Re: [oc] DPLL

[alexhu@alltek.com.cn]

----- Original Message ----- 
From: haoguang.guo@p...  
To: cores@o...  
Date: Thu, 15 Nov 2001 09:58:20 +0800 
Subject: Re: [oc] DPLL 

> 
> 
> Hi, 
>            I have a problem about  bit synchronization when use 
> QPSK in satellite communication. When design the demodulator , how 
> can i get the 
> bit clock?  Some one said because of the fading and unknown delay , 
> you can not synchroniza to the transmitter . so must  use the 
> equalizer to estimate the channel. Is it right? 
> 
> 
> 
> 
> 
> 
> 
> 
> "Sam Gladstone" <samg@t... >@opencores.org on 
> 11/15/2001 06:29:28 AM 
> 
> Please respond to cores@o...  
> 
> Sent by:  owner-cores@o...  
> 
> 
> To:     <cores@o... > 
> cc:      (bcc: Haoguang Guo/SHA/SC/PHILIPS) 
> Subject:  Re: [oc] DPLL 
> Classification: 
> 
> 
> 
> I take it you are demodulating back to a certain softbit size? 
> There is several books out there that are pretty good. I will find 
> the 
> one I used when we were writing an 802.11a phy for a company. 
> 
> The main idea is to demodulate each dimension of the 
> QPSKconstellation data 
> seperately by 
> breaking the real and imaginary up into two seperate demodulations. 
>  Linear 
> extrapolations can be used to generate softbits for a first order 
> method. 
> There are more cost effective, but 
> harder to understand methods available as well. 
> (Assuming that you have already done the proper power and phase 
> corrections.) 
> I think the number of softbits generated looks like this table. 
> BPSK - 1 softbit per constellation 
> QPSK - 2 softbits per constellation 
> QAM-16 - 4 softbits per constellation 
> QAM-64 - 6 softbits per constellation 
> (QAMs get nasty because they are like combinations of different 
> codings that 
> have 
> to have multiple softbits generated per demension because of grey 
> coding 
> with the 
> modulution module. Yuck! ) 
> 
> I will try to find the book name and send it out. 
> 
> Regards, 
>   Sam 
> 
> ----- Original Message ----- 
> From: <aolmo@g... > 
> To: <cores@o... > 
> Sent: Wednesday, November 14, 2001 9:24 AM 
> Subject: [oc] DPLL 
> 
> 
> > Hi, 
> > 
> > I take the liberty disturbing you. 
> > I am a friend from Taiwan. 
> > After reading your posts on Web, I know you are a professional 
> > communication designer. 
> > Now I am designing QPSK demodulator for wireless Lan with 
> verilog. 
> > Where can I find more helpful material, such as verilog code 
> for DPLL. 
> > Please kindly to give me some advice. 
> > Thank you a lot! 
> > 
> > 
> > 
> 
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