Small Cell

Small Cell LTE

Deployments Tightly Integrating Access and

Backhaul

Paul Trubridge

VP Product Management, Airspan

November 2012

2 Airspan Confidential information

A definition of Small Cells…

• There are many different definitions for small

cells - this is ours!

• In this classification there are three types of

small cells

1. Residential and Business Femto

• Indoor, Low Power (typically 100mW), Closed

User Groups

• These are traditional 3G Femto Cells

2. Open “Enterprise-Class” Femtos and Picos

• Outdoor and Indoor Cells, Open Access, Higher

power (1W)

• These are cells I focused on in this presentation

(and perhaps the future of Mobile Cellular

Networks)

3. Micro and Compact Macro Cells

• All-in-One Outdoor Base Stations

• Much higher power (2-10W), Open Access

• Optimized for non-traditional deployment

locations (Rooftops, Sides of Buildings etc…)

HISILICON SEMICONDUCTOR HUAWEI TECHNOLOGIES CO., LTD. Page 7 Huawei Confidential

Comprehensive Suite of Flexible Backhaul Products

Flexible Assembly

AD

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SL

FE / PO

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Small Cell

Radio Transport

＋

UE(TDD)

NLOS, PMP

eNB(TDD)

FDD

FDD

FDD

TDD FDD

FDD

FDD

Spectrum

In case of no wire line backhaul

xPON OLT

SFP

Copper

MicroWave

Optical

TDD Backhaul

ADSL/VDSL

FE / POE

Cable

Mobile Network Operators Demand a Portfolio of Backhaul Options Designed for Scenario

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3

Airspan is focused on Type 2 and Type 3 Small Cells


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Small Cell HetNets = Network Capacity Enhancement

• Small Cells will deliver huge network capacity increases…

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Macro-only

LTE Network

HetNet LTE

Network

Capacity Enhancement comes from

Aggressive Frequency Re-use


Dynamic

Resource Block

Allocation

The Power of LTE-Advanced: eICIC and SON

• LTE-A eICIC and SON enables

aggressive deployment of LTE

small cells

• Allowing Time and Frequency

resource block re-use.

• Closely Coupled (Macros)

• Typically a Tri-Sectored Base

Station – sectors share the same

frequency. X2 communication over

Ethernet or internal messages

between sector RRMs

• Loosely Coupled (Small Cells)

• Auto-Optimizing and Configuring

cells that share the same spectrum

(i.e. N=1 re-use). X2

communications over wide-area

backhaul to other cells

All

Resource

Blocks

All

Resource

Blocks All

Resource

Blocks

Loosely Coupled: Omni

Cells at different locations

Closely Coupled:

Sectors at same cell location

Dynamic

Resource Block

Allocation

Frequency

Time


LTE-Advanced: Small Cell Deployment Life Cycle

• Small cell deployment requires

LTE-Advanced eICIC and SON.

• Elimination of co-channel

Interference by inter-cell

coordination

• capacity enhancement by optimal

UE to eNodeB mapping

• Remove the need for Frequency

Planning by Self Optimisation and

Self Configuration

• Cells automatically get

configured by SON server as

they become active.

• Without impacting / interfering with

existing network

• Removes the need for complex

network design ahead of deployment

Step 1: Typical Tri-Sector Macro-cell

deployment. Release 8/9 ICIC auto

configures sector radio interfaces using

X2 comms between sectors and

dynamically schedules traffic. SON not

required. Uses SFR

Step 2: Omni small cells added to the

deployment. Small cells impact

resource block mapping. Static SON

and eICIC re-configs to ensure optimal

mapping. Uses ABS Patterns in areas

of co-channel overlap.

Step 3: Mass deployment of Omni small cells.

Dynamic SON and eICIC also drive Tx

powers and Range Extension bias to

best optimize resources across the

network. Uses ABS Patterns in areas

of co-channel overlap.


LTE-Advanced X2 Communications for eICIC

• At the heart of this LTE-Advanced eICIC is

extensive use of the X2 interface which

allows communications between RRMs

within each eNodeB.

• The X2AP interface was enhanced in Release 10

explicitly for eICIC and ABS

• X2 requires communications occur between

Macro and Pico, and Pico to Pico.

• The eICIC process ensures that traffic

scheduling by Macro and Pico eliminates

co-channel interference

• By stop simultaneously use of time/frequency

resource blocks in locations where interference

would occur.

X2 X2

X2

Release 10/11/12:

eICIC and SON X2 communications are

critical to LTE-A eICIC and

Small cell deployment.


Small Cell Networks: Capacity Enhancement

• LTE-Advanced eICIC and SON technology can deliver large capacity gains with even limited

numbers of Pico cells

• Macro cell footprint DL traffic boosted from 33Mbit/s to >130Mbit/s (with 4 Picos) – in Busy Hour

• Actual gains vary significantly depending on number of Pico cells deployed per Macro cell,

location of Pico cells, Busy Hour, versus Non-Busy Hour traffic patterns.

0x2x4x6x8x

10x12x14x16x18x20x

Downlink Uplink

Macro

Cell Edge

Median

Assumptions*:

N=1 reuse 10 MHz FDD

4 Pico cells per Macro cell

eICIC, SON, High Power

Macro, Hotspot Deployment

* 3GPP TS 36.814, Macro ISD 1500m, Full Buffer Model, Even UE Distribution, Cell Range Extension (12dB), 10 MHz (FDD) at 2.6 GHz

4x Gains using 4 Pico Cell per Macro Cell in Same Spectrum Allocation


Small Cell Backhaul Requirements

• Assumptions: LTE-A eICIC, Hot Spots Deployment, Urban Model

• Busy Hour vs. Non Busy Hour with statistical sharing of backhaul

• Typical Backhaul for LTE Small Cells is around 40 Mbit/s (for 10 MHz FDD)

• Non Busy Hour Pico backhaul traffic typically ~1.3 times Busy Hour

• Backhaul needed per Pico decreases as number of Pico increases

* 3GPP TS 36.814, Macro ISD 1500m, Full Buffer Model, Even UE Distribution, Cell Range Extension (12dB), 10 MHz (FDD) at 2.6 GHz

0

20

40

60

80

100

120

140

160

180

200

Macro Only 1 Pico 2 Pico 3 Pico 4 Pico

Busy Hour

Non Busy Hour

Average per Pico

Peak per Pico (90%)

Mb

it/s


Small Cells and Frequency Re-use: eICIC at Work

• Small cell capacity gains come from better frequency re-use.

• LTE-Advanced protocols map UEs to the optimal cell (Macro or Pico), i.e. with the best signal

conditions (better MCS and MIMO). Mapping is independent of RSSI (with Cell Range Extension).

• Small cells are typically “Buried in the clutter”, so that propagation is contained and extensive re-

use of frequencies can happen.

• LTE-Advanced eICIC and Almost Blank Sub-frames (ABS) features ensures potential areas of

interference between Macro-Pico, and Pico to Pico are “mapped out”.

Macro Cell Macro Cell

Pico Cells

Small Cells are deployed in locations that are generally Non-Line-of-Sight

from Macro Cells, or other Pico Cells to maximize capacity gains


4G Traffic: Everything is becoming real-time…

• Mobile Broadband data consumption is growing rapidly… It’s important

we understand why….

• What’s driving this growth?

• Smartphone adoption

• Introduction of tablets and Post-PC devices

• Broadband interfaces in non-PC devices (Gaming, Appliances, Cars…)

• Cloud Computing

• New Social Networking Applications and Networks

• Streaming Video and the death of the traditional broadcast TV

• Standard definition content becoming HD content

• Email and Messaging Multiplication

• Speech recognition (Siri and Google Voice)

• etc… etc…

• Most of today’s content must be delivered in real-time.

• This forces carriers care about “Quality of Service”. If they don’t, a

lot of applications stop working or become unusable.


QoS: Supporting Real Time Traffic

• Large percentage of traffic over a 4G network needs to have sub 300ms

response

• QoS classifications of traffic over the radio interface have become critical to

end user experience and service satisfaction.

• Small Pico cells, need to deliver traffic associated with LTE QoS Classes

(QCIs) just like Macro cells do…

• Guaranteed Bit Rate Services, Allocation and Retention Priority, Maximum Bit Rate

(MBR), Aggregate MBR, etc…


Ba

ck

ha

ul

Contended Backhaul and QoS

• If backhaul is contented (in any way), the QoS and

service reliability delivered over the LTE Uu interface

becomes impaired.

• If the backhaul randomly introduces latency and/or reduces the

capacity allocated to service flows (especially GBR), the service is

negatively impacted.

• THIS IS UNACCEPTABLE TO CARRIERS

• Therefore, any backhaul solution must ensure that the

LTE radio-interface QoS is respected and maintained

across contented backhaul.

• Typically this requires a detailed understanding of the LTE Air-

Interface

• Not something that can easily be done using code-point markings,

or other simple packet marking (ToS bits)

• Any contention based scheduling must take LTE Air-Interface QoS

needs into account.

• Ensuring Signaling gets and Real-Time / GBR service gets

served first

LTE QoS must be supported by any contented

backhaul solution for LTE Small Cells

eNodeB

Traffic

Instantaneous

Backhaul

Capacity

Instantaneous

Offered Load

S1 a

nd X

2,

Sync, M

gm

t

Real-T

ime a

nd G

BR

Serv

ices

Non R

eal-T

ime a

nd

Non-G

BR

Serv

ices


Small Cell Backhaul with End-to-End QoS

• The ideal arrangement for Small Cell

backhaul is a combination of LOS P-P links

and/or Fiber, feeding P-MP NLOS backhaul

links to the small cells

• Best economics with excellent ROI

• However, unless LTE Signaling and Real-

Time and GBR traffic is properly managed

and prioritized, ensuring QoS is honored the

solution is flawed.

• By tightly combining LTE Small Cell Access

technology of NLOS backhaul technology

the QoS can be solved

• The solution requires visibility of LTE QoS QCIs on a

service flow basis to be available to the P-MP NLOS

backhaul (and for LOS or Fiber to be uncontended)

Solution to Small Cell Backhaul is Tightly

coupled NLOS Backhaul technology

Fiber Uncontended

Metro Ethernet

NLOS P-MP NLOS P-MP

• We call this technology Cooperative QoS


Fiber

NLOS Wireless

Backhaul

Coverage

P-MP NLOS Backhaul: Cooperative QoS

• In Cooperative QoS mode the P-MP NLOS backhaul Scheduler maintains visibility of LTE Small Cell

scheduling requirements for UEs, tracking QoS commitments on bandwidth, latency and priority

• In addition the Backhaul Scheduler also has visibility of the iBridge backhaul radio interface and it’s

interference environment.

• The scheduling by the Pico cells takes accounts of both requirements to deliver high performance over

the backhaul and end-to-end QoS over the 4G LTE Pico access interface

LTE Pico

Access

Coverage

LTE Pico

Access

Coverage

LTE Pico

Access

Coverage

P-MP NLOS

Backhaul Base

Station Node

LTE QCI

Scheduler

Information

Real-Time LTE

QCI Service Flow

Data


Summary and Conclusions

• LTE-Advanced Small Cells can dramatically increase the capacity of Macro

LTE Networks

• X2 communications are increasingly important to achieve this.

• The enabling technology for LTE small cells is small-cell backhaul

• Unless the backhaul costs are right, small cell deployment won’t happen.

• Outdoor LTE Small Cells will mainly be deployed in NLOS locations

• Requires NLOS Backhaul technology, as Fiber based solution uneconomic

• A small amount (10-20MHz) of 2.x,3.x or 4.9GHz licensed spectrum can backhaul a network with

10-20 small-cells per macro-cell.

• Contended small-cell backhaul demands end to end QoS

• The backhaul requires access class latency aware QoS

• LTE and backhaul QoS must work cooperatively to deliver the ever increasing levels of real time

services.

The Core of any Small Cell deployment is NLOS P-MP Backhaul

Technology with QoS support augmented with Fiber and

P-P LOS Wireless Backhaul.


Thank you for your time!

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Small Cell