Keysight E6610A, Руководство пользователя и программирования

Страница: 104 / 108

Appendix C: AxC Configuration and Multicast Mode
Appendix C: AxC Configuration and Multicast Mode
The E6610A has two CPRI baseband arbitrary waveform generators which can each
be configured to play a waveform file. Typically these waveform files will contain IQ
data for one LTE frame which will be played repeatedly, and the size of the files will
depend on the bandwidth of the signal, which also dictates the sample rate. Each
waveform is transmitted as an antenna carrier (AxC) container group over CPRI, and
the data is routed to one antenna path in the RRH for conversion into an RF Tx output
signal.
The E6610A also offers a "multicast" mode (configurable using SCPI commands) that
allows it to generate four IQ data streams by duplicating the waveforms configured for
the CPRI Tx1 and CPRI Tx2 outputs into two additional data streams, subject to the
CPRI line rate being able to support the required data rate. This allows the E6610A to
support multi-carrier testing, or to transmit data to drive a RRH with up to 4 antenna
ports. Note that to prevent correlation peaks for multi-carrier testing, a multicast data
stream should not be routed to the same radio path in the RRH as the original
waveform that was duplicated. A brief review of CPRI frame structure will aid in
understanding the transmission capacity limitations for different CPRI line rates.
A CPRI basic frame consists of 16 words, with the first word being the control word
and the remaining 15 words being used to transmit IQ data. The length of one word T
depends on the CPRI line rate, as shown in the following table:
CPRI Line Rate CPRI line bit rate (Mbps) Length of Word T (bits)
1 614.4 8
2 1228.8 16
3 2457.6 32
4 3072.0 40
5 4915.2 64
6 6144.0 80
7 9830.4 128
Let M = the width of the I or Q data samples. The size of an antenna carrier (AxC) is
then equal to 2 x M per carrier/antenna.
CPRI basic frames are transmitted at a fixed clock rate of f
c
= 3.84 MHz, so to transmit
sufficient IQ samples for higher bandwidths and sample rates, multiple AxCs are
required for each IQ sample.
LTE Bandwidth (MHz)
Sampling Rate
fs (MHz)
# of AxCs in
AxC Container
5 7.68 = 2*fc 2
10 15.36 = 4*fc 4
20 30.72 = 8*fc 8
104 Keysight E6610A User and Programming Guide