OFDM(A) for wireless communication - Unik

OFDM(A) for wireless communicationFigure 36 Uplink reference signals are inserted within the fourth block of eachuplink slot [Dahl07]4.2 Mobile WiMAX 2Mobile WiMAX is based on the air interface of IEEE 802.16e-2005 and utilizesthe concept of scalable OFDMA (S-OFDMA). S-OFDMA supports a wide range ofbandwidths to flexibly address the needs in various frequency spectrums. TheWiMAX Forum has selected a subset of the 802.16e standard as mandatory inorder to ensure equipment interoperability and provides test and conformancespecifications. WiMAX Release 1 has been ready since 2006 and covers“profiles” for the system bandwidths 5, 7, 8.75 and 10 MHz and frequencybands 2.3, 2.5, 3.3 and 3.5 GHz [WiMAX06].Possibly important for future deployment of WiMAX technology is the fact thatITU-R at the Radio Assembly (RA) in October 2007 approved Mobile WiMAX tobe included into the IMT-2000 family under the name “OFDMA TDD WMAN” 3 .This means that the existing 3G frequency bands generally are open for thedeployment of Mobile WiMAX as a direct competitor to UTRA/WCDMA providedthat the national regulators’ license policies are technology neutral.Mobile uses OFDMA as the multiple access scheme both in uplink and downlink.Cyclic prefix is used in both directions to protect against ISI. Bandwidthscalability from 1.25 to 20 MHz is supported by adjusting the FFT size whilemaintaining fixed sub-carrier frequency spacing. The sub-carrier spacing ischosen to be 10.94 kHz, which defines the useful symbol length to be 91.4 μs.Since the resource unit sub-carrier bandwidth and symbol duration are fixed,the impact to higher layers is minimal when scaling the bandwidth. The OFDMAparameters applied by mobile WiMAX are summarized in Table 3.2 The presentation of mobile WiMAX is based on [WiMAX06], [Nua07], and [And07].3 ITU-R press release from RA-07 at: http://www.itu.int/newsroom/press_releases/2007/30.htmlTelenor R&I R 7/2008 - 31