Aeroflex 2050T SERIES Spezifikationen PDF herunterladen (Seite 11)

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34 and 35 for details of testing receiver sensitivity using audio

SINAD.

QQ33..99::

What is the difference between MER, BER and RBER?

AA33..99::

MER is Message Erasure Rate, and it applies to TETRA

channel types that include a parity check (e.g. the signalling chan-

nels such as SCH/F and the Class 2 bits in the speech frame). BER

is Bit Error Rate and it applies to TETRA channel types that do not

include a parity check (e.g. circuit data channels such as TCH/7.2

and the Class 1 and Class 0 bits in the speech frame). When

errors occur in the channels with parity checks, the whole mes-

sage is discarded (erased); when errors occur in the channels

without parity checks, one or more bits in the message are in

error.

BER tests on e.g. TCH/7.2 are much quicker than MER tests and

provide a direct test of the RF receiver performance. MER tests on

e.g. SCH/F take much longer because for every 432 bits in

TCH/7.2 there is only one message in SCH/F, so it takes 432 times

longer to acquire the same number of samples on SCH/F. For

example, the BS Class A TCH/7.2 BER test requires 5800 samples

(bits) which takes less than one second; the BS Class A SCH/F

MER test requires 6600 samples (messages) which takes 6 min-

utes and 36 seconds.

Hence the SCH/F MER test is normally only performed for R&D /

conformance testing because it takes too long. Manufacturing,

installation and maintenance testing normally uses the TCH/7.2 or

TCH/S Class 0 BER test because it is much quicker and provides

a direct test of the hardware. For performing acceptance tests /

installation tests on base stations the much fasterTCH/7.2 BER test

is normally more suitable than the slow SCH/F MER test.

RBER (Residual Bit Error Rate) applies only to the speech traffic

channel TCH/S, in which there are three different classes of bits

with different levels of protection. If bit errors occur in the Class 2

bits, this will normally be detected by the parity check and two

entire 30 ms speech frames will be erased. If RBER TT loopback

is selected, the mobile is instructed to signal erased frames by

substituting the loopback bits with all 1s in each speech frame,

hence it is only possible to measure BER of the Class 0 and Class

1 bits when frame erasure has not occurred. The Bit Error Rate,

measured only in those frames where frame erasure has not

occurred, is termed the Residual Bit Error Rate. If BER TT loopback

is selected, the mobile always loops back the received bits and

does not check for frame erasure. RBER measurement values are

likely to be limited compared to BER values, since higher BER val-

ues in Class 0 and Class 1 bits are statistically more likely to be

accompanied by bit errors (and hence frame erasure) in the Class

2 bits.

QQ33..1100::

Which types of T1 test signals are generated for mobile

testing?

AA33..1100::

The 2968 generates the following T1 signals for mobile

testing:

• T1 type 1: TCH/7.2 PRBS in TN1 FN1-17

• T1 type 2: SCH/F PRBS in TN1 FN1-17

• T1 type 4: TCH/2.4 PRBS in TN1 FN1-17

There is also another T1 signal defined which the 2968 does not

generate:

• T1 type 3: BSCH PRBS in SSN1 + SCH/HD PRBS in SSN2

in TN1 FN1-17

All four of these T1 signals have the following in common:

• AACH PRBS in BBK in TN1 FN1-18 in every multiframe

• BSCH (T1 sync info) in SSN1 in TN1 FN18 in every multi-

frame

• BNCH/T (T1 sys info) in SSN2 in TN1 FN18 in every mul-

tiframe

• TCH/7.2 PRBS + AACH PRBS in TN2, TN3 and TN4 FN1-

All T1 signals conform to ETSI EN 300 394-1 v2.3.1 subclause

5.3.2.1

QQ33..1111::

What is the content of the PRBS information generated by

the IFR 2968 T1 signals?

AA33..1111::

The IFR 2968 PRBS information conforms to ETSI EN 300

394-1 v2.3.1 subclauses 5.3.2.1 (T1 signal for mobile testing) and

5.3.2.2 (T1 signal for base station testing), which specify ITU-T

O.153 511 bit PRBS.

The hex data below represents 944 bits of the standard 511 bit

ITU-T O.153 PRBS, i.e. one complete sequence of 511 bits fol-

lowed by 433 bits of the next repetition of the sequence. Read

from left to right, i.e. binary sequence is

111111111 000001111 0111110 0 01 .....

ff83df17 32094ed1 e7cd8a91 c6d5c4c4 4021184e 5586f4dc 8a15a7ec

92df9353 3018ca34 bfa2c759 678fba0d 6dd82d7d 540a5797 7039d27a

ea243385 ed9a1de1 ff07be2e 64129da3 cf9b1523 8dab8988 8042309c

ab0de9b9 142b4fd9 25bf26a6 60319469 7f458eb2 cf1f741a dbb05afa

a814af2e e073

This data is pure O.153 PRBS not subject to any channel coding,

scrambling or framing. Mobile and base station equipment per-

forming internal or external self-measurement of BER should

expect to receive this sequence when there are no bit errors.

QQ33..1122::

Can the 2968 generate PRBS for testing AACH, BSCH

and SCH/HD channel types?

AA33..1122::

AACH PRBS is provided on all MS T1 signals. Note that

the AACH PRBS is over all 18 frames, unlike the other logical chan-

nels which have PRBS over frames 1 to 17 only.

The 2968 does not generate the T1 type 3 signal containing

BSCH PRBS and SCH/HD PRBS data. The BSCH and SCH/HD

channels are generated in all MS T1 signals, but only in frame 18,

and they contain T1 synchronisation and control information

rather than PRBS. However, for the purpose of performing an R&D

/ conformance test of BSCH and SCH/HD MER, the BSCH and

SCH/HD (BNCH/T) in frame 18 may be adequate, although the

test will be slower than with a T1 type 3 signal since BSCH and

SCH/HD are only present in frame 18.

QQ33..1133::

Can the IFR 2968 test base station receivers?

AA33..1133::

Yes. The IFR 2968 generates the uplink T1 type 7

(TCH/7.2) signal defined in ETSI EN 300 394-1 subclause 5.3.2.2

for testing base station receiver Bit Error Rate (BER), including

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 23 24

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