phase shift keying• The phase of the carrier is

changed in response to information and all else is kept fixed.

• To transmit 0, we shift the phase of the sinusoids by 180°.

• Phase shift represent the change in the state of the information signal.

phase shift keying

Phasor diagram

A phasor diagram is used to show the phase relationships between two or more sine waves having the same frequency.

Quarternary or QUADRATURE PHASE SHIFT KEYING (QPSK)

• With QPSK, four output phases are possible for a single carrier frequency.

• The binary input data for QPSK are combined into groups of 2.

Eight-Phase PSK (8-PSK)

• Eight-phase PSK is an M-ary encoding technique where M=8.

Research ASSIGNMENT:1 whole sheet of paper

-16-PSK-QAM-BANDWIDTH EFFICIENCY-TRELLIS CODE

TRELLIS code modulationTransmission rates of 56 kbps require a signal-to-noise ratio of 53 dB, which is virtually impossible to achieve over a standard telephone circuit.

Data transmission rates in excess of 56 kbps can be achieved, however, over standard telephone circuits using an encoding technique called trellis code modulation (TCM).

Dr. Ungerboeck at IBM Zuerich Research Laboratory developed TCM, which involves using convolutional (tree) codes, which combines encoding and modulation to reduce the probability of error, thus improving the bit error performance. I WILL CERTAINLY INCLUDE THIS IN THE 3RD QUARTER EXAMINATION. PLEASE STUDY, IT’S FOR YOUR OWN GOOD NOT MINE. RESEARCH MORE IF NECESSARY.

QUADRATURE AMPLITUDE MODULATION (QAM)

• Is a form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier.

8-QAM Truth table

Binary Input Output Phase Output Amplitude

Q I C

0 0 0 -135° 0.765 V

0 0 1 -135° 1.848 V

0 1 0 -45° 0.765 V

0 1 1 -45° 1.848 V

1 0 0 135° 0.765 V

1 0 1 135° 1.848 V

1 1 0 45° 0.765 V

1 1 1 45° 1.848 V

Research for the concept of 16-QAM.

BANDWIDTH EFFICIENCY

Is often used to compute the performance of one digital modulation technique to another. In essence, bandwidth efficiency is the ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme.

:::

• For 16-PSK and a transmission system with a 10 kHz bandwidth, determine the maximum bit rate.

CARRIER RECOVERY

Is the process of extracting a phase-coherent reference carrier from a receiver signal.

I WILL CERTAINLY INCLUDE THIS IN THE 3RD QUARTER EXAMINATION. PLEASE STUDY, IT’S FOR YOUR OWN GOOD NOT MINE. RESEARCH MORE IF NECESSARY.

Squaring loopA common method of achieving carrier recovery for BPSK is the squaring loop. The received BPSK waveform is filtered and then squared. The filtering reduces the spectral width of the received noise. The squaring circuit removes the modulation and generates the second harmonic of the carrier frequency.

I WILL CERTAINLY INCLUDE THIS IN THE 3RD QUARTER EXAMINATION. PLEASE STUDY, IT’S FOR YOUR OWN GOOD NOT MINE. RESEARCH MORE IF NECESSARY.

COSTAS LOOPA second method of carrier recovery is the Costas, or quadrature loop. This recovery scheme uses two parallel tracking loops (I and Q) simultaneously to derive the product of the I and Q components of the signal that drives the VCO.

I WILL CERTAINLY INCLUDE THIS IN THE 3RD QUARTER EXAMINATION. PLEASE STUDY, IT’S FOR YOUR OWN GOOD NOT MINE. RESEARCH MORE IF NECESSARY.

RemodulatorA third method of achieving recovery of a phase and frequency coherent carrier is the remodulator. The remodulator produces a loop error voltage that is proportional to twice the phase error between the incoming signal and the VCO signal. The remodulator has a faster acquisition time than either the squaring or the Costas loops.

I WILL CERTAINLY INCLUDE THIS IN THE 3RD QUARTER EXAMINATION. PLEASE STUDY, IT’S FOR YOUR OWN GOOD NOT MINE. RESEARCH MORE IF NECESSARY.

probability of error and bit error rate

Probability of error is a theoretical expectation of the bit error rate for a given system.

Bit Error Rate is an empirical record of a system’s actual bit error performance.

EXAMPLE:::For a QPSK system and the given parameters, determine:a. Carrier power in dBm.b. Noise power in dBm.c. Noise power density in dBm.d. Energy per bit in dBJ.e. Carrier-to-noise ratio in dB.f. Eb/No ratio.

C= 10-12 W fb = 60 kbpsN = 1.2 x 10-14 W B= 120 kHz

Pulse modulation:

Pulse modulation consists essentially of sampling analog information signals and then converting those samples into discrete pulses.

Sampling

The signal is sampled at regular intervals such that each sample is proportional to the amplitude of signal at that instant. This technique is called “sampling”.

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Sampling

There are 3 sampling methods:Ideal - an impulse at each sampling instant

Natural - a pulse of short width with varying amplitude

Flat top - sample and hold, like natural but with single amplitude value

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Sampling Rate• Nyquist showed that it is possible to

reconstruct a band-limited signal from periodic samples, as long as the sampling rate is at least twice the frequency of the of highest frequency component of the signal

PAM

The amplitude of a constant width, constant-position pulse is varied according to the amplitude of the sample of the analog signal.