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comm.GMSKTimingSynchronizer System object

Package: comm

Recover symbol timing phase using fourth-order nonlinearity method

Description

The GMSKTimingSynchronizer object recovers the symbol timing phase of the input signal using a fourth-order nonlinearity method. This block implements a general non-data-aided feedback method. This timing synchronization is a non-data-aided feedback method that is independent of carrier phase recovery, but requires prior compensation for the carrier frequency offset. You can use this block for systems that use Gaussian minimum shift keying (GMSK) modulation.

To recover the symbol timing phase of the input signal:

  1. Define and set up your GMSK timing synchronizer object. See Construction.

  2. Call step to recover the symbol timing phase of the input signal according to the properties of comm.GMSKTimingSynchronizer. The behavior of step is specific to each object in the toolbox.

Construction

H = comm.GMSKTimingSynchronizer creates a timing phase synchronizer System object™, H. This object recovers the symbol timing phase of the GMSK input signal using a fourth-order nonlinearity method.

H = comm.GMSKTimingSynchronizer(Name,Value) creates a GMSK timing synchronizer object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

SamplesPerSymbol

Number of samples representing each symbol

Specify the number of samples that represent each symbol in the input signal as an integer-valued scalar value greater than 1. The default is 4.

ErrorUpdateGain

Error update step size

Specify the step size for updating successive timing phase estimates as a positive real scalar value. Typically, this number is less than 1/SamplesPerSymbol, which corresponds to a slowly varying timing phase. The default is 0.05. This property is tunable.

ResetInputPort

Enable synchronization reset input

Set this property to true to enable resetting the timing phase recovery process based on an input argument value. The default is false.

When you set this property to true, you must specify a reset input value to the step method.

When you specify a nonzero value as the reset input, the object restarts the timing phase recovery process. When you set this property to false, the object does not restart.

ResetCondition

Condition for timing phase recovery reset

Specify the conditions to reset the timing phase recovery process as one of Never | Every frame. The default is Never.

When you set this property to Never, the phase recovery process never restarts. The object operates continuously, retaining information from one symbol to the next.

When you set this property to Every frame, the timing phase recovery restarts at the start of each frame of data. In this case, the restart occurs at each step method call. This property applies when you set the ResetInputPort property to false.

Methods

cloneCreate GMSK timing phase synchronizer object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
resetReset states of GMSK timing phase synchronizer object
stepRecover symbol timing phase using fourth-order nonlinearity method

Examples

Recover timing phase of an MSK signal.

 % Create System objects  
    hMod = comm.GMSKModulator('BitInput', true, ...
                    'SamplesPerSymbol', 14);
    timingOffset = 0.2; % Actual timing offset
    hDelay = dsp.VariableFractionalDelay;
    hSync = comm.GMSKTimingSynchronizer('SamplesPerSymbol', 14, ...
                    'ErrorUpdateGain', 0.05);
    phEst = zeros(1, 10);
    for i = 1:51
      data = randi([0 1], 100, 1); % generate data
      modData = step(hMod, data); % modulate data

 % data impaired by timing offset error
      impairedData = step(hDelay, modData, timingOffset*14); 
      % perform timing phase recovery
      [y, phase] = step(hSync, impairedData); 
      phEst(i) = phase(1)/14;
    end

    figure, plot(0.2*ones(1, 50));
    hold on; ylim([0 0.4])
    plot(phEst, 'r'); legend( 'original', 'estimated')
    title('Original and Estimated timing phases');

Algorithms

This object implements the algorithm, inputs, and outputs described on the MSK-Type Signal Timing Recovery block reference page. The object properties correspond to the block parameters, except:

See Also

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