MOBILE WIMAX AND IEEE 802.16 STANDARDS

The WiMAX Forum is an industry consortium promoting the IEEE 802.16 family of standards for broadband wireless access systems. Historical-ly, the first IEEE 802.16 standard (and associated 802.16c profile definitions) addressed primarily line-of-sight (LOS) environments at high fre-quency bands (10–66 GHz) via conventional quadrature amplitude modulation (QAM) single-carrier techniques. The limited market potential for millimeter-wave LOS systems resulted in the development of the IEEE 802.16a amendment to support non-LOS (NLOS) modes in radio bands between 2–11 GHz. The 802.16-2004 standard [1] (also known as 802.16d) made further, more rad-ical changes to 802.16 physical (PHY) layer oper-ation for low frequency (2–11 GHz) bands by adding two additional PHY modes: • A 256-point fast Fourier transform (FFT) orthogonal frequency-division multiplexing (OFDM) PHY mode • A 2048-point FFT orthogonal frequency-division multiple access (OFDMA) PHY mode The well understood goal of these develop-ments was to use OFDM for both downlink (DL) and uplink (UL) to enable relatively sim-ple high-performance receiver structures in the presence of frequency-selective fading channels. This new PHY capability was augmented by addition of several features: • Frequency-diverse and frequency-specific subchannelization schemes where respec-tive groups of physically distributed and physically adjacent subcarriers are used to construct subchannels. These schemes enable both frequency-diverse and frequen-cy-selective scheduling and resource alloca-tion methods. • Adaptive modulation and coding based on hybrid automatic repeat request (HARQ) techniques (previously used in Third Gen