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Evolution of LTE/4G Network Architecture: Key Technologies Explained

This introduction covers the transition from 3G to 4G, discussing IMT-Advanced requirements, peak spectral efficiencies, control plane latency, and the evolution of 3GPP specifications. It delves into LTE/SAE network architecture, including E-UTRAN, MME/S-GW, P-GW, HSS, and the functions of eNodeB. Also explained are OFDM, MIMO, SC-FDMA, and the reasons for using them in downlink and uplink transmissions.

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Evolution of LTE/4G Network Architecture: Key Technologies Explained

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  1. Introduction to

  2. No more Codes Key technologies…. • For Downlink : OFDM and MIMO • For Uplink : SC - FDMA

  3. Topics to discuss…

  4. 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

  5. Releases of 3GPP Specifications

  6. System Architecture Evolution (SAE)

  7. 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

  8. LTE/SAE Network Architecture Internet P-GW HSS MME/S-GW MME/S-GW EPC MME S-GW S11 S5 S6a S1 S1 S1 S1 E-UTRAN X2 X2 X2 eNodeB eNodeB eNodeB

  9. 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 Node Evolved 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

  10. 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

  11. What is Orthogonal Frequency Division Multiplexing (OFDM) ?

  12. OFDM Why ?

  13. ISI – Inter Symbol Interference Time domain : Data Rate ISI

  14. Time Spreading (Freq. Selective Fading) • When an impulse is transmitted , how does the average power received by Mobile vary as a function of time delay ζ ? Power Delay Profile • Freq. Selective Fading : Ts < ζ0 • Non Freq. Selective Fading : Ts > ζ0

  15. Spaced Freq. Correlation function Power Delay Profile FT Inside Coherence BW channel passes all freq. components with equal gain and linear phase • Freq. Selective Fading : W > f0 • Non Freq. Selective Fading : W < f0

  16. 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

  17. Single carrier transmission Vs OFDM Transmission :Single Carrier Transmission 0 1 1 1 : OFDM Transmission 0 1 t

  18. Sub carrier Pulse shape and Spectrum Subcarrier BW < Coherance BW

  19. Why “Orthogonal” ? Two modulated OFDM subcarriers and are mutually orthogonal over the time interval m ≤ t < (m+1) Subcarriers “Orthogonal” in the time domain In OFDM, Subcarriers are overlapped in Frequency domain while maintaining orthogonality in time domain

  20. Overlapping subcarriers in Freq. domain Overlapping Subcarriers Spectral Efficiency

  21. OFDM Symbol • Generated by Multiplexing several overlapping subcarriers and a Cyclic Prefix (CP). • 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 . CP Modulated Subcarriers

  22. 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.

  23. What is Multiple-Input Multiple-Output (MIMO) ?

  24. 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

  25. Why MIMO? • Significant increase in Spectral efficiency and data rates - Spatial Multiplexing • High QoS- Spatial diversity • Wide Coverage - Spatial diversity SISO Channel Capacity : MIMO Channel Capacity (MIMO system with M×N antenna configuration) : B : Channel Bandwidth SINR : Signal to Interference plus Noise ratio

  26. Received signal y at the receiver when signal x istransmitted, = • Channel impulse responses (are determined by transmitting reference signals from each transmitting antenna.

  27. What is Single Carrier FDMA (SC – FDMA)?

  28. 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

  29. 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.

  30. User Multiplexing in SC-FDMA • Localized Transmission : • Distributed Transmission : User 2 User 1 User 1 User 2 User 3 User 3

  31. LTE Physical Layer Overall RAN Protocol Architecture

  32. LTE Physical Layer Processing

  33. Available DL BW and Physical Resource Blocks (PRBs)

  34. 1 Frame (10 ms) Generic Frame Structure 1 Slot (0.5 ms) 0 2 1 n 18 19 1 Sub Frame (1 ms) 0 1 3 6 5 4 2 7 OFDM symbols

  35. Resource Grid 7 OFDM symbols Time F R E q R E S O U R C E B L O C K R E S O U R C E G R I D Resource Element

  36. 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.

  37. LTE Radio Access : An Overview

  38. 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

  39. 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 Reuse Coordination: Inner Region Outer Region

  40. 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.

  41. Special Features in LTE – A (Rel.10) Carrier Aggregation : Relaying:

  42. 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

  43. Heterogeneous Networks

  44. 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

  45. THANK YOU! Nadisanka Rupasinghe Engineer – Network Optimization

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