Coordinated multipoint (CoMP) is one technique that can be used to extend the coverage area by solving the Inter Cell Interference (ICI) problem occurring at the cell-edge. On the other hand, Distributed Space-Time/Frequency Block Coding (DSTBC/DSFBC) technique is used to improve the reliability in large modern wireless networks e.g. 3GPP LTE advanced. The cell-edge user is usually power limited. Hence, reducing processing load in such a terminal is preferable. In this paper, we propose a low complexity decoding method named Adaptive K-Best Sphere Decoder (AKBSD) to serve a high mobility cell edge user facing different varying frequency selective channels from multiple base stations. AKBSD adapts the number of K-paths the decoder processes while performing the tree search depending on the estimated received signal strengths and the channel quality of each transmission link in a DSFBC open-loop CoMP environment. The simulation results confirm a good trade-off between performance and complexity achieved by AKBSD under this scenario where about 20% reduction in complexity is achieved over a high K-value fixed KBSD for the price of 0.4 dB reduction in performance at BER value of 10-4.