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Despite almost two decades of research, multiple challenges remain unresolved in Cognitive Radio (CR) scenarios, especially the fundamental problem of reliable spectrum sensing. Hence we propose a channel partitioning scheme (CPS) based CR relying on realistic imperfect spectrum sensing. The channels licensed to the primary user (PU) are partitioned into two sets. Channels in one of the sets are exclusively reserved for the PU, while those in the other can be accessed by both the PU and the secondary user (SU) after spectrum sensing. The PU prioritizes its transmissions over the two sets by first transmitting using the channels in the reserved set and then moves on to the unreserved set, if required. It is shown that this simple policy significantly improves the overall detection performance as well as the simultaneous achievable rates and reduces the overhead associated with sensing.

Abstract-A new information-theoretic model is proposed for5 underlay-based cognitive radio (CR), which imposes rate limita-6 tion on the secondary user (SU), whereas the traditional systems

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A piece of user equipment (UE), typically, has access to multiple radio access technologies (RATS). Moreover, apart from the standard primary cellular network, the secondary cellular networks can assist the primary network in downlink UE communications. In this way, the data can reach the UE through multiple entities. This paper exploits the multiple entities' idea by proposing a cross-layer scheme that combines data to improve the block error rate (BLER) and the throughput. For this, we define a new entity, called the super-MAC, just above the Medium Access Control (MAC) layer. More specifically, we propose data duplication (at the transmitter) and combining (at UE) at the super-MAC, where the super-MAC gets the Radio Link Layer protocol data unit (RLC-PDU) and sends multiple-copies across various interfaces to different MAC-entities. In doing so, the super-MAC attaches a unique sequence number to a group of RLC-PDUs together. At the UE, the data from different MAC entities are combined at super-MAC to clear any block error. The super-MAC operates in between the Cyclic Redundancy Check and Forward Error Correction stages of the HARQ process. The additional complexity introduced by the scheme is negligible in front of the existing operations. Moreover, the average latency improves due to the significant improvement in the Block Error rate (BLER) that the combining scheme offers over the BLER of the conventional standalone system. Also, since the errors significantly reduce, the throughput shows significant improvement. Finally, the proposed scheme is an advancement in HARQ to reduce retransmissions, and hence it is suitable for the next-generation networks like B5G or 6G to adopt the super-MAC.