Tham khảo tài liệu 'cellular networks positioning performance analysis reliability part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Providing Emergency Services in Public Cellular Networks 289 more accurately using the lognormal distribution. Consult Mitchell et. al. 2001 where Matrix-Exponential distributions can be added to standard Markov chains like the one here to model virtually any arrival or service process. However in reality the exponential distribution assumption for sessions is still mostly used both in analysis-based study like Tang Li 2006 and simulation-based study like Nyquetek s report Nyquetek 2002 . For this work similar to what is used widely and also assumed in Nyquetek 2002 all session durations and inter-arrival times are independently identically and exponentially distributed. Adaptive probabilistic scheduling In FCC 2000 the FCC provided recommendations and rules regarding the provision of the Priority Access Service to public safety personnel by commercial providers. It required that at all times a reasonable amount of CMRS Commercial Mobile Radio Service spectrum is made available for public use. To meet the FCC s requirements when emergency traffic demand is under a certain protection threshold high priority should be given to emergency traffic when the emergency traffic is extremely high so that it can take most or all of the radio resources a corresponding strategy should be taken to avoid the starvation of public traffic by guaranteeing a certain amount of radio resources will be used by public. The protection threshold can be decided by each operator and thus is changeable. So our strategy should be able to deal with the above requirement for any protection threshold value this is why we introduce an adaptive probabilistic scheduling strategy instead of fixed scheduling like in Nyquetek 2002 . Description and modeling of APS Fig. 1. Probabilistic scheduling The basic APS scheme is illustrated in Fig. 1. In the figure Ảpmg Ảno Org represent the arrival rate of emergency public handoff and public originating sessions respectively. When an incoming session
