Satoshi Denno

A decoding for low density parity check codes over impulsive noise channels

Power line channel often suffers from impulsive interference generated by electrical appliances. Therefore, power line communication makes degradation due to such impulsive interference. We introduce Middletons class a noise model into a statistical model of impulsive noise environment. In this paper, we apply LDPC (low density parity check) codes and sum-product decoding to additive white class a noise (AWAN) channels. We propose a sum-product decoding which is suitable for AWAN channels. In addition, we show the BER (bit error rate) performance of the proposed sum-product decoding in class a noise environment by computer simulation.

Wireless network coding in slotted aloha with two-hop unbalanced traffic

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.

A fast bit loading algorithm synchronized with commercial power supply for in-home PLC systems

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.

Performance Evaluation of Wavelet OFDM Using ASCET

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.

A Virtual Layered Space Time Receiver with Maximum Likelihood Channel Detection

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.

Throughput Analysis of Wireless Relay Slotted ALOHA Systems with Network Coding

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 influence of time-varying channels synchronized with commercial power supply on PLC equipments

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.

Throughput Analysis of Two-Hop Wireless CSMA Network Coding

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.

Performance analysis of slotted ALOHA and network coding for single-relay multi-user wireless networks

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.

A bit-Loaded OFDMA for in-home power line communications

The in-home broadband power line communication (PLC) is drawing attention to us lately. The broadband PLC has regulation issues for the coexistence with shortwave wireless systems. Therefore, orthogonal frequency division multiplexing (OFDM) is adopted for the broadband PLC. On the other hand, the power line channels suffer from frequency selective fading. It is effective to load appropriate bits on each subcarrier in the OFDM for PLC. In this paper, we propose a bit loading algorithm that maximizes the bit rate by optimizing not only the bit quantity on each subcarrier but also the whole code rate of the forward error correction (FEC) code subject to constraints on the total bit error rate (BER) and power on each subcarrier. Furthermore, we investigate orthogonal frequency division multiple access (OFDMA) as a multiple access scheme on the in-home power line networks. We show that the proposed OFDMA scheme is superior to a time division multiple access (TDMA) scheme from the viewpoint of throughput by computer simulations.