COMPARİSON OF BER PERFORMANCES OF 

64-PSK AND 64-QAM İN AWGN CHANNELS

EE451 Communication Systems II

Berk SOYSALYiğitcan AYDOĞMUŞ

OUTLINE

1 INTRODUCTION2 BINARY MODULATION3 M-ARY MODULATION4 M-PSK MODULATION5 M-QAM MODULATION6 AWGN CHANNEL EFFECT7 BIT ERROR RATE8 RESULTS9 CONCLUSION

   

INTRODUCTION

• What is digital communication ?

• Digital communication is the transmission of information that has been encoded digitally, and passed through digital devices such as computers.

INTRODUCTION

• What is modulation ?

• Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal with an information bearing signal.

• Why do we need modulation ?

• Low frequency signals are more immune to noise.

• Prevent interference.• Reduce the antenna size in designed

transceivers.

BINARY MODULATION

M-ARY MODULATION

• In general, M-ary communication is used when one needs to design a communication system that is bandwidth efficient.

• However, the gain in bandwidth is accomplished at the expense of error performance.

M-ARY MODULATION

• To use M-ary modulation, the bit stream is blocked into groups of λ bits.

• The number of bit patterns is M = 2λ

• The symbol transmission rate is;Rs = 1/Ts = 1/(λTb) = Rb/λ symbols/sec

There is a bandwidth saving of 1/λ compared to binary modulation.

M-PSK MODULATION

• In this modulation type, the information is encoded in the phase of the transmitted signal.

M-PSK MODULATION

• The signals lie on a circle of radius √Es, and are spaced every 2π/M radians around the circle. Constellation Diagram of 64-PSK;

Decision Regions for M-PSK receiver;

M-QAM MODULATION

• In this modulation type, the information is encoded in both the amplitude and the phase of the transmitted signal.

• In QAM the transmitted signal has the form:• This signal is demodulated by multiplying with a cosine signal;• Or equivalently;

• Applying LPF removes the sine and cosine terms and leaves only the message term.

64-QAM MODULATION

• In 64 QAM there are 64 signal points in the constellation that are equally divided into four quadrants.

• Since the constellation is divided equally into four quadrants, normalizing the energy in a single quadrant will simplify things.

Constellation Diagram of 64-QAM;

Calculating the total energy in any one of the quadrant;

The average energy is and the normalization factor will be .

AWGN CHANNEL EFFECT

Additive white Gaussian noise (AWGN) is a channel modelin which the only impairment to communication is a linear addition of wideband or white noise with a constant spectral density and a Gaussian distribution of amplitude.

Noisy Constellation Diagrams;

BIT ERROR RATE

• The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval.

• Bit error rate (BER) is a parameter which gives an excellent indication of the performance of a data link.

THEORETHİCAL BER OF M-QAM & M-PSK

k=log2M

THEORETHİCAL BER GRAPH OF M-PSK

THEORETHİCAL BER GRAPH OF M-QAM

RESULTS

M-PSK VERSUS M-QAM

Bandwidth and Power Efficiency of M-PSK Signals

Bandwidth and Power Efficiency of M-QAM Signals

SHANNON’S LIMIT

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