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Device-to-Device (D2D) communications are considered one of the key technologies for 5G wireless communication systems. In this paper, a resource sharing mechanism, which applies different policies for different cases (thus being categorized), is proposed. In this scheme, all D2D pairs are divided into three groups by comparing the minimum transmit power with the maximum transmit power of each cellular UE. The proposed mechanism enables multiple D2D pairs in the second group to share the resource with cellular user equipment (UE) simultaneously, by adjusting the transmit powers of these D2D transmitters. At the same time, D2D pairs in the first group and the third group share resource with cellular UE based on the transmit power minimization principle. Simulation results show that the proposed scheme can achieve relatively higher network throughput and lower transmit power consumption of the D2D system.

The increasing demand for higher data rates within local area and the gradually increasing spectrum congestion have triggered research activities on improving the spectral efficiency and interference management. In recent years, D2D (Device-to-Device) communications have gained much attention [

However, D2D links may yield significant interference to the communication system. Therefore, resource management scheme, which supports the resource reuse by taking the intracell interference into account, has a great impact on the overall network performance. So far, major efforts are to be aimed at interference control through resource sharing mode selection [

In this paper, to further improve spectrum utilization and system capacity, a resource sharing method, which enables multiple D2D links to share resource with cellular UE simultaneously, is proposed. Firstly, the minimum transmit power of a D2D transmitter is calculated by the required minimum Signal-to-Interference-plus-Noise Ratio (SINR) and the interference from cellular UE which shares the resource with the D2D link. Secondly, based on the interference threshold of eNodeB, the maximum transmit power of a D2D transmitter is calculated. Thirdly, by comparing the minimum transmit power with the maximum one on the resource of each cellular UE, a set of cellular UE devices that can share resource with the D2D link is attained. Then, the D2D pairs are divided into three groups according to the comparison result.

Finally, when many D2D links can only share resource with some special cellular UE or the number of D2D links is larger than the number of cellular UE devices, the transmit powers of these D2D transmitters are adjusted to ensure that the cumulative interference to eNodeB is below a threshold; and the minimum SINR value of each D2D link is met as well. After that, they can share resource with the cellular UE simultaneously. Simulation results show that the proposed scheme can achieve a higher network capacity and lower transmit power consumption of the D2D system.

Then, we can summarize the main contributions in the following:

Different from the existing works, we analyze the resource sharing from the feasibility of transmit power and design the power bound principle by the requirement of minimum SINR and maximum interference, which provides a novel power management scheme.

According to the different geometry distribution (distances of various nodes in the system), the resources are divided into 3 groups based on the power bound principle, thus fully utilizing the UE resources.

Taking advantage of the adjustable transmit power of D2D, the proposed mechanism enables multiple D2D pairs in the second group to share the resource with cellular UE simultaneously. In addition, D2D pairs in the first group and the third group can share resource with cellular UE based on the transmit power minimization principle, which further improves the power efficiency.

The remainder of this paper is organized as follows. The next section describes the system model. The resource sharing method between cellular UE and D2D pairs is presented in Section

Considering an OFDMA based cellular network, which is frequency division duplex (FDD), and concentrating on a single cell served by eNodeB as depicted in Figure

Device-to-Device communication scenarios in a cellular network.

In this work, we focus on the factor of path loss due to the different distance between the D2D pairs and UE. The different distances lead to the different channel gains and thus can further affect the transmit power. According to Figure

We define

We define a

Here,

According to the condition for sharing resource between the cellular link

First group (if all

Second group (if part of

Third group (if all

For further understanding, according to the geography distribution (distances of the various nodes), we then draw Figure

Grouping illustration for a cellular network.

Now, the resource sharing model, which enables multiple D2D UE devices to reuse the resource of cellular UE and minimizes the total transmit power of D2D system, is presented. We concentrate on resource sharing between cellular UE and D2D links in the second group. We construct an

In Algorithm

The matrix

A set of minimum transmit power

(

(

(

(

(

(

(

(

(9)

(10)

(11)

(12)

(13)

(14)

(15) add the subscript

(16)

(17)

(18)

(19)

In Algorithm

Thus, according to (

As mentioned above, the target of the resource sharing method is not only to improve the system capacity but also to minimize the transmit power of D2D system. In order to minimize the total transmit power of D2D system, D2D links in the second group and the third group share resource with cellular UE based on the power minimization principle. The exclusive resources prefer to be allocated to the D2D UE of smaller transmit power in the first group, while each of the remaining cellular UE devices prefers to share resource with the D2D UE of smaller transmit power in the third group.

The matrix

A set of minimum transmit power

(

(

(

(

(

In this section, the performance of the proposed resource sharing mechanism is evaluated. First, the simulation parameters are set and then the simulation results are presented and analyzed. All the simulations are operated under the MATLAB environment.

There are

Simulation parameters.

Cell radius | 500 m |

Maximal distance between one D2D pair | 50 m |

Number of cellular users | 25 |

Number of D2D pairs | 25 |

Bandwidth per RB | 180 kHz |

Path-loss model | |

Target bit error rate | |

The probability threshold | |

Power level of thermal noise | |

The mean | |

The standard deviation | |

The simulation results are plotted in Figures

The number of D2D pairs in each group.

System sum rate with the number of D2D under different interference thresholds.

The number of accessed D2D pairs.

Transmit power of D2D transmitter.

Average transmit power with the number of D2D for different methods.

System sum rate with the number of D2D for different methods.

In Figure

The system sum rate with the number of D2D under different interference thresholds can be found in Figure

In Figure

The average transmit power of D2D transmitter is presented in Figure

At the end, we have compared the proposed method with the methods proposed in [

In this paper, a mechanism where multiple D2D links share resource with a cellular link in cellular network is proposed. Firstly, a minimum transmit power matrix and a maximum transmit power matrix are constructed, and D2D UE devices are divided into three groups by comparing each element of matrix. We construct a minimum transmit power matrix according to D2D pairs in the second group. By circular searching of the minimum value in matrix and comparing it with the corresponding maximum transmit power, the minimum transmit power values are obtained. Then, we adjust the transmit power of D2D transmitters that belong to the same column, and the D2D pairs share resource with cellular UE by the subscript of the selected minimum transmit power. In order to minimize the transmit power of D2D system, D2D UE devices in the first group and third group share resource with cellular UE based on the transmit power minimization principle. Finally, the simulation results show that the proposed policy can achieve a relatively higher network capacity and lower transmit power of D2D system.

The authors declare that there are no competing interests regarding the publication of this paper.

This work was partially supported by the National 863 Program under Grant 2015AA01A705 and China Scholarship Council. The work of H. Li was supported by the National Science Foundation under Grants ECCS-1407679, CNS-1525226, CNS-1525418, and CNS-1543830.