Difference between CDMA pilot channel acquistion and tracking
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From: Laron on 26 Feb 2010 03:55 Hi all, Did acquisition and tracking with pilot channel sharing the same process in CDMA2000? the acquisition using xcorr find the coarse delay,but how does tracking action? Plan to using 8x oversampling,then fed the stream to a digital matched filter to find best one from the eight. But really have no idea with the tracking process, do i need to using xcorr again when tracking? or pass the eight stream to the digital matched filter to find the best one? when using 256bit DMF, case chip by chip input, tracking will cause the stream chosen vary frequency; case 256 size buffer,then block by block input, tracking will introduce a certain mount of delay. How should i do. Wish your idea and thanks a lot. B. R. Laron
From: John on 26 Feb 2010 05:33 On Feb 26, 3:50 am, "Laron" <jason.pi...(a)inbox.com> wrote: > Hi all, > > Did acquisition and tracking with pilot channel sharing the same > process in CDMA2000? the acquisition using xcorr find the coarse delay,but > how does tracking action? > Plan to using 8x oversampling,then fed the stream to a digital matched > filter to find best one from the eight. But really have no idea with the > tracking process, do i need to using xcorr again when tracking? or pass the > eight stream to the digital matched filter to find the best one? > when using 256bit DMF, case chip by chip input, tracking will cause the > stream chosen vary frequency; case 256 size buffer,then block by block > input, tracking will introduce a certain mount of delay. How should i do. > > Wish your idea and thanks a lot. > > B. R. > Laron The cross-correlation will need to run continuously, so that you get a new peak for each repetition of of the shortcode. John
From: Laron on 27 Feb 2010 19:00 >On Feb 26, 3:50=A0am, "Laron" <jason.pi...(a)inbox.com> wrote: >> Hi all, >> >> =A0 =A0 Did acquisition and tracking with pilot channel sharing the same >> process in CDMA2000? the acquisition using xcorr find the coarse delay,bu= >t >> how does tracking action? >> =A0 =A0 Plan to using 8x oversampling,then fed the stream to a digital ma= >tched >> filter to find best one from the eight. But really have no idea with the >> tracking process, do i need to using xcorr again when tracking? or pass t= >he >> eight stream to the digital matched filter to find the best one? >> when using 256bit DMF, case chip by chip input, tracking will cause the >> stream chosen vary frequency; case 256 size buffer,then block by block >> input, tracking will introduce a certain mount of delay. How should i do. >> >> Wish your idea and thanks a lot. >> >> B. R. >> Laron =A0 =A0 > >The cross-correlation will need to run continuously, so that you get a >new peak for each repetition of of the shortcode. > >John The 32768 xcorr will take a certain long time, should we all use the 32768 size xcorr during both acquisition and tracking, this will introduce certain amount of delay. Another question is when everytime xcorr, we get a new delay, then shall we shift the local generated pn sequence or shift the input data to align with local sequence when despreading? Thanks. B. R. Laron
From: John on 27 Feb 2010 20:02 On Feb 27, 7:00 pm, "Laron" <jason.pi...(a)inbox.com> wrote: > >On Feb 26, 3:50=A0am, "Laron" <jason.pi...(a)inbox.com> wrote: > >> Hi all, > > >> =A0 =A0 Did acquisition and tracking with pilot channel sharing the > same > >> process in CDMA2000? the acquisition using xcorr find the coarse > delay,bu= > >t > >> how does tracking action? > >> =A0 =A0 Plan to using 8x oversampling,then fed the stream to a digital > ma= > >tched > >> filter to find best one from the eight. But really have no idea with > the > >> tracking process, do i need to using xcorr again when tracking? or pass > t= > >he > >> eight stream to the digital matched filter to find the best one? > >> when using 256bit DMF, case chip by chip input, tracking will cause the > >> stream chosen vary frequency; case 256 size buffer,then block by block > >> input, tracking will introduce a certain mount of delay. How should i > do. > > >> Wish your idea and thanks a lot. > > >> B. R. > >> Laron =A0 =A0 > > >The cross-correlation will need to run continuously, so that you get a > >new peak for each repetition of of the shortcode. > > >John > > The 32768 xcorr will take a certain long time, should we all use the 32768 > size xcorr during both acquisition and tracking, this will introduce > certain amount of delay. > Another question is when everytime xcorr, we get a new delay, then shall > we shift the local generated pn sequence or shift the input data to align > with local sequence when despreading? > > Thanks. > B. R. > Laron Find the XC peak location and then thin off 32678 input samples (those that went into the XC) starting from the one at the peak location and striding by whatever your samples per chip is. Now you have a complex 32k vector that is aligned with the shortcode. You can get complex data symbols as sum(input x conj(sc * w64)) where sc is the shortcode, w64 is the walsh code, and input is your 32k vector. The sum is computed over blocks of N inputs depending on the symbol repetition. N might be 64 (no repetition, one symbol per walsh sequence) or 256 (one symbol per four walsh sequences). So you get a new symbol for every N symbols in the 32k inputs. Now comes the part you asked about earlier. You need to multiply these symbols by conj(pilot) to remove the phase & frequency offset. Pilot is just w0, so you can just compute a pilot symbol for every data symbol. HTH, John
From: Laron on 28 Feb 2010 00:44
>On Feb 27, 7:00=A0pm, "Laron" <jason.pi...(a)inbox.com> wrote: >> >On Feb 26, 3:50=3DA0am, "Laron" <jason.pi...(a)inbox.com> wrote: >> >> Hi all, >> >> >> =3DA0 =3DA0 Did acquisition and tracking with pilot channel sharing th= >e >> same >> >> process in CDMA2000? the acquisition using xcorr find the coarse >> delay,bu=3D >> >t >> >> how does tracking action? >> >> =3DA0 =3DA0 Plan to using 8x oversampling,then fed the stream to a dig= >ital >> ma=3D >> >tched >> >> filter to find best one from the eight. But really have no idea with >> the >> >> tracking process, do i need to using xcorr again when tracking? or pas= >s >> t=3D >> >he >> >> eight stream to the digital matched filter to find the best one? >> >> when using 256bit DMF, case chip by chip input, tracking will cause th= >e >> >> stream chosen vary frequency; case 256 size buffer,then block by block >> >> input, tracking will introduce a certain mount of delay. How should i >> do. >> >> >> Wish your idea and thanks a lot. >> >> >> B. R. >> >> Laron =3DA0 =3DA0 >> >> >The cross-correlation will need to run continuously, so that you get a >> >new peak for each repetition of of the shortcode. >> >> >John >> >> The 32768 xcorr will take a certain long time, should we all use the 3276= >8 >> size xcorr during both acquisition and tracking, this will introduce >> certain amount of delay. >> =A0 Another question is when everytime xcorr, we get a new delay, then sh= >all >> we shift the local generated pn sequence or shift the input data to align >> with local sequence when despreading? >> >> Thanks. >> B. R. >> Laron > >Find the XC peak location and then thin off 32678 input samples (those >that went into the XC) starting from the one at the peak location and >striding by whatever your samples per chip is. Now you have a complex >32k vector that is aligned with the shortcode. > >You can get complex data symbols as sum(input x conj(sc * w64)) where >sc is the shortcode, w64 is the walsh code, and input is your 32k >vector. The sum is computed over blocks of N inputs depending on the >symbol repetition. N might be 64 (no repetition, one symbol per walsh >sequence) or 256 (one symbol per four walsh sequences). So you get a >new symbol for every N symbols in the 32k inputs. > >Now comes the part you asked about earlier. You need to multiply these >symbols by conj(pilot) to remove the phase & frequency offset. Pilot >is just w0, so you can just compute a pilot symbol for every data >symbol. > >HTH, > >John Hi John That's very very helpful and a large step ahead. still 2 points confused me listed below. 1.Cause the pilot symbols(all zeros) only transmitted on I-channel and i q use different sequence, so how could we make out i channel's imagine part from the complex sampled data? 2.Cause the sync channel's frame head align with 1 after 15 consecutive zeros of short code, so we don't need to do symbol timing and just align walsh code with the short pn sequence, is this right? Thanks B. R. Laron |