Low Latency PRACH Design for Unlicensed Spectrum
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Solution Overview
Problem
In wireless cellular communication systems, particularly in unlicensed spectrum, the Physical Random Access Channel (PRACH) procedure experiences high latency due to Listen-Before-Talk (LBT) procedures, which limit uplink transmissions and hinder efficient data rate improvement in next-generation networks like 5G.
Innovation Solution
The implementation of low-latency PRACH designs for MulteFire systems, which include two-step and single-step PRACH procedures that perform contention resolution and UL grant allocation, reducing latency by optimizing PRACH preamble and data transmission within UL subframes using Orthogonal Frequency Division Multiplexing (OFDM) symbols and interlaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional four-step PRACH procedure is used in unlicensed spectrum, then LBT procedures can be performed to ensure fair access, but PRACH latency increases significantly
Solution Approach 1:
The patent merges multiple PRACH steps into a single step by combining preamble transmission, contention resolution, and UL grant allocation into one simultaneous transmission. This eliminates the sequential LBT procedures required in traditional four-step PRACH, reducing latency while maintaining fair access through the LBT mechanism performed once before the combined transmission.
Solution Approach 2:
The patent performs preliminary actions by transmitting the preamble and associated control information in advance within the same subframe, enabling the base station to prepare and allocate resources beforehand. This preliminary transmission of control data allows for faster subsequent data transmission without waiting for separate LBT cycles.
2Speed
If PRACH procedure is simplified to reduce latency, then uplink transmission speed improves, but contention resolution may be compromised
Solution Approach 1:
The patent combines contention resolution information with the preamble transmission in a single integrated message. By merging the preamble with UL grant allocation and contention resolution data, the system maintains reliable contention resolution while enabling faster transmission, as all necessary control information is transmitted simultaneously rather than sequentially.
Solution Approach 2:
The patent makes the PRACH transmission multi-functional by incorporating preamble signaling, contention resolution, and UL grant allocation into a single transmission. This universal message structure allows one transmission to serve multiple purposes: establishing the uplink connection, resolving contentions, and allocating resources, thereby maintaining reliability while improving speed.
3Adaptability or versatility
If PRACH uses traditional OFDM symbol allocation, then compatibility with existing LTE is maintained, but data rate improvement is limited
Solution Approach 1:
The patent segments the PRACH transmission into multiple interlaces within a UL subframe, allowing parallel transmission of preamble and data across different frequency resources. This segmentation enables the system to maintain LTE compatibility through structured resource allocation while improving data rate through parallel transmission, as multiple data symbols can be sent simultaneously across different interlaces.
Solution Approach 2:
The patent introduces a new dimension to PRACH transmission by utilizing multiple interlaces across frequency resources rather than traditional single-symbol allocation. This dimensional expansion allows the system to transmit data in parallel across multiple frequency slots within the same time subframe, maintaining LTE compatibility while significantly improving data rate capability.
Data Source
AI summary
Described is an apparatus of an Evolved Node-B (eNB) operable to communicate with a User Equipment (UE) on a wireless network. The apparatus may comprise a first circuitry and a second circuitry. The first circuitry may be operable to initiate a Listen-Before-Talk (LBT) procedure on a bandwidth of the wireless network, the bandwidth being unlicensed spectrum. The second circuitry may be operable to generate a transmission if the LBT procedure indicates that the bandwidth is idle, the transmission comprising a Physical Random Access Channel (PRACH) preamble portion and a message portion.