The performance of device-to-device (D2D) communication in a cellular network depends on the resource sharing between D2D links and cellular users. Existing researches on resource sharing mainly focus on power control between the D2D users and cellular users that operate in the same frequency band. However, the D2D outage probability performance is hampered by the cellular interference to D2D links. Therefore, the D2D users may not achieve satisfactory SINR performance when D2D users and cellular users are geographically located in a small area; as a result, the outage probability performance would be significantly degraded. In this paper, we provide a novel resource sharing strategy to mitigate the interference from cellular users to D2D receivers by utilizing the low energy characteristics of signals in the guard band and analyze the D2D outage probability performance mathematically. Both the mathematical analysis and numerical results show that the proposed resource sharing strategy provides 1.2 dB SNR gain in D2D outage probability performance while guaranteeing the cellular throughputs.

Device-to-device communication underlying the cellular network is a promising technology in future wireless networks to improve the resource utilization efficiency and extend coverage areas [

Resource allocation methods for D2D users can be categorized into two schemes: the orthogonal resource sharing and the nonorthogonal resource sharing. The former assigns dedicated resources to D2D users, and the latter requires them to share resources with cellular users. The nonorthogonal resource sharing scheme achieves better resource utilization efficiency [

In [

In communication systems, to reduce the impact of adjacent channel interference, nearly 10 percent of the system bandwidth at the edge of the allocated bandwidth is reserved as the guard band. For example, 3GPP TS 25.101 regulates that the adjacent carrier spacing is 5 MHz, but the actual occupied bandwidth is

In contrast to existing works, this paper considers the low energy characteristics of WCDMA signals in the guard band and presents a novel resource sharing strategy to mitigate cellular user-induced interference at the D2D receiver. In addition, the D2D outage probability performances are discussed mathematically in both flat-fading and frequency-selective channels. Numerical results show that the proposed resource sharing strategy outperforms the conventional strategy.

In cellular networks, uplink resource sharing is a common technique, since uplink resources tend to be underutilized in frequency division duplexing (FDD) based cellular networks [

This paper will explore resource sharing problems in one cell, leaving intercell interference out of discussion. Consider a scenario involving a fully loaded cellular network, where

D2D links sharing uplink resources with cellular users.

In what follows, we use

The distance between

Let

The system has a guard band between two adjacent channels to suppress interferences between them. The carrier frequency of the cellular user

In this part, we will first present the conventional resource sharing technique and then propose a new one to improve the reliability of D2D communications. For convenience, the two strategies are denoted as

In

Conventional resource sharing strategy

In

Proposed resource sharing strategy

If a guard band exists between two adjacent channels with center frequencies

For convenience, we calculate the parameter

According to (

Equation (

Calculation of

Let

The TSPC scheme is also applied to the D2D link. Two lemmas are utilized to derive the D2D outage probability.

Let

The proof is presented in Appendix

Let

The proof is presented in Appendix

The D2D conditional outage probability is given by (

The difference between

In

The outage probability of

In

Similarly, when averaging over the positions of

When the system’s communication bandwidth is much larger than the coherence bandwidth, the channel has a frequency-selective characteristic. In this case, the channel is modelled as a multipath fading channel, and the received signal is given by

Intersymbol interference originates from multipath signals whose delays exceed one chip period. This set can be defined as

Substitute (

In

Substitute (

Substitute (

This section presents a performance comparison between

Simulation parameters.

Parameters | Values |
---|---|

Cell radius | 500 m |

Maximum cellular power | 20 dBm |

Distance between D2D TX and RX | ~ |

Distance between D2D TX and BS | ~ |

Channel spacing | 5 MHz |

Pulse shaping filter | RRC |

Gaussian noise powers | |

D2D SINR threshold | 0 dB |

Figure

D2D outage probability in a flat-fading channel.

Figure

Cellular capacity improvement factor in a flat-fading channel.

The frequency-selective channel is modelled in accordance with the Ped B model defined by ITU. Table

Ped B channel parameters.

Path number | Relative delay | Average power |
---|---|---|

1 | | |

2 | | |

3 | | |

4 | | |

5 | | |

6 | | |

Since WCDMA has a chip period of 260.42 ns, the first three paths (1, 2, and 3) are located in set

Figure

D2D outage probability in a frequency-selective channel.

This paper investigated resource sharing strategies for D2D communications in a cellular network. In contrast to previous research, we aimed at mitigating cellular interference on the basis of the low energy characteristics of signals in the guard band and proposed a novel resource sharing strategy. Mathematical analysis and simulation results show that, in a flat-fading channel, the proposed strategy could improve the outage probability performance. And in a frequency-selective channel, the advantage of the proposed method was obvious in low and moderate SNR regions.

Let

Let

The authors declare that they have no competing interests.

This work was supported by the 973 Program under Grant no. 2013CB329003 and the National Science and Technology Major Project under Grant no. 2012ZX03003011-004.