Column Control DTX

Multi-Coded Waveform Quality and Code Domain Measurements for cdma2000

Technical Overviews

Introduction

Waveform quality and code domain measurements in TIA/EIA-95-B

Waveform quality is the basic measure of the performance of a CDMA system transmitter. The success of a CDMA system lies in its efficient use of power, and the waveform quality measurement gives the percent of power that correlates to the ideal code.

The figure of merit for waveform quality is known as rho (ρ). Rho indicates how well the CDMA signal’s power distribution matches the ideal power distribution.

Standards generally specify rho as a percentage, and require a value greater than 0.944 for acceptable performance.

The basic measurement is usually conducted as shown in figure 1. First the mobile station starts transmitting known data on the reverse channel. The test equipment demodulates and decodes the transmitted signal to some level (the level depends on the implementation). The test equipment then re-encodes and mathematically regenerates the signal, thus creating an essentially ideal signal. The actual transmitted signal is compared to this ideal signal, producing the rho measurement. Typically this measurement also produces a number of other measurements such as frequency accuracy, static time offset, amplitude error, phase error and carrier feedthrough.

There are two primary methods of measuring waveform quality: test mode rho and traffic channel rho.

Test mode rho is a method that decodes down to the short code. This method is easy to implement, and can be performed while the mobile station is either on a call or in a special test mode. Disadvantages of test mode rho are that it cannot detect hidden coding errors and cannot accurately measure low levels of rho (less than 0.90).

Traffic channel rho can be measured only when a call is active. The signal is decoded down to the input of the 64-ary modulator. By decoding this far we have already recovered most of the original transmitted bits, and have corrected for errors. When it is mathematically regenerated into the ideal signal, it is nearly perfect, and much better than the test mode rho signal. This measurement can measure much lower rho values (about 0.70). This measurement can detect coding errors in the transmitted signal that would otherwise have been missed.

Traffic channel rho is measured on the traffic channel with no other channels active because there is only one channel in the reverse link of IS-95-B.

For more information about TIA/EIA-95-B waveform quality, see the appendix A: TIA/EIA-95-B waveform quality and correlation.

Code domain measurements for TIA/EIA-95-B are derived from the same data as the rho measurement. These measurements indicate the relative power for each code in the CDMA system.

Waveform quality and code domain measurementsfor cdma2000

The reverse channel of cdma2000 differs from IS-95’s because its new radio configurations always transmit at least two channels, except during a handoff. There can be up to five channels active at once. Refer to figure 3, cdma2000 reverse channel coding, to see how the various reverse channels are combined. The R-pilot and the R-FCH channels are typically transmitted when a call is in progress. The other three channels, R-DCCH, R-SCH1 and R-SCH2 are optional.

Since there are multiple channels transmitted on the reverse link in a cdma2000 system, it seems impossible to measure waveform quality like the IS-95 does on an active call. There is, however, one very short period of time in TIA/EIA-98-D in which only the pilot channel is transmitting. During a handoff, the pilot is the only channel transmitting during the preamble, so it is technically possible to measure IS-95 style waveform quality of the pilot signal. This is called test mode rho and is the measurement described in the TIA/EIA-98-D standard.

Because traffic channel rho and test mode rho are defined only for a single coded channel, cdma2000 system manufacturers cannot have the full confidence in the tested signal that they once had in IS-95. Additionally, when multiple channels are transmitted, the crest factor of the mobile station is increased. Increased crest factor makes it harder to design output amplifiers that are sufficiently linear and low noise.

A waveform quality measurement that works while multiple codes are active would greatly increase design confidence. Keysight Technologies, Inc. has developed a multi-coded rho measurement that restores the ability to test the whole signal. This measurement is similar to traffic channel rho, but can be used while the signal is normally transmitting.

The E1962B test application of the Keysight 8960 series test set measures both the test mode rho and the multi-coded rho.

×

Please have a salesperson contact me.

*Indicates required field

Preferred method of communication? *Required Field
Preferred method of communication? Change email?
Preferred method of communication?

By clicking the button, you are providing Keysight with your personal data. See the Keysight Privacy Statement for information on how we use this data.

Thank you.

A sales representative will contact you soon.

Column Control DTX