Auction-Based Time Scheduling for Backscatter-Aided RF-Powered Cognitive Radio Networks

Auction-Based Time Scheduling for Backscatter-Aided RF-Powered Cognitive Radio Networks

Abstract: This paper investigates the time scheduling for a backscatter-aided radiofrequency-powered cognitive radio network, where multiple secondary transmitters transmit data to the same secondary gateway in the backscatter mode and the harvest-then-transmit mode. With many secondary transmitters connected to the network, the total transmission demand of the secondary transmitters may frequently exceed the transmission capacity of the secondary network. As such, the secondary gateway is more likely to assign the time resource, i.e., the backscattering time in the backscatter mode and the transmission time in the harvest-then-transmit mode, to the secondary transmitters with higher transmission valuations. Therefore, according to a variety of demand requirements from secondary transmitters, we design two auction-based time scheduling mechanisms for the time resource assignment. In the auctions, the secondary gateway acts as the seller as well as the auctioneer, and the secondary transmitters act as the buyers to bid for the time resource. We design the winner determination, the time scheduling, and the pricing schemes for both the proposed auction-based mechanisms. Furthermore, the economic properties, such as individual rationality

and truthfulness, and the computational efficiency of our proposed mechanisms are analytically evaluated. The simulation results demonstrate the effectiveness of our proposed mechanisms.

Existing system: However, with more and more devices connected to the network [4], the time resource becomes more congested, and it may not satisfy all the transmission demands of the STs. Since the channel conditions and quality of services (QoS) requirements are different for STs, the STs may value the time resource differently, and the SG is more likely to assign the time resource to the STs with higher valuations in their transmissions, which bring more social welfare to the network.

Therefore, auction is expected to be an effective and fair method to the time resource assignment. Note that existing time scheduling strategies for backscatteraided RF-powered CR networks do not take the specific transmission demands of STs into account. Additionally, existing strategies are not able to ensure important economic properties that are desirable for resource allocation.

Proposed system: We develop a heuristic fixed-demand time scheduling mechanism and an optimal variable-demand time scheduling mechanism for STs. Both the WDTS strategy and the pricing scheme are developed for the two mechanisms. Specifically, in the fixed-demand case, we heuristically solve the formulated WDTS problem, which is a mixed-integer problem, and calculate the payments for winner STs based on the critical valuation. In the variable-demand case, we optimally solve the formulated WDTS problem, which is convex, and calculate the payments for STs using the generalized Vickrey-Clarke- Groves (VCG) pricing scheme. We analytically evaluate the economic properties and the computational complexities for our proposed two mechanisms. We prove that both two time scheduling mechanisms are individually rational and truthful. Also, we show that both our proposed mechanisms.

Advantages: We evaluate and compare the performance between our proposed heuristic fixeddemand and optimal variable demand time scheduling mechanisms by extensive

simulations. Also, we find that the computational complexity in the heuristic fixeddemand time scheduling mechanism is only a small fraction of that in the optimal fixed-demand time scheduling mechanism. Nonetheless, the average social welfare gap between these two mechanisms is very minor. Furthermore, we evaluate the impact of network parameters on the performance, which provides useful guidance for the time scheduling in backscatter-aided RF-powered CR networks.

Disadvantages: We develop a heuristic fixed-demand time scheduling mechanism and an optimal variable-demand time scheduling mechanism for STs. Both the WDTS strategy and the pricing scheme are developed for the two mechanisms. Specifically, in the fixed-demand case, we heuristically solve the formulated WDTS problem, which is a mixed-integer problem, and calculate the payments for winner STs based on the critical valuation. In the variable-demand case, we optimally solve the formulated WDTS problem, which is convex, and calculate the payments for STs using the generalized Vickrey-Clarke- Groves (VCG) pricing scheme.

Modules: Winner determination and time scheduling: We propose, for the first time, an auction model for a backscatter-aided RFpowered CR network, where the STs act as buyers, and the SG acts as the seller as well as the auctioneer. In the auction model, each ST submits its transmission demand and its unit data valuation, i.e., the valuation of transmitting unit data, to the SG to compete for the time resource. The SG is responsible for collecting the bids, performing the winner determination and time scheduling (WDTS), and calculating the payments for winner STs. We develop a heuristic fixed-demand time scheduling mechanism and an optimal variable-demand time scheduling mechanism for STs. Both the WDTS strategy and the pricing scheme are developed for the two mechanisms.

Vickrey – Clarke – Grove: Specifically, in the fixed-demand case, we heuristically solve the formulated WDTS problem, which is a mixed-integer problem, and calculate the payments for winner STs based on the critical valuation. In the variable-demand case, we

optimally solve the formulated WDTS problem, which is convex, and calculate the payments for STs using the generalized Vickrey-Clarke- Groves (VCG) pricing scheme. We analytically evaluate the economic properties and the computational complexities for our proposed two mechanisms. We prove that both two time scheduling mechanisms are individually rational and truthful. Also, we show that both our proposed mechanisms.

Quality of service: As a typical network setting, there usually exist multiple STs transmitting data to the same secondary controller, e.g. the secondary gateway (SG). Therefore, the time resource of the primary channel needs to be assigned to the STs to satisfy their transmission demands in the backscatter-aided RF-powered CR network.

However, with more and more devices connected to the network, the time resource becomes more congested, and it may not satisfy all the transmission demands of the STs. Since the channel conditions and quality of services (QoS) requirements are different for STs, the STs may value the time resource differently, and the SG is more likely to assign the time resource to the STs with higher valuations in their transmissions, which bring more social welfare to the network. Therefore, auction is expected to be an effective and fair method to the Time resource assignment.

Note that existing time scheduling strategies for backscatter-aided RF-powered CR networks do not take the specific transmission demands of STs into account.

Additionally, existing strategies are not able to ensure important economic properties that are desirable for resource allocation.

Secondary Transmitter: Cognitive radio (CR), which dynamically empowers the secondary transmitters (STs) to utilize the underused spectrum, can significantly improve the resource utilization efficiency, and therefore it has been acknowledged as a promising technique to meet the increasing wireless service demand. Among various CR networks, the radio-frequency (RF) powered CR network has received growing attention with the rapid progress of the RF energy harvesting technology. The RF energy harvesting technology enables devices to harvest energy from RF signals, which can greatly prolong and/or sustain the operations of the devices.

Specifically, in RF-powered CR networks, when a primary channel is busy, the STs harvest energy from the signal emitted by the primary transmitter (PT).

Analysis of Economic Properties: The economic properties, including individual rationality and truthfulness, can stimulate the entities, including the STs and the SG, to participate in the data transmission and sustain a stable and efficient network operation. In particular, if the individual rationality cannot be guaranteed, the STs may lose motivation to join the data transmission. This can lead to an inefficient or even unsustainable network operation and cause degradation of network performance. If the truthfulness cannot be guaranteed, the STs may misreport their transmission demands or unit data valuations. As a result, the mechanism can be disordered and the time scheduled can be maliciously manipulated. In the following, we analytically evaluate the individual rationality and the truthfulness of our proposed heuristic fixed-demand time scheduling mechanism.