Help! Difference between Walsh and Hadamard Codes?

Hello I hope you're all doing fine

Now, my question is, what is the difference between Walsh codes and
Hadamard
codes and the so-called Walsh-Hadamard codes, they all look the same
to me.

Can some one explain?

Also, something that has been nagging me for a while, that we scramle
our spread
data because:

1) We dont have too many orthogonal codes and after scrambling we can
re-use
them in next BS

2) Secondly, orthogonal codes lose their orthogonality under multipath
conditions, where after the detrimental effects of multipath the codes
have
non-zero cross correlation. So, my question is that "Is this also a
MAJOR reason
why we need to have scramling on top of spreading? since 'time shifted
versions
of pn sequences has little correlation'"

3) Orthogonal sequences, when time-shifted have very large cross-
correlation value and therefore become unsuitable to use in practical
wireless system with multi-paths and time synch problems and therefore
NEED pn scrambling to help these orthogonal codes, which as I
mentioned have little correlation pn after time shift

Please correct my statements if there are incorrect or deviate from
the point

Thanks and Cheers to all my fellow group members

On Mar 15, 10:13�am, Communications_engineer
<communications_engin...@yahoo.com> wrote:
> Hello I hope you're all doing fine
>
> Now, my question is, what is the difference between Walsh codes and
> Hadamard
> codes and the so-called Walsh-Hadamard codes, they all look the same
> to me.
>
> Can some one explain?

I believe they are the same thing.  Walsh codes come from Walsh
functions,
which is used to compute the Hadamard transform.

>
> Also, something that has been nagging me for a while, that we scramle
> our spread
> data because:

I don't understand what you mean by "scramle our spread data," can
you explain this again please.  Scrambling of a sequence of data
bits is used typically so that the output of the scrambler is equi-
probable.
This helps with synchronization and spectrum shaping to avoid
harmonics.

>
> 1) We dont have too many orthogonal codes and after scrambling we can
> re-use
> them in next BS

Yes, the number of orthogonal codes is limited by the length of
the sequences.

>
> 2) Secondly, orthogonal codes lose their orthogonality under multipath
> conditions, where after the detrimental effects of multipath the codes
> have
> non-zero cross correlation. So, my question is that "Is this also a
> MAJOR reason
> why we need to have scramling on top of spreading? since 'time shifted
> versions
> of pn sequences has little correlation'"

Probably because of what I said above.

But you are correct that orthogonality is lost not only because of
multipath, but also because of synchronization mismatch.
There's a huge treatment on this by researchers of "multiuser
detection".

>
> 3) Orthogonal sequences, when time-shifted have very large cross-
> correlation value and therefore become unsuitable to use in practical
> wireless system with multi-paths and time synch problems and therefore
> NEED pn scrambling to help these orthogonal codes, which as I
> mentioned have little correlation pn after time shift

To some extent, yes, but you have to state this quantitatively.
Nothing is perfect and nothing comes for free.  The cost-benefit is
what matters.

>
> Please correct my statements if there are incorrect or deviate from
> the point
>
> Thanks and Cheers to all my fellow group members

On Mar 18, 5:35=A0pm, julius <juli...@gmail.com> wrote:
> On Mar 15, 10:13=A0am, Communications_engineer
>
> <communications_engin...@yahoo.com> wrote:
> > Hello I hope you're all doing fine
>
> > Now, my question is, what is the difference between Walsh codes and
> > Hadamard
> > codes and the so-called Walsh-Hadamard codes, they all look the same
> > to me.
>
> > Can some one explain?
>
> I believe they are the same thing. =A0Walsh codes come from Walsh
> functions,
> which is used to compute the Hadamard transform.
>
>
>
> > Also, something that has been nagging me for a while, that we scramle
> > our spread
> > data because:
>
> I don't understand what you mean by "scramle our spread data," can
> you explain this again please. =A0Scrambling of a sequence of data
> bits is used typically so that the output of the scrambler is equi-
> probable.
> This helps with synchronization and spectrum shaping to avoid
> harmonics.
>
>
>
> > 1) We dont have too many orthogonal codes and after scrambling we can
> > re-use
> > them in next BS
>
> Yes, the number of orthogonal codes is limited by the length of
> the sequences.
>
>
>
> > 2) Secondly, orthogonal codes lose their orthogonality under multipath
> > conditions, where after the detrimental effects of multipath the codes
> > have
> > non-zero cross correlation. So, my question is that "Is this also a
> > MAJOR reason
> > why we need to have scramling on top of spreading? since 'time shifted
> > versions
> > of pn sequences has little correlation'"
>
> Probably because of what I said above.
>
> But you are correct that orthogonality is lost not only because of
> multipath, but also because of synchronization mismatch.
> There's a huge treatment on this by researchers of "multiuser
> detection".
>
>
>
> > 3) Orthogonal sequences, when time-shifted have very large cross-
> > correlation value and therefore become unsuitable to use in practical
> > wireless system with multi-paths and time synch problems and therefore
> > NEED pn scrambling to help these orthogonal codes, which as I
> > mentioned have little correlation pn after time shift
>
> To some extent, yes, but you have to state this quantitatively.
> Nothing is perfect and nothing comes for free. =A0The cost-benefit is
> what matters.
>
>
>
> > Please correct my statements if there are incorrect or deviate from
> > the point
>
> > Thanks and Cheers to all my fellow group members

Thanks SC, I owe you

Now, just as a suggestion, what are the future mobile wireless
technologies (I have 4G in my mind) for multiple access.

Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
confused about OFDM and OFDMA, I'll have to read some posts over here
regarding the topic), some people have also suggested IDMA and MC-
IDMA. CDMA seems to have missed out. What do you think?

On Mar 18, 5:35&#4294967295;pm, julius <juli...@gmail.com> wrote:
> On Mar 15, 10:13&#4294967295;am, Communications_engineer
>
> <communications_engin...@yahoo.com> wrote:
> > Hello I hope you're all doing fine
>
> > Now, my question is, what is the difference between Walsh codes and
> > Hadamard
> > codes and the so-called Walsh-Hadamard codes, they all look the same
> > to me.
>
> > Can some one explain?
>
> I believe they are the same thing. &#4294967295;Walsh codes come from Walsh
> functions,
> which is used to compute the Hadamard transform.
>
>
>
> > Also, something that has been nagging me for a while, that we scramle
> > our spread
> > data because:
>
> I don't understand what you mean by "scramle our spread data," can
> you explain this again please. &#4294967295;Scrambling of a sequence of data
> bits is used typically so that the output of the scrambler is equi-
> probable.
> This helps with synchronization and spectrum shaping to avoid
> harmonics.
>
>
>
> > 1) We dont have too many orthogonal codes and after scrambling we can
> > re-use
> > them in next BS
>
> Yes, the number of orthogonal codes is limited by the length of
> the sequences.
>
>
>
> > 2) Secondly, orthogonal codes lose their orthogonality under multipath
> > conditions, where after the detrimental effects of multipath the codes
> > have
> > non-zero cross correlation. So, my question is that "Is this also a
> > MAJOR reason
> > why we need to have scramling on top of spreading? since 'time shifted
> > versions
> > of pn sequences has little correlation'"
>
> Probably because of what I said above.
>
> But you are correct that orthogonality is lost not only because of
> multipath, but also because of synchronization mismatch.
> There's a huge treatment on this by researchers of "multiuser
> detection".
>
>
>
> > 3) Orthogonal sequences, when time-shifted have very large cross-
> > correlation value and therefore become unsuitable to use in practical
> > wireless system with multi-paths and time synch problems and therefore
> > NEED pn scrambling to help these orthogonal codes, which as I
> > mentioned have little correlation pn after time shift
>
> To some extent, yes, but you have to state this quantitatively.
> Nothing is perfect and nothing comes for free. &#4294967295;The cost-benefit is
> what matters.
>
>
>
> > Please correct my statements if there are incorrect or deviate from
> > the point
>
> > Thanks and Cheers to all my fellow group members

Thanks SC, I owe you

Now, just as a suggestion, what are the future mobile wireless
technologies (I have 4G in my mind) for multiple access.

Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
confused about OFDM and OFDMA, I'll have to read some posts over here
regarding the topic), some people have also suggested IDMA and MC-
IDMA. CDMA seems to have missed out. What do you think?

On Mar 18, 5:35=A0pm, julius <juli...@gmail.com> wrote:
> On Mar 15, 10:13=A0am, Communications_engineer
>
> <communications_engin...@yahoo.com> wrote:
> > Hello I hope you're all doing fine
>
> > Now, my question is, what is the difference between Walsh codes and
> > Hadamard
> > codes and the so-called Walsh-Hadamard codes, they all look the same
> > to me.
>
> > Can some one explain?
>
> I believe they are the same thing. =A0Walsh codes come from Walsh
> functions,
> which is used to compute the Hadamard transform.
>
>
>
> > Also, something that has been nagging me for a while, that we scramle
> > our spread
> > data because:
>
> I don't understand what you mean by "scramle our spread data," can
> you explain this again please. =A0Scrambling of a sequence of data
> bits is used typically so that the output of the scrambler is equi-
> probable.
> This helps with synchronization and spectrum shaping to avoid
> harmonics.
>
>
>
> > 1) We dont have too many orthogonal codes and after scrambling we can
> > re-use
> > them in next BS
>
> Yes, the number of orthogonal codes is limited by the length of
> the sequences.
>
>
>
> > 2) Secondly, orthogonal codes lose their orthogonality under multipath
> > conditions, where after the detrimental effects of multipath the codes
> > have
> > non-zero cross correlation. So, my question is that "Is this also a
> > MAJOR reason
> > why we need to have scramling on top of spreading? since 'time shifted
> > versions
> > of pn sequences has little correlation'"
>
> Probably because of what I said above.
>
> But you are correct that orthogonality is lost not only because of
> multipath, but also because of synchronization mismatch.
> There's a huge treatment on this by researchers of "multiuser
> detection".
>
>
>
> > 3) Orthogonal sequences, when time-shifted have very large cross-
> > correlation value and therefore become unsuitable to use in practical
> > wireless system with multi-paths and time synch problems and therefore
> > NEED pn scrambling to help these orthogonal codes, which as I
> > mentioned have little correlation pn after time shift
>
> To some extent, yes, but you have to state this quantitatively.
> Nothing is perfect and nothing comes for free. =A0The cost-benefit is
> what matters.
>
>
>
> > Please correct my statements if there are incorrect or deviate from
> > the point
>
> > Thanks and Cheers to all my fellow group members

Thanks SC, I owe you

Now, just as a suggestion, what are the future mobile wireless
technologies (I have 4G in my mind) for multiple access.

Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
confused about OFDM and OFDMA, I'll have to read some posts over here
regarding the topic), some people have also suggested IDMA and MC-
IDMA. CDMA seems to have missed out. What do you think?

On Mar 18, 5:35=A0pm, julius <juli...@gmail.com> wrote:
> On Mar 15, 10:13=A0am, Communications_engineer
>
> <communications_engin...@yahoo.com> wrote:
> > Hello I hope you're all doing fine
>
> > Now, my question is, what is the difference between Walsh codes and
> > Hadamard
> > codes and the so-called Walsh-Hadamard codes, they all look the same
> > to me.
>
> > Can some one explain?
>
> I believe they are the same thing. =A0Walsh codes come from Walsh
> functions,
> which is used to compute the Hadamard transform.
>
>
>
> > Also, something that has been nagging me for a while, that we scramle
> > our spread
> > data because:
>
> I don't understand what you mean by "scramle our spread data," can
> you explain this again please. =A0Scrambling of a sequence of data
> bits is used typically so that the output of the scrambler is equi-
> probable.
> This helps with synchronization and spectrum shaping to avoid
> harmonics.
>
>
>
> > 1) We dont have too many orthogonal codes and after scrambling we can
> > re-use
> > them in next BS
>
> Yes, the number of orthogonal codes is limited by the length of
> the sequences.
>
>
>
> > 2) Secondly, orthogonal codes lose their orthogonality under multipath
> > conditions, where after the detrimental effects of multipath the codes
> > have
> > non-zero cross correlation. So, my question is that "Is this also a
> > MAJOR reason
> > why we need to have scramling on top of spreading? since 'time shifted
> > versions
> > of pn sequences has little correlation'"
>
> Probably because of what I said above.
>
> But you are correct that orthogonality is lost not only because of
> multipath, but also because of synchronization mismatch.
> There's a huge treatment on this by researchers of "multiuser
> detection".
>
>
>
> > 3) Orthogonal sequences, when time-shifted have very large cross-
> > correlation value and therefore become unsuitable to use in practical
> > wireless system with multi-paths and time synch problems and therefore
> > NEED pn scrambling to help these orthogonal codes, which as I
> > mentioned have little correlation pn after time shift
>
> To some extent, yes, but you have to state this quantitatively.
> Nothing is perfect and nothing comes for free. =A0The cost-benefit is
> what matters.
>
>
>
> > Please correct my statements if there are incorrect or deviate from
> > the point
>
> > Thanks and Cheers to all my fellow group members

Thanks SC, I owe you

Now, just as a suggestion, what are the future mobile wireless
technologies (I have 4G in my mind) for multiple access.

Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
confused about OFDM and OFDMA, I'll have to read some posts over here
regarding the topic), some people have also suggested IDMA and MC-
IDMA. CDMA seems to have missed out. What do you think?

On Mar 18, 5:35&#4294967295;pm, julius <juli...@gmail.com> wrote:
> On Mar 15, 10:13&#4294967295;am, Communications_engineer
>
> <communications_engin...@yahoo.com> wrote:
> > Hello I hope you're all doing fine
>
> > Now, my question is, what is the difference between Walsh codes and
> > Hadamard
> > codes and the so-called Walsh-Hadamard codes, they all look the same
> > to me.
>
> > Can some one explain?
>
> I believe they are the same thing. &#4294967295;Walsh codes come from Walsh
> functions,
> which is used to compute the Hadamard transform.
>
>
>
> > Also, something that has been nagging me for a while, that we scramle
> > our spread
> > data because:
>
> I don't understand what you mean by "scramle our spread data," can
> you explain this again please. &#4294967295;Scrambling of a sequence of data
> bits is used typically so that the output of the scrambler is equi-
> probable.
> This helps with synchronization and spectrum shaping to avoid
> harmonics.
>
>
>
> > 1) We dont have too many orthogonal codes and after scrambling we can
> > re-use
> > them in next BS
>
> Yes, the number of orthogonal codes is limited by the length of
> the sequences.
>
>
>
> > 2) Secondly, orthogonal codes lose their orthogonality under multipath
> > conditions, where after the detrimental effects of multipath the codes
> > have
> > non-zero cross correlation. So, my question is that "Is this also a
> > MAJOR reason
> > why we need to have scramling on top of spreading? since 'time shifted
> > versions
> > of pn sequences has little correlation'"
>
> Probably because of what I said above.
>
> But you are correct that orthogonality is lost not only because of
> multipath, but also because of synchronization mismatch.
> There's a huge treatment on this by researchers of "multiuser
> detection".
>
>
>
> > 3) Orthogonal sequences, when time-shifted have very large cross-
> > correlation value and therefore become unsuitable to use in practical
> > wireless system with multi-paths and time synch problems and therefore
> > NEED pn scrambling to help these orthogonal codes, which as I
> > mentioned have little correlation pn after time shift
>
> To some extent, yes, but you have to state this quantitatively.
> Nothing is perfect and nothing comes for free. &#4294967295;The cost-benefit is
> what matters.
>
>
>
> > Please correct my statements if there are incorrect or deviate from
> > the point
>
> > Thanks and Cheers to all my fellow group members

Thanks SC, I owe you

Now, just as a suggestion, what are the future mobile wireless
technologies (I have 4G in my mind) for multiple access.

Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
confused about OFDM and OFDMA, I'll have to read some posts over here
regarding the topic), some people have also suggested IDMA and MC-
IDMA. CDMA seems to have missed out. What do you think?

On Mar 18, 12:39�pm, Communications_engineer
<communications_engin...@yahoo.com> wrote:
>
> Thanks SC, I owe you

Who's "SC"?

> Now, just as a suggestion, what are the future mobile wireless
> technologies (I have 4G in my mind) for multiple access.
>
> Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
> confused about OFDM and OFDMA, I'll have to read some posts over here
> regarding the topic),

You should either take a class or read textbooks or papers
instead of reading posts on this newsgroup.

> some people have also suggested IDMA and MC-
> IDMA. CDMA seems to have missed out. What do you think?

Whether one option is better than the other is usually not clear
until one considers all the analytical, practical, and economical
constraints.  That's why a lot of research and engineering is
needed.

If I recall correctly, CDMA lost its popularity for many reasons,
and one  of them is the difficulty of doing power control when
there are synchronization errors in multipath.

Julius

On Mar 18, 12:39=A0pm, Communications_engineer
<communications_engin...@yahoo.com> wrote:
>
> Thanks SC, I owe you

Who's "SC"?

> Now, just as a suggestion, what are the future mobile wireless
> technologies (I have 4G in my mind) for multiple access.
>
> Like from some quarters we hear SC-FDMA, OFDMA, OFDM (I'm still a bit
> confused about OFDM and OFDMA, I'll have to read some posts over here
> regarding the topic),

You should either take a class or read textbooks or papers
instead of reading posts on this newsgroup.

> some people have also suggested IDMA and MC-
> IDMA. CDMA seems to have missed out. What do you think?

Whether one option is better than the other is usually not clear
until one considers all the analytical, practical, and economical
constraints.  That's why a lot of research and engineering is
needed.

If I recall correctly, CDMA lost its popularity for many reasons,
and one  of them is the difficulty of doing power control when
there are synchronization errors in multipath.

Julius

julius wrote:

> If I recall correctly, CDMA lost its popularity for many reasons,
> and one  of them is the difficulty of doing power control when
> there are synchronization errors in multipath.

The whole GSM/CDMA war was actually about the key patent holders and the 
licensing fees. From the very beginning it was apparent that in the 
realistic environment the CDMA IS-95 couldn't provide any performance 
advantage over GSM. Furthermore, for the equal QOS, the IS-95 
infrastructure has to be more complex and expensive. Soft handovers, 
rake receivers and such had to be used because of the bitter necessity, 
not because it was good.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com