Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
It is for UMTS based standard LTE (20MHz bandwidth) which has 30.72Msps and this is beyond USRP2's instantaneous bandwidth (25MHz). I am simulating LTE (10MHz bandwidth) where I can halve the sampling rate of 15.36Msps. Reading the earlier mail threads and responses from Matt I understand that it is better to handle the sample rate converters at the software level rather than doing at the FPGA level in the USRP2 code. LTE is based on OFDM and is not using any spectral shaping filter, instead the samples generated for OFDM symbols at the above rate are directly read/write into DAC/ADC. I could successfully do the above by performing downlink and uplink using interpolation factor 16 which boils down to 6.25Msps but when I used the interpolation factor 6 (or 8) it gives the overflowing errors. I am using Quadcore PC (2.6GHz), can you suggest any other high end PC that can handle the above processing? Regards Krishna S --- On Fri, 9/4/10, John Orlando j...@epiq-solutions.com wrote: From: John Orlando j...@epiq-solutions.com Subject: Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc To: Johnathan Corgan jcor...@corganenterprises.com Cc: Krishna S krishna2...@yahoo.com, gnu discuss-gnuradio@gnu.org Date: Friday, 9 April, 2010, 4:15 PM snip If what you really mean is that you have a host PC generated sample stream at 15.36 Msps and need to transmit it with the USRP2, then yes, you'd set the USRP2 FPGA interpolation to 6, then fractionally resample from 15.36 Msps to 16 Msps on the host. Depending on what the last DSP processing stage in your application is, you may be able to fold this resampling into the prior stage. For example, if the last step in your signal processing chain is a spectral shaping filter, like a root-raised-cosine filter, then you can reimplement this using a polyphase resampler and use the output filter taps there. This would combine the filter and resampling operation in one block and eliminate the need for a very high CPU resampling block. Where does the figure of 15.36 Msps come from? Just a guess, but that sounds like 4x the UMTS chip rate (which is 3.84 Mchips/sec). If this is the case, there is an RRC filter at the last DSP stage typically, so your suggestion for folding this re-sampling in is spot-on. -- Regards, John Orlando CEO/System Architect Epiq Solutions www.epiq-solutions.com Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
Hi Thanks for your response. I have following queries on the sampling rates in USRP2. 1. I set the interpolation rate to 6. Does that mean baseband signal is fed to DAC at the rate of 100MHz/6 = 16.66 Msps? 2. I want actually feed 15.36 Msps to DAC which is not possible as the interpolation factor becomes non-integer. So do you suggest me to use ‘resampler’ to convert 16.66 Msps to 15.36Msps? I appreciate your feedback. Krishna S --- On Thu, 8/4/10, Johnathan Corgan jcor...@corganenterprises.com wrote: From: Johnathan Corgan jcor...@corganenterprises.com Subject: Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc To: Krishna S krishna2...@yahoo.com Cc: Per Zetterberg per.zetterb...@ee.kth.se, gnu discuss-gnuradio@gnu.org Date: Thursday, 8 April, 2010, 3:30 PM As i am dealing with RF communication i need to know exactly what sampling rate the USRP2 is sampling the data and sending over the air ? This has been detailed before on this list, so you can find a more complete explanation by searching the archives. On the transmit side, there are *two* sample rate conversions occurring in the USRP2. The DAC operates internally at 400 Msps, but is configured to interpolate samples presented by the FPGA by a factor of four, so the FPGA must present samples at 100 Msps to the DAC interface bus. This is the DAC rate parameter referred to above. Since it is not possible to provide the USRP2 itself with 100 Msps of data over the GbE communications interface (this would be 3.2 Gbps plus overhead), the USRP2 FPGA implements a configurable interpolation rate digital upconverter, allowing an interpolation rate between 4 and 512. In the case it is configured to interpolate by 4, then the USRP2 will consume samples from the GbE port at 25 Msps, or 800 Gbps + overhead. Since the signal sample format is complex baseband (I and Q in quadrature), the Nyquist criteria allows up to 25 MHz of signal bandwidth to be represented using 25 Msps (not 12.5 MHz, which would be the case for a real signal.) As the interpolation rate in the FPGA is decreased, the USRP2 consumes samples from the GbE at lower and lower rates, and the amount of RF signal bandwidth that can be represented in the sample stream goes down accordingly. In the limit, at an interpolation rate of 512, one would generate a sample stream representing ~183 KHz (100 MHz/512) for further host processing. The receive side is similar, but in the other direction, and there is only one sample rate conversion. The ADC sample rate is 100 Msps, and the configurable digitial downconverter in the USRP2 FPGA filters and decimates the digitized sample stream by a factor between 4 and 512. Thus, at the input to the FPGA, the digitized sample stream is 100 MHz wide, but the DDC reduces and resamples this to between 25 MHz (decimation 4) and ~183 KHz (decimation 512). This is a long way of saying that you should use the same decimation and interpolation rate on the transmitter and receiver to achieve the same sample rate/bandwidth to and from the host PCs. Johnathan Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
On Fri, Apr 9, 2010 at 01:25, Krishna S krishna2...@yahoo.com wrote: 1. I set the interpolation rate to 6. Does that mean baseband signal is fed to DAC at the rate of 100MHz/6 = 16.66 Msps? Not quite. It means that the FPGA is interpolating and creating 6 samples on the DAC bus for every sample that is sent to it over the GbE. Since the DAC is consuming samples at 100 Msps, the FPGA is consuming samples at 100 Msps/6 from the GbE. Thus, you need to generate (and being able to sustain) a sample stream on the host at 100 Msps/6, and by the Nyquist limit, it can contain up to ~16.666 MHz of spectral content. 2. I want actually feed 15.36 Msps to DAC which is not possible as the interpolation factor becomes non-integer. So do you suggest me to use ‘resampler’ to convert 16.66 Msps to 15.36Msps? The DAC always runs at 100 Msps. You need to understand this to know what needs to happen upstream. If what you really mean is that you have a host PC generated sample stream at 15.36 Msps and need to transmit it with the USRP2, then yes, you'd set the USRP2 FPGA interpolation to 6, then fractionally resample from 15.36 Msps to 16 Msps on the host. Depending on what the last DSP processing stage in your application is, you may be able to fold this resampling into the prior stage. For example, if the last step in your signal processing chain is a spectral shaping filter, like a root-raised-cosine filter, then you can reimplement this using a polyphase resampler and use the output filter taps there. This would combine the filter and resampling operation in one block and eliminate the need for a very high CPU resampling block. Where does the figure of 15.36 Msps come from? Johnathan ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
On Fri, Apr 9, 2010 at 08:58, Johnathan Corgan jcor...@corganenterprises.com wrote: If what you really mean is that you have a host PC generated sample stream at 15.36 Msps and need to transmit it with the USRP2, then yes, you'd set the USRP2 FPGA interpolation to 6, then fractionally resample from 15.36 Msps to 16 Msps on the host. Correction: resample from 15.36 Msps to 16. Msps on the host. Johnathan ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
snip If what you really mean is that you have a host PC generated sample stream at 15.36 Msps and need to transmit it with the USRP2, then yes, you'd set the USRP2 FPGA interpolation to 6, then fractionally resample from 15.36 Msps to 16 Msps on the host. Depending on what the last DSP processing stage in your application is, you may be able to fold this resampling into the prior stage. For example, if the last step in your signal processing chain is a spectral shaping filter, like a root-raised-cosine filter, then you can reimplement this using a polyphase resampler and use the output filter taps there. This would combine the filter and resampling operation in one block and eliminate the need for a very high CPU resampling block. Where does the figure of 15.36 Msps come from? Just a guess, but that sounds like 4x the UMTS chip rate (which is 3.84 Mchips/sec). If this is the case, there is an RRC filter at the last DSP stage typically, so your suggestion for folding this re-sampling in is spot-on. -- Regards, John Orlando CEO/System Architect Epiq Solutions www.epiq-solutions.com ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
Hi, So, if i am setting interpolation rate 16 at transmitter side(tx_samples.cc), according to the equation the program is sampling at Sampling rate = 400/16 = 25M samples/sec. but, I am able to receive the data only at the same decimation rate 16(rx_streaming_samples.cc) , for which the program is sampling at Sampling rate =100/16 =6.25M samples/sec But for me to transmit and receive data i have to send and receive at 25M samples /sec right ?? if i try to do that i.e., at receiver side samp rate = 100/4 = 25M samples /sec I don't receive at all ...? everything boils down to one question ? the sampling rate what we are talking here is the sampling rate at which the samples have been sampled before sending to RF as discussed in COMMUNICATION THEORY (following the Nyquist Criteria) or the sampling rate calculated to find the allowed no.of samples/sec the ETHERNET can take to connect the host to USRP2. but inside the sampling rate is different ? As i am dealing with RF communication i need to know exactly what sampling rate the USRP2 is sampling the data and sending over the air ? Thanks KRISHNA S --- On Wed, 7/4/10, Per Zetterberg per.zetterb...@ee.kth.se wrote: From: Per Zetterberg per.zetterb...@ee.kth.se Subject: Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc To: Krishna S krishna2...@yahoo.com Cc: gnu discuss-gnuradio@gnu.org Date: Wednesday, 7 April, 2010, 7:52 AM Krishna S wrote: Hi, i am trying to calculate at what sampling rate does the tx_sampless.cc and rx_streaming samples.cc are sending the data (file). from 1 USRP2 to another USRP2. i am setting interpolation as 16 at transmitter side (tx_samples.cc) and decimation rate of 16 at receiver side (rx_streaming_samples.cc) according to formula what i have learnt from WEB is Tx Side : Sampling Rate = DAC rate/ Interpolation rate; Rx Side : Sampling Rate = ADC rate/ Decimation rate; are the above equation are correct for determining the sampling rate Thank You Regards KRISHNA S Your Mail works best with the New Yahoo Optimized IE8. Get it NOW! http://in.rd.yahoo.com/tagline_ie8_new/*http://downloads.yahoo.com/in/internetexplorer/. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio Yes, it is the sample-rate on the host-side. DAC rate and ADC rate is 100MHz. BR/ Per Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
Krishna, My understanding is that we can regard the sample rate of the DAC and ADC as 100MHz (although the DAC uses internally a larger rate, this is what I have read). Thus the rate at which samples are leaving or entering the RF sections at are 100MHz. The maximum rate at the host side is 25MHz, then that rate is interpolated/decimated in the FPGA to/from the 100MHz. The tx_sampless.cc and rx_streaming_sampless.cc reads and writes from file and therefore 25MHz host sample-rate may not be possible. Thus you should typically use the same interpolation/decimation factor in the transmitter and receiver. BR/ Per Krishna S wrote: Hi, So, if i am setting interpolation rate 16 at transmitter side(tx_samples.cc), according to the equation the program is sampling at Sampling rate = 400/16 = 25M samples/sec. but, I am able to receive the data only at the same decimation rate 16(rx_streaming_samples.cc) , for which the program is sampling at Sampling rate =100/16 =6.25M samples/sec But for me to transmit and receive data i have to send and receive at 25M samples /sec right ?? if i try to do that i.e., at receiver side samp rate = 100/4 = 25M samples /sec I don't receive at all ...? everything boils down to one question ? the sampling rate what we are talking here is the sampling rate at which the samples have been sampled before sending to RF as discussed in COMMUNICATION THEORY (following the Nyquist Criteria) or the sampling rate calculated to find the allowed no.of samples/sec the ETHERNET can take to connect the host to USRP2. but inside the sampling rate is different ? As i am dealing with RF communication i need to know exactly what sampling rate the USRP2 is sampling the data and sending over the air ? Thanks KRISHNA S --- On *Wed, 7/4/10, Per Zetterberg /per.zetterb...@ee.kth.se/* wrote: From: Per Zetterberg per.zetterb...@ee.kth.se Subject: Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc To: Krishna S krishna2...@yahoo.com Cc: gnu discuss-gnuradio@gnu.org Date: Wednesday, 7 April, 2010, 7:52 AM Krishna S wrote: Hi, i am trying to calculate at what sampling rate does the tx_sampless.cc and rx_streaming samples.cc are sending the data (file). from 1 USRP2 to another USRP2. i am setting interpolation as 16 at transmitter side (tx_samples.cc) and decimation rate of 16 at receiver side (rx_streaming_samples.cc) according to formula what i have learnt from WEB is Tx Side : Sampling Rate = DAC rate/ Interpolation rate; Rx Side : Sampling Rate = ADC rate/ Decimation rate; are the above equation are correct for determining the sampling rate Thank You Regards KRISHNA S Your Mail works best with the New Yahoo Optimized IE8. Get it NOW! http://in.rd.yahoo.com/tagline_ie8_new/*http://downloads.yahoo.com/in/internetexplorer/. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org /mc/compose?to=discuss-gnura...@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio Yes, it is the sample-rate on the host-side. DAC rate and ADC rate is 100MHz. BR/ Per Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
As i am dealing with RF communication i need to know exactly what sampling rate the USRP2 is sampling the data and sending over the air ? This has been detailed before on this list, so you can find a more complete explanation by searching the archives. On the transmit side, there are *two* sample rate conversions occurring in the USRP2. The DAC operates internally at 400 Msps, but is configured to interpolate samples presented by the FPGA by a factor of four, so the FPGA must present samples at 100 Msps to the DAC interface bus. This is the DAC rate parameter referred to above. Since it is not possible to provide the USRP2 itself with 100 Msps of data over the GbE communications interface (this would be 3.2 Gbps plus overhead), the USRP2 FPGA implements a configurable interpolation rate digital upconverter, allowing an interpolation rate between 4 and 512. In the case it is configured to interpolate by 4, then the USRP2 will consume samples from the GbE port at 25 Msps, or 800 Gbps + overhead. Since the signal sample format is complex baseband (I and Q in quadrature), the Nyquist criteria allows up to 25 MHz of signal bandwidth to be represented using 25 Msps (not 12.5 MHz, which would be the case for a real signal.) As the interpolation rate in the FPGA is decreased, the USRP2 consumes samples from the GbE at lower and lower rates, and the amount of RF signal bandwidth that can be represented in the sample stream goes down accordingly. In the limit, at an interpolation rate of 512, one would generate a sample stream representing ~183 KHz (100 MHz/512) for further host processing. The receive side is similar, but in the other direction, and there is only one sample rate conversion. The ADC sample rate is 100 Msps, and the configurable digitial downconverter in the USRP2 FPGA filters and decimates the digitized sample stream by a factor between 4 and 512. Thus, at the input to the FPGA, the digitized sample stream is 100 MHz wide, but the DDC reduces and resamples this to between 25 MHz (decimation 4) and ~183 KHz (decimation 512). This is a long way of saying that you should use the same decimation and interpolation rate on the transmitter and receiver to achieve the same sample rate/bandwidth to and from the host PCs. Johnathan ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
On Thu, Apr 8, 2010 at 08:30, Johnathan Corgan jcor...@corganenterprises.com wrote: In the case it is configured to interpolate by 4, then the USRP2 will consume samples from the GbE port at 25 Msps, or 800 Gbps + overhead. Um, that would be 800 Mbps + overhead. But one could wish :-) Johnathan ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
Hi, i am trying to calculate at what sampling rate does the tx_sampless.cc and rx_streaming samples.cc are sending the data (file). from 1 USRP2 to another USRP2. i am setting interpolation as 16 at transmitter side (tx_samples.cc) and decimation rate of 16 at receiver side (rx_streaming_samples.cc) according to formula what i have learnt from WEB is Tx Side : Sampling Rate = DAC rate/ Interpolation rate; Rx Side : Sampling Rate = ADC rate/ Decimation rate; are the above equation are correct for determining the sampling rate Thank You Regards KRISHNA S The INTERNET now has a personality. YOURS! See your Yahoo! Homepage. http://in.yahoo.com/___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] sampling rate of tx_sampless.cc and rx_streaming_sampless.cc
Krishna S wrote: Hi, i am trying to calculate at what sampling rate does the tx_sampless.cc and rx_streaming samples.cc are sending the data (file). from 1 USRP2 to another USRP2. i am setting interpolation as 16 at transmitter side (tx_samples.cc) and decimation rate of 16 at receiver side (rx_streaming_samples.cc) according to formula what i have learnt from WEB is Tx Side : Sampling Rate = DAC rate/ Interpolation rate; Rx Side : Sampling Rate = ADC rate/ Decimation rate; are the above equation are correct for determining the sampling rate Thank You Regards KRISHNA S Your Mail works best with the New Yahoo Optimized IE8. Get it NOW! http://in.rd.yahoo.com/tagline_ie8_new/*http://downloads.yahoo.com/in/internetexplorer/. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio Yes, it is the sample-rate on the host-side. DAC rate and ADC rate is 100MHz. BR/ Per ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
