2. ABSTRACT:
Device-to-device (D2D) communications was initially proposed in cellular networks as a
new paradigm for enhancing network performance.
The emergence of new applications such as content distribution and location-aware
advertisement introduced new user cases for D2D communications in cellular networks.
D2D communications has advantages such as increased spectral efficiency and
reduced communication delay.
The feasibility of D2D communications in Long-Term Evolution Advanced(LTE-A) and
Third Generation Partnership Project (3GPP) is being studied by academia, industry,
and standardization bodies.
This study provide a taxonomy based on the D2D communicating spectrum and review
the available literature extensively under the proposed taxonomy.
.
2
3. D2D communication in cellular networks is defined as direct communication
between two mobile users without traversing the Base Station (BS).
Advantages of D2D Communications:
1.Highly increase the spectral efficiency of the network.
2.potentially improve throughput, energy efficiency and fairness.
3.Similar to the existing short-range wireless transmission techniques(e.g., WiFi Direct,
Bluetooth, and ultra wide bandwidth, UWB), D2D communications can also bring
low transmission delay.
4.D2D communications utilize the licensed spectrum bands, and thus can guarantee
uniform service provision and quality of service (QoS).
5.D2D communications can offload traffic and avoid congestion in the cellular core
network.
6.D2D communications have also been considered as a cost effective solution for
public safety service in case of lack of network coverage in 3GPP, LTE-Advanced.
A cellular network or mobile network is a wireless network distributed over
land areas called cells, each served by atleast one fixed location
transceiver , known as a cell site or base station.
3
11. Access Methods:
The D2D networks can be configured in three ways to allow or restrict
their usage by certain users:
Self-organized:
D2D users themselves realizes the communications in a self-
organizing way by finding the empty spectrum hole.
Network Assisted :
The D2D users operates in a self-organized way, and exchanges
with cellular system limited controlling information for resource
management.
cellular network can obtain the status of D2D communications
for better control purposes.
Network Controlled:
The base station and the core network control the
communication signaling setup and the there after resource
allocation for both cellular and D2D users.
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12. Mode selection criteria:
• Cellular Mode: The mobile works in a traditional cellular way relaying data by a
BS.
• D2D Mode: The mobiles exchanges information directly.
• Mode Adaptation: The mobiles can select the right mode for communication
according to the predefined criterions.
Typically, all the UEs are implemented with two modes, i.e. cellular mode, and D2D
mode, and can adaptively utilize the proper way for transmission.
Mode Selection: 12
13. 1. For D2D communications, network time synchronization is necessary
1. between cellular networks and D2D users
2. among D2D users themselves
3. to minimize multi-access interference, as well as for the proper performance
of handoffs.
2. The fundamental problem of device discovery is that
1. the two peer devices have to meet in space, time, and frequency. Without
any coordination
2. this can be made possible via some randomized procedure and one of the
peers assuming the responsibility of sending the beacon.
3. The approaches in IEEE 802.11 can be readily adopted to enable the
synchronization among mobiles.
Device Discovery and Synchronization: 13
14. 4. Traditional peer discovery:
In both the ad hoc and the cellular cases, the discovery is made possible by
one party transmitting a known synchronization or reference signal
sequence (the beacon).
5. In the case of network assisted D2D, the network can mediate in
the discovery process by
• recognizing D2D candidates.
• coordinating the time and frequency allocations for sending/scanning for
beacons.
• making the pairing process more energy efficient and less time
consuming.
6. Typical procedure:
• Use direct signal to discover peer.
• Set transmission power so that UEs in coverage can hear the broadcast.
• Whoever receives the broadcast confirm that with the eNodeB.
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15. 7. From the aspect that there is response from discovering UE or not,
two discovery approaches could be classified:
• Beacon-based discovery
• Request-based discovery
8. According to whether there is network participation for
identification detection, discovery procedure could be
categorized into:
• Network-assistance detection
• Non-Network-assistance detection
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16. D2D Implementation Challenges in Real World:
• Interference Management
• Power Allocation
• Resource Allocation
• Modulation Format
• Channel Measurement
• Energy Consumption
• HARQ
16
17. CONCLUSION:
• Types of D2D transitions
• Advantages and Disadvantages of transitions
• Applications
• Access methods
• Mode selection
• Device Discovery and Synchronization
• How Far is D2D From a Real World Implementation
• D2D Implementation Challenges in Real World
REFERENCES:
1. IEEE COMMUNICATION SURVEYS, VOL. 16, NO. 4, FOURTH QUARTER 2014
2. IEEE Communications Magazine • April 2014
3.“Architecture and protocols for LTE-based device to device communication”,
B.Raghothamanetal in Proc. ICNC, 2013, pp. 895–899.
4. “Advances in D2D communications: Energy efficient service and device discovery radio,”
K.Doppler, C. B. Ribeiro, and J. Kneckt, in Proc. Wireless VITAE, 2011, pp. 1–6.
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