Wireless local loop (WLL), originally defined as providing a local loop facility without wires, over the past few years has become synonymous with the term “fixed cellular,” technology used to provide telephone service to end users in urban and semi-urban areas with enough potential subscribers to justify the initial network investment. One U.S-based company, however, argues that neither term adequately defines systems needed by developing countries for rural areas.
“A rural area is defined as one with a low population density dispersed over a large geographic area,” explains Lauren McCabe, sales manager-Latin America for Telemobile Inc. Telemobile is a 35-year-old manufacturer of wireless telecommunications equipment, based in California.
“Rural telecommunications implies greater distance, more challenging terrain and few subscribers. The limited number of subscribers over a larger area requires low population density solutions that are more economical than the original cellular concept.”
To that end, McCabe said her company now uses the term “wireless rural loop” (WRL), with the definition of providing a local loop facility without wires to a small number of subscribers over a large geographic area. McCabe provided three examples of when a WRL system would be applicable for a developing country.
Rural region, multiple villages
The first example would work for an area where there are clusters of towns or population centers within the same geographic area, McCabe explained.
For instance, suppose there is a rural area of 5,000 people that wants initial phone service. The area comprises 10 different villages, approximately 10 to 15 kilometers apart. Each village has between 300 and 700 inhabitants and would require at least one pay phone or public calling office.
Based on this information, McCabe explained, it is determined a TDMA (Time Division Multiple Access) point-to-multipoint system is the best solution. TDMA enables a large number of time slots over a point-to-multipoint system, thereby extending service to a greater number of subscribers, she said.
The system would supply phone service to 400 initial subscribers sharing a certain number of trunk lines. Of these 400, there would be a mix of residential and business users, with each subscriber wanting full functionality from the telephone-including voice, fax and high-speed Internet access.
The system would be implemented, she said, with one remote outstation in each of the 10 villages. The maximum distance between an outstation and the terminal or repeater is 30 kilometers. Each subscriber would be hard-wired to the remote with a maximum distance of 3 kilometers. Based on these requirements, this WRL system would have 28 trunk lines.
Total cost: US$267,000, making the cost per subscriber US$667, according to McCabe.
Remote village
In the second application, there is a remote rural village of 500 inhabitants, and the village wants voice, fax and potentially low-speed data services.
For this application, the objective is to provide basic communications services while minimizing costs and maximizing revenue, explained McCabe. Due to the closeness of the subscribers, initial capital investment can be kept down by using a point-to-point system with adaptive differential pulse code modulation (ADPCM) at 16 kilobits per second to maximize bandwidth usage, she continued.
“This kind of system can extend service up to 50 kilometers from the central office.”
The system would have 40 subscribers sharing eight trunk lines. Each subscriber would be wired to the remote station. The village will have 10 pay phones, with the remaining 30 subscribers being both residential and commercial.
Total cost: US$30,000, making the cost per subscriber US$750.
Public Internet access
In the final example she presented, the objective is to increase the payback time of a system by installing revenue-generating equipment. A public Internet kiosk could meet this requirement, McCabe explained, but added that it then would reduce the number of standard voice lines.
As the number of subscribers per system decreases, the cost for each of these subscribers then would increase; however, by using different types of systems and technologies, the overall cost for a smaller-capacity system can be kept reasonable, she said.
The primary difference between this example and the second is that in this application a combination of pulse code modulation (PCM) and ADPCM operation is used. PCM allows the carrier to offer high-speed data services to the village, thus permitting installation of an Internet kiosk. The trade-off, again, is fewer trunk lines for voice.
The system would have four trunk lines for voice and/or fax, as well as one dedicated high-speed data line. Fifteen subscribers would share the four trunk lines; five subscribers would operate pay phones or telephones located in a public calling office.
Total cost: US$25,000. Since there are fewer subscribers over which this cost can be distributed, the individual subscriber cost, not including the Internet line, increases to about US$1,667.
“While cost per subscriber has increased, the existence of a public Internet kiosk will shorten the payback on this investment,” McCabe said.
