Antenna Systems & Technology - Fall 2012 - (Page 9)

FEATURE ARTICLE Base Station Antenna Evolution and Revolution By David Barker, CTO • Quintel Technology Ltd. Moore’s Law successfully predicted the growth in processing power over the last three decades and it still holds true today and for the foreseeable future. This growth in processing power has in turn enabled the mobile data consumption explosion, which emerged a few years ago, and today we are all predicting on what logarithmic order this will grow at. The demand is being addressing on a number of fronts in the industry: 1. Governments are putting in place policy and commitments to ensure that more cellular/wireless spectrum bands become available. The US, UK and India for example have all indicated that another 500 MHz of UHF spectrum will made available by the end of the decade. Spectrum efficiency gains can be exploited as operators move from 3G to 4G access technologies. LTEAdvanced offers up to 8x8 MIMO schemes and advanced Interference Mitigation features. Small cell and Het-Net network topologies are very much at the heart of LTE and LTE-Advanced. Cell splitting, and Macro cell offload to LTE small cells ensures spectrum can be re-used cost-effectively. Also, Wi-Fi is evolving, and while already a small cell, it too is becoming smarter to help take demand off the cellular layers as part of the Het-Net. Figure 1. Use of Radio Spectrum Past, Present and Future for Europe. 2. 3. In this article, we provide a discussion on the first two areas as summarized above, with a focus being on the base station antenna. Radio Spectrum: The Past, Present And Future Figure 1 depicts where we have been and perhaps where we are headed in terms of spectrum bands, access technologies and spectral efficiency techniques, for a European context. Two decades ago, there was only GSM technology in the 900 MHz band in Europe. The base station antenna feature of the day was Uplink space diversity, as a means of extending coverage. The mid 1990s saw 1,800 MHz band being introduced for additional GSM capacity, then mid-2000s 3G in the UMTS flavor emerged in the 2,100 MHz band. The base station antenna innovation of this era was perhaps triple band X-Polar with variable/ remote electrical tilt features. Europe has now introduced two further bands; 800 MHz and 2,600 MHz where LTE will be deployed. Bands such as 700 MHz, 1,500 MHz and 2,300 MHz being exploited in other areas of the world and are expected to become available in Europe too, leveraging economies of scale globally. For example, the Digital Dividend two band at 700 MHz is an agenda item at WRC16. White Space spectrum at the lower UHF frequencies opens up innovation in cognitive and co-operative radio access techniques too. LTE-Advanced supports carrier aggregation for spectrum re-farming in legacy bands, and a wide variety of MIMO techniques at the base station and UE. This is illustrated at the right aiming to illustrate in-band spectral efficiency evolution. One could conclude that at the end of the decade, we may need Macro base station antennas supporting 10 bands, legacy technologies and offer high order MIMO including spatial multiplexing and beamforming. More Spectrum: But it May Come with More Interference As more spectrum will be consumed in more spectrum bands, as using higher power PA’s then this creates more intersystem and intra-system RF interference issues that need to be addressed. A recent example of inter-system interference issues include LightSquared’s proposed use of the MSS 1,500 MHz band as a terrestrial cellular network being spectrally close to GPS and the fact GPS receivers do not have sufficient Adjacent Channel Selectivity (ACS). Another example in Europe is the Digital TV band only has a 1 MHz guard band between it and the LTE800 band which can create, similar to LightSquared’s case, adjacent channel interference. The US also has a similar issue concerning 700 MHz band lower A-Block being proximate to Channel 51 Digital TV broadcast. There are also numerous FDD/ TDD and TDD/TDD proximate spectrum interference issues. Intra-system interference issues include Passive Intermodulation (PIM) interference. PIM has always been a concern, but as more spectrum is being used and at higher powers, PIM is becoming increasing difficult to mitigate or control. Antenna and antenna line component (cables, connectors, etc.) PIM specifications are bound by laws of physics and cannot be made perfectly linear. By way of an example, Figure 2 depicts an operator with 2x45 MHz of 1,800 MHz band and 2x35 MHz WWW.ANTENNASONLINE.COM FALL 2012 ANTENNA SYSTEMS & TECHNOLOGY 9 http://WWW.ANTENNASONLINE.COM

Table of Contents for the Digital Edition of Antenna Systems & Technology - Fall 2012

Antenna Systems & Technology - Fall 2012
Table of Contents
Editor’s Choice
Performance Evalutaion of Antenna Integration of Mobile Devices Through Full-Wave Analysis
Base Station Antenna Evolution and Revolution
Antennas
Mobile Antenna Systems 2012 - Conference Preview
Manufacturing/Design
Components
Test & Measurement
Wireless Communication
Industry News
Marketplace

Antenna Systems & Technology - Fall 2012