HI, here People usually estimate the SINR in the OFDM systems in the following way. 1. Estimate over each specific pilot subcarrier of different OFDM symbols. (i.e. CINR estimation) 2. Then average over all pilot subcarriers (i.e. average CINR) to approximate the SINR. The problem is, most CINR estimation algorithms are based on a simpliied channel model assumption. That is, "y = h*a + w", where, y denotes the received signal after FFT transformation; h denotes the equivalent time-varying channel coefficients a denotes the transmitted signal before IFFT transformation. w denotes the AWGN noise. (There is theoretical real SINR for this simplified channel model, SINR=E{(ha)*(ha)} / E{w*w}; Also, h could be regarded as perfect channel estimation.) ====== However, I am going with a practical system. That means, I should justify the SINR estimation method in a complex channel model (not in a simplified linear version). Original transmitted signal -> IFFT -> Multipath channel (may result in ICI here)-> FFT -> Received sigmal. In this practical channel model. (It's hard to find theoretical real SINR, also hard to find the perfect channel estimation, which means it is hard for me to justify my SINR channel estimation method in the practical systems.) Could anyone give me some highlight on this problem?
SINR estimation in OFDM systems
Started by ●May 20, 2007
Reply by ●May 20, 20072007-05-20
>HI, here > >People usually estimate the SINR in the OFDM systems in the following >way. >1. Estimate over each specific pilot subcarrier of different OFDM >symbols. (i.e. CINR estimation) >2. Then average over all pilot subcarriers (i.e. average CINR) to >approximate the SINR. > >The problem is, most CINR estimation algorithms are based on a >simpliied channel model assumption. That is, "y = h*a + w", where, >y denotes the received signal after FFT transformation; >h denotes the equivalent time-varying channel coefficients >a denotes the transmitted signal before IFFT transformation. >w denotes the AWGN noise. >(There is theoretical real SINR for this simplified channel model, >SINR=E{(ha)*(ha)} / E{w*w}; Also, h could be regarded as perfect >channel estimation.) > >====== > >However, I am going with a practical system. That means, I should >justify the SINR estimation method in a complex channel model (not in >a simplified linear version). > >Original transmitted signal -> IFFT -> Multipath channel (may result >in ICI here)-> FFT -> Received sigmal. > >In this practical channel model. >(It's hard to find theoretical real SINR, also hard to find the >perfect channel estimation, which means it is hard for me to justify >my SINR channel estimation method in the practical systems.) > >Could anyone give me some highlight on this problem? > >I would implment the OFDM receiver, demodulate the signal and subtract it from the received signal to get an estimate of all noise plus interference corresponding to your specific receiver structure and the real-world conditions. The calculation of the SINR is then trivial. LBB _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?
Reply by ●May 20, 20072007-05-20
> I would implment the OFDM receiver, demodulate the signal and subtract it > from the received signal to get an estimate of all noise plus interference > corresponding to your specific receiver structure and the real-world > conditions. The calculation of the SINR is then trivial.=== Hmmm... "implmenting the OFDM receiver, demodulate the signal" sounds easy, but as to "Subtract it from the received signal", hmmm, I can't see where is the received signal. Do you mean that after we get the received signal(say y) from the channelthen we do the FFT transfomation, demodulate the signal, and then modulate the signal again, do the IFFT transformation again(say the result is x'), So, we can subtract x' from the received signal y to do the SINR estimation? -- Jia
Reply by ●May 20, 20072007-05-20
To LBB, Moreover, the way you said is something like "Non-data-aided" SINR estimation method. However, I want to do some "Data-aided" SINR estimatiion method, which means I know some transmitted pilots beforehand. ===== And also, the channel is fading channel, not AWGN channel. So, we may not just subtract the demodulated signal from the received signal directly. We need to know the channel fading coefficient. --- Jia
Reply by ●May 20, 20072007-05-20
>To LBB, > >Moreover, the way you said is something like "Non-data-aided" SINR >estimation method. > >However, I want to do some "Data-aided" SINR estimatiion method, which >means I know some transmitted pilots beforehand. > >===== > >And also, the channel is fading channel, not AWGN channel. So, we may >not just subtract the demodulated signal from the received signal >directly. We need to know the channel fading coefficient. > >--- > >Jia > >Sorry for the oversimplified answer. Ususaaly after the time/frequency synchronization, channel coefficient estimation, one-tap frequency domain equalization you get a series of decision variables for all subcarriers within one OFDM symbol duration, based on which you can make symbol detection, demapping, deinterleaving, decoding and so on. Then you can use the decoded bit stream to reconstruct the signal on each subcarrier by re-interleaving, re-coding and re-mapping. This reconstructed signal is supposed to be subtracted from the decision variable, which leads to the estimate of the noise plus interference. The assumption here is a quasi-error free reception after the decoding, meaning you can really extract the transmitted signal by your receiver under the given transmission condition. Otherwise you should expect a large deviation of the estimated SINR. But if you intend to use a training sequence you don't need to reconstruct the signal any more. Instead you can subtract the training sequence, which is usually defined in the frequency domain, from the decision variable, and this simplifies the whole story quite a lot. Yes, there will be frequency selective fading for multipath channels and fast/slow fading for mobile channels. By the reconstruction and subtraction mehtod you can work out an average SINR over time and frequency. You can also estimate the SINR of a specific subcarrier over time if you like. As mentioned, the statics become trivial once you reconstruct the signal. LBB _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?
Reply by ●December 13, 20072007-12-13
no, the answer is not correct. People doesn't concern SINR but CINR, and the definition of CINR is: CINR= power(H*X)/power(W+I) also, CINR = power(H)/(power(W+I)/X) we can't just subtract the X from the received signal in frequency domain to find out the value of (W+I). We should subtract (H*X)which is useful signal. The difficulty is that H is a variant in a real channel. Some people study the relation between adjacent subcarriers,and other study the time domain channel impulse response characteristic.But all of this studies are not perfect. If you are interested it,please contact me. wanghui263@hotmail.>>To LBB, >> >>Moreover, the way you said is something like "Non-data-aided" SINR >>estimation method. >> >>However, I want to do some "Data-aided" SINR estimatiion method, which >>means I know some transmitted pilots beforehand. >> >>===== >> >>And also, the channel is fading channel, not AWGN channel. So, we may >>not just subtract the demodulated signal from the received signal >>directly. We need to know the channel fading coefficient. >> >>--- >> >>Jia >> >> > >Sorry for the oversimplified answer. > >Ususaaly after the time/frequency synchronization, channel coefficient >estimation, one-tap frequency domain equalization you get a series of >decision variables for all subcarriers within one OFDM symbol duration, >based on which you can make symbol detection, demapping, deinterleaving, >decoding and so on. Then you can use the decoded bit stream toreconstruct>the signal on each subcarrier by re-interleaving, re-coding andre-mapping.>This reconstructed signal is supposed to be subtracted from the decision >variable, which leads to the estimate of the noise plus interference.The>assumption here is a quasi-error free reception after the decoding, >meaning you can really extract the transmitted signal by your receiver >under the given transmission condition. Otherwise you should expect a >large deviation of the estimated SINR. But if you intend to use atraining>sequence you don't need to reconstruct the signal any more. Instead youcan>subtract the training sequence, which is usually defined in thefrequency>domain, from the decision variable, and this simplifies the whole story >quite a lot. > >Yes, there will be frequency selective fading for multipath channels and >fast/slow fading for mobile channels. By the reconstruction and >subtraction mehtod you can work out an average SINR over time and >frequency. You can also estimate the SINR of a specific subcarrier over >time if you like. As mentioned, the statics become trivial once you >reconstruct the signal. > >LBB > >_____________________________________ >Do you know a company who employs DSP engineers? >Is it already listed at http://dsprelated.com/employers.php ? >