Smart phones and tablets are becoming devices of choice for consumers and road warriors. Whether they are at the local mall, Starbucks, or Panera, consumers have come to expect that when they use their portable device that they will be able to use social media, surf the net, and utilize applications that were specifically designed to entertain them and make their lives easier.

Today, we automatically assume that we can access applications and the Internet if we have a connection. But with the rapid adoption of smart phones and tablets, will the network be able to handle it? Or will our applications just time out, stall, or take forever to run? Operators are still trying to figure out how to meet the anticipated demand.

One solution to the evolving wireless broadband capacity crunch is a heterogeneous access network comprising macrocells, plus a range of small-cell solutions: microcells and picocells, carrier Wi-Fi, and femtocells to add capacity and performance. Wireless operators are starting to implement small-cell access solutions, though adoption has slowed down due to the lack of cost-effective backhaul solutions. Fiber has proven to be too expensive, and microwave isn’t technically feasible in many urban environments where line-of-sight is not possible.

There are three major design elements that need to be addressed to solve the small-cell backhaul challenge: architecture, self-organizing networks, and spectrum.

Architecture

Currently, mobile backhaul solutions such as microwave and fiber utilize a point-to-point (PTP) architecture where basestations have full utilization of dedicated backhaul bandwidth. PTP is provisioned based on peak volume, so during off-peak times the excess spectrum is idle.

Point-to-Multipoint (PMP) is the ability to backhaul several basestations through a single backhaul hub by creating multiple links that share the hub bandwidth (Fig. 1). PMP backhaul is intelligent, based on sharing resources, and ideal technically and economically for small-cell backhaul.

Technically, traffic patterns on for small-cell basestations are very different from macrocell basestations. Compact, below-roofline basestations such as microcells or picocells transmit at low power and are mounted at low height. This means their coverage area is small. Small coverage area means less interference with adjacent cells, and that’s why compact basestations provide up to double the capacity of macro basestations.

Macrocells have a low peak-to-average traffic ratio whereas small cells have a high peak-to-average traffic ratio. On average, there are fewer users served by small cells, but the performance is better (i.e., better download and upload speeds). When a small cell peaks, it does so for a very short period of time but can sustain rates above those of a macro cell.

Furthermore, traffic patterns for data services are not as predictable as those of voice networks. For example, voice networks have busy hours that typically happen at known times during the day where subscribers drive up the traffic on several basestations at the same time. This is different in data networks where traffic patterns are not predictable. Data consumption can happen at any time and is different between basestations.

Based on the described traffic patterns, it would be extremely inefficient to dedicate bandwidth to each compact basestation independently, especially if the dedicated bandwidth is designed to match the peak traffic performance that can only be achieved for very a brief moment with small-cell architectures. Given that peak traffic on any basestation can only occur when network utilization is low—that is, when adjacent basestations aren’t very busy—it becomes advantageous to use PMP backhaul. 

In this case, several basestations share the bandwidth, which is fine given that they don’t peak at the same time, and if they do, it’s only for a very brief period of time where traffic on adjacent basestations is low. PMP configuration is made more efficient by using “dynamic bandwidth allocation,” which shifts resources from a basestation with low traffic requirements to one with high traffic demand. This enables optimization of bandwidth to serve the basestation with highest traffic requirements at any particular moment in time.