Points / Symbol (Digital Demod)

Points / Symbol determines the number of points displayed between symbols for digitally demodulated data.

Points / Symbol does not apply to 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) or cdma2000 demodulation.

Minimum (except OQPSK Offset Quadrature Phase Shift Keying: A type of QPSK modulation that offsets the bit streams on the I and Q channels by a half bit. This reduces amplitude fluctuations and helps improve spectral efficiency.):	1 point per symbol
Minimum (OQPSK):	2 points per symbol
Maximum:	20 points per symbol
EDGE Enhanced Data for Global Evolution: A technology that gives GSMA and TDMA similar capacity to handle services for the third generation of mobile telephony. EDGE was developed to enable the transmission of large amounts of data at a high speed, 384 kilobits per second. (It increases available time slots and data rates over existing wireless networks.) default (see Additional Detains below):	1 point per symbol

For example, if the value of Points / Symbol is 1, each display point corresponds to a symbol. If the value is 2, every other display point corresponds to a symbol In this case, an IQ time trace would show 1 display point between each symbol, as shown in the following illustration.

The effect of Points / Symbol can be seen by displaying an IQ trace and pressing an arrow key (on the keyboard) or turning the mouse wheel to move the marker between symbols. If the number of points per symbol is 2, moving the marker would reveal 1 distinct display points between symbols.

For details about IQ diagrams, see IQ (Polar) Diagrams.

Additional Details

Here are some additional details:

Measurement Effects: For details about how Points / Symbol affects measurement data, see IQ Meas Time.
Saving Points / Symbol: When a digitally demodulated trace is saved , the Points / Symbol value used to create the trace is saved with the trace. When the trace is recalled, the VSA displays the trace with the Points / Symbol used to create the trace. The VSA DOES NOT use the current value of Points / Symbol.
OQPSK Demodulation: For OQPSK, an even number of Points / Symbol are required due to the offset between I and Q. If an odd value for Points / Symbol is specified, the VSA chooses the next lower even value.
EDGE demodulation: For the EDGE demodulation format, the Points / Symbol is set to 1 (default). The IQ Meas Time, IQ Mag Error, IQ Phase Error, and Syms/Err trace data results are the ISI Inter-Symbol Interference: An interference effect where energy from prior symbols in a bit stream is present in later symbols. ISI is normally caused by filtering of the data streams. (inter-symbol interference) compensated values. That is, when the points/symbol is set to 1 (default), the VSA removes the effects of ISI (inter-symbol interference), which provides a "clean" IQ Meas Time constellation diagram. For points/symbol greater than one, the trace data results are not compensated for the effects of ISI. For values greater than 1 point/symbol, the symbols in EDGE constellation diagrams may appear randomly placed due to the effects of ISI.
Couple to Gain Imb. / Quad Skew: This measurement parameter selection controls the number of Points / Symbol used to calculate the IQ Gain Imbalance and Quadrature Skew symbol error data results. For further information, see Couple to Gain Imb. / Quad Skew, IQ Gain Imbal, and Quad Err.

Also, see the Error Summary Data topic, Error Information at Symbol Times section.