A15.7.1 ACIR methodology

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 455.

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The combination of these two parameters, in the form of

            (Eq. 186)

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).

The ACS of a receiver is defined as the ratio of the receiver’s filter attenuation over its pass-band divided by the receiver’s filter attenuation over an adjacent frequency channel. It can be readily shown that ACIR-1 = ACLR-1+ ACS-1. The victim link receiver blocking attenuation is used in SEAMCAT to input the ACS.

The ACIR is defined as the ratio of the power of an adjacent-channel interferer as received at the victim, divided by the interference power experienced by the victim link receiver as a result of both transmitter and receiver imperfections.

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 455.

Figure 455: Interference as a result of limited ACLR and ACS

Note: This kind of description of the adjacent frequency bands parameters for compatibility issues is widely used in the 3GPP standardization.