LTE Advanced - D2D                            Home : www.sharetechnote.com

 

 

 

D2D stands for 'Device to Device'. It implies 'Direct communication between Devices'. In current implementation (i.e, without D2D), every communication between devices has to go through the full path of the network. Conceptually, ideal goal of D2D would be to establish the communication path between them without any intermediate component (e.g, eNB etc). Probably Bluetooth can be regarded as the best example of D2D just in terms of concept (Of course, we don't take Bluetooth as a part of 3GPP D2D) and now you may hear a lot of Direct WiFi. However, in reality it seems likely that D2D would get at least a few of intermediate component (e.g, eNB) between the devices.

 

However in the context of LTE (or any other wide scale wireless communication), it is not that simple to achieve D2D. Probably followings would be the biggest hurdles to overcome.

  • How to make money (Business Model).
  • How to handle Security (Authentication, Ciphering)
  • What kind of radio protocol should be used. (You may refer to TR 36.843 for D2D Radio currently being researched).

With these factors being considered, the concept being formally proposed/investigated in 3GPP seems to assume that it would be difficult (almost impossible) to completely exclude network involvement but it would be possible to minimize it.

 

I will try to keep posting things being investigated/proposed by 3GPP rather than putting too much fancy stories.

 

 

Who will be the master ? Network or UE ?

 

In normal LTE and other celluar communication, Network is almost always the master and it controls everything. What about in D2D ? Will the situation still be the same ? or Will UE get more controling power ?

At least in current specification, it seems that Network still hold the controlling power. It means the control signaling (e.g, Initial access, authentication, connection control, resource reservation) is handled by the network.

 

One possible except would be the case for public safty area such as emergency/disaster case. In this situation, there might be the situation where the network is down. Even in this csae, communication between security forces should still be possible. Therefore, there is some possibility that the future specification would support an autonmous control by UEs or a hybrid approach with the distributed control between network and UEs. (Reference [3])

 

 

Data Path

 

Following is the possible configuration proposed by TR 22.803 Feasibility Study for Proximity Services (ProSe). The final requirement can be different as it moves forward to TS document. But this can be a good start for you to think of as many possibilities as possible.

 

Possible Configuration

Description

In this configuration, Two UEs (or more than two) UEs takes separate path up to SGW/PGW and get directly connected at the level of SGW/PGW. In this case, considerable portions of data path is same as the current (non D2D) use mode. Then, what would be the advantage of D2D in this configuration as apposed to other kind of presense service ? (How about using RCS showing the presense and the location of the device ?)

In this configuration, Two UEs exchange data directly with each other without going through any part of LTE network.

Then, the question is "What kind of Radio they use for this communication since there is no direct communication among UEs at Radio level ?" (Probably LTE Direct ?)

How Network operator can make money in this case ?

In this configuration, two UEs belogn to same eNB and direct data exchange can be done at the level of eNB.

It seems to be the most practical to me (personally) since it can still use LTE radio for communication and hops between the two UE is also very small. But how to handle those situations where two UEs are in proximity (near to each other) but belong to different eNB ?

 

 

Control Path

 

Following is the possible configuration proposed by TR 22.803 Feasibility Study for Proximity Services (ProSe). The final requirement can be different as it moves forward to TS document. But this can be a good start for you to think of as many possibilities as possible.

 

Possible Configuration

Description

When multiple ProSe capable UEs are within the coverage of the same eNB, the system can perform ProSe Communication using control information exchange between the UE, eNB and EPC (e.g, session management, authorization, security)

When multiple ProSe capable UEs are connected to different eNBs, the system still can perform ProSe Communication as indicated by solid lines and arrows.

In this case, the multiple eNB can talk to each other ether via EPC or via direct communication as indicated in dotted arrow.

Even when network coverage is not available, the control path can exist directly between Public Safety UEs.

In this configuration, the Public Safety UEs can rely on pre-configured radio resources to establish and maintain the ProSe Communication. Alternatively, a Public Safety Radio Resource Management Function within UE can manage the allocation of radio resources for Public Safety ProSe Communication as shown with the dashed arrows

 

 

Reference