## 1 Introduction
In the optical MMW, (a) when the optical carrier has two sidebands, it is regarded as the generalization DSB; (b) when there are two sidebands without an optical carrier, it is regarded as the generalization OCS; (c) when there is one sideband with the optical carrier, it is regarded as the generalization SSB. In the conventional modulation format of data in ROF, fiber chromatic dispersion causes not only the fading effect [33] but also the bit walk-off effect [34]. DSB modulation's optical MMW suffers from both the periodical fading effect and the bit walk-off effect [35]. SSB and OCS modulation's optical MMWs are immune to the fading effect [35], but there is the bit walk-off effect, which limits their transmission distance [36]. To avoid the bit walk-off effect, data signals have to be modulated on only one sideband of the optical MMW. Many schemes were proposed to modulate data signals onto only one of the two optical sidebands [37; 38]. In the methods presented above, one of the optical sidebands was picked out with an optical filter first, and then the data signal was modulated on it [39; 40]. The use of a filter will make the system very complicated, limit the frequency tuning speed, and lead to large insertion losses. Modulating data on one of two sidebands of the optical MMW without a filter has been the hot research issue in ROF in recent years. Two schemes were proposed with a dual parallel MZM (DPMZM) [41; 42]. The structures of these schemes are complicated. To simplify the structure and increase the FMF, [PERSON]. et al. proposed to generate optical MMW filterless schemes in which the data are modulated only on the \(-\)n\({}^{\text{th}}\)-order sidebands to overcome chromatic dispersion [43; 44; 45; 46]. Intheir scheme, by properly adjusting the bias voltages of the MZM, as well as through the amplitudes and phases of the RF driving signal and the gain of the electrical gainer, the baseband data are only modulated on \(-\)n\({}^{\text{th}}\)-order sidebands. Their schemes can overcome the bit walk-off effect. However, the repetitive frequency of the optical MMW is only two times [43], four times [44], eight times [45], and twelve times [46] that of the RF signal. To influence the BER and Q factor, most parameters are related to the phase modulation index and the gain of the baseband signal. These were not considered in the literature. To reduce the cost, the carrier reuse technique is often used in ROF systems at the BS. In the conventional frequency multiplication ROF system, one of the most common methods is that a part of the power of the idle sidebands is filtered out by an FBG for carrier reuse at BS [43; 44]. One of the problems introduced by this method is that the center frequency of the FBG must be changed with the frequency of the idle sidebands. The frequency of the idle sidebands is changed with that of the RF driving signal. This limits the tunability of the system. There is another problem caused by this method. The carrier reuse is realized by reflecting part of the idle sidebands with the FBG. This method will cause a power imbalance between the two sidebands and reduce the performance of the downlink. To reduce the frequency of the RF signal and the cost of the ROF system, it is necessary to increase the FMF of the optical MMW and the tunability of the system. The problems to be solved in this paper are as follows: (1) the bit walk-off effect caused by fiber dispersion in a frequency 16-tupling MMW ROF system; (2) the performance degradation of the downlink of ROF caused by the conventional carrier reuse in ROF. The innovations of our proposed scheme are as follows: (1) the bit walk-off effect has been overcome in the frequency 16-tupling MMW ROF system, which greatly increases the transmission distance of the system; (2) the novel method of inserting guide frequency to realize carrier reuse can effectively improve the performance of the downlink of the system.