4G LTE Device to Device, D2D

- 4G LTE Advanced device to device, D2D communication for high data rate local direct communications using LTE devices.

One of the schemes that is being researched and considered for 4G LTE Advanced is the concept of Device to Device communications.

This form of communication using the LTE system is used where direct communications are needed within a small area.

LTE D2D communications is a peer to peer link which does not use the cellular network infrastructure, but enables LTE based devices to communicate directly with one another when they are in close proximity.

One of the particular applications where LTE device to device communications is for the emergency services. With proprietary systems like TETRA being expensive to maintain because of the separate infrastructure required, the LTE is becoming increasingly attractive as a result of cost, and performance. The main issue is that of reliability.

LTE device to device communication is also being investigated for applications where peer discovery is required for commercial applications in the presence of network support.

LTE D2D was a feature that appeared in LTE REl 12.

Benefits of D2D communications

Direct communications between devices can provide several benefits to users in various applications where the devices are in close proximity:

  • Data rates:   Devices may be remote from cellular infrastructure and may therefore not be able to support high data rate transmission that may be required
  • Reliable communications:   LTE Device to Device can be sued to communicate locally between devices to provide high reliability communications especially if the LTE network has failed for any reason - even as a result of the disaster.
  • Instant communications:   As the D2D communications does not rely on the network infrastructure the devices could be used for instant communications between a set number of devices in the same way that walkie-talkies are used. This is particularly applicable to t e way communications may be used by the emergency services.
  • Use of licensed spectrum:   Unlike other deveice to device systems including Wi-Fi, Bluetooth, etc, LTE would use licensed spectrum and this would enable the frequencies to be used to be less subject to interference, thereby allowing more reliable communications.
  • Interference reduction:   By not having to communicate directly with a base station, fewer links are required (i.e. essentially only between devices) and this has an impact of the amount of data being transmitted within a given spectrum allocation. This reduces the overall level of interference.
  • Power saving :   Using device to device communication provides energy saving for a variety of reasons. One major area is that if the two0 devices are in close proximity then lower transmission power levels are required.

LTE D2D basics

4G LTE device to device, D2D would enable the direct link of a device, user equipment UE, etc to another device using the cellular spectrum. This could allow large volumes of media or other data to be transferred from one device to another over short distances and using a direct connection.. This form of device to device transfer would enable the data to be transferred without the need to run it via the cellular network itself, thereby avoiding problems with overloading the network.

Other examples of direct communication include Wi-Fi Direct, Bluetooth, etc. Networks can be formed in many ways.

Diagram showing the concept of LTE device to device communications using direct links between two devices to reduce the load on the network.
LTE device to device, D2D concept

The D2D system would operate in a manner where devices within a locality would be able to provide direct communications rather than transmitting via the network. The cellular infrastructure, if present, may assist with issues like peer discovery, synchronisation, and the provision of identity and security information.

LTE D2D issues

The addition of the LTE D2D or device to device communication capability impacts the whole of the network and is therefore not a trivial addition, Issues like authorisation and authentication are currently handled by the network and the overall LTE system would need to be extended to accommodate device to device to communication without the essential presence of the network.

Another issue would be that of direct communication between devices that are under subscriptions with different operators, although this is unlikely to occur in the event of public service or emergency services.

By Ian Poole

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