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The W-CDMA Radio Access Network from Siemens consists of the Radio Network Controllers (RNC), the Radio Base Stations (RBS) and an Operation and Maintenance System, similar to that in the GSM network. The OSS is applied for handling operation and maintenance tasks in the W-CDMA network. The main accumulation of the RNC is to manage the user data transport and to optimize the radio network resources by controlling a number of RBS's. It is also the physical link to the core network and is connected to the RNC via an interface. The RBS includes all equipment for maintaining the radio link and connects the mobile station, for example a mobile phone or a laptop with the network.

As I got well acquainted to both radio systems used in Cyprus, I was taken with my colleagues on-site to different base stations that had some specific fault. Each day the department of operation and maintenance receives a report from the base station controllers specifying faults detected in different base stations. As the fault report was checked by the department, the critical faults were chosen first and split up between the different members in the department. According to the location of the faults some were given more than one base station. I was given the chance to go on-site with all the members throughout my training period and visited most of the base stations that the department was responsible for.

When the source of a fault was know, it included just a simple replacement of the faulty hardware card installed in the base station, which ranged from Transmission Receiver Unit (TRU) cards up to channel cards and the Combining and Distribution Unit (CDU) cards. Sometimes the source of the fault is not known, that is when an important tool called the Operation and Maintenance Terminal (OMT) is used.

The OMT is a software tool for installation, testing, site acceptance and diagnostics of the base station. A computer, connected to the Radio Base Station, enables the field engineer to read out the Installation Data Base file (IDB). The IDB includes all information about the applied hardware in the RBS. Furthermore all settings and adjustable parameters are saved and controlled by the IDB, and can be monitored by the OMT. Different kinds of views can be displayed by the software. The Cabinet View shows the hardware items in the RBS. The MO View shows the application objects and the service objects. These objects are also in the BSC's model of the RBS. The Hardware View shows the RBS's schematic structure. The hardware view is the most useful to detect a fault or a failure in the hardware of the whole RBS.

Some base stations we visited had unknown faults and thus we experienced the use of the OMT software, monitoring the values that passed through the different parts of the system. After debugging the system using this software, the fault is easily detectable, and the process returns to the simple replacement of the faulty card.

Sometimes the fault involves the cable and antenna system. The cable and antenna system plays an important role in the overall performance of the cell site. Small changes of the antenna system can affect the signal coverage area and eventually cause dropped calls. Furthermore, replacing a whole feeder cable and the antenna system is not as easy as replacing faulty cards of the RBS. The Wiltron is a portable frequ