In this paper we study and implement real-time adaptation schemes for video encoding and channel selection that work in tandem to facilitate HD and 360$°$ video streaming for secondary users in a dynamic spectrum access network. Out-of-band feedbacks on instantaneous pathloss of the signal between the transmitter and the receiver, the received signal strength indicator (RSSI) at the receiver, and the quality of the reconstructed video, are used to continuously determine the best possible encoding parameters. Similarly, the radio transmitter continuously adjusts the channel parameters (i.e., center frequency and channel bandwidth) based on the transmission activities of the primary users who are prioritized on these channels. We consider the physical limitations of the encoder and the channel statistics to determine when to change the encoder parameters and when to switch to a new channel. We propose a multi-level threshold based mechanism to find the optimal number of encoding bit rates. We also propose a threshold based algorithm to find the best available channel between the transmitter–receiver pair. We validate our theoretical propositions on an indoor testbed using universal software radio peripherals (USRPs) and GNU Radio. Live videos captured with a web-cam and a 360$°$ VR camera were encoded with open source H.264 software libraries and streamed using GStreamer. The signal was transmitted over the 915 MHz ISM bands with omni-directional antennas. We used two B210s (from Ettus Research) for the transmitter and the receiver. Another B210 was programmed to sense the energy levels on all the channels in order to detect the presence of primary user transmissions. GNU Radio was used to build the initial flow-graph of all the signal processing modules, both at the transmitter and the receiver. We used Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index (SSIM) to measure the video quality. Experimental results show that (i) the video encoder and the USRP transmitter–receiver pair were able to adapt to the changing RF conditions, (ii) the adaptation schemes yielded better video quality than non-adaptive schemes, and (iii) the USRPs could switch the channels fast enough allowing uninterrupted video streaming even when the primary users preempted the secondary user’s transmission. We also present a simulation study to show that the proposed encoder and channel adaptation algorithms can be scaled to larger networks.

在本文中，我们研究并实现了视频编码和频道选择的实时自适应方案，这些方案可以协同工作以促进HD和360$°$动态频谱访问网络中辅助用户的视频流。有关发射器和接收器之间的信号的瞬时路径损耗，接收器处的接收信号强度指示器（RSSI）以及重构视频的质量的带外反馈用于连续确定最佳可能的编码参数。类似地，无线电发射机基于优先于这些信道的主要用户的传输活动来连续地调整信道参数（即，中心频率和信道带宽）。我们考虑编码器的物理限制和通道统计信息，以确定何时更改编码器参数以及何时更改切换到新频道。我们提出了一种基于多级阈值的机制来找到编码比特率的最佳数量。我们还提出了一种基于阈值的算法，以在收发器对之间找到最佳的可用信道。我们使用通用软件无线电外围设备（USRP）和GNU Radio在室内试验台上验证了我们的理论主张。使用网络摄像头和360捕获的实时视频$°$VR摄像机使用开源H.264软件库进行编码，并使用GStreamer进行流传输。该信号通过全向天线在915 MHz ISM频段上传输。我们使用了两个B210（来自Ettus Research）作为发送器和接收器。另一个B210被编程为感测所有通道上的能量水平，以便检测主要用户传输的存在。GNU Radio用于在发射机和接收机处构建所有信号处理模块的初始流程图。我们使用峰值信噪比（PSNR）和结构相似性指数（SSIM）来测量视频质量。实验结果表明（i）视频编码器和USRP收发器对能够适应不断变化的RF条件，（ii）与非自适应方案相比，自适应方案产生的视频质量更好；并且（iii）USRP可以足够快地切换频道，即使主要用户抢占了次要用户的传输，视频流也不会中断。我们还提出了一项仿真研究，以表明所提出的编码器和信道自适应算法可以扩展到更大的网络。