Question

I am currently trying to retrieve the signal strength from a wireless access point using the wlanapi.dll WlanQueryInterface call.

Here is my api declaration

    [DllImport("wlanapi.dll", SetLastError = true)]
private static extern UInt32 WlanQueryInterface(IntPtr hClientHandle, ref Guid pInterfaceGuid, WLAN_INTF_OPCODE OpCode, IntPtr pReserved, out Int32 pdwDataSize, ref IntPtr ppData, IntPtr pWlanOpCodeValueType);

The problem is when I look at the wlanSignalStrength entry in the WLAN_ASSOCIATION_ATTRIBUTES structure it is set to 5400. Microsoft API documentation says that it should be a value between 0 – 100.

Here is my structure declaration:

    /// <summary>
/// Structure contains association attributes for a connection.
/// </summary>
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private struct WLAN_ASSOCIATION_ATTRIBUTES
{
    /// <summary>
    /// A DOT11_SSID structure that contains the SSID of the association.
    /// </summary>
    public DOT11_SSID dot11Ssid;
    /// <summary>
    /// A DOT11_BSS_TYPE value that specifies whether the network is infrastructure or ad hoc.
    /// </summary>
    public DOT11_BSS_TYPE dot11BssType;
    /// <summary>
    /// A DOT11_MAC_ADDRESS that contains the BSSID of the association.
    /// </summary>
    public DOT11_MAC_ADDRESS dot11Bssid;
    /// <summary>
    /// A DOT11_PHY_TYPE value that indicates the physical type of the association
    /// </summary>
    public DOT11_PHY_TYPE dot11PhyType;
    /// <summary>
    /// The position of the DOT11_PHY_TYPE value in the structure containing the list of PHY types.
    /// </summary>
    public ulong uDot11PhyIndex;
    /// <summary>
    /// A percentage value that represents the signal quality of the network.
    /// </summary>
    public Int32 wlanSignalQuality;
    /// <summary>
    /// Contains the receiving rate of the association.
    /// </summary>
    public ulong ulRxRate;
    /// <summary>
    /// Contains the transmission rate of the association.
    /// </summary>
    public ulong ulTxRate;
}

Here is my call to WlanQueryInterface:

    Int32 iDataSize;
    IntPtr ppData = IntPtr.Zero;
    WLAN_CONNECTION_ATTRIBUTES wcaAttributes = new WLAN_CONNECTION_ATTRIBUTES();
    String[] sReturn = new String[4];

    if (WlanQueryInterface(pClientHandle, ref gInterfaceGUID, WLAN_INTF_OPCODE.wlan_intf_opcode_current_connection, IntPtr.Zero, out iDataSize, ref ppData, IntPtr.Zero) == ERROR_SUCCESS)
    {
        wcaAttributes = (WLAN_CONNECTION_ATTRIBUTES)Marshal.PtrToStructure(ppData, typeof(WLAN_CONNECTION_ATTRIBUTES));

        sReturn[0] = wcaAttributes.wlanAssociationAttributes.dot11Ssid.ucSSID;
        sReturn[1] = wcaAttributes.strProfileName;
        sReturn[2] = String.Format("{0:X2}-{1:X2}-{2:X2}-{3:X2}-{4:X2}-{5:X2}", wcaAttributes.wlanAssociationAttributes.dot11Bssid.bOne, wcaAttributes.wlanAssociationAttributes.dot11Bssid.bTwo, wcaAttributes.wlanAssociationAttributes.dot11Bssid.bThree, wcaAttributes.wlanAssociationAttributes.dot11Bssid.bFour, wcaAttributes.wlanAssociationAttributes.dot11Bssid.bFive, wcaAttributes.wlanAssociationAttributes.dot11Bssid.bSix);
        sReturn[3] = wcaAttributes.wlanAssociationAttributes.wlanSignalQuality.ToString(); //This returns 5400 when the actual strength is ~99

        WlanFreeMemory(ppData);

        return sReturn;
    }
    else
    {
        throw new Exception("Unable to get interface connected SSID.");
    }

Does anyone see what I am doing wrong? Thanks in advance!

Answer 1

I finally got it fixed. I had to set the LayoutKind for the WLAN_ASSOCIATION_ATTRIBUTES to Explicit and set the charset to Unicode.

    [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Unicode)]
private struct WLAN_ASSOCIATION_ATTRIBUTES
{
    /// <summary>
    /// A DOT11_SSID structure that contains the SSID of the association.
    /// </summary>
    [FieldOffset(0)]
    public DOT11_SSID dot11Ssid;
    /// <summary>
    /// A DOT11_BSS_TYPE value that specifies whether the network is infrastructure or ad hoc.
    /// </summary>
    [FieldOffset(0x24)]
    public DOT11_BSS_TYPE dot11BssType;
    /// <summary>
    /// A DOT11_MAC_ADDRESS that contains the BSSID of the association.
    /// </summary>
    [FieldOffset(40)]
    public DOT11_MAC_ADDRESS dot11Bssid;
    /// <summary>
    /// A DOT11_PHY_TYPE value that indicates the physical type of the association
    /// </summary>
    [FieldOffset(0x30)]
    public DOT11_PHY_TYPE dot11PhyType;
    /// <summary>
    /// The position of the DOT11_PHY_TYPE value in the structure containing the list of PHY types.
    /// </summary>
    [FieldOffset(0x34)]
    public ulong uDot11PhyIndex;
    /// <summary>
    /// A percentage value that represents the signal quality of the network.
    /// </summary>
    [FieldOffset(0x38)]
    public Int32 wlanSignalQuality;
    /// <summary>
    /// Contains the receiving rate of the association.
    /// </summary>
    [FieldOffset(60)]
    public ulong ulRxRate;
    /// <summary>
    /// Contains the transmission rate of the association.
    /// </summary>
    [FieldOffset(0x40)]
    public ulong ulTxRate;
}