This technical report discusses WiFi Direct technology, which allows devices to directly communicate with each other over WiFi without an Internet connection or wireless access point. It describes how WiFi Direct uses device discovery, role negotiation, and security provisioning to enable devices to form groups and communicate securely. WiFi Direct supports data rates up to 250Mbps and has a coverage range of about 200 meters. It works in the 2.4GHz band and implements power management features to reduce power consumption for portable devices.

1. WiFi Direct technology
A technical report
Angelos Alevizopoulos

2. WiFi Direct technology
Device 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

3. WiFi Direct technology
D2D 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

4. WiFi Direct technology
Background
 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)

5. WiFi Direct technology
versus Bluetooth 4.0
Properties WiFi Direct Bluetooth 4.0
Low 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

6. 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

7. WiFi Direct technology
Group formation
Picture 3. Group formation https://goo.gl/DGtlUx
1. Discovery
2. Role negotiation
3. WPA2 Provisioning
4. Connected
Device detection
Service detection
Group creation
Power management

8. WiFi Direct technology
Layer 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)

9. 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

10. WiFi Direct technology
Application expectations
https://goo.gl/WVHNeS

11. WiFi Direct technology
Miracast

12. WiFi Direct technology
Miracast topology
https://goo.gl/Lt57l4

13. 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

14. 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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