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Can wi-fi really be used to backhaul cellular voice?

Louis Au | Jan. 31, 2012
Under the strain of a mobile data onslaught, the move to small cells is opening the door to new and unexpected uses of smarter wi-fi.

Using the unlicensed band for transporting licensed band traffic?

Exactly. Wi-fi has evolved to become an ideal solution for this small cell backhaul problem - if done properly.

New wi-fi technology has been developed that combines integrated adaptive directional antennas with smart meshing technology and predictive channel management - all used within the channel-rich 5GHz 802.11n spectrum. The combination of these technologies makes the use of wi-fi for both line-of-sight and non-line of sight backhaul applications advantageous.

Adaptive antenna arrays deliver more reliable connectivity at longer ranges by focusing and steering RF energy only where it helps deliver the best throughput across a specified link. As the environment changes, these smart antennas mitigate wi-fi and non-wi-fi interference, constantly selecting better signal paths that yield the highest data rates and lowest latency at any given time. When used within the 5GHz band, these antenna arrays become ideal for constructing highly resilient, long range, adaptive backhaul connections between wi-fi nodes.

Predictive channel management is then used to optimise RF channel selection by maximising network capacity specifically in high-density, noisy public wi-fi environments. It does this by measuring actual channel throughput and building a statistical model that allows access points to learn over time what channel will yield the highest capacity. By relying on real-time, observed capacity on all 2.4 and 5GHz frequencies, backhaul links can be automatically moved to a better channel with less interference thereby realising higher data rates.

Utilising smart mesh techniques with adaptive antenna arrays as an alternative to fixed PtP links eliminates much of the complexity associated with aiming and alignment during the installation process. This also results in a much more affordable solution with greater resiliency in crowded urban environments given its intrinsic capabilities to dynamically adjust to changing conditions by choosing alternate paths to the network.

In live field trials with multiple network operators today, this small cell wi-fi backhaul approach has proven to deliver reliable, carrier grade transport of 3G mobile data and circuit switched voice traffic along with the prioritised transport of timing signals (eg. IEEE 1588v2/PTP or NTP) necessary for small cell network synchronisation.

Wi-fi backhaul technology is currently being built into small cell nodes housing cellular and wi-fi access - within a fairly small footprint. This allows operators to deploy a single box to provide wi-fi access, cellular access and backhaul together. 

Ultimately with small cells and better backhaul, mobile subscribers should enjoy higher speeds with more coverage in more places. In turn, mobile operators can reduce subscriber churn and increase revenue by having visibility into both cellular and wi-fi traffic - giving the customers more options to connect in more places.

Louis Au is vice president - Asia Pacific, Ruckus Wireless.


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