Frequency Domain Equalization and Adaptive OFDM vs. Single Carrier Modulation

Frequency Domain Equalization and Adaptive OFDM vs. Single Carrier Modulation

Inderjeet Kaur (Ajay Kumar Garg Engineering College, India)
DOI: 10.4018/978-1-60960-563-6.ch009
OnDemand PDF Download:


In the present article an attempt is made to compare multi-carrier and single carrier modulation schemes for wireless communication systems with the utilization of fast Fourier transform (FFT) and its inverse in both cases. With the assumption that in OFDM (orthogonal frequency division multiplexing), the inverse FFT transforms the complex amplitudes of the individual sub-carriers at the transmitter into time domain, the inverse operation is carried out at the receiver. In case of single carrier modulation, the FFT and its inverse are used at the input and output of the frequency domain equalizer in the receiver. Different single carrier and multi-carrier transmission systems are simulated with time-variant transfer functions measured with a wideband channel sounder. In case of OFDM, the individual sub-carriers are modulated with fixed and adaptive signal alphabets. Furthermore, a frequency-independent as well as the optimum power distribution are used. Single carrier modulation uses a single carrier, instead of the hundreds or thousands typically used in OFDM, so the peak-to-average transmitted power ratio for single carrier modulated signals is smaller. This in turn means that a SC system requires a smaller linear range to support a given average power. This enables the use of cheaper power amplifier as compared to OFDM system.[Article copies are available for purchase from]
Chapter Preview


The basic recipe followed in this article is as follows:

  • 1.

    For investigating the transmission of digital signals we have used wideband frequency-selective radio channels.

    • It has been observed that the frequency-selective fading caused by multipath time delay spread degrades the performance of digital communication channels by causing inter-symbol interference, thus results in an irreducible BER and imposes an upper limit on the data symbol rate.

  • 2.

    We have compared the performance of single carrier and multi-carrier modulation schemes for a frequency-selective fading channel considering un-coded modulation scheme.

    • Our analysis shows that the un-coded OFDM loses all frequency diversity present in the channel which results in a dip in the channel. As a result of this, the information data on the subcarriers, affected by the dip, is erased. Further, this erased information cannot be recovered from the other carriers. Consequently, it results in a poor Bit Error Rate (BER) performance. However, we can recover frequency diversity and improve the BER performance by adding sufficiently strong coding which spreads the information over multiple subcarriers.

Alternatively, the performance of OFDM can also be improved significantly by using different modulation schemes for the individual sub-carriers. In this scenario, the modulation schemes have to be adapted to the prevailing channel transfer function. Moreover, each modulation scheme provides a trade off between spectral efficiency and the bit error rate. The spectral efficiency can be maximized by choosing the highest modulation scheme that will give an acceptable (BER). In a multipath radio channel, frequency selective fading can result in large variation in the received power of each carrier.

The article is organized as follows: In section II the fixed and adaptive OFDM transmitters are described. A brief description of a single carrier system with frequency domain equalization is given in section III. Section IV deals with the simulations results. Finally, the main conclusions are drawn in section V.


Adaptive Ofdm Transmission

Figure 1 shows the block diagram of the OFDM transmitter used. As can be seen, Binary data is, first, fed to a modulator which generates complex symbols on its output. The modulator either uses a fixed signal alphabet (QAM) or adapts the signal alphabets of the individual OFDM sub-carriers. Both, signal alphabets and power distribution can be optimized corresponding to the channel transfer function. Because of the slow variation of transfer function with time (as shown by the propagation measurements of radio channels with fixed antennas), it is safe to assume that the instantaneous channel transfer function can be estimated at the receiver and can be communicated back to the transmitter. The third block transforms the symbols into time-domain using inverse fast Fourier transform (FFT) at the transmitter. The next block inserts the guard interval. The output signal is transmitted over the radio channel. At the receiver, the cyclic extension is removed and the signal is transformed back into frequency domain with an FFT. Prior to demodulation, the signal is equalized in frequency domain with the inverse of the transfer function of the radio channel corresponding to a zero-forcing equalizer.

Figure 1.

Block diagram of a) an OFDM and b) a single carrier transmission system with frequency domain equalization

In this article, we have considered two different adaptive modulator/demodulator pairs A and B. In modulator A, the distribution of bits on the individual sub-carriers is adapted to the shape of the transfer function of the radio channel. Modulator B optimizes simultaneously both, the distribution of bits and the distribution of signal power with respect to frequency.

Complete Chapter List

Search this Book:
Table of Contents
Ismail Khalil, Edgar R. Weippl
Chapter 1
V. S. Anitha, M. P. Sebastian
This chapter proposes a scenario-based and diameter-bounded algorithm for cluster formation and management in mobile ad hoc networks (MANETs). A (k... Sample PDF
Multi-Purpose DS-Based Cluster Formation and Management in Mobile Ad Hoc Networks
Chapter 2
P. P. Abdul Haleem, M. P. Sebastian
Conservation of resources such as bandwidth, energy and memory are of a concern in Resource Constrained Networks (RCNs). Wireless mobile devices... Sample PDF
Optimizing Resource Consumption for Secure Messaging in Resource Constrained Networks
Chapter 3
Manu J. Pillai, M. P. Sebastian
The nodes are expected to transmit at different power levels in heterogeneous mobile adhoc networks, thus leading to communication links of... Sample PDF
Improving Energy Efficiency and Throughput in Heterogeneous Mobile Ad Hoc Networks
Chapter 4
Kais Mnif, Michel Kadoch
This paper proposes to use virtual backbone structure to handle control messages in ad hoc networks. This structure is effective in reducing the... Sample PDF
Performance Enhancement of Routing Protocols in Mobile Ad hoc Networks
Chapter 5
Qin Danyang, Ma Lin, Sha Xuejun, Xu Yubin
Mobile Ad Hoc Network (MANET) is a centerless packet radio network without fixed infrastructure. In recent years tremendous attentions have been... Sample PDF
Realization of Route Reconstructing Scheme for Mobile Ad hoc Network
Chapter 6
Mohammad Anbar, Deo Prakash Vidyarthi
Cellular IP networks deal with the concepts of micro-mobility. Buffer management in Cellular IP networks is very crucial as its proper usage not... Sample PDF
Buffer Management in Cellular IP Network using PSO
Chapter 7
Ibrahim Y. Abualhaol, Mustafa M. Matalgah
Cooperative communications among group of teleoperated unmanned ground vehicles (UGVs) allows to exploit spatial diversity in wireless fading... Sample PDF
Throughput Optimization of Cooperative Teleoperated UGV Network
Chapter 8
Péter Fülöp, Sándor Imre, Sándor Szabó, Tamás Szálka
The efficient dimensioning of cellular wireless access networks depends highly on the accuracy of the underlying mathematical models of user... Sample PDF
The Accuracy of Location Prediction Algorithms Based on Markovian Mobility Models
Chapter 9
Inderjeet Kaur
In the present article an attempt is made to compare multi-carrier and single carrier modulation schemes for wireless communication systems with the... Sample PDF
Frequency Domain Equalization and Adaptive OFDM vs. Single Carrier Modulation
Chapter 10
Joel Penhoat, Olivier Le Grand, Mikael Salaun, Tayeb Lemlouma
Fixed Mobile Convergence is an important challenge for telecommunication operators given the heterogeneity of access networks technologies and the... Sample PDF
Definition and analysis of a Fixed Mobile Convergent architecture for enterprise VoIP services
Chapter 11
Reza Rawassizadeh, Amin Anjomshoaa, A Min Tjoa
There are many mobile applications currently available on the market, which have been developed specifically for smart phones. The operating system... Sample PDF
A Qualitative Resource Utilization Benchmarking for Mobile Applications
Chapter 12
Ahmed Swilem
Vector quantization (VQ) is a well-known compression method. In the encoding phase, given a block represented as a vector, searching the closest... Sample PDF
Fast Vector Quantization Encoding Algorithms for Image Compression
Chapter 13
Ghaida A. Al-Suhail, Martin Fleury, Salah M. Saleh Al-Majeed
All-IP networks are under development with multimedia services in mind. Video multicast is an efficient way to deliver one video simultaneously to... Sample PDF
Mobile Video Streaming Over Heterogeneous Networks
Chapter 14
Siham Ouamour, Halim Sayoud, Mhania Guerti
Results show the importance of the high spectral resolution in noisy environment and telephonic bandwidth, while the current research works have... Sample PDF
Automatic Talker Identification Using Optimal Spectral Resolution: Application in noisy environment and telephony
Chapter 15
Ahmed A. Radwan, Ahmed Swilem, Mamdouh M. Gomaa
This article presents a very simple and efficient algorithm for codeword search in the vector quantization encoding. This algorithm uses 2-pixel... Sample PDF
A Fast Image Encoding Algorithm Based on the Pyramid Structure of Codewords
Chapter 16
Harilaos Koumaras, Charalampos Skianis, Anastasios Kourtis
In future communication networks, video is expected to represent a large portion of the total traffic, given that especially variable bit rate (VBR)... Sample PDF
Analysis and Modeling of H.264 Unconstrained VBR Video Traffic
Chapter 17
Halim Sayoud, Siham Ouamour
This chapter describes a new Speaker Discrimination System (SDS), which is a part of an overall project called Audio Documents Indexing based on a... Sample PDF
Speaker Discrimination on Broadcast News and Telephonic Calls Based on New Fusion Techniques
Chapter 18
Ivan Tomek, Elhadi Shakshuki
Pervasiveness of Internet and increasing geographical dispersal of work teams result in continuously growing importance of groupware - software that... Sample PDF
FCVW: Experiments in Groupware
Chapter 19
Nabeel Farouq Al-Mushasha, Shahizan Hassan
It is generally known that accessibility and mobility are the main barriers for effective implementation of electronic learning. However, the advent... Sample PDF
A Model for Mobile Learning Service Quality in University Environment
Chapter 20
Theodoros I. Kavaliotis, Anastasios A. Economides
Many people communicate among themselves using wireless networks. They have developed e-communities in order to discuss issues about their network... Sample PDF
Evaluating E-Communities of Wireless Networks Worldwide
Chapter 21
Vijayan Sugumaran, Shriram Raghunathan
The evolution of mobile devices has opened new opportunities for collaboration, communication and computation on the move. Increasing device... Sample PDF
Typology and Challenges in Developing Mobile Middleware Based Community Network Infrastructure
Chapter 22
Qi Wei, Ahmed Patel
Mobile agents raise security issues such as the protection of platform/host that runs the mobile agent against attacks which can harm or use its... Sample PDF
A Secure and Trustworthy Framework for Mobile Agent-Based E-Marketplace with Digital Forensics and Security Protocols
About the Contributors