sistelbanda at mwc15

Moving Carrier Networks to the Enterprise

Unlicensed bands: A Brave new world for LTE Small Cells

A Brief Analysis of License-Assisted Access

Small Cell Zone at Mobile World Congress March 2015 Oscar Carrasco - CTO

CONFIDENTIAL © Sistelbanda S.A. 2015


Principles of License-Assisted Access

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Unlicensed Spectrum Unlicensed Frequency Bands •  The 5GHz frequency band has a lot of unlicensed spectrum available globally. This band is frequently

referred as 5GHz UNII (Unlicensed NaPonal InformaPon Infrastructure) band, having 3 sub-‐bands (1,2 & 3) •  Most Regulatory Areas offer a large amount of spectrum in the 5 GHz band •  In Europe there is 455 MHz of spectrum available, and 580MHz in the US •  The use of unlicensed spectrum usually carries some regulatory requirements, such as being able to detect

if a radar system is using the band or being able to co-‐exist with other users of the band •  In some regulatory areas, like Europe and Japan, there is a specific requirement for supporPng LBT (Listen-‐

Before-‐Talk) or Clear Channel Assessment (CCA) at milliseconds scale is required •  In other regulatory areas, like US, Korea and China, there are no such requirements •  Other techniques are also needed like DFS (Dynamic Frequency SelecPon) in UNII-‐2 sub-‐band for opPmizing

the co-‐existence between different systems or technologies



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Reasons for using unlicensed spectrum with LTE

Benefits •  Beaer spectrum efficiency than the current technologies in use with the 5 GHz band, achieving both higher

data rates and at the same Pme higher spectral efficiency, also in the unlicensed band. •  Beaer coverage, especially when combined with the use of licensed band operaPon •  In terms of network management, using the unlicensed band with LTE instead of an alternaPve radio

technology, provides a fully integrated soluPon to the operator easing the management of security, authenPcaPon and end-‐to-‐end services, leading to OPEX reducPons.

•  The use of LAA is fully transparent to the LTE core network. •  Allows Managing only one Network •  LTE technology can meet the regulatory requirements for the unlicensed band allowing coexistence with

the other LTE systems as well as other technologies, such as Wi-‐Fi, operaPng on the same frequency band. •  Beaer User Experience, providing high reliability and quality with the support of Mobility, QoS, robust

fallback etc. •  The Cross-‐Carrier Scheduling allows a fully integrated Mobility & QoS management, as the C-‐Plane is kept in

the Primary Carrier (Licensed Carrier). •  SimulaPon results show that this soluPon fits opPmally with the deployment of low power nodes, the small

cells. Unlicensed spectrum can be used as performance booster in operator-‐deployed small cells



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LTE Licensed-Assisted Access Main ideas behind the use of LTE over unlicensed spectrum

•  LTE operaPon on the unlicensed band is built on top of LTE-‐Advanced carrier aggregaPon o  Always accompanied by a licensed

carrier – no focus on stand-‐alone operaPon

•  Primary carrier uses licensed spectrum (FDD or TDD) o  Control signaling, mobility management,

user data •  Secondary carrier(s) use unlicensed

spectrum o  Best-‐effort user data (DL and potenPally

UL)

SECONDARY CELLUnlicensed Spectrum

PRIMARY CELLLicensed Spectrum

DLUL

CARRIER AGGREGGATION



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LTE Licensed-Assisted Access Main ideas behind the use of LTE over unlicensed spectrum

•  When operaPng with downlink only on the unlicensed band (supplemental downlink), the LTE Small Cell can perform most of the necessary operaPons to ensure reliable communicaPons, including checking whether the intended unlicensed channel is free from other use

•  The LTE eNodeB should aim to select a channel that does not have another network operaPng on it with a high interference level, but rather select a channel that is either free or only slightly loaded. Having selected the channel, the LBT operaPon must be performed before transmission is possible, as well as the other necessary procedures

•  The LTE terminal capable of operaPng on the unlicensed band needs to be able to make the necessary measurements to support unlicensed band operaPon, including providing feedback when the terminal is in the coverage area of a LTE eNodeB transmigng with the unlicensed spectrum.

•  Channel Quality InformaPon (CQI) feedback will allow the eNodeB to determine what kind of quality could be achieved on the unlicensed band compared to the licensed band.



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Coexistence Mechanisms Techniques for ensuring a fair and friendly coexistence •  A criPcal element of the LTE operaPon in unlicensed band is to ensure LTE-‐U co-‐exists with

current access technologies such as WiFi on “fair” and “friendly” bases •  The unlicensed operaPon should also support a fair coexistence between operators •  There are some features to achieve such a friendly coexistence, being a “good-‐neighbor” to

Wi-‐Fi when using the same channel •  At the same Pme, the operaPon in unlicensed band also needs to factor in the regulatory

requirements of a given region o  DFS or Dynamic Frequency SelecPon for detecPng interference from radar systems (radar

detecPon) and to avoid co-‐channel operaPon with these systems, providing on aggregate a near-‐uniform loading of the spectrum (Uniform Spreading)

o  TPC or Transmit Power Control is a mechanism to ensure a miPgaPon factor of at least 3 dB on the aggregate power from a large number of devices. A common TPC value is 12dB

o  Channel Sensing and AdapPve TDM transmission algorithmics for regulatory regions where LBT is not applied



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Channel Access Mechanism for LBT Frame Based Equipment according to ETSI EN 301 893 V1.7.1

•  LBT AdapPvity is an automaPc channel access mechanism by which a radio device avoids transmissions in a channel in the presence of transmissions from other radio systems in that channel

•  LBT AdapPvity is not intended to be used as an alternaPve to DFS to detect radar transmissions

•  Transmissions are only allowed providing they are not prohibited by the DFS funcPon



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Channel Access Mechanism for LBT Frame Based Equipment according to ETSI EN 301 893 V1.7.1 1.  Before starPng transmissions on an OperaPng Channel, the equipment shall perform a Clear Channel

Assessment (CCA) check using "energy detect". The equipment shall observe the OperaPng Channel(s) for the duraPon of the CCA observaPon Pme which shall be not less than 20 μs.

2.  If the equipment finds an OperaPng Channel occupied, it shall not transmit on that channel during the next Fixed Frame Period

3.  The total Pme during which an equipment has transmissions on a given channel without re-‐evaluaPng the availability of that channel, is defined as the Channel Occupancy Time. The Channel Occupancy Time shall be in the range 1 ms to 10 ms and the minimum Idle Period shall be at least 5 % of the Channel Occupancy Time used by the equipment for the current Fixed Frame Period.

4.  The energy detecPon threshold for the CCA shall be proporPonal to the maximum transmit power (PH) of the transmiaer: for a 23 dBm e.i.r.p. transmiaer the CCA threshold level (TL) shall be equal or lower than -‐73 dBm/MHz at the input to the receiver (assuming a 0 dBi receive antenna). For other transmit power levels, the CCA threshold level TL shall be calculated using the formula: TL = -‐73 dBm/MHz + 23 -‐ PH (assuming a 0 dBi receive antenna and PH specified in dBm e.i.r.p.).



Simulation of a realistic LAA HetNet

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LAA LTE-Advanced HetNet Simulation Scenario

Assumptions for Simulating a Realistic environment for LAA operation •  For providing a proper simulaPon scenario, the METIS 2020 Dense urban

informaPon society Test Case layout has been used •  A future urban segng where the need to handle high traffic volumes and high

experienced data rates are necessary in order to fulfil the foreseen requirements at a reasonable cost in these urban regions.

•  RealisPc urban environmental model considering buildings (with entrances), roads, park, bus stops, metro entrances, sidewalks and crossing lanes.

•  This scenario is defined as Madrid Grid environmental model •  This scenario provides a much more realisPc environment than the classical

synthePc scenarios used at the ITU-‐R M.2135 or 3GPP TR 36.872



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METIS 2020 Dense urban information society

Technology Baseline •  Network infrastructure with a three-‐sector macro staPon that is

complemented with twelve pico staPons as shown in the figure. Each pico-‐staPon can have a 802.11ac WiFi AP or a LAA cell.

Propagation •  ITU-‐R UMi, UMa, InH (below 6 GHz) •  Ray tracing based pathloss maps for macro and micro are available Traffic •  CombinaPon of bursty user and applicaPon driven traffic with video,

sensors and permanent traffic Mobility •  RealisPc movement of cars, buses and pedestrians provided via shared

mobility traces User Distribution •  Indoor: 75 %, On the move: 25 % (4.25% Walking, 2% standing at Bus

Stop or traffic lights, 6.25% In the Park, 12,5% In a vehicle)

Realistic urban environment setting with very high traffic volumes and high experienced data rates



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System-Level Configuration

Basic Assumptions •  2x10MHz (FDD) carrier in licensed band of 2GHz shared between Macro and Small Cells using

LTE-‐Advanced HetNet FeICIC/IC techniques (RP-‐ABS) •  Each Small Cell has a Primary Component Carrier (PCC) operaPng in the same licensed EARFCN

as the Macrocell, along with either WiFi or a Secondary Component carrier (SCC) operaPng at the 5GHz unlicensed band

•  The Small Cell support unlicensed carriers in the same band, either as a Wi-‐Fi AP or LTE-‐U SDL •  Wi-‐Fi uses 802.11ac with the LDPC coding and channel selecPon •  LTE-‐U and Wi-‐Fi support 2x2 MIMO with max rank 2 transmission •  Fast & Slow fading and realisPc rate control for Wi-‐Fi and LTE are modeled •  3 situaPons have been modelled: WiFi offloading Only, 50% of LAA Small Cells and LAA Small

Cells only. The users are using different technologies depending on the camped Small Cell •  ConfiguraPon and Tx power

Detailed configuration for the System-Level simulation



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System-Level Configuration Detailed configuration for the System-Level simulation

Parameter Value Licensed Carrier (PCC) 2GHz

TX power (Ptotal per carrier) 46dBm

Antenna Gain 14 dBi

Unlicensed Carriers (SCC) (LTE-‐U, Wi-‐Fi) 12x40 MHz @ 5 GHz

Unlicensed Channel SelecPon & LBT FuncPon Supported

DL Antenna ConfiguraPon 2x2

Noise Figure 9dB

TXOP(Wi-‐Fi) / TTI(LTE) duraPon 3ms / 1ms

AP/SC EIRP 27dBm

UE receiver MMSE-‐IRC



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Channel Modelling Residential

building

Public area

Lamp post

Bus Stop

Office Building

1. indoor 3. Macro O2I

4. Micro outdoor

5. Micro O2I

7. d2d



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Channel Models

BS-‐M

S

Urban Micro O2O PS#1

Urban Micro O2I PS#2

Urban Macro O2O PS#3

Urban Macro O2I PS#4

Indoor Office PS#7

D2D

Urban O2O (also V2V) PS#9

Urban O2I PS#10

Indoor Office PS#13

PS Model CorrelaCon length #1 ITU-‐R UMi 10

#2 ITU-‐R UMi O2I 10

#3 ITU-‐R UMa 50

#4 ITU-‐R UMa 50

#7 ITU-‐R InH 10

#9 ITU-‐R UMi * 10

#10 ITU-‐R UMi O2I * 10

#13 ITU-‐R InH * 10

Small scale parameters


Moving Carrier Networks to the Enterprise PS#3 – Urban Macro O2O Model The total transmission loss is expressed as the sum of

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Δhb

Δhm

b x

r

R

θ

α

l

hb hr

•  free space loss, •  diffracPon loss from rooyop to the street •  reducPon due to mulPple screen diffracPon past rows of buildings.

0( )

0fs rts msd rts msd

fs rts msd

L L L if L LL R

L if L L+ + + >⎧⎪

= ⎨ + ≤⎪⎩



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PS#4 – Urban Macro O2I Model The pathloss is calculated as

PL = PLout + PLthr +Plin where PLout uses the PS#3 model assuming that the building within which the user is disappears but Δhm equals the actual height above terrain of the user, and

where din is the distance form the wall, that is closest to the transmiaer, to the receiver

( ) ( )( )2109.82 5.98log 15 1 sinth cPL f θ= + + −

0.5in inPL d=

50 100 150 200

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40

60

80

100

120

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200

220

105

110

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120

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155

50 100 150 200

20

40

60

80

100

120

140

160

180

200

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105

110

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120

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130

135

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0

0.5

1

1.5

2

2.5

3

LTE HetNet + WiFi Only

50% LTE HetNet + WiFi 50% LTE HetNet

+LTE-U

100% LTE HetNet + LTE-U

LTE HetNet+WiFi Users

LTE HetNet+LTE-U Users

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Simulation Results Simulation Results for Median Users of the Madrid Grid Scenario with LAA & WiFi

Thro

ughp

ut M

ultip

lyin

g Fa

ctor

x2.4

x2.8

x1 x1



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Simulation Results Simulation Results for Cell Edge Users of the Madrid Grid Scenario with LAA & WiFi

0

0.5

1

1.5

2

2.5

3

3.5

LTE HetNet + WiFi Only

50% LTE HetNet + WiFi 50% LTE HetNet

+LTE-U

100% LTE HetNet + LTE-U

LTE HetNet+WiFi Users

LTE HetNet+LTE-U Users

Thro

ughp

ut M

ultip

lyin

g Fa

ctor

X2.5

X3.1

x1 x1



Conclusions on License-Assisted Access

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Conclusions License-Assisted Acess… A brave new world for LTE Small Cells! •  LTE License Assisted Access (LAA) allows co-‐existence with Wi-‐Fi without any specific coordinaPon, meePng

all the regulatory requirements for 5 GHz unlicensed band operaPon. This enables the deployment in the same scenarios as Wi-‐Fi networks, such as dense urban shopping malls and enterprise environment.

•  SimulaPons show that the interference effect on a Wi-‐Fi network from a LTE network is similar to the interference from another Wi-‐Fi network. In that sense, an LTE system with LBT is implemenPng the same techniques than other WiFi APs in the 5GHz band.

•  LTE networks provide higher capacity than a Wi-‐Fi network, having also a bigger coverage footprint. Thus, installing unlicensed band capable LTE Small Cells will lead to reduce the number of nodes in the network, reducing as well the operaPonal costs for the operator.

•  Especially in an environment where the traffic density is high, LAA is an aaracPve soluPon to tap the unused potenPal of the 5 GHz spectrum. With the ability to control the kinds of systems installed, such as in a corporate environment, finding fully empty channels from the 5 GHz band will be relaPvely easy, allowing LTE to reach its full performance.

•  LTE for unlicensed band will reuse the exisPng LTE core network and the exisPng LTE security and authenPcaPon framework.

•  The use of LTE unlicensed together with the licensed band operaPon brings a major capacity boost from the unlicensed band while sPll ensuring end user quality of service, regardless of the interference situaPon in the unlicensed band.


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Thanks!

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sistelbanda at mwc15

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