gsmFrame

Create GSM waveform

Syntax

gsmWaveform = gsmFrame(gsmCfg)

gsmWaveform = gsmFrame(gsmCfg,numFrames)

Description

gsmWaveform = gsmFrame(gsmCfg) creates a GSM waveform with one TDMA frame based on the input GSM configuration object. The encrypted bit field of the transmission data bursts is filled with random data. For more information, see GSM Frames, Time Slots, and Bursts.

gsmWaveform = gsmFrame(gsmCfg,numFrames) creates a GSM waveform, with numFrames identically configured TDMA frames. In each frame, the encrypted bit field of the transmission data bursts is filled with random data. For more information, see GSM Frames, Time Slots, and Bursts.

Examples

Create GSM Uplink Waveform

Create a GSM uplink TDMA frame configuration object with default settings, and then create a GSM waveform containing one TDMA frame. GSM TDMA frames have eight time slots, each separated by a guard period of 8.25 symbols or about 30.46x10e-3 ms. Plot the GSM waveform.

Create a GSM uplink TDMA frame configuration object with default settings.

cfggsmul = gsmUplinkConfig

cfggsmul = 
  gsmUplinkConfig with properties:

           BurstType: [NB    NB    NB    NB    NB    NB    NB    NB]
    SamplesPerSymbol: 16
                 TSC: [0 1 2 3 4 5 6 7]
         Attenuation: [0 0 0 0 0 0 0 0]
         PulseLength: 4
            RiseTime: 2
           RiseDelay: 0
            FallTime: 2
           FallDelay: 0

Display information about the configured gsmUplinkConfig object by using the gsmInfo function. Assign the sample rate to a variable, Rs, for use in computing the plot timescale.

wfInfo = gsmInfo(cfggsmul)

wfInfo = struct with fields:
              SymbolRate: 2.7083e+05
              SampleRate: 4.3333e+06
    BandwidthTimeProduct: 0.3000
    BurstLengthInSymbols: 156.2500
       NumBurstsPerFrame: 8
    BurstLengthInSamples: 2500
    FrameLengthInSamples: 20000

Rs = wfInfo.SampleRate;

Create the GSM waveform by using the gsmFrame function, and then plot the GSM waveform.

waveform = gsmFrame(cfggsmul);

t = (0:length(waveform)-1)/Rs*1e3;
subplot(2,1,1)
plot(t,abs(waveform))
grid on
axis([0 5 0 1.2])
title('GSM Uplink Waveform - Amplitude')
xlabel('Time (ms)')
ylabel('Amplitude')
subplot(2,1,2)
plot(t,unwrap(angle(waveform)))
grid on
title('GSM Uplink Waveform - Phase')
xlabel('Time (ms)')
ylabel('Phase (rad)')

Create GSM Uplink Waveform Containing Five TDMA Frames

Create a GSM downlink TDMA frame configuration object with default settings, and then create a GSM waveform containing five TDMA frames. GSM TDMA frames have eight time slots, each separated by a guard period of 8.25 symbols or about 30.46x10e-3 ms. Plot the GSM waveform.

Create a GSM uplink TDMA frame configuration object, specifying 3 dB of attenuation in the last time slot to help identify the end of each frame.

cfggsmul = gsmUplinkConfig('Attenuation',[0 0 0 0 0 0 0 3])

cfggsmul = 
  gsmUplinkConfig with properties:

           BurstType: [NB    NB    NB    NB    NB    NB    NB    NB]
    SamplesPerSymbol: 16
                 TSC: [0 1 2 3 4 5 6 7]
         Attenuation: [0 0 0 0 0 0 0 3]
         PulseLength: 4
            RiseTime: 2
           RiseDelay: 0
            FallTime: 2
           FallDelay: 0

Display information about the configured gsmUplinkConfig object by using the gsmInfo function. Assign the frame length in samples to a variable, spf, for use in computing the plot timescale.

wfInfo = gsmInfo(cfggsmul)

wfInfo = struct with fields:
              SymbolRate: 2.7083e+05
              SampleRate: 4.3333e+06
    BandwidthTimeProduct: 0.3000
    BurstLengthInSymbols: 156.2500
       NumBurstsPerFrame: 8
    BurstLengthInSamples: 2500
    FrameLengthInSamples: 20000

spf = wfInfo.FrameLengthInSamples;

Create the GSM waveform by using the gsmFrame function, and then plot the GSM waveform. The last time slot of each frame is 3 dB less than the other time slots in that frame.

numFrames = 5;
waveform = gsmFrame(cfggsmul,numFrames);

t = 8*(0:length(waveform)-1)/spf;

numTS = 8*numFrames;
subplot(2,1,1)
plot(t,abs(waveform))
grid on
axis([0 numTS 0 1.2])
title('GSM Uplink Waveform - Amplitude')
xlabel('Time Slots')
ylabel('Amplitude')
subplot(2,1,2)
plot(t,unwrap(angle(waveform)))
grid on
title('GSM Uplink Waveform - Phase')
xlabel('Time Slots')
ylabel('Phase (rad)')

Create GSM Downlink Waveform

Create a GSM downlink TDMA frame configuration object with default settings, and then create a GSM waveform containing one TDMA frame. The GSM TDMA frame has eight time slots, each separated by a guard period of 8.25 symbols or about 30.46x10e-3 ms. Plot the GSM waveform.

Create a GSM downlink TDMA frame configuration object with default settings.

cfggsmdl = gsmDownlinkConfig

cfggsmdl = 
  gsmDownlinkConfig with properties:

           BurstType: [NB    NB    NB    NB    NB    NB    NB    NB]
    SamplesPerSymbol: 16
                 TSC: [0 1 2 3 4 5 6 7]
         Attenuation: [0 0 0 0 0 0 0 0]
         PulseLength: 4
            RiseTime: 2
           RiseDelay: 0
            FallTime: 2
           FallDelay: 0

Display information about the configured gsmDownlinkConfig object by using the gsmInfo function. Assign the sample rate to a variable, Rs, for use in computing the plot timescale.

wfInfo = gsmInfo(cfggsmdl)

wfInfo = struct with fields:
              SymbolRate: 2.7083e+05
              SampleRate: 4.3333e+06
    BandwidthTimeProduct: 0.3000
    BurstLengthInSymbols: 156.2500
       NumBurstsPerFrame: 8
    BurstLengthInSamples: 2500
    FrameLengthInSamples: 20000

Rs = wfInfo.SampleRate;

Create the GSM waveform by using the gsmFrame function, and then plot the GSM waveform.

waveform = gsmFrame(cfggsmdl);

t = (0:length(waveform)-1)/Rs*1e3;
subplot(2,1,1)
plot(t,abs(waveform))
grid on
axis([0 5 0 1.2])
title('GSM Downlink Waveform - Amplitude')
xlabel('Time (ms)')
ylabel('Amplitude')
subplot(2,1,2)
plot(t,unwrap(angle(waveform)))
grid on
title('GSM Downlink Waveform - Phase')
xlabel('Time (ms)')
ylabel('Phase (rad)')

Input Arguments

gsmCfg — GSM configuration

gsmUplinkConfig object | gsmDownlinkConfig object

GSM configuration, specified as a gsmUplinkConfig or gsmDownlinkConfig object.

numFrames — Number of TDMA frames

16 (default) | positive integer

Number of TDMA frames in the waveform, specified as a positive integer.

Data Types: double

Output Arguments

gsmWaveform — Output time-domain waveform

complex-valued column vector

Output time-domain waveform, returned as a complex-valued column vector of length N_s, where N_s represents the number of time-domain samples. The function generates this waveform in the form of complex in-phase quadrature (IQ) samples.

More About

GSM Frames, Time Slots, and Bursts

In GSM, transmissions consist of TDMA frames. Each GSM TDMA frame consists of eight time slots. The transmission data content of a time slot is called a burst. As described in Section 5.2 of 3GPP TS 45.011, a GSM time slot has a 156.25-symbol duration when using the normal symbol period, which is a time interval of 15/26 ms or about 576.9 microseconds. A guard period of 8.25 symbols or about 30.46 microseconds separates each time slot. The GSM standards describes a symbol as one bit period. Since GSM uses GMSK modulation, there is one bit per bit period. The transmission timing of a burst within a time slot is defined in terms of the bit number (BN). The BN refers to a particular bit period within a time slot. The bit with the lowest BN is transmitted first. BN0 is the first bit period, and BN156 is the last quarter-bit period.

This image from 3GPP TS 45.011 shows the relationship between different frame types and the relationship between different burst types.

This table shows the supported burst types and their characteristics.

Burst Type	Description	Link Direction	Useful Duration
NB	Normal burst	Uplink/Downlink	147
FB	Frequency correction burst	Downlink	147
SB	Synchronization burst	Downlink	147
Dummy	Dummy burst	Downlink	147
AB	Access burst	Uplink	87
Off	No burst sent	Uplink/Downlink	0

Useful duration, described in Section 5.2.2 of 3GPP TS 45.002, is a characteristic of GSM bursts. The useful duration, or useful part, of a burst is defined as beginning halfway through BN0 and ending half a bit period before the start of the guard period. The guard period is the period between bursts in successive time slots. This figure, from Section 2.2 of 3GPP TS 45.004, shows the leading and trailing ½ bit difference between the useful and active parts of the burst.

For more information, see GSM TDMA Frame Parameterization for Waveform Generation.

Training Sequence Code (TSC)

Normal bursts include a training sequence bits field assigned a bit pattern based on the specified TSC. For GSM, you can select one of these eight training sequences for normal burst type time slots.

Training Sequence Code (TSC)	Training Sequence Bits (BN61, BN62, …, BN86)
0	(0,0,1,0,0,1,0,1,1,1,0,0,0,0,1,0,0,0,1,0,0,1,0,1,1,1)
1	(0,0,1,0,1,1,0,1,1,1,0,1,1,1,1,0,0,0,1,0,1,1,0,1,1,1)
2	(0,1,0,0,0,0,1,1,1,0,1,1,1,0,1,0,0,1,0,0,0,0,1,1,1,0)
3	(0,1,0,0,0,1,1,1,1,0,1,1,0,1,0,0,0,1,0,0,0,1,1,1,1,0)
4	(0,0,0,1,1,0,1,0,1,1,1,0,0,1,0,0,0,0,0,1,1,0,1,0,1,1)
5	(0,1,0,0,1,1,1,0,1,0,1,1,0,0,0,0,0,1,0,0,1,1,1,0,1,0)
6	(1,0,1,0,0,1,1,1,1,1,0,1,1,0,0,0,1,0,1,0,0,1,1,1,1,1)
7	(1,1,1,0,1,1,1,1,0,0,0,1,0,0,1,0,1,1,1,0,1,1,1,1,0,0)

For more information, see Section 5.2.3 in 3GPP TS 45.002.

Extended Capabilities

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

Version History

Introduced in R2019b

R2024a: Gaussian filter pulse length and roll-off shape

This update allows you to optimize the spectral occupancy of your design by selecting the pulse length. When generating downlink and uplink GSM frames with the gsmFrame function, you can specify the pulse length in the GMSK modulator for the Gaussian filter with the gsmDownlinkConfig and gsmUplinkConfig configuration objects by setting the PulseLength property. The default value sets pulse length to 4. The gsmFrame function now also implements raised cosine roll-off instead of sine roll-off for the spectral shape of the rise and fall mask.

Previous releases used a static pulse length of 1 in the GMSK modulator and sine-shaped spectral rise and fall masks. The raised cosine roll-off shape and pulse length of 4, improves the out-of-channel and out-of-band spectral rejection.