T-Mobile accused of interfering with Sirius XM's signal at certain cell towers

T-Mobile US  (NYSE:TMUS) is under fire from satellite radio firm Sirius XM over what Sirius claims is interference caused by certain T-Mobile cell towers that are using the AWS-1 spectrum.

In a regulatory filing with the FCC, Sirius said that the company's satellite radio customers in several large urban markets are reporting disruptions to their radios, and the company's tests indicate the problem is caused by T-Mobile's cell phone transmitters. T-Mobile has said that the potential interference is not its responsibility because the problem is occurring within Sirius radios, which should be engineered to block these anomalies. The satellite firm has asked the FCC to intervene in the dispute.

T-Mobile has been using the AWS band as its primary band to support LTE, which it launched in March 2013. The company's LTE network now covers 280 million POPs, and the company aims to reach 300 million by year-end. In addition to the AWS band (Band 4), T-Mobile's LTE network also runs on the 700 MHz A Block (Band 12) and 1900 MHz PCS (Band 2).

Steve Sharkey, T-Mobile's senior director of engineering and technology policy, told the Wall Street Journal that the company is operating within the FCC's rule and the problem is "inadequate filtering" in Sirius XM's receivers. Nevertheless, Sharkey said T-Mobile is working with Sirius to resolve the problem.

Experts say that intermodulation is likely the cause of the problem. Intermodulation happens when two spectrum frequencies combine to create a third frequency. Equipment installers typically test for passive intermodulation among other things when they install equipment yet the problem is escalating as networks adopt higher orders of modulation and add more frequency bands.

For more:
- See this WSJ article (sub. req.)

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