CPM
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From: Vladimir Vassilevsky on 25 Apr 2010 20:28 I was trying to design a bandlimited pseudorandom signal with constant envelope for radar/sonar and like applications. I.e. frequency modulation with smoothed transitions. The problem is closely related to CPM for data transmission, however the optimization criteria are not quite the same. In particular, it turns out that optimal value for normalized deviation is higher then 0.5, optimal h ~0.6..0.7. Another observation: the binary CPM signal with BT ~ 0.3 and h ~ 0.8 makes for the best possible (?) rectangular spectrum shape, however its autocorrelation properties are worse then optimal. Could you suggest a good reading on this matter? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: John on 25 Apr 2010 20:53 On Apr 25, 8:28 pm, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: > I was trying to design a bandlimited pseudorandom signal with constant > envelope for radar/sonar and like applications. I.e. frequency > modulation with smoothed transitions. The problem is closely related to > CPM for data transmission, however the optimization criteria are not > quite the same. In particular, it turns out that optimal value for > normalized deviation is higher then 0.5, optimal h ~0.6..0.7. > Another observation: the binary CPM signal with BT ~ 0.3 and h ~ 0.8 > makes for the best possible (?) rectangular spectrum shape, however its > autocorrelation properties are worse then optimal. > > Could you suggest a good reading on this matter? > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultanthttp://www.abvolt.com http://books.google.com/books?id=RwMpVSOXdJQC&printsec=frontcover&dq=digital+phase+modulation&source=bl&ots=7qKVpiwre8&sig=kqxvTHpdWkgcWYxNryZSxyaSk8c&hl=en&ei=k-PUS6uMEYT48AbgssSqDw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CB4Q6AEwAw#v=onepage&q&f=false John
From: John on 25 Apr 2010 20:56 On Apr 25, 8:28 pm, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: > I was trying to design a bandlimited pseudorandom signal with constant > envelope for radar/sonar and like applications. I.e. frequency > modulation with smoothed transitions. The problem is closely related to > CPM for data transmission, however the optimization criteria are not > quite the same. In particular, it turns out that optimal value for > normalized deviation is higher then 0.5, optimal h ~0.6..0.7. > Another observation: the binary CPM signal with BT ~ 0.3 and h ~ 0.8 > makes for the best possible (?) rectangular spectrum shape, however its > autocorrelation properties are worse then optimal. > > Could you suggest a good reading on this matter? > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultanthttp://www.abvolt.com BTW, I came to the conclusion on a prior project that CPM cannot have impulse-like autocorrelation. For my project I switched to SQPSK with a PN sequence (different on I and Q) and accepted suboptimal peak/avg ratio in exchange for ideal autocorrelation. John John
From: Steve Pope on 25 Apr 2010 21:42 Vladimir Vassilevsky <nospam(a)nowhere.com> wrote: >I was trying to design a bandlimited pseudorandom signal with constant >envelope for radar/sonar and like applications. I.e. frequency >modulation with smoothed transitions. The problem is closely related to >CPM for data transmission, however the optimization criteria are not >quite the same. In particular, it turns out that optimal value for >normalized deviation is higher then 0.5, optimal h ~0.6..0.7. >Another observation: the binary CPM signal with BT ~ 0.3 and h ~ 0.8 >makes for the best possible (?) rectangular spectrum shape, however its >autocorrelation properties are worse then optimal. > >Could you suggest a good reading on this matter? I have no idea as to literature, but I likewise have had trouble sometimes receiving an h = 0.5 signal as well as I would like or would have expected, and had to push to a higher value of h. I assume it's simply because I don't know the best algorithms for what I'm trying to do. Steve
From: Vladimir Vassilevsky on 25 Apr 2010 22:07
John wrote: > On Apr 25, 8:28 pm, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: > >>I was trying to design a bandlimited pseudorandom signal with constant >>envelope for radar/sonar and like applications. I.e. frequency >>modulation with smoothed transitions. The problem is closely related to >>CPM for data transmission, however the optimization criteria are not >>quite the same. In particular, it turns out that optimal value for >>normalized deviation is higher then 0.5, optimal h ~0.6..0.7. >>Another observation: the binary CPM signal with BT ~ 0.3 and h ~ 0.8 >>makes for the best possible (?) rectangular spectrum shape, however its >>autocorrelation properties are worse then optimal. > BTW, I came to the conclusion on a prior project that CPM cannot have > impulse-like autocorrelation. Can you clarify? I am getting the main autocorrelation lobe just like it supposed to be according to the bandwidth, however there is a second lobe at ~ -7dB, a third at -20..-30 dB and so on till it gets to the autocorrelation floor. > For my project I switched to SQPSK with > a PN sequence (different on I and Q) and accepted suboptimal peak/avg > ratio in exchange for ideal autocorrelation. I thought about it. With or without offset, filtered QPSK has near gaussian amplitude distribution. It is not very obvious if better autocorrelation will compensate for PAPR. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com > > John > > John |