questions on constellation diagram

On 1/10/2012 2:02 PM, robert bristow-johnson wrote:
> On 1/9/12 9:40 PM, glen herrmannsfeldt wrote:
>> robert bristow-johnson<rbj@audioimagination.com>  wrote:
>>
>> (snip)
>>> i remember when i first learned that "constellation" didn't mean
>>> "constellation".  it was in an EE colloquium about some keying or coding
>>> about 3 decades ago.  since then i have heard some other uses in the
>>> social and political realm.
>>
>>> i'm no expert, but to answer the OP a little, i think that one of the
>>> issues in designing a constellation is to have a maximum distance metric
>>> between the points in the constellation so that when noise is added, it
>>> minimizes the probability of selecting the wrong symbol.
>>
>> I believe so. Maybe it is at least a little bit obvious, or maybe not,
>> that the noise in amplitude/phase space (I-Q in rectangular coordinates)
>> works out such that noise has circular symmetry.
> 
> so a Euclidian distance metric is the appropriate metric.
> 
>> That is, such that the
>> optimal patterns have equal distance between points on a 2D graph.
> 
> i would think then that the constellation points should be arranged in a 
> hexagonal honeycomb fashion, where, if you imagine the points to be in 
> equally-spaced rows, that every alternate row should have their points 
> horizontally offset by 1/2 the horizontal spacing.  like this:
> 
> 
>    *     *     *     *     *     *     *     *     *
> 
>       *     *     *     *     *     *     *     *     *
> 
>    *     *     *     *     *     *     *     *     *
> 
>       *     *     *     *     *     *     *     *     *
> 
>    *     *     *     *     *     *     *     *     *
> 
>       *     *     *     *     *     *     *     *     *
> 
>    *     *     *     *     *     *     *     *     *
> 
>       *     *     *     *     *     *     *     *     *
> 
>    *     *     *     *     *     *     *     *     *
> 
> 
>      ^
>    I |        Q -->
> 
> 
> then the vertical spacing of the rows can be packed a little tighter 
> (0.866 of the horizontal spacing between points) and you can pack in 
> more symbols for the same maximum signal power (or, for a given number 
> of symbols and a given maximum signal power, you can increase the 
> spacing the to the most and get a lower error rate).
> 

  It's also the best way to plant your leafy green vegetables to
maximize weed resistance and crop yield!

aizza ahmed wrote:

> Hi,
>     All Experts, Thanks for answering my question in last post
> (especially Eric Jacobsen Sir), I have few questions on constellation
> diagram. Please let know the the article/paper to understand below
> points
> 
> if you know the answer,please help me out
> 
> 1. How is the shape of constellation diagram decided? What are its
> implications?
> 2,  Why not 0 - phases in a 4-point QAM? Why ?

Constellation diagram is what monkey see in the eyes when he falls down 
fron a tree.

On Jan 11, 7:22&#4294967295;am, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> aizza ahmed wrote:
> > Hi,
> > &#4294967295; &#4294967295; All Experts, Thanks for answering my question in last post
> > (especially Eric Jacobsen Sir), I have few questions on constellation
> > diagram. Please let know the the article/paper to understand below
> > points
>
> > if you know the answer,please help me out
>
> > 1. How is the shape of constellation diagram decided? What are its
> > implications?
> > 2, &#4294967295;Why not 0 - phases in a 4-point QAM? Why ?
>
> Constellation diagram is what monkey see in the eyes when he falls down
> fron a tree.

Hi,
   All Experts thanks for answers. now i am onto understanding of why
the constellation shape is decided.

Thanks a lot,
aizza ahmed