This paper proposes a novel compressing and expanding (companding) system for OFDM wireless communications that minimizes the compression distortion and so reduces the peak power of OFDM symbols. OFDM systems suffer from large variations in instantaneous peak power. Such transients distort the signals when they are passed through a nonlinear high power amplifier (HPA) prior to transmission. Existing companding systems are far from perfect since the receiver can not accurately estimate the degree of compression applied by the transmitter and thus can not regenerate the original signal by expansion; the key problems are the band pass filter (BPF), HPA, and the noise component enhanced by the channel compensation filter. In the proposed companding system, each symbol is divided into segments, and series of consecutive segments are grouped into clusters. Each cluster is multiplied by a weight equal to the inverse of the largest instantaneous power within the cluster. The receiver estimates the weight used for each time cluster. The weights for all clusters are averaged to mitigate the weight estimation error. As a result, the proposed expander can accurately estimate the weights used and thus well suppress the compression distortion.

This paper clarifies properties of the quantum state control communication systems such as the quantum coherent communication systems (QCCS) and the photon communication systems (PCS). We compare properties of these two systems in the case of uncoded and coded schemes. In the former case, the energy-information efficiencies of both systems are given, taking into quantum state control account, and the Fano factor of PCS which corresponds to the same performance to the ideal QCCS is given. In the latter case, the reliability functions of both systems are considered. As a result, it is shown that effects of error correcting code in the PCS are much larger than that in the QCCS.

Trellis-Coded Modulation (TCM) schemes become popular in digital transmission systems to improve error performance. However, demodulation of Trellis-Coded signal is rather difficult. Because TCM schemes need many signal points compared with the uncoded schemes. This leads to a comparatively high probability of cycle slips. In addition, large loop delay caused by decoding can not be avoided when decision feed back type demodulators are used. This paper proposes a novel demodulation method for TCM signal using block demodulation. The block demodulation scheme is a kind of off-line demodulation, which has many advantages. The Viterbi decoder in the proposed block demodulator is used not only for Viterbi decoding but also for carrier estimation. Such a combined processing is done twice for high performance. In addition, a block demodulation scheme is not affected by processing delay. Therefore in the proposed system, carrier estimation becomes accurate, and Viterbi decoding also becomes correct. As a result, it can get coding gains which cannot be obtained by conventional block demodulation methods. And the proposed system can demodulate not only PSK signal but also QAM signal. The performance of the proposed demodulator is confirmed by computer simulation.

This paper shows a Direct-Sequence Spread-Spectrum (SS-DS) demodulator using block signal processing. One of the difficulties in applying SS-DS techniques to the packet radio network is that each packet needs a long initial-acquisition time for despreading. The acquisition time causes the large degradation of the data transmission efficiency. Our proposed SS-DS demodulator uses the block signal processing, unlike the conventional SS-DS demodulators using real time signal processing. Received signal demodulated quasi-coherently is once stored in memory, and after extracting matched-pulse timing and estimating carrier offset, the signal is demodulated. Incoming data, therefore, are all demodulated without being lost by the initial-acquisition time, and our proposed SS-DS demodulator can provide the higher data transmission efficiency.

In this paper, we propose a method of unicast and broadcast packet sharing for the orthogonal frequency division multiplexing (OFDM) multi-base station (BS) indoor wireless communication system using an adaptive array antenna on mobile terminals. The adaptive array antenna placed on the mobile terminal allows quality improvement due to the diversity effect when the data transmitted from all BSs are the same, and provides capacity improvement by channel sharing when the data from each BS are different. In the proposed sharing method, unicast packets are transmitted independently from multiple BSs in order to increase the communication capacity, and broadcast packets are transmitted simultaneously with other BSs in order to enhance the communication quality without retransmission. Furthermore, by modifying the packet assignment procedure, we confirm that quality can be improved for unicast packets in a low traffic environment.

This letter clarifies properties of cutoff rate R0 of photon channels using coherent state and photon number state as quantum state of light. The relation between cutoff rate improvement and energy saving rate is found, when one uses the number state instead of coherent state.

The plan of High Altitude Platform Station (HAPS) is considered as a revolutionary wireless system plan with several economic and technological advantages over both space- or ground-based counterparts. In this paper, we propose a joint system of terrestrial and HAPS cellular for Wideband-CDMA mobile communication. This system makes the conventional terrestrial W-CDMA cellular area smaller and the remainder area covered by HAPS to increase the total capacity. Furthermore in down link channel, we introduce the polarized wave and doughnut-like radiation. However, in the proposed system, the performance would be dependent on the terminal position especially near the boundary of doughnut-like cell zone. To overcome this, site diversity that uses both signals from terrestrial Base Station and HAPS Base Station is also introduced. To confirm the availability of the proposed system, we evaluate the system performance by computer simulation.

Transmit diversity gain can be obtained in cooperative communication by cooperating the multiple users with single antenna. In cooperative communication, in the first step, each mobile station (MS) transmits its own data to both the base station (BS) and the other MS. In the second step, each MS's data is transmitted from the other MS to BS. As a result, transmit diversity gain can be obtained without implementing multiple transmit antennas at MS. In the conventional relay method, if error is detected within the received packet by using cyclic redundancy check (CRC) code, MS transmits its own data to BS instead of relaying the other MS's data in the second step. As a result, transmit diversity gain cannot be obtained. In this paper, we propose a novel cooperative method. In the proposed method, if the CRC decoder detects error within the received packet, MS transmits soft decision symbol which is obtained from the decoded data in second step. As a result, the transmit diversity gain always can be obtained. From the computer simulation, we show that the proposed method can achieve the better error rate performance than the conventional one.

We propose Direct Sequence CDMA with Optical Multicarriers and Parallel Forward Error Correcting (PFEC) coding technique. Proposed DS-CDMA with OPTICAL MULTICARRIERS, is new in lightwave systems and its alliance with PARALLEL FEC codes, makes it further unique. Optical multicarriers approach is effective to increase throughput by combating dispersion and ISI (Intersymbol Interference), whereas FEC is effective to increase reliability by diluting interactions among optical multicarriers. Till now, both the techniques in lightwave systems have been discouraged. The former because of the wandering effect of optical multicarriers owing to unstability of laser diodes and later because it involves insertion of parity bits that changes data rate and results in insertion distortion that is not desirable in optical systems. To avoid change due to spreading code we also propose to take spreading code equal to serial to parallel converted streams. It bounds initial data (before S/P conversion) to data per carrier (after S/P conversion and spreading) on one hand and relaxes the requirement of high speed electronics on the other. The alliance of optical multicarriers with suitably applied FEC that we refer as Parallel FEC (PFEC) is effective as the beneficial aspects of each mitigate the shortcomings of the other and make the system practicable. Theoretical treatment confirms that the proposed approach is fundamentally sound and holds the potential for promising network performance.

Multiple-input multiple-output (MIMO) multiplexing has recently been attracting considerable attention for increasing the transmission rate in a limited bandwidth. In MIMO multiplexing, the signals transmitted simultaneously from different transmit antennas must be separated and detected at a receiver. Maximum likelihood detection with QR-decomposition and M-algorithm (QRM-MLD) can achieve good performance while keeping computational complexity low. However, when the number of surviving symbol replica candidates in the M-algorithm is set to be small, the performance of QRM-MLD degrades compared to that of MLD because of wrong selection of surviving symbol replica candidates. Furthermore, when channel estimation is inaccurate, accurate signal ranking and QR-decomposition cannot be carried out. In this paper, we propose an iterative QRM-MLD with decision directed channel estimation to improve the packet error rate (PER) performance. In the proposed QRM-MLD, decision feedback data symbols are also used for channel estimation in addition to pilot symbols in order to improve the channel estimation accuracy. Signal detection/channel estimation are then carried out in an iterative fashion. Computer simulation results show that the proposed QRM-MLD reduces the required average received Eb/N0 for PER of 10-2 by about 1.2 dB compared to the conventional method using orthogonal pilot symbols only.

The Orthogonal Frequency Division Multiplexing (OFDM) system is one of several suitable candidates for use in broadband wireless communications. However, due to multipath propagation, the received signal suffers from frequency-selective fading which causes significant degradation of system performance. Antenna diversity reception is widely used to solve this problem. However, this approach is not suitable for the downlink, because it increases the complexity and power consumption of the mobile station (receiver). In this paper, we consider closed-loop mode transmit diversity for OFDM, instead of diversity reception, to improve the performance in the downlink. The base station (transmitter) has several transmit antennas and each antenna is weighted by a weighting factor calculated based on feedback information (FBI). This system is a closed loop, since the FBI is fed back from the receiver. We propose a new weight generation scheme by making use of the correlation between adjacent OFDM subcarriers. The performance is evaluated under a broadband wireless channel model by computer simulation. The results show that the proposed weight generation scheme exhibits better performance than the conventional weight generation scheme without increasing the number of the FBI bits in the uplink.

Recently, there have been intensive studies on protocol methods and applications of short range inter-vehicle communication network (SR-IVCN) and systems. The purpose of the studies is to improve the safety of road traffic systems and the smooth control of the traffic flow by providing information to vehicles. Spread spectrum (SS) communication systems are able to simultaneously communicate and measure the distance between the terminals, thus it is advantageous to apply the spread spectrum technique to inter-vehicle communications. This paper assumes that the vehicles incidentally close to each other, form and manage a locally autonomous decentralized dynamic network. An R-ALOHA (Reservation-ALOHA) protocol for the spread spectrum inter-vehicle communication network using head spacing information is proposed which improve the conventional slot reservation methods. Since the near-far problem in SS communication is one reason for the degradation of system performance, this proposed scheme is shown to improve the efficiency of communication. The performance of the proposed system in the environment where the vehicles are assumed to run freely on a highway is verified by computer simulation. It is shown that inter-vehicle communication can be smoothly carried out between one vehicle and the surrounding vehicles using the propose method.

This paper proposes a new multi-band received signal strength (MRSS) fingerprinting based indoor location system, which employs the frequency diversity on the conventional single-band received signal strength (RSS) fingerprinting based indoor location system. In the proposed system, the impacts of frequency diversity on the enhancements of positioning accuracy are analyzed. Effectiveness of the proposed system is proved by experimental approach, which was conducted in non line-of-sight (NLOS) environment under the area of 103 m2 at Yagami Campus, Keio University. WLAN access points, which simultaneously transmit dual-band signal of 2.4 and 5.2 GHz, are utilized as transmitters. Likewise, a dual-band WLAN receiver is utilized as a receiver. Signal distances calculated by both Manhattan and Euclidean were classified by K-Nearest Neighbor (KNN) classifier to illustrate the performance of the proposed system. The results confirmed that Frequency diversity attributions of multi-band signal provide accuracy improvement over 50% of the conventional single-band.

A computational cost reduction scheme for a post-distortion type nonlinear distortion compensator of OFDM signals is proposed, and compared with the conventional sub-optimum detection scheme. The proposed scheme utilizes the principle that a complex OFDM signal can be demodulated with not only both I-phase (real part) and Q-phase (imaginary part) components, but also either of them. Usually each phase of an OFDM signal exhibits different signal envelope and they are distorted differently by the nonlinearity of a power amplifier. Consequently, three output sequence patterns can be obtained at the receiver. By comparing these outputs, we can know the erroneous positions of these sequences to some extent. By the aid of this comparison, we need to evaluate only a limited number of replicas for the compensation process of the post-distortion type nonlinear distortion compensator, which results in the computational cost reduction. We have proposed four new compensation schemes based on this idea and derived their performance in terms of the bit error rate and the average number of calculations.

Recently, many researches on associative memories have been made a lot of neural network models have been proposed. Bidirectional Associative Memory (BAM) is one of them. The BAM uses Hebbian learning. However, unless the traning vectors are orthogonal, Hebbian learning does not guarantee the recall of all training pairs. Namely, the BAM which is trained by Hebbian learning suffers from low memory capacity. To improve the storage capacity of the BAM, Pseudo-Relaxation Learning Algorithm for BAM (PRLAB) has been proposed. However, PRLAB needs long learning epochs because of random initial weights. In this paper, we propose Quick Learning for BAM which greatly reduces learning epochs and guarantees the recall of all training pairs. In the proposed algorithm, the BAM is trained by Hebbian learning in the first stage and then trained by PRLAB. Owing to the use of Hebbian learning in the first stage, the weights are much closer to the solution space than the initial weights chosen randomly. As a result, the proposed algorithm can reduce the learning epocks. The features of the proposed algorithm are: 1) It requires much less learning epochs. 2) It guarantees the recall of all training pairs. 3) It is robust for noisy inputs. 4) The memory capacity is much larger than conventional BAM. In addition, we made clear several important chracteristics of the conventional and the proposed algorithms such as noise reduction characteristics, storage capacity and the finding of an index which relates to the noise reduction.

In this paper, we propose a multiple access technique using a simple interference canceller for common code transmission. In the proposed system, we adopt a common code for a receiver oriented system. All the transmitters utilize the same pseudo noise (PN) code to communicate with a receiver. Here the receiver structure becomes very simple with only one matched filter (MF). The proposed system has two very important merits. One is to avoid packet collisions by means of an interference cancellation method based on a common code chip shift transmission technique. That is, in order to avoid interference, which occurs because all the received signals have the same PN code, the same data with different timing are transmitted in two channels. In this study, we define and evaluate three types of packet collision which can be reduced by the canceller. The other merit is to reduce the system degradation due to the correlation side-lobes by means of a side-lobe canceller. In spread spectrum (SS) communication systems with PN codes like M-sequences, the correlation side-lobes appear at the detector in the case of the polarity data changing from 1 to 1 . The side-lobes degrade the system quality. Therefore in this system a interference canceller operates to cancel the correlation side-lobes and attempts to reduce the system degradation. Finally, by our cancellation method it becomes possible to realize a simple multiple access using only one PN code under the condition of a receiver oriented system without a base station.

CATV networks are considered as promising transmission channels in that they permit wide bandwidth and high quality data communications. In apartment houses, however, the ingress noise in the up-links due to the tree and branch structure of a network deeply degrades the transmission performance of data communication channels. This is a serious problem especially in apartment houses which are often equipped with old coaxial cables. It permits the noise generated from electrical appliances to disturb up-link data communications. In this paper, we propose a wireless CATV system. In the proposed system, the noise generated in the room of a subscriber does not intrude into a trunk line. We analyze the upstream channels of this system. Based on the results of numerical analyses, we found that the proposed system is suitable and practical for up-link operation in CATV networks for apartment houses.

High speed home networks may lead high speed non-public networks (consumer communication networks) in this ten years. We find many high speed audio and visual machines in the home which should be connected each other and to personal computers by a home network. On the other hand, people's work is rapidly changing to work including teleworking. Home is becomming a part of office which needs a high speed network to access to the Internet, broadcasting, home database and so on. IEEE 1394 is a standard for high speed wired network in the home and should be extended to a wireless standard. Wireless 1394 discussed recently is shown in this paper.

In this paper, a method of Transmission Power Control (TPC) for Orthogonal Frequency Division Multiplexing Direct Sequence Code Division Multiple Access (OFDM-DS-CDMA), in order to compensate for power attenuation at each subcarrier, is proposed. Instead of assigning same power levels for all-subcarriers, different transmission power levels are assigned to different subcarriers, according to the attenuation of the subcarriers. System performance, in terms of Bit Error Rate (BER), has been evaluated by Monte Carlo simulation. The simulation results presented significant improvement, the proposed system performed much better than the system without TPC. It is shown that the Each Carrier TPC performs better than All Carriers TPC, which all carriers are controlled uniformly, hence Each Carrier TPC is more suitable for OFDM-DS-CDMA system.