GMSK in UMTS?

[ritgail]

can you guys help me out with the following :

1. Why GMSK is not used in WCDMA besides bit rate? What is the disadvantage?

2. How IQ modulation is effected by QPSK/QAM modulation?

[firstmaxim]

Unlike GSM, the duty cycle of WCDMA is 100 percent, and QPSK has a better spectral efficiency. However, on the uplink we use dual -BPSK for the reasons of bio-medical compatibility.



can you guys help me out with the following :

1. Why GMSK is not used in WCDMA besides bit rate? What is the disadvantage?

2. How IQ modulation is effected by QPSK/QAM modulation?

[Mctest]

Unlike GSM, the duty cycle of WCDMA is 100 percent, and QPSK has a better spectral efficiency. However, on the uplink we use dual -BPSK for the reasons of bio-medical compatibility.
Could you give us more details on bio-medical compatibility?

[firstmaxim]

Could you give us more details on bio-medical compatibility?

On the uplink if DPCCH and DPDCH were Time Division Mutliplexed like in downlink, and when DPDCH is not transmitted, DPCCH transmission in every slot would result in harmonic generation, since there are 15 slots in one 10 ms frame in WCDMA UMTS. The resulting harmonic of 15/10ms = 1500 Hz, fall in the audio region, with potential to interfere with hearing devices, and also pacemakers.

Adoption of I and Q modulation technique using dual-BPSK technique overcomes the above mentioned problem, by transmitting DPDCH on a continual basis (on the Q chain), even when DPDCH (on the I chain) is not being transmitted. Since there is DPCCH transmission on a continuous basis, harmonics are not generated.