## 1 Introduction
### Review of Related Works
Likewise, the SSB signal transmitters that are based on an electrical \(IQ\) mixer and optical \(IQ\) modulator are being studied [53]. Apart from the bias-induced generation being considered, digital virtual and optical generation schemes have been discussed [54]. Moreover, detailed theoretical derivations of the SSB-based modulation, as well as the relationship between the device parameters and the CSPR have been presented [55; 56]. Furthermore, SSBN mitigation/receiver-based digital linearization schemes for the direct-detection-based systems have been considered [12; 21; 22; 29; 30; 46; 54; 57; 58; 59]. For instance, the SSBN cancellation schemes based on the frequency gap insertion and iterative SSBN cancellation algorithm have been presented [12]. Similarly, the KK detection, iterative SSBN cancellation, and joint iterative SSBN cancellation have been analyzed [54]. Moreover, Refs. [22; 29] focused on the performance of the direct-detection-based transceivers with electronic dispersion compensation (EDC) and DSP-based receiver linearization techniques. Furthermore, the receiver DSP (Rx-DSP) with the KK scheme and EDC has been considered [21; 30; 46]. The iterative SSBN cancellation and KK field reconstruction techniques have been analyzed [57]. As previously mentioned, several efforts have been presented in the literature regarding SCOH optical transceivers. Nevertheless, there are still some issues that demand further consideration. For instance, Ref. [47] focused on an increase in the DWDM system AIR through a corresponding increase in the SE. In the work, direct detection, constant-IM, and COH detection were studied, while other simplified schemes were not considered. Furthermore, the reviews in [7; 10; 22] centered mainly on the principle of COH optical communications and the related DSP. Furthermore, most of the configurations presented in [32; 33; 34; 60] are mainly applicable to the passive access network systems. The supported transmission distance [32; 33; 60] or AIR [32; 60] is also limited. In spite of the fact that a variety of optical SCOH subsystems is being reviewed [9; 11; 12; 13; 14; 19; 26; 33; 34; 37; 38], the KK scheme and the associated signal processing chains have not been considered in the majority of the contributions. The optical SSB signal generation and mitigation were only presented briefly in a small number of works. Furthermore, the work in [24] focused on the SV-DD scheme and the signal recovery in the Stokes space, while other related SCOH subsystems were briefly reviewed. Likewise, the means of addressing spectral broadening in the KK algorithm were well attended to in [18; 21; 44; 45; 46]; however, most of them did not consider the demand for a strong CW tone, but also contributed to the issue [43]. Although measures by which the required CSPR in the conventional KK system can be lowered have been presented [48; 49; 50; 51], the spectral broadening and the need to reduce the required digital upsampling have not been considered. Despite the fact that a joint optimization for the CSPR and DSP resampling rate has been considered [30; 61], detailed information regarding the fundamental concept demands further consideration. Apart from the fact that the presented work in [14] was brief, some salient concepts of the simplified transceivers such as carrier/SSB signal generation, SSBN mitigation, spectral broadening, CSPR optimization, and field and polarization recoveries were not discussed. Moreover, the great majority of the contributions focused on one- or two-optical-SSB-signal generation [12; 53; 54; 55; 56], while most also presented one or two SSBN mitigation/digital linearization schemes [12; 21; 22; 29; 30; 46; 54; 57; 58; 59]. Furthermore, in [55; 56], the SSB signal generation was well presented, while little or no consideration was given to the SSBN mitigation/digital linearization schemes.