| Summary: | 碩士 === 國立中正大學 === 通訊工程研究所 === 104 === Two-layer cell architecture has been proposed as a candidate for future 5G systems, where the system constitutes of macro cells and small cells. Macro cells use the existing 4G system while small cell use 5G technology to provide higher high data rate and system capacity. A user first camps 4G systems through contention-based random access mechanism, and when very high data rate is needed it is handed over to 5G systems via contention-free random access. Whether the current 4G random access design is able to cope with the very large number of users anticipated in the future 5G systems is theme of this research.
In this thesis, the performance of random access in the two-layer cell architecture is studied in realistic channel environment, with MTC (Machine-Type Communications) traffic model proposed by 3GPP. The performance indexes include access success probability, collision probability, the access delay and total power consumption. Numerical results show that the current 4G random access design is not able to achieve the 5G requirements because of high collision probability, and excessive access delay and power consumption. One remedy is to increase the random access opportunity (RAO). Our results show that with 3-times RAO, access success rate is increased to 96%, and collision probability is decreased to 17%, and that significantly improves the random access performance.
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