World Academy of Science, Engineering and Technology 62 2012                     Design and Performance Evaluation        ...
World Academy of Science, Engineering and Technology 62 2012                                                              ...
World Academy of Science, Engineering and Technology 62 2012 C. Spectrum (Bandwidth) Requirements.                        ...
World Academy of Science, Engineering and Technology 62 2012                                                              ...
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Design and Performance Evaluation Of Modulation Techniques Suitable For ADSL modem


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Design and Performance Evaluation Of Modulation Techniques Suitable For ADSL modem

  1. 1. World Academy of Science, Engineering and Technology 62 2012 Design and Performance Evaluation Of Modulation Techniques Suitable For ADSL modem. Mr. Ashraf S M Touba Prof. Ivan Bagaric technologies. Each of the DSL technologies mixesAbstract — One of the significant problems in ADSL modem different. Asymmetrical digital subscriber line (ADSL) is adesign is the demand for bandwidth for high speed data communication system that transfers both analog andcommunications and interactive media transmission which digital information on a copper wire pair. The analoghas been growing explosively. The objective of this paper , is information can be a standard POTS or ISDN signal. Theto achieve the high bit rate in demand of bandwidth which maximum downstream digital transmission rate (data ratedepends on design and evaluating the Modulation /Demodulation – Regardless of the including any types of to the end user) can vary from 1.5 Mbps to 9 Mbpscoding techniques and Filters - and simulated reaching to the downstream and the maximum upstream digitalappropriated technique which will has been considered to transmission rate (from the customer to the network) variesdesign requirements of ADSL Up/Down stream specifications from 16 kbps to approximately 800 kbps. The datausing Matlab coding . transmission rate varies depending on distance, line Keywords — ADSL ,Up /Down stream, Mathlab, Bit rate. distortion and settings from the ADSL service provider. I. INTRODUCTION II. ADSL TECHNOLOGY.Digital subscriber line is the transmission of digital A. What does meaning of ADSL Modem?information, usually on a copper wire pair. Although the The idea behind the Asymmetrically that In ADSL, thetransmitted information is in digital form, the transmission data throughput in the upstream direction, (the direction tomedium is usually an analog carrier signal (or the the service provider) is lower, hence the designationcombination of many an analogue carrier signals) that is of asymmetric service, Figure 1 shown the means ofmodulated by the digital information signal. Digital Asymmetrically ;the digital data sent over analogy mediasubscriber line (DSL) was first used in the 1960s to that enables faster data transmission over copper telephonydescribe the T-1 circuits that were extended to the line than a conventional voice band modem can provide. Itcustomer premises. Later the same term was used to does this by utilizing frequencies that are not used by adescribe ISDN basic rate interface (BRI) (2B+D, 144 voice telephone call that will being the subscriber lineKbps) and primary rates interface (PRI) (23B+D, 1.544 same to on the lines. In general; the speed factors dependMbps). There are several different digital subscriber line type and thickness of copper wire ,situation of carryingtechnologies. Each of these DSL technologies usually has a wire (external noises and interfaces)and depends on theprefix to indicate the specific variant of DSL technology. distance from the local exchange , maximum range ofHence, the “x” in xDSL indicates that there are many ADSL without a repeater is 5.5Km,as a distance decreasesforms of xDSL technology. DSL transmission allows high- toward the telephone company office the data ratespeed data transmission over existing twisted pairtelephone wires. This has the potential providing high- increases .speed data services without the burden of installing new In July 2002, the ITU completed G.992.3 and G.992.4,transmission lines (e.g., for Internet access). DSL service two new standards for ADSL technology collectivelydramatically evolved in the mid 1990s due to the called “ADSL2”. In January 2003, as users of ADSLavailability of new modulation technology and low cost chipsets based on the first generation of ADSL standardselectronic circuits that can do advanced signal processing passed the 30-million mark, G.992.5 officially joined the(e.g., echo canceling and multiple channel demodulation). ADSL2 family as ADSL2plus, (or ADSL2+ as it isThis has increased the data transmission capability of commonly known).Several other features andtwisted pair copper wire to over 50 Mbps. improvements were also incorporated in the form of newThe data transmission capability of a DSL system varies Annexes. Carriers, service providers,[6] and subscribersbased on the distance of the cable, type of cable used, and have played a key role in the completion of ADSL2,modulation technology. There are several different DSL having provided valuable feedback from the field that the ITU in turn incorporated into the standards in the form ofAshraf Touba PhD student, University of Singidunum ,Belgrade ,Serbia new features and performance improvements.(E-mail: Bagaric ,Full professor ,University of Singidunum ,Belgrade,Serbia(E-mail: 1956
  2. 2. World Academy of Science, Engineering and Technology 62 2012 Fig.2. Constellation diagram for MPSK (Illustrated for M=8).Fig.1. The Downstream/Up stream of ADSL Modem Each message point is spaced (2π/M) distance from its adjacent message point. The receiver block diagram of B. The Modulation schemes are used in ADSL MPSK is given below: Modem.Digital modulation schemes are classified into two largecategories: constant envelope and non-constant envelope.Under constant envelope class, there are three subclasses:FSK, PSK, and CPM. Under non-constant envelope class,there are three subclasses: ASK, QAM, and other non-constant envelope modulations. In M-ary phase shiftkeying systems, the phase of the carrier is allowed to take Fig.3. Receiver Block diagram for MPSK.on one of the (M) possible values; Since the in-phase and quadrature components of M-ary (1) QAM are independent, the Pc(1-Pe)2 where the Pe is the probability of error of either component. The constellationThus (M) possible signals that would be transmitted during for the in-phase (or) quadrature component has geometryeach has signaling interval of similar to (PAM) with corresponding number of amplitude (T) is: levels. Consider a quaternary signaling scheme in which the (2) received signal is defined by x(t) =ai+w(t);0≤ t ≤T Where the amplitude ai = ± a/2 ± 3a/2 and w(t)is the sample function of a white Gaussian noise process of zero meanE =energy per symbol and usually M is taken as power of 2 and power spectral density N0/2. The signal space,i.e. M =2k . representing the signal component of x(t) has twoRecognizing that each Sk(t) may be written in terms of a characteristic features. It is one-dimensional in that thesinusoid and co-sinusoid , which are orthogonal and then signal component is scaled of time function;suitably scaling to fulfill the conditions of (3) (8)The appropriate form for the orthogonal waveformsφi(t) and φj(t) is given by : There are four message points, (9) (4) (5) The signal space diagram is as depicted below:The coordinates of the message points can be calculated by (6) (7)A constellation diagram is a representation of a signalmodulated by a digital modulation scheme. It displays thesignal as a two-dimensional scatter diagram in the complex Fig.4 Signal Space diagram for M -ary QAM.plane at symbol sampling instants thus will given as : 1957
  3. 3. World Academy of Science, Engineering and Technology 62 2012 C. Spectrum (Bandwidth) Requirements. meet the (ITU G.992.4) as standard for splitter lessThe signal bandwidth for the communications channel ADSL2 with data rate mandatory capability reduced toneeded depends on the symbol rate, not on the bit rate. 1.536 Mb/s downstream , 512Kb/s Up stream. ThatAn example of how symbol rate influences spectrum modem considered the 512-QAM Modulation in Upstreamrequirements can be seen in eight-state Phase Shift Keying and 1024-QAM downstream in AWGN channel without(8PSK). It is a variation of PSK. The phase of the signal any types of filters, Error correction code andcan take any of eight values at any symbol time. Since 23= decode…etc.8, there are three bits per symbol. This means the symbolrate is one third of the bit rate. This is relatively easy todecode. Bandwidth efficiency describes how efficiently theallocated bandwidth is utilized or the ability of amodulation scheme to accommodate data, within a limitedbandwidth, as shown in ( table 1) below the theoreticalbandwidth efficiency limits for the main modulation types;as we have more number of bits per symbol means themodulation will increasing in the order and the followingbandwidth efficiency of power spectrum density has Fig.6. Modem design of M-QAMreduced powerfully as shown in (Figure 5) Table 1. Bandwidth efficiency corresponding to the symbol rate . Modulation Theoretical Bandwidth Format Efficiency limits BPSK 1 bit/sec/Hz QPSK 2 bit/sec/Hz 8 PSK 3 bit/sec/Hz 16 PSK 4 bit/sec/Hz 32 PSK 5 bit/sec/Hz Fig.7(a) Time domain waveforms of 16QAMFig.5 Power Spectrum of Selected M-ary ModulationSchemes. III. DESIGN AND IMPLEMENTATION Clearly have been identified that to producing an ADSLmodem which has a efficient bandwidth meeting a higherbit data rate should design the proper digital modulation.In this paper that examined each type of M-ray Mod/Dempractically .The different types of M-ray Modem start byBPSK to 256 QAM ; that has been designed separately interms of Modem design as shown in (Figure .6),Time/Frequency domain waveforms as shown in Fig.7(b)Frequency domain waveforms of(Figure.7), Bit error rate (BER) in theoretically and 16QAMpractically as shown in (Figure .8) the bit error rate for M-QAM starting with BPSK to 1024 QAM ; theoretical andsimulation. The proper modem which has been chosen to 1958
  4. 4. World Academy of Science, Engineering and Technology 62 2012 The modem has been designed and the parameters calculated to introducing the simulated frequency spectrum which measured from null to null approach as upstream part of 512 QAM ,Downstream of 1024QAM The practical frequency spectrum shown in (Figure .10) is clearly demonstrated the availability of high order modulation as feature to have high data rate in amount of channel bandwidth. IV. CONCLUSION Fig.8 The theoretical and practical BER of M-QAM The needs of the broadband come to involves of digital The consideration parameters and result of simulation of modulation techniques, which most have been worked out specifically ADSL2 Modem shown in (table.2). the range to get acquainted which best modem could be considered of down/up streams will have bandwidth channels (960 to leads to have the appropriate bandwidth efficiency as kHz , 116 kHz) respectively; ITU G.992.4 ADSL2 increasing of order of M-ary. The aim of these paper to Modem theoretically spectrum shown in (Figure.9). introduce the main process of efficient design that could uses as base which easily implemented with any filters Table .2 the design parameters and results. ,error correction parts to enhancing data rate and less complexity .ADSL Data Channel Ratio of M-rayParameters Rate(Rb) Bandwidth(B (2Rb/2) technique REFERENCES ) [1] T. Starr, J. M. Cioffi, and P. Silverman,Upstream 520Kb/s 116kHz 9 512QAM Understanding Digital Subscriber Line Technology, Prentice-Hall PTR, USA, 1999.Downstream [2] J. M. Cioffi, “A multicarrier primer”, White Paper, 4.5Mbps 960kHz 10 1024QAM Amati Communications Corporation and Stanford University, Nov 1999. [3] Nextep Broadband Networks Group, “XDSL modulation technique ,May 2001. [4] R. Laroia, S. Trenter, and N. Farvardin, “A Simple and Effective Preceding Scheme for Noise Whitening on Inter symbol Interference. [5] IEEE Spectrum , Always on - Living in a networked World, Vol 38, No. 1, January 2001. [6] The Jamaica Gleaner, Centennial to invest $millions in Jamaica June 26, 2001. [7] Cable and Wireless Jamaica, Reference Interconnect Fig .9. The theoretical frequency spectrum considered Offer (RIO). [8] Jianhau Lu, K. B. Letaif, Justin C-I Chuang, Ming L. Liou, “MPSK and M-QAM BER Computation Using Signal-Space Concepts”, IEEE Trans. Com., Vol. 47, No. 2 (1999). [9] ITU-T g.992.2 Standard, “Digital Transmission System for ADSL Transmission on Metallic Local Loops with Provisioning to Facilitate Installation and Operation in Conjunction with Other Services.” [10] O. Sallent, J. Perez-Romero, R. Agusti, and F. Casadevall, RRM strategies for 3G W-CDMA,” IEEE Commun.Mag. vol. 41,no. 2, pp. 100–106, 2003. [11] Karim JABER, Ahmed FAKHFAKH and Nouri MASMOUDI” VHDL-AMS Behavioral Modeling and Simulation of M-QAM transceiver system” IEEE Fig .10 ITU G.992.4 ADSL2, simulated spectrum Conference March 25-29, 2007 TUNISIA. 1959