Simulation of 802.16e (WiMax) HARQ Mechanism Students: Guy Carmel & Aviv Castro External Supervisor – Mr. Erez Ben-Tovim Internal Supervisor– Prof. Ran Giladi Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Project Goals The project deals with HARQ (Hybrid Automatic Repeat ReQuest) feature in 802.16e (WiMax) protocol The project’s goals are: Specify the implementation of HARQ module in 802.16e 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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

HARQ Overview Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Combining Methods Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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). Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

HARQ main components combining methods Incremental Redundancy (IR) - instead of straightforward retransmission, additional redundancy is sent in every step. Usually implemented by puncturing. Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

N-SAW HARQ– IEEE 802.16e Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

N-SAW HARQ (N=2) Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Project Description Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

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 Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Project Description Simulation Environment Transmitter AWGN channel Receiver Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Results & Conclusions Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Results and conclusions number of retransmissions – HARQ retransmission gain FER = FEC Error Rate [dB] Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Results and conclusions CC vs. CTC – Turbo code performance is better than Convolution code Rate = ½ Block size = 480 bits CC CTC Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Results and conclusions Memory optimization – decreasing memory size without performance degradation Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

Questions? Thanks for listening Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement

www.comsysmobile.com Comsys confidential and proprietary information Subject to Mutual Confidentiality Agreement