Regulation: IFET R2019 A Academic Year: 2023-2024
IFET COLLEGE OF ENGINEERING
(An Autonomous Institution)
Department of ECE
Subject Code/ Name: 19UECPE632 /Advanced Communication Techniques
Year/Sem: III / VI
UNIT III - SPACE TIME BLOCK CODES
PART- A
1. Estimate the distance between signal points in QPSK.
The ability to determine a bit without error is measured by the distance between two nearest
possible points in the signal space. Such points differed in a single bit for example. Single points ‘A’
and ‘B’ are the two nearest points since they differ by a single bit be(t).
d 2 Eb
2. In a signal integration scheme the voice signal is modulated using a modulation scheme
which has even step size. Express the modulation that is used.
An analog to digital conversion technique where quality is not of primary importance is a delta
modulation.Delta modulation transmit only one bit per sample. That is the present sample value
is compared with previous sample and the indication whether the amplitude is increased or
decreased is sent. Input signal is approximated to step signal by delta modulator. This step size is
fixed
3. Euclid about the modulation technique in which gain is decreased or increased based on
the polarity. (or) Which modulation technique uses the polarity sign for decreasing or
increasing its gain and write about it?
In some case, the variable gain circuit is discrete the gain changes occurs on a pulse to pulse
basis and are said to be instantaneous. The controller has a 1 bit memory. By considering the fact
that slope overload leads to a sequence of output pulses of identical polarity, it compares the
polarity of each transmitted pulse with preceding one.
If they have the same polarity the controller indexes the gain circuit to a large gain value. If the
polarity is not the same, a sign reversal takes place and gain is decreased to a lower value. This
method is also called as constant factor delta modulation.
4. Examine the coding system that can be employed in adaptive coding technique and discuss
the operation of the same
The coding system which can be employed in adaptive coding technique is subband coding. The
subband decoder consist of the decoder as the first stage, where each encoded subband is first
decoded. Then the signal is up-sampled by a factor of two. This increases the sampling rate by a
factor of two. Then the two signals are combined. Thus the entire subbands are combined in the
same hierarchy as they are generated at the transmitter.
, Regulation: IFET R2019 A Academic Year: 2023-2024
5. A Speech signal is given as an input to a coding system at encodes the given input signal
and produces the output data with low bit rate. Inscribe about the transmitter unit of the
corresponding coding.
The speech signal x(k) is the digitized signal. It is obtained by sampling the continuous time
speech signal. Thus x(k) is the sequence of speech samples. It is applied to the analyzer. The
analyzer determines parameters for the synthesizer. Based on these parameters, the synthesizer
reconstructs the speech signal x(k). The reconstructed signal xq(k) and the original signal x(k)
are compared and the error Ɛ(k) is obtained. The analyzer parameters and the error signal is
multiplexed and transmitted. This signal is called LPC signal.
6. Illustrate the receiver circuit of a coding scheme which encodes the data at very low data
rate with signal sound.
In the receiver of Linear Predictive coding, the received LPC signal is applied to the
Demultiplexer (or decoder). It separates filter parameters and error signal. The parameters are
given to the synthesizer. The output of synthesizer is added to error signal which gives speech
signal. Basically the analyzer is a digital filter. This filter parameters are updated every 10 to 25
msec. For a reasonable speech quality, 10-12 parameters are used. This produces the bit rate of
about 3 to 8 K bits/sec.
7. Illustrate a coding scheme which accounts for the problem occurred by complement of
data in which comparison of present and past bits occur.
When serial data is passed through many circuits along a communication channel, the waveform
is often unintentionally inverted (i.e. data complemented). This result can occur in a twisted pair
transmission line channel just by switching the 2 leads at a connection point when a polar line
code is used. (such switching would not affect the data of a bipolar signal). To eliminate this
problem differential encoding is often employed. Each digit in an differential encoded sequence
is obtained by comparing the present input bit with the past encoded bit.
8. For the special case of a complex symbol at the output of the kth space–time channel,
Show that a decoupled pair of scalar channels that are statistically independent of each
other.
The space–time channel is decoupled into a pair of scalar channels that are statistically
independent of each other:
1. The complex symbol at the output of the kth space–time channel is identical to the complex
symbol transmitted by the kth antenna for k = 1, 2; the decoupling shown clearly in (9.97) is
attributed to complex orthogonality of the Alamouti code.
2. Assuming that the original channel noise is white Gaussian, then this statistical
characterization is maintained in the modified noise appearing at the output of the kth space–
time channel for k = 1, 2; this maintenance is attributed to the processing performed in the
receiver.
9. Show that twofold statement hinges on the premise that the receiver has knowledge of the
channel matrix H.
This twofold statement hinges on the premise that the receiver has knowledge of the channel
matrix H. Moreover, with two transmit antennas and one receive antenna, the Alamouti code
achieves the same level of diversity as a corresponding system with one transmit antenna and
two receive antennas. It is in this sense that a wireless communication system based on the
Alamouti code is said to enjoy a two-level diversity gain.
IFET COLLEGE OF ENGINEERING
(An Autonomous Institution)
Department of ECE
Subject Code/ Name: 19UECPE632 /Advanced Communication Techniques
Year/Sem: III / VI
UNIT III - SPACE TIME BLOCK CODES
PART- A
1. Estimate the distance between signal points in QPSK.
The ability to determine a bit without error is measured by the distance between two nearest
possible points in the signal space. Such points differed in a single bit for example. Single points ‘A’
and ‘B’ are the two nearest points since they differ by a single bit be(t).
d 2 Eb
2. In a signal integration scheme the voice signal is modulated using a modulation scheme
which has even step size. Express the modulation that is used.
An analog to digital conversion technique where quality is not of primary importance is a delta
modulation.Delta modulation transmit only one bit per sample. That is the present sample value
is compared with previous sample and the indication whether the amplitude is increased or
decreased is sent. Input signal is approximated to step signal by delta modulator. This step size is
fixed
3. Euclid about the modulation technique in which gain is decreased or increased based on
the polarity. (or) Which modulation technique uses the polarity sign for decreasing or
increasing its gain and write about it?
In some case, the variable gain circuit is discrete the gain changes occurs on a pulse to pulse
basis and are said to be instantaneous. The controller has a 1 bit memory. By considering the fact
that slope overload leads to a sequence of output pulses of identical polarity, it compares the
polarity of each transmitted pulse with preceding one.
If they have the same polarity the controller indexes the gain circuit to a large gain value. If the
polarity is not the same, a sign reversal takes place and gain is decreased to a lower value. This
method is also called as constant factor delta modulation.
4. Examine the coding system that can be employed in adaptive coding technique and discuss
the operation of the same
The coding system which can be employed in adaptive coding technique is subband coding. The
subband decoder consist of the decoder as the first stage, where each encoded subband is first
decoded. Then the signal is up-sampled by a factor of two. This increases the sampling rate by a
factor of two. Then the two signals are combined. Thus the entire subbands are combined in the
same hierarchy as they are generated at the transmitter.
, Regulation: IFET R2019 A Academic Year: 2023-2024
5. A Speech signal is given as an input to a coding system at encodes the given input signal
and produces the output data with low bit rate. Inscribe about the transmitter unit of the
corresponding coding.
The speech signal x(k) is the digitized signal. It is obtained by sampling the continuous time
speech signal. Thus x(k) is the sequence of speech samples. It is applied to the analyzer. The
analyzer determines parameters for the synthesizer. Based on these parameters, the synthesizer
reconstructs the speech signal x(k). The reconstructed signal xq(k) and the original signal x(k)
are compared and the error Ɛ(k) is obtained. The analyzer parameters and the error signal is
multiplexed and transmitted. This signal is called LPC signal.
6. Illustrate the receiver circuit of a coding scheme which encodes the data at very low data
rate with signal sound.
In the receiver of Linear Predictive coding, the received LPC signal is applied to the
Demultiplexer (or decoder). It separates filter parameters and error signal. The parameters are
given to the synthesizer. The output of synthesizer is added to error signal which gives speech
signal. Basically the analyzer is a digital filter. This filter parameters are updated every 10 to 25
msec. For a reasonable speech quality, 10-12 parameters are used. This produces the bit rate of
about 3 to 8 K bits/sec.
7. Illustrate a coding scheme which accounts for the problem occurred by complement of
data in which comparison of present and past bits occur.
When serial data is passed through many circuits along a communication channel, the waveform
is often unintentionally inverted (i.e. data complemented). This result can occur in a twisted pair
transmission line channel just by switching the 2 leads at a connection point when a polar line
code is used. (such switching would not affect the data of a bipolar signal). To eliminate this
problem differential encoding is often employed. Each digit in an differential encoded sequence
is obtained by comparing the present input bit with the past encoded bit.
8. For the special case of a complex symbol at the output of the kth space–time channel,
Show that a decoupled pair of scalar channels that are statistically independent of each
other.
The space–time channel is decoupled into a pair of scalar channels that are statistically
independent of each other:
1. The complex symbol at the output of the kth space–time channel is identical to the complex
symbol transmitted by the kth antenna for k = 1, 2; the decoupling shown clearly in (9.97) is
attributed to complex orthogonality of the Alamouti code.
2. Assuming that the original channel noise is white Gaussian, then this statistical
characterization is maintained in the modified noise appearing at the output of the kth space–
time channel for k = 1, 2; this maintenance is attributed to the processing performed in the
receiver.
9. Show that twofold statement hinges on the premise that the receiver has knowledge of the
channel matrix H.
This twofold statement hinges on the premise that the receiver has knowledge of the channel
matrix H. Moreover, with two transmit antennas and one receive antenna, the Alamouti code
achieves the same level of diversity as a corresponding system with one transmit antenna and
two receive antennas. It is in this sense that a wireless communication system based on the
Alamouti code is said to enjoy a two-level diversity gain.
