brief presentation about key techniques in 4g/lte

Key Techniques in 4G/LTE

(Oct 2011)

google.me/+SendilKumar

Outline

- Wireless Communication

- Multiuser Communication

- Key techniques in 4G/LTE

- Detecting & Latching to LTE n/w

- Channel Adaptation Techniques

- MIMO techniques

- Miscellaneous Developments

Wireless Channel : Property

Broadcast interface

• Everyone can listen to the medium

• One emitting source for a region

Shared resource

• All share the resources

• Need resource management to optimize the best utilization

Dynamic properties compared to wired

medium

• Adapt to the nature of the channel

• Need feedback of the user link quality

3Sendil Kumar, TCOE-IIT Madras

Wireless Channel - Terrain

Large Scale : Path Loss, Shadowing Small Scale : Stationary and Mobile objects

Wireless Channel - Impairments

Time Selective

• Relative speed of the transmitter and receiver

• Measured in terms Doppler frequency

Frequency Selective

• Multipath channel

• Measured in terms of the delay spread of the channel

Wireless Channel - Constraints

• Transmit power

– Both from base-station and terminal (FDD)

– TDD !!

• Bandwidth

• Diverse topography

Resource Plane & Elements

Sendil Kumar, TCOE-IIT Madras 7

Duration

RP dimensions ≈ BW x Duration

Signal Received at UE

Channel Mask

Noise + Interference

Y1=H1X1 +N1

Multiplexing physical symbols

How many BITS can be “reliably” transmitted ???

DELIVER RELIABLE BITS

• Measure of reliability of Bits

• Efficient usage of the channel

Capacity of a Wireless Channel

R C = log2(1 + ) b/s/Hz

Reliable communication rate

Post (receiver) processing SINR

Shannon-Hartley capacity relation

Capacity vs. SNR

Tune power or rate ??

Channel Quality

Transmit Power Data Rate

Power Control

Rate Control

Power ControlTransmit power inversely proportional to channel conditionsGood for circuit switched mode of communication

Rate ControlTransmit at fixed power levelGood for data traffic , Long term data rate

MULTIUSER COMMUNICATION

• Multiplexing multiple users’ data

• Basis of smart “picking” of users

Characteristics of Multiple access

• Static or Dynamic, equal/unequal sharing of the resource (BW x Duration)

• Orthogonality within intra-cell downlink

• Control overhead with increasing number of users

Scheduler – “Key Ingredient”

• Single User

– Adapt Rate based on Channel

• Multiple Users

– Adapt Rate also select which user(s) in a TTI

• Multi-cell

– Co-operation with adjacent cells for Interference Management

– Resource partition with small cells

Scheduler : Other metrics

• Diversity in the users’ channel

• Queue Size of data for the user

• Quality of service

– Mean delay at upper layers

– Reliability of the data

• Maintain the system capacity by efficiently sharing resources

Scheduling : Intra Cell

Frequency

Time Time Unit

User 4User 3User 2User 1

Scheduling : Inter-cell Interference Management (1/2)

Scheduling : Inter-cell Interference Management (2/2)

Cell-edge UE

Fractional Frequency Reuse

In-cell

KEY 4G TECHNIQUES

• More than as a 4G standard

• Flexibility to vendors, operators

4G systems (1/3)

Packet only network

(always on NET)

MIMO capabilities

Higher order modulation

Efficient Uplink

transmission

Using wide bandwidth ~

Scalable bandwidth

4G systems (2/3)

Spectral Efficiency in reuse-1

deployment

Cell Edge interference management

Improve mean cell-throughput

Co-operative communication

HetNET deployments

Pico cells

Portable base-stations

(Femtocell, Relays)

Remote Radio Heads

Inter-technology handoff

UMTS/HSDPA

EVDO (xHRPD)

1xCDMA voice

Proprietary techniques :

Resource Partitioning, Handoff

between Macro/HETNET,

inter-RAT mobility

4G systems : Addons (3/3)

Green technology

M2M communication

Network offloading WIFI

Self-Organizing Network (SON)

NUMERICAL COMPATIBILITY

• 4G timings with 3G, CDMA2000

• Multimode devices

Numerical Compatibility

Channel Bandwidth [MHz]

No. of Occupied Subcarriers

including DC (NSC)

FFT Size (N)

Sampling Rate [MHz]

No. of Resource Blocks

½ 3.84

2x3.84

4x3.84

6x3.84

8x3.84

HSDPAEVDO

3G - HSDPA : 5MHz : 2ms Subframe2560*3 /2= 3840 chips /1ms= 240 symbols /ms

LTE 5MHz : 600*14 =8400 symbols in 1ms Subframe

RESOURCE PLANE

• Symbols

• Slots, Subframe

• Frame

Timing definition

Shorter TTI => Fast user switching

Time-Frequency view (DL)

Physical Resources

frequency

Resource element

Resource Block

Resource block

(180 KHz x 0.5 ms)12x7 (subcarrier x symbols)

The grouping of resources allowsreduce the address size whenscheduling data, when indicatingcontrol information

DETECTING & LATCHING TO LTE

• Align reception with BS

• Determine Cell Info

UE procedures (1/2)

• some signature !!

• Periodic correlation

• Energy detection

Device Discovers N/w

• Sync time & frequency

• slot alignment

• System frame sequence

Device Reads N/w parameter (Public

Read) • Random Access

• Collision

• N/w detects

• Reliable channel to listen

Try to push request to “Associate”

UE procedures(2/2)

• All UE UL data arrives at same time at eNodeB

• UL Power Control

Timing Alignment

• Decode Data if scheduled

• Feedback of UL data

Listen to Control/Paging • Quality of Channel

• Supported Data rate

• ACK/NACK of DL data

Report Measurement

Downlink Transmission

Signals

• Pilots

• Synchronization (Primary & Secondary)

Control Channels

• System Information

• Scheduling

• Power control, ACK/NACK

Shared Data Channels

• Data Traffic

• Multicast Traffic

Synchronization / Cell Search

• Frequency stability

– Within regulatory & 3GPP requirements

– Handover

• Timing Synchronization

– UL and DL associated transmission

Cell Sync & Read Info

• Scalable Bandwidth operation

– Common Resource Blocks 72 carrier at centre

– Correlation – Energy Maximation

• Slot Boundary & Frame boundary

• Read Broad Cast channel

• Determine 1/504 cell ID

“Proprietary” way of doing this Esp. in multi-mode devices

Primary & Secondary Sync Signals

Twice in a Frame duration - Centre of the Bandwidth- Centre of the Time (Frame & Subframe)(5 ms interval) to look for other RAT

Sync & Broadcast channels

TV80-W1738-1 Rev B MAY CONTAIN U.S. AND INTERNATIONAL EXPORT CONTROLLED INFORMATION

12*6 = 72 subcarriers1.08MHz

Immediate Symbol after SYNC - provides necessary system information(like MIB, overall DL BW, Sys Frame Number)

Step. A Detect 1 of 3 Primary CodeStep. B Detect 1 of 168 using Sec Sync

Primary SYNC

Secondary SYNC

Broadcast Info BS :Deployment can help quick

cell searchUE: ability to demap BCH

faster

CHANNEL ADAPTATION

• Update link Quality

• Measurement Reporting

Flexible Channel Adaption

Feedback– Wideband CQI

– Band based CQI

– UE selected Band CQI

– Periodic Reporting, aperiodic reporting

– Multiple code-block transmission

Scheduling– Dynamic

– Semi persistent

– Localized, Distributed

E.g. CASES – When & What is used

Wideband CQI

• Maps to the best MCS supported for distributed mapping

• Kind of fall-back metric if eNodeB cant grant the best to the UE

Best Band CQI

• Group RBs, report CQI for each/best Group

• Frequency selective channels

eNodeB triggered bands only

• e.g restricted bands available

• FFR zones

GSM BW : 200KHz, 1 slot = 0.58ms (4.615ms/8)

vs1 RB-pair : 180Khz for 1ms subframe

E 2E 3E 4E

1 1/2 1/3 1/3

1 1 1 1Net code rate

Net code rate

Accumulated energy

Transmitted bits

Input to decoder

CRC Insertion, turbo coding; Rate 1/3

Depending on the PRB

locations ,eBcan decide what

Pilot/Reference Signals (RS)

• Measure Channel Response

– Along time & frequency

– Sufficient density for interpolation

• Distinguish multiple cells

– Orthogonal sequence across cells

– High Auto-correlation & Zero cross-correlation

• 168*3 = 504 sequences

Smart Planning of cells with Reusing the 504 sequences !!

For quick search

Pilot Symbol physical locations

-Distance between two RS-Freq : Urban / Mutlipath Env.-Maximum speed

-Pilots Orthogonal by locations -No Pilot to Pilot interference in same cell

1 Tx Antenna 2 Tx Antenna

What about adjacent sector

Pilots & More antennas ??

Inter-antenna Pilot Interference Management

With Multiple Receive Antenna – Estimate Correlated Channel

Response !!

Transmit Antennas

Receive Antennas

Adjacent Sector Pilot Interference Management

Sector 0 Sector 1 Sector 2

Deployment Planning

Informing the UE on PDCCH

• Information : PRBs and MCS to each UE• UE monitors the PDCCH(s) to find possible

allocation

• No. of allocation & size of allocation• Control Channel Address by CCE : 9*(4 RES)• Power control, uplink grant, etc..

3 to 4 OFDM symbols fn of BW4/14 = 28%

MIMO TECHNIQUES

For reliability

For capacity

MIMO Abilities – Improve SNR

Diversity for improvedsystem performance

Beamforming for improvedcoverage

Rx : Equalization , Tx : Open Loop (Alamouti like)

Low mobility or High Mobility users

Transmit “rotates” the signal for better signal reception at the UE

Codebook based, non-codebook based

MIMO Abilities – Increase Capacity

Beamforming for improvedcoverage

SDMA for improved capacityMulti-layer transmission for

High data-rate

Capacity !! : a) Smart Pick two users who can

tolerate/cancel interference on the same Resource

b) Artifical channel for the interfering data

Capacity !! : Assign two Streams to the

same user

MIMO Data Mapping

Turbo Coded Block : CW1

Turbo Coded Block : CW2

M = 1,2,3,4 LayersK = 1,2 Code Words N = 1,2, or 4 Antennas

4 Tx antenna

Receive Antennas

Y1=H1X1 + H2X2 + H3X3 + H1X4

4 Tx antenna

Receive Antennas

Y1=H1X1 + H2X2 + H3X3 + H1X4

Single Antenna Transmission

Open Loop Transmit Diversity

4 Tx antenna

Receive Antennas

Y1=H1A1 + H2A2 + H3X3 + H1X4

X1 A1,A2=fn(X1)

BEAMFORMING

4 Tx antenna

Receive Antennas

Y1=H1A1 + H2A2 + H3X3 + H1X4

A1=P1X1

Feedback of P1, P2

X1 A2=P2X1

4 Tx antenna

Receive Antennas

Y1=H1A1 + H2A2 + H3X3 + H1X4

Closed Loop , Two Streams (Spatial MUX)

Feedback of P by Hypothesis

Y2=G1A1 + G2A2 + G3X3 + G1X4

Transmission Modes

Open Loop

• Mode 1: Single antenna port

• Mode 2: Tx Diversity (Alamouti-like )

• Mode 3: Spatial multiplexing

• Transmissions using spatial multiplexing (2 CW). (RI , - )

• Exploit Cyclic Delay Diversity (CDD) transmissions

Closed Loop

• Mode 4: Spatial multiplexing (SU- MIMO) : (RI, PMI), 2CW, 4Layers, 4Tx

• Mode 5: Multi-user MIMO

• CL MU-MIMO / (SDMA)

• Mode 6: ( ~ Mode4 : (-,-) ) Rank=1 precoding

• Mode 7: Single antenna port; port 5 ( ~Mode1 : DRS)

Physical Resource Planes

Precoding based on CodeBook (Looktable )

Closed LoopOr

Open Loop

Phy Ant 1 : RP

Phy Ant 0 : RP

Data Layer X1,X2, X3..

MIMO Implementation

A very flexible and Vendor specific Implementation ,

- Cell Capacity - Multiple UE serving- Slow mobile terminals, - Rural / Urban channels

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