Efficient Spectrum Utilization Methods And Performance Analysis In Cognitive Wireless Networks

Driven by the devices such as smart phones, tablet PC and the services such as social networking, streaming media and online game, the amount of mobile traffic is increasing exponentially, which gives birth to the fifth generation mobile networks (5G). One of the QoS (Quality of Service) requirements of 5G is the 1000X capacity improvement compared with 4G. And the approaches of capacity improvement are heterogeneous networking, new spectrum resources and efficient transmission technologies. The heterogeneous networking and new spectrum resources contribute most to the capacity improvement compared with other technologies. Note that cognitive wireless network (CWN) aims at solving these two problems, in order to improve the spectrum efficiency and capacity of wireless networks.CWN can acquire the multi-domain (including wireless domain, network domain, policy domain and user domain, etc.) environment and resource information, which is called cognitive information in this paper. With the accurate and efficient cognitive information acquirement, CWN can reconfigure the network parameters, communication protocols, network topology and even hardware structure via learning, decision and implementation procedures. Thus CWN can adapt dynamically changing environment and improve the network capacity. In terms of the spectrum resource in wireless domain, fast and accurate cognitive information acquirement and delivery is the premise of efficient spectrum utilization. Efficient access to the spectrum opportunities in the dimensions of space, time, direction and height is the approach of efficient spectrum utilization. Capacity improvement is the goal of efficient specreum utilization in CWN. Thus in order to realize efficient spectrum utilization in CWN, we firstly address the cognitive information acquirement and delivery in CWN, then we study multi-dimensional spectrum access, meanwhile, we analyze the capacity improvement of multi-dimensional spectrum access.The main contents of this paper are as follows.(1) Representation, measurement and delivery of cognitive information in CWN.In order to realize fast and accurate cognitive information acquirement and delivery, we address the representation and measurement of cognitive information. Firstly, we address the representation of cognitive information, which mainly focus on the space and time spectrum information. We use the notions of geographical entropy and temporal entropy to represent the uncertainty of space and time spectrum information. We use the radio parameter error to denote the represent error of cognitive information. Then we achieve the mathematical properties of geographical entropy, temporal entropy and radio parameter error. Secondly, we establish the cognitive information measurement theory, which measures the multi-dimensional cognitive information when the cognition is imperfect. We derive the relations between the cognitive information measurement and the system parameters such as spectrum efficiency and interference probability. Besides, we apply the cognitive information measurement in the parameter optimization of spectrum sensing. Finally, we design the cognitive information delivery scheme based on the representation of cognitive information in order to realize the efficient cognitive information delivery in the mobile environment.(2) Space-time spectrum opportunities of CWN.Space-time spectrum access can improve the capacity of CWN. However, in the previous research, the calculation of the locations of space-time spectrum holes remains blank. We design a black-gray-white three regions scheme for space-time spectrum sensing and access. Only primary users (PUs) are allowed to be deployed in black region. In gray region, secondary users (SUs) have temporal spectrum opportunities. In white region, SUs have space spectrum opportunities. We have derived the bounds of three regions theoretically. Besides, we have achieved the existence condition of transition zone between gray region and white region. And we have derived the optimal radius of balck region via the view of dynamic spectrum lesing. Finally, we have verified that the space-time spectrum access can fill the capacity gap of primary networks, thus can improve the spectrum efficiency and capacity.(3) Directional spectrum opportunities of CWN.In order to extend the transmission freedom of CWN and improve the capacity of CWN, we study the capacity scaling laws of CWN with directional transmission for the first time. We firstly analyze the statistics of directional spectrum holes and achieve the probability density function (PDF) and expectation of directional spectrum holes. Then we analyze the impact of SUs on PUs when the directional spectrum holes are utilized and design the network protocol of primary network and secondary network to guarantee the operations of primary network and secondary network. Finally, we analyze the throughput capacity scaling laws and connectivity of primary network and secondary network. The research in this part has proved that the capacity of CWN with directional transmission is improved compared with space-time spectrum access.(4) Spectrum opportunities of CWN in the dimension of height.To improve the capacity of CWN, we study the CWN with the hight transmission freedom for the first time. We have constructed the 3D (Three Dimensional) CWN to fully use the transmission dimension of height. Firstly, we design the network protocols to guarantee the normal operation of primary network and secondary network. Then we achieve the throughput capacity scaling laws of primary network and secondary network via the analysis of routing density and interference. The research in this part has proved that the capacity of 3D CWN is improved compared with the CWN with 2D deployment.Finally we summarize this paper and present the future work.