Question

Q2 Fig.2 is a simplified diagram of a WCDMA system downlink signalling 20 construction, in which different channelization code CensF are used to PAPER CODE: EEE326/17-18/S2/ exam Page 2 of 6 separate different physical channels in downlink whilst the scrambling code Sa is used to differentiate the BSs. Each physical channel is assigned to different user with a gain factor Gi. Assume QPSK modulation is employed for digital transmission and the spectrum is 3.84 MHz. One user has a data rate of 30 Kbits/s before spreading. Meddaion Mappe one dowink plysical chanel frt plysical chamels Σ Fig.2 Downlink physical channels Determine the transmission bandwidth with and without spreading for one user, assuming Sinc pulse shaping. Determine the spread ing factor for the user. b) addictive white Suppose that the CDMA signal is received with an c) Gaussian noise (AWGN). Assume the signal power received at digital baseband is -60 dBm whilst the noise power is -50 dBm. Suppose that the CDMA signal is received with an addictive white Gaussian noise (AWGN). Assume the signal power received at digital baseband is -60 dBm whilst the noise power is -50 dBm. Determine the signal to noise ratio (SNR) in dB before and after dispreading at the receiver using the spreading code in b). Assume a wireless channel as shown in Q1. Determine the d) number of consecutive symbols that inter-symbol interference may spread over for the user with and without spreading, and whether it is flat fading or frequency selective fading for the user signal with and without spreading. PAPER CODE: EEE326/17-18/S2/exam Page 3 of 6

Answer 1

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b SF ISK Smbols one Sec 3.84 chps One sec 3.84x(000 3 84x IS SF Co,256 C chi SF

Bеbе Sprendlig sksps Rs Symbdae Troreani ttian Ba Rg SKНЗ яrua rовя- РN 3S о рass jonbs Tearsmiim B 3.84 M

Lefore desprodg Receved paldin Noise Re ceuca -Godan- (-50dn) SNR Siual -lo den SNR

Receivad despresd After noise SNR O dgm tve dom SP)dsm-Cdn SNR Sp Np SNR O dm

Solve To need dhamel chasactesstics we е аяune dhamol anel B 3 > dkam go fSiqual Tsansmiemy B Flat Fadug dhannel B Siqual TSans BO Frepueng selccfive falp