Takuro Sato

Cognitive interference management in 3G femtocells

We study a method of cognitive interference management in user-deployed 3G femtocell networks. Each femtocell cognitively recognizes an interference signature from the network environment and opportunistically allocates the proper channel patterns for interference minimization. Simulation results show great channel SINR improvement by implementing our opportunistic channel scheduler. The approach offers a novel view of autonomous spectrum management based on cognitive interference recognition and adaptive channel management.

Performance of handoff algorithm based on distance and RSSI measurements

The performance of a proposed handoff algorithm based on both the distance of a mobile station to neighboring base stations and the relative signal strength measurements is evaluated. The algorithm performs handoff when the measured distance from the serving base station exceeds that from the candidate base station by a given threshold and if the measured signal strength of the adjacent base station exceeds that of the serving base station by a given hysteresis level. The average handoff delay and average number of handoffs are used as criteria for performance. Numerical results are presented to demonstrate the feasibility of the distance-based handoff algorithm, including results for an additional criterion based on relative signal strength. The proposed algorithm is compared with an algorithm based on absolute and relative signal strength measurements and with a solely distance-based algorithm. It is found that the proposed handoff algorithm performs well in a log-normal fading environment when the distance estimate error is modeled by wide-sense stationary additive white Gaussian noise.

Energy Efficiency and Spectral Efficiency Tradeoff in Device-to-Device (D2D) Communications

In this letter, we investigate the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in device-to-device communications underlaying cellular networks with uplink channel reuse. The resource allocation problem is modeled as a noncooperative game, in which each user equipment is self-interested and wants to maximize its own EE. Given the SE requirement and maximum transmission power constraints, a distributed energy-efficient resource allocation algorithm is proposed by exploiting the properties of the nonlinear fractional programming. The relationships between the EE and SE tradeoff of the proposed algorithm and system parameters are analyzed and verified through computer simulations.

Rate Adaptive Reliable Multicast MAC Protocol for WLANs

IEEE 802.11b standard provides 1, 2, 5.5, 11 Mbps data rates. These data rates can be made possible by using different modulation techniques: DBPSK, DQPSK, CCK5.5 and CCK11 respectively. Rate adaptation is the process of dynamically selecting a proper modulation scheme depending on channel conditions in order to improve total throughput. Current rate adaptation protocols deal with unicast links rather than multicast. Channel conditions can be estimated by measuring the received signal strength (RSS) of a feedback message (CTS, ACK). However, IEEE 802.11 standard does not provide feedback messages for MAC layer recovery on multicast frames. This is due to collisions which may occur to simultaneous feedback messages from multicast group members. Therefore, in order to rate adapt multicast, a reliable multicast MAC protocol has to be introduced. In this paper, we propose a protocol which provides multicast reliability to WLANs and enhances its throughput by using rate adaptation. Further, we evaluate our protocol by throughput analysis and computer simulation. Simulation results suggest that our protocol performs better than a related/existing protocol in both throughput as well as reliability performances

Advanced CDMA scheme based on interference cancellation

The pseudorandom noise (PN) code is used for a CDMA scheme to spread the spectrum of user data. When the number of users increases, the signals of other users cause interference noises. The fundamental factor of the interference is dependent on the cross-correlation characteristics of the PN code. A scheme for improving the capacity is proposed, based on interference cancellation. The scheme is evaluated on the characteristics of bit-error-rate (BER) vs number of simultaneous users by computer simulations. It is found that around 60 users are available per cell by the proposed method without error correction and voice activity control. Around eight times the capacity of the conventional correlation scheme is achieved. The configuration of the personal station is effectively reduced in size and cost, because the complicated voice activity control is not necessary, and the IC is installed in the base station.

Wideband CDMA system for personal radio communications

This article describes a wideband spread code-division multiple access (W-CDMA) system for high-capacity and high-quality personal radio communication. This system has been authorized as an EIA/TIA Interim Standard IS-665, T1P1 Trial Use Standard J-STD-015, and ITU-R Recommendation M 1073. The system uses wideband spreading to accomplish good interference immunity, high-quality speech, and high-speed data transmission. The system uses coherent detection (CD) and an interference canceller system (ICS) to enhance the capacity. The CD and ICS use continuous pilot signals in the forward/reverse links to estimate the propagation path parameters. PN and Hadamard sequences are used as the spreading code for minimal mutual interference between traffic and pilot/sync/paging channels. A robust 32 kb/s waveform speech coder, ITU-T COM101+, has been developed to achieve toll-quality speech in the radio environment. This system provides up to 128 voice channels per cell and data transmission up to 64 kb/s by 5 MHz spreading. Unification of low- and high-mobility applications and reduced complexity of system and hardware configurations are accomplished.

Game-theoretic approach to energy-efficient resource allocation in device-to-device underlay communications

Despite the numerous benefits brought by device-to-device (D2D) communications, the introduction of D2D into cellular networks poses many new challenges in the resource allocation design because of the co-channel interference caused by spectrum reuse and limited battery life of user equipments (UEs). Most of the previous studies mainly focus on how to maximise the spectral efficiency and ignore the energy consumption of UEs. In this study, the authors study how to maximise each UEs Energy Efficiency (EE) in an interference-limited environment subject to its specific quality of service and maximum transmission power constraints. The authors model the resource allocation problem as a non-cooperative game, in which each player is self-interested and wants to maximise its own EE. A distributed interference-aware energy-efficient resource allocation algorithm is proposed by exploiting the properties of the nonlinear fractional programming. The authors prove that the optimal solution obtained by the proposed algorithm is the Nash equilibrium of the non-cooperative game. The authors also analyse the tradeoff between EE and SE and derive closed-form expressions for EE and SE gaps.

An Intelligent Hybrid MAC With Traffic-Differentiation-Based QoS for Wireless Sensor Networks

In this paper, we present the Intelligent Hybrid MAC (IH-MAC), a novel low power with quality of service guaranteed medium access control protocol for wireless sensor networks (WSNs). The IH-MAC achieves high energy efficiency under wide range of traffic load. It ensures shorter latency to critical and delay-sensitive packets. The IH-MAC protocol achieves high channel utilization during high traffic load without compromising energy efficiency. The IH-MAC does it by using the strength of CSMA and TDMA approach with intelligence. The novel idea behind the IH-MAC is that it uses both the broadcast scheduling and link scheduling. Depending on the network loads, the IH-MAC protocol dynamically switches from broadcast scheduling to link scheduling and vice versa in order to achieve better efficiency. The scheduling is done in the IH-MAC with a novel decentralized approach where the nodes locally use the clock arithmetic to find the time slot, allocated for it. Furthermore, the IH-MAC uses Request-To-Send, Clear-To-send handshakes with methods for adapting the transmit power to the minimum level necessary to reach the intended neighbor. Thus, the IH-MAC reduces energy consumption by suitably varying the transmit power. The IH-MAC also uses the concept of parallel transmission that further reduces delay. The analytical and simulation results corroborate the theoretical idea, and show the efficiency of our proposed protocol.

Throughput analysis method for hybrid ARQ schemes over burst error channels

A definition of a burst error channel using a Markov model was presented by T. Sato et al. in a previous paper (1991). A throughput analysis method of hybrid automatic repeat request (ARQ) under the burst error channel using the three-state Markov model is described. The hybrid ARQ is studied for the random and burst error correction codes as the forward error correction (FEC) code, and multiframe rejection (MREJ) as the ARQ. The throughput efficiency is obtained with both an infinite buffer memory and a finite buffer memory. The applicable range of the burst error channel is clarified for the hybrid ARQ using random and burst error correction codes. >

A Key Management Scheme for Secure Communications of Information Centric Advanced Metering Infrastructure in Smart Grid

The Advanced Metering Infrastructure (AMI) is the core component in Smart Grid. The cyber security is one of the major concerns and challenges should be prior considered. The Information Centric Networking (ICN) is a promising architecture for the future Internet that disseminates content based on named data instead of named hosts. It will be involved into Smart Grid because its excellent congestion control and self-security can enable more scalable, secure, collaborative and pervasive networking. This paper aims at proposing an Information Centric AMI (ICN-AMI) structure and a novel key management scheme (KMS) for a large number of smart meters (SMs) in this system to ensure confidentiality, integrality and authentication. To validate the scheme, the security analysis, comparisons and NDNsim simulation are done to demonstrate that the proposed ICN-KMS is possible solution for ICN-AMI system.