Smashing the small cell backhaul brick wall
WiFi offload is being openly embraced, RAN sharing is increasing in popularity, spectrum is being re-farmed and LTE technology is being deployed. Small cell deployments, as part of a heterogeneous network layer, have also been heralded as a key mobile network capacity driver. But as Shayan Sanyal, CCO at backhaul specialists Bluwan, points out; when it comes to small cell deployments, operators are coming up against a backhaul brick wall.
Small cell salvation
Small cells are becoming increasingly commonplace in next generation network architectures. They deliver targeted network coverage and capacity in areas where it is needed most. There are hundreds, in some cases thousands of small cells beginning to span most major cities in the developed world. Each small cell works much like a miniaturised, short range base station, beaming concentrated coverage and capacity to support areas of heavy mobile data demand.
The backhaul brick wall
Like any macro cell however, small cells require a supporting backhaul infrastructure. Macro cells rely on established fibre and copper networks supplied by a variety of wholesale providers. Delivering this supporting fibre infrastructure is incredibly expensive, particularly in urban areas where trenches need to be physically dug to lay supporting cables, or where the cost of wholesale fibre is prohibitive. Delivering fibre backhaul to hundreds (potentially thousands) of small cells is therefore not commercially viable.
Microwave technology is the most feasible way to extend the reach of wholesale fibre infrastructure. It brings its own OPEX challenges however, especially when considering the cost of supporting equipment and site rental costs. Point-to-point (PTP) microwave backhaul is restricted by the amount of spectrum available to it and the narrow channels providing limited capacity. These are combined with a high total cost of ownership (TCO) associated with site rental and spectrum licensing costs. In the past, point-to-multi-point (PMP) microwave backhaul technologies have struggled to penetrate developed markets due to the lack of bandwidth availability to support geometric increases in demand for mobile data, especially for advanced applications such as 3G+ or LTE, but this is set to change.
The answer is 42
Advancements in microwave technology are now leveraging 42 GHz millimetre wave spectrum to address the small cell backhaul conundrum. PMP microwave solutions now exist that leverage this vastly under-utilised spectrum band to serve the needs of the most data-hungry of mobile subscriber.
42 GHz millimetre wave PMP technology provides a practical and cost effective means to deliver backhaul capabilities to potentially thousands of small cells in a typical mobile network. By utilising the ultra-wide 42 GHz spectrum, which is widely available for the carrier market, operators can enable high speed transmission of high quality data and video content in dense urban areas.
With performance capability of up to 8 Gbps wireless backhaul throughput from the transmission hub and from 100 Mbps (scalable to several hundreds of megabits) to individual cell sites, PMP millimetre wave delivers up to 10 times more capacity in a cell sector than existing PMP solutions. Dedicated bandwidth to each site can be tailored dynamically to optimise spectrum use and manage subscriber demand. As trenching for the laying of fibre cable is not needed it is easy to install and provision new cell sites in near real-time.
This is particularly pertinent for areas such as Europe where operators with access to the 42GHz band, can now provide backhaul to multiple service providers will be able to deliver up to 400 Mbps to a single site. As it supports multiple transmission technologies, PMP backhaul also has enough capacity to service multiple sectors, boosting capacity requirements of a macro RAN and enabling enhanced RAN infrastructure sharing. Operators can not only support current RAN sharing services but also make use of multi-technology RAN – 2G, 3G and 4G – on the same site and eventually plan their migration to cloud RAN.
Making small cells financially feasible
The cost reduction and benefits of millimetre wave PMP technology are significant. It requires less OPEX and CAPEX expenditure than PTP wireless solutions, especially when compared to alternatives such as xDSL, PTP microwave, fibre and leased line. As it uses one antenna, serving a cluster of base stations in a single sector from a central transmission hub, PMP requires less equipment than other microwave PTP options. This correlates into more efficient use of limited cell tower space, lower site rental and lower maintenance. Single ended installations means the technology can be deployed in less time than other wireless networks. As it provides carrier-grade, multi-gigabit fibre-like speeds and capacity across wide areas, and removes the need to lay cables to each cell site, it has a faster time to market. Additionally, as it operates in the 42 GHz bands it is utilising more cost effective spectrum.
A recent analysis of the total cost of ownership (CAPEX and OPEX) of various small cell technologies found that millimetre wave PMP small cell backhaul is three times more cost effective than fibre backhaul and twice as cost effective as PTP microwave backhaul over a five year period.
Operators are up against a myriad of challenges as they migrate to LTE. Not only do they need to meet business objectives – deliver flexible services and enable rapid customer acquisition – but they have to ensure maximum revenue per unit of capacity at the lowest cost per unit. Utilising existing spectrum and getting smarter with what they have will certainly help and small cells are certainly part of the network mix, but only by thoroughly evaluating and deploying new technologies will operators be able to deliver the capacity gains needed for LTE.
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