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Difference between Underlay D2D and Overlay D2D communication

This page compares Underlay D2D vs Overlay D2D communication and mentions difference between Underlay D2D and Overlay D2D communication.

Introduction:
Cellular networks have evolved over the years and it has become essential for devices to communicate. Due to increase in subscribes exponentially, it has become immediate requirement to offload cellular traffic to manage capacity. The D2D is the new concept in cellular networks. It helps devices to communicate directly with or without network (i.e. BS or eNB) involvement. This increases data rate of D2D links and allows devices to communicate at very low latency. Based on spectrum allocation for D2D and cellular communications there are two types viz. Inband and Outband.

D2D Communication

InBand D2D Communication : In this type, both cellular communication and D2D use same licensed spectrum. There is interference between D2D and cellular uses which is very challenging to handle. Moreover resource allocation algorithms are very complex to develop.
OutBand D2D Communication : In this type, D2D uses unlicensed spectrum (2.4 GHz ISM band or 38 GHz mmwave band) where as cellular uses licensed spectrum as given by network operator. There is no interference issue between cellular and D2D. However D2D users are affected by other ISM band users of wifi and bluetooth which is uncontrollable.

Difference between Inband D2D vs Outband D2D

The figure depicts spectrum allocations for cellular communication, Inband D2D and Outband D2D communication.

InBand D2D communication is further categorized into two types viz. Underlay and Overlay as described below.

Difference between Underlay D2D and Overlay D2D

Underlay D2D communication

• In this subtype, licensed spectrum is not divided for D2D and Cellular use.
• The technique is more spectrum efficient but it is challenging to implement resource allocation between D2D and Cellular users.
• The Underlay D2D increases spectral efficiency by utilizing spatial diversity.

Overlay D2D communication

• In this subtype, licensed spectrum is divided into non-overlapping parts as shown for D2D and cellular links.
• This technique is very simple to implement due to separate resource allocations.
• The overlay D2D reduces chances of interference between D2D and cellular users.
• This technique requires more focus on avoiding wastage of resource.



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