Complex-Valued Spreading Sequences for CDMA Interference Reduction
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Solution Overview
Problem
Current multi-user code division multiple access (CDMA) systems face challenges in achieving good access performance due to high multi-user interference and system overload, particularly because binary pseudo-noise real number sequences with shorter lengths have poor cross-correlation properties, leading to degraded demodulation performance and increased interference as the number of users increases.
Innovation Solution
The use of complex-valued spreading sequences, where each element is a complex number with real and imaginary parts from an M-element set of real numbers, is introduced to improve cross-correlation properties and reduce interference, allowing for better separation of user information and increased system capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If binary pseudo-noise real number sequences are used for spreading, then the spreading process is simple, but the cross-correlation properties are poor leading to high multi-user interference
Solution Approach 1:
The patent changes the parameter of spreading sequence values from binary real numbers to complex numbers with multiple possible values (M-PSK modulation). This transformation improves cross-correlation properties and reduces multi-user interference while maintaining system complexity at an acceptable level through the use of well-established complex signal processing techniques.
2Quantity of substance
If spreading sequence length is shortened, then the system overhead is reduced, but the cross-correlation properties deteriorate leading to degraded demodulation performance
Solution Approach 1:
The patent changes the parameter space of spreading sequences from real numbers to complex numbers. This allows for better cross-correlation properties even with shorter sequence lengths, as the complex domain provides more degrees of freedom for sequence design, thereby maintaining demodulation performance while reducing overhead.
3Productivity
If more users are accommodated in the system, then the system capacity increases, but the multi-user interference increases leading to system overload
Solution Approach 1:
The patent employs complex-valued spreading sequences with M-PSK modulation to improve cross-correlation properties. This allows for better separation of user signals even when many users are simultaneously active, thereby increasing system capacity while controlling multi-user interference through superior sequence orthogonality in the complex domain.
4Object-affected harmful factors
If complex-valued spreading sequences are used, then the cross-correlation properties improve and interference is reduced, but the device complexity increases
Solution Approach 1:
The patent replaces complex multi-user detection algorithms with simpler receivers by using complex-valued spreading sequences with improved cross-correlation properties. The better inherent orthogonality of these sequences allows for simpler correlation-based detection, substituting algorithmic complexity with mathematically superior sequence design.
Data Source
AI summary
A multi-user code division multiple access communication method, and corresponding transmitter and receiver include: the transmitter determines a complex-valued spreading sequence to be used by the transmitter, herein each element of the complex-valued spreading sequence is a complex number and values of real and imaginary parts of all elements in the complex-valued spreading sequence are from an M-element set of real numbers, and M is an integer larger than or equal to 2; the transmitter performs spreading processing on data symbols to be sent by using the complex-valued spreading sequence to generate a spread symbol sequence; and sends the spread symbol sequence. The receiver receives signals transmitted by multiple transmitters, and performs reception detection by using an interference cancellation signal detector, herein the complex-valued spreading sequences used by the multiple transmitters are used during detection.