The Orthogonal Frequency Division Multiplexing (OFDM). Introduction and explanation of five different types of techniques

Thesis (M.A.), 2019

124 Pages, Grade: 9



Chapter 1
1.1 Overview of OFDM
1.1.1 Modulation and Demodulation of OFDM
1.1.2 Advantage of OFDM System
1.2 History of Channel Estimation and Selection
1.2.1 Pilot Assisted Channel Estimation
1.2.2 Cyclic Prefix
1.3 Overview of PAPR
1.4 Motivation
1.5 Objective of the Research Work
1.6 Methodologies of Research Work
1.6.1 Addition of Cyclic Prefix
1.6.2 Comb type and Block type Pilot Schemes
1.6.4 Clipping based SLM PTS Technique
1.7 Thesis Organization

Chapter 2
2.2 Review on Inter Carrier Interference Reduction in OFDM
2.3 Survey on Peak Cancelation Techniques
2.4 Overview of Power Line Communication System in OFDM
2.5 Review on MIMO OFDM System
2.6 Existing Techniques for BER and SNR Analysis
2.7 Survey of Earlier Schemes for PAPR Reduction
2.8 Summary

Chapter 3
3.1 Problem Statement
3.2 Contribution of the Research Work
3.3 Significant Principle of an OFDM System
3.4 Overview of Power Line Communication
3.4.1 Single Carrier Technology
3.4.2 Spread Spectrum Technique
3.5 FFT and IFFT based Peak Cancellation
3.6 Traditional ICI Reduction Techniques
3.6.1. Frequency Domain Equalization
3.6.2 Time Domain Windowing
3.6.3 Maximum Likelihood Estimation
3.7 Proposed Communication Quality and Capacity Enhancement Techniques
3.7.1 Wavelet OFDM for Power Line Communication
3.7.2 Peak Cancellation of the Digital OFDM Symbol
3.7.3 ICI Reduction Technique for OFDM with Phase Noise over Fading Channels
3.8 Result and Discussion
3.8.1 Evaluation Metrics
3.8.2 Performance Analysis of Wavelet Transform for PLC
3.8.3 Performance Analysis of Peak Cancellation of the OFDM
3.8.4. Performance Analysis of ICI Cancellation of the OFDM
3.9 Summary

Chapter 4
4.1 Problem Statement
4.2 Contribution of the Research Work
4.3 Overview of MIMO OFDM
4.3.1 Channel Estimation
4.4. Wavelet Technique in OFDM
4.5 Existing HAAR DWT Technique in OFDM
4.6 Proposed Techniques for Turbo HAAR DWT
4.6.1 System Model
4.6.2 Turbo Code using MIMO OFDM System
4.6.3 Modulation
4.6.4 Proposed HAAR DWT Technique in the MIMO OFDM System
4.6.5 Orthogonal Space Time Block Code
4.6.6 Turbo Decoder
4.7 Result and Discussion
4.7.1 Evaluation Metrics
4.7.2 System Specification
4.7.3 Performance Analysis of BER vs SNR for Different modulations with AWGN Channel
4.7.4 Performance Analysis of BER vs. SNR for Different Modulations with Rician Channel
4.7.5 Performance Analysis of BER vs. SNR for Different Modulations with combination of AWGN and Rician Channel
4.8 Summary

Chapter 5
5.1 Problem Statement
5.2 Contribution of the Research Work
5.3 Definition of PAPR
5.3.1 Impact of PAPR
5.3.2 Basics for PAPR Reduction Method Selection
5.3.3 PAPR Reduction based on Traditional SLM PTS Technique
5.4 Proposed Clipping SLM PTS Technique
5.4.1 Clipping with SLM PTS technique
5.4.2 Analysis of the Computational Complexity
5.5 Result and Discussion
5.5.1 Experimental Setup
5.5.2 Evaluation Metric
5.5.3 Performance Analysis of Existing and Proposed PAPR Reduction Technique
5.6 Summary

Chapter 6
6.1 Conclusion
6.2 Future Scope


The Orthogonal Frequency Division Multiplexing (OFDM) is an important aspect of multicarrier digital data transmission system where a single data stream is transmitted into a several number of lower rates subcarrier signals. This kind of new standard of transmission of data is the first one to perform with OFDM in data packet based communication system. In wireless communication network, the abstraction of parallel transmission of data symbols is implemented to attain high throughput and effective transmission quality. The OFDM is a method to deal with parallel transmission. In this thesis, there are five different types of the techniques has introduced to strengthen the communication quality and capacity.

The First technique proposed is Power Line Communication (PLC) with Wavelet OFDM. This approach excludes the use of Cyclic Prefix and with this also enhances the performance of the PLC transmission. The proposed PLC model is described for rapid and effective data transmission system over the power line communication channels.

Second proposed technique is clipping of Sub Carrier signals and peak windowing of carrier signals. These techniques were used for minimizing of non linear distortion caused on OFDM signal. As a result of these techniques, some of the data bits will become out of band radiation. This unwanted effect of out of band radiation can be diverted by operating a linear peak cancellation of subcarrier signals technique, wherein a time shifted base signal and scaled reference function signal is detract from the signal which is to be transmitted. So the detracted reference function signal diminishes the peak power of at least one signal constellation.

In third proposed technique is the issue of decreasing the effects of phase noise which take place in OFDM system, when the OFDM system is operated with frequency selective fading channel is forwarded. The proposed technique for combined estimation of channel and Common Phase Error (CPE) is done first and clear out of Inter Carrier Interference (ICI) is done in the second step.

In fourth technique, Turbo coding for encoding process and one dimensional (1D) HAAR Discrete Wavelet Transform (HAAR DWT) was used to Multiple Input Multiple Output OFDM system. This DWT based MIMO OFDM is much suitable for mitigating interferences being Inter Carrier Interference (ICI) which happens with Carrier signals and Inter Symbol Interference (ISI) which take place with Data symbols.

In fifth proposed technique is Clipping based Selective Mapping (SLM) which separates data symbols with PAPR within the threshold value and Partial Transmit Sequence (Clipping SLM PTS) technique is introduced to reduce PAPR in OFDM system.

Chapter 1


Orthogonal Frequency Division Multiplexing (OFDM) is used commonly in digital wireless communication systems because of important features such as high data rate transmission efficiency with the high bandwidth capability and its stability with respect to the multi path delay which take place in digital communication system. An innovative strategy is significantly employed in both wired and wireless communication systems. In Wireless Communication System (WCS), challenging tasks are to maintain more number of Sub Carriers (SCs) and provide the satisfied Quality of Service (QoS) requirements in corresponding to Bit Error Rate (BER) in frequency spectrum. An Orthogonal Frequency Multiplexing Division (OFDM) scheme maximizes the system capacity as well as diversity gain through merging the antenna arrays at the receiver as well as transmitter in time variant along with frequency selective channels. The present research work, the significant objectives are highlighted on reducing the information loss, Peak to Average Power Ratio (PAPR) reduction in both carrier and data signals, Bit Error Rate (BER) which has to be within the threshold and Signal to Noise Ratio (SNR) analysis in Multiple Input Multiple Output OFDM signals.

The following section describes about the modulation and demodulation of OFDM signal.

1.1 Overview of OFDM

The main objective of OFDM system be about to divide maximum rate of data into small data rates, after that transfer of these data in parallel employing numerous orthogonal SCs which is also known as Parallel Transmission. This Parallel Transmission technique involves the time period of data symbol rises therefore reduces the correlative amount of scattering of period affected by delay which happen in multipath spread. An OFDM is possible to use in multiplexing strategy or modulation technique. The approach of utilizing parallel data transmission as well as OFDM was introduced in the mid period of 1860s. U S patent was filled but has issued during January 1970. Currently in conventional parallel data transmission system, entire signal bandwidth or frequency band is separated into number of frequency sub channels which are non overlapping 1.

Every frequency sub channels are modified along with distinct symbol after that the sub channels are frequency multiplexed. By this the overlapping spectral can be reduced, Inter Carrier Interference (ICI) is minimized to better extent, channels are removed from SCs thus leads to ineffective support of the enable spectrum 2.

1.1.1 Modulation and Demodulation of OFDM

The OFDM systems are effectively combined with all SCs and monitored to sustain the orthogonality of the carriers. Hence, OFDM generates an efficient spectrum depending on modulation, demodulation scheme and inputs. Each of the carrier is transmitting the assigned data to the particular destination. After that, in consequence of modulation scheme the required amplitude as well as carrier phase is estimated. The general modulation techniques used in OFDM systems are Binary Phase Shift Keying (BPSK) which is used for wide frequency range, Quadrature Amplitude Modulation (QAM) In which bandwidth is doubled, and etc. The selected amplitude signal is converted into time domain signal, and this is done by using Inverse Fast Fourier Transform (IFFT). IFFT scheme efficiently performs the time domain signal transformations and maintains the orthogonality in carriers 3. The FFT method helps in converting time domain signal to frequency domain signal. This transformation helps to find the equivalent waveform and produces the mean orthogonal sinusoidal components. In time domain signal, the frequency spectrums are indicated by amplitudes and phase of sinusoidal components of the data symbol. The IFFT transformation method does reverse process of FFT. The general structure of modulation and demodulation process of OFDM is presented in the Figure 1.1.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.1 General Structure of Modulation and Demodulation components of OFDM System

The modulation and demodulation process of OFDM system includes several significant components and it’s described in the following sections.

- OFDM Transmitter

The modulation is the variations in signal waves that are transmitted over communication medium or channel to reduce noise effect and it is represented in Figure 1.1. This process involves determining the received data which is demodulated; after receiving the primary data. OFDM transmitter attained through data modulation as well as appropriate modulation strategy. So that averting the Inter Symbol Interference (ISI) and give a Cyclic Prefix (CP) is delivered to constellations or signal.

- Communication Channel

The vision of communication is to support information exchange between devices. A communicator encodes the data as well as then transfers the data through a channel to the different communicator after that they decode the data.

- OFDM Receiver

In modulation strategy, an input data is improved against the modulated symbols and signal is received by the receiver. In this condition, the received data symbols are initially given to the low pass filter as well as CP is eliminated. The Fast Fourier Transform of the data signal is taken then the receiving of signal completed with the process of entering to the serial to parallel converter.

- Inter Symbol Interference (ISI)

ISI is the process in which distortion of a signal consisting of single symbol restricts with subsequent symbols. This phenomenon is undesirable condition as the prior symbols have same influence as noise, therefore creating the signal transmission with lesser amount of reliability. The term ISI is normally affected through propagation or built in non linear frequency reaction of channel affecting sequential symbol leading to distortion.

- Inter Carrier Interference (ICI)

In digital OFDM system, ICI is one of the significant problem to diminish the transmission performance. The ICI causes the loss of orthogonality among the neighboring SCs also, and observe the interferences between the SCs.

- Inverse Fast Fourier Transform (IFFT)

An operation of OFDM in the baseband frequency domain is the modified QPSK data symbol that are served towards the SCs which are orthogonal. An IFFT method is a linear transformation, which is applied in OFDM system with no difficulty since the receiver end consists of FFT and due to attain input data at the receiver end based on frequency domain.

1.1.2 Advantage of OFDM System

Leading advantage of OFDM system is less rate of modulations are least sensitive to multipath in signals. An improved method forward several less rate data streams in parallel transmission than forwarding individual high rate wave 4. A few OFDM system benefits are addressed below,

- Saving of Bandwidth

The SCs overlap with each other due to its orthogonality feature. An overlapping of SCs, utilization of bandwidth decreased significantly as well as minimizes the use of guard bands which place significant role in separation of SCs.

- Easy to implement Modulation and Demodulation

“Data Transmission” is a term which is effectively executed using FFT as well as IFFT without using of group modulators at the source end as well as de modulators at the destination end.

- Easy Equalization

In OFDM system, the wideband communication channel is separated into number of flat fading sub channels. This results in decreasing the difficulties which take place in equalization at the receiver side. By this it is possible to achieve maximum probable decoding with feasible complications.

- Susceptible to Frequency Selective Fading

The capacity of parallel transmission (every SCs signal have limited bandwidth in comparison with total signal bandwidth) OFDM is very sensitive towards frequency selecting channel fading. The OFDM system converts a frequency selective fading channel into number of flat fading sub channels.

1.2 History of Channel Estimation and Selection

In WCS, the estimation of channel is essential to calculate the impact of the communication channel on the signal. The wireless channels include the significant features such as abnormality that happens in frequency domain and time domain 5. The common unreliable channel and partial channel state information’s are identified. The several channels include the uncertain nature i.e, inaccurate channel model, measurement errors, channel variations and etc. Pilot based channel estimation is one of the most common method and it includes different types. These are explained in the further sections.

1.2.1 Pilot Assisted Channel Estimation

Pilot Assisted Channel Estimation (PCE) schemes are significantly depends on the pilot symbols and its transmitted data over a signal. So to track the variations about radio channel statistics, pilot symbols are inserted into particular positions of the transmitted signals. The receiver has aware of the pilot symbol as well as pilot positions hence it’s easy to calculate the depending pilot sequences in channel 6. The pilot arrangements includes different structures. In which three significant structures are,

- Block Type PCE
- Comb Type PCE
- Lattice Type PCE Block Type PCE

This form of PCE is tested with the OFDM system and all SCs are periodically transmitted for effective channel estimation. The particular pilots help to perform time domain interpolation which helps to estimate or calculate the channel along with time as the reference. The graphical representation of Block Type Pilot channel estimation is shown in the Figure.1.2.

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Figure 1.2 Sample of Block Type Pilot channel estimation arrangement

The fast fading channels are sustained with lot of upward to record the channel fluctuation away decreasing the period of pilot symbols. Comb Type PCE

Comb type of pilot channel arrangement is graphically represented in Figure.1.3. Each transmitted symbol includes pilot tones are occasionally repeated with the SCs, which are used to calculate the channel with frequency along with the help of frequency domain interpolation. In comb type, the pilot symbols are placed frequently as coherent bandwidth.

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Figure 1.3 Sample of Comb Type Pilot channel estimation arrangement Lattice Type Pilot Channel Estimation

This type of PCE is preferred with respect to time as well as frequency axes with certain time period. The additional pilot tones are inserted and distributed in one and the other time and frequency axes helps to calculate the time/frequency domain interpolations. The graphical representation of Lattice type PCE is shown in Figure.1.4.

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Figure 1.4 Sample of Lattice Type Pilot channel estimation arrangement

1.2.2 Cyclic Prefix

The frequency selective channel is divided to indicate the frequency flat channel fading and it effectively removes the ISI. However, the fading channel indicates the average errors with delay distortion and loss of orthogonality among SCs in ICI. The CP removes the delay distortion using addition of Guard Interval. The CP based Guard Interval helps to reduce the ICI. After that with the help of FFT, sub channels are separated at receiver end. The power of every sub channel is widely spread to the nearby channel because of multi path fading [7-8]. The CP is known as Guard Interval and it is a repeated expansion of the OFDM symbol. It is included in transmitter at the front of the symbol as well as eliminated at the receiver end. The CP of before demodulation is shown in Figure.1.5.

Figure 1.5 Cyclic Prefix before demodulation

The significant benefits of Cyclic Prefix are mentioned below:

(i) The CP performs like a Guard Interval and it eliminates ISI against the earlier symbol.
(ii) CP attained at the end of the symbols are repeated, hence allowing the linear convolution of multi path channel featured as circular convolution. This is transmitted along with the support of frequency domain based method like FFT.

1.3 Overview of PAPR

OFDM is the kind of MCM technique and it contributes to the maximum efficiency of spectrum, reduced implementation ramification, minimum susceptibility and non linear distortion. With these benefits of OFDM signal, it is used in different applications in both wired and wireless communication. The significant problem of OFDM system is high PAPR. Higher value of PAPR will increase complexity in Analog to Digital Converter power dissipation and also the power dissipation in Digital to Analog converter [9-11].

1.4 Motivation

In WCS, numerous researchers have done work to enhance the spectral efficiency. Since the bandwidth availability is rare and expensive hence, high need for data rate is ensured by maximum counts of sub carriers imturn large bandwidth is required for multimedia applications. The conventional OFDM based techniques are difficult to reach its capabilities. Moreover, still numerous ways are available for minimize PAPR and ICI of that take place between OFDM signals. This research work proposes a method for reduction in PAPR in OFDM signal is the prime objective. The existing clipping as well as filtering method decrease the PAPR but impact of BER is not minimized. This research work proposes three different techniques and they are listed as

(i) Addition of CP to improve the communication capacity and quality.
(ii) Clipping based Selective Mapping and Partial Transmit Sequence technique to acheive PAPR minimization in OFDM Signal.
(iii) Turbo HAAR Discrete Wavelet Transform (DWT) for BER and SNR analysis.

1.5 Objective of the Research Work

Significant objective of this research work is described by the following sections.

- Design and develop an efficient channel estimation and selection technique to reduce the information losses in the channel.
- Effective transmission of data is achieved by the addition of CP and Improve in communication quality as well as capacity.
- A comparison of Comb type channel and Block type Pilot channel Schemes are made for the effective transmission of data. FFT and IFFT algorithms are enhanced to higher radix for the generation of Constellations.
- Design an efficient PAPR reduction technique with orthogonality of OFDM signals are expected to maintain over the communication channel. The reduction of PAPR with the increase in the ADC and DACs computational complexity and decreased efficiency of radio frequency power amplifier. Therefore, an efficient clipping based technique is used for PAPR reduction.

1.6 Methodologies of Research Work

In this section, the novel methods are proposed for reduce the information loss, improve the communication channel capacity and quality. The proposed methods are significantly reduced the PAPR, BER, and SNR in the MIMO OFDM signal. The proposed methodologies are depicted in the consecutive segments.

1.6.1 Addition of Cyclic Prefix

In WCS, the technique of OFDM is significantly used in broadband applications. In OFDM communication system to minimize the High Data Rate (HDR) effect of dispersive channel distortion, the CP is used also, avoids the ISI. An insertion of CP helps to copy the last region of IFFT packet for start of an OFDM data and carrier signal. Modulation of OFDM includes two operations such as IFFT process as well as CP insertion. The data packets are forwarded towards FFT to perform signal demodulation before that CP is removed at OFDM receiver.

The Table 1.1 indicates the CP configuration and variations of 3GPP Long Term Evolution (LTE) within every slot. OFDM symbol includes the specific CP length and 2048 time periods. Also, observes the same kinds of CP structures in WiMAX modulation and demodulation systems.

Table 1.1 Configuration of Cyclic Prefix

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In transmitter data path, IFFT method is performed in reverse order and stored into single buffer successively. The ordered samples are performed and preceding OFDM symbols are trashed at the concurrent period taken from dual port RAM. The CP generated, FFT performance is delayed using Avalon ST backpressure. In OFDM symbols, the CPs are inserted and sent to the digital converter for transmission. In addition, the CP removal process to find the beginning point OFDM signal and provides the data demodulation.

1.6.2 Comb type and Block type Pilot Schemes

The channel estimator requires several prior information of pilot symbols as reference. A fading channel needs the pilot information’s for tracking the continuous channels so that estimate the decision of channel. The information of pilot channel helps to reduce the error propagation. But, updated channels are calculated to transmit the pilot symbols rather than the data found at particular part of OFDM time scale and frequency scale lattice. The updated channel information’s are visible in Pilot Symbol Assisted Modulation (PSAM) of single carrier. The PSAM is to analyze the single carriers and observe the pilot symbols efficiently. An initial Digital Video Broadcast (DVB) standards, pilot information’s are improves the SCs transmission performance. The improved SCs include the pilot information’s transmitted at maximum power than data.

1.6.3 Turbo HAAR Discrete Wavelet Transform Method

The MIMO OFDM is one of the efficient digital communication systems with multi carrier signals, which associates extensive low data rate carrier to make a high rate digital communication system. A large number of orthogonal SCs are spaced firmly to propogate several data through parallel communication medium or channel. A low data rate of every carrier can remove ISI. To design of better communication system, noise power is significantly minimum and the signal transmission performance is maximum. The improvement of the bandwidth efficiency is required hence, the OFDM system is used and efficient channel estimator is applied i.e. capacity of spectrum. However the need of several tranceivers utilizes MIMO to meet the ongoing requirements in the 4G technology. OFDM system faces the ISI in the data uplink and downlink because of data congestion. Traditionally, several techniques are used in OFDM systems to reduce ISI and ICI induced by a communication channel, which limits its spectral efficiency. To overcome this problem, turbo coding for encoding process and one dimensional (1D) HAAR DWT is implemented in the MIMO OFDM system, this DWT based MIMO OFDM is much suitable for mitigating interference hence, Turbo HAAR DWT technique is proposed.

1.6.4 Clipping based SLM PTS Technique

The conventional PAPR reduction techniques have some drawbacks such as less PAPR reduction in maximum transmit power, reduced data rate, boosted BER and increased computation complex. Hence to overcome these issues Clipping based SLM and PTS technique is introduced to minimize PAPR in OFDM system.The clipping selective mapping and partial transmission sequencing technique has selected a limited number of samples in the input signal depending on samples length. That sample has been given to the SLM PTS technique.

1.7 Thesis Organization

In this section, organization of the thesis is branched as six chapters and every chapter is described with respect to specific objective. Every chapter’s detailed descriptions are discussed below.

Chapter 1 describes the introduction of OFDM, Channel Estimation, Modulation and Demodulation of OFDM. Also, defines proposed research techniques, motivation to carry the study and objective of research work.

Chapter 2 explains about exhaustive survey of the different PAPR reduction techniques, ICI reduction techniques, Peak Cancellation approaches, analysis of Bit Error Rate and Signal to Noise Ratio approaches.

Chapter 3 describes the improvements of communication capacity as well as quality in OFDM signal. An addition of CP is used for efficient data transmission in OFDM signal and improve the communication capacity. Also explains the experimental results of existing and proposed methods.

Chapter 4 describes the Turbo Coding for encoding process and one dimensional HAAR DWT is implemented in MIMO OFDM system, MIMO OFDM with DWT is much suitable for mitigating interference. The experimental results are evaluated and measured using efficient evaluation metrics.

Chapter 5 describes the SLM PTS technique based PAPR minimization in MIMO OFDM System. Compare to individual SLM and PTS method, the suggested hybrid SLM PTS method significantly reduce the PAPR.

Chapter 6 describes Conclusion and enhancement of research work in future.

Chapter 2


In communication technology, Orthogonal Frequency Division Multiplexing is most demanding approach because it transmits huge data signals. An OFDM is one of the essential method in Multi Carrier Modulation (MCM) and closely spaced SCs and overlapping spectra therefore, permitting multiple access. The MCM functions based on the principle of propagation of digital data through separating the large stream of data into few small streams of bits. Every stream consists minimum data bit rate as well as utilizing these sub streams to modify the many carrier signals. OFDM system is susceptible even to minute changes in carrier frequency that occur as an offset between carrier frequencies of transmitter and receiver disturbing the orthogonality of subcarrier signals, thereby it produces ICI. The intervention of ICI in the OFDM system causes a significant degradation in the overall performance. In this chapter, different kinds of existing techniques are analyzed such as ICI reduction technique, PC reduction technique, PAPR reduction technique, and etc. An essential objective of this investigation work is to minimize PAPR with computational complexity which happens in OFDM system. All existing techniques of MIMO OFDM and PLC systems are analyzed in the following sections.

2.1 Industrial Survey

An Industrial Survey is done with Bharat Sanchar Nigam Ltd. (BSNL) and Texas instruments to have insight of current trends happening in the digital communication Industry, practical challenges, and recommendations to improvise the performance of the system.

2.1.1 BSNL Regulation for Signal Transmission

Bharat Sanchar Nigam Ltd. (BSNL) was established on 15th of September 2000. The objective of the corporation is to provide business of telecom services and management of network from Departments of Telecom Services (DTS), Central Government of India and Telecom Operations (DTO), the corporation providing services effect from 1st of October 2000. BSNL is one of the principle public sectors in India providing comprehensive range of telecom services.

BSNL Telecom Regulatory Authority of India ... on 6th of December 2013.

Author: G Singhvi

Bench: G.S. Singhvi, B.S. Chauhan, Fakkir Mohamed Kalifulla

Government of India released a Regulatory Act to ensure fast advancement of usage of telecommunications services in the country and adopting the advanced technology, in coinciding with ensuring the concern of the consumers and service providers. The applications have been registered by Bharat Sanchar Nigam Limited (BSNL) to abide by the governance confined by Telecom Regulatory Authority of India. The very purpose of this regulation Act is to identify the technical parameters of the communication system and how to improvise quality, capacity and efficiency without violating some of the threshold values framed for the technical parameters.

Recommendations on regulatory Framework for Internet Telephony, prescribed by Telecom Regulatory Authority of India, New Delhi, 24th of October 2017.

The Article released by Telecom Regulatory Authority of India gives insight of Technical aspects of Internet Telephony, Evolution of Internet telephony, investigation of problems and endorsement, managerial and framework, Security Issues, Access to emergency services, Quality of Service, Global regulatory Practices in Internet Telephony.

The article gives some important technical parameters which are considered for efficient communication system. The parameters and its significance are listed below:

- Packet Loss: during communication, there exists possibility of disappearance of packets. Highly balanced media like optical fiber minimizes packet loss to essentially zero.
- Delay: Delay refers to transmission time, along with the time taken to collect the packets at arrival and remunerate for variations in transit times of the data signal (this overall transit time preferably lower than 400 ms). Such delays depend on network and care must be taken while designing the network.
- Jitter: fluctuation in the packet receiving delay. The Network Synchronization is essential to reduce jitter.
- Echo: Echo specifies the delay between the signal transmission and same signal receipt at the receiver side. Effective echo minimization or elimination can be achieved by designing well planned networks.

The article presents three types of service models distribution schemes for Internet Protocol (IP) Telephony. They are

- PC to PC Internet Telephony
- IP over Phone to Phone
- PC to Phone and Phone to PC Internet Protocol Telephony


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The Orthogonal Frequency Division Multiplexing (OFDM). Introduction and explanation of five different types of techniques
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orthogonal, frequency, division, multiplexing, ofdm, introduction
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Dr. Lokesh Chikkananjaiah (Author), 2019, The Orthogonal Frequency Division Multiplexing (OFDM). Introduction and explanation of five different types of techniques, Munich, GRIN Verlag,


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