In this study, the spectral efficiency (SE) and energy efficiency (EE) tradeoff in full‐duplex (FD) two‐hop decode‐and‐forward (DF) relaying system is studied by considering the influence of residual self‐interference. In order to increase the SE of the traditional DF relaying system, firstly, an optimal power allocation (OPA) method is proposed, and the SE and EE analyses of the system are obtained. Secondly, by applying an unified SE–EE tradeoff metric, the multi‐object joint SE and EE maximisation problem is formulated as a single‐objective joint maximisation problem for SE and EE. Furthermore, the optimal total transmission power of the single‐objective joint SE and EE maximisation problem is obtained according to the tradeoff factors. Theoretical analysis and numerical results show that the proposed OPA method significantly improve the system's SE and EE. At the same time, it reveals that the tradeoff between the SE and EE can be flexible by setting the tradeoff factors.

For cognitive wireless networks, it is a crucial task to optimize the communication performance of secondary users while providing effective delay service quality for primary users. In this paper, we propose a resource allocation strategy based on effective capacity under the scenario of secondary user's parallel transmission. Subject to the constraints of total power, minimum secondary user's satisfaction capacity and effective capacity, the model not only guarantees the effective delay service of the main user, but also reasonably distributes the channel and power resources to maximize the secondary user's channel capacity. Genetic algorithm is introduced to solve this model. Simulation results show that the cognitive wireless network resource allocation strategy based on effective capacity has better performance under different transmission power of main users and different resource allocation strategies.

It has been shown that amplify‐and‐forward (AF) transmission is a viable transmission protocol for wireless networks incorporating distributed spatial diversity. However, a drawback of this relatively simple protocol is identified, the destination node is only to combine a part of the signal, while the other part of the signal has been regarded as interference for delay, leading to the lower utilisation of the resource inevitably, which manifests in the bigger noise, lower signal‐to‐noise ratio, and higher bit error rate. A revised AF relay protocol has been proposed for it could fully combine signal and eliminate delay at destination node through caching signal. A multi‐user single‐relay transmission model could demonstrate the superior performance of this protocol, which is in a hotspots region of a cognitive radio network. The closed‐form solution of the channel transmission rate is obtained with the form of matrix multiplication, and it can ensure that even if without any interference cancellation operation it still can improve the transmission rate. Analytical expression of downlink transmission energy efficiency (DLEE) has been derived. Numerical simulation results show that the transmission performances and DLEE have been improved by proposed protocol compared with the conventional AF relay protocol and direct transmission.