Transmitter Space-Time Coding for CPM Full Diversity
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Solution Overview
Problem
Existing wireless communication systems face challenges in achieving full rate transmit diversity for Continuous Phase Modulation (CPM) signals, especially in non-linear modulation schemes and channels with intersymbol interference, where prior art methods are limited or undefined.
Innovation Solution
A full rate transmit diversity scheme is developed that uses a novel space-time code to provide full diversity gains for CPM signals, applying the Lindskog-Paulraj technique to non-linear CPM signals and enhancing spectrum efficiency by dividing user code bits into multiple sequences for transmission through multiple antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmit diversity is implemented for CPM signals using prior art methods, then diversity gains are achieved in linear modulation schemes, but the methods are limited or undefined for non-linear CPM signals and channels with intersymbol interference
Solution Approach 1:
The patent changes the fundamental parameters of the transmit diversity scheme by applying time-reversal and conjugation operations to the CPM signal constellation. This transforms the signal processing approach to be compatible with non-linear CPM modulation while maintaining diversity gains, making the system adaptable to previously unsolvable cases.
Solution Approach 2:
The patent segments the transmitted signal into multiple paths with different time-reversed and conjugated versions of the CPM signal. Each path carries the same information but with transformed characteristics, enabling diversity reception even in challenging channel conditions with intersymbol interference.
2Productivity
If user code bits are divided into multiple sequences for transmission through multiple antennas, then spectrum efficiency is enhanced and full diversity gains are achieved, but the implementation complexity increases
Solution Approach 1:
The patent creates a universal signal processing framework where the same time-reversal and conjugation operations can be applied to any CPM signal regardless of specific modulation parameters. This multi-functional approach handles various CPM variants (GMSK, ETCM, etc.) through a unified method, managing complexity while achieving full diversity gains.
Solution Approach 2:
The patent maintains continuous phase modulation throughout the signal processing chain, ensuring that the CPM signal's constant envelope property is preserved. This continuity allows the use of non-linear power amplifiers and maintains spectral efficiency while implementing transmit diversity.
3Reliability
If time-reversal and conjugation operations are applied to CPM signals, then full diversity gains are achieved in interference-limited environments, but the processing complexity at the transmitter increases
Solution Approach 1:
The patent applies time-reversal and conjugation operations in advance during signal generation at the transmitter, before the signal is modulated and transmitted. This preliminary processing prepares the signal for optimal reception in interference-limited environments, shifting complexity to the transmission phase where it can be managed more effectively.
Solution Approach 2:
The patent introduces intermediate signal representations that facilitate the application of time-reversal and conjugation operations. These intermediate forms serve as mediators between the original CPM signal and the final transmitted signal, simplifying the processing steps while achieving the desired diversity performance.
Data Source
AI summary
A transmitter and a method therein for transmitting CPM signals to a receiver. The transmitter divides bits into first and second bit sequences; obtains third and fourth bit sequences by appending bits to the first and second bit sequences. First and second intermediate sequences are generated based on the third and fourth bit sequences. The transmitter time-reverses the first and second intermediate sequences. The time-reversed first sequence is mapped to a third intermediate sequence, and the time-reversed second sequence is mapped to a fourth intermediate sequence. The transmitter generates fifth and sixth bit sequences from the third and fourth intermediate sequences. First and second CPM signals corresponding to first and second CPM bursts are created, which first burst is based on the third and sixth bit sequences, and which second burst is based on the fourth and fifth bit sequences. CPM signals are transmitted through a respective antenna.