Ahmed El Shafie

Optimal Random Access for a Cognitive Radio Terminal with Energy Harvesting Capability

We consider a cognitive radio scenario with an energy harvesting secondary user (SU) attempting to access a primary channel randomly. We assume multipacket reception (MPR) capability and investigate a system in which the SU may or may not exploit the primary feedback messages. The access probabilities are obtained to maximize the secondary throughput under the constraints of primary queue stability and such that the primary queueing delay is kept below a specified value in order to guarantee a certain quality of service (QoS) for the primary user (PU). We investigate the impact of the energy queue arrivals, MPR capability, and the primary queueing delay constraint on the maximum secondary throughput.

Optimal selection of spectrum sensing duration for an energy harvesting cognitive radio

In this paper, we consider a time-slotted cognitive radio (CR) setting with buffered and energy harvesting primary and CR users. At the beginning of each time slot, the CR user probabilistically chooses the spectrum sensing duration from a predefined set. If the primary user (PU) is sensed to be inactive, the CR user accesses the channel immediately. The CR user optimizes the sensing duration probabilities in order to maximize its mean data service rate with constraints on the stability of the primary and cognitive queues. The optimization problem is split into two subproblems. The first is a linear-fractional program, and the other is a linear program. Both subproblems can be solved efficiently.

Cooperative cognitive relaying with ordered cognitive multiple access

We investigate a cognitive radio system with two secondary users who can cooperate with the primary user in relaying its packets to the primary receiver. In addition to its own queue, each secondary user has a queue to keep the primary packets that are not received correctly by the primary receiver. The secondary users accept the unreceived primary packets with a certain probability and transmit randomly from either of their queues if both are nonempty. These probabilities are optimized to expand the maximum stable throughput region of the system. Moreover, we suggest a secondary multiple access scheme in which one secondary user senses the channel for τ seconds from the beginning of the time slot and transmits if the channel is found to be free. The other secondary user senses the channel over the period [0, 2τ] to detect the possible activity of the primary user and the first-ranked secondary user. It transmits, if possible, starting after 2τ seconds from the beginning of the time slot. It compensates for the delayed transmission by increasing its transmission rate so that it still transmits one packet during the time slot. We show the potential advantage of this ordered system over the conventional random access system. We also show the benefit of cooperation in enhancing the networks throughput.

On the coexistence of a primary user with an energy harvesting secondary user: a case of cognitive cooperation

In this paper, we consider a cognitive scenario where an energy harvesting secondary user shares the spectrum with a primary user. The secondary source helps the primary source in delivering its undelivered packets during periods of silence of the primary source. The primary source has a queue for storing its data packets, whereas the secondary source has two data queues: a queue for storing its own packets and the other for storing the fraction of the undelivered primary packets accepted for relaying. The secondary source is assumed to be a battery-based node, which harvests energy packets from the environment. In addition to its data queues, the secondary user has an energy queue to store the harvested energy packets. The secondary energy packets are used for primary packets decoding and data packets transmission. More specifically, if the secondary energy queue is empty, the secondary source can neither help the primary source nor transmit a packet from the data queues. The energy queue is modeled as a discrete-time queue with Markov arrival and service processes. Because of the interaction of the queues, we provide inner and outer bounds on the stability region of the proposed system. We investigate the impact of the energy arrival rate on the stability region. Numerical results show the significant gain of cooperation.Copyright

On spectrum sharing between energy harvesting cognitive radio users and primary users

This paper investigates the maximum throughput for a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable power supply. The SU maintains a finite energy queue and harvests energy from natural resources and primary radio frequency (RF) transmissions. We propose a power allocation policy at the PU and analyze its effect on the throughput of both the PU and SU Furthermore, we study the impact of the bursty arrivals at the PU on the energy harvested by the SU from RF transmissions. Moreover, we investigate the impact of the rate of energy harvesting from natural resources on the SU throughput. We assume fading channels and compute exact closed-form expressions for the energy harvested by the SU under fading. Results reveal that the proposed power allocation policy along with the implemented RF energy harvesting at the SU enhance the throughput of both primary and secondary links.

Energy-efficient cooperative relaying protocol for full-duplex cognitive radio users and delay-aware primary users

This paper considers a network in which a primary user (PU) may cooperate with a cognitive radio (CR) user for transmission of its data packets. The PU is assumed to be a buffered terminal operating in a time-slotted fashion. We develop an energy-efficient protocol that involves cooperation and coordination between primary and secondary users. To satisfy certain quality-of-service requirements, users share time slot duration and frequency bandwidth. Moreover, the secondary user (SU) may leverage the primary feedback channel. The proposed protocol is designed such that the secondary rate is maximized and the primary queueing delay is maintained less than the queueing delay in case of non-cooperative PU. In addition, the proposed protocol guarantees the stability of the primary queue and maintains the average energy emitted by the CR user below a certain predefined value that depends on the application. The proposed protocol provides more robust and potentially continuous service for SUs compared to the conventional practice in cognitive networks where SUs transmit in the spectrum holes and silence sessions of the PUs. We include primary source burstiness and sensing errors to the analysis of the proposed cooperative cognitive protocol. Numerical results show the beneficial gains of the cooperative protocol in terms of SU rate and PU throughput, PU queueing delay, and PU average energy savings.

Space–Time Coding for an Energy Harvesting Cooperative Secondary Terminal

In this letter, we consider a cognitive scenario where an energy harvesting secondary user (SU) shares the channel with a primary user (PU). The SU is equipped with two antennas. It maintains a finite capacity energy queue and two infinite capacity data queues: one for storing its own data packets and the other for storing the primary undelivered data packets. The PU communicates with its destination whenever it has data at its queue head. During idle sessions of the PU, if the secondary energy queue maintains at least K packets, the SU employs the Alamouti coding scheme over two of its data packets. The optimization problem for secondary throughput maximization is stated under the stability of all queues in the network and a specific end-to-end queueing delay for the primary packets.

Maximum throughput of a secondary user cooperating with an energy-aware primary user

This paper proposes a cooperation protocol between a secondary user (SU) and a primary user (PU) which dedicates a free frequency subband for the SU if cooperation results in energy saving. Time is slotted and users are equipped with buffers. Under the proposed protocol, the PU releases portion of its bandwidth for secondary transmission. Moreover, it assigns a portion of the time slot duration for the SU to relay primary packets and achieve a higher successful packet reception probability at the primary receiver. We assume that the PU has three states: idle, forward, and retransmission states. At each of these states, the SU accesses the channel with adaptive transmission parameters. The PU cooperates with the SU if and only if the achievable average number of transmitted primary packets per joule is higher than the number of transmitted packets per joule when it operates alone. The numerical results show the beneficial gains of the proposed cooperative cognitive protocol.

Optimal spectrum access for a rechargeable cognitive radio user based on energy buffer state

This paper investigates the maximum throughput for a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable power supply. The SU maintains a finite energy queue and harvests energy from natural resources, e.g., solar, wind and acoustic noise. We propose a probabilistic access strategy by the SU based on the number of packets at its energy queue. In particular, when the energy queue is in a certain state, the SU probabilistically uses a total number of energy packets that is at most equal to the number of packets at its energy queue. The probability of using certain amount of energy in a given state is optimizable. We investigate the effect of the energy arrival rate, the amount of energy per energy packet, and the capacity of the energy queue on the SU throughput under fading channels.

Power-optimal feedback-based random spectrum access for an energy harvesting cognitive user

In this paper, we study and analyze cognitive radio networks in which secondary users (SUs) are equipped with energy harvesting (EH) capability. We design a random spectrum sensing and access protocol for the SU that exploits the primary links feedback and requires less average sensing time. Unlike previous works proposed earlier in literature, we do not assume perfect feedback. Instead, we take into account the more practical possibilities of overhearing unreliable feedback signals and accommodate spectrum sensing errors. Moreover, we assume an interference-based channel model where the receivers are equipped with multi-packet reception (MPR) capability. Furthermore, we perform power allocation at the SU with the objective of maximizing the secondary throughput under constraints that maintain certain quality-of-service (QoS) measures for the primary user (PU).