Fixed WiMAX (16d) vs Mobile WiMAX (16e): Key Differences

This page outlines the differences between Fixed WiMAX (802.16d) and Mobile WiMAX (802.16e) technologies.
There are several versions of WiMAX standards, including:

• IEEE 802.16-2001
• IEEE 802.16-2004
• IEEE 802.16e-2005
• IEEE 802.16-2009

IEEE 802.16-2004 is known as Fixed WiMAX (16d), and IEEE 802.16e-2005 is known as Mobile WiMAX (16e). 802.16m is an upgraded version of 802.16-2009 and is referred to as WiMAX Advanced. Both Fixed WiMAX and Mobile WiMAX systems are used for broadband data communication.

As the names suggest, Fixed WiMAX systems have subscriber terminals located at fixed locations, while Mobile WiMAX systems have mobile subscriber terminals.

Mobile WiMAX is often considered a 4G technology due to its higher data rates and broader coverage. These improvements were achieved with the help of MIMO (Multiple-Input Multiple-Output) and beamforming technologies.

The figures above depict the frame structure used in Fixed WiMAX and Mobile WiMAX systems. As shown, resource allocation in Fixed WiMAX is primarily time-based, while in Mobile WiMAX, it’s both time and frequency-based.

The unit of resource allocation in Fixed WiMAX is the OFDM (Orthogonal Frequency-Division Multiplexing) symbol. In contrast, the unit of resource allocation in Mobile WiMAX is the slot. A slot comprises OFDM symbols on the time axis and subchannels on the frequency axis. A subchannel consists of more than one subcarrier.

Both technologies are based on the IEEE 802.16 standard, but Fixed WiMAX employs OFDM at the Physical layer, while Mobile WiMAX employs OFDMA (Orthogonal Frequency-Division Multiple Access). The Fast Fourier Transform (FFT) size is 256 in Fixed WiMAX systems. In Mobile WiMAX, sizes of 128, 512, 1024, and 2048 are available. 512 and 1024 FFTs are commonly adopted by manufacturers of Mobile WiMAX equipment.

Channel bandwidths of 3.5 MHz and 7 MHz are typically used by manufacturers of Fixed WiMAX equipment, while 5, 7, 8.75, and 10 MHz are adopted by Mobile WiMAX equipment manufacturers.

As illustrated in the figures, both systems have a frame consisting of a preamble, a header, and one or more bursts. The header is 24 bits in Mobile WiMAX, while it’s about 88 bits in Fixed WiMAX. The header carries information such as modulation and coding rates (mod-code) and the position of bursts.

Both Fixed WiMAX and Mobile WiMAX frames start with a known sequence called the preamble. The preamble is used for time, frequency, and channel estimation and equalization at the receiver. Mobile WiMAX has a total of 114 PN (Pseudo-Noise) sequences, one of which is randomly selected as the preamble for transmission. Fixed WiMAX defines specific patterns for short and long preambles, where the long preamble is used for the downlink subframe, and the short preamble is used for uplink bursts.

Both systems utilize a cyclic prefix or guard interval to mitigate the effects of delay spread. Refer OFDM preamble generation as per fixed wimax specifications.

Mobile WiMAX supports various zones such as PUSC (Partially Used Subchannelization), FUSC (Fully Used Subchannelization), and AMC (Adaptive Modulation and Coding) in both uplink and downlink directions. Fixed WiMAX does not have any zone concept.

Mobile WiMAX employs Convolutional Turbo Codes (CTC) and Convolutional Codes (CC) for forward error correction, while Fixed WiMAX uses Reed-Solomon codes and CC. Both systems use modulation techniques such as Binary Phase-Shift Keying (BPSK), Quadrature Phase-Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (16QAM), and 64QAM.

MIMO and beamforming techniques are employed in Mobile WiMAX. Most Fixed WiMAX systems do not utilize MIMO or beamforming.