Akira Yamaguchi

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.

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.

Novel TCP method to suppress the time delay effect in heterogeneous radio systems

The heterogeneous radio system is one approach to cognitive radio and a great candidate for creating a new fundamental network that improves the efficiency of frequency resource usage. In this paper, our target is to aggregate the adaptive link of multiple radio systems into a single rich link. Generally, time delays differ among multiple different radio systems, which cause the TCP performance to deteriorate. We propose two schemes to avoid the degradation. The first is delay adjustment and the second is TCP customizing. The delay adjustment scheme eliminates the time delay difference among multiple or between two links, while the customized TCP scheme performs the function to turn the slow start process of TCP on/off adaptively. When the slow start process is turned off, the congestion window is updated for the effective throughput, based on estimation from the radio environment information instead of the slow start process.

Novel cognitive mobile router and its efficient use in a heterogeneous wireless network

In this paper, we discuss the efficient use of a mobile router with multiple radio access technologies (RATs), called a cognitive mobile router (C-MR). In a heterogeneous wireless network, where various infrastructure-based RATs have already been deployed, C-MR selects a high quality RAT from among those available and provides a high quality mobile communication to connecting Wi-Fi user terminals. However, considering the significant growth in mobile data traffic, a huge amount of mobile data passes through C-MR and critical packet losses may occur due to its limited computational resources. Moreover, if the quality of the selected RAT is insufficient, incoming packets are stacked in C-MR and this leads to performance degradation due to packet loss, timeout and so forth. In this paper, we propose two novel schemes to avoid such redundant performance degradation, one is a novel packet queuing scheme that operates such a huge amount of mobile data traffic properly even with the limited computational resources. The other is an energy-efficient and accurate RAT quality selection method that avoids miss-selection of a suitable RAT. Through computer simulations, we have confirmed that C-MR deployment can realize more 40% packets delivery with higher priority compared with the no C-MR situation even while maintaining lower infrastructure load and lower power consumption of user terminals.