References 2 Material Related to LTE comes from 3GPP LTE: System - PowerPoint PPT Presentation

1 References 2 ¨ Material Related to LTE comes from ¤ “3GPP LTE: System Overview, Product Development and Test Challenges,” Agilent Technologies Application Note , 2008. ¤ IEEE Communications Magazine, February 2009 ¤ IEEE Communications Magazine, April 2009 ¤ Bell Labs Technical Journal, Vol. 13, No. 4, 2009 ¤ LTE: The UMTS Long Term Evolution, Ed. S. Sesia et al , John Wiley and Sons, 2011 UMTS and LTE What is UMTS? UMTS Architecture 3 4 ¨ UMTS stands for Universal Mobile Telecommunications System ¨ The UMTS System ¤ 3G cellular standard in the US, Europe, and Asia ¤ Consists of many logical network elements similar to the 2G systems ¨ Outcome of several research activities in Europe ¤ Logical network elements have “open interfaces” ¤ Assisted the standardization efforts ¨ There are three components ¨ Most of the standardization work was focused in 3GPP (3 rd Generaration ¤ User Equipment (UE) Partnership Project) ¤ UMTS Terrestrial Radio Access Network (UTRAN) ¤ Core Network (CN) ¤ 3GPP refers to the physical layer as UTRA – UMTS Terrestrial Radio Access n Heavily borrows from GSM ¤ There are two modes – FDD and TDD UMTS User Terrestrial Core Equipment RAN Network Uu Iu

Summary of WCDMA – I 5 Detailed Network Elements 6 ¨ WCDMA is somewhat different compared to IS-95 Uu Iu ¨ It is a “wideband” direct sequence spread spectrum system ¤ Supports up to 2 Mbps using Node n Variable spreading MSC/ B GMSC PLMN n Multicode connections VLR RNC PSTN Node ¨ The chip rate is 3.84 Mcps USIM B ¤ Approximate bandwidth is 5 MHz Cu Iur ¤ Supports higher data rates/capacity HLR Iub Node ME B Internet RNC SGSN GGSN Node UE B UTRAN CN WCDMA Air Interface Summary of WCDMA – II Long Term Evolution (LTE) 7 8 ¨ It is an evolution of UMTS ¨ Supports variable data rates or bandwidth on demand ¨ Many terms, ideas, entities, borrowed from UMTS ¤ Transmissions are in frames of 10 ms ¤ Simplified architecture compared to UMTS ¤ The data rate is constant for 10 ms ¤ Data rate can change from frame to frame ¨ Protocol stack is similar to UMTS Power/ Rate User 4 User 4 User 4 User 3 User 3 User 4 User 2 User 2 User 2 User 1 User 1 User 1 User 1 time f 10 ms

10 LTE – Summary Mossberg’s Measurements 9 ¨ Average using ¨ Only packet data traffic on the air (no circuit switching) different versions of ¨ All IP core network that can interface better with technologies such as WiFi and WiMax iPhone 5S, 20 ¨ Use of OFDMA as the medium access/modulation scheme downloads per phone ¨ Flexibility to deploy it in as little spectrum as 1.4 MHz and as much as 20 MHz of spectrum ¨ Sprint Spark in 2015 ¨ Support for true “broadband” with improved spectrum efficiency Expected Downlink Data Rates in LTE FDD Downlink Peak Data Rates Using 64 QAM Antenna Configuration SISO 2 × 2 MIMO 4 × 4 MIMO November 13, 2013 Data Rate (Mbps) 100 172.8 326.4 LTE Network Architecture LTE Network Architecture 11 12 ¨ Evolved Packet System (EPS) consists of two parts X2 interface ¤ E-UTRAN – Evolved UMTS Terrestrial Radio Access Network Home ¤ EPC – Evolved Packet Core Subscriber MME/ S-GW Server ¨ E-UTRAN ¤ Consists of only one kind of node: eNode-B Part of the IP Multimedia Subsystem ¨ EPC E-NodeB EPC ¤ Fully based on IP – consists of elements PDN-GW n MME – Mobility Management Entity (like SGSN) E-NodeB n S-GW & PDN-GW: Serving and Packet Data Network Gateways MME/ n Home subscriber server (HSS) S-GW ¤ Voice and real-time applications will make use of the IP E-NodeB Multimedia Subsystem (IMS) E-UTRAN

Orthogonal Frequency Division Channel Bandwidths Multiplexing 13 14 ¨ Idea in frequency domain: ¤ Coherence bandwidth limits the maximum data rate of the channel ¨ Can vary from 1.4 MHz to 20 MHz ¤ Send data in several parallel sub-channels each at a lower data rate and different carrier frequency ¨ Resource Block (RB) ¨ Idea in time domain: ¤ 180 kHz wide and 0.5ms long ¤ By using several sub-channels and reducing the data rate on each channel, the symbol duration in each channel is increased ¤ 12 subcarriers spaced at 15 kHz (24 at 7.5 kHz possible ¤ If the symbol duration in each channel is larger than the multipath delay spread, later) we have few errors ¨ Data rate limited by User Equipment (UE) categories ¨ OFDM enables ¤ Spacing carriers (sub-channels) as closely as possible ¤ Implementing the system completely in digital Channel BW (MHz) 1.4 3.0 5 10 15 20 Resource Blocks 6 15 25 50 75 100 What is OFDM? OFDM Advantages 15 16 ¨ Modulation/Multiplexing technique ¨ Bandwidth efficiency ¨ Usual transmission ¨ Reduction of ISI ¤ Transmits single high-rate data stream over a single carrier ¤ Needs simpler equalizers ¨ With OFDM ¨ Robust to narrowband interference and frequency ¤ Multiple parallel low-rate data streams selective fading ¤ Low-rate data streams transmitted on orthogonal ¨ Possibility of improving channel capacity using adaptive subcarriers bit loading over multiple channels ¤ Allows spectral overlap of sub-channels

18 How can we increase data rates? What is MIMO? 17 ¨ Traditional ways ¨ So far we have considered Single Input Single Output or ¤ Reduce the symbol duration SISO systems n Needs larger bandwidth ¤ Both transmitter and receiver have one antenna each n Leads to a wideband channel and frequency selectivity - ¤ Simplest form of transceiver irreducible error rates architecture ¤ Increase the number of bits/symbol ¨ Single input multiple-output n Error rates increase with M for the same E b / N 0 (SIMO) systems ¨ MIMO systems ¤ Receiver has multiple antennas ¨ Multiple input multiple output ¤ There is no need to increase the bandwidth or power (MIMO) systems n But what are the limitations? ¤ Both transmitter and receiver ¤ Use multiple transmit (Tx) and receive (Rx) antennas have multiple antennas ¤ Strictly: Each antenna has its own ¤ Increases spectral efficiency to several tens of bps/Hz RF chain (modulator, encoder and so on) Performance enhancements due to LTE Frame Structure MIMO 19 20 One Radio Frame = 10 ms ¨ Diversity gain one sub-frame = 1 ms ¤ Ability to receive multiple copies of the signal with independent fading Each sub-frame has two slots of 0.5 ms each time slot = 0.5 ms ¨ Spatial multiplexing gain ¤ Send different information bits over different antennas and recover the information resource block ¨ Interference reduction frequency ¤ Reduce the region of interference thereby increasing resource 12 carriers each with BW 15 kHz element capacity time OFDM symbol cyclic prefix

Detailed Downlink Frame Structure Downlink Multiple Access: OFDMA (FDD) 21 22 Source: Agilent Application Note Note users don’t have to be assigned resource blocks that are together Source: Agilent Application Note Multi-user Diversity with OFDMA Flexible Resource Allocation in OFDMA 23 24 frequency MS 8 MS 7 MS 8 H(f) H(f) MS 7 MS 3 f MS 6 f MS 6 MS 2 H(f) MS 5 f MS 4 MS 3 MS-3 MS-1 MS 3 MS 1 MS-2 MS 2 subcarrier MS 2 • Allocate subsets of carriers to users over different MS 1 times time – Preferably, allocate carriers that have good channel Slot characteristics

Uplink Multiple Access: Single Carrier 25 Other Downlink Features FDMA 26 ¨ Support for MIMO ¨ Frequency and time selective scheduling ¤ Transmit diversity ¤ MS reports channel ¤ Beamforming quality for resource ¤ Spatial multiplexing blocks ¤ Combos ¨ Fractional frequency ¨ Link adaptation reuse (FFR) ¤ Various modulation ¤ A fraction of frequency schemes and code rates resources are not reused in every cell (or are used with low transmit power) Source: Agilent Application Note Why SC-FDMA Other Uplink Features 27 28 ¨ Intra-cell orthogonality ¨ Avoid high peak-to-average power ratio (PAPR) in ¤ Unlike CDMA, there is only interference from outside MS the cell, not within the cell ¤ No need for fast power control (compare with CDMA) n Still has slow power control ¨ Frequency and time selective scheduling using wideband channel sounding signal by mobile stations ¨ Mobile is always “online” ¤ Has idle and connected states Source: Agilent Application Note

LTE Simplified Protocol Stack (Control 29 Flow of user data (“our data”) Information) 30 E-NodeB Shaded stack is called the ¨ UE E-NodeB “access stratum” - AS, upper Internet S-GW layers are called “non- S1 UE access stratum” – NAS PDN-GW MME RRC = Radio Resource End-to-End Between UE and Service End-point using IP ¨ Control Bearer between PDN-GW and UE that defines QoS (IP) ¤ Includes measurements Mobility and Session Management on signals PDCP PDCP GTP GTP GTP GTP S1- S1- RRC RRC PDCP = Packet Data ¨ bearer Bearer RLC RLC IP IP IP IP Convergence Protocol PDCP PDCP GTP GTP Note that there is MAC MAC Layer 2 Layer 2 Layer 2 Layer 2 RLC = Radio Link Control no RRC here ¨ RLC RLC IP IP PHY PHY Layer 1 Layer 1 Layer 1 Layer 1 GTP = GPRS Tunneling ¨ MAC MAC Layer 2 Layer 2 Protocol Radio Bearer PHY PHY Layer 1 Layer 1 Tunnel (GTP based) Radio Bearer LTE Physical Signals LTE Physical Channels 31 32 Source: Agilent Application Note Source: Agilent Application Note