安卓手机开发APP能否获取周边WiFi AP的CSI信息及PHY层无线通信数据？

Great question—let's break this down clearly, since CSI is such a powerful tool for indoor positioning compared to basic RSSI.

Core Answer: Native Android APIs Don't Support CSI #

First, the hard truth: Android's public WiFi APIs (like WifiManager, WifiScanResult) do not expose PHY-layer CSI data. These APIs only give you upper-level metrics like RSSI, SSID, MAC address, and channel number—no access to subcarrier CSI values, packet timestamps, or PHY-layer payload details.

The reason for this is simple: CSI is deeply tied to the hardware-specific WiFi chipset (Qualcomm, MediaTek, Broadcom, etc.) and their proprietary drivers. Android's framework doesn't abstract this low-level data into a universal API, as it's not needed for consumer-facing apps.

Workarounds for Getting CSI on Android #

While native APIs don't support it, there are a few (limited) paths forward, depending on your technical comfort and device access:

1. Chipset-Specific Private APIs/Drivers #

Major WiFi chipmakers like Qualcomm or MediaTek may offer private SDKs or driver interfaces that expose CSI data—but these are almost exclusively for OEM partners or enterprise developers. You'd need to reach out to the chip manufacturer directly for access, and the APIs will vary drastically between chipsets (no cross-device compatibility).

2. Custom ROM/Kernel Modifications #

If you're comfortable with low-level system hacking, you can modify the Android kernel or WiFi driver to expose CSI data:

• Many Android devices use open-source Linux WiFi drivers (e.g., ath9k, ath10k for Atheros chips). You can modify these drivers to add code that captures CSI and exposes it via sysfs nodes or custom ioctl commands.
• Once the driver is modified, you'd need to unlock your device's bootloader, flash a custom ROM with the modified kernel, then build an app that reads the exposed CSI data (via JNI or direct file reads).

This approach has high barriers—you'll need kernel development experience, and it only works for specific devices with open-source drivers.

3. Open-Source Research Projects #

Several academic research projects have built tools to capture CSI on specific Android devices. For example:

• Projects targeting Qualcomm QCA-series chips (common in many flagship phones) often use root access to call proprietary driver functions or read hidden sysfs entries.
• These tools are usually device-specific, require root, and are maintained for research purposes rather than production use.

Example Code Snippets (Conceptual) #

Since there's no universal code, here's a conceptual example of how you might access CSI via JNI on a rooted, modified device:

JNI Layer (C Code) #

#include <jni.h>
#include <sys/socket.h>
#include <linux/wireless.h>
#include <netpacket/packet.h>

JNIEXPORT jobjectArray JNICALL
Java_com_yourpackage_CsiHelper_fetchCsiData(JNIEnv *env, jobject thiz) {
    // Create a raw socket to interact with the WiFi driver
    int sock_fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    if (sock_fd < 0) {
        // Handle error (likely permission/root issue)
        return NULL;
    }

    // Use chip-specific ioctl commands to request CSI data
    // Note: This will vary wildly between chipsets—this is just a placeholder
    struct wireless_ext we;
    // Populate we with chip-specific parameters
    ioctl(sock_fd, SIOCGIWPRIV, &we);

    // Parse the returned CSI data (subcarrier values, timestamps, etc.)
    // Convert to a Java String array to pass back to the app
    jobjectArray csi_results = (*env)->NewObjectArray(env, num_subcarriers, (*env)->FindClass(env, "java/lang/String"), NULL);
    // Populate the array with parsed CSI values

    close(sock_fd);
    return csi_results;
}

Android App Layer #

public class CsiHelper {
    static {
        System.loadLibrary("csihelper"); // Load the JNI library
    }

    public native String[] fetchCsiData();
}

// In your Activity/Fragment:
private void startPeriodicCsiScan() {
    new Timer().scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            CsiHelper helper = new CsiHelper();
            String[] csiData = helper.fetchCsiData();
            
            if (csiData != null) {
                // Process CSI data (log, store, or use for positioning)
                runOnUiThread(() -> {
                    // Update UI if needed
                });
            }
        }
    }, 0, 1000); // Scan every 1 second
}

Key Notes #

• Permissions: You'll need ACCESS_WIFI_STATE, CHANGE_WIFI_STATE, and root access for most low-level CSI capture methods.
• Device Compatibility: Only a small subset of Android devices (usually with open-source WiFi drivers) can be modified to capture CSI. Most consumer phones block this access by default.
• Alternative: If CSI isn't feasible, consider combining RSSI with sensor data (accelerometer, gyroscope) or Bluetooth beacons for indoor positioning—though accuracy will be lower than CSI.

内容的提问来源于stack exchange，提问作者Mohsen Ali