The deliberate introduction of controlled intersymbol interference (ISI) in Tukey signalling enables the recovery of signal amplitude and (in part) signal phase under direct detection, giving rise to significant data rate improvements compared to intensity modulation with direct detection (IMDD). The use of an integrate-and-dump detector makes precise waveform shaping unnecessary, thereby equipping the scheme with a high degree of robustness to nonlinear signal distortions introduced by practical modulators. Signal sequences drawn from star quadrature amplitude modulation (SQAM) formats admit an efficient trellis description that facilitates codebook design and low-complexity near maximum-likelihood sequence detection in the presence of both shot noise and thermal noise. Under the practical (though suboptimal) allocation of a 50% duty cycle between ISI-free and ISI-present signalling segments, at a symbol rate of 50 Gbaud and a launch power of -10 dBm the Tukey scheme has a maximum theoretically achievable throughput of 200 Gb/s with an (8,4)-SQAM constellation, while an IMDD scheme achieves about 145 Gb/s using PAM-8. Note that the two mentioned constellations have the same number of magnitude levels and the difference in throughput is resulting from exploiting phase information under using a complex-valued signal constellation.

翻译：Tukey信令中刻意引入受控符号间干扰（ISI），使得在直接检测条件下能够恢复信号幅度及（部分）信号相位，相比强度调制直接检测（IMDD）显著提升了数据速率。采用积分-清除检测器无需精确波形整形，从而赋予该方案对实际调制器引入的非线性信号畸变的高度鲁棒性。源自星型正交幅度调制（SQAM）格式的信号序列具有高效的网格图描述，有利于码本设计，并在散粒噪声与热噪声并存条件下实现低复杂度的近最大似然序列检测。在ISI-free与ISI-present信令段之间采用50%占空比的次优分配方案下，当符号速率为50 Gbaud且发射功率为-10 dBm时，采用（8，4）-SQAM星座的Tukey方案最大理论吞吐量达200 Gb/s，而采用PAM-8的IMDD方案约为145 Gb/s。需指出两种星座具有相同幅度级数，吞吐量差异源于复数信号星座对相位信息的利用。