Costas loop software implementation

This method is fully digital, fpgafriendly, and process and resource efficient, and consumes resources. Coherent detection of differentially encoded bpsk debpsk. A novel method is presented for implementing the costas carrier recovery loop for software radio application. Before we get into the tests, lets remember that in an ideal situation a coherent demodulator like the costas loop performs better than a non coherent decoder like the dot product demodulator. Implementation of costas loop for bpsk receivers using fpga. The designed costas loop for bpsk detection is able to detect and demodulate data rates up to 50mbps. The adcrl combines classic closedloop carrier recovery circuit, all digital costas loop adcol, with frequency feedward loop, maximum likelihood frequency estimator mlfe so as to make the best use of the advantages of the two types of carrier recovery loops and obtain a more. The demodulator consists of a costas loop for carrier recovery, data recovery, and phase detection. Digital implementation of costas loop with carrier recovery. The carrier signal extraction is the main problem in synchronous demodulation in design of. It is a very simple yet fast and effective approach to apply costas loop to dsbsc signal with unknown carrier wave phase offset.

In this post, assume that we want to demodulate 4qam symbols having 1. Chapter 6, the costas loop, is another example project provided with the system generator. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Simulating bpsk costas loop in matlab stack exchange.

Design and implementation of a costas loop for wireless. Design and implementation of costas loop for bpsk demodulator. The costas loop relies on feedback concepts related to the pll 5. The proposed costas loop are implemented in fpga chip and verified by altera builtin signaltap logic analyzer. Digital implementation of costas loop with carrier recovery ijerd. The loop filter is usually a proportionalintegral pi filter providing both frequency and phase tracking of the costas loop. Demodulator circuit is a basic building block of wireless communication.

This paper presents an efficient all digital carrier recovery loop adcrl for quadrature phase shift keying qpsk. Costas loop implementation for synchronous detection of. Digital implementation of a secondorder costas loop demodulator. Here, the same carrier signal which is used for generating dsbsc signal is used to detect the message signal. Loop pll or frequency lock loop fll is used to track the carrier wave of the gps signal. The structure in question is the costas loop, named for j. A costas loop is basically a special use of a phase lock loop pll for estimating.

When transmitter or receiver in motion, it is difficult for demodulator to generate carrier signal same in frequency and phase as transmitter carrier signal due to doppler shift and doppler rate. Both the differential encoding and differential decoding blocks, illustrated in figures 1 and 2, are linear timeinvariant filters. Fpgabased implementation of alldigital qpsk carrier recovery. Fpgabased implementation of alldigital qpsk carrier. A phaselocked loop or phase lock loop pll is a control system that generates an output signal whose phase is related to the phase of an input signal. Design and implementation of digital costas loop and bit synchronizer in fpga for bpsk demodulation 1roshna t r 2nivin r 3sherly joy 4dr. Following is the block diagram of the coherent detector. The frequency offset is the main problem of the conventional. On the basis of analyzing the mathematical models of costas loop, a method to model and simulate it by matlab is put forward. Digital iq demodulator carrier recovery using costas loops.

That is, a costas pll is insensitive to navigation bit transitions 6. In order to improve convergence speed and tracking stability for highorder quadrature amplitude modulationqam demodulation carrier recovery,a new kind of costas loop is designed based on software radio thought and the basic principle of traditional costas loop. Gmsk demodulator using costas loop for softwaredefined radio. I am new to digital comms and i am learning to implement costas loop in software. The block diagram of the costas loop is shown in fig. Digital iq demodulator carrier recovery using costas. It turns out that a multiplierless phase detector can be implemented in. This method is fully digital, fpgafriendly, and process and resourceefficient. Fpgabased implementation of alldigital qpsk carrier recovery loop combining costas loop and maximum likelihood frequency estimator. The loop discriminator is implemented as an arctangent discriminator because of its high accuracy and insensitivity. Mathworks is the leading developer of mathematical computing software for engineers and scientists. Loop seems to oscillate rather than locking, even though the loop is closed. Thus this column explores a pll structure suitable for such a software implementation.

For testing ive taken a very long dft, and used that to narrow the initial phase accumulator step to be as close as possible costas loop where it should be in lock, and watched what is happening. I believe understanding the mechanics of something as fundamental as a phaselocked loop implemented using digital signal processing techniques in a lowlevel language is a great skill for any engineer. Project 1 costas loop implementation university of rhode. Design and implementation of the digital costas loop based on software defined radio. It is not a prerequisite to read the rf amplifier report before reading the costas loop report. This is a python implementation of an 8psk costas loop made as on oot module for gnuradio.

Digital implementation of costas loop with carrier. The power consumption of the costas loop bpsk detector was found to be 144mw. For low data rates, we have tested the scheme on a tis dsp tms320c67. Dec 09, 2012 design and implementation of costas loop for bpsk demodulator abstract. Now, i am trying to design costas loop for carrier synchronization. Pdf design and implementation of digital costas loop and. The numerically controlled oscillator nco is designed using the cordic algorithm, which provides the advantages of increased precision and of decreased memory.

Design and implementation of the digital costas loop based on. The lock time of the costas loop depends on how the pi loop filter is tuned. Due to the limited scope of this blog post, ill leave pi filter design and tuning problems to the readers. Sep 20, 2011 it is a very simple yet fast and effective approach to apply costas loop to dsbsc signal with unknown carrier wave phase offset. The first report begins on the next page, while the costas loop report starts on page 24.

Digital iq demodulator carrier recovery using costas loops nutaq. Design and implementation of digital costas loop and bit. Documentation for liquiddsp already includes a basic tutorial for writing a phaselocked loop. In order to validate the scheme, a matlab simulation and a hardware description code have for been developed. For testing ive taken a very long dft, and used that to narrow the initial phase accumulator step to be as close as possible carrier and timing recovery using fpgas chris dick xilinx inc.

This paper describes the design and implementation of digital costas loop for carrier recovery and demodulation of the data with bit synchronizer for clock recovery in field programmable gate. Here the digital implementation of costas loop for qpsk demodulation in. In the classical implementation of a costas loop, a local voltagecontrolled oscillator vco provides quadrature outputs, one to each of two phase detectors, e. Following is the matlab implementation of the waveform simulation model for the method discussed above. Software defined radio, doppler shift, doppler rate, phase locked loop i. These models enable designers to test circuits prior to building breadboards or prototypes, accelerating the. Gmsk demodulator using costas loop for softwaredefined. This project describes the digital implementation of a secondorder costas loop demodulator using simulation software systemview by elanix. The carrier signal extraction is the main problem in synchronous demodulation in design of demodulator based on software defined radio. Digital implementation of costas loop with carrier recovery lakulish m. I have read a lot of theory and i am using a dsp library to implement costas loop. Modified pll, costas loop, is used in this research.

Citeseerx digital implementation of costas loop with. I checked all signals widths and made sure that they do not overflow. Chapter 7, filter, demonstrates the effects of applying a. Block diagram of costas loop the digital implementation architecture of the costas loop is shown in fig. The author discusses all three variants of the costas loop and describes their dynamic behavior, using newly developed mathematical models. Here the digital implementation of costas loop for qpsk demodulation in continuous mode is discussed with. Design and implementation of costas loop for bpsk demodulator abstract.

Implementation of costas loop using cordic algorithm for software radio applications abstract. The same phase of the input signal is also applied to both phase detectors and the output of each phase detector is passed through a lowpass filter. Software pll design using c2000 mcus single phase grid. Stepbystep design procedures and simulink models are included for every type of costas loop. Software phase locked loop design using c2000 microcontrollers for single phase grid connected inverter a functional diagram of a pll is shown in figure 1, which consists of a phase detect pd, a loop filter lpf, and a voltage controlled oscillator vco.

Costas loop some mathematics will demonstrate how the costas loop works. The costas loop technique is adopted for developing the digital demodulator because unlike in square loop technique, in this the carrier recovery and data demodulation can be done simultaneously with simple blocks level design. Here the digital implementation of costas loop for qpsk. Fixedpoint data type is used in the implementation, 16. If time allows, you may want to run the costas loop simulations and look at a larger design that uses elements from the xilinx blockset as well as simulink blocks. Nov 24, 20 in this example, we will create a c implementation of a phaselocked loop without the dependencies on any external libraries, including liquid. The loop can track with in the vco frequency range of 1. After the costas loop locks to the transmit if carrier, the 4qam demodulator outputs the expected 4qam symbols at i and q rails. Also, a new procedure has been introduced to generate dynamic test. The block diagram of the costas loop used for carrier tracking loop is shown in fig. This paper presents an efficient all digital carrier recovery loop adcrl for. The oscillator generates a periodic signal, and the phase detector compares the.

The costas loop containing a carrier loop discriminator, a carrier loop. Carrier tracking the carrier tracking block of the software receiver is implemented as a costas phase lock loop pll. The second, discusses the design and implementation of a software costas loop for audio frequencies. The project builds two gnuradio blocks, an 8psk threshold block to carry out phase detection along with a complete working costas loop which uses the threshold code. The sampling frequency of the system is set to 10 mhz.

Dsp based implementation of gaussian minimum shift keying gmsk demodulator using costas loop has been described. Simulation of the carrier recovery using decisiondirected costas loop. Pdf digital implementation of costas loop with carrier. This paper introduced a scheme of bpsk binary phase shift keying carrier synchronization based on all digital costas loop.

Costas loop is a basic thing which takes 5 lines of code. Design and implementation of the digital costas loop. A typical example applying the software defined radio sdr based on fpga to. Hence, this process of detection is called as coherent or synchronous detection. Here the digital implementation of costas loop for qpsk demodulation in continuous mode is discussed with carrier recovery using phase locked loop. Pdf gmsk demodulator using costas loop for softwaredefined. Setting up the tools introduction to simulink and the xilinx. It is designed with sign phase detector instead of the traditional. In order to validate the scheme, a matlab simulation and a.

So we know that with a long steady signal a costas loop will decode more frames. The digital system design is simulated in matlab and the vhdl code developed in actel libero software is simulated in modelsim simulator. Digital implementation of demodulator is attracting more attention for the significant advantages of digital systems than analog systems. In this example, we will create a c implementation of a phaselocked loop without the dependencies on any external libraries, including liquid.

The costas loop presented in this work can sense both 0. A costas loop is a phaselocked looppll used for carrier phase recovery from suppressedcarrier modulation signals, such as from doublesideband suppressed carrier signals. Through the analysis of principle of digital costas loop, a method of design and implementation of costas loop has been proposed. Pdf gmsk demodulator using costas loop for software. Coherent detection of differentially encoded bpsk signal. The paper presents hardware design of digital signal processing based psk demodulator using costas loop. Implementation of costas loop using cordic algorithm for. Thus the costas loop carrier recovery circuit overcomes the 180. For the implementation with altera cyclone iv ep4ce115f29c7n chip, the entire digital costas loop only occupies a very small part of fpga resources. Software defined radio, doppler shift, doppler rate, phase locked loop. And this is the loop filters output, you can see how it is oscillating. Introduction the function of demodulator is to demodulate the received signal from wired or wireless link which. Pdf design and implementation of digital costas loop and bit.