n Interference Causes:
Improperly Configured Transmitter: Operator X is transmitting on operator Y’s frequency unknowingly due to a fault or an incorrect setting; and the operator of the transmitter would be happy to correct it to restore his own service level. Interference in mobile equipment poses some problems other than that in base station testing. While most of the same techniques used at the BTS can be used in the field, there are some limitations. For example, it is not as easy to disable a channel to clear out intended signals. Most interference is relatively localized, so the mobiles will have acceptable call quality everywhere except in the trouble area

Unauthorized Transmitter: Operator X is transmitting on operator Y’s frequency intentionally in the same frequency band.

Cell Overlap: A cell from network exceeds specified coverage in one or more channels. Incorrect antenna tilt, excess transmitter power, or a change in the environment can cause overlap.

Intermodulation from Another Transmitter: Intermodulation interference can be the result of one or more external radio signals getting into the antenna feeder coax and entering the offending transmitter’s nonlinear final amplifier stage. The external signals mix with each other and with the transmitter’s own signal, creating intermodulation products that appear as "new" (and often very undesirable) frequency components in the communications band.

OSI Layer 1 and Techniques Audit Parameter Test Instruments Type of Test s Local Area Networks s Twisted Pair Cable length Cable tester out-of-service Near-end Crosstalk (NEXT) Cable tester out-of-service Signal-to-noise Ratio (SNR) Cable tester out-of-service| Attenuation cable tester out-of-service s Coaxial CableCable length Cable tester out-of-service Reflections at connectors cable tester out-of-service Number of nodes protocol analyzer, in-service s LAN Probes s Fiber Optic Cable length OTDR out-of-service Total attenuation OTDR out-of-service Splice attenuation OTDR out-of-service s Wide Area Networks Signal level interface tester out-of-service Signal condition interface tester out-of-service Bit error parameters BER tester out-of-service s OSI Level 1 Stress Tests (at capacity load) Ethernet Network load sent=record CS errors: Collisions Protocol analyzer in-service r Token Ring Token rotation time Beacon packets:jitter protocol of analyzer in-service r FDDI Beacon packets: jitter, wrapping protocol analyzer in-service r ATM Cell BERT SDH frame alarms AIS: yellow alarm protocol analyzer in-service r Protocol analyzer in-service r X.25 CRC error monitoring REJ-packets protocol analyzer in-service y Protocol analyzer in-service Rame Relay protocol tester in-service CRC packets protocol tester in-service s ISDN CRC error monitoring in-service

Intermodulation in a Rusty Fence, Roof: The intermodulation effects from physical structures such as the rust between the individual roof sections are difficult to locate.

Intermodulation in Antennas or Connectors: Minor corrosion in a coaxial connector or the antenna itself can create a fault. The corrosion can act like a very poor diode and cause just a little bit of intermodulation.

Overload from a Legitimate Transmitter: Sometimes, strong signals from a transmitter at any frequency can overload a neighboring system. The only solution is to install a filter on the receiver antenna cable that will pass the intended signals and attenuate the overload signal.

Adjacent Channel Power from a Neighboring Transmitter: If the allocated spectrum becomes crowded, there can be some problems too.

Harmonics from Broadcast Transmitters: Also high-powered commercial broadcast stations can produce substantial energy in harmonics of their signals. For example, a 5-megawatt transmitter can easily generate 5 watts of harmonics – more than enough to interfere with nearby mobile communications.

n The Solutions: Interference can be categorized by its own characteristics. It can be found at the base station and in the air interfaces with the mobiles. Interference signals only affect receivers—even when they are physically close to a transmitter, the transmission will not be affected. The frequency of the offender is the most common indicator of the source and consequences of the interference. The solutions lie in hunting for sources of interference in the networks and fixing them. There are test tools and techniques for managing the same. The field transmitter and interference tester can be used.

Data Link Layout Audit Measurements: (OSI Layer2)
Ethernet	Token Ring	FDDI	ATM	WAN
Capacity User Activity Statistics Communications matrix Collisions FCS Errors Runits Jabliers Misalignment Errors Broadcasts Multicasts Number Nodes	Capacity User Activity Statistics Communications matrix Beacons FCS Errors Ring Purges Claim Token Frames Receiver Congestion Token Rotation Time Number of Nodes	Capacity User Activity Statistics Communications matrix Beacons FCS Errors Claim Frames SMT and Void Frames Token Potation Time Number of Nodes	Capacity User Activity Statistics Communications matrix SDH Parameters: - Frame Loss E2 - LineAIS D7 - PathAIS - LineEBE - LineER - PathER Total calls - Idle Calls - Busy Calls HEC Errors Cell Syn Loss Cell BERT Test Cell intersection (o.19)c [measurement of cell loss and cell delay]	ER Capacity User Activity Statistics Communications matrix Connections Statistics [number of completed of failed connection set ups] CRC Errors Transmission Delay Measurements

Measurements at the Base Station Receiver: The best way to hunt for interference in the base station receiver is to disable traffic on the channel to be measured. This will assure that no calls are assigned to it and the only signals that you will see are the interfering ones.

Using Automatic Spectrum Analysis: A BTS tester can be used for this purpose. There is no need to adjust controls such as resolution bandwidth or video bandwidth as these are automatically set internally. If the signals are constantly changing amplitude (as with GSM, for example), one may not catch the signals at their maximum when you press AutoLevel. If the levels increase beyond range, a warning banner on the screen will ask to decrease the reference level.

Finding Overlap in the Network: One of the more difficult problems to resolve is overlapping coverage. If a BTS is located on high ground, its coverage may unintentionally exceed the engineering plan. If the coverage is so great that it overlaps a cell that has the same control channel (BCCH for GSM), then the mobile can no longer distinguish between the two and is put out of service in the area of overlap. A directional antenna will let you determine the source of each of the overlapping signals. Moving in those directions will confirm which of the base stations is causing the extended overlap.

EXPERTS PANEL Vishnu K Goel, managing director, Acterna India and director, South Asia-Pacific, Acterna V Srinivasan, director, South Asia, Tektronix Shankar Roy Chowdhury, marketing manager (India), Agilent Technologies