MaxLinear has released a whitepaper showing how LTE transmissions from base stations and user equipment can interfere with DTV reception.
Not surprisingly, one way to reduce the interference is to use MaxLinear DTV tuners. Brian Sprague, MaxLinear Vice President and General Manager, Broadband and Consumer Products, said: “Countries moving from analog to digital television coverage are discovering that LTE signals can interfere with digital TV reception. MaxLinear has developed advanced tuner technology that can mitigate this interference, allowing digital TV and STB OEMs to provide a higher quality picture that keeps customers happy.”
The MaxLinear whitepaper, LTE Interference on Digital TV in Brazil, was written by Dr. Glenn Chang, director of technical marketing at MaxLinear and Professor Gunnar Bedicks, chief researcher at the DTV laboratory, at MacKenzie University. It examines several possible scenarios that cover combinations of interference from LTE base stations and user equipment to DTV reception with indoor and outdoor antennas with and without an amplifier. Interference to an amplified master antenna system from an LTE base station is also examined.
Two types of interference are analyzed--overload from LTE signals that can be more than 60 dB stronger than the effective −79 dBm receiver sensitivity and on-channel third-order intermodulation products created when strong base station and user equipment signals mix in the receiver.
Solutions discussed include filters, which are rejected due to cost and signal loss, and the protection of desired-to-undesired (D/U) that’s inherent within the tuner.
The whitepaper does not contain any test data or spectrum analyzer plots. If you’re expecting a Charlie Rhodes treatment of the subject, you’ll be disappointed, but the calculated D/U ratios in the whitepaper could provide a starting point for some real world testing.
If you want to see some real-world LTE signal levels measured in Los Angeles, see my Sept. 6, 2011 TV Technology magazine article 4G Interference to UHF DTV. LTE signals are also visible in Fig. 3 from my more recent article Testing TV Antennas With Nifty Gadgets.
Note that the TV signals were relatively strong both in both tests. The Brazilian analysis is based reception at threshold assuming a DTV receiver sensitivity of −79 dBm. This figure was used rather than the −83 dBm sensitivity, which only accounts for the noise figure of the receiver. The 4 dB degradation in sensitivity allows for real-world impairments such as ambient noise, fading, and other sources of interference.
Overload and intermodulation are likely to become more of a problem as TV stations are packed into a smaller amount of spectrum with LTE base stations and user equipment nearby. It would be interesting to see how different tuner designs will handle this challenging environment.
