Introduction to LTE
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Introduction to LTE






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  • Driving force towards LTE
  • EPC : Evolved Packet CoreSAE : System Architecture Evolution
  • SAE : System Architecture EvolutionSome of the RNC functions in UMTS have been brought to the eNodeB and some of the functions to the MME.One eNodeB can be connected to multiple MMEs/S-GW for the purpose of load sharingS1 –c: S1 control for MME ; S1- u : S1 user for S-GW
  • PCRF : Policy and charging rules Function : Responsible for QoS handling and charging
  • Multipath propagation
  • When data rate increases ISI also increases.
  • Multi path intensity profile
  • -. Cross Correlation of AWGN is an impulse response. What is the meaning of this?-. Spaced freq. Correlation function is generated by cross correlating two carriers which are separated by Delta(f)-. Disadv. Of single carrier transmission??
  • -. Symbol periods are now longer compared to single carrier. but bits are txd parallel in order to achieve the desired data rate. -. As Ts is high ISI can completely be removed from the system.-. Depending on the channel condition each subcarrier can be modulated using different modulation schemes (QPSK, 16QAM, 64 QAM etc..)
  • -. Each OFDM symbol is a liner combination of instantaneous signals on each of the subcarriers in the channel.
  • - Multi carrier systems with non overlapping sub carriers :- Spectrally inefficient
  • Frequency Selective fading is not an issue for Subcarriers (𝐵𝑊𝑠𝑢𝑏𝑐𝑎𝑟𝑟𝑖𝑒𝑟 < 𝐵𝑊𝐶𝑜h𝑒𝑟𝑒𝑛𝑐𝑒)Frequency Selective fading is not an issue for Subcarriers (〖𝐵𝑊〗_𝑠𝑢𝑏𝑐𝑎𝑟𝑟𝑖𝑒𝑟 < 〖𝐵𝑊〗_𝐶𝑜ℎ𝑒𝑟𝑒𝑛𝑐𝑒)
  • One Resource Grid per antenna.
  • QoS : Beam forming
  • PAR : Peak to Average Power RatioDFTS-OFDM : DFT-Spread-OFDM
  • Target : Lower PAPR and Use the benefit of OFDM transmission using multiple carriers.
  • -. 1 resource grid per antenna.

Introduction to LTE Introduction to LTE Presentation Transcript

  • Introduction to
  • No more CodesKey technologies….For Downlink : OFDM and MIMOFor Uplink : SC - FDMA
  • Topics to discuss…
  • IMT – Advanced Requirements Support for at least 40 MHz Bandwidth Peak Spectral Efficiencies :  DL : 15 bits/s/Hz (600 Mbps)  UL : 6.75 bits/s/Hz(270 Mbps) Control Plane Latency < 100ms User Plane Latency < 10ms
  • Releases of 3GPP Specifications Rel. 8 LTE EPC/SAE Location Multi- Rel.9 Services MBMS Standard BS Rel.10 LTE - A Carrier Aggregation Relays Enhanced Intra Band Rel.11 Carrier Aggregation Carrier Aggregation
  • System Architecture Evolution (SAE)
  • From 3G to 4G… UTRAN in 3G,E-UTRAN in 4G CN in 3G, EPC in 4G NodeB in 3G, E-NodeB in 4G No RNC as in 3G RNC tasks perform by eNodeB and EPC
  • LTE/SAE Network Internet Architecture P-GW HSS MME S-GW EPC S5 S6aMME/S-GW MME/S-GW S1 S1 S1 S1 X2 E-UTRAN X2 X2 eNodeB eNodeB eNodeB
  • Evolved UTRAN (E-UTRAN) eNodeB :  Directly connected to the Core via S1 interface  No RNC as in WCDMA  eNodeBs interconnected via X2 interface  Handovers are handled by eNodeBs it self, communicating via X2 interface  This is an intelligent NodeEvolved Packet Core (EPC)Supports only packet switched domain only Mobility Management Entity (MME) :  Control Plane Node of the EPC  handling connection/release of bearers to a terminal  handling of IDLE to ACTIVE Transition  handling of security keys
  •  Serving Gateway(S-GW) :  User plane node which connects EPC to E-UTRAN  Acts as a mobility anchor when Terminals move between eNodeBs  Mobility Anchor for other 3GPP technologies (GSM,HSPA)  Collecting information for charging purposes Packet Data Network Gateway (P-GW) :  Connects EPC to the Internet  Allocation of the IP address for a specific terminal  QoS handling Home Subscriber Service (HSS) :  A database containing subscriber information
  • What is Orthogonal FrequencyDivision Multiplexing (OFDM) ?
  • OFDMWhy ?
  • ISI – Inter Symbol InterferenceTime domain : Data Rate ISI
  • Time Spreading (Freq. SelectiveFading)• When an impulse is transmitted , howdoes the average power received by Power Delay ProfileMobile vary as a function of time delay ζ ? Freq. Selective Fading : Ts < ζ0 Non Freq. Selective Fading : Ts > ζ0
  • Power Delay Profile Spaced Freq. Correlation function FTInside Coherence BW channel passes all freq. components withequal gain and linear phase Freq. Selective Fading : W > f0 Non Freq. Selective Fading : W < f0
  • • Symbol rate not increased in order to achieve high data rates.• Instead of that Available BW breaks in to many narrower subcarriers and modulate generated symbols to these subcarriers.• These subcarriers then combine linearly and transmit (OFDM symbol). OFDM Modulation OFDM demodulation
  • Single carrier transmission Vs OFDMTransmission : Single Carrier 1 0 1 Transmission 1 : OFDM Transmission 0 1 t
  • Sub carrier Pulse shape and Spectrum Subcarrier BW < Coherance BW
  • Why “Orthogonal” ? Subcarriers “Orthogonal” in the time domainIn OFDM, Subcarriers are overlapped in Frequencydomain while maintaining orthogonality in time domain
  • Overlapping subcarriers in Freq.domain Overlapping Subcarriers Spectral Efficiency
  • OFDM Symbol • Generated by Multiplexing several overlapping subcarriers and a Cyclic Prefix (CP). CP Modulated Subcarriers • Cyclic Prefix added to the beginning of the OFDM symbol in order to eliminate IBI • At the Receiver CP is removed and only the information bearing part is further processed .
  • OFDM as a Multiple Access Scheme(OFDMA) OFDMA : In each OFDM symbol interval, Different subsets of the overall set of available subcarriers are used for transmission to different terminals.
  • What is Multiple-Input Multiple-Output (MIMO) ?
  • Main Transmission TechniquesSpatial Diversity : Signal copies are transmitted at multiple antennas or received at more than one antenna. Spatial Multiplexing : Transmit independent and separately encoded data streams over different antennas
  • Why MIMO?  Significant increase in Spectral efficiency and data rates - Spatial Multiplexing  High QoS - Spatial diversity  Wide Coverage - Spatial diversity
  • Received signal y at the receiver when signal x is transmitted,
  • What is Single Carrier FDMA(SC – FDMA)?
  • SC – FDMA (DFTS-OFDM)Why not Multi Carrier OFDM in Uplink ? One of the main drawbacks in OFDM : Large instantaneous power variations in the Transmitting signal This leads to High Peak-to-Average-Power Ratio (PAPR) in the Power Amplifier. Power Amplifier Efficiency Power Amplifier Cost Hence Multicarrier OFDM is not a Viable solution for Low power Mobiles
  •  In OFDM, each subcarrier carries information relating to one specific Symbol In SC-FDMA, each subcarrier contains information of All Transmitted symbols. Hence no need of transmitting with High Power. Signal energy is distributed among sub carriers.
  • User Multiplexing in SC-FDMA  Localized Transmission :  Distributed Transmission :User 1 User 2 User 3 User 1 User 2 User 3
  • LTE Physical LayerOverall RAN Protocol Architecture
  • LTE Physical Layer Processing
  • Available DL BW and Physical Resource Blocks(PRBs)Bandwidth (MHz) 1.25 2.5 5.0 10.0 15.0 20.0Subcarrier BW (kHz) 15PRB BW (kHz) 180No. of available RBs 6 12 25 50 75 100
  • Generic Frame Structure 1 Frame (10 ms) 1 Slot (0.5 ms) 0 1 2 n 18 19 1 Sub Frame (1 ms) 0 1 2 3 4 5 6 7 OFDM symbols
  • Resource Grid 7 OFDM symbols TimeFREq R E S O U R C R E E S B O L U O R C C K E G R I DResource Element
  •  Physical Resource Block (PRB) allocation is done by the scheduling function in eNodeB PRB is the smallest element of resource allocation assigned by the base station scheduler.
  • LTE Radio Access : An Overview
  •  Channel dependent Scheduling and Rate adaptation :  Depending on the channel conditions, time – frequency resources are allocated to users by the scheduler  Scheduling decisions taken once every 1ms with frequency domain granularity of 180 kHz.  Scheduler allocates resources depending on the Channel State Information(CSI) provided by the UE
  •  Inter Cell interference Coordination (ICIC) :  In LTE, Frequency Reuse Factor equals to one (full spectrum availability at each Cell)  This leads to high performance degradation specially the Users in cell edge.  ICIC reduce ICI at cell edge applying certain restrictions on resource assignment.Adaptive Fractional Frequency ReuseCoordination: 3 1 2 Inner Region Outer Region
  •  Multicast / Broadcast Single frequency Network (MBSFN) As Identical information is transmitted from transmitters (time aligned), UEs in Cell edge can utilize received power of several surrounding cells to detect / decode broadcasted data.
  • Special Features in LTE – A (Rel.10)Carrier Aggregation : Relaying:
  • Extended Multi Antenna Transmission :  DL Spatial Multiplexing has been expanded to support up to 8 transmission Layers.Heterogeneous Deployments :Ex : Pico Cell placed inside a Macro Cell
  • References : . “4G LTE/LTE-Advanced for Mobile Broadband” by Erik Dhalman, Stefan Parkvall, Johan Skold “Overview of the 3GPP Long Term Evolution Physical Layer ” by Jim Zyren, Dr.Wes McCoy “Wireless Communication” by Andrea Goldsmith
  • THANK YOU! Nadisanka Rupasinghe Engineer – Network Optimization