Question Topics :
All Questions
Answer: Dear Shashank nishad, there are basic questions in digital communications. for this you need to go through the pre-requisite course on digital communications and communication systems available on nptel
Answer: Dear Ahmed, This course is on 3G and 4G. GSM, GPRS are 2G. Hence, they are not discusses. you have to check the pre-requisite course for this for wcdma lte wi max, please check the cdma and ofdm sections ie lecture 13 onwards
Answer: Answer: using bpsk, send 4 bits over 4 subcarriers in the first ofdm symbol time, another four in the next symbol and finally the ramaining one bit. alternatively, you can encode 3 bits per symbol using 8 level PAM or 4 bits per symbol using 16-QAM and send them during one ofdm symbol time itself. it depends on the system
Answer: Answer: no effect. channel across each subcarrier will be FFT of delta(n) which is 1 for all K. Hence, it will be an AWGN channel for each subcarrier
Answer: dear siva, there is nothing similar between CDMA and OFDMA. CDMA is based on spreading codes while OFDMA is based on orthogonal subcarriers thanks,
Answer: yes, if the bandwidth is available
Answer: we are only considering inter OFDM symbol interference. this is because the initial samples will be affected by interference from previous samples
Answer: yes, to avoid inter ofdm symbol interference
Answer: 4g has higher bandwidth and data rate than 3g. Data rate of 4g is approximately 75-100 Mbps while that of 3G is 5-30 Mbps
Answer: videos can be downloaded from nptel site at http://nptel.iitm.ac.in/courses/117104099/
Answer: Dear anup, it is not possible to cover all topics. Please refer to the paper below for sphere decoding http://authors.library.caltech.edu/1636/1/HASieeetsp05.pdf
Answer: Dear hibetullah, please search either in IEEE explore or google for more information on this topic thanks,
Answer: Dear poornima, pilot symbols are used for channel estimation in OFDM systems. please refer to presentation at link below for more details www.winlab.rutgers.edu/~spasojev/courses/projects/CE_OFDM.ppt
Answer: dear shu, yes, typically there is not need for an equalizer. however, for case of a very large delay spread an equalizer of few taps may be used thanks,
Answer: dear satish, this question is not related to the course and hence i cannot answer this
Answer: souradeep, they are not analog signals. they become analog after D/A conversion after IFFT
Answer: dear neeraj, bpsk etc are digital modulation schemes. the ifft block removes the need for analog modulators corresponding to the subcarriers thanks,
Answer: dear aman, cellular and FM frequencies are different. hence they need different antennas
Answer: dear sharma, please refer to fundamentals of wireless communications by david tse and pramod vishwanath. the details are in chapter 3 thanks,
Answer: dear durgesh, once you switch the integrals, a is a constant in the inner integral where x is a variable. hence this is possible
Answer: please go through the reference textbook fundamentals of wireless communications by david tse thanks,
Answer: modulation is before the ifft block. the information symbols 0,1 are mapped to -1 and +1 for bpsk respectively and scaled by the power factor sqrt{P}. thanks,
Answer: Dear Rahim, there is no time and frequency domain. it is only for east of understanding. if one can think of the ifft as going from frequency to time, then basically adding an fft block in front of it represents going from time to frequency thanks,
Answer: The course is finished. all 40 lectures have been posted thanks,
Answer: Dear sridhar, this is because, in SC-FDMA, finally we also need to do IFFT to recover the transmitted symbols. If we do not equalize before the IFFT, there will be distortion
Answer: vinod, large delay spread means many multipath components. Deep fade implies destructive interference leading to cancellation of signal resulting in low signal power
Answer: Jitender, no, for single tap it is not necessary
