E-DCH Shared Channel for High-Speed Random Access
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Solution Overview
Problem
Current wireless communication systems, particularly in Release 99, face limitations with low data rates on the random access channel (RACH), significant retransmission delays, and substantial setup times from CELL_FACH to CELL_DCH, making them unsuitable for large packet transmissions and impacting user experience, especially for TCP-based applications.
Innovation Solution
The implementation of a high-speed random access channel (HS-RACH) using existing physical channels as shared channels, where uplink E-DPDCH and E-DPCCH are used for data transmission, and downlink L1 feedback channels for power control and capacity allocation, enabling higher bit rates and reducing delays by assigning dedicated mode channels for random access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional RACH is used for random access, then device compatibility is maintained, but data rate remains very low (16 kbps)
Solution Approach 1:
The E-DCH is configured to serve dual purposes: functioning as a dedicated channel for scheduled data transmission and as a shared random access channel (E-RACH) for initial access. This multi-functionality allows the system to achieve high data rates while maintaining compatibility with devices expecting traditional RACH behavior.
Solution Approach 2:
The system dynamically switches the operational mode of the E-DCH between dedicated mode (for high-rate data transmission) and shared random access mode (for initial access). This dynamic adaptation allows the channel to optimize performance based on current operational requirements while maintaining backward compatibility.
2Loss of time
If traditional RACH setup procedure is used, then protocol compatibility is maintained, but setup time from CELL_FACH to CELL_DCH is substantial
Solution Approach 1:
The system performs random access procedures preliminarily over the E-DCH while the UE remains in CELL_FACH state, rather than requiring a subsequent transition to CELL_DCH. This preliminary action eliminates the time-consuming state transition delay while maintaining compatibility with the existing protocol framework.
Solution Approach 2:
The invention extracts the random access functionality from the traditional RACH pathway that requires CELL_FACH to CELL_DCH state transition, and relocates it to the E-DCH. This separation allows high-speed random access to occur independently of the slow state transition mechanism, reducing overall setup time.
3Speed
If E-DCH is used for random access, then data rate increases to hundreds of kbps or Mbps, but channel configuration complexity increases
Solution Approach 1:
The E-DCH is configured to serve dual purposes: functioning as a dedicated channel for scheduled data transmission and as a shared random access channel (E-RACH) for initial access. This multi-functionality allows the system to achieve high data rates while maintaining compatibility with devices expecting traditional RACH behavior.
Solution Approach 2:
The system utilizes existing E-AGCH and E-HICH channels that are already part of the HSUPA framework to provide capacity allocation and feedback for the E-RACH operations. This self-service approach leverages existing infrastructure rather than requiring completely new control mechanisms, thereby reducing overall system complexity.
4Loss of time
If traditional RACH is used, then implementation simplicity is maintained, but retransmission delay is significant
Solution Approach 1:
The system implements fast feedback mechanisms through the E-HICH channel, which provides rapid acknowledgment and retransmission commands for E-RACH transmissions. This feedback loop operates much faster than traditional RACH retransmission mechanisms, significantly reducing retransmission delay while maintaining implementation feasibility through standardized HSUPA components.
Solution Approach 2:
The system dynamically adjusts the operational mode of the E-DCH between dedicated mode (for high-rate data transmission) and shared random access mode (for initial access). This dynamic adaptation allows the channel to optimize performance based on current operational requirements while maintaining backward compatibility.
Data Source
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AI summary
Apparatus, methods and computer program products in a wireless communications system provide an enhanced dedicated channel (E-DCH) for use by user equipment operating in the wireless communications system for use in conjunction with the random access procedure. The user equipment has circuitry to request a HS random access channel and, in response to receiving an assignment from a Node B of a dedicated mode channel for use as the random access channel, to send uplink data in a random access fashion over the assigned dedicated mode channel while receiving feedback from the Node B over at least one downlink L1 feedback channel. The Node B has circuitry to assign to the UE the dedicated mode channel for use as the random access channel, to receive uplink data in a random access fashion over the assigned dedicated mode channel, and to send feedback information to the UE over at least one downlink L1 feedback channel.