Block Equalization for Chip-Interleaved CDMA Signals
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Solution Overview
Problem
In multi-user wireless communication systems, especially in CDMA systems, frequency selective channels cause inter-chip interference (ICI) and multiple user interference (MUI), leading to data loss and inefficiencies due to non-orthogonal waveforms, and existing solutions are complex and power inefficient.
Innovation Solution
The implementation of block equalization techniques on block-spread wireless communication signals after de-spreading, allowing for one-step processing to generate symbol estimates, which reduces complexity and enhances orthogonality among user signals, thereby mitigating MUI and inter-cell interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multi-user detectors are used to suppress MUI, then MUI suppression is improved, but device complexity and implementation cost increase
Solution Approach 1:
The patent segments the equalization process into block-based processing rather than per-chip processing. By grouping chips into blocks and applying equalization to blocks after de-spreading, the system reduces the complexity of multi-user detection while maintaining MUI suppression capability. The block equalizer processes multiple chips simultaneously in a structured manner, simplifying the overall detector architecture.
Solution Approach 2:
The patent applies de-spreading operation before block equalization. By removing the spreading code first, the system prepares the signal in advance to make subsequent equalization simpler and more effective. This preliminary action separates the user signal from the spreading code, enabling simpler equalization to handle remaining interference.
2Productivity
If frequency selective channels are used to increase transmission rate, then data rate is improved, but inter-chip interference increases
Solution Approach 1:
The patent changes the equalization approach by using block-based processing with multiple taps that adapt to frequency selective fading. The block equalizer uses channel information to adjust equalization parameters for different frequency components, compensating for ICI caused by frequency selective channels while maintaining high transmission rates.
Solution Approach 2:
The patent introduces a block equalizer as an intermediary component between the de-spreading operation and symbol detection. This equalizer acts as a mediator that processes the de-spread signal, correcting frequency selective distortion and ICI effects before final detection, thereby enabling high data rates in frequency selective channels.
3Reliability
If soft handoff mode is used to improve transmission quality, then transmission quality is improved, but processing complexity increases
Solution Approach 1:
The patent merges the processing of multiple base station signals into a unified block equalization process. Instead of handling each base station's signal separately, the system combines signals from multiple base stations and applies a single block equalizer to process them together, reducing processing complexity while maintaining the quality benefits of soft handoff.
Solution Approach 2:
The block equalizer serves multiple functions simultaneously: it performs equalization, handles soft handoff processing, and prepares signals for de-spreading. This multi-functional approach reduces overall system complexity by consolidating operations that would otherwise require separate processing stages.
4Loss of time
If conventional chip-level equalization is used, then equalization is performed early, but overall system complexity increases
Solution Approach 1:
The patent performs de-spreading before block equalization, which is a more efficient sequence. By removing the spreading code first, the system reduces the amount of data that needs to be processed by the equalizer, thereby reducing complexity while maintaining timely equalization performance.
Solution Approach 2:
The patent transitions from chip-level processing to symbol-level block processing. By operating at the symbol level after de-spreading, the system reduces the dimensionality of processing requirements, making equalization less complex while maintaining effectiveness in correcting frequency selective distortion.
Data Source
AI summary
Techniques are described for performing block equalization on a received wireless communication signal formed according to interleaved chips generated from sub-blocks of symbols. For example, a one-step block equalization process is described which produces estimates of the information-bearing symbols from a wireless communication signal received from two or more transmitters in a soft handoff environment. The techniques provide improved performance in high load, soft handoff environments with low complexity, highly flexible equalization. The wireless communication signal may be a CIBS-CDMA signal in which a symbol block is divided into sub-blocks and spread by a user-specific block-spreading matrix. The CIBS signal is received through M subchannels and a de-spreading matrix is applied to produce a multi-user interference (MUI) free sub-block output for the mth channel. One-step block equalization comprises forming a single block from the m de-spread sub-blocks and performing block equalization on the single block.