Communication Time Slots Research Articles

Lower and upper bounds for deterministic convergecast with labeling schemes

In wireless networks, broadcast and convergecast are the two most used communication primitives. Broadcast instructs a specific sink (or root) node to send a message to each node in the network. Convergecast instructs each node in the network to send a message to the sink. Due to the collision, without labels, deterministic convergecast is impossible even in a three-node network. Therefore, networking solutions for convergecast are based on probabilistic approaches or use underlying probabilistic medium access protocols such as CSMA/CA or CSMA/CD.In this paper, we focus on deterministic convergecast algorithms enhanced with labeling schemes for wireless networks in collision-presence environment. We investigate two communication modes: half-duplex (nodes either transmit or receive but not both at the same time) and full-duplex (nodes can transmit and receive data at the same time). For these two modes we investigate lower and upper bounds for the time and size of labeling. Even though broadcast and convergecast are similar, we prove that, contrary to broadcast, deterministic convergecast cannot be solved with short labels for some topologies. That is, Ω(log⁡(Δ)) bits are necessary to solve deterministically convergecast where Δ is the maximal degree of a node in the network. We also prove that Ω(n) communication time slots are required, where n is the size of network. We provide solutions that are optimal in terms of time (transmission rounds), and by far, the closest to the lower bound in terms of space (message size) for arbitrary scenarios.

Throughput Maximization for the Full-Duplex Two-Way Relay System with Energy Harvesting

The full-duplex technique can improve the transmission capacity of the communication systems, and energy harvesting (EH) is a promising operation to prolong the lifespan of a wireless node by utilizing the radio-frequency signals. In this paper, the throughput performance of a full-duplex two-way energy EH capable relay system is investigated. In particular, a practical EH protocol, named the time-switching-based relaying (TSR) protocol, is used for EH and the decode-and-forward (DF) policy for information transmission. The outage probability is successfully obtained, and the corresponding system throughput for TSR protocol can be derived by it. The derived throughput is a function of different system parameters, including the time-switching (TS) ratio, power allocation ratio, and the length of the communication time slot. Meanwhile, the throughput is used to characterize a joint time and power allocation scheme for the system, and we aim to find the optimal time and power allocation to achieve the optimal throughput. Due to the existence of three variables and the integral form of throughput expression, an optimization for the throughput is difficult. However, a modified simulated annealing-based search (SABS) algorithm can be used to optimize the throughput. The modified SABS algorithm overcomes being highly impacted by the initial point, and derives the optimal solution fast. Simulation results show that the analytical throughput expression is related with the TS ratio, power allocation ratio, and the length of the communication time slot. The analytical curve of the throughput matches with the simulated one well, which shows that the obtained analytical system throughput for the TSR protocol is valid. Meanwhile, the proposed modified SABS algorithm could be used to derive accurate throughput when SNR is higher than 10 dB.

An Adaptive Topology Optimization Strategy for Inter-Satellite Links in GNSS

Inter-satellite links (ISLs) are an effective way for the Global Navigation Satellite System (GNSS) to reduce its dependence on ground infrastructures, which guarantees constellation orbit determination and satellite communication. When the number of onboard Ka-band antennas is less than that of visible satellites, ISL assignment of GNSS cause a problem. For the problem of ISL scheduling, considering that the result of the allocated link has a feedback effect on the subsequent link assignment as a priori knowledge, an adaptive topology optimization Algorithm Based on Signed Variance (ABSV) is proposed. In order to meet the requirements of communication and ranging performance, the time slots are divided into communication time slots and ranging time slots. Taking the communication time delay (TD) form overseas satellites to anchor satellites and Position Dilution of Precision (PDOP) as measurement indexes, the proposed strategy is simulated for 10080 min. The results show that the ranging performance of this strategy is better than other recently published methods, which verifies the effectiveness of signed variance for adaptive link planning and is also beneficial to the survivability of constellation.

BER Performance of Full-Duplex Cognitive Radio Network With Nonlinear Energy Harvesting

In this paper, the bit error rate (BER) performance of a full-duplex (FD) overlay cognitive radio (CR) network with linear/nonlinear energy harvesting (EH) capability is investigated. The considered overlay CR network consists of a primary transmitter/receiver (PT/PR) pair, a secondary transmitter (ST) and an FD mode operated secondary receiver (SR) where ST harvests energy from both PT and SR during the first communication time slot. In the second communication time slot, SR receives its intended signal from ST while cooperating with PT by transmitting its signal to PR. The bit error probability (BEP) expressions for the primary/secondary users (PU/SU) are analytically derived and validated through Monte-Carlo simulations according to both linear and nonlinear EH models applied at ST. In addition, the optimum distance value between PT and ST is determined considering the objective of minimizing BER of both PU and SU. Moreover, corresponding system performances are obtained regarding a power allocation coefficient at SR to obtain the trade-off between EH and information processing. The results show that the proposed FD-CR system with nonlinear EH improves the PU BEP performance compared to the non-cooperative (direct transmission) case while the SU benefits from the spectrum of PU with a significant BER performance.

LILAC: computable capabilities based high performance protocol for CRFID

Compared with traditional radio frequency identification (RFID), computational RFID (CRFID) tag has more powerful computing capability, but it shows poor performance when it follows EPC Class-1 Generation-2 protocol especially transmitting large amounts of data. In fact, the operation of the CRFID tag entirely depends on the state of energy. For this point, this study proposes an optimised protocol called LILAC. LILAC allows tags to select the communication time slot according to their current voltage value measured by using an analogue-to-digital converter rather than randomly selecting, the authors proposed a more reasonable time slot mapping algorithm for LILAC that increases the success rate of tag responding. In addition, they design a data transmission format that can be retransmitted to improve the uplink throughput. Finally, they implemented LILAC on a CRFID platform and practically measured several parameters to compare with the existing well-known protocol. The results of experiments show that LILAC increases the maximum communication distance by more than half in the access phase and doubles the goodput of the backscatter link in both the inventory and access phase.

Weight-Based Link Scheduling for Convergecast in WirelessHART Network

WirelessHART is considered to be one of the most promising wireless network protocols for its high robustness comparing to other similar wireless networks. Convergecast is an efficient approach for industrial control. But in WirelessHART specifications, no scheduling algorithms are defined for convergecast. In this paper, an efficient link arrangement strategy for packet delivering named WBLSS (Weight-Based Link Scheduling Strategy) is proposed. In order to improve the communication reliability and assign time slots to nodes in the network evenly, WBLSS considers network topology for time slot assignment. Nodes with more children in the communication tree have more time slots for communication, which improves the global throughput dramatically. As compared to the existing link arrangement strategy in WirelessHART, both the throughput of the network and the real-time performance are improved in WBLSS.

Efficient 3-D Bus Architectures for Inductive-Coupling ThruChip Interfaces

Wireless 3-D network-on-chips (NoCs) with inductive-coupling ThruChip interfaces provide a large degree of flexibility for customizing the number of arbitrary chips in a package after chips have been fabricated. To simplify the vertical communication interfaces, static time division multiple access (TDMA) is used for the vertical broadcast buses, while arbitrary or customized topologies can be used for the intrachip network. This paper proposes two techniques to break through the simple static TDMA-based vertical buses while maintaining a simple communication interface. The first technique is headfirst sliding (HS) routing to reduce the waiting time for acquiring the communication time-slot. HS routing selects the best vertical bus based on the current time, taking advantage of static TDMA. The second technique extends carrier sense multiple access with collision detection (CSMA/CD) for vertical broadcast buses. We introduce a packet collision detection technique for inductive-coupling buses and propose two retransmission strategies to reduce the waiting time for packet retransmissions caused by collisions. Network simulation results show that HS routing reduces the communication latency by 39.1% compared with the conventional static TDMA bus-based 3-D NoC that uses the shortest path routing. The proposed CSMA/CD bus also improves the latency by 52.5% and throughput by 34.1%. The full-system simulation results show that HS routing and the proposed CSMA/CD technique reduce the application execution time accordingly while maintaining the average flit transfer energy overhead modest.

A Study of the Model which Can Improve LEACH Protocol

In the application process of wireless sensor network, LEACH protocol solves the problem of data fusion well, and reduces data exchanges between nodes and bases. Based on the research, this paper proposes an advanced LEACH protocol, which is fused by the data of cluster head, and each time when transmits data to the neighbor shortest cluster head, this protocol gets reduction in the aspects of theoretical existing and energy consumption, and improvement in using efficiency. The LEACH protocol Low Energy Adaptive Clustering Hierarchy (LEACH) [1] is designed by Hein Zelman W et al from college of electronic engineering and computer science of MIT University for the wireless sensor network. The protocol divides all nodes in the network into several clusters, in which the cluster members are responsible for the collection of user needs in the news, and the cluster head is responsible for the management of cluster member cluster members, for the allocation of communication time slot to receive the cluster members messages, and these messages are forwarded to fusion processing, the processed data to the base station node. Compared with the planar routing, the cluster structure through data fusion, can eliminate redundant data, reduce network traffic, effectively save energy, and prolong the network survival time. But the protocol still has some problems, such as the burden of cluster heads is too heavy, more energy consumption, cost of frequent building clusters bring and network load balancing.

Energy Management Policies for Harvesting-Based Wireless Sensor Devices with Battery Degradation

Energy Harvesting Wireless Sensor Devices are increasingly being considered for deployment in sensor networks, due to their demonstrated advantages of prolonged lifetime and autonomous operation. However, irreversible degradation mechanisms jeopardize battery lifetime, calling for intelligent management policies, which minimize the impact of these phenomena while guaranteeing a minimum Quality of Service (QoS). This paper explores a mathematical characterization of these devices, focusing on the interplay between the battery discharge policy and the irreversible degradation of the storage capacity. We propose a stochastic Markov chain framework, suitable for policy optimization, which captures the degradation status of the battery. We present a general result of Markov chains, which exploits the timescale separation between the communication time-slot of the device and the battery degradation process, and enables an efficient optimization. We show that this model fits well the behavior of real batteries for what concerns their storage capacity degradation over time. We demonstrate that a degradation-aware policy significantly improves the lifetime of the sensor compared to greedy policies, while guaranteeing the minimum required QoS. Finally, a simple heuristic policy, which never discharges the battery below a given threshold, is shown to achieve near-optimal performance in terms of battery lifetime.

The General Monitoring Method of the Signal of TDMA Satellite Communication System

The current satellite communication systems generally use TDMA signal multiplexing method to improve the frequency efficiency. The system described in this paper has build a signal monitoring platform of TDMA satellite communication system by using general-purpose instruments, the platform has a flexible structure, strong real-time and high levels intelligent. Instead of the traditional monitoring method which uses the communication quality of the entire channel to replace the quality of each time slot inside the channel, it can monitor the signal quality of all the satellite communication time slots inside the monitoring channels. Practice has proved that the platform improves the efficiency of spectrum testing staff; it has realized a high degree of standardization and generalization, also it has reliable and stable operation.

Allocation of multi-objective cross-layer wireless sensor network resource based on chaotic parallel genetic algorithm

A chaotic parallel genetic algorithm for the allocation of a multi-objective cross-layer wireless sensor network resource is provided, in which chaotic sequence and parallel genetic algorithm are used to dynamically adjust target selection, communication time slots and other parameters for optimizing the global cross-layer resource allocation. Simulations are conducted to compare the chaotic parallel genetic algorithm method with random allocation algorithm, dynamic programming algorithm, T-MAC protocol and the S-MAC protocol separalely. The simulation results show that the chaotic parallel genetic algorithm has a small communication delay and high success rate of target detection, which reduces the power consumption and improves the real-time characteristic of wireless sensor network.

Collaborative Quickest Spectrum Sensing via Random Broadcast in Cognitive Radio Systems

Quickest detection is applied in spectrum sensing in cognitive radio systems when multiple secondary users collaborate with limited communication time slots. When the transmissions of sensing results are not coordinated to avoid confliction, random broadcast is used to exchange information. A necessary condition for the optimal broadcast probability, as a function of the log likelihood ratio of local observation, is obtained using variational analysis. To alleviate the difficulty of computing the optimal broadcast probability, a simple threshold broadcast scheme is proposed. Simulation shows that the proposed threshold broadcast scheme can achieve substantial performance gain (less than 60% in detection delay for the same false alarm rate) over schemes of random broadcast without regulation and single-user spectrum sensing.

Directed complete bipartite graph decompositions: Indirect constructions

Edge-decompositions of the complete λ -fold directed graph K ⇒ n into (uniform) directed complete bipartite subgraphs K ⇒ a , b form a model for wireless communication in sensor networks. Each node can be in one of three states: asleep (powered down), listening, or transmitting. Communication requires that the sender be transmitting, the destination listening, and no other node near the receiver transmitting. We represent nodes of the network as the vertices of K ⇒ n , and time slots for communication as blocks of the graph decomposition. A block with out-vertices A and in-vertices B corresponds to a slot in which the nodes in A are transmitting, those in B are receiving, and all others are asleep. Thus, such a decomposition of λ K ⇒ n guarantees that every ordered pair of nodes in the associated network can communicate in λ time slots. Additional constraints are needed to minimize interference by a third node. Some recursive constructions for these graph decompositions are established, with particular emphasis on properties minimizing interference.