Stbc.pptx(1)

Space-Time Block Codes for
Orthogonal Design
Prepared by:
Rathang Shah
140110705018

INTRODUCTION
Space–time block coding is a technique used in
wireless communications to transmit multiple copies of a
data stream across a number of antennas and to exploit the
various received versions of the data to improve the
reliability of data-transfer.
Transmitted signal must traverse a potentially difficult
environment. Receiver combines all the copies of the
received signal in an optimal way to extract as much
information from each of them as possible

CODE REPRESENTATION
An STBC is usually represented by a matrix. Each row
represents a time slot and each column represents one
antenna's transmissions over time.
Here, Sij is the modulated symbol to be transmitted in time slot i
from j antenna .

ORTHOGONALITY
Orthogonality means that the STBC is designed such that the
vectors representing any pair of columns taken from the coding
matrix is orthogonal.
It is a rate-1 code. It takes 2 time-slots to transmit 2 symbol.
The result of this is simple, linear, optimal decoding at the
receiver.
Code Rate – If the block encodes k symbols,code rate = k/T

Higher order STBC
These codes achieve rate-1/2 and rate-3/4 respectively,
as for their 3 TRANSMIT ANTENNA

Quasi-orthogonal STBCs
The code is full-rate and still only requires linear processing at
the receiver, although decoding is slightly more complex than
for orthogonal STBCs

Benefits of Space-Time
Block Codes
 Space-time block coding utilizes multiple transmit
antennas to create spatial diversity.
 This allows a system to have better performance in a
fading environment.
 Benefits:
 Good performance with minimal decoding complexity.
 Can achieve maximum diversity gain equivalent to
space-time trellis codes.
 Receivers that use only linear processing.

Block Diagram of STC
Transmission
X1 X2
0 T 2T
X1 -X2
*
X2 X1
*
0 T 2T
Ant 1
Ant 2
Data
STC encoder
Data STC
encoder
Fading αi
AWGN n
STC decoder
x rModulation
Encoder matrix:






−
= *
1
*
2
21
2
xx
xx
G

Comparison of BER
MISO SISO MIMO
-5 0 5 10 15 20
10
-4
10
-3
10
-2
10
-1
10
0
Eb/No, dB
BitErrorRate
BER for BPSK modulation using orthogonal STBC (Rayleigh channel)
(MIMO 2*2)
(MISO 2*1)
(SISO)

RESULT ANALYSIS
 As we can see from the graph SISO system has
more bit error rate than MIMO
 Orthogonal space time block code used in MIMO
(2*2) bit error rate reduces compared to MIMO
(2*1) it means if we increase the number of receiver
error further reduces.
 As STBC order increases we have to compromise
with code rate

References
[1] S. M. Alamouti, “A simple transmitter diversity scheme for wireless
communications,” IEEE J. Select. Areas Commun., vol. 16, pp. 1451–1458, Oct.
1998.
[2] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codes from
orthogonal designs,” IEEE Trans. Inform. Theory, vol. 45, pp. 1456–1467, July
1999.
[3] S. Sandhu and A. Paulraj, “Space-time block codes: A capacity perspective,” IEEE
Commun. Lett., vol. 4, pp. 384–386, Dec. 2000.
[4] Jesús Pérez, Jesús Ibáñez, Luis Vielva, and Ignacio Santamar´ıa, “Closed-form
Approximation for the Outage Capacity of Orthogonal STBC”, IEEE COMMUN
LETTERS, VOL. 9, NO. 11, NOVEMBER 2005
[5] Anna Papaioannou, George D. Papadopoulos, and Fotini-NioviPavlidou,
“Performance of Space-Time Block Coding in Powerline and Satellite
Communications”, IEEE JOURNAL OF COMMUNICATION AND
INFORMATION SYSTEMS, VOL. 20, NO. 3, 2005

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