Random Access Preamble Generation via Frequency and Sub-carrier Shifts
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Solution Overview
Problem
Current LTE systems have a limited number of available orthogonal random access preambles, leading to increased collision probabilities and constrained random access channel capacity, especially in larger cell sizes and 5G systems.
Innovation Solution
The method involves generating random access preambles through frequency shifts and sub-carrier shifts of root sequences, allowing for a significant increase in the number of available preambles, with the number of preambles potentially doubling or increasing n times with n sub-carrier shifts, thereby improving the random access success rate and reducing implementation complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the frequency allocation for random access preamble is increased to allow longer root sequences, then the number of available random access preambles increases, but the linear increase limits the scalability for large cell sizes and 5G systems
Solution Approach 1:
The patent transitions from one-dimensional cyclic shifts in the time domain to two-dimensional frequency shifts and sub-carrier shifts in the frequency domain. This dimensional change allows generating multiple distinct preambles from a single root sequence by applying different frequency shifts and sub-carrier shifts, thereby exponentially increasing the number of available preambles without linearly increasing the frequency allocation.
Solution Approach 2:
The patent changes the parameters used for preamble generation from cyclic shift values to frequency shift values and sub-carrier shift values. By varying these frequency-domain parameters, the system can generate a larger number of orthogonal preambles from the same root sequence, effectively increasing preamble capacity without proportionally increasing resource allocation.
2Reliability
If multiple nodes select the same random access preamble, then collision occurs resulting in random access failure, but increasing the number of preambles requires larger frequency allocation
Solution Approach 1:
By introducing frequency shifts and sub-carrier shifts as new dimensions for preamble differentiation, the system can distinguish more preambles within the same frequency allocation. This allows nodes to select from a larger pool of orthogonal preambles, reducing collision probability without expanding the frequency resources.
Solution Approach 2:
The system changes from using cyclic shift parameters to using frequency shift and sub-carrier shift parameters for preamble generation. This parameter transformation enables the same root sequence to generate multiple orthogonal preambles, increasing the effective number of preambles available for node selection and thereby reducing collisions.
3Quantity of substance
If frequency shifts and sub-carrier shifts are applied to generate more preambles, then the number of available preambles increases significantly, but the complexity of preamble detection and processing increases
Solution Approach 1:
The patent designs the random access preamble structure to be compatible with existing FFT-based detection mechanisms used for other uplink channels. The repeated short sequence structure allows the same detection hardware and algorithms to process both random access preambles and regular uplink data, eliminating the need for separate specialized processing paths and reducing overall system complexity.
Solution Approach 2:
The patent uses a repeated short sequence structure where a base sequence is copied multiple times to form the complete preamble. This copying approach allows the detection process to reuse the same correlation operations multiple times on different segments, reducing the computational complexity compared to processing a single long sequence directly.
Data Source
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AI summary
A node and an access node and methods therein for handling random access is disclosed. A method in a node for random access in a wireless network comprises, determining a set of sub-carrier shifts, wherein each sub-carrier shift indicates a shift with respect to a starting position in frequency domain for transmitting a random access preamble. The method further comprises selecting a sub-carrier shift from the set of sub-carrier shifts. The method further comprises transmitting a random access preamble to an access node， wherein the random access preamble is transmitted according to the selected sub-carrier shift.