brief presentation about key techniques in 4g/lte
DESCRIPTION
Brief presentation about Key Techniques in 4G/LTE and where there is space for proprietary way of tuning it. Note it was presented about 2years back !!TRANSCRIPT
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
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Wireless Channel - Terrain
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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
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Wireless Channel - Constraints
• Transmit power
– Both from base-station and terminal (FDD)
– TDD !!
• Bandwidth
• Diverse topography
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Resource Plane & Elements
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Duration
Spe
ctru
m
RP
RE
RP dimensions ≈ BW x Duration
Signal Received at UE
RP
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Channel Mask
UE
Noise + Interference
Y1=H1X1 +N1
Multiplexing physical symbols
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How many BITS can be “reliably” transmitted ???
DELIVER RELIABLE BITS
• Measure of reliability of Bits
• Efficient usage of the channel
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Capacity of a Wireless Channel
R C = log2(1 + ) b/s/Hz
Reliable communication rate
Post (receiver) processing SINR
Shannon-Hartley capacity relation
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Capacity vs. SNR
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Tune power or rate ??
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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
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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
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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
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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
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Scheduling : Intra Cell
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Frequency
Time Time Unit
User 4User 3User 2User 1
Scheduling : Inter-cell Interference Management (1/2)
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Scheduling : Inter-cell Interference Management (2/2)
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Cell-edge UE
Fractional Frequency Reuse
In-cell
KEY 4G TECHNIQUES
• More than as a 4G standard
• Flexibility to vendors, operators
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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
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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
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Proprietary techniques :
Resource Partitioning, Handoff
between Macro/HETNET,
inter-RAT mobility
4G systems : Addons (3/3)
Green technology
M2M communication
Network offloading WIFI
n/w
Self-Organizing Network (SON)
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NUMERICAL COMPATIBILITY
• 4G timings with 3G, CDMA2000
• Multimode devices
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Numerical Compatibility
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Channel Bandwidth [MHz]
No. of Occupied Subcarriers
including DC (NSC)
FFT Size (N)
Sampling Rate [MHz]
No. of Resource Blocks
(NRB)
1.4
73
128
1.92
½ 3.84
6
3
181
256
3.84
15
5
301
512
7.68
2x3.84
25
10
601
1024
15.36
4x3.84
50
15
901
1536
23.04
6x3.84
75
20
1201
2048
30.72
8x3.84
100
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
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Timing definition
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Slide 13
Shorter TTI => Fast user switching
Time-Frequency view (DL)
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Physical Resources
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frequency
Tslot
Resource element
time
Resource Block
Group
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
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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”
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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
(CQI)
• Supported Data rate
• ACK/NACK of DL data
Report Measurement
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Downlink Transmission
Signals
• Pilots
• Synchronization (Primary & Secondary)
Control Channels
• System Information
• Scheduling
• Power control, ACK/NACK
Shared Data Channels
• Data Traffic
• Multicast Traffic
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Synchronization / Cell Search
• Frequency stability
– Within regulatory & 3GPP requirements
– Handover
• Timing Synchronization
– UL and DL associated transmission
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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
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“Proprietary” way of doing this Esp. in multi-mode devices
Primary & Secondary Sync Signals
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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
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Slide 24 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
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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
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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
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GSM BW : 200KHz, 1 slot = 0.58ms (4.615ms/8)
vs1 RB-pair : 180Khz for 1ms subframe
HARQ
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IR
CC
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
to do
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
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Smart Planning of cells with Reusing the 504 sequences !!
For quick search
Pilot Symbol physical locations
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-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
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With Multiple Receive Antenna – Estimate Correlated Channel
Response !!
Transmit Antennas
UE
Receive Antennas
Adjacent Sector Pilot Interference Management
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Sector 0 Sector 1 Sector 2
Deployment Planning
Informing the UE on PDCCH
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• 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
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MIMO Abilities – Improve SNR
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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
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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
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Turbo Coded Block : CW1
Turbo Coded Block : CW2
M = 1,2,3,4 LayersK = 1,2 Code Words N = 1,2, or 4 Antennas
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4 Tx antenna
Receive Antennas
UE
Y1=H1X1 + H2X2 + H3X3 + H1X4
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4 Tx antenna
Receive Antennas
UE
Y1=H1X1 + H2X2 + H3X3 + H1X4
Single Antenna Transmission
Open Loop Transmit Diversity
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4 Tx antenna
Receive Antennas
UE
Y1=H1A1 + H2A2 + H3X3 + H1X4
X1 A1,A2=fn(X1)
BEAMFORMING
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4 Tx antenna
Receive Antennas
UE
Y1=H1A1 + H2A2 + H3X3 + H1X4
A1=P1X1
Feedback of P1, P2
X1 A2=P2X1
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4 Tx antenna
Receive Antennas
UE
Y1=H1A1 + H2A2 + H3X3 + H1X4
Closed Loop , Two Streams (Spatial MUX)
Feedback of P by Hypothesis
Y2=G1A1 + G2A2 + G3X3 + G1X4
X1
X2
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)
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Physical Resource Planes
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Precoding based on CodeBook (Looktable )
Closed LoopOr
Open Loop
Phy Ant 1 : RP
Phy Ant 0 : RP
Data Layer X1,X2, X3..
MIMO Implementation
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A very flexible and Vendor specific Implementation ,
- Cell Capacity - Multiple UE serving- Slow mobile terminals, - Rural / Urban channels
BACKUP SLIDES
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