Scheduling Algorithms and Radio Resource Management in WiMAX

Scheduling Algorithms and Radio Resource Management in WiMAX

Yasser Sadri (Islamic Azad University, Iran) and Mohammdhossein Norouzibeirami (Islamic Azad University, Iran)
DOI: 10.4018/978-1-4666-4888-3.ch012
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Abstract

The IEEE 802.16 has defined wireless access systems called WiMAX. These systems provide high-speed communications over long distances. To support multimedia applications, some service classes with Quality of Service (QoS) requirements are defined in IEEE 802.16, but the QoS scheduler is not standardized. The scheduling mechanism has a significant effect on the performance of WiMAX systems for use of bandwidth and radio resources. Some scheduling algorithms have been introduced by researchers. This study focuses on scheduling techniques proposed for WiMAX. The authors analyze a number of WiMAX scheduling algorithms in the Point-to-Multi-Point (PMP) mode and highlight their main points.
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Background

WiMAX stands for Wireless Metropolitan Area Networks (Wireless MAN). This system supports PMP architecture with an optional mesh topology. In PMP mode, a BS centrally allocates Downlink (DL, from the BS to the SSs) and Uplink (UL, from the SSs to the BS) resources to SSs. All SSs are only allowed to communicate with a BS. In mesh mode, multi-hop communication is possible between SSs. In this section, we provide a description of the Physical (PHY) and MAC layers of the IEEE 802.16 standard.

WiMAX PHY Layer

Under the PMP mode, the standard supports a range of frequencies from 2 to 66 GHz, which includes the licensed and license-exempt bands. Depending on the range of frequencies, a Line-Of-Sight (LOS) or Non-Line-Of-Sight (NLOS) propagation mode may be used. Three types of modulation can be used: QPSK, 16-QAM, and 64-QAM. QPSK is the only mandatory modulation defined by the standard.

IEEE 802.16 defines five different PHY techniques:

  • 1.

    Wireless MAN-SC (Single Carrier): In this technique, PHY layer single carriers are used to transmit information for frequencies beyond 11GHz in a LOS condition.

  • 2.

    Wireless MAN-SCa: This technique also relies on a single carrier transmission scheme, but for frequencies between 2 GHz and 11GHz.

  • 3.

    Wireless MAN-OFDM (Orthogonal Frequency Division Multiplexing): This technique is based on a Fast Fourier Transform (FFT) with a size of 256 points. It is used for PMP links in a NLOS condition for frequencies between 2 GHz and 11GHz.

  • 4.

    Wireless MAN-OFDMA (OFDM Access): This technique, also referred to as mobile WiMAX, is also based on a FFT and possesses a size of 2048 points. It is used in a NLOS conditions for frequencies between 2 GHz and 11GHz.

  • 5.

    Wireless MAN-SOFDMA (Scalable OFDMA): This technique employs an OFDMA PHY layer that has been extended in IEEE 802.16e, where the size is variable and can take different values: 128, 512, 1024, and 2048.

Both communications, DL and UL, are time multiplexed by means of Time Division Multiple Access (TDMA). Both sub-frames may use Time-Division Duplexing (TDD), where the DL and UL sub-frames share the same frequency but are separated in time or Frequency-Division Duplexing (FDD), in which both channels operate on separate frequencies.

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