# Cooperation-Assisted Spectrum Handover Mechanism in Vehicular Ad Hoc Networks
## 1 Introduction  
Due to the rapid development of wireless communication technology, a variety of application services have been proposed. Vehicular ad hoc networks (VANETs) are classified as an application of mobile ad hoc networks (MANETs) [1] that have the potential to improve road safety and to provide comfort to travelers. VANET has the following unique characteristics [2]: predictable mobility, providing safe driving, improving passenger comfort and enhancing traffic efficiency, no power constraints, variable network density, rapid changes in network topology, large scale network, and high computational ability. Recently, the Internet of Vehicles (IoV) has received much attention from industry, government, academics, and research units. Unfortunately, there are still many application services encountering bottlenecks in VANETs due to the bandwidth limitations of the wireless spectrum. Therefore, it calls for increasing the utilization rate of the spectrum to satisfy these services as much as possible. Although cognitive radio technology has been proposed to improve spectrum utilization, there are still many issues that need to be addressed. For example, when a vehicle hands over the base stations (BSs), the issue of spectrum handover needs to be considered. The network performance gets worse as the vehicle moves faster.  
2019 is the first year of 5G. Various telecom operators spared no expense to obtain a concentrated and relatively large spectrum in the 5G spectrum, which led to a record high in bidding amount. In other words, this also highlights the high value of the wireless spectrum. The significant features of IMT-2020 (also called 5G) [3] include enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLCC), and massive machine-type communications (mMTC). Obviously, 5G technology will play an important role in the IoV environment.  
According to the statistical results of the Federal Communications Commission in the United States (FCC) [4], the spectrum utilization efficiency of 0 to 6 GHz is about 15% to 85%. The results mean that the part of the frequency spectrum is overcrowded, but the partof the frequency spectrum shows a sharp contrast that is rarely used. It can be seen that the existing method of using fixed spectrum allocation will result in very uneven spectrum utilization. Therefore, if the wireless communication equipment of the vehicle is capable of detecting the use of the local spectrum and can make full use of the idle spectrums, it will improve the overall network performance and maximize the benefits of the spectrum. In the vehicular network, the issue of the spectrum handover needs to be considered when a vehicle hands over the BSs. The network performance gets worse as the vehicle moves faster. Given this, we will propose a novel spectrum handover method based on cognitive and cooperative techniques, called cooperation-assisted spectrum handover (CASH). The detailed operations of CASH will be described in the following sections.  
The remainder of this paper is organized as follows. Section 2 provides a review of related work. In Section 3, we describe the proposed spectrum handover scheme and in Section 4 we show the performance results. Section 5 contains some concluding remarks.