Hybrid Repeaters in the Spotlight

Repeaters are moving from their traditional supporting role to taking the lead in digital cellular and PCS deployments. As digital technology brings increased capacity, repeaters offer a way to spread that capacity in suburban, rural, rural highway and in-building areas for much less than the cost of building and operating base stations.

Traditionally, RF repeaters have been added after build-out to improve networks and fill in coverage holes. But increasingly, service providers are adding repeaters during the initial design phase.

By building out networks with a hybrid repeater network, which is a design that combines repeaters and base stations, you can expand cell size and coverage, minimize excess capacity, and reduce real estate requirements and your initial capital outlay, said Dave Bolan, Repeater Technologies vice president of marketing.

Hybrid repeater networks also present a few challenges. Designing the networks is not easy, and they may not be ideal in every situation. Still, many carriers are considering repeater build-out to provide subscribers with better service.

APPLICATIONS & BENEFITS With the advent of high-capacity digital systems, service providers may have more capacity than required for a given coverage area. Sometimes, building base stations is like constructing an expensive 8-lane freeway when a 2-lane hybrid road would suffice.

"With the judicious use of repeaters, the service provider is able to provide full coverage and do it in a way that the economics are more attractive than trying to do that exclusively with base stations," said Doug Morais, Ortel wireless unit president.

According to Bolan, you will end up with better coverage because you can fine tune the RF footprint by putting more repeaters into a network and get the RF exactly where you need it.

Bolan said when you have non-homogeneous coverage requirements, a hybrid repeater network is ideal.

"You don't need a ubiquitous RF blanket everywhere if it is not where people go," he said.

Repeaters are attractive particularly in rural and suburban environments because there is a need for coverage but less need for capacity, Morais said.

On the fringes of a main urban area, repeaters could be used to extend that coverage at a significantly lower cost than a base station. Another application would be on a highway, where, more so than in an urban or suburban environment, the issue is coverage, not capacity. In that situation, you can interweave repeaters with base stations. With a combination of base stations and repeaters, the base-station count can drop by half for suburban or rural coverage and by two-thirds for rural highways over a traditional all-base-station deployment.

Hybrid repeater-base-station build-out solves three major problems. It improves the No. 1 reason for churn -- lack of coverage. It reduces the No. 1 capital cost item -- base stations -- and minimizes the No. 1 expense for operation cost -- backhaul. Many manufacturers are offering customized repeater networks that solve all of these problems.

Morais said more carriers are deploying these types of hybrid repeater networks because they recognize coverage issues.

"They are turning toward the most economical solutions," he said. "As a result of that, (service providers) are paying more attention to repeaters and how repeaters can help them."

If you deploy base stations in every event, it is a significant capital expenditure and recurring cost. The cost of base stations includes switches, software, monthly operation costs, T1 backhaul, electricity and rent for lease space. With repeaters, that backhaul cost disappears because the repeater is picking up the signal that already is radiating and is re-radiating that signal. Also, because repeaters are smaller than base stations, the site-acquisition costs and installation cost structure tends to be considerably lower for repeaters.

"In order for carriers starting to build-out in second- and third-tier cities to be successful, they know how many subscribers they can expect, how much revenue per subscriber they can expect, and that they can support only 'x' amount of dollars of build-out," Bolan said. "To make their business plans viable, they have to cut their costs 30% to 40% over a conventional deployment." According to Bolan, cost savings with hybrid networks range from 25% for suburban areas to 50% for rural highways.

"If you put a base station where repeaters are located, you have more RF than you need, and you would be wasting your RF energy and spending more money to get the RF coverage you need," he explained.

Bolan said the 5-year total cost to cover 1,000 square miles would require 221 base stations at $120 million. Carriers can do the same with a network of 115 base stations and 345 repeaters for $80 million.

But cost savings can vary. Morais said Ortel's analysis shows that if a carrier used a CDMA-based system on a rural highway and deployed two repeaters instead of a base station -- one repeater taking a signal from an adjacent base station in one direction and another repeater doing the same in the other direction -- it could save $300,000 per site.

SUCCESS STORIES F-block PCS provider LifeCom in St. Cloud, MN, uses suburban/rural hybrid repeater network coverage. The carrier has a hybrid network consisting of 21 repeaters and five base stations, averaging almost two repeaters for every sector of base stations. Repeaters supply most of the coverage, with base stations providing the capacity.

If LifeCom had deployed all base stations, the network would have required 12 base stations at almost $5 million. But with a hybrid repeater network, the carrier's cost was just $3.12 million, said Bill Casto, general manager.

The hybrid network covers downtown St. Cloud as well as its suburbs and feeder highways. In St. Cloud, LifeCom leveraged coverage from various designs, including six repeaters off of a single cell site and repeaters with omnidirectional antennas.

"It is the first CDMA network to deploy a ratio of four repeaters per base station, making it the most concentrated usage to date," Repeater Technologies' Bolan said.

And LifeCom gained a much larger footprint and a smaller capital outlay to cover a geographical area, said Casto.

"The plus side (of hybrid repeater/base-station build-out) is you do not have to provide your infrastructure until capacity becomes an issue, and once it does, all of these repeater sites are already wired and antennaed for base stations," Casto said. "So you just pull off the repeater and plug in a base station."

Casto reported that LifeCom's deployment has been successful so far, though he admitted it also has been a learning process for the carrier, which just completed a pre-commercial launch in July.

"We were already a cellular carrier and could utilize a lot of the existing sites. However, CDMA is a different animal, and propagation of 1,900MHz versus 800MHz is smaller," he said. "With CDMA being as dynamic as it is, the more people that use a site, the smaller the site becomes, so you have to take that into your planning (considerations) when you design a network."

Clearnet Communications, a nationwide PCS provider in Canada, owns hundreds of base stations and just began deploying repeaters a few months ago, according to Stephen Howe, director of technology development.

Clearnet has been operating on the PCS side since October 1997, but Howe says it is in an intense build-out that will include more repeaters. He said the repeaters will allow better coverage and call quality and, ultimately, lower prices for subscribers because of a more efficient network.

DESIGNING HYBRID NETWORKS The design of hybrid repeater-base-station build-out will depend on each carrier's circumstances. However, there are some basic concepts all carriers should consider.

Bolan said to make hybrid repeater networks a reality, repeaters must enhance coverage without degrading network performance. Repeaters need to be designed like base stations,and not casually dropped in and treated like black boxes. In addition, repeaters must be managed because they become a critical network element.

"It is an important part of your coverage, not just a fill in," said Bolan.

Morais said network management is one of the biggest concerns when carriers deploy repeaters. It is important to service providers to be able to monitor repeaters in the same way they monitor base stations. Morais said Ortel offers a software program that manages all repeaters in the network.

Repeater Technologies also employs a system that can monitor up to 1,000 repeaters remotely. According to Bolan, the vendor designs a handset inside the repeater for carriers to call. Repeater Technologies pumps all of the data through the handset, through the network or over a wireline phone to talk to the network-monitoring site through a technician's laptop or at a regional center.

Testing and working with your vendor are important phases of designing your network.

"We thoroughly tested (repeaters) with (the vendor), so it is not like we just bought it off the shelf and (stuck) it up there," said Clearnet's Howe. "I have not seen any problems to date. It really comes down to working with the vendor. They know a lot more than you do, at least at first."

OUTLOOK With evolving technology, the future looks promising for repeaters, Morais said. But vendors must continue to make products more user friendly, and easier to install with more "plug and play" capabilities. In the past, repeaters were "dangerous machines."

"They were not channel selective, for example, and there was a possibility that they would transmit everything in sight, not just the desired signal," Morais said. "Unfortunately, repeaters got a not-so-excellent reputation."

Morais said that just a year or two ago, vendors ran into a repeater "stigma. " But he said that attitude is disappearing as more repeaters are deployed successfully and fears are allayed.

According to Clearnet's Howe, the flexibility of deployment options offered by hybrid repeater networks is making them increasingly attractive to carriers. A lot of people are more interested in repeaters now than a year ago, he added.

Vendors admit that hybrid repeater networks are not easy endeavors.

"One of the biggest challenges is designing from a systems standpoint," said Andrew Singer, Celwave director of technical marketing. You should ask yourself what sort of power repeater do you really need? What sort of coverage can you get out of it? What do you need to do with the distributed antenna system?

Designing hybrid repeater systems may be challenging, but doubts about how base stations and repeaters will work together may present a bigger roadblock.

Singer said network engineers are wary of how well repeaters will work and communicate with base stations. With a hybrid approach, he said, you are not just trying to fill a small hole, you are trying to cover a sizable area with repeaters, which become very intertwined with your whole system of base stations and the communication among those base stations.

"Engineers have a bit of mistrust in doing that," he said.

Bill Casto, LifeCom general manager, agreed that the biggest challenge was convincing the engineering staff to try it because their past experience using repeaters in a frequency-specific-type application was not very favorable.

According to Casto, another challenge when you design a network using repeaters, especially with a CDMA/PCS operation that overlays a cellular/analog system, is taking into consideration that when the mobiles get to the edge of the digital coverage, you should hand down to analog.

"If you do not place your repeaters properly, you end up with a problem where you are handing down prior to when you need to, based on the constraints of your switches' software," he said.

Another challenge is deciding whether hybrid networks will work for you.

"Cost is a major concern obviously, but there is no relevancy to cost if the quality is not there," Casto said. "If you can't provide the consumer with a high-quality product and that is your tradeoff, then don't trade off."

Casto said so far, LifeCom's hybrid network has been excellent. "But you have to be careful; you can overdo it," he warned. "You can have too many repeaters and not enough base stations. Keep in mind that each repeater is actually sucking the strength off of a base station someplace, and that strength is its capacity."

There can be a potential problem if the need for capacity increases significantly, said Doug Morais, Ortel wireless unit president. For example, if a developer comes along and puts in a large mall, suddenly there are more customers that use service. Ultimately, he said, because repeaters get capacity from the base station, that base station will run over capacity and potential subscribers in the new mall might get a lot of busy signals. The service provider would need to replace the repeater with a base station and then re-deploy the repeater.

Repeaters can be a viable option for expanding an existing network, but, when designing a new system or building onto an existing GSM PCS 1900 network, remote radios are another alternative. A remote radio coupled with a high-capacity broadband transceiver system (BTS) can provide quality performance, high flexibility and low operating expenses. Remote radios retain features of mini base stations (diversity, handoffs and coverage area), but without backhaul requirements.

Remote radios implement a low-cost, single-RF-channel base station using a narrowband radio transceiver with an integrated backhaul transceiver. The remote radio is used with high-capacity BTSs. Essentially, the radio serves as a remote single-channel BTS.

The remote radio fully implements a conventional base station. Other than additional backhaul frequency coordination, RF planning for system deployment is performed as it is with a typical base station. Mobile handovers are performed between remote radio sites or between remote radio and BTS sites. System performance is not compromised. Diversity processing counters the effects of multipath fading. Processing within the BTS compensates for the in-band backhaul delays and other signal variations so that timing and power adjustments are performed in relation to the remote radio site and not the serving BTS site.

Remote radios with a single BTS are a cost-effective method of providing RF coverage. One BTS can support up to 12 cell sites, each with a single TRX. One TRX will support up to seven simultaneous voice channels with one control and access channel. With the BTS supporting traffic within its own site, you can use a maximum of 11 remote radios with the BTS, which provides maximum coverage of 12pr2 square miles (1,100 square miles at 1.9GHz, under ideal conditions). Because the remote radio provides only a transceiver and none of the electronics required for baseband processing, it costs significantly less than a BTS. In addition, because remote radios use available spectrum for backhauls to the BTS, there is only one T1 or E1 backhaul to the BSC for all 12 cell sites. Therefore, backhaul operating costs are reduced up to 91%.

The remote radio concept incorporates distributed networking capabilities. You can position the primary BTS(s) in high-density areas with remote radios extended across the suburban/rural overlap region. If the suburban population increases, you can expand the BTS(s) capacity (up to 96 available channels).

As rural usage increases, you can deploy a second site. The original 12 cell sites can be split into two groups of six sites, with each group served by its own BTS. Remote radios that are replaced by a BTS are re-deployed to increase capacity in other cells or to provide additional coverage in the network.

Repeaters work with all digital technologies (CDMA, TDMA and GSM) to extend coverage at a lower cost than base stations. But there are some differences.

Andrew Singer, Celwave director of technical marketing, said there is a significantly higher usage of repeaters for GSM systems in Europe than in the United States because of higher penetration rates. As penetration rates go up in North America, Singer said new users will expect better service and more coverage, and more repeaters will be necessary, regardless of the technology.

According to Singer, repeater use provides a unique application for CDMA in supplying a dominant pilot as one way to handle pilot pollution, which does not occur with GSM or TDMA.

"One of the biggest challenges in the optimization phase for operators has been this phenomenon known as pilot pollution," he said. The portable CDMA phones have a 4-finger raked receiver. One of the fingers is used for scanning, to look for pilots. The other three can hold three pilot signals, whether three individual pilots or strong multipath reflections from pilots. If more than three pilots appear with similar and strong signals, the portable has problems with that information and can drop calls.

According to Doug Morais, Ortel wireless unit president, each base station has a pilot tone, and there are certain areas where a sub-scriber's phone becomes confused because there are so many pilot tones, and none is dominant. The portable does not know which base station to log onto. In that situation, a carrier can choose one pilot tone from a particular base station to be dominant, take a repeater and repeat the signal in that gray area so it is no longer gray.

"One way to create a dominant pilot is to use an outdoor repeater to saturate a particular trouble spot with a pilot from one particular sector," Singer said.

Morais said such situations tend to occur in urban environments where there are many base stations.

"It is a network-design problem, and one of the most economical ways to address it is to use a repeater," Morais said.