6.6 The Physical Layer and MAC Extensions
On layer 1, the physical layer, there are different modulation standards, as shown in Section 6.2, which are defined in the IEEE 802.11b, g, a and n standards.
6.6.1 IEEE 802.11b—11 Mbit/s
The breakthrough of WLAN in the consumer market was triggered by the introduction of devices compliant with the 802.11b standard, with a maximum speed of up to 11 Mbit/s. More recent physical layers described in the 802.11g or 802.11a standards can achieve even higher speeds with the same bandwidth requirement of 22 MHz. The different physical layers are discussed later in detail. The following list shows some basic WLAN parameters and compares some of them to similar parameters of other systems:
- WLAN maximum transmission power is limited to 0.1 W. Mobile phone power, on the other hand, is limited to 1–2 W. GSM and UMTS base stations have a typical power output of 40–60 W per sector and frequency.
- Each channel has a bandwidth of 22 MHz. Up to three access points can be used at close range in the ISM band without interfering with each other. GSM uses 0.2 MHz (200 kHz) per channel, and UMTS uses 5 MHz.
- Frame size is 4–4095 B. However, IP frames do not usually exceed 1500 B. This value is especially interesting for comparison with other technologies: A GPRS packet, as shown in Section 2.3.3, consists of four bursts of 114 bits each and thus can only contain 456 bits. If coding scheme 2 for error detection and correction is used, only 240 bits or 30 B remain ...