As the first standardized underwater acoustic communication protocol, JANUS aims to become the reference means of communication between underwater devices. Its specification focuses on the physical aspects of transmission for compatibility across multiple manufacturers and ease of implementation. Currently, JANUS does not include specification of any layers above Medium Access Control (MAC). Therefore, reliable communication in JANUS-based Underwater Acoustic Networks (UANs) can only be enabled by developing protocols, such as Automatic Repeat reQuest (ARQ), on top of the JANUS standard. This paper proposes a novel JANUS-compatible ARQ protocol featuring Multi-User Packed ACKnowledgment (MUPACK), bitfield-based selective retransmissions and header loss recovery to improve the reliability of UANs powered by JANUS.Our proposed ARQ protocol addresses the challenges of high roundtrip latency and low throughput associated with underwater acoustic communication. Through implementation and simulation, we demonstrate that the proposed ARQ scheme, combined with a Carrier Sense Multiple Access (CSMA)-based MAC protocol, vastly outperforms Stop-and-Wait (SW) and Selective Repeat (SR) ARQ in throughput and latency while maintaining compliance with the JANUS specification, thus making it wellsuited for practical deployment in UANs.

Conventional coverage and capacity from a high altitude platform (HAP) over an extended coverage area suffer significantly from inter-cell interference (ICI), antenna beam broadening, and uneven cell loading, which results in poor edge performance. In this paper, we show how a single antenna array on a HAP can be used to mitigate against these and achieve ubiquitous coverage by forming two tiers of a homogeneous contiguous cellular structure. We propose separate algorithms that implement the two-tier architecture with many antenna beams, which are used to form cells, and associate users with an appropriate cell and tier. A user associates with the cell and tier, which offer the best carrier power-to-noise ratio (CNR) and carrier power-to-interference-plus-noise ratio (CINR) respectively. The performance of the architecture, which is evaluated using simulation, is compared with a typical one-tier architecture. The results show that the two-tier architecture achieves over 30% higher user throughput and enhances throughput fairness and edge-of-cell connectivity by centralising as many users as possible within cells compared to the typical one-tier architecture. These benefits are better exploited by ensuring spectrum orthogonality between the two tiers.

For direction of arrival (DOA) estimation based on graph signal processing (GSP), it has been assumed that there is a phase shift between adjacent snapshots of the received signals. However, this assumption does not hold for narrowband signals and thus affects the performance of the corresponding algorithms. To improve the performance, a new GSP-based DOA estimation method is proposed. By building a periodic directed graph based on a graph shift operator and computing the spectrum using the Kronecker product, the relationship between the input narrowband signals and the graph adjacency matrix of different direction coefficients is constructed. Simulation results show that this method performs better than existing algorithms based on GSP.

This paper presents a lightweight cross-layer protocol relIable Routing with coordInated medium acceSs control (IRIS) which is designed for long-range pipeline Wireless Sensor Networks (WSNs) with extremely low power budget, typically seen in a range of monitoring applications. IRIS includes functions of network discovery, medium access control and routing designed for heavily energy constrained networks. The protocol is able to operate with less than 1% duty cycle, thereby conforming to ISM band spectrum regulations in the 868MHz band. The duty cycle can be flexibly configured to meet other regulations/power budgets as well as to improve the route forming performance. Simulation results show a guaranteed route formation in different network topologies with various protocol configurations. An analytical model is presented to validate the simulation results of route formation time. System robustness against unreliable wireless connections and node failures are also demonstrated by simulations. A network of 71 attenuated LoRa nodes is implemented to evaluate the capability of IRIS. Long-term operation of the network shows consistent performance compare with the simulations.

Machine-type communications (MTC) is considered as one of the promising technologies over the next decade and these MTC devices are continuously increasing. When a large number of MTC devices try to access a cellular base station simultaneously using the existing LTE/LTE-A Random Access Channel (RACH), the collision probability among Machine-to-Machine (M2M) and Human-to-Human (H2H) device increases drastically. Thus the performance of RACH degrades sharply which causes significant blocking and huge access delay. Delay-critical applications, cannot therefore be served using the legacy RACH protocol. The present work aims at solving this delay issue for a specific user group by proposing a Prioritised Dynamic Random Access scheme (PD-RACH) that improves the conventional RA procedure in order to minimize the delay and offer priority to the specific user group. Simulation results show that the proposed scheme can significantly reduce the access delay for the priority user group.

Internet-of-Underwater-Things (IoUT) systems comprising tens or hundreds of underwater acoustic communication nodes will become feasible in the near future. The development of scalable networking protocols is a key enabling technology for such IoUT systems, but this task is challenging due to the fundamental limitations of the underwater acoustic communication channel: extremely slow propagation and limited bandwidth. The aim of this article is to propose the JOIN protocol to enable the integration of new nodes into an existing IoUT network without the control overhead of typical state-of-the-art solutions. The proposed solution is based on the capability of a joining node to incorporate local topology and schedule information into a probabilistic model that allows it to choose when to join the network to minimize the expected number of collisions. The proposed approach is tested in numerical simulations and validated in two sea trials. The simulations show that the JOIN protocol achieves fast convergence to a collision-free solution, fast network adaptation to new nodes, and negligible network disruption due to collisions caused by a joining node. The sea trials demonstrate the practical feasibility of this protocol in real underwater acoustic network deployments and provide valuable insight for future work on the tradeoff between control overhead and reliability of the JOIN protocol in a harsh acoustic communication environment.

In this paper, we propose a scheme for beam-pointing from a high altitude platform (HAP) for contiguous coverage delivery within an extended service area. The scheme, which illuminates cells, considers the broadening of beams on the ground from the HAP-based antenna array. A predetermined degree of overlap is introduced between neighbouring cells to minimize user outages when moving between cells. In order to evaluate the performance of the scheme, users are randomly distributed at a density of λ users/km2over a service area of radius R. We compare the cell overlap, users' carrier-to-noise ratio (CNR), and carrier-to-interference-plus-noise ratio (CINR) with those of other cell-pointing schemes. The results show that cell overlap is better managed using our proposed schemes. In addition, the proposed scheme significantly improves user CNR and CINR, achieving a CINR improvement of 5-15dB compared with the other schemes.

A farmer's decision on whether to control a pest is usually based on the perceived threat of the pest locally and the guidance of commercial advisors. Therefore, farmers in a region are often influenced by similar circumstances, and this can create a coordinated response for pest control that is effective at a landscape scale. This coordinated response is not intentional, but is an emergent property of the system. We propose a framework for understanding the intrinsic feedback mechanisms between the actions of humans and the dynamics of pest populations and demonstrate this framework using the European corn borer, a serious pest in maize crops. We link a model of the European corn borer and a parasite in a landscape with a model that simulates the decisions of individual farmers on what type of maize to grow. Farmers chose whether to grow Bt-maize, which is toxic to the corn borer, or conventional maize for which the seed is cheaper. The problem is akin to the snow-drift problem in game theory; that is to say, if enough farmers choose to grow Bt maize then because the pest is suppressed an individual may benefit from growing conventional maize. We show that the communication network between farmers' and their perceptions of profit and loss affects landscape scale patterns in pest dynamics. We found that although adoption of Bt maize often brings increased financial returns, these rewards oscillate in response to the prevalence of pests.

To enhance channel throughput, end to end delay and energy efficiency for wireless networks based on a single-hop topology, this paper proposes a distributed reservation multiple access scheme with adaptive switching requests (DRMA-ASR). The DRMA-ASR scheme uses a repeating frame structure with a reservation period and a data transmission period based on the principles of the ALOHA-reservation scheme. To improve performance, this scheme proposes an adaptive or skipped reservation period with the probability based on a hidden Markov model (HMM). In addition, request packets are transmitted based on a permission probability to increase the probability with which the reservation period can be reduced in duration or skipped, and energy saving is achieved by putting terminals into a low power sleep mode when they are not required to transmit during the data transmission period. The scheme applies a virtual carrier sensing mechanism and does not require physical sensing. Simulation results show that DRMA-ASR provides better performance in terms of channel throughput, end to end delay, and energy efficiency than CSMA/CA with both small and large interference ranges.

In this paper, a novel interference aware, energy efficient resource allocation scheme based on signal to interference plus noise ratio (SINR) rank restrictions is proposed for beyond next generation mobile networks. The relationship between the choice of base stations (when their ranking and selection is based on SINR) and inter-cell interference is examined. It is observed that lower SINR choices result in higher interference in the network and vice versa. Based on the observed relationship, the capability of the proposed scheme to mitigate inter-cell interference and achieve energy saving is evaluated with different SINR based choice restriction policies. The energy efficiency and quality of service (QoS) performance of the proposed scheme is compared with schemes without interference awareness features. The results show that the proposed scheme can achieve up to 65% energy savings at low offered traffic and can also provide significantly higher QoS over a wide range of traffic loads than the schemes without interference awareness.

This study introduces two novel approaches, pre-partitioning and weight-driven exploration, to enable an efficient learning process in the context of cognitive radio. Learning efficiency is crucial when applying reinforcement learning to cognitive radio since cognitive radio users will cause a higher level of disturbance in the exploration phase. Careful control of the tradeoff between exploration and exploitation for a learning-enabled cognitive radio in order to efficiently learn from the interactions with a dynamic radio environment is investigated. In the pre-partitioning scheme, the potential action space of cognitive radios is reduced by initially randomly partitioning the spectrum in each cognitive radio. Cognitive radios are therefore able to finish their exploration stage faster than more basic reinforcement learning-based schemes. In the weight-driven exploration scheme, exploitation is merged into exploration by taking into account the knowledge gained in exploration to influence action selection, thereby achieving a more efficient exploration phase. The learning efficiency in a cognitive radio scenario is defined and the learning efficiency of the proposed schemes is investigated. The simulation results show that the exploration of cognitive radio is more efficient by using pre-partitioning and weight-driven exploration and the system performance is improved accordingly.

The purpose of this paper is to present a modified scheduling algorithm, called Traffic-oriented scheduling algorithm for Aerial platform based Routing and MAC (APRMAC) protocol for Wireless Sensor Networks (WSNs) to maximise throughput. This algorithm keeps the characteristics of APRMAC, which is energy efficient, contention free and inherent routes establishment. The advantages of APRMAC and the novel scheduling algorithm are analysed. A simulation is carried out for both crossing chain and random topologies to validate the scheme and for comparison of performance with the original delay-oriented APRMAC and a well-known schedule-based MAC protocol, TRAMA. The results show that APRMAC offers higher energy efficiency against TRAMA. The results also show that the traffic-oriented scheduling algorithm can provide better throughput performance then the original delay-oriented one.

In this paper, we consider a general cooperative wireless sensor network (WSN) and the problem of channel estimation. We develop a matrix-based set-membership normalized least mean squares (SM-NLMS) algorithm for the estimation of the complex channel parameters in order to reduce the computational complexity significantly and extend the lifetime of the WSN by reducing its power consumption. The proposed SM-NLMS channel estimation method requires the setting of a bound for appropriate performance. However, an inappropriate and fixed error bound will result in overbounding and underbounding problems which degrade the performance significantly. Therefore, we present and incorporate an error bound function into the SM-NLMS channel estimation method which can adjust the error bound automatically with the update of the channel estimates. Computer simulations show good performance of our proposed algorithms in terms of convergence speed and steady state, reduced complexity and robustness to the time-varying environment and different signal-to-noise ratio (SNR) values.

This study analyses a cognitive radio scenario based on non-persistent carrier sense multiple access (CSMA) and time division multiple access (TDMA) systems sharing a single-channel wireless network. TDMA users are considered as primary users who can access the channel at any time, and non-persistent CSMA users are considered as secondary users who can share the channel when it is free. New expressions for the individual and aggregate throughput performance of this combined system have been developed, and the system performance is evaluated for a variety of proportions of non-persistent CSMA and TDMA traffic levels. Simulation and analytical results are presented and the ways in which both schemes suffer negative effects as a result of the interaction are shown, primarily caused by increased number of collisions arising from the other scheme.

This paper investigates the ways of improving the Grade-of-Service (GoS) in a coexistence scenario with different user types in a multiple High Altitude Platforms (HAPs) system with shared coverage area and radio spectrum. It is achieved through the exploitation of HAP diversity. An analytical model based on a two-dimensional state-transition-rate diagram is developed to describe system behaviour of a coexistence scenario containing two user groups, which have full and limited HAP availability. On the basis of the analytical model, a novel restriction mechanism is implemented in order to achieve a fair balance of GoS to the two user groups using connection admission control (CAC). The mechanism restricts access to the channel resource for users with full HAP choice in order to give more chance of access to users with a more limited HAP selection. Different types of restriction function are analysed and the paper shows that a step restriction function is the most suitable mechanism to provide a balanced low blocking probability performance to both user groups simultaneously. Furthermore, the mechanism can potentially provide a certain level of GoS guarantee for the users if adequate flexibility is available within the whole system.

This paper introduces the Reservation Packet Medium Access Control (RP-MAC) protocol for Wireless Sensor Networks (WSNs). The protocol incorporates a periodic listen/sleep schedule to conserve energy and employs a novel channel reservation mechanism to enhance the rate at which packets can be transferred over multiple hops, thereby improving throughput and reducing end-to-end delay. To evaluate the performance of RP-MAC, it is compared with the established S-MAC protocol through simulation. Results show that RP-MAC can support much higher traffic loads as a direct result of its higher throughput capability along with reduced end-to-end delay for packet transmissions across a multi-hop link. These benefits come at the expense of higher energy consumption, but this is maintained at an acceptable level.

Two spectrum etiquettes are developed for the use on the downlink of coexisting high-altitude platform (HAP) and terrestrial fixed broadband systems that are intended for future application with cognitive radio-based user terminals with directional antennas. The spectrum etiquettes are based on the interference to noise ratio and carrier to interference plus noise ratio levels at the receiver of an incumbent user. Antenna beamwidths and multiple modulation scheme levels determine the parameter settings for coexistence performance. It is shown that coexistence performance can be improved by exploiting the surplus transmitter power of the terrestrial system, thereby enabling the incumbent terrestrial system to accommodate additional interference arising from a newly activated HAP system.

This paper investigates the feasibility of coexistence of co-channel time division synchronous code-division multiple access (TD-SCDMA) and wideband code division multiple access (WCDMA) systems operating in a macro cell environment. A Monte-Carlo simulation is performed for a TD-SCDMA network, a WCDMA network, and the coexistence network comprising both systems for both the uplink and downlink. The impact of eight interference modes is considered. The pole capacity in each case is calculated and compared with each other. From the comparison and analysis, it is found that the combined system can achieve comparable performance to that of the individual systems, and the WCDMA cells and TD-SCDMA cells can effectively share the same spectrum resources.

We propose and evaluate a vertical handover mechanism for TCP, based on receiver bandwidth delay product (BDP) measurement and congestion control using the receiver's advertised window. It addresses the negative impact of abrupt changes in link capacity and latency on TCP performance during make-before-break vertical handover in heterogeneous networks, enabling TCP to seamlessly adapt to new conditions. It resolves the problem of buffer overflow in a low capacity network on handover from a high capacity network, and the under-utilisation problem on handover in the reverse direction. All modifications are restricted to the mobile device, and the proposed technique is fully interoperable with existing TCP and mobile IP infrastructure. It maintains end-to-end semantics, supports IP security, and can be easily deployed

The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an original approach to DAMA, which eliminates the fundamental end-to-end delay bound associated with the traditional DAMA techniques. Whilst they offer significant improvements in the achievable delay/utilisation performance for bursty packet transmission over satellite, they are constrained by the initial build up of packets at the start of traffic bursts. In this paper, we introduce the adaptivity to the uplink frame that enables the proportion of alternative types of capacity allocation to be varied on a dynamic basis. Sufficient demand assigned capacity is assigned to meet the instantaneous user requirements, with spare capacity allocated by an alternative strategy to assist with initial throughput at the start of bursts. Results show that this approach enhances the end-to-end delay distribution and delay jitter performance compared with the conventional static frame BTDAMA schemes.

This paper presents a detailed performance evaluation of the burst targeted demand assignment multiple-access (BTDAMA) schemes, which employ an original approach to implementing demand assignment multiple-access (DAMA), suited to supporting ON/OFF type traffic over a broadband geostationary satellite link. A novel analytical model is introduced which can be used to predict and evaluate the delay performance of rate-based medium access control schemes, and is applied to BTDAMA to investigate the potential performance enhancements offered by introducing free assigned capacity to the scheme. Results show that BTDAMA eliminates the end-to-end delay bound of traditional DAMA techniques, offering significantly superior performance compared with conventional schemes, with free assignment effective in improving the delay performance for a wide range of traffic burst durations.

This paper explores the relative performance of the combined free/demand assignment multiple access (CFDAMA) protocol with random access and with packet accompanied request strategies in supporting self-similar traffic over a geostationary satellite link. It Is shown that both request strategies have certain advantages and are suited to different levels of channel loading. A new scheme is proposed, CFDAMA with combined requests (CFDAMA-CR), which combines the two request strategies to gain the benefits of both. Simulation results show that the CFDAMA-CR scheme can achieve better delay/throughput performance for a satellite channel than either of the standard schemes.

This paper introduces the burst targeted demand assignment multiple access scheme with pure demand assigned slots (BTDAMA-PD), which employs a different approach to implementing DAMA, suited to handling long bursts from on-off type data traffic sources. Its delay/throughput performance is compared with a variant of the combined free/demand assignment multiple access (CFDAMA) schemes. Simulation results show that BTDAMA-PD can achieve better delay/throughput performance of geo-stationary satellite channels carrying data traffic, with an excellent distribution of end-to-end delay values and low variation in the end-to-end delay of consecutive packet transmissions.

This paper examines the relative performance of the Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol with different terminal request strategies. A new scheme is proposed employing round robin assignment of request slots (CFDAMA-RR), which is compared with the standard schemes incorporating random, packet accompanied, and Combined Requests (CFDAMA-CR). It is shown that the CFDAMA-RR scheme can offer improved delay/utilisation performance of a satellite channel due to its inherent fairness and contentionless nature. Simulation results are presented with three different source traffic models, Poisson, self-similar (Pareto ON-OFF) and exponential ON-OFF. The results indicate that the ON-OFF nature of a traffic model has a more significant impact on Medium Access Control (MAC) protocol performance than the specific distribution of ON and OFF times.