Bit Error Rate Analysis for 5G New Radio Interface Augmented by a Spread Spectrum Underlay

This paper presents an analytical analysis of a spread spectrum underlay channel designed to coexist with the 5G New Radio (NR) Orthogonal Frequency Division Multiplexing (OFDM) waveform. This coexistence is intended for scenarios where this underlay channel is utilized by either a 5G base station or users. This analytical investigation plays a crucial role in designing the underlay-5G OFDM waveform and facilitates decisions related to the relative average symbol energy levels of the 5G channels, i.e., Physical Downlink Shared Channel (PDSCH) and underlay, the choice of modulation schemes, and spreading factors based on the target reliability of the channels and the signal-to-noise ratio (SNR) at the receiver. We derive and present the bit error rate (BER) expressions for the PDSCH and the underlay channels. Monte Carlo simulation results show that the proposed BER expressions are highly accurate. The expression for the BER of the PDSCH is generalized for M-QAM modulation schemes, and the BER of the underlay with BPSK/QPSK is presented. Our findings provide insight into the appropriate parameterization of underlay symbol energy level and spreading factors to avoid degradation to the PDSCH channel as a function of the PDSCH modulation scheme and the received SNR.