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Free Space Path Loss

Apply free space path loss to complex signal

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  • Free Space Path Loss block

Libraries:
Communications Toolbox / RF Impairments and Components

Description

The Free Space Path Loss block applies a free space path loss to a complex signal. The block simulates the loss of signal power due to the distance between the transmitter and receiver. The Mode parameter indicates whether you specify the loss in decibels or as a computation that is based on distance and the RF signal frequency.

Examples

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This example uses:

Open Model

The model applies free space path loss to a QPSK modulated signal.

The Free Space Path Loss block applies a free space path loss that is computed based on the distance and frequency mode setting.

Run the model and display the signal level after free space path loss is applied.

The Free Space Path Loss configuration settings are:

Mode: Distance and Frequency
Distance: 0.500
Frequency (MHz): 1920

The calculated free space path loss is 92.09 dB.

This example uses:

Open Script

This example applies RF impairments to a signal modulated by the differential quadrature phase shift keying (DQPSK) method. To show the RF impairments, the example applies exaggerated levels that are not typical levels for modern radios.

In this example, the slex_rcvrimpairments_dqpsk model DQPSK-modulates a random signal and applies various RF impairments to the signal. The model uses impairment blocks from the RF Impairments library. The InitFun callback function initializes simulation variables. For more information, see Model Callbacks (Simulink).

After the impairment blocks, the signal forks into two paths. One path applies DC blocking, automatic gain control (AGC), and I/Q imbalance compensation to the signal before demodulation. The signal on the correction path is adjusted by the DC Blocker, AGC, and I/Q Imbalance Compensator blocks. Because the signal is DQPSK modulated, no carrier synchronization is required. The second path goes directly to demodulation. After demodulation, an error rate calculation is performed on both signals. The model includes Constellation Diagram blocks after modulation, before correction, and after correction so that you can analyze the constellation.

When the model runs, constellation diagrams plot the signal at these stages in the simulation:

  • The After Modulation constellation diagram shows the reference DQPSK-modulated signal constellation.

  • The Before Correction constellation diagram shows the attenuated and distorted signal constellation.

  • The After Correction constellation diagram shows the signal has been amplified and improved after the correction blocks.

The error rate for the demodulated signal without AGC is primarily caused by free space path loss and I/Q imbalance. The QPSK modulation minimizes the effects of the other impairments.

Error rate for corrected signal:   0.000
Error rate for uncorrected signal: 0.042

To explore the model try:

  • Adjusting RF impairment settings, rerun the model, and notice the changes to the constellation diagrams and error rates.

  • Modifying the model to add an equalizer stage before the demodulation. Equalization has inherent ability to reduce some of the distortion caused by impairments. For more information, see Equalization.

Extended Examples

Impact of RF Effects on Communication System Performance

Impact of RF Effects on Communication System Performance

Model thermal noise, phase noise, and nonlinearity impairments of an RF transceiver in Simulink®.

Ports

Input

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Complex signal, specified as a scalar or column vector.

Data Types: double | single
Complex Number Support: Yes

Output

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Output signal, returned as a scalar or column vector. This output is the same dimension and data type as the input signal.

Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Loss calculation mode, specified as one of these options.

  • Decibels — The loss is specified using the Loss (dB) parameter.

  • Distance and Frequency — The loss is computed using the Distance (km) and Carrier frequency (MHz) parameters.

Power loss in decibels, specified as a scalar. The decibel amount shown on the block icon is rounded for display purposes only.

Dependencies

To enable this parameter, set the Mode parameter to Decibels.

Distance between the transmitter and receiver in kilometers, specified as a scalar.

Dependencies

To enable this parameter, set the Mode parameter to Distance and Frequency.

Carrier frequency in megahertz, specified as a scalar.

Dependencies

To enable this parameter, set the Mode parameter to Distance and Frequency.

Block Characteristics

Data Types

double | single

Multidimensional Signals

no

Variable-Size Signals

no

Algorithms

The free-space path loss, L, in decibels is:

L = 20log10(4πR/λ).

This formula assumes that the target is in the far-field of the transmitting element or array. In the near-field, the free-space path loss formula is not valid and can result in a loss smaller than 0 dB, equivalent to a signal gain. For this reason, the loss is set to 0 dB for range values R ≤ λ/4π.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a

See Also

Functions

Blocks