FPGA Central

For CDMA system, if the transmission is synchronous and orthogonal code i
applied, will different number of users of the system give any effect t
the BER performance in AWGN channel? Or the BER performance in this cas
should be the regardless of the number of users in the system?

Please help. Thanks.

On Dec 31, 12:45 am, "Richard_K" <ngy...@hotmail.com> wrote:
> For CDMA system, if the transmission is synchronous and orthogonal code is
> applied, will different number of users of the system give any effect to
> the BER performance in AWGN channel? Or the BER performance in this case
> should be the regardless of the number of users in the system?

In a perfect system, with perfect synchronisation (all signals arrive
at the receiver at the same time) and a perfect receiver (infinite
dynamic range), then the BER is independent of the number of users.
"Orthogonal" by definition means that there is zero cross-correlation
between the codes, so a correlating receiver will not be affected by
the other users.

--
Oli

Richard_K wrote:
> For CDMA system, if the transmission is synchronous and orthogonal code is
> applied, will different number of users of the system give any effect to
> the BER performance in AWGN channel? Or the BER performance in this case
> should be the regardless of the number of users in the system?
>
> Please help. Thanks.

In a real system, you will never have pure orthogonality, due to issues
like timing errors between users, finite system bandwidth that distorts
the spreading waveforms, etc. So, for each user that is added to the
system, all other users will experience some level of interference. For
a specific user, the interference is related to the cross-correlation
values between the user's correct spreading waveform and the actual
received spreading waveforms for all other users. A way to model this
is a gradual increase in the system noise level as the number of users
in the system is increased.

Jason