Ultra reliable low latency communication (URLLC) and enhanced mobile broadband (eMBB) are new services in the fifth generation mobile communications. One important design issue is how to multiplex eMBB and URLLC traffics. Preemption-based schemes have been proposed to solve the problem. This paper investigates an indicator-free preemption-based method with enhanced reliability. The main idea is to conduct a correlation-based space-frequency block code (CB-SFBC) at transmitter such that the receiver can blindly recognize URLLC data and at the same time improve the diversity. Since CB-SFBC constitutes an equivalent multiple-input and multiple-output system, it can be treated as a coding process and seen as an inner code. Combined with the channel code as an outer code, iterative detection and decoding can be conducted to improve the bit-error-rate performance. Simulation results show that the proposed methods can have low classification error rate and at the same time achieve reliable transmissions.