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.
This commit is contained in:
Atis Elsts
parent
29c9907c08
commit
c7c3ef3b9c
2 changed files with 374 additions and 4 deletions
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@ -0,0 +1,370 @@
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/*
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* Copyright (c) 2014, Uppsala University
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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*/
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package org.contikios.cooja.mspmote.interfaces;
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import java.util.Random;
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import org.apache.log4j.Logger;
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import org.contikios.cooja.ClassDescription;
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import org.contikios.cooja.Mote;
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import org.contikios.cooja.Simulation;
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import org.contikios.cooja.radiomediums.AbstractRadioMedium;
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import org.contikios.cooja.mspmote.MspMoteTimeEvent;
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import org.contikios.cooja.mspmote.interfaces.Msp802154Radio;
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/**
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* Extension of MSPSim 802.15.4 radio wrapper with bit-level errors.
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*
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* Only errors due to signal fading are supported (as opposed to errors to interference).
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* Interesting modelling effects can obtained if this is used together with a dynamic
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* channel fading model.
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*
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* @author Atis Elsts
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*/
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@ClassDescription("IEEE 802.15.4 Bit Error Radio")
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public class Msp802154BitErrorRadio extends Msp802154Radio {
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private static Logger logger = Logger.getLogger(Msp802154Radio.class);
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private static final double NOISE_FLOOR = AbstractRadioMedium.SS_WEAK;
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private static final double GOOD_SIGNAL = NOISE_FLOOR + 15.0;
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private Random random = null;
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public Msp802154BitErrorRadio(Mote m) {
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super(m);
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random = getMote().getSimulation().getRandomGenerator();
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}
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/* The MSK-transformed symbol-to-codeword table.
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* It's used for mapping between symbols and codeword by some popular
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* 802.15.4 radios such as CC2420 and CC2520. */
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private static final int[] mskEncodeTable = {
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1618456172,
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1309113062,
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1826650030,
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1724778362,
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778887287,
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2061946375,
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2007919840,
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125494990,
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529027475,
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838370585,
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320833617,
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422705285,
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1368596360,
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85537272,
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139563807,
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2021988657
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};
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/* Calculates the Hamming distance between two words */
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private int hammingDistance(int x1, int x2) {
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return Integer.bitCount(x1 ^ x2);
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}
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/* Send a symbol over the air with a specific bit error rate */
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private int transceiveSymbolWithErrors(int txSymbol, double bitErrorRate) {
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/* First, transmit (encode and randomly corrupt) it */
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int chipSequence = mskEncodeTable[txSymbol];
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/* Note: loop until 31, not until 32 here, as the highest bit in the codeword
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* is irrelevant for MSK encoded data, and therefore should not come into
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* the Hamming distance calculations. */
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for (int i = 0; i < 31; ++i) {
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double p = random.nextDouble();
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if (p < bitErrorRate) {
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chipSequence ^= (1 << i);
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}
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}
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/* Now receive (decode) it */
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int bestRxSymbol = 0;
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int bestHammingDistance = 32;
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for (byte i = 0; i < 16; ++i) {
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/* Resolve ties in a specific order:
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* s7, s6, ... , s0, s15, s14 , ..., s8 */
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int rxSymbol = i < 8 ? 7 - i : 15 - i + 8;
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int hd = hammingDistance(chipSequence, mskEncodeTable[rxSymbol]);
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if (hd < bestHammingDistance) {
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bestRxSymbol = rxSymbol;
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bestHammingDistance = hd;
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if (hd == 0) {
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break;
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}
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}
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}
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return bestRxSymbol;
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}
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/* This is the probability that a bit will received incorrectly, for
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* -95.0, -94.9, -94.8, ..., -80.0 dBm signal levels.
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* It is modelled as Additive White Gaussian Noise (AWGN) channel
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* with constellation size = 4, and log2(4) = 2 bits per over-the-air symbol.
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* (See "Digital Communications" by Proakis, page 311)
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*
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* The table was generated with the following Python code:
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*
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* noise_floor = -95.0
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* good_signal = noise_floor + 15.0
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*
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* # chips per second / carrier frequency
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* # In this case:
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* # 250 kbps * symbols_per_bit / 5 MHz 802.15.4 channel bandwidth
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* spectral_efficiency = 250000 * (32 / 4) / 5000000.
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*
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* def snr_from_rssi(signal):
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* return signal - noise_floor
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*
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* def combinations(n, k):
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* return math.factorial(n) / (math.factorial(k) * math.factorial(n - k))
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*
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* def chip_error_rate(signal):
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* M_sk = 4 # constellation size
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* K_b = 2 # bits per symbol
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* snr = snr_from_rssi(signal) * spectral_efficiency # signal-noise ratio
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* result = 0.0
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* for k in range(1, M_sk):
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* result += ((-1)**(k + 1) / (k + 1.0)) * combinations(M_sk - 1, k) * math.exp(- (k / (k + 1.0)) * K_b * snr)
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* return result * (M_sk / 2) / (M_sk - 1)
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*
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* for signal in range(int(noise_floor), int(good_signal + 1)):
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* for decimal_part in range(10):
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* s = signal + decimal_part / 10.0
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* print("{}: {:.16}".format(s, chip_error_rate(s)))
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*/
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private static final double[] bitErrorRateTable = {
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0.5000000000000000,
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0.4857075690874351,
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0.4717195981917559,
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0.4580362793082289,
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0.4446572346573086,
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0.4315815642818357,
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0.4188078906959320,
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0.4063344007440545,
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0.3941588848209507,
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0.3822787735959348,
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0.3706911723779558,
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0.3593928932511307,
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0.3483804851041035,
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0.3376502616704103,
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0.3271983276911817,
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0.3170206033059785,
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0.3071128467721474,
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0.2974706756080624,
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0.2880895862507204,
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0.2789649723135144,
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0.2700921415256470,
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0.2614663314303489,
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0.2530827239151328,
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0.2449364586434322,
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0.2370226454533358,
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0.2293363757856961,
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0.2218727332005190,
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0.2146268030374602,
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0.2075936812732179,
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0.2007684826257659,
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0.1941463479526962,
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0.1877224509883067,
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0.1814920044616803,
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0.1754502656356323,
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0.1695925413041991,
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0.1639141922842669,
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0.1584106374348990,
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0.1530773572360710,
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0.1479098969566969,
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0.1429038694401250,
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0.1380549575336883,
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0.1333589161873203,
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0.1288115742448300,
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0.1244088359500270,
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0.1201466821885792,
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0.1160211714852698,
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0.1120284407751141,
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0.1081647059657158,
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0.1044262623071727,
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0.1008094845848469,
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0.0973108271493890,
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0.0939268237974889,
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0.0906540875160106,
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0.0874893101013543,
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0.0844292616651377,
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0.0814707900365929,
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0.0786108200713800,
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0.0758463528759084,
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0.0731744649556428,
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0.0705923072953072,
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0.0680971043783837,
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0.0656861531527741,
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0.0633568219490458,
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0.0611065493572223,
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0.0589328430676567,
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0.0568332786811473,
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0.0548054984930601,
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0.0528472102558939,
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0.0509561859243809,
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0.0491302603869077,
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0.0473673301867607,
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0.0456653522364111,
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0.0440223425278144,
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0.0424363748414465,
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0.0409055794565784,
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0.0394281418650815,
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0.0380023014908522,
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0.0366263504167641,
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0.0352986321208818,
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0.0340175402235017,
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0.0327815172464461,
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0.0315890533858807,
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0.0304386852998058,
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0.0293289949112408,
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0.0282586082280085,
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0.0272261941799208,
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0.0262304634740650,
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0.0252701674687994,
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0.0243440970669807,
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0.0234510816288642,
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0.0225899879050480,
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0.0217597189897583,
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0.0209592132947168,
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0.0201874435437662,
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0.0194434157883799,
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0.0187261684441326,
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0.0180347713481601,
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0.0173683248375987,
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0.0167259588489542,
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0.0161068320383143,
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0.0155101309222909,
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0.0149350690395443,
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0.0143808861327198,
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0.0138468473506013,
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0.0133322424702643,
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0.0128363851389939,
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0.0123586121357148,
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0.0118982826516654,
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0.0114547775900349,
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0.0110274988842702,
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0.0106158688347500,
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0.0102193294635131,
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0.0098373418867231,
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0.0094693857045423,
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0.0091149584080853,
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0.0087735748031163,
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0.0084447664501541,
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0.0081280811206428,
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0.0078230822688482,
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0.0075293485191375,
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0.0072464731683002,
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0.0069740637025694,
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0.0067117413290037,
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0.0064591405208906,
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0.0062159085768378,
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0.0059817051932169,
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0.0057562020496316,
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0.0055390824070828,
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0.0053300407185094,
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0.0051287822513842,
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0.0049350227220528,
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0.0047484879415055,
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0.0045689134722762,
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0.0043960442961698,
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0.0042296344925230,
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0.0040694469267080,
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0.0039152529485966,
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0.0037668321007033,
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0.0036239718357372,
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0.0034864672432910,
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0.0033541207854084,
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0.0032267420407699,
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0.0031041474572487,
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0.0029861601125883,
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0.0028726094829638,
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0.0027633312191911,
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0.0026581669303560,
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0.0025569639746388,
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0.0024595752571165,
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0.0023658590343307,
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0.0022756787254125
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};
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private double getBitErrorRate(double signal) {
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if (signal <= NOISE_FLOOR) {
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return 0.5;
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} else if (signal >= GOOD_SIGNAL) {
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return 0.0;
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} else {
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long position = Math.round((signal - NOISE_FLOOR) * 10.0);
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return bitErrorRateTable[(int)position];
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}
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}
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public void receiveCustomData(Object data) {
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if (!(data instanceof Byte)) {
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logger.fatal("Bad custom data: " + data);
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return;
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}
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lastIncomingByte = (Byte) data;
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final byte inputByte;
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if (isInterfered()) {
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inputByte = (byte)0xFF;
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} else {
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double bitErrorRate = getBitErrorRate(currentSignalStrength);
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if (bitErrorRate == 0.0) {
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inputByte = lastIncomingByte;
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} else if (bitErrorRate >= 0.5) {
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inputByte = (byte) 0xFF;
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} else {
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/* convert to an unsigned int in order to prettify subsequent operations with bits */
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int incomingByteAsInt = lastIncomingByte;
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if (incomingByteAsInt < 0) incomingByteAsInt += 256;
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/* a byte consists of 2 symbols; independently transceive each of them */
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int firstSymbol = transceiveSymbolWithErrors(incomingByteAsInt >> 4, bitErrorRate);
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int secondSymbol = transceiveSymbolWithErrors(incomingByteAsInt & 0xf, bitErrorRate);
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inputByte = (byte)((firstSymbol << 4) + secondSymbol);
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}
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}
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mote.getSimulation().scheduleEvent(new MspMoteTimeEvent(mote, 0) {
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public void execute(long t) {
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super.execute(t);
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radio.receivedByte(inputByte);
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mote.requestImmediateWakeup();
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}
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}, mote.getSimulation().getSimulationTime());
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}
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}
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@ -69,16 +69,16 @@ public class Msp802154Radio extends Radio implements CustomDataRadio {
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private RadioEvent lastEvent = RadioEvent.UNKNOWN;
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private final MspMote mote;
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private final Radio802154 radio;
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protected final MspMote mote;
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protected final Radio802154 radio;
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private boolean isInterfered = false;
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private boolean isTransmitting = false;
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private boolean isReceiving = false;
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private boolean isSynchronized = false;
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private byte lastOutgoingByte;
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private byte lastIncomingByte;
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protected byte lastOutgoingByte;
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protected byte lastIncomingByte;
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private RadioPacket lastOutgoingPacket = null;
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private RadioPacket lastIncomingPacket = null;
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