That same time period also saw the first attempts at wireless communication. The radio pioneers had access to any spectrum they needed as all of it lay fallow. Interfering with other users was of no concern. Fortunately so, since their spark gap transmitters could create a good deal of Out-Of-Band Emissions (OOBE) even when skillfully tuned.
We can usually count on history to repeat itself and consequently, frequency spectrum is now a precious commodity. Everyone needs to stay within their licensed boundaries without trespassing upon the neighbors. In certain situations, avoiding such infringement requires the use of Interference Mitigation Filters (IMF). One typical case for IMFs is where one user’s transmit (downlink) band is too close in frequency to another’s receive (uplink) band.
Not so long ago I was called upon to help solve a case here in the heart of Texas. In this instance a cellular carrier had installed a Distributed Antenna System (DAS) on a university campus. When the DAS was turned up, it was discovered that the uppermost carrier with downlink close to 894 MHz was interfering with public utility uplink radio channels near 896 MHz. Those radios suffered a degradation of at least 15 dB due to OOBE from the cellular transmitters. The emission levels complied with regulations – the two radio systems were just too close to each other in location and in frequency.
Because modern-day Texans are known for civility, the two radio operators did not reach for their six-shooters to settle this territorial conflict—they reached out to CommScope. Their situation was not unlike what we encounter in a number of countries around the world using a varying mix of 850 and 900 MHz cellular spectrum. Because of the variability, we developed a flexible IMF design platform that was, in this case, adapted to provide over 30 dB rejection of the offending signals. An on-site trial confirmed the solution was 100 percent effective. This was of course a relief for the “victim” but no less so for the cellular carrier who could now safely turn up that top channel and regain much needed traffic capacity.
Across the world, spectrum is being reallocated to meet capacity demands. At CommScope, we are ready to pin that tin star on our chest and help make peace along the fence lines—in Texas and elsewhere. Job done, we can all mount up together and ride off into the sunset.
Have you considered where new interference scenarios can occur with broadcast and two-way operators, on co-location sites and in cross-border regions?