Wireless Extension Cord

Extend PCS coverage using microwave transmission over unlicensed bands.

The vast majority of metropolitan areas and many suburban areas boast available, if not ubiquitous, coverage for wireless communications. As wireless subscribers travel from place to place, they can be assured of receiving coverage throughout the local metropolitan area. But what happens when they travel outside that area, venturing into the sometimes-barren wireless wasteland that will leave them with dropped calls or "no service available" messages displayed on their handsets? These "mobility corridors" have quickly become a differentiating service issue for attracting and retaining wireless customers.

Traditionally, the cost/benefit analysis for extending wireless networks along highways or low-population areas has made this a tough sell. Revenues typically derived from mobility corridors are outstripped by the significant investment in building, operating, and maintaining core wireless networks, as well as the significant backhaul costs. Corridors are traditionally one of the last portions of a wireless network to be adequately completed. Unfortunately for the wireless customer, this usually means dropped calls or roaming charges while traveling outside a constrained footprint. For wireless operators, the result is limited customer attraction, customer dissatisfaction, high rates and unrealized revenues from reduced minutes on the network. Thanks to new, innovative wireless architectures, however, it doesn't have to be that way.

PCS Over Microwave
In a landmark deployment last winter, Triton PCS adopted a PCS-over-microwave system, employing a wireless architecture that uses microwave transmission over unlicensed bands to move call capacity away from donor base-station sites.

The system creates an "extension cord" effect for the service provider's network. This results in a tool to improve the life cycle of the radio network and to provide coverage in a cost-effective manner while creating more revenue and service differentiation.

Here's how it works. The unit employs unlicensed 2.4GHz or 5.8GHz bandwidth for a bi-directional connection between a single donor base station and two adjacent repeater sites. These microwave links take unused PCS call capacity, in the form of TDMA channel signals, from the donor base station (located either at an existing macrocell site or at a centralized base-station facility) and extend the capacity to the repeater sites.

The signal conversion is straightforward at both the donor base station and repeater sites. In the downlink scenario, the hub unit converts the base station's PCS RF signal to a digital data stream and transmits it over the microwave data link to the repeater sites. There, the received data stream is converted back to RF for retransmission at high-power PCS frequencies. Uplink PCS signals (traveling from the handset) go through the inverse sequence, back to the base station and into the network.

The unit gives the service provider a revenue-generating tool for building out mobility corridors. Because the system uses one base station per three sites, the provider has the ability to substantially extend the life cycle of the radio network. The equipment-site costs to support the corridor traffic are less than half of the traditional scenario, while the backhaul costs are reduced by about two-thirds. These cost savings offer an improved life cycle for the network, making the build-out of mobility corridors an economically attractive initiative. The extension-cord philosophy also can be used to ease changing out base stations; the system has been designed for EIA/TIA-136 compliancy and compatibility, easing base-station-replacement scenarios.

The Wireless Data Evolution
Demand for high-speed wireless data is increasing, and the necessary network infrastructure to support this continues to challenge service providers. Every two seconds a new customer has expectations for phone calls and text messages — and expectations for wireless data are likewise on the rise. Superior coverage allows service providers to attract, maintain and smoothly expand customers usage from voice into voice and data.

Currently, the wireless Internet consists of low-speed content from a limited set of sites for stock quotes, sports scores, and driving directions. The PCS industry is emerging with higher-speed data protocols such as EDGE, which will allow both push and pull data applications at speeds running several times those of today's circuit-switched and SMS.

As a result, the wireless data market, which reportedly could be worth well over $1 billion in three to five years, will depend on cost-effective distribution and transmission tool suites to attract new customers. The wireless industry already is seeing development of some PCS data services and applications. Without superior quality error rates offered to market all coverage areas, the PCS data market will be trapped in small metropolitan coverage areas that have many service providers offering similar services.

It's reasonable to assume that the adoption of wireless data and the wireless Internet will proceed much like the adoption of wireless voice, with the need for ubiquitous coverage. New customers will demand reliability, and in turn, service providers will need to provide the most complete coverage possible. Providers must be forward thinking in their network architectures and selection of tool suites.

Implications of Data
Wireless customers are demanding ubiquitous coverage, more services, better prices and higher reliability. The demand is for wireless networks to be as efficient and complete as wireline services. This opens a myriad of opportunities for wireless-network operators. Service providers such as Triton PCS and others that can find, develop and deploy systems that give their customers what they want and need will be competitively positioned and can differentiate themselves to their customers. Service providers that do not use a fuller, differentiating tool suite will have to compete in a landscape filled with look-alikes — companies offering similar services with replicated business models and limited coverage areas.

Reynolds is Transcept director of product planning.