ATA field (Figure 3.4). The rates are derived from the two sequences by employing puncturing. Puncturing is a procedure for omitting some of the encoded bits in the transmitter and inserting bits at ZERO into the convolutional decoder on the receive side in place of the omitted bits. encoded scrambled DATA A scrambled encoded scrambled DATA B Figure 3.4. Convolutional encoder diagram 3.1.2.4. Interleaving All encoded data bits shall be interleaved by a block interleaver with a block size corresponding to the number of bits in a single OFDM symbol (NCBPS). Wi-Fi Integration to the 4G Mobile Network The interleaver is defined by a two-step permutation. The first permutation ensures that adjacent coded bits are mapped onto non-adjacent sub-carriers. The second ensures that adjacent coded bits are mapped alternately onto less and more significant bits of the constellation, and therefore long runs of low-reliability (LSB) bits are avoided. 3.1.2.5. Modulation and coding scheme The modulation and coding scheme determines the rate of the DATA field (Table 3.2). The sub-carriers are modulated using phase modulation (BPSK or QPSK) or mixed phase and amplitude modulation (16-QAM or 64-QAM). Forward error correction (FEC) is a convolution code used with a coding rate of 1/2, 2/3 or 3/4. Number of Number of Number of Coding DATA bits Modulation bits per sub- encoded per OFDM (Mbps) carrier DATA bits symbol 16-QAM 16-QAM 64-QAM 64-QAM Table 3.2. Parameters of the modulation and coding scheme 802.11a/g Interfaces 3.1.2.6. Structure of the preamble and OFDM symbols The preamble consists of a short learning sequence of TSHORT duration and a long learning sequence of TLONG duration. The short learning sequence contains 10 short symbols t1 to t10. The long learning sequence consists of a guard time TGI2 and two long symbols T1 and T2 (Figure 3.5 and Table 3.3). The SIGNAL symbol, of TSIGNAL duration, and the different symbols DATA, of TSYM duration, start with a guard time TGI (Figure 3.5 and Table 3.3). Short SIGNAL training sequ