Contention Resolution Research Articles

Complexity analysis for recent ALOHA random access techniques in satellite communications

SummaryIn this paper, we study the the complexity of packet localization at reception, for recent synchronous Random Access (RA) techniques based on the protocol ALOHA for satellite communications. The promising CRDSA (Contention Resolution Diversity Slotted ALOHA) offers better throughput, in comparison to the traditional slotted ALOHA protocols, thanks to the use of Successive Interference Cancellation (SIC) along with multireplica transmission. MARSALA (Multi‐replicA decoding using corRelation baSed locALizAtion) is one of the many variants and enhancement schemes of CRDSA that have been proposed in the literature. It is applied to CRDSA each time a decoding deadlock situation is reached (when no packets can be retrieved by CRDSA). MARSALA first localizes the replicas of collided packets on a chosen reference time slot using correlations. Then it performs coherent signal combination of packet replicas prior to decoding. However, despite the good performance offered by MARSALA, its localization process adds a significant complexity to the receiver in terms of correlation operations. R‐SPOTiT (Random Shared POsition Technique for Interfered random Transmissions) mitigates this complexity by introducing a shared information between the receiver and each of the transmitters, about all potential packets' locations on the frame, without any additional signaling overhead. We focus in this paper on the analysis of the total number of correlations which are needed to localize packets' replicas for both MARSALA and R‐SPOTiT, with a single or with multiple Gold preambles. This should include preamble detection operations that are performed at CRDSA with a coarse and fine tracking. The results show that the most suitable system to use is the multi‐preamble R‐SPOTiT with two preambles.

Measurement of water content in heavy oil with cavity resonator

The study of optical microcavity sensors in current micro optical electromechanical systems (MOEMS) devices is an important research direction in this field. In this study, a surface plasmon optical waveguide structure with MIM (Metal Insulator Metal), semi-circular resonator, and T-shaped resonator was examined. The effects of the coupling distance, the geometrical size of the T-shaped cavity and its asymmetry, and the radius of the semi-circular cavity on the Fano resonance spectrum were analyzed numerically. The sensitivity of the refractive index sensor was up to1066.67nm/RIU. The detection of the water content of the heavy oil found that the Fano resonance line shifted to the short-wave direction as the volume percentage of the contained water increased. The volume percentage resolution of the sensor's heavy oil water content could be as low as2.05×10-9. The proposed structure can overcome the shortcomings of common refractive index sensors and therefore has great application prospects in chemical and biological sensing.

Uncertainty analysis of UMRS parameters and its application for water detection in the tunnel

As a novel geophysical exploration technology, the underground magnetic resonance sounding (UMRS) method has been applied to detect water inrush in underground construction over the past 10 years. Non-invasive UMRS technology has found potential use in preventing water inrush disasters in tunnel due to its direct sensitivity to water molecules. Small water bodies are often the origin of severe water inrush disasters in tunnels. In most cases, UMRS signals have a low SNR, yielding high uncertainties that are important to be correctly estimated for an optimal interpretation of the water distribution. In this paper, we describe a method by which to evaluate the uncertainty of UMRS parameters for advanced water detection in tunnels, calculating for the quasi-whole space model. The key point is that the response caused by water surrounding the tunnel is non-negligible. In addition, we discuss the resolution of water content as the main inverted parameter for UMRS advanced detection. In order to guide the configuration of the acquisition settings, the influences of some parameters, including coil size and turns, tunnel size, water content surrounding the tunnel lane, as well as the noise level, on the uncertainty of the advanced target, are analyzed. Finally, we invert a set of measurement data related to a case of tunnel advanced detection, and analyze the uncertainty of the results.Based on the study results, we have concluded that during the advanced detection the water content surrounding the tunnel may significantly increase the uncertainty of the target. In addition, the increasing coil size and number of turns cause an increase in the amplitude of the signal, and also provide a reduction in the uncertainty of the water content. However, at the same time, these also introduce a higher noise level, which may offset the improvement. For these reasons, it is necessary to conduct the parameter uncertainty analyses according to different tunnel environmental conditions before performing the field test, so as to obtain reliable UMRS results.

A Node-Regulated Deflection Routing Framework for Contention Minimization

Optical Burst Switching (OBS) paradigm coupled with Dense Wavelength Division Multiplexing (DWDM) has become a practical candidate solution for the next-generation optical backbone networks. In its practical deployment only the edge nodes are provisioned with buffering capabilities, whereas all interior (core) nodes remain buffer-less. In that way the implementation becomes quite simple as well as cost effective as there will be no need for optical buffers in the interior. However, the buffer-less nature of the interior nodes makes such networks prone to data burst contention occurrences that lead to a degradation in overall network performance as a result of sporadic heavy burst losses. Such drawbacks can be partly countered by appropriately dimensioning available network resources and reactively by way of deflecting excess as well as contending data bursts to available least-cost alternate paths. However, the deflected data bursts (traffic) must not cause network performance degradations in the deflection routes. Because minimizing contention occurrences is key to provisioning a consistent Quality of Service (QoS), we therefore in this paper propose and analyze a framework (scheme) that seeks to intelligently deflect traffic in the core network such that QoS degradations caused by contention occurrences are minimized. This is by way of regulated deflection routing (rDr) in which neural network agents are utilized in reinforcing the deflection route choices at core nodes. The framework primarily relies on both reactive and proactive regulated deflection routing approaches in order to prevent or resolve data burst contentions. Simulation results show that the scheme does effectively improve overall network performance when compared with existing contention resolution approaches. Notably, the scheme minimizes burst losses, end-to-end delays, frequency of contention occurrences, and burst deflections.

Complimentary code keying of spectral amplitude coding signals in optical buffering with increased capacity

Signal buffering services such as contention resolution and congestion avoidance are essential in optical packet switching networks. In this paper, an optical memory scheme based on spectral amplitude coding (SAC) and complementary code keying (CCK) is proposed to increase the buffer capacity. CCK is applied to packet buffering by selecting an available code set and encoding the payload bits with either an SAC signal or its complementarity. The capacity constraint is effectively released, as the usable codes for queuing packets are twice those for the conventional code-domain buffers. To minimize system costs by reducing the codec number, a shared structure based on an arrayed waveguide grating (AWG), which is capable of processing both the typical and complimentary coded signals simultaneously, is also investigated.

Analysis of a PPLN-based cSFG/DFG wavelength conversion for capacities beyond 100 Gb/s

Wavelength division multiplexing-based networks suffer from blocking probability due to wavelength contention resolution. Such a problem can even be worth when the advanced coherently modulation formats such as M-array quadrature amplitude modulation is used to increase the channel capacity beyond 100 Gbit/s. This paper presents theoretical study of cascaded sum frequency generation and difference frequency generation based tunable wavelength conversion in a periodically poled lithium niobate waveguide as a trivial solution to the wavelength blocking problem when advanced signal modulation formats are considered. It is shown numerically that wavelength conversion of single channel up to 1 Tbit/s would be possible with a 3 cm long wavelength converter.

An approach to reduce exploration risk using spectral decomposition, prestack inversion, and seismic facies classification

Petroleum companies have invested heavily in the exploration of frontier offshore basins in Brazil. Uncertainties associated with geologic complexity, lithostratigraphy, fluid content, and seismic resolution in these basins are the most common challenges. Many methods have been used to circumvent these issues, such as assessing seismic attributes, seismic inversion, spectral decomposition, and the integration of these methodologies to accomplish an optimal approach. Because of the complex geology of these areas, it is very difficult to identify potential reservoirs within one specific geologic formation. Hence, applying spectral decomposition to frontier basins of high geologic complexity can help overcome the challenges because in the frequency domain, it is possible to better define variability and lateral discontinuities. The correct choice of the spectral decomposition optimization approach is critical for accurate target zone representation as well as selection of the appropriate transform. Prestack inversion, spectral decomposition, and attribute seismic facies classification were applied to evaluate the extent of a reservoir and analyze whether an appraisal well has been sited at a good location. The results showed that the new appraisal well was planned at a good location but that its facies were not as good as those of the first discovery well, as confirmed after drilling.

Reducing neighbor discovery time in sensor networks with directional antennas using dynamic contention resolution

Reducing neighbor discovery time in sensor networks with directional antennas using dynamic contention resolution

Demonstration of SDN-Enabled Hybrid Polling Algorithm for Packet Contention Resolution in Optical Data Center Network

We propose and experimentally demonstrate a Software-Defined Network (SDN) enabled Hybrid Polling Algorithm for packet Contention Resolution (HPACR) in optical Data Center Network (DCN) based on Fast Optical Switches (FOS). Fast Semiconductor Optical Amplifier (SOA)-based buffer-less FOS with nanoseconds reconfiguration time are employed for interconnecting Top-Of-the Racks (TORs) switches with distributed flow control. Under the realistic 10 Gb/s server traffic, the network performance of the DCN employing the proposed HPACR algorithm is experimentally assessed. Results show that the HPACR increases 13.6% throughput at the high load of 1.0 and decreases the 75% contention ratio for the load >0.5 with respect to the traditional packet contention resolution methods. Based on the experimental parameters, a simulation platform is built to numerically evaluate the HPACR performance of DCN with 64 TORs connecting 1280 servers. The results show that HPACR improves the system performance by increasing the throughput by 5% compared with existing algorithms, reducing the TOR-to-TOR latency by 18.5%, and decreasing the packet loss by 14.1% at the load of 1.

Packet Blocking Performance of Cloud Computing Based Optical Data Centers Networks under Contention Resolution Mechanisms

Abstract In data center networks use of optical communication has revolutionized the data transfer mechanism. Optical communication heavily relies on enormous bandwidth of optical fiber. Wavelength Division Multiplexing (WDM) technique can be used for utilization of huge bandwidth. To employ WDM which uses distinct set of wavelengths to carry data wavelength converters are required. However as the tunable range of wavelength converter increases both cost and technological design complexity rises exponentially. Therefore, both Limited Range Wavelength Converter (LRWC) and Full Range Wavelength Converter (FRWC) are considered. However, under higher loading conditions buffering is also required as using wavelength converter (WC) blocking can be reduced significantly. This paper presents comprehensive analysis of blocking performance under various types of wavelengths converters and buffering of contending packets.

Nanosatellite-5G Integration in the Millimeter Wave Domain: A Full Top-Down Approach

This paper presents a novel network architecture for an integrated nanosatellite (nSAT)-5G system operating in the millimeter-wave (mmWave) domain. The architecture is realized adopting a delay/disruption tolerant networking (DTN) approach allowing end users to adopt standard devices. A buffer aware contact graph routing algorithm is designed to account for the buffer occupancy of the nSATs and for the connection planning derived from their visibility periods. At the terrestrial uplink, a coded random access is employed to realize a high-capacity interface for the typically irregular traffic of 5G users, while, at the space uplink, the DTN architecture is combined with the contention resolution diversity slotted Aloha protocol to match the recent update of the DVB-RCS2 standard. To achieve a reliable testing of the introduced functionalities, an accurate analysis of the statistic of the signal to interference-plus-noise ratio and of the capture probability at each mmWave link is developed by including interference, shadowing, fading, and noise. The application of the designed architecture to data transfer services in conjunction with possible delay reduction strategies, and an extension to inter-satellite communication, are finally presented by estimating the resulting loss/delay performance through a discrete-time discrete-event platform based on the integration of Matlab with Network Simulator 3.

Construction of Subexponential-Size Optical Priority Queues With Switches and Fiber Delay Lines

All-optical switching has been considered as a natural choice to keep pace with growing fiber link capacity. One key research issue of all-optical switching is the design of optical buffers for packet contention resolution. One of the most general buffering schemes is optical priority queue, where every packet is associated with a unique priority upon its arrival and departs the queue in order of priority, and the packet with the lowest priority is always dropped when a new packet arrives but the buffer is full. In this paper, we focus on the feedback construction of an optical priority queue with a single $\boldsymbol{(M+2)\times (M+2)}$ optical crossbar Switch and $\boldsymbol{M}$ fiber Delay Lines (SDL) connecting $\boldsymbol{M}$ inputs and $\boldsymbol{M}$ outputs of the switch. We propose a novel construction of an optical priority queue with buffer $\boldsymbol{2^{\Theta(\sqrt{M})}}$, which improves substantially over all previous constructions that only have buffers of $\boldsymbol{O(M^c)}$ size for constant integer $\boldsymbol{c}$. The key ideas behind our construction include (i) the use of first in first out multiplexers, which admit efficient SDL constructions, for feeding back packets to the switch instead of fiber delay lines, and (ii) the use of a routing policy that is similar to self-routing, where each packet entering the switch is routed to some multiplexer mainly determined by the current ranking of its priority.

Multi-dimensional mechanism design via random order contention resolution schemes

Already in 1981 Myerson gave a characterization of the optimal mechanism for a single parameter Bayesian mechanism design. However, till today we have no idea for how such a characterization for the multi-dimensional setting could even look like. Moreover, it wasn't until no that long time ago that we could not develop mechanisms for such setting with any reasonable and provable performance guarantees. The seminal work of [Chawla et al. 2009] on sequential posted pricing mechanisms gave us an approach for approximately solving the Bayesian multi-parameter unit-demand mechanism design problem (BMUMD). The paper left open the question on how to obtain a constant approximation for the matroid setting. Two mathematically beautiful results from combinatorial optimization under uncertainty where devised in order to answer this question. First, Kleinberg and Weinberg in 2011 extended the classical Prophet Inequality result into the matroid setting to give a 2-approximation for BMUMD for a single matroid setting. Second, Feldman, Svensson and Zenklusen in 2016 adapted the Contention Resolution Scheme framework for online settings. We add to this line of work by considering the Contention Resolution Scheme framework in the random order setting. The most impressive implication of this research are the new algorithms for BMUMD which improve the previous results in the multimatroid setting. Although the range of implications of the CR Scheme framework in the random order is reasonably wide, we shall focus in this letter on presenting only the single matroid setting and how it is connected to BMUMD.

A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)

VHF Data Exchange System (VDES) is considered as an important component of the future maritime communication system by the International Maritime Organization (IMO). On the basis of the existing Automatic Identification System (AIS), VDES adds the other two higher capacity subsystems: Application Specific Message (ASM) and VHF Data Exchange (VDE). The Random Access Channel (RACH) of VDE was first introduced in the International Telecommunication Union (ITU) Recommendation M.2092-0. As the slot planning principle of RACH in VDE is by interval, which is significantly different from the continuous slot map for access algorithms in AIS, the existing slot access algorithms cannot meet the requirements of VDE. The simulation results show that the VDE slot map can reduce the normalized throughput of the existing algorithm by 39%. A novel random access algorithm called Adaptive Traffic Load Contention Resolution Diversity Slotted ALOHA (ATL-CRDSA) is proposed in this paper. The algorithm combines the load control strategy and contention resolution scheme to overcome the challenges of the new RACH of VDE. Simulation results show that ATL-CRDSA has remarkable improvement on RACH, making it very efficient and providing low latency of the packets. The insights gained from this study may be of assistance to the Media Access Control (MAC) layer design for upcoming versions of VDES standard.

Fruit Battery Method for Oil Palm Fruit Ripeness Sensor and Comparison with Computer Vision Method.

Oil palm ripeness’ main evaluation procedure is traditionally accomplished by human vision. However, the dependency on human evaluators to grade the ripeness of oil palm fresh fruit bunches (FFBs) by traditional means could lead to inaccuracy that can cause a reduction in oil palm fruit oil extraction rate (OER). This paper emphasizes the fruit battery method to distinguish oil palm fruit FFB ripeness stages by determining the value of load resistance voltage and its moisture content resolution. In addition, computer vision using a color feature is tested on the same samples to compare the accuracy score using support vector machine (SVM). The accuracy score results of the fruit battery, computer vision, and a combination of both methods’ accuracy scores are evaluated and compared. When the ripe and unripe samples were tested for load resistance voltage ranging from 10 Ω to 10 kΩ, three resistance values were shortlisted and tested for moisture content resolution evaluation. A 1 kΩ load resistance showed the best moisture content resolution, and the results were used for accuracy score evaluation comparison with computer vision. From the results obtained, the accuracy scores for the combination method are the highest, followed by the fruit battery and computer vision methods.

Topology control for constructive interference-based data dissemination in WSN

Data dissemination is a fundamental service in wireless sensor networks. Traditional protocols often suffer severe medium contention problem or incur significant overhead in contention resolution. Constructive interference (CI) enables concurrent transmissions to interfere constructively, so as to enhance network performance. It has been proved that leveraging CI can achieve near-optimal network flooding latency. However, recent studies show that redundant nodes transmitting simultaneously may degrade the dissemination performance and also consume extra energy. Considering the limited energy of sensor nodes, how to choose the appropriate nodes for simultaneous transmission is important for CI-based data dissemination schemes. In this paper, we formulate this problem as a multi-objective combinatorial optimisation problem theoretically. Considering the complexity of the problem, we design a distributed greedy node selection algorithm to select suitable nodes which forward simultaneously based on CI in each time slot. The main idea of the algorithm is that, by maintaining RecSet and unRecSet in the two-hop neighbour, each node selects suitable nodes from RecSet to transmit simultaneously, such that the maximum number of nodes in unRecSet can receive the packet. Numerical simulations show the efficiency of our proposed algorithm.

Analysis of the information content and vertical resolution of the ground-based spectroscopic IR method for the CO2 vertical structure retrieval

Analysis of the information content and vertical resolution of the ground-based spectroscopic IR method for the CO2 vertical structure retrieval

Randomly Pre-Coded Packets Based Random Access Scheme for IoT-Oriented Satellite Networks

In this article, a novel random pre-coding (RPC) based random access (RA) scheme is proposed to improve the system performance in the Internet of Things-oriented satellite networks. In this scheme, each device randomly selects a non-orthogonal multi-level complex sequence from a pre-defined pre-coding sequence set to pre-code the transmitted packets in a sub-frame, by which multiple superimposed packets in the sub-frame can be successfully decoded by using the minimum mean squared error (MMSE) based successive interference cancellation (SIC) detection algorithm. Besides, by combining the proposed RPC with the existing contention resolution diversity slotted ALOHA (CRDSA) scheme, which the RPC-CRDSA scheme is generated. The SIC processing should be carried out across sub-frames to remove the received signals that are already recovered, which can further significantly improve the system throughput. The performance of the RPC-RA scheme is evaluated via both theoretical analysis and computer simulation. The collision probabilities of both preamble and pre-coding sequences and an upper bound of throughput are derived, respectively. Simulation results show that the peak normalized throughput of RPC-CRDSA with the pre-coding sequence length $L = 8$ can reach 1.87 bits/symbol, which largely outperforms traditional schemes.

An Efficient Reservation-Based MAC Protocol for Multi-Priority Traffic in Slotted Multi-Channel Distributed Cognitive Radio Networks

Cognitive radio network (CRN) is developed to improve the scarce but under-utilized wireless spectrum due to rapidly developing wireless networks. This paper proposes a reservation-based MAC protocol for traffic having multiple classes of priorities in CRN. One channel called control channel is used for contention resolution between secondary users (SUs). In this protocol, an SU having data packets with different class of priorities transmits its control packet containing the priority value through the control channel. The order of access to primary channels is determined based on the priority of the data packet and the position of the non-colliding control packet. The access order determines the idle primary channel that an SU uses to transmit its data packet. In this protocol, there is no performance degradation either from SUs choosing a busy primary channel or multiple SUs choosing the same idle primary channel. Moreover, even though the SU cannot transmit its data packet because there is no idle primary channel that the SU can utilize, it can re-transmit its control packet without having concern over additional collision. Multi-state Markov chain is used to analyze the throughput and performance of the proposed protocol and the analytical results show that higher priority traffic can be transmitted first ahead of the lower priority traffic. Notwithstanding the above, the maximum sum of the throughput of SUs with different classes of priorities is almost equal to the available capacity, and therefore the proposed protocol can take advantage of almost all of the available portion of primary channels.

Optimal Group Paging Frequency for Machine-to-Machine Communications in LTE Networks With Contention Resolution

Group paging is a baseline solution proposed by the long-term evolution (LTE) standardization body for supporting machine-to-machine (M2M) communications in the current-generation and the next-generation cellular networks. Yet, in conventional group paging scheme, upon the reception of paging message, all machine-type devices (MTDs) in a group will simultaneously access the base station, leading to severe network congestion and intolerably low access efficiency. To handle this issue, in this article, we propose a dynamic group paging mechanism, where only the MTDs with packets to send will join the contention process, and the collisions in the random access channel are addressed by the contention resolution scheme. Explicit expressions of key performance measures including the mean access delay of each MTD are derived as functions of the length of waiting period (interval between two consecutive paging periods) $T_{W}$ , where a smaller $T_{W}$ indicates a higher frequency of group paging. It is shown that $T_{W}$ is a key system parameter that determines the crucial tradeoff between the signaling overheads of the system during the paging period and the access delay performance of each MTD. To study how to properly tune the waiting period length, a utility-based analytical framework is established by taking the aforementioned tradeoff into consideration. The optimal waiting period length for maximizing the network utility is derived and verified by simulation results. The analysis in this article reveals that the network should increase the group paging frequency as the traffic becomes heavier or the number of preambles decreases. Providing more preambles can indeed improve the delay performance, while the gain becomes marginal if the number of preambles is large.