Multiple Systems Sensing for Cognitive Radio Networks
Date Issued
2008
Date
2008
Author(s)
Yu, Chung-Kai
Abstract
Cognitive radios (CRs) with capability of spectrum sensing to fully utilize radio spectrum have been considered as a key technology toward future wireless communications. We can further leverage CRs to form cognitive radio networks (CRN) which optimizes the total network instead of spectrum efficiency in conventional cognitive radios. When we consider CRN, there are two critical parts to sense the multiple systems environment: system/network sensing and radio resource sensing. In system/network sensing, CRs should identify the potential primary and secondary systems for construction of time-varying CRN. This is an important initial step in CRN since the cooperative routing transmission is allowable in the heterogeneous systems. In this thesis, we propose a general sensing algorithm to identify active systems under a multiple-systems coexisting environment over Rayleigh fading channel. We exploit unique characteristics of systems consisting of fundamental frequency, power spectrum density and four-order cumulant to accomplish the multiple systems sensing. This algorithm can also be applied in Detect and Avoid (DAA) for UWB with a priori knowledge of system parameters. On the other hand, cognitive radio networks may severely suffer from hidden terminal problem like transmission sensing wireless networks to degrade the outage performance. The function to determine the available radio resource for secondary system operation is the radio resource sensing which is similar to the spectrum sensing in conventional cognitive radio and should cope with the hidden terminal problem meanwhile. Modifying the concept from carrier sense multiple access (CSMA) networks, along with the cooperative communications, we propose aggressive sensing and cooperative adaptive modulation coding (AMC) to significantly enhance system outage probability performance and system capacity. CRs will transmit a pseudo carrier under acceptable interference level to primary system (PS). Then PS may cooperatively adjust modulation and coding parameters (MCP) so that CRs can determine optimal utilization of system power (and thus possible rate) under acceptable interference to PS. Consequently, the outage performance of PS in time duration and outage probability, and utilization of radio resource for CRs can be greatly enhanced.
Subjects
Cognitive radio networks
Spectrum efficiency
Network efficiency
Multiple systems sensing
Hidden terminal problem
Aggressive sensing
Cooperative adaptive modulation and coding
Type
thesis
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