WiFi Direct technologyA technical report

Angelos Alevizopoulos

WiFi Direct technologyDevice to Device (D2D) communication

D2D communication in cellular networks is defined as direct communication between two User Equipments (UEs) without the information passes through the Base Station (BS) or core network

Primarily designed for reducing traffic of the cellular infrastructure and then offloads it to UEs

D2D can associate with network infrastructure to exchange control functions like synchronization, session setup, resource allocation, routing

WiFi Direct technologyD2D communication

WAN + WLAN D2D (LTE + WiFi Direct)

WLAN D2D (WiFi Direct, Bluetooth)

WAN D2D (3GPP LTE D2D)

Picture 1. D2D communication https://goo.gl/38EbrM

WiFi Direct technologyBackground

Defined by the Wi-Fi Alliance also known as WiFi Peer-to-Peer

2009 : WiFi Direct specification introduced

Coverage range of about 200 m and maximum data rate up to 250Mbit/s as traditional WiFi

Working in the unlicensed 2.4 GHz Industrial, Scientific, and Medical (ISM) band

Allows devices to talk to each other without the need for wireless Access Point (AP)

WiFi Direct technologyversus Bluetooth 4.0

Properties WiFi Direct Bluetooth 4.0Low Energy (BLE)

Bit Rate 250 Mbps 25 Mbps

Range 200 m 50 m

Set-Up Time = 1 s <0.003 s

Security AES 256-bit AES 128-bit

Backwards Compatibility

All wireless protocols Not compatible

Power Short battery life Low Energy consumption

Standardization Body WiFi Alliance Bluetooth SIG

WiFi Direct technology Technical overview

WiFi Direct device has to implement both the role of a P2P Client and the role of an AP namely Group Owner (P2P GO)

All group members are able to communicate with each other by exchanging messages relayed by the GO

The main procedure of communication configuration is device discovery, role negotiation, service discovery, security provisioning and power saving

WiFi Direct technologyGroup formation

Picture 3. Group formation https://goo.gl/DGtlUx

1. Discovery2. Role negotiation3. WPA2

Provisioning4. ConnectedDevice detection

Service detection

Group creation

Power management

WiFi Direct technologyLayer two service discovery

Allowing devices to discover available services prior to establishing a P2P Group

Devices can broadcast the services that they provide, which helps other devices discover suitable peers more easily

Enables higher layer service advertisement protocols such as Bonjour and Universal Plug and Play (UPnP)

Service discovery queries transported to data link layer using the Generic AdvertiSement protocol (GAS)

WiFi Direct technology Concurrent operation

A P2P Device can operate concurrently with a WLAN (infrastructure network)

The concurrent operation requires a device to support multiple MAC entities that handles different transport channels

Allowing devices to maintain simultaneous connections to different Wi-Fi Direct networks

WiFi Direct technologyApplication expectations

Picture 4. https://goo.gl/WVHNeS

WiFi Direct technologyMiracast

Picture 5. https://goo.gl/fpJvP2

WiFi Direct technologyMiracast topology

Picture 6. https://goo.gl/Lt57l4

WiFi Direct technology Security provisioning and encryption

Wi-Fi Direct supports secure communication using WPA2 encryption

AES-Counter Mode CBC-MAC Protocol (CCMP) as the encryption cipher

Uses a randomly generated Pre-Shared Key (PSK) for mutual authentication

WiFi Direct technology Power management

P2P power management supports power save mechanisms for P2P Group Owners and P2P Clients

Power saving capabilities critical in portable devices like mobile phones

Use of protocol schemes Opportunistic Power Save and Notice of Absence that allows the P2P GO to be absent for defined periods

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