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Wireless Telecommunications Symposium, 2009. WTS 2009

Date 22-24 April 2009

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Displaying Results 1 - 25 of 76
  • Use of extrinsic information transfer chart to predict behavior of turbo codes

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (953 KB) |  | HTML iconHTML  

    In this paper, we consider turbo codes that are now introduced in various international standards, including the UMTS standard for third generation personal communications and the ETSI DVB-T standard for Terrestrial Digital Video Broadcasting, and review the method of extrinsic information transfer. The convergence properties of the iterative decoding process associated with a given turbo-coding scheme are assessed using the so-called extrinsic information transfer (EXIT) chart analysis technique. This approach provides an opportunity to foresee the bit error rate (BER) of a turbo code system using only the EXIT chart. It is shown that EXIT charts are powerful tools to analyze and optimize the convergence behavior of iterative systems utilizing the turbo principle, i.e., systems exchanging and refining extrinsic information. The idea is to consider the associated SISO stages as information processors that map input a priori LLR's onto output extrinsic LLR's, the information content being obviously assumed to increase from input to output, and introduce them to the design of turbo systems without the reliance on extensive simulation. Compared with existing methods for generating EXIT functions, a suggested approach provides insight into the iterative behavior of linear turbo systems with substantial reduction in numerical complexity. View full abstract»

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  • Modeling and simulation of self-similar wireless IP network traffic

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1382 KB) |  | HTML iconHTML  

    The paper examines self-similar properties of real telecommunications network traffic data over a wide range of time scales. These self-similar properties are very different from the properties of traditional models based on Poisson and Markov-modulated Poisson processes. The algorithms for modeling fixed-length sequence generators that are used to simulate self-similar behavior of wireless IP network traffic are developed and applied. Numerical examples and simulation results are provided. View full abstract»

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  • Analysis of threshold of regular and irregular LDPC codes using Gaussian approximation

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    We present the formulas for searching for the thresholds of regular and irregular low-density parity-check (LDPC) codes under message-passing (MP) algorithm. A Gaussian approximation is applied to studying the evolution of the means of the messages of the variable nodes and the check nodes. Accurate numerical integration methods by using transformations are shown for evaluating the expected values of the message of the check nodes. Tables are built first and interpolations are used for further evaluations. Two curves are used to locate the threshold. We utilize an iterative decoding tunnel between these two curves and study the decoding performance by evaluating conditions of the derivatives of these two curves. Using this method the performance of both regular and irregular LDPC codes can be studied in a unified manner without using simulation. View full abstract»

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  • Soft iterative channel estimator for BICM-ID-SSD over time-varying flat fading channels

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (988 KB) |  | HTML iconHTML  

    This paper proposes an iterative estimator for bit interleaved coded modulation (BICM) with an iterative soft-input soft-output (SISO) receiver over time-varying flat fading channels. More specifically, the system implements signal space diversity (SSD) where the QAM symbols are rotated. The use of an iterative Kalman filter shows good results using superimposed training sequence and Gauss-Markov channel model for fast tracking of the channel variation. The proposed soft iterative estimator uses the soft extrinsic information from the decoder as well as the superimposed training sequence to update the channel coefficients for data detection. To analyze the results, an analytical bound for the asymptotic bit error rate (BER) for BICM-ID-SSD over correlated fading channels is computed with perfect channel state information (CSI). View full abstract»

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  • Packet retransmission with interference cancellation for MIMO-OFDM systems

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (975 KB) |  | HTML iconHTML  

    This paper proposes a packet retransmission scheme with interference cancellation for OFDM systems based on the basic principle of spread spectrum technique. The proposed design orthogonally spreads packets in transmission-domain to separate the desired signal from the interferences. Almost without increasing complexity, it outperforms the conventional packet retransmission scheme. View full abstract»

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  • Two signatures' codes linear decorrelator detector for CDMA systems

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1587 KB) |  | HTML iconHTML  

    Code Division Multiple Access (CDMA) is a widely used multiple access method in a lot of nowadays vital applications. The systems that are designed based on CDMA are suffering from multiple access interference (MAI) problem. A lot of CDMA detectors are designed to overcome the (MAI) problem. But as the capability of CDMA detector in (MAI) cancellation increases, the complexity of the detector increases too. This paper gives a proposal of a new linear CDMA detector that has the same multiple access interference (MAI) cancellation capability as CDMA decorrelator detector. The structure complexity of this new proposed detector is as simple as the matched filter detector structure. Solving the (MAI) problem in CDMA system with simple detector structure at the receiver helps on increasing the CDMA system capacity. The new proposed detector operation is based on the symmetry property of CDMA signatures' codes cross-correlation matrix. View full abstract»

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  • Achieving higher HSDPA performance and preserving R99 soft handover control by large scale optimization in CPICH coverage planning

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB) |  | HTML iconHTML  

    Common pilot channel (CPICH) power is a crucial parameter in coverage planning of today's UMTS networks that implement both HSDPA and R99 services. Adopting a non-uniform allocation of cell CPICH power and minimizing its amount necessary for coverage, the resulting power saving significantly improves HSDPA performance. At the same time, it is vital to have the desired level R99 soft handover, which is heavily influenced by CPICH. In this paper, we demonstrate how large scale optimization can deal with both tasks. Our approach focuses on enhancing cell-edge HSDPA data rate, subject to requirements of CPICH coverage and the level of R99 soft(-er) handover. We present a solution algorithm that optimizes CPICH allocation for HSDPA performance, and, in parallel, offers accurate control of R99 soft handover. Experimental results for large and realistic network planning scenarios demonstrate the benefit of our optimization approach. View full abstract»

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  • Comparison of mobile TV deployment strategies in 3G LTE networks

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1309 KB) |  | HTML iconHTML  

    In this paper, we propose a cross-layer analytical model to assess the capacity of a cellular network offering both TV and unicast (voice, data) services. Different mobile TV deployment strategies are then studied. This includes unicast-based TV and two broadcast/multicast approaches based on 3GPP MBMS, namely, single cell point to multipoint (SC-PtM) and MBSFN (MBMS over single frenquency networks). We compare the different strategies from two points of view: 1. the quality of service (QoS) they insure for TV users and their impact on unicast services and 2. the trade off between the QoS needs of the different services is discussed and the best TV deployment strategy is given for different traffic scenarios. View full abstract»

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  • Adaptive rate control (ARC) over DVB-RCS on satellite links

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1625 KB) |  | HTML iconHTML  

    The Digital Video Broadcasting Return Channel via Satellite (DVB-RCS) is a flexible technology offering broadband Internet access to a large community of users with a relative low cost. However, the spreading of the multimedia network is required the mechanism to guarantee a certain level of Quality of Service (QoS) to the end users. This paper will propose the ARC mechanism which is acting like a gate to control bandwidth by investigating the available channel parameter, and delay time for reused the other available channels at Network Communication Center (NCC). The other co-parameters such as number of packet drop, mean queue time and throughput are investigated in situation of congestion. The results of ARC mechanism will compare with regular mechanism, as Connection Admission Control (CAC) mechanisms. Finally we obtained the impressive results over the proposed mechanism. View full abstract»

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  • An enhanced MBMS power control mechanism towards Long Term Evolution

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6582 KB) |  | HTML iconHTML  

    Long Term Evolution (LTE) promises the delivery of rich multimedia services in a more power and spectral efficient way than its predecessor Universal Mobile Telecommunication System (UMTS). To this direction, the newly introduced Enhanced - Multimedia Broadcast/Multicast Service (E-MBMS) framework is envisaged to play a fundamental role during the LTE standardization. E-MBMS constitutes the successor of MBMS which was introduced in the Release 6 of UMTS in order to deliver multimedia data from a single source entity to multiple destinations. This paper proposes a novel mechanism for efficient radio bearer selection during E-MBMS transmissions in LTE networks. The proposed mechanism is based on the concept of transport channels combination (point-to-point and/or point-to-multipoint radio bearers) in any cell/sector of the network in which multicast users are residing. The mechanism is evaluated through several realistic scenarios and is compared with several radio bearer selection mechanisms in order to highlight the enhancements that it provides. View full abstract»

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  • Interference mitigation in co-working IEEE 802.11n WLANs

    Page(s): 1 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1224 KB) |  | HTML iconHTML  

    In a densely deployed Wireless Local Area Network (WLAN) environment, Access Points (APs) could be so close to cause significant channel interference. In the next generation IEEE 802.11n WLANs, inter-cell interference decreases spectral efficiency. By applying common transmission weight vectors in all sub-carriers at a set of users, the paper proposes a new distributed algorithm that permits interfering APs to select appropriately their operating frequency and suppress interference in co-working IEEE 802.11n WLANs. Our method increase system performance and significantly reduces implementation complexity and power consumption. Simulation results in a strong interference environment show substantial gain for our proposed strategies. View full abstract»

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  • A hierarchical and topological classification of linear sensor networks

    Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2039 KB) |  | HTML iconHTML  

    Considerable advancements in the technology of wireless sensor networks (WSNs) are taking place due to smaller, and more efficient electronic devices which are capable of increased processing power, and communication capabilities. In addition, the cost of such devices is constantly decreasing, which makes it possible to employ large quantities of networked sensors in numerous commercial, environmental, military and health care applications. A lot of these applications involve lining up the sensor nodes in a linear structure giving rise to a new class of WSNs, which is defined in this work as Linear Sensor Networks (LSNs). This paper identifies some of the applications that might use such networks and offers a classification of the different types of LSNs from a topological and hierarchical points of view. Finally, a motivation for designing specialized protocols that take advantage of the linearity of such networks in order to increase reliability, efficiency, energy savings, and network lifetime is offered along with the new research issues, challenges and opportunities that exist in this field. View full abstract»

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  • A flexible object-oriented design of an event-driven wireless network simulator

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1513 KB) |  | HTML iconHTML  

    Different simulation tools are available to the research community which can be used to validate, test and evaluate networking protocols. Such simulation software packages include OPNET, ns-2 and others. These programs are capable of performing relatively accurate simulations of networking architectures including wireless, ad hoc, and sensor networks. Although they are very useful for a wide range of experiments which involve performance evaluation of existing protocols, selecting them to verify and test the performance of new platforms and protocols that are not implemented in these programs tend to impose considerable restrictions and limitations. Therefore, implementing these protocols in existing simulator packages could be relatively difficult and time consuming. This paper presents an object-oriented framework to design an event-driven network simulator that can be used to evaluate different wireless networking architectures and protocols. The design of the simulator allows for a considerable increase in flexibility for the researcher who is able to include particular aspects and implementations of the corresponding protocols. The different classes that constitute the simulator application along with the main methods, and relationships are presented. In addition, design strategies for simulating node mobility using the popular Waypoint model are also presented. View full abstract»

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  • Value analysis of technology evolution: Case mobile peer-to-peer communications

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1756 KB) |  | HTML iconHTML  

    We developed a value analysis framework based on existing literature. We used our framework to analyze novel mobile peer-to-peer communications technologies on three distinct evolution paths. According to our analysis, the telecom-driven evolution path concentrates on preserving established business models of current telecom operators; the Internet-driven and proprietary paths initiate competing business models where the service operator partially replaces the service provision value generation mode of the network operator. The value networks of the proprietary and the telecom-driven paths are centralized on one actor, whereas the value network of the Internet-driven path is more balanced and establishes value generation opportunities for more actors. View full abstract»

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  • End-to-end network simulator for conversational quality measurements

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (894 KB) |  | HTML iconHTML  

    End-to-end telecommunication network simulator design and realization is described in the paper. The main applications of the simulator are conversational tests e.g. as per ITU-T P.800 and demonstrations. The simulator can be also used as a replacement of telecommunication chain part that is missing during end-to-end testing or measurements. Examples of achieved subjective test results are presented. View full abstract»

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  • Reducing handover drops by utilizing Comparative Queuing

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1370 KB) |  | HTML iconHTML  

    In heavy traffic cellular networks low priority handover requests will increase handover drops. In current handover queuing schemes, slow signal strength changing mobile units with low priority handover requests can occupy the handover queue space. As a result, high priority requests will be dropped. This effect could be eliminated utilizing a new scheme called comparative queuing. Prioritization method has been modified to include the possibility of termination of calls for the mobile units waiting in the handover queue. This scheme with lower queue sizes outperforms the existing dynamic priority queuing schemes under heavy traffic conditions. Simulation is conducted for a cluster of seven cells to incorporate interaction between cells. Simulation results confirm the reduction in handover drops. View full abstract»

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  • On network processor based protocol stack implementation for 4G base stations

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (102 KB) |  | HTML iconHTML  

    This paper deals with the implementation of protocol handling in radio link control and medium access control layers using network processing elements, where the focus is on 4G wireless system parameters. We describe the software design and implementation for the Intel IXP2350 processor as an example and provide implementation results. Results are given in terms of feasible and achieved throughput, processor element utilization, thread execution times and memory bus utilization. For the protocol functionality we use the LTE (Advanced) draft standard as a guideline. The software design criteria and consequential implementation choices (such as number of threads and memory access budgets) are easily adaptable to other network processors and similar wireless standards. View full abstract»

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  • Parallel decoding of turbo codes using multi-point trellis termination and collision-free interleavers

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB) |  | HTML iconHTML  

    The UMTS turbo encoder is composed of parallel concatenation of two Recursive Systematic Convolutional (RSC) encoders which start and end at a known state. This trellis termination directly affects the performance of turbo codes. This paper presents performance analysis of multi-point trellis termination of turbo codes which is to terminate RSC encoders at more than one point of the current frame while keeping the interleaver length the same. For long interleaver lengths, this approach provides dividing a data frame into sub-frames which can be treated as independent blocks. A novel decoding architecture using multi-point trellis termination and collision-free interleavers is presented. Collision-free interleavers are used to solve memory collision problems encountered by parallel decoding of turbo codes. The proposed parallel decoding architecture reduces the decoding delay caused by the iterative nature and forward-backward metric computations of turbo decoding algorithms. Our simulations verified that this turbo encoding and decoding scheme shows bit error rate (BER) performance very close to that of the UMTS turbo coding while providing almost %50 time saving for the 2-point termination and %80 time saving for the 5-point termination. View full abstract»

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  • Adding indoor location capabilities to an IEEE 802.11 WLAN using real-time RTT measurements

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1650 KB) |  | HTML iconHTML  

    An accurate real-time application which locates mobile users in an indoor environment is highly demanded in hospitals, warehouses, etc., provided that minor changes in their infrastructure are required. Most present-day location techniques require a great calibration effort, or special devices which are not cost-effective. Avoiding these needs, this paper implements an autonomous positioning technique based on IEEE 802.11 RTS/CTS two-frame exchange in a real scenario. Two estimators of the delay profile measured are analyzed and a linear regression of them at each distance is performed from which the distance between a mobile user and an access point is estimated. Experimental results, without any tracking information nor nonline-of-sight mitigation, reveal the effectiveness of the proposed method. View full abstract»

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  • Theoretical derivation of bit error rate in MB-OFDM UWB system

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB) |  | HTML iconHTML  

    This paper derives the theoretical bit error rate (BER) of the multiband orthogonal frequency division multiplexing (MB-OFDM) system for ultra wideband (UWB) communication. The proposed derivation takes into account the fading correlation caused by time and frequency spreading, which is one of the most significant factors in MB-OFDM UWB system. Moreover, the proposed formula gives consideration to the frequency characteristics of propagation loss that are not negligible in UWB systems. The theoretical results by the proposed approach are compared with the computer simulation results in order to confirm the validity of the proposed derivation. View full abstract»

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  • Quantization based reliable equalization algorithm for turbo DFE and dual-mode blind equalizers

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    In this paper we propose a new adaptive equalization technique for turbo decision feedback equalizers (TDFE) and dual-mode blind equalizers, that takes the advantage of quantization in the probabilistic scheme. In generating the error signal the proposed technique considers the likelihood between the quantized equalizer output and all the constellation points, thus making the receiver insensitive to the decoding errors. The proposed technique achieves lower BER with less computations than other TDFE algorithms. Also a more reliable soft transition between start-up and decision directed (DD) mode in blind equalizers is proposed. This technique has been compared with Benveniste-Goursat, Stop-and-Go and Lim's soft transition algorithm. It is shown that the proposed approach is superior and more robust under different channel and SNR conditions. View full abstract»

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  • Switch over implementation and analysis for hybrid wireless network of optical wireless and GHz links

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (395 KB) |  | HTML iconHTML  

    High bandwidth optical wireless communication links are of prime importance, having tremendous potential to serve for the future huge data transmission requirements especially for the next generation optical networks. The inherent electromagnetic nature of the transmitted optical signals and the stochastic nature of the earth atmosphere create a number of technical challenges preventing widespread acceptance of technology and its implementation. One of the major concerns for Free Space Optics (FSO) links is fog that causes very high attenuation over non-negligible amounts of time. Another technology offering negligible fog attenuation and acceptable data rates is license free ISM band, which can be used as back up link. However, a switch-over mechanism is required for optimal selection of any link depending on weather condition and link quality maintaining an acceptable data rate. Moreover, synchronization of transceivers is the basic requirement of a communication link. This paper presents an implementation of a self-synchronizing switch-over system and the behaviour of this hybrid network is simulated for measured fog events. View full abstract»

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  • Low energy clustering adaptation protocol for an adhoc wireless sensor network

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    Energy dissipation in a Wireless Sensor Network is an active research field. Energy dissipation is related to the network topology and protocol used to route data. So, two criteria are proposed to elect a relay. A linear or a random choice from a set of potential nodes to become a relay based on their energy level above a mean threshold energy. These criteria improve the organization of the node communications and the lifetime of the network. The criteria and the protocol called the Self Organization One Hop Low Energy Clustering Adaptation (SOORLECA) are explained. The SOORLECA is designed for environmental and military monitoring with precise requisite measures at each node. No mean data or smoothing data technique is required at the Sink Node (SN). Random topology of the network for 100 nodes over 100m2 are simulated to show the protocol performances compared to direct transmission of the node to the SN, short routing path and static clustering protocols. The lifetime and the dissipated energy of the network are our criteria to measure the performance of the WSN. It is shown that the SOORLECA ACMET1 improves 2x the lifetime of network with 61% dissipated energy after 50% of nodes have dead. View full abstract»

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  • Laboratory performance of wi-fi point-to-point links: A case study

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2467 KB) |  | HTML iconHTML  

    Experimental laboratory measurements are made about several performance aspects of IEEE 802.11a, b, g point-to-point links, using Enterasys Networks access points (RBTR2). Detailed results are presented and discussed at OSI levels 1, 3, 4 and 7: SNR, latency, ICMP packet loss, TCP throughput, jitter, percentage datagram loss, and FTP transfer rate. View full abstract»

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  • Automotive multi-standard RF front-end for GSM, WCDMA and Mobile WiMAX

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (618 KB) |  | HTML iconHTML  

    The vastly growing amount of RF wireless communications standards and respective frequencies will demand the availability of multi-standard transceivers. A multi-frequency RF Front-end receiver supporting EGSM, WCDMA and Mobile WiMAX standards in the range from 935 MHz to 2.69 GHz is presented in this document. The multi-standard architecture aims for maximum hardware sharing and design reuse, adaptable to the various wireless channels and conceived as a reconfigurable smart radio aiming to provide full wireless connectivity in the framework of automotive communication environments. The RF front-end receiver features two CMOS switches and SAW filters for band selection and a shared LNA, I/Q-demodulators and analog baseband chain that meet the specifications spread spectrum (e.g. WCDMA) and OFDM(A) (e.g. WiMAX) systems as well as for the GSM narrow spectrum system with modulation scheme GMSK. View full abstract»

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