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Software Defined Radio DSP choice / sizing
I'm working on a SDR design using the AD9874 to
digitize the IF producing 280 Ksamples/sec and am trying to size the DSP. I'm leaning towards the ADSP-BF532 which is a fixed point DSP rated at 400 MIPS / 800 MMACS and is available in a LQFP package. I'd like to be able to handle everything from decoding standard shortwave SSB signals to broadcast FM stereo signals (including RDS). 1) Any pointers to information which can be used to size the DSP in terms of MIPS, program RAM, and data RAM? Something like a minimum of X MIPS are needed to do a reasonable job handling broadcast FM stereo signals (which I'm assuming require more MIPS than SSB) would be useful to know. 2) Anyone have a specific DSP they favored for this type of application? Keep in mind I need the DSP to be in a package I can handle using home equipment. It would be nice if the DSP was flexible enough so that it can be used for general purpose things such as controlling the keyboard and LCD instead of adding a microcontroller. I'm not looking to use a FPGA at this time. -- John ------------------------------------------------------------------------- | Feith Systems | Voice: 1-215-646-8000 | Email: | | John Wehle | Fax: 1-215-540-5495 | | ------------------------------------------------------------------------- |
Software Defined Radio DSP choice / sizing
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Software Defined Radio DSP choice / sizing
On Thu, 21 Jun 2007 17:44:13 -0700, john wrote:
I'm working on a SDR design using the AD9874 to digitize the IF producing 280 Ksamples/sec and am trying to size the DSP. I'm leaning towards the ADSP-BF532 which is a fixed point DSP rated at 400 MIPS / 800 MMACS and is available in a LQFP package. I'd like to be able to handle everything from decoding standard shortwave SSB signals to broadcast FM stereo signals (including RDS). 1) Any pointers to information which can be used to size the DSP in terms of MIPS, program RAM, and data RAM? Something like a minimum of X MIPS are needed to do a reasonable job handling broadcast FM stereo signals (which I'm assuming require more MIPS than SSB) would be useful to know. 2) Anyone have a specific DSP they favored for this type of application? Keep in mind I need the DSP to be in a package I can handle using home equipment. It would be nice if the DSP was flexible enough so that it can be used for general purpose things such as controlling the keyboard and LCD instead of adding a microcontroller. I'm not looking to use a FPGA at this time. 1. I generally do this by prototyping the algorithms using Scilab, or designing them on paper, then figuring out the number of operations (for MIPS) and data storage requirements. You'll probably find that the FM demodulation takes the most processor time, unless you're decoding multiple SSB channels for some odd reason. 2. I make a conscious effort to not fall in love with any particular processor. Look at a few different choices in your target word size and data type, and try to get a feel for how much time it'll take to run your algorithms. 1 & 2. _Don't_ forget the 'regular processor' stuff when you're sizing memory and processor bandwidth! Wouldn't you feel silly if you had 20 times the RAM you needed for your DSP, but didn't have the buffer space necessary for your TCP/IP stack, or if your algorithm took up 500 words of memory but you ran out of space for menu lines in ROM? Generally with these mixed-target DSP projects you can expect 1% of the code to take 95% of the consumed processing power; you need to make sure you have the code space for the other stuff. -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html |
Software Defined Radio DSP choice / sizing
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Software Defined Radio DSP choice / sizing
Vladimir Vassilevsky wrote:
Why don't you start learning DSP with something simple like FIR or IIR filter? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com Probably because he finds a "Software Defined Radio" to be fascinating. I know that's my motivation for applying fft's to speech and GPS errors. I'd lay odds that the majority of scientific/technical progress is due to amateurs. { please check your etymology before opening fire ; Think about bio's of ancient Greek philosophersetymology;, membership of Royal Society(astronomers particularly came to mind), Einstein, Goddard, Avins, Lyons, Allnor ... thru eons of grad students and even some professors with Phd's. |
Software Defined Radio DSP choice / sizing
On Jun 22, 10:58 am, Vladimir Vassilevsky
wrote: wrote: I'm working on a SDR design using the AD9874 to Fair performance is guaranteed. Do you mean "fair" as in good performance or as in marginal performance? If you mean good performance, then I quite happy to hear it's guaranteed. :-) |
Software Defined Radio DSP choice / sizing
wrote: On Jun 22, 10:58 am, Vladimir Vassilevsky wrote: wrote: I'm working on a SDR design using the AD9874 to Fair performance is guaranteed. Do you mean "fair" as in good performance or as in marginal performance? I mean this toy will work however the performance of the classic analog receiver of the communication class is much better. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com |
Software Defined Radio DSP choice / sizing
On Jun 22, 8:23 pm, Vladimir Vassilevsky
wrote: I mean this toy will work I'm willing to accept some tradeoffs for the sake of simplifying the design (i.e. the AD9874 integrates an ADC and digital filter which is convenient though less flexible then a ADC coupled with a FPGA). however the performance of the classic analog receiver of the communication class is much better. That seems to imply some type of fundamental limitation exists with using the AD9874. Care to be more specific? For example the AD9874 spec claim 95 dB dynamic range, there are certainly radios which claim a higher dynamic range. However I'm imagining that a 95 dB dynamic range should work for a lot of signals. |
Software Defined Radio DSP choice / sizing
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Software Defined Radio DSP choice / sizing
Paul Keinanen wrote:
... Even with a proper S&H (ten nanosecond sampling and several microsecond hold times) for decimation, the 280 Ksamples/s sounds a bit low for FM broadcast detection. The higher order (Bessel function) sidebands are still quite strong with the modulation indexes used, so truncating the bandwidth to the 100-140 kHz range might not be a good idea. ... The IF passband of an FM receiver needs to be at least 200 KHz for good quality and -- counterintuitive to me -- I'm told that the capture ratio improves as the bandwidth increases. Back in the 50s, one premium receiver -- the first I knew of to use semiconductor diodes in the detector -- had a half-MHz IF. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
Software Defined Radio DSP choice / sizing
On Jun 23, 6:17 am, Paul Keinanen wrote:
Even with a proper S&H (ten nanosecond sampling and several microsecond hold times) for decimation, the 280 Ksamples/s sounds a bit low for FM broadcast detection. The IF is 1.7 MHz which is sampled using a 13.6 MHz clock by the AD9874 and decimated by a factor of 48 to produce the 280 Ksamples/s output. Looking at: http://en.wikipedia.org/wiki/Fm_broadcasting I see that FM audio goes from 0 to 53 KHz and RDS is at 57 KHz. The AD9874 decimation filter should prevent any signal from aliasing into the bandwidth of interest and the resulting sample rate is above Nyquist. I'm missing something ... assuming no aliasing problems why is a higher sampling rate necessary for recovering the audio and RDS? -- John |
Software Defined Radio DSP choice / sizing
On Jun 23, 11:42 am, Jerry Avins wrote:
Paul Keinanen wrote: ... Even with a proper S&H (ten nanosecond sampling and several microsecond hold times) for decimation, the 280 Ksamples/s sounds a bit low for FM broadcast detection. The higher order (Bessel function) sidebands are still quite strong with the modulation indexes used, so truncating the bandwidth to the 100-140 kHz range might not be a good idea. ... The IF passband of an FM receiver needs to be at least 200 KHz for good quality and -- counterintuitive to me -- I'm told that the capture ratio improves as the bandwidth increases. Back in the 50s, one premium receiver -- the first I knew of to use semiconductor diodes in the detector -- had a half-MHz IF. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Assuming cochannel signals with small power difference, as the BW increases the weaker one will hit threshold (knee in the SNRout vs SNRin curve) first. Does that explain it? John |
Software Defined Radio DSP choice / sizing
writes:
On Jun 23, 6:17 am, Paul Keinanen wrote: Even with a proper S&H (ten nanosecond sampling and several microsecond hold times) for decimation, the 280 Ksamples/s sounds a bit low for FM broadcast detection. The IF is 1.7 MHz which is sampled using a 13.6 MHz clock by the AD9874 and decimated by a factor of 48 to produce the 280 Ksamples/s output. Looking at: http://en.wikipedia.org/wiki/Fm_broadcasting I see that FM audio goes from 0 to 53 KHz and RDS is at 57 KHz. The AD9874 decimation filter should prevent any signal from aliasing into the bandwidth of interest and the resulting sample rate is above Nyquist. I'm missing something ... assuming no aliasing problems why is a higher sampling rate necessary for recovering the audio and RDS? You're looking at the audio baseband bandwidth, i.e., the signal after being FM demodulated. From your description the signal you're getting has not yet been FM-demodulated. Thus you need to account for the +/- 75 kHz peak deviation of the FM signal, at a minimum. If you can swallow up the whole 200 kHz, you gain slightly better performance due to the admission of more the bessel function sidebands, as others have noted. -- % Randy Yates % "Maybe one day I'll feel her cold embrace, %% Fuquay-Varina, NC % and kiss her interface, %%% 919-577-9882 % til then, I'll leave her alone." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr |
Software Defined Radio DSP choice / sizing
On Fri, 22 Jun 2007 13:51:36 GMT, John Ferrell
wrote: On Thu, 21 Jun 2007 17:44:13 -0700, wrote: I'm working on a SDR design using the AD9874 to digitize the IF producing 280 Ksamples/sec and I am way behind you guys on the DSP-SDR subject but I appreciate every scrap of information you share. I am currently trying to puzzle out the strategy used in acquiring data from a sound card. Using C++, it's not that hard. This page of my website, http://sdeyoreo.tripod.com/id5.html gives the steps and code to capture sound and fill an array with the samples from the soundcard. Fell free to ask me more if you want. I have successfully built the Softrock Lite 40 meter receiver and am ever so slowly working on a Softrock RXTX Ver 6.2 40 M transceiver. John Ferrell W8CCW "Life is easier if you learn to plow around the stumps" |
Software Defined Radio DSP choice / sizing
wrote in message ups.com... I'm working on a SDR design using the AD9874 to digitize the IF producing 280 Ksamples/sec and am trying to size the DSP. I'm leaning towards the ADSP-BF532 which is a fixed point DSP rated at 400 MIPS / 800 MMACS and is available in a LQFP package. I'd like to be able to handle everything from decoding standard shortwave SSB signals to broadcast FM stereo signals (including RDS). 1) Any pointers to information which can be used to size the DSP in terms of MIPS, program RAM, and data RAM? Something like a minimum of X MIPS are needed to do a reasonable job handling broadcast FM stereo signals (which I'm assuming require more MIPS than SSB) would be useful to know. 2) Anyone have a specific DSP they favored for this type of application? Keep in mind I need the DSP to be in a package I can handle using home equipment. It would be nice if the DSP was flexible enough so that it can be used for general purpose things such as controlling the keyboard and LCD instead of adding a microcontroller. I'm not looking to use a FPGA at this time. -- John Can you use one of the blackfin stamp boards ? http://blackfin.uclinux.org/gf/project/stamp Digikey sells the BF537 stamp board for US$226 http://www.digikey.com/scripts/DkSea...440505&Site=US http://www.analog.com/en/prod/0,2877...DSTAMP,00.html Could always try and make a network interface for controlling the radio. I'm just starting to look at what I need for getting a similar set up but A.M and ssb only for students to use in a lab to introduce them to the bascs of sdr. The lecturers want the students to program different modules , different types of modulation , encoding and decoding, set different sampling rates etc They want the students to be able use both c and matlab. Looks like we'll be using a c6713 dsk as the base (thanks to TI providing free software) I just get to assemble/build/integrate what gets specified. Someone in the faculty has a couple of lyrtech signalwave boards which they aren't using(been sitting in their filling cabinet for a few years), have to see if we can prise them off them. Then see what it costs to get support (need the up to date software). http://www.lyrtech.com/DSP-developme...signalwave.php Alex |
Software Defined Radio DSP choice / sizing
On Sat, 23 Jun 2007 11:56:21 -0700, wrote:
The IF is 1.7 MHz which is sampled using a 13.6 MHz clock by the AD9874 and decimated by a factor of 48 to produce the 280 Ksamples/s output. With 1.7 MHz IF you are going to have to construct your own LC band pass filters in front of the AD9874, if 1.7 MHz is the first IF. If this is the second IF and you have proper filtering (ceramic or crystal) at the first IF, say 10.7 MHz, a very simple filter at 1.7 MHz should be sufficient. Due to not so spectacular performance of that chip, I would suggest using a selectable IF filter at 10,7 MHz (or whatever the first IF is), to even roughly match the required bandwidth of the transmission. If the IF filter would be 110-280 kHz wide to allow broadcast FM reception, using such receiver in Europe to receive the 7.0-7.1 MHz amateur band when there are very high power international broadcasters starting at 7.1 MHz, might give quite disappointing results, since those strong broadcast signals would control the AGC reducing sensitivity and you still would get a lot of intermodulation products. It also appears that the quoted dynamic range applies only to certain AGC settings. The use of 1.7 MHz IF with a very wide input filter may be problematic at least in countries that are still using the AM broadcast band actively, with very strong signals up to 1.6 MHz. On the other hand, local 1.8 MHz amateur radio signals may be quite strong. In any superheterodyne receiver, there is always a risk for signal break-through from the environment to the IF stage at that frequency range. For this reason, common IF frequencies, such as 10.7 MHz and 455 kHz, are usually excluded from transmitter frequency assignments. Looking at: http://en.wikipedia.org/wiki/Fm_broadcasting I see that FM audio goes from 0 to 53 KHz and RDS is at 57 KHz. While the modulation index for the RDS signal is quite low, thus producing only the first order Bessel sidebands at +/- 57 kHz from the carrier, the stereo difference signal S can have a quite high modulation index, thus producing the first pair of Bessel sidebands below +/-53 kHz from the carrier but also producing some significant second order Bessel sidebands below +/-106 kHz and possibly even the third order at +/-159 kHz. Of course, this requires that there is a strong high pitch tone only in one audio channel to get a huge difference signal. Paul OH3LWR |
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