.M w w w 91 tk ar st ed ia w M w w st ia ed tk 91 ar .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad .tk 91 ar st ia M ed w w w www.vsofts.net oldroad [...]... its home system and becomes a roamer in a neighboring system Also, compatibility between the two MSCs must be determined before implementing an intersystem handoff Chapter 10 demonstrates how intersystem handoffs are implemented in practice Prioritizing Handoffs w M 3.4.1 ed ia st ar Different systems have different policies and methods for managing handoff requests Some systems handle handoff requests... control channel and 160 voice channels would be assigned to each cell w (b) For N = 7, four cells with three control channels and 92 voice channels, two cells with three control channels and 90 voice channels, and one cell with two control channels and 92 voice channels could be allocated In practice, however, each cell would have one control channel, four cells would have 91 voice channels, and three cells... is terminated) Time w w (b) Proper handoff situation Received signal level w M (a) Improper handoff situation Received signal level 91 tk signal for acceptable voice quality at the base station receiver (normally taken as between –90 dBm and –100 dBm), a slightly stronger signal level is used as a threshold at which a handoff is made This margin, given by ∆ = Pr handoff – Pr minimum usable , cannot... is too large, unnecessary handoffs which burden the MSC may occur, and if ∆ is too small, there may be insufficient time to complete a handoff before a call is lost due to weak signal conditions Therefore, ∆ is chosen carefully to meet these conflicting requirements Figure 3.3 illustrates a handoff situation Figure 3.3(a) demonstrates the case where a handoff is not made and the signal drops below... excessive delay by the MSC in assigning a handoff or when the threshold ∆ is set too small for the handoff time in the system Excessive delays may occur during high traffic conditions due to computational loading at the MSC or due to the fact that no channels are available on any of the nearby base stations (thus forcing the MSC to wait until a channel in a nearby cell becomes free) Level at which handoff is... subscriber and the base station, and other time varying effects Chapter 5 shows that even when a mobile user is stationary, ambient motion in the vicinity of the base station and the mobile can produce fading; thus, even a stationary subscriber may have a random and finite dwell time Analysis in [Rap93b] indicates that the statistics of dwell time vary greatly, depending on the speed of the user and the... used to scan and determine signal strengths of mobile users which are in neighboring cells The locator receiver is controlled by the MSC and is used to monitor the signal strength of users in neighboring cells which appear to be in need of handoff and reports all RSSI values to the MSC Based on the locator receiver signal strength information from each base station, the MSC decides if a handoff is necessary... Tuesday, December 4, 2001 2:17 PM Handoff Strategies 65 time The MAHO method enables the call to be handed over between base stations at a much faster rate than in first generation analog systems since the handoff measurements are made by each mobile, and the MSC no longer constantly monitors signal strengths MAHO is particularly suited for microcellular environments where handoffs are more frequent 91 tk... station This handoff operation not only involves identifying a new base station, but also requires that the voice and control signals be allocated to channels associated with the new base station Processing handoffs is an important task in any cellular radio system Many handoff strategies prioritize handoff requests over call initiation requests when allocating unused channels in a cell site Handoffs must... service as perceived by the users, various methods have been devised to prioritize handoff requests over call initiation requests when allocating voice channels w w One method for giving priority to handoffs is called the guard channel concept, whereby a fraction of the total available channels in a cell is reserved exclusively for handoff requests from ongoing calls which may be handed off into the ... managing handoff requests Some systems handle handoff requests in the same way they handle originating calls In such systems, the probability that a handoff request will not be served by a new... intersystem handoff Chapter 10 demonstrates how intersystem handoffs are implemented in practice Prioritizing Handoffs w M 3.4.1 ed ia st ar Different systems have different policies and methods... which a handoff is made This margin, given by ∆ = Pr handoff – Pr minimum usable , cannot be too large or too small If ∆ is too large, unnecessary handoffs which burden the MSC may occur, and if