Interference-The Solution

 
Interference-The Solution
The recommendation of the Interference Protection Working Group of the FCC's Spectrum Policy Task
Force was that FCC should consider using the interference temperature metric as a means of quantifying
and managing interference. As introduced in this report, interference temperature is a measure of the RF
power available at a receiving antenna to be delivered to a receiver, that is, power generated by other
emitters and noise sources. More specifically, it is the temperature equivalent of the RF power available
at a receiving antenna per unit bandwidth, measured in units of °Kelvin (K). As conceptualized by the
Working Group, the terms interference temperature and antenna temperature are synonymous.
Interference temperature is a more descriptive term for interference management.
Interference temperature can be calculated as the power received by an antenna (watts) divided by the
associated RF bandwidth (hertz) and Boltzman's Constant (equal to 1.3807 wattsec/°Kelvin).
Alternatively, it can be calculated as the power flux density available at a receiving antenna (watts per
meter squared), multiplied by the effective capture area of the antenna (meter squared), with this quantity
divided by the associated RF bandwidth (hertz) and Boltzman's Constant. An interference temperature
density could also be defined as the interference temperature per unit area, expressed in units of °Kelvin
per meter squared and calculated as the interference temperature divided by the effective capture area of
the receiving antenna (which is determined by the antenna gain and the received frequency). Interference
temperature density could be measured for particular frequencies using a reference antenna with known
gain. Thereafter, it could be treated as a signal propagation variable independent of receiving antenna
characteristics.
As illustrated in Figure 9-1, interference temperature measurements could be taken at receiver locations
throughout the service areas of protected communications systems, thus estimating the real-time
conditions of the RF environment.
Figure 9-1: Interference temperature Source- FCC
Like other representations of radio signals, instantaneous values of interference temperature vary with
time and, thus, need to be treated statistically. The Working Group envisions that interference
thermometers could continuously monitor particular frequency bands, measure and record interference
temperature values, and compute the appropriate aggregate value(s). These real-time values could
govern the operation of nearby RF emitters. Measurement devices could be designed with the option to
include or exclude the on-channel energy contributions of particular signals with known characteristics
such as the emissions of users in geographic areas and bands where spectrum is assigned to licensees
for exclusive use.
The FCC could use the interference temperature metric to set the maximum acceptable levels of
interference, thus establishing a worst-case environment in which a receiver would operate. Interference
temperature thresholds could therefore be used, where appropriate, to define interference protection
rights.
The time has come to consider an entirely new paradigm for interference protection. A more forwardlooking
approach requires that there be a clear quantitative application of what is acceptable interference
for both license holders and the devices that can cause interference. Transmitters would be required to
ensure that the interference level (or interference temperature) is not exceeded. Receivers would be
required to tolerate an interference level.
Rather than simply saying your transmitter cannot exceed a certain power, the industry instead would
utilize receiver standards and new technologies to ensure that communication occurs without
interference, and that the spectrum resource is fully utilized. So, for example, perhaps services in rural
areas could utilize higher power levels because the adjacent bands are less congested, therefore
decreasing the need for interference protection.[2]
From a simplistic and physical standpoint, any transmission facility requires a transmitter, a medium for
transmission, and a receiver. The focus on receiver characteristics has not been great in past spectrum
use concerns; hence, a shift in focus is in order. The Working Group believes that receiver reception
factors, including sensitivity, selectivity, and interference tolerance, need to play a prominent role in
spectrum policy.[