#include <Decider80211.h>
Inheritance diagram for Decider80211:
Depending on the minimum of the snr included in the PhySDU this module computes a bit error probability. The header (1 Mbit/s) is always modulated with DBQPSK. The PDU is normally modulated either with DBPSK (1 and 2 Mbit/s) or CCK (5.5 and 11 Mbit/s). CCK is not easy to model, therefore it is modeled as DQPSK with a 16-QAM for 5.5 Mbit/s and a 256-QAM for 11 Mbit/s.
Protected Member Functions | |
virtual void | initialize (int) |
Initialization of the module and some variables. | |
virtual void | handleLowerMsg (AirFrame *, SnrList &) |
In this function the decision whether a frame is received correctly or not is made. | |
double | dB2fraction (double) |
converts a dB value into a normal fraction | |
bool | packetOk (double, int) |
computes if packet is ok or has errors | |
Protected Attributes | |
double | bitrate |
should be set in the omnetpp.ini | |
double | snirThreshold |
should be set in the omnetpp.ini; everthing below this threshold can't be read and is therefor considered as a collision |
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converts a dB value into a normal fraction
00137 {
00138 return pow(10.0, (dB / 10));
00139 }
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In this function the decision whether a frame is received correctly or not is made. Handle message from lower layer. The minimal snir is read in and it is computed wether the packet has collided or has bit errors or was received correctly. The corresponding kind is set and it is handed on to the upper layer. Reimplemented from BasicDecider. 00058 { 00059 00060 double snirMin; 00061 00062 //initialize snirMin: 00063 snirMin = receivedList.begin()->snr; 00064 00065 for (SnrList::iterator iter = receivedList.begin(); iter != receivedList.end(); iter++) 00066 { 00067 if (iter->snr < snirMin) 00068 snirMin = iter->snr; 00069 } 00070 EV << "packet from: " << ((Mac80211Pkt *) (af->encapsulatedMsg()))-> 00071 getSrcAddr() << " snrMin: " << snirMin << endl; 00072 00073 //if snir is big enough so that packet can be recognized at all 00074 if (snirMin > snirThreshold) 00075 { 00076 if (packetOk(snirMin, af->encapsulatedMsg()->length())) 00077 { 00078 EV << "packet was received correctly, it is now handed to upper layer...\n"; 00079 sendUp(af); 00080 } 00081 else 00082 { 00083 EV << "Packet has BIT ERRORS! It is lost!\n"; 00084 af->setName("ERROR"); 00085 af->encapsulatedMsg()->setKind(BITERROR); 00086 sendUp(af); 00087 } 00088 } 00089 else 00090 { 00091 EV << "COLLISION! Packet got lost\n"; 00092 af->setName("COLLISION"); 00093 af->encapsulatedMsg()->setKind(COLLISION); 00094 sendUp(af); 00095 } 00096 }
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Initialization of the module and some variables. First we have to initialize the module from which we derived ours, in this case BasicDecider. This decider also needs the bitrate and some 802.11 parameters are initialized Reimplemented from BasicDecider. 00036 { 00037 BasicDecider::initialize(stage); 00038 00039 if (stage == 0) 00040 { 00041 EV << "initializing stage 0\n"; 00042 bitrate = par("bitrate"); 00043 if (bitrate != 1E+6 && bitrate != 2E+6 && bitrate != 5.5E+6 && bitrate != 11E+6) 00044 error("Wrong bitrate!! Please chose 1E+6, 2E+6, 5.5E+6 or 11E+6 as bitrate!!"); 00045 snirThreshold = dB2fraction(par("snirThreshold")); 00046 } 00047 }
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computes if packet is ok or has errors
00100 { 00101 double berHeader, berMPDU; 00102 00103 berHeader = 0.5 * exp(-snirMin * BANDWIDTH / BITRATE_HEADER); 00104 //if PSK modulation 00105 if (bitrate == 1E+6 || bitrate == 2E+6) 00106 berMPDU = 0.5 * exp(-snirMin * BANDWIDTH / bitrate); 00107 //if CCK modulation (modeled with 16-QAM) 00108 else if (bitrate == 5.5E+6) 00109 berMPDU = 0.5 * (1 - 1 / sqrt(pow(2.0, 4))) * erfc(snirMin * BANDWIDTH / bitrate); 00110 else // CCK, modelled with 256-QAM 00111 berMPDU = 0.25 * (1 - 1 / sqrt(pow(2.0, 8))) * erfc(snirMin * BANDWIDTH / bitrate); 00112 //probability of no bit error in the PLCP header 00113 double headerNoError = pow(1.0 - berHeader, HEADER_WITHOUT_PREAMBLE); 00114 00115 //probability of no bit error in the MPDU 00116 double MpduNoError = pow(1.0 - berMPDU, lengthMPDU); 00117 EV << "berHeader: " << berHeader << " berMPDU: " << berMPDU << endl; 00118 double rand = dblrand(); 00119 00120 //if error in header 00121 if (rand > headerNoError) 00122 return (false); 00123 else 00124 { 00125 rand = dblrand(); 00126 00127 //if error in MPDU 00128 if (rand > MpduNoError) 00129 return (false); 00130 //if no error 00131 else 00132 return (true); 00133 } 00134 }
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should be set in the omnetpp.ini
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should be set in the omnetpp.ini; everthing below this threshold can't be read and is therefor considered as a collision
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