## 2 Related Work on Buffer-Aided CRN  
In the recent past, relays with a buffer were incorporated into cooperative relaying, which provided an additional degree of freedom in the selection of links [9] and resulted in improved throughput and a reduction in interference and outage probability, but at the expense of an increase in packet delay. Furthermore, the incorporation of buffers at the relays, i.e., buffer-aided (BA) relaying has resulted in further improvements in cognitive radio's (CR) performance as well. The fundamental concept is to store packets when conditions are unfavorable and wait till the time when conditions become suitable for transmission. This increases the network resiliency, throughput, and diversity. In [10], the authors discussed the diversity and delay-related problems associated with a BA relay selection scheme. They proposed a unique relay selection policy based on limiting the buffer size at the relay nodes. This scheme results in reducing delay, however at the cost of increased dropping probability. The work in [11] discussed an improved version of max-link that takes into account a predetermined level of interference (\(\alpha\)) that can be accepted by the primary network. The authors in [12] arbitrarily selected a relay for the primary network, and for the secondary network, selection was done from the remaining available relays. A cognitive max-ratio policy was proposed in [13], in which link selection was based on the maximum channel gain between the secondary transmitter-receiver pair over the product of the interference powers received by the secondary and primary networks In our work, we aim to provide a better insight into the whole process. Cognitive BA schemes can perform well in delay-tolerant networks (DTN); however, for time sensitive communication, there is a need to improve the delay performance in these relaying schemes. To accomplish this, it would be necessary to somehow increase the data transmission rate while keeping outage to a minimum. The scheme in [14] proposed to give higher priority to the relay-to-destination links. Source-to-relay links are considered when no relay-to-destination link can be selected. The authors assumed that this will resulted in reducing the packet queue lengths at the relay buffers, which in turn will reduce the average packet delay. However, the authors considered these relays in isolation and did not take into account accumulation of packets at the source. The practical source will have finite storage (buffer) and a finite packet arrivals/generation rate, and ignoring packet drops and delays at the source is not realistic. Moreover, it is assumed that all the relays have a fixed buffer size and do not have their own packets to transmit. Thus, this scheme does not represent a realistic scenario and may result in inefficient use of radio resources. Alternatively, if relays can operate in full-duplex mode, simultaneously transmitting and receiving data in each time slot, then throughput can be increased while keeping delay to a minimum. A general representation of full-duplex relaying is shown in Figure 1, but practically, such an implementation is very challenging because there will be strong self-interference between the transmitting and receiving RF chains  
Recent works [15; 16] discusses how the effect of self-interference can be minimized in full-duplex relays by employing a mixed analog-digital method. First, some analog partial self-interference  
Figure 1: Self-interference in dual-hop full-duplex relaying. cancellation technique is employed, thus preventing the receiver's analog-to-digital conversion (ADC) from being saturated by the transmitter power. This is then followed by digital self-interference cancellation in the baseband domain. In some schemes, self-interference is effectively canceled out by utilizing multiple antennas for transmitting signals. Now, the transmitted signal will superimpose out of phase and therefore cancels at the receiver antennas.