Cooperative Multigroup Multicast Transmission in Integrated Terrestrial-Satellite Networks

In this paper, we investigate the downlink cooperative multigroup multicast transmission in the integrated terrestrial-satellite network, in which base stations (BSs) and the satellite provide the multicast service for ground users in a cooperative manner while reusing the entire bandwidth. For both terrestrial BSs and the satellite, multiantennas are equipped and beamforming techniques are utilized for improving the system performance. Based on the architecture, we formulate a weighted max-min fair (MMF) beamforming design problem to jointly optimize the beamforming vectors of BSs and the satellite, which is solved based on the relation between the quality of service problem and the MMF problem. When it comes to the large scale case, where large numbers of BSs are distributed within the coverage of the satellite, we propose a time division cooperative multigroup multicast scheme consisting of two phases for the BSs and the satellite. Then, an iterative algorithm is proposed to solve the weighted MMF problem in the time division case. Finally, numerical results are provided to evaluate the cooperative multicast schemes as well as the proposed algorithms.

I. Introduction

With the rapid development and popularity of smart mobile devices like smartphones and tablets, as well as the development of wireless communication technology, wireless services are extended from traditional connection-centric communications, such as phone calls, e-mails, and web browsing, to content-centric communications, including music streaming, video streaming, and mobile TV [1]. Compared with traditional connection-centric communications of relatively low data rate, content-centric communications generally create much more data traffic, and thus incur more pressure to the existing wireless networks. It is predicted that the wireless data traffic will increase by 1,000 fold by 2020. On the other hand, for content-centric communications, the required contents are not unique in many cases. Instead, identical contents may be requested by multiple users simultaneously, especially when it comes to popular videos or TV programs, which is referred to as content reuse in [2]. Taking advantage of the property of content reuse, wireless multicast transmission becomes one promising solution for the rapidly increasing content-centric communications [3]. By means of multicast transmission, the same content can be transmitted to multiple users simultaneously without extra resources, which can significantly improve the system performance compared with the point-to-point transmission. It can be envisioned that multicast transmission will play an important role in the next generation wireless networks.