Adjacent channel power

ACP measurement of a UMTS FDD carrier In
addition to the UMTS carrier signal, the picture also shows the cut-off frequencies of the two lower and upper adjacent channels (see example ACP measurement ).

As Adjacent Channel Power ( ACP ), also adjacent channel power , adjacent channel leakage power ratio ( ACLR ) and Adjacent Channel Power Ratio ( ACPR called) is in mobile radio networks , the ratio of the transmitted GSM -, W- CDMA - or UMTS -Sendekanal power to Adjacent channel power.

The power that the transmission channel "radiates" into its adjacent channel must be as small as possible so that any transmission signal in the adjacent channel can still be properly detected.

ACP measurement

The measurement is carried out with signal analyzers that have already integrated the corresponding measurement routines and the required hardware . Root raised cosine filters ( RRC for short ) are used as measuring filters in the transmission channel and the adjacent channels . The RRC have a bandwidth which corresponds to the chip rate of the carrier signal of 3.84 MHz and a roll-off factor of = 0.22 (excessive bandwidth). The frequency spacing between the channels is 5 MHz. The measurement bandwidth of the signal analyzer when measuring W-CDMA carriers is 30 kHz. ${\ displaystyle \ alpha}$

The power of a channel ( CHP or CHPwr ; English Channel Power ) corresponds to the integration of the power over its bandwidth. The following formula can therefore be used for measurements with the signal analyzer:

${\ displaystyle CHP / {\ rm {dBm}} = 10 \ cdot \ log \ left ({\ frac {CHBW} {RBW \ cdot k_ {n}}} \ cdot {\ frac {1} {N}} \ cdot \ sum _ {i = 1} ^ {N} {10 ^ {\ frac {P_ {i}} {10}}} \ right)}$

CHP is the channel power, CHBW the channel bandwidth, RBW the resolution bandwidth, k _n the correction factor for the equivalent noise bandwidth of the resolution filter used, N the number of pixels in the channel and P _i the level of the i-th pixel in the channel in dBm.

The ratio of the carrier to the adjacent channel power is specified in dB , with ACP Low standing for the lower adjacent channel and ACP Up for the upper adjacent channel. The measurement specification, i.e. the settings of the measuring device and the filters, for ACP measurement of UMTS signals has been written down in the 3GPP specification TS 25.101.

Graphic representation

Schematic

The picture shows the measurement spectrum of an ACP measurement of a W-CDMA signal. The bandwidth of the individual channels is 3.84 MHz, whereby the center frequency of the channels is always 5 MHz apart. The power of the spectrum is given in dBm ( dB related to 1 mW power). The channel power is the total power within the channel bandwidth.

Example ACP measurement

Measurement result of an ACP measurement for a UMTS carrier with a signal analyzer. The signal analyzer displays the spectrum, the boundary lines of the channels and the measurement result.

Channel power

The channel services are highlighted here in color. The transmission channel has a green background, while the yellow and red areas represent the lower and upper adjacent channels, respectively.