SC-FDMA Single Carrier FDMA in LTE - Ixia

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IntroductionSC-FDMA is anew technologyused for uplink inLTE. This whitepaper exploresthis technology,its use in LTE andits extension fromOFDM.Single Carrier Frequency Division Multiple Access (SC-FDMA) is a promising technique forhigh data rate uplink communication and has been adopted by 3GPP for it next generationcellular system, called Long-Term Evolution (LTE). SC-FDMA is a modified form of OFDMwith similar throughput performance and complexity. This is often viewed as DFT-codedOFDM where time-domain data symbols are transformed to frequency-domain by a discreteFourier transform (DFT) before going through the standard OFDM modulation. Thus,SC-FDMA inherits all the advantages of OFDM over other well-known techniques such asTDMA and CDMA. The major problem in extending GSM TDMA and wideband CDMA tobroadband systems is the increase in complexity with the multipath signal reception. Themain advantage of OFDM, as is for SC-FDMA, is its robustness against multipath signalpropagation, which makes it suitable for broadband systems. SC-FDMA brings additionalbenefit of low peak-to-average power ratio (PAPR) compared to OFDM making it suitablefor uplink transmission by user-terminals.3GPP Long Term EvolutionLTE is a next generation mobile system from the 3GPP with a focus on wireless broadband.LTE is based on Orthogonal Frequency Division Multiplexing (OFDM) with cyclic prefix (CP)in the downlink, and on Single-Carrier Frequency Division Multiple Access (SC-FDMA) withcyclic prefix in the uplink. It supports both FDD and TDD duplex modes for transmission onpaired and unpaired spectrum.The generic radio frame has a time duration of 10 ms, consisting of 20 slots of each 0.5ms. Two adjacent slots form a sub-frame of 1 ms duration, which is also one transmit-timeinterval(TTI). Each slot consists of seven OFDM symbols with short/normal cyclic prefix(CP) or six OFDM symbols with long/extended CP.One radio frame - 10msSlot = .05ms#0#1 #2 #18 #19OFDM symbols in a slot#0 #1 #2 #3 #4 #5 #6OFDM symbolsCyclicprefixcopyingFigure 1. LTE Frame Format4
Uplink TransmissionThe uplink transmission scheme is based on single-carrier FDMA, more specifically DFTS-OFDM. The uplink sub-carrier spacing Δf = 15 kHz. There are two cyclic-prefix lengthsdefined: normal cyclic prefix and extended cyclic prefix corresponding to seven and sixSC-FDMA symbols per slot,N ULsymbrespectively. The cyclic prefix timings for uplink are the same as for the downlink.For short cyclic prefix: T CP= 160×Ts for OFDM symbol l = 0= 144×Ts for OFDM symbol l = 1, 2,…6For long cyclic prefix: T CP-e= 512×Ts for OFDM symbol l = 0, 1…5T s= 1/ (2048 × Δf) is the sampling time for 20 MHz system.DFTSub- CarrierMappingIFFTCPinsertionSymbolsFigure 2. Transmitter scheme of SC-FDMAThe sub-carriers are grouped into sets of 12 consecutive sub-carriers, corresponding tothe uplink resource blocks. 12 consecutive sub-carriers in one slot correspond to oneuplink resource block – the same as in the downlink – which is depicted in Figure 3. In thefrequency domain, the maximum number of resource blocks, N RB, can range from N RB-min= 6 to N RB-max= [110]. Each element in the resource grid is called a resource element andis uniquely defined by the index pair (k,l) in a slot where k and l are the indices in thefrequency (subcarrier) and time domain (symbol), respectively.5
Page 3: ContentsIntroduction...............
Page 7 and 8: Why OFDM is most favored for broadb
Page 9 and 10: SC-FDMA ModulationSC-FDMA is a new
Page 11 and 12: OFDM to SC-FDMAThe main difference
Page 13 and 14: Single Carrier ModulationBased on S
Page 16: Ixia Worldwide Headquarters26601 Ag

SC-FDMA Single Carrier FDMA in LTE - Ixia

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