channel and 64-QAM (quadrature amplitude modulation) can width is 312.5 kHz, SO the occupied channels have a total present six data bits as a single data unit on a subcarrier. width of 16.5625 (53 X 312.5 kHz) MHz. Naturally, transmitting many subcarriers on a channel For accommodating a wide range of data rates, four of given width brings up the problem of interference modulation schemes are used-BPSK, QPSK, 16-QAM between those subcarriers. There will be no interference and 64-QAM, requiring 1, 2, 4, and 6 data bits per between them if all the subcarriers are orthogonal-that symbol, respectively. Forward error correction (FEC) is, if the integral of any two different subcarriers over coding is employed with OFDM, which entails adding the symbol period is zero. It is easy to show that this code bits in each symbol. Three coding rates: 1/2, 2/3, condition exists if the frequency difference between and 3/4, indicate the ratio of data bits to the total adjacent subcarriers is the inverse of the symbol period. number of bits per symbol for different degrees of coding CHAPTER 5.2 Short-range wireless applications and technologies SERIAL BIT TO QUADRATURE GUARD CODING SYMBOL MAP MODULATOR INTERVAL LOCAL OSCILLATOR SYMBOL REMOVE TO BIT GUARD QUADRATURE DECODING DEMAP INTERVAL DEMODULATOR Figure 5.2-15 OFDM system block diagram. performance. FEC permits reconstruction of the correct the world, 802.1 specifically refers to the regulations message in the receiver, even when one or more of the of the FCC and the Japanese MPT. ETSI (European 48 data channels have selective interference that would Telecommunications Standards Institute) developed otherwise result in a lost symbol. Symbol bits are in- a high-speed wireless LAN specification, called terleaved SO that even if adjacent subcarrier bits are HIPERLAN/2 (high performance local area network), demodulated with errors, the error correction procedure which meets the European regulations and in many ways will still reproduce the correct symbol. A block diagram goes beyon