Research And Implementation Of Algorithm For Handoff In Wireless Network On Android

As the intelligent terminal devices are being widely used,Wi-Fi has become an easy and predominant way of internet connection.In order to overcome the limitation of a single access point(AP)in the coverage of range,multiple APs are distributed in a large range to form a network to guarantee internet connection through an AP in any desired location.Connecting to only one AP at each time results in the handoff process among APs when an intelligent terminal device is moving within the range.This handoff process determines the quality of communication,and thus,its optimization is important especially for VoIP and video streaming transmission communication network.The currently used algorithm of handoff process,termed as “fixed threshold method” in this study,is that the intelligent terminal device starts to scan and identify a target AP when the strength of the signal connected to the current AP is less than a critical level.The disadvantages of this method are as follows.(1)The frequency of handoff process increases when the critical level increases for the purpose of high quality communication,and consequently,the handoff process begins too early to make communication unstable.(2)On the other hand,when the critical level decreases for the purpose of a stable communication,the triggering of the handoff process becomes late,and consequently,the limited time left for handoff process will result in failure in handoff and the communication stays at low quality level for long time.Along with this,the intelligent terminal devices consider the signal strength value as the condition,when select the target AP.It will bring the problems that too much devices will connect the AP which has the better signal value but the performance of communication is terrible,then will make the communication worse.The objectives of this study are:(1)to propose a new algorithm of the handoff process to overcome the disadvantage of the current “fixed threshold method”;and(2)to implement and test this new algorithm on Android operating system.The new algorithm is to start the handoff process at a certain level of signal strength if signal strength is decreasing and will reach the critical level in a certain time.This method was termed as “dynamic threshold method” since the signal strength to trigger a handoff process is not a fixed value which was obviously different from the “fixed threshold method”.This algorithm used the history of signal dynamics and accordingly determined the correct time to start the scanning and identifying steps of the handoff process.The advantages of this dynamic threshold method were as follows.Due to the correct starting time,the dynamic threshold to trigger handoff process is at acceptable level even too early or too late.Thus,the system stability of the new method is better than the “fixed threshold method”.Second,in order to avoid too many devices connect to the AP which signal value is better but has heavy load,it was possible for the algorithm to include other factors such as the load of a target AP for a comprehensive evaluation of the target AP and to repeat this calculation for multiple target APs till a desired AP was found.The new algorithm is coded and tested on Android operation system,and is compared with the “fixed threshold method”.The experimental results show that the new method increases the stability of system and significantly improves the quality of communication.This new method can be implemented at intelligence terminal devices with different operation systems.It shows high potential in business service.