From c7c3ef3b9cac5d71f50e602ea10b5777ee77d75c Mon Sep 17 00:00:00 2001 From: Atis Elsts Date: Thu, 31 Mar 2016 13:41:08 +0300 Subject: [PATCH] Cooja: add Msp802154BitErrorRadio interface The interface more accurately models bit errors due to signal fading as observed in IEEE 802.15.4-compatible radios, such as CC2420 and CC2520. --- .../interfaces/Msp802154BitErrorRadio.java | 370 ++++++++++++++++++ .../mspmote/interfaces/Msp802154Radio.java | 8 +- 2 files changed, 374 insertions(+), 4 deletions(-) create mode 100644 tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154BitErrorRadio.java diff --git a/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154BitErrorRadio.java b/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154BitErrorRadio.java new file mode 100644 index 000000000..53b971755 --- /dev/null +++ b/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154BitErrorRadio.java @@ -0,0 +1,370 @@ +/* + * Copyright (c) 2014, Uppsala University + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. Neither the name of the Institute nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + */ + +package org.contikios.cooja.mspmote.interfaces; + +import java.util.Random; + +import org.apache.log4j.Logger; + +import org.contikios.cooja.ClassDescription; +import org.contikios.cooja.Mote; +import org.contikios.cooja.Simulation; +import org.contikios.cooja.radiomediums.AbstractRadioMedium; + +import org.contikios.cooja.mspmote.MspMoteTimeEvent; +import org.contikios.cooja.mspmote.interfaces.Msp802154Radio; + + +/** + * Extension of MSPSim 802.15.4 radio wrapper with bit-level errors. + * + * Only errors due to signal fading are supported (as opposed to errors to interference). + * Interesting modelling effects can obtained if this is used together with a dynamic + * channel fading model. + * + * @author Atis Elsts + */ +@ClassDescription("IEEE 802.15.4 Bit Error Radio") +public class Msp802154BitErrorRadio extends Msp802154Radio { + private static Logger logger = Logger.getLogger(Msp802154Radio.class); + + private static final double NOISE_FLOOR = AbstractRadioMedium.SS_WEAK; + private static final double GOOD_SIGNAL = NOISE_FLOOR + 15.0; + + private Random random = null; + + public Msp802154BitErrorRadio(Mote m) { + super(m); + + random = getMote().getSimulation().getRandomGenerator(); + } + + /* The MSK-transformed symbol-to-codeword table. + * It's used for mapping between symbols and codeword by some popular + * 802.15.4 radios such as CC2420 and CC2520. */ + private static final int[] mskEncodeTable = { + 1618456172, + 1309113062, + 1826650030, + 1724778362, + 778887287, + 2061946375, + 2007919840, + 125494990, + 529027475, + 838370585, + 320833617, + 422705285, + 1368596360, + 85537272, + 139563807, + 2021988657 + }; + + /* Calculates the Hamming distance between two words */ + private int hammingDistance(int x1, int x2) { + return Integer.bitCount(x1 ^ x2); + } + + /* Send a symbol over the air with a specific bit error rate */ + private int transceiveSymbolWithErrors(int txSymbol, double bitErrorRate) { + /* First, transmit (encode and randomly corrupt) it */ + int chipSequence = mskEncodeTable[txSymbol]; + /* Note: loop until 31, not until 32 here, as the highest bit in the codeword + * is irrelevant for MSK encoded data, and therefore should not come into + * the Hamming distance calculations. */ + for (int i = 0; i < 31; ++i) { + double p = random.nextDouble(); + if (p < bitErrorRate) { + chipSequence ^= (1 << i); + } + } + + /* Now receive (decode) it */ + int bestRxSymbol = 0; + int bestHammingDistance = 32; + for (byte i = 0; i < 16; ++i) { + /* Resolve ties in a specific order: + * s7, s6, ... , s0, s15, s14 , ..., s8 */ + int rxSymbol = i < 8 ? 7 - i : 15 - i + 8; + + int hd = hammingDistance(chipSequence, mskEncodeTable[rxSymbol]); + if (hd < bestHammingDistance) { + bestRxSymbol = rxSymbol; + bestHammingDistance = hd; + if (hd == 0) { + break; + } + } + } + return bestRxSymbol; + } + + /* This is the probability that a bit will received incorrectly, for + * -95.0, -94.9, -94.8, ..., -80.0 dBm signal levels. + * It is modelled as Additive White Gaussian Noise (AWGN) channel + * with constellation size = 4, and log2(4) = 2 bits per over-the-air symbol. + * (See "Digital Communications" by Proakis, page 311) + * + * The table was generated with the following Python code: + * + * noise_floor = -95.0 + * good_signal = noise_floor + 15.0 + * + * # chips per second / carrier frequency + * # In this case: + * # 250 kbps * symbols_per_bit / 5 MHz 802.15.4 channel bandwidth + * spectral_efficiency = 250000 * (32 / 4) / 5000000. + * + * def snr_from_rssi(signal): + * return signal - noise_floor + * + * def combinations(n, k): + * return math.factorial(n) / (math.factorial(k) * math.factorial(n - k)) + * + * def chip_error_rate(signal): + * M_sk = 4 # constellation size + * K_b = 2 # bits per symbol + * snr = snr_from_rssi(signal) * spectral_efficiency # signal-noise ratio + * result = 0.0 + * for k in range(1, M_sk): + * result += ((-1)**(k + 1) / (k + 1.0)) * combinations(M_sk - 1, k) * math.exp(- (k / (k + 1.0)) * K_b * snr) + * return result * (M_sk / 2) / (M_sk - 1) + * + * for signal in range(int(noise_floor), int(good_signal + 1)): + * for decimal_part in range(10): + * s = signal + decimal_part / 10.0 + * print("{}: {:.16}".format(s, chip_error_rate(s))) + */ + private static final double[] bitErrorRateTable = { + 0.5000000000000000, + 0.4857075690874351, + 0.4717195981917559, + 0.4580362793082289, + 0.4446572346573086, + 0.4315815642818357, + 0.4188078906959320, + 0.4063344007440545, + 0.3941588848209507, + 0.3822787735959348, + 0.3706911723779558, + 0.3593928932511307, + 0.3483804851041035, + 0.3376502616704103, + 0.3271983276911817, + 0.3170206033059785, + 0.3071128467721474, + 0.2974706756080624, + 0.2880895862507204, + 0.2789649723135144, + 0.2700921415256470, + 0.2614663314303489, + 0.2530827239151328, + 0.2449364586434322, + 0.2370226454533358, + 0.2293363757856961, + 0.2218727332005190, + 0.2146268030374602, + 0.2075936812732179, + 0.2007684826257659, + 0.1941463479526962, + 0.1877224509883067, + 0.1814920044616803, + 0.1754502656356323, + 0.1695925413041991, + 0.1639141922842669, + 0.1584106374348990, + 0.1530773572360710, + 0.1479098969566969, + 0.1429038694401250, + 0.1380549575336883, + 0.1333589161873203, + 0.1288115742448300, + 0.1244088359500270, + 0.1201466821885792, + 0.1160211714852698, + 0.1120284407751141, + 0.1081647059657158, + 0.1044262623071727, + 0.1008094845848469, + 0.0973108271493890, + 0.0939268237974889, + 0.0906540875160106, + 0.0874893101013543, + 0.0844292616651377, + 0.0814707900365929, + 0.0786108200713800, + 0.0758463528759084, + 0.0731744649556428, + 0.0705923072953072, + 0.0680971043783837, + 0.0656861531527741, + 0.0633568219490458, + 0.0611065493572223, + 0.0589328430676567, + 0.0568332786811473, + 0.0548054984930601, + 0.0528472102558939, + 0.0509561859243809, + 0.0491302603869077, + 0.0473673301867607, + 0.0456653522364111, + 0.0440223425278144, + 0.0424363748414465, + 0.0409055794565784, + 0.0394281418650815, + 0.0380023014908522, + 0.0366263504167641, + 0.0352986321208818, + 0.0340175402235017, + 0.0327815172464461, + 0.0315890533858807, + 0.0304386852998058, + 0.0293289949112408, + 0.0282586082280085, + 0.0272261941799208, + 0.0262304634740650, + 0.0252701674687994, + 0.0243440970669807, + 0.0234510816288642, + 0.0225899879050480, + 0.0217597189897583, + 0.0209592132947168, + 0.0201874435437662, + 0.0194434157883799, + 0.0187261684441326, + 0.0180347713481601, + 0.0173683248375987, + 0.0167259588489542, + 0.0161068320383143, + 0.0155101309222909, + 0.0149350690395443, + 0.0143808861327198, + 0.0138468473506013, + 0.0133322424702643, + 0.0128363851389939, + 0.0123586121357148, + 0.0118982826516654, + 0.0114547775900349, + 0.0110274988842702, + 0.0106158688347500, + 0.0102193294635131, + 0.0098373418867231, + 0.0094693857045423, + 0.0091149584080853, + 0.0087735748031163, + 0.0084447664501541, + 0.0081280811206428, + 0.0078230822688482, + 0.0075293485191375, + 0.0072464731683002, + 0.0069740637025694, + 0.0067117413290037, + 0.0064591405208906, + 0.0062159085768378, + 0.0059817051932169, + 0.0057562020496316, + 0.0055390824070828, + 0.0053300407185094, + 0.0051287822513842, + 0.0049350227220528, + 0.0047484879415055, + 0.0045689134722762, + 0.0043960442961698, + 0.0042296344925230, + 0.0040694469267080, + 0.0039152529485966, + 0.0037668321007033, + 0.0036239718357372, + 0.0034864672432910, + 0.0033541207854084, + 0.0032267420407699, + 0.0031041474572487, + 0.0029861601125883, + 0.0028726094829638, + 0.0027633312191911, + 0.0026581669303560, + 0.0025569639746388, + 0.0024595752571165, + 0.0023658590343307, + 0.0022756787254125 + }; + + private double getBitErrorRate(double signal) { + if (signal <= NOISE_FLOOR) { + return 0.5; + } else if (signal >= GOOD_SIGNAL) { + return 0.0; + } else { + long position = Math.round((signal - NOISE_FLOOR) * 10.0); + return bitErrorRateTable[(int)position]; + } + } + + public void receiveCustomData(Object data) { + if (!(data instanceof Byte)) { + logger.fatal("Bad custom data: " + data); + return; + } + lastIncomingByte = (Byte) data; + + final byte inputByte; + if (isInterfered()) { + inputByte = (byte)0xFF; + } else { + double bitErrorRate = getBitErrorRate(currentSignalStrength); + if (bitErrorRate == 0.0) { + inputByte = lastIncomingByte; + } else if (bitErrorRate >= 0.5) { + inputByte = (byte) 0xFF; + } else { + /* convert to an unsigned int in order to prettify subsequent operations with bits */ + int incomingByteAsInt = lastIncomingByte; + if (incomingByteAsInt < 0) incomingByteAsInt += 256; + + /* a byte consists of 2 symbols; independently transceive each of them */ + int firstSymbol = transceiveSymbolWithErrors(incomingByteAsInt >> 4, bitErrorRate); + int secondSymbol = transceiveSymbolWithErrors(incomingByteAsInt & 0xf, bitErrorRate); + + inputByte = (byte)((firstSymbol << 4) + secondSymbol); + } + } + + mote.getSimulation().scheduleEvent(new MspMoteTimeEvent(mote, 0) { + public void execute(long t) { + super.execute(t); + radio.receivedByte(inputByte); + mote.requestImmediateWakeup(); + } + }, mote.getSimulation().getSimulationTime()); + + } +} diff --git a/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154Radio.java b/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154Radio.java index 31aa30377..baa9676a9 100644 --- a/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154Radio.java +++ b/tools/cooja/apps/mspsim/src/org/contikios/cooja/mspmote/interfaces/Msp802154Radio.java @@ -69,16 +69,16 @@ public class Msp802154Radio extends Radio implements CustomDataRadio { private RadioEvent lastEvent = RadioEvent.UNKNOWN; - private final MspMote mote; - private final Radio802154 radio; + protected final MspMote mote; + protected final Radio802154 radio; private boolean isInterfered = false; private boolean isTransmitting = false; private boolean isReceiving = false; private boolean isSynchronized = false; - private byte lastOutgoingByte; - private byte lastIncomingByte; + protected byte lastOutgoingByte; + protected byte lastIncomingByte; private RadioPacket lastOutgoingPacket = null; private RadioPacket lastIncomingPacket = null;