Wireless Broadband Technologies: Wimax
5. Adaptive modulation and coding (AMC): WiMAX supports
a number of modulation and forward error correction (FEC)
coding schemes and allows the scheme to be changed on a
per user and per frame basis, based on channel conditions.
AMC is an effective mechanism to maximize throughput in
a time-varying channel.
6. Link-layer retransmissions: WiMAX supports automatic
retransmission requests (ARQ) at the link layer for connections
that require enhanced reliability. ARQ-enabled connections
require each transmitted packet to be acknowledged by the
receiver; unacknowledged packets are assumed to be lost
and are retransmitted.
7. Support for TDD and FDD: IEEE 802.16-2004 and IEEE
802.16e-2005 supports time division duplexing and frequency
division duplexing, as well as a half-duplex FDD, which
allows for a low-cost system implementation.
8. WiMAX uses OFDM: Mobile WiMAX uses orthogonal frequency
division multiple access (OFDM) as a multiple-access technique,
whereby different users can be allocated different subsets
of the OFDM tones. Flexible and dynamic per user resource
allocation: Both uplink and downlink resource allocation
are controlled by a scheduler in the base station. Capacity
is shared among multiple users on a demand basis, using
a burst TDM scheme.
9. Support for advanced antenna techniques: The WiMAX
solution has a number of hooks built into the physical-layer
design, which allows for the use of multiple-antenna techniques,
such as beam forming, space-time coding, and spatial multiplexing.
10. Quality-of-service support: The WiMAX MAC layer has
a connection-oriented architecture that is designed to support
a variety of applications, including voice and multimedia
11. WiMAX system offers support for constant bit rate,
variable bit rate, real-time, and non-real-time traffic
flows, in addition to best-effort data traffic.