A Control Method for Transmission Timing of Control Packets to Prevent the Concentration of Control Packets for Bluetooth MANETs

Abstract

Bluetooth MANETs are Bluetooth-based mobile ad hoc networks (MANETs) which consist of mobile terminals such as Bluetooth-enabled smartphones. In Bluetooth MANETs, a method to quickly establish a connection for Classic Bluetooth (Classic), which has a wide communication bandwidth, and by using Bluetooth Low Energy (BLE) for terminal discovery (Existing method) has been proposed. Bluetooth MANETs are effective as a temporary communication method in time of disaster because terminals can communicate without using communication infrastructure such as base stations. The existing method improves the speed of connection establishment and re-establishment of Classic between terminals, which is expected to occur more frequently compared to Wi-Fi and other technologies in the communication range of Blue- tooth. On the other hand, there is a problem of establishing connections with a large number of terminals in high density areas, which is likely to occur when the network size increases. However, the existing method does not consider the problem of establishing connections with a large number of terminals in a high terminal density area. In this paper, we provided the following contributions. (1) By conducting real terminal-based experiments, we observed the problems that occur when Bluetooth MANETs are applied to a large network size, i.e., when the network size of the existing method is increased, and discussed the causes. In addition, we proposed a method to mitigate the problem and verified the effect of the method using actual terminals. In this paper, we first prepared 50 Android terminals to check the problems that occur when the network size increases, and carefully measured the behavior and problems of the existing method. As a result, in an environment where there are many terminals that applied the existing method, while a terminal executes the process of a Classic connection establishment, re- quests from other terminals to establish a Classic connection (hereinafter referred to as “control packets”) are concentrated. Terminals must execute processes of connection establishment with multiple terminals simultaneously (hereinafter referred to as “concentration of control packets”). At that time, due to the specification of the profile used in Bluetooth MANETs, the success rate of established connections drops rapidly when multiple connection establishment processes are performed simultaneously. As a result, we found that it is difficult to establish connections in an environment where there are many terminals around, making it difficult to disseminate data packets. (2) To solve this problem, we propose a method to establish a connection more reliably by controlling the transmission of control packets (hereinafter referred to as “our proposed method”). First, we investigated the least number of terminals that can reproduce the situation where connection establishment becomes difficult in order to evaluate our proposed method. As a result, we confirmed that when the existing method is conducted with 6 terminals, the same problem occurs as when 50 terminals are used. Therefore, in this paper, we first implement our proposed method on 6 Android terminals and evaluate the performance. (3) In order to evaluate the applicability of our proposed method in an environment with many terminals, we increased the number of terminals from 6 and conducted experiments on actual terminals. As a result, we confirmed that our proposed method can be applied even when there are up to 14 terminals in the communication range.