ABSTRACT
SU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 7.2.4 Problem 2: Resource Allocation for Multiuser OFDM-Based
Cognitive Radio Networks with Heterogeneous Services . . . . 214 7.2.4.1 Subchannel Allocation Scheme . . . . . . . . . . . . . . . 216 7.2.4.2 Optimal Power Allocation . . . . . . . . . . . . . . . . . . . 217 7.2.4.3 Efficient Approximations and Algorithms for
Power Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . 221 7.2.4.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
7.2.5 Problem 3: Resource Allocation for Heterogeneous
Cognitive Radio Networks with Imperfect Spectrum Sensing 228
7.2.5.1 Optimal Power Allocation Using Fast Barrier
Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
7.2.5.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
The concept of cognitive radio (CR) was first proposed as “the point in which wireless personal digital assistants (PDAs) and ubiquitous networks are sufficiently computationally intelligent about radio resources and related computer-to-computer communications to: (a) detect user communications needs as a function of use context, and (b) provide radio resources and wireless services most appropriate to those needs” [1]. However, the concept of CR is not limited to wireless devices such as PDAs. There is disagreement on how to clearly define CR. As a result, many different definitions have been given by various organizations or even outstanding individuals [2]. The working definition of CR, constructed by the Software Define Radio (SDR) Forum Cognitive Radio Working Group [3], allows for future evolution of CR as well as strictly defining the concept:
In a CR system, secondary users (SUs) are allowed to sense the spectrum regis-
tered by primary users (PUs) and use the idle part of the spectrum in an opportunistic
manner [4]; that is, if an SU detects the presence of a PU in the channel that the SU is
using, it releases the channel and switches to a vacant one, or stops transmitting data
if no vacant channel is available. However, owing to the inherent feedback delays,
estimation errors, and quantization errors in practical wireless systems, there are in-
evitable sensing errors, which can lead to heavy interference to the PUs. To avoid
unacceptable performance degradation of the PUs, the interference generated by the
SUs should be regularly controlled, and the physical layer of CR systems should be
very flexible to meet these requirements.
