Comp IQ Meas Time and IQ Ref Time (W-CDMA(3GPP)/HSPA)

When W-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.(3GPP) Demodulation is enabled, the composite IQ Meas Time and IQ Ref Timecomposite trace data are the time data results of W-CDMA(3GPP) demodulation for the composite signal. IQ Meas Time is the data results for the measured input signal. IQ Ref Time trace data is the data results that would be derived from an ideal input signal (reference signal).

The trace data is computed from the first slot in the Measurement Interval after the Measurement Offset.

MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. Measurements ( only): There is a seperate trace result for each measurement Antenna (x).

Concepts

The VSA's demodulator produces two signals: I/Q Measured and I/Q Reference.

IQ measured signal

The IQ measured signal is the result of resampling the data to one point per chip and applying carrier locking, symbol locking, IQ origin offset compensation, filtering, and system gain normalization to the incoming signal.

IQ reference signal

IQ reference signal is the ideal signal that the VSA generates from the IQ measured signal demodulated data bits. The VSA detects bits from the measured IQ signal and reconstructs a sequence of ideal I and Q states. These are then treated as ideal impulses and are baseband filtered according to the reference filter and added together to form the IQ reference signal. The resultant IQ reference signal is then used compare and analyze against the IQ measured signal.

Online help for Digital Demodulation includes a block diagram that shows how I/Q measured and I/Q reference data are generated.

Time Domain Displays

The VSA's demodulator produces fime domain data. If composite IQ Meas Time is selected, the VSA shows the composite IQ measured signal in the time domain. Likewise, if composite IQ Ref Timeis selected, the VSA shows the composite IQ reference signal in the time domain.

The data can be displayed in a variety of trace data formats, including I-Q, Constellation, Q-Eye, I-Eye, and Trellis-Eye formats. (See Trace Formats (Digital Demodulation)).

If normalization is off, the VSA shows the instantaneous magnitude. If normalization is on, the VSA scales the composite IQ measured and composite IQ reference traces so that the RMS level is one, which produces a unitless y-axis.

For further details about normalization, see Normalize IQ Traces.