Changing the FEC to LDPC, help me convincing the RF Guy

Started by recoder April 28, 2009
Dear All,
 We have a Solar Power operated X Band qpsk transmitter in a remote
region.
The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps.
I want to increase the effective bitrate and improve BER by switching
to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also
the Project Manager).
 Since the device is Solar powered, the power consumption of the X
Band transmitter is critical. The RF Guy argued that there will be no
change in power consumption. I think he is too lazy to do the RF
design changes.
I am not sure but as the Bandwidth reduces to nearly the half, should
also the Microwave Transmitters power consumption drop???
 Please give an argument to convince the lazy RF guy, please please
pleaaaase...
On Apr 28, 5:20&#2013266080;am, recoder <kurtulmeh...@gmail.com> wrote:
> Dear All, > &#2013266080;We have a Solar Power operated X Band qpsk transmitter in a remote > region. > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. > I want to increase the effective bitrate and improve BER by switching > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also > the Project Manager). > &#2013266080;Since the device is Solar powered, the power consumption of the X > Band transmitter is critical. The RF Guy argued that there will be no > change in power consumption. I think he is too lazy to do the RF > design changes. > I am not sure but as the Bandwidth reduces to nearly the half, should > also the Microwave Transmitters power consumption drop??? > &#2013266080;Please give an argument to convince the lazy RF guy, please please > pleaaaase...
If the coding gain is increased by X dB, the transmit power can be decreased by X dB. John
On 28 Nisan, 12:38, John <sampson...@gmail.com> wrote:
> On Apr 28, 5:20&#2013266080;am, recoder <kurtulmeh...@gmail.com> wrote: > > > Dear All, > > &#2013266080;We have a Solar Power operated X Band qpsk transmitter in a remote > > region. > > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. > > I want to increase the effective bitrate and improve BER by switching > > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also > > the Project Manager). > > &#2013266080;Since the device is Solar powered, the power consumption of the X > > Band transmitter is critical. The RF Guy argued that there will be no > > change in power consumption. I think he is too lazy to do the RF > > design changes. > > I am not sure but as the Bandwidth reduces to nearly the half, should > > also the Microwave Transmitters power consumption drop??? > > &#2013266080;Please give an argument to convince the lazy RF guy, please please > > pleaaaase... > > If the coding gain is increased by X dB, the transmit power can be > decreased by X dB. > > John
The coding gain has not changed much, but the Bandwidth nearly halved. Assuming the output rf power is the same, will there be a drop in power consumption? Is there not a relationship with the RF Bandwidth to input power in a microwave amplifier?
On Apr 28, 5:57&#2013266080;am, recoder <kurtulmeh...@gmail.com> wrote:
> On 28 Nisan, 12:38, John <sampson...@gmail.com> wrote: > > > > > On Apr 28, 5:20&#2013266080;am, recoder <kurtulmeh...@gmail.com> wrote: > > > > Dear All, > > > &#2013266080;We have a Solar Power operated X Band qpsk transmitter in a
remote
> > > region. > > > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. > > > I want to increase the effective bitrate and improve BER by switching > > > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also > > > the Project Manager). > > > &#2013266080;Since the device is Solar powered, the power consumption of the
X
> > > Band transmitter is critical. The RF Guy argued that there will be no > > > change in power consumption. I think he is too lazy to do the RF > > > design changes. > > > I am not sure but as the Bandwidth reduces to nearly the half, should > > > also the Microwave Transmitters power consumption drop??? > > > &#2013266080;Please give an argument to convince the lazy RF guy, please
please
> > > pleaaaase... > > > If the coding gain is increased by X dB, the transmit power can be > > decreased by X dB. > > > John > > The coding gain has not changed much, but the Bandwidth nearly halved. > Assuming the output rf power is the same, will there be a drop in > power consumption? > Is there not a relationship with the RF Bandwidth to input power in a > microwave amplifier?
I don't believe there's any power-consumption gain by decreasing the bandwidth of the signal you're transmitting. However, while you may not have any additional coding gain, you will get a gain in signal-to- noise ratio due to the smaller bandwidth of your transmitted signal. Think of it like this: the power that your amplifier outputs is spread over a smaller bandwidth, so the ratio of the signal power to the noise power spectral density (assuming AWGN) in the signal's bandwidth is higher. Assuming you tighten up filters in the receiver to filter out the excess noise, you could then ostensibly cash in the gain in SNR for some savings in transmit power at the other end of the link. Jason
On Tue, 28 Apr 2009 02:57:13 -0700, recoder wrote:

> On 28 Nisan, 12:38, John <sampson...@gmail.com> wrote: >> On Apr 28, 5:20&nbsp;am, recoder <kurtulmeh...@gmail.com> wrote: >> >> > Dear All, >> > &nbsp;We have a Solar Power operated X Band qpsk transmitter in a remote >> > region. >> > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. I >> > want to increase the effective bitrate and improve BER by switching >> > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is >> > also the Project Manager). >> > &nbsp;Since the device is Solar powered, the power consumption of the X >> > Band transmitter is critical. The RF Guy argued that there will be no >> > change in power consumption. I think he is too lazy to do the RF >> > design changes. >> > I am not sure but as the Bandwidth reduces to nearly the half, should >> > also the Microwave Transmitters power consumption drop??? >> > &nbsp;Please give an argument to convince the lazy RF guy, please please >> > pleaaaase... >> >> If the coding gain is increased by X dB, the transmit power can be >> decreased by X dB. >> >> John > > The coding gain has not changed much, but the Bandwidth nearly halved. > Assuming the output rf power is the same, will there be a drop in power > consumption? > Is there not a relationship with the RF Bandwidth to input power in a > microwave amplifier?
The efficiency of the RF stage is more or less independent of the bandwidth, for all but really wideband signals (which these aren't). So no, neither the input nor output power will change with bandwidth. About the only gain that I can see is if the new modulation method that you propose gives a better SNR at the receiver because of the reduced bandwidth (I'm not familiar with the modulation); if this is the case then you could lower the transmit power (which isn't necessarily trivial if the RF stage is already designed and highly optimized) to get the same raw bit error rate and the same overall link performance. -- http://www.wescottdesign.com
STUPIDENT

recoder wrote:

> Dear All, > We have a Solar Power operated X Band qpsk transmitter in a remote > region. > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. > I want to increase the effective bitrate and improve BER by switching > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also > the Project Manager). > Since the device is Solar powered, the power consumption of the X > Band transmitter is critical. The RF Guy argued that there will be no > change in power consumption. I think he is too lazy to do the RF > design changes. > I am not sure but as the Bandwidth reduces to nearly the half, should > also the Microwave Transmitters power consumption drop??? > Please give an argument to convince the lazy RF guy, please please > pleaaaase...
Vladimir Vassilevsky wrote:
>> Dear All, >> We have a Solar Power operated X Band qpsk transmitter in a remote >> region. >> The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. >> I want to increase the effective bitrate and improve BER by switching >> to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also >> the Project Manager). >> Since the device is Solar powered, the power consumption of the X >> Band transmitter is critical. The RF Guy argued that there will be no >> change in power consumption. I think he is too lazy to do the RF >> design changes. >> I am not sure but as the Bandwidth reduces to nearly the half, should >> also the Microwave Transmitters power consumption drop??? >> Please give an argument to convince the lazy RF guy, please please >> pleaaaase...
> > STUPIDENT > > recoder wrote: > Vladimir, I'm happy for you that you're more perfect than God. But could you please not rub our noses in it? Perhaps you could start a 'comp.dsp.perfect-people-only' newsgroup. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Tue, 28 Apr 2009 02:57:13 -0700 (PDT), recoder
<kurtulmehtap@gmail.com> wrote:

>On 28 Nisan, 12:38, John <sampson...@gmail.com> wrote: >> On Apr 28, 5:20&#2013266080;am, recoder <kurtulmeh...@gmail.com> wrote: >> >> > Dear All, >> > &#2013266080;We have a Solar Power operated X Band qpsk transmitter in a
remote
>> > region. >> > The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. >> > I want to increase the effective bitrate and improve BER by switching >> > to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also >> > the Project Manager). >> > &#2013266080;Since the device is Solar powered, the power consumption of the X >> > Band transmitter is critical. The RF Guy argued that there will be no >> > change in power consumption. I think he is too lazy to do the RF >> > design changes. >> > I am not sure but as the Bandwidth reduces to nearly the half, should >> > also the Microwave Transmitters power consumption drop??? >> > &#2013266080;Please give an argument to convince the lazy RF guy, please
please
>> > pleaaaase... >> >> If the coding gain is increased by X dB, the transmit power can be >> decreased by X dB. >> >> John > >The coding gain has not changed much, but the Bandwidth nearly halved. >Assuming the output rf power is the same, will there be a drop in >power consumption? >Is there not a relationship with the RF Bandwidth to input power in a >microwave amplifier?
I'd think a good way to do the analysis that'd make sense to an RF guy is to do a full link budget analysis for both cases. The bandwidth reduction will provide some power concentration and the change in coding will also affect margin. The net affect is hard to say without knowing the specifics of the code performance. As has been mentioned, any net gain in link margin can be traded as a transmit power reduction. You might also consider that an LDPC encoder takes a lot more power to run than a Convolutional Encoder, which is trivial. If you want something that provides more gain but perhaps not as much power consumption in the modulator as an LDPC, you may want to look at Turbo Codes. In that case there's just two trivial convolutional encoders and an interleaver, which might be lower power consumption than an LDPC encoder. FWIW, if it were me I'd insist on something rigorous like a link budget analysis comparison before reaching a conclusion. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php
On Apr 28, 1:21&#2013266080;pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:

> You might also consider that an LDPC encoder takes a lot more power to > run than a Convolutional Encoder, which is trivial. &#2013266080; If you want > something that provides more gain but perhaps not as much power > consumption in the modulator as an LDPC, you may want to look at Turbo > Codes. &#2013266080; In that case there's just two trivial convolutional encoders > and an interleaver, which might be lower power consumption than an > LDPC encoder.
Eric, Is this necessarily true? I'd say that there are some LDPC codes with relatively low complexity (regular repeat-accumulate codes come to mind). In that case, yes, it's slightly more complex than a convolutional encoder, but not too much more so. Wouldn't the main driver for encoder complexity (I'm thinking of an FPGA implementation here) be the block size, which drives interleaver design and such? In that case, turbo codes would be approximately on the same footing as an LDPC code. Or I might be showing my ignorance. Jason
cincydsp@gmail.com wrote:
> On Apr 28, 1:21 pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote: > >> You might also consider that an LDPC encoder takes a lot more power to >> run than a Convolutional Encoder, which is trivial. If you want >> something that provides more gain but perhaps not as much power >> consumption in the modulator as an LDPC, you may want to look at Turbo >> Codes. In that case there's just two trivial convolutional encoders >> and an interleaver, which might be lower power consumption than an >> LDPC encoder. > > Eric, > > Is this necessarily true? I'd say that there are some LDPC codes with > relatively low complexity (regular repeat-accumulate codes come to > mind). In that case, yes, it's slightly more complex than a > convolutional encoder, but not too much more so. Wouldn't the main > driver for encoder complexity (I'm thinking of an FPGA implementation > here) be the block size, which drives interleaver design and such? In > that case, turbo codes would be approximately on the same footing as > an LDPC code. > > Or I might be showing my ignorance.
An interleaver wouldn't necessarily require much active logic -- just a honking big chunk of memory. That may or may not have much effect on power, depending on whether the FPGA is already chosen, how it's connected, and how hard you want to flog it when you use it. (I'm assuming an FPGA -- in the case of an ASIC it's probably easier, because you can just count up the number of gates you light up, instead of worrying about all the parasitic loads that an FPGA presents). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html