COVERAGE ANALYSIS OF HANDOFF ALGORITHM WITH ADAPTIVE HYSTERESIS MARGIN Shyam Lal & Deepak Kumar Panwar Electronics & Communication Engineering Department, NIT Kurukshetra (Haryana) INDIA-136119 [shyam_rao24@rediffmail.com & deepakdeeppanwar@hotmail.com] Abstract The handoff initiation in cellular systems depends on many environmental and system parameters. Various handoff initiation algorithms are available and most of them are based on relative signal strength (RSS) measurements. Some hysteresis margin in handoff decision criterion is allowed to avoid the ping-pong effect and hence frequent handoff requests from single user. The value of hysteresis margin plays a key role in handoff performance and affects the coverage of the cellular system. It is very difficult to choose a particular value for it. In this paper, the coverage of a handoff algorithm with dynamic hysteresis margin, based on the distance information between the mobile station and the serving base station, is analyzed for microcellular environment. Handoff probability is taken as performance parameter to evaluate handoff algorithms analytically. KEY WORDS: Handoff, adaptive hysteresis, handoff probability, Relative Signal Strength (RSS), shadow fading. I. Introduction The development in the field of wireless communications has been nothing short of astonishing in the past decades. The primary goal of any wireless network is to provide fixed network access to a large number of mobile or stationary users. Mobility is one of the key characteristics of the wireless networks. In the wireless mobile communication system, mobile users move around in the service area and time to time require communication services in the form of a wireless connection to the fixed network. Here the fixed base stations (BS), distributed over the geographical area, provide the physical two-way connection between mobile users and network. Problems arise in context to mobility when a mobile user moves around from the service area of one BS into others. Handoff, or handover, in cellular communication is the process whereby a mobile subscriber communicating with one BS is switched to another BS, which is providing the better link quality during a call. Handoff management is a challenging aspect in wireless networks to provide the mobility, as the available resources, at any cell site, are limited. The handoff initiation is based on various factors of BS i -MS link [1-4], such as, distance of MS from the BS, relative signal strength, absolute signal strength, and the estimate quality levels of the concerned radio link, etc. A call in progress could be forced to abort during handoff if sufficient resources cannot be allocated in the new wireless cell. A properly designed handoff algorithm is essential in reducing the switching load of the system while maintaining the quality of service (QoS).Handoffs are broadly classified into two categories: hard and soft handoff. A hard handoff is essentially a ‘‘break before make’’ connection. In a hard handoff, the link to the prior BS is terminated before or as the user is transferred to the new BS; the MS is linked to no more than one BS at any given time. With hard handoff, a definite decision is made on whether to handoff or not. In contrast to hard handoff, a soft handoff is a ‘‘make before break’’ method. With soft handoff, the MS can establish multiple connections with neighboring BSs. Depending on the changes in pilot signal strength from the two or more BSs involved, a hard decision will eventually be made to communicate with only one. In the interim period, the user has simultaneous traffic channel communication with all candidate BSs. In this paper hard handoffs in a cellular system are concentrated on. The term handoff is henceforth used to refer to hard handoff. When a MS is traveling from its serving BS to the target adjacent BS, the probability of handoff is generally designed to maximize at the cell boundary. In general, handoff includes two steps: handoff initiation and execution. In the initiation phase, the RSS is measured according to radio propagation-based methods, and a new candidate BS is chosen if necessary. In the execution phase, a new radio channel will be assigned, and the call will be handed over to another BS. The handoff initiation phase is defined as monitoring the radio channel, making a decision for initiating the handoff process and selecting a new BS. Therefore, the handoff initiation algorithm is extremely 10th International Conference on Information Technology 0-7695-3068-0/07 $25.00 © 2007 IEEE DOI 133 10th International Conference on Information Technology 0-7695-3068-0/07 $25.00 © 2007 IEEE DOI 10.1109/ICIT.2007.68 133 10th International Conference on Information Technology 0-7695-3068-0/07 $25.00 © 2007 IEEE DOI 10.1109/ICIT.2007.68 133 10th International Conference on Information Technology 0-7695-3068-0/07 $25.00 © 2007 IEEE DOI 10.1109/ICIT.2007.68 133