By Topic

Communications and Networks, Journal of

Issue 1 • Date March 2007

Filter Results

Displaying Results 1 - 20 of 20
  • [Front cover]

    Page(s): c1
    Save to Project icon | Request Permissions | PDF file iconPDF (58 KB)  
    Freely Available from IEEE
  • [Front inside cover]

    Page(s): c2
    Save to Project icon | Request Permissions | PDF file iconPDF (59 KB)  
    Freely Available from IEEE
  • Subsidiary maximum likelihood iterative decoding based on extrinsic information

    Page(s): 1 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1234 KB) |  | HTML iconHTML  

    This paper proposes a multimodal generalized Gaussian distribution (MGGD) to effectively model the varying statistical properties of the extrinsic information. A subsidiary maximum likelihood decoding (MLD) algorithm is subsequently developed to dynamically select the most suitable MGGD parameters to be used in the component maximum a posteriori (MAP) decoders at each decoding iteration to derive the more reliable metrics performance enhancement. Simulation results show that, for a wide range of block lengths, the proposed approach can enhance the overall turbo decoding performance for both parallel and serially concatenated codes in additive white Gaussian noise (AWGN), Rician, and Rayleigh fading channels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comprehensive analysis of turbo TCM over two typical channels

    Page(s): 11 - 17
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1183 KB) |  | HTML iconHTML  

    In this paper, system performance of turbo trellis coded modulation (turbo TCM) is presented and analyzed through computer simulations over two typical channels, namely additive white Gaussian noise (AWGN) and Rayleigh fading channels. We use and compare different mapping strategies based on Ungerboeck partitioning (UP), block partitioning (BP), mixed partitioning (MP), Gray partitioning (GP), and Ungerboeck-Gray partitioning (UGP) of the signal constellation of the turbo TCM system. Furthermore, taking 8PSK modulation of turbo TCM as an example, our simulation results show that turbo TCM with UP can obtain better performance than turbo TCM with BP, MP, GP, and UGP in both AWGN and Rayleigh fading channels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A square root normalized LMS algorithm for adaptive identification with non-stationary inputs

    Page(s): 18 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2945 KB) |  | HTML iconHTML  

    The conventional normalized least mean square (NLMS) algorithm is the most widely used for adaptive identification within a non-stationary input context. The convergence of the NLMS algorithm is independent of environmental changes. However, its steady state performance is impaired during input sequences with low dynamics. In this paper, we propose a new NLMS algorithm which is, in the steady state, insensitive to the time variations of the input dynamics. The square soot (SR)-NLMS algorithm is based on a normalization of the LMS adaptive filter input by the Euclidean norm of the tap-input. The tap-input power of the SR- NLMS adaptive filter is then equal to one even during sequences with low dynamics. Therefore, the amplification of the observation noise power by the tap-input power is cancelled in the misadjustment time evolution. The harmful effect of the low dynamics input sequences, on the steady state performance of the LMS adaptive filter are then reduced. In addition, the square root normalized input is more stationary than the base input. Therefore, the robustness of LMS adaptive filter with respect to the input non stationarity is enhanced. A performance analysis of the first- and the second-order statistic behavior of the proposed SR-NLMS adaptive filter is carried out. In particular, an analytical expression of the step size ensuring stability and mean convergence is derived. In addition, the results of an experimental study demonstrating the good performance of the SR-NLMS algorithm are given. A comparison of these results with those obtained from a standard NLMS algorithm, is performed. It is shown that, within a non- stationary input context, the SR-NLMS algorithm exhibits better performance than the NLMS algorithm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Intersymbol decorrelating detector for asynchronous CDMA systems

    Page(s): 28 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (670 KB) |  | HTML iconHTML  

    Estimated channel information, especially multipath length and multipath channel of the desired user, is necessary for most previously reported linear blind multiuser detectors in code division multiple access (CDMA) systems. This paper presents a new blind intersymbol decorrelating detector in asynchronous CDMA systems, which uses the cross correlation matrix of the consecutive symbols. The proposed detector is attractive for its simplicity because no channel estimation is required except the synchronization of the desired user. Compared with other reported multiuser detectors, simulation results show that the proposed detector provides a good performance when the active users have significant intersymbol interference and the multipath length is short. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • BER performance of OFDM combined with TDM using frequency-domain equalization

    Page(s): 34 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1341 KB) |  | HTML iconHTML  

    Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM), in this paper called OFDM/TDM, can overcome the high peak-to-average-power ratio (PAPR) problem of the conventional OFDM and improve the robustness against long time delays. In this paper, the bit error rate (BER) performance of OFDM/TDM in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays. It is also shown that the performance of OFDM/TDM de- signed to reduce the PAPR can bridge the conventional OFDM and single-carrier (SC) transmission by changing the design parameter. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Enhanced client polling with multilevel pre-fetching algorithm for wireless networks

    Page(s): 43 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    The implementation of client polling as a weak cache coherence mechanism has two major drawbacks: Firstly, the cache may return a stale copy if the object is changed in the origin server while the cached copy is considered valid. Secondly, the cache can invalidate a cached copy that is still valid in the server. Therefore, we propose a multilevel pre-fetching (MLP) in conjunction with the client polling to refine these drawbacks. MLP is introduced to improve the level of freshness among the cached objects. The simulation results presented in this paper show that the proposed MLP significantly minimizes the number of stale objects and reduces the invalidation messages sent out to the server, i.e., increase the cache HIT rate. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Chip-interleaved self-encoded multiple access with iterative detection in fading channels

    Page(s): 50 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1014 KB) |  | HTML iconHTML  

    We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A scalable and robust approach to collaboration enforcement in mobile ad-hoc networks

    Page(s): 56 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (997 KB) |  | HTML iconHTML  

    Mobile ad-hoc networks (MANETs) have attracted great research interest in recent years. Among many issues, lack of motivation for participating nodes to collaborate forms a major obstacle to the adoption of MANETs. Many contemporary collaboration enforcement techniques employ reputation mechanisms for nodes to avoid and penalize malicious participants. Reputation in- formation is propagated among participants and updated based on complicated trust relationships to thwart false accusation of benign nodes. The aforementioned strategy suffers from low scalability and is likely to be exploited by adversaries. In this paper, we propose a novel approach to address these problems. With the proposed technique, no reputation information is propagated in the network and malicious nodes cannot cause false penalty to benign hosts. Nodes classify their one-hop neighbors through direct observation and misbehaving nodes are penalized within their localities. Data packets are dynamically rerouted to circumvent selfish nodes. As a result, overall network performance is greatly enhanced. This approach significantly simplifies the collaboration enforcement process, incurs low overhead, and is robust against various malicious behaviors. Simulation results based on different system configurations indicate that the proposed technique can significantly improve network performance with very low communication cost. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dual diversity over correlated Ricean fading channels

    Page(s): 67 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (982 KB) |  | HTML iconHTML  

    The performance of dual diversity receivers operating over correlated Ricean fading channels is analyzed. Using a previously derived rapidly converging infinite series representation for the bivariate Ricean probability density function, analytical expressions for the statistics of dual-branch selection combining, maximal-ratio combining, and equal-gain combining output signal-to-noise ratio (SNR) are derived. These expressions are employed to obtain novel analytical formulae for the average output SNR, amount of fading, average bit error probability, and outage probability. The proposed mathematical analysis is used to study various novel performance evaluation results with parameters of interest the fading severity, average input SNRs, and the correlation coefficient. The series convergence rate is also examined verifying the fast convergence of the analytical expressions. The accuracy of most of the theoretical performance evaluation results are validated by means of computer simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Reduced complexity signal detection for OFDM systems with transmit diversity

    Page(s): 75 - 83
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (987 KB) |  | HTML iconHTML  

    Orthogonal frequency division multiplexing (OFDM) systems with multiple transmit antennas can exploit space-time block coding on each subchannel for reliable data transmission. Spacetime coded OFDM systems, however, are very sensitive to time variant channels because the channels need to be static over multiple OFDM symbol periods. In this paper, we propose to mitigate the channel variations in the frequency domain using a linear filter in the frequency domain that exploits the sparse structure of the system matrix in the frequency domain. Our approach has reduced complexity compared with alternative approaches based on time domain block-linear filters. Simulation results demonstrate that our proposed frequency domain block-linear filter reduces computational complexity by more than a factor of ten at the cost of small performance degradation, compared with a time domain block- linear filter. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Steiner tree compilation of multicast under differentiated services constraints

    Page(s): 84 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1236 KB) |  | HTML iconHTML  

    This paper deals with the creation of multicast trees in a differentiated services (DiffServ) domain. Initially, we model the integration problems of multicast & DiffServ and give a general description of our framework for multicast provisioning in DiffServ domains. Within this framework, we introduce a novel heuristic algorithm which calculates the multicast trees efficiently. The multicast tree's format and the bandwidth constraints per service class are modeled. The heuristic is based on the Dijkstra's shortest path algorithm and aims to produce the cheapest possible trees (Steiner tree problem) that conform to the defined model. The produced trees can be considered as DiffServ-customized Steiner trees. Furthermore, we evaluate the algorithm with theoretical and experimental analysis and finally, we present our conclusions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Survivable traffic grooming in WDM ring networks

    Page(s): 93 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (895 KB) |  | HTML iconHTML  

    Traffic grooming, in which low-rate circuits are multiplexed onto wavelengths, with the goal of minimizing the number of add-drop multiplexers (ADMs) and wavelengths has received much research attention from the optical networking community in recent years. While previous work has considered various traffic models and network architectures, protection requirements of the circuits have not been considered. In this paper, we consider survivable traffic grooming, or grooming traffic which contains a mix of circuits that need protection and that do not need protection. We assume a unidirectional ring network with all-to-all symmetric traffic with t >; 1 circuits between each node pair, of which s require protection. As it turns out, survivable traffic grooming presents a significant tradeoff between the number of wavelengths and the number of ADMs, which is almost non-existent in non-survivable traffic grooming for this type of traffic. We explore this tradeoff for some specific cases in this paper. We also present some new results and solution methods for solving certain non-survivable traffic grooming problems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Call for papers

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (67 KB)  
    Freely Available from IEEE
  • Call for papers

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (50 KB)  
    Freely Available from IEEE
  • IEEE copyright transfer form

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (32 KB)  
    Freely Available from IEEE
  • [Advertisement]

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (49 KB)  
    Freely Available from IEEE
  • Journal of Communications and Networks (JCN)

    Page(s): c3
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
    Save to Project icon | Request Permissions | PDF file iconPDF (51 KB)  
    Freely Available from IEEE

Aims & Scope

The Journal of Communications and Networks is published six times per year, and is committed to publishing high-quality papers that advance the state-of-the-art and practical applications of communications and information networks.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
H. Vincent Poor
Princeton University