What is offset quadrature amplitude modulation?
What is offset quadrature amplitude modulation?
Offset quadrature amplitude modulation (offset-QAM) is a group of modulation formats in general communications [9], and has been investigated in multicarrier systems [10–12]. Recently, this concept was introduced to optical communications [13–17].
What is the main problem in using Quadrature Amplitude Modulation?
Explanation: Quadrature Amplitude Modulation (QAM) is widely used for combining two amplitude modulated waves into a single channel. It is both an analog and digital modulation technique. It has many advantages over other modulations such as PSK but its disadvantage is its incompability with ordinary radio waves.
What is a IQ modulator?
An IQ modulator is a device that converts baseband information into RF signals. Internally, two double-balanced mixers are combined as shown below. By modulating with both in-phase (I) and quadrature (Q) inputs, any arbitrary output amplitude and phase can be selected.
Why is DPSK scheme of carrier modulation used?
DPSK is a technique of BPSK, in which there is no reference phase signal. Here, the transmitted signal itself can be used as a reference signal. DPSK encodes two distinct signals, i.e., the carrier and the modulating signal with 180° phase shift each.
What kind of modulation does WiFi use?
WiFi systems use two primary radio transmission techniques. 802.11b (<=11 Mbps) − The 802.11b radio link uses a direct sequence spread spectrum technique called complementary coded keying (CCK). The bit stream is processed with a special coding and then modulated using Quadrature Phase Shift Keying (QPSK).
Why QPSK is called quadrature shift keying?
Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which two bits are modulated at once, selecting one of four possible carrier phase shifts (0, 90, 180, or 270 degrees). QPSK allows the signal to carry twice as much information as ordinary PSK using the same bandwidth.
What are quadrature signals?
A pair of periodic signals are said to be in “quadrature” when they differ in phase by 90 degrees. The “in-phase” or reference signal is referred to as “I,” and the signal that is shifted by 90 degrees (the signal in quadrature) is called “Q.” What does this mean and why do we care?
