LTE Radio Interface

Introduction

LTE Radio Interface?Different from other technologies

New structures

Some similarities

?

Scope and objectivesDescribe OFDM/OFDMADescribe SC-FDMAExplain Flexible Spectrum UsageExplain Hybrid ARQ (HARQ)Present Radio Interface StructureDescribe Channel StructureObjectivesScopeDownlink and Uplink Transmission TechniqueFlexible Spectrum UsageHARQRadio Interface and Channel Structure

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Overview

LTE Radio InterfaceInterface between UE and eNodeB

Hybrid ARQ

Multi Antenna Possibility

Flexible spectrum usage

LTE Radio Interface

Downlink transmission techniqueFlexible bandwidth operation Different regions Different frequency bands & bandwidths

OFDM

OFDMA

Uplink transmission techniqueIntra-cellorthogonality

Bandwidth flexibility1.4 MHz

FDDfDL/ULTDDTime-domain structure- more overhead and latency+ radio channel reciprocity+ simpler to deploy in limited available spectrum

Excersize

Multi Antenna PossibilitiesRXMIMO

Segmentation, ARQCipheringHeader Compr.Hybrid ARQHybrid ARQMAC multiplexingAntenna and resrouce mappingCoding + RM Data modulation Antenna and resource mapping Coding Modulation User #1User #2Concatenation, ARQDecipheringHeader Compr.Hybrid ARQHybrid ARQMAC demultiplexingAntenna and resrouce mappingCoding + RM Data modulation Antenna and resource demapping Decoding Demodulation eNodeBUERadio interface structureMACMACRLC #1PHYRLCPHYPDCP #1PDCP

Radio interface Control Signaling

3 7 2 6 1 5 9 Datastream 0 4 8 The HARQ Principle

Excersize

Channel structurePHYMACRLCPhysical Channels/ SignalsTraffic

Summary

SummaryOFDM/OFDMA in DLSC-FDMA in ULSix different bandwidthsFDD, TDD and Half-duplex FDDMultiple antenna solutionsLayered interface structure

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*In this module, we will overview the LTE radio interface. We will take a look on the main concepts in regard to spectrum usage, transmission techniques interface structure. *Introduction*What is happening in the LTE Radio Interface. At a first glance the LTE radio interface might feel completely different from other radio access technologies. There are for example new physical channels and modifications made to the protocols. But you will probably also recognise some concepts like Hybrid ARQ if you are familiar with HSPA. Throughout this module and the following modules in LTE Air Interface we will help you to achieve a better understanding of the LTE Radio Interface.*On completion of this module the students will be able to:Describe the principle for OFDM/OFDMADescribe the principle for SC-FDMAExlain the flexible spectrum usageExplain Hybrid ARQ (HARQ) Present the radio interface strucuture Describe the channel structureSpend your time well. Answer a few questions to se if you already now master the learning objectives of this module. Based on that you will either be recommended to take this course or not. Good luck! **Click on the left button to go to the first topic in the course, or Click on the right button to skip the course and go to EriColl to register your attempt.Make your choice!

* *Overview*The radio interface is the interface between the UE and the eNodeB. It enables both signalling and transfer of user data. This is achieved by using different physical channels. Other functions that enables and enhances this are for example Hybrid ARQ, multiple antenna solutions and the possibility for a flexible spectrum usage.

**IPTV Template2008-12-09*The LTE radio interface is based on OFDM (Orthogonal Frequency Division Multiplex) and OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink (DL).These techniques are well suited for a flexible bandwidth operation, and it enables operators to deploy LTE in different regions with different frequency bands and bandwidths available.*IPTV Template2008-12-09*OFDM has very good performance in highly time dispersive radio environments (i.e. many delayed and strong multipath reflections).That is because the data stream is distributed over many subcarriers.*IPTV Template2008-12-09*The users in DL are separated with OFDMA, which means that each user has its own time- and frequency resources, so called scheduling blocks.Dynamic channel dependent scheduling allocates a number of these time- and frequency resources to different users at different times. In that way it is possible to schedule users on the frequencues they experience the best quality on during a certain time intervall.The LTE radio transmissions are based on a very short TTI (Transmission Time Interval) of 1ms, which speeds up the operation of all functions. The short TTI also reduces the radio interface latency.*IPTV Template2008-12-09*The uplink transmission technique, SC-FDMA, is realized in a similar manner as for the downlink and is also called DFTS-OFDM (Discrete Fourier Transform Spread OFDM).The time domain structure is also similar in uplink and downlink. One of the reasons for the choice of SC-FDMA for the uplink is that it enables the UE to be made more power efficient and manufactured at a lower cost since the Peak to Average Power Ratio (PAPR) is lower than for OFDMA.In contrary to WCDMA, the uplink transmissions in LTE are, thanks to the SC-FDMA solution, perfect separated within a cell (intra-cell orthogonality). This leads to a less extensive power control operation.*IPTV Template2008-12-09*The support for operation in six different bandwidths, 1.4, 3, 5, 10, 15 and 20 MHz, plays an important role of the spectrum flexibility part in the standardization of the radio interface. Actually, the LTE radio interface implementation supports operation in any bandwidth between 1.4 and 20 MHz in steps of one resource block, which corresponds to 12 subcarriers or 180 kHz.The maximum number of Resource Blocks that can be allocated is 100. The 10 remaining RBs (since 20 MHz corresponds to 110 RBs) are used as guard bands.*IPTV Template2008-12-09*Both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) is supported, which opens up for deployment in both paired and unpaired spectrum. In FDD, different frequency bands are used for UL and DL. In TDD the UL and DL transmissions are separated in time.There are pros and cons with both methods. TDD has some more overhead and latency, due to the frequent switching in time.On the other hand, the TDD mode enables radio channel reciprocity, which means that uplink measurements can be used for downlink transmissions, and vice versa.The TDD mode is also simpler to deploy in areas with limited available spectrum since it can utilize unpaired frequency bands.A half duplex FDD mode (HD-FDD) is also defined, where the UE does not have to transmit at the same time as it receives. Therefore, more cost effective UEs can be manufactured since a duplex filter is not needed.*IPTV Template2008-12-09**IPTV Template2008-12-09*To increase the spectrum efficiency, capacity and overall data rates the use of multiple antennas MIMO (Multiple Input Multiple Output) is included in the standard.With these multiple antennas and advanced signal processing, the radio channel can be separated into several layers, or data pipes. Up to four layers can be utilized. This corresponds to up to four times higher data rates for a given bandwidth.*IPTV Template2008-12-09*The radio interface is structured in a layered model (similar to WCDMA), with the EPS Bearer Service (a layer 2 bearer) carrying layer 3 data and the end-to-end service.The EPS bearer is carried by the E-UTRA Radio Bearer Service in the radio interface. The E-UTRA radio bearer is carried by the radio channels. The radio channel structure is divided into logical, transport and physical channels The logical channels are carried by transport channels, which in turn are carried by the physical channels.The protocols performing the functions in the radio interface are: PDCP (Packet Data Convergence Protocol), RLC (Radio Link Protocol), MAC (Medium Access Control) and the physical layer.*IPTV Template2008-12-09*For control signaling the RRC (Radio Resource Control) protocol is used to transfer the NAS (Non Access Stratum) information over the radio interface.*IPTV Template2008-12-09*The Hybrid ARQ (HARQ) protocol is very similar to the solution adopted for HSDPA, i.e., the protocol uses multiple stop-and-wait hybrid ARQ processes.In this case, we have a received datastream that is processed by HARQ and demultiplexed into logical channels and forwarded to the RLC protocol for re-ordering. The motivation for the HARQ protocol is to allow continuous transmission, which cannot be achieved with a single stop-and-wait scheme, while at the same time having some of the simplicity of a stop-and-wait protocol.HARQ works with several processes at the same time. In this example only 4 processes are shown. For FDD it will be up to 8 parallel processes but for TDD it will differ depending on the configuration.*IPTV Template2008-12-09**IPTV Template2008-12-09*The physical layer provides transport channels to the layer 2 (L2).These transport channels differ in their characteristics how data is transmitted and are mapped to different logical channels provided by the MAC layer. Logical channels describe which type of data is conveyed.The logical channels can be divided into control channels and traffic channels. The control channels are used for transfer of control plane information and the traffic channels are used for the transfer of user plane information.An effort has been made to keep a low number of transport channels in order to avoid unnecessary switches between different channel types, which are found to be time consuming in UMTS. In fact there is currently only one transport channel in downlink and one in uplink carrying user data, i.e., channel switching is not needed.The physical layer defines physical channels and physical signals. A physical channel corresponds to a set of physical resources used for transmission of data and/or control information from the MAC layer. A physical signal, which also corresponds to a set of physical resources, is used to support physical-layer functionality but do not carry any information from the MAC layer. *Summary*IPTV Template2008-12-09*In summary:The LTE radio interface is based on OFDM and OFDMA transmission technique in downlinkThe corresponding transmission technique is SC-FDMA in uplink, which is less power consuming for the UELTE is flexible regarding bandwidth with support for operation in six different bandwidthsIt supports both FDD, TDD and Half-duplex FDD, making it easier to adapt to the operators specific requirementsThe use of multiple antennas increase spectrum efficiency, capacity and overall data ratesThe radio interface is structured in a layered model with different protocols and channels performing specific functions. **When clicking next you will be directed to an EriColl page. It is important that you fill in the form and click OK. This will register your successful attempt. 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