Cyclic Shift Demodulation Reference Signal for LTE Random Access
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Solution Overview
Problem
In LTE wireless communication systems, contention-based random access procedures often result in collisions when multiple mobile stations select the same preamble, leading to delayed contention resolution and increased latency due to the inability of the base station to correctly decode messages from contending mobile stations.
Innovation Solution
Each mobile station randomly selects a cyclic shift for the demodulation reference signal when transmitting the random access message, allowing the base station to distinguish between channel responses and improve the probability of successful decoding, thereby reducing contention and latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple mobile stations use the same preamble for random access, then the random access procedure can be initiated, but collision occurs and decoding fails leading to increased latency
Solution Approach 1:
The patent segments the random access procedure by introducing cyclic shift differentiation. Mobile stations that collide on the same preamble are segmented into different groups based on their cyclic shift values, allowing the base station to separately process and decode each group's message, thereby resolving collisions and reducing delay
Solution Approach 2:
The patent applies dynamics by making the cyclic shift value a variable parameter that changes based on message type and transmission conditions. The cyclic shift is dynamically adjusted to provide orthogonal reference signals for different messages, enabling the system to adapt to collision scenarios and improve decoding success rate
2Reliability
If the base station attempts to decode messages from contending mobile stations using the same preamble, then decoding may fail, but increasing processing attempts increases latency
Solution Approach 1:
The patent applies preliminary action by pre-configuring multiple cyclic shift values and their corresponding orthogonal relationships before random access occurs. The base station prepares the decoding matrix and cyclic shift mappings in advance, so when collisions occur, it can immediately apply the pre-prepared differentiation without additional processing delay
Solution Approach 2:
The patent changes the cyclic shift parameter to differentiate between contending mobile stations. By varying this parameter based on message type and collision detection, the system transforms identical preambles into distinguishable signals, improving decoding reliability without requiring multiple retransmission attempts
Data Source
AI summary
A method and apparatus for accessing a wireless communication system, and for processing random access attempts. A mobile communication device detects random-access information transmitted by a base station, transmits a random-access preamble to the base station according to the random-access information, and receives a random-access response from the base station. The random-access response includes at least an allocation of uplink resources to be used for the next step in the random access procedure. The mobile device also selects a reference signal sequence index from a pre-determined set of sequence indexes, and transmits a first message to the base station using the uplink resource allocation provided in the random-access response. The first message includes a device identifier and a first demodulation reference signal derived from a base reference sequence shifted according to the selected sequence index.