A novel efficient power‐saving MAC protocol for multi‐hop MANETs

Following recent advances in the performance of ad hoc networks, the limited life of batteries in mobile devices poses a bottleneck in their development. Consequently, how to minimize power consumption in the Medium Access Control (MAC) layer of ad hoc networks is an essential issue. The power‐saving mode (PSM) of IEEE 802.11 involves the Timing Synchronization Function to reduce power consumption for single‐hop mobile ad hoc networks (MANETs). However, the IEEE 802.11 PSM is known to result in unnecessary energy consumption as well as the problems of overheating and back‐off time delay. Hence, this study presents an efficient power‐saving MAC protocol, called p‐MANET, based on a Multi‐hop Time Synchronization Protocol, which involves a hibernation mechanism, a beacon inhibition mechanism, and a low‐latency next‐hop selection mechanism for general‐purpose multi‐hop MANETs. The main purposes of the p‐MANET protocol are to reduce significantly the power consumption and the transmission latency. In the hibernation mechanism, each p‐MANET node needs only to wake up during one out of every N beacon interval, where N is the number of beacon intervals in a cycle. Thus, efficient power consumption is achieved. Furthermore, a beacon inhibition mechanism is proposed to prevent the beacon storm problem that is caused by synchronization and neighbor discovery messages. Finally, the low‐latency next‐hop selection mechanism is designed to yield low transmission latency. Each p‐MANET node is aware of the active beacon intervals of its neighbors by using a hash function, such that it can easily forward packets to a neighbor in active mode or with the least remaining time to wake up. As a consequence, upper‐layer routing protocols can cooperate with p‐MANET to select the next‐hop neighbor with the best forwarding delay. To verify the proposed design and demonstrate the favorable performance of the proposed p‐MANET, we present the theoretical analysis related to p‐MANET and also perform experimental simulations. The numerical results show that p‐MANET reduces power consumption and routing latency and performs well in extending lifetime with a small neighbor discovery time. Copyright © 2011 John Wiley & Sons, Ltd.     

A hop‐by‐hop delay‐constrained routing algorithm with explicit loop avoidance and backup routing information

QoS Routing is crucial for QoS provisioning in high‐speed networks. In general, QoS routing can be classified into two paradigms: source routing and hop‐by‐hop routing. In source routing, the entire path to the destination node of a communication request is locally computed at the source node based on the global state that it maintains, which does not scale well to large networks. In hop‐by‐hop routing, a path‐selecting process is shared among intermediate nodes between the source node and the destination node, which can largely improve the protocol scalability. In this paper, we present the design of hop‐by‐hop routing with backup route information such that each intermediate node can recursively update the best known feasible path, if possible, by collectively utilizing the routing information gathered thus far and the information that it locally stores. Such a route is kept as a backup route and its path cost is used as a reference to guide the subsequent routing process to search for a lower‐cost constrained path and avoid performance degradation. In this way, the information gathered is maximally utilized for improved performance. We prove the correctness of our presented algorithm and deduce its worst message complexity to be O(∣V∣²), where ∣V∣ is the number of network nodes. Simulation results indicate that, however, the designed algorithm requires much fewer messages on average. Therefore it scales well with respect to the network size. Moreover, simulation results demonstrate that the cost performance of our algorithm is near‐optimal. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparative performance analysis of cooperative and multi dual‐hop relay networks using MGF approach

In this paper, we analyzed and compared the performance of cooperative diversity systems such as cooperative and multi dual‐hop networks with non‐regenerative relay nodes. The contributions of this study are twofolds. Firstly, analytical expressions of outage probability P_out and average symbol error rate ASER are derived using moment generating function (MGF) analysis of the received SNR with the assumption that the channel experiences Weibull fading and the best relay selection is used. Then, using the analytical results, comparative performance evaluation of cooperative and multi dual‐hop relay networks is done for varying number of relay nodes and different receive diversity schemes such as maximal ratio combining (MRC) and selection combining (SC). The results show that the cooperative relay network has better performance than a multi dual‐hop relay network in terms of P_out and ASER. The results also show that the multi dual‐hop network can achieve the same performance as the cooperative network with the requirement that it needs the deployment of three times more relay nodes.     

The Effect of Methyl Functionalization on Microporous Metal‐Organic Frameworks' Capacity and Binding Energy for Carbon Dioxide Adsorption

The design, synthesis, and structural characterization of two new microporous metal‐organic framework (MMOF) structures is reported; Zn(BDC)(DMBPY)_0.5·(DMF)_0.5(H₂O)_0.5 (1; H₂ BDC = 1,4‐benzenedicarboxylic acid; DMBPY=2,2′‐dimethyl‐4,4′‐bipyridine) and Zn(NDC)(DMBPY)_0.5·(DMF)₂ (2; H₂NDC = 2,6‐naphthalenedicarboxylic acid, DMF=N,N,‐dimethylformamide), which are obtained by functionalizing a pillar ligand with methyl groups. Both compounds are 3D porous structures of the Zn₂(L)₂(P) type and are made of a paddle‐wheel Zn₂(COO)₄ secondary building unit (SBU), with the dicarboxylate and DMBPY as linker (L) and pillar (P) ligands, respectively. Comparisons are made to the parent structures Zn(BDC)(BPY)_0.5·(DMF)_0.5(H₂O)_0.5 (3; BPY = 4,4′‐bipyridine) and Zn(NDC)(BPY)_0.5·(DMF)_1.575 (4) to analyze and understand the effect of methyl functionalization. CO₂‐adsorption studies indicate substantially enhanced isosteric heats of CO₂ adsorption (Q_st) for both compounds, as a result of adding methyl groups to the BPY ligand. The CO₂ uptake capacity, however, is affected by two opposing and competing factors: the enhancement due to increased MMOF–CO₂ interactions (higher Q_st values) and detraction due to the surface area and pore‐volume reduction. For 1′ (the guest‐free form of 1), the positive effect dominates, which leads to a significantly higher uptake of CO₂ than that of its parent structure 3′ (the guest‐free form of 3). In 2′ (the guest‐free form of 2), however, the negative effect rules, which results in a slightly lower CO₂ uptake with respect to 4′ (the guest‐free form of 4). All four compounds exhibit a relatively high separation capability for carbon dioxide over other small gases, including CH₄, N₂, and O₂. The separation ratios of CO₂ to O₂ and N₂ (at 298 K and 1 atm) are 39.8 and 23.5 for compound 1′, 57.7 and 40.2 for 2′, 25.7 and 29.5 for 3′, 89.7, and 20.3 for 4′, respectively. IR and Raman spectroscopic characterization of CO₂ interactions with 1′ and 2′ provides indirect support of the importance of the methyl groups in the interaction of CO₂ within these systems.     

Cross-layer Routing Design in Cognitive Radio Networks by Colored Multigraph Model

In this paper, the cross-layer design routing in cognitive radio(CR) networks is studied. We propose a colored multigraph based model for the temporarily available spectrum bands, called spectrum holes in this paper. Based on this colored multigraph model, a polynomial time algorithm with complexity O(n ²) is also proposed to develop a routing and interface assignment, where n is the number of nodes in a CR network. Our algorithm optimizes the hop number of routing, meanwhile, the adjacent hop interference (AHI) is also optimized locally.

Interference analysis of cognitive radio networks

In spite of spectrum sensing, aggregate interference from cognitive radios (CRs) remains as a deterring factor to the realization of spectrum sharing. We provide a systematic approach of evaluating the aggregate interference (I _aggr) experienced at a victim primary receiver. In our approach, we model the received power versus propagation distance relations between a primary transmitter, primary receiver, and CRs. Our analytical framework differs from the previous works in that we have formulated the relationship between I _aggr and the sensing inaccuracy of CRs. Energy detector is assumed for the purpose of spectrum sensing. I _aggr is expressed explicitly as a function of the number of energy samples collected (N ) and the threshold signal‐to‐noise ratio level used for comparison (SNR_ε ). The theoretical analysis is then applied to a practical scenario of spectrum sharing between digital TV broadcast and the IEEE 802.22 wireless regional area network systems. The impact on digital TV reception is evaluated in terms of signal‐to‐interference ratio. The proposed method allows us to determine the appropriate wireless regional area network operating conditions that fulfill the signal‐to‐interference ratio requirement imposed by regulator. Copyright © 2016 John Wiley & Sons, Ltd.     

A high‐performance switch architecture based on mesh of trees

With emergence of various new Internet‐enabled devices, such as tablet PCs or smart phones along with their own applications, the traffic growth rate is getting faster and faster these days and demands more communication bandwidth at even faster rate than before. To accommodate this ever‐increasing network traffic, even faster Internet routers are required. To respond for these needs, we propose a new mesh of trees based switch architecture, called MOTS(N) switch. In addition, we also propose two more variations of MOTS(N) to further improve it. MOTS(N) is inspired by crossbar with crosspoint buffers. It forms a binary tree for each output line, where each gridpoint buffer ? ? Because the fabric of MOTS(N) switch is not pure crossbar, we call the buffers in the same location in pure crossbar gridpoint buffers. Details will be presented in the following sections.
is a leaf node and each internal node is 2‐in 1‐out merge buffer § § 2‐in 1‐out merge buffer can accommodate two memory writes and one memory read simultaneously by using its modularized architecture 31 .
emulating FIFO queues. Because of this FIFO characteristic of internal buffers, MOTS(N) ensures QoS like FIFO output‐queued switch. The root node of the tree for each output line is the only component connected to the output port where each cell is transmitted to output port without any contention. To limit the number of buffers in MOTS(N) switch, we present one of its improved (practical) variations, IMOTS(N) switch, as well. For IMOTS(N) switch architecture, sizes of the buffers in the fabric are limited by a certain amount. As a downside of IMOTS(N), however, every cell should go through log ₂N + 1 number of buffers in the fabric to be transmitted to the designated output line. Therefore, for even further improvement, IMOTS(N) with cut‐through, denoted as IMOTS‐CT(N), is also proposed in this paper. In IMOTS‐CT(N) switch, the cells can cut through one or more empty buffers to be transferred from inputs to outputs with simple 1 or 2 bit signal exchanges between buffers. We analyze the throughput of MOTS(N), IMOTS(N), and IMOTS‐CT(N) switches and show that they can achieve 100% throughput under Bernoulli independent and identically distributed uniform traffic. Our quantitative simulation results validate the theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

Multi‐interface cognitive radio for enhanced routing in multi‐hop cellular networks

Multi‐hop cellular network (MCN) is a wireless communication architecture that combines the benefits of conventional single‐hop cellular networks and multi‐hop ad hoc relaying networks. The route selection in MCN depends on the availability of intermediate nodes and their neighborhood connectivity. Cognitive radio (CR) is an emerging communication paradigm that exploits the available radio frequencies opportunistically for the effective utilization of the radio frequency spectrum. The incorporation of CR and mobile ad hoc network routing protocols in MCN could potentially improve the spectrum utilization and the routing performance of MCN. This paper firstly presents the proposed model for the multi‐interface CR mobile node with transceiver synchronization and then investigates its opportunistic spectrum utilization and routing performance in MCN. Copyright © 2015 John Wiley & Sons, Ltd.     

Secure multicast routing protocols in mobile ad‐hoc networks

A mobile ad‐hoc network (MANET) is a collection of autonomous nodes that communicate with each other by forming a multi‐hop radio network. Routing protocols in MANETs define how routes between source and destination nodes are established and maintained. Multicast routing provides a bandwidth‐efficient means for supporting group‐oriented applications. The increasing demand for such applications coupled with the inherent characteristics of MANETs (e.g., lack of infrastructure and node mobility) have made secure multicast routing a crucial yet challenging issue. Recently, several multicast routing protocols (MRP) have been proposed in MANETs. Depending on whether security is built‐in or added, MRP can be classified into two types: secure and security‐enhanced routing protocols, respectively. This paper presents a survey on secure and security‐enhanced MRP along with their security techniques and the types of attacks they can confront. A detailed comparison for the capability of the various routing protocols against some known attacks is also presented and analyzed. Copyright © 2013 John Wiley & Sons, Ltd.     

A load awareness medium access control protocol for single‐hop wireless ad hoc networks

A contention‐based wireless ad hoc medium access control (MAC) protocol, such as carrier sense multiple access with collision avoidance (CSMA/CA), has excellent efficiency when the system is light loaded. The main drawback of such protocols is their inefficiency and unbounded delay when the system load is heavy. On the other hand, a contention‐free MAC protocol, such as token passing, has a better and fair throughput when the system is heavy loaded. The main drawback of such protocols is their inefficiency when only a small amount of users want to transmit. In this paper, we propose a new load awareness single‐hop wireless ad hoc MAC protocol (which is called the LA protocol) that exploits the benefits of both contention‐based and contention‐free protocols. A contention‐based MAC protocol is used when the system is light loaded and a contention‐free one is used otherwise. Our LA protocol, which operates in a distributed fashion and is fully compatible with the IEEE 802.11 wireless local area network (WLAN) standard, can switch smoothly between the contention‐based protocol and the contention‐free one. Simulation results show that our protocol indeed extracts the better part of two kinds of protocols. Copyright © 2006 John Wiley & Sons, Ltd.     

Synchronization among neighbouring RNCs in a TD‐CDMA mobile network

In the paper, we use zone concepts, and also consider multiple‐bunch in a TD‐CDMA mobile network. In the multiple‐bunch environment, we need a synchronization mechanism to avoid inter‐RNC interferences. Here, we use an Informed‐of message to transmit local resource allocation results to other neighbouring RNCs through a high‐speed network. Thus, inter‐RNC interferences can be avoided and the global resource allocation can be made with the message passing. Within the resource allocation algorithm, we also find maximal compatible cliques to achieve the best resource utilization, using the graph algorithm finding maximal cliques in graph theory. Through the simulation, we found that the SRU classification using Conservative strategy matching the SRU allocation using Aggressive strategy has the best performance among all combinations. Copyright © 2006 John Wiley & Sons, Ltd.     

An optimum design of deep‐space downlinks affected by tropospheric attenuation

In the paper, we propose an optimum design of deep‐space downlinks made with 2 hops, at K_a band and above, in which each hop should be designed for providing half of the total noise‐to‐signal power ratio. We have derived this result from maximizing the ratio between the tropospheric attenuation in the 2‐hop downlink and that in the 1‐hop downlink. The design of the 1st hop (free‐space) of the 2‐hop downlink can reduce the spacecraft power, for the same antennas physical size, by increasing the carrier frequency from K_a band (32 GHz) to W band (80 GHz). This choice is not available in 1‐hop downlink design because of the huge Earth tropospheric attenuation expected in the W frequency band. To show a practical design, we have applied the theory to compare 1‐hop downlink design at 32 GHz to 2‐hop downlink design that adopts 32 or 80 GHz in the 1st hop. The calculations refer to spacecrafts located at two astronomical units (300×10⁶ km, about planet Mars) and to NASA and ESA receiving stations located in Goldstone (California), Cebreros (Madrid, Spain), Canberra and New Norcia (Australia). At 0.1% outage probability, in an average year or in the worst month, 1‐hop downlinks show performance critical or close to fail, because of the large tropospheric attenuation (except at Goldstone), while 2‐hop downlinks always work. Copyright © 2009 John Wiley & Sons, Ltd.     

Deep‐space communications with a 2‐hop downlink with high link‐availability

We recall and discuss the theory of a 2‐hop downlink in deep‐space communications. The first hop (length d₁) links the deep‐space spacecraft to either a geostationary satellite or to a low Earth orbiting satellite. The second hop (length d₂, with d₂ ? d₁) links the satellite to the Earth receiver through a transparent or regenerative transponder, in slant paths affected by troposphere attenuation. If we adopt a BPSK or QPSK modulation scheme and the same carrier frequencies in the two hops with a transparent transponder, a particular value of the carrier frequency makes the noise‐to‐signal ratio minimum. A better choice is to assign a low carrier frequency (X‐band) to the second hop and a high one (W‐band) to the first hop. A 2‐hop downlink is superior to a 1‐hop downlink with a large power gain proportional to (d₁/d₂)² ? 1 at high microwave frequencies and large troposphere attenuation (high link‐availability). Shannon's capacity theorem provides the same large gain independently of the choice of the carrier frequencies in the two hops, if we use a regenerative transponder. The carrier frequencies of a 2‐hop downlink need not be those reserved to deep‐space communication, because the spacecraft could communicate as if it were transmitting ‘from the Earth’ through a conventional satellite connection. We have applied the theory to a first‐order design in the frequency range 10–100 GHz, slant path elevation angles 30°, 45° and 90° at Gera Lario or Fucino (Italy), and downlinks form Mars and Saturn, although the general findings and methodology are of global applicability. Copyright © 2005 John Wiley & Sons, Ltd.     

Improved ACE and ICF low complexity joint algorithm to reduce PAPR of CO-OFDM system

Active constellation expansion (ACE) and iterative clipping and filtering (ICF) are simple and effective techniques for reducing the peak-to-average ratio (PAPR) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems, but effective PAPR suppression requires a lot of iterations. To overcome this shortcoming, a joint algorithm based on improved active constellation expansion (IACE) and ICF (IACE-ICF) is proposed. The simulation results show that at the complementary cumulative distribution function (CCDF) of 10-4, the PAPR of IACE-ICF (G=4, iter=4) algorithm is optimized by 1.507 dB, 1.13 dB and 0.204 dB compared with that of the IACE, ICF (iter=4) and ICF-IACE (G=4, iter=4) algorithms, respectively. Meanwhile, when the bit error rate (BER) is 10-3, the optical signal to noise ratio (OSNR) of the proposed scheme is optimized by 2.04 dB, 1.75 dB and 1.4 dB compared with that of clipping, ICF (iter=4) and ICF-IACE (G=4, iter=4) algorithms, respectively. On the other hand, the proposed scheme can reduce the number of complex multiplications by 14.29% and complex additions by 28.57% compared with the ICF (iter=14) scheme.     

An improved algorithm for multicast topology discovery from end‐to‐end measurements

We present a new multicast topology inference algorithm called binary loss tree classification with hop count (HBLT). HBLT improves the previous algorithm of binary loss tree classification (BLT) not only in time complexity but also in misclassification probability and inference accuracy. The time complexity of HBLT is O(l²) instead of O(l³) required by BLT in the worst case, and O(l · log l) instead of O(l³) by BLT in the expected case, where l is the number of receivers in the multicast network. The misclassification probability of HBLT decreases more quickly than that of BLT as the number of probe packets increases. For correct classification, the inference accuracy of HBLT is always 1, i.e. the inferred tree is identical to the physical tree, whereas that of BLT is dependent on the shape of the physical tree and inversely proportional to the number of internal nodes with single child. We also show through simulation that HBLT requires fewer probe packets to infer the correct topology and hence has a lower misclassification probability and higher inference accuracy than BLT. Copyright © 2006 John Wiley & Sons, Ltd.     

HSG‐ad hoc network: A novel hierarchical star graph ad hoc network with self‐organization and routing discovery free

In ad hoc wireless networks, most data are delivered by multi‐hop routing (hop by hop). This approach may cause long delay and a high routing overhead regardless of which routing protocol is used. To mitigate this inherent characteristic, this work presents a novel ad hoc network structure that adopts dual‐card‐mode, self‐organization with specific IP naming and channel assignment to form a hierarchical star graph ad hoc network (HSG‐ad hoc). This network not only expedites data transmission but also eliminates the route discovery procedure during data transmission. Therefore, the overall network reliability and stability are significantly improved. Simulation results show that the proposed approach achieves substantial improvements over DSDV, AODV, and DSR in terms of average end‐to‐end delay, throughput, and packet delivery ratio. Copyright © 2009 John Wiley & Sons, Ltd.     

Mixing greedy and predictive approaches to improve geographic routing for VANET

In recent years, thanks to the development and popularization of wireless network technologies, the issue of vehicular ad hoc network (VANET) has received great attention, and more and more VANET‐related researches have been brought up. Generally speaking, the biggest difference between VANET and traditional ad hoc network is the velocity of carriers because in VANET, the velocity of vehicles, the carriers, is much higher than those in traditional ad hoc. Therefore, it would be a great challenge to forward data efficiently in VANETs and many researches proposed have focused on the development of routing protocols. The current proposed routing protocols are all assumed to simulate in a distributed and ideal environment. As for the complex geographic environments, such as urban scenarios, extra amendments must be needed to improve the efficiency of the routing protocols. Thus, the main purpose of this paper is to design a suitable routing protocol for urban scenarios with better performance and adaptability. For this reason, greedy on straight roads and predictive at the intersections (GSPI) routing protocol is proposed to use greedy mode on straight roads and to use predictive mode at the intersections. In greedy mode, we choose the next hop according to the weight value that combines the distances and multi‐rate. In predictive mode, we predict the directions of the vehicles to determine the next hop. The simulation results reveal that our proposed algorithm indeed proves its feasibility. Copyright © 2010 John Wiley & Sons, Ltd.     

Engineering of Self‐Assembled Domain Architectures with Ultra‐high Piezoelectric Response in Epitaxial Ferroelectric Films

Substrate clamping and inter‐domain pinning limit movement of non‐180° domain walls in ferroelectric epitaxial films thereby reducing the resulting piezoelectric response of ferroelectric layers. Our theoretical calculations and experimental studies of the epitaxial PbZr_xTi_1–xO₃ films grown on single crystal SrTiO₃ demonstrate that for film compositions near the morphotropic phase boundary it is possible to obtain mobile two‐domain architectures by selecting the appropriate substrate orientation. Transmission electron microscopy, X‐ray diffraction analysis, and piezoelectric force microscopy revealed that the PbZr_0.52Ti_0.48O₃ films grown on (101) SrTiO₃ substrates feature self‐assembled two‐domain structures, consisting of two tetragonal domain variants. For these films, the low‐field piezoelectric coefficient measured in the direction normal to the film surface (d₃₃) is 200 pm V^–1, which agrees well with the theoretical predictions. Under external AC electric fields of about 30 kV cm^–1, the (101) films exhibit reversible longitudinal strains as high as 0.35 %, which correspond to the effective piezoelectric coefficients in the order of 1000 pm V^–1 and can be explained by elastic softening of the PbZr_xTi_1–xO₃ ferroelectrics near the morphotropic phase boundary.     

Importance‐based data transmission optimization in multi‐source single‐sink wireless sensor networks

Energy‐efficient routing becomes one of the most critical technologies for sustaining the overall network lifetime of wireless sensor networks. In this paper, we propose a novel data transmission scheme between a number of specified source nodes and the single sink, which can efficiently restrict the usage frequency of each relay node, measured by the number of source nodes using it for data transmission. On the basis of the importance of source nodes that is closely related to deployed location, they form a descending sequence such that each node finds the minimum energy path earlier than the succeeding one. Then, the energy‐efficient multiple path algorithm with the computational complexity of O(n³) is developed for deriving the minimum energy paths, where n is the number of nodes in the network. Also, a polynomial algorithm is presented for deriving the range of the feasible values of N₀ serving as the threshold of the usage frequency of relay nodes, in which each can guarantee the existence of the solution. Further, we theoretically investigate the existence of the solution and the tree‐structured solution using m‐ary tree. Extensive simulation results show that our proposed scheme can achieve significant performance enhancement. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrical Properties and Structure of p‐Type Amorphous Oxide Semiconductor xZnO·Rh2O3

p‐Type conduction in amorphous oxide was firstly found in zinc rhodium oxide (ZnO·Rh₂O₃) (Adv. Mater. 2003 , 15, 1409), and it is still the only p‐type amorphous oxide to date. It was reported that an ordered structure at the nanometer scale was contained and its electronic structure is not clear yet. In this paper, optoelectronic and structural properties are reported in detail for xZnO·Rh₂O₃ thin films (x = 0.5–2.0) in relation to the chemical composition x. All the films exhibit positive Seebeck coefficients, confirming p‐type conduction. Local network structure strongly depends on the chemical composition. Transmission electron microscopic observations reveal that lattice‐like structures made of edge‐sharing RhO₆ network exist in 2–3 nm sized grains for rhodium‐rich films (x = 0.5 and 1.0), while the zinc‐rich film (x = 2) is completely amorphous. This result indicates that excess Zn assists to form an amorphous network in the ZnO–Rh₂O₃ system since Zn ions tend to form corner‐sharing networks. The electronic structure of an all‐amorphous oxide p‐ZnO·Rh₂O₃/n‐InGaZnO₄ junction is discussed with reference to electrical characteristics and results of photoelectron emission measurements, suggesting that the p/n junction has large band offsets at the conduction and valence bands, respectively.