In this letter, we present a method to generate sets of sequences suitable for multicode transmission in quasi-synchronous (QS) CDMA systems. We focus on Gold code but extension to orthogonal Gold code is straightforward. We show that by appropriate classification of sequences, it is possible to have sets whose cross correlation is small in QS situations.

This paper describes an analytical method to estimate the amount of interference in multibeam non-geostationary satellite systems. The performance of CDMA is compared with that of FDMA (or TDMA) by employing the maximum acceptable number of users per cell in uplink as a measure. Numerical examples shows that the maximum acceptable number of users in FDMA (or TDMA) systems varies according to the altitude of the satellites, while the performance is insensitive to the altitude in CDMA systems. Then, it is found that the superior multiple access scheme depends on the altitude of the satellite.

This manuscript presents a simple scheme to improve the performance of a feedback control system that uses power line channels for its feedback loop. The noise and attenuation of power lines, and thus the signal to noise ratio, are known to be cyclostationary. Such cyclic features in the channel allow us to predict virtually error free transmission instants as well as instants of high probability of errors. This paper introduces and evaluates the effectiveness of a packet transmission scheduling that collaborates with a predictive control scheme adapted to this cyclostationary environment. In other words, we explore the cooperation between the physical and application layers of the system in order to achieve an overall optimization. To rate the control quality of the system we evaluate its stability as well as its ability to follow control commands accurately. We compare a scheme of increased packet rate against our proposed scheme which emulates a high packet rate with the use of predictive control. Through this comparison, we verify the effectiveness of the proposed scheme to improve the control quality of the system, even under low signal to noise ratio conditions in the cyclostationary channel.

Energy harvesting technology was introduced into wireless sensor networks (WSNs) to solve the problem of the short lifetimes of sensor nodes. The technology gives sensor nodes the ability to convert environmental energy into electricity. Sufficient electrical energy can lengthen the lifetime and improve the quality of service of a WSN. This paper proposes a novel use of mutual information to evaluate data transmission behavior in the energy harvesting WSNs. Data at a sink for a node deteriorates over time until the next periodic transmission from the node is received. In this paper, we suggest an optimized intermittent transmission method for WSNs that harvest energy. Our method overcomes the problem of information deterioration without increasing energy cost. We show that by using spatial correlation between different sensor nodes, our proposed method can mitigate information deterioration significantly at the sink.

This paper proposes a new spectrum sharing scheme which uses one-sided collaboration. In the proposed system, the transmitter of the secondary system relays the primary signal and overlays its own data on the retransmitted primary signal. The results of the theoretical analysis show that the proposed scheme with regenerative relay allows the secondary system to communicate at the same speed as the primary system that disregards the presence of the secondary system.

In this manuscript, a layered macro/micro diversity scheme is introduced at the receiver side of a MIMO STBC wireless control system under fading and shadowing environment. The combination of the outputs of micro diversity is based on soft-decision values, while the macro diversity branches are combined based on hard decision values. As a measure of the reliability of the system, the outage probability of frame-error rate is employed. The performance of the proposed system is analytically and numerically evaluated and the impact of the macro diversity in the outage probability is clarified.

Image sensor communication (ISC), derived from visible light communication (VLC) is an attractive solution for outdoor mobile environments, particularly for intelligent transport systems (ITS). In ITS-ISC, tracking a transmitter in the image plane is critical issue since vehicle vibrations make it difficult to selsct the correct pixels for data reception. Our goal in this study is to develop a precise tracking method. To accomplish this, vehicle vibration modeling and its parameters estimation, i.e., represetative frequencies and their amplitudes for inherent vehicle vibration, and the variance of the Gaussian random process represnting road surface irregularity, are required. In this paper, we measured actual vehicle vibration in a driving situation and determined parameters based on the frequency characteristics. Then, we demonstrate that vehicle vibration that induces transmitter displacement in an image plane can be modeled by only Gaussian random processes that represent road surface irregularity when a high frame rate (e.g., 1000fps) image sensor is used as an ISC receiver. The simplified vehicle vibration model and its parameters are evaluated by numerical analysis and experimental measurement and obtained result shows that the proposed model can reproduce the characteristics of the transmitter displacement sufficiently.

We consider a distributed transmission of data packet to a sink where the distance of a sensor node to a sink is much longer than the maximum communication range of each sensor node. We give a simple modification to the transmitter, i.e., multiplication of random phase before the transmission. Thanks to Turbo Code, it is possible to extend the transmission range as the received amplitude varies symbol by symbol for our scheme while whole data packet may be lost for the conventional scheme. In this letter, we report the experimental results of our scheme equivalently developed using visible light communication.

The noise on power-lines is non-stationary, while the instantaneous noise power in different frequency bands are dependent. Under such noise environments, the instantaneous noise power in a frequency band can be estimated by observing the noise in other frequency bands. In this paper, we propose a receiver structure which uses the estimated instantaneous noise power in the decoding process and show its superiority in BER performance to conventional systems.

Throughput analysis of CDMA Unslotted ALOHA with channel load sensing protocol (CLSP) is presented in consideration of the effect of the access timing delay. The access timing delay is defined as the sum of the process time and the propagation time for the packet access control. As CLSP is the scheme to control packet generation by the channel state information from the hub station, the effect of the access timing delay is significant. In our analysis, we extend a continuous-time Markov chain model and queueing systems. As a result, we found degradations of the throughput performance due to the access timing delay. For the value of CLSP threshold, we show that it is smaller than the case without the access timing delay in order to achieve satisfactory throughput. Furthermore, for a large access timing delay, CLSP makes no sense and the throughput is worse than the system without employing CLSP.

Packet-recognition/code-acquisition (PR/CA) is one of the most important issues in packet communication systems. In a CDMA Unslotted ALOHA system, Multiple Access Interference (MAI) may bring about errors in PR/CA. The MAI mainly stems from already recognized packets and newly arriving packets under the execution of PR/CA. This characteristic of asynchronous transmission in CDMA U-ALOHA systems implies that only one or a few packets arrive at the receiver within a short interval of a execution. Furthermore, newly arriving packets are recognized and code-acquired by using a short preamble part. Consequently, the MAI from the packets under the execution of the PR/CA will be small. Focusing on that point, this paper proposes applying the IC scheme in order to suppress the MAI from the already recognized and code-acquired packets. A performance evaluation demonstrates that such an application is valid due to the small amount of MAI from the packets under the execution of PR/CA. In addition, we demonstrates that the scheme reduces false recognition rather than mis-recognition. Such a scheme improves the performance of not only PR/CA, but also the throughput.

This paper discusses the reduction of the amount of transmitted information for the efficient use of frequency resources in wireless feedback control systems, and clarify the effect of the reduction of the amount of transmitted information. As a typical example of the underactuated controlled object, a rotary inverted pendulum is considered. We propose a reduction method for state information fed back from the controller to the controlled object. It estimates angle or velocity state from the previous state. In addition, we propose a reduction method that temporally omits less important control information and state information. Numerical examples clarify the effect of the reduction methods on the control quality. And we show that the reduction methods achieve large reduction of the amount of transmitted information with small disadvantage of the control quality.

In a sensor network, a certain area or environment are observed by a lot of distributed sensor nodes and a sink collects data observed by sensor nodes. The observed data sequences that sensor nodes generate may have space- and/or time-dependent correlation. This correlation is regarded as redundant information and can be used for channel error correction by joint decoder using correlation. In this paper, we propose the joint decoding scheme using the time-dependent correlation consisting of the consecutive data sequences generated by a sensor node. We also propose a power control scheme using the time-dependent correlation for reduction in energy consumption. We evaluate the packet error rate and the energy consumption ratio, and clarify the effect of our proposed schemes.

In narrow band power-line communication (PLC) systems, which use frequency band below a few hundred kHz, the noise on power-line is non-white and non-stationary. Under such environment, the performance of Orthogonal Frequency Division Multiplex (OFDM) modulation system is analyzed, and time and frequency dependence of bit error rate (BER) is clarified. In addition, the possibility of performance improvement with the symbol level repetition coding employing cyclo-stationary feature of power-line noise is presented.

In this letter, we present bit error analysis (BER) of orthogonal multi-carrier direct sequence code division multiple access (DS-CDMA) system with multi-rate (multimedia) traffic. Analysis is carried out with random signature codes for an AWGN channel. Interference in such a system is severe because all users of all media transmit over the same assigned sub-carriers. This makes the analysis difficult. In our analysis, we divide this interference into different types and carry out our analysis to obtain the BER taking into account all these types. We show that the performance of the system is improved as the number of assigned sub-carriers M increases until a limit where the improvement does not continue even when M increases more. This is because of, as we show, the interference due to other sub-carriers becomes constant even in the case of M , and the interference in a multi-rate multi-carrier system is bigger than that in a single-carrier (M=1) by a factor of π2/3.

For reducing bit errors on wireless channels, we have proposed the multiroute coding scheme on multiple routes for wireless multihop networks. In this paper, we introduce ARQ to our multiroute coding scheme. In our multiroute coding scheme, a destination node combines and decodes subpackets which are encoded and divided by a source node. Each intermediate node relays a subpacket, that is, only a part of a packet. Therefore, intermediate nodes cannot detect packet errors, and only a destination node can do so after combining and decoding subpackets. We propose an ARQ scheme between a source node and a destination node. We analyze the proposed ARQ scheme and evaluate the system performance.

We propose a new analytical model of Transmission Control Protocol (TCP) in wireless environments where transmission errors occur frequently. In our proposed model, we consider the exponential increase of a congestion window and the exponential increase of a timeout back-off. Finally, we have clarified the behavior of TCP mechanisms of different versions and TCP throughput characteristics analytically. From our result, the behavior of TCP mechanisms is different in each implementation version. These differences mean that the required characteristics of wireless links are different in each implementation version. Therefore, our proposed model is a base analysis of designing wireless link mechanisms.

The one of the problems in the satellite packet communication system is the existence of a long time delay, which may cause an improper packet access control resulting in a great deal of degradation of the system performance. In this paper, we clarify the effect of long time delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we show that a significant improvement in the throughput performance was obtained with MCLSP even in the presence of a long time delay.

In an attempt to improve the performance under frequency selective fading environment, we develop in this paper an orthogonal frequency division multiplex (OFDM) system in which adaptive interleaving is applied. The adaptive interleaving is a method that assigns symbols adaptively to the subcarriers in order to cope with frequency selective fading based on a channel state information (CSI) sent back from the reception end. The concept of adaptive interleaving is to maximize a free Euclidean distance in the limited interleave size. In this paper, we extend the method by an introduction of bit interleaving and multiple trellis coded modulation (MTCM). MTCM assigns two or more symbols to one trellis branch and shows good performance in frequency selective fading. If we could assign those set of symbols with an aid of the adaptive interleaving, the performance improvement can be expected. Another improvement method considered in this paper is the use of bit interleaving. The bit interleaving techniques randomize the effect of channel more efficiently compared to the case of symbols interleaving. Thus the further performance improvement is expected. One draw back is that since the interleaving process is done in bit level, bit interleaving can not be applied to TCM nor MTCM. In this paper, we mainly focus on adaptive bit and symbol interleaving and discuss the performance from the point of interleaving effect, and the error correcting code (convolutional code and MTCM).