Mobile Initiated Priority Access Solutions for Cellular Networks zyx Hsuan-Jung Su Department of Electrical Engineering National Taiwan University Taipei, Taiwan hjsu@cc.ee.ntu.edu.tw zyxwvuts Abstract- The rapid growth zyxwvutsrq of the wireless communication networks has provided subscribers with economical and nearly ubiquitous wireless access throughout the world. As a result, not only the individual subscribers but also the subscribers in the government and public organizations have become dependent on the commercial wireless services to perform their duties. With this said, the commercial wireless service becomes a more cost- etrective means to assist national security and emergency preparedness as compared to the costly development of a private network. Sharing the commercial wireless services, however, could result in blocking of the security or emergency calls during or after a disaster when heavy traMc demand is placed zyxwvut on the surviving systems. In this paper, we discuss enhancements to the mobile stations that will make the user initiated priority access possible. These enhancements can operate with or without the priority access provisioned in the current or ongoing standards, and the additional complexity they impose is very marginal. With the combination of these enhancements, different levels of emergency call service can be provided to guarantee the success of emergency calls and shorten their setup time. 1. MOTIVATION The rapid growth of the wireless communication networks has provided subscribers with economical and nearly ubiquitous wireless access throughout the world. As a result, not only the individual subscribers hut also the subscribers in the government and public organizations have become dependent on the commercial wireless services to perform their duties. With this said, the commercial wireless service becomes a more cost-effective means to assist national security and emergency preparedness as compared to the costly development of a private network. Sharing the commercial wireless services, however, could result in blocking of the security or emergency calls during or after a disaster when heavy traffic demand is placed on the surviving systems. It is therefore necessary to equip the commercial wireless service with a priority access mechanism to ensure the connection of a government emergency call. Priority access is also desirable in the third gcneration wireless networks which support mixed services with different quality of services. In the existing commercial wireless network standards [7], or the standards in progress [4][5], priority access is provisioned. However, as will he detailed later, these priority access provisions are more for the purpose of traffic and overload control. The individual users may not be guaranteed to establish an emergency call when needed. Moreover, with the priority access functions not currently widely available, it is necessary to provide govemment officials or emergency workers with equipments that can always make emergency calls no matter the connecting network has priority access On-Ching Yue Department of Information Engineering Chinese University of Hong Kong Hong Kong onching@ie.cuhk.edu.hk functions implemented or not. In this paper, we discuss enhancements to the mobile stations that will make the mobile initiated priority access possible. These enhancements can operate with or without the priority access provisioned in the current or ongoing standards, and the additional complexity they impose is very marginal. With the combination of these enhancements, different levels of emergency call service can be provided to guarantee the success of emergency calls and shorten their setup time. Under normal random access channel load, these performance enhancing techniques can reduce the mean acquisition timc by up to 68%. When the random access channel is overloaded, these techniques also improve substantially the probability of successful access attempts. zyx 11. BACKGROUND The current wireless networks separate the communication between a mobile station and a base station into two stages: access stage and traffic stage. When a mobile station enters a network, it listens to the pilot and synchronization channels broadcasted from the base station. Once the mobile station synchronizes with the network, it can extract from the base station’s broadcast messages the information it needs to get access to the network. During the access stage, the mobile station transmits on the reverse link Random Access Channels (RACH) trying to make the base station aware of its existence. Since the base station does not have any information (e.g., timing, mobile identification, etc.) about the mobile station before the access stage, the access stage involves search and detection of the mobile access message. Once the base station successfully detects the access message, a traffic channel will be assigned to this mobile station and the regular call establishment process starts. As the access and traffic stages are separated, they both impose a bottleneck on the network capacity. As a result, priority access can he performed on both stages. For the access stage under normal RACH load, the high priority mobile stations can increase their chance to be detected by the base station by using higher power or more frequent transmission. In the situation when the RACH is overloaded, individual priority enhancement may no longer work because the RACH is contention based and the heavy traffic on the RACH causes too high a mutual interference for any mobile station to he detected. A proper centralized priority access control is necessary in this situation. This so-called “overload control” is handled by the base station by assigning different transmission ~7803-8255-2J046u).Oo 02004 zyxwvutsr IEE. 1589