LTF Sequence Generation via Frequency Domain CDM
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In 802.11ac wireless local area networks, the generation of Very High Throughput-Long Training Fields (VHT-LTF) in time domain Code Division Multiplexing (CDM) mode leads to increased signaling overheads and delays due to longer cyclic prefixes required for outdoor multipath effects, which are not effectively addressed by existing technologies.
Innovation Solution
A transmission device and method that utilize both frequency domain and time domain transforms to generate a Long Training Field (LTF) sequence for channel estimation in multiple-input multiple-output (MIMO) scenarios, reducing the number of LTF symbols and thereby minimizing signaling overheads and reception delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If VHT-LTF is generated in time domain CDM mode to support multiple users in MU-MIMO scenario, then channel estimation capability is improved, but signaling overheads increase and data field reception is delayed due to multiple CPs required
Solution Approach 1:
The patent transitions from time-domain CDM to frequency-domain CDM for generating VHT-LTF. In frequency domain, multiple users are distinguished by assigning different frequency subcarriers rather than using multiple time-domain symbols with cyclic prefixes. This dimensional change from time to frequency domain eliminates the need for multiple CPs while maintaining multi-user channel estimation capability.
Solution Approach 2:
The patent changes the fundamental parameter of LTF generation from time-domain processing to frequency-domain processing. By modifying the domain in which CDM is applied (from time to frequency), the system achieves the same user differentiation function without requiring multiple cyclic prefixes, thereby reducing signaling overhead and reception delay.
2Measurement precision
If VHT-LTF is generated in time domain CDM mode to distinguish multiple streams in SU-MIMO scenario, then spatial stream separation is improved, but signaling overheads increase due to multiple LTF symbols
Solution Approach 1:
The patent applies frequency-domain CDM instead of time-domain CDM to generate VHT-LTF for SU-MIMO scenarios. By using frequency domain separation, multiple spatial streams are distinguished through frequency subcarrier allocation rather than through multiple time-domain LTF symbols, thereby reducing signaling overhead while maintaining stream separation capability.
Solution Approach 2:
The patent fundamentally changes the generation domain of VHT-LTF from time domain to frequency domain. This parameter change allows the system to achieve spatial stream differentiation through frequency domain code division multiplexing, eliminating the need for multiple LTF symbols in the time domain and thus reducing signaling complexity.
3Reliability
If CP length is increased to avoid interference between OFDM symbols in outdoor environment, then signal interference resistance is improved, but LTF sequence length increases causing more signaling overheads
Solution Approach 1:
The patent addresses outdoor multipath interference by changing from time-domain LTF generation to frequency-domain LTF generation. In frequency domain, the system can maintain adequate frequency spacing between subcarriers to avoid interference without necessarily extending the time-domain sequence length, thus reducing signaling overhead while maintaining reliability in outdoor environments.
Data Source
Figure 1~3
Figure 4
Figure 5~6
AI summary
The present invention discloses a transmission device and a method for transmitting a data frame, which relate to the communications field, reduce signaling overheads, and reduce a delay in reception of a data field. A specific solution is: an acquiring unit acquires LTF parameters, and acquires a start position I of allocated subcarriers, where the LTF parameters include a frequency domain transform parameter and a time domain transform parameter that are required for generating an LTF sequence; a frequency domain transform unit performs, according to the frequency domain transform parameter and the start position I, a frequency domain transform on an LTF basic sequence to obtain an LTF symbol; a time domain transform unit performs, according to the time domain transform parameter, a time domain transform on the LTF symbol to obtain the LTF sequence; and a sending unit adds the LTF sequence to a first data frame, and sends the first data frame to a second device, so that the second device determines the LTF basic sequence according to the LTF sequence and performs channel estimation according to the LTF basic sequence. The present invention is used in a transmission process of a data frame.