Polyphase Subband Encryption for Mobile Voice Confidentiality
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Solution Overview
Problem
Existing voice encryption technologies based on polyphase filter banks face challenges in achieving optimal speech quality and confidentiality due to subband permutation inefficiencies, leading to recognizable speech and high processing complexity, especially in mobile devices with limited resources.
Innovation Solution
The proposed method employs polyphase subband filters derived from a prototype filter, with adaptive subband configuration and permutation based on signal energy distribution, and optional noise injection to ensure confidentiality, using FPGA-based devices for efficient processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If subband permutation is used for encryption, then confidentiality is improved, but speech quality deteriorates due to non-optimal reconstruction
Solution Approach 1:
The speech signal is divided into multiple subbands using polyphase filter banks, allowing independent processing of each subband. This segmentation enables permutation operations on individual subbands while maintaining the ability to reconstruct the original signal through complementary synthesis filters.
Solution Approach 2:
The invention changes the permutation parameters by using complementary synthesis filters that are specifically designed to reverse the analysis filter effects. The synthesis filters have frequency responses that are complementary to the analysis filters, ensuring that after permutation, the subbands can be perfectly reconstructed without quality loss.
2Reliability
If complex encryption algorithms are used, then confidentiality is improved, but processing complexity and energy consumption increase
Solution Approach 1:
By segmenting the signal into subbands, the encryption process becomes simpler as each subband can be processed independently with basic permutation operations, avoiding the need for complex cryptographic algorithms while still achieving good confidentiality.
Solution Approach 2:
The invention changes from complex cryptographic parameter transformations to simple permutation operations on subband indices. The encryption key determines the permutation pattern, but the actual operation is computationally lightweight compared to traditional encryption methods.
3Reliability
If subband permutation is used for encryption, then confidentiality is improved, but processing power requirements increase
Solution Approach 1:
The polyphase filter bank structure segments the processing into parallel subband channels, allowing efficient utilization of processing resources. Each subband can be permuted independently, reducing the overall computational burden compared to processing the entire signal spectrum together.
Solution Approach 2:
The invention changes the processing approach from complex time-domain encryption to frequency-domain permutation, which is computationally more efficient. The permutation operation involves simple index rearrangement rather than complex mathematical transformations, significantly reducing processing power requirements.
4Ease of manufacture
If existing polyphase filter bank encryption is used, then encryption functionality is provided, but speech remains recognizable due to insufficient permutation
Solution Approach 1:
The signal is segmented into multiple subbands that are then permuted according to a key-dependent pattern. This segmentation and permutation approach ensures that no single subband contains recognizable speech characteristics, as the perceptually important frequency components are scattered across different subbands.
Solution Approach 2:
The invention changes the permutation strategy by using a more comprehensive permutation pattern that operates on all subbands rather than selecting only certain ones for modification. This ensures that the entire speech spectrum is adequately scrambled, preventing recognizable speech while maintaining decryption capability through the complementary filter bank structure.
Data Source
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AI summary
The invention relates to techniques for encrypting and decrypting information signals, for example digital voice signals in mobile communications, based on polyphase filter banks. A method embodiment of the invention for encrypting information signals comprises the steps of splitting, based on multiple analysis subband filters, an input information signal into a set of signal subbands; performing an encryption operation on one or more subbands of the set of subbands; and synthesizing, based on multiple synthesis subband filters, the encrypted set of subbands into an output information signal, wherein a particular synthesis filter is the product of all analysis filters except the analysis filter corresponding in subband to the particular synthesis filter.