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Air-Sampling for Automatic Detection of Performance Degradation and RF Intermodulation Products in a UMTS Base Station Installation.

IP.com Disclosure Number: IPCOM000004824D
Original Publication Date: 2001-Jun-19
Included in the Prior Art Database: 2001-Jun-19
Document File: 3 page(s) / 239K

Publishing Venue

Motorola

Related People

Neil Turner: AUTHOR [+2]

Abstract

This paper shows how an automatic system can be incorporated into a cellular base station to detect degradation of the antenna cabling with time. This can be measured in terms of the IP3 of the cabling by detecting the presence and magnitude of rf third-order products using the loopback system. Power loss due to degradation and water ingress can also be measured. A key element in this system is air-sampling of the actual transmitted signal and any associated spectral impurities.

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This is the abbreviated version, containing approximately 35% of the total text.

"Air-Sampling" for Automatic Detection of Performance Degradation and RF Intermodulation Products in a UMTS Base Station Installation.

Neil Turner, Chris Brice

Abstract

This paper shows how an automatic system can be incorporated into a cellular base station to detect degradation of the antenna cabling with time. This can be measured in terms of the IP3 of the cabling by detecting the presence and magnitude of rf third-order products using the loopback system. Power loss due to degradation and water ingress can also be measured. A key element in this system is air-sampling of the actual transmitted signal and any associated spectral impurities.

Introduction

The antenna connection of a cellular base station can be exposed to harsh climatic conditions, which have undesirable effects upon dissimilar metallic surfaces used at cable interfaces or within the antenna structure. Corrosion and oxidation cause a deterioration in the passive intermodulation performance of these joints and their effect will be to decrease the overall third-order intercept point (IP3) of the transmit chain. This can lead to unwanted products falling within the receive band, blocking the desired uplink service and causing a reduction in service. This is especially a problem with UMTS as W-CDMA relies on high linearity elements in the transmit chain. Any degradation in linearity, even in the antenna or associated cabling, will potentially cause degradation in the spectral mask performance, reducing the quality of the link. Degradation (including water ingress) can also significantly reduce the transmit power and received signal strength due to the effective insertion loss of the antenna and cabling.

Problem to be Solved

Given that the base station, cabling, and antenna system is exposed to a variety of weather conditions, it is inevitable that the metalwork will degrade over time. Currently, this needs to be checked and replaced periodically by staff on-site. An automatic system is required.

Proposed Solution

Consider the effect of these non-linearities. Unwanted products can be generated by two or more carriers in the base station, or by one transceiver and other co-sited transmitters out of the control of the cellular operator. This is an increasingly likely scenario given the economic and environmental pressures on operators to share existing antenna masts, and the proliferation of operators and standards.

This effect can be tested using a base-station with 2 carriers on adjacent channels, with frequencies at F1 and F2. Third order products will be generated at 2.F1 F2 and 2.F2 F1. For a UMTS system with carriers spaced 5 MHz apart, these products will be at 5 MHz above and below these carriers. Due to the advancement of the corrosion described above, these products will increase in amplitude. Once the amplitude reaches a predetermined threshold, maintenance can be performed.<...