IEEE Std. 802.16 Technique Overview
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系統暨網路管理實驗室 Systems & Network Management Lab
Reporter:黃文帥2007/09/18
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Contents
What is WiMAX1
Physical Layer2
Frame Structure3
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What is WiMAX
Scope: - Specifies the air interface, MAC (Medium Access Control), PHY (Physical Layer).
Purpose: - Enable rapid worldwide deployment of cost-effective broadband wireless access product.
- Facilitate competition in broadband access by providing alternatives to wireless broadband access.
Main advantage: - Fast deployment, dynamic sharing of radio resources and low cost.
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What is WiMAX
Deployment
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What is WiMAX
Adaptive Modulation Maximize throughput. Minimize average power. Minimize average bit error rate.
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What is WiMAX
802.11 is not strictly synchronized.
802.16 is a slotted system and all the transmission must be synchronize.
802.11 uses two-way (Data/ACK) or four-way (RTS/CTS/Data/ACK) handshaking to access channel and transmit data.
802.16 uses a three-way handshaking to set up connection before data transmission (Request/Grant/Transmit).
802.11 does not distinguish control channel and data channel.
In 802.16, the control channel and data channel are separated.
In 802.11, a station must compete for every packet.
In 802.16, a station can reserve multiple slots for the following packets.
802.11 vs 802.16
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Physical Layer
Support framing. Support both Time Division Duplex (TDD) and Frequency
Division Duplex (FDD), as well as half-duplex FDD (H-FDD).
Burst transmission format which supports adaptive burst profiling.
- Data allocations within a frame are referred as bursts.
- Transmission parameters, including the modulation and coding schemes (burst
profiles), may be adjusted individually to each SS on a frame-by-frame basis.
- Burst profiles are broadcast via MAC management messages Downlink Channel
Descriptor (DCD) and Uplink Channel Descriptor (UCD) periodically.
- The actual transmission bandwidth is allocated by BS and broadcast in MAC
management messages Downlink MAP (DL-MAP) and Uplink MAP (UP-MAP) in
each frame.
- Adapt to multiple modulation levels : BPSK, QPSK, QAM-16, QAM-64.
Introduction
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Physical Layer
TDD - The UL and DL transmissions occur at different times and usually share
the same frequency. (SS does not receive and transmit data at the same
time)
- A TDD frame has a fixed duration and contains one DL and one UL
subframe, whose durations can vary.
FDD - The UL and DL channels are located on separate frequencies.
- A fixed duration frame is used for both UL and DL transmissions.
- The H-FDD SS does not receive and transmit data at the same time.
PHY Duplexing Option
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Physical Layer
TDD Frame Structure
PS (Physical Slot) - A unit of time, depend on the PHY specification, for allocating bandwidth.
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Physical Layer
FDD Bandwidth Allocation
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Frame Structure
Downlink Subframe
TTG/RTG (Transmit/Receive Transition Gap) - A gap between the downlink burst and the subsequent uplink burst in a time division duplex (TDD) transceiver.
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Frame Structure
Uplink Subframe
SSTG (Subscriber Station Transition Gap)
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Frame Structure
OFDMA Frame Structure