Abstract
Nonorthogonal multiple access (NOMA) is a promising candidate for future wireless networks due to its ability to improve the spectral efficiency and network connectivity. Nevertheless, the error rate performance of NOMA depends significantly on the power assignment for each user, which requires accurate knowledge of the channel state information (CSI) at the transmitter, which can be challenging for several applications, such as wireless sensor networks (WSNs) and Internet of Things (IoT). Therefore, this article proposes a power-tolerant NOMA by adaptively changing the signal power of each user to reduce the system sensitivity to inaccurate power assignment. The power adaptation in the power-adaptive NOMA (PANOMA) is performed based on the transmitted data, and it does not require accurate CSI. To quantify its potential, the bit error rate (BER) and the lower bound capacity performance, over Rayleigh fading channels, are derived in exact closed forms for two and three users scenarios. The results demonstrate that PANOMA provides a tangible BER performance improvement over conventional power-domain NOMA when both schemes use suboptimal power assignment, which is typically experienced in practical scenarios involving channel time variation and CSI estimation errors. Specifically, it will be shown that both schemes provide similar BERs using optimal assignment, but the PANOMA offers BER reduction by a factor of 10 for certain scenarios when suboptimal power values are assigned. The integrity of the analytical results is verified via matching extensive Monte Carlo simulation experiments.
Highlights
I T is widely acknowledged that the number of devices connected to mobile networks will continue to grow at a tremendous pace
The analysis in this paper focuses on binary phase shift keying (BPSK) for both the Non-orthogonal multiple access (NOMA) and power-adaptive NOMA (PANOMA), and it is straightforward to extend it to quadrature phase shift keying (QPSK)
The performance of a single user (SU) orthogonal multiple access (OMA) with maximum transmit power and located at a distance d1 from the base station is used as a benchmark
Summary
I T is widely acknowledged that the number of devices connected to mobile networks will continue to grow at a tremendous pace. Fixed power assignment has low complexity and does not require prior knowledge of the channel state information (CSI) at the transmitter [12], [13], [16], [18], [20] It cannot satisfy the users’ BER requirements or minimize the average BER. Robust NOMA design with respect to sum rate and energy efficiency is considered in [22]– [24] Such schemes are not generally applicable to the BER scenario, and they require substantial computational power. The presented results show a significant BER improvement at the expense of substantial additional complexity Such design is based on the assumption that each symbol experiences independent and identically distributed (i.i.d.) channels, which is a limiting assumption as the channel coefficients are highly correlated in slow fading channels, unless interleavers with very depth are used
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