Analysis of slot antennas on a radial transmission line

Two methods for the analysis of slot-array radial-line antennas are presented. A moment method (MM) analysis is performed using a cosine basis function for each slot and the Galerkin method. The analysis can be extended to incorporate thickness of the metal plate supporting the slots. Closed form formulas are also derived to model the slot antenna as a multiport network. This model allows a faster antenna analysis when a large number of slots are present. The multiport model has been validated with the MM analysis in a two-slot case and through the measurements of a more complex antenna problem. © 1996 John Wiley & Sons, Inc.     

The value of location in keyword auctions

Sponsored links on search engines are an emerging advertising tool, whereby a number of slots are put on sale through keyword auctions. This is also known as contextual advertising. Slot assignment and pricing in keyword auctions are then essential for the search engine’s management since provide the main stream of revenues, and are typically accomplished by the Generalized Second Price (GSP) mechanism. In GSP the price of slots is a monotone function of the slot location, being larger for the highest slots. Though a higher location is associated with larger revenues, the lower costs associated with the lowest slots may make them more attractive for the advertiser. The contribution of this research is to show, by analytical and simulation results based on the theory of order statistics, that advertisers may not get the optimal slot they aim at (the slot maximizing their expected profit) and that the GSP mechanism may be unfair to all the winning bidders but the one who submitted the lowest bid.     

Topology-transparent reservation time division multiple access in multihop ad hoc networks

In this paper, an optimal topology-transparent reservation time division multiple access (OTTR-TDMA) protocol is proposed for multihop ad hoc networks. Our MAC protocol is based on a slotted TDMA architecture in which every slot is divided into reservation phase and data transmission phase. Every node not only transmits data in its assigned slots that are computed by Chlamtac’s algorithm, but it also utilizes free slots among its non-assigned slots through reservation. Through theoretical analysis, we derive the proper parameter for the best performance. We compare our protocol with other TDMA protocols and find that it gives better performance. Simulation results show that they are consistent with our analytical results.     

Dynamic routing and spectrum (re)allocation in future flexgrid optical networks

Future flexible-grid elastic optical networks are very promising due to their higher spectrum efficiency and flexibility comparing to the rigid spectrum grid optical networks realized with the traditional wavelength division multiplexing (WDM) technology. The maturity of key system components enabling flexgrid optical networks, such as advanced modulation techniques and multi-granular switching, is already high enough and thus their deployment is expected in the near future. The main feature of such networks is the removal of fix grid-space assignment (in general 50 GHz) to the optical connections independently of the required bandwidth. In fact, the available optical spectrum in flexgrid network is divided into frequency slots of a fixed spectrum width and an optical connection can be allocated into the number of slots that better matches the actual bandwidth of the connection demand. Nonetheless, such allocation must satisfy two constraints, i.e. the slots must be (i) contiguous in the spectrum domain and (ii) continuous along the links on the routing path. These constraints result in a need for dedicated Routing and Spectrum Allocation (RSA) algorithms able to operate under dynamic traffic conditions. From the network design perspective, an important issue is the selection of the frequency slot width which may have an impact on the network performance. Last but not least, network dynamicity entails spectrum fragmentation, which significantly reduces the network performance. In this paper we address these topics and, in particular: (1) we present an RSA algorithm to be used in dynamic network scenarios, (2) we study the optimal slot width as a function of the foreseen traffic to be served, and (3) we propose an algorithm to reallocate already established optical connections so that to make room in the spectrum for the new ones. Exhaustive simulation results reveal that the proposed approach improves the blocking probability performance in flexgrid optical networks.     

FlexiTP: A Flexible-Schedule-Based TDMA Protocol for Fault-Tolerant and Energy-Efficient Wireless Sensor Networks

FlexiTP is a novel TDMA protocol that offers a synchronized and loose slot structure. Nodes in the network can build, modify, or extend their scheduled number of slots during execution, based on their local information. Nodes wake up for their scheduled slots; otherwise, they switch into power-saving sleep mode. This flexible schedule allows FlexiTP to be strongly fault tolerant and highly energy efficient. FlexiTP is scalable for a large number of nodes because its depth-first-search schedule minimizes buffering, and it allows communication slots to be reused by nodes outside each other's interference range. Hence, the overall scheme of FlexiTP provides end-to-end guarantees on data delivery (throughput, fair access, and robust self-healing) while also respecting the severe energy and memory constraints of wireless sensor networks. Simulations in ns-2 show that FlexiTP ensures energy efficiency and is robust to network dynamics (faults such as dropped packets and nodes joining or leaving the network) under various network configurations (network topology and network density), providing an efficient solution for data-gathering applications. Furthermore, under high contention, FlexiTP outperforms 2-MAC in terms of energy efficiency and network performance.     

Energy-efficient initialization protocols for single-hop radionetworks with no collision detection

A radio network (RN, for short) is a distributed system consisting of n radio stations. We assume that the stations are small, bulk-produced, hand-held devices running on batteries and cannot be distinguished by serial or manufacturing number. Since recharging batteries may not be possible while on mission, we are interested in designing protocols that are highly energy-efficient. The initialization problem is to assign each of the n stations in the RN a unique ID. The initialization problem is nontrivial since the stations are assumed to be indistinguishable. The problem is fundamental, since practically all communication protocols for RNs proceed under the assumption that the RN has been initialized in advance. The main contribution of this work is to propose energy-efficient randomized initialization protocols for single-hop RNs lacking collision detection capabilities. First, we show that if the number n of stations is known beforehand, the single-channel RN can be initialized by a protocol that terminates, with probability exceeding 1-¹/_n in O(n) time slots, with no station being awake for more than O(log log n) time slots. We then go on to address the multichannel case and show that if k, (k⩾1), channels are available, an n-station RN can be initialized, with probability exceeding 1-¹/_n, in O(ⁿ/_k+log n) time slots, with no station being awake for more than O(log log n) time slots     

An energy-efficient permutation routing protocol for single-hop radio networks

A radio network (RN) is a distributed system where each station or node is a small hand-held commodity device called a station. Typically, each station has access to a few channels for transmitting and receiving messages. By RN(p, k), we denote a radio network with p stations, where each station has access to k channels. In a single-hop RN, every station is within the transmission range of every other station. Each station consumes power while transmitting or receiving a message, even when it receives a message that is not destined for it. It is extremely important that the stations consume power only when it is necessary since it is not possible to recharge batteries when the stations are on a mission. We are interested in designing an energy-efficient protocol for permutation routing, which is one of the most fundamental problems in any distributed system. An instance of the permutation routing problem involves p stations of an RN, each storing n/p items. Each item has a unique destination address which is the identity of the destination station to which the item should be sent. The goal is to route all the items to their destinations while consuming as little energy as possible. We show that the permutation routing problem of n packets on an RN(p, k) can be solved in 2n/k+(p/k)/sup 2/+p+2k/sup 2/ slots and each station needs to be awake for at most 6n/p+2p/k+8k slots. When k/spl Lt/p/spl Lt/n, our protocol is more efficient, both in terms of total number of slots and the number of slots each station is awake compared to a previously published protocol by Nakano et al. (2001).     

New broadband circularly polarized antenna with an inverted F‐shaped feedline

In this article, we present a new broadband CP square‐slot antenna with an inverted F‐shaped feed‐line. The antenna is composed of an inverted F‐shaped feed‐line, pairs of isosceles triangular chamfers, I‐shaped slots, rectangular slots and triangular patches, and a Z‐shaped strip. By introducing these strips and slots into the square‐slot, multiple CP modes can be stimulated simultaneously, which eventually enhances 3‐dB ARBW and 10‐dB impedance bandwidth (IBW) of the presented antenna. The measured results show that its IBW (|S₁₁| < ?10 dB) is about 7.2 GHz (87.8% from 4.6 to 11.8 GHz) and its ARBW (AR < 3 dB) is 8.3 GHz (96% from 4.5 to 12.8 GHz).     

Multiphase transfer of control signal for adaptive power control in CDMA systems

Capacity improvment in cellular networks is highly dependent on the effectiveness of power control. A power control procedure is needed to compensate for the fluctuation of a mobile's transmitting power received at a base station and to increase the capacity of the mobile communication system via decreasing intra- and inter-cellular interference. Here we consider fuzzy set theory based delayed adaptive step-size closed loop power control scheme(s). In this scheme transmitters adjust their power step sizes according to the received multiphased power control signals (delayed commands) from base stations. Code division multiple access (CDMA) system standards (cdmaOne, CDMA2000 and ETSI UMTS/UTRAN) limit the number of bits to two for the length of the control command in time slots. Hence, the number of commands is limited to four per time slot (in practise to two: up and down fixed amount, the rest are zero and unused values) when a sign and magnitude binary word format is used. In the developed algorithm, the number of commands is enlarged to 16 per two sequential time slots (four bits) without an increase in the standardized control bit rate by transmitting control commands in two sequential phases (time slots). First two bits of the command are transmitted in the current time slot and a receiver stores them and waits for the next time slot, which includes the last two bits of the control signal. The receiver interprets control command after receiving all 4 bits. Therefore, the control frequency is decreased (delayed control) to half of the original but respectively the dynamic scale is increased to 4 times larger (in practise 7 times: 7 values up and 7 down, 1 value for zero and 1 unused) for the sign and magnitude binary coding. A single transmitter's control results with the developed controller in a frequency selective fading channel in a CDMA network with interfering nodes and Gaussian noise are compared to the predefined step size power control scheme, which is a de facto standard the power control in cellular networks.     

A wideband compact horizontally polarized omnidirectional antenna for 2G/3G/LTE

A compact horizontally polarized omnidirectional slot antenna with a wide working band is presented in this article. The proposed antenna consists of 4 shorter driven cross‐shaped slots, 4 longer parasitic cross‐shaped slots, and a feeding network. Four shorter slots, placed on the same side of a circular substrate, are fed by a feeding network printed on the other side with uniform phase and magnitude. To enhance the bandwidth of the antenna, 4 longer cross‐shaped slots are inserted between adjacent longer slots to produce an additional resonant frequency. All 8 slot radiators placed symmetrically along the circumference results in an omnidirectional horizontal polarized radiation pattern. By utilizing cross‐shaped slots, a compact size of 0.53λ_L × 0.53λ_L × 0.005λ_L (λ_L is the free space wavelength at the lowest operational frequency) is achieved. The prototype of the proposed antenna is fabricated and measured. The measured results reasonably agree with the simulated results. The measured working band for |S₁₁|<–10dB is from 1.62 to 2.81 GHz which successfully covers the 1.7 to 2.7 GHz 2G/3G/LTE bands. The measured gain variation in azimuthal angle is <1.7 dB within 1.7 to 2.7 GHz, and the cross polarization level is <–27 dB in the horizontal plane.     

Energy-efficient permutation routing in radio networks

A radio network (RN, for short) is a distributed system populated by small, hand-held commodity devices running on batteries. Since recharging batteries may not be possible while on mission, we are interested in designing protocols that are highly energy efficient. One of the most effective energy-saving strategies is to mandate that the stations go to sleep whenever they do not transmit or receive messages. It is well known that a station is expending power while its transceiver is active, that is, while transmitting or receiving a packet. It is perhaps surprising at first that a station is expending power even if it receives a packet that is not destined for it. Since, in single-hop radio networks, every station is within transmission range from every other station, the design of energy-efficient protocols is highly nontrivial. An instance of the permutation routing problem involves p stations of an RN, each storing n/p items. Each item has a unique destination which is the identity of the station to which the item must be routed. The goal is to route all the items to their destinations while expending as little energy as possible. Since, in the worst case, each item must be transmitted at least once, every permutation routing protocol must take n/k time slots. Similarly, each station must be awake for at least n/p time slots to transmit and/or receive packets. Our main contribution is to present an almost optimal energy-efficient permutation routing protocol for a k-channel, a p-station RN that routes n packets in at most (2d+2b+1)n/k+k time slots with no station being awake for more than (4d+7b-1)n/p time slots, where d=[(logp/k)/(logn/p)], b=[(log k)/(logn/p)] and k⩽√(p/2). Since, in most real-life situations, the number n of packets to route, the number p of stations in the RN, and the number k of channels available satisfy the relation k≪p≪n, it follows that d and b are very small     

Hypercube computations on partitioned optical passive stars networks

This paper shows that an n=2/sup k/ processor partitioned optical passive stars (POPS) network with g groups and d processors per group can simulate every bidirectional move of an n processor hypercube using one slot when dg. Moreover, the same POPS network can simulate every monodirectional move of a processor hypercube using one slot when d=g. All these results are shown to be optimal. Our simulations improve on the literature whenever d/spl ne/g and directly yield several important consequences. For example, as a direct consequence of our simulations, a POPS network, n=dg and d相似文献   

SIW cavity‐backed 24° inclined‐slots antenna for ISM band application

In this article, a novel resonant series slot linearly polarized antenna is realized using substrate integrated waveguide (SIW) technology for industrial scientific medical radio band (ISM) at 5.8 GHz. The proposed antenna consists of two 24° inclined slots and two metallic vias to produce alternate inductive and capacitive loads. The rectangular slots are introduced at the top metallic surface at an angle of 24° from the Y‐axis to excite a hybrid mode (TE₁₁₀ + TE₁₂₀) near to the modified cavity mode TE₁₂₀. The resonant slots are excited with the help of an inset microstrip feedline which retain its planar integrability. The slots are excited to resonate in the TE₁₂₀ mode at 5.8 GHz. To enhance the bandwidth, the location of two shorting vias are optimized in proximity to the slots. These vias help to couple the hybrid mode and the cavity modes in the desired frequency band, which leads to enhancement in the bandwidth significantly. The proposed geometry is fabricated and experimentally verified. The measured and simulated results depict a good co‐relation which show measured ?10 dB fractional bandwidth of 5.2% with a maximum gain of 7.15 dBi and the front to back ratio better than 15 dB at 5.8 GHz.     

Feature recognition from CAD models

This article presents a system dubbed IF² (Integrated Incremental Feature Finder), which functions as a feature recognizer or a feature model converter depending on whether the input CAD data contains design features. IF² recognizes three types of machining features: holes, slots and pockets. This article discusses recognition algorithms for slots and pockets. Recognition algorithms for holes are similar to those of slots (Han, 1996)     

TRAP: a high performance protocol for wireless local area networks

The fixed number of available random addresses for randomly addressed polling (RAP) poses a significant problem in terms of scalability in case of many active stations. In such cases, the protocol's performance is significantly degraded. In this paper, we propose a TDMA-based randomly addressed polling (TRAP) protocol. The protocol employs a variable-length TDMA-based contention stage with the length based on the number of active stations. At the beginning of each polling cycle, the base station invites all active mobile stations to register their intention to transmit via transmission of a short pulse. The base station uses the aggregate received pulse in order to obtain an estimate of the number of contending stations and schedules the contention stage to comprise an adequate number of time slots for these stations to successfully register their intention to transmit. Then it transmits a READY message carrying the number of time slots P. Each mobile station calculates a random address in the interval [0…P−1], transmits its registration request in the respective time slot and then the base station polls according to the received random addresses. Simulation results are presented that reveal the superiority of TRAP against the RAP protocol in case of medium and high offered loads. Furthermore, the implementation of the proposed protocol is much simpler than that of CDMA-based versions of RAP, since no extra hardware is needed for the orthogonal reception of the random addresses.     

A formal model for the interoperability of service clouds

Large-scale service-oriented computing is based on the idea that services from various servers are combined into one distributed application. Referring to a collection of services on one server as a ??service cloud??, the problem investigated in this paper is to define formal high-level specifications of such distributed applications and to enable the location of suitable services for them. Based on the language-independent model of Abstract State Services (AS²s), which serves as a universal integrated model for data and software as services, we extend AS²s by high-level action schemes called ??plots?? as a means to specify permitted sequences of service operations. On these grounds, we develop a model for service mediators, that is, specifications of composed services in which service slots have to be filled by actual services, and investigate matching conditions for slots of mediators and services. For a services to match a slot in a mediator, a (generalised) projection of the mediator must comply with the plot of the service. Furthermore, the service must be semantically adequate, which requires the use of a service ontology.     

Compositional reasoning using intervals and time reversal

Interval Temporal Logic (ITL) is an established formalism for reasoning about time periods. We investigate some simple kinds of ITL formulas which have application to compositional reasoning and furthermore are closed under conjunction and the conventional temporal operator known both as “box” and “always”. Such closures help us modularly construct formulas from simple building blocks in a way which preserves useful compositional properties. The most important class considered here is called the 2-to-1 formulas. They offer an attractive framework for analysing sequential composition in ITL and provide the formal basis for most of the subsequent presentation. A key contribution of this work concerns a useful and apparently new and quite elementary mathematical theorem that 2-to-1 formulas are closed under “box”. We also use a natural form of time symmetry with 2-to-1 formulas. This extends known facts about such formulas by looking at them in reverse. An important example involves showing that 2-to-1 formulas are also closed under a variant of “box” for prefix subintervals rather than suffix ones. We then apply the compositional formulas obtained with time symmetry to analyse concurrent behaviour involving mutual exclusion in both Peterson’s algorithm and a new and more abstract one. At present, our study of mutual exclusion mainly serves as a kind of experimental “proof of concept” and research tool to develop and illustrate some of the logical framework’s promising features. We also discuss how time symmetry sometimes assists in reducing reasoning in ITL to conventional linear-time temporal logic.     

A computer‐aided approach for designing dielectric‐covered planar array antennas consisting of longitudinal slots

A straightforward design approach is proposed to design arrays of longitudinal slots covered with dielectric slabs. The design of the arrays is accomplished via linking the slotted array antennas fed by the waveguides to a corresponding array of the loaded slots cut in an infinite ground plane and covered with dielectric slab. In this regard, the Elliott's design equations are modified for the dielectric‐covered longitudinal slotted array antennas. The introduced design equations are employed to find the final dimensions of the slot antennas while the updated mutual admittances of the corresponding array of the loaded slots are used iteratively in the design equations. Employing the introduced design equations, a two by three slotted array antenna was designed, simulated and tested. The proposed design approach is verified by the simulation and the measurement results.