Suppose you build an OFDM system with a total system bandwidth of 50 MHz operating in a channel with
Suppose you build an OFDM system with a total system bandwidth
of 50 MHz operating in a channel with maximum excess delay Tm = 0.55 _sec.
a. Is this an indoor or an outdoor channel?
b. How many subchannels are needed so that subchannels
suffer flat fading? Flat fading assumption implies that _fc _
10_f , where _f=1/T denotes the subchannel bandwidth, which is
assumed to be equal to the inverse of the OFDM symbol duration T. Noting that
FFT/IFFT requires that the number of subcarriers N should be equal to an
exponent of 2, that is, N=2n where n is an integer, determine the appropriate
Suppose you build an OFDM system with a total system bandwidth
of 50 MHz operating in a channel with maximum excess delay Tm = 0.55 _sec.
a. Is this an indoor or an outdoor channel?
b. How many subchannels are needed so that subchannels
suffer flat fading? Flat fading assumption implies that _fc _
10_f , where _f=1/T denotes the subchannel bandwidth, which is
assumed to be equal to the inverse of the OFDM symbol duration T. Noting that
FFT/IFFT requires that the number of subcarriers N should be equal to an
exponent of 2, that is, N=2n where n is an integer, determine the appropriate
value of N that can be used in practice.
c. Determine the duration TG of the cyclic prefix to ensure
no ISI between FFT blocks? If the duration of a cyclic prefix can assume one of
the values TG/T=1/32, 1/16, 1/8 or 1/4, determine the appropriate duration of
the cyclic prefix.
d. If the maximum Doppler shift should be less than 1% of
the subchannel bandwidth, determine the maximum mobile speeds that this system
can support.
