Nowadays, several positioning systems are available for outdoor localization, such as the global positioning system (GPS), assisted GPS (A-GPS), and other systems working on cellular networks, for example, time difference of arrival (TDOA), angle of arrival (AOA) and enhanced observed time difference of arrival (E-OTD). However, with the increasing use of mobile computing devices and an expansion of wireless local area networks (WLANs), there is a growing interest in indoor wireless positioning systems based on the WLAN infrastructure. Wireless positioning systems (WPS) based on this infrastructure can be used for indoor localization to determine the position of mobile users. In this paper, we present a novel wireless positioning system, based on the IEEE 802.11b standard, using a novel access point (AP) with two transceivers to improve the performance of WPS in terms of accuracy of the location estimation and to avoid service connectivity interruption. In our proposed system, the novel AP uses the second transceiver to find information from neighboring mobile stations (STAs) in the transmission range and then sends information in advance to associated APs, which estimate the location of the STA based on an internal database. We also use a TDOA technique to estimate the location of the STA when there is not enough information in the database (in this case, the STA moves into a new area where the system has not run the calibration phase). Using TDOA, the database can be generated and updated automatically. The initial results from our simulations show that the proposed system provides higher accuracy of location estimation than other related work and does not interrupt the Internet connection for end users in contrast with other proposed schemes.

Recently, wireless LANs based on the IEEE 802.11 standard have become popular and widely used, and Voice over IP (VoIP) is one of the most promising to be used in mobile devices over wireless networks. Up to date, new technologies have improved providing high data rate to support various kind of real-time applications. However, besides the need for higher data rates, seamless handoff is another important issue to be addressed in order to continue supporting realtime services across wireless LANs. In this paper, we proposed a Seamless Handoff Scheme that uses Access Point (AP) Module with 2 transceivers in order to improve network efficiency in terms of supporting seamless handoff and balancing the traffic load in wireless network. In our proposed scheme, APs use the second transceiver to search for information of neighbor STAs in the transmission range, and later send the result back to associate AP, which in turn compare and analyze whether the STA should perform a handoff or not. The initial results from our simulations show the proposed handoff scheme is more effective than the conventional scheme in terms of low latency and traffic load is fairly balanced.

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Recently, new technologies improve WLANs to provide efficiency, we also analyzed the increased traffic load affect to high quality of service (QoS) and support real time applications.the STA and the AP, and traffic load sharing supported by our In this paper, we improve network efficiency in terms of reducing proposed scheme.the latency time in handover process and support traffic load sharing among neighbor Access Points (APs). We neglect both detection phase and search phase in the conventional handover II. HANDOVER PROCEDURE scheme by proposing a Pre-Active Scan Phase, which works during normal connectivity. This phase will scan for the The handover is a function or process refers to the information of neighbor APs, which in turn is used to decide mechanism or sequence of messages exchanged by the AP whether to perform a handover or not. The results from our and the STA resulting in a transfer of physical layer simulation show the proposed handover scheme is more effective connectivity and state information from one AP to another AP than the conventional one in terms of providing low latency time with respect to the STA in consideration. In the conventional and support traffic load sharing among neighbor APs.handover scheme, the handover process has been divided into three phases [3] as shown in Figure. 1. Detection phase is the Keywords -h discover phase for the need of handover (the station detects the reason of frame loss), Search phase covers the acquisition I. INTRODUCTION of the information needed to perform the handover (STA use active scan mode to find APs in range), and Execution phase Wireless Local Area Networks (WLANs) based on IEEE 802.11 standard are now becoming popular and widely used perform handover (reassociation and authentication). for mobile internet services. There are many hotspots in many STA Current AP convenient places including train stations, airports, hotels and coffee shops for mobile access to the internet via PCs and R D PDAs. Hotspot enables PC and PDA users to enjoy broadband Rt noAckinternet access in wireless environments, and in near future, voice based applications will be available in wireless networks R oAclsuch as Voice over WLAN (VoWLAN) and E-conference. noCIS~' > Last RTS Supporting Real-Time applications with continuous mobility implies that the total latency (layer 2 and layer 3) of handover CTS --process must be fast. Specifically, the overall latency should All APs in Range Probe Request (broadcast) 7 not exceed 50ms to prevent excessive delay and jitter. P R (broadcast) > Unfortunately, the vast majority of IEEE 802.11 based ....Ronetworks do not currently meet this goal, that mean the layer 2 + _.--------latencies contributing approximately 90% of the overall latency which exceeds lOOms when the handover involve layer Probe Request (broadcast) 3 latencies by an average 15.37ms [5].-------ProbeReP To accomplish this handover latency time issue, we + ----proposed a novel handover scheme to improve network Current AP efficiency in terms of reducing the latency ti...