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Motivation

There is no doubt that WLAN becomes a major technology in the field of industrial wireless communication. A lot of products are available in the automation market. Within a joint project with the german magazine “Elektronik” the Institut Industrial IT want to carry out a Benchmark Test of Industrial WLAN equipment. Using comprehensible and transparent test procedures, we are going to create an unbiased picture of the current state of the art for realtime communications using WLAN. In case of participation, vendors have the following advantages:

• Neutral testing of their products
• Increased customer confidence
• Driving the industry acceptance of WLAN
• No costs (except of providing the equipment and a contact person for technical support)

Our Approach

The analysis of existing wireless networks is very difficult, because of different disruptive influences caused by many factors. In order to provide valid and reproducible information about different relevant performance metrics, it is necessary to exclude such influences. Hence, our measurement system consists of three anechoic chambers in order to allow a conducted setup. The different HF signals of the WLAN devices are interconnected via HF cables and a controlable attenuator matrix, which simulate the real channel, leading to a reproducible environment.

Measurement System

The Azimuth Systems W-Series 802.11 test platform will be used for testing and  has the following characteristics:

• Isolated test chambers for DUTs
• Precise attenuators
• Metrics for single devices and whole systems
• Precise timestamps of received frames
• Exclusion of disruptive influences
• Absolute metrics in a conducted environment

Used Metrics

1. Latency of single MAC layer frames as a function of the attenuation, traffic direction and frame size with a resolution of 1µs. Calculation of the average latency and mean deviation of a whole burst of frames.
2. Jitter of MAC layer frames as a function of the attenuation, the traffic direction and the frame size as defined in IEEE 802.11.2 and RFC 3550.
3. Throughput versus attenuation with different traffic patterns and calculation of “Goodput” as defined in RFC 2647. This metric is only applicable to a setup with a station and an access point.
4. Packet Loss as a function of MAC layer throughput and attenuation. This metric is applicable to single devices.
5. BSS transition time from the last successful transmitted frame of the old AP to the first successful transmitted frame of the new AP. All different phases, e.g. authentication, association and probe frames will be seperately reported.

These metrics can be performed with different security settings or roaming thresholds. Packet Loss, Latency and Jitter are metrics designed for single devices, but can be applied for a whole system as well.

Project partner

German Magazine ELEKTRONIK, Publisher: Weka