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This article presents the design and implementation of PCube, a phase-based parallel packet decoder for concurrent transmissions of LoRa nodes. The key enabling technology behind PCube is a novel air-channel phase measurement technique that is able to extract phase differences of air-channels between LoRa nodes and multiple antennas of a gateway. PCube leverages the reception diversities of multiple receiving antennas of a gateway and scales the concurrent transmissions of a large number of LoRa nodes, even exceeding the number of receiving antennas at a gateway. As a phase-based parallel decoder, PCube provides a new dimension to resolve collisions and supports more concurrent transmissions by complementing time and frequency-based parallel decoders. PCube is implemented and evaluated with synchronized software defined radios and off-the-shelf LoRa nodes in both indoors and outdoors. Results demonstrate that PCube can substantially outperform state-of-the-art works in terms of aggregated throughput by 4.9× and the number of concurrent nodes by up to 5×. More importantly, PCube scales well with the number of receiving antennas of a gateway, which is promising to break the barrier of concurrent transmissions. [ABSTRACT FROM AUTHOR]

This paper presents a novel bluetooth low energy (BLE) protocol enabling a BLE node to perform RF fingerprint acquisition by measuring the received signal strength (RSS) from its neighboring nodes and simultaneously broadcast the acquired fingerprint via its advertising packet. However, the fingerprint acquisition and broadcast process in a dense BLE network is very challenging owing to: 1) the likelihood of packet collision; and 2) the length-constrained packet. To this end, we exploit a compressive sensing (CS) framework allowing each node to acquire no more than $M$ M measurements from a very dense network, in which the number of nodes $N$ N is far greater than $M$ M . By aggregating the $M$ M -dimensional compressed fingerprint vector from $s

The large propagation delay in underwater acoustic networks results in spatial and temporal uncertainty between communication links. This uncertainty, in turn, leads to problems with spatial unfairness and packet collision in media access control (MAC) solutions. To address these issues, this research paper proposes a spatially fair and low-conflict media access control (SFLC-MAC) protocol. Within the protocol, a contention window spatial fairness adjustment strategy is designed, including random and fair states. Nodes autonomously adjust their contention states based on the perceived network information. Nodes in the fair state increase their listening time to ensure that nodes in the random state can successfully access the channel, thereby overcoming the fairness issues in channel access. A method based on postponing data packet transmission is proposed to avoid collisions between data packets and neighbors’ control packets. By scrutinizing the spatio-temporal constraints pertinent to these conflicts, the exact duration of the delay required for this method is ascertained. Simulation results demonstrate that SFLC-MAC effectively improves network throughput, reduces end-to-end delay, decreases network energy consumption, and enhances channel access fairness among nodes.

Pulsed-Coupling Oscillators (PCOs) are recently considered as the best energy efficient source of unregulated syncs in Wireless Sensor Network (WSN). PCO utilizes firefly-sync to draw complices. In any case, for sensor networks, a PCO is not feasible, as synchronous transmission costs cannot be borne by WSNs and the processing of information. For certain situations, the exhaustion of a node's battery energy policy (due to the packet collision) is a nonsensical substitute of batteries. To prevent this, A novel process named this analysis the Desynchronization-Traveling-Wave-Pulse-Coupled-Oscillator (DTWPCO) algorithm, an energy-efficient WSN self-organizer that uses Travelling-Wave-Pulse-Coupled-Oscillator (TWPCO) phases locking and the PCO antiphase desynchronization process. The plan aims to reduce the high-power consumption within the network in order to display signs of improved data collection during data transmission for the sensor nodes (SNs). The results of the computer simulation showed that the proposed DTWPCO mechanism was able to achieve 50% and 58% reduction in energy by increasing the amount of transmitted data by SNs, in contrast to TWPCO and PCO methods. The method also increases the data processing ratio by up to 73% and 70% in comparison to the TWPCO and PCO methods, respectively.

Packet collisions caused by the standard Distributed Coordination Function (DCF) protocol in wireless local area networks (WLANs) have been a challenging problem leading to congestion and reduced throughput. To solve this problem, we propose a novel backoff state generation algorithm, called adaptive virtual backoff algorithm (AVBA), operating in an access point. The virtual contention window size in the algorithm is automatically adjusted based on the number of synchronized active nodes in a cell. Backoff counts generated by AVBA operating in the access point are sent by the access point to each active node in the cell to try to synchronize transmissions and minimize packet collisions. The evaluation results show that the AVBA improves the throughput performance compared to the existing collision resolution techniques, such as the deterministic backoff and centralized random backoff (CRB), when the number of active nodes is large. Moreover, the results show that it maintains a high level of fairness in terms of channel access opportunities between nodes using AVBA and nodes using the DCF protocol when they coexist in a mixed wireless network scenario.

In this article, we investigate the performance of massive machine type communications (mMTC) in status update systems, where massive machine type communication devices (MTCDs) send status packets to the BS for system monitoring. However, massive MTCDs sending status packets to the BS will cause severe packet collisions, which will have a negative impact on status update performance. In this case, it is necessary to carry out reasonable access control and resource allocation scheme to improve the status update performance for mMTC. In this article, taking the features of mMTC into consideration, we first analyze access control, packet collisions and packet errors in mMTC respectively, and derive the closed-form expression of the average age of information for all MTCDs as the performance metric, and then propose a joint access control, frame division and subchannel allocation scheme to improve the overall status update performance. Simulation and numerical results verify the correctness of theoretical results and show that our proposed scheme can achieve almost the same performance as the exhaustive search method and outperforms benchmark schemes. [ABSTRACT FROM AUTHOR]

Previous studies showed that the packet collision probability in the 802.11 Distributed Coordination Function (DCF) can approach zero by adopting Centralized Random Backoff (CRB), which improves the total throughput performance. Moreover, it was reported that wireless networks using CRB maintain a high level of compatibility to legacy wireless local area networks (WLANs) when they coexist. However, little attention has been paid to relations between the performance of CRB and the retransmission limit, although the number of retransmission limit is an essential parameter that must be carefully chosen when implementing CRB for efficient WLANs. This article presents more realistic Markov chain models, and studies the impact of retransmission limit on the performance of CRB. These relations are also investigated by Monte Carlo simulation in more practical scenarios. Results show the trade-off that the total throughput increases with the retransmission limit when the number of nodes is larger than 15; whereas, the channel access opportunities in the mixed network scenario are more unevenly distributed between nodes as the retransmission limit increases. It is also shown in the simulation results that the throughput degradation caused by the hidden node problem is alleviated as the retransmission limit increases. [ABSTRACT FROM AUTHOR]

Localization plays a more and more important role in underwater wireless sensor networks (UWSNs). But in the large-scale UWSNs, the localization algorithm can’t be realized for the continuous packet collision. Therefore, we need to consider the impact of MAC protocol on the positioning algorithm. First, this paper proposes a multi-layer positioning model based on the underwater network architecture. Then according to the non-synchronous localization scheme, we analyze the reason of packet collisions and propose the variable interval ALOHA (VI-ALOHA) protocol based on the Poisson distribution. The VI-ALOHA protocol reduces the collision by adding random space–time. Through the comparison of localization coverage, packet loss, and localization time, this paper evaluates the impact on the localization result in equal interval ALOHA (EI-ALOHA) and VI-ALOHA. Our simulation results show that the MAC protocol has a significant influence on localization; besides, the localization coverage and the packet loss of VI-ALOHA protocol are above 20% better than the EI-ALOHA.

With the delayed channel state information at transmitters, an effective interference management approach, realized in the packet interference network and with a specific physical layer model (i.e., destinations have the flexibility to utilize past receptions), began to emerge. Meanwhile, the capacity region of this packet interference network can provide best interference management approach. Thus, in this paper, we concentrate on the capacity region of the two-user interference network with the past reception based physical layer model. To this end, we first derive the capacity outer bound, by exhibiting that the bound for the binary fading interference channel is exactly the desired one for the packet interference network. We then examine its linear network coding (LNC) capacity, by exploiting a linear-space-based approach, which unifies the problem of finding a capacity outer bound and devising the achievability scheme into a single linear programming problem. Finally, by analyzing the properties of linear spaces of coding vectors and some pure algebraic arguments, we prove that the LNC capacity region matches the derived outer bound, implying that the derived LNC capacity region is indeed the true capacity of the studied network.

Stability region is an important and practical measure of the transmission capacity of wireless networks with stochastic flows. On the other hand, an effective interference mitigation approach, realized in the physical layer model with the flexibility to utilize past receptions, began to emerge. Nevertheless, there is still a lack of the investigation on the stability region of the interference network in this physical layer model. Thus, in this paper, we concentrate on the stability region of the two-user interference network for the aforementioned physical layer model. To this end, we first design a physical layer linear coding scheme to fully utilize past receptions. Next, on the basis of the proposed coding scheme, a queue-based transmission strategy is presented. Then, by leveraging the virtual network mechanism, we derive the stability region of the system for the proposed transmission strategy. Meanwhile, a Lyapunov-function-based stabilizing policy is presented. Finally, we compare the stability region with the information-theoretical outer bound by a numerical method. The simulation results reveal that their relative difference is no larger than 3%, and is below 0.1% under the specific setting of the probability that packets successfully arrive at each receiver, implying that the transmission strategy could essentially achieve the outer bound from the practical perspective. In particular, the stability region of the system is almost identical to its information-theoretic throughput region under the specific setting.

We study the capacity region of the two-user binary fading (or erasure) interference channel, where the transmitters have no knowledge of the channel state information. We develop new inner bounds and outer bounds for this problem. We identify three regimes based on the channel parameters: weak, moderate, and strong interference regimes. Interestingly, this is similar to the generalized degrees of freedom of the two-user Gaussian interference channel, where transmitters have perfect channel knowledge. We show that for the weak interference regime, treating interference as erasure is optimal while for the strong interference regime, decoding interference is optimal. For the moderate interference regime, we provide new inner and outer bounds. The inner bound is based on a modification of the Han–Kobayashi scheme for the erasure channel, enhanced by time-sharing. We study the gap between our inner bound and our outer bounds for the moderate interference regime and compare our results to that of the Gaussian interference channel. Deriving our new outer bounds has three main steps. We first create a contracted channel that has fewer states compared with the original channel, in order to make the analysis tractable. We then prove the correlation lemma that shows an outer bound on the capacity region of the contracted channel and also serves as an outer bound for the original channel. Finally, using the conditional entropy leakage lemma, we derive our outer bound on the capacity region of the contracted channel. [ABSTRACT FROM AUTHOR]

This paper is focused on a vehicle-to-vehicle (V2V) communication system operating at a road intersection, where the communication links can be either line-of-sight (LOS) or non-line-of-sight (NLOS). We present a semi-empirical analysis of the packet delivery ratio of dedicated short-range communication (DSRC) safety messages for both LOS and NLOS scenarios using a commercial transceiver. In a NLOS scenario in which the reception of a safety message may be heavily blocked by concrete buildings, direct communication between the on-board units (OBUs) of vehicles through the IEEE 802.11p standard tends to be unreliable. On the basis of the semi-empirical result of safety message delivery at an intersection, we propose two relaying mechanisms (namely, simple relaying and network-coded relaying) via a road-side unit (RSU) to improve the delivery ratio of safety messages. Specifically, we designed RSU algorithms to optimize the number of relaying messages so as to maximize the message delivery ratio of the entire system in the presence of data packet collisions. Numerical results show that our proposed relaying schemes lead to a significant increase in safety message delivery rates.

Packet collision is a well-known severe impairment in ALOHA-based networks and, more generally, in any random access network. As a consequence, several methodologies have been considered with the aim of lowering the resulting performance degradation. A novel multiuser detection scheme exploiting channel diversity to separate collided signals is proposed here to enable multiple packet reception capability in random access schemes. The performance of this approach is analytically derived and optimized in terms of network throughput, and compared with that of different alternatives. The overall performance in terms of throughput shows the effectiveness of the proposed scheme in different operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the capture effect through experiments conducted with Iris nodes equipped with AT86RF230 radio transceivers. It is shown that the first arriving packet in a collision can capture the radio channel for equal power transmissions and may be decoded depending on the amount of overlap. A new 3-packet-capture scenario is introduced and implemented. To be able to understand the impact of capture on the throughput performance of wireless sensor networks, we present an analysis of the capture coefficient using our practical results. For real-world implementations, the throughput of pure ALOHA considering a finite number of users is presented in analytical form. The capture coefficient is then applied to pure ALOHA as a case study. Using analytical and practical implementations of the capture effect on ALOHA, a very good match in channel throughput performance enhancement is demonstrated over the non-capture effect case. TinyOS-2.x is used to program the nodes and to observe data exchange on a computer through a base station. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of cooperation among vehicles in VANET using QoS-OLSR protocol in the presence of selfish nodes. QoS-OLSR is a proactive protocol that considers the Quality of Service (QoS) of the nodes while electing the cluster-heads and selecting the Multi-Point Relay (MPRs) nodes. Cluster-heads and MPRs might misbehave on the roads by over-speeding or under-speeding. Classical and generous Tit-for-Tats are proposed to analyze the interaction among vehicles. However, both strategies are not able to enforce the cooperation due the fact that they (1) count on individual watchdogs monitoring, (2) rely on the node-to-node cooperation decision, (3) and ignore the high mobility and packet collisions. Therefore, we propose a Dempster-Shafer based Tit-for-Tat strategy that is able to improve the decision and regulate the cooperation in the vehicular network. This is done by (1) launching a cooperative watchdogs monitoring, (2) correlating the observations of the different watchdogs using Dempster-Shafer theory, and (3) propagating the decisions among clusters. Thereafter, we compare the Dempster-Shafer based strategy with several strategies derived from the original Tit-for-Tat. Simulation results prove that the Dempster-Shafer based strategy is able to maintain the survivability of the vehicular network in the presence of high mobility and packet collisions with minimal time and overhead. [ABSTRACT FROM AUTHOR]

ZigBee/IEEE 802.15.4 is one of the most used standards for low‐power applications. However, full function devices must be always active to route data in a mesh network. The objective of this work is to implement a sleeping technique at the application layer that enables sleep mode for all nodes of a ZigBee network. A time synchronisation mechanism to deal with the clock drift of the sensor nodes was developed. The technique also enables the recovery of lost messages. A large network is organised into smaller groups to reduce latency and packet collisions. The active interval of each node is dynamically adapted to the network operation to optimise the energy consumption. The proposed technique was applied to a real testbed and the increase in energy efficiency was evaluated. The results demonstrated energy savings of about 95% for networks containing up to 20 nodes per group and wake up periods longer than 2 min. [ABSTRACT FROM AUTHOR]

Systematic packet collisions constitute a major problem in wireless flooding, which is a key mechanism for information dissemination in wireless mesh and multi-hop ad hoc networks. Since this cannot be solved only through classic MAC collision avoidance mechanisms, the IETF has proposed and standardized in RFC 5148 jittering techniques to handle it. These techniques are widely used in protocols for wireless communication such as OLSR, AODV or LOAD, and have proven useful for reducing collisions. They lead however some undesirableside effects that may harm substantially the flooding performance. To the best of our knowledge, no research effort has been deployed to understand and analyze these effects. This paper addresses this issue. It motivates and introduces a theoretical model of flooding with jitter in a wireless interface, as specified in RFC 5148, and explores the probabilistic characterization of additional flooding delay caused by jitter. It mostly provides two analytical bounds for the per-interface additional jitter delay. Presented results, which are validated by way of a discrete-event simulation, enable a better understanding of the performance trade-offs (between packet collisions and additional delay, in particular) underlying the use of jitter in wireless flooding. [ABSTRACT FROM AUTHOR]

In this paper, we examine an algorithm for estimating the location of packet collisions, in the presence of bandlimited multipath channels. We propose an improvement to the collision localization algorithm to further enhance its performance to compensate for the increased impairments of the multipath channel. We then examine the collision localization algorithm in conjunction with two common wireless LAN standards, 802.11b and 802.11a/g. We show that for the 802.11b standard, the collision localization algorithm performs well, even in the presence of a multi-path channel. We also show that the 802.11 a/g standards are compatible with collision localization. However, we will see that the IFFT/FFT operations required to perform OFDM transmission limit the effectiveness of collision localization. We therefore also investigate collision localization in conjunction with block-based single carrier transmission, a comparable technology to OFDM, and offers some advantages when used with collision localization. In addition, we also investigate two applications of collision localization. First, we will show that collision localization in conjunction with Viterbi decoding with erasures can, in many cases, allow for corrupted packets to be completely recovered at the receiver. Second, we will also demonstrate that collision localization can be used to combat narrow-band interference, such as Bluetooth, in 802.11 a/g networks. [ABSTRACT FROM AUTHOR]

The Precision Time Protocol (PTP) distributes a time reference across a network. It specifically addresses demanding environments, where it can reach sub microsecond precision using appropriate technologies. Its scalability is primarily limited by packet delay variations induced by packet collisions. While it is possible to avoid collisions with non-PTP packets using traffic management technologies, collision between PTP packets is an open problem in large systems with critical clock precision requirements. We propose a coordination algorithm that avoids the occurrence of such collisions. It assumes that the master clock, which is the timing reference source, can send a packet in multicast to the slaves: this is not a restrictive hypothesis, since PTP itself takes advantage of this kind of connectivity, and it is also compatible with typical wireless environments. The algorithm operates without introducing additional traffic, it ensures an upper bound to the time between two successive synchronizations of any given slave, it does not alter the structure of the standard PTP messages, it envisions a dynamic number of slaves, it tolerates the replacement of the master with a hot spare in case of failure, and does not rely on specialized hardware. The algorithm has a footprint that does not insist on activities that are already time sensitive, and its operation is mostly concentrated on the master. The algorithm inherits security and fault tolerance limits from PTP: in particular this refers to malicious nodes, and to broken devices that may jam the network. [ABSTRACT FROM AUTHOR]

In this paper, we derive an algorithm for estimating the location of events which cause burst errors, such as packet collisions and multipath fades in wireless packets. Effective localization algorithms have a range of applications, and could lead to network performance improvements through techniques such as error control coding and cross-layer design between the physical and medium access control layers. Given that a collision or fade occurs in a packet, the algorithm finds the maximum-likelihood estimate of the start time and duration of the collision or fade. Due to the computational complexity of this optimal estimate, we also derive an efficient sub-optimal algorithm which decouples the estimation of the collision or fade duration from the estimation of its starting position within the packet of interest. Both algorithms are able to isolate collision locations within the packet when the signal-to-noise ratio is high enough for the link to operate at a BER of ~10 in the absence of collision. An extension to M-QAM demonstrates similar effectiveness for constellation sizes up to 128. [ABSTRACT FROM AUTHOR]

This work presents a wireless token-passing protocol, named Ripple, for wireless mesh networks (WMNs). In contrast to existing random-access approaches, Ripple uses a decentralized controlled-access approach to protect nodes from unintentional packet collisions and maximize the spatial reuse. The performance of Ripple under an error-free wireless channel was investigated and the accuracy of the analysis was verified by simulation. Simulation results also indicated that Ripple achieved throughput, stability, and QoS enhancement than that of 802.11 DCF under a highly loaded situation [ABSTRACT FROM PUBLISHER]