16-QAM Modem Loopback

Random bytes through QAM Mod, a noisy channel with a frequency offset, and QAM Demod. The constellation sink shows the 16 points after the channel; raise the noise or the offset to watch them smear and the demodulated bits go wrong. The time sink shows the sent bits above the received ones -- slide Align until they line up, since the modem's filters and clock recovery delay the stream.
Author Marc
Category Digital
Blocks 17
Connections 11
File digital/qam_loopback.grc
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Blocks used

Block	Module	Used
QT GUI Range	`GNU Radio`	3
Char To Float	`GNU Radio`	2
Variable	`GNU Radio`	2
Channel Model	`GNU Radio`	1
Delay	`GNU Radio`	1
GUI Layout	`GNU Radio`	1
QAM Demod	`GNU Radio`	1
QAM Mod	`GNU Radio`	1
QT GUI Constellation Sink	`GNU Radio`	1
QT GUI Time Sink	`GNU Radio`	1
Random Source	`GNU Radio`	1
Throttle	`GNU Radio`	1
Unpack K Bits	`GNU Radio`	1
Flowgraph source

digital/qam_loopback.grc
options:
    parameters:
        author: Marc
        comment: ''
        copyright: ''
        description: Random bytes through QAM Mod, a noisy channel with a frequency offset, and QAM Demod. The constellation sink shows the 16 points after the channel; raise the noise or the offset to watch them smear and the demodulated bits go wrong. The time sink shows the sent bits above the received ones -- slide Align until they line up, since the modem's filters and clock recovery delay the stream.
        generate_options: qt_gui
        id: fg_16_QAM_Modem_Loopback
        title: 16-QAM Modem Loopback
    states:
        coordinate: [10, 10]
        rotation: 0
        state: enabled
blocks:
-   name: align
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Align sent bits to received (bits of delay)
        min_len: '240'
        orient: QtCore.Qt.Horizontal
        rangeType: int
        start: '0'
        step: '1'
        stop: '400'
        value: '68'
        widget: counter_slider
    states:
        coordinate: [610, 10]
        rotation: 0
        state: enabled
-   name: freq_offset
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Channel frequency offset
        min_len: '240'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '-0.01'
        step: '0.0005'
        stop: '0.01'
        value: '0'
        widget: counter_slider
    states:
        coordinate: [900, 10]
        rotation: 0
        state: enabled
-   name: noise
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Channel noise voltage
        min_len: '240'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '0'
        step: '0.005'
        stop: '0.5'
        value: '0.05'
        widget: counter_slider
    states:
        coordinate: [1180, 10]
        rotation: 0
        state: enabled
-   name: samp_rate
    id: variable
    parameters:
        comment: ''
        value: '32000'
    states:
        coordinate: [1480, 10]
        rotation: 0
        state: enabled
-   name: sps
    id: variable
    parameters:
        comment: ''
        value: '2'
    states:
        coordinate: [1670, 10]
        rotation: 0
        state: enabled
-   name: bits
    id: qtgui_time_sink_x
    parameters:
        affinity: ''
        alias: ''
        alpha1: '1'
        alpha10: '1'
        alpha2: '1'
        alpha3: '1'
        alpha4: '1'
        alpha5: '1'
        alpha6: '1'
        alpha7: '1'
        alpha8: '1'
        alpha9: '1'
        autoscale: 'False'
        axislabels: 'True'
        color1: blue
        color10: dark blue
        color2: red
        color3: green
        color4: black
        color5: cyan
        color6: magenta
        color7: yellow
        color8: dark red
        color9: dark green
        comment: ''
        ctrlpanel: 'False'
        entags: 'True'
        grid: 'True'
        label1: Received bits
        label10: Signal 10
        label2: Sent bits (delayed to line up)
        label3: Signal 3
        label4: Signal 4
        label5: Signal 5
        label6: Signal 6
        label7: Signal 7
        label8: Signal 8
        label9: Signal 9
        legend: 'True'
        marker1: '1'
        marker10: '-1'
        marker2: '4'
        marker3: '-1'
        marker4: '-1'
        marker5: '-1'
        marker6: '-1'
        marker7: '-1'
        marker8: '-1'
        marker9: '-1'
        name: Sent bits vs received bits
        nconnections: '2'
        size: '100'
        srate: samp_rate/sps*4
        stemplot: 'False'
        style1: '0'
        style10: '1'
        style2: '0'
        style3: '1'
        style4: '1'
        style5: '1'
        style6: '1'
        style7: '1'
        style8: '1'
        style9: '1'
        tr_chan: '0'
        tr_delay: '0'
        tr_level: '0'
        tr_mode: qtgui.TRIG_MODE_FREE
        tr_slope: qtgui.TRIG_SLOPE_POS
        tr_tag: ''
        type: float
        update_time: '0.1'
        width1: '1'
        width10: '1'
        width2: '1'
        width3: '1'
        width4: '1'
        width5: '1'
        width6: '1'
        width7: '1'
        width8: '1'
        width9: '1'
        ylabel: Amplitude
        ymax: '1.2'
        ymin: '-0.2'
        yunit: ''
    states:
        coordinate: [1950, 540]
        rotation: 0
        state: enabled
-   name: bits_to_float
    id: blocks_char_to_float
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        maxoutbuf: '0'
        minoutbuf: '0'
        scale: '1'
        vlen: '1'
    states:
        coordinate: [1900, 410]
        rotation: 0
        state: enabled
-   name: bytes
    id: analog_random_source_x
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        max: '256'
        maxoutbuf: '0'
        min: '0'
        minoutbuf: '0'
        num_samps: '10000'
        repeat: 'True'
        type: byte
    states:
        coordinate: [10, 390]
        rotation: 0
        state: enabled
-   name: channel
    id: channels_channel_model
    parameters:
        affinity: ''
        alias: ''
        block_tags: 'False'
        comment: ''
        epsilon: '1'
        freq_offset: freq_offset
        maxoutbuf: '0'
        minoutbuf: '0'
        noise_voltage: noise
        seed: '0'
        taps: '[1.0]'
    states:
        coordinate: [1070, 370]
        rotation: 0
        state: enabled
-   name: qam_demod
    id: digital_qam_demod
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        constellation_points: '16'
        differential: 'True'
        excess_bw: '0.35'
        freq_bw: '0.005'
        log: 'False'
        maxoutbuf: '0'
        minoutbuf: '0'
        mod_code: gray
        phase_bw: '0.0628'
        samples_per_symbol: sps
        timing_bw: '0.0628'
        verbose: 'False'
    states:
        coordinate: [1450, 330]
        rotation: 0
        state: enabled
-   name: qam_mod
    id: digital_qam_mod
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        constellation_points: '16'
        differential: 'True'
        excess_bw: '0.35'
        log: 'False'
        maxoutbuf: '0'
        minoutbuf: '0'
        mod_code: gray
        samples_per_symbol: sps
        verbose: 'False'
    states:
        coordinate: [630, 360]
        rotation: 0
        state: enabled
-   name: received
    id: qtgui_const_sink_x
    parameters:
        affinity: ''
        alias: ''
        alpha1: '1'
        alpha10: '1'
        alpha2: '1'
        alpha3: '1'
        alpha4: '1'
        alpha5: '1'
        alpha6: '1'
        alpha7: '1'
        alpha8: '1'
        alpha9: '1'
        autoscale: 'False'
        axislabels: 'True'
        color1: '"blue"'
        color10: '"dark blue"'
        color2: '"red"'
        color3: '"green"'
        color4: '"black"'
        color5: '"cyan"'
        color6: '"magenta"'
        color7: '"yellow"'
        color8: '"dark red"'
        color9: '"dark green"'
        comment: ''
        grid: 'False'
        label1: ''
        label10: ''
        label2: ''
        label3: ''
        label4: ''
        label5: ''
        label6: ''
        label7: ''
        label8: ''
        label9: ''
        legend: 'True'
        marker1: '0'
        marker10: '0'
        marker2: '0'
        marker3: '0'
        marker4: '0'
        marker5: '0'
        marker6: '0'
        marker7: '0'
        marker8: '0'
        marker9: '0'
        name: 16-QAM after the channel
        nconnections: '1'
        size: '1000'
        style1: '0'
        style10: '0'
        style2: '0'
        style3: '0'
        style4: '0'
        style5: '0'
        style6: '0'
        style7: '0'
        style8: '0'
        style9: '0'
        tr_chan: '0'
        tr_level: '0'
        tr_mode: qtgui.TRIG_MODE_FREE
        tr_slope: qtgui.TRIG_SLOPE_POS
        tr_tag: ''
        update_time: '0.1'
        width1: '1'
        width10: '1'
        width2: '1'
        width3: '1'
        width4: '1'
        width5: '1'
        width6: '1'
        width7: '1'
        width8: '1'
        width9: '1'
        xmax: '2'
        xmin: '-2'
        ymax: '2'
        ymin: '-2'
    states:
        coordinate: [1450, 190]
        rotation: 0
        state: enabled
-   name: sent_delay
    id: blocks_delay
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        delay: align
        maxoutbuf: '0'
        minoutbuf: '0'
        type: byte
        vlen: '1'
    states:
        coordinate: [890, 580]
        rotation: 0
        state: enabled
-   name: sent_to_float
    id: blocks_char_to_float
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        maxoutbuf: '0'
        minoutbuf: '0'
        scale: '1'
        vlen: '1'
    states:
        coordinate: [1210, 580]
        rotation: 0
        state: enabled
-   name: throttle
    id: blocks_throttle2
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        ignoretag: 'True'
        limit: time
        maximum: '0.1'
        maxoutbuf: '0'
        minoutbuf: '0'
        samples_per_second: samp_rate/sps/2
        type: byte
        vlen: '1'
    states:
        coordinate: [300, 390]
        rotation: 0
        state: enabled
-   name: unpack
    id: blocks_unpack_k_bits_bb
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        k: '8'
        maxoutbuf: '0'
        minoutbuf: '0'
    states:
        coordinate: [600, 580]
        rotation: 0
        state: enabled
-   name: wasm_gui_layout_0
    id: wasm_gui_layout
    parameters:
        affinity: ''
        alias: ''
        columns: '12'
        comment: ''
        layout: '{"align":[3,6,9,1],"bits":[0,0,12,4],"freq_offset":[3,5,9,1],"noise":[3,4,9,1],"received":[0,4,3,4]}'
        row_height: '60'
    states:
        coordinate: [320, 10]
        rotation: 0
        state: enabled
connections:
- [bits_to_float, '0', bits, '0']
- [bytes, '0', throttle, '0']
- [channel, '0', qam_demod, '0']
- [channel, '0', received, '0']
- [qam_demod, '0', bits_to_float, '0']
- [qam_mod, '0', channel, '0']
- [sent_delay, '0', sent_to_float, '0']
- [sent_to_float, '0', bits, '1']
- [throttle, '0', qam_mod, '0']
- [throttle, '0', unpack, '0']
- [unpack, '0', sent_delay, '0']
metadata:
    file_format: 1
    grc_version: 3.11.0.0