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Communications, IEE Proceedings-

Issue 1 • Date 2 Feb. 2006

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Displaying Results 1 - 22 of 22
  • Novel packet coding scheme immune to packet collisions for CDMA-based wireless ad hoc networks

    Publication Year: 2006 , Page(s): 1 - 4
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    A novel packet coding scheme for DS-CDMA ad hoc networks is developed. The scheme facilitates collision resolution by embedding the information of both transmitter and receiver in the coding scheme so that the receiver can identify packets addressing to it without actually decoding the information symbol bits. In addition, the present scheme also avoids the transmitter's retransmissions by resolving all packet collisions and avoids receivers wasting time in receiving a packet to completion if the packet is not addressed to it which causes additional battery energy consumption. A bank of matched filters is used to identify intended receivers, even though, any multiuser detection algorithm can easily be applied. The present scheme is evaluated and compared to an existing scheme through computer simulations. View full abstract»

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  • Design of an adaptive PI rate controller for streaming media traffic based on gain and phase margins

    Publication Year: 2006 , Page(s): 5 - 14
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    An adaptive proportional-integral (PI) rate controller for best-effort streaming media traffic in the Internet is proposed. Classical control theory is employed in the control design, which allows the user to achieve good performance of active queue management (AQM) in the router by specifying the proper gain and phase margins. The proposed adaptive PI rate controller will self-tune only when the number of active controlled source nodes changes or the average round trip time becomes longer. The adaptive PI rate controller located in the router can calculate the advertised source transmission rate for the streaming media traffic based on the instantaneous queue length of the buffer, which clamps the steady value of the queue length around the target buffer occupancy. Every controlled source node always transmits streaming media traffic through IP packets into the network at the maximum allowed transmission rate, thus providing the best-effort service traffic and maximising the bandwidth utilisation of the Internet. Our OPNET simulations demonstrate that the rate-based AQM control system can adapt to the fluctuation of the uncontrolled guaranteed traffic very well, thus providing the network with good stability robustness. View full abstract»

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  • Performance of STBCs with antenna selection: spatial correlation and keyhole effects

    Publication Year: 2006 , Page(s): 15 - 20
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (197 KB)  

    Both the spatial fading correlation and keyhole effects can reduce the performance of multiple-input multiple-output (MIMO) wireless channels. A comprehensive performance analysis of orthogonal space-time block codes with receive antenna selection in the presence of spatial correlation at the receiver and keyhole effects is presented. Assuming one best receive antenna that maximises the instantaneous received signal-to-noise is selected and using ordered statistics, a closed-form expression and an upper bound for the bit-error rate (BER) performance of spatially correlated MIMO channels are derived. The outage probability analysis for spatially correlated MIMO channels is also presented. Furthermore, an approximated BER performance formula for the keyhole MIMO channels is derived. Finally numerical results to verify the analysis are presented. View full abstract»

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  • Performance of Hermitian codes using combined error and erasure decoding

    Publication Year: 2006 , Page(s): 21 - 30
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (247 KB)  

    The authors have previously implemented a hard-decision decoder and have shown with simulation results that Hermitian codes perform well over the AWGN and Rayleigh fading channel, owing to their large code lengths. However, further increases in coding gain can be achieved by using a combined error and erasure decoding algorithm instead. In the paper a combined error and erasure decoding algorithm for Hermitian codes is implemented and simulation results over the AWGN and Rayleigh fading channel for the (64, 49, 10), (64, 44, 15) and (512, 314, 171) Hermitian codes are presented. The results show only a small increase in performance over the AWGN channel but more significant coding gains can be achieved over a Rayleigh fading channel. View full abstract»

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  • Dynamically negotiated security service for multicast application in the active network

    Publication Year: 2006 , Page(s): 31 - 38
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (194 KB)  

    Many cryptography and integrity algorithms have been suggested to enhance the security of active networks. Since senders and receivers of multicast applications may own different security processing capabilities and use different security services to communicate with each other, different security services must be negotiated among these receivers and senders before communication is implemented in the active network. However, this problem may not be validly solved by using general session protocols, key distributed and general multicast security mechanisms, because the premise of general security mechanisms presumes that senders and receivers of multicast applications all use the same security algorithms (i.e. the same security service). To address this problem, the paper proposes a novel mechanism to provide the needed mechanism of quality of security service and dynamically negotiated quality of security service for the senders and receivers of multicast application in the active network. It also provides different quality of security service resolutions for different receivers with different security service needs and includes six different negotiation styles. View full abstract»

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  • Decision feedback MLSE for spatially multiplexed MIMO frequency selective fading channel

    Publication Year: 2006 , Page(s): 39 - 48
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    A new decision feedback maximum likelihood sequence estimation (DF-MLSE) scheme for spatially multiplexed MIMO frequency selective fading channel has been proposed. A single trellis processor is required in the proposed receiver instead of multiple NT parallel processors as required in existing low complexity receivers, where NT is the number of transmitter antennas. The bit error rate (BER) performance of the proposed algorithm is the same as standard MLSE, but the computational complexity has been reduced significantly. For a model MIMO system (four transmitter and four receiver antennas) the computational complexity has been reduced by 95% in comparison to standard MLSE exploiting the proposed detection algorithm. Unlike the decision feedback equaliser (DFE) and the delayed decision feedback sequence estimation (DDFSE), the proposed algorithm has no signal-to-noise ratio (SNR) penalty while achieving the same BER performance as standard MLSE. View full abstract»

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  • Hybrid DFE with variable length feedback filter

    Publication Year: 2006 , Page(s): 49 - 54
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (223 KB)  

    In the paper, a hybrid decision feedback equaliser (DFE) with a feedback filter (FBF) whose length can be dynamically adjusted is presented and investigated. The equaliser is an adaptive DFE with a feedforward filter (FFF) implemented in the frequency domain with its length fixed by the FFT/IFFT size and a feedback filter (FBF) in the time domain. The FBF length is adjusted according to the achieved mean squared error (MSE). In addition, the impact of small FBF coefficients on system BER performance is taken into account so that a shorter filter length can be considered. Computer simulations show that the proposed approach is capable of adjusting the feedback filter length to a satisfactory level in terms of MSE and system BER performance and is able to track channel changes successfully. View full abstract»

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  • Edge-based active queue management

    Publication Year: 2006 , Page(s): 55 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    In this paper, a new framework of active queue management, namely, edge-based active queue management (EAQM), is proposed. Conventional AQM schemes are required to be deployed at all routers in the network, and this involves significant upgrading to current drop-tail routers. The new approach only needs to modify the edge routers and at the same time provides similar or better performance as compared to conventional AQM schemes. Furthermore, EAQM can reduce the throughput bias against TCP connections with longer round trip times, and this cannot be achieved by current available AQM approaches. View full abstract»

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  • Channel assignment for cellular mobile networks with nonuniform cells - an improved heuristic algorithm

    Publication Year: 2006 , Page(s): 61 - 68
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (274 KB)  

    A heuristic sequential algorithm for fixed channel assignment in cellular mobile networks with nonuniform cells, i.e., cells of different sizes and shapes, is presented. The channel assignment is treated as a nonbinary constraints satisfaction problem. The algorithm uses both the co-channel and adjacent channel interference levels and the number of channel requirements per cell to define the corresponding sequence of assignment. The effects of intercell overlapping and complex propagation mechanisms on the channel assignment results are investigated too. View full abstract»

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  • Variable LDPC coding rate performances for multicarrier systems using HD decoding

    Publication Year: 2006 , Page(s): 69 - 73
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    An adaptive coding scheme minimising the BER of a bit-interleaved coded modulation OFDM system performing hard-decisions (HD) after the demodulation and ideal interleaving is proposed. The subcarrier code rate levels subject to a rate constraint are varied according to perfect channel state information at the transmitter. The derived adaptive scheme uses low-density parity-check codes. A modified bit-flipping algorithm provides HD decoding and can be applied either alone or combined with a power loading scheme. It is shown by Monte Carlo simulations that, for broadband systems with Rayleigh fading, the loading procedure provides a signal-to-noise ratio gain up to 3dB for an average BER level of 10-5. View full abstract»

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  • Performance analysis for MIMO systems using zero forcing detector over fading channels

    Publication Year: 2006 , Page(s): 74 - 80
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (226 KB)  

    In the paper, the performance of multiple-input-multiple-output (MIMO) systems using a zero forcing detector is studied over Rayleigh and Rice fading channels. Approximation to the distribution of non-central complex Wishart distribution is used to derive the distribution of the post-detection signal-to-noise (SNR) ratio. A closed-form expression of bit error rate is obtained in terms of the hypergeometric and Gamma functions. The performance of MIMO systems under the scenario that the individual sub-channels are correlated is also investigated. It is shown that, for the exponential correlation channel model, an increase in channel correlation between the transmission paths results a decrease in SNR at the receiver. It is concluded that with the same SNR at the receiver, the performance of MIMO systems over a Rice fading channel degrades compared to that over an independent and identical distributed (i.i.d.) Rayleigh fading channel. View full abstract»

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  • Editorial: Ultra wideband systems technologies and applications

    Publication Year: 2006 , Page(s): 81 - 82
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (230 KB)  

    First Page of the Article
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  • Exact evaluation of M-ary TH-PPM UWB systems on AWGN channels for indoor multiple-access communications

    Publication Year: 2006 , Page(s): 83 - 92
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (286 KB)  

    Analysis of ultra-wideband (UWB) time-hopping spread-spectrum code division multiple-access system using binary PPM signaling has been considered previously. However, the representation of the multiple-access interference was based on assuming Gaussian random processes that resulted in inaccuracies in some scenarios. This analysis was improved by a more precise statistical analysis that dispensed with approximations based on using Gaussian process statistics. In the paper, this precise statistical analysis is extended for general M-ary PPM UWB modulations. Performance metrics of symbol error rate and capacity are evaluated. It is shown that there is a significant error in using the Gaussian approximation as it overestimates the capacity of the M-ary PPM modulation. View full abstract»

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  • Frequency domain channel estimation and equalisation for direct sequence ultra wideband (DS-UWB) system

    Publication Year: 2006 , Page(s): 93 - 98
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Recently, the single-carrier transmission with frequency domain equalisation has attracted much attention for reasons of being able to obtain an excellent performance even in strong frequency selective channels. In the paper, the authors evaluate the performance of direct sequence - ultra wideband (DS-UWB) with frequency domain channel estimation (FDCE) and equalisation (FDE) in the UWB multipath channel and compare it to that of conventional DS-UWB with time domain channel estimation (TDCE) and RAKE receiver. The authors purpose is to compare the performances of both schemes under fair conditions. In particular, we focus on the computational complexity of frequency domain process (FDP) that uses FDCE and FDE and compare it to that of time domain process (TDP) that uses TDCE and RAKE receiver. The authors simulation results show that when Eb/N0 is high, DS-UWB with FDP has significantly less computational complexity and achieves a better performance than DS-UWB with TDP; conversely when Eb/N0 is low, DS-UWB with TDP has significantly more computational complexity and achieves a better performance than DS-UWB with FDP. View full abstract»

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  • Angular-spectral antenna effects in ultra-wideband communications links

    Publication Year: 2006 , Page(s): 99 - 106
    Cited by:  Papers (20)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (941 KB)  

    In traditional approaches to antenna characterisation, spectral and angular dispersion are modelled separately. In the paper, the dependence of the power radiated from ultra wideband (UWB) antennas jointly on frequency and direction is established experimentally. It is demonstrated that both omni-directional and directional antennas typically exhibit higher directivity with frequency, with the former experiencing a seven-fold increase with respect to the lowest frequency in the FCC UWB frequency range (3.1-10.6 GHz). The consequences of this behaviour are highlighted and the effect on the communications link is quantified. The effective available bandwidth of a system is found to be highly sensitive to the angular disposition of the antenna at each end of the link. It is shown that the bandwidth is severely limited in some directions, and careful orientation of the antennas is required to achieve full UWB operation for a range of antenna designs. The 10 dB bandwidth of a vertically polarised UWB antenna can be as little as 2 GHz in the equatorial plane when the joint dispersion is considered. The distortion caused to a UWB signal is investigated and significant variation in the radiated signal waveform with angle is demonstrated. View full abstract»

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  • UWB on-body radio propagation and system modelling for wireless body-centric networks

    Publication Year: 2006 , Page(s): 107 - 114
    Cited by:  Papers (68)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (449 KB)  

    Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal area community. Researchers and designers have been investigating radio propagation characterisation and modelling owing to its importance in developing and designing efficient and reliable radio systems. The paper presents an experimental investigation of ultra-wideband (UWB) on-body radio propagation. Channel models with respect to large scale and delay analysis have been derived from measured parameters. Effects of different antenna types on channel behaviour are also demonstrated. Results and analyses highlight the consequences of changes in body postures and positions in addition to antenna orientations on the communication channels. Measurement data are also used in predicting the performance of potential UWB wireless systems and their applications in body-centric networks. It is indicated that bi-phase modulation for UWB body-centric networks performs better than pulse position modulation systems. The study also concludes that the use of hybrid antenna types for different on-body links will provide better system performance. View full abstract»

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  • On time estimation and synchronisation of UWB signals

    Publication Year: 2006 , Page(s): 115 - 119
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (171 KB)  

    The paper examines the problems of symbol timing estimation and timing recovery for ultra wideband signals. Two different approaches based on the maximum likelihood technique are investigated, the first approach is based on derivative matched filter and the second approach takes advantage of early-late technique. Further, two non-coherent timing recovery circuits are proposed and discussed, the first circuit is based on early-late technique and the second circuit is a digital delay-locked loop. Finally, performance analysis for IEEE 802.15.3a channel models in terms of the minimum squared error is provided. View full abstract»

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  • Complex multipath effects in UWB communication channels

    Publication Year: 2006 , Page(s): 120 - 126
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (289 KB)  

    Multipath effects in complex environments can result in distortion and time elongation of received UWB pulses. These effects have been analysed using a ray tracing channel model with a PPM-TH modulation scheme and a RAKE receiver architecture. The resultant BER has been calculated using both this model and a generalised statistical model from the literature. Results indicate that the late arrival multipath components allowed for in the ray tracing model have a significant effect on system performance for bit rates of the order 100 Mbit/s. The generalised channel model is shown to be in general agreement with the ray tracing approach for low bit rate systems but somewhat optimistic for high bit rates in a complex multipath scenario. View full abstract»

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  • Design and performance analysis of a space-time block coding scheme for single band UWB

    Publication Year: 2006 , Page(s): 127 - 135
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Ultra wide-band (UWB) systems have recently attracted much research interest owing to their appealing features in short-range mobile communications. These features include high data rates, low power consumption, multiple access communications, and precise positioning capabilities. Space-time coding techniques, such as the block coding scheme or the trellis coding scheme, are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. So far, few contributions have looked over multiple-inputs-multiple-outputs UWB systems. In the paper, a method to adapt the space-time block coding technique to single band UWB signalling is proposed. A space-time block codec, based on orthogonal pulses to achieve spatial diversity and collect the multipath diversity is developed. A theoretical analysis is conducted to enlighten the performance enhancements provided by the proposed scheme compared to the classic single link scheme. Simulations support analysis, for various numbers of transmit and receive antennas, several types of channel scenarios, and different detection techniques. In a typical studied UWB environment, the results revealed that the proposed scheme improves the bit error rate performances compared to those of a single link scheme and it provides a strong immunity against timing jitter. View full abstract»

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  • Comparison of UWB transmitted reference schemes

    Publication Year: 2006 , Page(s): 136 - 142
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    The paper provides a theoretical comparison of different schemes for ultra wideband transmitted reference that utilise correlation based receivers. The performance comparison is based on a simplified analysis of signal-to-noise ratio (SNR) derivations of receiver output for different signal repetition structures using binary pulse position modulation. The results show that a scheme based on pair-wise combination of pulses for which succeeding pulses form the reference for subsequent pulses, significantly outperforms other schemes. The results also show that a pulse repetition scheme with equal power pulses in a doublet structure does not provide a good solution from the perspective of SNR degradation. View full abstract»

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  • Power loss modelling of short-range ultra wideband pulse transmissions

    Publication Year: 2006 , Page(s): 143 - 152
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (279 KB)  

    Narrowband path loss models are not applicable to the link budget calculation of ultra wideband (UWB) signals. In the paper, a rigorous analysis reveals the power loss behaviour of short-range UWB pulse systems when operated in a rich multi-path environment. A novel breakpoint is derived that is within the vicinity of the transmitter, and is shown to influence the UWB link budget considerably. Furthermore, it is shown that the power delay profile does not generally follow a simple negative exponential dependency. Also, the effects of perfect and imperfect correlator onto the overall UWB pulse power loss are considered. View full abstract»

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  • Co-existence measurements between UMTS and UWB systems

    Publication Year: 2006 , Page(s): 153 - 158
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (243 KB)  

    The paper presents results of a co-existence measurement study between multiple ultra wideband (UWB) transmitters and a universal Mobile Telecommunications System (UMTS) mobile phone. Two environments were explored: an anechoic chamber with one operating UMTS link and a true operational UMTS network. A large number of FCC compatible UWB transmitters were used to generate interference for an active UMTS connection. In an anechoic chamber, only the voice service was studied between a radio communication analyser (used as a base station) and a mobile terminal. In the true commercial UMTS network case, both the voice and data services were investigated in a shelter having a low UMTS signal level. The results clearly show that UMTS and high pulse repetition rate UWB devices can co-exist at link level when a moderate number of simultaneously active UWB devices operate in close proximity of the UMTS 'victim' receiver. The results also show that the activity factor of the UWB transmitter disproportionately impacts the effective interference. When using low activity factors, even with high pulse repetition rates and very large numbers of UWB devices, it is difficult to detect UMTS link performance degradation. As the activity factors grow beyond 5%, the impact of the UWB interference becomes visible. However, this study covers only one active UMTS link in both environments but does not report on the UWB impact on the UMTS radio access network. View full abstract»

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