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Eliminate the Backhaul Link

Bennet Wong
10/01/1999
Wireless Review
Copyright 1999 by Intertec Publishing Corporation, a PRIMEDIA Company. All rights reserved.

Whether you use T1 lines or dedicated fixed microwave, backhaul costs typically range from $500 to $2,000 per link per month. Considering that every BTS in a network needs a backhaul link, this expense is often the main impediment to rapid build-out. As much as 30% of a carrier's recurring expense is associated with backhaul.

But soon this will be a problem of the past. Software-defined broadband technology is the key to unlocking a backhaul-free infrastructure solution. By using this new technology, you can eliminate the physical link to every base station in the network.

BROADBAND VS. NARROWBAND

Traditional analog systems require banks of radio equipment, each hosting a single link between the cellular user and the public switched telephone network (PSTN). Today's digital systems improve capacity by squeezing more conversations into a single narrowband channel. Although digital protocols use spectrum more efficiently than analog protocols, they still are tied to narrowband channel transmission.

Rather than being restricted to a distinct narrowband channel, a broadband radio receives RF spectrum containing many channels at one time. The intermingled channels are isolated and forwarded to the MSC for routing to the PSTN. An inverse algorithm combines separate narrowband signals for transmission to remote handsets.

For example, a broadband base station with an RF front end tuned across a 5MHz range of spectrum supports up to 12 GSM (200kHz) carriers, each divided into eight time slots for a total of 96 channels. In this case, one broadband transceiver does the work of 12narrowband transceivers.

By using digital-signal-processor-based technology, a software-defined base station processes many channels at a low cost. Not only are they more cost-effective than hardware-intensive narrow-band base stations, but you can upgrade to new 3G protocols easily. And software-defined broadband base-station prices are dropping rapidly.

Because a broadband software-defined base station supports many channels, this extra low-cost capacity provides a solution to the backhaul problem: You can use the additional channels to carry backhaul traffic, and avoid the high cost of T1 lines and fixed microwave links.

You can install a specialized remote base station to interface with the high-capacity broadband BTS and associate more than one with the same broadband software-defined BTS. A 12-carrier GSM base station can support 11 remote 8-channel GSM base stations leaving one carrier (eight channels) on the broadband BTS for local traffic. Although the broadband BTS needs a T1 line or microwave link to the base-station controller (BSC), all remote base stations provide backhaul-free coverage.

This type of network is inherently modular and gives you more deployment flexibility than traditional, T1-dependent architectures. If a remote cell reaches full capacity, you have two options: Add another remote backhaul-free base station to increase capacity, or move the original remote base station to a new cell and replace it with a broadband software-defined BTS.

UBIQUITOUS COVERAGE

When you deploy an initial-coverage infrastructure for a new market, you should deploy a footprint large enough to interest potential subscribers. At a minimum, this must include a community of interest such as a city, the surrounding suburbs and the highway corridors that connect them. You must deploy an infrastructure with the lowest operating and capital costs with the ability to add additional capacity as the subscriber base grows. You must provide ubiquitous coverage and address the demand for wireline substitution. In addition, rapid, flexible infrastructure deployment is an essential attribute because it allows you to launch service sooner.

A backhaul-free solution solves all of these problems. It allows you to build out networks quickly and cost-effectively. Secondary markets and coverage-limited suburban dead zones will benefit the most from the backhaul-free revolution. Free from the restrictions of costly T1 connections, build-outs in areas that generate less wireless traffic are not only practical, but even profitable.

Adding coverage is particularly expensive for PCS carriers because RF propagation is more limited at these higher frequencies. Up to four times as many base stations are required to cover the same area vs. the number required at 800MHz. Clearly, you need an infrastructure solution that can provide low-population-density coverage with low operating costs.

One solution is to place a broadband software-defined BTS in a higher-traffic area and expand coverage with backhaul-free remote base stations. The only T1 line in this example goes from the broadband BTS to the BSC, which means one T1 line is used more efficiently than using multiple T1 lines to each base station. This approach could save up to $16,000 per month.

Today, many stretches of highway are still without wireless coverage. Light traffic loads and the need for seamless coverage made highway build-outs an unattractive proposition, because of the high cost of backhaul. Eliminating the need for a physical backhaul link greatly reduces the deployment and operational costs for highway coverage. You can stretch remote base stations along highways and communicate with a broadband software-defined BTS located in a population center. This is especially efficient when the BTS is located near a highway junction. This type of highway architecture gives subscribers the coverage they want and gives you what otherwise would have been lost revenue.

HIGH-SPEED DATA

An additional advantage of the broadband software-defined base station is its inherent adaptability to new wireless standards and high-speed data networks.

As you move toward 3G and deploy new services with data speeds reaching 2Mb/s, you overlay the existing network. Using today's narrowband base stations, this overlay scheme could mean multiple base stations located at each cell site. One base station would support a legacy voice protocol, and one or more new base stations would support high-speed data protocols.

A carrier with a GSM BTS supporting voice and low-speed data would have to add a second base station to support high-speed data. That same carrier might have to add a third base station to support 3G ultra-high-speed data. An overlay scheme requiring multiple base stations will be expensive and inefficient.

The software-defined base station is an ideal solution because it can support multiple protocols on one hardware platform, which allows you to roll out high-speed data services as subscribers demand them. This solution also allows you to transition capacity from one type of service to another as subscribers adopt each new standard. All you need is a software upgrade.

By eliminating backhaul, this new architecture paves the way to truly ubiquitous coverage at a price that won't kill your bottom line. Free backhaul today, with a low-cost upgrade, is the path to new high-speed data services tomorrow.

TECHNOLOGY AT WORK IN LIBERAL, KS

Panhandle Telecommunications Systems has been operating a backhaul-free GSM network in Liberal, KS, for more than a year. After researching narrowband solutions, air interface technologies and infrastructure vendors, Ron Strecker, Panhandle CEO, said the decision came down to business, not technology. With T1 costs hovering around $600 to $1,200, Panhandle discovered a substantial savings in both deployment and ongoing operating costs.

"If we deployed our initial system using a traditional architecture with a bunch of T1 lines going everywhere, it would take forever for us to capitalize the build-out of the rest of our network," Strecker said.

In the Panhandle system, one broadband software-defined BTS is located in Liberal and provides standard base-station coverage. The BTS acts as the network's central hub, allowing Panhandle to deploy up to 11 remote base stations using only one T1 line.

The network's growth flexibility was one of the advantages that attracted Panhandle. When the carrier needs another remote base station, it simply installs 100-foot monopoles or leasing towers and aligns the antennas.

"It's that simple," Strecker added. "It's very inexpensive."

Panhandle decided that coverage was its first concern, because it needed to provide enough coverage to attract customers. It will address capacity issues as it grows and adds high-speed data applications.

"In high-traffic cells, we'll replace our remote base station with a broadband software-defined base station and move the remote base station a little farther on down the highway," Strecker said. "(The solution) gives us the ability to roll out service when needed, as needed."

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