 types of channel distortion. transmission in 802.11b. It is this 11 Mcps modulation The concept of CCK modulation and demodulation is that gives the 22 MHz null-to-null bandwidth. However, shown in Figures 5.2-12 and 5.2-13. It's explained below in contrast to the original specification, the symbol rate in reference to a data rate of 11 Mbps. The multiplexer of when sending data at 5.5 or 11 Mbps is 1.375 Msps. Eight Figure 5.2-12 takes a block of eight serial data bits, en- chips per symbol are transmitted instead of eleven chips tering at 11 Mbps, and outputs them in parallel, with per symbol as when sending at 1 or 2 Mbps. In "standard" updates at the symbol rate of 1.375 MHz. The six latest DSSS as used in 802.11, the modulation, BPSK or QPSK, data bits determine 1 out of 64 (26) complex code words. is applied to the group of eleven chips constituting a Each code word is a sequence of eight complex chips, symbol. The series of eleven chips in the symbol is always having phase angles al through ag and a magnitude of the same (the Barker sequence previously defined). In unity. The first two data bits, do and di determine an contrast, high-rate DSSS uses a different 8-chip sequence angle, a's which, in the code rotator (see Figure 5.2-12), in each symbol, depending on the sequence of data bits rotates the whole code word relative to ag of the previous that is applied to each symbol. Quadrature modulation is code word. This angle of rotation becomes the absolute used, and each chip has an I value and a Q value which angle ag of the present code word. The normalized I and represent a complex number having a normalized ampli- Q outputs of the code rotator, which after filtering are tude of one and some angle, a, where a = arctangent input to a quadrature modulator for up-conversion to the (Q/I). a can assume one of four values divided equally carrier (or intermediate) frequency, are: around 360 degrees. Since each complex bit has four possible values, there are a total of 48 = 65536 possible I = cos(ai), Qi = sin(