0. Simulation of 802.16e (WiMax) HARQ Mechanism
Students: Guy Carmel & Aviv Castro
External Supervisor – Mr. Erez Ben-Tovim Internal Supervisor– Prof. Ran Giladi
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1. Results and Conclusions
Agenda
Project Goals
HARQ Overview
General description and major benefits
Combining methods
Retransmission methods
Project description
Results and Conclusions
Chase combining analysis
Complexity and tradeoffs
Performance
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2. Project Goals
The project deals with HARQ (Hybrid Automatic Repeat ReQuest) feature in e (WiMax) protocol
The project’s goals are:
Specify the implementation of HARQ module in e
Examine the performance gain that achieved by HARQ (FEC Error Rate, SNR)
Examine the differences between HARQ methods (CC and CTC, Chase and IR)
Memory optimization research
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3. HARQ Overview Comsys confidential and proprietary information
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4. HARQ Overview
HARQ (Hybrid Automatic Re-transmission reQuest) is defined as any combination of ARQ and FEC (Forward Error Correction) that saves failed decoding attempts for future joint decoding
HARQ is practically an implicit link adaptation technique
HARQ improves performance by allowing the receiver to combine multiple ARQ transmissions
The HARQ holds a component that sums up the soft values of the retransmissions (namely, “Combiner”) before entering the decoder
This summation embodies a summation of the retransmissions’ SNRs and by that it improves the performance
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5. Combining Methods Comsys confidential and proprietary information
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6. HARQ main components combining methods
Chase combining – each retransmission is self decodable and is an exact retransmission (also called H-ARQ-type III with one redundancy version).
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7. HARQ main components combining methods
Incremental Redundancy (IR) - instead of straightforward retransmission, additional redundancy is sent in every step. Usually implemented by puncturing.
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8. HARQ main components retransmission method
Stop and Wait (SAW)
simplest forms of ARQ requiring very little overhead
the transmitter operates on the current block until the block has been received successfully
one-bit sequence number that identifies the current or the next block and one bit for Ack/NAck
Disadvantage – Low throughput
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9. N-SAW HARQ– IEEE e
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10. N-SAW HARQ (N=2) Comsys confidential and proprietary information
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11. Chase Combining Analysis - Model
We observe the retransmissions as a single transmission in parallel channels
Each channel is characterized by its SNR
Channels are independent.
Only SNRi = Pi/Ni is of interest
For simplicity we assume Pi is constant and Ni varies
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12. Project Description Comsys confidential and proprietary information
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13. Project Description
The project deals with HARQ feature in IEEE802.16e standard with OFDMA PHY layer
The project includes the design and programming of a standalone HARQ simulation with a FEC level simulated environment
The simulation is used for research and optimization of the HARQ components and algorithms, in light of the future integration of the HARQ module in Comsys’ chip
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14. Project Description
The HARQ simulation envelopes the BE (modem Backend) simulation by adding CRC, buffers, feedback channel, combining components and N-SAW mechanism, all of which enabling the operation of the HARQ N-SAW “mighty” mechanism
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15. Project Description Simulation Environment Transmitter AWGN channel
Receiver
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16. Results & Conclusions Comsys confidential and proprietary information
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17. Results and conclusions
number of retransmissions – HARQ retransmission gain
FER = FEC Error Rate
[dB]
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18. Results and conclusions
CC vs. CTC – Turbo code performance is better than Convolution code
Rate = ½
Block size = 480 bits CC
CTC
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19. Results and conclusions
Memory optimization – decreasing memory size without performance degradation
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20. Questions? Thanks for listening
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21. www.comsysmobile.com Comsys confidential and proprietary information
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