 Hello everyone, welcome to a video lecture on channel assignment and handoff strategies. I am K. R. Biradhar, Assistant Professor, Department of Electronics and Telecommunication Engineering, Walsh and the Institute of Technology, Sallapur. Let us start with the learning outcomes first. At the end of this video, you will be able to identify channel assignment strategy depends upon requirement. Also, you will be able to explain handoff mechanism in cellular system. Channel assignment strategies. To begin with, definition of channel assignment strategy. Channel assignment strategy means to allocate the available channels to the cells in a cellular system. Here, when a user wants to make a call request, then by using channel assignment strategies, their requests are fulfilled. For efficient spectrum utilization, frequency use scheme should be consistent with 2 objectives. Those are by increasing system capacity and also by minimizing interference. Types of channel assignment strategies. Mainly, there are 2 types of channel assignment strategies. First one, fixed channel assignment strategy. Second one, dynamic channel assignment strategy. Let us see fixed channel assignment are simply FCA first. In fixed channel assignment strategy, each cell is allocated a free defined set of voice channels. If any call attempt can only be served, if unused channel in that cell is available. If all the channels are occupied, then the call is blocked. Several variations or changes exist like borrow a free channel available in the neighboring cell. A cell is allowed to borrow a channel from neighboring cell if all its channels are occupied by mobile stations. A MSC supervises or handles such procedure and without disturbing other ongoing calls. Dynamic channel assignment strategy. Here voice channels are not allowed permanently to any of the cells. On each call request from mobile station, the base station requests a channel from mobile switching center and then mobile switching center releases the channel on demand. Mobile switching center only allocates a free channel. That means, if that is not present in use in the cell which fails within minimum restricted distance of frequency use. It reduces the likelihood of call blocking by increasing trunking capacity of the system. List out some advantages and disadvantages of dynamic channel assignment strategies. Pause the video think and write your answer. Thank you. You might have written the answer dynamic channel assignment. In this slide, we will discuss advantages and disadvantages of dynamic channel assignment. Some of the advantages of dynamic channel assignment over fixed channel assignment are reduces call blocking that is reduces call blocking means at the same time increases trunking capacity and also increases voice quality. Some of the disadvantages are increases storage and computational load of MSC because it requires some real time data from entire network related to channel occupancy, traffic distribution, radio signal, strength, indication, RSSI, rules for channel assignment. Some of rules to be followed while assigning channels. Do not assign co-channel or adjacent channel at the same cell site. If you assign co-channel cells and adjacent channel cells in the same cell that creates interference in the network. Avoid adjacent channel assignment in adjacent cell sites. Do not assign co-channels in adjacent cell sites. These three are not applicable for CDMA. Do not mix and match channel groups in a cell or sector. Maximize the distance between reusing cell sites. Maintain proper channel separation for any channel assignment for a sector or site. Handoff strategies. First we shall see the definition of handoff. Handoff refers to a process of transforming an ongoing call or data session from one channel connected to the core network to the another. Process of transferring a mobile station from one base station to another, the mobile switching center automatically transfers the calls to the new base station, but also requires that the voice and control signals be allocated to channels associated with new base station. This is also called a handover. In this slide we shall see how handoff situation occurs. One where handoff occurs successfully in figure 1B and second one handoff fails as shown in the figure 1A. Let us first see lower curve. Remember two reasons, base station 1 and base station 2. In figure 1B, when mobile station is at cell 1, the base station 1 will be given service. As mobile station moves and reaches end of cell 1 and crosses and reaches out to cell 2. Then automatically service will be switched over to the base station 2. This situation is the successful handoff. Therefore, in successful handoff the signal from base station 1 fails below a threshold level. Before reaching to this threshold, there is a jump in the signal and there is a service from base station 2. But in the figure 1A, where the case of improper handoff signal drops drops drops then reaches the signal well below the minimum acceptable point. And there is a disconnection in the call case 1, handoff successful. The figure shows handoff successful and this diagram detailed view of the previous diagram. In this the value of delta is large enough, when the received signal power is reached to handoff threshold the MSC the mobile switching center initiates the handoff. Case 2, handoff unsuccessful. This diagram depicts the handoff unsuccessful. In this case the MSC mobile switching center was unable to perform the handoff before the signal level dropped below the minimum usable level and so the call was lost. There are various reasons for handoff failure those are when delta is too small or even it is too big also because there may be insufficient time to complete a handoff before a call is lost due to weak signal condition. When moving with very high speed suppose a mobile user is moving with very high speed while call is in progress there is chance of failure in handoff. Excessive delay at MSC due to high traffic level, unavailability of channels at the time of switching there may be chance of channels not freely available. These are the references I referred to prepare the above presentation. Thank you.