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.

In the Evolved UTRA (UMTS Terrestrial Radio Access) downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference and flexible accommodation of different spectrum arrangements. This paper presents the optimum adaptive modulation and channel coding (AMC) scheme when resource blocks (RBs) is simultaneously assigned to the same user when frequency and time domain channel-dependent scheduling is assumed in the downlink OFDMA radio access with single-antenna transmission. We start by presenting selection methods for the modulation and coding scheme (MCS) employing mutual information both for RB-common and RB-dependent modulation schemes. Simulation results show that, irrespective of the application of power adaptation to RB-dependent modulation, the improvement in the achievable throughput of the RB-dependent modulation scheme compared to that for the RB-common modulation scheme is slight, i.e., 4 to 5%. In addition, the number of required control signaling bits in the RB-dependent modulation scheme becomes greater than that for the RB-common modulation scheme. Therefore, we conclude that the RB-common modulation and channel coding rate scheme is preferred, when multiple RBs of the same coded stream are assigned to one user in the case of single-antenna transmission.

Orthogonal Frequency Division Multiplexing-Direct Sequence/Code Division Multiple Access (OFDM-DS/CDMA) systems provide frequency diversity gain avoiding inter symbol interference (ISI) in a frequency selective fading channel. However, path diversity gain can not be obtained by using conventional OFDM-DS/CDMA schemes. This paper proposes a new multiple antenna transmission system with combined path diversity and frequency diversity. Signal of each antenna is delayed by several chips to create artificial path diversity as well as frequency diversity of multi-carrier transmission in which can then be combined by using a RAKE receiver. Therefore multiple antenna transmission scheme creates a path diversity effect on uncorrelated signals in multi-carriers from each antenna. The received uncorrelated signals can be processed by Maximum Ratio Combining (MRC) diversity without ISI at a RAKE receiver even when we use FFT modulation. As a result, we can obtain combined path diversity and frequency diversity gain effectively by the RAKE system with the combination of multiple antennas.

In this paper, three multiple access schemes, single carrier (SC)-CDMA, multicarrier (MC)-CDMA, and frequency & time spread (FTS)-CDMA, with space time transmit diversity (STTD) are presented for a broadband mobile communication system. In general, broadband communication systems are easily affected by severe frequency selective fading which results in the degradation of the system performance due to the multipath. In order to improve the system performance in such a fading environment, STTD is applied to these CDMA systems. Computer simulation is carried out to evaluate the system performance, and the BER results are compared with each other. From the simulation results, it is found that the performance of MC-CDMA with STTD is better than that of the other systems, and SC-CDMA cannot improve the system performance by using STTD.

In this paper, we evaluate the performance of asymmetric Time Division Duplex (TDD) system that employs Adaptive Modulation and Coding (AMC) and Hybrid ARQ, with consideration of the effect of control delays in TDD. Channel reciprocity characteristic in TDD allows utilization of open loop channel estimation to choose appropriate modulation and coding scheme (MCS) level for AMC. However, control delay in AMC and HARQ depends on TDD time slot allocation formats. Large control delay in AMC will result in false MCS selection due to the poor channel correlation between measured channel state from the received signals and instantaneous channel state of actual transmission with the MCS selected based on the measured channel state. We present an analytical approach to calculate the probability of MCS level selection error in different channel conditions for different asymmetric time slot allocations. From the theoretical and simulation results, it is shown that the instantaneous throughput per slot depends not only on maximum Doppler frequency but also on asymmetric slot allocations. Average delay time that yields error free packet reception in the downlink increases as the number of continuous downlink slots increases.

In this paper, we propose a novel peak-to-average power ratio (PAPR) reduction method for multi-rate orthogonal frequency division multiplexing (OFCDM) based on an orthogonal variable spreading factor (OVSF) code. In the method, the base station assigns two signs of code sequence to each user to maintain the orthogonality among the code sequences that have different lengths. After that, one sign of the code sequence is selected for reducing the PAPR of the OFCDM symbol. Based on theoretical analysis and computer simulation, we show that the proposed method reduces the PAPR for two data rate classes.

A channel coding which combines convolutional coding and M-ary PSK/orthogonal multi-carrier (MPSK/OMC) transmission is proposed. A coding gain is achieved without sacrificing the data rate or occupying extra bandwidth. The proposed coding formula is that the imformation data bits of bit interval Ts are serial to parallel converted to P parallel branches where each branch has a bit interval Tp = PTs. The data bits of the parallel branches are encoded through a rate nP/(n + 1)(2P - 1) convolutional encoding process and the total (n+1)(2P-1) symbol of the encoder output is transmitted by 2P - 1 OMCs where each carrier is modulated by MPSK/OMC (M = 2n + 1). Following performance analysis of a coding form using rate P/(2P - 1) convolutional encoder and BPSK/OMC modulation, a general channel coding combining convolutional coding and MPSK/OMC modulation is discussed.

Capacity of Cellular DS/CDMA systems depends on an amount of co-channel interference (CCI). One of the effective schemes to eliminate the CCI and improve the capacity is CCI cancellers which remove the CCI by subtracting all the regenerated signals of the interfering users. These cancellers, however, suffer from the residual interference due to the symbol errors in the initial decision. Therefore, a canceller which employed error correction in the initial decision has been proposed. In this system, two Viterbi decoders per one user are needed. Therefore, the amount of calculation increases and this causes additional signal processing delay which is not preferable, especially for voice transmission. Here we propose three fast decoding methods by simplifying the second Viterbi decoder which is used for decoding after the cancellation. Method-1 uses information of the first Viterbi decoder. Method-2 utilizes information of the second correlator instead of that of the first Viterbi decoder. Method-3 is the combination of method-1 and method-2. It uses information from both the first Viterbi decoder and the second correlator. The results obtained from the computer simulation show that the ACS reduction ratio reaches up to 80% within 0.5 dB degradation in Es/No.