This paper investigates the effect of fast cell selection (FCS) associated with fast packet scheduling methods and hybrid automatic repeat request (HARQ) with Chase combining, in which the optimum cell (or sector) transmitting a slot-assigned downlink shared channel (DSCH) is selected based on the received signal-to-interference power ratio (SIR), in high-speed downlink packet access (HSDPA). The Round robin (RR), Proportional fairness (PF) and Maximum carrier-to-interference power ratio (CIR) schedulers are used as the scheduling algorithm. The simulation results elucidate that although almost no additional diversity gain through FCS is obtained for the PF and Maximum CIR schedulers, the improvement in throughput by FCS coupled with the RR scheduler is achieved. Furthermore, we elucidate that the effect of FCS is small when only inter-sector FCS is performed; however, inter-cell FCS is effective in improving the radio link throughput for the access users with a lower received SIR near the cell edge. The radio link throughput at the cumulative distribution of 20% of soft handover users when both inter-sector and inter-cell FCS are performed is increased by approximately 20% and 60% for PF and RR schedulers, respectively, compared to that without FCS, i.e. with hard handover. We also show that when a traffic model such as the modified ETSI WWW browsing model is taken into account, the effect of FCS associated with the decreasing effect of fast packet scheduling is greater than that assuming continuous packet transmission. The user throughput at the cumulative distribution of 20% employing both inter-sector and inter-cell FCS is increased by approximately 60% compared to that without FCS.

A simple system configuration was used to generate transform-limited optical pulses at 160 Gbit/s in the sub-picosecond range (625 fs). Pulse compression was achieved by broadening the spectrum using supercontinuum generation followed by a linear frequency chirping compensation.

Terrestrial radio links with sparsely distributed multipath delays can be represented by a tapped-delay line with a few significant tap coefficients. This letter presents criteria and performance of identification methods that determine channel taps with significant power. In particular, a tap identification method derived from the maximum-likelihood criterion and its closed form error probabilities are presented. Performance improvement over a previously reported scheme is quantified using the derived error probabilities.

This paper proposes a stable rate allocation algorithm for ABR service in ATM networks. The main goals in designing this algorithm are to speed up the convergence according to the max-min fairness criterion and to maximize the network utilization while the switch queue length can be properly controlled. Importantly, the set goals should be achieved in a wide range of network conditions without the need for adjusting the algorithm parameters. The algorithm is targeted to work in various networking environments with additional criteria as extended from the work of E-FMMRA (Enhanced Fast Max-Min Rate Allocation) and ERICA+ (Explicit Rate Indication for Congestion Avoidance) . The additional design criteria include the ability to enhance a large number of ABR connections and staggered TCP connections as well as to perform an accurate traffic averaging. The algorithm is analytically proved to be convergent. Simulation results indicate that the proposed algorithm achieves the goals in all evaluated configurations. However, it has some limitations when working in the large-scale network due to its per-connection accounting. It is not recommended to implement the algorithm with a switch that has a small buffer size due to its relatively long averaging interval.

A voltage-mode universal biquadratic filter using single current-feedback amplifier (CFA), two capacitors and three resistors is presented. The new circuit has four inputs and one output and can realize all the standard filter functions, that is, lowpass, bandpass, highpass, notch and allpass filters, without changing the circuit topology. The use of only one current-feedback amplifier simplifiers the configuration.

Subband adaptive array (SBAA) has been realised as a promising method to perform space-time signal processing in mobile communications. Recently, several schemes of SBAA have been introduced. However, theoretical analysis of SBAA performance has been only limited to case of SBAA without using decimation. In this paper, we introduce a novel method to analyse the performance of SBAA using critical sampling with localised feedback scheme. We first provide a detailed analysis of the SBAA performance in the case of single path and multipath fading environment. The simulation results are then presented to verify the proposed method.

In SoC (system-on-a-chip) design, interfacing among IP (Intellectual Property) blocks is one of the most important issues. Since most IP's are provided by different vendors, they generally have different interface schemes and different operating frequencies. In this paper, we propose a new interface synthesis method with two features: 1) generation of the interface between IP's with different operating frequencies, and 2) minimization of the hardware resource required for the interface. We have demonstrated the proposed algorithm through its application to an MP3 decoder design example, where the IIS (Inter-IC Sound)-to-PCI (Peripheral Component Interconnect) protocol converter was successfully implemented using the proposed method.

It is widely known that the family of projection filters includes the generalized inverse filter, and that the family of parametric projection filters includes parametric generalized projection filters. However, relations between the family of parametric projection filters and constrained least squares filters are not sufficiently clarified. In this paper, we consider relations between parameter estimation and image restoration by these families. As a result, we show that the restored image by the family of parametric projection filters is a maximum penalized likelihood estimator, and that it agrees with the restored image by constrained least squares filter under some suitable conditions.

This paper introduces an automatic and multi-instrument snowfall observation system and proposes techniques that could be used in the estimation of snowfall characteristics. The instruments used in this study include two microwave radars, an optical lidar, a CCD camera based imaging system and high-accuracy electrical balances for reference data. The emphasis has been on obtaining good temporal resolution and synchronization accuracy of separate datasets. In most research done so far, this has not been a principal point, either because only very long snowfall events have been measured, or wide area estimates were desired, or due to limitations in manual sampling methods and other technical issues. The measurements were also contained in a small area to make sure that all instruments record data from the same target. One radar and the optical lidar recorded an atmospheric profile up to 6000 m, while the other radar, the imaging system and the two balances recorded snowfall on the ground level. The combination of optical, microwave and direct visual observations of snowfall show that a change in cloud conditions can result in snowfall having different characteristics. The lidar backscatter was used as main indicator of transitions in cloud conditions. A direct visual evaluation of snowflake size distribution using a CCD camera shows that it is extremely helpful in order to interpret radar data. The camera observed velocity distribution showed no large variations between snowfall events, however, it could be useful in detecting graupel and hail precipitations which have much faster terminal velocities. This paper will conclude with a discussion on further elaborating the use of lidar and visual data to complement radar observations of snowfall.

We propose a buffer management mechanism, called V-WFQ (Virtual Weighted Fair Queueing), for achieving an approximately fair allocation of bandwidth with a small amount of hardware in a high-speed network. The basic process for the allocation of bandwidth uses selective packet dropping that compares the measured input rate of the flow with an estimated fair share of bandwidth. Although V-WFQ is a hardware-efficient FIFO-based algorithm, it achieves almost ideal fairness in bandwidth allocation. V-WFQ can be implemented in the high-speed core routers of today's IP backbone networks to provide various high-quality services. We have investigated V-WFQ's performance in terms of fairness and link utilization through extensive simulation. The results of simulation show that V-WFQ achieves a good balance between fairness and link utilization under various simulation conditions.

Pilot-aided adaptive prediction channel estimation is proposed for coherent detection in a frequency-nonselective fading channel. It is an extension of the conventional weighted multi-slot averaging (WMSA) channel estimation and consists of 3 steps. A block of Np pilot symbols is periodically transmitted, each pilot block being followed by Nd data symbols to form a data slot. In the first step, the instantaneous channel gain is estimated by coherent addition of Np pilot symbols. Using the K past and K future estimated instantaneous channel gains, the second step predicts the instantaneous channel gains at the end and beginning of data slot of interest by a forward predictor and a backward predictor, respectively. The tap-weights of forward prediction and backward prediction are adaptively updated using the normalized least mean square (NLMS) algorithm. Finally, in the third step, the instantaneous channel gain at each data symbol position within the data slot of interest is estimated by simple averaging or linear interpolation using the two adaptively predicted instantaneous channel gains. The computer simulation confirms that the proposed adaptive prediction channel estimation achieves better bit error rate (BER) performance than the conventional WMSA channel estimation in a fast fading channel and/or in the presence of frequency offset between a transmitter and a receiver.

In this paper, a new adaptive method is suggested using the complementally transformed minimum variance technique for the purpose of suppressing interference in additive white and colored Gaussian noise channels. The method is based on interference suppression by way of the resulting projection weight. The multiple access causes an interference problem in the code-division multiple access systems. An efficient adaptive algorithm should be used to suppress this interference for the improvement of system performance. Analytical and simulation results show that the new adaptive method has fast convergence rate and offers significant performance gain over the conventional detector, the MMSE detector, and the linear decorrelator. Finally, multipath fading induced performance loss, which leads to error probability floor, is established for the proposed method with combining schemes and shown by computer simulation.

Providing a fair allocation of bandwidth among different connections over the Internet without affecting link efficiency has been a challenging issue in the area of network performance improvement. Congestion signaling is essential for the purpose. Conventional TCP uses packet loss as an implicit indication of congestion. Several enhancements to TCP have been proposed for faster congestion recovery and thus to improve the network performance. However, packet loss reduces TCP goodput and adds large delay. Also the variance in the share of bandwidth obtained by each connection may become unaccepatbly high. To the contrary, Explicit Congestion Notification (ECN) indicates a congestion explicitly before it actually occurs. Therefore, ECN facilitates a faster congestion detection and contributes to the network performance improvement. In this paper, we consider the performance implications of employing different ECN strategies along with several TCP enhancement schemes. We also introduce a new ECN packet marking strategy FIM and evaluate its relative performance and suitability for deployment along with different TCP enhancements. Simulation results show the superiority of FIM over other existing marking strategies with different TCP enhancement schemes by providing the best fairness without hampering link efficiency. We also observe FIM maintains a more consistent delay bound than other strategies and as such, is more suitable for application in practical purposes.

The performances of M-ary PSK (MPSK) and QAM (MQAM) systems using L-branch selection combining (SC) diversity reception in frequency-nonselective slow Nakagami fading channels are derived theoretically. For integer values of the Nakagami fading parameter m, the general formula for evaluating symbol error rate (SER) of MPSK signals in the independent branch diversity system comprises numerical analyses with the integral-form expressions. An exact closed-form SER performance of MQAM signals under the effect of SC diversity via numerical integration is presented.

In this paper, a hybrid FDMA/CDMA system and a wideband CDMA (W-CDMA) system in the frequency selective Rayleigh fading are considered. The bit error rate (BER) and coded symbol error rate performance of a coherent BPSK RAKE receiver under the various number of receiver fingers are derived and evaluated. In addition, a multiple access control (MAC) protocol based on packet-switched network is proposed and computer simulation is performed. Then, the results of performance evaluation are compared. The numerical analysis shows that the performance of the hybrid system is better than that of the W-CDMA in situation when the RAKE receiver complexities are kept constant in both systems. As noted, when each system has as many fingers as paths, the performance of the full-fingered W-CDMA is best. The 2- or 3-subspectrum FCDMA, however, has almost the same performance compared with the full-fingered W-CDMA when we applied the proposed MAC protocol to the system.

We propose using a soft decision-directed least-mean-square algorithm in a code-aided equalization scheme for fading channels. Soft-output Viterbi algorithm (SOVA) is modified and applied to strengthen the second-stage equalizer adaptation in the scheme. Simulation results are presented for bit error rate performance in a multipath environment for various normalized fade rates. The proposed equalizer scheme is shown to provide significant bit error rate improvement compared to conventional equalization schemes.

This paper proposes a multipath interference canceller (MPIC) for orthogonal code multiplexed channels in the W-CDMA forward link and evaluates by computer simulation the improvement in BER performance owing to the multipath interference (MPI) suppression effect obtained by the MPIC. The simulation results show that a one-stage MPIC, which removes the MPI from the common pilot channel (PICH), common control channel (CCH), and synchronization channel (SCH), achieves a sufficient MPI suppression effect, and that the required received Eb/N0 of the traffic channel (TCH) at the average BER of 10-3 using the MPIC for the common channels is decreased by approximately 6.5 dB compared to that with a matched filter (MF)-based Rake receiver (the transmit power ratio of each common channel to TCH: ΔPICH/TCH=0 dB, ΔCCH/TCH=5 dB, ΔSCH/TCH=3 dB, without fast transmit power control (TPC) and antenna diversity reception). We also show that by using MPIC, the required transmit Eb/N0 at the average BER of 10-3, when the ratio of the target Eb/I0 of the 9-interfering users to desired user is ΔInt/Des=6 dB with fast TPC, is increased by only approximately 0.6 dB compared to that when ΔInt/Des=0 dB. This implies that the preferential MPI suppression from high-rate TCHs that abates the increase in complexity in a mobile terminal is effective in increasing the link capacity in the forward link.

Methods that precisely compensate for propagation distortion using pilot symbols are widely used in mobile communications. We describe such a pilot-symbol-assisted technique for precise compensation of flat fading and frequency offset. This technique provides a wide range of offset compensation. Conventional methods using fast Fourier transform (FFT) compensate for both slow and fast fading, but their tolerable range of frequency offset is very limited. By composing a system with an approximate frequency estimator, we can estimate and compensate for fading and a large frequency offset at the same time. The estimation and compensation are carried out by periodic pilot symbols and no other index sequences are needed. This method enables high-data-rate transmission. We describe the method and provide a theoretical analysis for the compensable range of fading and frequency offset for a transmission frame structure with pilot symbols. Then, we evaluate the method by computer simulation.

Transmitter power control is an effective scheme to improve the performance of cellular DS/CDMA systems. In the reverse link, pilot symbols are used to assist the estimation of received signal power in order to improve the performance of power control. In this paper, we propose a model for the evaluation of the performance of a power-controlled reverse link CDMA system in the presence of Rayleigh flat fading. The model allows analysis of design parameters such as the number of pilot symbols, the power control updating frequency and the maximum allowable transmitted power. Analysis result shows that when transmitter power control is used, system capacity can be increased by more than 40% for typical normalised Doppler frequency in cellular communications.

In this paper, we propose a new fair queueing algorithm to improve cell delay variation (CDV) for real-time service categories and to make efficient use of system resources for multimedia traffic in high speed ATM networks. The proposed algorithm is called the delay variation-based fair queueing (DVFQ) algorithm, which is based on per-VC queueing to improve CDV and fairness for each VC of real-time services such as CBR and rt-VBR. In DVFQ algorithm, we define two fairness indexes, which indicate the degree of the fairness of CDV at the rate of each VC, and the degree of impartially sharing the bandwidth between the scheduled cells for each VC. The simulation results for both heavily and lightly loaded conditions show that DVFQ algorithm provides better performances in terms of the CDV, the CDV fairness, and the service fairness than those of FCFS for real-time service.