presented at: wireless @ virginia tech 2012 symposium & summer school on wireless communications

Presented at:

Wireless @ Virginia Tech2012 Symposium & Summer

School on Wireless Communications

May 31, 2012

Kenneth R. Baker, PhDUniversity of Colorado at BoulderInterdisciplinary Telecommunications Program

Wireless Antenna Distribution and LTE HetNets

CU-Boulder

2Ken Baker (http://morse.colorado.edu/~kkbaker/)May 31, 2012

Thesis

Indoor Distribution as path for LTE HetNets• An introduction to Indoor and Outdoor

Distributed Antenna Systems.

• State of the art today

• Describe how these systems form a migration path to hierarchical cell structures planned for 4G/LTE cellular networks.

• A review of LTE HCS related standards


DAS Systems

A Distributed Antenna System (DAS) is a network of spatially separated

antenna nodes connected to a common source via a transport medium that

provides wireless service within a geographic area or structure (the DAS

Forum)

Provide better coverage in environments like:

• Outdoor: Highways, Downtowns, Subways, Tunnels, University Campuses

• Indoor: Corporate Offices, Stadiums, Shopping Complexes, Airports,

Convention Centers, Hospitals, Hotels etc.

60% of voice traffic and 90% of data traffic from indoors. (ABI Research)

DAS systems with overall market value of $5.5 billion comprises 96% of

indoor systems (ABI Research)

DAS Concept was introduced by Saleh etal in 1987 as a solution for better indoor

coverage using leaky coax cable to simulcast the RF signal. (A.A.M. Saleh, A.J. Rustako, and

R.S. Roman, “Distributed antennas for indoor radio communications,” IEEE Trans. Commn., vol. 35, pp. 1245–1251,

Dec. 1987)

3


Why DAS is needed?

Indoor:

• Poor coverage in basements, higher floors (above 25 floors), elevators, inner rooms (due to wall attenuations).

• Large reflections from walls, roofs, tinted glass windows.

Outdoor:

• Other buildings block the coverage in dense areas like downtowns.

• To provide coverage to long Highways/tunnels.


DAS Components

Donor Unit

• BSS, External Antennas

Interconnection Network

• Active & Passive Head

Ends and Distribution

Units

• Coax/Fiber/Repeaters

• Star or Cascade

Connections

Remote Unit

• RAUs & multi/wide band

antennasImage source: http://www.accu-tech.com/das/

5

http://www.accu-tech.com/das/


Example Airport DAS


Example: Outdoor DAS

Outdoor DAS serving a University Campus

• Neutral Host System• Two Cellular

Operators share the transport infrastructure

• They also share antennas


Interconnection Media

Coax

• Cables: 50 ohm (RG174, RG58, LMR240, Standard Heliax etc)

• Connectors: SMA, BNC, TNC, N, 7/16 etc.

• Other Components: Couplers, Splitters, Bi-Directional Amplifiers

Optic Fiber

• Cables: Single Mode, Multimode, Step Index, Graded Index

• Connectors: FC,SC, ST, LC or MTRJ

• Other Components: Splicers, Splitters, Attenuators, WDM multiplexers, Laser Diodes

Over the Air (RF)

• Repeaters or Bi-Directional Amplifiers (BDA),

• Antennas: Isotropic, Dipole, Yagi, Panel, Leaky Coax

Hybrid Fiber Cable (HFC): CATV Networks


Benefits of DAS (Chow, et al. 1994)

RADIO RADIO

Single Antenna System DAS

• Consider single slope propagation model:

d

• PT = Transmitted Power• PR = Received Power• C = Path loss at reference

distance• γ = Path loss exponent

• d = radius of the macro-cell• A = area of the macro-cell = πd2


Benefits of DAS (contd.)

Improvement in Coverage:• Area of coverage of single antenna is given by:

• Assuming transmitted power is equally divided between N antennas of the DAS, area covered by each individual antenna is given by:

= = …. =

• Therefore, total area:

• Thus, coverage is increased by a factor of:


Benefits of DAS (contd.)

Reduction in Transmit Power (Forward Link):For single antenna system: Assuming transmitted power is equally divided between N antennas of the DAS:

• Therefore, total area:

• Thus, transmitted power is reduced by a factor of:

• On Reverse Link, assuming that path loss is reciprocal, mobiles have to transmit only 1/N of the base station to communicate to a single DAS antenna. Thus power is reduced by a factor of:


Q. What’s the vision? A. Small Cells

Heterogeneous Networks• a.k.a. Multi-Tier Networks

• Better Coverage, More Capacity

Incorporated in 3GPP LTE Standards• Includes New Network Elements

• Includes Interference and Mobility Management Techniques


Indoor Distribution Today

• Outdoor DAS

• Indoor DAS

• Neutral Host vs. Single Carrier

• Passive vs. Active

The first steps to HetNets …• WIFI Off-load in Stadiums

• Femtocells (Home Node-B’s)



• Outdoor DAS

• Indoor DAS






Sports Stadium as a Specific Example


Stadium Traffic Facts (with 60-90K Fans)

Traffic Statistics from a Sports Stadium

Example Traffic profiling look at data services usage during a game

42%

24%

15%

12%6% 2%

Streaming Web browsing

App Store Access Smartphone Apps

Email Other

Voice calls: 30-60K

SMS: 200-600K

Data Volume: 4-9 GB

Data Calls: 300K-1M

Numbers are cumulative over the duration of a game

Data services used during events

Data services on Smartphones are driving the traffic today

Background traffic from applications like Twitter, Email, etc. is a significant contributor


Stadium Traffic Will Continue to Increase

It is expected that mobile video will account for the majority of data growth


Stadium Antennas


Bowl Design and Some Statistics

Stadium No. WiFi APs No. SectorsNo. 1.25 MHz

Carriers (Voice/Data)

U. Michigan ~ 15 5/7

Met Life ~ 12 8/9

Lucas Field 1020 15 5/9

Mile High 500 12 6/8


Super Bowl Data Usage

(One of three operators)


Offload will get easier: “Hot Spot 2.0”

Three components:1. IEEE 802.11u

• Pre-association

• published on February 25, 2011

2. Wi-Fi Protected Access 2 (WPA2)-Enterprise3. Extensible Authentication Protocol (EAP)

• EAP-SIM (GSM)

• EAP-AKA (UMTS)

Mobility Services Advertisement Protocol (MSAP)• transported via IEEE 802.11u Generic Advertisement

Service (GAS)

See also: IEEE 802.21• enables seamless handover between networks



• Outdoor DAS

• Indoor DAS






Femtocell Overview

Femtocell• Ethernet Backhaul

• In-home base station

• Enterprise Base Station

Minimal Customer Requirements: • Any wireless handset or data device

• A broadband connection and router

Femtocell

ISP

xDSL/Cable Modem

Core Network

GPS

3 Satellites


Example: Dual-Mode EvDO product

Bottom Line: It’s a Plug and Play Cellular Base Station


Femtocell Interference

Femtocells as two tier network• Open: Any cell phone can attach

• Closed: Only specified cell phones can attachBS of

Macro cell

Femto Cell Femto Cell

Femto Cell Femto Cell

Femto BS

Legend

Connection to BS

Interference from Macro to Femto and Femto to

Macro

Interference form Femto to Femto

User of Macro cell

Femto BS

Femto BS

Femto BS

User of Femto cell

Downlink Femtocell Interference


Femtocell Summary

3G Femtocells Today:• Can hand out to the macro layer

• Cannot hand-in from the macro layer

4G (LTE) Femtocells:• Will enable both hand-in and hand-out between the

femto layer and the macro

• Femto to Femto handover should also be possible.


Looking ahead to LTE

• Carrier Aggregation

• Higher Order Modulation

• 4G

• MIMO

IEEE 802.16Fig. after Nokia Siemens


Why LTE?


LTE, LTE-A, and 4G


LTE Network

MME: Mobility Management Entity• Manages mobility, UE Identity and

Security Parameters

S-GW: Serving Gateway• Evolved Packet Core Interface to E-

UTRAN

P-GW: Packet Gateway• Evolved Packet Core Interface to

Packet Data Network

eNB: Evolved Node B• Performs all Radio Interface Related

Functions

Interfaces• X2: between eNBs

• S1: between eNB and MME/S-GW


Network Elements

Element Backhaul Coverage Antennas

Macro-Cell S1* ≥ 500mAt or above rooftop level

Pico-Cell S1*≤ 500m, Indoors

Rooftop or below

Femtocell IP Indoors Tabletop

Relay LTE≤ 500m, Indoors

Below rooftop

*S1-C: Stream Control Transmission Protocol / IP (SCTP/IP) stack*S1_U: GSRP Tunneling Protocol/UDP5/IP stack


Pico-Cells … Heterogeneous Networks

Increasing data rate requirements• Need better SNR

Increasing capacity requirements• Need more cells

Ergo: Put cells where the users are• Trend is to complement

macro network with picocells

• Possible with LTE Rel.8

• Enhancements with Rel. 11

Picocells• S1 interface for backhaul,

not ethernet

Picocells exist today in 3G networks


Relay Nodes

Donor eNB uses LTE as backhaulEither in-band or out-of-band

RNB

RUEMUE(Donor) eNB

Backhaul Link(Un)

Relay Node Access Link(Uu)

Macro UE Relay UE

Relay Cell

Donor Cell

(Uu)


Example Application: Public Safety

See: Order and Fourth Further Notice of Proposed Rule Making, FCC11-6, “In the Matterof Service Rules for the 698-746, 747-762 and 777-792 MHz Bands; Implementing aNationwide, Broadband, Interoperable Public Safety Network in the 700 MHz Band;Amendment of Part 90 of the Commission’s Rules,” January 25, 2011


Outage Probability as a Function of No. of Relays

Ref. Tin-Ei Wang, unpublished work


LTE Heterogeneous Networks

Network Elements• Relays

• Pico Cells

• Femtocells (Home Node B)

Need tight coordination for Handover and Interference management

• Negative Impact at small cell edges

• Small cells need handover management


LTE Heterogeneous Networks

LTE Network Solutions:• Soft Cell

• Enhanced Inter Cell Interference Coordination (eICIC)

• CoMP

• Self-Organizing Networks (SON)

• Dynamic Load Balancing

• Carrier Aggregation


Enhanced Local Access: Soft Cell

In LTE Advanced:Pico does not create a new cell but is an extension of an overlaid macrocell• Macro – basic coverage (system info, data, control

• Pico – enhanced capacity and data rates

Consider this a macro assisted pico layer


Inter-cell Interference Coordination (ICIC)

Release 8 (LTE)• Interference mitigation by coordinating DL control and

data channels

• lowering the power of a part of the sub-channels in the frequency domain

Release 10 (LTE-A)• coordinate blanking of sub-frames in the time domain

in the macro cell

• Only legacy broadcast signals and channels are transmitted to support legacy Rel 8 UEs


Originalreuse

ICIC Example

ICIC Rel. 8 SINR Distribution Example

-5 dB 20 dB


CoMP

Coordinated Multipoint TransmissionIncreases Data Rate

• coordinating and combining signals from multiple antennas


Rel. 10/11 CoMP

Downlink• joint processing (JP)

• coordinated scheduling (CS)

• coordinated beamforming (CB)

Uplink• joint reception (JR)

• Coordinated scheduling (CS)


Self-Optimizing Networks (SON)

“Self-Optimizing and Self-Configuring”• Needed to manage tiersIdentified Use Cases:• Energy Savings

• Interference Reduction

• Automated Configuration of Physical Cell Identity

• Mobility robustness optimization

• Mobility Load balancing optimization

• RACH Optimization

• Automatic Neighbor Relation Function

• Inter-cell Interference Coordination

3GPP TR 36.902 V9.3.1 (2011-03)

Note: HCS is not mentioned specifically in 36.902


Dynamic Load Balancing

• Between tiers• Listed as a function of the X2 interface:“This function allows exchanging overload and traffic load information between eNBs, such that the eNBs can control the traffic load appropriately. This information may be spontaneously sent to selected neighbour eNBs, or reported as configured by a neighbour eNB.”

• 3GPP TS 36.420 V10.2.0 (2011-09)


Carrier Aggregation

Between bandsBetween tiers


DAS or Femto?

1. ABIresearch2. IBW Solution and Capacity Offload in 3G and LTE (IBW symposium)

Summary of solution comparison

Metric Femto DAS

Equipment + Labor Costs1 $.05-$.1 per sq. foot

Active DAS - $0.25 - $ 0.5 per sq. foot.

FlexibilityHigh, technology, coverage and capacity can be added as needed

Medium, Coverage should be planned at onceCapacity can be modified through sectorization plan Adding technology depends on selected DAS

Multi-operator support2 Requires multiple Femtos Possible

Deployment ModelPlug and play solution, with limited setting for Enterprise Femto

Requires planning and extensive deployment support (installation, commissioning….)


One Slide About Backhaul

• The backhaul network needs to be able to support the wireless throughput.

• Backhaul is one of the major expenses for wireless network operators

Max. 802.11b


Motivations for HetNets

Better performance:1. Better coverage

• Chow, et. al, 1994

2. Better SNR• Madhusudhanan, et. al, 2011

Madhusudhanan, P.; Restrepo, J.G.; Youjian Liu; Brown, T.X.;Baker, K.R.; , "Multi-Tier Network Performance Analysis Using a Shotgun Cellular System," Global Telecommunications Conference(GLOBECOM 2011), 2011 IEEE , vol., no., pp.1-6, 5-9 Dec. 2011.


Challenges in Studying a Multi-tier Network

Simulation study of the entire system is computationally infeasible.Ideal hexagonal grid model is not a good model anymore.Certain entities of the network are essentially random in nature.

e.g. the location of the femtocell BSs.


Motivations for considering a Shotgun Cellular System Inspired Model

Shotgun Cellular System (SCS): [Brown 2000] The cellular system where the BS placement is according to a 2-D homogeneous Poisson point process.SCS is a good model the femtocell BSs in the network.The SCS is a surprisingly good model for the macrocell network:

SCS provides a natural lower bound to the cellular performance.

[Brown 2000] The SCS model provides a fair idea about the actual macrocell network. In the strong shadow fading regime, the downlink performance in

an SCS converges to ideal hexagonal grid model. In the normal shadow fading regime, the gap between the

downlink performance in an SCS and in an ideal hexagonal grid model is small.


System Model

Multi-tier network with tiers of heterogeneous networks.Each tier is an SCS independent of the other tiers.

BS density: .

BS transmission power:

SINR threshold: (same for all tiers)Received power at a distance from a BS of the tier is

Background noise -

Shadow fading factor Path-loss exponent


Performance Metric

Carrier-to-Interference-ratio at the mobile user located at origin

Carrier-to-Interference-plus-noise-ratio Problem:

For the multi-tier network, Characterize the success probabilities: and

(or) the outage probabilities: and .

‘s’ the tier corresponding to the strongest signal at the MS Total interference

power due to the rest of the BSs in the multi-tier network.


Approach

Step1

• , 1-tier network, w/o shadow fading.• , 1-tier network, w/o shadow fading.

Step 2

• 1-tier network, arbitrary fading distribution. • 1-tier network, arbitrary fading distribution.

Step 3

• multi-tier network, arbitrary fading distribution. • multi-tier network, arbitrary fading distribution.


Multi-tier Networks

Having thoroughly studied the single-tier network, we move on to

the multi-tier network.

Multi-tier network with tiers of independent SCSs, represented as

is the number of tiers. is the BS density of the tiers.

is the path-loss exponent.

is the BS transmission powers for the tiers.

is the noise power.

is the shadow fading factor with arbitrary distribution.

ASSUMPTION: The SINR threshold is the same for all tiers.

Theorem: The multi-tier network

is equivalent to a single-tier network where Equivalent BS density

Transmission power of each BS is an i.i.d. random variable such that


Multi-tier Networks: Important Implications

Inclusion of the additional tiers of wireless network: Does not affect the success probability.Improves the success probability when

There is no shadow fading.

The arbitrary shadow fading distribution is such that For example, log-normal shadow fading factors with 0 mean and standard deviation satisfy the above condition.


Madhusudhanan, et. al Conclusions

We have studied the and success probability of a multi-tier network by systematically reducing the network to equivalent networks and finally to a single-tier network that we understand well.As a result, for a multi-tier network where the SINR thresholds of all the tiers are the same, we have

Derived the semi-analytical expression for the and success probabilities for SINR threshold .

Obtained a simple closed form expression for success probability for SINR threshold

The above result matches the results obtained by [Dhillon, Ganti, Baccelli, Andrews, 2011] and [Mukherjee, 2011] who approached the problem in different ways with results restricted only to Rayleigh fading distributions.

Further, we have derived an approximation for the success probability and show the approximation is tight.

All the results derived in the paper hold for arbitrary fading distribution.


The Path From Today to HetNet

Indoor DASOutdoor DASFemtocellsPicocells

Soft CellsBetter FemtocellsIndoor / IP Connected

HetNetsSONICICCoMPRelays

3G

…

L

TE

...

LTE-

A


If I were a cellular network operator …

All Technology Decisions are Business drivenFuture will be built upon combining networks1) Entrenched equipment and technology will

drive future deployments1) Capital investment to be fully effectuated.

2) Engineering staff that knows the current technology cannot be redirected instantaneously

2) Leveraging technology to mitigate expenses1) WiFi off-load


Research Issues

Research Issues• Backhaul

• Simulation of Indoor and Outdoor Network Interaction

• Improving Small Cell Handover and Control

• Managing Handover Between Tiers

• Managing Interference Between Tiers

• Taking SON Concepts Across Tiers

• Traffic steering– RAT handovers– layer handovers– resource availability


Bibliography (1/3)

P. Chow, A. Karim, V. Fung, and C. Dietrich. Performance advantages of distributed antennas in indoor wireless communication systems. In IEEE Proceedings of Vehicular Technology Conference, 1994, volume 3, pages 1522 – 1526, June 1994. Timothy X Brown, “Cellular performance bounds via shotgun cellular systems”, IEEE Journal on Selected Areas in Communications, vol. 18, no. 11, pp. 2443-2455, Nov 2000. H. S. Dhillon, R. K. Ganti, F. Baccelli, J. G. Andrews, “Modeling and analysis of K-tier downlink heterogeneous networks”, IEEE Journal on Selected Areas in Communications, to appear in Apr 2012.S. Mukherjee, “Downlink SINR distribution in a heterogeneous cellular wireless network with max-SINR connectivity”, Allerton Conference on Communication, Control, and Computing, Sep 2011.Madhusudhanan, P.; Restrepo, J.G.; Youjian Liu; Brown, T.X.; Baker, K.R.; , "Multi-Tier Network Performance Analysis Using a Shotgun Cellular System," Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE , vol., no., pp.1-6, 5-9 Dec. 2011.


Bibliography (2/3)

Blaze Vincent, Reverse Link Analysis and Modeling of CDMA based Distributed Antenna Systems. Thesis (M.S.)--University of Colorado, Dec. 2011. See also references therein.Tin-Ei Wang, CU Boulder, unpublished work, 2012Ching-Pu Wu, K. Baker, “Comparison of LTE Performance Indicators and Throughput in Indoor and Outdoor Scenarios at 700 MHz,” to be published: Proc. IEEE 76th Vehicular Technology Conference, VTC2012-Fall, Québec City, Sept. 2012.Christophe Chevalier, “Expanding 3G Coverage: Indoor and High Capacity Venues,” Presentation material, Qualcomm Inc.Jon M. Peha, et. al, “The Public Safety Nationwide Interoperable Broadband Network: A New Model for Capacity, Performance and Cost,” FCC White Paper: DOC-298799A1, June 2010. http://transition.fcc.gov/pshs/docs/releases/DOC-298799A1.pdfJames Arden Barnett, Jr., Jennifer A. Manner, FCC Public Safety and Homeland Security Bureau, Presentation to: 2010 UASI National Conference, New Orleans, LA, June 22, 2010S. Kishore, L. Greenstein, H. Poor, and S. Schwartz, “Uplink user capacity in a CDMA macrocell with a hotspot microcell: exact and approximate analyses,” IEEE Trans. Wireless Commun., vol. 2, no. 2, pp. 364–374, Mar. 2003.——, “Uplink user capacity in a multicell CDMA system with hotspot microcells,” IEEE Trans. Wireless Commun., vol. 5, no. 6, pp. 1333–1342, June 2006.


Bibliography (3/3)

S. Kishore, L. J. Greenstein, H. V. Poor, and S. C. Schwartz, “Uplink user capacity in a CDMA system with hotspot microcells: effects of finite transmit power and dispersion,” IEEE Trans. Wireless Com., vol. 5, no. 2, pp. 417–426, Feb. 2006.Claussen, H., "Performance of Macro- and Co-Channel Femtocells in a Hierarchical Cell Structure," Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on, pp.1-5, 3-7 Sept. 2007.Kaneko, M.; Popovski, P.; , "Radio Resource Allocation Algorithm for Relay-Aided Cellular OFDMA System," Communications, 2007. ICC '07. IEEE International Conference on , vol., no., pp.4831-4836, 24-28 June 2007.Chandrasekhar, V.; Andrews, J.; "Uplink capacity and interference avoidance for two-tier femtocell networks," Wireless Communications, IEEE Transactions on, vol.8, no.7, pp.3498-3509, July 2009.“The Future of Hotspots: Making Wi-Fi as Secure and Easy to Use as Cellular,” Cisco Whitepaper, http://www.cisco.com/en/US/solutions/collateral/ns341/ns524/ns673/white_paper_c11-649337.html

presented at: wireless @ virginia tech 2012 symposium & summer school on wireless communications

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better indoor coverage

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indoor radio communications

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