Abdoulaye Bagayoko

Power Control of Spectrum-Sharing in Fading Environment With Partial Channel State Information

This paper addresses the spectrum-sharing for wireless communication where a cognitive or secondary user shares a spectrum with an existing primary user (and interferes with it). We propose two lower bounds, for the primary user mean rate, depending on the channel state information available for the secondary-user power control and the type of constraint for spectrum access. Several power control policies are investigated and the achieved primary-user mean rates are compared with these lower bounds. Specially, assuming all pairs of transmitter-receiver are achieving real-time delay-sensitive applications, we propose a novel secondary-user power control policy to ensure for both users, at a given occurrence, predefined minimum instantaneous rates. This power control uses only the secondary-user direct links gains estimations (secondary-to-secondary link and secondary-to-primary link).

Impact of shadowing on the primary exclusive region in cognitive networks

In this paper we use the spatial dimension of spectrum sharing to allow the re-use of a radio frequency spectrum, first licensed to a primary user, by several secondary or cognitive users, while providing an outage performance to the primary user. In particular, we consider a primary receiver in the center of an exclusive region (or no-talk zone) and a guard band, within which there is no secondary transmitter, in order to protect the primary transmission against strong interference. Outside the exclusive region and the guard band, N cognitive transmitters are distributed randomly. Moreover, the primary service is protected by an outage constraint making the primary rate to be greater, most of the time, than a minimal necessary rate C0. We study the effects of shadowing and path-loss exponent on the primary exclusive region.

On the achievable rate region of the Gaussian interference channel: the two- and three-user cases

This paper addresses the problem of computing the achievable rates for two and three users sharing the same frequency band without coordination and interfering with each other. It is primarily related to the field of cognitive radio studies as we look for the achievable increase in the spectrum use efficiency. It is also strongly related to the longstanding problem of the achievable rate region of a Gaussian interference channel (GIC) because of the assumption of no user coordination and the underlying assumption that all signals and interferences are Gaussian. We give a geometrical description of the signal to interference-plus-noise ratio region for the two-user and three-user channels. This geometric approach provides a simple closed-form expression of the achievable rate region of the two-user interference channel and an insight of known optimal power allocation scheme. A closed-form expression of the contour lines of the achievable rate region is also given for the three-user channel.

Simultaneous outage performance in a spectrum-sharing fading environment

We consider two different users sharing the same spectrum resource, interfering with each other, under outage performance requirements for both the users. We derive a practical condition to enable the spectrum-sharing under simultaneous outage performance. Furthermore, when the condition is fulfilled, we provide equations to define the two-dimensional region of allocated powers (P1, P2), for the two users, where a given simultaneous outage performance is achievable. Numerical examples are given to illustrate our results. The framework presented in this paper covers more general settings and the results can be used to build power scheduling and sharing rules for licensed or unlicensed bands.

Spectrum-sharing power control with outage performance requirements and direct links CSI only

This paper addresses the spectrum-sharing for wireless communication with a licensee-primary and a secondary users interfering with each other. We propose a new practical power control policy for the secondary user, under outage performance requirements for both users, with partial knowledge of channel state information.