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channel type 8 (SCH/F) in frame 18 in timeslot 1. It does not gen-

erate an uplink T1 type 8 (SCH/F) signal in frames 1 to 17 for test-

ing base station receiver Message Erasure Rate (MER), although

the SCH/F in frame 18 could be used for this purpose. The 2968

synchronises the timing of its uplink T1 type 7 signal to that

expected by the base station. Base stations normally perform their

own BER measurement on the uplink signal that they receive, so

the IFR 2968 does not expect the BS to perform RF loopback on

the T1 signal, and does not perform BER measurement on signals

transmitted by the base station.

QQ33..1144::

What is the synchronisation connection between the

base station and the IFR 2968?

AA33..1144::

Two synchronisation methods are provided in the IFR

2968.

The IFR 2968 can synchronise its timing to a synchronisation

pulse generated by the base station. The BS sync pulse is defined

in ETSI EN 300 394-1 v2.3.1 subclause 4.1.1 (6th bullet point). The

repetition rate is the multiframe rate (1.02s) but the pulse width is

undefined - only the rise and fall times are defined (<50 ns). The

2968 can be triggered on either the rising edge or the falling

edge of the pulse. It is the timing of this edge that matters, so if

the timing is defined w.r.t. the rising edge then the timing of the

falling edge (and hence the pulse width) is irrelevant. The syn-

chronisation pulse is connected to the IFR 2968 via the rear panel

ACCESSORY connector (25 way D-type), pin 2 is the pulse input,

pin 4 is signal ground. For full details refer to issue 10 of the IFR

2968 Operating Manual TETRA supplement for Phase 3.2, chap-

ter 5.

The 2968 can also synchronise automatically to the signal gener-

ated by the BS. However, the automatic synchronisation only

works for a BS that is generating a signal according to ETSI EN

300 394-1 subclause 5.2.1.2, and that is expecting to receive a

signal according to ETSI EN 300 394-1 subclause 5.3.2.2.

QQ33..1155::

How do I perform a test on a base station receiver with

the IFR 2968?

AA33..1155::

This will depend on the type of base station. Typically you

will need a control program or a terminal emulator running on a

PC with a serial port connection to a test / control port on the

base station. For some base stations you will need to connect a

synchronisation pulse lead between the base station and the IFR

2968 ACCESSORY socket. For other base stations you will be able

to synchronise the 2968 automatically to the signal generated by

the base station. Ensure that the IFR 2968 system parameters

menu item "SYNC TO BASE STATION" is set to PULSE or AUTO as

appropriate. For full details refer to issue 10 of the IFR 2968

Operating Manual TETRA supplement for Phase 3.2, chapter 5.

For the specific details of operating a particular base station in a

receiver testing mode you should refer to the base station manu-

facturer. For some TETRA base stations, IFR can supply application

notes on request for testing the base station with the IFR 2968.

However, please note that since these contain manufacturers'

proprietary details we can only supply this information to autho-

rised persons; normally this is restricted to the base station man-

ufacturer's personnel or authorised agents.

QQ33..1166::

What is the purpose of the base station system parame-

ters "SYNC PULSE OFFSET" and "AUTO SYNC PATH DELAY" ?

AA33..1166::

The SYNC PULSE OFFSET defines the time between the

rising or falling edge of the sync pulse and the start of the IFR

2968 uplink T1 signal (frame 1, timeslot 1, symbol number 0). The

sync pulse output by the base station has an arbitrary, but fixed,

relationship to the expected timing of the uplink T1 signal. You

should refer to the base station manufacturer for the required

value of this parameter if you are using pulse synchronisation. This

parameter is irrelevant if you are using auto synchronisation.

The AUTO SYNC PATH DELAY defines a delay in the generation

of the IFR 2968 uplink T1 signal when it is synchronised to the

downlink signal generated by the base station. With zero delay, the

start of the IFR 2968 uplink T1 signal (frame 1, timeslot 1, symbol

number 0) occurs exactly two timeslots after the start of the base

station downlink T1 signal. However, base stations in a receiver

testing mode may expect to receive the uplink signal later than

this time (as with a mobile some distance from the base station).

You should refer to the base station manufacturer for the required

value of this parameter if you are using auto synchronisation. This

parameter is irrelevant if you are using pulse synchronisation.

QQ33..1177::

Why does the base station indicate a BER measurement

of around 50% even though the IFR 2968 is synchronised and

the signal level is above the reference sensitivity level?

AA33..1177::

50% BER is normally an indication that there is no corre-

lation between the received data and the expected data, i.e. the

received data appears to be completely random rather than the

expected PRBS. This can occur because the receiver is not receiv-

ing the expected sequence, or because the receiver's compari-

son with the expected sequence is not synchronised to the

received sequence. These problems can occur if the base station

receiver and the 2968 signal generator are using different scram-

bling sequences. Scrambling is a TETRA process that is used on

all traffic and signalling channels, which applies a particular bit

pattern (the scrambling sequence) to invert some of the data bits.

Scrambling is used to ensure that the modulation is randomised,

and to guard against inadvertent co-channel reception from an

unwanted base station using a different scrambling sequence.

Check the setting of the "MCC-MNC-BCC UPDATE" parameter in

the base station system parameters menu. It is essential that the

2968 uplink T1 signal is scrambled with the same scrambling

sequence that the base station is using to de-scramble the signal,

otherwise the data content of the signal will be uncorrelated with

the PRBS that the base station is expecting to receive. If the base

station conforms to ETSI EN 300 394-1, subclause 5.2.1.2, it indi-

cates the expected scrambling sequence by means of the MCC,

MNC and BCC parameters in its synchronisation burst. If the IFR

2968 is set to MCC-MNC-BCC UPDATE: AUTO, it will automati-

cally set the scrambling of its uplink signal according to these

parameters in the signal received from the base station. However,

if the base station does not conform to subclause 5.2.1.2, or if the

base station receiver is to be tested separately from the base sta-

tion transmitter, the IFR 2968 must be set to MANUAL update,

and the required values of MCC, MNC and BCC must be set to

match those expected by the base station.

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