Acknowledgement Research Articles

Jamming-Resistant Multiradio Multichannel Opportunistic Spectrum Access in Cognitive Radio Networks

For achieving optimized spectrum usage, most existing opportunistic spectrum sensing and access protocols model the spectrum sensing and access problem as a partially observed Markov decision process by assuming that the information states and/or the primary users' (PUs) traffic statistics are known a priori to the secondary users (SUs). While theoretically sound, the existing solutions may not be effective in practice due to two main concerns. First, the assumptions are not practical, as before the communication starts, PUs' traffic statistics may not be readily available to the SUs. Second and more serious, existing approaches are extremely vulnerable to malicious jamming attacks. By leveraging the same statistic information and stochastic dynamic decision-making process that the SUs would follow, a cognitive attacker with sensing capability can sense and jam the channels to be accessed by SUs, while not interfering PUs. To address these concerns, we formulate the antijamming, multichannel access problem as a nonstochastic multi-armed bandit problem. By leveraging probabilistically shared information between the sender and the receiver, our proposed protocol enables them to hop to the same set of channels with high probability while gaining resilience to jamming attacks without affecting PUs' activities. We analytically show the convergence of the learning algorithms and derive the performance bound based on regret . We further discuss the problem of tracking the best adaptive strategy and characterize the performance bound based on a new regret . Extensive simulation results show that the probabilistic spectrum sensing and access protocol can overcome the limitation of existing solutions and is highly resilient to various jamming attacks even with jammed acknowledgment (ACK) information.

Gateway-Assisted Retransmission for Lightweight and Reliable IoT Communications.

Message Queuing Telemetry Transport for Sensor Networks (MQTT-SN) and Constrained Application Protocol (CoAP) are two protocols supporting publish/subscribe models for IoT devices to publish messages to interested subscribers. Retransmission mechanisms are introduced to compensate for the lack of data reliability. If the device does not receive the acknowledgement (ACK) before retransmission timeout (RTO) expires, the device will retransmit data. Setting an appropriate RTO is important because the delay may be large or retransmission may be too frequent when the RTO is inappropriate. We propose a Gateway-assisted CoAP (GaCoAP) to dynamically compute RTO for devices. Simulation models are proposed to investigate the performance of GaCoAP compared with four other methods. The experiment results show that GaCoAP is more suitable for IoT devices.

Estimation and LQG Control Over Unreliable Network With Acknowledgment Randomly Lost.

In this paper, we study the state estimation and optimal control [i.e., linear quadratic Gaussian (LQG) control] problems for networked control systems in which control inputs, observations, and packet acknowledgments (ACKs) are randomly lost. The packet ACK is a signal that is transmitted from the actuator to notice the estimator the occurence of control packet loss. For such systems, we obtain the optimal estimator, which is consisted of exponentially increasing terms. For the solvability of the LQG problem, we come to a conclusion that in general even the optimal LQG control exists, it is impossible and unnecessary to be obtained as its calculation is not only technically difficult but also computationally prohibitive. This issue motivates us to design a suboptimal LQG controller for the underlying systems. We first develop a suboptimal estimator by using the estimator gain in each term of the optimal estimator. Then we derive a suboptimal LQG controller and establish the conditions for stability of the closed-loop systems. Examples are given to illustrate the effectiveness and advantages of the proposed design scheme.

A new explicit congestion notification scheme for satellite IP networks

Longer transmission delay and higher link errors affect data communication performance over satellite links. The problem gets compounded in case a congestion occurs in the corresponding data path. Taking preventive measures before a congestion actually occurs can help in avoiding such situations. Irrespective of the network characteristics, Explicit Congestion Notification (ECN) either through ICMP messages or through marking packets aims to achieve this objective. However, use of ICMP messages for explicit congestion notification leads to vulnerability to attacks by malicious hosts. On the other hand, use of conventional marking schemes that mark data packets in the forward direction can be slow as they have to traverse the satellite links. In this manuscript, we propose a new mechanism of ECN for an even faster notification of an incipient congestion over satellite IP networks. Our proposal, Mark-Reverse ECN, marks packets corresponding to acknowledgement (ACK) segments in the reverse direction to the sender. This leads to a reduction of the latency between detection and actual notification. As such, our mechanism leads to a more accurate and effective approach to congestion control. In addition, our proposed mechanism is free from vulnerability to malicious attacks. We also develop a new analytical model for Mark-Reverse ECN on TCP Reno for performance prediction and validation of simulation outcomes. Simulation results show that our proposed mechanism (i) leads to up to 25% improvement of TCP performance, (ii) reduces packet loss at the congested router by down to about 0% and (iii) helps to improve the performance of conventional TCP when deployed together.

Modeling RTT for DTN Protocol Over Asymmetric Cislunar Space Channels

Extensive work has been done in the performance evaluation of delay-/disruption-tolerant networking (DTN) technologies in cislunar and deep-space communications using simulation or emulation file transfer experiments. However, little work has been seen for studying in an analytical manner the performance of DTN protocols for space communications characterized by asymmetric channel rates. Accurate estimate of file delivery latency [i.e., round trip time (RTT)] is essential for efficient transmission control, reliable delivery, and bandwidth usage optimization of a protocol. In this paper, we present a performance analysis of the main DTN convergence layer adapter (CLA), i.e., Licklider transmission protocol (LTP) CLA (LTPCL adapter), over cislunar space channels, focusing on RTT estimates, in the presence of asymmetric channel rates. Analytical models are built for the RTT estimate of LTPCL transmissions with the effect of delay caused by space channel-rate asymmetry, channel impairment, and link disruption taken into consideration. The models are validated by file transfer experiments using a PC-based test bed. It is found that a smaller LTP data block size results in a longer delay in acknowledgement (ACK) transmission and thus a longer RTT. With a block size equal to or larger than a calculated threshold size, the ACK delay is avoided; thus, their RTT is consistently very low, leading to significantly shorter file delivery time and goodput advantage.

Constraints of nonresponding flows based on cross layers in the networks

In the active queue management (AQM) scheme, core routers cannot manage and constrain user datagram protocol (UDP) data flows by the sliding window control mechanism in the transport layer due to the nonresponsive nature of such traffic flows. However, the UDP traffics occupy a large part of the network service nowadays which brings a great challenge to the stability of the more and more complex networks. To solve the uncontrollable problem, this paper proposes a cross layers random early detection (CLRED) scheme, which can control the nonresponding UDP-like flows rate effectively when congestion occurs in the access point (AP). The CLRED makes use of the MAC frame acknowledgement (ACK) transmitting congestion information to the sources nodes and utilizes the back-off windows of the MAC layer throttling data rate. Consequently, the UDP-like flows data rate can be restrained timely by the sources nodes in order to alleviate congestion in the complex networks. The proposed CLRED can constrain the nonresponsive flows availably and make the communication expedite, so that the network can sustain stable. The simulation results of network simulator-2 (NS2) verify the proposed CLRED scheme.

Mitigating Intra Flow Interference Over Multi Hop Wireless Ad Hoc Networks.

Transmission Control Protocol (TCP) is a predominant transport layer protocol for data transmission. The burst nature of TCP congestion control mechanism has often lead to heavy link layer contentions over multi hop ad hoc networks. Acknowledgements (ACK) that compete with the data packets for medium access in the reverse path, further add up to the contention levels. Such intense contention paves way to interference and reduces the throughput. In this paper, we propose a framework that ties up rate controlled cross layer transport solution (CLTSP) with opportunistic network coding to minimize the intra flow interference over wireless ad hoc networks. CLTSP performs rate controlled transmission to prevent self interference among data packets by spacing them out at an appropriate interval. The time interval between the deliveries of successive data packets is dynamically measured based on four hop propagation delay and an appropriate correction factor that are collected from intermediate nodes. Besides, we perform network coding over the data and ACK packets pertaining to the same connection to reduce intra flow contention. We use the basic idea of piggy code and incorporate effective buffer management which is opportunistic with CLTSP. We evaluate the performance of our protocol with TCP New Reno, Piggy code and show significant improvement in terms of throughput, Packet Delivery Ratio, Packet drops and Link layer collisions.

Analysis for TCP in data center networks: Outcast and Incast

The unfairness caused by bandwidth sharing via TCP in data center networks is called TCP Outcast problem. Some researchers show that the throughput of a flow with small Round Trip Time (RTT) is less than that with large RTT which is completely contrary to the classic Transmission Control Protocol (TCP) protocol, and they believe that the Outcast problem is caused by port blackout in data center. However, we find that there are more important reasons for outcast which are an unfair distribution of the flows with different RTT on physical link and the differences in congestion window size when finishing the transmission of current block. TCP Incast is a throughput collapse that occurs when many flows arrive at the switch destined for the same output port. Incast deteriorates the performance of networks by increasing the queuing delay of flows and decreasing the throughput of applications. In this paper, we develop an analytical model for goodput when TCP Outcast occurs. Then we propose a new protocol based on window notification mechanism called TCP congestion window replacement (TCP-CWR), which can improve the goodput of the flows with small RTT to solve the outcast problem. Second, we propose a new transport layer protocol based on acknowledgment (ACK) reply changing rate to solve the Incast problem named TCP with Acknowledgment Changing Rate (TCP-ACR). The TCP-ACR protocol adjusts the current congestion window according to the changing rate of ACK and the theoretical maximum congestion window, and it can alleviate the congestion in data center networks. Last, we conduct simulation experiments to verify our proposed schemes. The results show that our analysis of Outcast is correct and our proposed protocols for Outcast and Incast are effective and practical.

Modified Bi-directional Routing with Best Afford Path (MBRBAP) for Routing Optimization in MANET

A Mobile Adhoc NETwork (MANET) is an independent wireless network in which mobile nodes can communicate with each other by forwarding the packets without support of any infrastructure. Since it is a dynamic mobile network, it cannot assure seamless packet transmission between the mobile nodes; making the open network vulnerable to various malicious attacks. MANET uses acknowledgement based schemes, for the assurance of packet transmission by overriding the malicious attacks. Since most of the existing intrusion detection systems (IDS) use two hop information for acknowledging the packets, flooding over multiple outgoing paths and acknowledgement (ACK) overhead occurs when transmitted over a long distance and finally it doesn’t have any prevention system to solve the malicious attacks. In this paper, Modified Bi-directional Routing Abstraction method is proposed to resolve these problems by reducing the ACK overhead and eliminating the malicious attacks. The Best Afford Path using cluster heads is embraced with the proposed technique which utilizes the maximum bandwidth to transfer the packets by routing the nodes around clockwise and anticlockwise routing procedures that detects and overcomes the malicious attacks with an IDS/IPS coupled mechanism. This technique utilizes the cluster heads that are used to get the ACK from the cluster nodes when the packets are sent through it. The proposed technique reduces the ACK overhead, eliminates the malicious attack, increases the bandwidth utilization and improves the delivery of packet with minimum delay compared with the existing schemes.

Linear Estimation of Clock Frequency Offset for Time Synchronization Based on Overhearing in Wireless Sensor Networks

The overhearing mechanism in time synchronization has been an active research area for wireless sensor networks (WSNs), for it can save a significant amount of energy by exploiting the wireless medium broadcast property. Recently, based on acknowledgment (ACK) mechanism, a synchronization scheme has been proposed for practical WSNs that the timestamps can be directly inserted into the data frame and the corresponding ACK, instead of dedicated synchronization packet. Consequently, the overhead of time synchronization could be further reduced. Motivated by this, in this letter, we analyze the synchronization of inactive nodes overhearing the pairwise synchronization on the basis of ACK mechanism, and present a linear estimation algorithm of clock frequency offset with the nodes’ clock adjusted at every synchronization. Furthermore, assuming Gaussian delays, the linear estimation for frequency offset and the corresponding Cramer–Rao lower bound are derived. Simulation results verify that the estimator is efficient.

ICP: Instantaneous clustering protocol for wireless sensor networks

Wireless sensor network (WSN) is one of the mainstay technologies in Internet of Things. In WSNs, clustering is to organize scattered sensor nodes into a cluster-topology network for communications. Existing efforts on clustering intensively focus on the energy-efficiency issue. However, in mission-critical applications, a fast clustering scheme, which can not only gather sensory data immediately after deployment but also reduce the energy consumption, is more desired. In this paper, we study the clustering problem considering both time- and energy-efficiency. We propose a novel instantaneous clustering protocol (ICP) that groups sensor nodes into single-hop clusters in a parallel manner. ICP can instantaneously complete the clustering due to two key designs. First, to determine the cluster heads locally. Existing methods require a long duration on cluster head voting. To waive the voting consumption, a cluster head in ICP is locally determined by the pre-assigned probability and its present status. Second, to minimize the amount of transmissions. Parallel transmissions from different cluster heads and acknowledgments (ACKs) from multiple cluster members lead to severe time and energy consumption. On the contrary, ICP gets rid of the ACK mechanism, instead, only cluster heads contend to broadcast during a given period. This period is elaborately derived to guarantee the connectivity. Experiments on a 64-node testbed and simulations on large-scale WSNs are extensively conducted to evaluate ICP. Performance results demonstrate that ICP significantly outperforms existing clustering methods by reducing up to 55% time consumption and 89% amount of transmissions for energy-saving.

AVATARS: a software-defined radio based teleoperating cyber-physical system for disaster environment exploration

In this paper, we develop a software-defined radio (SDR)-based teleoperating cyber-physical system (CPS) for disaster environment exploration, named AVATARS, which includes a telerobot and a teleoperator. The telerobot of AVATARS can be sent into some dangerous or inaccessible disaster environments for search and rescue tasks. Assisted by the environment information collected by the telerobot, the teleoperator can have a better understanding of the detected disaster environment, and the telerobot can be teleoperated more precisely to accomplish tasks effectively. Wireless communications play a vital role for AVATARS to guarantee its flexibility and scalability. To support reliable wireless transmission and real-time wireless teleoperation, we design an efficient and reliable wireless link to enhance the effective throughput of AVATARS. In the link, wireless communication efficiency is improved by using the packets pipelining and accumulative acknowledgement strategy based on the traditional stop-and-wait ARQ protocol. Sequentially, cognitive radio techniques are explored, and an adaptive channel switching mechanism is proposed to mitigate channel interferences in the crowded ISM band. Furthermore, three different kinds of control information are integrated into a single acknowledgement (ACK) packet to reduce communication overhead. The wireless link is implemented on SDR platforms, and extensive experiments under different conditions are carried out to evaluate its performance. The effective throughput of AVATARS can be enhanced more than four times compared with the traditional stop-and-wait ARQ protocol. We also present a video demo to show the powerful and interesting performance of AVATARS.

A Correlation-based Coverage Aware and Energy Balanced Probabilistic Flooding Algorithm

Aiming at the costly explicit and implicit acknowledgements (ACKs) and the serious energy imbalance of the existing flooding algorithm, a correlation-based coverage-aware and energy-balanced probabilistic flooding algorithm (CCEP) is proposed in this paper. CCEP distinguishes previous flooding algorithms with three features: (1) it exploits the link correlation between neighbours; the one-hop neighbours that have high link correlation are assigned to an aggregate explicit or implicit acknowledgement (aggregate ACK), thus effectively ameliorating the ACK implosion problem and saves energy on both data transmit and ACKs; (2) it balances the residual energy of sensor nodes; (3) it achieves target reliability and energy efficiency by tracking real-time aggregate ACKs and probabilistically deciding whether to retransmit a packet. The simulation results reveal that CCEP saves more than 50% energy on explicit and implicit ACKs in most cases while achieving target reliability; CCEP simultaneously reduces network variance of residual energy, thus prolonging the network lifetime.

A Game-Theoretic Approach to Fake-Acknowledgment Attack on Cyber-Physical Systems

A class of malicious attacks against remote state estimation in cyber-physical systems is considered. A sensor adopts an acknowledgement (ACK)-based online power schedule to improve the remote state estimation performance under limited resources. To launch malicious attacks, the attacker can modify the ACKs from the remote estimator and convey fake information to the sensor, thereby misleading the sensor with subsequent performance degradation. One feasible attack pattern is proposed and the corresponding effect on the estimation performance is derived analytically. Due to the ACKs being unreliable, the sensor needs to decide at each instant, whether to trust the ACK information or not and adapt the transmission schedule accordingly. In the meanwhile, there is also a tradeoff for the attacker between attacking and not attacking when the modification of ACKs is costly. To investigate the optimal strategies for both the sensor and the attacker, a game-theoretic framework is built and the equilibrium for both sides is studied.

A Remote Monitoring System for Greenhouse Based on the Internet of Things

The Internet of Things (IOT) is considered as a great opportunity for the development in the information field nowadays, and has been applied widely in many fields. The IOT can be applied to monitor and control the microclimate factors of greenhouse remotely. In this paper, a wireless monitoring network is designed in the perception layer of the IOT. The nodes are developed based on the Mica2 hardware and the TinyOS software. The LPL (low power listening) technology is adopted to reduce the energy consumption of the relay node which is powered by a solar panel. The ACK (Acknowledgement) mechanism is used in the software to improve the quality of wireless communications. A remote monitoring terminal is developed by using Java technology. The monitoring terminal is easy to operate with good interactivity. The system has been installed in a glass greenhouse. The actual operation results show that the system is stable and reliable, which lays a good foundation for the development of remote control strategies in future.

Transmission Power Control for Link-Level Handshaking in Wireless Sensor Networks

In practical wireless sensor networks (WSNs), the main mechanism for link-level data exchange is through handshaking. To maximize the network lifetime, the transmission power levels for both data and acknowledgement (ACK) packets should be selected optimally. If the highest transmission power level is selected then the handshake failure is minimized, however, minimizing handshake failure does not necessarily result in the maximized lifetime due to the fact that for some links selection of the maximum transmission power may not be necessary. In this paper, we investigate the impact of optimal transmission power assignment for data and ACK packets on network lifetime in WSNs. We built a novel family of mathematical programming formulations to accurately model the energy dissipation in WSNs under practical assumptions by considering a wide range of energy dissipation mechanisms. We also investigate the validity of a commonly made assumption in wireless communication and networking research: lossless feedback channel (i.e., ACK packets never fail). Our results show that the global optimal assignment of data and ACK packets can be replaced with link scope power level assignment strategies without any significant deterioration of network lifetime. The assumption that ACK packets do not fail is shown to be misleading.

PHACK: An Efficient Scheme for Selective Forwarding Attack Detection in WSNs.

In this paper, a Per-Hop Acknowledgement (PHACK)-based scheme is proposed for each packet transmission to detect selective forwarding attacks. In our scheme, the sink and each node along the forwarding path generate an acknowledgement (ACK) message for each received packet to confirm the normal packet transmission. The scheme, in which each ACK is returned to the source node along a different routing path, can significantly increase the resilience against attacks because it prevents an attacker from compromising nodes in the return routing path, which can otherwise interrupt the return of nodes’ ACK packets. For this case, the PHACK scheme also has better potential to detect abnormal packet loss and identify suspect nodes as well as better resilience against attacks. Another pivotal issue is the network lifetime of the PHACK scheme, as it generates more acknowledgements than previous ACK-based schemes. We demonstrate that the network lifetime of the PHACK scheme is not lower than that of other ACK-based schemes because the scheme just increases the energy consumption in non-hotspot areas and does not increase the energy consumption in hotspot areas. Moreover, the PHACK scheme greatly simplifies the protocol and is easy to implement. Both theoretical and simulation results are given to demonstrate the effectiveness of the proposed scheme in terms of high detection probability and the ability to identify suspect nodes.

OppCode: Correlated Opportunistic Coding for Energy-Efficient Flooding in Wireless Sensor Networks

Existing work on flooding in wireless sensor networks (WSNs) mainly focuses on single-packet problem, while the work on sequential multipacket problem is surprisingly little. This paper proposes OppCode , a new opportunistic network-coding-based flooding architecture for multipacket dissemination in WSNs, where both unreliable and correlated links commonly exist. Instead of flooding a single packet each time, each node encodes multiple native packets chosen from a specific fixed-size page to an encoded packet and then rebroadcasts it further. The key idea consists of two parts. One is opportunistically coding decision , in which each node grasps every possible coding opportunity greedily to maximize its aggregate coding gain of all neighbors based on the probabilistic estimation of packets each neighbor already has. The other is paged collective acknowledgements (ACKs), in which one rebroadcast acts as not only an implicit ACK of successful disseminations of all packets in the entire page for the sender, but also probabilistic ACK to update page-scale per-packet coverage estimations for its neighbors in a batch. Experiments based on extensive simulations and 21-node testbed show that OppCode significantly increases performance of multipacket flooding in terms of reliability, transmission overhead, delay, and load balance.

Clock Skew Estimation of Listening Nodes with Clock Correction upon Every Synchronization in Wireless Sensor Networks

Time synchronization is a significant component in Wireless Sensor Networks (WSNs) for maintaining synchrony among nodes. Most time synchronization protocols in WSNs utilize dedicated synchronization packets for clock accuracy optimization. However, in practical WSNs, the joint design of time synchronization and Media Access Control layer protocols should be considered. One approach is adding timestamps directly into data packets and the corresponding acknowledgements (ACKs). Therefore, communication and energy overhead could be saved greatly and time synchronization could be seamlessly integrated into networks. In this letter, we investigate the time synchronization scheme of listening nodes overhearing the neighboring two-way timing packet exchange based on periodical ACK mechanism and present an efficient clock skew estimation algorithm with clock correction upon every synchronization. The Maximum Likelihood Estimator (MLE) of clock skew for Gaussian random packet delay is derived, and the corresponding Cramer-Rao Lower Bound (CRLB) is obtained. In addition, the MLE shows that the clock skew could be estimated without any prior knowledge of the fixed packet delay and the time of adjustment. Simulation results verify that the MLE is efficient.

Opportunistic Spectrum Access with Discrete Feedback in Unknown and Dynamic Environment：A Multi-agent Learning Approach

This article investigates the problem of opportunistic spectrum access in dynamic environment, in which the signal-to-noise ratio (SNR) is time-varying. Different from existing work on continuous feedback, we consider more practical scenarios in which the transmitter receives an Acknowledgment (ACK) if the received SNR is larger than the required threshold, and otherwise a Non-Acknowledgment (NACK). That is, the feedback is discrete. Several applications with different threshold values are also considered in this work. The channel selection problem is formulated as a non-cooperative game, and subsequently it is proved to be a potential game, which has at least one pure strategy Nash equilibrium. Following this, a multi-agent Q-learning algorithm is proposed to converge to Nash equilibria of the game. Furthermore, opportunistic spectrum access with multiple discrete feedbacks is also investigated. Finally, the simulation results verify that the proposed multi-agent Q-learning algorithm is applicable to both situations with binary feedback and multiple discrete feedbacks.