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Modeling Smart Antennas in Synchronous Ad Hoc Networks Using OPNET ’ s Pipeline Stages
| Content Provider | Semantic Scholar |
|---|---|
| Author | Stine, John A. |
| Copyright Year | 2005 |
| Abstract | Smart antennas have been proposed as a physical lay er device that can increase the capacity of ad hoc networks. The effectiveness of smart antennas depends on whether acc ss mechanisms create the conditions that enable receiv rs to adapt to both desired signals and interfering signals and enable transmitters to discern where they must avoid causi ng interference. The ease of implementing solutions a nd modeling the antennas are both affected by whether the acces s s hemes are asynchronous or synchronous. Asynchronous access mechanisms are more difficult since they allow new transmitters to begin transmissions during ongoing exchanges. T hus, past adaptation becomes irrelevant and current adaptatio n is done with insufficient information. Arbitrating the eff ects in simulation requires detailed models of antenna adap t tion and the resulting power patterns. Synchronous access m chanisms, however, overcome these shortcomings because they f orce ongoing exchanges to conclude before new exchanges start and because they cause all new exchanges to occur simul taneously. Receivers can sample both the desired signals and t he interfering signals to arrive at a weighting solution. Since c onditions do not change after adaptation, the adaptation is more eff ective and simulation models can be more abstract. In this pa per we describe how we built models of adaptive antennas i OPNET using a radio process model and the radio pipeline stages. We use this model in conjunction with our Synchronous Collision Resolution (SCR) medium access control protocol and evaluate the relative merits of different antenna technologi es and capabilities. We found that those technologies that improve capture soonest in an exchange most improve the cap acity. Introduction Directional and smart antennas have been proposed a s a means to enhance performance of wireless ad hoc networks including increasing capacity, increasing the range of commun ications, reducing the susceptibility to detection, intercept ion, and jamming, conserving energy, and resolving collision . Properties of antennas that have been identified to support these benefits include: antenna directivity, increased ga in, nd a host of capabilities enabled with arrayed antennas and s ignal processing techniques including beam forming, null steering, diversity, spatial processing, and multiple input m ultiple output (MIMO). Direct modeling of these effects and the a lgorithms that make them work is prohibitive requiring detail ed models of the environment, the antennas, and the scenario, th eir effect on the bit streams that are transmitted and then the r esults of the algorithms that operate on the bit streams. This l evel of detail is difficult to create for just the analysis of algori thms let alone to combine it with a comprehensive network model with multiple transceivers transmitting and receiving simultaneou sly. Abstractions that can capture the effectiveness of these techniques are necessary to assess their contributi on to the performance of mobile ad hoc networks (MANETs). In this paper, we propose a modeling abstraction that accou nts for directional and smart antenna effects when using sy chronous access. We build these models into a radio process model and OPNET's radio transceiver pipeline stages. Our presentation of this material begins with an ov erview of directional and smart antenna technologies. Next, we describe how smart antennas are modeled abstractly and then how we model them in OPNET. We describe the Synchronous C ollision Resolution (SCR) approach to access and identify ho w it creates the conditions that enable smart antennas to be exp loited and the models we described earlier to be valid. We conclu de with a description of simulation experiments we conducted to study the effect of smart antenna performance on SCR capacity . Directional and Smart Antennas The mobility of nodes in ad hoc networks will cause th relative direction between nodes to change. Exploiting dire ctional antennas in mobile ad hoc networks (MANET) will inv olve intelligence to discern where to point an antenna a nd mechanisms to subsequently point it in that directi on. Antennas that can do this are considered smart. Smart anten nas have varying levels of intelligence. This intelligence is frequently divided into three levels: switched beam, dynamic p hased array, and adaptive array [1]. A review of the difference s and the types of intelligence follows. Switched Beam Antennas In switched beam antennas, there is a predefined se t of directions in which an antenna can be pointed. Use of these a ntennas in ad hoc networks requires MAC and possibly routing prot oc ls to track which antenna sectors point toward other node s. Dynamically Phased Arrays An array of antenna elements can be pointed in a di rection by changing the phase of the signals emitted from each lement so that they arrive on the wavefront in the preferred direction at the same time thus constructively interfering in the po inting direction and destructively interfering elsewhere. Any arrangement of antennas can be used; however, they must be calibrated to support beamforming. Weighting of th e excitation signal at each antenna can be used to affect the sh ape and amplitude of the mainlobe and sidelobes. The enhancement in intelligence that comes with dyn amically phased arrays is the ability to determine the direc tion of the arrival (DOA) of signals so that the antennas can a dapt and immediately point toward the source. This capabili ty does not require protocols to track network state. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.mitre.org/sites/default/files/pdf/05_1045.pdf |
| Alternate Webpage(s) | https://www.mitre.org/sites/default/files/pdf/05_1045.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
