MIMO Features In WiMAX and LTE

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Presentation on MIMO features in WiMAX (IEEE 802.16m) and 3GPP LTE

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MIMO Features In WiMAX and LTE

  1. 1. ET4275 :Advanced Topics in Digital Wireless Communications: Case Study Technological University of DelftMIMO Features in WiMAX and LTE: An Overview PRESENTED BY :ANANTHAKRISHNAN RAMKUMAR - 4119568 &PRAVEEN KALYANASUNDARAM - 4118863 January 2011
  2. 2. Trends in Mobile Communications Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  3. 3. 4GHigher data rates, mobility, spectral efficiency and bettercell coverage compared to 3G.High quality of service for next generation multimediasupport (real time audio, high speed data, HDTV videocontent, mobile TV, etc.)High usability: anytime, anywhere, and interoperabilitywith existing wireless standardsBased on an all-IP packet switched network.Two technologies that are expected to fulfill the 4Grequirements are: Mobile WiMAX and 3GPP LTE Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  4. 4. Mobile WiMAX (IEEE 802.16m)IEEE 802.16m known as Mobile WiMAX is an extension of IEEE802.16-2004 (fixed WiMAX). Mobile WiMAX introduces new featuresto support enhanced Quality of Service to provide high mobility at veryhigh data rates.Rapidly growing broadband wireless access technology that replacesthe current existing systems such as Wi-Fi and 3G.Key features are : Use of MIMO Technology OFDMA with CP (both uplink and downlink) Scalable bandwidth Adaptive Modulation and Coding Support for TDD and FDD Hybrid-ARQ, Integrated Security for voice and data transmission Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  5. 5. Long Term Evolution(3GPP-LTE)3GPP Long Term Evolution (LTE)-developed by the 3rd GenerationPartnership Project is the latest standard in the mobile networktechnology targeting 4G.LTE-Advanced (Release 10) is still being developed primarily to meetthe requirements of the International Telecommunications Union(ITU) for IMT fourth generation (4G).Key Features Use of MIMO Technology OFDMA with CP in downlink, SC-FDMA in uplink Scalable bandwidth Adaptive Modulation and Coding Support for TDD and FDD Hybrid-ARQ, Integrated Security for voice and data transmission Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  6. 6. Table of features Aspect WiMAX LTELegacy GSM/GPRS/EDGE/UMTS/HSPA IEEE 802.16 a through eAccess Technology DL-OFDMA, UL-SC-FDMA DL-OFDMA, UL-OFDMAAntenna Scheme MIMO: MIMODL 2x2,4x2,4x4 2x2,4x2,4x4UL 1x2,1x4, 2x2 1x2,1x4,2x2 ,Frequency Band Existing (800,900,1800,1900 MHz) and 2-11 GHz new bands (Range 800 MHz to 2.62 GHz)Mobility: Up to 350 Km/h with inter-cell soft Up to 120 Km/h with optimized hard handovers handoversChannel Bandwidth Scalable from 1.25 to 20 MHz with Scalable from 1.25 to 20 MHz with system profiles 1.25,1.4,2.5,3.5,10, 15 system profiles 1.25,2.5, 5, 10and 20 and 20 MHz MHzDL Spectral Efficiency 1.57 bps/Hz/Sector (2x2) MIMO2 1.59 bps/Hz/Sector (2x2) MIMOUL Spectral Efficiency 0.64 bps/Hz/Sector (1x2) SIMO2 0.99 bps/Hz/Sector (1x2) SIMORadio Access Mode TDD and FDD TDD and FDD Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  7. 7. MIMO Technology: An Introduction • A MIMO is a technique to improve communication performance by using multiple antennas at the transmitter and receiver Features: • Exploits multipath effects instead of mitigating it • High spectral efficiency • High speed data transmission • Higher Channel capacity (i.e., min (M,N)) •Diversity in both the transmit and receive sides Channel011001 - - 011001 Matrix ‘H’ - - - - ‘N’ Transmitters ‘M’ Receivers Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  8. 8. Classification of MIMO Techniques Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  9. 9. Spatial MultiplexingA high data rate stream is split into several low data rate streams where each ofthe individual streams is transmitted by a different transmit antenna in thesame frequency channel.At the receiver the data streams can be separated by the equalizer providedeach of the data stream has undergone fading independent of each other.This technique is used to increase the overall capacity of the channel. In asystem with N transmit antennas and M receive antennas the maximum spatialmultiplexing order is given by Ns = min (M,N) where Ns is the number ofstreams which can be transmitted in parallel Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  10. 10. Transmit DiversityImprovement of link reliability by adding more redundancy to informationgoing through the channel.Space Time block Code (STBC) or Alamouti Code: the data stream to betransmitted is encoded in blocks, which are distributed among spaced antennasand across time.The frequency domain version of STBC is called Space Frequency Block Code(SFBC).Pair of adjacent subcarriers are coded together instead of time slots. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  11. 11. BeamformingSignal processing technique that takes advantage of the fading channelsto improve received signal gain and coverage.Transmission radiation pattern from an array of antennas is focused inthe direction of specific user by constructively interfering in thatspecific direction.Using feedback from the receiver, a precoder matrix is constructed toachieve beamforming Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  12. 12. Pilot/Reference SignalUsed for measuring the spatial channel and helps in coherent demodulation at theterminal. Perform the operation of supervision, control, equalization,synchronization within a transmission system.The reference signals can be classified asCommon reference signal (CRS):used by all UEs within a cell.Dedicated reference signal (DRS): used by a specific UE within the cellFurther classified as precoded or non-precoded. If the pilot/RS is also multiplied bythe precoding matrix before transmission then it is called precoded pilot.In WiMAX and LTE specific sub-carriers are allocated as pilots/RS. Their location ischanged from symbol to symbol. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  13. 13. Open Loop MIMOIn Open Loop (OL) transmission technique, the transmitterhas limited or no knowledge of the channel.To obtain knowledge of the channel, an open-looptransmission scheme uses the idea of the channelreciprocity available in TDDOL transmission is suitable for high mobility scenarioOL-MIMO techniques include-Spatial Multiplexing-Transmit Diversity (e.g Space-Time codes)-Random Beamforming Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  14. 14. Random Beamforming/Precoder CyclingRandom beamforming is a method to increase channel selectivity bychanging beams within allocated time/frequency resources. It is used inopen loop MIMO scheme where there is no feedback available.Precoder cycling is a random beamforming technique.A predefined set of precoders are chosen from a predefined codebookand are cyclically allocated to a group of adjacent subcarriers.The Chordal distance (separation between beams) property of the setof precoders must be good in order to increase the order of thediversity.Used to provide Beam diversity gain :Predefined precoders in each localized frequency band form different beams Beam selection gain: Localized resource allotted to user terminal based on the CQI feedback for preferred subbands Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  15. 15. WiMAX and LTE: Overview of OL-MIMOSFBC adopted for transmit diversity using pair of sub-carriers- Fast changing channel destroys orthogonality of code in STBCIn 802.16m SFBC with precoder cycling is employed with precodedpilotsPrecoder cycling creates a fixed set of two virtual antennas (streams)across all subcarriers and changes the virtual antennas by usingdifferent precoder weightsIn LTE, SFBC with FSTD is employed with non-precoded CRS.FSTD cycles transmissions over pairs of transmit antennas- Tradeoff: Reduced overhead using precoded pilots vs wider range ofinterpolation in the frequency domain for finer channel estimationusing non-precoded CRS. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  16. 16. Closed Loop MIMOAn important MIMO scheme that uses feedback from the receiver toobtain Channel State Information (CSI) and hence uses it for increasingthroughput or coverage.The challenge here lies in efficiently obtaining the CSI in order toconstruct a precoder matrix.For overhead reduction, the whole beamforming matrix is quantized bya vector codebook. The factors to be considered for the base codebookdesign are performance gain, overhead, robustness and complexity. User Base Station Channel Equipment/ Receiver CQI - Channel Quality Indicator CQI,PMI,RI PMI - Preferred Matrix Indicator RI - Rank Indicator Feedback Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  17. 17. WiMAX and LTE: Overview of CL-MIMOThe index of the selected quantization codeword is fed back. An L bit codebookconsists of 2L codewords, where L is the required number of bits for indexingeach codeword. Precoding codebook for transmission on two antennas .802.16m defines 3-bit feedback for 2-transmit antennas (2-Tx) as well as 4-bitand 6-bit feedbacks for 4-transmit antennas (4-Tx), while LTE defines 2-bitand 4-bit feedbacks for 2-Tx and 4-Tx, respectively.- More the number of bits in codebook index, more the codewords. This giveswider range for choosing the best precoder at the cost of signaling overhead. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  18. 18. Overview of CL-MIMO. . ContdBase codebooks can be dynamically generated using a few parameters.Also, high rank codewords with more columns include the low rankcodewords with a few columns as subset.Reduces the storage complexity and the complexity of searching forthe best number of spatial streams.Adaptive codebook is defined in 802.16m:codeword distributionchanged according to long-term channel statistics.More codewords are steered in the ideal beamforming directions802.16m has adopted differential feedback, where the correlationbetween consecutive beamforming reports is exploited- the incrementalchange between the current and previous matrices is fed back.- Adv: Lower feedback overhead- Disadv: Error propagation effect Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  19. 19. Block diagram for downlink MIMO Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  20. 20. Block diagram for Uplink MIMO Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  21. 21. Single User MIMO: An Introduction• The Time/Frequency resources are dedicated to a single User Equipment (UE)/ Advanced Mobile Station (AMS) so as to achieve peak user spectral efficiency.• Encompass techniques such as transmit diversity, spatial multiplexing and beamforming• Based on the MIMO channel conditions and modulation type, the user terminals need to have an appropriate receiver mechanism so as to reduce the average processing power.• The various detectors that are considered in SU-MIMO include - Maximum Likelihood Detector (MLD), - Minimum Mean Squared Error – Successive Interference Cancellation (MMSE - SIC) Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  22. 22. WiMAX and LTE: Overview of SU-MIMO WiMAX 802.16m LTE• Uses Vertical Encoding • Uses Multiple Code Word (MCW)(VE)/Single Code Word (SCW) transmission• A MLD gives better performance • Lower complexity and bettercompared to MMSE-SIC for the performance of MMSE-SIC receiversadvanced receiver with SCW with MCW transmission.- Better in case of correlated channels - Modeling of effective SNR per codeword is difficult in MLD• HARQ process is simplified andonly a single report of the CQI is • One CQI report and one HARQrequired for all multiplexed layers process required for each FEC codeword and hence more overhead Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  23. 23. Multi User MIMO: An Introduction• The time – frequency resources are shared by multiple users to exploit the multi-user diversity in the spatial domain• Provides enhanced throughput under heavy data traffic• The multiple users are selected at the base station with the help of precoder matrix that is constructed by the orthogonal PMI’s reported by different users. Two schemes are observed in MU-MIMO:• Linear scheme in MU-MIMO include Zero- Forcing(ZF) technique wherein the data symbols are precoded with the pseudo inverse of the channel in order to cancel out the interference of other users.• Non-linear MU-MIMO uses Dirty Paper Coding (DPC) that pre-cancels known interference without additional power once the transmitter is assumed to know the interference signal regardless of the CSI at the receiver. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  24. 24. WiMAX and LTE: Overview of MU-MIMODOWNLINK:Both standards use a scheduler to select users with good spatialseparation and perform pseudo inversion of the combined channelmatrix to obtain the precoding matrix. The CQI reported by each user isthen adjusted at the base station to fit the channel quality afterprecoding. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  25. 25. WiMAX and LTE: Overview of MU-MIMOUPLINK:For uplink MU-MIMO, both WiMAX and LTE allow multiple users to transmitsimultaneously in the same uplink resource. The base station distinguishes thesignals from different user terminals through the pilots/RSs allocated to eachterminal and separates them using an advanced receiver which is MLD in case of802.16 and MMSE in LTE. Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  26. 26. SUMMARY Parameter LTE WiMAX ExplanationCapacity +++ +++ Use of MIMO TechnologySpectral Efficiency Use of Spatial Multiplexing,Uplink ++ +++ Beamforming. OFDMA in downlink inDownlink +++ +++ both. But LTE uses SC-FDMA in uplink.Mobility +++ ++ Use of Open-Loop techniques,SFBCReceiver ++ + MLD (higher computational complexity)Complexity used in WiMax. MMSE in LTE.Feedback ++ +++ Differential feedback in 802.16m leads to lesser overhead compared to LTEPower ++ ++ Transmit power control.Consumption Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  27. 27. Conclusions802.16m and 3GPP LTE are both capable technologies tomeet the requirements of 4G, in terms of data rates,spectral efficiency and mobilityBoth standards are technically similar when it comes toemploying MIMO techniquesTwo technologies however differ in terms of legacy andtime to market Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar
  28. 28. ReferencesQinghua Li; Guangjie Li; Wookbong Lee; Moon-il Lee; Mazzarese, D.; Clerckx, B.; Zexian Li; ,"MIMO techniques inWiMAX and LTE: a feature overview," Communications Magazine, IEEE , vol.48, no.5, pp.86-92, May 2010Alamouti, S.M.; , "A simple transmit diversity technique for wireless communications ,"Selected Areas in Communications, IEEE Journal on , vol.16, no.8, pp.1451-1458, Oct 1998Q. H. Spencer et al., “An Introduction to the Multi- User MIMO Downlink” IEEE Commun.Mag., vol. 42, no. 10, Oct.2004, pp. 60–67.Jim Zyren, Freescale Semiconductor, ”Overview of 3GPP Long Term Evolution Physical Layer“,white paper.Juho Lee, Jin-Kyu Han, and Jianzhong (Charlie) Zhang, “MIMO Technologies in 3GPP LTE andLTE- Advanced,”EURASIP Journal on Wireless Communications and Networking, vol. 2009Qinghua Li; Xintian Lin; Jianzhong Zhang; Wonil Roh; , "Advancement of MIMO technology inWiMAX: from IEEE 802.16d/e/j to 802.16m," Communications Magazine, IEEE , vol.47, no.6,pp.100-107, June 2009 Property of Praveen Kalyansundaram & Ananthakrishnan Ramkumar

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