qam constellation mapping

qam constellation mapping插图

How do I map a QAM constellation to another constellation?

This is usually achieved by converting the input symbols to Gray coded symbols and then mapping it to the desired QAM constellation. But this intermediate step can be skipped altogether by using a Look-Up-Table (LUT) approach which properly translates the input symbol to appropriate position in the constellation.

How to construct a mqam constellation using MATLAB?

The Matlab function constructQAM.m given in the book implements ( refer the book Digital Modulations using Matlab for the full Matlab code, python code is available in the book Digital Modulations using Python) the walk type 1 for constructing a MQAM constellation.

What causes amplitude imbalance in a constellation diagram?

In a constellation diagram, amplitude imbalance shows by one signal component being expanded and the other one being compressed. This is due to the fact that the receiver AGC makes a constant average signal level.

What is interference in a QAM signal?

Interferers are understood to be sinusoidal spurious signals occurring in the transmission frequency range and superimposed on the QAM signal at some point in the transmission path. After demodulation, the interferer is contained in the baseband form of low-frequency sinusoidal spurious signals.

What causes phase jitter in QAM?

Phase Jitter or phase noise in the QAM signal is caused by transponders in the transmission path or by the I/Q modulator. It may be produced in carrier recovery, a possibility that is to be excluded here. In contrast to the phase error described above, phase jitter is a statistical quantity that affects the I and Q path equally. In the constellation diagram, phase jitter shows up by the signal states being shifted about their coordinate origin. Image below – Constellation Diagram — 64 QAM signal with Phase Jitter (PJRMS = 1.73°)

What is QAM signal?

Each state is defined by a specific amplitude and phase. This means the generation and detection of symbols is more complex than a simple phase or amplitude device. Each time the number of states per symbol is increased the total data and bandwidth increases. The modulation schemes shown occupy the same bandwidth (after filtering), but have varying efficiencies (in theory at least).

Is there always a combination of modulation errors that may be difficult to separate and identify?

In practice, there is always a combination of modulation errors that may be difficult to separate and identify, as such, it is recommended to evaluate the measured constellation diagrams using mathematical and statistically methods.

Does Questtel have liability?

QuestTel shall have no liability for any error or damage of any kind resulting from the use of this document.

What is QAM in a signal?

QAM is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme.

What is QAM in telecommunications?

What is QAM? Quadrature amplitude modulation ( QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. QAM is both an analog and a digital modulation scheme.

How many bits are in 64QAM?

The QAM modulation converts input bits into complex symbols which represent bits by variation in amplitude/phase of the time domain waveform. Using 64QAM converts 6 bits into one symbol at transmitter.

Why is QAM used in radio communications?

This is because QAM achieves a greater distance between adjacent points in the I-Q plane by distributing the points more evenly.

What is 64-QAM mapper?

The 64-QAM mapper takes binary input and generates complex data symbols as output. It uses above mentioned encoding table to do the conversion process. Before the coversion process, data is grouped into 6 bits pair. Here, (b5, b4, b3) determines the I value and (b2, b1, b0) determines the Q value.

What algorithms are needed for higher modulation?

In addition to high SNR, higher modulation techniques need very robust front-end algorithms (time, frequency and channel) to decode the symbols without errors.

What is data mapping in RF?

Data mapping or modulation process is done before the RF upconversion (U/C) in the transmitter and PA. Due to this, higher order modulation necessitates use of highly linear PA (Power Amplifier) at the transmit end.

How to restrict erroneous symbols in M-QAM?

In any M-QAM constellation, in order to restrict the erroneous symbol decisions to single bit errors, the adjacent symbols in the transmitter constellation should not differ by more than one bit. This is usually achieved by converting the input symbols to Gray coded symbols and then mapping it to the desired QAM constellation. But this intermediate step can be skipped altogether by using a Look-Up-Table (LUT) approach which properly translates the input symbol to appropriate position in the constellation.

How does MQAM work?

The M-QAM modulator transmits a series of information symbols drawn from the set , with each transmitted symbol holding k bits of information ( ). To restrict the erroneous receiver decisions to single bit errors, the information symbols are Gray coded. The information symbols are then digitally modulated using a rectangular M-QAM technique, whose signal set is given by

Which constellation is more efficient?

There exist other constellation shapes (like circular, triangular constellations) that are more efficient (in terms of energy required to achieve same the error probability) than the standard rectangular constellation. Rectangular (symmetric or square) constellations are the preferred choice of implementation due to its simplicity in implementing modulation and demodulation.

Who is Mathuranathan Viswanathan?

Mathuranathan Viswanathan, is an author @ gaussianwaves.com that has garnered worldwide readership. He is a masters in communication engineering and has 12 years of technical expertise in channel modeling and has worked in various technologies ranging from read channel, OFDM, MIMO, 3GPP PHY layer, Data Science & Machine learning.

What is a QAM constellation?

Any rectangular QAM constellation is equivalent to superimposing two Amplitude Shift Keying (ASK) signals (also called Pulse Amplitude Modulation – PAM) on quadrature carriers. For example, 16-QAM constellation points can be generated from two 4-PAM signals, similarly the 64-QAM constellation points can be generated from two 8-PAM signals.

What is generic baseband simulation?

A generic complex baseband simulation technique, to simulate all M-ary QAM modulation techniques is given here. The given simulation code is very generic, and it plots both simulated and theoretical symbol error rates for all M-QAM modulation techniques.

What are the two types of detection techniques used for digitally modulated data?

Generally the two main categories of detection techniques, commonly applied for detecting the digitally modulated data are coherent detection and non-coherent detection.

When should the same reference constellation be used?

The same reference constellation should be used if coherent detection is selected as the method of demodulating the received data vector. On the other hand, in the non-coherent detection, the receiver is oblivious to the reference constellation used at the transmitter.

Which constellation is more efficient?

There exist other constellation shapes (like circular, triangular constellations) that are more efficient (in terms of energy required to achieve same the error probability) than the standard rectangular constellation. Rectangular (symmetric or square) constellations are the preferred choice of implementation due to its simplicity in implementing modulation and demodulation.

Who is Mathuranathan Viswanathan?

Mathuranathan Viswanathan, is an author @ gaussianwaves.com that has garnered worldwide readership. He is a masters in communication engineering and has 12 years of technical expertise in channel modeling and has worked in various technologies ranging from read channel, OFDM, MIMO, 3GPP PHY layer, Data Science & Machine learning.

What is baseband signal?

The complex signal that leads to the figures at the end of the article What is a Constellation Diagram? is called a baseband signal. For BPSK, this baseband signal is simply a series of complex values taken from the set { 1, ? 1 }. These complex values are the symbols of BPSK. The figures at the end of What is a Constellation Diagram? use the set { i, ? i } for BPSK. This is completely equivalent, since it is just a rotation of the constellation by 90 degrees. However, typically { 1, ? 1 } is used (although it must be said that using { i, ? i } makes it easier to not forget that the signal should always be treated as complex in this context, even though the values happen to be real). This makes mapping bits to BPSK simply

Why is gray coding used in constellations?

For larger constellations such as 16-QAM, the mapping table gets larger, and Gray coding is also used to limit the number of bit errors that are caused by a symbol error.

How many bits are encoded in QPSK?

For QPSK, two bits are encoded in each symbol, according to the following table.