Interference in the ISM Band: Mitigation Strategies By Charles Foreman More and more, the ISM bands are being used for wide area, wireless networks in the oil patch. Because the ISM bands are unlicensed, anyone can use them so long as they comply with the FCC regulations. This can lead to potential RF interference between operators in the same geographical area, on the same frequency band, using different modulation techniques. Fortunately there are techniques and strategies to minimize the effects of the interference.
is required so that the operator can model the reservoir with higher resolution.
In the past, gathering a few data points from an oil or gas well once an hour was adequate to operate the field. “Good oil field practices” did not require large amounts of data to manage the reservoir. This has not been true for some time. As the oil and gas become more valuable, even small percentages in extraction efficiencies contribute significantly to hydrocarbon recovery from the reservoir and hence to the company’s bottom line. In order to improve extraction, more data, more often
The challenge becomes one of: how do you collect the data from thousands of wells spread over hundreds of square miles with no connectivity back to the central operations location? Plus the connectivity must be highly reliable. Typically, the wells are located in remote areas without any commercial infrastructure to support mission critical, high throughput data.
Industrial, Scientific, and Medical bands are at 900 MHz, 2.4 GHz, and 5.8GHz. Equipment is unlicensed but must be FCC compliant.
Personal safety and environmental protection have always been important. The negative impact of an accident can take years to rectify. By recognizing that an “event” has occurred at the well head in a matter of minutes, instead of hours, the operator can take corrective action in a timelier manner and, hopefully, minimize the impact.
One solution is to use radios to provide the connectivity. In the past, low speed (9600 baud), FCC licensed radios were adequate to meet the operator’s needs. While this solution
did not always guarantee interference-free transmission of data, it allow for remediation through the FCC. Low speed data is no longer adequate to operate the field. The operators need more data, and it has to be closer to realtime. This requires higher bandwidth and higher polling rates. At the present time, the commercially available radios that economically fill this need are in the unlicensed ISM bands. While this unlicensed operation makes for one less step in the deployment process, it leaves operators in congested areas nervous about the ability to control potential interference from neighboring operators. Depending upon the terrain, frequency, power availability, and RF interference, commercially available, point-to-multipoint radio systems can support from 512kbps to ≈12Mbps connectivity. Choosing the right frequency band, antenna height, and hardware can satisfy most of the system requirements for data throughput. RF interference can be much trickier. RF interference is a fact of life. It cannot be completely eliminated nor avoided. Any unwanted signals or background noise may introduce errors into the transmission path. These errors will decrease the system’s throughput due to the need for retransmissions, or in the worst case, block all throughput because the receiving radio cannot discriminate the data. Fortunately there are techniques incorporated in the radio equipment to mitigate the effects of RF interference. 21