CDMA Pilot Symbol Allocation for Interference Mitigation
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Solution Overview
Problem
Conventional CDMA-based communication systems are interference-limited due to non-orthogonal spreading codes, leading to degraded receiver performance and increased multiple access interference (MAI), especially in scenarios with a high number of users, where existing multi-user receivers are complex and inefficient in mitigating MAI.
Innovation Solution
The method involves allocating different pilot symbol sequences to each user entity, similar to a frequency division multiple access (FDMA) technique, to mitigate MAI by ensuring orthogonality and reducing cross-correlation between spreading codes, thereby improving channel estimation and synchronization accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If orthogonal spreading codes are used for separating users in CDMA-based communication systems, then user separation capability is improved, but multiple access interference increases due to non-orthogonality in frequency-selective channels and delay spread
Solution Approach 1:
The invention segments the frequency spectrum into multiple subbands and assigns different pilot symbol sequences to different subbands. This segmentation allows orthogonal spreading codes to maintain their orthogonality properties within each subband, reducing multiple access interference caused by frequency-selective fading and delay spread across the entire bandwidth.
Solution Approach 2:
The invention applies local quality by ensuring that each user's pilot symbols are transmitted on specific frequency subbands where their orthogonal spreading codes maintain orthogonality. This local optimization of signal quality in frequency-selective channels reduces the harmful effects of non-orthogonality and multiple access interference in specific frequency regions.
2Productivity
If the number of users in a cell increases, then system capacity is improved, but receiver performance degrades due to increased multiple access interference
Solution Approach 1:
The invention introduces an additional dimension for user separation by combining orthogonal spreading codes in the code domain with orthogonal pilot symbol sequences in the frequency domain. This two-dimensional separation approach allows the system to accommodate more users while maintaining receiver performance, as users are separated both by their spreading codes and by their assigned frequency subbands for pilot transmission.
3Object-affected harmful factors
If conventional multi-user receivers are used to reduce multiple access interference, then interference mitigation capability is improved, but system complexity increases due to complex interference cancellation algorithms
Solution Approach 1:
The invention applies preliminary action by assigning orthogonal pilot symbol sequences to different users before transmission begins. This pre-assignment of orthogonal frequency resources for pilots eliminates multiple access interference in the pilot signals, providing accurate channel estimates that enable simpler receiver structures to effectively mitigate interference in data signals without requiring complex iterative cancellation algorithms.
Data Source
AI summary
A solution for radio access in a code division multiple access (CDMA)-based telecommunication system, in which orthogonal spreading codes are used for separating data of a plurality of user entities, is provided. According to the solution, a different pilot symbol sequence is allocated to each user entity, and the pilot symbol sequences of user entities are selected by allocating different frequencies for pilot symbol sequences of different user entities according to a frequency division multiple access (FDMA) technique in order to mitigate the effect of multiple access interference.