Evaluation of Transmission Performance for Digital Terrestrial Television Broadcasting System in the Presence of Inter-modulation Noise

Abstract

When an orthogonal frequency division multiplexing (OFDM) signal passes through a non-linear power amplifier, inter-modulation (IM) occurs. Third distortion components of the IM exist in the OFDM band, degrading the bit error rate (BER). Because the in-band IM cannot be measured directly, this phenomenon has not been analyzed thoroughly. The TM is introduced into the OFDM by the non-linearity of the transmission equipment. It changes the C/N of each carrier, leading to variations in their BERs. The overall BER of the OFDM signal is calculated by adding and averaging the carrier BERs. Using mathematical representations of the above, we have theoretically and experimentally shown that the equivalent C/N degradation due to IM from the reference C/N (22 dB), where the BER of error correction-free 64 QAM-OFDM is 9.7 × 10^-3, can be obtained directly by measuring the IM near the OFDM band, without measuring the carrier BERs.