclic prefix (CP) are becoming attractive procedures for their ability to eliminate both inter-symbol interference (ISI) and inter-block interference (IBI). In this paper, we present joint blind channel estimation and interference suppression for single carrier block transmission using both ZP and CP. The proposed estimators take the same form, which gives flexibility for application to either one with minor changes. Our approach uses a generalized multichannel minimum variance principle to design an equalizing filterbank. Channel estimate is then obtained by deriving an asymptotically tight lower bound of the filterbank output power. Numerical examples show that the proposed schemes exhibit low sensitivity to unknown narrowband interference and compare favorably with sub-space blind channel estimators View full abstract»

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  • Finite-alphabet and decision-feedback based channel estimation for space-time coded OFDM systems

    Page(s): 64 - 67
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A novel blind channel estimation scheme is presented for space-time coded OFDM (STC-OFDM) systems. This scheme is composed of coarse channel estimation by exploiting the finite-alphabet property of information signals and fine channel estimation by using decision-directed method, which employs the priori knowledge of the transmitted signals other than the finite-alphabet property of mapping constellation. At the cost of a little more computational complexity, it achieves better performance than the competitive one. The scheme is tested with simulations and also compared with the subspace-based channel estimation View full abstract»

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  • Modeling dual polarization wireless fading channels using quaternions

    Page(s): 68 - 71
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In the letter we describe signal transmitted between two dual-polarized antennas using a quaternion notation. The channel can then be modeled by a single quaternion gain, instead of a matrix of four complex gains as it is done in a classical approach. The model is very useful as it allows for a simple accommodation of any polarization twist between the transmit and receive antennas, as well as, modeling random fading in both polarizations with or without cross-polar scattering View full abstract»

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  • Probability of signal-to-interference ratio in mobile cellular systems

    Page(s): 72 - 75
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (199 KB) |  | HTML iconHTML  

    The probability functions of a sum of co-channel interference signals in a mobile cellular network are analyzed under the assumption that the signal variations follow the Rayleigh distribution and the mean power decreases as dn where n = -3.5. On numerical examples if is shown that the probability function of the sum of interfering signal can be approximated with a Rayleigh distribution with the mean roughly equal to the mean of the strongest interference signal. A comparison of efficiency between two cellular systems is carried out based on these facts View full abstract»

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  • MC-CDMA system with double spreading codes for MAI reduction in the multi-path fading downlink channel

    Page(s): 76 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB) |  | HTML iconHTML  

    Most of the techniques for multiple access interference (MAI) reduction in code-division multiple access (CDMA) systems are applicable to the uplink, where the base-station knows the signature of all users and can apply a multi-user detection (MUD) strategy. A technique is proposed here to reduce the influence of MAI on the downlink of a multi-carrier CDMA (MC-CDMA) system, without resorting to MUD. The technique is based on the use of a spreading sequences pair for each subscriber. Its limiting factor is that the system capacity, in terms of the active users' maximum number, is halved as compared to the case in which a single spreading code per user is adopted View full abstract»

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  • UWB spatial multiplexing by multiple antennas and RAKE decorrelation

    Page(s): 80 - 83
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    An ultra wide band (UWB) spatial multiplexing architecture employing multi-elements antennas (MEA) at the emitter side is presented and analyzed in this paper. This work evaluates the performance of the demultiplexing process at the receiver side, as ensured by multiple parallel RAKE receivers in order to achieve channel decorrelation. The quality of signal restitution, the sub-channels isolation and the quality of the communication links are evaluated by a normalized similarity coefficient, an inter-channel interferences level ratio and a bit error rate (BER) curve respectively View full abstract»

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  • Performance evaluation of two-dimensional quasi orthogonal complete complementary codes in fading channels

    Page(s): 84 - 87
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    A novel MC-CDMA architecture based on complete complementary codes (CCC) was proposed. The benefits of using CCC for both time and frequency domain are known and include features like MAI free transmission, easy rate matching using the unique offset stacked spreading (shift-and-add modulation), low peak-to-average power ratio and low dynamic range of the signal. Two-dimensional (time-frequency) spreading received some attention for its inherent ability to combat negative effects in hostile mobile radio channels. The performance of 2D-MC-CDMA system based on two-dimensional orthogonal CCC (2D-OCCC) in a fading channel was already examined. In this paper we evaluate the performance of two-dimensional quasi orthogonal CCC (2D-QOCCC) for different equalization methods. The system performance is evaluated using an uncorrelated fading channel model View full abstract»

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  • Multicarrier multiuser modulation performance in severely fading channels

    Page(s): 88 - 91
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    In this paper, we investigate the performance of two popular multicarrier transmission schemes, OFDMA, and MC-DS-CDMA, on severely fading channels. Channel models are drawn from our experimental work measuring the wireless channel in the 5 GHz band, around airport surface areas. Results indicate that multicarrier schemes can outperform their single-carrier counterparts, particularly when configured to account for the channel characteristics View full abstract»

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