Spektrumanalys och Dynamiska Management-system med Cisco Radio Resource Management och CleanAir

Sammanfattning: Interference is one of the most common causes of performance issues and reliability issues in wireless networks. Interference and background noise can be localized by performing spectrum analysis to measure amplitude and frequency characteristics of electromagnetic signals. Initially a theoretical description of spectrum analysis and site survey was performed. Manual spectrum analysis was also examined by performing practical measurements and creating graphs with Metageek Wi-Spy and Chanalyzer. Signals from 802.11 units were observed with spectrum analysis, and were analyzed according to their visual interference levels. This was compared to the actual interference impact of the units. This analysis showed that manual spectrum analysis could be hard to interpret when it comes to interference, as signals from units that looked harmful were in fact not. The channel access method of the units, in this case CSMA/CA, contributed to a low impact of interference, since the units waited for the medium to be free before sending, which reduced the probability of collisions. Cisco CleanAir technology has built-in spectrum analysis functionality, to detect, classify and avoid radio frequency interference. Dynamic interference detection and avoidance reduces costs in operating and network outages. This is made possible by Cisco Radio Resource Management (RRM) - a system consisting of multiple protocols that can dynamically change frequency channel and power. The protocols of RRM were examined and discussed relative to the lab measurement. The measurements showed that the Cisco Aironet 2700 access point was more robust against interference compared to a D-Link router for small offices and home use. The robustness of an access point depends on its wireless standard, modulation and dynamic management protocols. Wireless communication is a complex subject, where multiple factors has an impact on network performance. Therefore, it might not be appropriate to draw any hard conclusions from the laboratory measurements that were performed. For future studies, similar lab measurements should be carried out by creating interference from non-802.11 units to compare the interference impact from CSMA and non-CSMA communication.