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OFDM and MC-CDMA : A Primer
Abstract
This concise volume provides a widely accessible introduction to OFDM and MC-CDMA. Based on the authors’ experience in researching OFDM in the context of various applications, it systematically converts the lessons of Shannon’s information theory into practical wireless system design examples. Comprehensive coverage of OFDM, MIMO-OFDM and MC-CDMA is presented, incorporating radically new research-oriented principles. A further strength of this primer is that it considers the ambitious aim of achieving near-maximum-likelihood multi-user MIMO-OFDM performance at a modest complexity, proposing an advanced extension of the Complex Sphere Detector (CSD). This technique allows the system to support a higher number of OFDM/MC-CDMA users than the number of antennas even in the case of high-throughput QAM schemes.
The design and performance of OFDM modems are highlighted, covering both Gaussian and wideband fading channels, frequency domain synchronization as well as adaptive single- and multi-user OFDM
Offers a comparative study of OFDM and MC-CDMA, discussing spreading sequences, adaptive modulation and the attainable performance in synchronous environments
Contains an advanced section on genetic algorithm aided joint multi-user channel estimation techniques for multi-user SDMA-OFDM
Introduces an avant-garde design principle, which aims for directly minimizing the bit error ratio (BER) at the output of the multi-user OFDM system
As an introductory treatment of the complex subject of OFDM, this primer text will be attractive to a wide readership, including postgraduate students, systems and development engineers, as well as communications managers and practitioner.
... In Maximal Ratio Combining (MRC) scheme, the diversity combiner assigns a higher weight to stronger signal than a weaker signal, because a stronger signal provides a more reliable communication [8,9]. The corresponding equalisation gain, g n , is given as: ...
... Although the MRC scheme optimally combines the multi-path components to maximise the SNR, it may further impair the orthogonality of the codes. In order to avoid this problem, Equal Gain Combining (EGC) detector can be used because it can correct phase distortions of the signal introduced in the channel [8,11]. Thus, the equalisation gain of EGC detector, is given by: (11) where, ...
Multi-carrier code-division multiple access system support multiple users at the same time over same frequency band. It is a multiple access scheme used in OFDM-based telecommunication systems. Though it is a promising wireless communication technology with high spectral efficiency and system performance, it is prone to multiple access interference (MAI). So, this paper mainly aims to design a MC-CDMA receiver to mitigate MAI. The classical receivers like maximal ratio combining (MRC), equal gain combining (EGC), and minimum mean square error (MMSE) fails to cancel MAI when the MC-CDMA is subjected to non-linearistic degradations. In this case, the neural network (NN) receivers could be a better alternative. The efficiency and effectiveness of the proposed ELM (Extreme Learning Machine) Algorithm based receiver is studied thoroughly and explained in detailed for the MC-CDMA with non-linearistic degradations.
... Multi-Carrier Code Division Multiple Access (MC-CDMA) [1][2][3], a prominent transmission technique that amalgamates Direct Sequence CDMA (DS-CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) [4][5][6][7], is presently incorporated in Non-Orthogonal Multiple Access (NOMA) systems [8]. In the quest for delivering high-speed multimedia services and wireless Internet, broadband mobile wireless systems are expected to provide high data rates. ...
This study explores a composite space-time and frequency-domain spreading strategy, designed to augment the capacity of multicarrier 5G systems operating over frequency-selective Rayleigh fading channels. The focus is directed towards a comprehensive analysis of the Bit Error Rate (BER) performance of the proposed system, with adjustments made to various parametric values. In tandem, receiver optimization techniques are meticulously studied, and their outcomes are positioned against existing literature. Within this context, the Parallel Interference Canceller (PIC) emerges as a viable alternative to the De-correlating Detector (DD), a shift primarily driven by the latter's heightened complexity and noise amplification. Additionally, this study demonstrates the acquisition of a larger number of users exclusively employing transmission diversity, thereby eliminating the need for receiving diversity and additional code sets. This approach incrementally augments hardware complexity at both ends of the transmission link, a minor trade-off for the benefits garnered. The efficacy of this scheme is substantiated through MATLAB simulations, indicating a promising avenue for improving the capacity of multicarrier 5G systems. The findings pave the way for significant advancements in the development of efficient and robust communication systems for the 5G era and beyond.
... These technologies comprises of advanced capabilities like beam forming, beam management (beam switching, recovery and refinement) and mMIMO at mmWave frequencies and sub-6 GHz spectrum bands. The fully integrated radio arrays having more than 100 trans receivers and antenna elements are capable of supporting 8 [24][25][26][27][28][29][30][31][32][33][34] UFMC [11,12] Power allocation [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] f-OFDM [13,14] Cooperative NOMA [50][51][52][53][54][55][56] Pulse Shaping FBMC [15,16] Code domain Low density signature sequence based CDMA(LDS-CDMA) [57] QAMFBMC [17] Low density spreading OFDM (LDS-OFDM) [58] GFDM [18,19] Sparse code multiple access (SCMA) [59] Pulse shaped OFDM [20] Trellis coded multiple access (TCMA) [60] Interleave Division Multiple Access (IDMA) [61] Spectrally Precoding design OFDM SP-OFDM [21] Pattern division multiple access [62] Multiuser shared access (MUSA) [63] Delay Doppler Domain OTFS [22] NOMA Multiplexing in multiple domain BOMA [64,65] Guard Interval Shortening GIDFT-S-OFDM [23] LPMA [66][67][68] concurrent streams at 20 Gbits/s downloads and 4 concurrent streams at 10 Gbits/s uploads [77]. 5G era will demand for tighter integrations of RF electronics and antennas known as Integrated Antenna and Base Station (IAB) techniques, in order to meet the requirements of mMIMO and mmWaves. ...
Due to exponential increase in the capacity demands raised by the smart devices and multimedia applications of new generations, existing cellular networks are facing significant burden. To provide a solution to the challenges faced by 4th generation (4G) networks, there is utmost need of improving existing technologies as well as developing new technologies to meet the key requirements of 5th generation (5G) networks as well as the Next Generation Mobile Networks (NGMNs). Networks having high capacity, low latency, faster data rates and better quality of service is the vision of 5G mobile networks. In order to achieve this, we will need wider bandwidths as offered by millimeter wave bands, more spatial diversity as offered by Massive multiple input multiple output technology, denser networks as designed in dense small cell deployment technology, new waveforms using efficient coding techniques such as filtered orthogonal frequency division multiplexing and filter bank multiple carrier, a new architecture supporting virtualization and advance computing techniques as in network function virtualization, software defined networks, cloud radio access networks. Many more technologies are yet to be introduced. This tutorial gives an insight to the candidate technologies proposed by researchers till date and the progress made, for defining the standards to meet the requirements of 5G and NGMNs. It explains the basic concept of the technology and the latest development in the industry to support this technology.
... However, OFDM performance is sensitive to receiver synchronization. Carrier frequency offset causes intercarrier interference (ICI) and errors in timing synchronization can lead to inter-symbol interference (ISI) [5]. Therefore, synchronization is critical to the performance of OFDM systems as well as L-DACS1. ...
L-band Digital Aeronautical Communication System type-1 (L-DACS1) is an emerging standard that aims at enhancing air traffic management (ATM) by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. L-DACS1 employs modern and efficient orthogonal frequency division multiplexing (OFDM) modulation technique to achieve more efficient and higher data rate in comparison to the existing aeronautical communication systems. However, the performance of OFDM systems is very sensitive to synchronization errors. L-DACS1 transmission is in the L-band aeronautical channels that suffer from large interference and large Doppler shifts, which makes the synchronization for L-DACS more challenging. This paper proposes a novel computationally efficient synchronization method for L-DACS1 systems that offers robust performance. Through simulation, the proposed method is shown to provide accurate symbol timing offset (STO) estimation as well as fractional carrier frequency offset (CFO) estimation in a range of aeronautical channels. In particular, it can yield excellent synchronization performance in the face of a large carrier frequency offset.
In this paper, we review radio resource optimization methods for energy-efficient wireless communication in links and networks using the Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) techniques. We first consider the energy-efficiency metrics and optimization goals. We discuss the increasingly complex systems, starting from (i) a single OFDM link, (ii) an OFDMA single-hop network to (iii) multi-hop relay OFDMA interference networks. In each case, we elaborate on the transmission rate estimation, power consumption modelling, existing optimization constraints and the optimization solutions. Specifically, in the power-consumption modelling, we include the signal-processing (and related computing) power.We discuss the practicality of the considered solutions. We also touch upon the problem of nonlinear power amplifier characteristics (causing distortions typical for OFDM signals) to be taken into account for energy-efficient resource allocation. We discuss trade-offs and provide recommendations for future energy-efficient OFDM networks design. We also discuss the future works and challenges in the context of energy efficiency resource allocation for OFDM/OFDMA and their derivative techniques.We conclude that the presented design practices should include computational awareness in the networks to trade-off between information communication, information processing and the required network management energy-efficiency.
Confidentiality of information must be maintained when it is required to be transmitted over a communication channel or when it is stored in a computer for further information access. Establishing a highly reliable and secure means of wireless communication for the transfer of digital data (text, images, audio, and video) from source to destination is becoming a prime requirement in present‐day wireless communications. Security can be achieved at the network level as well as at the data level. Data‐level security is made through cryptographic techniques. This paper emphasizes data‐level security aspects in a wireless communication system for the secure transmission of images over an AWGN channel condition. Here, a crypto orthogonal frequency division multiplexing system (crypto‐OFDM system) is designed using Rubik's cube encryption algorithm scheme for secured transmission of images under the MATLAB environment. The quality of the image transmission is analyzed using peak signal to noise ratio (PSNR) and BER at different SNR conditions. The quality of the encryption algorithm was also tested with statistical metrics, which are the histogram, NPCR, UACI, entropy, correlation coefficient analysis, etc. The numerical results reveal that a DCT‐based crypto‐OFDM system with Rubik's cube algorithm show a better performance over earlier cryptosystems and also perform superior to the original/basic OFDM system. The statistical analysis tests prove that Rubik's cube algorithm is one of the most robust algorithms for security point of view and is easy to implement, as Rubik's cube algorithm makes use of natural characteristics of pixel values, which form the basis for designing the secret key.
This chapter introduces an alternative technique, the orthogonal frequency division multiplexing (OFDM) modulation. It first introduces the formulation for OFDM and discusses time domain equalization, which is an addition to the basic OFDM receiver to deal with excessive channel dispersion. The chapter shows that OFDM can address channel dispersion in a simple way, and can reach near‐optimum data rate. It provides a more detailed comparison between OFDM and the single‐carrier modulation with the decision feedback equalizer. The chapter then discusses practical issues with OFDM: channel estimation and synchronization. It presents two OFDM implementation challenges, the peak‐to‐average ratio and the sidelobes. The chapter also considers improvement alternatives. It extends OFDM to multiuser cases and discusses the orthogonal frequency division multiple access (OFDMA) scheme. OFDMA has the additional challenge of synchronization among multiple transmitters. Such challenge motivates a generalization of OFDM, the filter bank multicarrier modulation.
With the passage of previous several decades it is analyzed that the upcoming generation of mobile communication should provide high data rates as well as capacity of data transmission. As far as Generalized Frequency Division Multiplexing (GFDM) is concerned, the pulse shaping filters plays a significant role in it. The Bit Error Rate (BER) performance of GFDM is worse as compared to OFDM due to the lack of initial orthogonality in the subcarriers. This can be made better with the usage of different pulse shaping filter. This paper presents the implementation of the Raised Cosine (RC), Square Root Raised Cosine (SRRC) and Gaussian filter along with the MRC combining scheme of MIMO for GFDM. The simulation results show that the different SNR values can be obtained for the respective BER in GFDM.
Multicarrier code division multiple access (MC-CDMA) is a novel wireless communication technology with high spectral efficiency and system performance. However, all multiple access techniques including MC-CDMA were most likely to have multiple access interference (MAI). So, this paper mainly aims at designing a suitable receiver for MC-CDMA system to mitigate such MAI. The classical receivers like maximal-ratio combining and minimum mean square error fail to cancel MAI when the MC-CDMA is subjected to nonlinear distortions, which may occur due to saturated power amplifiers or arbitrary channel conditions. Being highly nonlinear structures, the neural network (NN) receivers such as multilayer perceptron and radial basis function networks could be better alternative for such a case. The possibility NN receiver for a MC-CDMA system under different nonlinear conditions has been studied with respect to both performance and complexity analysis.
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