Variable Propagation Delay Research Articles

MixMatch: Flow Matching for Mixnet Traffic

Mixnets provide communication anonymity against network adversaries by routing packets independently via multiple hops, delaying them artificially at each hop, and introducing cover traffic. We show that these features (particularly the use of cover traffic) significantly diminish the effectiveness of state-of-the-art flow correlation techniques developed to link the two ends of a Tor connection. In this work, we propose novel methods to determine whether a set of endpoints exchanges packets via a mixnet and demonstrate their effectiveness by applying them to the Nym mixnet. We consider Nym in both an idealized lab setup and the official live network, and propose and compare three classifiers to conduct flow matching on it. Our statistical classifier tests whether egress packet timestamps are consistent with ingress timestamps and the (known) routing delay characteristic of the mixnet. In contrast, our two deep learning (DL) classifiers learn to distinguish matched from unmatched flow pairs from collected datasets directly, rather than relying on priors that describe the delay distribution. All three classifiers use our flow merging technique, which enables testing a match for sets of communicating endpoints of any cardinality. Considering a use case where two observed endpoints communicate exclusively to exchange a file through Nym, we find that flow matching is fast and accurate in the idealized lab setup. If flow pairs are aligned using all network observations in a download, we achieve a TPR of circa 0.6 (DL) and 0.47 (statistical) at an FPR of 10^-2 after only processing 100 observations. We evaluate classifier performance under key variations of this setup: the absence of loop cover traffic, an increased or decreased average per-mix delay, larger communicating sets (three endpoints) with faster responders, and the presence of realistic network effects (live network). The classifiers' matching performance diminishes on the live network where packet losses and variable propagation delays exist, reducing DL TPR to circa 0.26 and statistical TPR to circa 0.28 at an FPR of 10^-2. Informed by the insights of our analyses, we outline countermeasures that can be deployed in mixnets such as Nym to mitigate flow matching threats.

An On-Demand Scheduling-Based MAC Protocol for UW-WiFi Networks

Underwater Internet-of-Things (UIoT) is an extension of Internet-of-Things technology in underwater. The underwater acoustic network with WiFi architecture (UW-WiFi), as a specific deployment of UIoT, has been proved to be a promising technique for wide-ranging marine applications. However, due to the unique features of underwater acoustic channel, such as long and variable propagation delay, low available bandwidth and high bit error rate, conventional medium access control (MAC) protocols designed for terrestrial WiFi networks need an overhaul to work efficiently for UW-WiFi networks. In consideration of the aforementioned channel features, different demands of nodes to occupy channel resources and the reliability of data transmission, a time sequence-based dynamic on-demand assignment (SDDA) MAC protocol for UW-WiFi networks is proposed in this paper. In SDDA, the collision-free scheduling is integrated with the reservation mechanism, aiming to address the issue of various access requirements of diverse task nodes on channel resources in the UW-WiFi network system. The designed protocol employs propagation delays and the amount of data to be sent by terminal nodes to achieve non-conflict transmissions of control packets and on-demand scheduling of data packets. Additionally, the scheme does not require extra overhead for time synchronization. Comparison simulations demonstrate that SDDA provides considerable benefits in terms of channel utilization, end-to-end delay and packet delivery ratio. At last, the SDDA protocol is implemented and a UW-WiFi network system is set up in the marine environment. The ocean field experiment results agree well with the simulated ones and also verify that the proposed protocol achieve conflict-free on-demand scheduling, fairness among terminal nodes at different ranges and the practicability in actual environments.

High-Speed 16-bit Carry Bypass Adder Design

Adders are one of the most significant blocks in a logical arithmetic unit. These are employed in a wide range of applications, from incrementing the value of a program variable to high-speed applications such as video-encoding, digital-signal. There are various adders with varying propagation delays. As a result, selecting an efficient adder is critical for system performance. This research compares the latency of several 16 bit adders that are available. The delay of logic gates in 180nm technology has been quantitatively modelled utilizing logical effort. The delay is then utilized to calculate the delay of various adders in Virtuoso Cadence while simulating. Virtuoso Cadence was used to perform functional verification on adders. Each adder's route delay has also been determined. Based on this research, a new carry bypass adder has been developed to reduce propagation delay. The suggested carry bypass adder reduces combinational path latency by 7.2 percent and logical effort delay by 29.5 percent, respectively. Keywords: Algorithms for 16-bit adders, logical effort, propagation delay, carry skip adder

Review of ALOHA-based MAC Protocols for Underwater Wireless Sensor Networks. (Dept.E. Computer)

The aquatic environment has become clearer and more controllable since Underwater Wireless Sensor Networks (UWSNs) intervened to detect them, because underwater wireless sensor networks are efficiently providing and supporting many civilian and military applications, and many have been decomposed and extracted for helping to avoid falling into many problems, causing many physical and economic losses. Media Access Control (MAC) protocol plays a fit role to enhance the performance of the network which helps to quickly accomplish the tasks that are required from the network and without additional cost. Low and limited bandwidth, energy, limited memory, long and variable propagation delay, and high bit error rate are some challenges that face the designing of the MAC protocol for UWSNs. ALOHA protocol is one of the most popular MAC protocols. In this article, we focus on providing a review of the state of art of the most recent developments of ALOHA protocols for UWSNs from recent literature. These protocols are P-ALOHA, S-ALOHA, ALOHA–CS, ALOHA-AN, BUFFERED-ALOHA, SLOTTED-CS-ALOHA, VI-ALOHA, L-ALOHA, ST-SLOTTED-CS-ALOHA, MODIFIED-SLOTTED-ALOHA, SLOTTED-BUFFERING-ALOHA, and BUFFERING_SLOTTED_ALOH. A discussion of the characteristics and restrictions of every ALOHA protocol in addition to explaining comparisons among all these protocols according to different performance metrics is also presented in this paper. The performance metrics used are the average delay, the energy consumption ratio, the number of dropped nodes, and the throughput ratio.

A TDMA-Based Data Gathering Protocol for Molecular Communication via Diffusion-Based Nano-Sensor Networks

This paper explores the application of molecular communication via diffusion-based nano-sensor networks (MCSNs) for data gathering applications in in-body medical systems. For MCSNs, the large and varying propagation delay in the channel presents a fundamental challenge for channel access, leading to packet collisions. Although packet collisions are well-studied for traditional wireless sensor networks, to date, there are no such studies conducted for MCSNs. Another fundamental challenge is the limited capabilities of the nano-sensors, rendering the existing solutions inefficient. Therefore, a novel light-weight time-division multiple access (TDMA)-based data gathering multiple access control (MAC) protocol is proposed. Light-weight here implies that long information, such as timestamps, is not exchanged. TDMA-based here implies that each nano-sensor is designated an exclusive time-slot. The lack of a channel model for spherical transmitters impairs theoretical analysis of the probability of packet collisions. To overcome this, the propagation delay is approximated as a Normal distribution. The model is validated using the widely popular particle-based simulation, which is also used to determine the packet duration considering ON-OFF shift keying. Building upon these analyses, a system-level simulator is developed to evaluate the proposed MAC protocol. For the first time, the packet collision probability is characterized under varied distances and diffusion coefficients. A key finding is the correlation between the channel utilization and the time-slot occupancy ratio, which can be used as a tool to optimize the performance of an MCSN. Finally, comparisons with conventional TDMA reveals that the proposed protocol can offer better performance.

RPCP‐MAC: Receiver preambling with channel polling MAC protocol for underwater wireless sensor networks

SummaryTo design a reliable and energy efficient medium access control (MAC) protocol for underwater wireless sensor networks (UWSNs) is an active research area due to its variety of applications. There are many issues associated with underwater acoustic channels including long and variable propagation delay, attenuation, and limited bandwidth which pose significant challenges in the design of MAC protocol. The available sender‐initiated asynchronous preamble‐based MAC protocols for UWSNs are not reliable and energy‐efficient. This is due to the problems caused by transmission of preambles for longer duration and collision of preambles from hidden nodes in sender‐initiated preamble‐based MAC protocols. To resolve these issues, the paper proposed an asynchronous receiver‐initiated preamble‐based MAC protocol named Receiver Preambling with Channel Polling MAC (RPCP‐MAC) protocol for shallow underwater monitoring applications with high data rates. The protocol is proposed to resolve data packet collision and support reliability in an energy‐efficient way without using any transmission schedule. The proposed protocol is based on the following mechanisms. Firstly, receiver preambling mechanism is adopted to reduce idle listening. Secondly, channel polling mechanism is used to determine missing data frame during its sleeping period and to minimize the active time of node and reduces energy wastage. Finally, a back‐off mechanism is applied to resolve collision when preambles are received simultaneously. In addition, performance analysis through Markov chain together with its validation with simulation‐based studies is reported in the paper. Both the analytical and simulation results have demonstrated the reliability achievable with RPCP‐MAC while providing good energy efficiency.

LAVR: link failure avoidance and void recovery routing protocol for underwater sensor networks

Recently, underwater wireless sensor network (UWSN) has paved the way for researchers towards a new era of exploring ocean realm targeting envisioned landscape of underwater applications. These applications can be made viable through underwater communication by using acoustic waves, giving rise to several design challenges like limited bandwidth, large and variable propagation delay, frequent connectivity loss, etc. Reliable data delivery in UWSN is always a tempting issue to be addressed, which is jeopardised by link failures and communication void. Under this context, Link failure Avoidance and Void Recovery (LAVR) routing protocol is proposed that uses link quality as forwarding factor, computed using Triangle Metric, to achieve reliability. A void node recovery procedure is proposed to displace the void node to a new depth to increase the packet delivery ratio. Simulations are performed in Aqua-Sim simulator and LAVR outperforms other existing protocols in terms of packet delivery ratio and network lifetime.

LAVR: link failure avoidance and void recovery routing protocol for underwater sensor networks

Recently, underwater wireless sensor network (UWSN) has paved the way for researchers towards a new era of exploring ocean realm targeting envisioned landscape of underwater applications. These applications can be made viable through underwater communication by using acoustic waves, giving rise to several design challenges like limited bandwidth, large and variable propagation delay, frequent connectivity loss, etc. Reliable data delivery in UWSN is always a tempting issue to be addressed, which is jeopardised by link failures and communication void. Under this context, Link failure Avoidance and Void Recovery (LAVR) routing protocol is proposed that uses link quality as forwarding factor, computed using Triangle Metric, to achieve reliability. A void node recovery procedure is proposed to displace the void node to a new depth to increase the packet delivery ratio. Simulations are performed in Aqua-Sim simulator and LAVR outperforms other existing protocols in terms of packet delivery ratio and network lifetime.

Stability of S‐Aloha with variable propagation delay

State-of-the-art variants of slotted Aloha (S-Aloha) for underwater acoustic networks do not consider the joint effect of retransmission and distance-dependent propagation delay variability, which is one of the most important parameters that affect the performance of any medium access control protocol. In this study, the authors analyse the stability of S-Aloha in a network environment, such as underwater, where propagation delay and its variance are not negligible. A finite number of unbuffered transmitters are considered. Through mathematical analysis, supported by discrete event simulations, they compare the utilisation and stability with S-Aloha in radio frequency environments where propagation delay, as well as delay variance, are negligible. The comparison results indicate that the stability region is appreciably shifted and also there is a significant decrease of utilisation in the presence of retransmission and distance-dependent propagation delay variability.

LDMAC: A propagation delay-aware MAC scheme for long-distance UAV networks

Unmanned aerial vehicles (UAVs) are gaining increasing importance in military and civilian applications. A challenging problem is the efficient communication between multiple UAVs and terrestrial base station (BS), where a wireless link has to cover hundreds of miles. These long-distance wireless networks suffer from heterogeneous and varying propagation delays, making conventional medium access control (MAC) protocols inappropriate. In this paper, a propagation delay-aware access scheme, LDMAC, is designed for long-distance UAV networks. It is a joint design of random access and collision-free time slot allocation. UAVs contend for time slots based on improved Irregular Repetition Slotted Aloha (IRSA), and subsequently the BS makes a collision-free, fair and optimized time slot allocation with temporal reuse. Both of the processes take full advantage of propagation delay to efficiently improve system throughput. Simulation results show that LDMAC achieves up to 30% improvement over IRSA with respect to successful decoding rate (SDR), and outperforms competing protocols that include IRSA and dynamic time division multiple access (D-TDMA) in terms of throughput in mobile wireless networks.

A Stateless Opportunistic Routing Protocol for Underwater Sensor Networks

Routing packets in Underwater Sensor Networks (UWSNs) face different challenges, the most notable of which is perhaps how to deal with void communication areas. While this issue is not addressed in some underwater routing protocols, there exist some partially state‐full protocols which can guarantee the delivery of packets using excessive communication overhead. However, there is no fully stateless underwater routing protocol, to the best of our knowledge, which can detect and bypass trapped nodes. A trapped node is a node which only leads packets to arrive finally at a void node. In this paper, we propose a Stateless Opportunistic Routing Protocol (SORP), in which the void and trapped nodes are locally detected in the different area of network topology to be excluded during the routing phase using a passive participation approach. SORP also uses a novel scheme to employ an adaptive forwarding area which can be resized and replaced according to the local density and placement of the candidate forwarding nodes to enhance the energy efficiency and reliability. We also make a theoretical analysis on the routing performance in case of considering the shadow zone and variable propagation delays. The results of our extensive simulation study indicate that SORP outperforms other protocols regarding the routing performance metrics.

Trade-off Analysis of Underwater Acoustic Sensor Networks

In the last couple of decades, Underwater Acoustic Sensor Networks (UASNs) were started to be used for various commercial and non-commercial purposes. However, in underwater environments, there are some specific inherent constraints, such as high bit error rate, variable and large propagation delay, limited bandwidth capacity, and short-range communications, which severely degrade the performance of UASNs and limit the lifetime of underwater sensor nodes as well. Therefore, proving reliability of UASN applications poses a challenge. In this study, we try to balance energy consumption of underwater acoustic sensor networks and minimize end-to-end delay using an efficient node placement strategy. Our simulation results reveal that if the number of hops is reduced, energy consumption can be reduced. However, this increases end-to-end delay. Hence, application-specific requirements must be taken into consideration when determining a strategy for node deployment.

Beacon‐based routing protocols for underwater acoustic sensor networks

SummaryUnderwater Acoustic Sensor Networks (UW‐ASN) are provisioned with limited bandwidth, long variable propagation delay, limited available energy, highly unreliable acoustic channels, and random node mobility. Consequently, efficient data routing between source destination pair requires UW‐ASN to apply a technology different than terrestrial networks. For the past few years researchers have proposed many robust and efficient routing protocols for UW‐ASN, thus reviewing the challenges posed by stringent underwater environment. These protocols can be broadly categorized into localization based and localization‐free protocols. This paper presents a critical review of beacon‐based localization‐free routing protocols and suggest possible solution to improve the working of studied beacon based protocols. This work categorizes beacon based protocols into hop‐by‐hop, end‐to‐end, single, and multiple parameters based forwarding protocols. This categorization will help to differentiate and identify the requirements for the development of new beacon‐based protocols. Finally, this paper presents performance comparison based on simulation results and outlines the research gap and future directions.

Asynchronous Cooperative Aloha for Multi-Receiver Satellite Communication Networks

Satellite communication networks suffer from heterogeneous and varying propagation delay, which makes slotted random access (RA) protocols being no longer favorable, especially in the multi-receiver scenario. Different from other train of thoughts for RA algorithms, an asynchronous RA scheme named asynchronous cooperative Aloha (ACA) is introduced to benefit from the heterogeneous and varying propagation delay in satellite communication networks. A specific packet is transmitted only once with the concept of spatial diversity, and multiple receivers are used to receive the packets. Cooperative interference cancellation technique combined with sliding correlation scheme is adopted to efficiently resolve packet collisions at the gateway. The performance of ACA scheme is evaluated via mathematical analysis and simulations. Simulation results show that ACA outperforms the conventional asynchronous RA scheme in terms of throughput and packet loss ratio.

Accurate and Robust Time Reconstruction for Deployed Sensor Networks

The notion of global time is of great importance for many sensor network applications. Time reconstruction methods aim to reconstruct the global time with respect to a reference clock. To achieve microsecond accuracy, MAC-layer timestamping is required for recording packet transmission and reception times. The timestamps, however, can be invalid due to multiple reasons, such as imperfect system designs, wireless corruptions, or timing attacks, etc. In this paper, we propose ART, an accurate and robust time reconstruction approach to detecting invalid timestamps and recovering the needed information. ART is much more accurate and robust than threshold-based approach, especially in dynamic networks with inherently varying propagation delays. We evaluate our approach in both testbed and a real-world deployment. Results show that: 1) ART achieves a high detection accuracy with low false-positive rate and low false-negative rate; 2) ART achieves a high recovery accuracy of less than 2 ms on average, much more accurate than previously reported results.

수중 통신 시스템을 위한 가변 길이를 갖는 Slotted ALOHA

In this letter, we consider a random access scheme for underwater acoustic network, in which a slotted ALOHA with variable slot length is designed to enhance the random access performance for the nodes with the varying propagation delay.

Pressure Based Routing Protocol for Underwater Wireless Sensor Network: A Survey

Underwater wireless sensor networks (UWSNs) are similar to the terrestrial sensor networks. Nevertheless, there are different characteristics among them such as low battery power, limited bandwidth and high variable propagation delay. One of the common major problems in UWSNs is determining an efficient and reliable routing between the source node and the destination node. Therefore, researchers tend to design efficient protocols with consideration of the different characteristics of underwater communication. Furthermore, many routing protocols have been proposed and these protocols may be classified as location-based and location-free routing protocols. Pressure-based routing protocols are a subcategory of the location-free routing protocols. This paper focuses on reviewing the pressure-based routing protocols that may further be classified into non-void avoidance protocols and void avoidance protocols. Moreover, non-void avoidance protocols have been classified into single factor based and multi factor based routing protocols. Finally, this paper provides a comparison between these protocols based on their features, performance and simulation parameters and the paper concludes with some future works on which further study can be conducted.

A Handshake Based Ordered Scheduling MAC Protocol for Underwater Acoustic Local Area Networks

Underwater acoustic local area networks (UA-LANs) can be used to improve the coverage of an underwater network by introducing a tier of local area communications. Media access control (MAC) is a crucial issue for UA-LANs. Existing MAC protocols for terrestrial WLANs cannot be directly applied to UA-LANs due to the acoustic channel features of limited bandwidth and high and variable propagation delay. In this paper, we propose a handshake based ordered scheduling MAC (HOSM) protocol for UA-LANs. The nodes with data packets to be transmitted first reserve the channel in a channel reservation phase. Then an order list is calculated, and the data packets of these nodes are transmitted according to this order list. We develop a control packets transmission adjustment mechanism to reduce collisions of control packets. The key idea of this mechanism is to utilize the information of propagation delay to adjust the time instant of control packets transmitting. To improve channel utilization, we present a variant Max-Min Ant System algorithm to calculate an optimal order for each data transmission round. Simulation results have confirmed that the proposed protocol can achieve high throughput with low delay and good spatial fairness.

τ-NEAT: Initial experiments in precise temporal processing through neuroevolution

Neuroevolution of Augmenting Topologies (NEAT) has been a very successful algorithm for evolving Artificial Neural Networks (ANNs) that adapt their structure and processing to the task that is required from them. However, this algorithm is not always reliable when handling time related processes and this may be due to its lack of explicit temporal elements within its structure. Of course, NEAT can handle time dependent phenomena through the use of recurrences within the networks it builds, but it is well known that simple recurrences do not easily allow for precise temporal processing due to the history effect they induce on the networks. Many authors have argued for the introduction of other mechanisms, which are also present in natural systems, such as variable or trainable propagation delays in the synapses of the networks that must deal with precise temporal processing. In this paper, we carry out an initial study of a new implementation of NEAT called ?-NEAT that includes the possibility of introducing variable delays in the synapses of the networks NEAT constructs. These delays can affect both, regular direct synapses or recurrent connections. To evaluate the performance of this implementation several tests are carried out over different types of temporal functions and the results of the traditional version of NEAT and ?-NEAT are compared.

Geographic Routing Protocols For Underwater Wireless Sensor Networks: A Survey

Underwater wireless sensor networks (UWSN), similar to the terrestrial sensor networks, have different challenges such as limited bandwidth, low battery power, defective underwater channels, and high variable propagation delay. A crucial problem in UWSN is finding an efficient route between a source and a destination. Consequently, great efforts have been made for designing efficient protocols while considering the unique characteristics of underwater communication. Several routing protocols are proposed for this issue and can be classified into geographic and non-geographic routing protocols. In this paper we focus on the geographic routing protocols. We introduce a review and comparison of different algorithms proposed recently in the literature. We also presented a novel taxonomy of these routing in which the protocols are classified into three categories (greedy, restricted directional flooding and hierarchical) according to their forwarding strategies.