Techniques Modeling of Adaptive Modulation and Coding and Hybrid-ARQ

Among communication system engineering, AMC and HARQ are the cross-sectional techniques that are applied on wireless communication system and they are aimed at improving the efficiency and reliability of the data transmission. Modulation, coding and retransmission methods cooperate and adjust adaptively modulation scheme, coding rate and retransmision methods according to the channel condition which improve system efficiency. Let’s dive into each of these techniques in detail:Let’s dive into each of these techniques in detail:

Adaptive Modulation and Coding (AMC)

• Modulation: Modulating is the activity of converting digital data in the anglicarrier with this purpose of facilitating the transmission. It performs its function by translating digital data bits into analog signals which are suitable for transmission over the given communication channel. Different modes of operation can be used, e.g. BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16-QAM (Quadrature Amplitude Modulation) and 64-QAM, all of them representing different combinations of spectral efficiency and susceptibility to noise and interference.
• Coding: Redundancy, which is sent with message serves as an instrument for correcting errors at the receiver side. ECC algorithms like Reed-Solomon algorithms, Turbo codes, and LDPC (Low Density Parity-Check) codes are the main tools for this task. These codes that the transmitter sends are able to make it possible for the receiver to regenerate unchanged the original data even if errors occur during transmission. The modification of coding rate allows for more redundant data to be incorporated which could lead to better error correction, although at the efficiency of the effective data rate.

Hybrid Automatic Repeat Request (HARQ)

• HARQ is a method of receiving data without error on the unreliable channels such as the wireless channels that are associated with the degradation of signal through the continuous fading, interference and noise.
• HARQ consists of two principles: ARQ and FEC. They are commonly used nowadays by mobile networks operators to make the data transfer faster and reliable. According to traditional ARQ, even if the receiver detects the presence of fetal in the messages received, the retransmission of the entire packet will be asked for. Nevertheless, unlike HARQ, which retransmits only the corrupted bits, in the latter one, only the erroneous bytes are requested to be retransmitted, leading to much lower overhead than in retransmissions.
• HARQ operates in two modes: Combining (soft combining) and Redundancy incrementally (IR) are types of forward error correction (FEC) algorithms. However, the multipath interference that results from the combination of retransmitted data and the original data by the receiver can be improved to the signal to noise ratio through Chase Combining. In Incremental Redundancy, we send along more redundancy bits for each repetition to acquire precise decoding process pitch.
• HARQ schemes can dynamically alter the transmission parameters by the means of adaptive modulation and coding techniques and this enables the system to be provided with good performance in different channel conditions. Such as the cases when the overall channel quality improves, higher modulation orders and coding rates could be used and data rate will be increased. Concurrently, when the channel quality decreases, lower modulation and coding orders are chosen to ensure error-free connection.
• Through the inherent union of AMC and HARQ, the spectrum efficiency of communication systems can be high while being reliable at different fading circumstances. These are the key techniques that are the building blocks of the modern wireless communications standards such as LTE (long-term evolution) and 5G (5th generation) where maximizing data throughput and getting rid of delay are the fundamental objectives.

One of the solutions allowing the growing demands related to data rates, reliability, and spectral efficiency to be met with constant evolution in the field of telecommunications is adaptive modulation. Adaptive Modulation is the dynamic change of modulation parameters with the change of channel conditions.

This article presents the Adaptive Modulation in-depth concept, reasons behind the use of Adaptive Modulation, and methods of implementing this scheme and how it works.