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In this study, we propose a novel positioning and searching system for emergency location services, namely the hyper-enhanced local positioning system (HELPS), which is applicable to all mobile phone users, including legacy feature phone users. In the case of an emergency, rescuers are dispatched with portable signal measurement equipment around the estimated location of the emergency caller. Each signal measurement device measures the uplink signal from the mobile phone of the caller. After calculating the rough location of the caller's mobile phone based on these measurements, rescuers can efficiently search for the caller using the received uplink signal strength. Thus, the positioning accuracy in a conventional sense is not a limitation for rescuers in finding the caller. HELPS is not a traditional positioning system but rather a system with humans in the loop designed to reduce search time in emergencies. HELPS can provide emergency location information even in environments where the GPS or Wi-Fi is not functional. Furthermore, for HELPS operation, no hardware changes or software installations are required on the caller's mobile phone., Comment: Submitted to IEEE Wireless Communications

Code division multiplexing (CDM)-based random access is used in many practical wireless systems. With CDM-based random access, a set of sequences is reserved for random access. A remote station transmits a random access packet using a randomly selected sequence among the set. If more than one remote stations transmit random access packets using the same sequence simultaneously, performance degrades due to sequence collision. In addition, if more than one remote stations transmit random access packets using different sequences simultaneously, performance also degrades due to interference. Therefore, the performance of CDM-based random access is dependent on both sequence collision and interference. There has been no previous research to analyze the performance of CDM-based random access considering both sequence collision and interference. In this paper, throughput of CDM-based random access is investigated considering both sequence collision and interference based on a signal to interference plus noise ratio (SINR) capture model. Analysis and numerical simulation compare the throughputs of several random access schemes including conventional and channel-adaptive random access. The results show that channel-adaptive random access can achieve significantly higher throughput than conventional random access. In addition, based on the results of this paper, it is possible to analyze the trade-off between the throughput and implementation complexity with increased number of sequences., Comment: 24pages