Microwave Engineering Europe - January/February 2008 - (Page 30)

30 WiMAX WiMAX update 2008 WiMAX promises much to a wide range of mainstream and niche wireless sector players. It also presents some signiﬁcant challenges from an RF and network planning perspective, writes Jörg Springer of Radio Frequency Systems (RFS). By Jörg Springer, VP Global Marketing & Communications, Radio Frequency Systems (RFS) iMAX is a strongly standardsbased broadband wireless technology that is predicted to satisfy a wide range of applications. Policed by the industry body, the WiMAX Forum, the WiMAX standard is offered in two variants: one for ﬁxed/portable applications (the IEEE 802.6d ‘ﬁxed/portable WiMAX’) and the other for mobile (the IEEE 802.16e ‘mobile WiMAX’). Theoretically, the IEEE 802.16 can realize data throughput rates as high as 72 Mbps with cell sizes as broad as 50 km. In practicality, the standard has demonstrated data throughputs of 40 Mbps in the ﬁxed/ portable variant, for cells ranging in size from three to 10 km, and 15 Mbps in cells up to 3 km in size with ‘mobile WiMAX’. While such performance might imply that WiMAX could go head-to-head with 3G cell-based technologies such as UMTS and CDMA2000, market analysts suggest that WiMAX will ﬁnd its greatest application as a ‘cable- and DSL-alternative’ for ﬁxed/ portable broadband data applications. The strongest business case currently for WiMAX will see it deployed in localized hot-spots where market demand is greatest. Advanced technology Perhaps WiMAX’s most distinctive characteristic is the modulation technique on which it is founded: ‘orthogonal frequency division multiple access’ (OFDMA). OFDMA is the key RF air interface deﬁned for both 3GPP LTE and ‘ultra mobile broadband’ (UMB) 4G technologies, and for good reason. When compared with conventional code- or time-division modulation systems, OFDMA provides signiﬁcant improvements in spectral efﬁciency, non line-of-sight (NLOS) performance, and data throughput. The ‘WIMAX mobile’ standard also supports ‘multiple-input/multiple-output’ MIMO antenna signal processing. Such MIMO base station/handset architectures will push spectral efﬁciency, throughput W and quality of service into an entirely new performance domain. WiMAX proﬁles support both ‘frequency division duplex’ (FDD) and ‘time division duplex’ (TDD) implementations, although it is believed that — in a data-centric market — TDD will dominate. TDD brings spectral convenience in that it is more spectrally efﬁcient for the bursty asymmetric nature of data services. From a bandwidth and spectrum allocation perspective, WiMAX is particularly ﬂexible. There is no uniform global license spectrum for WiMAX; it is broadly deﬁned across a expanse of spectrum that spans 2 to 6 GHz and 10 to 66 GHz, although the WiMAX forum has published three spectrum proﬁles for 2.3, 2.5 and 3.5 GHz. It also allows scalable channel bandwidths, which can range in size from 5 to 20 MHz. WiMAX’s distinctive throughput, physical range, data-centric nature and ﬂexibility carve out exciting market prospects. It offers great potential for greenﬁeld operators in niche markets; it presents great opportunity for coverage in areas previously unserviced by traditional broadband services; and it will offer commercial enterprises new levels of broadband access diversity. It is for these reasons that the technology has attracted a broad range of industry supporters, including large and small OEMs, chip suppliers and service providers, plus a clutch of global software players. The latter is most telling in a wireless market that is quickly moving from voice to data. At end-2007, more than 350 WiMAX trials and deployments were underway in over 65 countries around the world. Leading adopters were USA, Spain, Brazil and Australia — all ‘big geography’ countries with widely distributed populations. The ﬂexibility challenge Ironically, the inherent ﬂexibility of the WIMAX platform that is so attractive to carriers and spectrum regulators, presents Currently, the strongest business case for WiMAX will see it deployed in localized hotspots — typically high-density commercial zones (Sao Paulo pictured — where market demand is greatest. serious challenges to technology developers. The absence of a single dominant WiMAX licensed spectrum and channel bandwidth thwarts the economy-of-scale advantages typically enjoyed by global technologies, and slows development. This impacts on all fronts: base station technologies, handsets and RF/tower-top systems. Further WiMAX challenges stem from its elevated frequency allocations. These present RF technology groups with link-budget problems and reduced cell sizes, while base station OEMs face signiﬁcant challenges in developing the higher powers required in the power ampliﬁers (PAs), particularly at 3.5 GHz and above. Small cell sizes and low power levels result in radiating-point intensive and granular WiMAX networks. Microwave Engineering Europe ● January/February 2008 ● www.mwee.com 030_031_MWEE.indd 30 24/01/08 15:24:08 http://www.mwee.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - January/February 2008

Microwave Engineering Europe - January/February 2008 Contents News Comment Radio: Raising the Bar for the Radio: Making 802.11n Work Cover Feature: The RF-System-In-Package Trend - Efficient Design with Advanced Design System 2008 Wireless Sensor Networks: The Zigbee PRO Feature Set: More of a Good Thing Very Fast Measurements of Wireless Devices with Small Antennas in Reverberation Chambers WiMAX Update 2008 Bridging the Gap from the CMOS DSP to the Antenna in OFDM Systems Products Calendar

Microwave Engineering Europe - January/February 2008

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