OFDM Transmitter Sampling Phase Control for Lower NB-IoT Rates
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Solution Overview
Problem
Current solutions for Narrowband IoT (NB IoT) systems face challenges in reducing sampling rates while maintaining compatibility with legacy LTE systems, leading to increased processing costs and power consumption, especially in low-cost Machine-Type Communication (MTC) devices.
Innovation Solution
A transmitter architecture that adjusts the sampling phase during cyclic prefixes, allowing for a lower sampling rate than the traditional 1.92 MHz, using a digital-to-analog converter with non-uniform sampling and adjusting the sampling phase to maintain integer samples per cyclic prefix, thereby reducing the overall sampling rate while ensuring compatibility with LTE numerology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the traditional sampling rate of 1.92 MHz is used to generate both cyclic prefixes with integer samples, then compatibility with legacy LTE systems is maintained, but power consumption and processing costs increase
Solution Approach 1:
The patent changes the sampling rate parameter from the traditional 1.92 MHz to a lower rate, and introduces variable cyclic prefix lengths (first CP length for first sequence, second CP length for second sequence) to maintain integer sample counts. This parameter adjustment reduces power consumption while preserving LTE compatibility through careful selection of CP lengths that work with the new sampling rate.
Solution Approach 2:
The patent implements dynamic cyclic prefix length adjustment where different sequences of OFDM symbols use different cyclic prefix lengths. The first sequence uses a first cyclic prefix length and the second sequence uses a second cyclic prefix length, allowing the system to adapt to the lower sampling rate while maintaining integer sample requirements for both sequences.
2Use of energy by moving object
If a lower sampling rate is used to reduce power consumption, then processing costs decrease, but maintaining integer samples per cyclic prefix becomes difficult
Solution Approach 1:
The patent selects specific cyclic prefix lengths (first CP length and second CP length) that are mathematically compatible with the lower sampling rate to ensure integer sample counts. This careful parameter selection simplifies the processing by avoiding complex fractional sample handling while still achieving power reduction through the lower sampling rate.
3Productivity
If different cyclic prefix lengths are used for different sequences, then lower sampling rate is achieved, but system complexity increases
Solution Approach 1:
The patent divides the OFDM symbols into two sequences: a first sequence with a first cyclic prefix length and a second sequence with a second cyclic prefix length. This segmentation allows each sequence to be optimized for the lower sampling rate while maintaining integer sample requirements, achieving better sampling rate efficiency without requiring complete system redesign.
Data Source
AI summary
A method in a transmitter circuit of generating a signal comprising a first sequence of OFDM symbols, which are to be transmitted within a frequency sub band of a second sequence of OFDM symbols is disclosed. A first cyclic prefix (CP) of the second sequence of OFDM symbols has a first duration, and a second CP of the second sequence of OFDM symbols has a second duration. In order to generate both the first and the second cyclic prefix with an integer number of equidistant samples, a first sampling rate is required. The method comprises generating the signal comprising the first sequence of OFDM symbols at a second sampling rate, lower than the first sampling rate, and adjusting a sampling phase during CPs.