FD-LTDA-MAC: Full-Duplex Unsynchronised Scheduling in Linear Underwater Acoustic Chain Networks

In-band full-duplex communication offers significant potential to enhance network performance. This paper presents the full-duplex linear transmit delay allocation MAC (FD-LTDA-MAC) protocol for full-duplex based underwater acoustic chain networks (FD-UACNs) for subsea pipeline monitoring. This incorporates a number of extensions to the LTDA-MAC protocol in order to fully exploit advantages of full-duplex communication to enhance the efficiency of underwater facility monitoring. The protocol uses a greedy optimisation algorithm to derive collision-free packet schedules for delivering data packets to the sink node of the underwater chain network. The purpose of this paper is to show the significant improvement that can be achieved in packet scheduling by exploiting temporal spectrum re-use of an underwater acoustic channel through full-duplex communication. Simulation results show that more efficient packet scheduling and reduced end-to-end packet delays can be achieved in large scale scenarios using FD-LTDA-MAC compared with LTDA-MAC and LTDA-MAC with full-duplex enabled nodes. It can provide much higher monitoring rates for long range underwater pipelines using low cost, mid range, low rate, and low power acoustic modems.

Mathematical model of delay based on a system with gamma distribution

This article is devoted to the analysis of a queuing system formed by two flows with density functions of the gamma distribution law in order to derive a solution for the average delay of requests in the queue, which is the main characteristic for any queuing system. According to this characteristic, for example, packet delays in packet-switched networks are estimated when they are modeled using the queuing system. In queuing theory, studies of G/G/1 systems are especially relevant because there is no solution in the final form for the general case. Therefore, in the study of such systems, various particular distribution laws are used as an arbitrary distribution law for G. In the study of G/G/1 systems, an important role is played by the method of spectral decomposition of the solution of the Lindley integral equation, and most of the results in the theory of queuing were obtained using this method. The article presents the derivation of the calculation formula for the average delay of requests in the queue in the system under consideration, also based on the spectral decomposition method.

Reducing Conservatism in Analysis of Networked Control Systems Using Order Constraints

This paper deals with the analysis of the stability of networked control systems (NCS). In NCS, the signal transmission between the plant and the controller is done through a communication network. Usually, this data transmission faces packet delay and dropout. Two types of NCS modeling for networks with packet dropout and one type of modeling for networks with packet delays are introduced. These models are of discrete-time switched linear types and there may be constraints on the order of the subsystems’ occurrence. The analysis will be conservative if these constraints are not taken into account. It is shown that by considering these constraints, the stability analysis will be less conservative. Both deterministic and stochastic analyses are considered and compared.

Practical cross-layer testing of HARQ-induced delay variation on IP/RTP QoS and VoLTE QoE

As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may impose additional delay when their code-block retransmissions occur, the arising question is whether these significantly contribute to IP and consequently RTP packet delays, and finally degrade the overall application-layer end-to-end QoE, especially when voice is transmitted over LTE? With this regard, we propose and demonstrate a VoLTE QoS and QoE test procedure based on PHY/MAC/RLC/IP/TCP-UDP/RTP cross-layer protocol analysis and perceptual speech quality QoE measurements. We identified monotonic relationship between the paired observations: QoE and HARQ RTT, i.e. between the PESQ voice quality rating and the IP/RTP packet latency, for given BLER of the received MAC/RLC code-blocks. Specifically, we found out that, for the HARQ RTT value of about 8 ms, only up to 2 HARQ retransmissions (and consequently no RLC-ARQ one) is appropriate during any voice packet, otherwise delay accumulation might not be accordingly “smoothed out” by jitter/playback buffers along the propagation path.

Supporting Real-Time Data Transmissions in Cognitive Radio Networks Using Queue Shifting Mechanism

As cognitive radio networks are conceptualized to make use of the opportunistic spectrum access, the users of these networks may face problems in satisfying their quality of service (QoS) requirements. Some services of users like real-time audio and video which cannot tolerate inter-packet delays will be affected more due to this. The problem occurs due to the non-availability of channels to these applications at some instants. This problem can be addressed if the available channels are judiciously distributed among the competing users. One such mechanism that dynamically allocates the competing users to multiple queues, and shifting the users to higher-level queues as the time elapses is introduced in this work. This is found to help the users of cognitive radio networks to communicate reasonably well even when fewer channels are available for opportunistic use. Results are indicated in terms of blocking probabilities of real-time data. Markov chain-based analysis and discrete event simulation studies are carried out.

Queue Scheduling Algorithms: A Comparative Analysis

Congestion control and reduction is paramount in enhancing the performance and speed of communication networks. Despite its efficiency in improving the speed and performance of communication networks, it is imperative to mention that the technique exhibit several issues, such as scheduling algorithms. This paper presents a comparison of different results associated with different scheduling algorithms. Multisource was used to simulate and test different scheduling algorithms, including First In First Out (FIFO), Random Packet Drop, and Last In First Out (LIFO). The comparison was made by analyzing different results, including the average delay vs arrival rate, average buffer utilization vs arrival rate, and packet loss ration vs arrival rate. According to the results, it is evident that the average buffer utilization and average packet delays increased as the rate of data transmitted through the network increased. There was no significant change noticed in the average buffer utilization in all the three algorithms. However, the packet loss ratio was high in Random Packet Loss algorithm than in both FIFO and LIFO for slower arrival rates below 1000. Similarly, FIFO exhibited a significantly high average packet delay than both LIFO and Random Packet Drop algorithms.

A STUDY ON GEOGRAPHICAL ROUTING WITH ADAPTIVE POSITION UPDATE

Geographical Routing is a routing methodology mainly used for wireless mobile networks (Mobile Adhoc Networks, MANETs). MANETs are comprised of mobile nodes or mobile computing devices which are free to move randomly and thus the network's wireless topology may also change randomly. In Geographical Routing, nodes need to maintain the current positions of their neighbors for making forwarding decisions and hence the Adaptive Position Update (APU) method is proposed. Based on the flexibility of the nodes and the forwarding decisions made in the network, APU dynamically keeps in track of the rate of position updates. It is based on nodes with movements which are complex to predict their updated positions frequently and also the nodes which are closer to forwarding paths and update their positions more frequently. The APU is validated by network simulations showing that APU can potentially reduce the traffic load and acknowledge the mobility of nodes. It also improves the routing performance in terms of packet delivery ratio and packet delays.