OQPSK Constellation Display, how is it done?
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From: Mark on 23 Jun 2010 12:39 For standard QPSK, the I and Q channels are (conceptually speaking) displayed as XY on a scope and the scope beam is turned on at the symbol instant. Ideally the combination of I and Q will be at one of the 4 corner symbol locations during the symbol time. The scope beam can also be turned on dimly during the trajectory between symbol times....so far so good. Now for OQPSK, the I and Q symbols are staggered in time. So when the I channel is at its symbol value, the Q channel is in transition. The two channels are never both at the symbol value at the same time. So how does one create a constellation display for OQPSK showing the 4 symbol points? Does it require a 1/2 symbol delay to one channel? thanks Mark
From: Tim Wescott on 23 Jun 2010 13:20 On 06/23/2010 09:39 AM, Mark wrote: > For standard QPSK, the I and Q channels are (conceptually speaking) > displayed as XY on a scope and the scope beam is turned on at the > symbol instant. Ideally the combination of I and Q will be at one of > the 4 corner symbol locations during the symbol time. The scope beam > can also be turned on dimly during the trajectory between symbol > times....so far so good. > > Now for OQPSK, the I and Q symbols are staggered in time. So when the > I channel is at its symbol value, the Q channel is in transition. > The two channels are never both at the symbol value at the same > time. So how does one create a constellation display for OQPSK > showing the 4 symbol points? > > Does it require a 1/2 symbol delay to one channel? One would certainly assume so. I've always done this in digital-land, so I just show a scatter plot of the values of the channels at the sampling instants, which automagically takes care of the delay. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Eric Jacobsen on 24 Jun 2010 00:46 On Wed, 23 Jun 2010 09:39:13 -0700 (PDT), Mark <makolber(a)yahoo.com> wrote: >For standard QPSK, the I and Q channels are (conceptually speaking) >displayed as XY on a scope and the scope beam is turned on at the >symbol instant. Ideally the combination of I and Q will be at one of >the 4 corner symbol locations during the symbol time. The scope beam >can also be turned on dimly during the trajectory between symbol >times....so far so good. > >Now for OQPSK, the I and Q symbols are staggered in time. So when the >I channel is at its symbol value, the Q channel is in transition. >The two channels are never both at the symbol value at the same >time. So how does one create a constellation display for OQPSK >showing the 4 symbol points? > >Does it require a 1/2 symbol delay to one channel? > >thanks > >Mark Yes, typically the delay is removed so that it becomes equivalent to QPSK. The display is then identical to QPSK. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
From: Mark on 25 Jun 2010 12:14
On Jun 24, 12:46 am, eric.jacob...(a)ieee.org (Eric Jacobsen) wrote: > On Wed, 23 Jun 2010 09:39:13 -0700 (PDT), Mark <makol...(a)yahoo.com> > wrote: > > > > > > >For standard QPSK, the I and Q channels are (conceptually speaking) > >displayed as XY on a scope and the scope beam is turned on at the > >symbol instant. Ideally the combination of I and Q will be at one of > >the 4 corner symbol locations during the symbol time. The scope beam > >can also be turned on dimly during the trajectory between symbol > >times....so far so good. > > >Now for OQPSK, the I and Q symbols are staggered in time. So when the > >I channel is at its symbol value, the Q channel is in transition. > >The two channels are never both at the symbol value at the same > >time. So how does one create a constellation display for OQPSK > >showing the 4 symbol points? > > >Does it require a 1/2 symbol delay to one channel? > > >thanks > > >Mark > > Yes, typically the delay is removed so that it becomes equivalent to > QPSK. The display is then identical to QPSK. > > Eric Jacobsen > Minister of Algorithms > Abineau Communicationshttp://www.abineau.com- Hide quoted text - > > - Show quoted text - thank you thank you Mark |