Table 4.1:OFDM Symbol Parameters
Parameters Nominal Channel Bandwidth, BW Number of Used Subcarrier, Nused Sampling Factor, n Ratio of Guard time to useful symbol time, G NFFT(smallest power of 2 greater than Nused) Sampling Frequency, Fs Subcarrier Spacing, f Useful Symbol Time, Tb CP Time, Tg OFDM Symbol Time, T s Sampling Time
Value 1.75 MHz 200 8/7 1/4 ,1/8, 1/16, 1/32 255 Floor(n.BW/8000) X 8000 Fs/NFFT 1/ f G.Tb Tb+Tg Tb/NFFT
4.2 Physical Layer Setup
The structure of the baseband part of the implemented transmitter and receiver is shown in Figure 4.1. This structure corresponds to the physical layer of the IEEE 802.162004 WirelessMANOFDM air interface. In this setup, we have just implemented mandatory features of the specification, while leaving the implementation of optional features for future work. Channel coding part is composed of three steps randomization, Forward Error Correction (FEC) and interleaving. FEC is done in two phases through the outer ReedSolomon (RS) and inner Convolutional Code (CC). The complementary operations are applied in the reverse order at channel decoding in the receiver end. The complete channel encoding setup is shown in Figure 4.2 while corresponding decoding setup is shown in Figure 4.3. Through the rest of the sections, the individual block of the setup will be discussed with implementation technique.