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ldpc
====


 LDPC codes are Low Density Parity Check codes used in favor of
convolutional codes. They are quite experimental and not widely
tested. Furthermore this module is not optimsed at all!


ldpc_decode
-----------

 Tries to decode the received slot. As it is really slow to do this,
this module should be SUBS_MSG_THREADed so that it has more than one
slot's time to decode.

Inputs:
	SYMBOL_COMPLEX

outputs:
	U8

Config:
	channel_param<double>: 0.07
		either 'p' for a BSC or 'a/variance' for AWGN

	channel_type<int>: 1
		The type of channel.
		1 - BSC ( Binary Symmetric Channel )
		2 - AWGN ( Average White Gaussian Noise )

	drop_blocks<int>: 0
		How many blocks to drop

	iterations<int>: 30
		The number of iterations that are done to decode the message.
		Each iteration contains a cnode->vnode->cnode cycle

	ldpc_code_id<int>: 1
		The index of the ldpc-code. For the moment, three codes
		are implemented:
		1 - rate .25, size 4000
		2 - rate .5, size 3992
		3 - rate .75, size 3992

	mafi<int>: -1
		Define the matched filter to calculate the correct a/variance


Stats:
	snr<double>:
		The calculated SNR in case of a AWGN channel


ldpc_encode
-----------

 Encodes a slot. Needs to have a modulator-module with a QPSK
modulation.

Inputs:
	U8

outputs:
	U8

Config:
	ldpc_code_id<int>: 1
		The index of the ldpc-code. For the moment, three codes
		are implemented:
		1 - rate .25, size 4000
		2 - rate .5, size 3992
		3 - rate .75, size 3992