H.2 Basic principles
38.176-13GPPIntegrated Access and Backhaul (IAB) conformance testingNRPart 1: conducted conformance testingRelease 17TS
The process is based on the comparison of the actual output signal of the TX under test, received by an ideal receiver, with an ideal signal, that is generated by the measuring equipment and represents an ideal error free received signal. All signals are represented as equivalent (generally complex) baseband signals.
The description below uses numbers and illustrations as examples only. These numbers are taken from a TDD frame structure with normal CP length, 30 kHz SCS and a transmission bandwidth configuration of 100 MHz (NRB = 273). The application of the text below, however, is not restricted to this parameter set.
H.2.1 Output signal of the TX under test
The output signal of the TX under test is acquired by the measuring equipment and stored for further processing. It is sampled at a sampling rate which is the product of the SCS and the FFT size, and it is named . The FFT size is determined by the transmission bandwidth in table 6.5.3.5-2 for 15 kHz SCS, table 6.5.3.5-3 for 30 kHz SCS and table 6.5.3.5-4 for 60 kHz SCS. In the time domain, it comprises at least 10 ms. It is modelled as a signal with the following parameters:
– demodulated data content,
– carrier frequency,
– amplitude and phase for each subcarrier.
For the example in the annex, the FFT size is 4096 based on table 6.5.3.5-3. The sampling rate of 122.88 Msps is the product of the FFT size and SCS.
H.2.2 Ideal signal
Two types of ideal signals are defined:
The first ideal signal is constructed by the measuring equipment according to the relevant TX specifications, using the following parameters:
– demodulated data content,
– nominal carrier frequency,
– nominal amplitude and phase for each subcarrier.
It is represented as a sequence of samples at the sampling rate determined from annex H.2.1 in the time domain. The structure of the signal is described in the test models.
The second ideal signal is constructed by the measuring equipment according to the relevant TX specifications, using the following parameters:
– nominal demodulation reference signals (all other modulation symbols are set to 0 V),
– nominal carrier frequency,
– nominal amplitude and phase for each applicable subcarrier,
– nominal timing.
It is represented as a sequence of samples at the sampling rate determined from annex H.2.1 in the time domain.
H.2.3 Measurement results
The measurement results, achieved by the in-channel TX test are the following:
– Carrier frequency error
– EVM
– Resource element TX power
– OFDM symbol TX power (OSTP)
Other side results are: residual amplitude- and phase response of the TX chain after equalisation.
H.2.4 Measurement points
The resource element TX power is measured after the FFT box as described in figure H.2.4-1. The EVM shall be measured at the point after the FFT and a zero-forcing (ZF) equalizer in the receiver, as depicted for FR1 in figure H.2.4-1. The FFT window of FFT size samples out of (FFT size + cyclic prefix length) samples in the time domain is selected in the "Remove CP" box. The FFT size and the cyclic prefix length are obtained from table 6.5.3.5-2 for 15 kHz SCS, table 6.5.3.5-3 for 30 kHz SCS and table 6.5.3.5-4 for 60 kHz SCS.
In one subframe, there are two symbols with the length of the cyclic prefix larger than the values listed in tables 6.5.3.5-2, 6.5.3.5-3 and 6.5.3.5-4. Table H.2.4-1 lists the slot number and the symbol number and the formula how to compute the length of cyclic prefix for those two symbols according to the sampling rate.
Table H.2.4-1: Slot number and symbol number identifying the longer CP length for normal CP
|
SCS (kHz) |
# slots in subframe |
Symbol # and slot # with longer CP |
Longer CP length |
|
15 |
1 |
(symbol 0, slot 0) |
CP length + FFT size / 128 |
|
30 |
2 |
(symbol 0, slot 0) |
CP length + FFT size / 64 |
|
60 |
4 |
(symbol 0, slot 0) |
CP length + FFT size / 32 |
For the example used in the annex, the "Remove CP" box selects 4096 samples out of 4384 samples. Symbol 0 has 64 more samples in the cyclic prefix than the other 13 symbols in the slot (the longer CP length = 352).
Figure H.2.4-1: Reference point for FR1 EVM measurements