Rohde & Schwarz CMU-K20, Руководство по эксплуатации

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CMU-K20/K21/K22/K23/K24
Signalling: Receiver Quality Measurements
1115.6088.12 4.119 E-12
RBER Ib = Erroneous class Ib bits (RF) / total number of class Ib bits (RF) * 100%
The Block Error Ratio (BLER) is the ratio of blocks that the MS receives in error to
the total number of received blocks, where a block is defined as received in error if
the error detection functions in the receiver indicate an error as a the result of the
Block Check Sequence (BCS, see GSM 11.10):
BLER = Blocks received in error / total number of blocks * 100%
The Data Block Error Rate (DBLER) is the ratio of data blocks that contain bit
errors in their data field to the total number of transferred blocks in percent:
DBLER = Blocks with erroneous data fields / total number of blocks * 100%
The USF Block Error Rate (USF BLER) is the ratio of GPRS packet data blocks
that contain bit errors in their Uplink State Flag (USF) to the total number of
transferred blocks in percent:
USF BLER = Erroneous blocks / total number of blocks * 100%
Statistical Testing
Bit error rate tests are based on the assumption of statistical independence of the single bit
error events: The probability of a bit error is equal for each received bit. The exact bit error
rate is given by the limit of the ratio <bit errors>/<no. of received bits>, where the number of
received bits tends to infinity. As test times are limited, any real bit error rate test necessarily
provides an approximation to the exact bit error rate.
The CMU is not only capable of measuring (approximate) bit error rates for a fixed number of
received bits but can also use the preliminary results to predict a confidence interval for the
exact bit error rate. Confidence BER tests can reduce test times considerably. For more
information and application examples see section
Statistical BER Tests
on p. 4.125 ff.
BLER and
BER/DBLER
mode
The BLER and the BER/DBLER measurements assess the receiver quality for
packet data traffic channels (PDTCHs) both in circuit switched or packet data
mode. For a detailed explanation of these measurements see section
BER Tests of
PDTCHs
on p. 4.120 f.
Note: For circuit switched channels, the reduced signalling scheme
(
Signalling Channel
= NONE
, see p.
4.176
) and one of the packet data
coding schemes CS1 to CS4 or MCS1 to MCS9 must be used (see
Traffic Mode softkey
4.170
).
Packet switched data channels (GPRS and EGPRS channels) can be
analyzed with option CMU-K42 and CMU-K43.
Burst by Burst
mode (fast BER)
In the
Burst by Burst
mode, the CMU transmits only bits without error protection
(class II bits); no guard bits are used. The internal test loop of the MS is closed
before any channel decoding/encoding (see GSM 04.14 and
Fig. 4-55 below
), so
the bit error rate is evaluated on a burst by burst basis. This increases the number
of bits measured per unit of time and thus considerably enhances the measurement
speed.
Note: The
Burst by Burst
bit error rate test is specified for GSM phase II and
phase II+ mobiles. Not all mobiles support this test mode. If a mobile
does not support the
Burst by Burst
bit error rate test, the
measurement fails (like for very low signal levels) and an error
message is generated:
Too many errors. Measurement halted !
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