The Cost of Noise and the Value of Silence

In this latest addition to the LTE Best Practices blog series, Erik Lilieholm introduces the subjects of noise and interference mitigation in wireless networks. He explains why the subject is so important to network operators, especially after they have spent billions of dollars acquiring spectrum. Readers can access the complete LTE Best Practices ebook for advice about limiting noise and interference.

Cabin-in-the-woodsHidden in the woods, miles away from city lights and busy highways, there is a 100-year old cottage to which I return every year. As night falls and the wind dies, the absence of noise – both acoustic and optical – becomes very noticeable. Or rather, I notice what I can then hear and see, like a faint creak in the timbers, an owl hooting in the distance and a million stars against the blackness of space. I highly value this experience which no money can buy in the urban environment I otherwise inhabit.

The above illustrates the importance of Signal-to-Noise Ratio (SNR). How well we perceive is not determined just by absolute loudness or brightness but more importantly by the contrast of an object or signal against its surrounding environment. In a radio receiver when noise levels rise, weaker signals cannot be reliably received and eventually become undetectable. Merely amplifying does not help at this point because the levels of signal and noise are equally raised and SNR does not improve.

Like interference, noise disrupts the reception of desired signals, causing errors and dropouts. Engineers often treat interference and noise together, using terms such as Signal(Carrier)-to-Noise-and-Interference Ratio (SNIR, CNIR). This highlights the similarity between the two, but there are also important differences that shape the methods we have at hand for interference control and noise mitigation, respectively. In the LTE Best Practices ebook, the #1 Best Practice is focused on noise mitigation.

LTE supports very high data rates enabled by high order modulations and coding schemes. High spectral efficiency can be attained and maximum throughput achieved in a limited slice of radio spectrum. To get the highest data rates, 64-point Quadrature Amplitude Modulation (64-QAM) is used and the receiver must continuously and correctly detect what is transmitted from a constellation of 64 possible symbols. As the difference is small between the symbols, a little noise in the radio channel can cause frequent misdetections and result in high Block Error Rate (BLER) and communication failure. Fortunately, LTE can adapt to the reduced radio link quality by switching to 16-QAM where the symbols are further apart and more tolerant to noise. Unfortunately, spectral efficiency then becomes much lower and throughput suffers.

What is the cost of noise? Consider the value that operators place on spectrum assets as recently manifested in the record-setting auction of AWS-3 spectrum in the United States. The value of that spectrum is in the throughput it can support. Every decibel (dB) of unmitigated noise detracts from that value. We must realize that in the world of LTE, noise has become very costly. Noise mitigation best practices should be high on your agenda and a good place to begin is with the LTE Best Practices ebook. Get your copy today for free after a brief registration.

Noise mitigation in LTE networks is easily justified in pure commercial terms. The silent stillness of a cabin in the woods has a different value that is not monetary, yet if you ask me, I find it high enough to justify the cost of my annual retreat.

Is noise threatening the return on your LTE investment? How can we help?