By
Vikram Karri
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Introduction
Collaboration Diagram
Superposition Coding
Principle
Design and Implementation
Platform For SC System
Transmitter Operation
Receiver Operation
Conclusion
Reference
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Information coding is a rule for converting a piece
of information into another form or representation
not necessarily of the same type.
In communications and information processing,
encoding is the process by which information from
a source is converted into symbols to be
communicated.
Decoding is the reverse process, converting these
code
symbols
back
into
information
understandable by a receiver.
• All C++ blocks that can be used in GR graphs are listed here or in
the subcategories below.
• Collaboration diagram for GNU Radio C++ Signal Processing Blocks:
Collaboration Diagram
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Collaboration diagram for Information Coding and
Decoding:
Information Coding is to convert the message into
some signals & Information Decoding is to convert
it into the original form.
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Superposition coding is a well-known capacity
achieving coding scheme for stochastically
degraded broadcast channels.
A software-radio based design of a superposition
coding system on the GNU Radio platform with the
Universal Software Radio Peripheral acting as the
transceiver frontend.
The packet error performance and discuss some
issues that arise in this implementation.
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A single transmitter to communicate with multiple
receivers is Superposition Coding (SC), which is known
to be the optimal communication strategy for
stochastically degraded1 broadcast channels.
SC works by exploiting the relative disparities in
channel quality to different receivers to optimally
allocate transmit power among them, while using the
entire bandwidth for each receiver.
Receivers decode the messages meant for all those
receivers whose channel quality is poorer than theirs,
before decoding their own message.
The SC system design and implementation has the following
benefits.
• The SD procedure is also beneficial in other scenarios. For
example, it is the optimal decoding scheme for the
multiple-access channel and has been shown to improve
link throughput in ad hoc scenarios.
• SC sets the foundation to experiment with more
sophisticated medium
access schemes that are pointto multipoint, or even multipoint-to-multipoint.
Platform For SC System
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All the signal processing algorithms at the baseband are
implemented digitally using GNU Radio on a generalpurpose computer.
This approach use several built-in libraries that come
with the GNU Radio package, including the USRP
interface.
OFDM offers a high degree of bandwidth scalability and
implementation flexibility, especially given its relative
ease of time- and frequency-synchronization, channel
estimation and equalizer design
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The figure shows that our SC system gives very
good performance (Packet Error Rate achieves
10−2). Clearly, the far user has a lower PER than
the near user (for the same SNR).
Transmitter Operation
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The payloads are provided to the physical layer by
the link layer. Each user’s payload is assigned a
modulation type, code rate, and the fraction of the
transmit power.
In time domain, the signals are weighted by the
fraction of power allocation factors (√ 1 − α for the
near user signal, and √α for the far user signal),
added and transmitted.
Receiver Operation
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The receiver front end is implemented in hardware
using the USRP, while the physical layer is
implemented using a single GNU Radio signal
processing block.
The USRP downconverts and digitizes signals in the
frequency band of operation.
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I have presented a design that leverages the flexibility
of the GNU Radio/USRP platform to implement physical
layer of a communication system that uses
superposition coding.
The performance of the implementation was measured
using packet error rates for each of the streams.
I found that the limitations of the USRP hardware have
implications for the design of training sequences, and
the software environment imposes constraints on the
degree of modularity allowed in the system
implementation.
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Ganti, R.K.; Gong, Z.; Haenggi, M.; Lee, C.; Srinivasa, S.; Tisza, D.;
Vanka, S.; Vizi, P.; , "Implementation and Experimental Results of
Superposition Coding on Software Radio," Communications (ICC),
2010 IEEE International Conference on , vol., no., pp.1-5, 23-27 May
2010
doi: 10.1109/ICC.2010.5502330
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5
502330&isnumber=5501741
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http://gnuradio.org/doc/doxygen/group__coding__blk.html
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Seeger, A.; , "Information theoretic based design of hierarchical
channel coding and modulation on mobile radio channels," Wireless
Image/Video Communications, 1996., First International Workshop
on , vol., no., pp.85-90, 4-5 Sep 1996
doi: 10.1109/WIVC.1996.624658
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6
24658&isnumber=13577
Thank You