Joint non-orthogonal multiple access (NOMA) & Walsh-Hadamard transform: enhancing the receiver performance

Non-orthogonal multiple access (NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation (5G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation (SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform (WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor (OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate (BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio (PAPR) of the user signal. The results are discussed in terms of comparison between the conventional NOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.