LPWA Random Access Channel Design With Two-Step RACH
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Solution Overview
Problem
Existing random access channel designs for low power wide area (LPWA) communications face challenges such as high access latency, signaling overhead, network congestion, and increased collision risks, particularly in dense deployment scenarios, which are not adequately addressed by conventional four-step RACH procedures.
Innovation Solution
A two-step RACH procedure is introduced, combining the first and third messages of the four-step RACH into a single message (MsgA) for the UE and the second and fourth messages into a single message (MsgB) for the network, utilizing hashing techniques for preamble selection and interleaving uplink data transmission across different sets of PUSCH occasions to reduce collisions and latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a four-step RACH procedure is used for random access, then the access process is comprehensive and reliable, but the access latency is high and power consumption is increased
Solution Approach 1:
The patent combines the four-step RACH procedure into a two-step procedure by merging Message 1 and Message 3 into a single MsgA (containing preamble and uplink data), and merging Message 2 and Message 4 into a single MsgB (containing random access response and contention resolution). This reduces the number of round-trip transmissions from four to two, directly reducing access latency while maintaining access reliability through integrated transmission of all necessary information in each message exchange.
Solution Approach 2:
The patent enables the UE to transmit both the preamble and uplink data payload in MsgA simultaneously, rather than waiting for separate grants. The network processes both the random access preamble and the uplink data in parallel, preparing the contention resolution identifier in advance based on the received uplink data. This preliminary processing reduces the time required for sequential operations in the traditional four-step procedure.
2Reliability
If conventional RACH procedures are used in dense deployment scenarios, then network coverage is maintained, but collision risks increase and network congestion occurs
Solution Approach 1:
The patent changes the parameter of message structure by including the uplink data payload directly within MsgA alongside the preamble, rather than transmitting data in a separate subsequent message. This parameter change allows the network to process contention resolution based on the actual uplink data content, enabling more sophisticated collision resolution mechanisms that can differentiate between overlapping transmissions, thereby reducing collision impact in dense deployments.
Solution Approach 2:
The network generates a contention resolution identifier in MsgB based on the uplink data payload received in MsgA and transmits it back to the UE. This feedback mechanism allows the UE to verify whether its transmission was successfully received and differentiated from other UEs. In dense deployment scenarios, this feedback enables rapid detection and resolution of collisions, reducing the impact of harmful interference and retransmission requirements.
3Reliability
If multiple PUSCH occasions are allocated for uplink data transmission, then transmission reliability is improved, but signaling overhead and device complexity increase
Solution Approach 1:
The patent merges the random access preamble transmission and uplink data transmission into a single MsgA transmission event, even though the data may be transmitted across multiple PUSCH occasions. The network allocates multiple PUSCH occasions for the uplink data payload but treats the entire sequence as part of a single random access procedure, reducing the need for separate signaling for each transmission occasion and simplifying the overall procedure while maintaining reliability through redundant transmission opportunities.
Data Source
AI summary
Various aspects of the present disclosure relate to random access for low power wide area (LPWA) communications. A user equipment (UE) can determine a first set of physical uplink shared channel (PUSCH) occasions. Additionally, the UE can determine a first random access channel (RACH) occasion. Moreover, the UE can determine a second set of PUSCH occasions based at least in part on one or more of the first set of PUSCH occasions, the first RACH occasion, and a first PID associated with the first RACH occasion. Subsequently, the UE can transmit a first random access message during a random access procedure. The first random access message can include a preamble and an uplink data payload. The preamble can be transmitted during the first RACH occasion and the uplink data payload can be transmitted during the second set of PUSCH occasions. The preamble can be associated with the first PID.