【Advanced】Design and Simulation of Multicarrier Communication Systems in MATLAB

# Introduction to Multicarrier Communication Systems Multicarrier communication systems are a type of technology that decomposes a high bit-rate data stream into multiple lower bit-rate subcarriers. These subcarriers are transmitted simultaneously and employ Orthogonal Frequency Division Multiplexing (OFDM) to avoid mutual interference. Multicarrier communication systems offer advantages such as high spectrum efficiency and strong resistance to multipath fading, and are widely used in wireless communications, radar, and other fields. # Theoretical Foundations of Multicarrier Communication Systems ### 2.1 Principles of OFDM Systems #### 2.1.1 Principles of OFDM Modulation and Demodulation OFDM (Orthogonal Frequency Division Multiplexing) is a multicarrier modulation technique that breaks down a broadband data stream into multiple narrowband subcarriers, each carrying part of the data. The OFDM modulator maps the input data stream onto multiple subcarriers, with each subcarrier using a different orthogonal carrier for modulation. There is no mutual interference between orthogonal carriers, thereby enhancing the system's spectrum efficiency and its resistance to multipath fading. The OFDM demodulator receives the modulated signal and decomposes it into individual subcarriers through a Fourier transform. It then demodulates each subcarrier to restore the original data stream. #### 2.1.2 Spectrum Characteristics of OFDM Systems OFDM systems have unique spectral characteristics consisting of multiple discrete subcarriers with guard intervals between them. The guard intervals prevent interference between adjacent subcarriers, ensuring independent data transmission for each subcarrier. The spectral characteristics of OFDM systems offer the following advantages: - High spectrum efficiency: Orthogonality between subcarriers allows multiple subcarriers to be transmitted within the same frequency band, enhancing spectrum utilization. - Multipath fading resistance: As the subcarriers are orthogonal, multipath signals experience different phase shifts on different subcarriers. Equalization techniques can effectively eliminate the effects of multipath fading. - Robustness: OFDM systems have strong robustness against channel noise and interference, maintaining good communication performance even in adverse channel conditions. ### 2.2 Multicarrier Modulation Techniques #### 2.2.1 QAM Modulation QAM (Quadrature Amplitude Modulation) is a digital modulation technique that maps digital signals onto different points on a complex plane. The QAM modulator decomposes the input data stream into two orthogonal signals, amplitude modulates each signal, and then combines them into a complex signal for transmission. Advantages of QAM modulation include: - High spectrum efficiency: QAM can transmit multiple bits simultaneously, enhancing spectrum utilization. - Noise resistance: QAM has better noise resistance than other modulation techniques, maintaining good communication performance even at low signal-to-noise ratios. #### 2.2.2 PSK Modulation PSK (Phase Shift Keying) is a digital modulation technique that maps digital signals onto different phase shifts. The PSK modulator decomposes the input data stream into multiple bits, each corresponding to a phase shift, and then modulates the phase shifts onto the carrier for transmission. Advantages of PSK modulation include: - Strong interference resistance: PSK has strong resistance to phase noise and interference, maintaining good communication performance under adverse channel conditions. - Simple implementation: PSK modulators and demodulators are relatively simple to implement, with lower costs. ### 2.3 Multicarrier Channel Coding #### 2.3.1 Convolutional Coding Convolutional coding is a linear forward error correction code that encodes the input data stream through convolution operations. A convolutional encoder consists of a shift register and a feedback function. The shift register stores the input data stream, and the feedback function linearly combines the output of the shift register to generate the encoded bit stream. Advantages of convolutional coding include: - High coding efficiency: Convolutional coding has high coding efficiency, effectively improving channel transmission efficiency. - Noise resistance: Convolutional coding has strong resistance to channel noise, effectively reducing the bit error rate. #### 2.3.2 Turbo Coding Turbo co