Direct Sequence Spread Spectrum Communication System with Interference

In this experiment, we will design a direct sequence spread spectrum communication system with interference. The PN code will be generated using an m-sequence generator and transmitted through an additive white Gaussian noise channel. At the receiver end, the received signal contains "useful signal + Gaussian white noise + interference." We will perform despreading and decision-making on the received signal to obtain the user's signal detection results. Subsequently, we will plot the bit error rate versus Eb/N0 curves for different spreading gains (gain values of 10, 30, and 50).

Implementation approach: The system can be implemented using MATLAB's Communications Toolbox with key functions including pngen for PN sequence generation, awgn for channel noise simulation, and custom functions for spreading/despreading operations. The m-sequence generator utilizes linear feedback shift registers to create pseudo-random sequences with good autocorrelation properties. The despreading process involves correlating the received signal with the locally generated PN sequence, followed by threshold-based decision making for signal detection. Performance evaluation will involve Monte Carlo simulations to calculate bit error rates across varying Eb/N0 ratios.

Through this experiment, we can better understand the performance characteristics of direct sequence spread spectrum communication systems, particularly their interference rejection capabilities and the relationship between spreading gain and bit error rate performance.