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WiFi Testing | compliance, radio, protocol, interoperability

This article covers wifi testing. This wifi compliance testing covers Wifi radio conformance testing, wifi protocol conformance testing and wifi interoperability testing. This wifi testing is useful for WLAN device manufacturers, wifi software developers and test and measurement companies etc.

Introduction:
The term WiFi is given to the wifi alliance which manages and develops IEEE 802.11 family of standards. There are different versions with different data rate, range, carrier frequency, bandwidth and other system requirements. The table-1 mentions some of these parameters of different 802.11 standard versions.


WLAN Standard Features
802.11a Frequency:5.3,5.8 GHz
BW: 20 MHz
Data rate: 54 Mbps
802.11b Frequency: 2.4 GHz
BW: 20 MHz
Data rate: 11 Mbps
802.11g Frequency: 2.4 GHz
BW: 20 MHz
Data rate: 54 Mbps
802.11n Frequency: 2.4 GHz or 5GHz
BW: 20 MHz or 40 MHz
Data rate: 248 Mbps for 2 MIMO streams
802.11ac Frequency: 5 GHz
BW: 20/40/80/160 MHz
Data varies based on BW and number of streams
802.11ad Frequency: 60 GHz
BW: 2.16 GHz

There are two devices which make WLAN system viz. Client or Station and Access Point (AP) or Router. The AP interfaces with the internet backbone and all the stations obtain the internet service through AP. As there are two operating modes in WLAN i.e. Infrastructure and Ad-hoc. The WLAN devices are testing in both of these modes in order to ascertain they can be used to form both of these type of networks. The figure-1 below depicts WLAN protocol stackin general used across different versions. Modulation technique at PHY and RF carrier frequency/bandwidth vary as per different standard flavors.

WiFi Radio Conformance Testing


WLAN protocol stack

Following are the generic WiFi transmitter and receiver tests performed on the device. These tests are used to validate RF and Physical layer (i.e. baseband layer) specifications of the WLAN device as per standard specifications. These set of tests are useful for pre-compliance testing as well as for pre-certification of the device before sending it for certification to the certified labs.

The purpose of wifi testing for radio conformance is to ascertain that the WLAN device works efficiently as per desired RF layer/PHY layer performance limits defined in the standard and required in the WLAN network.

WLAN RF/PHY Transmitter tests during wifi testing are as follows:
• Transmit power spectrum mask
• Spectral flatness or gain response
• Transmit power level and its control range
• Transmitter RF carrier and Symbol clock frequency tolerance
• Transmitter carrier leakage
• EVM (Error Vector Magnitude) or RCE (Relative Constellation Error)
• Spurious compliance limit
• Power Ramp Up/Down test

WLAN RF/PHY Receiver tests during wifi testing are as follows:
• Receiver input sensitivity (min.) or PER
• Adjacent and non-adjacent channel rejection test
• Max. input power level to the receiver
• Clear Channel Assessment Sensitivity test

For 802.11a/b/g SISO tests are done. For 802.11n/ac/ad SISO as well as MIMO tests need to be carried out. Refer SISO testing vs MIMO testing for more information.

WiFi testing for Protocol Conformance compliance

The main purpose of WLAN protocol conformance is to verify MAC layer and above as per standard requirements. In MAC, one need to ascertain that all the MAC control and management messages are simulated and worksas desired. Moreover once connection is established the WLAN device supports stable data connection for short and long period of time.

As we know WLAN MAC frame consists of MAC header, Frame Body carrying mac message or data payload and FCS. Various MAC analyzer or sniffer applications are available which analyzes/decodes the MAC frames and display various parameters of the frame. The WLAN MAC frame generator applications are used to configure various MAC layer frames in order to test MAC functionalities of the WLAN device under development e.g. Association Request/Request frame, Authentication, Beacon, Probe etc.

WiFi Interoperability Testing

The WLAN interoperability tests ascertain that products from different vendors co-exist together in a WLAN network without any issues. For example, WLAN Stations from Linksys (or cisco) can connect with WLAN router from D-LINK and viceversa.

The radio conformance, protocol conformance and interoperability for wifi testing mentioned in this article can also be applied to other wireless standards viz. WiMAX, GSM, LTE, CDMA, Zigbee, Zwave, IoT etc. The specific limits or specifications may vary as per different wireless standards and as per their network as well as RF carrier frequency requirements. The performance requirements of different systems may also differ as per user and quality of service requirements.



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