Mobile markets in major countries have become zero-sum games in which the simplest way for a carrier to grow revenues is by luring away customers from another carrier. Against this backdrop, carriers also are trying to increase ARPU by adding new, 3G data plans along with mobile video, GPS and other services. The challenge, of course, is to layer on these new services without disrupting existing subscribers, and to add new service capabilities at a reasonable cost.
From an architectural standpoint, one of the key problems is that today's macro cellular networks are built on an old model with the goal of providing relatively low-frequency voice coverage over large public areas. As demand for capacity grows in a given area, the coverage cell is split and carriers deploy another cellular base station and antenna. There are several problems with this approach when it comes to providing 3G voice and data services:
"¢ scaling coverage or capacity requires adding base station/antenna combinations, when in fact only more coverage or capacity may be required;
"¢ newer voice and data services operate at higher radio frequencies, and these are more susceptible to service interruptions due to obstructions such as buildings or other geographical features. As a result, subscribers within a given coverage area may not get good service because they're behind a wall, in an underpass or in other locations;
"¢ geographically dispersed base stations increase maintenance and backhaul costs, because each station must be serviced individually;
"¢ backhaul facilities for existing base stations are typically T1 lines (1.544 Mbps), which don't have enough bandwidth to handle the increasing mix of voice and video services from 3G devices.
Nevertheless, carriers can look at 3G service demand as an opportunity to migrate toward new service infrastructure that reduces costs, adds flexibility and increases service scalability.
Rethinking the cell tower
The first step is to reconsider the design of base station towers in light of new demands. 3G services need more backhaul and better coverage, and given the myriad challenges of providing coverage inside buildings and public facilities, it is likely that there will be far more antennas needed than network capacity.
Since this is the case, why not abandon the one base station/one antenna model and use distributed radio systems to extend coverage and capacity to where the consumer requires service‾ By distributing coverage and capacity where needed, carriers can solve several problems:
"¢ they can place remote antennas anywhere coverage is needed. Low-cost wall-mount, ceiling-mount, or pole-mount antennas can be placed in buildings, in subway tunnels, or in overbuilt urban areas to provide excellent signal strength where macro antennas can't reach;
"¢ they can get the most out of expensive and maintenance-intensive base station equipment by extending out from it with remote antennas rather than always adding new base stations. . This reduces maintenance and property costs;
"¢ use of small, distributed radio points greatly reduces site development expenses;
"¢ they can scale up backhaul through the use of fibre, metro Ethernet, millimetre wave radio, or other technologies to gain adequate bandwidth for new services with bandwidth-on-demand flexibility.
The large mobile network vendors already have upgraded their base station offerings to accommodate new 3G services along with legacy services. The distribution network is the missing ingredient. Fortunately, there are several antenna systems that can provide frequency distribution at low cost.
Inside buildings, carriers or enterprises can deploy distributed antenna systems (DAS) to deliver clear, strong, and consistent mobile coverage within their premises. DAS systems are often deployed by the carrier, but a growing number of enterprises are paying for the DAS deployment and then connecting it to the carrier's network signal with on-site.
The carrier signal is delivered either with carrier-supplied base stations or via rooftop antennas that grab a macro network signal which is then repeated inside the building via the DAS.
Another approach is for enterprises to buy their own picot base stations and then connect them to the carrier's network via Ethernet or DSL. In this scenario, the enterprise "owns" the mobile network capacity for its building and simply backhauls the traffic to the carrier's network. As with carrier-supplied base stations, pico base stations can be used in conjunction with a DAS to extend coverage throughout a building.
Outside buildings, carriers will need to fill in coverage gaps in alleys, subways and other public areas that aren't adequately served by macro cell towers. For this application, a new generation of remote radio heads can deliver legacy and 3G coverage from centralised radio suites, making the most efficient use of fibre resources.
Carriers could also use small, hardened micro base stations with simple DSL or Ethernet backhaul to the network. Ideally, the radio head or microBTS should offer modular bays to support 2G and 3G services in various flavours (such as CDMA, GSM, EDGE, EV-DO, HDPA, LTE) from the same unit to support the wide array of offerings and minimise carrier CAPEX and OPEX.
Wherever possible, carriers will want to maximise their investments in existing macro base stations, but when upgrading to LTE, WiMAX and other 3G-4G technologies, they will need far better coverage than those macro towers provide. In time, using remote antenna systems and pico or micro cells to bring coverage and capacity closer to the customer will allow operators to maximise existing resources and reduce site development.
LeFebvre is director of Product Management for ADC Active Infrastructure. [email protected]