Access Strategies for Spectrum Sharing in Fading Environment: Overlay, Underlay, and Mixed

Abstract

In this paper, we analyze the achievable capacity of the secondary service for overlay and underlay access strategies. We then propose a novel mixed access strategy in which in contrast to the underlay strategy, the secondary service transmits during the idle periods without considering the interference threshold constraint. In contrast to the overlay strategy, mixed strategy makes transmission during the busy periods with a probability p a subject to satisfying the interference threshold constraint. Parameter p a is a secondary service parameter, which can be adjusted based on the spectrum status. Moreover, we show that the secondary service can adjust p a to select appropriate access strategy with the objective of maximizing the achieved capacity based on the interference at the secondary service receiver, I, imposed by the primary service transmitter. The proposed spectrum-sharing technique developed in this paper based on I significantly reduces the system complexity comparing to the system in which for spectrum sharing, the imposed interference at the primary receiver is required. We further suggest a simple power allocation scheme for the mixed strategy that its achieved capacity is very close to the maximum achievable capacity of the secondary service.

Downlink Beamforming in Underlay Cognitive Cellular Networks

“…In order to show the convergence of the above sequence {p (n)},w eÞrst introduce the following lemma. (23), is a standard-interference function 2 .…”

Cognitive Radio Systems: Multicarrier Modulation and Power Allocation Challenges

“…Therefore, either in ISS or USS scheme the spectrum cannot be fully exploited. To address this problem MSS scheme is proposed in order to utilize the spectrum more efficiently [4]. Unlike the USS scheme, SU in the MSS scheme transmits without taking the ITC into consideration during idle periods and ITC is imposed during busy periods in contrast to the ISS scheme.…”

“…However, in the ISS scheme where the spectrum is only accessible by the SU once it is left by the PU, the achievable rate cannot be guaranteed due to the dependency on γ. Based on γ, a switch access scheme (between ISS and USS) is proposed in [4]. When γ is small, USS schemes achieves higher capacity than the ISS scheme (even zero at γ=0), while ISS scheme outperforms USS scheme when γ is high.…”

“…The amount of interference introduced by the SU subcarriers into the PUs band depends on three factors, i.e., power allocated in that subcarrier, spectral distance between that particular subcarrier and the PUs band, and location of the PU (whether it is detectable or not by the SU). To address this issue, different power allocation schemes have been proposed in the literature where Gaussian inputs are assumed to maximize the SU data rate for a given interference threshold values [4,5]. However, the Gaussian input assumption is unrealistic, whereas, Finite Symbol Alphabet (FSA) input is more applicable to practical systems.…”

Ergodic Sum Capacity of Spectrum-Sharing Multiple Access with Collision Metric

“…However, this faster convergence comes at the cost of smaller ergodic sum capacity. This is mainly because for Θ > 1 the algorithm 5 ∈ R + is a sufficiently small number.…”