The worldwide availability of the Industrial Scientific and Medical (ISM) bands has prompted the proposal of several communication systems for indoor application at the 2.4 and 5 GHz bands. Although adaptive array antennas have been thoroughly investigated for various outdoor scenarios, their application to indoor communications has been overlooked. Experimental results indicating that conventional array antenna techniques exhibit poor performance when implemented indoors have recently been published. An important peculiarity of the indoor channel is the coexistence of both near-field and far-field propagating waves. Therefore, algorithms that can indifferently cope with both near-field and far-field wavefronts for source location and beamforming are desirable. In this paper, the following are presented. First, a mathematical analysis of the performance of array antennas in the indoor environment is taken up. Second, a new, simple, cost-effective and statistically coherent scheme, the Adaptive Sampling algorithm, is proposed for location estimation of sources anywhere from near field to far field. It is shown that the proposed algorithm achieves ubiquitous source location, allowing for symmetric uplink/downlink beamforming with seamless performance. Finally, the performance of the proposed Adaptively Sampled Array Antenna is performance analyzed via computer simulations under the specifications of the IEEE802.11b DS Wireless Local Area Network (W-LAN).

This paper investigates the improvement of the radiation pattern design of transmitting array antenna beamforming and transmission power control (TPC) for forward link of DS-CDMA/FDD system. Optimum transmission beamforming and TPC can be derived from the information of the propagation channel for the forward link, in terms of outage probability minimization. It is assumed that the channel is static and then all mobile stations (MS's) report channel characteristics measured in the forward link to a base station (BS) that can control signal to interference plus noise ratios (SINR's) received by individual MS's using that measured information. Then, for the multi-user environment of a single cell, goal programming (GP) is applied to derive an optimum weight vector of the transmitting array antenna and optimum TPC such that outage probability can be minimized.

This paper presents an overview of research, development, standardization and regulation activities on ultra wideband (UWB) technologies in National Institute of Information and Communications Technology (NICT). NICT started a project on UWB technologies since 2002, and organized UWB consortium in cooperation with more than 20 companies and 7 universities in Japan. Up to now, we have been conducting numerous UWB R&D including the following main works: i) key technology development such as MMIC chips, antennas and other devices, ii) measurement and channel modeling for UWB signal propagation, iii) standardization in international activities of IEEE 802.15, ITU-R TG1/8 as well as in a national regulatory committee of Ministry of Internal Affair and Communications (MIC). The UWB systems we have studied occupy frequency bands range from microwave band (3-5 GHz) to quasi-millimeter wave band (24-29 GHz). Various prototype UWB systems including multi-functional terminals have been developed. The output of NICT has been succeeded by industrial parties with with national and international standardization and regulation.

PSK coherent demodulation has difficulty in achieving high speed carrier extraction and symbol synchronization when implementing to slow FH-SS radio system. On the other hand, implementation to FPGA has the requirement of a small gate size to design because of FPGA cost issue. We developed a QPSK coherent demodulation digital modem for FH-SS radio systems using FPGA by solving problems. The designed modem performs symbol synchronization with no carrier extractions, under the limitation of the small gate size requirement. The modem employs shift arithmetic operation and a comb digital BPF to achieve very good synchronization lock-up performance with small gate size. In this paper, the symbol synchronization and the carrier tracking scheme are mainly discussed. Analysis of its performance and stability are also explained. The achievement of its very good performance is presented by experimental measurement.

This paper proposes and investigates an intelligent error-controlling scheme according to different importance of segmental information. In particular, the scheme is designed for facial images encoded by model-based coding that is a kind of intelligent compression coding. Intelligent communication systems regard the contents of information to be transmitted with extremely high compression and reliability. After highly efficient information compression by model-beaed coding, errors in the compressed information lead to severe semantic errors. The proposed scheme reduces semantic errors of information for the receiver. In this paper, we consider Action Unit (AU) as a segment of model-based coded facial image of human being and define the importance for each AU. According to the importance, an AU is encoded by an appropriated code among codes with different error-correcting capabilities. For encoding with different error controlling codes, we use three kinds of constructions to obtain unequal error protection (UEP) codes in this paper. One of them is the direct sum construction and the others are the proposed constructions which are based on joint and double coding. These UEP codes can have higher coderate than other UEP codes when minimum Hamming distance is small. By using these UEP codes, the proposed intelligent error-controlling scheme can protect information in segment in order to reduce semantic errors over a conventional error-controlling scheme in which information is uniformly protected by an error-correcting code.

This paper proposes and investigates optimum modulation assignment and band allocation scheme according to subband channel status for BST-OFDM system. The proposed system can adaptively optimize modulation assignment and band allocation according to the conditional parameter under independently fading subband channels. Specifically, in this paper only two optimization problems are treated in terms of modulation assignment. At first, an optimization criterion is a total Bit Error Rate (BER) subject to the constraint conditions of a desired total information bit rate under a fixed effective bandwidth. Another optimization problem is the maximization of a total information bit rate to satisfy a desired BER under a fixed effective bandwidth. Knowledge of the subband channel status is assumed to be updated by the feedback information from a receiver. This paper shows that the proposed system can overperform the conventional system in which all subbands employ the same modulation schemes in terms of BER. In addition, it is shown that the proposed system improves the overall information bit rate, which is not accomplishable in the conventional system.

Multilevel RLL (Runlength Limited) sequences are analyzed. Their noiseless capacity and lower bounds on the channel capacity in the presence of additive white Gaussian noise are given. Moreover, the analytical power spectra formulae for those sequences which generalize the previously derived one for binary sequences are newly derived. We conclude from the analysis of the power spectra that multilevel RLL sequences are attractive from the point of view that they increase information rate while keeping low DC-content and self-clocking capability of binary RLL sequences.

An adaptive array antenna should be applied for suppression of CCI in the spatial domain. However, the adaptive array antenna has some problems as follows. Because the adaptive array antenna takes a long time to converge to the optimum antenna weights, it's hard to track in case of quick varying channel. On the other hand, processing burden increases with the number of elements in the array antenna. To solve these problems, we propose an adaptive array antenna using array antenna as element antennas, the so-called "Layered array antenna." At the 1st layer, sector area are defined. We can change the sector areas according to the DOA distribution, because the sector areas are defined by the antenna weights. At the 2nd layer, MMSE is performed. Interference that couldn't be suppressed at the 1st layer is suppressed at the 2nd layer. By the proposed system, we confirmed higher convergence speed while relieving processing complexity.

An implantable WBAN path-loss model for a capsule endoscopy which is used for examining digestive organs, is developed by conducting simulations and experiments. First, we performed FDTD simulations on implant WBAN propagation by using a numerical human model. Second, we performed FDTD simulations on a vessel that represents the human body. Third, we performed experiments using a vessel of the same dimensions as that used in the simulations. On the basis of the results of these simulations and experiments, we proposed the gradient and intercept parameters of the simple path-loss in-body propagation model.

In order to achieve adaptive channel coding and adaptive modulation, the main causes of degradation to system performance are the decoder selection error and modulator estimation error. The utilization of supplementary information, in an estimation system utilizing channel estimation results, blind modulation estimation, and blind encoder estimation using several decoders information and encoder transitions have been considered to overcome these two problems. There are however many issues in these methods, such as the channel estimation difference between transmitter and receiver, computational complexity and the assumption of perfect Channel State Information (CSI). Our proposal, on the other hand, decreases decoder and demodulator selection error using a Hidden-Markov Model (HMM). In order to estimate the switching patterns of the encoder and modulator, our proposed system selects the maximum likelihood encoder and modulator transition patterns using both encoder and modulator transition probability based on the HMM obtained by CSI and also Decoder and Demodulator Selection Error probabilities. Therefore, the decoder and demodulation results can be achieved efficiently without any restraint on the pattern of switching encoder and modulation.

This paper proposes and investigates the adaptive multi-user equalizer based on the multi-dimensional IIR adaptive lattice filter in order to suppress the co-channel interference (CCI) in asynchronous DS/CDMA system. An asynchronous DS/CDMA system with multi-user receiver is modeled as multi-dimensional or multi-input/out system with cross-coupling that is co-channel interference. From the system model it is shown that the multi-user detection is reduced into a problem of multi-dimensional equalization for multiaccess interference as well as intersymbol interference. The proposed multi-user equalizer can improve the equalizing error of the filter, comparing with that of the multi-dimensional FIR transversal filter of which number of tap is finite. The multi-dimensional lattice filter can adaptively achieve fast and stable convergence with less taps. Since the filter can resolve correlative multiple input into orthogonal output stage by stage, CCI can be removed. Computer simulations show performance of the proposed scheme.

This paper proposes and investigates a vehicular radar system that can measure the distance to, the relative speed of and the direction of arrival (DOA) of the reflected waves from multiple targets or vehicles using the direct-sequence spread spectrum (DS-SS) technique. In particular, we propose a DOA estimation scheme using a multi-beam antenna. In order to show that the proposed system can accurately measure the above mentioned quantities, the performance is evaluated numerically in a multipath environment. Moreover, optimal multi-beam pattern is derived to minimize error probability of DOA estimation.

This letter proposes and investigates a method of estimating the direction of arrival (DOA) of wideband signals such as spread spectrum signals, in a multipath channel. The DOA estimation method can reduce the effect of signal distortion due to bandwidth of signals by creating a spatial spectrum wihch satisfies the sampling theory in the time domain. The DOA estimate calculated from this spatial spectrum is robust against signal distortion due to multipath. Computer simulations numerically evaluate the proposed method. In comparison with conventional MUSIC algorithm, the proposed method achieves superior performance in a multipath channel.

In this paper performance of M-stage detection for DS/CDMA is considered in terms of near-far resistance. Asymptotic multiuser efficiency (AME) of M stage detection over fading multipath channel is calculated and it is shown that even in the fading case the detector is near-far resistant i.e., insensitive to the relative energies of the users. The idea is extended to cellular environment. The effect of power control imperfection is investigated. It is shown that capacity can be increased if near-far resistant technique is employed in conjunction with limited power control.

A major drawback with linear precoding in a downlink multi-user MIMO system is the increase in the transmit power when a channel is correlated. On the other hand, nonlinear trellis precoding in downlink multi-user MIMO systems is capable of minimizing the transmit power by adding a shaping sequence to the original transmit sequence. However, conventional trellis precoding cannot be directly applied to existing bit-interleaved coded MIMO-OFDM systems since the trellis precoding and error correcting codes should be designed separately. In this paper, we proposed to embed trellis precoding into the error correcting codes that are used in the original multi-user MIMO-OFDM system employing linear precoding. Major advantage of this approach is that the receiving procedure at user terminals designed for the original system need not be changed up to the error correcting decoder to support our trellis precoding. Computer simulations show that the proposed trellis precoding provides improvements of 2 dB and 2.5 dB in 22 and 33 MIMO configurations, respectively.

Hands-free communications between cellular phones must be robust enough to withstand echo-path variation, and highly nonlinear echoes must be suppressed at low cost, when acoustic echo cancellation or suppression is applied to them. This paper proposes a spectrum-selective nonlinear echo suppression (SS-ES) approach as a solution to these issues. SS-ES is characterized by the selection of either a spectrum of the residual signal from an adaptive filter or a spectrum of the sending input signal depending on the amount of linear echo cancellation in an adaptive filter. Compared to conventional methods, the objective evaluation results of the SS-ES approach show an improvement of approximately 0.8-2.2dB, 0.23-2.39dB, and 0.26-0.50 in average echo return loss enhancement (ERLE), average root-mean-square log-spectral distortion (RMS-LSD), and the perceptual evaluation of speech quality (PESQ) value, respectively, under echo-path variation and double-talk conditions.

Spread spectrum systems have been recently studied and developed for commercial applications, because they have some advantages such as robustness against interference and a noise, low probability of intercept, realization of code-division multiple access, high accuracy ranging and so on. In this paper we analyze the information security of spread spectrum systems into confidentiality, untraceability, authenticity, and antijamming property and present some measures to achieve these properties using cryptographic techniques. We show that the spreading sequences play central role in the information security issues of spread spectrum systems. A generation method of the spreading sequence having high-security property is proposed.

The application of Orthogonal Space-Time Block Codes (O-STBC) as the encoding scheme in the presence of "non-quasi-static" fading was considered. A simple and efficient adaptive method of channel estimation based on the interpolation of estimates acquired at the pre-amble and post-amble of framed blocks of information is developed. Moreover, the proposed method is proven, both theoretically and by simulations, to outperform the alternative of channel tracking, despite its significant low complexity.

As a center of mobile multimedia of the 21st century, it is very much looking forward to explosion of R&D and business of the next generation of mobile communication systems and the ITS (Intelligent Transport Systems) because ITS will enable information-oriented in the field of the road, traffic and vehicles, by using the most advanced technologies of mobile communications and devices, for the various purposes such as decrease of the traffic accident, the reduction of traffic jam, the increase in efficiency of the logistics and the harmony with the earth environment. This invited paper will first briefly introduce evolution of mobile communications and ITS in ministries, industries and academia in Japan. Then core communication technologies for ITS will be overviewed such as spread spectrum CDMA, adaptive antenna array, and software radio or software defined radio. Demands of SoC (System on a Chip) to carry out the core technologies will be addressed.