Mobile Communications: Long Term Evolution Part 1 Motivation for LTE Evolution of the standards...

Mobile Communications: Mobile Communications: Long Term EvolutionLong Term Evolution

Part 1 • Motivation for LTE• Evolution of the standards • Requirements and targets• Competing standards• Frequency bands• System architecture

Part 2 • LTE enabling technologies

– OFDM – MIMO– SC-FDMA

Chair Systemswww.tu-cottbus.de/systeme

Motivation for LTE

• For consumers– Fast data access (several megabytes in just some seconds)

– Flexible media access (access to any media content from everywhere)

– Real time services (streaming, VoIP, videoconferencing, etc.)

• For network operators– Flexibility (scalable bandwidth from 1.25MHz to 20MHz)

– Efficiency (more standard voice customers, more data, more services)

– Cost savings (cheaper infrastructure, migration to an All-IP-Network)

Monday 10 April 2023winter term 2010/11 – Mobile Communication Systems II


IMT-2000 to IMT-Advanced(source: ITU-R M. 1645)


High

Low

Mobility

1 10 100 1000

Peak useful datarate (Mbps)

IMT-2000 EnhancedIMT-2000

NewMobileAccess

IMT-A

New Nomadic / LocalArea Wireless Access

Enhancement

new capabilities of systems beyond

IMT-2000


Cellular wireless system evolution


1G

2G

2.5G / 2.75G

3G

3.5G / 3.75G

3.9G

AnalogCellular

DigitalCellular

DigitalCellular

Wide-BandDigital

Cellular

Wide-BandDigital

Cellular

Wide-BandNetwork

· Voice· AMPS, TACS

· Voice· Pager· 10kbps data· 3GPP: GSM · 3GPP2: cdmaOne

· Voice· E-mail· Photos· Web· ~100kbps data· 3GPP: GPRS, EDGE· 3GPP2: CDMA 2000 1x

· Video· M-pixel cam.· 3D· 300kbps 14Mbps· 3GPP: W-CDMA (UMTS)· 3GPP2: CDMA 2000 1x EV-DO

· Video· High-end gaming· 100Mbps, 10msec· Flexible bandwidth· All IP Network· 3GPP: Super 3G / LTE· 3GPP2: UMB· IEEE: Mobile WiMAX

(802.16e)

· Ubiquitous data· Flexible Spectrum use· Enhanced apps.· 100Mbps – 1Gbps· OFDM· Meet IMT-A requirements· 3GPP: LTE-A· IEEE: 802.16m

4G

Wide-BandDigital

Cellular

· Video· Mobile broadband· 3GPP: HSPA

(HSDPA / HSUPA)· 3GPP2: CDMA 2000

1x EV-DO Rev. A / B· IEEE: Mobile WiMAX

(IEEE 802.16e)


Evolution of UMTS towards packet only system

• First version of LTE is documented in 3GPP specifications Rel-8• Former specifications of LTE are known as E-UTRA and E-UTRAN


Release Functional freeze

Main features of release

Rel-99 Mar 2000 · Basic 3.84 Mcps W-CDMA (FDD & TDD) Rel-4 Mar 2001 · 1.28 Mcps narrow band version of W-CDMA (TD-SCDMA) Rel-5 Jun 2002 · HDSPA as packet-based data services for UMTS Rel-6 Mar 2005 · Completion of packet data service with HSUPA (E-DCH) Rel-7 Dec 2007 · first work on LTE / SAE with completion of feasibility studies

· HSPA+ (downlink MIMO, 64QAM downlink, 16QAM uplink) Rel-8 Dec 2008 · LTE work item – OFOMA/SC-FDMA air interface

· SAE work item – new IP core network · HSPA features (dual cell HSDPA, 64QAM with MIMO)


Requirements and targets(source: TR 25.912 and 25.913)


• Peak data rate

• LatencyC-Plane latency: less than 100ms camped-to-active transition and less than 50ms dormant-to-active transition (excluding DL and paging delay)U-Plane latency: less than 5ms in upload condition

• Capacity at least 200 active users per cell for spectrum allocations up to 5 MHz at least 400 users for higher spectrum allocations

FDD downlink peak data rates (64QAM, 20MHz bandwidth) Antenna configuration SISO 2x2 MIMO 4x4 MIMO Peak data rate Mbps 100 172.8 326.4

FDD uplink peak data rates (single antenna, 20MHzandwidth) Modulation depth QPSK 16QAM 64QAM Peak data rate Mbps 50 57.6 86.4


Requirements and targets(source: TR 25.913)


• Average user throughput per MHz and spectrum efficiency DL: 3 to 4 times Release 6 HSDPA. UL: 2 to 3 times Release 6 Enhanced Uplink

• Mobility Optimized for low mobile speed at 0 – 15km/h Support 15 – 120km/h with high performance 120 – 350km/h main mobility (500km/h depending on frequency band)

• Coverage Up to 5km: meet targets for throughput, spectrum efficiency and mobility Up to 30km: support full mobility, slight degradations of throughput and

more significant degradation of spectrum efficiency are acceptable

• Further enhanced MBMS Improved cell edge performance Defined interruption time when changing between different streams




• Deployment Scenarios Standalone (no interworking with UTRAN/GERAN) Integrated (existing UTRAN and/or GERAN in same geographical area)

• Spectrum flexibility Support for spectrum allocations of different size (1.25 (1.4?) – 20MHz) Support for diverse spectrum arrangements

• Spectrum deployment Co-existence and co-location with GERAN/3G and between operators

on adjacent channels

• Co-existence and interworking with 3GPP RAT Interruption time during handover between E-UTRAN and 3GPP-RAN

(real-time service < 300msec, non real-time service < 500msec)




• Architecture and migration Single E-UTRAN architecture (packet based) Simplified and minimized number of interfaces Minimized delay variation (jitter)

• Radio resource management requirements Enhanced end-to-end QoS Support efficient transmission and operation of higher layer protocols

over the radio interface (e.g. IP header compression) Support of load sharing and policy management across different Radio

Access Technologies

• Complexity Minimized number of options No redundant mandatory features Optimized terminal complexity and power consumption


Parameters in context(source: www.radio-electronics.com)


WCDMA (UMTS)

HSPA HSDPA / HSUPA

HSPA+ LTE

Maximum downlink speed 384 kbps 14 Mbps 28 Mbps 100 Mbps Maximum uplink speed 128 kbps 5.7 Mbps 11 Mbps 50 Mbps Latency round trip time approx. 150 ms 100 ms 50 ms (max) ~10 ms 3GPP releases Rel 99/4 Rel 5/6 Rel 7 Rel 8 Approx. years of initial roll out 2003/4 2005/6 HSDPA

2007/8 HSUPA 2008/9 2009/10

Access methodology CDMA CDMA CDMA DL: OFDMA UL: SC-FDMA


Monday 10 April 2023winter term 2010/11 – Mobile Communication Systems II 11

Complementary Access Systems

Switching between the layers need to be transparent to the user

Some existing standards and technologies for the different layers

Source ITU-R M.1645

IEEE 802.3

3GPP LTE

IEEE 802.11

Bluetooth*IEEE 802.15

IEEE 802.16

UWB mmWave

IEEE 802.21

3GPP2 UMB/IEEE 802.20


Competing 3.9G standards

• Different organizations - different standards?– 3GPP: LTE

– 3GPP2: UMB (discontinued)

– IEEE and WiMAX Forum: Mobile WiMAX™ (IEEE 802.16e)

• All have similar goals– Improved spectral efficiency

– Wide bandwidth

– Very high data rates

• Goals shall be achieved primarily by– Higher-order modulation schemes

– Multi-antenna technology

– Simplified network architecture



Comparison of the competitors(source: Technical overview of 3GPP LTE by Hyung G. Myung in May 2008)


3GPP LTE 3GPP2 UMB Mobile WiMAX R1 (802.16e)

Channel bandwidth 1.4, 3, 5, 10, 15, 20 MHz 1.25, 2.5, 5, 10, 20 MHz 5, 7, 8.75, 10 MHz DL multiple access OFDMA OFDMA OFDMA UL multiple access SC-FDMA OFDMA, CDMA OFDMA Duplexing FDD, TDD FDD, TDD TDD Subcarrier mapping localized localized, distributed localized, distributed Subcarrier hopping yes yes yes Data modulation QPSK, 16QAM, 64QAM QPSK, 8PSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM Subcarrier spacing 15 kHz 9.6 kHz 10.94 kHz FFT size (5 MHz) 512 512 512 Mobility support target: up to 350 km/h target: up to 300 km/h target: up to 120 km/h Channel coding convolutional, turbo convolutional, turbo, LDPC convolutional and

convolutional turbo, block turbo and LDPC (optional)

MIMO multi-layer precoded spatial multiplexing, space-time / frequency block coding, switched transmit diversity and cyclic delay diversity

multi-layer precoded spatial multiplexing, space-time transmit diversity, spatial division multiple access and beamforming

beamforming, space-time coding and spatial multiplexing


E-UTRA operating bands (source: TS 36.101)


E-UTRA Operating

Band Uplink (UL) operating band

BS receive UE transmit

Downlink (DL) operating band BS transmit UE receive

Duplex Mode

FUL_low – FUL_high FDL_low – FDL_high 1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD 2 1850 MHz – 1910 MHz 1930 MHz – 1990 MHz FDD 3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz FDD 4 1710 MHz – 1755 MHz 2110 MHz – 2155 MHz FDD 5 824 MHz – 849 MHz 869 MHz – 894MHz FDD 6 830 MHz – 840 MHz 875 MHz – 885 MHz FDD 7 2500 MHz – 2570 MHz 2620 MHz – 2690 MHz FDD 8 880 MHz – 915 MHz 925 MHz – 960 MHz FDD 9 1749.9 MHz – 1784.9 MHz 1844.9 MHz – 1879.9 MHz FDD 10 1710 MHz – 1770 MHz 2110 MHz – 2170 MHz FDD 11 1427.9 MHz – 1447.9 MHz 1475.9 MHz – 1495.9 MHz FDD 12 698 MHz – 716 MHz 728 MHz – 746 MHz FDD 13 777 MHz – 787 MHz 746 MHz – 756 MHz FDD 14 788 MHz – 798 MHz 758 MHz – 768 MHz FDD 17 704 MHz – 716 MHz 734 MHz – 746 MHz FDD

33 1900 MHz – 1920 MHz 1900 MHz – 1920 MHz TDD 34 2010 MHz – 2025 MHz 2010 MHz – 2025 MHz TDD 35 1850 MHz – 1910 MHz 1850 MHz – 1910 MHz TDD 36 1930 MHz – 1990 MHz 1930 MHz – 1990 MHz TDD 37 1910 MHz – 1930 MHz 1910 MHz – 1930 MHz TDD 38 2570 MHz – 2620 MHz 2570 MHz – 2620 MHz TDD 39 1880 MHz – 1920 MHz 1880 MHz – 1920 MHz TDD 40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD

FDD LTE frequency bands-Paired bands for simultaneous transmission on UL and DL -Separation reduces the impact of signals to the receiver performance

TDD LTE frequency bands-Unpaired because UL and DL share the same frequency but time separated

Overlapping frequency bands-(roaming) UE needs to detect whether to use TDD or FDD on a particular band


Additional information(source: www.radio-electronics.com)


TDD Band Description

33, 34 TDD 2000 (defined for unpaired spectrum in Rel 99 of the 3GPP specifications) 35, 36 TDD 1900 37, 38 PCS Center Gap (center band spacing between UL and DL pairs of LTE band 7) 39, 40 IMT Extension Center Gap

FDD Band Description

1 IMT Core Band (one of the paired bands defined for 3G UTRA and 3GPP Rel-99) 2 PCS 1900 3 GSM 1800 4 AWS (US & other, DL overlaps with DL for band 1 this facilitates roaming) 5 850 6 850 (Japan) 7 IMT Extension 8 GSM 900 9 1700 (Japan, overlaps with band 3 but has different band limits, enables roaming to be achieved more easily 10 3G Americas (extension to band 4, not available everywhere but allocated globally, increases bandwidth from 45 to 60 MHz (paired)) 11 (Japan, also allocated globally to the mobile service on a co-primary basis) 12, 13, 14 (previously for broadcasting, released as a result of the “digital dividend”, reversed duplex) 15, 16 (defined by ETSI for Europe, not adopted by 3GPP, combines two nominally TDD bands to provide one FDD band) 17 (previously for broadcasting, released as a result of the “digital dividend”) 20 (reversed duplex) 21 (Japan, also allocated globally to the mobile service on a co-primary basis) 24 (reversed duplex)


Frequency division in Germany (source: www.bundesnetzagentur.de 30.8.2010)


Frequency bands at 800 MHz and 900 MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz GSM-R5

MHz5

MHz5

MHz12,4MHz

12,4MHz GSM-R 5

MHz5

MHz12,4MHz

12,4MHz

790,0

791,0

FDD-downlink

A B-F A B-F

796,0

821,0

832,0

837,0

862,0

FDD-uplink FDD-uplink

873,1

880,1

914,9

FDD-downlink

918,1

925,1

959,9

MHz

5MHz

5MHz

5MHz

5MHz

5MHz

17,4MHz

5,4MHz

5MHz

17,4MHz

5MHz

5MHz

5MHz

5MHz

5MHz

17,4MHz

5,4MHz

5MHz

17,4MHz

FDD-uplink FDD-downlink

1710,0

1725,0

1730,1

1735,1

1758,1

1763,1

1780,5

MHz

1820,0

1825,1

1830,1

1853,1

1858,1

1875,5

1805,0

A-C D E A-C D E

Frequency bands at 1,8 GHz

Frequency bands at 2 GHz

5MHz

5MHz

5MHz

5MHz

9,9MHz

4,95MHz

4,95MHz

9,9MHz

4,95MHz

4,95MHz

9,9MHz

9,9MHz

E A B C D

FDD-uplinkTDD/FDD-uplink (extern)

14,2MHz

9,9MHz

4,95MHz

4,95MHz

9,9MHz

4,95MHz

4,95MHz

9,9MHz

9,9MHz

A B C D

FDD-downlink

MHz

2170,0

TDD / FDD-uplink (extern)

1900,01900,1

1905,1

1920,11920,3

1930,2

1935,15

1940,1

1950,0

1954,95

1959,9

1979,7

1980,0

2010,0

D

2010,5

2024,7

2025,0

2110,0

2110,3

2120,2

2125,15

2130,1

2140,0

2144,95

2149,9

2169,7

Frequency bands at 2,6 GHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

5MHz

A-N O-X A-N

FDD-uplink / TDD TDD / FDD-downlink (extern) FDD-downlink / TDD

2500,0

2570,0

2620,0

2690,0 MHz

Telekom Deutschland E-Plus-Gruppe Telefónica O2 Germany Vodafone konkret vergeben abstrakt vergeben


LTE network coverage in Germany (December 2011)

• E-Plus-Group (intended network expansion)

• Source: http://offensive-netzausbau.redaktionsservice-eplus-gruppe.de/4g-datennetz.php


• Telekom Deutschland• Source:

http://www.t-mobile.de/funkversorgung/inland/0,12418,15400-_,00.html)

• Vodafone• Source: www.vodafone-

lte.de/zum-onlineshop/netzabdeckung/vodafone-lte-netzabdeckung.htm)

• Telefónica O2 Germany (no map provided)


2G and 3G cellular network today (source: TR 23.882)


IMS

TE MT GERAN

R Um

MSC EIRHLR/AuC*

HSS*SMS-GMSC

SMS-IWMSC SMS-SCC

SGSNTE MT UTRAN

R Uu

GGSN

PCRF AF

BM-SC

Iu

Gb, IuGs Gf

GrGd

Gn / Gp

GcGx+ (Go / Gx)

Rx+ (Rx / Gq)

Gmb

Gi

PDN

Gi

SGSN

Gn

CGF*

Billingsystem*

Ga Ga

OCS*

GyMRFP

IMS-MGW

Mb

Mb

UE

P-CSCF CSCF

Gm

Mw

CDFHLR/AuC* HSS* SLF

Cx Dx

3GPP AAAProxy

3GPP AAAServer OCS*

Wf Wf

D / Gr Wx

Dw

Wd

Wo

WLANUE

WLAN AccessNetwork WAG PDG

Intranet/Internet

Ww

Wa

Wa

Wn

Wg

Wp

WmWy

WuCGF*

Billingsystem*

Wz

Wi

**

Traffic and signalingSignaling

* Elements duplicated for picture layout purposes only, they belong to the same logical entity in the architecture baseline

** is a reference point currently missing

• The 3GPP project “System Architecture Evolution” (SAE) shall simplify this complex architecture by defining an all-IP network called the Evolved Packet Core (EPC).

• The EPC is required for specific features of LTE

• The EPC supports LTE, UTRAN, GERAN and non-3GPP radio access networks such as cdma2000, 802.16


Logical high level architecture(source: TR 23.882)


•Mobility Management Entity (MME) manages and stores the UE control plane context, generates temporary Id, UE authentication, authorisation of TA/PLMN, mobility management

•User Plane Entity (UPE) manages and stores UE context, DL UP termination in LTE_IDLE, ciphering, mobility anchor, packet routing and forwarding, initiation of paging

•3GPP anchor is the mobility anchor between 2G/3G and LTE access systems

•SAE anchor is the mobility anchor between 3GPP and non 3GPP access systems (WLAN, WiMAX, etc.)

GERAN

UTRAN

Evolved RAN(LTE)

Trusted non 3GPPIP access

WLANAccess NW

MMEUPE

ePDG

Op.IP

Serv.(IMS,PSS,

etc …)

PCRF

HSS

3GPPanchor

SAEanchor

SGSN

GPRS CoreGb

Iu

S3 S4

S5a

S1

S5b S6

SGi

S2b

S2a

S7

Rx+

WLAN3GPP IPaccess

Evolved Packet Core(SAE)


Interfaces(source: TS 23.401)

• S1: – S1-MME is reference point between E-UTRAN and MME– S1-U is reference point between E-UTRAN and Serving GW for per bearer U-Plane

tunneling and inter eNB path switching during handover

• S2: mobility support between WLAN 3GPP IP access or non 3GPP access

• S3: user and bearer information exchange for inter 3GPP access system mobility

• S4: control and mobility support between GPRS Core and Inter AS Anchor

• S5: user plane tunneling and tunnel management between Serving GW and PDN GW

• S6: transfer of subscription and authentication data for user access to the evolved system

• S7:Transfer of (QoS) policy and charging rules from PCRF



The evolution of UTRAN


eNB eNB

eNB

MME / S-GW / P-GW MME / S-GW / P-GW

X2

X2 X2

S1 S1

S1

S1

NB NB NB NB

RNC RNC

SGSN

GGSN

UTRAN (UMTS) EPC and E-UTRAN (LTE)

E-UTRAN

EPC



System architecture of LTE-Rel8(source: TR 36.300)

• eNB provides E-UTRA U-Plane and C-Plane protocol terminations towards the UE

• X2 connects eNBs as mesh network, enabling direct communication between the elements and eliminating the need to tunnel data back and forth through a (RNC)

• S1 connects E-UTRAN to EPC (eNBs are connected to MME and S-GW elements through a “many-to-many” relationship)

eNB eNB

eNB

MME / S-GW / P-GW MME / S-GW / P-GW

X2

X2 X2

S1 S1

S1

S1

E-UTRAN

EPC


Overview of the functional split (source: TR 36.300)


• Yellow boxes depict the logical nodes

• white boxes depict the functional entities of the control plane

• blue boxes depict the radio protocol layers

Inter cell RRM

RB control

Connection mobility cont.

Radio admission control

eNB measurementconfiguration & provision

Dynamic resourceallocation (schedule)

RRC

PDCP

RLC

MAC

PHY

E-UTRAN

internet

Mobility anchoring

Serving gateway

SAE bearer control

Idle state mobilityhandling

NAS security

MME

EPC

S1

PND Gateway

UE IP address allocation

Packet filtering


Functions of the eNodeB(source: TR 36.300)

• Radio resource management• IP header compression and encryption• Selection of MME at UE attachment• Routing of user plane data towards S-GW• Scheduling and transmission of paging messages and broadcast

information• Measurement and measurement reporting configuration for mobility

and scheduling• Scheduling and transmission of ETWS messages



Functions of the MME(source: TR 36.300)

• Non-access stratum (NAS) signaling and NAS signaling security• Access stratum (AS) security control• Inter CN node signalling for mobility between 3GPP access networks• Idle mode UE Reachability• Tracking Area list management (for UE in idle and active mode)• PDN GW and Serving GW selection• MME selection for handovers with MME change• SGSN selection for handovers to 2G or 3G 3GPP access networks• Roaming• Authentication• Bearer management functions including dedicated bearer establishment• Support for ETWS message transmission



Functions of the S-GW(source: TR 36.300)

• Local mobility anchor point for inter eNB handovers• Mobility anchoring for inter 3GPP mobility• E-UTRAN idle mode DL packet buffering and initiation of network

triggered service request procedure• Lawful interception• Packet routing and forwarding• Transport level packet marking in the uplink and the downlink• Accounting on user and QCI granularity for inter-operator charging• UL and DL charging per UE, PDN and QCI



Functions of the P-GW(source: TR 36.300)

• Per-user-based packet filtering• Lawful interception• UE IP address allocation• Transport level packet marking in the downlink• UL and DL service level charging, ating and rate enforcement• DL rate enforcement based on APN-AMBR



Erweiterungen an dieser Stelle für das nächste Semester

• Protocol Stack– C-Plane– U-Plane

• Attach Procedure• Detach Procedure• Mobile Terminating Call• Mobile Originating Call• Handover



Identities of the UE

• International Mobile Subscriber Identity (IMSI) – unique permanent identity of the SIM card, stored in HSS

– used as little as possible when UE is communicating with the network

• Temporary Mobile Subscriber Identity (TMSI)– Alias used instead of IMSI

– temporary ID, allocated by the MME during the attach procedure

• Radio Network Temporary ID (RNTI)– To identify the UE on the radio

– Handed out by eNodeB, when UE establishes radio contact with eNodeB

• Access Point Name (APN)– IP address, allocated by PDN-Gateway as soon as UE is powered on



Attach procedure


UE eNodeB

S-GW

MME

PDN-GW

HSS

Internet1.

2.

3.

4.

1. UE contacts eNB it hears the strongest

2. eNB will then select an MME for the UE

3. MME will select a serving gateway

4. S-GW selects a PDN-GW which provides an IP to the UE (PDN-GW is selected from the APN parameter provided by the enduser or the operator)


LTE enabling technologies


• Orthogonal Frequency Division Multiple Access (OFDMA)• Single Carrier FDMA (SC-FDMA)• Multiple Input Multiple Output (MIMO)• …


OFDM

• Available spectrum is divided into multiple narrowband parallel channels (subcarriers)

• Information is transmitted on the subcarriers at a reduced signal rate

• Frequency responses of the subcarriers are overlapping and orthogonal


f

f

Single carrier

Multi carrier

W

W / N


OFDM(source: F. Khan, LTE for 4G Mobile Broadband, ISBN 978-0-521-88221-7)


• Example shows 5 OFDM subcarriers – Each subcarrier is modulated by a data

symbol

– The OFDM symbol is formed by adding the modulated subcarrier signals

– Here all subcarriers are modulated by data symbols 1‘s

• Resulting OFDM symbol signal has much larger signal amplitutde variations than the individual subcarriers– This characteristic of OFDM signal

leads to larger signal peakness

+


OFDM(source: F. Khan, LTE for 4G Mobile Broadband, ISBN 978-0-521-88221-7)

• Application of rectangular pulse in OFDM results in a sinc-square shape power spectral density

• This allows minimal subcarrier separation with overlapping spectra where signal peak for a given subcarrier corresponds to spectrum nulls for the remaining subcarriers



Cyclic prefix(source: F. Khan, LTE for 4G Mobile Broadband, ISBN 978-0-521-88221-7)

• Orthogonality of OFDM subcarriers can be lost when the signal passes through a time-dispersive radio channel due to inter-OFDM symbol interference (multipath propagation)

• A cyclic prefix extension of the OFDM signal can be performed to avoid this interference

• Cyclic prefix length is generally chosen to accomodate the maximum delay spread of the wireless channel



OFDM signal representation(source: TR 25.892)



OFDMA(source: http://cp.literature.agilent.com/litweb/pdf/5989-8139EN.pdf)

• Orthogonal Frequency Division Multiple Access (OFDMA) is a DL multi carrier transmission scheme for E-UTRA FDD and TDD modes based on conventional OFDM

• Incorporates elements of time division multiple access (TDMA) to avoid narrowband fading and interference

• OFDMA allows subsets of the subcarriers to be allocated dynamically among the different users on the channel (Frequency selective scheduling)

• Result is a more robust system with increased capacity



OFDM vs. OFDMA


subc

arrie

rs

symbols (time)

user 1

user 2

user 3

subc

arrie

rs

symbols (time)

OFDM OFDMA

• Data is modulated over sub-carriers and time slots Enables high data rate in a wireless channel

• Each subscriber can get different quantity of data Enables optimal balance of data forwarding between subscribers


SC-FDMA(source: http://cp.literature.agilent.com/litweb/pdf/5989-8139EN.pdf)

• Single Carrier – Frequency Division Multiple Access (SC-FDMA) is UL transmission scheme for LTE with structure and performance similar to OFDMA

• It combines the low Peak-to-Average Ratio (PAR) techniques of single-carrier transmission systems (GSM and CDMA), with the multi-path resistance and flexible frequency allocation of OFDMA

• Brief description: – Convert data symbols from time to frequency domain via DFT

– Map data symbols to desired location in overall channel bandwidth before they are converted back to time domain via IFFT

– Inserted cyclic prefix



OFDMA vs. SC-FDMA



SC-FDMA signal generation(source: http://cp.literature.agilent.com/litweb/pdf/5989-8139EN.pdf)


• Create time domain waveform (IQ representation) of SC-FDMA symbol

• Represent the symbol in frequency domain via DFT– DFT sampling frequency is chosen such that the time-domain waveform of

one SC-FDMA symbol is fully represented by M=4 DFT bins spaced 15 kHz apart, with each bin representing one subcarrier in which amplitude and phase are held constant for 66.7 μs

• Shift the symbol to the desired part of the overall channel bandwidth


MIMO(source: http://www.cs.wustl.edu/~jain/cse574-08/ftp/lte/index.html)

• Multiple antenna schemes that help to achieve higher spectral efficiency (throughput ) and link reliability (data quality)

• Key idea: Tx sends multiple data streams on multiple antennas and each stream goes through different paths to reach each Rx antenna

• The different paths taken by the same stream to reach multiple Rx allow canceling errors using superior signal processing techniques

• MIMO also achieves spatial multiplexing to distinguish among different symbols on the same frequency



MIMO formats


• Use spatial (antenna) diversity to transmit high quality data• Use spatial multiplexing to transmit many data

• Multipath propagation causes destructive interference (fading)– Affects SNR and error rate of the channel

• MIMO utilizes the different paths to improve– the robustness of the channel

• use multiple antennas to send the same signal on different paths• signals on the different paths will be affected in different ways • probability that all signals will be affected simultaneously is reduced

– the throughput • use the additional paths as additional channels for data transmission


The different antenna schemes(source: www.radio-electronics.com)

• SISO – Single Input Single Output– No diversity, no additional processing

– (+) simple, (-) channel performance is limited, (-) impact of interference and fading is significant

• SIMO – Single Input Multiple Output– Receive diversity (smart antennas)

– Types: switched diversity and maximum ratio combining– (+) simple implementation, (+) reduces effects of fading,

(-) processing needs to be done in Tx and Rx


Tx Rx

Tx Rx

...


• MISO– Transmission diversity

– Rx can receive optimum signal

– (+) multiple antennas and redundancy coding / processing is moved from Rx to Tx, (+) size, cost and battery consumption of the UE

• Full MIMO– more than one antenna on both sides (Tx and Rx)

– Channel coding to separate data from different paths

– (+) can improve robustness and throughput of the channel, (-) additional cost for processing and antennas


The different antenna schemes(source: www.radio-electronics.com)

Tx Rx

...

Tx Rx

... ...


Shannon‘s Law(source: www.radio-electronics.com)

• MIMO spatial multiplexing provides additional data capacity

• Achieved by using multiple paths as additional data channels

• Shannon’s Law defines maximum data rate on a radio channel


N

SBC 1log2

channel capacity [bps] bandwidth [Hz]

received signal power [W] or [V]

noise over the bandwidth [W] or [V]


MIMO spatial multiplexing(source: www.radio-electronics.com)


• MIMO systems utilize a matrix mathematical approach

• Transmit a number of n data streams t from n antennas• Each path has different channel properties h• Properties are processed to enable Rx to be able to differentiate

between the different data streams

t1

t2

tn

MIM

O-Tx

processing

MIM

O-Rx

processing

MIMO Channeldata streams to transmit received data streams

... ...

...

...

...

...

... ...

1

2

n

1

2

n

t1

t2

tn

h11

h21

hnn


MIMO spatial multiplexing(source: www.radio-electronics.com)


• rn is the signal received at antenna n

• To recover transmitted data stream tn

– Estimate individual channel transfer characteristic hij to determine the channel transfer matrix [H]

– Multiply received vector with inverse of the transfer matrix [H]

[T] = [H]-1 x [R]

...

...

...

...

r1 = h11t1 + h12t2 + … + h1ntn

rn = hn1t1 + hn2t2 + … + hnntn

...

r2 = h21t1 + h22t2 + … + h2ntn [R] = [H] x [T]



Enabling Technologies for LTE-Advanced

• Peak Data Rate improvement – DL 4x4 : LTE baseline 2x2– UL 2x4 : LTE baseline 1x2– 8 Tx antennas at eNode-B including 8x8 MIMO spatial multiplexing is also

considered

• Sector/cell throughput improvement– Advanced Downlink MU-MIMO: 8 Tx beam-forming– Uplink SU-MIMO– Hybrid OFDMA and SC-FDMA in uplink– Multi-stream MIMO SFN broadcast – Superposition of unicast and broadcast traffic

• Cell edge performance improvement– Multi-hop relay – coverage extension– Multi-cell MIMO (Network MIMO) – toward a cell without cell edge?

Mobile Communications: Long Term Evolution Part 1 Motivation for LTE Evolution of the standards...

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