Forums

The effect of hand around the antenna of a digital transceiver

Started by ytach February 20, 2009
Hello Guys,

I have built a basic DBPSK transceiver and I was verifying the
implementation when I found out that when I put my hand on the antenna, the
signal error rate goes up big time. My question to you guys, is it possible
to implement a basic DBPSK transceiver with no error correction or
equalization or AGC and yet can sustain the multipath and attenuation
effect of placing hand around the antenna? When do I need really these
components (Please guys let me know if my assumptions below are wrong):

1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go
from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are
fixed in place I did not implement AGC.

2- Synchronizer : I did not implement carrier equalization because I am
using differential coding so I can live without carrier synch with loss 3
dB. and I did not implement the symbol synch because I am clocking both TX
and RX from the same source so I do not need timing extraction.

3- Equalizer
The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt
cosine pulse shaping) which I am assuming less than the channel bandwidth
coherency in indoor environment so an equalizer can be ignored.

Is it is really possible to implement DBPSK in an indoor environment and
receive good BER without the components mentioned above? 

I am ready to provide any further technical details as needed and would
appreciate sharing your experience with me
>Hello Guys, > >I have built a basic DBPSK transceiver and I was verifying the >implementation when I found out that when I put my hand on the antenna,
the
>signal error rate goes up big time. My question to you guys, is it
possible
>to implement a basic DBPSK transceiver with no error correction or >equalization or AGC and yet can sustain the multipath and attenuation >effect of placing hand around the antenna? When do I need really these >components (Please guys let me know if my assumptions below are wrong): > >1- AGC : The TX and RX are so close (15 cm apart) and the TX power can
go
>from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are >fixed in place I did not implement AGC. > >2- Synchronizer : I did not implement carrier equalization because I am >using differential coding so I can live without carrier synch with loss
3
>dB. and I did not implement the symbol synch because I am clocking both
TX
>and RX from the same source so I do not need timing extraction. > >3- Equalizer >The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt >cosine pulse shaping) which I am assuming less than the channel
bandwidth
>coherency in indoor environment so an equalizer can be ignored. > >Is it is really possible to implement DBPSK in an indoor environment and >receive good BER without the components mentioned above? > >I am ready to provide any further technical details as needed and would >appreciate sharing your experience with me >
It might be that my question is a little unusual or seems too simple. But this implementation is done on a software radio platform and I am trying to get a sense of how good is the basic implementation done so far. It is really a nagging question for me to know if it is possible to have a basic PSK transceiver at this rate with good BER without implementing AGC, quantizer and with perfect timing synchronization. Does anybody have any idea?
On Feb 20, 7:31&#2013266080;pm, "ytach" <ytachw...@ou.edu> wrote:
> Hello Guys, > > I have built a basic DBPSK transceiver and I was verifying the > implementation when I found out that when I put my hand on the antenna, the > signal error rate goes up big time. My question to you guys, is it possible > to implement a basic DBPSK transceiver with no error correction or > equalization or AGC and yet can sustain the multipath and attenuation > effect of placing hand around the antenna? When do I need really these > components (Please guys let me know if my assumptions below are wrong): > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > fixed in place I did not implement AGC.
you probably don't need an AGC if nothing ever moves, but if you're going to wrap your hand around on of the ants, then you need an AGC. On the other hand, AGC is easy and could help a lot, why not put it in?
> > 2- Synchronizer : I did not implement carrier equalization because I am > using differential coding so I can live without carrier synch with loss 3 > dB. and I did not implement the symbol synch because I am clocking both TX > and RX from the same source so I do not need timing extraction. >
probably correct
> 3- Equalizer > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > cosine pulse shaping) which I am assuming less than the channel bandwidth > coherency in indoor environment so an equalizer can be ignored. >
probabyl correct
> Is it is really possible to implement DBPSK in an indoor environment and > receive good BER without the components mentioned above?
if the Tx and Rx are a fixed 15 cm apart, probably yes ... if by "indoor env" you mean moving around through various rooms then probabyl no.
> > I am ready to provide any further technical details as needed and would > appreciate sharing your experience with me
Your post exposes utter cluelessness and the total mix-up in your head.
Start with the basics:  something like 555 timer and flashing LED.

VLV




"ytach" <ytachwali@ou.edu> wrote in message
news:qMedndTRFu731gLUnZ2dnUVZ_tjinZ2d@giganews.com...
> Hello Guys, > > I have built a basic DBPSK transceiver and I was verifying the > implementation when I found out that when I put my hand on the antenna,
the
> signal error rate goes up big time. My question to you guys, is it
possible
> to implement a basic DBPSK transceiver with no error correction or > equalization or AGC and yet can sustain the multipath and attenuation > effect of placing hand around the antenna? When do I need really these > components (Please guys let me know if my assumptions below are wrong): > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > fixed in place I did not implement AGC. > > 2- Synchronizer : I did not implement carrier equalization because I am > using differential coding so I can live without carrier synch with loss 3 > dB. and I did not implement the symbol synch because I am clocking both TX > and RX from the same source so I do not need timing extraction. > > 3- Equalizer > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > cosine pulse shaping) which I am assuming less than the channel bandwidth > coherency in indoor environment so an equalizer can be ignored. > > Is it is really possible to implement DBPSK in an indoor environment and > receive good BER without the components mentioned above? > > I am ready to provide any further technical details as needed and would > appreciate sharing your experience with me
"ytach" <ytachwali@ou.edu> wrote in message
news:s6udnTxFlaJ2LwLUnZ2dnUVZ_uCdnZ2d@giganews.com...
> >Hello Guys, > > > It might be that my question is a little unusual or seems too simple. But > this implementation is done on a software radio platform and I am trying
to
> get a sense of how good is the basic implementation done so far. It is > really a nagging question for me to know if it is possible to have a basic > PSK transceiver at this rate with good BER without implementing AGC, > quantizer and with perfect timing synchronization. Does anybody have any > idea?
Get off the tree and learn how to walk first. VLV
ytach schrieb:
> Hello Guys, > > I have built a basic DBPSK transceiver and I was verifying the > implementation when I found out that when I put my hand on the antenna, the > signal error rate goes up big time. My question to you guys, is it possible > to implement a basic DBPSK transceiver with no error correction or > equalization or AGC and yet can sustain the multipath and attenuation > effect of placing hand around the antenna? When do I need really these > components (Please guys let me know if my assumptions below are wrong): > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > fixed in place I did not implement AGC. > > 2- Synchronizer : I did not implement carrier equalization because I am > using differential coding so I can live without carrier synch with loss 3 > dB. and I did not implement the symbol synch because I am clocking both TX > and RX from the same source so I do not need timing extraction. > > 3- Equalizer > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > cosine pulse shaping) which I am assuming less than the channel bandwidth > coherency in indoor environment so an equalizer can be ignored. > > Is it is really possible to implement DBPSK in an indoor environment and > receive good BER without the components mentioned above? > > I am ready to provide any further technical details as needed and would > appreciate sharing your experience with me
Well I try to post something constructive: If the RX and TX are only 15cm apart I suspect the RX is in the near-field of the TX (depending on your used carrier frequency), so all your nice models for multi-path propagation that hold for plane waves won't fit any longer. By the way only comparing the BER does not give you much insight about what really happened to your signal. Try to compare the transmitted and received bitstream (in time and frequency domain) to gain some more insight about what happened to your signal on the way from the TX to the RX . Greetz, Sebastian
On Feb 20, 7:31&#2013266080;pm, "ytach" <ytachw...@ou.edu> wrote:
> Hello Guys, > > I have built a basic DBPSK transceiver and I was verifying the > implementation when I found out that when I put my hand on the antenna, the > signal error rate goes up big time. My question to you guys, is it possible > to implement a basic DBPSK transceiver with no error correction or > equalization or AGC and yet can sustain the multipath and attenuation > effect of placing hand around the antenna? When do I need really these > components (Please guys let me know if my assumptions below are wrong): > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > fixed in place I did not implement AGC. > > 2- Synchronizer : I did not implement carrier equalization because I am > using differential coding so I can live without carrier synch with loss 3 > dB. and I did not implement the symbol synch because I am clocking both TX > and RX from the same source so I do not need timing extraction. > > 3- Equalizer > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > cosine pulse shaping) which I am assuming less than the channel bandwidth > coherency in indoor environment so an equalizer can be ignored. > > Is it is really possible to implement DBPSK in an indoor environment and > receive good BER without the components mentioned above? > > I am ready to provide any further technical details as needed and would > appreciate sharing your experience with me
A dose of reality: if you are clocking the TX and RX off of the same source, that implies some sort of physical connection between the two devices. If that's available, why not use that connection to carry your DBPSK signal instead? What I'm getting at is that you will (almost) never have perfect time synchronization. Your other questions, as to what you can "get away without having," will have differing answers depending upon the exact topology of your system; there's no single answer. You seem to have a basic communications system in place, which will work in the presence of AWGN and no channel dispersion or attenuation. Those additional challenges require solutions to combat them, so the answers to your questions are "yes, you need AGC/equalization/time sychronization" if the structure of your system demands it. Jason
On Fri, 20 Feb 2009 18:31:38 -0600, "ytach" <ytachwali@ou.edu> wrote:

>Hello Guys, > >I have built a basic DBPSK transceiver and I was verifying the >implementation when I found out that when I put my hand on the antenna, the >signal error rate goes up big time. My question to you guys, is it possible >to implement a basic DBPSK transceiver with no error correction or >equalization or AGC and yet can sustain the multipath and attenuation >effect of placing hand around the antenna? When do I need really these >components (Please guys let me know if my assumptions below are wrong):
Your physically touching the antenna? Depending on how your receiver is built you're probably screwing up the input impedance or something. As Sebastian mentioned, your antennas may already be in near-field, and your hand certainly is if you're touching the antenna. At that point, all bets are off.
>1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go >from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are >fixed in place I did not implement AGC.
Even wired systems implement AGC. AGC is pretty fundamental to getting deterministic receiver response. Deleting it implies that the operating conditions are unusually stable, and for a wireless system that means nothing changes in the environment, no people moving around, nobody ever opens or closes a door, etc., etc.
>2- Synchronizer : I did not implement carrier equalization because I am >using differential coding so I can live without carrier synch with loss 3 >dB. and I did not implement the symbol synch because I am clocking both TX >and RX from the same source so I do not need timing extraction.
As previously mentioned, use the timing connection to carry the data.
>3- Equalizer >The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt >cosine pulse shaping) which I am assuming less than the channel bandwidth >coherency in indoor environment so an equalizer can be ignored.
Maybe. Maybe not.
>Is it is really possible to implement DBPSK in an indoor environment and >receive good BER without the components mentioned above?
IMHO not for any practical application. If the connection exists for the synchronization, that's probably a good connection to use for the data, too. AGC is fundamental. Only in very unusual circumstances can you get away without an AGC if you want a practical system. Study "dynamic range" in receivers. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php
On Feb 21, 7:20&#2013266080;am, makol...@yahoo.com wrote:
> On Feb 20, 7:31&#2013266080;pm, "ytach" <ytachw...@ou.edu> wrote: > > > Hello Guys, > > > I have built a basic DBPSK transceiver and I was verifying the > > implementation when I found out that when I put my hand on the antenna, the > > signal error rate goes up big time. My question to you guys, is it possible > > to implement a basic DBPSK transceiver with no error correction or > > equalization or AGC and yet can sustain the multipath and attenuation > > effect of placing hand around the antenna? When do I need really these > > components (Please guys let me know if my assumptions below are wrong): > > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > > fixed in place I did not implement AGC. > > you probably don't need an AGC if nothing ever moves, but if you're > going to wrap your hand around on of the ants, then you need an AGC. > On the other hand, AGC is easy and could help a lot, why not put it > in? >
Thank you for the advice. I will be looking into the implementation of AGC. I am building the transceiver step by step and I want to make sure that I will not be adding AGC on top of a transceiver that was not built correctly. As a matter of fact, I have tried to connect the output of the DAC of the TX to the ADC of the RX (Since TX and RX are so close) and the receiver is working perfect with no problem (yes the connection here is pretty stable) but when I go wireless by connecting the digital converters to RF boards, then I have this problem at the receive, but you probably right since sometimes I can fix the receiption by tuning "manually" the gains of TX and RX but not always that works which makes me skiptical alittle bit and wondering what else could be wrong.
> > > > 2- Synchronizer : I did not implement carrier equalization because I am > > using differential coding so I can live without carrier synch with loss 3 > > dB. and I did not implement the symbol synch because I am clocking both TX > > and RX from the same source so I do not need timing extraction. > > probably correct > > > 3- Equalizer > > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > > cosine pulse shaping) which I am assuming less than the channel bandwidth > > coherency in indoor environment so an equalizer can be ignored. > > probabyl correct > > > Is it is really possible to implement DBPSK in an indoor environment and > > receive good BER without the components mentioned above? > > if the Tx and Rx are a fixed 15 cm apart, probably yes ... > if by "indoor env" you mean moving around through various rooms &#2013266080;then > probabyl no.
I am at the prototyping stage and both TX and RX are at the same room facing each other. so I "feel" that I should be able to establish pretty stable connection at such environment with noise immune modulation such as BPSK. If any clues from your experience could be shared I will be very greatful. Thank you very much for your reply.
> > > > > > > I am ready to provide any further technical details as needed and would > > appreciate sharing your experience with me- Hide quoted text - > > - Show quoted text -
On Feb 21, 8:44&#2013266080;am, Sebastian Doht <seb_d...@lycos.com> wrote:
> ytach schrieb: > > > > > > > Hello Guys, > > > I have built a basic DBPSK transceiver and I was verifying the > > implementation when I found out that when I put my hand on the antenna, the > > signal error rate goes up big time. My question to you guys, is it possible > > to implement a basic DBPSK transceiver with no error correction or > > equalization or AGC and yet can sustain the multipath and attenuation > > effect of placing hand around the antenna? When do I need really these > > components (Please guys let me know if my assumptions below are wrong): > > > 1- AGC : The TX and RX are so close (15 cm apart) and the TX power can go > > from -6dBm to 6 dBm and I am sending at -3 dBm. since the TX and RX are > > fixed in place I did not implement AGC. > > > 2- Synchronizer : I did not implement carrier equalization because I am > > using differential coding so I can live without carrier synch with loss 3 > > dB. and I did not implement the symbol synch because I am clocking both TX > > and RX from the same source so I do not need timing extraction. > > > 3- Equalizer > > The bandwidth of my signal is around 400kHz (using BPSK and 0.5 sqrt > > cosine pulse shaping) which I am assuming less than the channel bandwidth > > coherency in indoor environment so an equalizer can be ignored. > > > Is it is really possible to implement DBPSK in an indoor environment and > > receive good BER without the components mentioned above? > > > I am ready to provide any further technical details as needed and would > > appreciate sharing your experience with me > > Well I try to post something constructive: > If the RX and TX are only 15cm apart I suspect the RX is in the > near-field of the TX (depending on your used carrier frequency), so all > your nice models for multi-path propagation that hold for plane waves > won't fit any longer. By the way only comparing the BER does not give > you much insight about what really happened to your signal. Try to > compare the transmitted and received bitstream (in time and frequency > domain) to gain some more insight about what happened to your signal on > the way from the TX to the RX . > > Greetz, > Sebastian- Hide quoted text - > > - Show quoted text -
That is a good clue regarding the model of wireless channel in that range. I will be looking into it. I have simulated my design on a AWGN channel and it is working fine. (yes AWGN is basic but for a controlled setup like that where no mobility exists then I am assuming it is a reasonable test). and you are abosolutely right regarding looking at the bitstream. As a matter of fact, I tried different bitstreams to transmit to have a clue about what is going on. For example, I tried to send a stream of bytes of the value 1 to check if I am having framing synchronization problem, so if I received at the end a stream of 2 or 8 or 16 ... etc then I am having a problem with my framing and the error I am getting is due to frame synching. I am not doing yet any framing synch techniques such as using preamble, I have just added a delay that compensate the delay between TX and RX. I am sure that I need to do a frame synch later but since I am building the transceiver step by step, I am trying to verify that I am going to the right direction. Having said that, it turns out that there is no frame synch problem and the errors are quit random. Do you have any suggestions on what I can conclude from the bit stream? Thank you for your reply.