Abstract
In this study, it is mathematically shown that the detector inputs obtained using the matched filters in the Quadrature Amplitude Modulation (QAM) receiver are the same expressions as those obtained using the integrators if a rectangular pulse is used in the transmitter and the channel is Additive White Gaussian Noise (AWGN). Under the assumption that there is a perfect synchronization between the transmitter and the receiver. QAM is intensively used at the present time for the data transmission on subchannels in orthogonal frequency-division multiplexing (OFDM) communication systems such as digital subscriber lines (DSLs) modems, wireless local area networks (WLANs) and cellular wireless communication systems (e.g. 4G LTE). Cyclic-prefix OFDM is deployed in 4G LTE systems and the rectangular pulse is used in the time domain to shape all subcarriers of OFDM.
Highlights
Quadrature Amplitude Modulation (QAM) can be seen as a combination of digital-amplitude modulation and digital-phase modulation
Rectangular M-ary QAM signal constellations are preferable to nonrectangular constellations because they are generated and demodulated [2]
Third Generation Partnership Project (3GPP) standardized the Release-15 corresponding to 5G New Radio (NR) phase 1, and the Release-16 corresponding to 5G New Radio (NR) phase 2 is almost complete [5, 6]
Summary
QAM can be seen as a combination of digital-amplitude modulation and digital-phase modulation. In other words, this technique utilizes both phase and amplitude variations to carry information in QAM signalling [1, 2]. Assigning different QAM signal constellation sizes to different subchannels is often used currently by the communication industry, for example in DSL modems. The emerging 5G mobile communication system will be OFDM based like 4G and the expected use of QAM signal constellation sizes in 5G NR will be up to 1024 (10 bits/symbol) in the coming years
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