  In this paper, we consider multi-quality multicast beamforming of a video
stream from a multi-antenna base station (BS) to multiple single-antenna users
receiving different qualities of the same video stream, via scalable video
coding (SVC). Leveraging the layered structure of SVC and exploiting
superposition coding (SC) as well as successive interference cancelation (SIC),
we propose a layer-based multi-quality multicast beamforming scheme. To reduce
the complexity, we also propose a quality-based multi-quality multicast
beamforming scheme, which further utilizes the layered structure of SVC and
quality information of all users. Under each scheme, for given quality
requirements of all users, we formulate the corresponding optimal beamforming
design as a non-convex power minimization problem, and obtain a globally
optimal solution for a class of special cases as well as a locally optimal
solution for the general case. Then, we show that the minimum total
transmission power of the quality-based power minimization problem is the same
as that of the layer-based power minimization problem, although the former
incurs a lower computational complexity. Next, we consider the optimal joint
layer selection and quality-based multi quality multicast beamforming design to
maximize the total utility representing the satisfaction with the received
video quality for all users under a given maximum transmission power budget,
which is NP-hard in general. By exploiting the optimal solution of the
quality-based power minimization problem, we develop a greedy algorithm to
obtain a near optimal solution. Finally, numerical results show that the
proposed solutions achieve better performance than existing solutions.
