Selective Cyclic Prefix Extension for Wireless Co-Scheduling
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Solution Overview
Problem
Wireless communication networks face challenges in co-scheduling Long Range Low Power (LRLP) devices with 802.11ax devices due to differing cyclic-prefix length requirements and interference issues, particularly in OFDMA transmissions, where extending the cyclic prefix increases overhead and causes Inter-Symbol Interference (ISI).
Innovation Solution
A modified data-to-subcarrier mapping approach that selectively extends the cyclic prefix for receivers needing a longer effective channel delay spread without increasing the OFDM symbol length, allowing for concurrent scheduling of devices with varying bandwidth and power requirements by allocating different subcarriers for each receiver, with the second mapping considering only every m-th subcarrier for LRLP devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long cyclic prefix is used for all sub bands in OFDMA transmission to support LRLP STAs, then LRLP STAs can operate at longer ranges, but the overhead increases and capacity is wasted
Solution Approach 1:
The patent applies different cyclic prefix lengths to different resource units within the same OFDMA transmission. Specifically, LRLP STAs receive resource units with extended cyclic prefixes while 802.11ax STAs receive resource units with normal cyclic prefixes. This local differentiation allows each device type to operate optimally without forcing all devices to use the less efficient extended prefix format.
Solution Approach 2:
The patent segments the OFDMA transmission into multiple resource units, where each resource unit can be independently configured with appropriate cyclic prefix length based on the target STA type. This segmentation enables fine-grained control over overhead vs. reliability trade-offs for different device categories within the same transmission frame.
2Reliability
If different cyclic prefix lengths are used in the same OFDMA symbol, then LRLP STAs can have longer range, but inter symbol interference occurs
Solution Approach 1:
The patent divides the OFDMA transmission into multiple independent resource units, each targeting a specific STA type with appropriately configured cyclic prefix length. By segmenting the transmission at the resource unit level rather than using a single uniform prefix length for all subcarriers, the system avoids inter-symbol interference while still providing extended range capability for LRLP STAs.
3Adaptability or versatility
If LRLP STAs filter out allocated sub bands from wideband OFDMA signal, then narrowband operation is achieved, but receive filter shortens cyclic prefix and introduces ISI
Solution Approach 1:
The patent pre-extends the cyclic prefix length in the resource units allocated to LRLP STAs before the filtering operation occurs at the receiver. By establishing the extended prefix length in advance at the transmitter side, the system compensates for the prefix shortening effect that will occur when LRLP STAs apply narrowband filtering to extract their allocated subcarriers from the wideband OFDMA signal.
Data Source
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AI summary
A node in a wireless communication network uses a modified data-to-subcarrier mapping on at least a selective basis, wherein the modified mapping effectively extends the cyclic prefix (CP) of a transmission targeted to a given receiver without extending the CP of the Orthogonal Frequency Division Multiplex (OFDM) symbol in which the transmission is conveyed. This approach allows, for example, the node to use a first or normal data-to-subcarrier mapping for transmissions that are targeted to receivers that do not need an effective increase of the CP length, while using the modified mapping for those receivers that need a longer effective CP length, e.g., because of receiver type or channel conditions.