Pre-stored QPSK Sequences for LTE Uplink Reference Signals
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Solution Overview
Problem
In wireless communication systems, particularly in 3GPP LTE, existing technologies face challenges in efficiently generating reference signals with low cubic metric and good cross-correlation properties for user terminals, especially for allocations of one or two resource blocks, which require significant memory and complexity.
Innovation Solution
The use of pre-stored QPSK sequences with specific phase scaling factors and imaginary parts, allowing for the generation of uplink reference signals with reduced memory requirements by storing information representative of these sequences on user terminals, enabling efficient modulation on subcarriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If QPSK sequences are used for reference signal generation in 3GPP LTE user terminals, then memory requirements are reduced to 24 or 48 bits per sequence for 1 and 2 resource blocks respectively, but sequence properties such as cubic metric and cross-correlation are compromised
Solution Approach 1:
The patent pre-calculates and stores optimal phase scaling factors for QPSK sequences in lookup tables during system design or initialization. These pre-computed factors are then directly applied during reference signal generation without real-time calculation, achieving low cubic metric and good cross-correlation properties while using compact memory structures suitable for user terminals with limited resources
Solution Approach 2:
The patent optimizes specific parameters of the QPSK sequences by applying carefully selected phase scaling factors (such as 1, -1, j, -j) to different sequence elements. This parameter optimization maintains desirable sequence properties including low cubic metric and good cross-correlation, while keeping the memory footprint at acceptable levels for 1 and 2 resource block allocations
2Reliability
If Zadoff-Chu sequences are used for reference signal generation, then cubic metric and cross-correlation properties are improved, but memory requirements and device complexity increase
Solution Approach 1:
Instead of implementing complex Zadoff-Chu sequence generation algorithms that require significant memory and computational resources, the patent creates simplified QPSK sequences that copy the desirable correlation properties of ZC sequences. These approximated sequences are stored in compact lookup tables and applied directly, achieving similar performance benefits without the computational burden
Solution Approach 2:
The patent replaces expensive, complex ZC sequence generation with cheaper, pre-computed QPSK sequences that can be stored in small lookup tables. These simplified sequences are disposable in the sense that pre-computed tables can be easily replaced or reloaded without requiring complex generation logic, reducing overall device complexity while maintaining acceptable sequence properties
Data Source
AI summary
A wireless communication device including a controller communicably coupled to a transceiver. In one embodiment, the controller generates a QPSK sequence having multiple elements wherein each element includes real and imaginary parts. In another embodiment, the sequence is selected from a groups of sequences stored on a user terminal. Thereafter, the controller generates a reference signal based on the information representative of the selected QPSK sequence.