Explanation of using Gardner algorithm in Matlab code

[smallputin]

hello everybody,now i need to wirte the matlab code to realize timing recovery and baud recovery for qpsk signal.I have read the Garnder algorithm.But I can not apply it to code matlab program.anyone can draw code flow chart for me or explain the algorithm in detail.Thank you very much.

 

[fontp]

zero cross dpll bit

Use PLL after Gardner/ Like that

https://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=6742&objectType=file

or

https://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=10754&objectType=file

 

[priyankguddu]

what is zero cross dpll

Time recovery is easy , when you have data bits , you know the bit duration but its an integral value and you cannot find exacttly the zero crossing of the bits. So to find the zero crossing of the bits very pricisely you need the phase information (QPSK) and to know the phase exactly and to track it properly you need a PLL, Pll tracks the phase (zero crossing ) as it varies due to the noise in the communication channel, so QPSK modulation will provide with the phase information and PLL will track the phase , whos o/p u need to take and calculate exact timing for your synchronisation ..

If any doubts regarding the concept , I can help you, Implementation part is easy.. U need to design a DPLL .. of 2nd order ( order depends upon signal dynamics... i,e whether u r tracking ur signal sitting inside a moving car (2nd order) or a missile ( 4th order ) where there is accelaration / jerk..)

Once u decide the PLL order .. u need to determine the bandwith such that 3 sigma error in that should not be greater than 45 degree of phase else you will loose the lock)

I maynot able to provide you the matlab code but definetely the concept will help you in solving the problem


***PLEASE PRESS HELP IF U FEEL I WAS USEUL***

 

[smallputin]

matlab code for symbol timing recovery

i am puzzle about the Gardner algorithm to implement the timing recovery.can you explain it

 

[fontp]

zero crossing timing recovery

Idea is simple. You calculate timing error as

e = I(r-T/2)*(I(r)-I(r-T))+Q(r-T/2)*(Q(r)-Q(r-T))

and then you use PLL controlled by this signal

T-baud-interval

 

[smallputin]

zero crossing timing recovery

in one symbol period,if there is no zero-crossing point,what should I do?according to the gardner algorithm,in one symbol period,we should haver two zero-crossing points.Am I right?

 

[fontp]

zero crossing timing recovery

in one symbol period,if there is no zero-crossing point,what should I do?according to the gardner algorithm,in one symbol period,we should haver two zero-crossing points.Am I right?

Nothing. PLL low-pass filter will do if you once have no zero-crossing.
Positive and negative zero-crossings will be accumulated by low-pass filter with the same polarity

And you should be able to design PLL then