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Communications, IEE Proceedings-

Issue 2 • Date Apr 2002

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Displaying Results 1 - 10 of 10
  • Fuzzy-based adaptive partial parallel interference canceller for CDMA communication systems over fading channels

    Page(s): 111 - 116
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    The authors propose a fuzzy inference system (FIS) for the multistage partial parallel interference cancellation (PIC) multiuser detectors in a direct-sequence code-division multiple-access (DS-CDMA) communication system. The multistage PIC scheme is an effective method for the multiuser detection in the DS-CDMA systems, but the performance still suffers degradations in the near-far situations. The partial PIC (PPIC), which tries to reduce the cancellation error due to the wrong interference estimations in the earlier stages, outperforms the conventional PIC (CPIC) when the system load is high. An adaptive fuzzy inference mechanism is proposed to generate the adequate cancellation weights for the multistage PPIC by using the measured SNR and signals' amplitudes, which reveal the reliability of the received signals. Simulation results show that the proposed fuzzy-based PPIC (FB-PPIC) detector is more robust over the fading channels and is more near-far resistant than both the CPIC and constant weight PPIC (CW-PPIC) schemes. View full abstract»

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  • Dual-frequency sounder for UMTS frequency-division duplex channels

    Page(s): 117 - 122
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (867 KB)  

    A single-frequency wideband chirp sounder designed and implemented at UMIST was modified to carry out simultaneous measurements at the uplink and downlink frequencies of the UMTS bands. Measurements in the dense urban environment of Manchester city centre were carried out using both a trolley and a van, and power delay profiles were obtained over the two 60 MHz channels allocated for the frequency-division duplex links. Small-scale characterisation is determined from scattering functions and from power delay profiles. Both functions showed differences in the multipath structure between the two channels. Scattering functions with both sparse scattering and dense scattering were detected. The effects of moving vehicles on a stationary user are also presented. These results are preceded by a presentation of the sounder architecture and various back-to-back tests demonstrating its performance capabilities. These include linearity tests with multiple tones, and ambiguity functions of the two frequency bands. View full abstract»

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  • Generalised approach for evaluation of outage performance in micro- and pico-cellular networks

    Page(s): 123 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (639 KB)  

    Outage analysis is one of the primary objectives in the design and operation of the current generations of cellular mobile communications systems, in order to increase spectrum efficiency and meet the quality of service and the grade of service demands. A general and unified semi-analytical approach is presented for the direct evaluation of the outage probability in the presence of L mutually independent co-channel interferers for micro- and pico-cellular mobile radio environments that follow Rice or Nakagami (1960) models. Outage probability is evaluated in a nested mode via the Laguerre numerical integration technique, avoiding the calculation of complex functions. The proposed formulation can be efficiently applied to practical wireless applications with arbitrary statistical characteristics for the modelling parameters, in both the case of an interference-limited environment (no minimum power constraint) and the existence of a minimum power constraint. Comments, comparison with other existing techniques and useful curves are also presented. View full abstract»

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  • Noncoherent sequence detection of trellis-coded CPFSK with MRC diversity over fading channels

    Page(s): 92 - 98
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (757 KB)  

    Soft-decision differential phase detection (SD-DPD) with Viterbi decoding is proposed for the detection of trellis-coded FSK signals over a fading channel. The soft detector detects the differential phase and chooses a subregion among a preselected set of subregions at the end of every interval. The effect of the number of subregions is studied. The proposed system is analysed over a Rician channel with maximum ratio combining diversity. Numerical results indicate that SD-DPD with Viterbi decoding performs significantly better than hard-decision decoding, and diversity improves performance. Numerical results also indicate that a suboptimal receiver that maintains the same set of metrics for all signal-to-noise ratios performs close to optimal decoding View full abstract»

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  • Nonlinear orthogonal spreading sequence design for third generation DS-CDMA systems

    Page(s): 105 - 110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    Binary sequences with ideal autocorrelation can be defined as the incidence functions for Hadamard difference sets. The authors consider a length of the form M=2m-1, m=nk, such that N=2n-1 and T=M/N are relatively prime. Width analyses show that a N×T generating array can be formed with shifted (and decimated) versions of subsequences of length N as its columns except for zero column(s), to generate a Hadamard difference set sequence. The subsequences can be generated by utilising a general model for shift register sequence generators associated with shift sequences, σ and γ, which represent primitive connections and initial loadings of the shift registers, respectively View full abstract»

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  • Concatenated convolutional and differential codes in interference-suppressed DS-CDMA systems

    Page(s): 99 - 104
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (778 KB)  

    A serial concatenated convolutional and differential coding scheme is employed in a multi-user direct-sequence code-division multiple-access (DS-CDMA) system. The system consists of single-user detectors (SUDS), which are used to suppress multiple-access interference (MAI) with no requirement of other users' spreading codes, timing, or phase information. The differential code, treated as a convolutional code of code rate 1 and memory 1, does not sacrifice the coding efficiency and has the least number of states. The iterative process exchanges information between the differential decoder and the convolutional decoder. Both component decoders adopt the a posteriori probability (APP) algorithm. Numerical results in additive white Gaussian noise (AWGN) channels show that this concatenated coding scheme provides better performance and more flexibility than conventional convolutional codes in DS-CDMA systems, even in the sense of similar complexity. Further study shows that the performance of this coding scheme applied to DS-CDMA systems with SUDS improves by increasing the processing gain or the number of taps of the interference suppression filter, and degrades for higher near-far interfering power or additional near-far interfering users View full abstract»

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  • Power-spectrum-based neural-net connection admission control for multimedia networks

    Page(s): 70 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (699 KB)  

    Multimedia networks need sophisticated and real-time connection admission control (CAC) not only to guarantee the required quality of service (QoS) for existing calls but also to enhance utilisation of systems. The power spectral density (PSD) of the input process contains correlation and burstiness characteristics of input traffic and possesses the additive property. Neural networks have been widely employed to deal with the traffic control problems in high-speed networks because of their self-learning capability. The authors propose a power-spectrum-based neural-net connection admission control (PNCAC) for multimedia networks. A decision hyperplane is constructed for the CAC using power spectrum parameters of traffic sources of connections, under the constraint of the QoS requirement. Simulation results show that the PNCAC method provides system utilisation and robustness superior to the conventional equivalent capacity CAC scheme and Hiramatsu's (1990) neural network CAC scheme, while meeting the QoS requirement View full abstract»

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  • Bounds for finite block-length codes

    Page(s): 65 - 69
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    A tight bound for finite block-length codes is required when developing bandwidth efficient systems, and the paper describes an information-theoretic approach for determining the bound for binary codes. It is derived on the assumption that when the entropy loss in a binary symmetric channel equates to that in a soft-decision channel, the corresponding hard and soft-decision decoders must generate the same error probability. The bound agrees well with the Gallager (1968) bound at large block lengths, and is compared to the performance of iteratively decoded product codes. The paper also describes a recursive breakdown of Shannon's sphere packing bound that permits exact numerical evaluation for information block lengths up to 103 bits. The difference between the exact solution and Shannon's approximation is given up to this block length View full abstract»

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  • Explicit routing with QoS constraints in IP over WDM

    Page(s): 83 - 91
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (931 KB)  

    Generalised multiprotocol label switching (GMPLS) is being developed as a unified control architecture for the optical transport network and the layers above it. GMPLS supports traffic engineering (TE) by allowing explicit routing (ER) of data-bearing paths across networks, which will help to guarantee quality of service (QoS) for types of services in IP over WDM networks. Although there have been many approaches to allocate resources in optical data networks using constrained linear programs, these do not consider the delays at layer 3, which impacts QoS. In networks where it is not possible to create a virtual topology at layer 3 that is a full mesh, more than one lightpath will be required to route traffic between certain pairs of source and destination IP routers. The authors present a technique for traffic engineering in optical networks that support QoS considering the traffic flows with delay QoS requirements across optical networks. This technique provides real-time services with a specific optical label switched path and optimises an objective function including the queueing delay at layer 3 View full abstract»

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  • Efficient IP routing table lookup scheme

    Page(s): 77 - 82
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (719 KB)  

    One of the pertinent issues in IP router design is the IP routing table lookup. With high-speed multi-gigabit links required in the Internet, the lookup has become a great bottleneck. The authors propose a lookup scheme that can efficiently handle IP route lookup, insertion and deletion inside the routing table. This method is less complex in comparison to other schemes. By using careful memory management design, each of the IP routes are only stored once instead of the range that is used conventionally. Therefore, the required memory is reduced. In addition, a novel skip function is introduced to further decrease the memory size. The proposed scheme, which furnishes approximately 75 × 106 lookups/s, needs only a small memory size of 0.59 Mbyte. This scheme can be implemented in a pipeline hardware design and thus achieves one route lookup for every memory access. This lookup scheme can also be easily scaled to IPv6 in the future View full abstract»

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