Antonio Furtado

Towards a Realistic Primary Users' Behavior in Single Transceiver Cognitive Networks

Most of the models intended to describe the throughput of Primary (PUs) and Secondary (SUs) users of Cognitive Radio Networks (CRNs) assume that PUs only change their activity state (ON/OFF) in the beginning of each SUs operation cycle, admitting that PUs are synchronized with SUs operation cycle. This letter characterizes a more realistic scenario where PUs can randomly change their activity state during the SUs operation cycle. We derive an analytical model for the PUs throughput and its validation is assessed through simulation results. The analysis shows that assuming synchronized PUs leads to an undervaluation of the interference caused to PUs, and the interference decreases as more SUs operation cycles are performed per ON/OFF PUs activity state.

Energy-Efficient QoS Provisioning in Demand Assigned Satellite NDMA Schemes

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Hybrid Automatic Retransmission reQuest (H-ARQ) and time diversity multipacket reception approaches, such as Network Diversity Multiple Access(NDMA), improve the system performance by requesting additional retransmissions and combining all the signals received together. However, the high round trip delay time associated to satellite networks introduces limitations in the number of retransmission requests that may be issued by the terminals to fulfill the Quality of Service (QoS) requirements. This paper considers the design of hybrid protocols combining H-ARQ and NDMA for satellite networks with demand-assigned traffic. The satellite NDMA (S-NDMA) protocol is presented and analytical models are proposed for its performance. Energy efficient QoS provisioning is also analyzed. The proposed systems performance is evaluated for a Low Earth Orbit (LEO) network with a Single-Carrier with Frequency Domain Equalization (SCFDE) scheme, and compared to H-NDMA. Results show that the proposed system is energy efficient and can provide enough QoS to support high demand services such as video telephony.

Energy sensing parameterization criteria for cognitive radios

Energy-based sensing (EBS) has been a topic of strong research in the last years due to its importance to Cognitive Radios (CRs). While EBS has been used in several works, different parameterizations have been adopted. In this work we compare different parameterization criteria to determine the decision threshold to the energy detector. We compare their performance through simulations by characterizing the interference caused to primary users and the throughput achieved by the secondary users. We also assess their relative performance.

Successful Packet Reception Analysis in Multi-Packet Reception Wireless Systems

In this letter, we analyze the individual probability of receiving a packet when

The impact of transmission errors in MAC schemes for distributed wireless networks

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Performance analysis of a distributed MAC scheme for Multi-Packet Reception wireless networks

nodes transmit simultaneously to a single receiver and a multi-packet reception (MPR) scheme is adopted at the physical layer. The main contribution of this letter is the characterization of the average number of packets successfully received. The generic methodology proposed to compute the probability of successful reception of a packet is obtained taking into account the stochastic nature of the path loss due to the spatial distribution of the nodes, as well as shadowing and fast fading effects. The accuracy of the theoretical approach is finally assessed through simulations, showing that for a generic MPR system, there is an optimal number of transmitters that maximize the average number of received packets.

Performance analysis of Multi-Packet Reception wireless systems in far-field region

The Medium Access Control (MAC) protocol design for distributed wireless networks has been a topic of extensive research in the last years. The protocol design challenge relies on the infra-structureless nature of distributed wireless networks, which difficult the implementation of optimal throughput MAC schemes. However, interesting optimal-based MAC protocols have been proposed in the last years, including protocols such as AOB, Idle Sense, as well as a MAC scheme that we have recently proposed. Contrarily to previous works, where the existing optimal-based protocols are evaluated considering an ideal physical layer without transmission errors, this paper evaluates the performance of these protocols when transmission errors are considered. The analysis compares a recent optimal MAC scheme proposed by our team (OMACP - Optimal MAC Protocol) with two other optimal-based protocols (Idle Sense and AOB), extending the evaluation to two heuristic-based solutions (IEEE 802.11 MAC and GDCF protocol). A comparison is made for the throughput, delay and fairness index achieved by each protocol. The results evidence higher performance for optimal-based protocols, highlighting the good performance of our recently proposed protocol.

A distributed MAC protocol for multi-packet reception wireless networks

In this paper we propose two decentralized medium access control (MAC) schemes to coordinate the access of multiple transmitters adopting a Multi-Packet Reception (MPR) physical (PHY) layer. The proposed MAC schemes operate over a MPR-based PHY-layer and are divided in two stages. In the first stage the nodes indicate their willingness to transmit, while in the second one they jointly transmit. The MAC schemes differ by considering a Single-Packet Reception (SPR) or a MPR PHY-layer in the first stage. We analyze the throughput achieved by each MAC in a theoretical way. Several results obtained through simulation are also presented, which validate the numerical results obtained with the theoretical model. The results demonstrate the effectiveness of the proposed MAC schemes, and allow us to draw valuable conclusions about the design of distributed MPR systems.

Practical Assessment of Energy-Based Sensing through Software Defined Radio Devices

In recent schemes proposed to the physical layer of wireless systems the receiver node has the capability of simultaneously receiving multiple transmissions, which is commonly referred to as a Multi-Packet Reception (MPR) scheme. Assuming that the transmitters are randomly located in the far-field region and a generic signal-to-interference-plus-noise ratio (SINR) threshold-based criterion is used as the packet capture model, we derive the probability of successful reception of a packet considering path loss, shadowing and fading effects. Our approach relies on the characterization of the aggregate interference caused by the transmitters, which is used in the capture model in a simplified way. The probability of successful reception of a packet is then used to approximate the average number of packets simultaneously received. The proposed analysis is evaluated for different scenarios and compared with several results obtained through simulation. The simplicity of the model, as well as its accuracy, makes it a useful tool to assist the design of future medium access control mechanisms for MPR wireless systems.

Channel Availability Assessment for Cognitive Radios

In this paper we propose a decentralized medium access control (MAC) scheme to coordinate the access of multiple transmitters adopting a multi-packet reception (MPR) physical (PHY) layer. MPR receivers are able to decode multiple transmissions, and depending on the technique adopted at the PHY-layer, there is an optimal number of simultaneous transmissions that maximize the number of packets successfully decoded in a simultaneous way. The proposed MAC scheme admits an MPR PHY-layer and is divided in two stages. In the first one the nodes indicate their willingness to transmit, while in the second one they jointly transmit. Adopting a generic model for the PHY-layer, we characterize the throughput achieved by the proposed MAC when both MAC and PHY layers are considered. The formal characterization of the throughput is then used to optimize the duration of the first stage of the MAC scheme in order to optimize the throughput. In this way, the number of transmitters is regulated to optimize the cross-layer operation, taking into consideration the features of the MPR PHY-layer and the maximum performance achieved with the proposed MAC design. Several results obtained through simulation are presented, which validate the numerical results obtained with the proposed characterization. The proposed scheme is a first step to develop MAC protocols specifically designed to distributed MPR systems that operate in a cross-layer and improve the exploitation of current and future MPR techniques proposed for the PHY-layer.