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Convolutional codes are important channel codes to combat fading and noise in 3GPP 3.84/1.28 Mcps TDD systems. However, the design of the convolutional codes used in current specifications just obtain the best performance for BPSK modulation and the AWGN propagation channel. In 3GPP 3.84/1.28 Mcps TDD systems, QPSK modulation is adopted. Moreover, multipath fading channels are often encountered in practical communication environments. Therefore, convolutional codes used in the specifications cannot always achieve the best performance in practical 3GPP 3.84/1.28 Mcps TDD systems. We propose an improved convolutional encoder for the 3GPP 3.84/1.28 Mcps TDD downlink system by analyzing the integration effects of QPSK modulation and multipath fading channels on the code design. Performance analysis and simulation show that better system performance can be achieved by using the proposed encoder.