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58529-2_Datasheet PDF

发帖时间:2021-06-15 01:18:31

We have seen that reflection of a signal from the ground has a significant effect on the strength of the received signal. The nature of short-range radio links, which are very often installed indoors and use omnidirectional antennas, makes them accessible to a multitude of reflected rays, from floors, ceilings, walls, and the various furnishings and people that are invariably present near the transmitter and receiver. Thus, the total signal strength at the receiver is the vector sum of not just two signals, but of many signals traveling over multiple paths.

In most cases indoors, there is no direct line-of-sight path, and all signals are the result of reflection, diffraction, and scattering. From the point of view of the receiver, there are several consequences of the multipath phenomena:

58529-2_Datasheet PDF

Flat Fading In many of the short-range radio applications covered in this chapter, the signal bandwidth is narrow and frequency distortion is negligible. The multipath effect in this case is classified as flat fading. In describing the variation of the resultant signal amplitude in a multipath environment, we distinguish two cases: (1) there is no line-of-sight path and the signal is the resultant of a large number of randomly distributed reflections; (2) the random reflections are superimposed on a signal over a dominant constant path, usually the line of sight.

Short-range radio systems that are installed indoors or outdoors in built-up areas are subject to multipath fading essentially of the first case. Our aim in this section is to determine the signal strength margin that is needed to ensure that reliable communication can take place at a given probability. While in many situations there will be a dominant signal path in addition to the multipath fading, restricting ourselves to an analysis of the case where all paths are the result of random reflections gives us an upper bound on the required margin.

Rayleigh Fading The first case can be described by a received signal R (t), expressed as

58529-2_Datasheet PDF

where r and θ are random variables for the peak signal, or envelope, and phase. Their values may vary with time, when various reflecting objects are moving (people in a room, for example), or with changes in position of the transmitter or receiver that are small in respect to the distance between them. We are not dealing here with the large-scale path gain that is expressed in Eqs. (5.5) and (5.6). For simplicity, Eq. (5.7) shows a continuous wave (CW) signal as the modulation terms are not needed to describe the fading statistics. The envelope of the received signal, r, can be statistically described by the Rayleigh distribution whose probability density function is:

58529-2_Datasheet PDF

where σ2 represents the variance of R(t) in Eq. (5.7), which is the average received signal power. This function is plotted in Figure 5.6. We normalized the curve with σ equal to 1. In this plot, the average value of the signal envelope, shown by a dotted vertical line, is 1.253.

The remaining architecture is shown in Figure 13. The global resources include a PCI-to-PCI bridge and DMA/memory controller that couples PCI bus 1 to PCI bus 2. Attachedto the controller is a flash memory for storing the firmware needed to setup and run thebridge, a 32 Mbyte SDRAM used for staging data as it's moved to/from the nodes, and afront panel RS-232 serial interface. On PCI bus 2 is a 100 BaseT Ethernet interface and asecond RS-232 interface. Also on PCI bus 2 is a VME 64 interface that provides VMEslot-1 controller capability, and an optional RACE++ interface.

Whether using a C6203 or a PowerPC, the architectures shown provide exceptional datamovement capability, a critical requirement in many high-speed, real-time applications.A complete list of processor baseboards and VIM I/O modules can be found on thePentek web site at www.pentek.com.

Part 3 compares the tools, OSs, and support for the PowerPC and the C6000. It also looks at example applications for the processors. It will be published Thursday, January 3.

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