Multi-Carrier Spread Spectrum System Using Segmented ADCs
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Solution Overview
Problem
Current CDMA spread spectrum systems face challenges in processing high sample rates and bandwidths beyond the capabilities of commercially available devices, making it difficult to implement wide bandwidth communications effectively.
Innovation Solution
The system employs multiple digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) with lower sample rates to create multiple spread spectrum sub-bands across a wide bandwidth, using RF upconverters with different frequencies to form carriers with guard bands, allowing for the spreading and despreading of CDMA signals over extremely wide bandwidths using existing device technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CDMA spread spectrum signals are spread over very wide bandwidth (100's MHz to multiple GHz), then the processing gain and interference resilience improve, but the required sample rates and processing capabilities exceed current commercially-available device technology
Solution Approach 1:
The patent divides the wideband CDMA signal into multiple narrower bandwidth sub-bands, each processed by separate ADCs and DSP channels operating at lower sample rates. This segmentation allows the system to achieve wideband processing gain while using commercially-available lower-sample-rate devices, resolving the contradiction between interference resilience and device complexity
2Area of stationary object
If the bandwidth is increased to multiple GHz, then the communication range and user capacity increase, but the ADC and DAC sample rates required reach beyond current device technology capabilities
Solution Approach 1:
The total bandwidth is segmented into multiple sub-bands, each handled by a separate ADC operating at a lower, commercially-available sample rate. The sub-bands are then combined through digital processing to achieve the overall wideband performance, thus achieving multiple GHz bandwidth without requiring single ADCs with impractically high sample rates
Solution Approach 2:
The patent transitions from a single-dimensional high-sample-rate processing approach to a multi-dimensional approach using multiple parallel lower-sample-rate channels. By adding the dimension of parallel processing channels, the system achieves equivalent wideband performance without increasing the sample rate of individual devices beyond current capabilities
3Adaptability or versatility
If multiple unique spreading codes are used for multiple users, then the number of users within allocated spectrum increases, but the processing complexity for spreading and despreading increases significantly
Solution Approach 1:
The patent assigns different spreading codes to different sub-bands rather than requiring all users to be processed in a single high-sample-rate channel. This segmentation of user capacity across multiple lower-complexity parallel channels reduces the processing complexity per user while maintaining overall user capacity in the wideband system
Data Source
AI summary
A communications system may include a transmitter having spreading stages configured to spread a common modulated baseband input data stream based upon respective coefficient sequences; a plurality of upconverters, each having a different frequency; and an RF output stage that generates an RF output signal. A receiver may include an RF input stage that receives an RF input signal, a plurality of downconverters, a plurality of despreading stages, and a demodulator coupled to the despreading stages.