MDM‐Incorporated Quad Donut Modes OCDMA‐FSO Scheme for Secure High‐Altitude Platforms‐To‐Satellite Scenarios

ABSTRACT The next generation of communication networks is envisioned to be driven by high‐altitude platform (HAP)‐to‐satellite systems. License‐free narrow beam free space optics (FSO) can provide uninterrupted connectivity in satellite‐enabled Internet of Things scenarios. This work proposes a HAP‐to‐satellite hybrid mode division multiplexing–optical code division multiple access (MDM‐OCDMA) scheme employing zero cross‐correlation (ZCC) and multidiagonal (MD) codes. In high‐speed satellite communications, a 12 × 10‐Gbps hybrid MDM‐OCDMA scheme carrying four donut modes (0, 1, 2, and 3) enables high channel capacity, sufficient spectral efficiency, and data security under severe link conditions. Based on simulations, the hybrid MDM‐OCDMA scheme using the ZCC code achieves a greater FSO link distance of 420 m compared with when using the MD code at a 10e‐9 error correction limit under clear air and weak turbulent scenario. The reliable transmission distance of 250 m is achievable with the 120‐Gbps proposed system, assuming pointing errors of 2 mrad, 1‐dB receiver, and 2.5‐dB transmitter losses. The results also show that the system can sustain an additional loss of 1.5–2 dB over 250 m for all donut modes. Additionally, the system using ZCC code contributes to low power consumption over MD and variable weight ZCC code and thus requires a minimum received power of −4.02 dBm. It also offers high optical signal to noise of 42–52 dB, −11.58 to −22.20 dB of gain, 11.58–22.20 dB of noise figure, and −48.11 to −58.73 dBm of signal power at output over 200–700 m range up to 2 dB of additional loss. Comparative analysis indicates that the proposed system is more efficient, less complex, adequately distance‐friendly (=420 m), and capable of higher data rates (=120 Gbps) compared with other works. This makes it a promising solution for future high‐speed satellite communications considering the impact of link losses and atmospheric conditions.