This article explores the performance of the OFDM-IDMA method in wireless communications networks. In recent years, OFDMs such DC-OFDM, ACO-OFDM, and SSB-OFDM have been hot topic in between researchers, and they all make it possible to use a unipolar waveform. This research work proposes a coded phase-offset frequencydivision multiplexing (CP-OFDM) scheme to mitigate symbol interference (SI) and carrier interference (CI). The proposed method based on modified Low density parity check encoding and decoding. For the simulation of proposed method use matrix laboratory. The proposed method simulates the result on different FFT windows of sizes 128, 256, and 512. In this research work, we also compare the different modulation and demodulation techniques at different FFT window sizes. Due to its simplicity, the Binary Phase Shift Key (BPSK) modulation technology has a low bit error rate (BER) and a high signal-to-noise ratio (SNR). The higher window size effect also analyzed and discussed in this presented research work.

OFDM, BER, BPSK, QPSK, Carrier Interference (CI), CPOFDM, and Symbol Interference (SI).