lte air interface.pdf

8/10/2019 LTE Air Interface.pdf

http://slidepdf.com/reader/full/lte-air-interfacepdf 1/26TM51171EN02GLA2

Introduction

1



Introduction

2



Introduction

3



Introduction

4

The evolution of UMTS is termed Evolved Packet System (EPS).

In more detail, the evolution of the 3GPP radio technology is being specified under the

name Long Term Evolution (LTE). The Evolved Packet Core (EPC) describes the non-RAN aspects of the system.

EPS = LTE + EPC

EPS: Evolved Packet System (describes evolution of UMTS)LTE: Long Term Evolution (describes the new radio access technology)EPC: Evolved Packet Core

LTE/EPC is the 3GPP system for the years 2010 to 2020 and beyond.

LTE/EPC shall be ready for commercial launch around 2010.

The motivation of LTE/EPC is mainly driven by the need to stay competitive. In order tobe future-proof, UMTS shall be evolving towards a true mobile broadband packet accesssystem. In many aspects it will be superior compared with existing 3G alternatives.



Introduction

5

Fully packet-oriented mobile broadband network providing:

- Peak data rates of 100 Mbps (DL) and 50 Mbps (UL)

- Very low latency

- Seamless and lossless handover

- Sophisticated QoS to support important real time applications such as voice, video andinteractive gaming

- Support for terminal speeds of 150-500 Km/h and cell ranges of up to 100 Km.

- Reduced cost per bit:

LTE/EPC deploys a simplified architecture and open interfaces. It is full IP-based anduses IP transport. In this way it utilizes low-cost equipment and infrastructure. Additionallythis contributes to reduction of operational costs. Further sophisticated features like self-configuration / self-optimization capabilities are beneficial in this context.

- Maximized exploitation of frequency resources:

LTE provides high throughput per cell and supports flexible frequency bandwidths and inparticular allows for re-farming of existing and deployment of new frequency bands.Furthermore by means of OFDM, MIMO, HARQ etc. an outstanding spectrum efficiencycan be achieved.

- Extended interworking functionality: LTE/EPC provides seamless mobility with other3GPP access systems (UMTS, GPRS), with 3GPP2/cdma2000 and where possible withnon-3GPP (e.g. WLAN).

- Reduced terminal complexity. Due to the specific transmission schemes thecomplexity of the terminals is kept reasonable. Also the power consumption shall beminimized. Both contributes to cost reduction and makes it attractive for mass market

deployment.



Introduction

6



Introduction

7

LTE FDD and TDD modes have been harmonized in the sense that both modes share thesame underlaying framework including the radio access schemes (OFDM in DL and SC-

FDMA in UL for both), basic frame formats and protocols. As a clear indication of harmonisation the TDD mode is included together with the FDDmode in the same set of specifications . Protocols and procedures are kept the same forFDD and TDD and therefore it is expected a high level of commonalities for theimplementation. This will make possibile to implement FDD and TDD in the same mobileterminal with a big potential for roaming between FDD and TDD and the other wayarround. However the scenarios for coexistences still need to be further investigated.

Another key feature of TDD mode is the commonality with TD-SCDMA. This is a bigadvantege since China is already having TD-SCDMA so the gloabal roaming will bepossibile.



Introduction

8



Introduction

9

Generic:

The requirements input list for LTE/EPC contains the following crucial elements:

higher data rates: Obviously this is a general requirement requested from any newsystem.

quality of service, lower delay: To enable true convergence between real-time and non-real-time services quality of service awareness is of absolute importance. This mustalready be paid attention to during the design of the physical layer. So LTE/EPC will beQoS aware from the very beginning on and not have QoS as an add-on, which is usuallynot very efficient.

expected new spectrum allocation: It is expected to get some new frequency bandsassigned to 3G. LTE should be ready to use these bands.

flexible bandwidth usage: LTE should be able to deal with frequency bands of differentsize. So a fixed bandwidth ultra-wideband system is not of big use. Rather LTE should be

able to scale the frequency requirements dependent on the operator’s choice. reduced terminal complexity: 3G terminals are very complex and thus suffer often frompoor performance due to hardware limitations and very often also software limitations (orbugs). LTE terminals should have essentially lower complexity. This would also offer thepossibility to implement other performance enhancement techniques later on.

These points result in a long list of requirements for LTE/EPC. So 3GPP/ETSI demand tohave downlink bit rates of greater than 100 Mbps and uplink bit rates of 50 Mbps. Of highimportance is also to increase the cell edge bit rates compared to HSPA.



Introduction

10

The transition times between different levels of activity are also named C-plane latency.The one-way transit time can be seen as U-plane latency.

Furthermore for the C-plane capacity targets are stated as number of active users:

200 (5 MHz) and at least 400 for wider bands.

The UL/DL resource scheduling of course requires that the scheduler can handle anddistinguish different quality of service classes.



Introduction

11

Targets are defined related to the Rel. 6 baseline.

TIP!

Note, bit rates are defined for 20 MHz bandwidth and for smaller bands proportionalscaling applies.

2 Tx antennas at the Node B and 2 Rx antennas at the UE are assumed for DL. For ULthe targets are set considering a single Tx antenna at the UE and 2 Rx antennas at theeNB.



Introduction

12

Functionality:

eNB obtains the UE radio capabilities via:

- The S1AP initial setup request message

- The X2AP in case of handover

- The RRC in any other cases

eNB sends the UE radio capabilities to:

- The MME if it has been retrieved from RRC signalling

- The neighbour eNB in case of handover

UE category determines:

- MIMO settings

- PRB allocation and AMC limitation (e.g. 64QAM in UL)

- ROHC (Robust Header Compression) profile

- Inter RAT handover support



Introduction

13



Introduction

14



Introduction

15



Introduction

16



Introduction

17

BASED ON THE REQUIREMENTS 3GPP AGREED UPON STANDARD FEATURES:

OFDMA/SC-FDMA.

MIMO (Multiple Input Multiple Output)

HARQ (Hybrid Automatic Retransmission on reQuest)

Scalable bandwidth

Evolved Node B

IP transport layer

UL/DL resource scheduling

QoS awareness

Self configuration

Self optimization

Packet Switched Domain only

3GPP (GTP) or IETF (MIPv6) option

Non-3GPP access



Introduction

18



Introduction

19

SAE: System Architecture Evolution

SAE GW: Serving Gateway +PDN Gateway



Introduction

20

The LTE/EPC architecture is driven by the goal to optimize the system for packet datatransfer.

TIP!

There are no circuit switched components in LTE/EPC

There is a new approach in the inter-connection between radio access network and corenetwork. The EPS architecture is made up of an EPC (Packet Core Network, alsoreferred as EPC) and an eUTRAN Radio Access Network (also referred as LTE)

The CN provides access to external packet IP networks and performs a number of CNrelated functions (e.g. QoS, security, mobility and terminal context management) for idle

(camped) and active terminals. The RAN performs all radio interface related functions.

The LTE/EPC radio access network - Evolved UTRAN (E-UTRAN) - will only containNode Bs. No RNC is provided anymore. This means, that the evolved Node Bs take overthe radio management functionality.

This will make radio management faster and the network architecture simpler. E-UTRANexclusively uses IP as transport layer. Behind the EPC follow one or more IP networks. Amajor example will be IMS, that can benefit especially from the QoS awareness of LTE.



Introduction

21



Introduction

22



Introduction

23

The state-of-the-art design of the LTE air interface is characterised by OFDMA (DL) andSC-FDMA (UL) together with MIMO.

The downlink modulation is based on OFDMA (Orthogonal Frequency Division Multiple Access). OFDMA is a variant of OFDM which has the advantage that receiver complexityis at a reasonable level, it can handle scalable bandwidth requirements and it supportsvarious modulation schemes from BPSK, QPSK, 16QAM to 64QAM. This allows adaptivemodulation on a per user base. In uplink direction a variant of OFDMA called SC-FDMA(Single Carrier Frequency Division Multiple Access) is used. It has the advantage againstOFDMA to have a lower PAPR (Peak-to-Average Power Ratio), which leads to lowerpower consumption and less expensive RF amplifiers in the terminal.

LTE will support MIMO. It describes the possibility to have multiple transmitter andreceiver antennas in a system. Other names are beam-forming or smart antennas. Up tofour antennas can be used by a single LTE cell. This allows having spatial multiplexingand beam-forming. MIMO is considered to be the core technology to increase spectralefficiency. Currently the performance of MIMO for high mobility cases is still underinvestigation.

HARQ implements a protocol on layer 1/layer 2 that allows for fast retransmission.Furthermore blocks can be retransmitted with increased coding.

In contrast to UMTS where physical resources are either shared or dedicated, theEvolved Node B in EUTRAN handles all physical resource via a scheduler and assignsthem dynamically to users and channels. This provides greater flexibility than the oldersystem



Introduction

24


http://slidepdf.com/reader/full/lte-air-interfacepdf 25/26


http://slidepdf.com/reader/full/lte-air-interfacepdf 26/26

Introduction

lte air interface.pdf

Documents