As a blind linear-interference-canceller for DS-CDMA mobile communications, the orthogonal matched filter (OMF) minimizes the power of the output while maintaining constant power of the desired signal in the output. This paper studies the extension of OMF to an RAKE receiver (OMF-RAKE), which adaptively controls the steering vectors that determine the constraint. It also applies the QR-RLS algorithm to estimate the OMF-RAKE parameters and investigates a hardware implementation that employs a systolic array. Computer simulations show that OMF-RAKE with the QR-RLS algorithm and the systolic array structure can reduce the computational complexity to about a half that of the conventional RLS-type algorithm without degrading the BER.

This paper proposes a direct blind equalization algorithm based on the multiple-shift correlation (MSC) property of the received data. Employing adaptive beamforming technique, we develope a partially adaptive channel equalizer (PACE) which allows the number of the adaptive weights to be less than the number of all the channel parameters. The PACE is with fast convergence speed and low implementation complexity. This paper also analyzes the effect of mismatch of channel order estimation due to small head and tail of the channel impulse response. From the analysis, we show the performance degradation is a function of the optimal output signal-to-interference plus noise ratio (SINR), the optimal output power and the control vector. We also propose a simple iterative method to reudce the performance degradation. Analysis of this proposed iterative method is also performed. Some simulation examples are demonstrated to show the effectiveness of the proposed blind channel equalizer and the performance analysis.

Optical Burst Switching (OBS) has been developed as an efficient switching technique to exploit the capacity provided by Wavelength Division Multiplexing (WDM) transmission technology for the next generation optical Internet. One critical design issue in OBS is how to provide Quality-of-Service (QoS) on optical networks. In order to provide the service differentiation, we propose in this paper a buffer allocation algorithm to schedule bursts at the edge OBS nodes, a bandwidth allocation algorithm and a Fiber Delay Line (FDL) allocation algorithm to schedule bursts at the core OBS nodes. We also introduce a new burst assembly technique in which the burst is generated either when the sum of the collected packet sizes reaches the maximum threshold or when the burst assembling time reaches the timeout limit. Our simulation results show that the proposed algorithms achieve the controllable burst loss probability for different service classes. The bandwidth allocation algorithm performs very well at the core OBS nodes in terms of the low loss probability.

Recently, various types of traffic have increased on the Internet with the development of broadband networks. However, it is difficult to guarantee QoS for each traffic type in current network environments. Moreover, it has been reported that bandwidth can be allocated to flows unfairly, and this can be an important issue for QoS guarantees. Therefore, we have proposed a flow-based queue management scheme, called Dual Metrics Fair Queueing (DMFQ), to improve the fairness and QoS per flow. DMFQ discards arrival packets by considering not only the arrival rate per flow but also the flow succession time. In addition, we have confirmed the effectiveness of DMFQ through several computer simulations. In this paper, we implement DMFQ with hardware for high-speed operation. Concretely, we propose the design policies and show the hardware design results.

In this paper, we present a set of sequence pairs which produce zero correlation windows not only in the middle part of the sum of aperiodic correlation functions, but also in the two terminal parts. We name it "Ear Windows." In approximately synchronous CDMA communication system, this set of sequences is able to completely remove the inter-symbol interference (ISI) and multi-user interference (MUI) caused by the multi-path effect if the maximum delay is shorter than the length of the "Ear windows." In addition, it is also feasible in M-ary modulation. The inter-code interference will be mitigated drastically.

Two rotational transformations are used to derive a new expression for the symbol error probability (SEP) of an M-ary phase shift keying (MPSK) with an I-Q unbalance over additive white Gaussian noise (AWGN) and Rician fading channels. We used the new expression to investigate the effect of the I-Q unbalance on the MPSK SEP performance. Our investigation confirms that this approach is a convenient way to evaluate the average SEP of an MPSK for various cases of the Rician factor.

We derive and analyze a bit error rate (BER) expression of a Gray coded rectangular QAM (R-QAM) signal with maximal ratio combining (MRC) diversity reception over Nakagami-n (Rician) fading channels. The derived result is provided in terms of the Whittaker function and the confluent hypergeometric function. Because the derived expression is general, it can readily allow numerical evaluation for various cases of practical interest such as line-of-sight (LOS) or satellite communication channel analysis.

To provide better QoS management, we investigated network-level dynamic priority methods. We propose methods in which packets of the same type of application receive different treatment in the network, depending on the route information. They feature a simple mechanism, which enables the methods to be executed easily with a small processing load at the routers as well as a small amount of information stored in the packet header. The effectiveness of these methods is shown by numerical comparison with the existing static priority method as well as the dynamic priority method.

In this paper, a Dynamic Voltage and Frequency Management (DVFM) scheme introduced in a microprocessor for handheld devices with wideband embedded DRAM is reported. Our DVFM scheme reduces the power consumption effectively by cooperation of the autonomous clock frequency control and the adaptive supply voltage control. The clock frequency is controlled using hardware activity information to determine the minimum value required by the current processor load. This clock frequency control is realized without special power management software. The supply voltage is controlled according to the delay information provided from a delay synthesizer circuit, which consists of three programmable delay components, gate delay, RC delay and a rise/fall delay. The delay synthesizer circuit emulates the critical-path delay within 4% voltage accuracy over the full range of process deviation and voltage. This accurate tracking ability realizes the supply voltage scaling according to the fluctuation of the LSI's characteristic caused by the temperature and process deviation. The DVFM contributes not only the dynamic power reduction, but also the leakage power reduction. This microprocessor, fabricated in 0.18 µm CMOS embedded DRAM technology achieves 82% power reduction in a Personal Information Management scheduler (PIM) application and 40% power reduction in a MPEG4 movie playback application. As process technology shrinks, the DVFM scheme with leakage power compensation effect will become more important realizing in high-performance and low-power mobile consumer applications.

We have developed an estimation system of the electric parameters for liquid materials without a sensor connecting to the testing materials. A PC can be used for the calculation, and the calculation time is about 2 minutes. The accuracy is such that the estimated values are different from the nominal values by less than 2%.

Spatial correlation among antenna elements both at transmitter and receiver sides in MIMO communications is known to have a crucial impact on system performances. Another factor that can severely degrade receiver performances is the timing offset relative to the channel delay profile. In this paper we derive a novel receiver for turbo MIMO equalization in space-time-trellis-coded (STTrC) system to jointly address the problems described above. The equalizer is based on low complexity MMSE filtering. A joint detection technique of the several transmit antennas is used to reduce the receiver's sensitivity to the spatial correlation at the transmitter and receiver sides. Furthermore, only the significant portion of the channel impulse response (CIR) is taken into account while detecting signals. The remaining portion of CIR is regarded as the unknown interference which is effectively suppressed by estimating its covariance matrix. By doing this the receiver's complexity can be reduced since only a portion of the CIR has to be estimated and used for signal detection. Furthermore, by suppressing the interference from the other paths outside the equalizers coverage the receiver's sensitivity to the timing offset can be reduced. The proposed receiver's performance is evaluated using field measurement data obtained through multidimensional channel sounding. It is verified through computer simulations that the performance sensitivity of the joint detection-based receiver to the spatial correlation is significantly lower than with the receiver that detects only one antenna at a time. Furthermore, the performance sensitivity to the timing offset of the proposed receiver is shown to be significantly lower than that of the receiver that ignores the existence of the remaining multipath CIR components.

This letter considers frame synchronization in non-synchronized sampling discrete multi-tone (DMT) based asymmetric digital subscriber line (ADSL)/very high speed DSL (VDSL) systems in the presence of timing error. We propose a frame synchronization method which is based on the observation that the normalized correlation between two sequences separated by the FFT length is Cauchy random variable. The proposed approach uses less number of correlators, reducing computational complexity as well as demodulation delay than a previous approach. Therefore, ADSL/VDSL modems can be more power efficient and computationally less complex via the proposed frame synchronization method. Simulation results demonstrate the effectiveness of the proposed approach, comparing with the previous approach.

Multipath propagation of radio signal introduces frequency selectivity. OFDMA systems greatly suffer from frequency selective fading. It is an important limit factor of performance of OFDMA systems, especially in subband based multiple user access scehems. In this paper, we propose the method of subband selection and handover to improve the system performance over the frequency selective channel. Two subband selection algorithms are presented to accurately select the subband with high channel gain and avoid the channel notch. The random access procedure employing subband selection is presented as an example. The effects of the subband selection are also given. The selection effectively improves the performances of frame synchronization, frequency synchronization, channel estimation, and bit error rate (BER). The investigations show that the proposed scheme is promising to reliable communications over frequency selective fading channel.

We have fabricated Al-gate MOS capacitors with a Si quantum-dots (Si-QDs) floating gate, the number of dots was changed in the range of 1.6-4.81011 cm-2 in areal density with repeating the formation of Si dots and their surface oxidation a couple of times. The capacitance-voltage (C-V) characteristics of Si-QDs floating gate MOS capacitors on p-Si(100) confirm that, with increasing number of dots density, the flat-band voltage shift due to electron charging in Si-QDs is increased and the accumulation capacitance is decreased. Also, in the negative bias region beyond the flat-band condition, the voltage shift in the C-V curves due to the emission of valence electrons from intrinsic Si-QDs was observed with no hysterisis presumably because holes generated in Si-QDs can smoothly recombine with electrons tunneling through the 2.8 nm-thick bottom SiO2. In addition, we have demonstrated the charge retention characteristic improves in the Si-QDs stacked structure.

Active Queue Management (AQM) can maintain smaller queuing delay and higher throughput by purposefully dropping packets at the intermediate nodes. Most of the existing AQM schemes follow the probability dropping mechanism originated from Random Early Detection (RED). In this paper, we develop a novel packet dropping mechanism for AQM through designing a two-category classifier based on the Fisher Linear Discriminate approach. The simulation results show that the new scheme outperforms other well-known AQM schemes, such as RED, AdaptiveRED, AVQ, PI, REM etc., in the integrated performance. Additionally, our mechanism is simple since it requires few CPU cycles, which makes it suitable for the high-speed routers.

This paper presents a wavelength lock system using a Z-cut quartz etalon supported at the middle point. The Z-cut quartz etalon possesses the cavity length modulation and the low temperature coefficient. We propose a Z-cut quartz etalon supported at the middle point in order to improve the modulation index and response time. The mechanism of the center supported Z-cut quartz etalon is described. We also show that the etalon possesses a high modulation index, a high Q factor, and a rapid response time in experimental results. A self-tuning dither oscillator realized by using quartz etalon is also described.

In this paper, a new algorithm for MTMR adaptive array antenna (AAA) system combined with analog-type transmit power control (TPC) is proposed for DS-CDMA systems in order to employ high level modulation schemes like 64 QAM in wireless multimedia services. A conventional AAA system considering the strongest path as a target path cannot work effectively when angular dispersion between the strongest path and other delayed paths is large, that is, beam selectivity is so small due to severe frequency selective multipath fading. So, in order to solve such a beam selectivity problem, a beam directivity control scheme using a path manipulation technique is introduced for the BS and MS AAA combining in this paper, along with analog-type TPC. It utilizes virtual delay profiles which are modified from the measured complex delay profile and selects a desired path giving the maximum DUR with an optimized weight vector for BS and MS beamforming. We will show through computer simulation that the proposed scheme is very effective in enhancing the data throughput at the downlink of wideband DS-CDMA systems as compared with the conventional system.

This paper proposes a Voice Activity Detection (VAD) algorithm using Radial Basis Function (RBF) network. The k-means clustering and Least Mean Square (LMS) algorithm are used to update the RBF network to the underlying speech condition. The inputs for RBF are the three parameters a Code Excited Linear Prediction (CELP) coder, which works stably under various background noise levels. Adaptive hangover threshold applies in RBF-VAD for reducing error, because threshold value has trade off effect in VAD decision. The experimental results show that the proposed VAD algorithm achieves better performance than G.729 Annex B at any noise level.

The bit error rate (BER) degradations of fast frequency hopping multiple access (FFH-MA) systems due to the frequency and timing offsets are investigated over a Rician fading channel. It is shown that as the received average SNR increases, the BER is affected much larger by frequency and timing offsets. When the frequency offset or the timing offset exists alone, the BER of the FFH-MA system is degraded much more due to the timing offset than due to the frequency offset. The BER degradation due to both the frequency offset and the timing offset is larger than the sum of the degradations due to each offset.

In this letter, pilot-assisted adaptive prediction iterative channel estimation in frequency-domain is presented for the antenna diversity reception of orthogonal frequency division multiplexing (OFDM) signals. A frequency-domain adaptive prediction filtering is applied to iterative channel estimation for improving the tracking capability against frequency-domain variations in a severe frequency-selective fading channel. Also, in order to track the changing fading environment, the tap weights of frequency-domain prediction filter are updated using the simple NLMS algorithm. Updating of tap weights is incorporated into the iterative channel estimation loop to achieve faster convergence rate. The average bit error rate (BER) performance in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is confirmed that the frequency-domain adaptive prediction iterative channel estimation provides better BER performance than the conventional iterative channel estimation schemes.