Kanshiro Kashiki

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.

Testbed development and performance improvement of heterogeneous radio networks

Within categories of the cognitive radio system used to attain efficient use of restricted radio spectrum resources, this article introduces some technical results concerning cooperative heterogeneous radio networks. We have developed a testbed to affirm the functions of a heterogeneous radio network, which has abilities to select one system from multiple communication systems and to aggregate multiple systems. First of all, we introduce the activities in the ITU-R and DYSPAN, where the cognitive radio system is under discussion, and clarify the standpoint of our research regarding the heterogeneous radio network. Subsequently, we state the function and specification of the testbed developed. Some experimental results using the testbed are introduced. The testbed is composed of three different communication systems, a controlling system for selecting or aggregating the most appropriate system for the user terminal and networks, and its measurement system. The measurement system is a kind of link simulator to confirm the performance of the controlling system. We also describe an analytical example of evaluating the performance improvement by heterogeneous network controlling. Finally, we address some essential future study issues for practical realization of the heterogeneous radio network.

Heterogeneous wireless networks for reliable communications

This paper introduces the latest status of our undergoing project aiming at reliable communications by heterogeneous wireless networks. This project is one of the new Research and Development (R & D) projects in Japan to attain the efficient use of the precious and scarce radio spectrum resources. A test-bed facility has been developed and their features, specifications and some experimental results are also described. Our project focuses on cooperative heterogeneous wireless networks to improve the reliability of the radio communication links while ensuring efficient use of radio spectrum resources.

Channel occupancy estimation method for Wireless LAN

Channel occupancy is key information to realize efficient operation of the wireless system. Channel occupancy can be defined as the time occupancy ratio in the case of Wireless LAN (WLAN). We propose a novel passive method to estimate the time occupancy ratio of WLAN. The proposed method produces greater improvement in estimation accuracy compared with that of conventional methods. In this paper, we introduce the definition of the time occupancy ratio as the utilization index of a WLAN radio resource. Then, details of the proposal are introduced. Finally, the excellent evaluation results executed on an experimental system are introduced even when many loss packets exist.

Study on Inter-Base Station Link Capacity Sharing using Cognitive Radio Communication

This paper describes a study on beam switching scheme applicable to the cognitive radio communication, from the viewpoint of the efficient use of radio frequency resource, as a function of the response time of Web browsing. The beam switching is time division scheme of the assigned frequency bandwidth among one wireless link and another links. Regarding the radio network, we consider three types of topology. As a result of software simulations, we conclude that the radio beam switching have the better performance in frequency use, comparing with the case of the conventional fixed frequency allocation. Furthermore, we simulate the IP throughput characteristics and response time characteristics of Web browsing in the radio link affected by transmission error.

Downlink Link Aggregation Performance with Delay Adjustment Capability in Multi-Radio Access System

Heterogeneous radio network which efficiently utilizes the resources of multi-radio access systems is one of promising approaches for flexible, reliable and high-capacity communication. Regarding the cooperative controlling functionality in the heterogeneous system, two schemes are considered to be applicable to the efficient usage of multi-radio systems. One is a link selection and the other is a link aggregation which bundles multi-radio access systems. In this paper, the link aggregation is focused and its improvement of the Transmission Control Protocol (TCP) transmission performance over the aggregated link is discussed. The key function of the aggregation is a delay adjustment capability, which compensates the time delay difference among multiple links by addition of the time delay. The performance characteristics are measured by the experimental testbed including LTE, WiMAX and Wi-Fi. The throughput improvement provided by the link aggregation and the effect of the packet re-transmission caused by the link aggregation are addressed.

Experimental and analytical study regarding transmission quality of Wireless LAN system - For implementation of heterogeneous wireless network -

In order to implement the heterogeneous wireless network using multiple wireless systems, it is important to comprehend the transmission quality characteristics such as the transmission throughput and delay, because the network control managements are performed based on these qualities. In this paper, we address the study results regarding the transmission quality characteristics of the Wireless LAN (WLAN) system, which is one of multiple wireless systems. The study covers the experimental examination regarding the statistical distribution characteristic of the transmission quality, their mutual relationship and their time fluctuation characteristic. Based on the established analytical model obtained by the WLAN experiment, we also discuss the method to estimate the delay (or throughput) from the measured throughput (or delay) and its estimation accuracy.

Research project concerning cooperative heterogenious radio networks for reliability improvements

In Japan, several new Research and Development (R & D) projects have been started, whose main purpose is to attain the efficient use of the restricted resources of frequency bands. This paper introduces the objective and outline of the project in which we have been engaged. The test-bed facility has been developed and their features, specifications and some experimental results are also described. Our project focuses on cooperative heterogeneous radio networks to improve the reliability in the radio communication link. The technology developed in the project is considered to be advanced network technology that includes the cognitive radio system being studied in many research organizations.

Study of inter-base station beam switching considering asymmetric broadband transmission in cognitive radio

The authors considered applying cognitive radio to facilitate the efficient use of frequency resources over multiple radio links. They proposed a beam-switching scheme for radio links among inter-base stations and analyzed transmission performance characteristics by response time for Web browsing. The current modeling assumes mobile WiMAX transmissions to be a realistic and efficient form of broadband radio communications. In this paper, the transmission characteristics of inter-base station beam switching are evaluated by software simulations, assuming broadband asymmetric transmission of up- and downlinks. Furthermore, the evaluations extend to cascaded topologies applicable to disaster relief deployment. The results show that beam switching of broadband transmission has better transmission performance than fixed capacity assignment of a band-division transmission depending on conditions in basic and cascaded cases.

Performance characteristics of a signal detection scheme and its estimation method applicable to M-to-M communication System

In mobile radio systems, Machine-to-Machine (M-to-M) communication has recently attracted significant attention. This paper describes the performance characteristics of a signal detection scheme applicable to M-to-M communication, in which machine terminals search their possible operation area where the Base-Station-to-Mobile-Station (BS-to-MS) communication is not using a specific frequency band. The investigated signal detection scheme consists of a signal canceller and a feature detector. For such scheme, we describe the detection performance characteristics by an analysis based on stochastic theory. We also address the estimation method of the detection performance by using detected values in the signal detector. Its estimation accuracy is adequate from the viewpoint of real usage.