Bug 2151

Summary: Redundancy version in uplink HARQ not generated properly
Product: ns-3 Reporter: rouil
Component: lteAssignee: Marco Miozzo <mmiozzo>
Status: RESOLVED FIXED    
Severity: normal CC: bbojovic, ns-bugs
Priority: P5    
Version: ns-3.23   
Hardware: All   
OS: All   
Attachments: Test scenario
Proposed patch
proposed patch for Ul L1 sycnh

Description rouil 2015-07-08 15:24:12 UTC 
When HARQ performs multiple uplink retransmissions, the redundancy version is expected to increase (0 to 3) but the traces show that it does not go beyond 1. 

Using a small scenario with 1 packet sent in the uplink and forcing the receiver to treat the packet as corrupted generated the following results:

% time    cellId    IMSI    RNTI    layer    mcs    size    rv    ndi   correct
112     1       1       1       0       28      2292    0       1       0
119     1       1       1       0       28      2292    1       0       0
126     1       1       1       0       28      2292    1       0       0
133     1       1       1       0       28      2292    1       0       0

The issue seems to be that receiver (eNodeB) reads the HARQ history via LteHarqPhy:: GetHarqProcessInfoUl using process ID 0, lte-spectrum-phy.cc:963, but the function LteHarqPhy:: UpdateUlHarqProcessStatus stores the new information at the end (position 7), lte-harq-phy.cc:188. Therefore if there is retransmission, the history will contain at most 1 transmission which can impact the performance of the HARQ soft combining process.
Comment 1 rouil 2015-07-08 15:30:50 UTC 
Created attachment 2089 [details]
Test scenario

To run the test, it is also necessary to modify the lte-spectrum-phy.cc to force packet corruption by modifying the function EndRxData at line 972 to:
 (*itTb).second.corrupt = true;
Comment 2 rouil 2015-08-13 10:28:12 UTC 
Created attachment 2115 [details]
Proposed patch

The patch ensures that the previous history is inserted before storing status of the new transmission. The revision number is now increasing as expected.

% time  cellId  IMSI    RNTI    layer   mcs     size    rv      ndi     correct
112     1       1       1       0       28      2292    0       1       0
119     1       1       1       0       28      2292    1       0       0
126     1       1       1       0       28      2292    2       0       0
133     1       1       1       0       28      2292    3       0       0
Comment 3 Marco Miozzo 2017-11-09 07:39:21 UTC 
The patch is fine with me, the history of the HARQ block was lost when retransmitting.
Comment 4 Marco Miozzo 2017-11-09 11:08:40 UTC 
Created attachment 2951 [details]
proposed patch for Ul L1 sycnh

Actually Zoraze found another problem on the patch, it was storing the history of all packets for ever and ever. The correct patch is this one in attachment.
Comment 5 Biljana Bojović 2017-11-16 13:22:09 UTC 
Pushed to changeset 13176:3e32da1d3de6.