From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeon Date: Tue, 14 Jun 2016 02:00:04 +0900 Subject: [ath9k-devel] linearity of ath9k CSI phase Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ath9k-devel@lists.ath9k.org Dear ath9k developers, I am currently working with Atheros CSI Extraction Tool [1] to get a true phase of each subcarrier. - Background [2], [3] and many other papers claim that phase information from extracted CSI contains two components: true phase and unwanted phase offset due to subcarrier and time delay. i.e., measured_phase = true_phase + time_delay * subcarrier_index + phase_offset_due_to_txrx_mismatch This equation can be visualized as below: http://i.imgur.com/rk9Hh1M.png (Please note that this figure is based on CSI tool for Intel 5300 NIC.) It contains unwanted linear phase offset and constant phase offset. Since the true phase is relatively small, it seems that phase is monotonically increasing or decreasing in macro view due to the unwanted phase offsets. We cannot see a tiny true phase currently. To remove phase offset due to subcarrier, the mentioned papers are attempting to remove it with linear fitting ax + b, where a = slope of the figure, b = average of measured phase, and x = subcarrier index. After removing unwanted phase offset components, the true phase is estimated. This estimated true phase seems steady and consistent across a time duration shorter than < 100 - 1000 ms: http://i.imgur.com/AO89vYV.png Note that Y-axis scale is reduece from [-50, 10] to [5, -3] - My question I want to extract and manipulate CSI phase WITH ATH9K NIC. After extracting CSI from my ath9k NIC (AR9580 @ 2.4 GHz) with Atheros CSI extraction tool, I've tried various fitting methods to eliminate unwanted components and stacked results from nearly 100 packets: http://i.imgur.com/5r9eYwO.png