Normalize IQ Traces (Digital Demod)

Normalize IQ Traces enables or disables IQ trace normalization. Selecting the Normalize IQ Traces check box enables normalization; clearing the check box disables normalization.

When normalization is ON, the VSA normalizes, or scales, the demodulated trace data results. The normalization factor depends on the EVM Normalization Reference selection and the type of signal format.

Normalization is performed on these traces:

QAM Quadrature Amplitude Modulation/PSK Phase Shift Keying: A broad classification of modulation techniques where the information to be transmitted is contained in the phase of the carrier wave. formats
- Error Vector Spec and Error Vector Time
- IQ Meas Spec and IQ Meas Time
- IQ Ref Spec and IQ Ref Time
- IQ Mag Error
- The Instantaneous versions of any of these traces (like Inst IQ Meas Spec)
FSK Frequency Shift Keying: A form of modulation using multiple carrier frequencies to carry the digital information. The most common is the two frequency FSK system using the two frequencies to carry the binary ones and zeros. and CPM Continuous Phase Modulation (FM Frequency Modulation) formats
- FSK Meas Time and FSK Ref Time
- FSK Meas Spec and FSK Ref Spec
- Carrier Magnitude Error
- FSK Error Time and FSK Error Spec
- The Instantaneous versions of any of these traces (like Inst FSK Meas Time).
CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95. formats
- CDP and CDE traces for W-CDMA, cdma2000, 1xEV-DO and TD-SCDMA demodulation

Digital Demod and QAM/PSK formats

For Digital Demod (option AYA) analyzing QAM/PSK formats, normalization depends on the selection of the EVM Normalization Reference parameter.

When normalization is ON and the display is a vector or constellation diagram, the VSA displays cross-hairs or circles at the ideal constellation locations.

EVM Normalization Reference = Constellation Maximum

When EVM Normalization Reference is set to Constellation Maximum, the traces are normalized to the maximum constellation magnitude, which is the outermost state in the ideal (IQ Ref) constellation diagram. For example, the constellation for a 16QAM IQ Ref trace is shown below after normalization. All the points in the trace have been normalized by the magnitude of the outermost state, which sets the outermost states to 1.

$image\normalize_wmf.jpg$

A 32QAM constellation diagram does not have corner states. For these "cross-QAM" constellations, the VSA normalizes the constellation diagram to the corner state of an ideal, square constellation diagram. In other words, when normalization is ON for 32QAM, traces are normalized by the magnitude of the corner state of an ideal 36QAM constellation diagram. 128QAM is normalized to 144QAM. 512QAM is normalized to 576QAM, etc.

OQPSK Offset Quadrature Phase Shift Keying: A type of QPSK modulation that offsets the bit streams on the I and Q channels by a half bit. This reduces amplitude fluctuations and helps improve spectral efficiency. signals are normalized to the QPSK Quadrature phase shift keying constellation so that the corners of the QPSK constellation have a magnitude of one. For more information, see the OQPSK Offset note in the Error Vector Magnitude (EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format.) topic.

EVM Normalization Reference = Reference RMS

For modulation formats whose constellations have multiple magnitude levels (16QAM, APSK, StarQAM, etc.), EVM Normalization Reference can be set to Reference RMS. When this is selected, IQ traces are normalized by the RMS level of the constellation itself (EVM in the Syms/Errs table is still normalized to the RMS average of the IQ Reference symbol points).

In other words, the normalization value is an RMS average of all possible states in the IQ Ref Time ideal QAM constellation. This is in contrast with the normalization value used when EVM Normalization Reference is set to Constellation Maximum, which is the outermost constellation state of IQ Ref Time trace.

Since the normalization value for IQ traces differs from the normalization value for the EVM metric, the peak value of the Error Vector Time trace will not exactly match the peak EVM reported on the Syms/Errs trace, nor will placing a Band Power marker over all symbols in the Error Vector Time trace exactly match the EVM value.

Digital Demod and FSK formats

For FSK and CPM (FM), normalization scales the trace points as follows:

This FSK trace:	Is scaled by:
FSK measured time	Deviation
FSK reference time	Deviation
FSK measured spectrum	Deviation
FSK reference spectrum	Deviation
Carrier magnitude error	rms magnitude
FSK error time	Deviation

The links in the table above contain more information on normalization and FSK.

OFDM Demodulation

For OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. normalization (except LTE/LTE-A), each subcarrier is normalized so that the RMS level of the ideal constellation is 1. This is equivalent to setting EVM Normalization Reference to Reference RMS in Digital Demod.

Non-OFDM Demodulation

(W-CDMA, cdma2000, 1xEV-DO, TD-SCDMA, 802.11b/g DSSS Direct sequence spread spectrum. The data transmission scheme (sometimes referred to as a "'modulation" scheme) used in 802.11b WLANs. DSSS uses a radio transmitter operating at a fixed centre frequency, but using a relatively broad range of frequencies, to spread data transmissions over a fixed range of the frequency band. 802.11a and 802.11g (when not operating in 802.11b mode) use Orthogonal Frequency Division Multiplexing (OFDM)./CCK complementary code keying/PBCC packet binary convolutional code)

Except as noted below for composite trace data, non-OFDM measurement types perform the same normalization as Digital Demod with EVM Normalization Reference is set to Constellation Maximum.

Composite Trace Data for CDMA-based Demods

For composite time data in CDMA-based measurements, the ideal state positions vary depending on the CDMA channel configuration. Instead of normalizing the outermost state to have a magnitude of one, traces are normalized as follows:

Code domain trace data results
Code domain results (CDP Composite, CDP Layer, CDE Composite, and CDE Layer) are normalized to the total measured signal power. This means that the sum of all the values in a CDP Layer trace will be one.
Composite time trace data results
Composite time results (Composite Error Vector Time, Composite IQ Meas Time, Composite IQ Ref Time, and so on) are normalized to the composite reference signal power. This means that the RMS level of the Composite IQ Ref Time trace will be one.
Channel time trace data results
Channel time results (Channel Error Vector Time, Channel IQ Meas Time, Channel IQ Ref Time, and so on) are normalized to the Channel IQ Ref Time power. This means that the RMS level of the Channel IQ Ref Time trace will be one.

How Normalization Affects the Trace Measurement Units

For most configurations, the measurement data determines the units of the normalized trace. With normalization on, the y-axis units (for rectangular traces) or polar units (for polar traces) become unitless or are converted to a percentage. If the Log Mag trace format is selected, the units are decibels.

As mentioned previously, normalization scales the demodulated data onto the unit circle. This process of scaling yields a unitless scalar (number). For some traces, such as error vector time, the number is multiplied by 100 to display the percentage error. Thus an error vector of 0.10 is 10%.