CPM Pulse Shaping for Adjacent Channel Interference
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Solution Overview
Problem
Existing multi-user wireless communication systems face performance degradation due to adjacent channel interference (ACI), which limits bandwidth efficiency and channel capacity, as conventional pulse shapes are suboptimal for coded systems and increase receiver complexity.
Innovation Solution
A new pulse shape is introduced, derived as a linear combination of rectangular and raised-cosine phase pulses, which addresses the tradeoff between the width of the power spectral density (PSD) main lobe and the rate of side lobe decay, optimized using information theory to maximize channel capacity while minimizing interference, and implemented with a binary convolutional coder and CPM modulator using S-random bit interleaving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pulse shapes (RC or REC) are used in CPM systems, then the implementation is simple, but the coded performance in multi-user systems with ACI is suboptimal
Solution Approach 1:
The patent changes the fundamental parameter of pulse shape from conventional RC or REC to a new polynomial-based pulse shape defined by equation (1) with optimized coefficients. This parameter change improves coded performance in multi-user systems while maintaining implementation feasibility through the polynomial structure
Solution Approach 2:
The new pulse shape combines multiple polynomial terms with different coefficients (a0, a1, a2, a3) to create a composite pulse shape that achieves superior performance. The composite nature of the pulse shape allows it to simultaneously optimize for coded performance and manage ACI effects
2Productivity
If frequency separation between adjacent channels is reduced to achieve high bandwidth efficiency, then spectral efficiency improves, but ACI increases causing performance degradation
Solution Approach 1:
The patent changes the pulse shape parameter to optimize the power spectral density characteristics. The new pulse shape defined by polynomial coefficients creates a PSD that allows closer channel spacing while controlling ACI, thereby improving bandwidth efficiency without excessive interference
Solution Approach 2:
The new pulse shape design anticipates and cushions against ACI effects by optimizing the PSD main lobe width and side lobe levels beforehand. This preprocessing of the signal characteristics through pulse shape design reduces the harmful effects of ACI before they occur in the multi-user system
3Reliability
If new pulse shape is designed to optimize coded performance, then channel capacity increases, but implementation complexity may increase
Solution Approach 1:
The patent defines the pulse shape using polynomial coefficients (a0=0.5, a1=-1.0, a2=0.75, a3=-0.25) that can be pre-calculated and stored. This parameterization allows the complex pulse shape to be implemented through simple coefficient multiplication and addition operations, maintaining ease of implementation while achieving optimized channel capacity
Solution Approach 2:
The patent replaces complex analog pulse generation circuits with digital polynomial evaluation. The new pulse shape is generated through digital signal processing using the polynomial equation, substituting mechanical/analog complexity with programmable digital operations that are easier to implement and adjust
Data Source
AI summary
A new pulse shape for CPM is introduced which is obtained by a linear combination of well-known RC and REC pulse shapes. The new pulse shape addresses the tradeoff between the width of the PSD main lobe and the rate of decay of the side lobe to improve the coded performance of multi-carrier systems affected by ACI. Also, a methodology is proposed to design and evaluate the performance of the new pulse shape for multi-carrier, coded systems based on the modulation constrained capacity. Furthermore, a binary convolutional code and the CPM modulator are concatenated using an S-random bit interleaver to lower the error floor. Finally, Laurent representation of the new pulse shape is suggested such that by retaining only the principal pulses at the receiver, complexity of the receiver can be reduced.