中文摘要：

为了克服协作传输中的载波频率偏移，提出了一种采用正交幅度调制（QAIvI）的双差分协作传输（DDCT）方案。推导了误符号率（SER）的闭合表达式、SER的上界以及高信噪比（SNR）下的渐进近似。基于SER的渐进近似，推导了最佳功率分配（OPA）在SNR下的近似解。仿真结果显示，该0PA的近似解在实际中等的SNR环境中仍然有效。比较了DDCT分别采用相同调制阶数的QAM调制和PSK调制的SER。当调制阶数大于8时，DDCT-QAM比DDCT-PSK具有更好的SER性能。尤其当调制阶数等于64时，DDCT－QAM可以获得4．5dB的SNR增益。

英文摘要：

A double differential cooperative transmission （DDCT） scheme using quadrature amplitude modulation （QAM） is proposed to overcome carrier frequency offset in cooperative transmission. A closed-form symbol error rate （SER） formulation, an SER upper bound, and an asymptotic SER approximation at high SNR are derived. Based on the asymptotic SER approximation, an approximate solution of optimum power allocation （OPA） at high signal-to-noise ratio （SNR） is derived. The simulation results demonstrate that the approximate solution of OPA also provides a good solution to a realistic moderate SNR scenario. The SER performance of DDCT with QAM modulation and DDCT with phase shift keying （PSK） modulation is compared in condition of same modulation order. The comparison results demonstrate that DDCT-QAM outperforms the DDCT-PSK, when the modulation order is larger than 8. Specially, when the modulation order equals to 64, DDCT-QAM obtains a 4.5 dB SNR gain.