Duty Cycle (Channel Utilization) Testing of Medical RF Wireless Networks

Publish Date: May 08, 2013 | 0 Ratings | 0.00 out of 5 | Print | Submit your review

Overview

The following example shows an NI LabVIEW application that measures duty cycle, or channel utilization, for RF coexistence testing. The graphical programming paradigm of NI LabVIEW allows a developer complete control of RF waveforms for coexistence testing.

Table of Contents

  1. Example- Sweeping the ISM Band from 2.4 GHz to 2.48 GHz
  2. Tools for Medical RF Coexistence Testing
  3. Related Information

The transmission parameters of the wireless medical device, such as packet size, polling window, clear channel assessment threshold, and duty cycle, can alter the outcome of coexistence testing. Studies have shown that as the packet size increases, the probability of packet loss increases. Studies have also shown that as the polling window increases, the probability of packet loss decreases. Results indicate that when the interference level is below a certain level specified by the device sensitivity, the channel is sensed as idle or clear and the interference does not affect communication.

Duty cycle, or channel utilization, is mainly dependent on the amount of traffic generated and transmitted by the interfering wireless networks.  As the interfering device or network increases its duty cycle, the victim network packet loss ratio increases, causing either temporary or permanent interference. Therefore, use two transmission parameter settings during coexistence testing. These settings include typical or manufacturer-suggested default settings and worst-case-scenario settings, as suggested by previous work published in the literature.

1. Example- Sweeping the ISM Band from 2.4 GHz to 2.48 GHz

Find the number of times the measured power exceeds the noise floor for each WiFi channel. If the noise floor is exceeded more than a critical number of times, assume that a transmission has been captured. The result is an array of ones and zeros for each channel where ones indicate a busy channel and zeros indicate an idle channel. From runs of ones and zeros, determine the channel duty cycle and the inter-packet delay time statistics. Find the probability density function for the inter-packet delay times. Refer to the graphs in Figure 1 and Figure 2.

Figure 1.

 

Figure 2.

 

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2. Tools for Medical RF Coexistence Testing

Wireless Channel Characterization - This example uses the NI PXIe-5663E vector signal analyzer for channel duty cycle, inter-packet interval distribution, and network activity rate measurements. Other measurements that can help with coexistence testing include network/node density and distribution and wireless signal emulation. 

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3. Related Information

Originally Authored By: Greg Crouch, National Instruments

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rfdutycycle.zip

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