The system characteristics of 4G and beyond 4G broadband mobile system (BMS) are high data rate (throughput), low latency (delay), high mobility (speed), and high capacity. The current recognized 4G BMS needs to meet the requirements specified by IMT-Advanced of ITU-T. Those BMSs include 3GPP-LTE/LTE-Advanced and IEEE 802.16e/m (WiMAX 1/WiMAX 2). In the meantime, the smart device (smartphone and tablet) with powerful CPU/GPU, HD digital camera, digital compass, GPS, and various sensors are becoming rapidly popular. In addition, the architecture and capability of cloud computing are getting adopted in various applications and services, a cloud-based 4G/LTE is one example of telecommunications services. With the combination of more deployments of cloud-based BMSs and increasing usages of smart mobile devices, there are many potential appealing applications and services with real-time and/or interactive features can be created. In this article, we explore the technology and applications of mobile augmented reality (MAR) on the cloud-based 4G BMS (TD-LTE) and smart devices environment. The developed smart device-based MAR system (SD-MAR) with the 4G/TD-LTE experimental network testbed is located at MIRC/BML in the campus of National Chiao Tung University. This testbed consists of several brandy dongles/tablets/smartphones (as UE), two NSN TD-LTE base stations (as eNodeB), one core network (as EPC), and cloud-based servers and data center. To study the technology and applications on SD-MAR system, we have integrated research teams/people specialized in the areas of cloud computing, smart device technology, 4G broadband mobile system, computer vision and image processing, gesture recognition, computer graphics and rendering, and system integration. The applications discussed in the article include real-time accurate navigation/tourism for indoor and outdoor, collaborative urban design, and multiuser interactive motion learning system in the mobile environment.