Metrics Provided by CDMA Over Air Measurements
This section contains descriptions of the individual CDMA transmit parameters in the metric display of the screen. For expected result values and possible causes of error if the expected results are not met, see "Interpretation of CDMA Over Air Measurement Results"
Frequency Error
Frequency error is the frequency difference between your transmitter's actual center frequency and the frequency (or channel) you entered.
PN Offset
The PN Offset is a "short code" sequence that provides a unique identifier for each sector of each cell site. The PN Offsets are applied to the I and Q signals before modulation. PN Offsets are offset in time by 52.08 µs and they repeat every 26.666 ms. This yields 512 unique short code sequences (0-511). The mobile phone needs the PN Offset to decode information in the Sync and Paging channels, which are transmitted by the base station.
Time Offset
The Time Offset compares the PN Offset timing with the overall system time. This measurement checks the start of the PN offset in comparison to either the GPS signal or the Even Second clock signal. For example, PN Offset 0 should repeat exactly on the rising edge of the Even Second clock. PN Offset 1 should repeat 52.08 µs after the rising edge of the Even Second clock, and so forth. Any error in time from that event is reported as a Time Offset.
IS-95 specifies that the base station timing must be within +/-10 µs of its assigned value. Many base station manufactures specify that the timing must be within +/-3 µs. For example, if you are parked near the transmit antenna, the propagation delay is less than 1 µs. The measured value of delay should be within the recommended limit, which is greater than -10 µs and less than +10 µs. As you move away from the transmit antenna, propagation delay needs to be considered-about 1 µs for every 300 meters (1000 feet). So, if you are parked 800 meters (½ mile) from the transmit antenna, the additional propagation delay would be approximately 2.5 µs. The measured value of delay should be greater than -7.5 µs and less than +12.5 µs.
Below is a table showing various delays vs. distance.
Distance
Delay
161 meters (0.1 mile)
0.56 µs
402 meters (0.25 mile)
1.36 µs
805 meters (0.5 mile)
2.72 µs
1609 meters (1 mile)
5.28 µs
8047 meters (5 miles)
26.4 µs
Estimated Rho
Estimated Rho is the measure of the modulation quality for a CDMA transmitter. This measurement is analogous to measuring FM accuracy and distortion in an AMPS network or EVM in a TDMA system. A Rho value of 1.0 is perfect, indicating that all of the power is being transmitted correctly.
Carrier Feedthrough
Carrier Feedthrough is a result of the RF carrier signal feeding through the I/Q modulator and appearing at the transmitter port. Carrier Feedthrough is a common cause of bad Rho measurements.
Noise Floor
Noise Floor is the average power of all the inactive channels.
Channel Power
Channel Power is the total power within a defined bandwidth. For CDMA the channel bandwidth is defined to be 1.25 MHz. Channel Power measures the power the base station is transmitting across the entire 1.25 MHz CDMA channel.
Pilot Power
Pilot Power is the total power in the Pilot code channel, expressed in dBm. The transmit power of the Pilot Channel signal for a given base station is constant.
Pilot Ec/Io
The Pilot Ec/Io is the ratio of the pilot power to all the other power in the channel, expressed in dB. Since Ec and Io are measured individually, the system can detect poor signal quality and tell you if it is caused by low Ec or high Io. This helps you quickly resolve coverage versus interference issues.
Delta Page Power
Delta Page Power is the amplitude difference between the Paging Channel and Pilot Channel, expressed in dB. The transmit power of the Paging Channel is constant and can be set at a value relative to the Pilot Power. A common value is -4 dB relative to the Pilot. It is important to know what the intended settings are for each carrier and sector of your base station.
Delta Sync Power
Delta Sync Power is the amplitude difference between the Sync Channel and Pilot Channel, expressed in dB. The transmit power of the Sync Channel is constant and may be set at a value relative to the Pilot Power. A common value is -10 dB relative to the Pilot. It is important to know what the intended settings are for each carrier and sector of your base station.
Delta Quick Page Channel Power
Delta Quick Page Channel (QPCH) Power is the amplitude difference between the Quick Page Channel and Pilot Channel, expressed in dB. The QPCH is a bursted channel and is not on all the time. In order to capture the level of the QPCH, the statistic measures and holds the peak level of the QPCH. Until a QPCH has been measured, the value will be dashes. When "on", the level of the QPCH is constant and is set at a value relative to the Pilot Power. The QPCH digital gain level can be set to 2, 1, 0, -1, -2, -3, -4, and -5 dB relative to the Pilot. It is important to know what the intended settings are for each carrier and sector of your base station.
Amplifier Capacity
Assuming the Amplifier Capacity parameters are set properly, the Amplifier Capacity measurement is an estimate of the amount of power amplifier capacity that is being used, expressed in percent of maximum. When an amplifier is transmitting at maximum output power, it is said to be at 100% of its capacity. For example, an amplifier with a maximum output power of 12 watts would be at 50% of capacity when transmitting 6 watts and at 100% of capacity when transmitting at 12 watts.
The percentage of amplifier capacity increases as the number or level of the traffic channels increase.
Peak Amplifier Capacity
Peak Amplifier Capacity is the peak level of all the valid Amplifier Capacity measurements while on the same PN offset. In PN Offset Auto mode this measurement is reset if the PN offset changes or the Reset Metrics button is used. In PN Offset Manual mode this measurement is reset only if the Reset Metrics button is used.
Average Amplifier Capacity
Average Amplifier Capacity is the average level of all the valid Amplifier Capacity measurements while on the same PN offset. In PN Offset Auto mode this measurement is reset if the PN offset changes or the Reset Metrics button is used. In PN Offset Manual mode this measurement is reset only if the Reset Metrics button is used.
Utilization
Utilization is a ratio of the active Walsh codes to the total 128 Walsh codes, expressed in percent. Even though active control channels such as the pilot are included in the utilization measurement, utilization is an indication of the traffic that is being carried by the base station.
For example, a CDMA signal with a pilot, paging, and sync channel, two IS-95 traffic channels, and one eight-wide cdma2000 data channel, would use 18 Walsh codes. Each control channel would use two Walsh codes, each IS-95 channel would use two Walsh codes, and the cdma2000 channel would use 8 Walsh codes for a total or 18 Walsh codes. Eighteen Walsh codes in use out of the 128 total Walsh codes would result in a utilization of 14%.
Peak Utilization
Peak Utilization is the peak level of all the valid Utilization measurements while on the same PN offset. In PN Offset Auto mode this measurement is reset if the PN offset changes or the Reset Metrics button is used. In PN Offset Manual mode this measurement is reset only if the Reset Metrics button is used.
Average Utilization
Average Utilization is the average level of all the valid Utilization measurements while on the same PN offset. In PN Offset Auto mode this measurement is reset if the PN offset changes or the Reset Metrics button is used. In PN Offset Manual mode this measurement is reset only if the Reset Metrics button is used.