Despreading-on-demand Buffering for CDMA Spreading Factor Adaptation
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Solution Overview
Problem
In CDMA-based mobile radio communications, the existing despreading techniques face challenges due to the delay in determining the actual spreading factor for DPDCH channels, leading to inefficient buffering and resource allocation, especially with the introduction of enhanced dedicated channels and multi-code transmissions, which increases the complexity and cost of buffer sizing.
Innovation Solution
The despreading-on-demand technique allows for flexible and efficient despreading by storing the first frame of spread data at a lower rate and reading it out at a higher rate to quickly despread using the determined actual spreading factor, reducing delay and buffering requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the actual spreading factor is determined before despreading, then despreading can be performed accurately, but buffering requirements increase due to the need to store all received frames
Solution Approach 1:
The patent applies preliminary action by determining the actual spreading factor from control information before the despreading operation is performed. The receiver extracts transport format information including the spreading factor from downlink control information (DCI) or uplink control information (UCI) in advance, allowing the despreader to be properly configured before processing the data frames. This eliminates the need for large buffers while maintaining accurate despreading.
Solution Approach 2:
The patent implements dynamics by making the spreading factor adaptive and variable rather than fixed. The actual spreading factor is dynamically determined based on the transport format indicated by control information, allowing the system to adjust the spreading factor according to channel conditions and traffic requirements. This dynamic approach enables flexible resource allocation without requiring oversized buffers to accommodate all possible spreading factor scenarios.
2Adaptability or versatility
If large buffers are allocated to accommodate varying spreading factors, then all transmission scenarios can be handled, but system cost and complexity increase
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the spreading factor parameter based on control information rather than using fixed or pre-configured buffer sizes. The receiver determines the actual spreading factor from transport format indicators in control messages, then configures the despreader accordingly. This parameter-driven approach simplifies the system architecture by eliminating complex buffer sizing calculations and allows the system to adapt to different transmission scenarios using a single, consistently-sized buffer.
3Ease of operation
If data is read out at the same rate as received, then buffering is simple, but despreading delay increases
Solution Approach 1:
The patent applies preliminary action by completing the spreading factor determination from control information before the despreading operation begins. This advance determination allows the system to prepare the despreader configuration in advance, enabling faster processing when the actual data frames need to be despread, thereby reducing overall delay without complicating the buffering operation.
Data Source
AI summary
A flexible and resource-efficient despreading-on-demand (DoD) technique is described where only channels that actually contain data to be despread are despread, and only a single despreading operation need be performed using the actual spreading factor associated with that data. In one example, the data portion of the received signal is buffered for a frame so that an associated transport format, including the actual spreading factor, can be determined before the data is despread. The data is buffered in a memory at a first rate and then subsequently read out at a second rate that is considerably faster than the first rate. The fast data read-out allows despreading at a high rate so that the despread data symbols from the buffered frame are available for further processing shortly after the last sample belonging to the frame has been received.