Adaptive channel estimation filters are presented for coherent DS-CDMA reverse link using time-multiplexed pilot and parallel pilot structures. Fast transmit power control (TPC) is adopted in the reverse link. Fading statistical properties are not preserved when fast TPC is used. When fading is slow, the channel is similar to non-fading channel, but its starts to vary as fading become faster since fast TPC cannot track fading perfectly. A pragmatic approach is used in this paper to derive adaptive channel estimation filter. The filter coefficients are updated based on the measured autocorrelation function of the instantaneous channel estimate. The bit error rate (BER) performance under frequency selective Rayleigh fading is evaluated by computer simulation to show that the adaptive channel estimation filter provides superior performance to the previously proposed non-adaptive WMSA filter.

In multi-media systems, the type of interactive communication channels is found almost everywhere and plays an important role, as well as the type of unilateral communication channels. In this report, we shall construct a fluctuation theory based on the concept of set-valued mappings, suitable for evaluation, control and operation of interactive communication channels in multi-media systems, complicated and diversified on large scales. Fundamental conditions for availability of such channels are clarified in a form of fixed point theorem for system of set-valued mappings.

Coaxial-core erbium-doped fiber amplifiers (EDFA's) having a property of self-regulated gain spectrum are developed. The operation of a coaxial-core EDFA is based on the partial separation of the light paths for different wavelength channels in the directionally-coupled waveguides of a coaxial-core geometry. The degree of channel equalization depends on the geometrical and optical parameters of the coaxial-core EDFA and on relative channel power levels. A numerical analysis based on the coupled-mode theory and on the rate equation shows that, under fully optimized conditions, a coaxial-core EDFA provides equalization rates in excess of -0.4 dB per dB of input-power imbalance in the case with two WDM channels. A cascade experiment demonstrates the effect of coaxial-core EDFA's toward channel-power equalization in fiber links with a small number of WDM channels.

Coaxial-core erbium-doped fiber amplifiers (EDFA's) having a property of self-regulated gain spectrum are developed. The operation of a coaxial-core EDFA is based on the partial separation of the light paths for different wavelength channels in the directionally-coupled waveguides of a coaxial-core geometry. The degree of channel equalization depends on the geometrical and optical parameters of the coaxial-core EDFA and on relative channel power levels. A numerical analysis based on the coupled-mode theory and on the rate equation shows that, under fully optimized conditions, a coaxial-core EDFA provides equalization rates in excess of -0.4 dB per dB of input-power imbalance in the case with two WDM channels. A cascade experiment demonstrates the effect of coaxial-core EDFA's toward channel-power equalization in fiber links with a small number of WDM channels.

This paper presents an approach to the blind identification of multichannel communication systems by using partial knowledge of the channel. The received signal is first processed by a filter constructed by the known component of the channel and then a blind identification algorithm based on the second-order statistics is applied to the filtered signal. It is shown that, if the unknown component satisfies the identifiability condition, the channel can be identified even though the channel does not satisfy the identifiability condition. Simulation results are presented to show the performance of the proposed approach. A comparison to the existing approaches is also presented.

This paper proposes and investigates the adaptive single-user receiver with co-channel interference (CCI) canceller based on orthogonalizing matched filter (OMF) using the multi-dimensional (multi-D) lattice filters for DS/CDMA in a multipath environment. A conventional single-user receiver using OMF cannot correctly cancel CCI in the presence of multipath in a channel, because the desired user's signal component and other users' intersymbol interference (ISI), due to multipath, still remain at the output of OMF, and then a correct replica of CCI cannot be generated. The proposed receiver can solve this problem because a multi-D IIR lattice filter can distinguish the desired user's signal component from the other users' ones and remove the ISI of all users' signals by Gram-Schmidt orthogonalization. And a multi-D FIR lattice filter can selectively regenerate undesired users' signal components which contain neither the desired user's signal component nor ISI. The proposed receiver based on multi-D lattice filters can apply orthogonality property of the OMF to not only a direct wave but also to delayed waves in a multipath channel. Since the proposed receiver does not have to know spreading codes of multiusers except the desired user, it will be applicable at a mobile terminal in the forward link in a multipath environment. Computer simulations show the proposed receiver have capability to cancel the CCI and converges fast in a multipath channel.

In this paper, the performance of some communication systems using chaos synchronization is evaluated and compared. A new channel model taking the attenuation, impedance mismatch and noise into account, is proposed for the performance evaluation. The evaluation of bit error rate is done for both ideal and non-ideal conditions using the channel model. It is confirmed that some chaos-based communication systems have a good performance compared with conventional analog communication schemes.

In this paper, the performance of dynamic channel assignment for cellular systems with an array antenna is evaluated assuming realistic beamformer. A new dynamic channel assignment algorithm is proposed to improve the performance by forming a directional beam pattern to cancel stronger co-channel interference with higher priority. Performance comparison is carried out by computer simulations. Conventional algorithm shows 2.7 fold capacity increase compared with an omni antenna system, whereas proposed algorithm shows around 3.3 fold capacity increase, at the point of 3 percent blocking probability. The simulation results also denote that a shorter reuse distance can be achieved by the proposed algorithm, which indicates a more efficient utilization of channel resource.

In this letter, we propose the channel estimation technique in the uplink of a DS/CDMA system with M-ary orthogonal signaling over multipath fading channels. The channel estimation is carried out using the maximum correlator output of RAKE receiver. With the estimated channel parameters, the RAKE receiver can coherently combines the received multipath signals, resulting in a significant performace improvement. The hardware complexity of the proposed detection technique is slightly increased when compared to that of noncoherent detection.

This paper proposes an adaptive transmission control scheme for code-division multiple-access (CDMA) cellular slotted-ALOHA systems. This scheme adaptively controls the target received power and the processing gain according to both channel load and location of the mobile station. The target received power of each mobile station is controlled so that the difference between the target received powers by distance becomes large under heavy load conditions. As the distance from the base station increases, the target received power becomes smaller. The processing gain of transmitted packets is concurrently controlled with their target received powers. The packets transmitted with low signal power are spread by a large processing gain in order to reduce the unfairness in packet reception. The radio channels with distance attenuation, shadowing, slow Rayleigh fading and imperfect power control are taken into consideration in order to evaluate the performance of this scheme in the case that mobile stations transmit short massages to the base station in cellular environments. Computer simulation validates the effectiveness of this scheme: the capture effect can be achieved under heavy channel loads, and therefore, throughput performance is improved. Detailed evaluation of throughput, packet reception probability and transmission complete probability is presented. The effect of movement of mobile stations is also discussed. Calculated results show that the proposed scheme has superior characteristics and thus can expand the allowable load area in the cellular environments with slow Rayleigh fading channels.

This paper describes a forward subchannel control of multi-carrier scheme intended to compensate for phase/amplitude distortions under frequency selective fading. The forward subchannel control scheme is used for a Time Division Duplex (TDD) multi-carrier system on up-link. The forward subchannel control scheme provides forward subchannel control of phase/amplitude variation and subchannel assignment control. These controls are applied before transmission of an up-link signal. The forward control parameters are estimated by a preamble down-link signal. Simulation results clarify that the BER performance with the forward subchannel control scheme shows a superiority of more than one order at the condition of 22 dB of Eb/N0 and 400 Hz of fading frequency.

The feasibility of a dynamic zone configuration technique has been investigated. To make it easy to implement this technique in wireless communication systems, a simplified method for determining a suitable weight vector by using the least squares (LS) methods was developed. Simulations showed that the developed system is more effective than the present omni-directional zone system. Moreover, combining dynamic zone configuration technique with dynamic channel assignment strategy reduced blocking rate, forced call termination ratio, and required transmission power.

This paper reports the evaluation results of the channel boron distribution in the deep sub-0.1 [µm] n-MOSFETs for the first time. It has been found that the boron depletion effect becomes dominant and the reverse short channel effect becomes less significant in the deep sub-0.1 [µm] n-MOSFETs. It has been also found that the sheet charge distribution responsible for the reverse short channel effect is localized within a distance of 100 [nm] from the source/drain-extension junction.

The Joint CDMA/PRMA (JCP) protocol, proposed by Brand and Aghvami, is modified to increase the capacity for mobile communication systems. To reduce multiuser interference, the modified JCP uses an access channel additionally to the traffic channels, on which each mobile terminal reserves a unique slot and code. Furthermore, the modified JCP employs receiver-based code scheme. In the case of voice-only traffic, the throughput increases by up to 15% compared to that of the conventional JCP, when Ploss is 0.01. Also, for the mixed traffic case, the throughput increases about 20%.

In the basic user/network interface of ISDN (ITU-T Recommendation I. 430), the D-channel is shared by up to 8 terminals for signal and data packets. An analytical model is proposed to reveal the performance characteristics of the access control scheme for the D-channel. Numerical and simulation results are shown to demonstrate the performance differentiation of the terminals with different priorities. It is observed that the mean signal delay at low load may become large because of long service time for packets, and that the priority mechanism may not work properly when the loads at terminals are very asymmetric.

An optical receiver with a saturated electrical amplifier is studied for signal light that is distorted due to the use of a gain-saturated semiconductor optical amplifier or homowavelength crosstalk light. It is shown that less penalty is induced in a receiver with a DC-coupled saturated amplifier than in one with a linear amplifier, in a practical situation where the decision threshold is fixed at a value optimized for a back-to-back signal. The result suggests that a receiver with a saturated amplifier or a limitter is preferable to an automatic gain control circuit for detecting distorted signal lights.

This paper analyzes the performance of direct-detection optical CDMA systems with single optical hard-limiter using equal-weight orthogonal (EWO) signaling. Moreover, this paper clarifies the basic structure and the performance of the system using time-shifted versions of optical orthogonal code (OOC's) as EWO signaling. The system assigns the time-shifted versions of OOC's to the transmission of bits "0" and "1," respectively. Thus, the system does not require dynamic estimation of the receiver threshold. The performance is analyzed under the Gaussian approximation of an avalanche photodiode (APD) output where the effects of APD noise, thermal noise and interference are included. From the theoretical analysis and numerical results, it is shown that the system has good performance without dynamic estimation of the receiver threshold.

In this paper, the bit error rate (BER) of 16 differential amplitude phase shift keying (16DAPSK) modems in future mobile communication system is derived analytically. The channel employed in this paper is the frequency-selective and fast Rayleigh fading channel, corrupted by cochannel interference (CCI) and additive white Gaussian noise (AWGN). Exact expressions for the probability distributions of the differential phase and amplitude ratio are derived for the BER calculation. The BER and optimum boundary are obtained for various channel conditions. In addition, the results for the BER in the presence of CCI are provided.

The frequency-offset estimation of a wireless asynchronous transfer mode (ATM) modem based on the orthogonal frequency division multiplexing (OFDM) is discussed. For burst synchronization operating under the time-division multiple access (TDMA) medium access control (MAC), an OFDM preamble using a multistage frequency-offset estimation technique is proposed and shown to have a good accuracy with a large estimation range. And also an averaged decision-directed channel estimation (ADDCE) technique suitable for burst data is proposed.

Speech signals transmitted over telephone network often suffer from interference due to ambient noise and channel distortion. In this paper, a novel frame-dependent fuzzy channel compensation (FD-FCC) method employing two-stage bias subtraction is proposed to minimize the channel effect. First, through maximum likelihood (ML) estimation over the set of all word models, we choose the word model which is best matched with the input utterance. Then, based upon this word model, a set of mixture biases can be derived by averaging the cepstral differences between the input utterance and the chosen model. In the second stage, instead of using a single bias, a frame-dependent bias is calculated for each input frame to equalize the channel variations in the input utterance. This frame-dependent bias is achieved by the convex combination of those mixture biases which are weighted by a fuzzy membership function. Experimental results show that the channel effect can be effectively canceled even though the additive background noise is involved in a telephone speech recognition system.