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Understanding LTE Model Internals and Interfaces

Understanding LTE Model Internals and Interfaces

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1581 <strong>Underst<strong>and</strong>ing</strong> <strong>LTE</strong> <strong>Model</strong> <strong>Internals</strong> <strong>and</strong> <strong>Interfaces</strong>Appendix E: H<strong>and</strong>ling of UL HARQRetransmissionslte_enb_as_ul_frame_harq_rtx_process()Find all UEs that transmitted at n-8(ACK || max RTX exceeded) && (UEmade a “correct” transmission)*Else if UE made an “incorrect”transmission*ElseFree the HARQ process for newtransmissions.Send a fake ACK to this UE to stopfurther retransmissions <strong>and</strong> mark for“adaptive” retransmissionAttempt synchronous retransmission:lte_enb_as_ul_frame_harq_implicit_rtx_process()Failed due to collision with anotherRTX or RACHFor each open “segment”, attempt adaptiveretransmission:lte_enb_as_ul_frame_harq_explicit_rtx_process()ElseSend NACK. TheUE will retransmitimplicitlyFailedSend a fake ACK to stop retransmissionSucceededSend NACK <strong>and</strong> a grant forRTX with NDI = 0*Incorrect transmission: An incorrect transmission is a consequence of the following scenario: ACK to NACK <strong>and</strong> lost grant fornew data. In this case, the UE retransmits using a previous grant instead of doing a transmission using the new grant. In realsystems, HARQ/PHY can detect this by noting reception of a packet on wrong frequencies.CONFIDENTIAL ─ RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2010 OPNET Technologies, Inc.86

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