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We present a success prioritized binary exponential backoff algorithm of non-persistent carrier-sense multiple access (NP-CSMA) for vast-area large-scale data gathering with power-limited wireless sensors in order to simultaneously gain the transmission and energy efficiencies of the wireless communication devices in this paper. The proposed medium access control (MAC) mechanism does not require any additional physical-layer functions such as multiple antennas, interference canceller, etc. It has high flexibility and scalability without any complex configuration in an autonomous and distributed manner. In this paper, we provide a performance analysis model to estimate the throughput and consumed energy for the proposed backoff algorithm. We show the validity of the performance analysis model by comparing the analysis results with the simulation results for the number of active nodes more than 500 of interest to us.

Controller area network (CAN) is a communication protocol that has been widely introduced for in-vehicle networks. Recently, CAN with flexible data-rate (CAN FD) has been suggested and it achieves higher data rate. Electronic control units (ECUs) in a vehicle communicate with each other using CAN protocol. Since more ECUs are required to establish advanced vehicle functions, we need additional wiring in a car which leads to the increase of car cost and weight. Complicated wiring topology may make communication links always fail due to the ringing. We have proposed a bipolar NRZ line coding architecture in the data phase of CAN FD to reduce the ringing. However, we need further investigation to clarify its flexibility and scalability. The simulation results show that our proposed method with high-rate CAN FD works well for more flexible and scalable wiring topology with multistage branches.

We apply the L1oyd-Max quantization to a distributed collaborative interference canceller (DCIC) with digital higher-frequency radio (HR) forwarding in order to effectively use the HR-band resources. A destination terminal (DT) achieves higher throughput and earns higher diversity order by gathering the other received signals forwarded from surrounding relay stations (RSs) with HR band even though it mounts fewer receiving antennas than the transmitting antennas at the base station (BS). However enormous HR-band resources are required to forward the received signals which are digitally encoded at the surrounding RSs with sufficiently low latency. We need to develop technology to effectively use the HR-band resources. The simulation results show that L1oyd-Max quantization achieves higher data reliability as compared to the uniform quantization for MIMO-OFDM signal with high peak-to-average power ratio (PAPR).

For future machine-type communication systems, the frame duration will shorten because the sensor data size is small and the PHY rate gets higher. The contention interval caused by the propagation delay and the processing time becomes relatively larger as compared with the frame duration. The advantage of carrier sense function for random access protocols is impaired. To enhance the energy efficiency of wireless communication devices, the frequent use of carrier sense function will not be desirable because the receiver is active during sensing the wireless channel. In this paper, we propose a non-persistent slotted ALOHA (SALOHA) that the transceiver is in the sleep mode except for transmit and observation slots on the assumption of immediate ACK or self ACK. We incorporate a success prioritized backoff algorithm into SALOHA in order to enhance the throughput and reduce the energy efficiency and the delay. We clarify the closed-form expressions of network throughput and per-node consumed current for given saturated network traffic. A network simulator shows the unsaturated network performances such as the network throughput and the average delay. Furthermore, we design the contention window (CW) so as to maximize the network throughput.

Controller area network (CAN) is widely distributed as an in-vehicle communications standard. CAN with flexible data-rate (CAN FD) is defined in the ISO standards to achieve higher data rate than the legacy CAN. A number of CAN nodes are able to connect with a single transmission medium, i.e. CAN enables us to constitute cost-effective bus-topology networks. CAN puts carrier sense multiple access with collision resolution (CSMA/CR) into practice by using bit-wise arbitration based on wired logical AND in the physical layer. The prioritized message is delivered without interruption if two or more CAN nodes transmit messages at the same time thanks to the bit-wise arbitration. However, the scalability of CAN networks suffers from ringing caused by the signaling mechanism establishing the wired logical AND. We need to reduce networking materials in order to reduce the car weight, save the fuel and the cost, and develop a sustainable society by establishing more scalable CAN networks. In this paper, we show the reduced wiring technology for CAN to enhance the network scalability and the cost efficiency.

We propose a new design of success prioritized distributed coordination function (SP-DCF) based on the backoff mechanism of IEEE 802.11 DCF to prioritize the station (STA) after successful transmission, which is called success STA. A design parameter of contention-free threshold offers priority to the success STA. The proposed SP-DCF is a fully distributed control scheme and achieves a higher throughput and a lower frame discard rate as compared with the conventional DCF especially when STAs are densely deployed because the success STA has an opportunity to transmit the next frame without contention. We also develop a performance analysis model which enables to estimate the throughput, frame discard rate, and the number of failures per success under saturated traffic. The simulation results reveal the validity of the developed performance analysis model for the SP-DCF with contention-free threshold and the characteristics in the coexistence of the conventional DCF and the proposed SP-DCF.

Collaborative reception has been proposed to improve the frequency utilization efficiency in wireless networks. This paper proposes adaptive forward link formation that selects not only terminals to forward received signals to the destination but also higher frequency bands for the forward link. More-over, this paper proposes a complexity-reduced algorithm for the selection. The proposed formation achieves about 2-times higher frequency utilization efficiency than the fixed formation. While the proposed complexity-reduced algorithm attains similar frequency utilization efficiency as the exhaustive search, the proposed algorithm reduces the complexity of the selection to almost 1/200 of the exhaustive search.

In the IEEE 802.11 standards used for wireless local area networks (WLANs), an access point (AP) and stations (STAs) have opportunities to transmit the data frame in a basic service set (BSS) by carrier sense multiple access with collision avoidance (CSMA/CA). When there are a large number of STAs with high traffic in the BSS, the throughput from AP to a STA will deteriorate since its transmit opportunities are severely limited. We develop a mathematical model of access control to allocate bandwidth for the downlink from AP to STAs in the saturated traffic. The mathematical model enables us to derive a contention window (CW) size at AP with uniform backoff algorithm such that the downlink bandwidth is guaranteed even in the bidirectional saturated traffic. We show the validity of the CW size obtained from the mathematical model using a network simulator, ns3.

Controller area network (CAN) is a communication standard for in-vehicle networks and is widely employed by a number of vehicle lines. Recently, it is required for CAN to enhance bit rate because in-vehicle devices are becoming high quality and their number is increasing. CAN with flexible data-rate (CAN FD) has been recently developed to enhance the throughput in in-vehicle networks. However, higher bit rate in the data phase of CAN FD will cause severe inter-symbol interference (ISI) due to ringing, and the communication may be disabled. In this paper, symbol detection with OR rule is proposed to improve the bit reliability. The simulation results show that the proposed symbol detection attains higher bit rate than the conventional one for test networks.

Electronic control units (ECUs) in vehicles are interconnected with each other. Controller area network (CAN) is one of standards for in-vehicle networks and is widely employed. However, much more weight and space of wiring harness among CAN devices have been required as upgrading higher-performance networks. In this paper, we propose power over CAN (PoCAN), which is an implementation method of power over data lines (PoDL) under the review in IEEE P802.3bu, for twisted-pair (TP) cables among CAN devices to remove power lines. Unipolar non-return-to-zero (NRZ) line codes are employed in CAN and include mainly direct current (DC) component in the signals so that power superposed unipolar NRZ codes will not be suitable for PoDL. Bipolar alternate make inversion (AMI) and NRZ line codes are exploited for PoCAN because AMI-NRZ codes do not include DC component. The waveforms of PoCAN are analyzed in bus networks complied by a CAN standard with an analog mixed-signal (AMS) simulator. Moreover, experimental trials are conducted to evaluate frame transmission of PoCAN. The simulation and experimental results show that the proposed PoCAN can achieve the simultaneous transmission of data and DC power in one-pair TP cables.

In this paper, we propose a distributed coordination function with successful transmission priority (DCF-STP) based on IEEE 802.11 DCF. DCF-STP will enhance the throughput and reduce the frame discard rate (FDR) in wireless networks because the wireless station (WS) just after the successful transmission has an opportunity to transmit the next frame without contention. We also develop a performance analytical model which enables to estimate the throughput, FDR, and the average number of frame retransmissions with high accuracy for saturated wireless networks. The simulation results show the validity of the developed performance analytical model of DCF-STP and the characteristics in the coexistence of the conventional DCF and the proposed DCF-STP.

Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control.

Network coding is a promising technique for improving system performance in wireless multihop networks. In this paper, the throughput and fairness in single-relay multi-user wireless networks are evaluated. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding are used in the medium access control (MAC) sublayer in such networks. The fairness of wireless medium access among stations (STAs), the access point (AP), and the relay station (RS) results in asymmetric bidirectional flows via the RS; as a result the wireless throughput decreases substantially. To overcome this problem, an autonomous optimization of minimum contention window size is developed for CSMA/CA and network coding to assign appropriate transmission opportunities to both the AP and RS. By optimizing the minimum contention window size according to the number of STAs, the wireless throughput in single-relay multi-user networks can be improved and the fairness between bidirectional flows via the RS can be achieved. Numerical analysis and computer simulations enable us to evaluate the performances of CSMA/CA and network coding in single-relay multi-user wireless networks.

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.

Satellite communications is suitable for multicast communications which can achieve one-to-many delivery because it can broadcast to multiple receiving stations over a wide area. However, packet retransmission is inefficient for satellite communications because of its large delay and bit error rate. In order to avoid packet retransmission, FEC (forward error correction) exploiting error correcting codes have been put to practical use in satellite multicasting. Tornado-type codes are well known as a kind of error correcting codes suitable for multicasting. Tornado-type codes are encoded and decoded in packets. As a result, they are effective for combatting packet losses by buffer overflow or congestion control. Furthermore, their coding and decoding have low time complexity. On the other hand, the bit errors in the packet are processed as a packet loss in decoding because the Tornado-type codes are decoded packet-wise. In this paper, we propose an effective decoding method for bit errors in the packets for Tornado-type codes. We show by computer simulation that the proposed method is effective in bit error environments. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 57– 66, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20361

In this paper, an experiment is conducted to transmit and receive orthogonal frequency division multiplexing (OFDM) modulated packets in the 5 GHz band with a software defined radio (SDR) platform composed of universal software radio peripherals (USRPs) and GNU Radio. The OFDM modulation is complied with the 1:4 scale model of IEEE 802.11a standard. The observed OFDM signals do not satisfy the spectral mask of IEEE 802.11a standard so that an overlapped windowing will be required to satisfy it. The experimental results show that the received sensitivity of -59 dBm attains at the packet error rate (PER) of 1% when subcarriers are modulated by quadrature phase shift keying (QPSK) and the received sensitivity of -61 dBm attains at 1% PER when subcarriers are modulated by binary PSK (BPSK).

The device discovery in Bluetooth is needed before establishing data communications. Almost all Bluetooth slaves are battery-powered so that they should connect with a master through the device discovery for a short time. To prevent the worst case scenario with long device discovery in Bluetooth, the events with long device discovery should be estimated in advance. However, it is intractable to estimate the exact longest device discovery time with Monte Carlo simulations or mathematical analysis because of the probabilistic behavior. In this paper, we reveal the longest device discovery time and the maximum energy consumption in Bluetooth Low Energy (LE) with a probabilistic model checking tool, PRISM. The results show that some parameters in Bluetooth LE will largely affect the energy consumption so that their design criteria will be desired to reduce the energy consumption.

In this paper we consider a large number of wireless terminals that are interconnected by a multihop wireless network called an ad hoc network. Design of routing protocols is a crucial problem in ad hoc networks. Location information of wireless terminals is an effective measure for ad hoc network routing. This paper presents a method to identify network topology implying terminal location and connections among terminals. A modified Self-Organizing Map (SOM) algorithm is proposed to apply to the network topology identification. This method exploits information of the received power levels of the signals that are transmitted by other terminals. This paper has evaluated how network topology is identified by means of an example graph made by random numbers. The results show that only one bit information about the received power level in each terminal can identify network topology accurately with a mean error of about 10% for more terminals than a certain value. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 34–44, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10100

Ad hoc networks have excellent capabilities for data transmission in an environment with an incomplete communications infrastructure, and in mobility and portability of terminals. Routing protocols between terminals in an ad hoc network can be broadly divided into location-aware routing, based on location information on the terminals, and non-location-aware routing, which is not based on location information. In the former, routing can be made accurate and easy by effectively utilizing location information. Hitherto, the use of the global positioning system (GPS) has been most often treated as the means of acquiring terminal location information. However, in location estimation by GPS, electromagnetic waves from multiple location estimation satellites must be received, and the method cannot be applied effectively in an environment in which that condition is not satisfied. This paper proposes the following method of location estimation. Fixed access points whose absolute locations are already known are placed in the network. Then, by using self-organizing maps (SOM), the mutual location information among the terminals is organized, and the location of the home terminal is successively inferred. The feasibility and accuracy of estimation in the proposed method are examined by a computer simulation. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(4): 73–81, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10098

A transmission experiment of a multi-user MIMO system with user selection and linear spatial precoding is conducted and the results are reported. As a low-complexity user selection algorithm, the chordal distance-based user selection (CDUS) algorithm is employed. The testbed used in the experiment is implemented by taking full advantage of the software-defined radio. An amplify-and-forward-based simple channel estimation method is adopted. As a result of the experiment in a conference room, the CDUS algorithm improved both the power efficiency and the interference suppression accuracy compared to the round-robin user selection.

Controller area network (CAN) is one of communication standards for in-vehicle control networks and enables electronic control units (ECU) to communicate various control commands with each other via a CAN bus. It is currently expected to develop CAN with higher rate and higher multiplexing, but the communication may be disabled by inter-symbol interference (ISI) due to ringing. In this paper, short pulse line codes and their symbol detection by weighted majority decision are proposed to achieve CAN with higher rate and higher multiplexing. A network structure is extracted as an evaluation network, which has large ringing duration by analyzing the transmission characteristics. The numerical analysis on received signals shows that the proposed schemes achieve sufficiently high reliability in the evaluation network. A prototype ECU implementing the proposed schemes provide successful communication links which are disabled in the conventional ECU.

Transmit power control to minimize transmit power for multi-user distributed antenna systems (MU-DASs) is necessary to improve spectrum efficiency. In previous work, distributed transmit power control (DTPC) algorithm for cellular MIMO systems has been developed based on uplink-downlink duality. The performance of this DTPC algorithm in MU-DASs is evaluated in this paper because MU-DASs is different from cellular MIMO systems in terms of an effect of the co-channel interference (CCI). Computer simulations show that the sum of transmit power is decreased because of uplink-downlink duality assumption. In addition to this, an advantage of MU-DAS is shown. However, it is shown that the sum of transmit power is not always minimized without optimization of clustering.

In this paper, the end-to-end packet error rate (PER) performance of a space-time block code (STBC) based multi-hop cooperative relaying system is discussed. This system consists of a source, a destination, and two STBC based cooperative relays in each hop. These relays decode their received packets and forward the packets only when no error is found. In this system, there are conditions where the end-to-end PER performance improves with the number of hops. The theoretical end-to-end PER performance of this system have been derived analytically. However, in real-world wireless systems, various practical issues, e.g., timing synchronization and imperfect channel estimation, have a large impact on the performance. To confirm the end-to-end PER performance of this system in actual setup, an in-lab experiment using a fading emulator and four transceivers is performed under Rayleigh fading environment. The experimental results clarify the PER performance of the STBC based multi-hop cooperative relaying system. In addition, the theoretical PER performance is also verified from the experimental results.

Distributed antenna systems (DAS) are studied in order to improve the coverage area of wireless communication systems under transmit power constraint. In order to reduce the computational complexly among clusters, in DAS, it is imperative to control the inter-cluster interference in a decentralized way. In this paper, a distributed power control among clusters for single-user DAS based on Foschini-Miljanic's algorithm is proposed. The objective of the proposed algorithm is to mitigate the interference among clusters and satisfy the desired SINR at each mobile station (MS). In the algorithm, first signal power after MRC at MS in a cluster is calculated, then the transmit power of the BSAs in the corresponding cluster is updated according to the predefined transmit power ratio. In addition, the convergence condition is derived, and the performance of the proposed algorithm is evaluated through computer simulations.

This paper proposes a length aware packet aggregation and coding (LAPAC) scheme that uses packet aggregation and network coding (NC) to improve the throughput of single-relay multi-user wireless networks. Besides, this paper clarifies that the throughput is improved by optimizing the minimum contention window sizes in the IEEE 802.11 based single-relay multi-user wireless networks with LAPAC subject to the constraint achieving fairness between uplink and downlink flows. Computer simulation results show that the throughput of the LAPAC scheme is about 10% higher than that of the conventional ones. The optimized minimum contention window sizes are derived by computer simulations and theoretical analysis. The optimized minimum contention window sizes obtained from theoretical analysis are in good agreement with those obtained from computer simulations, when the number of wireless stations is less than or equal to 15. Furthermore this paper shows that LAPAC scheme outperforms the conventional ones in the case of not only single-rate networks but also multi-rate networks.

In-vehicle signal transmission requires dedicated communication cables such as twisted metal wires and optical fiber cables, which increase the weight and volume of wiring harnesses in vehicles. Low rate in-vehicle power line communication (PLC) systems are investigated to communicate the control data between electronic control units (ECUs) via in-vehicle power lines. To design low rate in-vehicle PLC systems, the communication channels are analyzed. It is shown that the channels are mainly characterized by frequency selective attenuation and narrowband impulsive noise. In this paper, a model of impulsive noise is presented for in-vehicle PLC and effects of carrier frequency selection and analog limiter on narrowband impulsive noise channels are analyzed in binary phase shift keying (BPSK), differential BPSK (DBPSK), and on-off keying (OOK). The simulation results show that DBPSK and differential detection with hard limiter achieve high reliable and cost-effective communications for low rate in-vehicle PLC systems.

Network coding is a promising technique for improving system performance in wireless multihop networks. In this paper, the throughput and fairness in single-relay multiuser wireless networks are evaluated. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding are used in the medium access control (MAC) sublayer in such networks. The fairness of wireless medium access among stations (STAs), the access point (AP), and the relay station (RS) results in asymmetric bidirectional flows via the RS; as a result the wireless throughput decreases substantially. To overcome this problem, an autonomous optimization of minimum contention window size is developed for CSMA/CA and network coding to assign appropriate transmission opportunities to both the AP and RS. By optimizing the minimum contention window size according to the number of STAs, the wireless throughput in single-relay multi-user networks can be improved and the fairness between bidirectional flows via the RS can be achieved. Numerical analysis and computer simulations enable us to evaluate the performances of CSMA/CA and network coding in single-relay multi-user wireless networks.

This paper proposes a medium access control (MAC) protocol with network coding on relay nodes for contention-based multihop wireless relay networks. The proposed protocol is called coded packet priority access (CPPA) protocol in which coded packets have higher transmission opportunity than non-coded native packets at relay nodes. In this paper, the performance of coded packet immediate access (CPIA) protocols, which are a subclass of CPPA protocols, is evaluated for single-relay bidirectional symmetric traffic and upper and lower bounds of analytical throughput are derived for any given node traffic. It is shown that the lower bound approximates to the throughput obtained from computer simulations with high accuracy. The conventional slotted ALOHA protocol with network coding (S-ALOHA/NC) is required to adapt the transmission probability of relay node to a rational function of node traffic so as to maximize the throughput whereas the CPIA protocol achieves the maximal throughput only if the relay node transmits no native packets. Furthermore it is clarified that the CPIA protocol is superior to the S-ALOHA/NC protocol in delay for given retransmission probabilities of user nodes.

In this paper, we introduce, a new method named “Complexity Reduction Method based on Compensation Distance” in order to reduce the complexity of the detection in virtual layered space-time receivers in multiple-input multiple-output (MIMO) systems. Moreover, this method is practical even when the number of transmitting streams is greater than that of receiving antennas. Computer simulations indicate that the proposed method can be used to reduce the complexity of detection to approximately 20% in [8×4] (the transmitter is equipped with 8 antennas and the receiver is equipped with 4 antennas) systems.

This paper considers two-hop wireless systems employing network coding and a carrier sense multiple access (CSMA) protocol. Network coding is a recent and highly regarded technology for the capacity enhancement of multiple unicast and multisource multicast networks. The two-hop wireless CSMA systems are often involved with the hidden node problem, but the impact of the hidden nodes on network coding has not been analyzed in theory. This paper provides explicit expressions of the throughput for single-relay two-hop wireless CSMA systems both without and with network coding. The throughput can be obtained from these expressions for given system parameters even when end nodes via the relay node are hidden each other. Furthermore it is shown that the transmit probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput for CSMA systems with network coding. It is clarified that the throughput for CSMA systems can be enhanced as compared with that for slotted ALOHA systems in case of non-hidden end nodes whereas it deteriorates considerably in case of hidden end nodes.

In-vehicle signal transmission requires dedicated communication cables such as twisted metal wires and optical fiber cables, which increase the weight and the volume of wiring harnesses in vehicles. Furthermore, the number of electronic control units (ECUs) and the other electronic devices in vehicles is increasing. As a result, in-vehicle networks are becoming more and more complex and unstable. In-vehicle power line communication (PLC) system has been proposed to carry out signal transmissions between ECUs via in-vehicle power lines. The in-vehicle PLC system simplifies in-vehicle networks and reduces the weight and the volume of wiring harnesses. To design communication systems, we analyze communication environments which are mainly characterized by propagation channels and additive noise. In this paper, the measurement and the analysis of frequency responses for in-vehicle power lines are presented to analyze the propagation channels. Thus we observe frequency-selective fading channels which have several notches in the frequency domain because of reflection of signals at impedance mismatching points.We also analyze the noise and the interference in order to design reliable communication systems. For this purpose, the measurement and analysis of the noise on in-vehicle power lines are presented. A lot of bursty impulsive noises are observed while actuators in vehicles are active. A time-frequency analysis is applied to the observed noise and we show time-varying frequency spectra of the observed noise. Finally, we discuss in-vehicle PLC schemes which are suitable for signal transmissions.

This paper presents achievable regions in slotted ALOHA throughput both without and with network coding for one-relay two-hop wireless networks between two end node groups. In this paper, there are no restrictions on the total traffic and the number of end nodes per group. It follows that the relay node will be generally involved with asymmetric bidirectional traffic. This paper derives closed-form expressions of the throughput and packet delay per group both without and with network coding from a theoretical perspective regardless of whether the buffer on the relay node is saturated or not. Furthermore, we show that the maximum throughput per group with network coding can be achieved at the boundary of the relay buffer saturation and unsaturation which is expressed as the solution of a polynomial equation in two group node traffics. As a result, we clarify the enhancement of the achievable region in slotted ALOHA throughput by applying network coding.

Control signal networks in vehicles using dedicated communication cables such as twisted wires and fiber optics cables have been built in order to communicate between electronic control units (ECUs). However, there are problems such as the increase in weight of the cable harness and the difficulty to insure the reliability of complicated network architectures. Communication systems using in-vehicle power lines have been investigated. This paper proposes an impulse detection scheme and its four criteria to decide the impulse occurrence in a communication cycle by using the two-state hidden Markovian-Gaussian noise model for noise on in-vehicle power lines. The new scheme involves the maximum a posteriori (MAP) estimation using the Baum-Welch (BW) algorithm and the moment method to estimate the model parameters. The proposed scheme is applied to noise generated from the hidden Markov model and noise observed on in-vehicle power lines and investigate their detection accuracy. It is shown that the detection accuracy is substantially improved by using an impulse occurrence criterion based on the number of free parameters.

In this study, we develop a virtual layered spacefrequency communication architecture. This architecture enables the decoding of transmitted OFDM (Orthogonal Frequency Division Multiplexing)-QPSK signals even if the number of antennas at the transmitter is twice the number of antennas at the receiver over multipath fading channels. Furthermore, we propose two detection schemes called "hard replica" and "soft replica." In addition, in order to improve the performance of this architecture, we propose an iteration in which the receiver decodes the detected signals; through such iterations, this architecture can obtain path diversity and achieve high performance. When the transmitter has four antennas and receiver has two antennas, the proposed architecture achieves BER of 8 × 10-4 using the soft replica at Eb/N0 = 15 dB. Furthermore, by performing more iterations, it provides additional gains of 3 dB. The performance of the proposed architecture is verified using computer simulations.

In this study, we develop a virtual layered space-frequency communication architecture. This architecture enables the decoding of transmitted OFDM (Orthogonal Frequency Division Multiplexing)-QPSK signals even if the number of antennas at the transmitter is twice the number of antennas at the receiver over multipath fading channels. Furthermore, in order to improve the performance of this architecture, we propose an iteration with prior probability in which the receiver decodes the detected signals; through such iteration, this architecture can obtain path diversity and achieve high performance. When the transmitter has four antennas and receiver has two antennas, the proposed architecture achieves BER of 8×10−4 at E b /N 0 = 13.5 dB. Furthermore, by performing more iterations, it provides additional gains of 5 dB. The performance of the proposed architecture is verified using computer simulations.

This paper deals with two representative bidirectional traffic cases in two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement of multiple unicast and multisource multicast networks. The relay nodes are generally involved with unbalanced multidirectional traffic, but the impact of the unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput of slotted ALOHA systems with network coding in two-hop bidirectional traffic cases.

This paper proposes a novel receiver architecture named as "Virtual layered space time reception" for MIMO wireless communication systems. In the proposed reception architecture, a transmission signal is regarded to comprise a sign signal and fractional phase shift. The phase shift combined with wireless channels are dealt as a virtual channel. Then, the sign signal which is assumed to be transmitted over the virtual channel is detected by a serial interference canceler (SIC) like V-BLAST. The receiver based on the proposed architecture can detect more data streams than the number of received antennas, even though the architecture applies the SIC. This means that the receiver based on the proposed architecture can form more communications channels between the transmitter and the receiver than the number of received antennas. Therefore, the proposed architecture has potential of increasing channel capacity. Actually, computer simulation result shows that the proposed receiver attains superior performance even when the number of transmit antenna is twice as many as that of the received antennas.

In this paper, we propose an initial acuisition method for channel synchronization on in-home broadband power line communication (PLC). It has been considered that the time fluctuation in the transfer function has been smaller than that in the noise on the in-home broadband PLC. However, we have observed that the extensively and rapidly time fluctuation across the whole frequency band appears in the in-home PLC at the half of power cycle intervals while connecting some switching power supply devices. Such largely and quickly time fluctuation makes the extensive degradation in performance of in-home PLC devices. Therefore, we should estimate the timing of time fluctuation and synchronize the in-home PLC systems with the estimated time fluctuation. We evaluate the performance of the proposed initial acquisition method under impulsive noise environments and investigate its feasibility for the real in-home PLC.

The regulation on power line communication (PLC) has been eased in Japan, and the frequency band between 2 and 30 MHz can be used for in-home PLC. Several different types of commercial PLC equipment are available in the market. Almost all of them include PLC adapters that interconvert Ethernet signals and power line signals. An in-home network can easily be constructed by using these PLC adapters because there are many power outlets in every room. However, there are various factors that tend to destabilize the communication among PLC adapters. These factors involve time-varying channel response and noise characteristics, which are both synchronized with the power frequency. In particular, it has been observed that the noise in a power line varies more significantly than the channel response. Therefore, many PLC adapters contain certain features to mitigate the time-varying noise in a power line. We show a number of examples of more significant variations in the channel response synchronized with the power frequency due to the switching regulators used. This paper deals with such a time-varying channel response synchronized with the power frequency. We show that the performance of the PLC adapters suffers due the time-varying channel response and analyze its influences on the PLC adapters.

The regulation on power line communication (PLC) has been eased in Japan and the frequency band between 2 and 30 MHz can be exploited for in-home PLC. Several commercial PLC equipments are available in the market. Almost all PLC equipments take on a form of PLC adapters interconverting Ethernet signals and power line signals. We can construct in- home network by these PLC adapters easily because there are many power outlets in every room. However there are various factors destabilizing the communication among PLC adapters. These factors involve time-varying channel response and noise characteristics which are synchronized with commercial power supply. In particular, it has been seen that the noise on power line has significant variations rather than the channel response. Therefore, many PLC adapters are taking some measures to mitigate the time-varying noise on power line. On the other hand, we show a number of examples of more significant variations of the channel response synchronized with power supply due to some kinds of switching regulators. In this paper, we deal with such the time-varying channel response synchronized with commercial power supply. We show that the PLC adapters suffer from the time-varying channel response and analyze its influence on the PLC adapters.

In-home PLC (power line communication) is one of the most attractive in-home networkings. However, there are a lot of technical issues for the realization of PLC with high rate and high reliability. These issues include the influence of frequency selective and linear periodically time-variant (LPTV) channel synchronized with commercial power supply. In particular, we show that some kind of switching power devices impact deep and deterministic time selectivity for power line channels. The combination of OFDM (Orthogonal Frequency Division Multiplexing) and bit loading algorithm is a powerful tool to increase the bit rate or reliability for quasi-static frequency selective channels including power line channels. However, a quick response will be required for the execution of bit loading algorithm since power line channels are synchronized with commercial power supply. In this paper, we propose a fast bit loading algorithm based on the fractional knapsack algorithm to enhance the bit rate under the condition that the transmitted power is constant. Furthermore, we evaluate the achievable bit rate of the proposed algorithm for the SNR over a power line channel and compare it with the achievable bit rate based on water filling theory.

This paper deals with a simple but essential two-hop wireless relay network employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement on multiple unicast and multisource multicast networks. However, the performance of network coding on wireless relay networks employing random access protocols has not been analyzed. This paper provides closed-form expressions for the throughput and delay on two- hop wireless relay networks both with and without network coding from a theoretical perspective of the slotted ALOHA protocol. The analytical results are derived by solving queueing systems for the buffer activity at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of slotted ALOHA with network coding on a two-hop wireless relay network. Furthermore, this paper clarifies that the throughput is enhanced by controlling the transmission probability of the relay node such that it has considerable opportunity for network coding.

The satellite communication is suitable for the multicast communication because it can broadcast multiple receiving stations over a wide area. The FEC (forward error correction) like tornado-like codes is effective for balk data transmission in the satellite multicast because the packet retransmission is inefficient. The tornado-like codes are exploited for the packet losses by the buffer overflow or congestion control. Yamato et al. proposed an effective decoding against bit errors remained in the packets for tornado-like codes by exploiting a bit-by-bit majority decision. We call this decoding Yamato decoding. In this paper, we propose a new decoding whose performance is improved for that of Yamato decoding. We show the performance of the proposed decoding by computer simulations and is superior to that of Yamato decoding.

Power line communication (PLC) is one of the most attractive communication methods for in-home networks. However, the emissions of unwanted electric waves from PLC system cause harmful interference to other radio communication systems with the same frequency band. Wavelet OFDM (Orthogonal Frequency Division Multiplexing) is expected to be an efficient modulation for PLC because it can make steep and deep notch for any frequency band in the transmit signal power spectrum. However, wavelet OFDM cannot implement the equalization by guard interval (GI) like OFDM and causes performance degradation in multipath channels including power line channels. In this paper, we apply ASCET (Adaptive Sine modulated / Cosine modulated filter bank Equalizer for Transmultiplexers) to wavelet OFDM and evaluate its performance over a multipath power line channel. In particular, we propose an estimation scheme of equalizer coefficients for ASCET that the required preamble becomes short. We compare the performance of OFDM with GI to that of wavelet OFDM with ASCET over the multipath power line channel by computer simulations. As a result, we show that the proposed scheme can achieve the approximately equivalent performance of OFDM with GI by using the shorter preamble as compared to the original scheme.

We propose applying pulse amplitude modulated code shift keying (CSK/PAM) to indoor power line communication (PLC) for the high-speed data transmission at the low electromagnetic wave leakage. However, CSK/PAM system using conventional binary sequence, for example Gold sequence and M sequence, has error floor for real power line channels even with rake receiver because of the poor properties of odd auto-and cross-correlation. Therefore, we propose extending binary sequence to real-valued sequence and we optimize performance in real-valued sequence by minimizing the even and odd, auto-and cross-correlation values. We show that the CSK/PAM system using the optimized real-valued sequence can achieve better BER (bit error rate) performance as compared with that using Gold sequence by computer simulation.

Residential power lines are one of the most attractive communication media for home networking, since every room in a house has multiple power outlets. In general, in-home power line networks have various network components which are not related to communications. The power line network includes many electrical appliances without communication facilities, switches, and so on. These components will cause electrical unbalance of the power line network and increase radiated emissions. We investigate that each power line network component has an impact on the electrical unbalance and the radiated emissions quantitatively by an experiment. As the result, we show that the radiated emissions and the electrical unbalance of the network vary significantly as the wired network components. Furthermore, our result indicates that the radiated emission is especially large in the case where the network contains a fluorescent light or a single-pole switch.