Kosuke Yamazaki

Adaptive Energy Centric Radio Access Selection for Vertical Handover in Heterogeneous Networks

This paper presents an energy efficient radio access network (RAN) selection for vertical handover between heterogeneous networks. The proposed RAN selection switches evaluation bases by application and adaptively selects a RAN with low energy consumption. In addition, the selection employs a penalty function that avoids discarded vertical handovers to reduce handover overhead and network loading by reducing the integrations.

Novel Communication System Selection Applying the AHP Algorithm in Heterogeneous Wireless Networks

In this paper, we propose a novel selection policy for a communication system in heterogeneous wireless networks, which applies the analytic hierarchy process (AHP) algorithm by taking into account the mobility of the user terminals. In particular, the AHP algorithm has excellent characteristics of improving overall performance within the existing wireless systems. We certify the performance improvement by applying the AHP through software simulations under the conditions where Wi-Fi and WiMAX are used in the heterogeneous wireless networks.

Novel Wi-Fi Throughput Estimation Method Considering CSMA/CA Behavior

Wi-Fi is one of the solutions to overcome the explosion of mobile data traffic and improvement of Wi-Fi performance intensifies the cellular data offload to Wi-Fi. Wi-Fi AP (Access Point) selection at the STA (STAtion) is a key function to improve Wi-Fi throughput. Our proposed method is practical for the AP selection. If an STA can know the throughputs between the STA and surrounding APs before exchanging Wi-Fi packets with an AP, the STA can select the optimum AP that promises high throughput. In this paper, we focus on a throughput estimation method that is applicable to AP selection, and discuss the accuracy of the estimated throughput. We propose a novel Wi-Fi throughput estimation method with passive measurement and without modification for the Wi-Fi standard. The proposed method consists of three stages: measurement of the time ratio used by each Wi-Fi device, selection of dominant Wi-Fi devices and calculation of estimated throughout. Our proposed method considers the influence of CSMA/CA that affects Wi-Fi throughput that changes based on the number of Wi-Fi devices sharing the same frequency band and the traffic load of each device. We evaluate the effectiveness of the proposed method by experiments (estimated before communication) and compare the estimated throughput and the actual throughput (measured during communication) in certain environments. The proposed method is effective for estimating Wi-Fi throughput. The RMSE (Root Mean Square Error) of the proposed method decreases to 29~33% that of conventional methods. Estimated throughput with our proposed method is always higher than measured throughput. Therefore, modification of the proposed method to decrease the difference between the estimated and measured value is a subject for future study. As some systems influence Wi-Fi, considering these influences in a throughput estimation process is also recommended.

Performance Evaluation of Centralized Control Algorithm for Channel Allocation in Pico-Cell System

In a pico-cell architecture, co-channel interference between adjacent cells can cause serious problems. With a centralized control approach based on interference information reported by each subscriber station (SS), we propose a novel channel allocation algorithm applying the graph theory. This method directly determines the optimal channel allocation and minimizes inter-cell co-channel interference. Both computer simulations and experiments based on the implementation demonstrate that our proposed algorithm is effective.

Energy efficient wireless link monitoring using probability inequality for vertical handover

This paper proposes a new way of measuring signal to interference and noise ratio (SINR) at a low level of power consumption for vertical handover. In order to select the most suitable radio access networks (RAN) in vertical handover, the SINR of the alternative RAN should be measured at a certain interval while communicating with the existing RAN. In our proposal, the SINR measurement interval for the alternative RAN is controlled on the basis of SINR fluctuations in order to maintain high tracking ability and reduce power consumption during monitoring operations for vertical handover. In addition, a simple probability inequality is applied to detect SINR fluctuations with high precision and achieve low computational complexity. The effectiveness of the proposed monitoring method was verified through computer simulations and the results showed that the averaged SINR could be measured to an accuracy of about 1 dB while maintaining sleep mode at about 30%.

Radio access selection method designed to enhance node availability in multi-mode wireless sensor network

To utilize wireless sensor networks (WSN) effectively, maximization of network lifetime and minimization of response time to data queries are very important issues. To enhance the functionality and availability of conventional WSNs, we propose the new concept of a Multi-Mode Wireless Sensor Network (MM-WSN) in which nodes with only limited battery power are equipped with different types of radio access technologies. Nodes in a MM-WSN can use both single-hop and multi-hop delivery of data and select the most suitable option according to the situation. In this paper, we show that our proposed method provides a radio access selection method that achieves energy-efficient and high-speed data reports. The effectiveness of our proposal is shown by means of computer simulations.

Performance Evaluation of Novel Frequency Channel Allocation Algorithm for Pico-Cell System

In pico-cell architecture, although utilizing a simple base station and a simplified allocation design help to reduce bit cost, frequency channel interference between/among adjacent cells becomes a serious problem. The pico-cell system is supposed to be used mainly for packet-based communication and the carrier to interference power ratio (C/I) degradation leads to poor network performance. To overcome this drawback, we propose a novel channel allocation algorithm, i.e., a centralized approach that works based on interference information reported by each subscriber station (SS). Both computer simulations and experiments based on implementation clarify that our proposed algorithm is effective

Systematic coexistence scheme for an additional radio system in the operating area of an existing radio communication system

This paper proposes a systematic coexistence scheme for a new radio communication system (secondary system), which is additionally introduced to the service area being operated by an existing communication system (primary system). The same frequency band is allocated for both systems. Our proposal is to protect the primary system from interference, on the basis that the primary and secondary systems work cooperatively with each other. For this objective, we propose the deployment of signal detectors in the operating area of the primary system and also the gathering of information regarding the signal detection. Such information is used for estimating the area, where an additional radio system is allowed to operate. A signal detection scheme with high sensitivity is also proposed that has the ability to detect a weak interference signal under the condition of mixed primary and secondary signals, to confirm that the secondary system does not causes harmful interference to the primary system. By using the concept of non-detection probability of the secondary system, we address the systematic scheme to introduce an additional radio system in the operating area of an existing radio communication system.

Evaluation of radio link selection with Analytic Hierarchy Process algorithm in heterogeneous radio networks

A multi-access radio network that efficiently utilizes radio resources is a promising approach to flexible, reliable, high-capacity communication. Regarding cooperative controlling functionality in a heterogeneous radio network, two schemes are considered to be applicable to the efficient usage of multi-radio systems: link selection and link aggregation. This paper focuses on link selection and its improvement of Transmission Control Protocol (TCP) throughput with an Analytic Hierarchy Process (AHP) algorithm in comparison with two conventional algorithms of the fixed priority scheme (Priority) and the maximum transmission rate scheme (MaxRate). Because the characteristics of transmission delay influence the behavior of the TCP protocol, the impact of three kinds of delay (RTT: round trip time, DL delay: downlink delay, and UL delay: uplink delay) are compared to find which delay is suitable for a metric of the AHP algorithm. According to the simulation results, using RTT as a metric shows 22% and 400%, at maximum, better improvement in throughput compared to MaxRate and Priority, respectively.

Feature Detection Scheme Using Cyclic Prefix (CP) in OFDM: Its Application and Performance

This paper describes study results regarding a feature detection scheme using a Cyclic Prefix (CP) that is appended to an OFDM signal. The detection scheme is especially important when used as a sensing technology in advanced systems such as Device-to-Device communication. Herein, several performance characteristics of the signal processing involved in the feature detection are described with an analytical expression and examined with software simulation. Then, supposing that two OFDM systems using different CP lengths are operated in the same frequency band, some applications are addressed such as an estimation method for the Input C/N (Carrier-to-Noise power ratio), a system discrimination scheme and a timing offset detection method.