Study On Power Allocation Schemes For Cognitive Radio Networks

With the continuous development of society, wireless communication plays a more and more important role in peoples’ lives with high standard and fast pace. The rapid growth of the usage of various wireless communication devices makes the spectrum resource become increasingly scarce. Fortunately, cognitive radio, a novel wireless communication technology, has great potentiality to solve the problem of spectrum scarcity in wireless communication.Cognitive radio is an intelligent wireless communication technology based on the classification of users, which can improve the spectrum utilization efficiency significantly. In the cognitive radio networks, there are two kinds of users, namely primary user(licensed user) and secondary user(unlicensed user or cognitive user). Without affecting the normal transmission of the primary users, the secondary users utilize the idle primary spectrum temporarily to complete their own communication through adjusting communication parameters. Spectrum sensing and power allocation are two key technologies in cognitive radio network. Using the spectrum sensing technology, the secondary users detect and analyze the spectrum resource of their surroundings to excavate communication opportunities as much as possible. Based on the results of spectrum sensing, power allocation technology is used to select the transmission power of secondary transmitter to satisfy secondary users’ communication needs as well as control the interference to primary user under a tolerable level. Around above problems, this thesis makes a detailed study, furthermore propose some schemes mainly for power allocation. The main contributions of this thesis are concluded as follows.1) In order to overcome the shortage that the convex optimization scheme is strict with the property of the optimal problem, this thesis study some power allocation schemes base on artificial intelligent algorithm. Under the interference temperature constraint proposed by each primary user and the total transmission power budget of secondary user, a power allocation scheme based on artificial fish swarm algorithm is researched for an OFDM-based modal where secondary user and all primary users co-existing side-by-side bands. Considering the limitations of artificial fish swarm algorithm and some superiority of other intelligent algorithms, we propose a power allocation scheme based on improved artificial fish swarm algorithm further. From the comparison to the simulation results of other algorithms, the proposed scheme performs better on both the calculation speed and performance of communication.2) Considering the problem that the traditional interference temperature constraint can not assure to protect the communication of primary user completely and there is hardly any calculate methods of it, the thesis proposes two power allocation schemes based on the novel constraints, namely the power allocation scheme based on primary transmission rate constraint and the one based on timeout probability constraint of primary users. Due to the uncertainty of channel parameters, we introduce the robust optimization theory to transform the power allocation scheme based on nominal parameters model to a robust optimization problem, which can make the scheme practical. In order to satisfy the needs of green communication in current society, we use the energy efficiency of cognitive radio network as the optimal object to allocate the power for secondary user. In addition, the relationship between the traditional interference temperature constraint and the two novel constraints, as a result, obtain a calculation method of interference temperature.3) In actual communication environment, the secondary user catches the instantaneous channel state information difficultly and can not analyze the detail primary users’ states through conventional binary decision of spectrum sensing technology. Inspired by the limited channel feedback and the multi-level spectrum sensing technology, we propose a power allocation scheme for secondary user based on the status sensing of primary user in a single-input single-output cognitive radio network. Instead of the conventional binary primary transmit power strategy, namely the sensed PU has only present or absent status, we consider a more practical scenario when primary users transmit with multiple levels of power and quantized side information known by SU in advance as a primary quantized codebook.