Random Access Preamble Transmission Using Tx Diversity
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Solution Overview
Problem
Current radio communications networks face challenges in utilizing uplink transmit diversity due to the lack of immediate feedback and knowledge about user equipment's multiple transmit antennas, which hinders the network's ability to benefit from this diversity during random access procedures.
Innovation Solution
The method involves a radio network node scanning for and detecting multiple random access preambles transmitted simultaneously or sequentially through different transmit antenna ports, allowing the user equipment to select the best antenna port based on feedback from the network, thereby enabling the use of transmit diversity for improved random access performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the user equipment transmits random access preambles using multiple transmit antennas with transmit diversity, then the random access performance and reliability are improved, but the device complexity increases due to the need for multiple transmit antennas and antenna weight management
Solution Approach 1:
The patent segments the random access procedure into two distinct parts: a first random access preamble transmitted without transmit diversity (using single antenna) and a second random access preamble transmitted with transmit diversity (using multiple antennas). This segmentation allows the system to achieve reliability improvements through transmit diversity only when necessary, while avoiding the complexity of managing multiple antennas for all random access attempts.
Solution Approach 2:
The patent applies preliminary action by first transmitting the initial random access preamble using a single antenna before attempting to use multiple antennas with transmit diversity. The network node evaluates the success of this initial transmission and only then proceeds to use the more complex multi-antenna approach if needed, thereby reducing overall device complexity while maintaining reliability improvements when necessary.
2Productivity
If the user equipment uses beamforming with multiple transmit antennas, then the network performance is maximized in terms of bitrate, but the device complexity increases due to requiring one Power Amplifier for each transmit antenna
Solution Approach 1:
The patent segments the transmit antenna usage into optional beamforming mode for the second random access preamble, allowing the user equipment to achieve higher bitrate through beamforming only when the network node requests it and when the device has the capability, rather than requiring full beamforming hardware for all operations.
Solution Approach 2:
The patent changes the operational parameters dynamically by switching between single-antenna and multi-antenna modes based on network feedback and device capability. The user equipment can adjust its transmit diversity configuration (including beamforming parameters) based on the random access response received from the network, thereby achieving high bitrate performance only when conditions permit, reducing overall device complexity requirements.
3Reliability
If the user equipment gradually increases transmission power for random access preamble, then the probability of successful access is improved, but the interference levels and energy consumption increase
Solution Approach 1:
The patent uses the first random access preamble transmitted at initial power levels to establish basic connectivity before attempting more powerful transmissions. By successfully completing the initial preamble transmission at lower power, the system reduces the need for subsequent high-power retransmissions, thereby lowering overall interference levels while maintaining access success probability.
Solution Approach 2:
The patent introduces the network node's random access response as an intermediary that provides feedback on the success of the initial preamble transmission. This intermediary mechanism allows the system to determine whether higher power transmissions are actually necessary, reducing unnecessary high-power transmissions and their associated interference, while still achieving reliable access when needed.
Data Source
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AI summary
Embodiments herein relate to a method in a user equipment (10) for requesting access to a radio communications network (1), which user equipment (10) comprises at least two transmit antenna ports. The user equipment (10) obtains one or more random access preambles to be used to access the radio communications network. The user equipment (10) transmits; in case of obtaining one random access preamble, the one random access preamble over the at least two transmit antenna ports. In case of obtaining more than one random access preambles, the user equipment (10) transmits each random access preamble over a separate antenna port out of the at least two transmit antenna ports.