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Communications, IEE Proceedings-

Issue 5 • Date 7 Oct. 2005

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Displaying Results 1 - 25 of 34
  • EXIT chart analysis and performance of precoded turbo equalisation systems for long block lengths

    Publication Year: 2005 , Page(s): 513 - 520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (417 KB)  

    The authors investigate the effect that the precoders' weights have on the convergence of turbo equalisation systems for long block lengths. A comparison is made between the trellis code capacities and the independent and identically distributed channel capacity. The extrinsic information transfer chart is used to analyse four precoded turbo equalisation systems. It is observed that the gradient of the transfer function at high input mutual information values, relating to the maximum a posteriori equalisation of a precoded channel, plays a greater role than the initial loss of information in determining the convergence of precoded turbo equalisation systems. Simulation results demonstrate that a low weight precoder converges at a lower signal-to-noise ratio in comparison to a high weight precoder. Further, it is noticed that the system trajectories only follow the bounds of the transfer functions on the extrinsic information transfer chart during the early iterations. The Kolmogorov-Smirnov test is used to study probability density function shapes of the extrinsic log-likelihood ratios during the iterative equalisation/decoding process. The authors also show that the extrinsic information transfer chart can be used to compute the trellis code capacity of a precoded channel. View full abstract»

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  • High capacity hotspots based on bluetooth technology

    Publication Year: 2005 , Page(s): 521 - 527
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    Bluetooth is a short range wireless interface that offers data transmission rates of the order of 721 kbit/s which is comparable with ADSL data rates, but which could be regarded as being too low for deployment as a limited range wireless access point. The capacity of a wireless access point based on Bluetooth technology can be increased significantly by co-locating a number of Bluetooth transducers in a hotspot scenario. This paper describes a technique which reduces mutual interference in co-located Bluetooth transducers by coordinating the hopping frequencies of the individual devices. Such a system can then provide attractive data transmission rates when deployed in wireless access point applications. View full abstract»

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  • Dual-hop wireless communications with combined gain relays

    Publication Year: 2005 , Page(s): 528 - 532
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (238 KB)  

    A dual-hop relayed wireless communication system is presented where the gain of the relay, called combined gain relay (CGR), is produced after combining the channel state information from both hops, depending on the mean hop's signal-to-noise ratio (SNR). The proposed scheme can be efficiently applied in dual-hop transmissions with unbalanced mean SNRs due to the long-term fading effects produced by the movement of the user in the area served by the wireless network. The overall system performance is studied in Rayleigh fading channels. Closed-form expressions are derived for important system performance metrics, such as average end-to-end SNR, average error probability and outage probability. The CGR's average power consumption is investigated which in certain cases is lower compared with existed relays. Numerical results and simulations show an improvement in the end-to-end system performance. View full abstract»

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  • Improved subspace-based channel estimation algorithm for DS/CDMA systems exploiting pulse-shaping information

    Publication Year: 2005 , Page(s): 533 - 540
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    An improved subspace-based channel estimation algorithm for DS/CDMA system is presented. The proposed algorithm is based on the Torlak/Xu algorithm for asynchronous DS/CDMA systems. The aim is to incorporate knowledge of the pulse-shaping filter into the Torlak/Xu subspace algorithm with the objective of reducing the variance of the channel estimates. The improved algorithm is developed from a system model of a DS/CDMA system where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is incorporated into the proposed channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu algorithm that does not exploit pulse-shaping filter information. A mathematical expression of the mean square error of estimation for the improved algorithm is also derived. It is shown that the analytical expression provides a good approximation of the actual mean square error for high SNR signals. View full abstract»

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  • Encoded diversity transmission for slow-frequency-hopped multiple access communication

    Publication Year: 2005 , Page(s): 541 - 547
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    In slow-frequency-hopped multiple access communication systems using M-ary FSK modulation, multiple access interference may lead to erroneous reception of symbols. An encoded diversity transmission scheme is proposed for reducing the probability of symbol error due to multiple access interference. Using this scheme, a transmitter encodes each symbol into a sequence of L symbols (L is called diversity degree), chooses a sequence of L frequency bins and transmits the L encoded symbols in the L chosen bins, respectively. In this manner, the transmitter can encode more information about each symbol for diversity transmission. The receiver can use this information to increase the chance of decoding the correct symbol in the presence of multiple access interference. It is demonstrated that the proposed scheme can significantly reduce the probability of symbol error caused by multiple access interference. View full abstract»

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  • Congestion control based on flow-state-dependent dynamic priority scheduling

    Publication Year: 2005 , Page(s): 548 - 558
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    The existing congestion control mechanism in the current Internet use is based on TCP congestion control mechanism, which is the key to the success of the Internet. However the TCP's end-to-end congestion control mechanism and the router assistant mechanism active queue management (AQM), such as random early detection (RED), cannot cope with flows that are unresponsive to congestion notification or non-TCP-compatible flows which are responsive but more aggressive than TCP. Unresponsive or non-TCP compatible flows could even cause congestion collapse. In this paper, a new mechanism is presented, namely source aware congestion control (SACC) based on a packet scheduling algorithm called flow-state-dependent dynamic priority scheduling (FDPS), which performs traffic monitoring, marking and scheduling at routers. Extensive simulation experiments are conducted based on ns-2 to examine SACC behaviour and evaluate its performance in a variety of scenarios. The numerical results illustrate that the proposed scheme can differentiate services and resolve congestion by gracefully discarding packets from non-conformant and best effort flows when unresponsive flows exist. View full abstract»

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  • IMD reduction coding to improve the error probability performance of nonlinearly distorted OFDM signals

    Publication Year: 2005 , Page(s): 559 - 566
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (255 KB)  

    Intermodulation distortion (IMD) reduction coding is proposed to improve the error probability performance of nonlinearly distorted orthogonal frequency division multiplexing (OFDM). In particular, two IMD reduction coding strategies are considered: one requires knowledge of the system nonlinearity, whereas the other does not. Simulation results demonstrate that in the presence of nonlinearities, the error probability of OFDM systems relying on IMD reduction coding is considerably lower than that of OFDM systems relying on peak-to-average power ratio (PAPR) reduction coding. Additionally, simulation results also demonstrate that in the presence of nonlinearities the average out-of-band power generated by IMD reduction coding is similar to that generated by PAPR reduction coding. View full abstract»

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  • Software performance characterisation of block cipher structures using S-boxes and linear mappings

    Publication Year: 2005 , Page(s): 567 - 579
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (274 KB)  

    A new framework is presented for evaluating the performance characteristics of block cipher structures composed of S-boxes and maximum distance separable (MDS) mappings. In particular, a novel performance metric is introduced and applied to nested substitution-permutation networks and Feistel networks with round functions composed of S-boxes and MDS mappings. Within each cipher structure, many cases are considered based on two types of S-boxes (4×4 and 8×8) and parameterised MDS mappings. In the study of each case, the performance is analysed based on a table lookup implementation. Although this implementation method is the typical approach used for software realisation, it may also be applicable to hardware realisation in some instances. Cipher security, in the form of resistance to differential and linear attacks, is applied as a basis which is used to normalise the performance in the analysis. Because the discussed structures are similar to many existing ciphers such as AES and Camellia, the analysis provides a meaningful mechanism for seeking efficient ciphers through a wide comparison of security, performance, and implementation methods. View full abstract»

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  • Method for yielding a database of location fingerprints in WLAN

    Publication Year: 2005 , Page(s): 580 - 586
    Cited by:  Papers (49)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Location fingerprinting in wireless LAN positioning has received much attention recently. One of the key issues of this technique is generating the database of fingerprints. The conventional method does not utilise the spatial correlation of measurements sampled at adjacent reference points, and the training process is not an easy task. A new method based on kriging is presented which can not only achieve more accurate estimation, but can also greatly reduce the workload and save training time. This can make the fingerprinting technique more flexible and easier to implement. View full abstract»

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  • Hybrid maximum likelihood frequency offset estimation in coherent OFDM systems

    Publication Year: 2005 , Page(s): 587 - 592
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    One of the well known problems in an orthogonal frequency division multiplexing (OFDM) system is its vulnerability to frequency offset. In practice, most coherent OFDM systems transmit pilot symbols on some of the subcarriers to estimate channel attenuation and also add a cyclic prefix (CP) to avoid intercarrier interference and intersymbol interference. A hybrid maximum likelihood estimation algorithm based on the redundancy of both cyclic prefix and pilot subcarriers is proposed for the correction of frequency offset. If the frame timing has been synchronised in advance, by considering the two kinds of redundancy simultaneously, the performance of the proposed hybrid algorithm could achieve significant improvement under low SNR and short CP. As to high SNR and long CP, the performance of this hybrid algorithm is almost identical to that of CP-based only algorithm. Some comparative simulations are given to illustrate the advantages of the proposed hybrid estimation scheme. View full abstract»

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  • On the use of partial unit memory codes for woven turbo codes with outer and inner warp

    Publication Year: 2005 , Page(s): 593 - 597
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (246 KB)  

    The encoding, decoding and performance analysis of concatenated partial unit memory (PUM) code structures for capacity approaching performance are investigated. PUM codes are known for their excellent distance properties and lower decoding complexity compared to equivalent multi-memory convolutional codes. Two capacity approaching concatenated structures are considered: turbo codes (TCs) and woven turbo codes (WTCs), both initially proposed with component convolutional codes. TCs consist of a number of parallel concatenated encoders. WTCs were originally proposed with outer warp, that is a number of outer encoders are parallel concatenated to one inner encoder. WTCs are also constructed with inner warp, i.e. one outer encoder is parallel concatenated to a number of inner encoders. An iterative max-log-maximum a posteriori decoding scheme is proposed for decoding PUM codes having multiple-input parallel branches in the trellis. The distance properties and bit error rate performance of the novel concatenated PUM codes are compared with known concatenated convolutional codes. It is observed that PUM structures, both TC and WTC with inner and outer warp, have better distance properties and hence improved performance over their equivalent convolutional counterparts. Performance as close as 1.25 dB from the Shannon limit is obtained for concatenated PUM structures with an interleaver size of only 4800 bits. View full abstract»

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  • Multiconstrained QoS routing using optimal supervisory control

    Publication Year: 2005 , Page(s): 598 - 604
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (225 KB)  

    To find feasible paths that satisfy multiple independent quality-of-service (QoS) constraints, the methodology of optimal supervisory control is applied. The network is modelled as a discrete event system (DES) and the penalties of the states and the disabling costs of the events of the DES are assigned considering the given metrics. After introducing the DES and assigning the penalties and the disabling costs, the feasible paths are found using the modified optimal supervisor design algorithm. View full abstract»

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  • Unsupervised, fast and efficient colour-image copy protection

    Publication Year: 2005 , Page(s): 605 - 616
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4855 KB)  

    The ubiquity of broadband digital communications and mass storage in modern society has stimulated the widespread acceptance of digital media. However, easy access to royalty-free digital media has also resulted in a reduced perception in society of the intellectual value of digital media and has promoted unauthorised duplication practices. To detect and discourage the unauthorised duplication of media, researchers have investigated watermarking methods to embed ownership data into media. However, some authorities have expressed doubt over the efficacy of watermarking methods to protect digital media. The paper introduces a novel method to discourage unauthorised duplication of digital images by introducing reversible, deliberate distortions to the original image. The resultant image preserves the image size and essential content with distortions in edge and colour appearance. The proposal method also provides an efficient reconstruction process using a compact key to reconstruct the original image from the distorted image. Experimental results indicate that the proposed method can achieve effective robustness towards attacks, while its computational cost and quality of results are completely practical. View full abstract»

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  • Outage-based fuzzy call admission controller with multiuser detection for WCDMA systems

    Publication Year: 2005 , Page(s): 617 - 623
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (231 KB)  

    An outage-based fuzzy call admission controller with multiuser detection (OFCAC-MUD) is proposed for wideband code division multiple access (WCDMA) systems. The OFCAC-MUD determines the new call admission based on the uplink signal-to-interference ratios from home and adjacent cells and system outage probabilities. The OFCAC-MUD possesses both the effective reasoning capability of a fuzzy logic system and the aggressive processing ability of MUD. Simulation results reveal that OFCAC-MUD without power control (PC) improves the system capacity by 70.5% as compared to an SIR-based CAC-RAKE with perfect PC. It also enhances the system capacity by 53.9% as compared to an OFCAC-RAKE with perfect PC, by 6.7% as compared to an SIR-based CAC-MUD without PC and by 12.9% as compared to an OFCAC-MUD with perfect PC, given the same outage probability requirements. Moreover, OFCAC-MUD can prevent the violation of outage probability requirements in the hotspot environment, which is hardly achieved by SIR-based CAC. View full abstract»

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  • Carrier frequency offset estimation for OFDM/SDMA systems using consecutive pilots

    Publication Year: 2005 , Page(s): 624 - 632
    Cited by:  Papers (4)  |  Patents (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Carrier frequency offsets (CFO) greatly degrade the performance of orthogonal frequency-division multiplexing (OFDM) systems because they may violate the orthogonality of subcarriers and introduce intercarrier interferences. CFO effects of uplink of a spatial-diversity multiple-access (SDMA) OFDM system are first approximated by the CFO-vectors which are the fast Fourier transform (FFT) of complex exponential functions associated with the CFO. Then, the CFO-vectors are optimally estimated in a minimum mean square error sense by appropriately designing pilots which are in fact the δ-sequences subject to a specified distribution. In addition, the estimation is further improved by imposing a window function on the received signals to reduce the side-lobe leakages of the CFO-vectors. Through simulations, it is shown that the new estimators provide a satisfactory CFO estimation for fine tracking of uplink of OFDM/SDMA systems. View full abstract»

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  • Optimising data processing in network performance monitoring systems

    Publication Year: 2005 , Page(s): 633 - 642
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Recent literature on the performance monitoring of communication networks focuses on exploiting compressibility of the collected data and its management on high-performance hardware. An alternative approach is to use summary structures referred to as intermediate information which support the reuse of semiprocessed information to optimise the calculation of nondistributive and nonalgebraic network delay statistics. Different intermediate-information structures possess different performance and accuracy characteristics. By selecting an appropriate structure on the basis of the query and the state of the intermediate-information cache, we show that significant improvements in the processing cost of a database of network measurements can be achieved. An approach to the dynamic selection of such a structure is presented and results showing the subsequent improvement in processing speed are given. View full abstract»

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  • Adaptive scheduling algorithms for Ethernet passive optical networks

    Publication Year: 2005 , Page(s): 643 - 647
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    Medium access control (MAC) is one of the most crucial issues in the design of Ethernet passive optical networks (EPONs). To prevent data from collision in the upstream direction, an EPON system must employ a MAC mechanism to arbitrate the access to the shared upstream channel and at the same time efficiently share the bandwidth of the upstream channel among all optical network units (ONUs). In this paper, two adaptive scheduling algorithms for MAC in an EPON system are presented. One is called the longest-queue-first (LQF) algorithm, which adaptively schedules the transmission order of different ONUs based on the instantaneous queue length of each ONU and polls the one with the longest queue first in each polling. The other is called the earliest-packet-first (EPF) algorithm, which adaptively schedules the transmission order based on the arrival time of the first packet waiting in each ONU queue and polls the one with the earliest packet first. It is shown through simulation results that the proposed scheduling algorithms can effectively improve the network performance in terms of packet delay compared with the most commonly-used round-robin scheduling algorithm. View full abstract»

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  • Optimal settings of maximum transfer unit (MTU) for efficient wireless video communications

    Publication Year: 2005 , Page(s): 648 - 654
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (218 KB)  

    Following its success over wired networks, the deployment of the Internet Protocol (IP) over wireless networks is an increasingly popular topic. Protocol optimisations implemented at this level only consider the traditional Internet applications. Path maximum transfer unit (MTU) discovery algorithms are designed to avoid packet fragmentation along the transmission path and hence improve protocol efficiency. However, the design criteria do not take into account the potentially significant influences on the performance over the wireless links. A theoretical analysis is presented of the effect of MTU size upon the performance of wireless video. The theoretical calculation is based on a distortion model, which accurately estimates the video quality in terms of average frame peak signal-to-noise ratio (PSNR). The theoretical analysis are validated for MPEG-4 coded video transmission over a simulated UMTS network. View full abstract»

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  • DO-WF2Q: delay-optimised WF2Q packet scheduling

    Publication Year: 2005 , Page(s): 655 - 660
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    Packet scheduling is an essential element of any QoS enabled packet-switched network. (QoS provisioning and packet scheduling play important roles in present and future Internet applications.) In terms of packet fair queueing, worst case fair WFQ (WF2Q) is better than weighted fair queueing (WFQ) in that it can provide a bounded worst-case fairness index (WFI). The delay property of these two queueing schemes are studied. To do this, the delay index (DI) and the worst-case delay index (WDI) are defined to measure the discrepancy between the delay using these queueing schemes and that obtained using generalised processor sharing (GPS). Simulations show that in some circumstances WF2Q has higher DI than that using WFQ. The reason why WF2Q sometimes experiences higher DI is analysed, and based on this, an adaptive packet queueing algorithm termed delay-optimised WF2Q (DO-WF2Q) is proposed. This algorithm aims to improve the delay index (DI) while maintaining the WFI bound provided by WF2Q. Verifications and simulations show that DO-WF2Q can reduce the DI while maintaining the WFI bound, and at the same time retaining the same complexity as WF2Q. View full abstract»

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  • Equalisation with adaptive time lag

    Publication Year: 2005 , Page(s): 661 - 667
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    In an adaptive equaliser, the time lag is an important parameter that significantly influences the performance. Only with the optimum time lag that corresponds to the best minimum-mean-square-error (MMSE) performance, can there be best use of the available resources. Many designs, however, choose the time lag either based on preassumption of the channel or simply based on average experience. The relation between the MMSE performance and the time lag is investigated using a new interpretation of the MMSE equaliser, and then a novel adaptive time lag algorithm is proposed based on gradient search. The proposed algorithm can converge to the optimum time lag in the mean and is verified by the numerical simulations provided. View full abstract»

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  • End-to-end rate-based congestion control using EWMA for multicast services in IP networks

    Publication Year: 2005 , Page(s): 668 - 672
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (262 KB)  

    In high-speed communication networks, the determination of a transmission rate using a congestion control scheme is critical for the stability of a closed-loop network system. A new rate-based congestion control scheme is proposed which employs an exponential weighted moving average algorithm. This scheme can be used to develop an efficient feedback control mechanism for congestion avoidance in high speed communication networks. The newly posited scheme ensures not only the stability of switch buffers but also higher link utilisation of the whole network system. View full abstract»

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  • Effective message routing in unstructured peer-to-peer overlays

    Publication Year: 2005 , Page(s): 673 - 678
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (175 KB)  

    There is a lack of efficiency in flooding-based unstructured peer-to-peer overlays, where loosely coupled nodes require high local autonomy. Two routing improvements are compared based on answer caching, where the cached metadata facilitates content-based routing of queries. Since peer nodes keep joining and leaving the overlay, a mechanism to keep the metadata valid is analysed. The problem area is reviewed, an overlay network model described, and related message routing issues and the simulation environment explained. Simulation results confirm expectations about the traffic reduction, while the user experience does not deteriorate. View full abstract»

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  • Performance of coherent fast frequency-hopped spread-spectrum receivers with partial-band noise jamming and AWGN

    Publication Year: 2005 , Page(s): 679 - 685
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    Performance analyses of coherent fast frequency-hopped spread-spectrum (FHSS) systems with the presence of partial-band noise jamming (PBNJ) and additive white gaussian noise (AWGN) are presented. Bit-error-rate expressions for the coherent maximum-likelihood (ML), linear-combination (LC), and hard-decision majority-vote (HDMV) receivers with binary phase-shift-keying are derived and validated by simulation results. Among the three proposed receivers, the coherent ML receiver gives the best performance under the worst-case PBNJ condition, followed by the coherent HDMV receiver and the coherent LC receiver. The BER results of the coherent ML receiver improve as the diversity level increases, although the incremental improvement in performance will diminish eventually when the diversity level is sufficiently large. The coherent LC receiver is incapable of providing diversity improvement under the worst-case PBNJ condition. For the coherent HDMV receiver it has been shown that there is an optimum diversity level under the worst-case PBNJ condition. The locus of the optimum diversity level for the coherent HDMV receiver is also presented, which allows one to obtain the optimum diversity level for the coherent HDMV receiver under different levels of signal-to-jamming ratio. It has been shown that the three coherent receivers significantly outperform the various existing noncoherent diversity-combining receivers under the worst-case PBNJ and AWGN conditions. View full abstract»

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  • Analysis of the channel bit-rate detection process in WCDMA

    Publication Year: 2005 , Page(s): 686 - 690
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    A critical task within receivers for third-generation W-CDMA systems is the detection of the respective channel parameters and bit-rate on the basis of decoding the transport format combination indicator (TFCI) bits associated with each 10 ms frame. Evaluation of hard and soft decoding of the TFCI bits is therefore the focus of this work. The probability of erroneous rate detection for each case is computed and supported by simulation results obtained in realistic scenarios specified by the 3GPP standardisation forum. It is shown that the improved performance provided by soft decoding over hard detection is in the range of 2 to 3 dB for a wide range of signal-to-interference-plus-noise ratios, and that for low data rates, where fewer TFCI bits are transmitted per slot, the decoding performance is inferior to that in high data rates. View full abstract»

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  • Explicit window adaptation algorithm over TCP wireless networks

    Publication Year: 2005 , Page(s): 691 - 696
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A feedback-based congestion control algorithm is described which improves TCP performance over wireless networks. An explicit feedback scheme is proposed for the fair sharing of the bandwidth by modifying the receiver's advertised window in TCP acknowledgments returning to the source. Using the feedback information, the proposed algorithm adapts the window size to avoid the congestion and sees the packet loss only due to the wireless link error. Based on the asymptotic analysis, it is shown that the proposed algorithm guarantees the fair sharing and improves wireless TCP performance. The effectiveness of the proposed algorithm is demonstrated by simulations. View full abstract»

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