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

Sendil Kumar, TCOE-IIT Madras

Dynamic properties
compared to wired
medium
• Adapt to the
nature of the
channel
• Need feedback of
the user link
quality

3

Wireless Channel - Terrain

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

4

Wireless Channel - Impairments
Time Selective

Frequency Selective

• Relative speed of the
transmitter and receiver
• Measured in terms
Doppler frequency

• Multipath channel
• Measured in terms of the
delay spread of the
channel


5

Wireless Channel - Constraints
• Transmit power
– Both from base-station and terminal (FDD)
– TDD !!

• Bandwidth
• Diverse topography


6

Spectrum

Resource Plane & Elements

RE

RP
Duration

RP dimensions ≈ BW x Duration


7

Signal Received at UE

Y1=H1X1 +N1

UE
RP

Channel Mask

Noise + Interference


8

Multiplexing physical symbols

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

9

• Measure of reliability of Bits
• Efficient usage of the channel

DELIVER RELIABLE BITS


10

Capacity of a Wireless Channel
Reliable communication rate

R  C = log2(1 + ) b/s/Hz
Post (receiver) processing SINR
Shannon-Hartley capacity relation


11

Capacity vs. SNR


12

Tune power or rate ??
Power Control
Transmit Power

Data Rate
Rate Control

Channel Quality

Power Control
Transmit power inversely proportional to channel conditions
Good for circuit switched mode of communication

Rate Control
Transmit at fixed power level
Good for data traffic , Long term data rate

13

• Multiplexing multiple users’ data
• Basis of smart “picking” of users

MULTIUSER COMMUNICATION


14

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


15

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

16

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


17

Scheduling : Intra Cell
User 4
User 3
User 2
User 1

Frequency
Time


Time Unit

18

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


19

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

Cell-edge UE

Fractional Frequency Reuse

20

• More than as a 4G standard
• Flexibility to vendors, operators

KEY 4G TECHNIQUES


21

4G systems (1/3)

Packet only
network
(always on
NET)

MIMO
capabilities

Higher order
modulation
64QAM

Efficient
Uplink
transmission


Using wide
bandwidth ~
20MHz

Scalable
bandwidth

22

4G systems (2/3)
Spectral Efficiency
in reuse-1
deployment

HetNET
deployments

Inter-technology
handoff

Cell Edge
interference
management

Pico cells

UMTS/HSDPA

Improve mean
cell-throughput

Portable basestations
(Femtocell, Relays)

EVDO (xHRPD)

Co-operative
communication

Remote Radio
Heads

1xCDMA voice


Proprietary
techniques :
Resource
Partitioning, Handoff
between
Macro/HETNET,
inter-RAT mobility

23

4G systems : Addons (3/3)

Green
technology

M2M
communication

Network
offloading WIFI
n/w


Self-Organizing
Network (SON)

24

• 4G timings with 3G, CDMA2000
• Multimode devices

NUMERICAL COMPATIBILITY


25

Numerical Compatibility
Channel Bandwidth [MHz]

1.4

3

5

10

15

20

73

181

301

601

901

1201

128

256

512

1024

1536

2048

Sampling Rate [MHz]

1.92
½ 3.84

3.84

7.68
2x3.84

15.36
4x3.84

23.04
6x3.84

30.72
8x3.84

No. of Resource Blocks
(NRB)

6

15

25

50

75

100

No. of Occupied Subcarriers
including DC (NSC)
FFT Size (N)

EVDO

HSDPA

3G - HSDPA : 5MHz : 2ms Subframe
2560*3 /2= 3840 chips /1ms= 240 symbols /ms
LTE 5MHz : 600*14 =8400 symbols in 1ms Subframe

26

• Symbols
• Slots, Subframe
• Frame

RESOURCE PLANE


27

Timing definition

Shorter TTI => Fast user switching
Slide 13

28

Time-Frequency view (DL)


29

Physical Resources
Tslot

The grouping of resources allows
reduce the address size when
scheduling data, when indicating
control information
Resource element
Resource block
(180 KHz x 0.5 ms)
12x7 (subcarrier x symbols)

Resource Block
Group

frequency

time

30

• Align reception with BS
• Determine Cell Info

DETECTING & LATCHING TO LTE


31

UE procedures (1/2)

• some signature !!
• Periodic correlation
• Energy detection

Device Reads N/w
parameter (Public
Read)

• Sync time &
frequency
• slot alignment
• System frame
sequence

Device Discovers N/w


• Random Access
• Collision
• N/w detects
• Reliable channel to
listen
Try to push request to
“Associate”

32

UE procedures(2/2)

• All UE UL data arrives
at same time at
eNodeB
• UL Power Control

Listen to
Control/Paging
• Decode Data if
scheduled
• Feedback of UL data

Timing
Alignment

• Quality of Channel
(CQI)
• Supported Data rate
• ACK/NACK of DL data

Report
Measurement


33

Downlink Transmission

Signals

• Pilots
• Synchronization
(Primary &
Secondary)

Control Channels

• System
Information
• Scheduling
• Power control,
ACK/NACK


Shared Data
Channels

• Data Traffic
• Multicast Traffic

34

Synchronization / Cell Search
• Frequency stability
– Within regulatory & 3GPP requirements
– Handover

• Timing Synchronization
– UL and DL associated transmission


35

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
“Proprietary” way
• Determine 1/504 cell ID
of doing this Esp. in
multi-mode devices


36

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


37

Sync & Broadcast channels
Immediate Symbol after SYNC - provides
necessary system information
(like MIB, overall DL BW, Sys Frame Number)
Step. A Detect 1 of 3 Primary Code
Step. B Detect 1 of 168 using Sec Sync
12*6 = 72 subcarriers
1.08MHz
Broadcast Info

Primary SYNC

BS :Deployment
can help quick
cell search
UE: ability to
demap BCH
faster

Secondary SYNC
Slide 24

TV80-W1738-1 Rev B

38

MAY CONTAIN U.S. AND INTERNATIONAL EXPORT CONTRO

• Update link Quality
• Measurement Reporting

CHANNEL ADAPTATION


39

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

40

E.g. CASES – When & What is used
Wideband CQI

Best Band CQI

• Maps to the
best MCS
supported for
distributed
mapping
• Kind of fall-back
metric if
eNodeB cant
grant the best to
the UE

• 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)
vs
1 RB-pair : 180Khz for 1ms subframe

41

HARQ

Depending on
the PRB
locations ,eB
can decide what
to do
Accumulated energy
Transmitted bits

CRC Insertion, turbo coding;
Rate 1/3
E

2E

3E

4E

Input to decoder
Net code rate

IR
1

1/2

1/3

1/3

CC
Net code rate

1

1


1

1

42

Pilot/Reference Signals (RS)
• Measure Channel Response
– Along time & frequency
– Sufficient density for interpolation

• Distinguish multiple cells
– Orthogonal sequence across the 504
Smart Planning of cells with Reusing cells sequences !!

– High Auto-correlation &searchcross-correlation
For quick Zero

• 168*3 = 504 sequences


43

Pilot Symbol physical locations
1 Tx Antenna

2 Tx Antenna

What about adjacent sector
-Distance between two RS
-Freq : Urban / Mutlipath Env.
Pilots & More antennas ??
-Maximum speed
-Pilots Orthogonal by locations
-No Pilot to Pilot interferenceKumar, TCOE-IITcell
Sendil in same Madras

44

Inter-antenna Pilot Interference
Management
Transmit Antennas

With Multiple Receive
Antenna – Estimate
Correlated Channel
Response !!

Receive Antennas
UE


45

Adjacent Sector Pilot Interference
Management

Sector 0

Sector 1

Sector 2

Deployment Planning


46

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 BW
4/14 = 28%


47

For reliability
For capacity

MIMO TECHNIQUES


48

MIMO Abilities – Improve SNR

Diversity for improved
system performance

Beamforming for improved
coverage

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


49

MIMO Abilities – Increase Capacity

Beamforming for improved
coverage

SDMA for improved capacity

Capacity !! :
a) Smart Pick two users who can
tolerate/cancel interference on the
same Resource
b) Artifical channel for the interfering
data

Multi-layer transmission for
High data-rate

Capacity !! :
Assign two Streams to the
same user

50

MIMO Data Mapping
Turbo Coded
Block : CW1
Turbo Coded
Block : CW2

K = 1,2 Code Words

M = 1,2,3,4 Layers

N = 1,2, or 4 Antennas


51

Y1=H1X1 + H2X2 + H3X3 + H1X4

4 Tx antenna

UE
Receive Antennas

52

Single Antenna Transmission
Y1=H1X1 + H2X2 + H3X3 + H1X4

4 Tx antenna

UE
Receive Antennas

53

Open Loop Transmit Diversity
X1

A1,A2=fn(X1)

Y1=H1A1 + H2A2 + H3X3 + H1X4

4 Tx antenna
UE
Receive Antennas

54

BEAMFORMING
A1=P1X1 A2=P2X1

X1

Y1=H1A1 + H2A2 + H3X3 + H1X4

4 Tx antenna
Receive Antennas
Feedback of P1, P2

UE
55

Closed Loop , Two Streams
(Spatial MUX)

X2
X1
Y1=H1A1 + H2A2 + H3X3 + H1X4
Y2=G1A1 + G2A2 + G3X3 + G1X4

4 Tx antenna
Feedback of P by
Hypothesis

UE
Receive Antennas
56

Transmission Modes

Open Loop
• Mode 1: Single antenna port
• Mode 2: Tx Diversity (Alamoutilike )
• 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)


57

Physical Resource Planes

Data Layer X1,X2, X3..
Phy Ant 1 : RP

Precoding based on
CodeBook (Looktable )
Closed Loop
Or
Open Loop

Phy Ant 0 : RP

58

MIMO Implementation
A very flexible and Vendor specific Implementation ,
- Cell Capacity
- Multiple UE serving
- Slow mobile terminals,
- Rural / Urban channels


59

BACKUP SLIDES


60

Brief presentation about Key Techniques in 4G/LTE

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