Zadoff-Chu Cyclic Shift Grouping for LTE RACH Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In wireless communication systems, particularly in LTE UL, the detection of RACH preambles is hindered by frequency offsets, leading to increased false alarm rates and missed detection probabilities due to the deterioration of autocorrelation properties of Zadoff-Chu sequences and restricted cyclic shifts in high velocity environments.
Innovation Solution
The method involves selecting cyclic shifts of a Zadoff-Chu root sequence such that the timing uncertainty windows of allowed cyclic shifts do not overlap with frequency cyclic shifts of +1 or -1, ensuring separate frequency cyclic shifts for each timing uncertainty window element, thereby improving preamble detection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cyclic shifts of Zadoff-Chu sequences are used for RACH preambles in high velocity environments, then multiple preambles can be obtained from a single base sequence, but frequency offsets cause timing uncertainty window overlaps leading to increased false alarm rates and missed detection
Solution Approach 1:
The patent segments the set of cyclic shifts into multiple groups, where each group is assigned to a different base Zadoff-Chu sequence. This segmentation prevents timing uncertainty window overlaps by ensuring that cyclic shifts within each group are spaced sufficiently apart, while still providing a large total number of preambles across all groups and sequences.
Solution Approach 2:
The patent introduces an additional dimension to the preamble space by using multiple base Zadoff-Chu sequences with different root indices, in addition to cyclic shifts. This multi-dimensional approach (sequences × cyclic shifts) allows the system to achieve the required number of preambles while maintaining adequate spacing to avoid timing uncertainty window overlaps in high velocity environments.
2Reliability
If cyclic shifts are restricted to avoid timing uncertainty window overlaps, then false alarm rates are reduced, but the number of available preambles decreases
Solution Approach 1:
The patent makes each base Zadoff-Chu sequence serve multiple functions by assigning it a dedicated group of cyclic shifts that are optimized for high velocity environments. Each sequence-group combination provides a set of preambles with guaranteed non-overlapping timing uncertainty windows, while the collection of all sequences and groups provides the total required number of preambles.
Solution Approach 2:
The patent dynamically assigns cyclic shifts to different base sequences based on the specific requirements of the cell and deployment scenario. The grouping strategy can be adapted to balance between the number of available preambles and the spacing required to avoid timing uncertainty window overlaps, allowing flexible optimization for different operational conditions.
3Device complexity
If a single 0.8 ms Zadoff-Chu sequence is used for RACH preamble, then the structure is simple, but frequency offsets cause the received sequence to become orthogonal to the transmitted one, leading to detection failures
Solution Approach 1:
The patent changes the parameters of the Zadoff-Chu sequences by using multiple base sequences with different root indices and applying specific cyclic shift patterns within each group. This parameter variation ensures that even under frequency offsets and high Doppler shifts, the correlation properties are preserved and detection reliability is maintained, while keeping the overall structure manageable.
Data Source
AI summary
In one, non-limiting exemplary embodiment, a method includes: obtaining a timing uncertainty window parameter; and selecting, using the obtained timing uncertainty window parameter, a preamble sequence including a cyclic shift of a Zadoff-Chu root sequence, wherein the cyclic shift is an allowed cyclic shift from a group of allowed cyclic shifts, wherein the allowed cyclic shifts have timing uncertainty windows with timing uncertainty window elements, wherein the timing uncertainty windows of the allowed cyclic shifts do not overlap with one other or with frequency cyclic shifts of +1 or −1 of the timing uncertainty window elements, and wherein the frequency cyclic shift of −1 of the timing uncertainty window elements of the allowed cyclic shifts does not overlap with the frequency cyclic shift of +1 of the timing uncertainty window elements of other allowed cyclic shifts.