Just as we have seen a trend towards distributed architectures in computing and content delivery, a similar shift is taking place in wireless networks. Small cell architectures (aka, microcells) have the promise to deliver significantly higher network capacity. By bringing the base station closer to the street level and into the users' direct environment and allowing for more frequent re-use of scarce radio access spectrum, microcell architectures are showing great promise for mobile operators.
As the industry discovered with public Wi-Fi mesh networks a few years ago, the economics of these types of network architectures are dependent on the backhaul, installation and access point/base station costs in roughly equal measure. The deployment constraints for such networks are very different from those of the macro network. Size, power, aesthetics, easy installation, zoning friendliness and total deployed network cost top the list of concerns. So, while microcellular architectures represent an attractive and cost-effective option for mobile operators, they also present a unique set of challenges that must be addressed when being installed.
Despite advances in mobile networks, there is a growing gap between end user demand and access bandwidth. Upgrading to higher capacity 3G and 4G networks significantly improves access capacity, but that alone will not provide sufficient throughput for media rich applications in high tele-density areas. Capacity issues will be further impacted by the advent of machine-to-machine applications, meaning a significant amount of future demand will come from "things" currently unconnected.
Street level base stations exist "below the clutter level" in microcellular networks and so offer much greater in-building penetration at lower transmit powers. This is particularly relevant to operators using higher-frequency access spectrum, such as 2.5 GHz and above. In fact, in-building penetration suffers significantly in traditional macrocellular architectures due to the lower propagation characteristics of these higher frequencies.
While some spectral efficiency gains are achieved with 4G networks and the use of MIMO technology, the majority of bandwidth increases result from larger channel sizes defined by these new standards. Microcelluar networks present a viable solution to the spectrum shortfall. Smaller cells operating below the clutter at street level enable operators to re-use radio access spectrum more frequently, resulting in higher spectral efficiency. Additionally, for deployments using microwave backhaul, the spatial separation between the microcells and macrocells allow operators to re-use the same backhaul spectrum for both – potentially leading to significant licensing savings.
This nascent technology does, however, require careful planning to ensure optimal site selection and compliance with city zoning requirements. Included in the planning process, operators should also adopt a flexible backhaul strategy to minimize capital and operational costs, while also recognizing that deployment timelines are essential for future bandwidth expansion and an improved mobile experience.
Because microcellular networks operate at street level, existing towers cannot be utilized, therefore operators must establish new installation locations on non-traditional structures such as street light poles, traffic light poles, bridges and exterior walls of buildings. For microcell units to operate in these locations, it's essential they be fully integrated, environmentally-hardened units for the outdoors, and contain the base station, backhaul radio and modem (in the case of microwave), battery backup, environmental alarms and local switching capabilities.
The high visibility of microcell units means operators must comply with city zoning placement requirements that generally dictate street light pole-mounted equipment must be contained within a single enclosure that meets strict space and weight requirements.
Installation must be rapid to minimize any disruption to city traffic and operations and also must be able to be installed and maintained by a single individual without the use of heavy equipment. Likewise, alignment and field replacement must also be fast and simple. The smaller cell size will result in a significant increase in the number of deployed units in a given network, meaning that operational simplicity and sophisticated remote management are paramount to the ongoing operation of the system.
The total cost for deployment depends on a large number of factors, including site acquisition, site leasing, installation and maintenance, power conditioning, spectrum licensing and, of course, equipment cost. The means of connecting the street level network with the macro or fiber-based network is also a significant factor. Costs for deployment should be weighed against those similar costs incurred in a macrocell deployment. Equipment cost, while important to the initial network cost, is not the dominant factor in the total cost of ownership. The form factor requirements imposed by city planners will drive us to higher levels of integration. Finally, the backhaul requires a flexible design that allows the use of fiber, point-to-point wireless, as well as point-to-multipoint wireless technologies in order to meet both performance and cost objectives.
Looking beyond initial deployments, which are focused primarily on high teledensity urban areas, it is highly probable that suburban, rural and underdeveloped regions can also benefit from these solutions, allowing mobile service providers to deliver 10 Mbps and beyond to the home.
Regardless of where microcellular networks are deployed, operators will rely on a combination of technologies to solve their backhaul challenges and it's clear that microwave will play a very important role in enabling the widespread buildout of these solutions.
Alan Solheim is vice president of Corporate Development for DragonWave.