IEEE 802.16-2004
IEEE 802.16-2004 is a completely revised version of 802.16d, as well as 802.16 and 802.16a. The revised version defines the frequency range between 2 GHz and 66 GHz for line-of-sight( LOS) andnon-line-of-sight ( NLOS) links.
The channels are scalable and have channel widths between 1.75 MHz and 20 MHz. 802.16-2004 distinguishes two transmission methods: Orthogonal Frequency Division Multiplex( OFDM) and Orthogonal Frequency Division Multiple Access( OFDMA). In OFDM multiplex, 200 subcarrier signals are available for data transmission and both time division duplex( TDD) and frequency division duplex( FDD) are used.
In OFDMA, subscriber groups can be formed to which specific carrier frequency groups are assigned. This technology works with 128, 512, 1,024 or 2,048 carrier frequencies. With a larger number of subcarriers, the individual frequency bands become narrower and the symbol duration longer. The longer symbol duration offers advantages in possible multipath propagation because it has a greater tolerance tosignalpropagationdelay. For example, 802.16 tolerates signal propagation times of up to 10 µs, compared to only 90 ns for 802.11.
Spectral efficiency is 3.75 bit/s/ Hz with line-of-sight links and a range of 30 km; without line-of-sight links, 2 bit/s/Hz is defined and a range of 6 km. This would correspond to a data rate of 75 Mbit/s (20 MHz channel), or of 40 Mbit/s.
System security will be enhanced by improved security algorithms and authentication.
802.16-2004 is used in WiMAX for fixed operation with a fixed antenna; 802.16-2004 is not suitable for mobile WiMAX because it does not have a handover feature that allows the subscriber to switch radio cells without interruption. This mobile WiMAX is supported by 802.16e-2005.