Frequency Selective Baseband Digital Communication System
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Solution Overview
Problem
Existing digital communication systems, particularly human body communication systems, face challenges in achieving a predetermined processing gain while reducing the complexity of analog transmission/reception blocks and power consumption, especially due to the inefficiency of time domain/frequency domain spreading methods and the need for intermediate frequency converters.
Innovation Solution
A digital communication system using frequency selective baseband that selects spread codes with dominant frequencies in the user's desired frequency band, employing a transmitter with a preamble/header processing unit and data transmission processing unit to spread data using frequency selective spread codes, and a receiver with demultiplexing and despreading units to recover data, thereby reducing the complexity of analog processing and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If intermediate frequency (fc) passband is used in human body communication system, then data transmission can be performed, but analog transceiver including DAC, ADC and intermediate frequency converter is needed which increases power consumption
Solution Approach 1:
The patent replaces the analog intermediate frequency conversion system with a digital direct baseband transmission system. Instead of using analog DAC, ADC, and intermediate frequency converters, the system transmits data directly in the baseband frequency range (5-40 MHz) through the human body channel, eliminating the need for complex analog transceiver components and significantly reducing power consumption.
Solution Approach 2:
The patent extracts and removes the intermediate frequency conversion stage from the communication system. By directly transmitting in the baseband frequency range without up-conversion to intermediate frequency and subsequent down-conversion, the system eliminates the analog transceiver components (DAC, ADC, intermediate frequency converter) that consume excessive power.
2Productivity
If time domain/frequency domain spreading method is applied to obtain processing gain, then processing gain is achieved, but data transmission rate cannot be increased and transmission/reception stability is limited due to limited frequency band
Solution Approach 1:
The patent segments the limited frequency band (5-40 MHz) into multiple orthogonal sub-carrier frequency bands and assigns different spread codes to each sub-carrier. This frequency-domain segmentation allows parallel data transmission across multiple sub-carriers, increasing the overall data transmission rate while maintaining transmission stability through the orthogonal properties of the sub-carriers.
Solution Approach 2:
The patent transitions from time-domain spreading to frequency-domain spreading by utilizing multiple orthogonal sub-carrier frequency bands. This dimensional change from time to frequency domain allows simultaneous transmission of multiple data streams in parallel, achieving both high data transmission rate and stable reception through frequency diversity.
3Reliability
If all spread codes are used in CDMA system, then processing gain is maximized, but complexity of code allocation and interference management increases
Solution Approach 1:
The patent assigns different spread codes to different users based on their allocated frequency sub-bands. Each user's spread code is optimized for their specific frequency range, creating local quality optimization. This approach maintains processing gain by using orthogonal spread codes while reducing code allocation complexity through systematic frequency-based code assignment.
Data Source
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AI summary
Provided are a digital communication system using frequency selective baseband and a method thereof. A transmitter of the digital communication system, includes: a preamble/header transmission processing unit for spreading a preamble for frame synchronization and a header including data information; a data transmission processing unit for spreading data by using spread codes having dominant frequency in a desired frequency band, i.e., frequency selective spread codes; and a multiplexer for multiplexing the spreaded preamble and the spreaded header from the preamble/header transmission processing unit and the frequency selective spreaded data from the data transmission processing unit and transmitting the multiplexed signal in digital.