Question 5: (20 marks) a) A particular mobile cell uses a downlink channel 30 MHz wide. Subcarrier separation is 15 kHz. How many subchannels are there in this cell? (4 marks) b) Assume that a cyclic prefix of 5us is used and the useful symbol period is 45us. What is the OFDM symbol period? (4 marks) c) If the cyclic prefix remains unchanged, how many OFDM symbols are there in a second? (4 marks) d) If 64-QAM is used, what is the data rate per subchannel (assuming a constant cyclic prefix)? (4 marks) e) What is the combined data rate across the 30 MHz channel? (4 marks)