Hello. I got these question while viewing old articles. Could anyone please answer next two ? 1. Under what conditions is the available bandwidth of a digital system Fs Hz instead of Fs/2 Hz? 2. What two PSK modulation orders differ exactly by a factor of two in spectral efficiency? Many thanks !
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Started by ●August 3, 2005
Reply by ●August 3, 20052005-08-03
johny wrote:> > Hello. I got these question while viewing old articles. Could anyone > please answer next two ? > > 1. Under what conditions is the available bandwidth of a digital system > Fs Hz instead of Fs/2 Hz?If you are sampling a complex analytic signal.> 2. What two PSK modulation orders differ exactly by a factor of two > in spectral efficiency?I'll leave that for someone else. Erik -- +-----------------------------------------------------------+ Erik de Castro Lopo nospam@mega-nerd.com (Yes it's valid) +-----------------------------------------------------------+ "C++ is history repeated as tragedy. Java is history repeated as farce." -- Scott McKay
Reply by ●August 3, 20052005-08-03
Erik de Castro Lopo wrote:> johny wrote: > >>Hello. I got these question while viewing old articles. Could anyone >>please answer next two ? >> >>1. Under what conditions is the available bandwidth of a digital system >>Fs Hz instead of Fs/2 Hz? > > > If you are sampling a complex analytic signal.In other words, when each sample counts for two. ... Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●August 4, 20052005-08-04
On 3 Aug 2005 03:54:17 -0700, "johny" <miranda.wu@gmail.com> wrote:>Hello. I got these question while viewing old articles. Could anyone >please answer next two ? > >1. Under what conditions is the available bandwidth of a digital system >Fs Hz instead of Fs/2 Hz?Been addressed previously, so...>2. What two PSK modulation orders differ exactly by a factor of two >in spectral efficiency?There are only three PSK modes in common use, BPSK, QPSK, and 8-PSK (16-QAM, as well as higher orders, is more efficient than 16-PSK, so it kinda stops there). Of those, QPSK gets double the number of bits in the same bandwidth as BPSK. 8-PSK is three times BPSK, and 1.5 times QPSK. Or, to continue to beat the horse, BPSK, one bit per symbol QPSK, two bits per symbol 8-PSK, three bits per symbol The question as posed assumes the symbol rates are equivalent. Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
Reply by ●August 7, 20052005-08-07
But in fact there are more issues to consider here, such as error sensitivity (robustness), average power & SNR, etc. Eric Jacobsen wrote:> On 3 Aug 2005 03:54:17 -0700, "johny" <miranda.wu@gmail.com> wrote: > > >>Hello. I got these question while viewing old articles. Could anyone >>please answer next two ? >> >>1. Under what conditions is the available bandwidth of a digital system >>Fs Hz instead of Fs/2 Hz? > > > Been addressed previously, so... > > >>2. What two PSK modulation orders differ exactly by a factor of two >>in spectral efficiency? > > > There are only three PSK modes in common use, BPSK, QPSK, and 8-PSK > (16-QAM, as well as higher orders, is more efficient than 16-PSK, so > it kinda stops there). > > Of those, QPSK gets double the number of bits in the same bandwidth as > BPSK. 8-PSK is three times BPSK, and 1.5 times QPSK. > > Or, to continue to beat the horse, > > BPSK, one bit per symbol > QPSK, two bits per symbol > 8-PSK, three bits per symbol > > The question as posed assumes the symbol rates are equivalent. > > > > > Eric Jacobsen > Minister of Algorithms, Intel Corp. > My opinions may not be Intel's opinions. > http://www.ericjacobsen.org
Reply by ●August 8, 20052005-08-08
On Sun, 07 Aug 2005 05:19:02 GMT, NS <NS@NoSpam.com> wrote:>But in fact there are more issues to consider here, such as error >sensitivity (robustness), average power & SNR, etc.The question, copied from the OP, was just:>>>2. What two PSK modulation orders differ exactly by a factor of two >>>in spectral efficiency?Spectral efficiency in this sense is independent of the things you're mentioning.> > >Eric Jacobsen wrote: >> On 3 Aug 2005 03:54:17 -0700, "johny" <miranda.wu@gmail.com> wrote: >> >> >>>Hello. I got these question while viewing old articles. Could anyone >>>please answer next two ? >>> >>>1. Under what conditions is the available bandwidth of a digital system >>>Fs Hz instead of Fs/2 Hz? >> >> >> Been addressed previously, so... >> >> >>>2. What two PSK modulation orders differ exactly by a factor of two >>>in spectral efficiency? >> >> >> There are only three PSK modes in common use, BPSK, QPSK, and 8-PSK >> (16-QAM, as well as higher orders, is more efficient than 16-PSK, so >> it kinda stops there). >> >> Of those, QPSK gets double the number of bits in the same bandwidth as >> BPSK. 8-PSK is three times BPSK, and 1.5 times QPSK. >> >> Or, to continue to beat the horse, >> >> BPSK, one bit per symbol >> QPSK, two bits per symbol >> 8-PSK, three bits per symbol >> >> The question as posed assumes the symbol rates are equivalent. >> >> >> >> >> Eric Jacobsen >> Minister of Algorithms, Intel Corp. >> My opinions may not be Intel's opinions. >> http://www.ericjacobsen.orgEric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
