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International Journal of Electronics and Communication Engineering.ISSN 0974-2166 Volume 4, Number 5 (2011), pp. 543-553© International Research Publication Househttp://www.irphouse.comPerformance Evaluation of Time Hopping UWBSystem in Underground Mine Channel1 Athar Ravish Khan and 2 Sanjay M. Gulhane1 Department of Electronics & Telecommunication,Jawaharlal Darda Institute of Engg. & Technology,Yavatmal Maharashtra, IndiaE-mail: mr.atharravishkhan@rediffmail.com2 Department of Electronics & TelecommunicationJawaharlal Darda Institute of Engg & Technology,Yavatmal Maharashtra, IndiaE-mail: smgulhane67@rediffmail.comAbstractIn order to effectively overcome the path loss, multi-path delay and differentchannels power attenuation of underground mines, wireless communicationUltra Wide Band system, based on Time Hopping Pulse Position Modulationfor coal mine is presented. Discrete time channel impulse response is used tobuild up revised channel model for underground mine which is based on theUWB Channel model proposed by IEEE802.15.3a with the observation thatusually multi-path contributions generated by the same pulse arrive at thereceiver grouped into cluster. With the revised channel model, we compare theperformance of the system in IEEE channel and mine channel and evaluate theperformance of a RAKE receiver employing maximal ratio combining(MRC).The log-normal fading statistics of multipath fading channel isconsidered with different RAKE finger and repetition code. Mean excessdelay and RMS delay spread are calculated to characterize the temporaldispersive properties of the multipath channel. The model of the system wassimulated in the complex environment of mine, simulation results and analysisshow that the underground wireless communication system of UWB based onTH-PPM can effectively with-stand multipath fading and has the advantagesof low bit-error rate.Keywords: TH-PPM Ultra-Wideband (UWB) system, IEEE802.15.3a UWBChannel, Modified Mine Channel

544 Athar Ravish Khan and Sanjay M. GulhaneIntroductionThe complex natural environment and operating conditions in coal mine restrict thedevelopment of mine wireless communication seriously. Ultra-Wide band (UWB)Wireless Communication with a high transfer rate, low power consumption, antiinterferenceis conducive to resolve the issue of radio communication under thecomplex environment in underground mines. Ultra-Wideband (UWB) technology hasgained much interest for its applications in wireless communications. The necessityfor wireless communications in underground mines is well understood. Somecompanies have started to deploy modern wireless networks in mine galleries with theobjective of increasing safety and productivity. Ultra wide band (UWB) wirelesscommunication system has became the principal scheme of short distance high speeddigital transmission, resisting on multipath interference as well as its low powerconsumption. The analysis and design of a UWB communication system requires, anaccurate channel model to determine the maximum achievable data rate, efficientmodulation schemes, and associated signal processing algorithms [1]. This paperevaluate a performance of an Ultra-Wideband (UWB) system in an underground minechannel. The remainder of the paper is organized as follows. In the next section wepresent modulate technique and Choice of UWB wave in coal mine. Section 3 dealswith channel modeling and receiver structure in Underground Mine and in Section. 4the paper ends with simulation results and conclusion.Choice of UWB Wave and Modulate Technique in UndergroundMineChoice of Modulate Technique and channel coderIn TH-UWB combine with binary PPM (2PPM-TH-UWB), the UWB signal can beschematized to be generated as shown in Figure(1).Given the binary sequence to betransmitted b= (..,b 0 ,b 1 ,…b k ,b k+1 ,…),generate at rate of R b =1/T b bits/sec, a firstsystem repeats each bit N s times and generates a binarysequence(.,b 0 ,b 0 ,…b 0 ,b 1 ,b 1 ,..,b k+1 ,b k+1 …b k+1 ,.)=(..a 0 ,a 1 …..a j ,a j+1 ) = a at the rate ofR cb =N s /T b =1/T s bits/s. This system introduce the redundancy and is a(N s ,1) blockcoder indicated as a code repetition coder in classical terminology this is channelcoder. A second block called a transmission coder applies an integer-valued codec=(..c 0 ,c 1, …c j ,c j+1 ,…) to the binary sequence a=(..a 0 , a1…..a j , aj +1 ) and generate a newsequence d. The generic element of the sequence d is express asd j =c j T c +a j ε (1)where T c and ε are constant terms that satisfy the condition c j T c + ε < T s for all c j Onealso has, in general, ε< T c , d is a real-valued sequence as opposed to a, which isbinary and to c, which is integer-valued, assume that c is a pseudorandom code, itsgeneric element c j being an integer verifying 0 ≤ c j ≤ N h - 1. The code c might beperiodic, and in that case, its period is indicated by N p . Two particular cases are worthdiscussing. The first corresponds to the absence of periodicity in the code, that is, N ptends to ∞ and the second to N p = N s . In the second case, which is the most commonly

Performance Evaluation of Time Hopping UWB System 545adopted, the periodicity of the code coincides with the length of the repetition code[7]. The coded real-valued sequence d enters a third system, the PPM modulator,which generates a sequence of unit pulses (Dirac pulses δ(t) ) at a rate of R p = N s /T b =1/T s pulses/s. These pulses are located at times jT s +d j , and are therefore shifted intime from nominal positions jT s by d j . Pulses occur at times (jT s +c j T c +a j ε). Note thatcode c introduces a TH shift on the generated signal, and it is for this reason that it isindicated as TH code. Note that the shift introduced by the PPM modulator, a j ε, isusually much smaller than the shift introduced by the TH code, c j T c , that is, a j ε < c j T c ,except for c j = 0. T c is called chip time refer figure(2). The last system is the pulseshaper filter with impulse response p(t). The impulse response p(t) must be such thatthe signal at the output of the pulse shaper filter is a sequence of strictly nonoverlappingpulses. The most commonly adopted pulse shapes is second derivative ofa Gaussian function.Figure 1: Proposed 2PPM-TH-UWB System model for Underground Mine0.080.06Ts= Frame timeTc =Chip TimeExample: THcode = [ 2 0 1 1 2 ]numbits = 2 number of bits generated by the source [1 0]Ns = 3; number of pulses per bitNp = 5; periodicity of the TH codeAmplitude [V]0.040.02Bit=1Tm =Pulse DurationBit=00-0.02TH1=2TH1=2TH2=0TH3=1 TH4=1 TH5=20 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8Time [s]x 10 -8Figure 2: 2PPM-TH with Pulse Shape.

546 Athar Ravish Khan and Sanjay M. GulhaneNarrow impulse waveNarrow impulse wave has great infection in UWB communication system, so it isvery important to choose the narrow impulse. The narrow impulse signal waves incommon used now include the Guass wave, Cosine wave, multi-period impulse waveand so on. The Gauss wave applied most commonly of these [1]. In the non-carrierwave impulse UWB communications, we usually modeling the transmitting andreceiving antenna to a differential operation. The Gauss impulse signal can beexpressed aspt 1e √2πσ √2αe Where α 2 =4πσ 2 is shape factor and σ 2 is variance ,to be radiate in efficient wayGaussian derivatives are suitable [7] the most currently adopted pulse shape ismodeled as the second derivative of a Gaussian function described byd ptdt 14π te α 3Ideally, a second derivative Gaussian pulse can be obtained at transmittingantenna if the antenna is fed with a current pulse shaped as the first derivative ofGaussian waveform ,the radiating pulse being proportional to the derivative of thedrive current in an ideal antenna(Immoreev and Sinyavin 2002) [7]. The signal s(t) atthe output of the cascade of the systems shown in Figure(1) can be expressed asfollows:st ptjT c T a εNote that the bit interval, or bit duration, that is, the time used to transmit one bitT b is: T b = N s T s . Also note that in Eq. (4), the term c j T c defines pulse randomization ordithering with respect to the nominal instances of time occurring at multiples of T s . Ifwe represent the time shift introduced by the TH code c j T c by a random TH dither η j ,which can be assumed to be distributed between 0 and T η < Ts, we obtain:st ptjT η a εAs noticed above, η j is usually much larger than ε. The global effect of these twoterms is to introduce a random time shift, distributed between 0 and T η + ε < Ts, whichwill be indicated by θ j leading to the following expression for the transmitted signalst ptjT θ 2456

Performance Evaluation of Time Hopping UWB System 547Receiver Structure and Channel Modeling in Underground MineChannel ModelingIn July 2003, the Channel-Modeling sub-commettee of study group IEEE 802.15.SGapublished the final report regarding the UWB indoor multi-path channel model (IEEE802.15.SG3a,2003).This model should be used for evaluating the performance ofdifferent physical layers as submitted to the IEEE 802.15.3 task group. IEEE channel-Modeling sub-commettee finally converged an a model based on the cluster approchproposed by Turin and others in 1972(Turin et.al.1972)and further formalized bySaleh and Valenzuela in 1987(Saleh and Valenzuela,1987)[7]in the seminal work onstatistical modeling for indoor multi-path propagation .The S-V model is based on theobservation that usually multi-path contributions generated by the same pulse arrive atthe receiver grouped into cluster. In this model the gain of the n th ray of k th cluster is acomplex random variable.To better fit the data resulting from UWB measurement campaign, the IEEEgroup proposed a few modifications to S-V model. In particular, a log-normaldistribution was suggested for characterizing the multi-path gain amplitude, and anadditional log-normal variable was introduced for representing the fluctuations of thetotal multipath gain. Finally, the channel coefficient was assumed to be real variablesrather than complex variables. The channel impulse response of the IEEE model canbe express as Where X is a lognormal distributed random variable representing the magnitudeof channel gain. N is the observed number of clusters. K(n) is the received number ofmultipath in the n th cluster. α nk is coefficients of the k th path in the n th cluster. T n is thearrival time of the nth cluster. τ nk is the k th path delay in the n th cluster. Table 1 showsthe parameter required for the setting of IEEE UWB Channel and Table 2 ShowsParameter for environmental characteristics of Underground Mine [6].7Table 1: Parameter required for the setting of IEEE UWB Channel.IEEE UWB ChannelΛ λ Г γ(1/ns) (1/ns)0.0233 2.5 7.1 4.3σ ξ (dB) σ ζ (dB) σ g (dB) Type3.3941 3.3941 3 LOSWhere Λ is the cluster average arrival rate, λ in pulse average arrival rate ,Г ispower delay factor for cluster, γ is power delay factor for pulse within a cluster, σ ξ isstandard deviation of the fluctuation of the channel coefficient for the clusters, σ ζ is

548 Athar Ravish Khan and Sanjay M. Gulhanestandard deviation of the fluctuation of the channel coefficient for pulse within a theclusters, σ g , is standard deviation of the channel amplitude gain.Table 2 Parameter for environmental characteristics of Underground MineModified UWB Channel forUnderground MineΛ λ Г γ(1/ns) (1/ns)0.0667 2.1 36 24σ ξ (dB) σ ζ (dB) σ g (dB) Type3.3941 3.3941 3 LOSThe mean excess delay and RMS delay spread are two important parameters useto characterize the temporal dispersive properties of the multipath channel. The RMSdelay spread parameter determines the frequency selectively of the channel whichdegrades the performance of digital communication systems. The RMS delay spreadlimits the maximum data transmission rate that can be reliably supported by thechannel figure (5) shows the RMS delay of Underground Mine Channel and figure (6)shows the Excess delay of Underground Mine Channel, simulated for 100 number ofchannel. The clustering of the multipath arrivals is evidence observed in figure (3),this validates the multi-paths arriving in clusters of UWB channel measurement data.It is the typical result in the multipath attenuation channel, any more the amplitudefading statistics of the channel impulse response are exponential. It can be seen thatbefore 300ns the amplitude fading lentamente, here the model is able to best fit thechannel propagation law, but after 300ns, the amplitude fading prick up and almostnear zero.Discrete Time Mine Channel Impulse Response10.80.60.4Amplitude G ain0.20-0.2-0.4-0.6-0.8-10 100 200 300 400Time [ns]Figure 3 Discrete time impulse response of Underground Mine Channel.

Performance Evaluation of Time Hopping UWB System 549IEEE UWB Channel Impulse Response10.80.60.4Amplitude Gain0.20-0.2-0.4-0.6-0.8-10 100 200 300 400Time [ns]Figure 4 Discrete time impulse response of IEEE UWB channel55RMS delay (nS)5045403530250 10 20 30 40 50 60 70 80 90 100Channel numberFigure 5 Root Mean Square delay of Underground Mine Channel.70Excess delay (nS)6560555045403530250 10 20 30 40 50 60 70 80 90 100Channel numberFigure 6 Excess delay of Underground Mine Channel.

Performance Evaluation of Time Hopping UWB System 551rt a s t τ nt9where n(t) is AWGN at the receiver input. Equation (8) can be rewritten for IRtransmission on the basis of statistical channel model discussed equation(7)rt X E a a p t jT φ τ nt10Where E TX Transmitted energy per pulse ,a j amplitude of j th transmitted pulse T s isaverage pulse repetition time, φ j is time dithering .Simulation ResultsFigure 8 is the curve of bit error rate (BER) with signal noise ratio (SNR) of the abovesystem for IEEE UWB Channel and Modified Underground Mine channelenvironment.10 0 E b/N 0IEEE ChannelMine Channel10 -1P r e10 -210 -310 -40 2 4 6 8 10 12 14 16 18 20Figure 8 BER performance in IEEE channel Vs Underground Mine ChannelFigure 9 and figure 10 is the curve of bit error rate (BER) with signal noise ratio(SNR) which evaluate the performance of RAKE receiver for different RAKE fingerand different value of repeat bits in the transmission coder respectively for modifiedUnderground Mine channel environment.

552 Athar Ravish Khan and Sanjay M. Gulhaneyg10 0 E b/N 0Srake(10-Branches)Srake(8-Branches)Srake(5-Branches)Srake(3-Branches)10 -1Pr e10 -210 -310 -40 2 4 6 8 10 12 14 16 18 20Figure 9: BER performance in Underground Mine Channel for different RAKEfinger10 0 10 -1E b/N 0Ns=50Ns=40Ns=30Ns=20P r e10 -210 -310 -40 2 4 6 8 10 12 14 16 18 20Figure 10: BER performance in Underground Mine Channel for different repetitioncoderConclusionIn this paper, the propagation of the UWB signal in Underground Mine is analyzed.The performance of a RAKE receiver for 2PPM-TH- UWB system was analyzed inUnderground Mine channel model and IEEE UWB channel based on an extensive setof indoor channel measurements. Simulation results and analysis show that theunderground wireless communication system of UWB based on TH-PPM can

Performance Evaluation of Time Hopping UWB System 553effectively with-stand multipath fading and has the advantages of low bit-error rate.Research is continuing into developing effective RAKE architectures to combinelarge numbers of multipath components with low complexity.AcknowledgmentThe authors would like to thank firstly, our GOD, and all friends who gave us anyhelp related to this work. Finally, the most thank is to our families and to our countryINDIA which born us.References[1] SUN Yanjing, PENG Li, LIU Xue “Wireless Channel Model of UWB forUnderground Tunnels in Coal Mine” IEEE 2009 978-1-4244-3693[2] A Saleh, R Valenzuela., “A Statistical Model for Indoor MultipathPropagation,” IEEE JSAC, 1987, vol.5, pp. 128-137.[3] Mathieu Boutin, Ahmed Benzakour, Charles L. Despins, “Radio WaveCharacterization and Modeling in Underground Mine Tunnels” IEEETransactions On Antennas And Propagation, pp-540-549 VOL. 56, NO. 2,February 2008[4] Rajeswaran A, Somayazulu V S, Foerster J R, “Rake performance for a pulsebased UWB system in a realistic UWB indoor channel,”ICC’03[C]. 2003,pp.2879-2883.[5] Abdellah Chehri, Paul Fortier, Pierre-Martin Tardif, “An Investigation ofUWB-Based Wireless Networks in Industrial Automation” IJCSNSInternational Journal of Computer Science and Network Security, VOL.8 No.2,February 2008[6] Yanjing Sun, Beibei Zhang “System Model of Underground UWB Based onMB-OFDM” Int. J. Communications, Network and System Sciences, 2011, 4,59-64[7] M.-G. Di Benedetto, G. Gianloca,“Understanding ultra wideband radiofundamentals”, Pearson Education LPE 2008 ISBN 978-81-317-2279-4[8] Wei Li, T. Aaron Gulliver and Hao Zhang, “Performance of Ultra-WidebandTransmission with Pulse Position Amplitude Modulation and RAKEReception” IEEE- ©2005 0-7803-9068[9] Ph. Mariage, M. Lienard, and P. Degauque, “Theoretic a1 and ExperimentalApproach of the Propagation of High Frequency Waves in Road Tunnels”IEEE Transactions On Antennas And Propagation, Vol. 42, No. 1 , January1994[10] A. Nezampour, M. Nasiri-Kenari and M.G. Shayesteh “Internally coded TH–UWB–CDMA system and its performance evaluation” IET Commun., 2007, 1,(2), pp. 225–232