NLoS Backhaul Needed for Small Cells
Over the past few months, I have been investigating the major challenges mobile operators face in deploying outdoor small cells as a capacity layer to handle data traffic growth in urban settings. As noted in my last Heavy Lifting note, operators such as Softbank have the advantage of leveraging existing fiber links to backhaul small-cell traffic to pooled baseband units in telco central offices in Tokyo's densely populated Ginza district. This "cloud RAN" architecture yields blazing fast download speeds, low latency, high quality, and performance even at the cell edge. (See Test Driving TD-LTE Advanced.)
But most operators cannot deploy fiber to backhaul small-cell traffic, especially in the dense core of most US cities. Even with aggregation points at hubs on tall buildings or towers, these carriers will need to establish multiple high-capacity, non-line-of-sight (NLoS) links to pole-mounted or street-level small cells over long distances that are frequently blocked by other buildings or trees. Small-cell backhaul links are often blocked by multiple buildings located about 1 km apart, yet they must deliver full capacity. I expect that the same requirements will emerge in European cities as well.
As major mobile carriers start deploying outdoor small cells in urban settings, they will require a "universal wireless transport" solution for backhaul that combines the following attributes:
- "True NLoS" -- Instances where a wireless link is completely blocked by multiple solid structures yet maintains the same dedicated high capacity as a line-of-sight (LoS) link at distances ranging from hundreds of meters to 1 km.
- Frequency Reuse -- The ability to support multiple simultaneous wireless links at full capacity using a single carrier frequency from a common hub location within an overlapping geographical service area. This feature is critical to enable carriers to maximize use of limited spectral resources within a service area as well as to minimize capital investments needed to achieve desired capacity.
This would provide a single toolkit to satisfy a wide range of small-cell backhaul requirements. The combination of NLoS backhaul capacity and range seems critical for cost-effective deployment of the next generation of outdoor small-cell LTE wireless infrastructure for maximum location flexibility. I would like your feedback on this analysis, as I will be looking for these attributes as I evaluate the available NLoS backhaul solutions from the perspective of operators deploying outdoor small cells in urban settings.
— Berge Ayvazian, Senior Analyst, Heavy Reading