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“Coexistence Mechanisms for Legacy and Next Generation Wireless networks Protocols”
by Alex Chia-Chun Hsu
December 2007
Effective usage of unlicensed bands (UB) has received a lot of attention due to its potential in ubiquitous computing and networking. One key issue in effective UB usage is the coexistence among devices of homogeneous or heterogeneous systems, e.g. wireless local area networks (WLAN) and wireless personal area networks (WPAN). To resolve the coexistence problem, we need to understand the interaction between concurrent transmissions in overlapping frequency bands. Although some basic interference resolving process is mentioned in the standards, further performance improvement can be achieved by careful system analysis and parameter selection. In this research, we analyze the coexistence problem that these systems face and devise coexistence mechanisms to enhance performance.We develop a suitable analytical model that can accurately model the interference phenomena between WLANs and WPANs. Then, we propose non-collaborative solutions for WLAN and WPAN, respectively. For WLAN, we propose a dynamic fragmentation (DF) mechanism to optimize the packet length such that Wi-Fi devices have better chance to avoid the interference caused by Bluetooth piconets. Both theoretical analysis and simulation results confirm that DF can significantly improve the performance of Wi-Fi in terms of throughput and transmission delay.For WPAN, we propose an adaptive hopset frequency hopping (AHFH) mechanism to avoid the interference from coexisting WLAN as well as the self-interference from collocating Bluetooth piconets. With AHFH, a piconet adjusts its hopset to minimize the interference adaptively. Results show that AHFH improves performance and adaptability to the dynamic changes in the environment.Stale and inefficient current spectrum regulation and the crowded ISM band make flexible "cognitive radio (CR)" the logical next step. Along this research direction, we propose a statistic channel allocation MAC (SCA-MAC) and a dynamic spectrum access MAC (DSA-MAC). Both protocols can exploit the "spectrum hole" on unlicensed bands and minimize their interference on incumbent users and collision with other CR nodes.SCA-MAC avoids interference with primary services through statistics, and improves spectrum efficiency. DSA-MAC further investigates strategies of the operation range assignment. Three strategies, namely, non-sharing (NS), partial sharing (PS) and full sharing (FS), were discussed and compared under various scenarios. It is shown that FS gives the best throughput.
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