IEEE 802.11b bandwidth and data rates

Question

I am self-studying on how 802.11b bandwidth and data rates are calculated, primarily those of 1 and 2 Mbps. These are my understandings, please correct them if they are wrong. Please keep in mind I am not an electrical engineer.

At 1 and 2 Mbps, DSSS performs signal spreading resulting with 11 and 22 mega bits (chips) per second for BPSK and QPSK, respectively. In both cases, this stream has to be modulated with mentioned modulations and equal symbol rates of 1 Mbaud per second.

Bandwith equals 2 times bits_per_second/number_of_bits_per_symbol (1 or 2 depending on modulation scheme). This "2" at the begining is because of null-to-null bandwidth of a modulated signal. For both cases, the bandwidth is 22 MHz.

The data rates are equal symbol_rates times bits_per_symbol, resulting with 1 and 2 Mbps.

Answer 1

The frequency spreading can be ignored for data rate calculation, only the symbol rate is relevant here.

Since the spreading pattern is multiplied onto the symbol stream, the frequency spectrum is the convolution of the symbol spectrum and the spectrum of the spreading pattern. The latter has higher bandwidth and thus is the dominant term when finding the bandwidth of the total signal (which is close to the sum of both bandwidths).