Rocco Di Taranto

Outage Performance in Cognitive Radio Systems with Opportunistic Interference Cancelation

In this paper, we investigate the problem of spectrally efficient operation of a cognitive radio, also called secondary spectrum user, under an interference from the primary system. A secondary receiver observes a multiple access channel of two users, the secondary and the primary transmitter, respectively. The secondary receiver applies Opportunistic Interference Cancelation (OIC) and Suboptimal Opportunistic Interference Cancelation (S-OIC) thus decoding the primary signal when such an opportunity is created by the rate selected at the primary transmitter and the power received from the primary transmitter. First, we investigate how the secondary transmitter, when using OIC and S-OIC for fixed transmitting power, should select its rate in order to meet its target outage probability under different assumptions about the channel-state-information available at the secondary transmitter. We study three different cases and for each of them identify the region of achievable primary and secondary rates. Second, we determine how the secondary transmitter should select its transmitting power not to violate the target outage probability at the primary terminals. Our numerical results show that the best secondary performance is always obtained when the secondary transmitter knows the instantaneous channel-state-information toward the intended receiver. We also evaluate the degradation in terms of achievable rate at the secondary receiver when it uses suboptimal decoding (S-OIC rather than OIC) and the interplay between the allowed power at the secondary transmitter (which depends on the target outage probability at the primary receiver) and the decodability at the secondary receiver.

Cognitive Mesh Network Under Interference from Primary User

In a commonly accepted usage scenario, a cognitive radio appears as a secondary user of certain spectrum which is licensed to another, primary system. A prominent example of cognitive system is a mesh network operating under the interference from primary system. For such a scenario, we propose techniques for efficient secondary usage of spectrum, which rely on the adaptive array antenna in order to reduce the interference between the primary and the cognitive system. In order to keep the hardware complexity as small as possible, the number of antennas at each cognitive node should be small. However, with the simplest 2-element linear adaptive array, the created antenna pattern can result in non-optimized pattern between cognitive nodes in the mesh network. In order to solve such a problem, this paper introduces a simple antenna pattern switching where each cognitive node is equipped with three antennas, and tries to select the antenna configuration constituting 2-element linear array with the best antenna pattern for each link. The proposed configuration requires three antennas but only two transceiver chains, which can reduce the hardware complexity. We also introduce 3-element linear array and design a simple procedure to heuristically select the pattern. Our numerical results show that the proposed techniques can significantly increase the available bandwidth and networking connectivity with small complexity when a cognitive mesh network is located inside the communication area of the primary system.

Outage margin and power constraints in cognitive radio with multiple antennas

In the commons model for spectrum usage, the cognitive (secondary) users are allowed to use the spectrum as long as the target performance in the primary system is not violated. In this paper we consider primary system that has a target outage performance and the transmission power of the secondary transmitter (STX) should be appropriately not to violate the target outage probability for the primary terminals (PT). We have considered two types of STX, with single antenna (SISO STX) and two antennas (MISO STX) and analyzed the allowed secondary power. In general, the power level allowed for the SISO STX differs from the total power level allowed for the MISO STX. Our analysis shows that the relation between these power levels changes as the direct component (the K-factor) of the Ricean fading in the primary channel changes. For a large K-factor in the primary system, the total power allowed for a MISO STX is higher than the power allowed for a SISO STX system. The situation is reversed when the fading in the primary system has a low value of the K-factor and moves towards Rayleigh fading. This implies that, for example, when the direct component in the primary system is substantial, the usage of multiple antennas in the cognitive system has additional benefit, as it can use a higher power.

Two players non-cooperative iterative power control for spectrum sharing

To cope with limited spectrum resources, inefficient spectrum usage and overcrowded wireless communication, the Federal Communications Commissions (FCC) has introduced a new way to manage RF resources: the interference temperature model. With this model the key point is to let unlicensed users use licensed frequencies, provided they can quantify and bound their interference toward the primary license holders. In this paper we study power control for spectrum sharing among two secondary users with interference temperature limit (ITL) at a measurement point. We model this scenario as 2-player non-cooperative game. The 2 players are selfish and rational and strive to maximize their own utility. The measurement point, upon violation of ITL, iteratively backs off a randomly selected secondary user. We identify the possible outcomes of this game and the conditions for the existence of unique/multiple Nash equilibria. We analyze the property of the Nash equilibria in our games, and compare their performances with the social optimal solution. Our simulation results demonstrate that the proposed solution can achieve a satisfactory performance in terms of the total transmitting rate of the two secondary users.