Hierarchical Modulation for Wireless Access Throughput
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Solution Overview
Problem
Current broadband wireless access systems, such as WiMAX, suffer from poor spectral efficiency and low average throughput due to suboptimal usage of the multi-user channel, particularly in cellular wireless access systems where channel quality varies significantly with location, leading to wasted capacity.
Innovation Solution
The method involves transmitting at least two data streams on the same radio resources using hierarchical or layered modulation and coding, allowing for different power levels and modulation schemes to optimize channel usage, enabling better utilization of the multi-user channel by combining and separating data streams based on channel conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If robust modulation and coding with low spectral efficiency is used for broadcast/multicast information to far terminals, then reliability is improved, but spectral efficiency deteriorates
Solution Approach 1:
The data stream is segmented into multiple layers with different reliability requirements. The first layer uses robust modulation and coding for reliable reception by all terminals, while the second layer uses less robust but more efficient modulation and coding for terminals with better channel conditions. This segmentation allows different parts of the data to be transmitted with different spectral efficiencies according to their reliability needs.
Solution Approach 2:
Different modulation and coding schemes are applied to different layers of the data stream based on local channel conditions. The first layer is designed with high reliability for far terminals, while the second layer optimizes for spectral efficiency for near terminals. This local quality approach allows the system to adapt the transmission characteristics to the specific needs of different terminal groups.
2Ease of operation
If time and frequency multiplex is used for multi-user channel access, then ease of operation is improved, but spectral efficiency deteriorates
Solution Approach 1:
Multiple data streams from different terminals are merged into a single composite signal that is transmitted over the same radio resources. The base station combines the data streams using different modulation and coding schemes, and the terminals separate and decode their respective streams. This merging allows simultaneous transmission to multiple terminals without requiring separate time or frequency slots, thereby improving spectral efficiency while maintaining ease of operation.
3Reliability
If separate radio resources are allocated to different users, then reliability is improved, but device complexity deteriorates
Solution Approach 1:
The same radio resources are made universal for transmitting multiple data streams to different terminals simultaneously. The base station and terminals are equipped with multi-functional capabilities to handle multiple layers: the base station can modulate and code multiple streams with different schemes, and terminals can separate and decode their designated streams from the composite signal. This universality eliminates the need for separate resource allocation while maintaining reliability through appropriate layer design.
Data Source
AI summary
The present invention relates to the field of wireless access systems and more particularly to a broadband wireless access system and a transmission method for such system. At least two data streams (2, 3, 4) are simultaneously transmitted in a multi-user channel (1) having a location dependent capacity. The data streams (2, 3, 4) are transmitted on the same radio resources. Preferably, the data streams are combined in a transmitter and separated in a receiver using different modulation and/or coding for the data streams.