vocabulary

terminology	meaning
cellular networks	蜂窝网络
bandwidth	带宽
base station	基站
two-tier	两层
macrocell tier	宏层（基站到设备的通讯）
device tier	设备层（设备到设备的通讯）
BS-to-device	基站到设备
device terminal relay	设备中继传递
massive ad hoc mesh	大型无线自组网
mobile broadband	移动宽带
closed access	闭路访问
open access	开路访问

Abstract

• Conventional cellular system
  devices are not allowed to directly communicate with each other in the licensed cellular bandwidth and all communications take place through the base stations.
• New
  a two-tier cellular network involves a macrocell tier and a device tier to realize a massive ad hoc mesh network
• Device terminal relaying makes it possible for devices in a network to function as transmission relays for each other and realize a massive ad hoc mesh network.

Challenges

• security of the user data must be maintained for privacy
• the two-tier network needs to be designed to ensure minimal impact on the performance of existing macrocell BSs. Attention to the management strategies and resource allocation schemes.
• pricing models should be designed to tempt devices to participate in.

Introduction

Growing demand for higher data rates and capacity

With the introduction of a myriad of smart handheld devices, user demands for mobile broad-band are undergoing an unprecedented rise. The drastic growth of bandwidth-hungry applications such as video streaming and multimedia file
sharing are already pushing the limits of current cellular systems. In the next decade, envisioned media-rich mobile applications such as tele-presence and 3D holography will require data rates simply not possible with fourth generation (4G)
networks.

Cooperative communications has such promise

Advantage of D2D communication

1. the number of context-aware services and applications is growing rapidly. These applications require location discovery and communication with neighboring
   devices, and the availability of such a functionality would reduce the cost of communication among devices.
2. play a vital role in mobile cloud computing and facilitate effective sharing of resources (spectrum, computational power, applications, social contents, etc.) for users who are spatially close to each other.
3. Service providers can further take advantage of D2D functionality to take some
   load off of the network in a local area such as a stadium or a big mall by allowing direct transmission among cell phones and other devices
4. D2D communication can be of critical use in natural disasters.

WiFi or Bluetooth have problem in the interference and QoS

In the current market, technologies such as WiFi or Bluetooth provide some D2D communication functionality. However, these work in unlicensed band, and the interference is uncontrollable. In addition, they cannot provide security and quality of service (QoS) guarantee as do cellular networks.

Main topic

• Some major challenges
• Discuss security, interference management, and resource allocation issues, and point out some directions for future research.
• Focus on pricing, and propose some pricing schemes tempting for both users and operators.

D2D Communicationg types and main technical challenges

• The macrocell tier communications as in a conventional cellular system.
• The device tier involves D2D communications.

Four main types of device-tier communications

Device relaying with operator controlled link establishment(DR-OC)

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Direct D2D communication with operator controlled link establishment (DC-OC)

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Device relaying with device controlled link establishment (DR-DC)

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Direct D2D communication with device controlled link establishment (DC-DC)

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Security

• One possible solution to ensure security is closed access for the devices that want to operated in the device tier.
• In closed access, a device has a list of “trusted” devices, and devices not on this list must use the macrocell tier to communicate with it. The devices in a group can set a proper encryption between each other to avoid divulging their information to other devices.
• In open access, on the other hand, each device can act as a relay for other devices without any restrictions. Since there is no type of supervision,
  security in such a case is a challenging open research problem. Security issues in D2D communication involve the identification of potential attacks, threats, and vulnerability of the system.

Interference Management

In DR-OC and DC-OC

resource allocation and call setup are performed by the BS. Therefore, the BS can
alleviate the problem of interference management to some extent using centralized methods, a well-established research area in wireless communications.

In DR-DC and DC-DC

there is no centralized entity to supervise the resource allocation between devices.
Operating in the same licensed band, devices will inevitably impact macrocell users. To ensure minimal impact on the performance of existing macrocell BSs, a two-tier network needs to be designed with smart interference management strategies and appropriate resource allocation schemes.

Between the macrocell and device tier

To address resource allocation for this type of communication, different approaches such as resource pooling , non-cooperative game or bargaining game , admission control and power allocation , cluster partitioning, and relay selection can be employed.

Pricing

Significance

the operators must answer the “pay for what” question before
they can push forward the operator-controlled D2D technology, which requires extensive analysis of usage cases and business models.

Pricing for DR-OC

Pricing for DC-OC

Pricing for DR-DC and DC-DC