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Communications, Computers and signal Processing, 2005. PACRIM. 2005 IEEE Pacific Rim Conference on

Date 24-26 Aug. 2005

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Displaying Results 1 - 25 of 168
  • Optimizing the performance of a cluster of hosts

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (435 KB) |  | HTML iconHTML  

    We evaluate the applicability of the dynamic rejuvenation algorithm introduced in A. Avritzer, et al. (2005) to clusters of identical systems operating in parallel. The dynamic rejuvenation algorithm triggers software rejuvenation events when degradation in the value of the response time is detected. View full abstract»

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  • Protocol and control mechanisms to save terminal energy in IEEE 802.16 networks

    Page(s): 5 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB) |  | HTML iconHTML  

    The IEEE 802.16-2004 standard (formerly 802.16d) has been approved to provide last-mile connectivity to fixed locations by radio links. Although the IEEE committee is working on a future 802.16e standard to support terminal mobility, we believe that adding mobility support to the present standard will offer a significant business opportunity for service providers by enabling them to serve a large pool of potential users whose laptops and PDAs are 802.16-2004 enabled. In our prior work, we have shown how to reuse commands from the 802.16-2004 standard to support handoff between access points without any change to the standard. However, given that the mobile terminals will be severely constrained by battery life, it is essential that new protocols and control mechanisms be devised to save terminal energy, based on the existing 802.16-2004 standard. To achieve this objective, in the present paper we propose protocols and use existing 802.16-2004 commands to put mobile terminals to "sleep" (to save energy) when they are idle, and "wake them up" when there is traffic destined for them. We also demonstrate how this "sleep/wakeup" cycle can is compatible with the handoff process. View full abstract»

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  • Bandwidth usage and network latency in a conveyor system with Ethernet-based communication between controllers

    Page(s): 9 - 12
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB) |  | HTML iconHTML  

    Switched Ethernets are increasingly being used in industrial applications such as the control of conveyor systems and the synchronization of axles in complex machinery. The timely delivery of control messages is a central concern in these applications. We show how a queueing model was used to predict traffic flow and delay in the control networks of a conveyor system. The model indicates that the anticipated level of bandwidth usage will be low on even the most heavily loaded links, and that the resulting end-to-end message latencies will be quite small. View full abstract»

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  • On performance of time-hoping impulse radio system with space time coding

    Page(s): 13 - 16
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    Impulse radio (IR) is a promising candidate for short-range, high data rate multiple-access wireless communications. In a multiuser scenario, there are pulses collisions between the signal of the desire user and the interfering users, which degrade the system performance. In this paper, space-time block coding (STBC) is employed in the IR system to exploit space-time diversity for improving performance. Several types of receivers are also proposed and their performances are studied. View full abstract»

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  • DS-PPM ultra-wideband communications with BCH Coding

    Page(s): 17 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    Ultra-wideband (UWB) transmission for short-range wireless communications has recently drawn great attention. This is due to advantages such as high speed, immunity to multipath fading, low cost, and the ability to coexist with narrowband wireless systems. In this paper, we improve the performance of a direct sequence spread spectrum pulse position modulation (DS-PPM) UWB system via the addition of a Bose-Chaudhuri-Hocquenghem (BCH) code. Both single user and multiple-access performance over an additive white Gaussian noise channel is considered. View full abstract»

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  • Performance of SC-FDE in UWB communications with channel estimation errors

    Page(s): 21 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    We analyze the performance of single carrier transmission with frequency domain equalizations (SC-FDE) over UWB communications with least-square (LS) channel estimation. The probability density functions (PDF's) of the frequency domain minimum mean-squared error (MMSE) equalizer taps are derived. The error probability of SC-FDE over UWB channels with LS channel estimation is presented and evaluated numerically. Simulation results validate the use of Gaussian approximation method in the performance analysis of the SC-FDE system with LS channel estimation. View full abstract»

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  • Accurate BER of time-hopping and direct-sequence UWB systems in multi-user interference

    Page(s): 25 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    An exact analysis is derived for precisely calculating the bit error probability of time-hopping and direct-sequence ultra-wideband systems with multi-user interference. This analysis differs from past work in that it is assumed that multiple pulses in a frame from an interfering user can cause interference to the desired user. The Gaussian approximation is shown to be inaccurate for predicting the bit error rate for medium and large signal-to-noise ratio values. The performances of time-hopping and direct-sequence modulation schemes are accurately compared for different numbers of users and frame lengths. View full abstract»

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  • Ultrawideband synchronization in dense multi-path environment

    Page(s): 29 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (533 KB) |  | HTML iconHTML  

    The ultra-short pulse shape of ultra-wideband makes system synchronization very difficult. In practice, UWB synchronization is much more challenging due to the dense multi-path environment of indoor wireless. This paper proposes a simple scheme using pilot codes as a transmitted reference (TR) to assist the frame and bit acquisitions. A new architecture, the reference aided matched filter (RAMF), is suggested. To optimize performance, an adaptive post detection integration (APDI) is designed to capture as much energy as possible for acquisition. In addition, a low complexity early-late gate tracking loop is embedded in both tracking and acquisition functions. System simulations using four IEEE UWB channel models show a fast acquisition time with a reasonable bit error rate. Sampling rate is at symbol speed for practical implementation of a simple digital receiver. View full abstract»

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  • Performance comparison of signal detectors for dependent Gaussian channels

    Page(s): 33 - 36
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (258 KB) |  | HTML iconHTML  

    The detection of weak signals is addressed in additive noise described by the first order moving average of a Gaussian process. We derive decision regions of the maximum likelihood (ML) and suboptimum ML (SML) detectors, and obtain specific examples of the ML and SML decision regions. The ML and SML detectors are employed in the antipodal signaling system, and compared in terms of the bit-error-rate in the dependent Gaussian noise environment. Numerical results show that the SML detector, despite its reduced complexity and simpler structure, exhibits practically the same performance as the optimum ML detector. View full abstract»

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  • Detection and arrival time estimation of a pulsed sinusoid

    Page(s): 37 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (397 KB) |  | HTML iconHTML  

    A novel double-FFT method is presented for the computationally efficient detection and time-of-arrival (TOA) estimation of a pulsed sinusoid. Starting from the time samples x(n), the first FFT produces X(k), whose magnitude is summed for detection. If a pulse is detected, a second complex FFT, of the X(k)2, produces a peak whose location corresponds to the TOA. Simulation results have been used to generate the ROC curves for the detector, and an evaluation of the TOA estimation accuracy. For SNR ≥ 5 db, the TOA root mean square errors are less than ten time samples. View full abstract»

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  • Decision regions for weak PSK signals with a novel M-ary detection criterion

    Page(s): 41 - 44
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (373 KB) |  | HTML iconHTML  

    In this paper, we derive and obtain specific examples of the decision regions of a novel detection criterion for weak M-ary signals. In the sense of minimizing the error probability, the detection criterion is optimum when the signal strength approaches zero. Assuming phase shift keying for convenience, specific decision regions are obtained for the detection of weak signals. It is shown that the proposed detection criterion has almost the same decision regions as the maximum likelihood detection criterion when the strength of signals are small. View full abstract»

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  • Non-coherent detection of MSK with transmit diversity in fast fading

    Page(s): 45 - 48
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (629 KB) |  | HTML iconHTML  

    We propose a minimum-shift keying (MSK) transmission scheme, motivated by the Alamouti-type block code structure. Taking advantage of the block-wise differential encoding on which the MSK transmission is based, the receiver is able to obtain non-coherent sequence estimates from a down-sampled subset of the received statistics. As a result of the sequence detection, the fast fading error floor associated with symbol-by-symbol differential detection is essentially eliminated. Furthermore, using the original received sequence and performing iterative channel estimation and sequence detection, the decisions are refined and further performance gains are observed. In fast fading, the results show that the proposed receiver performance is within 5 dB of the coherent detection lower bound, at a BER of 10-3. View full abstract»

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  • A new improved detector for the V-BLAST system

    Page(s): 49 - 52
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB) |  | HTML iconHTML  

    This paper proposes a new method for symbol detection in the Vertical Bell Labs layered space-time (V-BLAST) system. The performance of V-BLAST is limited by the worst subchannel, i.e. the first iteration, the diversity order of which is Nr - Nt + 1 where Nt and Nr are the number of transmit and receive antennas. A diversity order of Nr - Nt + 1 + T is achievable by delaying decisions by T stages. Considering the statistical properties of the error patterns, we present a new algorithm to delay the decisions to achieve higher diversity orders with reduced computational complexity. The performance-complexity measure of the proposed algorithm is compared with that of the V-BLAST detector and sphere decoder. View full abstract»

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  • Differential distributed space-time block coding

    Page(s): 53 - 56
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (483 KB) |  | HTML iconHTML  

    In this paper, differential distributed space-time block codes (DSIBCs) are introduced. These differential DSTBCs are designed for wireless networks which have a large set of nodes N but at any given time only a small, a priori unknown subset of nodes S ⊂ N can be active. Channel state information is not required at the cooperating nodes nor at the receiver. The signal transmitted by an active node is the product of an information-carrying code matrix and a unique node signature vector. It is shown that existing differential STBCs designed for Nc ≥ 2 co-located antennas are favorable choices for the code matrix guaranteeing a diversity order of d = min{Ns,Nc} if ns nodes are active. Efficient methods for the optimization of the set of signature vectors are provided. Possible applications of the proposed DSTBCs include ad hoc and sensor networks employing decode-and-forward relaying. View full abstract»

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  • Further discussion on the design of STBC-MLC scheme for different set partitioning

    Page(s): 57 - 60
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    This paper presents the concatenation scheme of space-time block codes (STBC) and multilevel codes/multi-stage decoding (MLC/MSD). We analyze the impact of different set partitionings, namely Ungerboeck's partitioning (UP) and block partitioning (BP), on the concatenation scheme by using product distance. Based on capacity rule, performances of the concatenation schemes with 8-ASK and 8-PSK are given for analyzing. View full abstract»

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  • A space constraint based block Tomlinson-Harashima precoding technique for the multi-user MIMO downlink

    Page(s): 61 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (446 KB) |  | HTML iconHTML  

    A space constraint based block Tomlinson-Harashima preceding technique (NS-BTHP technique) is proposed for the downlink of multi-user MIMO systems. Employing non-linear pre-processing at the base station this technique pre-eliminates multi-user interference (MUI) among different mobiles. Therefore, an equivalent point-to-point MlMO channel is realized for each mobile, and the spatial interference among the multiple data streams directed to each user (self-interference) can be eliminated using signal processing algorithms developed for point-to-point MlMO systems. The proposed nonlinear preceding approach results in an improvement of the space constraint technique (NS technique), in which linear pre-processing is used to pre-eliminate the MUI at the base station. The advantage of the NS-BTHP technique over the NS technique is explained and demonstrated by simulations. View full abstract»

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  • On the performance of the space time coded WCDMA downlink system over multi-path fading channel

    Page(s): 65 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    This paper presents performance results of space-time block coding (STBC) in the downlink WCDMA with linear receivers at the terminal. We analyze the bit-error probability performance for this system in frequency selective fading channels. We also present some numerical results. The results show that much better performance is achieved when linear channel equalization at the chip level is employed at the terminal's receiver instead of the conventional Rake receiver. For example, for voice conversations at a BER of 10-3, the capacity can be doubled by using channel chip equalizer. View full abstract»

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  • Polynomial constrained detection for MIMO systems using penalty function

    Page(s): 69 - 72
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB) |  | HTML iconHTML  

    In this paper, we develop a family of approximate maximum likelihood (ML) detectors for multiple-input multiple-output (MlMO) systems by relaxing the ML detection problem. Polynomial constraints are formulated for any signal constellation. The resulting relaxed constrained optimization problem is solved using a penalty function approach. Moreover, to escape from the local minima and to improve the performance of detection, a probabilistic restart algorithm based on noise statistics is proposed. Simulation results show that our polynomial constrained detectors perform better than several existing detectors. View full abstract»

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  • Improved BICM iterative decoding with hard-decision feedback

    Page(s): 73 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    Bit-interleaved coded modulation (BlCM) enables power- and bandwidth-efficient transmission over fading channels. Power efficiency can be further improved if iterative decoding (ID) is applied, so-called BICM-ID. In this paper, we consider BICM-ID with hard-decision feedback as originally proposed by Li and Ritcey (1999) for low-complexity ID. We analyze the reliability of the soft output of the hard-decision feedback aided demapper, the inner decoder of BICM-ID. From this we find that a simple truncation of these output values significantly improves reliability in subsequent decoding iterations and thus, enhances convergence of ID. We propose two pragmatic truncation schemes and show by means of simulations that gains of more than 3 dB in power efficiency over conventional BICM-ID are achieved for the Rayleigh fading channel with no increase in decoding complexity. View full abstract»

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  • Turbo decoding enhancement studies in satellite communications

    Page(s): 77 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (262 KB) |  | HTML iconHTML  

    Modern satellite communication systems require high-rate, accurate and reliable transmission in the presence of hostile environments. These requirements present a major challenge. To meet this challenge, we are presenting a simple enhancement of the turbo decoding algorithm which will significantly improve the end-to-end channel performance. Herein, we present an improved max-log-MAP turbo decoding in which the branch metrics are weight by a single scaling factor. The enhanced max-log-MAP decoder can provide a significant BER performance over the conventional max-log-MAP by improvement in the extrinsic information calculation. With negligible increase in complexity, this enhancement has significant advantage for advanced satellite communication applications. View full abstract»

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  • Performance evaluation of LDPC codes in the presence of colored noise

    Page(s): 81 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB) |  | HTML iconHTML  

    The class of low density parity check (LDPC) codes includes the most powerful capacity-approaching codes reported to date. As a result, LDPC codes have been considered for application in new communication standards such as 10GBASE-T Ethernet. However, the successful use of LDPC codes for such applications requires a better understanding of the effects of signal impairments on their error correction capabilities. In this paper, the performance of various LDPC codes in the presence of additive colored Gaussian noise (ACGN) is evaluated and compared with the effects of conventional additive white Gaussian noise (AWGN). The simulation results provide insight into the performance of LDPC codes in real systems in which the noise components can indeed be correlated. In particular, our results show that at the same signal-to-noise ratio (SNR), ACGN is more detrimental to the bit error rate (BER) performance than AWGN. View full abstract»

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  • Low-density parity-check convolutional codes for Ethernet networks

    Page(s): 85 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    In this paper we discuss the application of low-density parity-check convolutional codes to several communication protocols which employ the Ethernet frame format. We argue that these codes are more suited to such systems than their block counterparts. This is due, in part, to a reduced encoder complexity and the ability to operate on random lengths of data. We also discuss how we can use existing frame delimiters and interframe gaps to perform presetting and termination of the code. We present simulation results which suggest this may be used to improve error performance over the first and last bytes of the frame. View full abstract»

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  • Effect of imperfect CSI on iteratively decoded BICM over Nakagami fading channels

    Page(s): 89 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (374 KB) |  | HTML iconHTML  

    We investigate the impact of imperfect channel state information (CSI) on the bit error rate (BER) performance of uncoded and coded modulation schemes over Nakagami fading channels using the model proposed in C. Polprasert and JA Ritcey (2005). The analytical and asymptotic BER performance of uncoded M-PSK modulation is evaluated and verified by the simulation. For coded modulation, the error free feedback bound (EF bound) of the bit-interleaved coded modulation with iterative decoding (BICM-ID) for both perfect and imperfect CSI is developed. We show that asymptotically, the error floor generated due to imperfect CSI depends on the fading parameter and the power correlation coefficient between the fading coefficient and its estimate. View full abstract»

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  • Model description method based on a graphical language and a character based language together for a queueing network model

    Page(s): 93 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (245 KB) |  | HTML iconHTML  

    In existing queueing network evaluation system, a user selects the model for among sorts of prepared model and can describe for defining feature of model. Therefore, it is hard for the user to select adequate model, and representing connection between entities is so hard for the user that representing queueing network is difficult. So, we propose the model description method that the user can use in graphical user interface so as to compensate for such weak points. By using it, the user is possible to model easily and do not have to select which models the user want to use. And, representing connection between entities is easy. Then, we actually model with proposal method and show usefulness with comparing existing queueing network evaluation systems. View full abstract»

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  • Performance comparison of ECN-BLUE in both single bottleneck and multi-bottleneck networks

    Page(s): 97 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB) |  | HTML iconHTML  

    We investigate in this paper the application of ECN-BLUE, which uses packet marking to indicate congestion instead of dropping packets currently adopted by BLUE. We compare the performance of ECN-BLUE with BLUE in both a single bottleneck and a multi-bottleneck network. Our simulation results show that ECN-BLUE cannot further improve the performance of BLUE in terms of packet drop rate, average queue size and queue size stability. View full abstract»

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