Multiplexing CDMA and SC-FDMA Transmissions
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Solution Overview
Problem
Wireless communication systems face inefficiencies in supporting delay-sensitive and low data rate traffic flows due to high scheduling overhead and low channel utilization, particularly in protocols like SC-FDMA and OFDMA, which are not suitable for traffic such as VoIP and Layer-1/2 control signaling.
Innovation Solution
The method involves encoding symbols using a frequency division protocol and coding sequences with cyclic correlation properties, allowing for concurrent transmission of data symbols over shared time-frequency resources, reducing scheduling overhead and improving channel utilization by using CDMA and SC-FDMA protocols with CAZAC coding sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scheduling is implemented in SC-FDMA/OFDMA systems to allocate time-frequency resources, then spectral efficiency can be improved through adaptive modulation coding, but scheduling overhead increases and latency increases
Solution Approach 1:
The patent segments the transmission into two distinct parts: a first part using SC-FDMA with DFT precoding for high spectral efficiency, and a second part using CDMA without scheduling for low latency. This segmentation allows each part to serve its specific purpose independently, resolving the contradiction between spectral efficiency and latency.
Solution Approach 2:
The system dynamically switches between SC-FDMA mode (for high spectral efficiency when time is not critical) and CDMA mode (for low latency when scheduling overhead is problematic). This dynamic adaptation allows the system to optimize performance based on the specific traffic characteristics and timing requirements of each transmission.
2Productivity
If scheduling is implemented to allocate time-frequency resources, then spectral efficiency can be improved, but scheduling overhead increases
Solution Approach 1:
The patent divides the transmission into two segments: one using SC-FDMA with scheduling for high spectral efficiency, and another using CDMA without scheduling to eliminate scheduling overhead. This segmentation allows the system to achieve high spectral efficiency when needed while avoiding scheduling complexity for latency-sensitive traffic.
Solution Approach 2:
The patent extracts the scheduling mechanism from the transmission system and removes it entirely from the second part of the transmission. By taking out scheduling from the CDMA portion, the system eliminates scheduling overhead while maintaining spectral efficiency through the first SC-FDMA portion for appropriate traffic types.
3Device complexity
If semi-static allocation or interference avoidance schemes are used to support low data rate traffic, then scheduling overhead is reduced, but channel utilization decreases
Solution Approach 1:
The system dynamically adapts the transmission mode based on traffic characteristics. For low data rate traffic with latency requirements, it uses CDMA mode which provides flexible resource allocation without semi-static constraints, thereby maintaining high channel utilization while reducing scheduling overhead compared to semi-static allocation schemes.
Data Source
AI summary
The present invention provides a method and apparatus for multiplexing code division and frequency division transmissions. One embodiment of the method includes accessing at least one first symbol and at least one second symbol, encoding the at least one first symbol according to a frequency division protocol, and encoding the at least one second symbol using a coding sequence having a cyclic correlation property. The method also includes transmitting a radiofrequency signal indicative of the at least one encoded first symbol and the at least one encoded second symbol.