Performance Analysis of Terahertz Communication Systems With RSMA and Hardware Impairments

Terahertz (THz) communication has received much attention recently for its large bandwidth availability, high data-rate transmission, and alleviating the spectrum shortage, and it can meet the requirements of Internet of Things with large system capacity and networking capability. In this article, the performance of multiantenna THz communication systems with rate-splitting multiple access (RSMA) under the hardware impairments (HWIs) and imperfect successive interference cancelation (SIC) are investigated, where the THz channel is modeled as a composite fading channel, including the molecular absorption effects, misalignment fading and small-scale $\alpha - \mu$ fading. Taking the HWIs and imperfect SIC into account, the probability density function and cumulative distribution function of the effective channel gain are derived. A joint zero-forcing and maximum ratio transmission beamforming design is employed to eliminate the interference among devices. Then, with the performance analysis, the closed-form outage probability (OP) and diversity gain of the system are, respectively, deduced. By minimizing the OP, a closed-form power allocation (PA) scheme is proposed to adjust the PA coefficients between the common stream and private streams, and resultant lower OP is attained. Moreover, the closed-form expression of the ergodic sum rate (ESR) is derived by means of Fox-H function and the Meijer-G function. With this ESR expression, the asymptotic ESR at high signal to noise ratio (SNR) is also provided to gain further insights. Furthermore, a simple upper bound of the ESR is derived for performance evaluation based on the Jensen’s inequality. Simulation results show that the theoretical analysis is effective, and the proposed PA scheme can obtain lower OP. Besides, the impact of different system and fading parameters on the performance are also analyzed.