Interference Challenges at 700 MHz
Hello, my name is Abhijit Karandikar. I am a Sr. Product Manager here at Superconductor Technologies, Inc. There has been a lot of buzz regarding the interference challenges at 700 MHz. Today, I would like to talk briefly about the sources of interference as well as the different types of interference, with a particular focus on intermodulation distortion.
As the chart shows, some potential sources of interference are high power broadcast signals from digital television, MediaFLO and Public Safety. When high power signals are in proximity to low power receive bands, there is a potential for interference. In the 700 MHz spectrum, these low power basestation receive bands are vulnerable.
The main types of interference challenging wireless operators today are:
1. Co-channel interference from in-band signals
2. Broadband emissions from high power transmitters, and
3. High Power Near-band signals causing intermodulation distortion products, or intermods
These intermods are sometimes misunderstood and I would like to take a moment to talk about them.
In a receiver chain, intermods are created by the interaction of high power near-band signals, like MediaFLO, with non-linear elements like low noise amplifiers and mixers. Intermod spurs become a problem when they land in-band and are large enough to desensitize the receiver. These intermods raise the noise floor which reduces the signal to noise ratio.
The result is a reduction in basestation sensitivity, compromising coverage, data-throughput, and quality of service. One way to mitigate intermods is with high-order receive filtering. A high-order filter drops the power level of the intermod spurs so that they do not desensitize the receiver.
Here at STI, we understand the challenges of deploying a new network in the presence of interference. We hope this update has been helpful, and please contact us if you have any questions. Thank you and we look forward to speaking with you again.
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