Spectrum Liberalisation, UMTS900, Optimisation and the Need for Smarter Antenna Solutions 

David Barker, Director of Technology Applications,

 Quintel Technology Limited (UK)

Introduction

The spectrum liberalisation process occurring worldwide will mean the emergence of new wireless technologies, and through the “technology neutrality” debate, these new technologies will co-exist in the same spectrum bands used by today's wireless technologies. Spectrum de-regulation ultimately promises fair competition between rival technologies, better use of existing cellular spectrum bands, and better services for end users. This has already happened in certain parts of the world, either by regulator driven liberalisation policies, or by default, such as the US, Canada, South America and Australia, and we will ultimately see this happen in Europe and the rest of the world, where for example UMTS900 and HSDPA900 will be deployed in the current GSM900 bands.

Mobile operators wanting to, or considering the deployment of new wireless access technologies (e.g. Mobile TV, 3G, 3.5G, WiMax, etc.) in existing spectrum occupied by current cellular access technologies or for deployment of mixed access technologies in emerging technology neutral bands (e.g. 2500-2690MHz), will need independent RF tilt optimisation per access technology. This is because different wireless access technologies require different network optimisation targets, due to each technology serving different subscriber populations and demographics, having different air-interface characteristics, and different inter-technology and intra-technology interference tolerances. Moreover, when multiple access technologies are used by one operator and share the same limited spectrum then as spectrum is farmed from one technology to another technology, in response to technology migration, independent tilt optimisation per technology is paramount to maximise the re-farming process. To support new technologies in the same band an operator would have to deploy separate antennas, and feeder lines. This will mean additional costs and time penalties associated with the planning permission process, extra tower loading, rentals for new antennas and feeders, installation costs for new feeders, and the ever growing environmental pressure upon operators to minimise the quantity of antennas and masts.

Figure 1:Spectrum liberalisation = new technologies = need for independent tilt optimisation per technology = need for more antennas and feeders at sites = more costs, planning delays and loss in revenue

Quintel's QTilt technology provides the operator with a very compelling solution and an alternative to having to deploy multiple antennas and feeders, which can be deployed at lower cost, in less time, with less uncertainty, resulting in earlier revenues, and with an altogether more environmentally responsible solution.

QTilt Technology Sharing Applications

Quintel's QTilt technology provides two independently tilting beams, within the same cellular spectrum band, from one conventional sized panel antenna assembly to support the independent tilt optimisation of two different access technologies, or even two different operators using the same or different access technologies, and without the need to install additional feeder lines.

Figure 2: Principle of QTilt – Delivering two independently tilting beams from one conventionally sized panel antenna and a pair of (existing) feeders.

Examples of using the two independently tilting beams to optimise two logical radio layers include (but are not limited to) the following applications. The list also includes real world current examples of where two technologies are sharing the same band, most notable GSM 1900/UMTS 1900, and cdma1x 850/GSM 850:

Table 1: Examples of two wireless access technologies sharing the same spectrum band and requiring different tilt optimisation requirements

The QTilt technology has the unique ability to also support independent tilt for Uplink, Uplink Diversity and Downlink with each technology. This may be of particular interest where paired spectrum may have wide duplex splits, such as the Advanced Wireless Services (AWS) spectrum in the USA (1700 Uplink and 2100 Downlink), which can resort to link and elevation pattern imbalances with more conventional antenna designs. Also, for the more traditional space diversity head-frame sites where there are two antenna positions per sector, the QTilt solution can support two technologies with independent tilt yet maintain the advantages of spatial receive diversity (plus polarisation receive diversity if required) for each technology. Space diversity offers uplink advantages in less dispersive radio environments, for example in rural areas, and where UMTS900 may also be expected to be deployed.

Quintel's QTilt technology is completely unique in that it allows a doubling of independently tilting beams from the same antenna physical aperture dimensions, and within the same spectrum band. Conventional antenna solutions for the cellular industry offer only one tilting beam per band, and have to resort to using multiple antennas, multi-stack solutions, and use additional feeders to support multiple technologies with independent tilt in the same band. This means QTilt can be applied in a dual-band antenna to deliver four independently tilting beams; two beams for each band. Therefore, QTilt allows new wireless access technologies to be added within existing cellular spectrum bands with the comfort that:

• Planning approvals are minimised, thereby reducing any risks of planning delay, administration costs, or even planning rejections
• The site would not incur further wind loading, and hence remove the need to carry out potential mast redevelopments
• The site should not incur any extra rental charges which would be associated had extra antennas and feeders been deployed
• Earlier and more predictable cluster launches can be achieved guaranteeing earlier revenue and a competitive edge
• The site remains visually unchanged for the benefit of the public, land-owner, local authority, and operator.

QTilt Technology Optimisation Applications

Spectrum Liberalisation also promises spectrum trading, spectrum leasing, and spectrum sharing. This encourages operators to use spectrum more effectively and efficiently. Traditionally, as a network grows to serve increasing traffic for a single technology layer, operators must use more radio spectrum, or constantly improve the spectral efficiency of existing spectrum, which has primarily been delivered by adding more sectors per site and/or new sites. Quintel's QTilt technology offers an additional means to achieve enhanced spectral efficiency of limited spectral resources, reducing the significant costs associated with adding new sectors, new sites, or having to acquire, lease or use new spectrum.

The QTilt technology can be equally applied for the independent tilt of two different RF channels of the same technology, two beams of the same (W)CDMA based technology and RF channel (to create cell splitting in the elevation plane), or even two differently tilted beams for MISO or MIMO transmission diversity schemes for use with WiMax technologies in dispersive radio environments. Such intra-technology applications of QTilt are equivalent to exploiting the benefits of had separate antennas being deployed at site. These applications bring new optimisation freedoms and performance benefits to operators, in the form of spectrum efficiency, coverage and capacity. Such  applications include (but are not limited to) the following:

Table 2: Examples of how the same wireless access technology can benefit from exploiting two tilt freedoms

The prime driver for using QTilt in this manner is that it delivers enhanced cellular network performance; studies have shown that typically 30% performance gain can be delivered over a cluster of sites, and even further gains for individual hot-spot, high-traffic sites. This therefore enables improved utilisation of existing spectrum and site assets, which translates into an improved customer service experience and increased operator revenue.

Figure 3 illustrates the simple concept of “Radio Planning Diversity” at a macroscopic level using two UMTS RF channels, and two independent tilts per sector. The first UMTS channel is planned and tilt optimised for the expected traffic demand. The second UMTS channel is planned and tilt optimised completely differently (diversely), but still in an optimised manner. Where coverage and/or interference is marginal on the first channel under loading (i.e. cell edge boundaries), coverage and interference on the second channel under loading is not marginal, because the second channel cell boundaries are elsewhere. This is a simple but effective means of coverage and interference redundancy, which can deliver significant network performance gains.

Figure 3:UMTS Radio Planning Diversity Example using Two Tilts for Two RF Channels per Sector

Summary

Quintel's QTilt technology has been developed in response to the growing spectrum liberalisation, and technology neutrality debate, where operators can, or will be able to deploy different access technologies within their spectrum, and will ultimately need to optimise each technology layer independently, e.g. UMTS900 and GSM900 access technologies. Furthermore, where single technologies are used within the spectrum band, using two tilting beams can bring significant performance gains for coverage, capacity and interference rejection.

QTilt technology can be deployed at lower cost, in quicker time, and without visual change to existing site assets in order for new technologies to be deployed with independent tilt optimisation per technology, or deployed to make more efficient use of single technologies, and existing spectrum, when compared to the only real alternative of deploying new additional antennas and feeders.

Figure 4:Summary of key QTilt applications

Further Information please contact:

Quintel Technology Limited

Web:         www.quintel.co.uk

Email:       david.barker@quintel.co.uk

Tel:           +44 (0)795 841 8816