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Radio repeaters - old technology for new networks

Written by  Håkan Samuelsson
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Håkan SamuelssonIssue:Europe I 2010
Article no.:12
Topic:Radio repeaters - old technology for new networks
Author:Håkan Samuelsson
Title:CTO
Organisation:Axell Wireless
PDF size:169KB

About author

Håkan Samuelsson, the Chief Technology Officer of Axell Wireless, is the creator of some of the first cell enhancers in the industry more than 20 years ago. Mr Samuelsson began his career in wireless in the Swedish broadcasting industry. He later founded Avitec AB; Avitec merged with AFL to create Axell. Mr Samuelsson, an industry expert in both coverage solutions and wireless technology, is a frequent speaker at telecom conferences worldwide.

 

Article abstract

Mobile data traffic growth is forcing operators to upgrade their networks. Most mobile operators will eventually upgrade to LTE, but are holding back due to the high cost of deploying LTE using traditional network architectures. An old technology, radio repeaters, allied with a new digital technology, SDRs - software defined radios, provides an economical and technically robust way to provide coverage using existing antenna networks. SDRs can also be easily reconfigured - without hardware update - for use with future technologies.

 

Full Article

Consumer expectations of mobile services have irrevocably changed. Devices such as the iPhone, not to mention Android, BlackBerry and Windows Mobile smartphones, have created a plethora of ways in which to consume mobile broadband and data services. From the mobile network operators’ perspective this is good news, after all mobile broadband and data services represent one their most significant revenue generating opportunities. But this opportunity brings with it a new set of challenges. Customers expect data traffic speeds to support their chosen smartphone applications, whether that be low-demand services such as email and social networking apps or high-demand services including mobile TV. Due to network capacity limitations, operators cannot always guarantee sufficient bandwidth to customers and, as increasing numbers of mobile users adopt smartphones, this is a problem that will only get worse. Within the mobile communications industry there is little doubt as to how these bandwidth issues will ultimately be solved. The arrival of LTE (Long Term Evolution) will provide users with data-speeds previously only associated with fixed-line broadband connections. When LTE finally arrives, smartphone users will, in theory, be able to make full use of their handsets’ data hungry features without experiencing prohibitively slow data speeds at peak usage times. But only a small minority of operators are currently focused on LTE and for good reason - operators have some robust challenges to overcome before LTE becomes anything more than a technological possibility. Perhaps the most significant of these of these challenges is the huge cost of LTE rollout. These costs are mainly due to the fact that LTE, like all high-capacity wireless data networks, operates on a less propagation-efficient spectrum. As such, LTE base stations have to be deployed at more frequent intervals meaning significant investment in network hardware is required. In addition, greater base station density requires new cell mast locations and additional cost for the masts and sites to place them and a time consuming logistical challenge. A nation-wide LTE rollout is definitely a technological possibility, as recently demonstrated by Telia Sonera’s metropolitan deployments in the cities of Oslo and Stockholm, but the process can be expensive and logistically difficult. The scale of these challenges could set national LTE rollout back for years were it not for the various solutions available to operators. Each of these solutions brings a price tag and a unique set of benefits and disadvantages, which operators have to weigh. One prominent solution would be running LTE on lower frequency, more propagation efficient, spectrum. This mean fewer base stations would be required, lower costs and fewer logistical challenges, but in many regions in and around Europe, lower frequencies are already allocated for other purposes including broadcasting. Another issue with the lower frequencies is that they support less bandwidth and so would struggle to support broadband speeds in high user density areas. This drawback alone would bring into serious question the value of deploying LTE. An alternative would be to deploy a carrier grade distributed antenna system. These extend the reach of a single base station, but such systems rely on high capacity, high cost, fibre links between each network element. So, while overcoming black and grey coverage spots, costs would still be high, bringing into question the true value of distributed antenna systems in addressing LTE challenges. The adoption of pico and femtocells connected to fixed broadband routers is also a possible solution but, whilst viable for creating micro cells within buildings for a limited number of users, they are not economically scalable for larger numbers of users. In addition, pico and femtocells require operator to rely on a network over which it has no direct control - a scenario the majority of operators would like to steer clear of. An alternative solution has been less debated, but it offers a perhaps more feasible response to the challenges posed by LTE rollout is the use of radio repeaters. Repeaters are small, easy to place and, most importantly, inexpensive when compared to base stations. Repeaters can be used to propagate LTE coverage to grey and black spot areas between LTE base stations, which means LTE base stations can be placed on existing cell masts, eliminating the need to find new mast locations. By overcoming the cost and logistical challenges of LTE rollout, repeaters would appear to present a complete solution. Why, though, are operators holding back from fully endorsing the technology as a core component of LTE networks? Radio repeaters are an old technology, but they still play an important role today by extending wireless coverage indoors and into other radio network black spots. Repeaters are rarely used as a core or permanent part of macro cellular networks since traditional repeater technologies often raise interference issues. This means that repeaters work well for limited numbers of user or as a temporary fix for coverage issues, but ultimately cannot replace base stations. Recent advances in repeater technology however, directly address these problems and offer operators additional benefits. These advances are obtained through the use of software defined radio (SDR) technology. Interference cancellation features have historically been difficult to achieve in conventional repeaters. SDR repeaters make interference cancellation a relatively straightforward process. They also make the implementation of adaptive gain adjustment and advanced supervision and signal quality reporting easier. As such, all signals processed by SDR equipped repeaters reach their recipients clean and indistinguishable from a signal that has emerged directly from a base station. This factor alone makes SDR repeaters suitable for use as a core network component. SDR functionality goes beyond meeting the necessary requirements, extending coverage to the grey and black spots in the gaps between base stations, to support the deployment of LTE and provides operators with additional justifications for the permanent use of repeaters in mobile networks. In traditional radio based communications, network equipment such as base stations and repeaters operate on fixed standards, the standards are hardwired into the equipment and so cannot be changed without a physical upgrade. Today, numerous mobile telecommunications networks exist: GPRS and 3G not to mention the networks used by the emergency services such as Terrestrial Trunked Radio (TETRA). This means that for each of these standards, dedicated network equipment has to be strategically positioned to deliver coverage. Naturally, if a new network standard is introduced, additional network equipment has to be deployed - as in the case of LTE deployment. Such upgrades at a national level are both expensive and time consuming, which makes operators unsurprisingly slow to react. SDR provides a solution to this challenge by enabling operators to meet changes in network standards with almost immediate effect. With SDR, network operators can remotely change the radio standard that network components operate on simply by installing new software. This means that it is possible to accommodate future developments and enhancements in network functionality without replacing older equipment. In terms of future proofing networks and ensuring a return on investment in the network infrastructure, the benefits of SDR are clear. Regardless of future planned and unforeseen changes in the use of radio standards, with SDR the network hardware can accommodate these changes with little more than a click of a button. SDR makes repeaters a long-term solution - not just a temporary fix for the cost issues surrounding LTE. Once in place, SDR enabled network equipment provides operators with a solution that is good for LTE and whatever network standards follow LTE. In many ways this further justifies the deployment of digital SDR repeaters for LTE - a solution that provides both immediate and long-term cost saving advantages. So will digital repeaters become a core component of LTE networks? LTE is not a luxury. LTE is fast becoming a necessity for both mobile broadband users and mobile network operators since existing network infrastructures are increasingly overloaded by growing volumes of data traffic. As such, operators need to quickly deploy LTE, but to do so they need to first overcome the cost and logistical challenges. By bringing the tried and tested repeater into use as a core and permanent part of the mobile network infrastructure, LTE deployment costs can be significantly reduced and the logistics simplified, thereby eliminating the biggest barriers to deployment. The introduction of SDR technology ‘future-proofs’ the solution and further tips the balance in favour of repeaters. SDR will prove to be a boon for operators who still have unpleasant memories of the costs associated with 3G. It is still too early to say whether and how repeaters will feature in LTE networks. Nevertheless, this old technology, renewed by digital innovation, offers mobile operators a cost effective, viable solution. The old repeater is now a strong contender.

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