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Ivan Tam 2015

Wireless Network Infrastructure – An OverviewIVAN TAM

Fixed and Mobile Service Provider Architecture

InternetCoreService EdgeAggregationAccess

xDSL

Core RouterInternet Gateway

Transit Carrier Router

Internet Exchanges

• Access – provides cost/performance effective connectivity using copper, fiber to home and offices

• Aggregation –aggregate the traffic from various types of access terminating at CO/POP

• Service/edge – service management point where authentication, service quality, and service features are provided BNG ( Broadband Gateway)/VPN

PE (Provider Edge) or as MME, SGW and PGW in LTE

• AAA – where database of customers are stored and checked by service edge

• Value added service (VAS) –IPTV server, internet cache

• Core – national connectivity between data centers and service edge to each other and to the internet

• Transit – service provider interface with a number of transit carriers via own border routers. Transit carrier is responsible for routing traffic back and forth to destinations in the worls

Data Center

Central Office

Transit

Web site’s service provider

Web site’s hosting data center/ Cloud

Basestation

Backhaul

Fixed and Mobile Service Provider Architecture

InternetCoreService EdgeAggregationAccess

xDSL

Core RouterInternet Gateway

Transit Carrier Router

Internet Exchanges• AAA – where database of customers are stored and checked by service edge

• Value added service (VAS) –IPTV server, internet cache

Data Center

Central Office

Transit

Web site’s service provider

Web site’s hosting data center/ Cloud

Basestation

Backhaul

How does radio wave carries information?

How to track the location of user terminals?

How to mitigate interference between neighbor cells?

How does user terminal join the packet network?

How to ensure that user data can be transported to/from packet network as user moves ?

How to optimize on the amount of info over radio?

How to arbitrate the access of radio resource by user terminals?

How to maintain QOS of different traffic types?

Security and Authentication?

3GPP (3rd Generation Partnership Project) Releases – Technology Evolutions

UMTS (2000 – 2007) LTE + UMTS HSPA evolution LTE-Advanced 5G

Release 99 (2000)• UMTS (3G), 5Mhz• DL (384Kbps), UL (128Kbps)

Release 5,6 (2002-2004)• HSDPA with QAM 16(14Mbps), HSUPA

(5.7Mbps), IP architecture

Release 7 (2007)• HSPA+ with QAM64 DL (21Mbps),

QAM16 and 2x2MIMO (42Mbps)

Release 8 (2008)LTE – DL MIMO2x2 and 20Mhz (150Mbps), UL (75Mbps), all IP networkUMTS – 2xMIMO+QAM64 or Dual Carrier+QAM64 (42Mbps)

Release 9 (2009)LTE – Femto cell (HetNet)

UMTS – Dual Carrier multi-band with 2xMIMO DL + 64QAM (84Mbps)

Release 10 (2011)LTE Advanced – Carrier Aggregation (CA) , DL at 2x20Mbps (300Mbps)Self-Organizing Network (SON)Relaying – for cell without wireline backhaulHSPA+ Multicarrier (4)+2xMIMO+QAM64 (168Mbps)

Release 11 (2012)LTE Advanced – COMP, eICICHSPA – Multi-carriers (8) with 2xMIMO (336Mbps)

Release 12 (2012)M2MMobile RelayCA – 3 carrier DL, 2 carrier UL

UMTS2000-2007 – Mobile Broadband era• WCDMA using spread spectrum

technology over 5Mhz • Initially ATM transport but

moved to IP • Larger latency but reduced as

advanced to HSPA

LTE & HSPA2008-> Introduce LTE, full packet based and high bandwidth• OFDM – subcarrier scheduling, path

diversity, flexible at 1.4, 3, 5, 10,15,20Mhz

• Lower latency• Flat IP network• Voice over IP• Carrier aggregation (UMTS)

LTE Advanced2011-> Further optimization of LTE for performance• Small cells, hetnet• Inter-cell coordination on interference eICIC• Carrier aggregation (LTE)

3GPP Specifications and References

3GPP 36.2xx series – Physical Layer

36.3xx – Layer 2 and 3, 36.4xx S1 and X2 interfaces

36.1xx – Core performance requirements

36.5xx terminal conformance testing

http://www.3gpp.org/DynaReport/36-series.htm

4G Americas Industry trade organization with extensive technical and deployment reports

http://www.4gamericas.org/en/

http://www.3gpp.org/DynaReport/36-series.htm

http://www.4gamericas.org/en/

Agenda

Spectrum and Transmission Technologies Wired and wireless media, modulation, signal propagation

LTE Overall Architecture and 3GPP

Physical transmission, UL and DL channel allocations

Attachment, mobility tracking and handover

Moving on to LTE-A LTE-A Further Optimizations and more cell sites collaboration

Virtualization and change in architecture

Heterogeneous network, WiFi, LTE over unlicensed spectrum

Current Development

Modulation (simplified) Signal is transmitted over medium by modulating a carrier wave

Amplitude, phase, and frequency or combination of these on the carrier

Simple phase shift-keying modulate the phase of the carrier, e.g, BPSK shift the carrier wave 180 degree when info change between 0 and 1

QPSK allows phase shift in 4 values, e.g., 45, 135, 225, and 315 degree, with four different patterns hence representing two bits symbol, i.e., 2 bits represents 4 values

QAM further mix phase shift together with amplitude change, giving more patterns, e.g., in QAM 16 the combination of phase shift and amplitude change give us 16 patterns, representing a 4 bit symbol, i.e., 4 values, 2 , QAM64 support 6 bits per symbol

The more patterns we try to get a wave to exhibit, the closer these patterns are in terms of phase and amplitude and harder for receiver to decide especially when received signal is poor resulting in transmission error

Hence QAM 64 is used when the channel condition is good, and QPSK is used when high reliability is required, i.e., higher Signal to Noise Ratio (SNR)

Baud Rate - The number of time we modulate a carrier per second

When a carrier wave is modulated at a Baud rate B, it will “occupy” a spectrum range of B centered around the carrier frequency

E.g., say f is the carrier frequency, then the spectrum used is : ((f+B/2) - (f-(B/2))

E.g., a 20Mhz bandwidth allocated to and operator at 2540-2560Mhz when modulated at QAM 16 is able to carry up to 80Mbps

Actually useful data rate is smaller due to error check coding, overhead of channel etc.

QPSK

Q

I

QAM16 Q

I

1101 1111

1100 1110

0111 0101

0110 0100

0010 0000

0011 0001

1000 1010

1001 1011

0001

11 10

4

Information

Carrier

Phase modulation

Source: IDA Spectrum Management Handbook

Source: IDA, Singapore

3GPP LTE BandsLTE Band Uplink Band Downlink Band Duplex Mode Region

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD UMTS Core

2 1850 MHz – 1910 MHz 1930 MHz – 1990 MHz FDD US PCS

3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz FDD 1800

4 1710 MHz – 1755 MHz 2110 MHz – 2155 MHz FDD US AWS

5 824 MHz – 849 MHz 869 MHz – 894 MHz FDD US 850

6 830 MHz – 840 MHz 875 MHz – 885 MHz FDD Japan

7 2500 MHz – 2570 MHz 2620 MHz – 2690 MHz FDD 2600

8 880 MHz – 915 MHz 925 MHz – 960 MHz FDD GSM 900

9 1749.9 MHz – 1784.9 MHz 1844.9 MHz – 1879.9 MHz FDD Japan 1700

10 1710 MHz – 1770 MHz 2110 MHz – 2170 MHz FDD Extended AWS

11 1427.9 MHz – 1447.9 MHz 1475.9 MHz – 1495.9 MHz FDD Japan 1500

12 699 MHz – 716 MHz 729 MHz – 746 MHz FDD







21 1447.9 MHz – 1462.9 MHz 1495.9 MHz – 1510.9 MHz FDD



24 1626.5 MHz – 1660.5 MHz 1525 MHz – 1559 MHz FDD





29 Downlink Only 717 MHz – 728 MHz FDD


31 452.5 MHz – 457.5 MHz 462.5 MHz – 467.5 MHz FDD

32 Downlink Only 1452 MHz – 1496 MHz FDD

33 1900 MHz – 1920 MHz 1900 MHz – 1920 MHz TDD UMTS Core (TDD)

34 2010 MHz – 2025 MHz 2010 MHz – 2025 MHz TDD UMTS Core (TDD)

35 1850 MHz – 1910 MHz 1850 MHz – 1910 MHz TDD




39 1880 MHz – 1920 MHz 1880 MHz – 1920 MHz TDD China UMTS TDD

40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD China TDD





LTE Band Uplink Band Downlink Band Duplex Mode Region

LTE Architecture

SGW PGW

HSS

OCS

S1-U

S1-U

S1-MME

S1-MME

S6a

Core Router

S5

Internet Gateway

MME

S11

SGW (Serving Gateway)- Mobility anchor

PGW (Packet Data Network Gateway)- Interface to external packet network

eNodeB

SGi

X2

MME (Mobility Management Entity)-

HSS – Home Subscriber Server

Packet Data Network (PDN)

S1 BearerRadio Bearer S5/S8 Bearer

EPS (Evolved Packet System) Bearer

Uu

• EPS bearer is a “tunnel” that transport packets between UE and PGW. It connects the UE via PGW to the PDN. It is per UE base

PCRF

Gx

Gy

OCS (Online charging system)

PCRF (Policy and Charging Rules Function)

S1 BearerRadio Bearer S5/S8 Bearer

LTE Architecture

SGW PGW

HSS

S1-U

S1-U

S1-MME

S1-MME

S6a

Core Router

S5

Internet Gateway

MME

S11

eNodeB

SGi

X2


Radio Bearer S1 Bearer S5/S8 Bearer


Uu


OCSHow does radio wave carries information?









PCRF

LTE Architecture

SGW PGW

HSS

S1-U

S1-U

S1-MME

S1-MME

S6a

Core Router

S5

Internet Gateway

MME

S11



eNodeB

SGi

X2






Uu


Billing System









?

?


LTE – Physical Layer Range of spectrum bandwidth from 1.4Mhz, 3, 5, 10, 15, 20Mhz

Downlink (DL) via OFDM-A (Orthogonal Frequency Division Multi-Access) and Uplink (UL) DFTS-OFDM

OFDM-A divides spectrum into subcarriers of 15Khz

Info are divided and transmit in these subcarriers in parallel at each at lower rate rather than being modulated at very high rate using the whole bandwidth over single carrier

Each Subcarrier is structured in time domain as slot of 0.5ms with 7/6 symbols in each slot. Two slots forms a subframe (1ms)

A Resource block is 12 subcarriers (total 180Khz) for a duration of 1 slot (0.5ms)

Scheduler schedule resources in pairs of resource blocks, i.e., a subframe (1ms)

Different modulation schemes (QPSK, QAM16/64) can be used based on UE radio conditions

Much smaller symbol rate at 15khz rather than say full 20Mhz

Symbol duration 66.7us and 4.69us for CP (Cyclic Prefix)

CP “period” avoids symbol overlapping when signal are deflected during their propagation and resulting in multiple paths of different length

4.69us = 1.4km by speed of light, i.e., if a path of the first symbol is delayed less than 1.4km worth of distance then it will still not overlap with the data of the second symbol

Time Frames

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Subframe (1ms)Slot 0 Slot 1

One SymbolOne Resource Element

15Khz

Resource Block

6 R

eso

urc

e B

lock

s ~

1.1

MH

z1

00

Res

ou

rce

Blo

cks

~ 2

0M

hz

Resource Block

Resource Block

Resource Block

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Spectrum Bandwidth

1.4Mhz 3Mhz 5Mhz 10Mhz 15Mhz 20Mhz

No. of Resource Block

6 15 25 50 75 100

CP Symbol

• The CP of first symbol is longer at 5.2us• A longer CP option support larger cell (longer path) in expense of 6 symbols per slot

Larger Delay

UE 1

UE 2Resource Block

Resource BlockResource Block

UE 3

Inter-symbol Interference

LTE Control Data Channels Functional Overview Control information must be exchanged between basestations and UE For basestation to tell UE the control

parameters and how fields are formatted

For UE to be attached to the network to receiving service and tracked

For basestation to communicate resource allocations at DL and UL

Physical level control channels are critical and usually uses more robust QPSK (DL, UL) or even BPSK (UL)

Physical level shared channels carries control from upper layer and data, could use QPSK, QAM16 or QAM64 depending on the channel condition of the UEs sharing the channel

DL Control• Identify which UE transmits at which RB• UE power control• Acknowledge UL data• Grant to UE UL request

UL Control• Allow UEs to request for uplink transmission• UL Random access – allow unattached UE to establish initial radio link• CQI (Channel Quality Indication) – consist channel quality overall or specific UE selected set of

subcarriers. In addition PMI (Precoding matrix indicator) and RI (Rank Indicator) is reported when MIMO is used

DL Data• Voice, Video, Web

UL Data• Voice, Video, Web DL Broadcast

• Master information block

Power Cable Fiber

RRH (Remote Radio Head)

Antenna

Cabinet/ShelfBackup power

Cell 1

Cell 2

Cell 3Base Station Hotel-> C-RAN (Centralized RAN)-> vRAN (Virtualized RAN)

Pico cell radio head

RRH

Coaxial Cable

Mobile Radio Access Network Deployment

CPRI/Fiber

Backhaul

DL Control and Data121110

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15Khz

Resource Block

Resource Block

User A

User B

User C

Control Channels, e.g., PDCCH, PHICH occupy the first 1, 2 or 3 symbols of the subframe. Resource allocation to UE is done by PDCCH identifying it using RNTI (Radio Network Temporary Identifier) which is assigned to UE by eNB

Reference Signal (RS) pattern – known cell/antenna specific pattern for UE to asses channel quality, RS from different antenna locates differently in resource block to avoid inter-antenna RS interference

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(H)ARQ = (Hybrid) Automatic Repeat Request

User IP Packets

LTE Stack

RLC(Radio Link Control)

MAC(Medium Access Control)

PHY

PDCP(Packet Data

Convergence Protocol)

RRC(Radio Resource Control)

Segmentation/ConcatenationIn-sequence DeliveryRLC establishment

H-ARQPriority handlingMapping between logical to transport channel

Ciphering, in-sequence deliveryHeader compressionIntegrity protection for control plane

Paging, Radio Bearer ControlMobility functions (handover)UE measurement controlRRC connection set up

PBCH(Physical Broadcast Channel – Master

information Block for UE access, QPSK)

PDSCH(Physical Downlink Shared Channel,

QPSK, QAM16/64)

PDCCH(Physical Downlink Control Channel –

downlink allocation, uplink grant, power

control, QPSK)

PHICH(Physical Hybrid-

ARQ Indicator Channel – Data

acknowledgement, QPSK)

Physical level control channels

(Paging Control Channel –

paging for UE)PCCH

(Broadcast Control

Channel)BCCH

(Common Control Channel – for initial

control with UE before RRC attach)

CCCH

(Dedicated Traffic Channel –

bidirectional user data for one UE )

DTCH

(Dedicated Control Channel – for

control to UE after RRC attach)

DCCH

(Multicast Traffic Channel – multicast

user data )MTCH

(Multicast Control

Channel)MCCH

DL-SCH(Downlink Shared Channel – shared among logical channels carry both control and data, decide dynamic resource allocation, modulation, coding, support beamforming, sleep cycle)

BCH(Broadcast Control

Channel)

PCH(Paging Channel – support UE power saving, page to

cell coverage area)

PCFICH(Physical Control

Frame Indictor for location of the

PDCCH)

Transport Channels -Define transport characteristics like modulation, coding, antenna mapping MCH

PMCH

Logical Channels -

MAC LayerRLC

(Radio Link Control)

MAC(Medium Access Control)

PHY

PDCP(Packet Data

Convergence Protocol)

Transport Channels

RRC(Radio Resource Control)

eNodeBUE

NAS NAS

MME

User IP Packets

Maintaining connection with core, mobility managementNon Stratum Access Non Stratum Access

Logical channels

PDCP Header

RLC Header

PDCP Header

MAC Header

Transport Block

Scrambling, Modulation, Layering Mapping, Antenna Mapping

Uplink Control and Data

PUSCH(Physical Uplink Shared

Channel, QPSK, QAM16/64 )

PUCCH(Physical uplink Control

Channel – Quality feedback, scheduling

request, H-ARQ for DL, BPSK, QPSK)

(Common Control Channel – for initial

random access before attach)

CCCH

UL-SCH(Uplink Shared Channel – shared among UEs

carry both control and data, dynamic resource allocation, modulation, coding)

Control Downlink - format of frames, allocation of downstream and upstream subscarriers/slot,

acknowledgement of data received, paging for mobile terminals, reference pattern

Uplink – random access for attachment, bandwidth request, feedback on downlink channel quality

Data – both downlink and uplink

Transport Channels -Define transport characteristics like modulation, coding, antenna mapping

RACH(Random Access Channel – for initial

attachment from uplink)

PRACH(Physical Random Access Channel –

generates preambles for UE identification and provide random access)

(Dedicated Control Channel – for control to UE after attach)

DCCH

(Dedicated Traffic Channel – user data for

one UE )DTCH

MIMO – Multi-Input Multi-Output MIMO

Defined by convention as MxN in one direction

M means the number of transmitter and N is the number of receiver

Up to 4 antennas FDD and 8 antennas in TDD

Assume all UE support two receivers

MIMO make use of multiple antenna to achieve robustness of channel or higher capacity

Make use of multipath condition

SINR (Signal to Noise Ratio) When UE is in low SINR(Signal to Noise ratio)

E.g., cell edge, transmit diversity or beamforming provide benefits

High SINR environment SU MiMO or MU-MIMO can be used provide there are spatial diversity on

the paths (low correlation)

Close loop – feedback from UE Useful when UE not in high speed mobility

Transmit Diversity- Single data stream is coded differently on

two antennas for transmission, don’t assume feedback on channel quality

- Improve data reception at cell edge ( mainly for control channels) but not higher rate

Multi-user MU-MIMO- Multiple UE transmit at the same time with same

subcarriers- Rely on spatial diversity to achieve minimal

interference, double the throughput

Beam Forming- Improve coverage- Weighted phase and magnitude of individual

antennas, work with interference- Require known channel state information,

terminal estimate overall beamformed channel- Easier for TDD as downlink channel is same as

uplink channel

1 Transmission layer is based on rank which is the number of linearly independent path (spatial layer) between M antenna and N receivers based on feedback from UE2 Layers <= # Antennas, layers are split to antenna, single layer result in beamforming

SU-MIMO Spatial Diversity- Multiple data streams to antennas for simultaneous

transmission known as layers, Higher peak rate, layers <= number of antennas

- rate- Open or close loop feedback to precoder

1,2

Enhance cell edge performance

Enhance peak performance

LTE Cell CapacityLet’s find the theoretical downstream throughput of 20Mhz DL with 2x MIMO spatial diversity

- RB is 180Khz with 12 subcarriers at 7 symbols at 0.5ms slot, 1 subframe has 2 slots

- For 20Mhz channel, number of RB is : 100

- Assume optimistically that QAM 64 is used, which carries 6 bit per symbol

- Bandwidth per subframe = 100 RB x 12 subcarriers x 2 slots x 7 symbols x 6 bit per symbol

= 100800bits per ms

- Bandwidth per second = 100Mbps

- Factor in 25% overhead -> 75Mbps

- Assume 2x2 MIMO with spatial diversity => 75x2Mbps = 150Mbps

- Assume 4x4 MIMO with spatial diversity => 75x4Mbps = 300Mbps

• UE further away• Signal is weaker• QPSK used for robustness• Smaller Throughput

• UE nearby• Signal received well• QAM64 used • Higher Throughput

Basestation

In Reality, the actual capacity of a cell depends on:• Noise condition, Interference from other cells, location of the UEs within the cell• The modulation and coding scheme (MCS) of a channel is dependent on the feedback CQI

(Channel Quality Indicator) from the UEs that it serves

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One SymbolOne Resource Element

15Khz

Resource Block

6 R

eso

urc

e B

lock

s ~

1.1

MH

z1

00

Res

ou

rce

Blo

cks

~ 2

0M

hz

Resource Block

Resource Block

Resource Block

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UE 1

UE 2Resource Block

Resource BlockResource Block

UE 3

LTE Architecture

SGW PGW

HSS

S1-U

S1-U

S1-MME

S1-MME

S6a

Core Router

S5

Internet Gateway

MME

S11



eNodeB

SGi

X2






Uu


Billing System









?

?

?


?

UE Attachment Procedure

PCRF

Internet Gateway

eNodeB

4. eNodeB relay attach request to MME, add its own ID, PDN connection Request

5a. Authentication Request for the UE using IMSI. HSS assembles AUTH vector send to MME

6. Location update, HSS

8. MME request SGW create session, EPS bearer id, IMSI PGW address with APN, QOS

7. HSS reply with APN, QOS profile include AMBR (aggregated bit rate), QCI, PGW address with assigned static IP if specified

9. SGW request PGW Create session, default EPS bearer id,S5 SGW TEID APN, QOS profile

11. PGW reply with assigned IP and authorized QOS profile, S5 PGW TEID

12. SGW response to MME and pass S1 SGW TEID for eNodeB to create S1-U bearer

13. a)Attach request accept with GUTI, TA list, b) request default bearer from eNodeBto UE, c) initial context request to EnodeB with AMR, QCI, S1 SGW TEID

15. eNodeB and UE exchange messages on a) attach accept (NAS) with the assigned IP, TA list, GUTI, and b) reconfigure the RRC to activate default bearer

16b. eNodeB response initial context, include eNodeB TEID of S1-U bearer

1a. UE receives cell identify and master information block (MIB) with up and downlink control channel config via broadcast channel. 1b. Via the PDCCH, SIB is obtained which identify random access channel (PRACH) frequency and offset to make initial contact with eNB


17. MME sends update bearer request to SGW with S1 eNB TEID


2) UE performs random access secure uplink resource and setup RRC with eNB, obtain C-RNTI the UE identifier within the cell,

3). UE sent attach request including IMSI to MME

5b) MME sends AUTH vector for UE to verify, UE send response to MME for further checking

UE eNB MME

HSS

PGWSGW

S11 S5

14. UE and eNB set up security and encryption for RRC message and user data


Step 10/11Step 11,12,14,15Step 14

16a. eNodeB sends Attach complete to MME

(1). UE cell identification, synchronize physical layer parameters(2,3). UE set up Radio link with eNB and request for attachment (NAS) to the mobile network with MME(5) . MME checks with HSS to get authentication vector and mutual authentication with UE(6,7). MME updates the HSS on location and gets the profile of the UE, including APN, PGW address, QOS Profile etc.(8-12) MME set ups EPS bearer by first setting up the S11 and S5 bearer, it request SGW to create session with UE parameters from HSS. SGW and PGW set up the S5 bearer, PGW allocates IP address and check profile with PCRF. PGW response to SGW which then response to MME for bearer setup(13) MME verify bandwidth profile, set up bearer toward eNB and UE, sends request to eNB(14) eNB establish secure communication over radio with UE(15-17) UE and eNB set up the radio bearer, acknowledge the set up to MME, MME finalize the S1 bearer with SBW using info from eNB

IMSI – International Mobile Subscriber Identification consists of MCC (Mobile Country code, MNC (Mobile Network Code), MSIN (Mobile Subscriber Identification Number)TEID (Tunnel Endpoint ID) – is end point identification for GTP (GPRS Tunnel Protocol) tunnel implementing bearersQCI (QOS Class Identifier)APN (Access Point Name) – identifies PDN/service to be connectedGUTI – Globally Unique Temporary ID, MME’s identifiers for a UETA List – list of tracking areas within which UE don’t need to update MME

10 PGW checks with PCRF on policy using UE IP, IMSI, APN, QOS Profile. PCRF response with rules to be enforced in PGW

Tracking Area

TA-1

TA-2

TA-3TA-4

TA-5

Cells are grouped into individual tracking area (TA), a number of tracking areas (up to 15) put under a tracking area list

MME keeps track of a UE in terms of its current TA list, TA list is also given to UE when it register with the MME

UE updates the MME when it moves to a TA not in its TA list via an action called TAU (update) trade off on size of TA, TAL and TAU frequency)

When downstream data comes for an idle UE, the MME send a paging to cells on the TA in the UE’s TA list

Cell “page” for UEs using “paging occasions” on (PDSCH) and defined by (PDCCH)

A sleeping UE wakes up periodically and listen to paging, the period is called default paging cycle cycle length (DRX discontinuous receive cycle) trades response time against UE battery consumption

UE checks the paging occasions for its own identification, if found, it sends service request to MMETAU

TA List TA List

MME

Handover via X2 Procedure

SGW

PGWInternet Gateway

Source eNB



Step 9/10Step 11,12,14,15Step 13

1. UE sends Cell Measurement Report on source and neighbor eNB2. Source node identify better performance can be achieved if UE use a neighbor

eNB and initiate Switch Over Request to target node3. Target eNB checks resource to take in UE, send reply to Switch Over Request

together with target eNB own parameters4. Source eNB instructs UE to switch to target node with Radio Reconfigure Request

(RRC) with target eNB parameters5. Source eNB sends Transfer Status update to target eNB on transport status, relay

DL data to UE via X2 bearer to target node6. UE synch, attaches to target eNB running RRC confirm with target eNB7. Target eNB sends path switching request to MME8. MME sends Modify Bearer Request to SGW 9. S-1 bearer between SGW and target node is set, SGW ack Modify Bearer Request10. MME acknowledges the Modify Bearer Request to target node11. Target node instructs the source node to release the UE context


1

5

6

3

MME

8 97

24

11

Original traffic between source node and UE

DL traffic forwarded by source node to target node and to UE after step 6

UL traffic from UE via target node after step 6

DL traffic from UE via target node after step 9

10

Target eNB

LTE Architecture

SGW PGW

HSS

S1-U

S1-U

S1-MME

S1-MME

S6a

Core Router

S5

Internet Gateway

MME

S11



eNodeB

SGi

X2






Uu


Billing System









?

Frequency Reuse

S1

S2

S3

S1

S2

S3

S1

S2

S3

f1

f2

f3 f3

f2

f1

Refers to how frequency band are used in cell deployment Reuse of 1 => the same frequency is used in all sector

Reuse of 3 => frequency band is reused every 3 sectors – lower utilization of whole band

Inter-cell Interference (ICI) occurs when a UE is in the edge of a sector and is subceptable to the interference of a neighbor cell

Reuse of 1 result in high ICI

A reuse 3 approach divides the frequency band among 3 sectors eliminate ICI but result in much lower cell capacity

SFR (Soft Frequency Reuse) divide the frequency into minor and major band. Major band is used all the way up to cell edge by using higher power, and minor band is used in the cell center at lower power. Major bands can be derived by dividing whole band into 3 non overlapping bands.

Full capacity is harnessed at the cell center with a reuse of 1

At the edge due to the division of frequency, the reuse is >1, e.g., 3

Furthermore band power can be adjusted to change the extend of reuse depending on the inter-cell condition and UEs requirements

minor band

major band

minor bandminor band

minor band

Reuse 3Reuse 1 Reuse ~1 with SFR

Heterogeneous NetworkQuality of Experience issues

◦ Coverage problems at cell edge or indoor, e.g., terrace house and deep in office buildings, poor voice quality

◦ Capacity problem at hotspot, low mobile broadband throughput and poor user experience

Build more macro cell◦ Site acquisition issue and macro cells start to interfere

with each others

Heterogeneous Network - Small cells of lower power

◦ Macro (40W), Micro, Pico/metro (5-10W), and Femto(100mw)

◦ Serves smaller area providing or increase the capacity in hotspot

◦ A small cell is connected via wireline broadband network to core via a small cell gateway or alternatively, it is a radio head and connects via optical fiber to nearby basestation for baseband processing

◦ UE locked onto a small cell when signal is above threshold, use further bias configuration to bias UE towards connecting with small cell, thus offloading the traffic from macro cell, thus extending the range

◦ Issue with interference from macro cell at the small cell edge

Coverage Issue

Capacity Issue at hotspot Coverage and Capacity Issue

Build more macro cell

Heterogeneous Network- Build smaller calls of lower power

Potential interference from macro

Femto cell dedicated to private user group e.g., home or office UE

Lower power pico cell

Metro/Pico cell serves public UE in a hotspot area

Macro cell still provides overall coverage

Wireline broadband

Optical fiber

LTE-A - eICICeICIC (Enhanced Inter-cell Interference coordination)

◦ UE at pico/metro cell edge tends to suffer from interference from macro cell

◦ Interference onto the pico cell can be reduced if the macro cell refrain from using the subframesthat pico cell is using on it’s edge UE/s

◦ Pico cells exchange load info with macro cell which takes account of own load and Macro cell identify which resource blocks not to be used, called ABS (Almost Blank subframe)

◦ Pico cells near to the macro cell can allocate the same subframe corresponding to the ABS for UEs at the edge as there will be less interference from macro

◦ Synchronization between the pico and macro as both must now aligned on ABS subframe

Macro cell determines the ABS based on load of Pico and Macro cell

Macro eICICScheduling

Pico submit load and Macro cell informs ABS pattern

Corresponding subframe assigned to UE at Pico cell edge

LTE-A – CACA – Carrier Aggregation

- Operators often have license to multiple frequency blocks, may be in the same band or different band

- Being able to allocate them to UEs together increase peak rate of UEs, and potentially increase utilization efficiency

- Up to 5 carriers (component carriers) to transmit data down or upstream, currently up to 3 is defined

- Component carriers can be in same band or different band◦ e.g., GSM refarming, and newly acquired 2.6Ghz band

- Primary frequency known as PCell is responsible for signaling such as mobility management and allocate one more secondary frequency known as SCell to UE

- Algorithm runs in basestation to decide whether to activate CA configuration of UE depending on availability of resource and UE demand, deactivate when not needed to save UE power

- Multiple scenarios◦ Low band + high band -> low band provides coverage and high

band provides capacity

◦ FDD+TDD -> FDD at macro provides coverage and TDD as RRH provides additional capacity

◦ Macro+small cell using different frequency – macro provides coverage and small cell provides capacity

Intra-band contiguous

Intra-band non-contiguous

Inter-band non-contiguous

f1 - pCell

f2 - sCell

Pico/TDD RRH

macro

f1 - pCell

f2 - sCell

Low band + Highband

Pico+ Macro or FDD + TDD

LTE-Advanced - COMP COMP (Coordinated Multipoint Transmission)

Coordinates among a set of transmission (Tx) or receiving points (Rx) which can be intra or inter site to provide better performance at the cell edge by mitigating interference

Two major approaches – Coordinated Scheduling/Coordinated Beamforming achieving interference avoidance, Joint Processing/Joint Transmission or Joint Processing/Dynamic Point selection (DPS) where multiple Txs transmit to the cell sites

RRH_1RRH_2

JT – both Tx in a Frequency time resource

DCS – one Tx transmit at a time

eNodeB_2

Data stream to both Tx

Only the serving cell receive data stream and transmit other Tx points are coordinated at the scheduling or beamforming to reduce interference.

Serving cell transmission

Coordinated Scheduling/BeamformingJoint Processing – Joint Transmission/Dynamic Cell selection

UE Category

UE Category DL SpatialMIMO Layer

UL Spatial MIMO Layer

QAM 64DL

QAM 64UL

RF Bandwidth

DL Peak Rate

UL Peak Rate

Category 1 Optional No Yes No 20Mhz 10 5

Category 2 2x2 No Yes No 20Mhz 50 25



Category 5 4x4 No Yes Yes 20Mhz 300 75

Category 6 2x2 or 4x4 No Yes No 40Mhz 300 50

Category 7 2x2 or 4x4 2x2 Yes No 40Mhz 300 100

Category 8 8x8 4x4 Yes Yes 100Mhz 3000 1500

LTE-

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Up to Release 10

Further DevelopmentLTE in Unlicensed band (LTE-U)

◦ Licensed Assisted Access (LAA-LTE) where LTE runs on unlicensed band, 5GHz being considered

◦ Licensed band macro serve as primary cell for signaling and basic service, use local cell with unlicensed band as supplementary either only on downlink or with uplink as well, based on CA (carrier aggregation)

◦ 3GPP Release 13 work items

LTE and WiFi Aggregation (LWA)◦ Part of LTE traffic is “tunneled” via WiFI (hence still using WiFi medium access, AP etc.)

◦ LTE traffic at licensed band and those tunneled via WiFi is combined at the local eNB e.g., small cell

◦ Better coexistence of WiFi as there is no LTE RAN in the unlicensed band, no hardware change in UE

◦ 3GPP Release 13 work items

Machine to Machine communications, IOT (Internet of Things)◦ Still very loosely defined

◦ Huge number of devices at low bandwidth, sleep and communicate

◦ Reduce complexity on UE to reduce power, e.g., reduce bandwidth capability, transmission mode

◦ Support for longer distance

Documents

Fixed Network Infrastructure - NUS · PDF fileWireless Network Infrastructure –An Overview ... • Carrier aggregation (LTE) ... 3 íóíìD,ÌtíóôñD,Ì íôìñD,ÌtíôôìD,Ì