comm.OSTBCEncoder

Encode input using orthogonal space-time block code

Description

The comm.OSTBCEncoder System object™ encodes an input symbol sequence using orthogonal space-time block code (OSTBC). This system object maps the input symbols block-wise and concatenates the output codeword matrices in the time domain. For more information, see

To encode an input symbol sequence using OSTBC:

1. Create the comm.OSTBCEncoder object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

ostbcenc = comm.OSTBCEncoder

ostbcenc = comm.OSTBCEncoder(N)

ostbcenc = comm.OSTBCEncoder(___,Name=Value)

Description

ostbcenc = comm.OSTBCEncoder creates an OSTBC encoder System object, ostbcenc. This object maps the input symbols block-wise and concatenates the output codeword matrices in the time domain.

ostbcenc = comm.OSTBCEncoder(N) creates an OSTBC encoder object with the NumTransmitAntennas property set to N.

ostbcenc = comm.OSTBCEncoder(___,Name=Value) creates an OSTBC encoder object using any of the previous syntaxes and sets properties using one or more name-value arguments. For example, SymbolRate=1/2 sets the symbol rate of the code to 1/2.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

NumTransmitAntennas — Number of transmit antennas

2 (default) | 3 | 4

Number of transmit antennas, specified as 2, 3, or 4.

Data Types: double

SymbolRate — Symbol rate of code

3/4 (default) | 1/2

Symbol rate of the code, specified as 3/4 or 1/2.

Dependencies

To enable this property, set the NumTransmitAntennas property to a value greater than 2. When you set NumTransmitAntennas to 2, the symbol rate is 1.

Data Types: double

Fixed-Point Properties

OverflowAction — Action when fixed-point numeric values overflow

"Wrap" (default) | "Saturate"

Action when fixed-point numeric values overflow, specified as "Wrap" or "Saturate". This property specifies the action to be taken in the case of an overflow. Overflow occurs when the magnitude of a fixed-point calculation result does not fit into the range of the data type and scaling that stores the result.

Usage

Syntax

Y = ostbcenc(X)

Description

Y = ostbcenc(X) applies OSTBC encoding to the input data X, and returns the OSTBC-encoded data Y.

Input Arguments

X — Input data

column vector | matrix

Input data, specified as a complex-valued column vector or matrix of data type double, single, or signed fixed-point with power-of-two slope and zero bias. The input matrix can be of size F-by-T, where F is the additional dimension (typically the frequency domain) over which the encoding calculation is independent. Specify F as a positive integer. If you do not specify the additional dimension, specify the input as a T-by-1 column vector. The time domain length, T, of X must be a multiple of the number of symbols in each codeword matrix. Specifically, when you set the NumTransmitAntennas property to 2 or the SymbolRate property to 1/2, T must be a multiple of two, and when the SymbolRate property is 3/4, T must be a multiple of 3.

This object accepts variable-size inputs. After the object is locked, you can change the size of each input channel, but you cannot change the number of channels. For more information, see Variable-Size Signal Support with System Objects.

Data Types: single | double | fi
Complex Number Support: Yes

Output Arguments

Y — Output data

matrix | 3-D array

Output data, returned as a matrix or 3-D array. For a time or spatial domain input of size T-by-1, the encoded output data, Y, is a (T/SymbolRate)-by-NumTransmitAntennas matrix. When the input matrix size is F-by-T, the output is an F-by-(T/SymbolRate)-by-NumTransmitAntennas array.

Data Types: double | single | fi

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
clone	Create duplicate System object
isLocked	Determine if System object is in use
reset	Reset internal states of System object

Examples

Encode BPSK Modulated Data with OSTBC

Generate random binary data, modulate using the BPSK modulation scheme, and encode the modulated data using OSTBC.

Generate an 8-by-1 vector of random binary data.

data = randi([0 1],8,1);

Create a BPSK modulator System object and modulate the data.

bpskMod = comm.BPSKModulator;
modData = bpskMod(data);

Create an OSTBC encoder object and encode the modulated signal. As the default number of transmit antennas is 2, you can see that encData is an 8-by-2 matrix.

ostbcEnc = comm.OSTBCEncoder;
encData = ostbcEnc(modData)

encData = 8×2 complex

  -1.0000 + 0.0000i  -1.0000 + 0.0000i
   1.0000 + 0.0000i  -1.0000 - 0.0000i
   1.0000 + 0.0000i  -1.0000 + 0.0000i
   1.0000 + 0.0000i   1.0000 + 0.0000i
  -1.0000 + 0.0000i   1.0000 + 0.0000i
  -1.0000 + 0.0000i  -1.0000 - 0.0000i
   1.0000 + 0.0000i  -1.0000 + 0.0000i
   1.0000 + 0.0000i   1.0000 + 0.0000i

More About

Input-to-Output Dimensions

The OSTBC encoder supports time and spatial domains for OSTBC transmission and an optional dimension over which the encoding calculation is independent. This illustration indicates the supported input dimensions and resulting output dimensions.

• When you input a time or spatial domain signal of size T-by-1, the encoder outputs a (T/R)-by-N matrix.

• When you input a matrix of size F-by-T, the encoder outputs an F-by-(T/R)-by-N array.

• Where:

  • R — Symbol rate of the code, as specified by the SymbolRate property.

    • For N = 2, R must be 1.

    • For N = 3 or 4, R can be 3/4 or 1/2.

  • N — Number of transmit antennas, as specified by the NumTransmitAntennas property. N can be 2, 3, or 4.

  • T — Input symbol sequence length for the time domain. The time domain length T must be a multiple of the number of symbols in each codeword matrix.

    • For N = 2 or R = 1/2, T must be a multiple of 2.

    • For R = 3/4, T must be a multiple of 3.

  • T/R — Symbol sequence length in time domain for the output signal.

  • F — Additional dimension; typically the frequency domain. The encoding is independent of this additional dimension. F can be any positive integer.

Algorithms

OSTBC Encoding Algorithm

The OSTBC encoder algorithm implements the five different OSTBC codeword matrices shown in this table. The number of transmit antennas and the symbol rate determine the codeword matrix that the algorithm uses to encode the input data.

Number of Transmit Antennas	Symbol Rate	OSTBC Codeword Matrix
2	1	$$\left(\begin{array}{cc}{s}_1& s_2\\ -s_2^{*}& s_1^{*}\end{array}\right)$$
3	1/2	$$\left(\begin{array}{ccc}{s}_1& s_2& 0\\ -s_2^{*}& s_1^{*}& 0\\ 0& 0& s_1\\ 0& 0& -s_2^{*}\end{array}\right)$$
3	3/4	$$\left(\begin{array}{ccc}{s}_1& s_2& s_3\\ -s_2^{*}& s_1^{*}& 0\\ s_3^{*}& 0& -s_1^{*}\\ 0& s_3^{*}& -s_2^{*}\end{array}\right)$$
4	1/2	$$\left(\begin{array}{cccc}{s}_1& s_2& 0& 0\\ -s_2^{*}& s_1^{*}& 0& 0\\ 0& 0& s_1& s_2\\ 0& 0& -s_2^{*}& s_1^{*}\end{array}\right)$$
4	3/4	$$\left(\begin{array}{cccc}{s}_1& s_2& s_3& 0\\ -s_2^{*}& s_1^{*}& 0& s_3\\ s_3^{*}& 0& -s_1^{*}& s_2\\ 0& s_3^{*}& -s_2^{*}& -s_1\end{array}\right)$$

In each matrix, each (l, i) element indicates the symbol transmitted from the ith antenna in the lth time slot of the codeword block. Values for i are in the range [1,N], where N is the number of transmit antennas. Values for l are in the range [1,L], where L is the codeword block length.

When processing variable-size signals:

• If the input signal is a column vector, the first dimension can change, but the second dimension must remain fixed at 1.

• If the input signal is a matrix, both dimensions can change.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2012a