SIDEBAR 2: Unlicensed backhaul
One notable challenge for small cells and hetnets is, of course, getting them all connected in the first place. LTE-level throughput speeds demand fiber-level backhaul capacity, but assuming the fiber is available at every site location (let alone bonded copper), with small cells potentially number in the tens of thousands in a metro service area, connecting every site with fiber is costly.
Wireless broadband is the next obvious solution, but technologies like microwave and even Wimax (which has been touted and utilized as a backhaul option for Wi-Fi) require spectrum licenses that, generally, aren't cheap.
Consequently, some vendors are pushing unlicensed spectrum as a viable backhaul option for hetnets.
Ruckus Wireless, for example, recently announced its SmartCell solution that not only integrates cellular and Wi-Fi connectivity, but also uses Wi-Fi mesh technology to provide low-cost backhaul links on the unlicensed ISM bands.
Meanwhile, NEC uses the less-populated unlicensed 60-GHz band for small-cell backhaul. According to Keita Ito, NEC's program director of small-cell solutions, the high channel re-use characteristics of that spectrum band are "ideally suited" to deliver high capacity and low latency connections to hundreds of cell sites.
He says, "60-GHz is capable of delivering 100 Mbps and more to the small cell, using virtually zero-cost radio spectrum." Ito adds that 60-GHz spectrum allows the design of compact equipment that can be easily installed and "aesthetically concealed within a wide variety of urban environments."
One tough selling point for using unlicensed spectrum for backhaul is, of course, the fact that it's unlicensed - i.e. anyone can use it - which raises potential QoS issues.
Ruckus says that SmartCell's use of adaptive directional antennas, predictive channel management and Wi-Fi mesh technology deliver "reliable backhaul for licensed cellular and unlicensed Wi-Fi traffic in both line of sight and non-line of site environments."
Ito says NEC's 60-GHz solution includes features for "intelligent provisioning of backhaul resources and protection against performance degradations, resulting in improved capacity efficiency and elimination of costly manual maintenance and troubleshooting."