The fourth generation of wireless mobile networks (4G) or Long Term Evolution (LTE) as it is popularly called, has evolved rapidly to become the fastest growing cellular network technology. With increased adoption of LTE and advancement in the fifth generation of wireless networks (5G), the present day mobile networks have a high speed and throughput. However, the increased throughput should also support increased number of business cases for the service providers to adopt the latest in mobile technology.
With bandwidth demand for 4K resolution videos, connected car communications and home and enterprise automation going up sharply, the future mobile networks are set to become complicated and interesting. Device to Device (D2D) communication provides solutions to solve some of these problems. Device to device communication is not a new technology, with a host of existing standards (NFC, Bluetooth, Wi-Fi Direct etc.) and applications.
Release 12 of 3GPP standards proposes a D2D communication technology named LTE Direct. It is an innovative device-to-device connection technology that enables mobile devices to passively discover and interact with the world around them with hugely bigger data transfer rates and within a longer range.
LTE direct is a service layer discovery feature. LTE-Direct devices broadcast their needs or services using a 128-bit service layer identifier termed 'expressions'. LTE Direct is optimized for both LTE Time Division Duplex (TDD) and Frequency Division Duplex (FDD). It uses the LTE network for its initial attach.
Proximity-based services (ProSe) based reference architecture is shown in the above diagram.
PC1: Interface between ProSe APP in the UE/device and ProSe Application Server.
PC2: The reference point between ProSe Application Server and ProSe Function.
PC3: Using the PC3 interface, the UE contacts the ProSe Function
PC4: The interface between the EPC and the ProSe Function.
PC5: It is a one-to-many communication interface between two LTE Direct UEs.
In ProSe communications, User Equipment’s (UEs) that are near each other communicate directly rather than via the cellular network. The ProSe discovery process identifies UEs that are near each other and enables operators to provide a highly power-efficient, privacy-sensitive, spectrally efficient and scalable proximate-discovery platform.
User equipment needs to be in the RRC_CONNECTED mode to contact ProSe function. UE can see thousands of 'expressions' in its proximity. Each device can filter the expressions based on user preferences. The device alerts the user when an expression is detected and is relevant. An LTE Direct enabled device wakes up during a specific period, either to broadcast or to listen to services.
I would like to highlight below few benefits of using LTE direct:
- Low spectrum utilization
- Works seamlessly with existing LTE networks
- Better throughput
- Low energy consumption
- Enables peer-to-peer location-based applications and services
Few challenges for LTE-Direct:
- Needs UE/devices to be ON (RRC_Connected). This blocks a part of the LTE resource
- The number of devices supported and its impact on the normal LTE users
- Challenges of interoperability between devices of different make
Near Field Communication, Bluetooth and Wi-Fi Direct are being used in proximity-based services. They are also sufficient for local-area communications, but it is hard to support the number of proximity-based services with the limited reach of these technologies.
LTE direct has the potential of providing next generation services across an extensive set of use cases ranging from advertising, social networking, online gaming, education to many other Internet of Things(IoT) applications. Some of the technology companies have already started to build apps that use LTE direct. It will be very interesting to see how LTE direct emerges as a winner in D2D communication technologies space.
Aricent is the leading solution provider of wireless technologies and has extensive experience in device to device communication technologies and LTE product development and deployment. It also provides consultancy, design, engineering and testing services to its customers.