# Performance Analysis of Hybrid PDM-SAC-OCDMA-Enabled FSO Transmission Using ZCC Codes
## 2 Literature Review  
In this section, a literature review focused on different multiplexing techniques used in FSO communication systems will be presented. OFDM is incorporated into an FSO system using four-level-quadrature-amplitude modulation (4-QAM), as reported in [18]. A transmission capacity of 10 Gbps under clear and fog weather conditions is reported, and the results are obtained for single channel. In [15], SAC-OCDMA using enhanced double weight (EDW) code enabled by PDM is used in FSO transmission and the performance is estimated under clear weather, haze, fog, and rain conditions. Six channels assigned with different EDW code sequences are used. Each carry 10 Gbps and an overall capacity of 60 Gbps is achieved. Additionally, in [19], authors proposed hybrid SAC-OCDMA with PDM using permutation vector (PV) code. Eight channels are used and each carry 20 Gbps of information data. Clear sky, fog conditions, different dust storm events, and different snowfall rates are the weather conditions considered. A high transmission capacity of 160 Gbps achieved, but this code has a significant code length that require more components for code generation. In [17], SAC-OCDMA with two Laguerre Gaussian OAM is used in the FSO transmission link and the performance is investigated under various fog and dust storm conditions. The OCDMA technique using fixed right shift (FRS) code that has unity cross-correlation is used, so the SPD detection technique is required to cancel the MAI between users. Six channels are used, each carrying 10 Gbps of data, and the data are transmitted on two different OAM beams. An overall 60 Gbps transmission capacity is reported. A SAC-OCDMA with PDM is proposed in an FSO transmission in [16]. Ten channels are used. Each is assigned a random diagonal (RD) code sequence and carries 10 Gbps of data. The performance of the system is evaluated under the effect of clear sky and different fog conditions and a 100 Gbps transmission capacity is reported. In [20], a dense wavelength division multiplexing (DWDM) is used in a hybrid FSO and single mode fiber (SMF) communication system. Different fog conditions and clear sky weather conditions are considered, and shorter FSO propagation ranges are reported in the results. The OFDM technique with (4-QAM) is used with SAC-OCDMA in an FSO transmission system in [14]. Three channels are used, and each is assigned three different EDW codes. An SPD detection technique is used to cancel MAI that exist as EDW code has unity cross correlation. Clear sky, haze conditions, rain conditions, and fog conditions are considered and a 45 Gbps transmission capacity is reported. In [21], spectral slicing wavelength division multiplexing (SS-WDM) is used in FSO systems. Sixteen channels are used: each carries 1.25 Gbps of information data. The tropical weather conditions in southern India are considered and an approximately 25 Gbps transmission capacity is reported. In [22], the two multiplexing techniques, PDM and SAC-OCDMA are used in the FSO transmission communication system. The diagonal permutation shift (DPS) code is used with an SPD detection technique as this code has unity cross correlation. Different weather conditions such as rain, different fog levels, and different dust storms are considered and a 60 Gbps transmission capacity is reported. In [23], four Laguerre Gaussian OAM beams are used with a SAC-OCDMA system in an FSO transmission system. The three SAC-OCDMA channels are assigned with a DPS code and transmitted on four different OAM beams, each carrying 20 Gbps of information data. Weather conditions (different snowfall rates, different dust storms and tropical weather conditions) of different Indian and Saudi Arabia cities are considered and a 120 Gbps overall transmission capacity is reported. In [24], the FSO communication system based on the use of two multiplexing techniques; PDM and SAC-OCDMA are proposed.