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Where an interferer transmits at a frequency that lies outside the nominal pass-band of the wanted signal, the level of interference experienced is a function of a) the interferer’s spectral leakage, as defined by its emission power spectral density, and b) the frequency response of the filtering {XE "Filtering"} at the receiver. These two effects can be characterised by the interferer’s adjacent-channel leakage ratio (ACLR) {XE "ACLR"} and the receiver’s adjacent channel selectivity (ACS) {XE "ACS"} respectively, as illustrated in Figure 450455.
The combination of these two parameters, in the form of
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represents the fraction of the received interferer power which is experienced as interference by the receiver, and is referred to as the adjacent-channel interference ratio (ACIR {XE "ACIR"}).
The ACLR of a signal is defined as the ratio of the signal’s power (nominally equal to the power over the signal’s pass-band) divided by the power of the signal when measured at the output of a (nominally rectangular) receiver filter centred on an adjacent frequency channel. By setting up the unwanted emission mask in SEAMCAT, it is possible to display directly the ACLR (facility only available in the OFDMA module version).
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In other words, for a received interferer power at a frequency offset from the wanted signal, and for an ACIR (function of the frequency offset), the experienced interference power is reduced by the ACIR as sketched in Figure 450455.
Figure 450
Figure 455: Interference as a result of limited ACLR and ACSAnchor F455 F455
Note: This kind of description of the adjacent frequency bands parameters for compatibility issues is widely used in the 3GPP standardization.