Composite Error Vector Magnitude
Contents |
quality metric in digital communication error vector magnitude calculator systems. See the EVM metric in the Error Summary Table
Evm Error Vector Magnitude
topic in each demodulator for more information on how EVM is calculated for that modulation format. values; error vector magnitude matlab the RMS (root mean square) EVM, the Peak (largest) EVM, and the symbol number with the Peak EVM. A perfect ideal signal is synthesized at the chip level and identified as the reference signal. error vector magnitude definition The reference signal is subtracted from the measured signal to produce a time record of error phasors. The square root of the ratio of the mean power of the error signal to the mean power of the reference signal is computed and expressed as a percentage EVM. This parameter is similar to digital demodulation EVM except that it is computed at the chip rate instead of the symbol rate. See Digital Demodulation Error Vector Magnitude (EVM) for further information about this parameter. See Also Digital Demodulation Error Vector Magnitude (EVM) About Composite Summary Table 21.00 Copyright © 2000-2016 Keysight Technologies, Inc.
for more information on how EVM is calculated for that modulation format. is the Error Vector Magnitude for the composite signal (includes all Walsh Code Length (Symbol Rate) and Walsh Code Number). http://rfmw.em.keysight.com/wireless/helpfiles/89600B/WebHelp/subsystems/wcdma/content/wcdma_sym_tbl_comp_evm.htm The display shows these EVM values; the RMS (root mean square) EVM, the Peak (largest) EVM, and the symbol number with the Peak EVM. A perfect ideal signal is synthesized at the chip level and http://rfmw.em.keysight.com/wireless/helpfiles/89600B/webhelp/Subsystems/cdma2k/Content/cdma2000_sym_tbl_comp_evm.htm identified as the reference signal. The reference signal is subtracted from the measured signal to produce a time record of error phasors. The square root of the ratio of the mean power of the error signal to the mean power of the reference signal is computed and expressed as a percentage EVM. This parameter is similar to digital demodulation EVM except that it is computed at the chip rate instead of the symbol rate. See Digital Demodulation Error-vector magnitude (EVM) for further information about this parameter. See Also About Composite Error Summary Data Digital Demodulation Error-vector magnitude (EVM) 21.00 Copyright © 2000-2016 Keysight Technologies, Inc.
noise, interfering signals, nonlinear distortion and the load of the radio. It is a component of the 802.11 IEEE standard, and has become an industry standard measurement for cellular phones, cable television and wifi. EVM is typically measured in http://www.antenna-theory.com/definitions/evm.php decibels (dB), and sometimes in percent. An example will make this is clear, assuming you know a bit about digital modulation techniques (QAM, QPSK, PSK, etc). Suppose our radio is transmitting via a 16-QAM constellation. It would like to send the black dots below in the I-Q (In phase - Quadrature Plane) plane. However, due to our real-world (non-ideal) radio, suppose the radio actually transmits something a bit off of this point: Figure 1. Illustration of error vector A 16-QAM Constellation. In Figure 1, we have a 16-QAM constellation, which means we encode our 1's and 0's as 16 different symbols, with 4 bits per symbol. At this instant in Figure 1, suppose we are transmitting the symbol pointed to by the orange vector, or bits [0000]. In this case, we are transmitting exactly what our radio wants to transmit; simiarly this is what the receiver would expect to receive with no noise present. error vector magnitude Now, suppose that our radio is not perfect for whatever reason. Then we won't be exactly transmitting the symbol we want to send. The difference between the desired (ideal) signal vector and the actual signal vector is the error vector, as shown in Figure 2. And the magnitude of the error vector? This is EVM. Figure 2. Illustration of The Error Vector Magnitude (EVM). Now, if you have noise in your system, this disturbs your measurements as well. However, EVM is not noise. Noise arises from some external source and can be reduced via averaging or other techniques. We'll return to what causes EVM in a minute. EVM is typically measured in dB, as in: EVM=-28 dB. This means the error vector has a magnitude that is 28 dB less than the average signal vector (or, the average energy per symbol we transmit). Hence, we can write EVM mathematically as: EVM is typically less than -20 dB, and often much lower depending on the application. How does EVM relate to Antennas? As this website doesn't focus too much on radios, you may be wondering why the topic of EVM is being studied in an antenna theory website. Well it turns out that the antenna can significantly affect EVM. How? The antenna's impedance presents itself as a load to the radio. If the antenna has a poor impeda
be down. Please try the request again. Your cache administrator is webmaster. Generated Wed, 05 Oct 2016 23:48:28 GMT by s_hv999 (squid/3.5.20)