The benefits of continuous phase modulation (CPM), namely high power and spectral efficiencies, are often overshadowed by the high complexity that comes along with the nonlinearity of the modulation format. We tackle the problem of detection of a quaternary CPM signal in a frequency-selective fast fading channel. In particular, we derive a joint detector-equalizer using the Laurent principal pulse approximation. To handle time-selectivity, we adopt the well-known turbo-estimation approach. However, it turns out that classical turbo-estimation cannot be directly applied, but has to be modified beforehand. With the help of Monte Carlo bit error rate (BER) simulations, we show that using the modified turbo-estimation approach, the receiver is able to track channel variations within a transmit burst under fast fading conditions. This allows for a larger payload-to-overhead ratio. Since joint detection-equalization is practically feasible only for channels with short memory, we also consider a suboptimal approach which decouples detection from equalization.

中文翻译：

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频率选择性快速衰落信道上 CPM 的 Turbo 估计

连续相位调制 (CPM) 的优势，即高功率和频谱效率，通常被调制格式非线性带来的高复杂性所掩盖。我们解决了在频率选择性快速衰落信道中检测四进制 CPM 信号的问题。特别是，我们使用 Laurent 主脉冲近似推导出联合检测器均衡器。为了处理时间选择性，我们采用了众所周知的涡轮估计方法。然而，事实证明经典涡轮估计不能直接应用，而必须事先修改。在蒙特卡洛误码率 (BER) 模拟的帮助下，我们表明使用改进的 Turbo 估计方法，接收器能够在快速衰落条件下跟踪传输突发内的信道变化。这允许更大的有效载荷与开销的比率。由于联合检测均衡实际上仅适用于具有短内存的信道，因此我们还考虑了一种将检测与均衡分离的次优方法。