Tài liệu 03_01_ra41203en16agla0_air_interface

LTE Air Interface Slide 1 NokiaEDU LTE Air Interface LTE Radio Planning Essentials Course RA4120 FL16A/TL16A RA41203EN16AGLA0 RA41203EN16AGLA0 © Nokia 2016 1 LTE Air Interface Slide 2 Copyright and confidentiality The contents of this document are proprietary and confidential property of Nokia. This document is provided subject to confidentiality obligations of the applicable agreement(s). This document is intended for use of Nokia’s customers and collaborators only for the purpose for which this document is submitted by Nokia. No part of this document may be reproduced or made available to the public or to any third party in any form or means without the prior written permission of Nokia. This document is to be used by properly trained professional personnel. Any use of the contents in this document is limited strictly to the use(s) specifically created in the applicable agreement(s) under which the document is submitted. 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Other product and company names mentioned herein may be trademarks or trade names of their respective owners. © Nokia 2016 RA41203EN16AGLA0 2 LTE Air Interface Slide 5 RA4120 – Learning Elements list Introduction & Roadmaps LTE/EPS Overview LTE Air Interface Air Interface Overheads RRM overview LTE Link Budget Cell Range (Coverage Planning) Radio Capacity Planning Nokia eNodeB LTE Solution Initial Parameters Planning LTE Performance Simulations 5 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 3 LTE Air Interface Slide 6 Module Objectives After completing this module, the participant will be able to: • Describe the basics of the OFDM transmission technology • Explain how the OFDM technology avoids the Inter Symbol Interference • Recognise the different between OFDM & OFDMA • Identify the OFDM weaknesses • Review the key OFDM parameters • Analyze the reasons for SC-FDMA selection in UL • Describe the LTE Air Interface Physical Layer • Explain LTE Cell acquisition and call set up • Identify LTE Measurements • List the frequency allocation alternatives for FDD LTE 6 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 4 LTE Air Interface Slide 7 Module Contents • OFDM Basics • OFDM & Multipath Propagation: The Cyclic Prefix • OFDM versus OFDMA • OFDM Weaknesses • • • • • SC-FDMA LTE Air Interface Physical Layer LTE Cell acquisition and call set up LTE Measurements LTE Frequency Variants - FDD 7 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 5 LTE Air Interface Slide 8 Module Contents • OFDM Basics • OFDM & Multipath Propagation: The Cyclic Prefix • OFDM versus OFDMA • OFDM Weaknesses • • • • • SC-FDMA LTE Air Interface Physical Layer LTE Cell acquisition and call set up LTE Measurements LTE Frequency Variants - FDD 8 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 6 LTE Air Interface Slide 9 Multiple Access Methods TDMA • Time Division User 2 User 1 User 3 User .. OFDMA FDMA CDMA • Frequency Division • Code Division • Frequency Division • Orthogonal subcarriers f f f f t t t f f f t f OFDM is the state-of-the-art and most efficient and robust air interface 9 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 7 LTE Air Interface Slide 10 The Rectangular Pulse Fourier Transform spectral power density Frequency Domain amplitude Time Domain fs  Ts 1 Ts fs  time Advantages: + Simple to implement: there is no complex filter system required to detect such pulses and to generate them. + The pulse has a clearly defined duration. This is a major advantage in case of multipath propagation environments as it simplifies handling of inter-symbol interference. 10 RA41203EN16AGLA0 Inverse Fourier Transform frequency f/f s Disadvantage: - it allocates a quite huge spectrum. However the spectral power density has null points exactly at multiples of the frequency fs = 1/Ts. This will be important in OFDM. © Nokia 2016 RA41203EN16AGLA0 8 LTE Air Interface Slide 11 OFDM Basics • Transmits hundreds or even thousands of separately modulated radio signals using orthogonal subcarriers spread across a wideband channel Total transmission bandwidth 15 kHz in LTE: fixed Orthogonality: The peak ( center frequency) of one subcarrier … …intercepts the ‘nulls’ of the neighboring subcarriers 11 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 9 LTE Air Interface Slide 12 OFDM Basics - Data is sent in parallel across the set of subcarriers, each subcarrier only transports a part of the whole transmission - The throughput is the sum of the data rates of each individual (or used) subcarriers while the power is distributed to all used subcarriers - FFT ( Fast Fourier Transform) is used to create the orthogonal subcarriers. The number of subcarriers is determined by the FFT size ( by the bandwidth) Power bandwidth frequency 12 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 10 LTE Air Interface Slide 13 OFDMA Parameters in LTE - Channel bandwidth: DL bandwidths ranging from 1.4 MHz to 20 MHz - Data subcarriers: the number of data subcarriers varies with the bandwidth • 72 for 1.4 MHz to 1200 for 20 MHz 13 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 11 LTE Air Interface Slide 14 LTE Air Interface Specifications •The LTE radio interface is standardised in the 36-series of 3GPP Release 8. The detailed physical layer structure is described in five physical layer specifications. LTE is standardised in the 36-series of 3GPP Release 8: TS 36.1xx Equipment requirements (terminals, eNodeB) TS 36.2xx Layer 1 (physical layer) specifications TS 36.3xx Layer 2 and 3 specifications TS 36.4xx Network signaling specifications TS 36.5xx User equipment conformance testing OFDMA SCFDMA Subcarriers eNodeB Physical layer specifications: TS 36.201 Physical layer; General description TS 36.211 Physical channels and modulation TS 36.212 Multiplexing and channel coding TS 36.213 Physical layer procedures TS 36.214 Physical layer; Measurements Frequency 14 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 12 LTE Air Interface Slide 15 Module Contents • OFDM Basics • OFDM & Multipath Propagation: The Cyclic Prefix • OFDM versus OFDMA • OFDM Weaknesses • • • • • SC-FDMA LTE Air Interface Physical Layer LTE Cell acquisition and call set up LTE Measurements LTE Frequency Variants - FDD 15 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 13 LTE Air Interface Slide 16 Propagation delay exceeding the Guard Period 2 1 3 Time Domain Delay spread > Tg  ISI 4 TSYM Tg BOL 1 time 2 time Tg: Guard period duration ISI: Inter-Symbol Interference 3 time 4 time 16 RA41203EN16AGLA0 © Nokia 2016 The Guard Period should be designed such that it is always longer than the multipath delay spread, in order to avoid inter-symbol interference between successive OFDM symbols. Note that in the example of this slide, the Guard Period is too short, so there will be intersymbol interference! RA41203EN16AGLA0 14 LTE Air Interface Slide 17 OFDM symbol The Cyclic Prefix • In all major implementations of the OFDMA technology (LTE, WiMAX) the Guard Period is equivalent to the Cyclic Prefix CP. • This technique consists in copying the last part of a symbol shape for a duration of guard-time and attaching it in front of the symbol (refer to picture sequence on the right). • CP needs to be longer than the channel multipath delay spread (refer to previous slide). • A receiver typically uses the high correlation between the CP and the last part of the following symbol to locate the start of the symbol and begin then with decoding. OFDM symbol OFDM symbol OFDM symbol Cyclic prefix 17 RA41203EN16AGLA0 Part of symbol used for FFT processing in the receiver © Nokia 2016 RA41203EN16AGLA0 15 LTE Air Interface Slide 18 The OFDM Signal 18 RA41203EN16AGLA0 © Nokia 2016 •The OFDM signal is made of multiple subcarriers. •The distance between the center frequencies of the subcarriers is exactly the inverse of the Symbol period (Ts). Bigger Ts means subcarriers will allocated closer and more subcarriers could be allocated on a given spectrum bandwidth. •An OFDM symbol is the combination of “n” subcarrier Symbol being produced in parallel at the same time. RA41203EN16AGLA0 16 LTE Air Interface Slide 19 Module Contents • OFDM Basics • OFDM & Multipath Propagation: The Cyclic Prefix • OFDM versus OFDMA • OFDM Weaknesses • • • • • SC-FDMA LTE Air Interface Physical Layer LTE Cell acquisition and call set up LTE Measurements LTE Frequency Variants - FDD 19 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 17 LTE Air Interface Slide 20 OFDM Plain OFDM • OFDM stands for Orthogonal Frequency Division Multicarrier • OFDM: Plain or Normal OFDM has no built-in multipleaccess mechanism. • This is suitable for broadcast systems like DVB-T/H which transmit only broadcast and multicast signals and do not really need an uplink feedback channel (although such systems exist too). • Now we have to analyze how to handle access of multiple users simultaneously to the system, each one using OFDM. 1 UE 1 20 2 UE 2 3 UE 3 RA41203EN16AGLA0 subcarrier time . . . . . . . . . . . . ... ... ... ... . . . ... ... ... ... ... common info (may be addressed via Higher Layers) © Nokia 2016 RA41203EN16AGLA0 18 LTE Air Interface Slide 21 OFDMA® Orthogonal Frequency Multiple Access OFDMA® OFDMA® stands for Orthogonal Frequency Division Multiple Access • registered trademark by Runcom Ltd. • The basic idea is to assign subcarriers to users based on their time bit rate services. With this approach it is quite easy to handle high and low bit rate users simultaneously in a single system. But still it is difficult to run highly variable traffic efficiently. The solution to this problem is to assign to a single users so called resource blocks or scheduling blocks. • • such block is simply a set of some subcarriers over some time. A single user can then use 1 or more Resource Blocks. 1 UE 1 21 2 UE 2 3 UE 3 RA41203EN16AGLA0 subcarrier • • common info (may be addressed via Higher Layers) 1 1 1 . . 1. 1 3 3 3 1 1 1 . . 1. 1 3 3 3 ... 1 2 2 ... 1 2 2 ... 1 2 2 ... . . . . . . 1. . . ... 1 ... 3 3 3 ... 3 3 3 ... 3 3 3 ... Resource Block (RB) © Nokia 2016 RA41203EN16AGLA0 19 LTE Air Interface Slide 22 Module Contents • OFDM Basics • OFDM & Multipath Propagation: The Cyclic Prefix • OFDM versus OFDMA • OFDM Weaknesses • • • • • SC-FDMA LTE Air Interface Physical Layer LTE Cell acquisition and call set up LTE Measurements LTE Frequency Variants - FDD 22 RA41203EN16AGLA0 © Nokia 2016 RA41203EN16AGLA0 20