Understanding WiMAX (Chapter 8)

ENE 490

MON 13:30-16:30

Asst. Prof. Dr. Suwat Pattaramalai

Understanding WiMAX� PHY Layer of WiMAX

Understanding WiMAX� Channel coding

� Convolutional coding, Turbo, block Turbo, and LDPC codes .

Understanding WiMAX

Understanding WiMAX� Hybrid-ARQ

� Incremental redundancy: encoded bits is changed from one transmission to

the next to lower bit error rate (BER) and block error rate (BLER)

Understanding WiMAX� Interleaving

� Encoded bits are interleaved, provides frequency diversity

Understanding WiMAX� Symbol Mapping

Understanding WiMAX� OFDM Symbol Structure

Understanding WiMAX

Understanding WiMAX� Downlink Full Usage of Subcarriers

Understanding WiMAX

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Understanding WiMAX� Uplink Partial Usage of Subcarriers

Understanding WiMAX� Tile Usage of Subcarriers: identical to PUSC

� Band Adaptive Modulation and Coding

Understanding WiMAX� Slot and Frame Structure

� FDD: UL and DL subframes are transmitted simultaneously on different � FDD: UL and DL subframes are transmitted simultaneously on different

carrier frequencies.

� TDD: UL and DL subframes are transmitted on the same carrier frequency

at different times.

� H-FDD: is a basis FDD with the restriction the MS cannot transmit and

receive at the same time, Cheaper and less complex than it’s FDD

counterpart but peak data rate of UL and DL are less.

� Preamble: synchronization, initial channel estimation (noise&interference)

Understanding WiMAX� TDD frame structure

Understanding WiMAX� TDD frame structure

� FCH: carrying system control information (subcarriers used, ranging

subchannels, and length of DL-MAP message), BPSK R1/2 mode

� DL-MAP (UL-MAP): specify the data regions of the various users in DL

(UL) subframes of the current frame, MS can identify its’ subchannels

and symbols to use.

� Downlink channel descriptor, DCD (UCD): contains additional control � Downlink channel descriptor, DCD (UCD): contains additional control

infromation pertaining to the description of channel structure and

various burst profiles, not transmitted every DL frame.

� Transmit Diversity and MIMO

� AAS: multiple antenna, diversity, beamforming, spatial multiplexing

� Transmit diversity and Space/Time Coding:

� Two antenna open-loop schemes: equation (8.6) in figure 8.15

� Four antenna : equation (8.7)

� Horizontal and vertical encoding: figure 8.16

� Pilot are distributed transmitting among various antennas

Understanding WiMAX� Two antenna

Understanding WiMAX� Four antenna

Understanding WiMAX� Horizontal and vertical coding

Understanding WiMAX� Frequency-Hopping Diversity Code (FHDC)

Understanding WiMAX� Closed-Loop MIMO

Understanding WiMAX� Long-term feedback: maximum number of parallel streams, rank of the

precoding matrix to be used for DL transmissions

� Short-term feedback: precoding matrix weights to be used

Understanding WiMAX� Antenna selection: bandwidth-efficient feedback

� Antenna Grouping

Understanding WiMAX� Codebook Based Feedback: MS identify a precoding matrix that should be

used for DL transmissions to improve performance and efficiency

� Quantized Channel Feedback: MS inform BS its MIMO channel state

information

� Channel Sounding: MS’s transmitting a deterministic signal the can be

used by the BS to estimate the UL channel, most bandwidth-intensive

MIMO channel-feedback mechanism, maximum capacity gain

� Ranging

� Maintains the quality and reliability of the radio-link communication

between the BS and MS

� Estimate channel impulse response, SINR, time of arrival to adjust

any in the transmit power level or the timing offset.

� Guarantees no phase discontinuity at the boundary the two

consecutive symbols in creating two OFDM symbols of the ranging

subchannels

Understanding WiMAX� Ranging

Understanding WiMAX� Power control

� BS uses the UL ranging channel transmissions from various MSs to

estimate the initial and periodic adjustments for power control.

� BS uses dedicate MAC managements messages to indicate to the MS

the necessary power-level adjustment

Understanding WiMAX� Channel-Quality Measurements

� RSSI (received signal strength indicator) and SINR are need to provide

to the BS on request

� MS uses Channel quality feedback (CQI) to provide the BS

� Mean and standard deviation of the SINR are converted to the dB

before being reported to the BS

Understanding WiMAX� Summary and Conclusions

Understanding WiMAX