NDI Handling in LTE Random Access HARQ Processes
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Solution Overview
Problem
In mobile communication systems like LTE, the processing of new data indicators (NDI) during random access procedures can lead to errors in signal transmission and reception due to confusion between new data transmission and data retransmission, especially when NDI values received during the random access procedure are not properly handled.
Innovation Solution
A method where the user equipment ignores NDI values received using a temporary cell identifier during the random access procedure and relies on NDI values received using a cell identifier after the procedure to determine whether to perform retransmissions, ensuring accurate handling of new data transmission or retransmissions by toggling the NDI value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NDI values received during random access procedure are stored and used for retransmission determination, then HARQ retransmission control is enabled, but errors occur in signal transmission and reception due to confusion between new data and retransmission
Solution Approach 1:
The patent segments the NDI processing by creating separate handling paths for NDI values received during random access procedure versus those received after random access completion. NDI values received during random access (when temporary cell identifier is used) are stored in a separate buffer or handled separately from NDI values received after random access (when cell identifier is used), preventing confusion between the two types of NDI values and enabling reliable HARQ retransmission control.
2Ease of operation
If NDI values received using temporary cell identifier are processed like normal NDI values, then HARQ process is maintained, but incorrect retransmission decisions are made
Solution Approach 1:
The patent applies local quality by treating NDI values received during random access procedure differently from normal NDI values. Specifically, NDI values received using temporary cell identifier are either discarded, stored in a separate buffer, or marked with a special flag to indicate their special status. This localized differentiation ensures that these NDI values do not interfere with the accuracy of retransmission determination for actual data transmissions.
3Reliability
If all NDI values are used for retransmission determination, then complete HARQ control is achieved, but errors occur due to temporary cell identifier confusion
Solution Approach 1:
The patent implements preliminary action by identifying and filtering out NDI values received during random access procedure before they can cause confusion in retransmission determination. The system checks whether the currently received NDI is associated with a temporary cell identifier or random access procedure, and if so, handles it differently (discarding or separate storage) before the NDI is used for HARQ retransmission control decisions.
Data Source
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AI summary
A method for a user equipment, hereinafter called as UE, to receive a downlink signal, the method comprising: receiving a first physical downlink control channel using a temporary cell identifier, hereinafter called as Temporary C-RNTI, from a base station at a first timing associated with a first HARQ process, the first physical downlink control channel comprising a first downlink assignment signal having a new data indicator, hereinafter called as NDI with a first value (S901); and receiving a second physical downlink control channel using a cell identifier, hereinafter called as C-RNTI, from the base station at a second timing associated with the first HARQ process, the second physical downlink control channel comprising a second downlink assignment signal having the NDI with a second value (S902), the method being characterized by comprising: determining if the NDI with the second value has been toggled compared to a value of the NDI set with regards to the first HARQ process before the second timing, wherein the UE ignores the NDI with the first value received through the first physical downlink control channel using the Temporary C-RNTI (S903); and receiving the downlink signal based on the determining (S904).