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Trouble at the tower top As the FCC auctions wireless spectrum for future services in the US, the cocktail of co-located technologies and frequencies at the tower top could interact with each other in unpredictable ways—spawning unprecedented interference challenges. The contemporary demand for communications mobility is undeniably putting pressure on wireless spectrum. New technologies and services—such as WiMAX and mobile television—are joining third-generation (3G) cell-based mobile services in the jostle for bandwidth. Spectrum regulators are having to assess— and quickly—how best to reassign and redeploy spectrum and services to pave the way for future applications. An added complexity is the concurrent trend towards co-location of base station sites. Premium sites are in high demand, leading to physical congestion of tower structures and rooftops, as more and more antenna systems are deployed. What can result, says David Kiesling, Radio Frequency Systems Director Marketing and Technical Services, Americas North, is a cocktail of frequencies and technologies at the tower top that interact with each other in unpredictable ways—in many cases causing significant interference and degradation of services. US spectrum auctions According to Kiesling, a more widespread understanding of potential interactions and interference is required in order to minimize the impact on quality of service. “There have been scenarios where a particular service has been operating successfully for years, then is suddenly impacted by the introduction of a new service to the same site,” he says. “An example of this is the co-location of 800-MHz CDMA and GSM 900-MHz services in countries such as Brazil, China and India.” The CDMA/GSM co-location scenario is now well documented, and the solution has been proven to lie in the deployment of RF filters with sharp selectivity responses. However, says Kiesling, the situation in the United States is about to get very interesting with the planned 2006 auction of spectrum in the 1.7 and 2.1-GHz bands, and later the 2.4-GHz band, by the nation’s Federal Communications Commission (FCC). “There’s a very real possibility that carriers adopting 2.1-GHz spectrum for UMTS transmission will co-locate with existing PCS services,” says Kiesling. “If the antennas are positioned too closely together on the tower, the third order intermodulation harmonic created by the two signals stands to fall in the vicinity of the 1.7-GHz UMTS receive band.” (See Figure 1) WIRELESS COMMUNICATIONS The problem here is that the intermodulation signal is likely to be significantly stronger than the desired receive signals, leading to problems with blocking and receiver sensitivity. If the intermodulation signal falls out of the UMTS receive band, installation of a RF filter on the UMTS uplink will mitigate these interfering signals. However, if the interfering intermodulation signal happens to fall in-band, the situation becomes more challenging. Kiesling suggests that the only recourse for carriers may be to work together to better manage frequencies. Equipment vendors will also be under pressure to ensure their designs minimize passive intermodulation sources. Future outlook This scenario is but one predicted issue to arise from the assignment of new spectrum in the US. “The point is that we don’t know exactly what the outlook is for the future,” Kiesling says. “Once you’ve got five different technologies up on the same tower, you need a certain level of cooperation and shared knowledge in order to determine which services will cause interference to others.” Kiesling adds that the issue is influenced by a shifting culture in base station site ownership: in the US, around 70 percent of sites are now owned by independent tower real-estate companies, as carriers seek to release capital for deployment. “The site owners don’t necessarily come from a wireless background and they don’t necessarily understand all the issues,” he says. It all boils down to the fact that someone needs to take responsibility for how colocated services interact with each other, emphasizes Kiesling. In cases where RF filtering is not an option, this may be as simple as ensuring certain antennas are not positioned too close together, or operating at reduced power levels. The bottom line is that some degree of care will need to be taken to avoid trouble at the tower top. Broadband RF now, mobile TV later Impending analog switch-off will provide plenty of options for broadcasters seeking to utilize the released spectrum; but how can RF systems be made futureproof to accommodate the new services? As analog switch-off dates draw closer in some parts of the world, the deployment of digital terrestrial television (DTT) services is entering a new stage. The focus is starting to shift towards ‘life after analog’, and the opportunities that will arise from the released spectrum. One of the key issues for broadcasters is the capacity of existing multi-channel broadcast systems to incorporate whatever new services might be introduced—including mobile television. For those broadcasters deploying new networks: how can those systems be futureproofed? Multi-channel systems, where multiple analog and/or digital services are broadcast simultaneously from a shared RF broadcast infrastructure, are common across Europe and rising in popularity elsewhere. Utilizing broadband panel arrays and advanced RF combining technology, such broadband systems help minimize installation costs and optimize site real-estate. With little extra capital expenditure, decisions can be made now that will make the addition of future digital services—including the emerging Digital Video Broadcasting- Handheld (DVB-H)—easier and less costly. The future-proof system A number of important factors need to be considered when designing a future-proof system. From a practical perspective, there is the consideration of signal polarization and coverage: how likely is it that future services will have the same requirements as the existing channels? This question is particularly pertinent if DVB-H services are to be considered. It is still unclear as to whether DVB-H will be driven by broadcasters or the mobile telecommunications industry—or whether these industries are headed towards some form of convergence or cooperation. Distribution models utilizing various frequency bands have been developed by both parties: some based around mobile base stations, others based on central broadcast sites supported by translator sites in a manner similar to DTT. The issue of which form of polarization will provide the best reception for mobile television handsets deserves further consideration. In addition, determining optimum coverage is the subject of an increasing number of DVB-H trials around the world. Nevertheless, if the polarization and coverage requirements of DVB-H are the same as existing DTT services, it is certainly possible to use a common infrastructure. From a system design perspective, the issues of power handling, voltage capacity, and whether the combiner chain is able to be expanded, need to be considered for a future-proof system. Broadband antennas are available to cover the full UHF spectrum; however, the number of channels that the system can support is dependent on the power and voltage characteristics. Importantly, in multi-channel systems the voltage ratings become critical, plus digital services exhibit higher peak voltages than analog services with equivalent power. It is therefore beneficial if the planned digital replacement for analog services is factored into system design at the beginning. It doesn’t cost much to consider extra power and voltage handling when specifying an antenna and feeder system. Expanding combiners When it comes to expanding an existing combiner chain, there needs at the very least BROADCAST 14 15 Figure 1: The UMTS/PCS co-location challenge to be space available. Coaxial combiners—as most often seen in Europe—can be rearranged relatively easily to accommodate new modules, providing there is enough power and voltage handling in the final stages. On the other hand, it is far more difficult to insert channels into a high-power directional waveguide combiner system; in such systems, it is advisable to incorporate ‘blanking’ sections into the chain where additional channels can be inserted later. However, it is usually necessary to know the specific channel beforehand, since channel sequence is important. Although it is difficult to predict exactly what technologies are coming down the track, it is certainly possible—and perhaps advisable—to build-in extra capacity to multi-channel broadcast systems with very little up-front expenditure. At the very least, broadcasters should consider what services they plan to introduce in replacement of analog services, in order to ensure the system will support them.
Ukraine’s Kievo- Pecherskaya Lavra in Kiev Ukraine spreads the wireless word One of the fastest growing wireless markets in the world, Ukraine leans heavily on RFS technologies as the foundation for its nationwide RF networks. is a center of pilgrimage for Orthodox Christians from all over the world. digital age,” says Rivkina. “Now we're happy to be assisting all three carriers in Ukraine's dynamic telecommunications market.” Reputation for reliability Nine years of collaboration with the Ukrainian wireless carriers has given RFS a reputation for first-class quality and short Russia and CIS, as well as processing the orders. From a global RFS perspective, Ukraine is an important market, and that’s why the RFS name is so established here.” A large portion of RFS’s success in the region is due to its ability to meet Ukraine’s uniquely short delivery time requirements. In a country that from 2004 to 2005 increased its mobile subscriber base by 110 taken the time to analyze the trends and identify a series of products to maximize these fast-maturing networks.” Recently, both carriers have seen the value of using RFS’s range of highperformance boosters from its RF conditioning family of products. According to Rivkina, DCC/Astelit, being a new carrier with a young network, has seen the delivery times. “In this region—Ukraine, percent, fast delivery is of the utmost need for boosters and tower-mount The first form of wireless communication in (UMC) and Kyivstar—have continued Belarus and Moldova—trust is a very importance. “RFS has manufacturing amplifiers to increase its network capacity. Ukraine was a symbolic ‘human chain’ to maintain a duopoly now representing important part of business, and RFS, with facilities in Balabanovo, near Moscow, and “Our customers rely on us to keep formed by half a million Ukrainians joining 98 percent of Ukraine’s mobile subscriptions. its local sales partners, has proven itself over also in France, Denmark, Germany and so them abreast of new and interesting hands from the capital Kiev, to Lviv in the Originally the leading operator, UMC was and over again,” says Rivkina. on. So, by leveraging this global framework technologies. It’s a very open and trusting west. This occurred on January 22, 1990, forced in mid-2001 to stop accepting we can meet any order within the shortest relationship,” says Rivkina. and stretched over 500 kilometers pre-paid subscriptions for a period of delivery time,” says Rivkina. RFS regularly delivers presentations on new (310 miles). The act was in commemoration three months due to network capacity An important element of the spectrum of and next-generation technologies to the of the anniversary of the proclamation of problems. This paved the way for Kyivstar solutions provided by RFS to the Ukrainian Ukrainian carriers, keeping them up to Ukrainian independence in 1918. to take a strong position in the market. wireless communication sector is CELLFLEX date with progress in the industry. RFS Ending in 1920, the period of indepen- Since then, despite fierce competition foam-dielectric coaxial cable and acces- also holds annual installation training dence was short-lived, and it wasn’t until between the two, both GSM carriers sories. The popular and high-performance courses for the carriers’ subcontractors. the dissolution of the USSR in 1991, that have been on par, but their overall RFS feeder cable forms the backbone “That’s what sets RFS apart from the Ukraine finally regained independence. dominance has been almost unassailable. to the RF distribution of both UMC and rest, we go to the source of the issue With its freedom, the country also took Other carriers have since looked towards Kyivstar—and more recently DCC/Astelit. and work out from there—such as 16 REGIONAL FOCUS The Dnepr River is the Ukraine’s most significant river, and—at 2300 kilometers (1430 miles) long—one of Europe’s longest. 17 on a series of challenges to begin the Ukrainian wireless industry, although providing training to our customers’ upgrading its telecommunications sector. their success has been limited and, in most installation service providers,” says Rivkina. The national telecommunications develop- cases, transitory. The first to really make its More than just caring, RFS has the ment plan led first to the launch of analog mark in the Ukrainian wireless market advantage of foresight. “Being a global mobile telephony (using the Nordic Mobile has been Turkish Turkcell-backed Digital organization we have gone through Telephone (NMT) standard in 1993. Cellular Communication of Ukraine all stages of the wireless development The launch of global system for mobile (DCC)/Astelit, with its ‘Life’ network. lifecycle. We’ve found that our experience communications (GSM) digital networks in Launched in 2005, DCC/Astelit is the in Eastern Europe and the rest of the the 900- and 1800-MHz bands followed newest GSM carrier in Ukraine and is wireless world provides an important closely in 1996. This is also the year that currently deploying an aggressive network foundation for our work in Ukraine.” Radio Frequency Systems began to assist in roll-out incorporating 2.5 generation In order to keep abreast of the require- “Based on the reliability of the RFS trans- Over the coming five years, the Ukrainian the country’s roll-out of wireless networks. technologies. Determined to find a niche ments of the local operators, RFS mission lines, the Ukrainian carriers are now carriers are expected to continue increasing By 2001, two main GSM carriers had within this rapidly expanding sector, The Mikhailovski operates in the Ukraine through three starting to look into other RFS technologies both coverage and capacity of their secured the majority of the mobile market, DCC/Astelit has been marketing its Cathedral in Kiev sales partners: Radiochastotnyie Sistemyi to modernize their networks,” says Rivkina. GSM networks. Next on the cards is seizing more than 90 percent of the subscriber base between them. fashionable ‘Life’ brand, which targets students and young adults. The success of Ukraine, Stankotechimport and Actek C. These partners act as RFS’s ‘ears on the Capped capacity universal mobile telecommunications service (UMTS), with the first 3G license to Three’s a crowd the ‘Life’ network is all the more significant in light of Turkcell’s first Ukrainian wireless ground’, although RFS also maintains a tight focus on the region. “Ukraine is a very Of particular interest to the Ukrainian mobile sector in its current evolutionary be awarded very soon to the incumbent fixed line operator, Ukrtelecom, a new Ukraine’s total mobile subscriber base has venture in 2001—the ‘Novacell’ network— important country for us,” says Rivkina. stage is RFS’s suite of network optimization player in the mobile market. The company increased from just two million in 2001, to which folded within two years. “We have an area manager completely products. “Both UMC and Kyivstar are plans to launch commercial UMTS services more than 20 million in 2005, equating to According to Natalia Rivkina, RFS Regional dedicated to looking after RFS customers in continually rolling out new networks and by end-2006. “Just as we’ve been there all a mobile penetration increase from four Sales Manager, DCC/Astelit is a very new Ukraine, Belarus and Moldova. We also optimizing existing ones. Yet, as the along for the development of the country’s percent to nearly 50 percent in just carrier in the Ukrainian wireless market. have two customer service coordinators subscriber numbers increase relentlessly, 2G, we’ll be there also to facilitate Ukraine’s four years. Over this time, the two main “RFS has been involved with UMC and providing technical and commercial the demand for capacity remains the transition into 3G,” says Rivkina. carriers—Ukrainian Mobile Communications Kyivstar since the beginning of Ukraine's informational support to RFS customers in driving factor,” says Rivkina. “We’ve
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