Block Spreading CDMA Guard Symbols for MAI Reduction
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Solution Overview
Problem
In code division multiple access (CDMA) mobile communication systems, multiple access interference (MAI) significantly degrades signal quality and bit error rate (BER) as the number of users and paths increases, particularly in block spreading CDMA systems, where existing methods to reduce interference either increase system complexity or deteriorate bandwidth efficiency.
Innovation Solution
A method and apparatus that generate and receive traffic sequences using block spreading codes by inserting forward and backward guard symbols, where the first symbol is repeatedly copied and rear symbols are mirrored and inserted, to reduce interference from multiple paths without increasing system complexity, utilizing a chip spreading unit, symbol generating unit, maximum ratio combination detector, and feedback filter to process and filter symbols effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If block spreading CDMA is used to support more users and paths, then system capacity and data transfer speed are improved, but multiple access interference increases and degrades signal quality
Solution Approach 1:
The patent applies preliminary action by inserting guard symbols at the beginning and end of data blocks before transmission. These guard symbols are predetermined sequences that prepare the system to handle multipath interference in advance, allowing the receiver to distinguish between desired signals and delayed interference from other users or paths.
Solution Approach 2:
The guard symbols act as intermediary elements between the data blocks and the interference from multiple access. By placing these intermediary sequences at block boundaries, the system creates a buffer zone that mediates the interaction between transmitted signals and delayed replicas, preventing direct interference with data symbols.
2Object-affected harmful factors
If conventional interference reduction methods are applied, then multiple access interference is reduced, but system complexity increases
Solution Approach 1:
The patent segments the transmitted signal into distinct blocks with guard symbols separating them. This segmentation divides the continuous signal stream into manageable chunks, allowing simple block-level processing at the receiver without requiring complex continuous interference cancellation algorithms. Each block can be processed independently, reducing overall system complexity.
Solution Approach 2:
The invention changes the temporal parameter of signal transmission by introducing guard intervals (guard symbols) between data blocks. This parameter change transforms the interference problem from a continuous complex cancellation task into a discrete block-based problem that can be solved with simpler synchronization and correlation techniques.
3Object-affected harmful factors
If guard symbols are inserted to reduce interference, then signal quality is improved, but bandwidth efficiency deteriorates
Solution Approach 1:
The patent applies partial action by inserting guard symbols only at necessary block boundaries rather than continuously throughout the transmission. The length of guard symbols is optimized to be just sufficient to handle the expected multipath delay spread, avoiding excessive bandwidth consumption while providing adequate protection against interference.
Data Source
AI summary
An apparatus and method for generating and receiving traffic in a code division multiple access mobile communication system using a block spreading scheme. The apparatus and method for generating and receiving traffic sequences in a code division multiple access mobile communication system use a block spreading code, by a simple method, without increasing the complexity of a system, which is capable of improving receipt performance by reducing an MAI at maximum.