Gain Imb (802.16 OFDM)
Gain Imb (Gain Imbalance) compares the gain of the I signal with the gain of the Q signal, as follows:
Gain Imb is expressed as a logarithmic value so it may have a positive or negative value. Gain Imb is computed and stored as a linear ratio equal to (I Gain/Q Gain) and then displayed in dB equal to [20 Log (I Gain/Q Gain)].
GainImbalance for OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. demodulation differs from gain imbalance for single carrier modulation in that gain imbalance does not show up in the constellation diagram as a width different than height. That's because gain imbalance is in the time domain signal but OFDM constellations are in the frequency domain. In an OFDM signal, gain imbalance causes each subcarrier to interfere with its opposing subcarrier, causing each constellation point to spread into a miniature picture of the entire constellation.
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