Instantaneous ambiguity resolution techniques are methods employed to achieve real-time high-accuracy positioning. The advent of the Chinese BeiDou system enables us to evaluate the performance of the combined GPS/BeiDou/QZSS dual-frequency ambiguity resolution and BeiDou three-frequency ambiguity resolution. It is known that the increasing number of satellites used can increase the reliability as well as the availability of single-epoch real-time kinematic (RTK) information. Therefore, performance improvement of single-epoch RTK by adding BeiDou satellites is strongly expected because many BeiDou satellites are operated in Asian regions. The first objective of this study is to conduct an initial assessment of the single-epoch RTK performance, as well as standalone positioning/code relative positioning using GPS/BeiDou/QZSS. The second objective of this study is to evaluate the performance of the longer-baseline single-epoch ambiguity resolution using the three-frequency observation data. Furthermore, the possibility of future single-epoch RTK service is discussed in this paper.