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Two questions about WCDMA

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aomeen

aomeen

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Dear all,

I have two quistions...

1) Why CDMA systems (UMTS,IS-95,CDMA2000) use QPSK modulation technique while TDMA system (e.g GSM) use GMSK modulation?

2) Why modulation used in Downlink is different than that is used in Uplink? (as WCDMA DL use QPSK while WCDMA UL use BPSK).

Thanks in advance.
 

Re: WCDMA Quistions

1) QPSK can carry more data in same band

2) DL needs more speed than UL. The mobile terminal has to be simpler than BS
 

    aomeen

    aomeen

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Re: WCDMA Quistions

Hi,

I do agree with the answers given by aomeen.
For the first question, there are also a strategical aspects behind....
Regards.
 

Re: WCDMA Quistions

aomeen said:
Dear all,

I have two quistions...

1) Why CDMA systems (UMTS,IS-95,CDMA2000) use QPSK modulation technique while TDMA system (e.g GSM) use GMSK modulation?

2) Why modulation used in Downlink is different than that is used in Uplink? (as WCDMA DL use QPSK while WCDMA UL use BPSK).

Thanks in advance.
Click to expand...

1) GMSK is used in GSM for its less stringent requirement of the linearity of power amplifier. As to WCDMA, technology enables more spectral-efficient QPSK.

2) First UL is power limited and BPSK is more power-efficient. On the other hand, with BPSK for data and another BPSK for control data, both are modulated by channelization code. This has one advantage that using I/Q multiplexing, instead of TDMA, no audio interference is generated (those tone can be heared by stearo, e.g.).
 

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