Digital Radio System Design Pdf
In the case of a single carrier radio, no head room is required. With these thoughts in mind, how can the performance of a radio be determined and what tradeoffs can be made. Although a complete system would have additional components, this will serve this discussion. When considering overall system performance, a more generalized equation may be used. It provides an in-depth examination of the complete transceiver chain which helps to connect the two topics in a unified system concept.
Many receivers use proprietary schemes to further enhance performance through additional noise rejection and heterodyne elimination. Usually, aperture uncertainty is expressed in seconds rms. The table below also shows which cases cause spectral reversal. In some instances, these may not be realistic assumption but they do provide a starting point with which performance limits can be bench marked.
Since aperture uncertainty is wideband noise on the clock, it shows up as wideband noise in the sampled spectrum as well. The terms aperture jitter and aperture uncertainty are frequently interchanged in text. Multi-Carrier There are two basic types of radios under discussion. Another example of frequency planning can be found in undersampling.
These changes allow reduction of size, cost, managing successful projects with prince2 2009 edition pdf complexity and improve manufacturing by using digital components to replace unreliable and in-accurate analog components. Digital receivers can be used to receive any type of modulation including any analog or digital modulation standards. The radio and the digital processor.
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Therefore the focus of this analysis will be on overall noise contribution due to aperture uncertainty. In this case the following equation is valid. This is called reciprocal mixing.
Enter your email address below and we will send you your username. First, it is assumed that the receiver is noise limited.
Using this technique to cause harmonics to fall outside the Nyquist zone of interest allows them to be easily filtered as shown above. For additional reading on this subject matter, consult one of the references at the end of this article. If they are, then the frequency must be folded back into the first Nyquist zone by subtracting the result from f SampleRate. This is important because this is the reference point with which our receiver will be compared. However, this is a complete discussion in itself and not the focus of this article.
In this application, they have the same meaning. Another application might be surveillance receivers that typically use scanners to monitor multiple frequencies.
This is the noise present at the antenna and must be gained up by the conversion gain and degraded by the noise figure. There are two basic types of radios under discussion.
These spurs are unaffected by techniques such as dither and must be addressed to prevent disruption of receiver performance. If these specifications are met, then the performance should be equal to. Oversampling only simplifies matters by providing more spectrum for the harmonics to fall harmlessly within. That is that no spurs exist inband that would otherwise limit performance.
As can be seen, the second and third harmonics fall away from the band of interest and cause no interference to the fundamental components. Although synthesizer phase noise is similar to jitter on the encode clock, it has slightly different effects on the receiver, but in the end, the effects are very similar.
The frequency domain process of the mixer is convolution the time domain process of the mixer is multiplication. First, in a multi-carrier receiver, none of the channels can be expected to be correlated.
Likewise, the purpose of the digital processor is to take the digitized data and extract out the desired information. At the antenna, this is dBm.
As with jitter, the less phase noise the better. Better numbers can be achieved with low noise modules. In terms of phase accuracy and inter-symbol interference the effects of aperture uncertainty are small.
This can be observed in the before and after plots of dither as a slight increase in the average noise floor of the converter. Analysis starts with several assumptions. By analyzing the units, it can be seen that this yields unit of volts. If not specified, the insertion loss may be used, however, if a noise figure is supplied with the device, it should be used.
Anything beyond this is called Over Sampling. The second assumption is that the bandwidth of the receiver front end is our Nyquist bandwidth. Usually, it is specified in dB although in the computation of noise figure, the numerical ratio non-log is used. Although this is a simple equation, it provide much insight into the noise performance that can be expected from a data converter.
To start the analysis, the noise at the antenna port must be considered. Thus, the available noise from the previous section can be degraded directly using the noise figure. Since the energy of the spurs must be conserved, dither simply causes them to appear as additional noise in the floor of the converter. Under sampling is important because it can serve a function very similar to mixing. This is the source of this expression.
With each progressive stage through the receiver, this noise is degraded by the noise figure of the stage as discussed below. Thus in reality, the available noise power from the source in this case is independent of impedance for non-zero and finite resistance values. This applications allows simultaneous monitoring of many frequencies without the need for sequential scanning. Neither the noise factor or the gains are in log form at this point. This equation provides the resulting frequency in the first and second Nyquist zone.
If the address matches an existing account you will receive an email with instructions to retrieve your username. Many times, the Nyquist rate is quoted as the sample rate that is twice that of the highest frequency component. This paper attempts to explain how to calculate sensitivity and selectivity of such a receiver. However, noise figure is not independent of gain and an increase in the gain may also have an adverse effect on noise performance from additional gain stages.
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