CDMA (IS-95) has a multiple access scheme based on spread spectrum technology, which has been applied to digital cellular mobile communications since the early 1990s. The number of traffic channels used depends on the number of users in the cell. Thus the output signal of the IS-95 base station has a basically large peak-to-average power ratio (PAPR) because it consists of the signals from the multiple channels, which requires a linear power amplifier to transmit the signal without distortion.
In practice, it is impossible to avoid some signal distortion from the amplifier nonlinear characteristics. So, the occupied bandwidth (OBW) measurement is a main factor for spectrum monitoring of a transmitting radio system. The occupied bandwidth (OBW) is a measure of the bandwidth containing 99% of the integrated power for the transmitted spectrum, centered on the assigned frequency. The OBW of a base station has been measured directly at the RF monitoring port of a base station. Spectrum monitoring activities determine any violations of the assigned output bandwidth.
However, this measurement method has the disadvantages of requiring considerable manpower. Therefore, the monitoring of the OBW as an alternative to spectrum monitoring at the remote site is strongly advantageous. In practice, the multi-FA (Frequency Assignment) CDMA base stations are general cases and three-FA CDMA base stations are the most commonly used. Therefore, it is necessary to develop a measurement method of the OBW based on a three-FA CDMA signal from a remote station.
In this study, the proposed measurement method of the OBW is compliant with the 99 % bandwidth definition, which has been formulated by the ITU-R. The measured occupied bandwidth depends on the number of channels used and measurement duration.
Thus we take an average of the measured samples to represent the statistical characteristic of the OBW. And, the modified adjacent channel power (ACP) is used as a parameter to determine the reliable spectrum of the assigned bandwidth of a multi-FA CDMA base station. This Proposed ACP parameter takes into account environmental signal distortions within the measurement scan bandwidth.