Block Scrambling for OFDMA Inter-Cell Interference
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Solution Overview
Problem
In wireless communication systems, particularly Evolved-UMTS Radio Access (E-UTRA), inter-cell interference poses a significant challenge that affects system performance, such as cell average throughput and cell edge throughput, due to the similarity of block spreading codes used by user equipment in adjacent cells, leading to identical interference patterns across time slots.
Innovation Solution
Implementing cell-specific block scrambling codes, which are pseudo-random sequences of equal or greater length than the number of time periods, to decorrelate and randomize inter-cell interference by assigning different scrambling codes to user equipment in each cell, thereby separating signals and minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If block spreading codes are used to separate multiple users in OFDMA systems, then user separation and concurrent transmission capability are improved, but inter-cell interference increases due to identical interference patterns across time slots
Solution Approach 1:
The patent applies dynamics by introducing time-varying block scrambling codes that change across different time slots. Instead of using static spreading codes, the system dynamically scrambles the block spreading codes with cell-specific sequences that vary over time. This temporal variation transforms the interference pattern from static and identical across time slots to dynamic and different for each time slot, thereby reducing inter-cell interference while maintaining user separation capability.
Solution Approach 2:
The patent changes the parameter of the spreading code by introducing an additional scrambling dimension. The block spreading code is modified by multiplying it with a cell-specific block scrambling code that varies in time. This parameter change transforms the interference characteristics by ensuring that even though users in the same cell experience identical spreading codes, users in different cells experience different scrambled versions, thereby differentiating interference patterns across cells.
2Productivity
If cell-specific block scrambling codes are introduced to randomize inter-cell interference, then interference is reduced and system performance is improved, but device complexity increases due to additional scrambling processing
Solution Approach 1:
The patent uses copying by deriving the cell-specific block scrambling code from a cell identity parameter. Instead of requiring completely independent random codes for each cell, the system copies the structure of the scrambling code and instantiates it with cell-specific parameters. This allows multiple cells to use the same scrambling code structure while differentiated by their cell identity, reducing the complexity of code generation and management while still achieving cell-specific interference randomization.
Data Source
AI summary
A method of transmitting signals in a communication system over at least two time periods including generating a base signal comprising of at least two samples in each time period, selecting a scrambling sequence of length equal to or greater than the number of time periods, scaling all samples in said signal in a time period with one element of said scrambling sequence and transmitting the scaled signal in said time period. Different elements of the scrambling sequence are used to scale the base signal in different time periods. The signal in each time period is obtained by scaling a base signal. The scrambling sequence is preferably a pseudo-random sequence. The step of scaling all samples in said signal in a time period consists of multiplying all samples of said signal with an element of said scrambling sequence.