ofdm beacon receiver using software-凯发k8网页登录

rxsim.receiveonsdr = false;

filename = "capturedbeacons.mat";

if rxsim.receiveonsdr
    rxsim.sdrdevicename = "ad936x";        % sdr that is used for waveform reception
    rxsim.radioidentifier = '192.168.3.2';      % value used to identify radio, for example, ip address, usb port, or serial number 30ad2d5
    rxsim.radiosamplerate = 20000000;      % configured for 20e6 hz as this is beacon transmission bw
    rxsim.radiogain = 50;
    rxsim.frequencyband = 5;
    rxsim.channelnumbers = [32, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144, 149, 153, 157, 161, 165, 169, 173, 177];       % default scans all 5 ghz beacon channels
    rxsim.receiveantenna = 1;       % configure to work with only a single antenna
    rxsim.capturetime = milliseconds(100);          % value expected to be of type duration
    % derived parameters
    rxsim.centerfrequencies = wlanchannelfrequency(rxsim.channelnumbers,rxsim.frequencyband);
    rxsim.numsamplestocapture = seconds(rxsim.capturetime)*rxsim.radiosamplerate;
        
else
    rx = load(filename);
    rxsim.channelnumbers = rx.channels;
    rxsim.radiosamplerate = rx.radiosamplerate;
    rxsim.frequencyband = rx.band;
    % derived parameters
    rxsim.numsamplestocapture = size(rx.capturedwaveforms,1);
end
osf = rxsim.radiosamplerate/20e6;

retrievevendorinfo = true;

displayadditionalinfo = false;

displayscope = false;

if rxsim.receiveonsdr
    if matches(rxsim.sdrdevicename, ["ad936x", "fmcomms5", "pluto", "e3xx"])
        sdrreceiver = sdrrx( ...
            rxsim.sdrdevicename, ...
            basebandsamplerate=rxsim.radiosamplerate, ...
            gainsource="manual");
        if matches(rxsim.sdrdevicename, ["ad936x", "fmcomms5", "e3xx"])
            % when capturing a waveform, skip the fpga and have the data
            % sent straight to the host
            sdrreceiver.showadvancedproperties = true;
            sdrreceiver.bypassuserlogic = true;
            sdrreceiver.ipaddress = rxsim.radioidentifier;
        else
            sdrreceiver.radioid = rxsim.radioidentifier;
        end        
    else
        % for the usrp sdrs
        sdrreceiver = comm.sdrureceiver( ...
            platform=rxsim.sdrdevicename, ...
            enableburstmode=true);
        % determine burst capture values
        % each frame will have 100 symbols
        sdrreceiver.samplesperframe = 4e-6*rxsim.radiosamplerate*100;
        sdrreceiver.numframesinburst = rxsim.numsamplestocapture/sdrreceiver.samplesperframe;
        [sdrreceiver.masterclockrate, sdrreceiver.decimationfactor] = ...
            hgetusrprateinformation(rxsim.sdrdevicename,rxsim.radiosamplerate);
        if matches(rxsim.sdrdevicename, ["b200", "b210"])
            % change the serial number as needed for usrp b200/b210
            sdrreceiver.serialnum = rxsim.radioidentifier;
        else
            sdrreceiver.ipaddress = rxsim.radioidentifier;
        end
    end
    sdrreceiver.gain = rxsim.radiogain;
    sdrreceiver.outputdatatype = "double";
    sdrreceiver.channelmapping = rxsim.receiveantenna;
end

aps = struct(...
    "ssid",[],"bssid",[],"vendor",[],"snr_db",[],"beacon_channel",[], ...
    "operating_channel",[],"channel_width_mhz",[],"band",[],"mode",[], ...
    "mac_config",wlanmacframeconfig,"waveform",[],"offset",[]);

cbw = "cbw20";
cfg = wlannonhtconfig(channelbandwidth=cbw);
ind = wlanfieldindices(cfg);
indexap = 1;

for i = 1:length(rxsim.channelnumbers)    
    
    fprintf("scanning channel %d on band %.1f.\n",rxsim.channelnumbers(i),rxsim.frequencyband);
    if rxsim.receiveonsdr
        sdrreceiver.centerfrequency = rxsim.centerfrequencies(i);
        captureddata = capturewaveform(sdrreceiver,rxsim.numsamplestocapture);
    else
        captureddata = rx.capturedwaveforms(:,i);
    end
    
    % display spectrum and spectrogram
    if displayscope %#ok<*unrch>
        scope = spectrumanalyzer(viewtype="spectrum-and-spectrogram",samplerate=rxsim.radiosamplerate,...
            timespansource="property",timespan=rxsim.numsamplestocapture/rxsim.radiosamplerate);
        scope(captureddata);
    end    
   
    % resample the captured data to 20 mhz for beacon processing. 
    if osf ~= 1
        captureddata = resample(captureddata,20e6,rxsim.radiosamplerate);
    end
    searchoffset = 0;
    while searchoffset% recoverpreamble detects a packet and performs analysis of the non-ht preamble.
        [preamblestatus,res] = recoverpreamble(captureddata,cbw,searchoffset);
        
        if matches(preamblestatus,"no packet detected")
            break;
        end
        % retrieve synchronized data and scale it with lstf power as done
        % in the recoverpreamble function.
        syncdata = captureddata(res.packetoffset 1:end)./sqrt(res.lstfpower);
        syncdata = frequencyoffset(syncdata,rxsim.radiosamplerate/osf,-res.cfoestimate);
        
        % need only 4 ofdm symbols (lsig   3 more symbols) following lltf
        % for format detection
        fmtdetect = syncdata(ind.lsig(1):(ind.lsig(2) 4e-6*rxsim.radiosamplerate/osf*3));        
        
        [lsigbits, failcheck] = wlanlsigrecover(fmtdetect(1:4e-6*rxsim.radiosamplerate/osf*1), ...
            res.chanestnonht,res.noiseestnonht,cbw);
    
        if ~failcheck            
            format = wlanformatdetect(fmtdetect,res.chanestnonht,res.noiseestnonht,cbw);
            if matches(format,"non-ht")
                
                % extract mcs from first 3 bits of l-sig.
                rate = double(bit2int(lsigbits(1:3),3));
                if rate <= 1
                    cfg.mcs = rate   6;
                else
                    cfg.mcs = mod(rate,6);
                end
                
                % determine psdu length from l-sig.
                cfg.psdulength = double(bit2int(lsigbits(6:17),12,0));
                ind.nonhtdata = wlanfieldindices(cfg,"nonht-data");
                
                if double(ind.nonhtdata(2)-ind.nonhtdata(1))> ...
                        length(syncdata(ind.nonhtdata(1):end))
                    % exit while loop as full packet not captured. 
                    break;
                end
                
                nonhtdata = syncdata(ind.nonhtdata(1):ind.nonhtdata(2));                
                bitsdata = wlannonhtdatarecover(nonhtdata,res.chanestnonht, ...
                    res.noiseestnonht,cfg);
                [cfgmac, ~, decodestatus] = wlanmpdudecode(bitsdata,cfg, ...
                    suppresswarnings=true);
                
                % print additional information on all successfully packets
                if ~decodestatus && displayadditionalinfo
                   payloadsize = floor(length(bitsdata)/8);
                   [modulation,coderate] = getrateinfo(cfg.mcs);
                   fprintf("payload size: %d | modulation: %s | code rate: %s \n",payloadsize,modulation,coderate);
                   fprintf("type: %s | sub-type: %s",cfgmac.gettype,cfgmac.getsubtype);
                
                end
                % extract information about channel from the beacon.
                if ~decodestatus && matches(cfgmac.frametype,"beacon")
                    % populate the table with information about the beacon.
                    if isempty(cfgmac.managementconfig.ssid)
                        aps(indexap).ssid = "hidden";
                    else
                        aps(indexap).ssid = string(cfgmac.managementconfig.ssid);
                    end
                    fprintf("%s beacon detected on channel %d in band %.1f.\n",aps(indexap).ssid,rxsim.channelnumbers(i),rxsim.frequencyband);
                    
                    aps(indexap).bssid = string(cfgmac.address3);
                    if retrievevendorinfo 
                        aps(indexap).vendor = determinevendor(cfgmac.address3);
                    else
                        aps(indexap).vendor = "skipped"; 
                    end
                    [aps(indexap).mode, aps(indexap).channel_width_mhz, operatingchannel] = ...
                        determinemode(cfgmac.managementconfig.informationelements);
                    
                    if isempty(operatingchannel)
                        % default to scanning channel if operating channel
                        % cannot be determined.  
                        operatingchannel = rxsim.channelnumbers(i);
                    end
                    
                    aps(indexap).beacon_channel = rxsim.channelnumbers(i);
                    aps(indexap).operating_channel = operatingchannel;
                    aps(indexap).snr_db = res.lltfsnr;
                    aps(indexap).mac_config = cfgmac;
                    aps(indexap).offset = res.packetoffset;
                    aps(indexap).waveform = captureddata;
                    indexap = indexap   1;
                end
                % shift packet search offset for next iteration of while loop.
                searchoffset = res.packetoffset   double(ind.nonhtdata(2));
            else
                % packet is not non-ht; shift packet search offset by 10 ofdm symbols (minimum
                % packet length of non-ht) for next iteration of while loop.
                searchoffset = res.packetoffset   4e-6*rxsim.radiosamplerate/osf*10;
            end
        else
            % l-sig recovery failed; shift packet search offset by 10 ofdm symbols (minimum
            % packet length of non-ht) for next iteration of while loop.
            searchoffset = res.packetoffset   4e-6*rxsim.radiosamplerate/osf*10;
        end
    end
end

detectedbeaconsinfo = generatebeacontable(aps,rxsim.frequencyband,retrievevendorinfo)

if rxsim.receiveonsdr
    release(sdrreceiver);
end

function waveform = capturewaveform(sdrreceiver,numsamplestocapture)
% capturewaveform returns a column vector of complex values given an
% sdrreceiver object and a scalar numsamplestocapture value.
    % for a comm.sdrureceiver object, use the burst capture technique to
    % acquire the waveform
    if isa(sdrreceiver,'comm.sdrureceiver')
        waveform = complex(zeros(numsamplestocapture,1));
        samplesperframe = sdrreceiver.samplesperframe;
        for i = 1:sdrreceiver.numframesinburst
            waveform(samplesperframe*(i-1) (1:samplesperframe)) = sdrreceiver();
        end
    else
        waveform = capture(sdrreceiver,numsamplestocapture);
    end
end
function [modulation,coderate] = getrateinfo(mcs)
% getrateinfo returns the modulation scheme as a character array and the
% code rate of a packet given a scalar integer representing the modulation
% coding scheme
switch mcs
    case 0 % bpsk
        modulation = 'bpsk';
        coderate = '1/2';
    case 1 % bpsk
        modulation = 'bpsk';
        coderate = '3/4';
    case 2 % qpsk
        modulation = 'qpsk';
        coderate = '1/2';
    case 3 % qpsk
        modulation = 'qpsk';
        coderate = '3/4';
    case 4 % 16qam
        modulation = '16qam';
        coderate = '1/2';
    case 5 % 16qam
        modulation = '16qam';
        coderate = '3/4';
    case 6 % 64qam
        modulation = '64qam';
        coderate = '2/3';
    otherwise % 64qam
        modulation = '64qam';
        coderate = '3/4';
end
end
function vendor = determinevendor(mac)
% determinevendor returns the vendor name of the ap by extracting the
% organizationally unique identifier (oui) from the specified mac address.
persistent ouis
vendor = strings(0);
try
    if isempty(ouis)
        if ~exist("oui.csv","file")
            disp("downloading oui.csv from ieee registration authority...")
            options = weboptions("timeout",10);
            websave("oui.csv","http://standards-oui.ieee.org/oui/oui.csv",options);
        end
        ouis = readtable("oui.csv",variablenamingrule="preserve");
    end
    % extract oui from mac address.
    oui = mac(1:6);
    % extract vendors name based on oui.
    vendor = string(cell2mat(ouis.("organization name")(matches(ouis.assignment,oui))));
catch me
    % rethrow caught error as warning.
    warning(me.message "\nto skip the determinevendor function call, set retrievevendorinfo to false.",[]);
end
if isempty(vendor)
    vendor = "unknown";
end
end
function [mode,bw,operatingchannel] = determinemode(informationelements)
% determinemode determines the 802.11 standard that the ap uses. 
% the function checks for the presence of ht, vht, and he capability
% elements and determines the 802.11 standard that the ap uses. the element
% ids are defined in ieee std 802.11-2020 and ieee std 802.11ax-2021.
elementids = cell2mat(informationelements(:,1));
ids = elementids(:,1);
if any(ids==255)
    if any(elementids(ids==255,2)==35)
        % he packet format
        mode = "802.11ax";
    else
        mode = "unknown";
    end
    vhtelement = informationelements{ids==192,2};
    htelement = informationelements{ids==61,2};
    [bw,operatingchannel] = determinechannelwidth(htelement,vhtelement);
elseif any(ids==191)
    % vht packet format
    mode = "802.11ac";
    vhtelement = informationelements{ids==192,2};
    htelement = informationelements{ids==61,2};
    [bw,operatingchannel] = determinechannelwidth(htelement,vhtelement);
elseif any(ids==45)
    % ht packet format
    mode = "802.11n";
    htelement = informationelements{ids==61,2};
    [bw,operatingchannel] = determinechannelwidth(htelement);
else
    % non-ht packet format
    % exclude b as only dsss is supported
    mode ="802.11a/g/j/p";
    bw = "unknown";
    operatingchannel = [];
end
end
function [bw,operatingchannel] = determinechannelwidth(htelement,varargin)
% determinechannelwidth returns the bandwidth of the channel from the
% beacons operation information elements as defined in ieee std 802.11-2020
% table 11-23.
msbfirst = false;
% convert to bits to get sta channel width value in 3rd bit.
htoperationinfobits = int2bit(htelement(2),5*8,msbfirst);
operatingchannel = 0;
if nargin == 2
    vhtelement = varargin{1};
    % vht operation channel width field
    cw = vhtelement(1);
    % channel center frequency segment 0
    ccfs0 = vhtelement(2);
    % channel center frequency segment 1
    ccfs1 = vhtelement(3);
    if htoperationinfobits(3) == 0
        bw = "20";
        operatingchannel = ccfs0;
    elseif cw == 0
        % ht operation channel width field is 1
        bw = "40";
        operatingchannel = ccfs0;
    elseif ccfs1 == 0
        % ht operation channel width field is 1 and
        % vht operation channel width field is 1
        bw = "80";
        operatingchannel = ccfs0;
    elseif abs(ccfs1 - ccfs0) == 8
        % ht operation channel width field is 1 and
        % vht operation channel width field is 1 and
        % ccfs1 is greater than 0
        bw = "160";
        operatingchannel = ccfs1;
    else
        % ht operation channel width field is 1 and
        % vht operation channel width field is 1 and
        % ccfs1 is greater than 0 and
        % |ccfs1 - ccfs0| is greater than 16
        bw = "80 80";
    end
end
if operatingchannel == 0
    if htoperationinfobits(3) == 1
        bw = "40";
        secondarychanneloffset = bit2int(htoperationinfobits(1:2),2,false);
        if secondarychanneloffset == 1
            % secondary channel is above the primary channel.
            operatingchannel = htelement(1)   2;
        elseif secondarychanneloffset == 3
            % secondary channel is below the primary channel.
            operatingchannel = htelement(1) - 2;
        else
            warning("could not determine operating channel.")
        end
    else
        bw = "20";
        operatingchannel = htelement(1);
    end
end
end
function tbl = generatebeacontable(aps,band,retrievevendorinfo)
% generatebeacontable converts the access point structure to a table and
% cleans up the variable names.
tbl = struct2table(aps,"asarray",true);
tbl.band = repmat(band,length(tbl.ssid),1);
tbl = renamevars(tbl,["snr_db","beacon_channel","operating_channel","channel_width_mhz"], ...
    ["snr (db)","primary 20 mhz channel","current channel center frequency index", ...
    "channel width (mhz)"]);
if retrievevendorinfo
    tbl = tbl(:,1:9);
else
    tbl = tbl(:,[1:2,4:9]);
end
end