Orthogonal Cover Code Mapping for Reference Signal Latency
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Solution Overview
Problem
Current LTE systems face challenges in reducing latency during channel estimation and achieving full peak power randomization, especially in extended cyclic prefix cases and special subframes, which affects the efficiency of reference signal decoding and channel demodulation.
Innovation Solution
A low complexity OCC mapping pattern is introduced, allowing for per-slot processing and peak power randomization by permutating orthogonal cover codes across CDM subgroups, maintaining backward compatibility and enabling decoding within a single time slot, thereby reducing latency and improving channel estimation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If orthogonal cover codes are applied across the entire subframe (both time slots) for channel estimation, then channel estimation accuracy is improved, but detection latency increases because processing cannot begin until the second time slot is received
Solution Approach 1:
The patent segments the orthogonal cover code application into two parts: first CDM subgroup processed in the first time slot, and second CDM subgroup processed in the second time slot. This allows channel estimation to begin after receiving only the first time slot, reducing detection latency while maintaining estimation accuracy through sequential processing of both segments.
Solution Approach 2:
The patent performs preliminary channel estimation using the first CDM subgroup in the first time slot before the second time slot is received. This preliminary action enables earlier detection and processing, reducing overall latency while the second CDM subgroup provides complementary information to complete the estimation.
2Measurement precision
If reference signals are transmitted in all resource blocks, then channel estimation coverage is improved, but peak power randomization becomes insufficient leading to power allocation issues
Solution Approach 1:
The patent applies different orthogonal cover codes to different CDM subgroups within the same resource block. This local differentiation achieves peak power randomization at the resource block level while maintaining channel estimation coverage across all resource blocks, resolving the contradiction between coverage and power randomization.
3Object-generated harmful factors
If complex OCC mapping patterns are used to support full peak power randomization, then power allocation is improved, but processing complexity increases
Solution Approach 1:
The patent segments the CDM group into two subgroups with different orthogonal cover code assignments. This segmentation achieves peak power randomization through simple code differentiation rather than complex mapping patterns, reducing processing complexity while maintaining power allocation quality.
Data Source
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Figure 3(a)~3(b)
AI summary
In some embodiments, a method is provided in a radio network node for transmitting a reference signal over an antenna port, wherein the reference signal is transmitted in a code division multiplexing, CDM, group. The CDM group comprises at least two CDM subgroups, each CDM subgroup being transmitted on a different subcarrier. Each CDM subgroup comprises resource elements. In a first step, the radio network node transmits the reference signal over a first CDM subgroup using an orthogonal cover code. The first CDM subgroup comprises resource elements in a first time slot and a subsequent time slot. In a further step, the radio network node transmits the reference signal over a second CDM subgroup using a permutation of the orthogonal cover code. The second CDM subgroup comprises resource elements in the first time slot and the second time slot. The permutation of the orthogonal cover code is selected in such a way as to enable decoding of the reference signal in the frequency domain, by applying the orthogonal cover code only to resource elements in the CDM group which are comprised in the first time slot.