  In uplink non-orthogonal multiple access (NOMA) channels, the existing
cooperative successive interference cancellation (SIC) and power control (PC)
schemes lack the capability of achieving the full capacity region, which
restricts the outage performance of uplink NOMA users. For the uplink cognitive
radio (CR) inspired NOMA system, we propose a new rate splitting (RS) strategy
to maximize the achievable rate of the secondary user without deteriorating the
primary user's outage performance. Based on the interference threshold and its
own channel gain, the secondary user adaptively conducts RS, transmit power
allocation and SIC, which utilizes the transmit power efficiently. Closed-form
expression of the outage probability is derived for the secondary user.
Numerical results show that the proposed RS scheme achieves the best outage
performance for the secondary user among the existing cooperative SIC and PC
schemes.
