Slot Duration Research Articles

Performance analysis of a wireless sensor network with cognitive radio capabilities in structural health monitoring applications: A discrete model

This article studies the performance of a wireless sensor network with cognitive radio capabilities to gather information about structural health monitoring of buildings in case of seismic activity. Since the use of the local area network is intensive in office and home environments, we propose the use of empty cellular channels (primary system). As such, the structural health monitoring does not degrade the local communications. Thus, the wireless sensor network for structural health monitoring acts as secondary network. Two discrete-time analytical approaches are proposed and developed to evaluate the system performance in terms of both the average packet delay and average energy consumption. The first one is an approximation suitable for the case when the time slot duration is small relative to the mean call inter-arrival time. The second model is accurate for any time slot duration and inter-arrival times.

Random Pilot and Data Access in Massive MIMO for Machine-Type Communications

A massive MIMO system, represented by a base station with hundreds of antennas, is capable of spatially multiplexing many devices and thus naturally suited to serve dense crowds of wireless devices in emerging applications, such as machine-type communications. Crowd scenarios pose new challenges in the pilot-based acquisition of channel state information and call for pilot access protocols that match the intermittent pattern of device activity. A joint pilot assignment and data transmission protocol based on random access is proposed in this paper for the uplink of a massive MIMO system. The protocol relies on the averaging across multiple transmission slots of the pilot collision events that result from the random access process. We derive new uplink sum rate expressions that take pilot collisions, intermittent device activity, and interference into account. Simplified bounds are obtained and used to optimize the device activation probability and pilot length. A performance analysis indicates how performance scales as a function of the number of antennas and the transmission slot duration.

Link‐layer security in TSCH networks: effect on slot duration

AbstractThe IEEE802.15.4e‐2012 standard is widely used in multi‐hop wireless industrial Internet of things applications. In the time‐slotted channel hopping mode, nodes are synchronised, and time is cut into timeslots. A schedule orchestrates all communications, resulting in high reliability and low power operations. A timeslot must be long enough for a node to send a data frame to its neighbour, and for that neighbour to send back an acknowledgement. Shorter timeslots enable higher bandwidth and lower latency, yet the minimal timeslot duration is limited by how long link‐layer security operations take. We evaluate the overhead of link‐layer security in time‐slotted channel hopping networks in terms of minimal timeslot length, memory footprint and energy consumption. We implement full link‐layer security on a range of hardware platforms, exploring different hardware/software implementation strategies. Through an extensive measurement campaign, we quantify the advantage of hardware accelerations for link‐layer security and show how the minimal duration of a timeslot varies between 9 and 88ms for the most common configuration, depending on hardware support. Furthermore, we also highlighted the impact that the timeslot duration has on both high‐level application design and energy consumption. Copyright © 2016 John Wiley & Sons, Ltd.

Reliability and delay analysis of multicast in binary molecular communication

Molecular communication is a new and promising communication technology. However, we consider that molecular communication easily suffers from high unreliability and long delay due to the stochastic behavior of the molecules in a biological environment, thus it is essential to investigate the characteristics of reliability and delay in molecular communication. In this paper, we analyze the reliability and delay in multicast topology based on binary molecular communication model. First, we give the mathematical expressions of reliability and delay in different scenarios including a single link, a single path and multicast topology, respectively. In particular, we use retransmission mechanism for transmission failure. Then the numerical results derived from the simulation performances show how the parameters including diffusion coefficient, the distance between transmitter nanomachine and receiver nanomachine, the number of molecules emitted in each time slot, the number of slots and each time slot duration have impacts on reliability and delay. More importantly, under the same reliability, lower delay can be theoretically realized by binary molecular communication model compared to the concentration model of virus-based nanonetworks.

Content based Video Retrieval using Text Annotation and Low Level Features Technique

The information retrieval processes are playing essential role in the computer based database exploration or finding the essential contents from the databases. Now in these days a number of search techniques and retrieval models are exist by using which the users can find the data. According to the different data formats the information retrieval processes are also varying therefore different data format based retrieval process are works in different manner. In this presented work the content based video retrieval model is presented. In the content based video retrieval model the work is initiated from the segmentation of the videos into the set of frames. The segmentation of video is performed using the FFMPEG media library that works on the basis of two parameters first the video clip and second the time slot duration by which the frames are extracted. After segmentation to enable the text based query the text annotation concept is used and the individual frames of video is tagged with the user defined text. On the other hand to enable the query by example the low level features of individual frames are also computed. To compute the low level descriptors shape, color and texture analysis is performed. Thus the canny edge detection, local binary pattern and the color movement analysis techniques are used. Finally for classifying the relevant videos according to the user query the KNN classifier is implemented. That classifier accepts the user text query or the example query for classifying the similar video objects from the database. The implementation of the presented methodology is performed using JAVA technology. Additionally for finding the performance precision, recall, and f-measures are computed, according to the computed values the example based techniques provides more accurate outcomes as compared to text based query. In addition of that the resource consumption of the proposed technique is also computed in terms of time and space, according to the results the example based query processing consumes additional resources as compared to text based methods. Thus the proposed work is accomplished with the satisfactory performance.

A Distributed Opportunistic MAC Protocol for Multichannel Wireless Networks

We propose a distributed opportunistic medium access control (MAC) scheme for maximizing the expected aggregate throughput in a multichannel wireless network such as a clustered orthogonal frequency-division multiple access (OFDMA) network. In our proposed scheme, each user attempts to send only on its best channel and transmits if the best-channel gain is higher than a given threshold, which is dynamically updated depending on previous idle and collision situations. In this way, with our proposed scheme, in a homogeneous system where the channel fading distribution is identical for all users, the best user for each channel is obtained in a distributed manner. We also obtain the optimal values of the thresholds so that the probability of successful transmission is maximized and a minimal number of transmission opportunities are wasted (e.g., due to collision or idle transmissions). In the asymptotic limit of a large number of users and sufficiently long transmission slot duration, we show that, in comparison with the optimal centralized scheme, the throughput loss for our proposed scheme goes to zero. Furthermore, we extend our distributed opportunistic MAC scheme for a homogeneous system to that for a heterogeneous system where the channel fading distribution is heterogeneous across users. Throughput performances and signaling overhead are analyzed for the proposed distributed MAC schemes and compared with those of the existing schemes. Simulation results show that our proposed schemes significantly improve the average aggregate throughput when compared with the existing schemes.

An Adaptive Slot TDMA MAC Protocol for Underwater Sensor Networks

In this study, we introduce a new media access control (MAC) protocol that adaptively changes time division multiple access (TDMA) frame size and slot duration in order to upgrade performance of underwater sensor networks. Throughput of underwater sensor networks is very low compared to a radio frequency (RF) network; the reason is a very long propagation delay and a very low bit rate. To solve these problems, we modified the TDMA protocol and introduce a new TDMA MAC protocol (aTDMA). Basically, the TDMA MAC protocol provides a time slot to each node, and the node transmits data in the allocated time slot so transmission does not collide with another node’s transmission. But if a node has no data, it wastes its slot. For the propagation delay in underwater acoustic sensor networks, the length of each slot is very long, so the waste of a slot can cause a serious reduction in performance. The proposed protocol, aTDMA, can remove the wasting of slot times and can change slot duration according to the distance between nodes. Through experiments, aTDMA shows better performance than the conventional TDMA MAC protocol.

English

The personal area network (PAN) coordinator can assign a guaranteed time slot (GTS) to allocate a particular duration for requested devices in IEEE 802.15.4 beacon-enabled mode. The main challenge in the GTS mechanism is how to let the PAN coordinator allocate time slot duration for the devices which request a GTS. If the allocated devices use the GTS partially or the traffic pattern is not suitable, wasted bandwidth will increase, which degrades the performance of the network. In order to overcome the abovementioned problem, this paper proposes the Partitioned GTS Allocation Scheme (PEGAS) for IEEE 802.15.4 networks. PEGAS aims to decide the precise moment for the starting time, the end, and the length of the GTS allocation for requested devices taking into account the values of the superframe order, superframe duration, data packet length, and arrival data packet rate. Our simulation results showed that the proposed mechanism outperforms the IEEE 802.15.4 standard in terms of the total number of transmitted packets, throughput, energy efficiency, latency, bandwidth utilization, and contention access period (CAP) length ratio.

Throughput Maximization for Sensor-Aided Cognitive Radio Networks with Continuous Energy Arrivals.

We consider a Sensor-Aided Cognitive Radio Network (SACRN) in which sensors capable of harvesting energy are distributed throughout the network to support secondary transmitters for sensing licensed channels in order to improve both energy and spectral efficiency. Harvesting ambient energy is one of the most promising solutions to mitigate energy deficiency, prolong device lifetime, and partly reduce the battery size of devices. So far, many works related to SACRN have considered single secondary users capable of harvesting energy in whole slot as well as short-term throughput. In the paper, we consider two types of energy harvesting sensor nodes (EHSN): Type-I sensor nodes will harvest ambient energy in whole slot duration, whereas type-II sensor nodes will only harvest energy after carrying out spectrum sensing. In the paper, we also investigate long-term throughput in the scheduling window, and formulate the throughput maximization problem by considering energy-neutral operation conditions of type-I and -II sensors and the target detection probability. Through simulations, it is shown that the sensing energy consumption of all sensor nodes can be efficiently managed with the proposed scheme to achieve optimal long-term throughput in the window.

A Time and Capture Probability Aware Closed Form Frame Slotted ALOHA Frame Length Optimization

Minimizing the reading time in dense radio-frequency identification (RFID) networks is a critical issue. Commonly used RFID systems are based on frame alotted ALOHA (FSA) for tag anti-collision management. The usual approach for improved reading times with large tag populations is the optimization of the number of slots per frame. In real RFID systems, the slot duration depends on the slot type (i.e. idle, successful, or collided). In addition, collided slots might be converted to successful slots by capturing the strongest transponder, i.e. the so-called capture effect. Recent publications have proposed numerical solutions for obtaining the optimum frame length under these assumptions. The authors employ numerical solutions that require Multi-dimensional look-up tables for obtaining the optimum frame length. In this letter, we propose a closed form solution for the analytical calculation of the optimum frame length. The proposed solution gives a novel closed form equation for the frame length considering the different slot durations and the capture effect. Moreover, this letter presents a new method to calculate the capture probability per frame. Simulations indicate that the proposed solution gives accurate results for all relevant parameter configurations without any need for multi-dimensional look-up tables.

Energy-aware resource allocation for cooperative cognitive radio dynamic spectrum access networks

The resource allocation problem is investigated for cooperative cognitive radio networks, considering energy efficiency of the primary users (PUs) and spectrum efficiency of the secondary users (SUs). The cooperation framework involves a PU selecting a SU as the relay and allocating the spectrum access intervals for the selected SU as a reward. The above sequential decision procedure is formulated as a Stackelberg game. Based on the knowledge of the effects of PUs decision on the behavior of a SU, the leader (PU) determines a fraction of the time slot duration to be used for the primary. The follower (SU) is allowed to transmit its own data to the corresponding receiver in the remaining duration and determines its optimal transmission power. The outcomes of the proposed cooperative resource allocation scheme, including primary user and secondary user power control, as well as dynamic access spectrum, are analyzed. Numerical results demonstrate that, with the proposed resource allocation scheme, the PU can achieve high energy saving by cooperation with the SU.

Statistical method for performance analysis of WBAN in time-saturation

Performance analysis of carrier sense multiple access with collision avoidance (CSMA/CA) scheme based on IEEE 802.15.6 standard has been discussed in many literatures. In previous works on IEEE 802.15.6 and another standards, the performance was analyzed by using access probability in one slot duration and the Markov chain model was proposed to calculate the access probability in both saturation and non-saturation models. However, for both saturation and non-saturation models, the access probability or the packet arrival rate was assumed to be fixed and the effect of remained packets that was transmitted unsuccessfully due to busy channel or collision was not considered. In this paper, in order to evaluate the system performance more accurately, the effect of the remained packet is taken into account and a statistical method is proposed to calculate the successful probability of wireless body area networks (WBANs). Moreover, a time-saturation model is defined as a system model in which the system performance is changed following the operating time, and then, the change between three models, i.e., saturation, non-saturation, and time-saturation models, is analyzed. The calculation result indicates that the proposal method can achieve the same performance as the Markov chain method in both saturation and non-saturation models. However, in the time-saturation model, the proposal statistical method is more accurate.

Analytical Computation of the Mean Number of Tag Identifications During a Time Interval in FSA

We analytically compute the mean number of identifications when $N$ tags contend in a bounded time interval of $T$ seconds in RFID systems using framed slotted aloha. Usually, performance is described in terms of identifications per time-slot. However, slot duration notably varies depending on the event (identification, collision, or empty slot). Moreover, during the reading process, the number of tags contending dynamically changes since identified tags withdraw from the process, and the frame length may vary dynamically as well. These conditions have been included in the model and lead to an accurate analysis of real RFID systems.

Framed ALOHA Protocol with FIFO-Blocking and LIFO-Push out Discipline.

This paper considers the framed ALOHA protocol for a finite number of terminals. Terminals are single-buffered, i.e. each one can store only one packet. We derive the throughput and the delay under two types of queue disciplines, first-in-first-out (FIFO) and last-in-first-out LIFO. It is assumed that terminals are independent each other and generate packets of constant size according to a Bernoulli process. The one slot duration equals to the one packet transmission. The analysis is carried out by means of Markovian tools. Some discussion on the applicability of that protocol is addressed.

Visible light communications employing PPM and PWM formats for simultaneous data transmission and dimming

A visible light communication system with simultaneous brightness control and data transmission is experimentally demonstrated in this paper. A pulse-width modulation (PWM) scheme is adopted for brightness control of the light-emitting diode and pulse-position modulation (PPM) superimposed on top of PWM is used for data communications. We show that independent control of light dimming is possible while transmitting data within a typical room environment, provided the PWM dimming period is an integer multiple of the PPM slot duration. To validate this, we show the measured eye diagrams for a range of dimming levels. In addition, we qualitatively illustrate examples of different dimming levels by changing the dimming level while maintaining the PPM data stream.

Activity aware energy efficient priority based multi patient monitoring adaptive system for body sensor networks

According to WHO, Cardiovascular diseases are the major cause of death worldwide. Due to the increase in cardiac diseases, miniaturized and energy efficient remote cardiac monitoring systems are required. To develop an Activity Aware Energy Efficient priority based Multi Patient Monitoring protocol for Body Sensor Networks to monitor physiological signals continuously. The protocol must also be adaptive to allow for new connections and to renegotiate the nodes services. In this protocol, the ECG signals of multiple patients are monitored one after another in a cyclic order. Slots are allotted to each patient by means of a dynamic TDMA scheme where the slot duration is dependent upon the criticality of the patient. A Network configuration slot is provided at the end of each frame to reconfigure the network. Using the wearer's activity level, the sensor dynamically manages its activities namely, sampling of the ECG sensor, processing of the data, and wireless transmission to minimize overall power consumption. Additional energy efficiency is achieved by assigning priorities to the devices connected in the network and turning them on and off periodically based on their priorities. The protocol is implemented on Shimmer nodes and ECG signals of N patients are monitored. The reconfiguration of the node's priority and sampling rate based on the health condition of the patient are demonstrated. A comparison of energy consumption, packet delivery ratio and battery life time is made. Energy consumption and nodes lifetime are the parameters to be optimized in the case of BSN. The AAEEPMPM protocol for BSN has been designed and implemented in hardware platform for energy efficiency. The results obtained from the BSN shows that this protocol has higher energy efficiency and provides better lifetime for the network.

Slow hopping based cooperative sensing MAC protocol for cognitive radio networks

A slow hopping based cooperative sensing MAC (SHCS-MAC) protocol is proposed in order to improve aggregate throughput as well as achieve better coexistence with primary users (PUs) and other secondary users (SUs) in cognitive radio (CR) networks where each node has only one half-duplex radio. The proposed SHCS-MAC protocol includes indispensible CR-MAC features such as bootstrapping, multi-channel operation, cooperative sensing, and self-coexistence. Bootstrapping algorithm enables a new node to join a common hopping based network. Slow hopping based multi-channel (MC) operation improves aggregate throughput by enabling concurrent data exchange in different channels on common hopping sequence in which the slot duration can be flexibly selected. Furthermore, cooperative sensing protocol appropriate for the slow hopping based MC-MAC is devised to increase PU detection probability. The improved detection probability enables SUs to promptly evacuate from the channel in which a PU appears. Finally, self-coexistence algorithm is proposed to mitigate the performance degradation due to the interference among neighboring networks. By using extensive simulation and analysis, SHCS-MAC is shown to more efficiently increase network capacity, improve PU detection probability, and achieve self-coexistence with minimal radio cost.

A Stochastic Shortest Path Model to Minimize the Reading Time in DFSA-Based RFID Systems

RFID systems implementing Dynamic Frame Slotted Aloha (DFSA) can adjust the number of identification rounds (slots) within an inventory cycle (frame). The usual approach to reduce the identification time of the tag population is to select the frame size attaining the highest throughput in the frame. However, it is more accurate to minimize the identification time of all the tags considering an indefinite long decision horizon. This is done in this paper by means of a Stochastic Shortest Path (SSP) formulation that incorporates capture effect and differentiation among slot durations. Our results show that the optimal policy is even faster than previous approaches.

Signal-to-Noise Ratio Estimation Algorithm for Advanced DVB-RCS Systems

This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) systems using adaptive coding and modulation (ACM) in the reverse link of broadband satellite systems. Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided (DA) and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided (NDA) estimator that was previously proposed by the authors for binary phase shift keying (BPSK) and QPSK schemes is extended to 8-PSK in a decision directed manner. This estimator shows improved performance over existing estimators. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, i.e., using the proposed estimator at moderate/high values of SNR and the moments-based estimator ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.

Throughput Analysis for Cognitive Radio (CR) Systems

In cognitive radio networks, the secondary network (users) are allowed to utilize the frequency bands of primary network (users) when they are not currently being used. To support this function, the secondary users are required to sense the radio frequency environment, and once the primary user is found to be active, the secondary users have to vacate the channel within certain amount of time. There are two parameters related to channel sensing: probability of detection and probability of false alarm. The higher the detection probability, the better the primary users can be protected. However, from the secondary users’ perspective, the lower the false alarm probability, the more chances the channel can be reused, thus the higher the achievable throughput for the secondary users. In this paper, we study the fundamental tradeoff between sensing capability and achievable throughput of the secondary users. Also, we present a design for sensing slot duration to maximize the achievable throughput for the secondary users under the constraint that the primary users are sufficiently protected. Using energy detection scheme, an optimal sensing time which provides the best tradeoff is given. Cooperative sensing is also studied based on the methodology of the proposed sensing throughput tradeoff. Computer simulations are presented to evaluate the proposed tradeoff methodology.