고영배 교수(youngko@ajou.ac.kr)

아주대학교 SW융합학과

제3회 WLAN 최신기술 워크숍, 2014. 4. 3

Contents

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l WLAN D2D: What is it?

l Various WLAN D2D TechnologiesP Traditional WLAN ad-hoc modeP DLS/TDLSP Wi-Fi DirectP Wi-Fi Display (Miracast)

l Research Activities on WLAN D2Dü Opportunistic networks with Wi-Fi Directü LTE-WiFi Direct Offloadingü Cooperative data sharingü Dynamic power management

l Future Applications and Challenges of WLAN D2D

Importance of WLAN D2Dû Problems have arisen in conventional communication

methods because of:♦ Increase in wireless communication devices♦ Overhead in relay-based communication♦ Increase in network complexity♦ Delay-constraint P2P multimedia services

û Solution: WLAN Device-to-Device (D2D)!

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일반 통신 D2D 통신

Difference of relay-based and D2D communications

WLAN D2D Technologyû P2P/D2D Communication between devices equipped with

IEEE 802.11 interface

û Why use WLAN D2D?♦ Very High Throughput (VHT) available (1 Gbps)♦ Free-to-use ISM bands can be utilized (2.4 GHz, 5 GHz)♦ Future extensions in 60 GHz, White spaces♦ No need for pre-existing infrastructure♦ Android already defines Wi-Fi Direct♦ Can be used to synergize with future cellular networks

û Various technologies can be used to construct WLAN D2D♦ Wi-Fi ad hoc mode [1]♦ WLAN P2P in IEEE Std. 802.11-2012§ Direct Link Setup§ Tunneled Direct Link Setup

♦ Wi-Fi Direct in Wi-Fi Alliance [2]

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WLAN D2D Scenariosû Using these scenarios, various use cases can be defined

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Show (Wireless Docking)

Wireless Printing (Shared Peripherals)

Mirroring (Distributed Connection)

Data Transfer (Direct P2P)

Wi-Fi Ad hoc modeû IEEE 802.11 standard already defines the means of direct

communication through ad hoc mode [1]♦ Utilization of Independent Basic Service Set (IBSS)

û Problems♦ Never widely deployed with various services♦ Not concurrently setup with an infra mode (e.g., AP connections)♦ No sophisticated group formation protocol defined

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Direct Link Setup (DLS)û IEEE 802.11e defines DLS for better QoS support of

direct communication between client Wi-Fi stations♦ Handshake between AP and two clients enable direct

communication

û Problems♦ Never widely deployed with various services♦ Still requires AP infrastructure for initial association

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AP

STA STA

Data

Direct Connection Established

Tunneled DLSû 802.11z specification enhancing the DLS

♦ Used to secure direct links between two STAs♦ The control messages (DLS request, response, and teardown) are

ENCAPSULATED in a data frame

û Also, off-channel DLS is provided♦ Different channel to that of AP is used for the direct communication♦ Further increase efficiency

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AP

STA STA

Encapsulated Data Frame (DLS Request)

Encapsulated Data Frame (DLS Response)

CH6

Encapsulated Data Frame (DLS Confirm)

CH1 CH1

Wi-Fi Direct?û Wi-Fi Peer-to-Peer Technical Specification [2]

û Communication between two Wi-Fi devices via “pairing”♦ A virtual topology called a “group” is created♦ Association between Group Owner (GO) – many Group Clients

û D2D communication through various functions♦ Device Discovery♦ P2P Group Formation♦ Data Communication♦ Power Management

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Wi-Fi Direct Architectural Overview

ûWi-Fi Direct creates Wi-Fi P2P Groups for 1:N communication

û Device roles in Wi-Fi Direct♦ P2P Group Owner (GO) : Elected within the group to act as the

Access Point (AP). Also called soft-AP.♦ P2P Client : Connected to P2P GO and share data.

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Group Owner Group Owner (soft-AP)

Device discovery

û Initial connection between P2P devices by searching for each other♦ “Search” of different channels in the used frequency♦ Probe requests and responses are exchanged to search♦ Information is shared when they “meet” at the same channel

û Three phases are used for device discovery♦ Scan♦ Listen♦ Search

û In 2014 Wi-Fi Direct draft, NFC technology can be used to compliment Device discovery♦ Less power, less time consumed♦ Useful only when devices are in close proximity

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Group Formation

û After successful discovery, devices associate with each other to form a Group

û GO is elected between P2P devices via 3-way handshaking

û GO Intent value is used to decide who will be GO♦ Intent value : Value between 0-15, where higher intent value, higher

chance for GO.♦ Intent value configuration methods: An open issue

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Data Communication

û After discovery and group formation, data can be exchanged between devices

û Typical 802.11 PHY/MAC functions are utilized

û Group Owner manages the group via periodical beacon transmission

û Upon data exchange, WPA-2 security measures are used♦ AES-CCMP encryption cipher♦ Random PSK for mutual authentication

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Power Management

û Power management different to that of legacy 802.11 is defined♦ Power saving functions for soft-APs as well

û Wi-Fi Direct defines two types of power saving♦ Opportunistic power save (OppPS)♦ Notice of absence power save (NoA)

û Each power save mechanisms have different advantages/disadvantages♦ How can they be used in different use cases?♦ Which is more useful in which data traffic?

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Miracastû P2P Wireless Screencasting technology based on

WLAN D2D [3]♦ Created by Wi-Fi Alliance♦ Utilized by Intel’s Wi-Fi Display♦ Spec. compatible with Wi-Fi Direct and TDLS

û Used to “Display” multimedia from one device to another♦ Enable WLAN D2D♦ Capture screen content♦ Encode & Transmit♦ Receive & Decode♦ Render to Display

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Miracast functionsû Miracast is initiated with general Wi-Fi Direct functions

♦ Device Discovery♦ Service Discovery♦ Association

û Then, Miracast defines its own functions for streaming support♦ Capability Negotiation§ RTSP exchange for multimedia capability check

♦ Session Establishment§ RTSP SETUP & PLAY

♦ Security & Protection Features

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WiFi Direct based Opportunistic Networking [4]û To investigate the feasibility of creating opportunistic

networks with WiFi Direct in real-life scenarios♦ Exploits the current problems of Wi-Fi Direct in terms of

discovery and association

û Google Galaxy Nexus phones are used to estimate the association and discovery times® Android 4.2 implementation of Wi-Fi Direct® Multiple devices simultaneously start random discoveryà Therefore, their channels may not meet instantly

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Performance Evaluation

û The real-time experiments show that association can consume too much delay® Graph shows time taken for association according to number of

nodes® In (A,B,C,D,E,F) six-node case of incremental group formation,

association may take 1+ minute

û Therefore, discovery + association time must be reduced!21

Six-node experiment

LTE – WiFi Direct Offloading [5]û [5] shows that in shorter links, Wi-Fi can guarantee much higher

throughput than LTE ® So in short distance communication, WLAN D2D based

communication is much more beneficial® However, in opportunistic communication, association of WLAN D2D

must be done quickly® To support this, LTE association is used to obtain channel information

of D2D devices, so that discovery process is not required

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Utilizing D2D link for LTE offloading,with discovery assist

Throughput of Wi-Fi and LTE according to link length

Performance Evaluation

û Simulation based study♦ Offloading protocols are assumed to exist already

û Offloading via Wi-Fi Direct♦ As the percentage of LTE offload increases, D2D offloading can greatly

increase performance♦ Even with interference from Wi-Fi rogue nodes, better throughput and

energy efficiency can be achieved

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Cooperative Data Sharing [6]û Microcast: Cooperative video streaming on smartphone® Data is divided into segments ® Each D2D device receives different segments through a soft-AP

or cellular network® Devices share segments between each other through D2D

communications

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Data sharing between D2D phonesDifferent segments go to different devices

Performance Evaluation

û D2D Sharing strategy is compared with® BitTorrent method: other devices pull data segments® No-Cooperation: Data is directly received by all devices

û Utilizing D2D can increase efficiency and bandwidth utilization

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Overhead of network Goodput

Dynamic Power Management [7]û To propose a method of dynamically controlling the

NoA periods to support various data traffic rates

û Three NoA designs are proposed♦ Active state – NoA is always active♦ Static state – NoA absent/present intervals are fixed♦ Dynamic state – NoA intervals are variant depending on data

û Wi-Fi Direct testbed is designed♦ 802.11a/b/g D-Link PCMCIA card with Atheros Chipset♦ wpa_supplicant used to re-design NoA§ http://hostap.epitest.fi/wpa_supplicant/

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Dynamic NoA Management Evaluationû Various environments are emulated on testbed® Pedestrian, Urban, Vehicular® 3G channel emulation® Local intra-group data transmission

® Dynamic controlling of NoA can improve performance of Wi-Fi Direct, and also save more energy

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Dynamic Power Selection [8]û Evaluation and Scheme for Power Management

selection depending on data traffic♦ Dynamic NoA management [7] may not be suitable for bulky data

transmissions.♦ Opportunistic power save must also be used, depending on the data

û Proposed Scheme measures the performance of Wi-Fi Direct power management depending on the service♦ Periodic Data transmission à NoA method♦ Bulk data transmission à Opportunistic power save method

û Dynamic power save scheme is proposed♦ Selection of appropriate power save scheme based on services

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Dynamic Power Management Scheme

û GO selects the power management scheme depending on the client data transmissionû Data Initiation Notify (DIN) is exchanged to announce a new data trafficû At the next beacon interval, power mode is switchedû Upon a new data traffic, power mode is switched again, depending on the type of data

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GO

Client

Beacon (TIM

, NoA)

Beacon (TIM

)

Beacon (TIM

, NoA

)

Default

Start with NoA

Switch to NoA,

Calculate NoA Ratio using XMbps,

Switch to opportunistic

Doze Doze Doze

DATA (B

ulk)

CTWindow

DATA (B

ulk)

DATA (B

ulk, end)

DozeDoze

DozeDoze

DATA (Stream

ing)

DATA (Stream

ing)

Doze Doze Doze DozeDoze

DozeDoze

Used ModeNoA NoAOpportunistic

Bulk TxInitiated

Streaming TxInitiated

DIN

_reply

DIN

(Bulk)

DIN

(Streaming, XM

bps)

DIN

_reply

Power Efficient QoS [9]û Energy efficiency of Wi-Fi Direct can be improved even more, if

devices can sleep during data intervals♦ In OppPS, if data interval is high, idle time occurs♦ However, this must be done without causing delay in data

transmission, thus guaranteeing Power Efficient QoS

û We utilize temporary sleep intervals between data transmission periods to provide higher power efficiency♦ Outperforms OppPS in that [9] can reduce idle time♦ Outperforms NoA in that [9] can also support bulk data

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Opportunistic Power Save induces idle time

[9]: Doze according to the data interval and

timely wakeup

Wi-Fi Direct in the Future Networksû Standard for various future devices

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Flexible Future Phones Augmented Reality Devices

Future Home DevicesFuture Wearable Devices

Intelligent Transportation Systemsû High speed V2V, V2I Communication Support

♦ Short-range P2P data sharing between vehicles♦ Fast association / Group formation technology required

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Wireless Serial Busû Connection of USB protocol using Wi-Fi Direct

♦ Various activities such as Wireless Serial Extension (WSE) and Wireless Bus Extension (WBE) have been focused on this area

♦ USB applications and services can be seamlessly used, without the user knowing whether it is wired or wireless

û Research issues♦ Synchronizing USB data with Wi-Fi data transmission♦ USB power management issues

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Multimedia Display Servicesû Miracast is currently Implemented in Android 4.2

♦ Counterpart to Apple AirPlay in OS X♦ Various services are already introduced, with its uses bound to

increase in the future

û Research issues♦ How to reduce power consumption of handheld devices?♦ Latency requirements depending on different use cases?

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WLAN D2D with Hybrid Tech. û WLAN D2D with various communication technologies

♦ LTE – Wi-Fi Directà Mobile Data Offloading [10]

♦ Wi-Fi Direct – Soundwave Hybrid Servicesà Hybrid telecommunication [11]

♦ Wi-Fi Direct – Bluetooth Hybrid Servicesà Localization [12]

♦ Etc.

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Conclusionû WLAN D2D technology can solve the problems of

current communication systems♦ And realize various future networking services

û Future Work♦ WLAN can be utilized depending on many different services

and applications♦ Starting your research based on these services will be a great

way to realize the future of WLAN D2D!

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References[1] IEEE P802.11™-2012, Part 11: Wireless LAN medium access control (MAC) and physical layer (PHY) specifications, IEEE, 2012.

[2] Wi-Fi Alliance, P2P Technical Group, Wi-Fi Peer-to-Peer (P2P) Technical Specification v1.3,draft 33, 2014.

[3] Wi-Fi Alliance, Wi-Fi Display Technical Task Group, Wi-Fi Display Technical Specification v1.0, 2012.

[4] M. Conti, et al, “Experimenting opportunistic networks with WiFi Direct,” IFIP Wireless Days, 2013.

[5] A. Pyattaev, et al, “3GPP LTE Traffic Offloading onto WiFi Direct,” WCNC Workshop on Mobile Internet, 2013.

[6] L. Keller, et al, “MicroCast: Cooperative Video Streaming on Smartphones,” ACM Mobisys, 2012.

[7] D. Camps-Mur, et al., Device to device communications with Wi-Fi Direct: overview and experimentation, ” IEEE Wireless Comm. Mag. Vol. 20(3), June 2013.

[8] K. Lim, Y. Seo, Young-Bae Ko, J. Kim, J. Lee, "Dynamic Power Management in Wi-Fi Direct for Future Wireless Serial Bus," Springer Wireless Networks, March 2014 (published online).

[9] K. Lim, W. Jung, H. Kim, J. Han, Y.-B. Ko, “Enhanced Power Management for Wi-Fi Direct,” in IEEE WCNC, 2013.

[10] K. Lee, et al, “Mobile Data Offloading: How Much Can WiFi Deliver?,” in ACM CoNext 2010.

[11] J. Pulver, “Hybrid telecommunication system, method, and device,” US 8547893 B2, 2013.

[12] A. Baniukevic, et al, “Hybrid Indoor Positioning With Wi-Fi and Bluetooth: Architecture and Performance, ” in IEEE MDM 2013.

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