Successive interference cancelation (SIC) has been considered widely for the detection of downlink nonorthogonal multiple access (NOMA) signals. However, the sequential detection inherent to SIC process may introduce additional time delay for certain users, making the SIC unsuitable for communication systems with time delay constraints such as wireless networks that utilize unmanned aerial vehicles or low earth orbit satellites. Therefore, this article considers the performance of NOMA systems using a joint multiuser detector (JMuD), which can detect the signals of all users simultaneously and, hence, reduce the detection time requirements. The performance of the JMuD is evaluated in terms of bit error rate (BER), computational complexity, and processing time and compared to the SIC detector (SICD). The exact BER of the JMuD is derived analytically using quadrature phase shift keying modulation where closed-form expressions are derived for the two- and three-user scenarios for the air-to-ground channel, which is modeled as a Rician fading channels with order statistics. The obtained analytical results corroborated by Monte Carlo simulation confirm that the BERs of the JMuD and SICD are identical; however, the processing time of the SICD is 51% more than the JMuD for several cases of interest.