## 1 Introduction  
Non-orthogonal multiple access (NOMA) is currently being considered as a promising wireless multiple access technology capable of meeting the demands of 5G wireless systems. The fundamental idea of NOMA is multi-user spectrum sharing within a resource block through power-domain multiplexing [1]. This is different from orthogonal multiple access (OMA) schemes which rely on time-domain/frequency domain multiplexing. In comparison to orthogonal multiple access waveforms, non-orthogonal multiple access (NOMA) waveforms offer a set of desirable potential advantages such as enhanced spectrum efficiency, higher connectivity and reduced latency with high reliability. A slight variant of the power domain NOMA concept is the so-called Layer Division Multiplexing (LDM) technology for achieving a high data rate in the cloud transmission network [2; 3; 4]. Similar to conventional NOMA, in LDM, layers of signals with different power levels are superposed on each other, each layer delivering a different service. From an information-theoretic point of view, the approach is referred to as superposition coding (SC) [5]. An LDM system can comprise of 2 layers where the upper layer with higher power allocation may deliver mobile services and the lower layer may be used to serve high data rates such as HDTV [2; 3; 4]. The LDM concept has been standardized for the next generation American Digital Television standard ATSC 3.0 and has been initiated for the 3 GPP project under the then name Multi-User Superposition Transmission (MUST) [6; 7]. Apart from power-domain multiplexed NOMA or LDM, multi-user spectrum sharing can also be achieved through cognitive radio (CR) technology, where the secondary users (SU) can either opportunistically or collaboratively access the spectral bands occupied by the licensed user/primary user (PU) of that band. The primary objective of both NOMA and CR technology is efficient spectrum utilization. However, the enhancement of spectrum efficiency is achieved by these two closely related wireless technologies from two different perspectives. While CR facilitates the low-priority secondary access either in an opportunistic manner or collaborative manner, NOMA technology enables the simultaneous transmission of multiple users' waveforms by allocating different power levels. A clever combination of CR and NOMA, referred to as the cognitive NOMA, can lead to an improved spectrum sharing approach to further enhance spectrum utilization. Some of the advantages offered by the cognitive NOMA approach are improved spectrum efficiency, massive connectivity, low latency and greater fairness [6; 7; 8]. Moreover, by adopting a multicarrier waveform framework, the spectrum utilization of cognitive NOMA can be further improved in a fragmented dynamic spectrum access (DSA) scenario. Orthogonal Frequency Division Multiple Access (OFDMA) is the most popular multicarrier signaling scheme. However, owing to its use of rectangular pulse shaping filters, the conventional OFDMA suffers from high spectral side-lobes, which leads to undesirable adjacent channel interference (ACI). Hence, conventional OFDM based cognitive NOMA can lead to harmful interference to the primary users of the spectrum. Hence, an alternative adaptive and flexible physical layer waveform with high spectral efficiency is required to achieve interference avoidance and optimized spectrum utilization in a densely deployed 5G network. Filtered multicarrier waveforms with fast convolution-based processing are promising candidates for this purpose [9; 10]. The idea of a fast convolution-based filter-bank (FC-FB) is that the convolution of a long data sequence with a pulse shaping filter response can be achieved over frequency domain data blocks with overlapped block processing. Each sub-band can be easily configured for unequal bandwidths, different center frequencies and adjustable sample rate conversion factors [9; 10].