ece 4371, fall, 2013 introduction to telecommunication engineering/telecommunication laboratory zhu...

ECE 4371, Fall, 2013

Introduction to Telecommunication Engineering/Telecommunication Laboratory

Zhu Han

Department of Electrical and Computer Engineering

Class 24

Nov. 17th, 2014

OutlineOutline Device-to-Device Communications

– Overview

– Key Technologies

– Variety of Applications

Femtocells– Overview

– Standardization & Models

– Key Challenges

2015200520001995 2010

Standardization Facilitates Technology Standardization Facilitates Technology Evolution Evolution

Each new evolution builds on the established market of the previous

Backwards-compatible evolution

But larger technology steps require revolutions:

Frequency

Tim

e

Frequency

Tim

e

Frequency

Tim

e

From TDMA:

Frequency

Tim

e

Frequency

Tim

e

Frequency

Tim

e

to CDMA: to OFDMA:

Future Wireless ChallengesFuture Wireless Challenges Mobile Internet and Smart Phones

1. Bandwidth and data traffic boost (Cisco) Data traffic increases 2 times/per year, 1000 times by 2020

Wireless network cannot support that!

2. Information aggregate to hotspot and local area 70% in office and hotspot, over 90% in future

Hotspot QoS cannot be guaranteed!

Bandwidth demand over 1200MHz ， ITU assignment less than 600MHz

Bandwidth demand over 1200MHz ， ITU assignment less than 600MHz

Possible SolutionsPossible Solutions

Number of UE

Cell Capacity

Add fixed AP

Sum rates

P. Gupta and P. Kumar, “The capacity of wireless networks,” IEEE Transactions on Information Theory, vol. 46, no. 2, pp. 388-404, Mar. 2000.

Ad-hoc optimal rate

By “Shannon Theory” ， network capacity relies on bandwidth and APs

Current ： Add fixed APs

By “Shannon Theory” ， network capacity relies on bandwidth and APs

Current ： Add fixed APs

Combine Cellular and Ad-hoc

Combine Cellular and Ad-hoc

Definition and BenefitsDefinition and Benefits

Definition of Device-to-Device (D2D) Communications– D2D communications commonly refer to the technologies that

enable devices to communicate directly without an infrastructure of access points or base stations.

eNBeNB

eNBeNB

① Increase network capacity②Extend coverage③Offload data④ Improve energy efficiency⑤Create new applications

① Increase network capacity②Extend coverage③Offload data④ Improve energy efficiency⑤Create new applications

Deployment RoadmapDeployment Roadmap

Cellular unaware D2D Cellular network is not aware of

D2D 2 RATs, e.g. 3G + Wifi No cooperation between cellular

and D2D

Cellular aware D2D• Cellular network is aware of

D2D • 2 RATs, e.g. LTE + Wifi• Kind of cooperation between

cellular and D2D

Cellular controlled D2D• Cellular network fully controls

D2D• A single RAT, e.g. LTE-A• D2D is a part of cellular

communication

RAT1

RAT2

UE1UE2

flow1

flow2

Scenario A

RAT1

RAT2

UE1UE2

flow1

flow2

Scenario B

RAT1

UE1UE2

flow1

flow2

Scenario C

D2D Benefits Scenario A Scenario B Scenario C• Traffic offload• Unified & Simplified comm.• User experience improvement• Cellular capacity enhancement

RATs converging

Scenario A: Cellular UnawareScenario A: Cellular Unaware

App

3G 3G

Wifi Wifi

Example structure:

App

New App

• Typical applications– Data synchronization, Social

networking, Mobile advertising, Automation control, etc.

BSBS

BSBS

social networksocial network

Data synchronizationData synchronization

Mobile advertisingMobile advertising

• Key technology– D2D opportunity identification &

neighbor discovery– Flow distribution among different RATs

• Benefits/Gains– Offload cellular traffic– Unified & Simplified communications

• Node functionality– User device: application distribute

flows among different RATs– No impact on RAN & CN nodes

Scenario B: Cellular awareScenario B: Cellular aware

App LTE LTE

Wifi Wifi

Example structure:

App

Core Network

Core NetworkNew coordination

function/services

• Key technology– D2D opportunity identification – D2D coordination

• Benefits/Gains– Better user experience, e.g. QoS, mobility, etc.– Core network traffic offload – Unified & Simplified communications

• Node functionality– User device: new D2D coordination

function– RAN node: No impact– CN node: new D2D coordination function

• Typical applications– Cellular P2P: A, B, C receive data from CN,

and share the non-achieved data among themselves

NBNB

NBNB

AA BB CC

Core Network

Core Network

CN nodeCN node

Scenario C: Cellular controlledScenario C: Cellular controlled

App

Cellular

Example structure:

App

Core Network

Core Network

New Cellular D2D interface

New D2D control function/services

New D2D control function/services

• Typical applications– Cooperative transmission: Mobiles interact to jointly transmit

and/or receive information in cellular environments.

• Node functionality– User device: New D2D control &

interface– RAN nodes: New D2D control function– CN nodes: New D2D control function

• Benefits/Gains– Cellular capacity improvement– Better QoS, security & mobility support– Core network traffic offload – Unified & Simplified communications

• Key technology– D2D control – D2D air interface design– Cooperative transmission

eNBeNB

Key TechnologiesKey Technologies

Access Methods

Mode Selection

Neighbor Discovery

Spectrum Sharing

Interference Analysis

Power Control

MIMO Beamforming

Signal and Interference Model

Radio Resource Management

Operation Protocol

Access MethodsAccess Methods

The D2D networks can be configured in three ways to allow or restrict their usage by certain users:– Self-organized:

D2D users themselves realizes the communications in a self-organizing way by finding the empty spectrum hole.

– Network Assisted : The D2D users operates in a self-organized way, and

exchanges with cellular system limited controlling information for resource management.

cellular network can obtain the status of D2D communications for better control purposes.

– Network Controlled: the base station and the core network control the

communication signaling setup and the there after resource allocation for both cellular and D2D users.

Mode SelectionMode Selection

Mode selection criteria– Cellular Mode: The mobile works in a traditional cellular way

relaying data by a BS.

– D2D Mode: The mobiles exchanges information directly.

– Mode Adaptation: The mobiles can select the right mode for communication according to the predefined criterions.

Typically, all the UEs are implemented with two modes, i.e. cellular mode, and D2D mode, and can adaptively utilize the proper way for transmission.

Device Discovery and Synchronization (1)Device Discovery and Synchronization (1)

For D2D communications, network time synchronization is necessary – between cellular networks and D2D users

– among D2D users themselves

– to minimize multi-access interference, as well as for the proper performance of handoffs.

The fundamental problem of device discovery is that – the two peer devices have to meet in space, time, and frequency.

Without any coordination

– this can be made possible via some randomized procedure and one of the peers assuming the responsibility of sending the beacon.

The approaches in IEEE 802.11 can be readily adopted to enable the synchronization among mobiles.


Traditional peer discovery: – In both the ad hoc and the cellular cases, the discovery is made

possible by one party transmitting a known synchronization or reference signal sequence (the beacon).

In the case of network assisted D2D, the network can mediate in the discovery process by – recognizing D2D candidates

– coordinating the time and frequency allocations for sending/scanning for beacons

– making the pairing process more energy efficient and less time consuming


Typical procedure– Use direct signal to discover peer

– Set transmission power so that UEs in coverage can hear the broadcast.

– Whoever receives the broadcast confirm that with the eNodeB

From the aspect that there is response from discovering UE or not, two discovery approaches could be classified: – Beacon-based discovery

– Request-based discovery

According to whether there is network participation for identification detection, discovery procedure could be categorized into: – Network-assistance detection

– Non-Network-assistance detection

Spectrum SharingSpectrum Sharing

Spectrum sharing as an overlay: – The D2D users occupies the vacant cellular spectrum for

communication.

– completely eliminates cross-layer interference is to divide the licensed spectrum into two parts (orthogonal channel assignment).

– a fraction of the subchannels would be used by the cellular users while another fraction would be used by the D2D networks.

– Although optimal from a cross-layer interference standpoint, this approach is inefficient in terms of spectrum reuse.

Spectrum sharing as an underlay: – allows multiple D2D users to work as an underlay with cellular users,

and thus to improve the spectrum efficiency.

– co-channel assignment of the cellular and D2D users seems more efficient and profitable for operators, although far more intricate from the technical point of view.

Interference AnalysisInterference Analysis

Considering that these networks define two separate layers, interference can be classified as follows:– Cross-layer: This refers to situations in which the aggressor (e.g., a D2D

user) and the victim (e.g., a cellular user) of interference belong to different network layers.

– Co-layer: In this case the aggressor (e.g., a D2D user) and the victim (e.g., a neighboring D2D user) belong to the same network layer.

Combating the interference– Transmitter: Frequency, time, space, power etc, allocation

– Receiver: Signal processing for interference cancelation

Power ControlPower Control

Power control can be performed by two approaches:– Self-organized power control:

the D2D users make power changes in a self-organized way according to a predefined SINR threshold in order to meet the QoS, and meanwhile not affect the cellular users.

– Network managed power control: Both cellular and D2D users adaptively adjust the transmit power

according to the SINR report. Typically, the D2D users can control the transmit power at first, and

then the cellular users make change afterward. This iterative process terminates until all the users meet their SINR

requirements.

The first method is not going to change the behaviors of cellular users, such that D2D users are invisibly treated.

The second method allows all the users to adjust the transmit power, but requires a certain amount of signaling overhead

MIMO and Virtual MIMOMIMO and Virtual MIMO

By performing transmit or receive beamforming ,the use of multiple antennas at the eNB and the UE can – reduce the co-channel interference to other users

– improve spectrum efficiency

The methods can be summarized as follows:– eNB beamforming: This sort of multi-user MIMO like approach

can be performed at the cellular downlink to reduce the interference to D2D users, such that D2D communications can be allowed.

– D2D beamforming: This avoids the D2D transmission to disturb the cellular and other D2D users.

– Virtual D2D beamforming: This borrows the ideas of cooperative mobiles, such that multiple D2D users collaboratively form the beamforming matrices to improve the system performance.

Radio Resource Management (1)Radio Resource Management (1)

With regards to the underlay approach, to mitigate cross- and co-layer interference, there would be a central entity in charge of intelligently telling each cell which subchannels to use.

This entity would need to collect information from the D2D users, and use it to find an optimal or a good solution within a short period of time.

The presence of large number of D2D users, and the allowance of multiple D2D users coexistence with cellular user makes the optimization problem too complex.

Latency issues arise when trying to facilitate the D2D communication with the central subchannels broker throughout the backhaul.

A distributed approach to mitigate cross- and co-layer interference, where the D2D users can manage their own subchannels, is thus more suitable in this case (i.e., self-organization).

Radio Resource Management (2)Radio Resource Management (2)

In a non-cooperative solution, i.e. self-organized approach– each D2D user would plan its subchannels so as to maximize the

throughput and QoS for its users.

– this would be done independent of the effects its allocation that might cause to co-channel D2D and cellular users.

In a cooperative approach, i.e. network assisted approach– the D2D users can gather partial information about subcarrier

usage situation.

– may perform its allocation taking into account the effect it would cause to its co-channel neighbors.

– the average cellular and D2D users' throughput and QoS, as well as their global performance can be locally optimized.


– Overview




– History


– Key Challenges

Application ScenariosApplication Scenarios

There are two important services of ProSe. – The first one is proximity discovery with which users can

discovery each other in proximity.

– The second is direct communication with which users can communicate with each other in proximity.

There is no causality between proximity discovery and direct communication. – Proximity discovery can be stand alone services to users and

doesn’t always trigger direct communication.

– Users may initiate direct communication directly without proximity discovery.

– However, users can use direct communication easily when they know the proximity information.

Application ScenariosApplication Scenarios D2D scenarios include proximity discovery and direct

communication.

Application Scenarios (1)Application Scenarios (1)

Social Networking– Without specific target users:

ProSe applications discovery all the users in proximity and network helps to choose those of users’ interest.

– With specific target users: ProSe applications only discover the specific users, usually the friends of users and show the proximity information on the right of the target user.


Local Advertisement– The shops will

automatically distribute the advertisement to the passagers nearby.

– Applications in users’ terminal discover the advertisers automatically and receive the information from them, including introduction, menus, coupons, etc.


Location Enhancement – The D2D terminals

receive the real-time parking space information that helps finding one’s parking space easily.

– It can provide more information than a GPS based application by D2D.


Distance Based Applications– Members of a team or

group can obtain the sphere of activities for each other by D2D distance monitoring when touring, keeping a safe movement range to prevent occurring accident.

Application Scenarios (5)Application Scenarios (5) Enhance Network Capability (Offloading)

– D2D applications can provide coverage enhancement without increasing infrastructure cost, capacity enhancement by multiplexing D2D and cellular spectrum and user experience enhancement of link robustness and throughput.

e.g.•Concert Networks•Stadium Networks


Disaster and Public Safety – In case of disastrous

simulation, where the fixed infrastructures, such as BSs, are in failure, mobiles not in the coverage can possibly reach the BS with the aid of mobiles in the coverage area.

– This is similar to multi-hop relaying networks.

D2D

MME S-GW

Emergency Communications①Mobile Adhoc networks②Active BS is the final destination


– Overview




– History


– Key Challenges

Overview of FemtocellsOverview of Femtocells

Femtocells are low-power wireless access points that operate in licensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections.


Why femtocells is needed?– Exponentially increasing wireless data traffic.


Why femtocells is needed?– Data offload is real and measurable.


The key attributes of femtocells:– Mature mobile technology

– Operating in licensed spectrum

– Generating coverage and capacity

– Using internet-grade backhaul

– At competitive prices

– Fully managed by licensed operators

Question– What is the difference from WIFI: some control

– What is different from microcell: backhaul

A Brief History of FemtocellsA Brief History of Femtocells Early Origins

– 1980s: “Small cells” Cellular repeaters or “boosters”

– 1990s: A precursor to cellular picocells An indoor femtocell-like solution (Southwest Bell and

Panasonic)

The birth of modern femtocells– March, 1999

Alcatel announced that they would bring to market a GSM home base station.

– 2002 Motorola engineers in Swindon claimed to have built the

first complete 3G home base station

A Brief History of FemtocellsA Brief History of Femtocells

Development of modern femtocells– 2003

Chipset design company – picoChip – was demonstrating lower-cost 3G chipsets.

– Mid-2004 Ubiquisys and 3Way networks were formed in the UK

to develop their own 3G cellular home base stations.– 2007

Products were demonstrated at the 3GSM conference. The Femto Forum (www.femtoforum.org) was set up.

– August, 2008 Commercial service was launched first by Sprint in the

USA with their Airave CDMA offering.


Femtocell ecosystem


Femtocell products


Femtocell service deployments and commitments


– Overview





– Key Challenges

Femtocell StandardizationFemtocell Standardization Mission:

– The mission is to advance the development and adoption of small cells for the provision of high-quality 2G/3G/4G coverage and services within residential, enterprise, public and rural access markets.

3G and 4G

Femtocell StandardizationFemtocell Standardization

3GPP standards for UMTS femtocells– Interface between the femtocell (Home Node B - HNB) and the

femto network gateway (HNB Gateway, HNB-GW)

– Security protocols to authenticate femtocell (HNBs) and secure communications across the un-trusted Internet

– Management protocols for “touch free” Operations, Administration, and Management (OA&M) of femtocells (HNB devices)


3GPP2 standards for CDMA femtocells– SIP/IMS-based 1x circuit services architecture

– Packet data architecture

– Security framework

– Enhancements to mobile devices to make them more femto-aware

– Foundations of femtozone services (Local IP Access and Remote IP Access)

– Femtocell management architecture


The need for LTE femtocells– There is a limit to how many outdoor cell sites can be built;

– The spectrum available to any particular operator is limited;

– Cell site backhaul is expensive.

LTE is the first cellular technology which will be able to take full advantage of femtocell.– The large quantity of dynamically allocated time and frequency

slots.


LTE architecture with deployed HeNB GW

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

S1 S

1

X2

X2X2

E-UTRAN

HeNB HeNB

HeNB GW

S1 S1

S1 S

1

HeNB

S1S1

Femtocell ModelsFemtocell Models

Traditional hexagonal grid model– Dozens of systems parameters can be modeled;

– Other-cell interference can be modeled simply;

– The results is sufficiently accurate to enable the evaluation of new proposed techniques.

Multi-tiered cellular model– Macrocells

– Picocells

– Femtocells

– Possibly further radiating elements


Link level modeling– Channel status depend on a large number of factors

The propagation environment Range & distance Carrier frequency Antenna placement Antenna type


Femtocell access control model– Closed subscriber group (CSG)

Only pre-registered mobile users can use a certain femtocell.

– Open subscriber group (OSG) Any mobile can use any femtocell or at least one that

is “open”.


Femtocell network model– Keep the grid model for macro base stations, drop femtocells “on

top” of it, either randomly or in a deterministic fashion;

– Focus on a single femtocell dropped in the cellular network;

– Drop both the macrocells and femtocells randomly;

– Keep all the channel gains and possibly even the various per-user capacities general, without specifying the precise spatial model for the various base stations.


System level model


– Overview





– Key Challenges

Overview of Key ChallengesOverview of Key Challenges

– Interference scenario relationships


– Interference level With open-access and strongest cell selection,

heterogeneous, multi-tiered deployments do not worsen the over all interference conditions or even change the SINR statistics.

– Interference of femtocell networks in practice Unregistered mobiles cause significant interference to

the femtocell; The signaling for coordinating cross-tier interference

may be logistically difficult.


– Interference coordination 3G CDMA femtos

power control strategies Reserving a “femto-free” band

4G LTE femtos Backhaul-based coordination Dynamic orthogonalization Subband scheduling Adaptive fractional frequency reuse


– Spectrum: Femtocells can use any and all of these standardized bands

Opening up spectrum bands Re-using existing bands Spectrum and economic efficiencies Innovation and competition


– Cell association and biasing assign each user to the strongest base station signal it

receives


– Cell association and biasing Biasing: users are actively pushed onto small cells.


– Cell association and biasing How to inform a biased user its channel assignment? How much biasing is “optimal”?

The throughput/QoS metric of interest How users and the various base stations are distributed in space Traffic patterns in space-time The amount of adaptively and side information the mobiles and

small cell base stations are able to exploit


– Mobility and soft handover Femto-to-macro handover (outbound mobility) Macro-to-femto handover (inbound mobility) Possibly femto-to-femto handover

– The most difficult aspect of femtocell mobility Femtocells are not typically directly connected into the

core network Femtocells are typically unable to share a RNC with a

macrocell or other femtocells.


– Self-organizing networks (SON) Femtocells must support an essentially plug-and-play

operation

– Considerable research attention Automatic channel selection Power adjustment Frequency assignment for autonomous interference

coordination Coverage optimization The autonomous shutting down and waking up of base

stations for power savings


Economic and Regulatory Issues– Operator Business Case

The cost of femtocells must be outweighed by the savings from offloading traffic from the macrocell networks;

Femtocells can be used to delay costly initial capital costs on macrocell network for operators deploying new 4G technology.

– Subscriber and ISP incentives Subscribers and enterprises become responsible for

installing the femtocells while private ISPs provide the backhaul.


Economic and Regulatory Issues– Femto vs. WiFi and Whitespace

WiFi: best-effort service; Femto: managed service.

– Regulatory benefits Improved access Spectrum efficiency Innovation and opportunity


Economic and Regulatory Issues– Regulatory aspects:

What is the impact of femtocells on spectrum licensing?

What about public health concerns? What power levels do femtocells transmit? How do operators stop users transmitting with

femtocells on unauthorised frequencies or locations? Could femtocells be “hacked”? Do femtocells comply with existing standards? How about the need to register base station locations? What other regulatory issues should be considered?

ConclusionConclusion Demand for cellular data services skyrockets

Setbacks– plug-and-play deployment

– Highly democratic cost

– Possible chaos to the network

Forecast– Dense femtocell deployment

– Economic and capacity benefit


– Overview





– Key Challenges

Thanks!

ece 4371, fall, 2013 introduction to telecommunication engineering/telecommunication laboratory zhu...

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