Broad band theologies

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Broad band theologies


ADSL: - Asymmetric Digital Subscriber Line.

HDSL: - High bit rate Digital Subscriber Line.

VDSL: - very high bit-rate DSL

DSL: - Symmetric Digital Subscriber Line.

1. Introduction.

Broad band theologies are now available all over the word. Because of the technological development is giving more opportunities to improve communication development such as xDSL technologies. Implementation of Digital Subscriber Line technology originally was part of the Integrated Services Digital Network (ISDN) specification and it was published by published in 1984 CCITT and ITU.xDSL represents individual varieties of DSL technology such as ADSL,VDSL,RADSL…. etc.

Discreet multi tone DMT (Discrete Multi Tone) is a method of converting digital data into frequencies or tones that can be carried over telephone wire. [2] This method is more efficiency method than Carrier less amplitude and phase (CAP) modulation method. Because it has Higher Performance, Immunity to noise and line conditions, Simplicity in design and implementation, Flexibility etc. the sub carries are not equal in all xDSL technologies because depending on the speed the subcarriers are getting vary. But one DSL technology has fixed sub carries.

“Quadrature Amplitude Modulation (QAM) is a complex name for a simple technique”[6] that term is gives the real meaning of this modulation technique. Because Quadrature amplitude modulation is the combination of amplitude modulation and phase shift keying. It map the signal according to the constellation diagram.QAM has different levels such as 4, 8, 16, 32 ….etc.

IFFT and FFT are doing a great job in this simulation. That is converting the time domain signal in to frequency domain signals after that modulation the signal. In piratical situation the modulation is more important because our computers use digital data a MODEM (MOdulator-DEModulator) is needed to code and decode between digital and analogue signals before go the copper wire (transmission line). The Modulation is method of converting digital data into analogue signals which can be carried over the copper wire.

In this project manly focus on build a DMT transmitter and receiver using mat lab slimulink. After analyzing the bit Error rate by changing the parameters of the channel. If we add more noise to sub carries the bit error rate also getting increase. In this project mainly analyzed noise with subcarriers and the different level of QAM performances.


In XDSL technologies use different number of subcarriers to accomplish different purposes. Because there are different types of DSL technologies has different number of subcarriers. Those subcarriers need to modulate using different modulation methods. The modulation methods performance will analyze with SNR (signal to noise ratio) in this project.

DMT is a multi carrier modulation method that divides the transmission bandwidth in to a high number of narrow sub channels or tones. so need to analyze number of carries tones, etc
Rather than Transmitting data in single carrier in high data rate better to send data in different carrier in different rates. Because of that reason need to analyze data rate.
There are different QAM forms, the rectangular QAM used in conventional DMT. Analyze new cancellation form in rectangular QAM.
Design a DMT transmitter using math lab. Add different value of noise and analyze the performance of the QAM forms using the parameter signal to noise ratio.
Design a DMT receiver using math lab and analyze the Bit Error Rate (BER).

What is XDSL ?

The “x” in xDSL stands for the various kinds of digital subscriber line technologies such as ADSL, R-ADSL, HDSL, SDSL, and VDSL. These technologies most used to carry multimedia information through the internet in all over the world. Residential users and business users are major growing factor in this technology because of the differentiation of the technology.

Development History

xDSL was designed initially to provide video on- demand and interactive TV applications over twisted-pair wires because those days the cane TV customers are increased rapidly. The xDSL technologies and servicers were getting improved because of the fiber optic development arise.

Another boost came with the passage of the Telecommunications Reform Act of 1996, which allows local phone companies, long-distance carriers, radio/television broadcasters, cable companies; Internet/online service providers, and telecommunications equipment manufacturers in the United States and United Kingdom to compete in one another's markets.

The important factor is bandwidth on that time. In xDSL, telecommunications companies see a chance to leverage customer demand for faster data access that has resulted from the explosive growth of the Internet and the coming on of IP telephony. xDSL has the potential to transport high-speed data access and much more.

In 1998 introduced itself to the business and residential community offering high speed and affordable DSL service.Being one of the premier DSL providers in Southern California, has a tremendous amount of experience in dealing with Digital Subscribers Lines.xDSL. Net offers DSL service to anywhere GTE is located in the area of Southern California.If a Digital Subscriber Line is what you're looking for, has got the option that is right for your business or private use needs.

How XDSL work

There is mainly having two limitations in XDSL technologies. There are distance limitation between DSLAM and the customer premises and other one is line impairment of the channel. XDSL technologies are very popular because it is very cheap and installation is very easy because the gives through the copper wire. In developed or developing country every house has telephone line it means every house have a copper with connected to the exchange. If the telephone service provider need to provide XDSL servicers to the customers only need to do fixed a DSLAM to the exchange. From the DSLMP the data rate (downstream and upstream),XDSL technology ,signal to noise ratio …etc can be con.

XDSL with the lower data transmission rate like 1.5 Mbps is being used in the residences because are using internet for only browe and to download small files. The high data transmission XDSL provides transmission rate up to 50 Mbps and is being used in the business sector and the VDSL because they need redounded good internet connection to do their work properly. There are some other types of the XDSL, which includes VODSL (Voice DSL) and VDSL. Voice traffic has high priority over the data traffic to ensure the quality of service and the data transmission rate up to 1.5 Mbps but there is distance limitation up 3Km. Otherwise VDSL (Very High Bit Rate DSL) supports 13 Mbps to 55 Mbps over the twisted pair cable.





ADSL lite

Up to 1Mbps downstream

Up to 512Kbps upstream

18000 feet

Internet /intranet access. Web browsing. Ip technology. Video technology.


1.5-8Mbps downstream up to 1.544Mbps /upstream.

18,000 feet (12,000 feet for fastest speeds)

Internet/intranet access. Video on demand. Remote LAN access. VPNs, VoIP.


Up to 144 Kbps full duplex

18,000 feet (additional equipment can extend the distance)

Internet/intranet access, Web browsing, IP telephony, video telephony.


1.544 Mbps full duplex (T1)

2.048 Mbps full duplex (E1)

(uses 1 wire pair)

10,000 feet

Local, repeater T1/E1 trunk replacement, collaborative computing, LAN interconnect.


1.544 Mbps full duplex (T1)

2.048 Mbps full duplex (E1)

(uses 2-3 wire pairs)

12,000-15,000 feet

Local, repeatered T1/E1 trunk replacement, PBX interconnection Frame Relay traffic aggregator LAN interconnect.


13-52 Mbps downstream

1.5-2.3 Mbps upstream (up to 34 Mbps if symmetric)

1,000-4,500 feet (depending on speed)

Multimedia Internet access

high-definition television program delivery.

table 1. Technology and Application Comparison [1]

Background of ADSL (Asymmetric Digital Subscriber Line.)

What is ADSL

ADSL is now very popular internet access technology all over the world. That technology is more popular because of the telephone line. In every country have telephone (PSTN) line. That connects to the local exchange. In the local exchange there is a different path to split the signal in to data and the voice. In the customer premises need to split the signal voice and the data to access the internet. In ADSL the letter of ‘A' means asymmetric, which mean the Download speed, is greater than Upload speed. Normally download speed is range from 512 kbs to 2000 kbs and the upload speed for each product is 256kbs. That method is more benefit for the customers because the most of the customer are using the internet for the download thing than uploading. The internet services are mostly uses for communication purpose and the education purpose.

The most companies are using still using fax machines that is not effecting for that technology still they can sent the fax. In this technology have a big advantage that is the servicers can implement very chap and quick.

TO give ADSL servicers to customers need a DSLAM. That is in the local exchange. Depending on the product DSLAM multiplexers connect DSL lines with some combination of asynchronous transfer mode, frame relay or IP networks. From the DSLAM the signal to noise ratio, upstream bit rate, downstream bitrates.Etc like various kind of thing can change.
Initialisation and Synchronisation

There are mainly four stages to Synchronize between your router (modem) and the DSLAM. The four processes are handshake, transceiver training, channel analysis and exchange,

Handshake -This process is a very important process because in this process to synchronize with both end there is small mechanism used Basically saying 'hello can you hear me' and giving details about which technology are using and which protocols are going to use. Depending on the technology The DSLAM will define which sub-channels may be used because certain tones are deliberately not used.

Transceiver Training - there are lots of parameters to estimate before communication with each other those are Preliminary estimation of loop attenuation, reporting of upstream power levels, test data stream, power level adjustment. in order to reduce the risk of cross-talk Some sub-channels may have masks applied which limit the maximum power level at a particular frequency

Channel Analysis - in this process modem will respond and analysed the sub channels condition. Power levels reporting and SNR and attenuation calculating are the main analytical process. Depending line condition determines the amount of data bits that can be carried in each channel.

Exchange - Allocating total number of bits can carried across all the sub channels. Synchronization speed also setting up in this process. The DSLAM will check that the modem can receive data or not because the modem and DSLAM communication process need to compatible all the lie condition parameters. The dslam will check that the modem can receive data at that
speed ok and the router should reply and synchronisation is attained. If not the initialisation process happen successfully sync process repeated until sync is achieved.[2]


In November 2001 VDSL deployement over a existing PSTN copper wire approved by ITUT. Because it is a improvement of a DSL technology.VDSL is capable of supporting high band width such as high definition television because VDSL providing faster transmission rate up to 52Mbps and 16Mbps Upstream over a twisted paire copper wires.VDSL providing Voice over Ip servicers and internet acess over a sigle connection.VDSL oprate 400 feet (1200m) over the copper wire(shows in 7)

In VDSL DMT divides in to 247 separate Channels. Each channel have a 4KHz wide bandwidth.

Each channel is monitored and, if the quality is too impaired, the signal is shifted to another channel. This system constantly shifts signals, searching for the best channels for transmission and reception. In addition, some of the lower channels (those starting at about 8 KHz) are used as bidirectional channels, for both upstream and downstream information. Monitoring and sorting out the information on the bidirectional channels, and keeping up with the quality of all 247 channels, makes DMT more complex to implement than other carrier technologies, but also gives it more flexibility on lines of differing quality.


xDSL Modulation Techniques

Quadrature Amplitude Modulation (QAM)

Hardware Implementation

Quadrature Amplitude Modulation (QAM) is a complex name for a simple technique. In the simplest of terms, Quadrature amplitude modulation is the combination of amplitude modulation and phase shift keying. More technically, quadrature amplitude modulation is a system of modulation in which data is transferred by modulating the amplitude of two separate carrier waves.[6]

Quadrature amplitude modulation (QAM) needs to change the phase and amplitude of a carrier sine wave. To generate and mix two sine waves that are 90 degrees out of phase with one another is the easiest ways to implement QAM with hardware. Adjusting only the amplitude of either signal can affect the amplitude and phase of the resulting mixed signal.

These two carrier waves correspond to the in-phase (I) and quadrature-phase (Q) components of our signal. Separately each of these signals can be represented as:

I = A cos(φ) and Q = A sin(φ).

I and Q components are represented as cosine and sine because the two signals are 90 degrees out of phase with one another. Using the in-phase (I) and quadrature-phase (Q) identities apply for the following trigonometric identity.

cos(α + β) = cos(α)cos(β) - sin(α)sin(β),

rewrite a carrier wave A cos(2πfct + φ) as

A cos(2πfct + φ) = I cos(2πfct) - Q sin(2πfct).

As the equation above illustrates, the resulting identity is a periodic signal whose phase can be adjusted by changing the amplitude of I and Q. Thus, it is possible to perform digital modulation on a carrier signal by adjusting the amplitude of the two mixed signals.

1 shows a block diagram of the hardware required to generate the intermediate frequency (IF) signal. The “Quadrature Modulator” block shows how the I and Q signals are mixed with the local oscillator (LO) signal before being mixed together. The two LOs are exactly 90 degrees out of phase with one another. [5]

QAM involves sending digital information by periodically adjusting the phase and amplitude of a sinusoidal electromagnetic wave. 4-QAM uses four combinations of phase and amplitude. Each combination is assigned a 2-bit digital pattern. For example, suppose you want to generate the bit stream (1,0,0,1,1,1,0,1). Because each symbol has a unique 2-bit digital pattern, these bits are group in two's like so that they can be mapped to the corresponding symbols.[5] The original bit stream grouped into the four symbols (10, 01, 11, and 01).

In the above , 4-QAM consists of four unique combinations of phase and amplitude. These combinations—called symbols—are shown as the white dots on the constellation plot in the . The red lines stand for the phase and amplitude transitions from one symbol to another. Labelled (binary) on the constellation plot is the digital bit pattern that each symbol represents. Thus, by generating unique combinations of phase and amplitude digital bit pattern can be sent over a carrier signal.

What is DMT?

DMT (Discrete Multi Tone) is a technique of converting digital data into tones or frequencies that can be carried over telephone wire. In other words available bandwidth is split into large number of sub channels. The meaning of ‘Discreet' from the mathematical meaning of that term is distinct or separate. The meaning of the ‘Multi-tone' came because it splits the available frequencies into a defined number of smaller sub-channels or tones.

ADSL1 and ADSL2 :- 256 sub-channels

ADSL 2+ :- 512 sub-channels

DMT is a modulation method for Frequency Division Multiplexing (FDM) which is when multiple signals are combined and carried over the same medium. If DMT had applied FDM only for the higher sub-channels such as downstream.

How DMT works

The modulation technique that has become stand for ADSL is called the discreet multitone technique (DMT) which combines the QAM and FDM. There is Norway that the bandwidth of a system is divided. Each system can decide on its bandwidth division .typically, an available bandwidth of 1.104 MHz is divided I to 256 channels. Each channel uses a bandwidth of 4.312 KHz, as shown in . [3]

The bandwidth can be divided in to below categories. Those are shown in following diagram in frequency domain.[7] 4

Voice: - channel 0 is used for voice communication.

Idle: - channel 1 to 5 are not using because it is using for provide a gap between voice and data communication.

Upstream and data control: - channel 6 to 30 there is 25 channels those channels are use for upstream data transfer control such as One channel use for control and other 24 channels

Total bandwidth is 1.104 MHz and each carrier bin has bandwidth of 4.3125 kHz.

Total ADSL bandwidth : 1.104 × 106

Total number of tones : 1.104 ÷ 256

Single tone bandwidth : 4.3125 KHz used for data transfer.

For one channel bandwidth = 4.312 kHz

Number of data channel =24

Total channel bandwidth in upstream = 24 × 4.312 kHz

= 103.488 kHz

Downstream and data control:- channel 31 to 255 there is 225 channels those channels are use for upstream data transfer control such as One channel use for control and other 224 channels used for data transfer.

For one channel bandwidth = 4.312 kHz

Number of data channel = 224

Total channel bandwidth in upstream = 224 × 4.312 kHz

= 965.888 kHz

0-4 kHz: - voice.

4-25 kHz: - unused guard band.

25-138 kHz: - 25 upstream bin (7-31).

138-1107 kHz:- 224 downstream bins (33-255)

Common tones which are not use in total the DSL bandwidth.

In the total channel bandwidth the some tones are not used to transmitter the data because it used for important reasons mainly for guard band. Those are given below certain sub carrier channels are not used. Some of these are laid down in the g.DMT standard, whilst some others may depend upon the DSLAM/MSAN manufacturer and vary slightly. [2]
Common tones not in use are:-

(Tone 0) DC‘First Tone'.

(Tones 1 to 5) Guard Band. Tone 1 POTs (Plain old telephone service) and Tones 2-5 prevent cross talk between POTs + ADSL.

(Tone 32 - 138 kHz). Guard Band Prevents cross talk between upstream and downstream data.

(Tone 16 - 69kHz ) Upstream Pilot Tone.

(Tone 64 - 276 kHz). Downstream Pilot tone.

(Tone 59 - 254 kHz). Annex_M Stop Band. ADSL2+ Annex_M only.

Nyquist frequency (Final frequency tone)

Useful of DMT for VDSL

Using DMT for VDSL has big advantage because it giving to improve the technology in more efficient way.some of advanteges are given below.

Higher Performance

Immunity to noise and line conditions

v Simplicity in design and implementation

v Flexibility

v Rate adaptation capabilities

Higher Performance

Following shows practical and theory that it can provide higher performance than traditional single carrier modulation.

Upstream and Downstream throughput for DMT and SCM function of distance. DMT has higher performance because it has bit loading based on the water-filling algorithm .uses the Shannon capacity DMT or theory to covert in to channels smaller. There are other additional to reason for higher performance in DMT there are DMT can exploit a higher percentage of the available frequency spectrum during full duplex operation. the second on is DMT can achieve a higher density of bit/sec/Hz, which translate into higher bandwidth efficiency because of the higher spectrum utilization.
Immunity to noise and line conditions

Immune to narrow band interference is high in VDSL-DMT system because of the narrowband interference the sub channels are getting corrupt. DMT system will ignore a sub-channel without affecting to the other sub channels. To overcome this problem, use efficient interference cancellation techniques.

DMT has great flexibility to shape the frequency spectrum of the transmitted signal. There are lots of advantages because of the flexibility in spectral compatibility. The main advantage is any frequency band plan can be implemented using the same hardware. The other advantage is that the Upstream Power Back-Off (UPBO) is easier to implement in VDSL-DMT systems.

Mat lab simulink and parameters.

What is IFFT/FFT?

IFFT means inverse fast Fourier transform and FFT means fast Fourier transforms. The FFT is a nearer and faster version of the Discrete Fourier Transform (DFT). The FFT utilizes some clever algorithms to do the same thing as the DTF, but in much less time. Those are the main benefit of FFT and IFFT. [3]

MATLAB function of IFFT/FFT

Mat lab's FFT function is an effective tool for computing the discrete Fourier transform of a signal. The DFT is extremely important in the area of frequency (spectrum) analysis because it transforms the discreet signal in the time domain signal into discrete frequency domain.

The signal would not be able to compute the Fourier transform with a microprocessor or DSP based system without a discrete-time to discrete-frequency transform because it is the speed and discrete nature of the FFT that allows us to analyze a signal's spectrum with Mat lab or in real-time [3].

FFT algorithm

The Fast Fourier Transform have a computational algorithm apply to the Discreet Fourier Transform to an array of 2^N samples. Convert in 2^N samples allow transform time domain discreet signal to frequency domain signal. This algorithm has a complexity of O(N*log2(N)). the data needs to be prepared by an operation called bit-reversal because of that reson the complexity of the algorithm is a little higher.

The FFT is calculated in two steps. The first step is applying the bit reverse order math to transforms the original data array into a bit-reverse order array. This makes the mathematical calculations of the second step much easier. The second step is processes the FFT in N*log2 (N) operations from the Danielson-Lanzcos algorithm. In array of complex data the size of array must be in an N^2 order such as 2, 4, 8, 16, 32, 64, etc. In case the sample doesn't match that size then put it in an array with the next 2^N size and fill the remaining spaces with 0s.[4]

Bernulli Binary Generator

Bernoulli distribution is use to generate random binary numbers. The Bernoulli distribution with parameter p produces zero with possibility p and one with possibility 1-p. The Bernoulli distribution has variance p (1-p) and mean value 1-p. The Probability of a zero parameter specifies probability any real number between zero and one. Bernoulli binary generator is shows followers.

This block generate square wave pulses in FFT (Fast Fourier Transformation)

FFT along the vector dimension is Compute for sampled-based vector inputs. Compute the FFT along each Colum for all other inputs. When the “Inherit length from input dimensions”

Check box is selected; the input must have a power of 2 widths.

Input and Output Characteristics.

Inputs can be real or complex value and the value must be in linear order.

The dimension along which the block computes the DFT.

The output port rate must equal the input port rate.

The Frame Conversion block main function is Set sampling mode of the output signal. It can be either Frame-based or Sample-based. The values are changing using Sampling mode of output signal parameter in the frame conversion block.


The Display block shows the value of its input on its icon. The display is increase according to the valued to be display. In the above diagram shows the bit error rate is 0.1271 and error of bit is 1678 and the total number of transmitted bit is 1.32 ×104.

Error Rate Calculation.

The Error Rate Calculation block is used to compare input data from a transmitter side with input data from a receiver side. Bit error rate is the number of error bits dividing by total number of transmitted bit. In this block calculates the error rate as a running statistic, by dividing the total number of unequal pairs of data elements by the total number of input data elements from one source. This block does not consider the magnitude of the difference between input data elements so this is help to compute either symbol or bit error rate.

Complex to real-image

This block is convert the output in to real or imaginary according to the requirement of the output. for a example if the output is need to convert into complex for this block can be use directly to convert the values in to imaginary format. In this simulation the complex value cannot evaluate in scopes. To convert in to real values use this block. Using these block in the parameter output category need to change real to get the output in to real format before connecting to the scope.

This concatenate block helps to concatenate the signals at its inputs to create an output signal whose elements reside in contiguous locations in memory. This block operates in either vector or multidimensional array concatenation mode, depending on the setting of its Mode parameter. In either case, the block concatenates the inputs from the top to bottom, or left to right, input ports. In the above diagram shows number of inputs can be change according to required input.

Rectangular Qam modulator Base band

The rectangular Qam modulator Base band block modulate using M array quadrature amplitude modulation with a constellation such as M- 2,4,8,16,32…etc on a rectangular lattice. The output is a baseband representation of modulated signal. The rectangular QAM modulator base band block provides the capability to visualize a signal constellation from the block mask. This is very helpful to visualize a signal constellation for specific parameters.

Depending on the required signal level the M-ary number needs to be change. To create 4- Rectangular QAM Modulator the M-ary number has to be change 4 or 22 .in the modem between rectangular modulator to rectangular demodulator the communication type is double. Double should be overloaded for any object when it makes sense to change it in to a double-precision value. The constellation ordering settings should be in the binary. There are three types of settings to change in Normalization method; those are Mn.distance between symbols, average power and peak power. From these settings the mappnig place of the dots (area) will be change. If Mn.distance between symbols is select constellation viewing of the constellation diagram is in 8

Rectangular QAM demodulator Base Band.

In this block demodulate the signal and de mapping part also happening in this section.


The IFFT block computes the inverse fast Fourier transform (IFFT) of each row of a sampled based 1 by p input vector


The buffer block unbuffer an M array N frame based input in to a 1 by -N sampled base output. Then the inputs are unbufferd row wise. Finally the matrix row becomes an independent time sampled in the output. The rate at which produce output generally higher than block that receives input general.

The sample period is the equal at both the input and output, Tso=Tsi. Therefore, the output sample period for an input of frame size Mi and frame period Tfi is Tfi/Mi, which represents a rate Mi times higher than the input frame rate. According to the example above, the block receives inputs only once every three sample periods, but generate an output once every sample period. [8]

In the model below, the block unbuffers a frame-based input with frame size 3 and four-channel. The Initial conditions parameter is set to zero and the tasking mode is set to multitasking because of that reason the first three outputs are become zero vectors. unbuffers a frame-based input with frame size 3 and four-channel


The Scope block can have multiple axes (one per port) and all axes have a common time range with independent y-axes to observe the signal clearly. The Scope block allows you to adjust the amount of time and the range of input values displayed. To place the parameters can move and resize the Scope window and you can modify the Scope's parameter values during the simulation.

Simulation results.




Conclusion and further work

Further work.

There are different types of constellation mapping system in QAM modulation. This applying for conventional DMT and this method is NQAM modulation system. NQAM has low bit error rate with respect to conventional QAM especially in high signal to noise ratio.

If the channel bust noise change (length, power and the position of occurrence in the channel is different.) BER is changing. The NQAM of new constellation method has better performance than rectangular QAM. If the SNR is high NQAM has better performance than rectangular QAM.



[3] University of Rhode Island, 2008, FFT Tutorial, Last Update 28.04.2009 Available at [Access on 21 March 2010].

[4] THE CODE PROJECT, 2005, How to implement the FFT algorithm, Last update 2 feb 2005, Available at: [Accessed on 21 march 2010]

[5] National instruments.2010 Quadrature Amplitude Modulation (QAM) [online] (updated Oct 18, 2008) Available at: [accessed 29 January 2010].

[6] 2010 Quadrature Amplitude Modulation Available at: [accessed 29 January 2010].

[7] Behrouz A.forouzan,2007 ,Data communications and networking,4th edition ,McGraw-Hills Companies,inc.

[8] MATLAB ® simulink, version (R2009b) ,August 12,2009 , signal processing Blockset/blocks/signal manement/Buffers/Unbuffer.

[9] ,June 2005 ,Broad Band Technology overview, CORNING discovering Beyond Imagination. Available at: Accessed on: [1st of April 2010]