 pseudo-random sequence Figure 5.1-13 PBCC-11 convolutional code and cover sequence. CHAPTER 5. Wireless local area networks telephones, and microwave ovens, among others), would eventually result in serious interference problems in this band. The UNII band was (and is) relatively unoccupied and provides a considerable expansion in available bandwidth: in the United States, 300 MHz at the time PBCC11 versus 80 MHz available at ISM. CCK11 Rules for operating in the UNII band have changed significantly in the United States since the promulgation of the 802.11 standard: in November 2003, the FCC added 255 MHz to the available spectrum and imposed additional restrictions on operation in the existing 5.250- to 5.350-GHz band. The original and modified U.S. assign- ments are depicted in Figure 5.1-15. The allowed bands at the time of the standard consisted of a lower, middle, and S/N (dB) upper band, each with 100 MHz of bandwidth. The lower band was dedicated to indoor use only and limited to Figure 5.1-14 Error rate of uncoded QPSK, PBCC11, and CCK 40 mW output power. The middle band allowed dual use, 11 VS. (S/N) (after Heegard et al., in Bing 2002). and the upper band was targeted to outdoor uses with a much higher allowed output of 800 mW. but by pruning out the worst choices at each stage of the The FCC's changes in late 2003 added an additional trellis, the complexity of the algorithm is reduced to band, almost as big as what had been available, for dual use something manageable. However, implementation is at 200 mW. Use of this band, and retroactively of the old still rather more complex than in the case of a block code UNII mid-band, is only allowed if devices implement like CCK. transmit power control and dynamic frequency selection. The PBCC-11 code has slightly better performance The former reduces the power of each transmitting device than the corresponding CCK code: about 3.5 additional to the minimum needed to achieve a reliable link, reducing dB of coding gain (Figure 5.1-14). However, the com- overall 