IS-95 Filters (Digital Demod)

MeasSetup > Digital Demod Properties > Filter > Reference Filter

The VSA includes two filters that conform to US 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. digital cellular standard IS-95:

IS-95 Base Phase Compensating filter.
IS-95 Baseband (Chebyshev) filter.

These filters measure base stations or mobile phones that conform to US CDMA digital cellular standard IS-95. The IS-95 base-phase EQ filter is the inverse of the forward all-pass phase-compensation filter that is specified for IS-95 base-station transmission. The IS-95 Chebyshev filter is the filter specified in IS-95 that provides overall channel filtering for both base-to-mobile and mobile-to-base links.

The IS-95 base-phase EQ filter is applied to the I/Q measured signal. The IS-95 Chebyshev filter is applied to the I/Q reference signal.

To automatically configure the VSA for base-station or mobile measurements, display the Format tab in the Digital Demod Properties dialog box, then click Preset to Standard and select CDMA BASE or CDMA MOBILE.

IS-95 Base Phase Compensating filter

This filter is the inverse of the forward all-pass phase-compensation filter that is specified for IS-95 base-station transmission. IS-95 base-station transmit filters include a baseband filter followed by an all-pass phase-compensation filter which compensates for typical IF phase-distortion in a mobile phone.

The inverse all-pass phase-compensation filter selected with IS-95 Base Phase Compensating is an ideal digital implementation. While actual IF characteristics in mobile phones may vary, base- station filtering is a fixed standard in IS-95. Therefore, selecting IS-95 Base Phase Compensating configures the VSA to behave as an ideal measuring receiver for determining base-station compliance to IS-95 filtering.

The following illustration shows filtering for base stations as defined in IS-95. The illustration also shows how to use the VSA's IS-95 Base Phase Compensating and IS-95 baseband filters to measure base-station transmissions.

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Mobile transmitters do not use an all-pass phase filter. Therefore, when measuring mobile transmissions, set the demodulator's measurement filter to None.

Select CDMA BASE or CDMA MOBILE to automatically configure the VSA to measure CDMA base stations or mobile phones.

IS-95 Baseband (Chebyshev) filter

The IS-95 Chebyshev (baseband) filter is the filter specified in IS-95 that provides overall channel filtering for both base-to-mobile, and mobile-to-base links.

If demodulating a base station or mobile, select this filter for the reference filter.