Performance analysis of filtered Orthogonal Frequency Division Multiplexed LDPC codes for satellite communication in the Ka-Band

Abstract

The saturation of lower frequency bands and the growing demand for high data rates have presented the need to design future systems at Ka-band frequency, but Ka-band frequency is very fragile because of the millimeter wavelength. Ka-band frequencies range from 26 to 40 GHz, making the signal more susceptible to weather impairments and shadowing than lower frequency bands. Rain attenuation is a major problem in satellite communications systems operating at Ka-band, it causes major signal degradation because the raindrop is about the size of the Ka-band wavelength. To mitigate this problem, you must use powerful Forward Error Correction (FEC) codes such as Low Density Parity Check (LDPC) or Turbo codes. This research presents the performance of LDPC codes for satellite communications in the Ka-band, we enhance the system’s performance by adding adaptive modulation and filtered - Orthogonal Frequency Division Multiplexing (f-OFDM). This research study has been undertaken as follows: First, we studied the operation of LDPC codes, including different encoding and decoding techniques. We decided to use the Quasi Cyclic (QC) parity check matrix, allowing us to employ the QC-LDPC encoding technique, which reduces encoding complexity and improves coding efficiency. We explored various LDPC code decoding techniques and opted for soft decoding techniques, namely Belief Propagation, Layered Belief, Normalised Min-Sum, and Offset-Min Sum, as they are more effective in reducing errors compared to hard decision decoding. The Kaband satellite channel is modeled using the Gaussian distribution, considering that the signal envelope and signal phase change randomly after passing through the Ka-band channel. All parameters were set according to different weather conditions. For the simulations, we utilized the MATLAB software package. The uncoded 16-Quadrature Amplitude Modulation (QAM) OFDM system on moderate rain weather conditions achieved a gain of 4.3 dB against light snow and thunderstorm weather conditions at the BER 10−3. We applied f-OFDM, and the results show that LDPC codes achieve a gain of 2 dB when compared to Turbo codes and a gain of 3 dB compared to Convolutional Codes (CC) at the BER of 10−3 under moderate rain conditions in the Ka-band channel, we can see the effects of f-OFDM and LDPC codes. When adding the adaptive modulation into the system, modulation switches from 16 QAM to 64-QAM at Eb/No of -9 dB and switches from 64-QAM to 256-QAM at Eb/No of -5 dB thus improving spectral efficiency. The system is resilient and feasible in error correction at low Signal to Noise Ratio (SNR).