Have you ever had the experience where you walk into a bar, ask for a drink and the bartender simply can’t hear you because of all the background noise in the room? That is a good analogy for the kind of environment in which more and more backhaul microwave links are being deployed today and tomorrow. Your voice is like the radio signal trying to communicate with the core network. The background noise that prevents the bartender from hearing you is the interference threat in a microwave backhaul network.
For a microwave backhaul link, the threat of interference will vary depending on the environment and frequencies available. If we’re talking about rural areas with low radio congestion then the threat of interference from adjacent links is unlikely. Similarly, the background noise levels in a quiet country bar will be low, allowing the bartender to hear you easily. Moving in towards the suburbs of a town, the risk of interference increases to the extent that it becomes possible for interference – as it would be with the noise in the suburban bar. When we move into the busy urban environment then the threat of interference becomes likely – just like you’d experience in a busy city-centre club.
So what can we do to avoid these interference scenarios and increase our immunity to its effects?
CommScope released a white paper some time ago which discussed the comprehensive analysis of a European operator’s backhaul network containing over 10,000 microwave links operated in the 15, 18 and 23 GHz bands.
In it, we compared the impact of using low-cost antennas with known radiation pattern irregularities (bad side lobe control), with the well-defined and controlled radiation patterns of high-performance, well-engineered microwave antennas. We found that 19 percent of wireless backhaul in the 15GHz band failed to meet the required degradation threshold. It was 29 percent in the 18GHz band and 21 percent in the 23 GHz band. In all, an average of 23 percent of the wireless backhaul network failed to meet interference and availability objectives resulting in backhaul traffic being slowed down (adaptive code modulation throttling down) or even lost altogether (outages).
So the first and critical step is to ensure that you only install well-engineered antenna products from a reputable supplier who can clearly demonstrate that its antennas meet the side lobe specifications it claims they do over the deployment life time. Saving a few dollars upfront can result in considerable additional expense further down the line. Remember – a high quality radio will only be as good as the antenna it’s combined with in the system.
I will be speaking at length about the negative effect of side lobe interference on microwave network performance, and the opportunity that better antennas give, at the upcomingLTE North America 2012 conference in Dallas. My presentation will be part of Track 2 on Wednesday, November 14 from 3:25–3:45 p.m. Hope to see you there.