It is normal for Ping times to fluctuate when you are running continuous ping, this can be due to multiple reasons. Here are some steps from the Wireless adapter side that may improve this.
- Apply the settings from the advisory: What are the Recommended Settings for 802.11n Connectivity?
- Also in the Wireless adapter advanced settings, configure U-APSD support to "disabled"
- Set the Roaming aggressiveness to "Low" or "Medium-Low" and test the connection.
- If your network operates in the 2.4 GHz band, try disabling the Bluetooth Radio in your PC (this can be done with a switch in your PC/Keyboard, disabling it in Device Manager, or via Windows wireless configuration). Bluetooth also operates in 2.4 GHz and this may interfere with WiFi.