Underlay vs Overlay D2D Communication: Key Differences

This page compares Underlay D2D vs Overlay D2D communication and highlights the key differences between them.

Introduction

Cellular networks have evolved significantly over the years, making device-to-device (D2D) communication essential. With subscriber numbers increasing exponentially, offloading cellular traffic to manage capacity has become a pressing need. D2D communication emerges as a novel concept in cellular networks, enabling devices to communicate directly, with or without network (Base Station or evolved Node B) involvement. This direct communication boosts the data rate of D2D links and allows devices to communicate with very low latency.

Based on how spectrum is allocated for D2D and cellular communications, there are two main types: Inband and Outband.

InBand D2D Communication

In this approach, both cellular and D2D communication utilize the same licensed spectrum. This leads to interference between D2D and cellular users, presenting a significant challenge to manage. Furthermore, the resource allocation algorithms are complex to develop.

OutBand D2D Communication

Here, D2D uses unlicensed spectrum (like the 2.4 GHz ISM band or 38 GHz mmWave band), while cellular communication uses licensed spectrum allocated by the network operator. This eliminates interference between cellular and D2D communications. However, D2D users can be affected by other devices using the ISM band, like Wi-Fi and Bluetooth, which is uncontrollable.

The figure illustrates the spectrum allocations for cellular communication, Inband D2D, and Outband D2D communication. InBand D2D communication is further categorized into Underlay and Overlay types, as described below.

Underlay D2D Communication

• In this subtype, the licensed spectrum is not divided between D2D and Cellular use.
• This technique is more spectrum-efficient, but implementing resource allocation between D2D and Cellular users is more challenging.
• Underlay D2D increases spectral efficiency by taking advantage of spatial diversity.

Overlay D2D Communication

• In this subtype, the licensed spectrum is divided into non-overlapping parts for D2D and cellular links.
• This technique is simpler to implement due to separate resource allocations.
• Overlay D2D reduces the chances of interference between D2D and cellular users.
• This technique requires careful planning to avoid resource wastage.