You can examine handset and Node B performance at bit level, symbol level, chip
level, slot level, and frame level (as shown in Table 3.8), with the Node B exercised by
any one of the four reference measurement channels (12.2, 64, 144, and 384 kbps) and
the handset exercised by any one of five measurement channels (12.2, 64, 144, 384, and
The measurement terms are Eb = energy in a user information bit, Ec = energy in
every chip, Eb/No = ratio of bit energy to noise energy, and IO = interference + noise
density. You will also see the term Eb/Nt used to describe the narrowband thermal
noise (for example, in adaptive RAKE design).
Chip level error vector magnitude includes spreading and HPSK scrambling. It cannot
be used to identify OVSF or HPSK scrambling errors, but it can be used to detect
baseband filtering, modulation, or RF impairments (the analog sections of the transmitter).
It could, for example, be used to identify an I/Q quadrature error causing constellation
QPSK EVM measurement can be used to measure single DPDCH channels, but we
are more interested in representing the effect of complex channels. This is done using
the composite EVM measurement (3GPP modulation accuracy conformance test), as
shown in Figure 3.25.
A reference signal is synthesized, downconverted (I and Q recovery), and passed
through an RRC filter. Active channels are then descrambled, despread, and Binary
Phase Shift Key (BPSK) decoded down to bit level. The despread bits are perfectly
remodulated to obtain a reference signal to produce an error vector. Composite EVM
can be used to identify all active channel spreading and scrambling problems and all
baseband, IF, and RF impairments in the Tx chain.
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