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Inband vs. Outband D2D Communication: A Detailed Comparison

d2d inband outband communication spectrum

This article delves into the comparison of Inband and Outband Device-to-Device (D2D) communication, outlining their differences, advantages, disadvantages, and other relevant parameters.

Introduction to D2D Communication

D2D communication allows devices (mobile phones, vehicles, or User Equipment - UE) to communicate directly with each other, with or without the involvement of a Base Station (BS), evolved NodeB (eNB), or eNodeB. This co-exists with regular cellular communication.

D2D Communication

D2D links offer extremely low latency and high data rates between devices that are in close proximity. These links can utilize either licensed or unlicensed spectrum, as explained in the following sections.

Inband D2D Communication

  • In this approach, both D2D and cellular communication links operate within the licensed spectrum.
  • If the licensed spectrum is divided into distinct, non-overlapping segments for D2D and cellular allocations, it’s referred to as “Overlay.” This method is relatively straightforward to implement.
  • Conversely, if the licensed spectrum isn’t divided, it’s known as “Underlay.” This approach provides more efficient spectrum utilization, potentially increasing operator profits.
  • A key benefit of Inband D2D is that the network operator retains control over interference between D2D devices and cellular phones.

Outband D2D Communication

  • In this approach, D2D communication utilizes unlicensed spectrum, such as the 2.4 GHz ISM band or the 38 GHz mmWave band. Cellular communication continues to use its dedicated licensed spectrum.
  • This eliminates interference between D2D and cellular users.
  • However, interference from other wireless devices operating in the same unlicensed band (e.g., Bluetooth, Wi-Fi) can occur.
  • Network operators have limited control over interference in this setup.
  • Outband D2D is further categorized into “controlled” and “autonomous” types:
    • Controlled: The cellular network manages the D2D radio interface.
    • Autonomous: The cellular network only controls cellular links, while users themselves manage D2D links.

Difference between Inband D2D vs Outband D2D

Inband vs. Outband D2D: A Comparison

The figure above illustrates the different types of D2D communication: Inband (Underlay and Overlay) and Outband.

The following table highlights the key differences between Inband and Outband D2D:

FeaturesInband D2DOutband D2D
SpectrumLicensed spectrum is shared by D2D and cellular users.Unlicensed spectrum is used by D2D, while licensed spectrum is used by cellular users.
Types• Underlay • Overlay• Controlled • Autonomous
Advantages• QoS guaranteed as cellular spectrum is fully controlled by the BS. • Transmission distance of 1 Km and data rate of 1 Gbps • No need of new interface • Any cellular device can use inband D2D communication • In Underlay D2D communication, spatial diversity techniques are used to enhance spectral efficiency.• No interference issue between cellular and D2D • No need of resource allocation • Simultaneous D2D and cellular communication
Disadvantages• Challenge is to handle D2D and cellular interference • Algorithm is complex for resource allocation • Resource wastage cannot be avoided in overlay D2D • A user cannot have simultaneous cellular and D2D transmissions.• Unlicensed band interference uncontrollable • Two interfaces are required (cellular devices need two radio interfaces such as LTE and Wi-Fi to use out band D2D communication). • Power management between two wireless interfaces is crucial to control power consumption of the device. Hence it is not power efficient which leads to low transmitter distance and data rate.