A simple scheme for slot reuse without latency for a dual busconfiguration

A simple scheme for slot reuse without latency for the dual bus configuration is studied. The scheme relies on information read in the previous slot and will be referred to as previous slot information (PSI) slot reuse. The scheme requires a minimal addition to the station hardware and its reliability is high. The efficiency of PSI is checked over a wide range of parameters and is found to be almost as good as destination release. The scheme can be implemented with or without the addition of erasure nodes     

A study of isochronous channel reuse in DQDB metropolitan areanetworks

This paper investigates the isochronous channel reuse problem (ICRP) on the IEEE 802.6 distributed-queue dual-bus (DQDB) metropolitan area network (MAN). Given a set of established isochronous connections and a set of isochronous connections requests, using a minimal number of isochronous bandwidth to service all of the connections is attempted. On the other hand, given a limited isochronous bandwidth, establishing a maximal number of isochronous connections is of primary concern. Our previous study demonstrates that the ICRP is NP-complete by showing that the simplified ICRP (SICRP), in which all of the established isochronous connections and the isochronous requests are of the same bandwidth, is NP-complete. We recommend using a tight lower bound on the number of required isochronous channels for the SICRP. An efficient isochronous channel scheduling algorithm (ICSA), capable of providing a solution close to the lower bound, is also proposed. Simulation results indicate that for a limited isochronous bandwidth, the number of isochronous connections successfully established by the ICSA is significantly more than that of the isochronous channels allocation scheme in the DQDB standard     

Schemes for slot reuse in CRMA

Several schemes for slot reuse in CRMA are studied. A major challenge in CRMA is to incorporate slot reuse together with continuous message transmissions, i.e., to ensure that every message is transmitted in a stream of contiguous slots on the bus. Schemes based on the ideas of erasure nodes and destination release are developed and simulation results are presented     

DQDB networks with and without bandwidth balancing

It is explained why long distributed queue dual bus (DQDB) networks without bandwidth balancing can have fairness problems when several nodes are performing large file transfers. The problems arise because the network control information is subject to propagation delays that are much longer than the transmission time of a data segment. Bandwidth balancing is then presented as a simple solution. By constraining each node to take only a certain fraction of the transmission opportunities offered to it by the basic DQDB protocol, bandwidth balancing gradually achieves a fair allocation of bandwidth among simultaneous file transfers. Two ways to extend this procedure effectively to multipriority traffic are proposed     

A study of slot reuse in dual bus multiple access networks

In dual unidirectional bus networks, packets usually occupy fixed-length slots form the sending station to the end of the network. An erasure node is a specialized station which recognizes packets which have passed their destination stations and releases the slots for subsequent use. The authors derive the optimal locations for erasure nodes and show analytically, for uniform traffic, that only several erasure nodes are needed to achieve throughput close to twice the nominal network bandwidth. The results are tested by simulation of the DQDB (distributed queue dual bus) protocol, which demonstrates a realistic improvement of 40% with only three erasure nodes. Fair access among the stations is improved as well. The authors generalize the analytic results by providing an algorithm for determining the optimal erasure node locations and the throughput improvement, given any arbitrary traffic pattern. The application of this methodology to the related problem of bridged subnetworks is briefly discussed     

On the efficiency of slot reuse in the dual bus configuration

Slot reuse is a simple method to improve the efficiency of MACs designed for the slotted, dual bus configuration. The authors propose several schemes for the assignment of throughput to stations in this configuration, taking into account slot reuse and assuming uniform source destination distribution. The criteria for comparison of the schemes are throughput gain, worst averages of message queueing and access delays at stations and the fraction of blocked messages. On the average, it turns out that the scheme in which every station receives the same throughput is very attractive     

A queueing analysis of the performance of DQDB

A queueing model for the DQDB protocol with a single priority level is presented and analyzed. The state of a node is defined by the number of requests in the distributed queue prior to, and post generation of a segment. It is shown that the number of states that a node can be in, is finite and position dependent. Moreover, it is shown that the request rate and the network traffic that a node perceives at any particular moment are highly dependent on its state. An iterative technique is presented to calculate the request rate and network traffic for all the nodes in a DQDB network by carefully modeling the relationship between adjacent nodes. The node average waiting time and average throughput are analyzed as functions of the node position and state in the network. Our results illustrate the effect of the various parameters on the waiting time and throughput. Comparisons with simulation and existing analytical results are presented     

Bandwidth tuning for fairness of DQDB in client-server trafficenvironments

An effective fairness control method is proposed for distributed queue dual bus with general bandwidth demand patterns under client server traffic environments. This method is based on a bandwidth tuning mechanism under which an intermediate pattern is first obtained from a bandwidth occupation pattern. Then, the bandwidth demand pattern is matched with the intermediate pattern by bandwidth yielding or borrowing     

SOJOURN TIME ANALYSIS OF DQDB MAN FOR LANs INTERCONNECTION

The Distributed Queue Dual Bus(DQDB) Metropolitan Area Network(MAN) is a promising solution for the evolution from current networks to B-ISDN. The performance of the DQDB MAN for Local Area Networks(LANs) interconnection is analyzed. The effects of message length, traffic load of upstream and downstream nodes and the parameters of bandwidth balancing mechanism and network counters on the sojourn time of message in the buffer are investigated, which present a valuable reference for the implementation of the DQDB MAN.     

Design of shunt slot arrays without weak excitations

By using an appropriate objective function, simulated annealing is found to prevent the presence of weakly excited slots in feedmatched waveguide slot arrays designed to produce demanding power patterns     

PERFORMANCE ANALYSIS OF PRIORITIZED DQDB MAN FOR LANs INTERCONNECTION

The sojourn time of the prioritized OQDB MAN with bursty traffic input is studied in this paper. The expressions for the mean sojourn time of the message with two transmission priority are obtained. The conclusions drawn from the paper are that, the mean sojourn time of the message, at either higher or lower priority, is a linear function of the mean message length approximately, and the performance improvement by adopting the higher priority level for the user is remarkable, especially when the lower-priority traffic load from the downstream users is heavy.     

DQDB城域网暂态和稳态公平性分析

本文分析了DQDB城域网在大文件传输时的公平性。通过分析大文件传输时某一节点的性能及网络各节点的关联性,证明了网络经过一个暂态过程后将达到稳态,给出了各节点在稳态及暂态时的吞吐量、暂态过程长度的表达式。     

A reconfigurable slot antenna with switchable polarization

A novel reconfigurable slot antenna architecture allowing polarization switching is presented. The antenna shape consists of a slot-ring with perturbations which are switched on and off using pin-diodes. Two antennas allowing switching either between linear and circular polarization or between two circular polarizations are demonstrated. The antenna architecture is interesting for commercial wireless applications because it is compatible with modern fabrication processes and can be realized on low cost dielectric materials.     

A slot design for uniform aperture field distribution insingle-layered radial line slot antennas

A single-layered radial line slot antenna (RLSA) is proposed for a direct broadcast from a satellite (DBS) subscriber antenna. It utilizes a radially outward-traveling wave and the aperture field is intolerably tapered if the uniform slots are used. Two novel techniques are applied. First, the slot design for uniform aperture field distribution is introduced. Second, the radial line is terminated by a matching spiral, in place of a dummy load. It suppresses reflection and radiates all the residual power in circular polarization. For a model antenna of 600-mm diameter, the efficiency of 65% is observed     

Assessment and performance analysis of DQDB MAC protocols

Distributed queue dual bus (DQDB) has been adopted as the IEEE 802.6 standard for metropolitan area networks (MANs). The access mechanism is based on an implicit distributed queue maintained at each node. DQDB has been shown to achieve maximal aggregate throughput and minimal access delay independent of the size and speed of the network. However, as the size and load of the network increase, DQDB gives rise to throughput unfairness problems due to the long propagation delay. This paper initially presents a survey and assessment of recently proposed remedial DQDB mechanisms. These approaches are categorized as time division multiplexing (TDM)-oriented versus non-TDM-oriented, and exhaustive versus non-exhaustive operations. Regarding TDM as the most promising mechanism, the paper then provides the performance analysis of one TDM-oriented method, called multiple segment control (MSC), proposed by the authors. In the analysis, the network is modelled as a set of identicalM/G/1 queues, each with different services for transmitting the first and remaining segments in a busy period. The average aggregate access delay is then analyzed via an embedded Markov model. The paper shows simulation results to demonstrate the precision of the performance analysis and the performance superiority of MSC over non-TDM-oriented DQDB mechanisms. Furthermore, as will be shown, the network using the TDM-oriented method may incur bandwidth waste should active stations fail. The paper finally proposes a guardian reliability scheme to ensure the robustness of networks.     

A dual-polarized slot antenna for millimeter waves

We describe a new dual-polarized slot antenna to be used with quad-optical devices such as superconductor-insulator-superconductor (SIS) mixers at millimeter and submillimeter wavelengths. The radiation and impedance characteristics of the antenna were obtained from a moment-method calculation. The antenna has an excellent radiation pattern, a low impedance, wide bandwidth, and low cross polarization     

应用于带有闭合金属边框手机的缝隙天线

提出了无断开(闭合)金属边框情况下平面手机天线的模型,解决了在闭合金属情况下导致的传统平面天线带宽变窄的问题.通过天线折叠技术,将其面积缩小至手机应用的尺寸内.然后,进一步的阻抗匹配使在smith圆图上将天线的阻抗带宽调到了最大,使天线能够覆盖GSM850、GSM900、DCS、PCS、UMTS 5个频段.采用开槽天线将金属边框作为天线的一部分能解决金属框对天线的影响.实测结果表明,低频部分带宽为142 MHz,高频部分带宽有480 MHz,满足了常用频段的需要.同时,为了避免发生手握的影响,金属框和地的接地点置于电路基板顶段,从而降低了手握的影响.     

A waveguide transverse slot for array applications

The characteristics of a radiating rectangular transverse slot in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. The results are presented in terms of normalized resistance and reactance versus slot length and frequency. Excellent agreement with a previous pulse basis solution is found, as well as with measured data. An array of resonantly spaced transverse slots radiates large grating lobes. A spatial filter using baffles to suppress the grating lobes is described, suppressed. The effect of the baffles on the transverse slot impedance is analyzed for the case of baffles with infinite height     

A novel approach for miniaturization of slot antennas

With the virtual enforcement of the required boundary condition (BC) at the end of a slot antenna, the area occupied by the resonant antenna can be reduced. To achieve the required virtual BC, the two short circuits at the end of the resonant slot are replaced by some reactive BC, including inductive or capacitive loadings. The application of these loads is shown to reduce the size of the resonant slot antenna for a given resonant frequency without imposing any stringent condition on the impedance matching of the antenna. A procedure for designing this class of slot antennas for any arbitrary size is presented. The procedure is based on an equivalent circuit model for the antenna and its feed structure. The corresponding equivalent circuit parameters are extracted using a full-wave forward model in conjunction with a genetic algorithm optimizer. These parameters are employed to find a proper matching network so that a perfect match to a 50 /spl Omega/ line is obtained. For a prototype slot antenna with approximate dimensions of 0.05/spl lambda//sub 0//spl times/0.05/spl lambda//sub 0/ the impedance match is obtained, with a fairly high gain of -3dBi, for a very small ground plane (/spl ap/0.20/spl lambda//sub 0/). Since there are neither polarization nor mismatch losses, the antenna efficiency is limited only by the dielectric and ohmic losses.