I want to add a channel equalizer into my my BPSK receiver. I have a
confusion where to place this module. Either in pass-band or in
base-band? Currently my receiver performs following sequence of
1) The received pass-band signal r(t) is sampled at Fs (8 times the
symbol/bit rate fb) and demodulated using a Costas Loop carrier
recovery and LPF. This LPF filter gives a base-band stream, but still
2)The baseband stream at Fs, is Matched Filtered with a Root-Raised
Cosine filter operating at Fs.(A same RRC filter used to shape the
base-band pulse in the transmitter).
3)The output of the Matched filter is decimated to symbol rate fb,
under the control of a timing recovery loop.
4)These symbols at are fb are used for decisions.
Now where should i place an equalizer (if any?) ..should it be in the
pass-band? i.e. before the costas loop demodulation? or should it be
some where in baseband? like immediately before/after the Matched RRC
Any help would be highly appreciated.
Reply by Vladimir Vassilevsky●January 21, 20042004-01-21
> I want to add a channel equalizer into my my BPSK receiver.
Generally you don't need any equalization for BPSK.
> I have a
> confusion where to place this module. Either in pass-band or in
No difference. It is just the matter of convenience.
Make sure the equalizer don't interfere with the carrier and timing
DSP and Mixed Signal Design Consultant
Reply by JM●January 22, 20042004-01-22
> Generally you don't need any equalization for BPSK.
It depends on the channel you are looking at and the symbol period
(1/fb), not the modulation scheme. If your delay spread is no longer
negligible (in comparison to your symbol period) then you can suffer
the BER, or use some form of equalisation, or else consider
lengthening your symbol period by dropping the throughput or
multiplexing your throughput over multiple channels (OFDM?).
Granted BPSK shows favourable performance, when compared with other
modulations, [e.g. like QPSK,MSK in Chuang's 'The Effects of Time
Delay Spread on Portable Radio Communications Channels with Digital
Modulation', IEEE] but it still suffers.
From Rappaport('Wireless Communications', 1996, p.301), 'an equalizer
is usually implemented in baseband or IF in a receiver'. A good read.
hope this is of some help.
Reply by rider●January 23, 20042004-01-23
J_M_1967@hotmail.com (JM) wrote in message news:<firstname.lastname@example.org>...
> From Rappaport('Wireless Communications', 1996, p.301), 'an equalizer
> is usually implemented in baseband or IF in a receiver'. A good read.
> hope this is of some help.
Hi! Thans for everyone's replies. For an all digital BPSK receiver, If
I place the Equalizer in baseband, then what could be its exact
loaction: Is the following arrangement acceptable?
fs ------ fs ------ fs fb ------ fb -------
r(nTs)--->|DEMOD|----| MF |---/---| EQUZ |---|SLICER |--->
------ ------ ^ --- |- ------- |
^ | | |
| | `-----<---------`
| CR | | STR |
r(nTs)= Received pass-band Digital Samples at freq fs=1/Ts
fs = Sampling Frequency
fb = BPSK SYMBOL rate (bit rate) , fs >= 2.fb , fb=1/Tb , Tb=
DMOD= Mix with recovered carrier and LPF, operating freq=fs
CR= COSTAS LOOP CARRIER RECOVERY
MF=Root Raised Cosine Filter, operating at fs
STR= Symbol Timing recovery
EQUZ= Symbol Spaced Equalizer, operating at fb
SLICER= Hard decisions +/-1 V
1) Is this arrangement acceptable as one possible form of a BPSK
2) Since Equalizer is operating at Bit/Symbol rate fb, it is called a
Symbol rate equalizer. What if I want to use a FSE (Fractionally
Spaced Equalizer)? Say Tb/2 spaced(that Equalizer will give output at
rate fb=1/Tb). Where should i place it? Before the MF ? What would the
position of STR in that case(The output of FSE would already have
deimated to fb, so how to implement the STR)? Do i have to move STR in