Router CSI Lab
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Wi-Fi CSI explained: from channel state information to human sensing

2026-10-11 · 2 min read

Wi-Fi CSI (Channel State Information) is the per-subcarrier, per-antenna complex channel measurement taken by a Wi-Fi receiver. Where RSSI gives you one number (how strong the signal is), CSI gives you amplitude and phase for every subcarrier — which is why it can see motion, not just strength.

Everything on this site comes from a real lab: a GL-MT6000 (MT7986) router, 5 GHz / 80 MHz, 256 subcarriers, tx 0/1 × rx 0/1/2/3. A 10-minute run captured 57,293 frames at 95.5 fps with a 5.2 MB resident daemon (raw capture published [11]).

RSSI vs CSI

RSSI CSI
Output one scalar (dBm) complex I/Q per subcarrier
Frequency resolution none 256 subcarriers @ 80 MHz
Spatial resolution none per Tx/Rx chain
Typical use link quality activity, breathing, gestures, positioning

What it can and cannot do

Proven directions: presence/occupancy, activity and fall detection, respiration and heart rate (seated, still), gesture recognition, coarse localisation — all surveyed in the field's most-cited review [1].

Where projects fail:

  1. "Seeing through walls" is over-hyped — you detect channel changes caused by motion, not images.
  2. Models do not transfer across rooms, furniture or body poses.
  3. Sampling jitter destroys low-frequency analysis (breathing/heart rate).
  4. Different chips produce very different CSI — model portability is poor.

Five hardware routes

Route Bandwidth / subcarriers Cost Coverage
Intel 5300 CSI Tool [3] [5] 20 MHz / 30 used NIC one PC
Atheros CSI Tool [4] 40 MHz / 114 used NIC one PC
ESP32 (esp-csi / CSI Tool) [6] 20 MHz / 30–64 from $3 single point
Nexmon CSI (Pi/phone) [7] 80 MHz / 256 from $40 single point
Router (MT7986 + mt76 CSI) 80 MHz / 256 one router whole home
Research (PicoScenes / SDR) [8] any $1k+ bench

For long-running, whole-home sensing the router form factor wins: it is already powered 24/7, sits in the middle of the house and needs no extra hardware.

Pipeline

router (capture)                     host (analysis)
OpenWrt + mt76 CSI patch   --UDP-->  parse → buffer → features → detection
mt76-csi-daemon :8888                visualise (heatmap/waterfall/doppler) + storage

Three things are mandatory for CSI to work at all:

  1. a CSI-capable firmware (MT7986: the 2026-05-15 build),
  2. the frame-type filter (frame_type = 0,34) — without it the firmware reports nothing,
  3. the target station's MAC in the MAC filter list.

Start here

Standards and further reading

Please respect local law and ethics: do not use Wi-Fi sensing for non-consensual surveillance.

References and data sources

Every external claim carries a source and an evidence grade (grading scheme). Grade E marks first-party, reproducible measurements from this project.

  1. Grade A · standard/review WiFi Sensing with Channel State Information: A Survey
    W. Ma, W. Zhou, X. Wang · ACM Computing Surveys · 2019
    doi:10.1145/3310194 · citations 857 · verified: CrossRef API, 2026-10-11 · The field's most-cited CSI sensing survey (857 citations, verified via CrossRef).
  2. Grade A · standard/review IEEE 802.11bf — WLAN Sensing (standard project)
    IEEE Standards Association · IEEE 802.11 Working Group · 2020
    standards.ieee.org/ieee/802.11bf/10331/ · verified: standards.ieee.org HTTP 200, 2026-10-11 · Official project page for turning sensing into a WLAN standard capability (approved September 2020).
  3. Grade B · peer-reviewed Tool release: gathering 802.11n traces with channel state information
    D. Halperin, W. Hu, A. Sheth, D. Wetherall · ACM SIGCOMM Computer Communication Review · 2011
    doi:10.1145/1925861.1925870 · citations 1713 · verified: CrossRef API, 2026-10-11 · The formal paper for the Intel 5300 CSI Tool (1713 citations) — the widely reproduced starting point for CSI capture.
  4. Grade B · peer-reviewed Precise Power Delay Profiling with Commodity WiFi (Atheros CSI Tool)
    Y. Xie, Z. Li, M. Li · ACM MobiCom 2015 · 2015
    doi:10.1145/2789168.2790124 · citations 521 · verified: CrossRef API, 2026-10-11 · The paper behind the Atheros CSI Tool (521 citations); describes CSI / power-delay-profile capture at 40 MHz.
  5. Grade C · official docs dhalperi/linux-80211n-csitool-supplementary — Intel 5300 CSI Tool (code)
    D. Halperin et al.
    github.com/dhalperi/linux-80211n-csitool-supplementary · verified: GitHub API 2026-10-11 (stars 221, last push 2020-05-25) · Code repository for the Intel 5300 tool; its last commit was in 2020, which is the basis for calling it unmaintained.
  6. Grade C · official docs espressif/esp-csi — Applications based on Wi-Fi CSI
    Espressif Systems
    github.com/espressif/esp-csi · verified: GitHub API 2026-10-11 (stars 1,679) · The official README states: "All ESP32 series support CSI, including ESP32 / ESP32-S2 / ESP32-C3 / ESP32-S3 / ESP32-C5 / ESP32-C6 / ESP32-C61."
  7. Grade C · official docs seemoo-lab/nexmon_csi — CSI extraction on various Broadcom Wi-Fi chips
    SEEMOO Lab, TU Darmstadt
    github.com/seemoo-lab/nexmon_csi · verified: GitHub API 2026-10-11 (stars 475, last push 2026-09-30)
  8. Grade C · official docs PicoScenes — modern Wi-Fi ISAC research platform
    Z. Jiang et al. (PicoScenes project)
    ps.zpj.io/ · verified: ps.zpj.io HTTP 200, 2026-10-11 · Official site of a software/hardware platform for Wi-Fi ISAC research (the SDR route).
  9. Grade C · official docs WST — Hands-on Wireless Sensing with Wi-Fi (Tsinghua tutorial)
    Tsinghua University TNS group
    tns.thss.tsinghua.edu.cn/wst/ · verified: tns.thss.tsinghua.edu.cn HTTP 200, 2026-10-11 · A university-run hands-on Wi-Fi sensing course (slides and datasets); not a peer-reviewed paper.
  10. Grade D · preprint/wiki ruvnet/RuView — community Wi-Fi spatial-intelligence project
    r. u. v. (community maintainer) · 2026
    github.com/ruvnet/RuView · verified: GitHub API 2026-10-11 (stars 97,237; created 2025-06-07) · Community project, not peer-reviewed: its marketing claims (real-time “spatial intelligence” / vital signs) have no independent reproduction — treat as a lead, not a conclusion.
  11. Grade E · first-party measurement This project's 10-minute raw capture (57,293 records / 600.0 s, SHA-256 00373f83…95e2)
    Router CSI Lab · 2026
    csi.okwujun.pw/zh/datasets/ · verified: Reassembled chunks verified byte-identical (2026-10-11)

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