Comparative Study of OFDM and CDMA Technique

International Journal of computer science issues, 2012

There have been extensive research efforts on simulating Wireless Local Area Networks. Many papers have studied the performance of IEEE 802.11 WLANs by using simulation under different channels and for different modulations. In this paper we first simulate a simplified IEEE 802.11a standard based on Orthogonal Frequency Division Multiplexing (OFDM) with the cyclic prefix and IEEE 802.11b standard based on Direct-Sequence Code Division Multiple Accesses (DS-CDMA). Then a comparative study will be performed to evaluate them in Additive White Gaussian Noise (AWGN) channel with Rayleigh fading to resemble the real world scenario. We investigated their physical layer performances on the basis of Bit Error Rate (BER) and Signal-to-Noise Ratio (SNR). These parameters are discussed and compared in the two models. It has been demonstrated that OFDM system provides better performance in noisy conditions.

Journal of Electrical Engineering, Electronics, Control and Computer Science, 2021

At the present era of communication technology, every user wants a communication system that has higher data transmission capability and reliability. Orthogonal Frequency Division Multiplexing (OFDM) is a frequency division multiplexed multi carrier transmission method and each multiplexed signal is orthogonal to each other. This technology is known as core technology of the new generation wireless mobile communication systems. This technology has higher data transmission capability and reliability as well as has the ability to combat frequency selective fading or narrowband interference while maintaining high spectrum utilization. The aim of this paper is to analyze the performance of the OFDM technology using different modulation techniques. This paper is mainly focused on the calculation of the Bit Error Rate (BER) to analyze the performance of OFDM systems. In this paper, we considered BPSK, QPSK, 64-QAM, 128-QAM and 256-QAM modulation techniques. All the simulations has been accomplished by using the MATLAB framework.

The demand for high-speed mobile wireless communications is rapidly growing. Orthogonal Frequency Division Multiplexing (OFDM) technology promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for wireless communication systems ins the near future. This paper investigates the performance of OFDM-based system over static and non-static or fading channels. In order to investigate this, a simulation model has been created and implemented using MATLAB. A comparison has also been made between the performances of coherent and differential modulation scheme over static and fading channels. In the fading channels, it has been found that OFDM-based system's performance depends severely on Doppler shift which in turn depends on the velocity of user. It has been found that performance degrades as Doppler shift increase, as expected. This paper also performs a comparative study of OFDM-based system's performance on different fading channels and it has been found that it performs better over Rician channel, as expected and system performance improves as the value of Rician factor increases, as expected. As a last task, a coding technique , Gray Coding, has been used to improve system performance and it is found that it improves system performance by reducing BER about 25-32 percent. INTRODUCTION: Wireless communications is an emerging field, which has seen enormous growth in the last several years. The huge uptake rate of mobile phone technology, Wireless Local Area Networks (WLAN) and the exponential growth of the Internet have resulted in an increased demand for new methods of obtaining high capacity wireless networks. Most WLAN systems currently use the IEEE802.11b standard, which provides a maximum data rate of 11 Mbps. Newer WLAN standards such as IEEE802.11a and HiperLAN2 [1], [2] are based on OFDM technology and provide a much higher data rate of 54 Mbps. However systems of the near future will require WLANs with data rate of greater than 100 Mbps, and so there is a need to further improve the spectral efficiency and data capacity of OFDM systems in WLAN applications. For cellular mobile applications, we will see in the near future a complete convergence of mobile phone technology, computing, Internet access, and potentially many mul-timedia applications such as video and high quality audio. In fact, some may argue that this convergence has already largely occurred, with the advent of being able to send and receive data using a notebook computer and a mobile phone. Although this is possible with current 2G (2 nd Generation) Mobile phones, the data rates provided are very low (9.6 kbps – 14.4 kbps) and the cost is high (typically $0.20-$1.30 AUD per minute) [3], [4], limiting the usefulness of such a service. The goal of third and fourth generation mobile networks is to provide users with a high data rate, and to provide a wider range of services, such as voice communications, videophones, and high speed Internet access. The higher data rate of future mobile networks will be achieved by increasing the amount of spectrum allocated to the service and by improvements in the spectral efficiency. OFDM is a potential candidate for the physical layer of fourth generation mobile systems. This thesis presents techniques for improving the spectral efficiency of OFDM systems applied in WLAN and mobile networks. BASIC PRINCIPLES OF OFDM: Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier transmission technique, which divides the available spectrum into many carriers. The information is modulated onto the sub-carrier by varying the phase, amplitude, or both. Each sub-carrier then combined to gather by using the inverse fast fourier transform to yield the time domain wave form that is to be transmitted. To obtain a high spectral efficiency the frequency response of each of the sub-carriers are overlapping and orthogonal. This orthogonality prevents interference between the sub carriers (ICI) and is preserved even when the signal passes through a multi-path channel by introducing a Cyclic Prefix, which prevents Inter-symbol Interference (ISI) on the carriers. This makes OFDM especially suited to wireless communications applications. SIMULATION RESULTS: An OFDM system has been modeled using Matlab to allow various parameters of the system to be varied and tested. The aim of doing the simulations is to measure the performance of OFDM under different channel conditions, and to allow for different OFDM configurations to be tested. The effect of different modulation techniques and modulation level on OFDM has also been tested. Moreover, different techniques have been employed to reduce BER (Bit Error Rate) rate. When OFDM performance has been tested in fading environment

2015

Future wireless communication systems must be able to accommodate a large number of users and simultaneously to provide the high data rates at the required quality of service. Multi-carrier code division multiple access(MC-CDMA) is a promising technique for future 4G broadband multiuser communication systems.MC-CDMA is a combination of orthogonal frequency-division multiplexing(OFDM) and code division multiple accesses (CDMA), it has been considered as an important technique for the future generation wireless systems due to its combined advantages of MC and CDMA techniques: high spectral efficiency, robustness in frequency selective channels with a lowcomplexity at receiver considering a simple one-tap equalization, multiple access capability with high flexibility, narrow-band interference rejection. The aim of this paper is to study the performance of MC-CDMA under the effect of Rayleigh fading channel and Additive White Gaussian Noise (AWGN) using MATLAB. Keywords-Multi-carrier code division multiple access (MC-CDMA), Orthogonal frequency division multiplexing (OFDM), Binary phase shift key (BPSK), Peak to average power ratio (PAPR), Additive white Gaussian noise (AWGN), Rayleigh fading. I.

IOSR Journal of Electronics and Communication Engineering, 2014

Recent advances in wireless communication need such kind of techniques which support higher data rate transmission. In this paper study of orthogonal frequency division multiplexing (OFDM) & multicarrier code division multiple access (MC-CDMA) has been done. MC-CDMA is scheme which works more efficiently in case of mobile environment. A novel approach of Adaptive OFDM is proposed here which provide better SNR performance.

2012

Many reasons cause multi- carrier CDMA to be the best technology in the latest mobile generations known by fourth generation for mobile. As well known, the greatest enemy for any wireless communication is multi- path fading which usually result in distortion in time- domain, or in frequency domain or even in both. Therefore any new technique applied into mobile communication system is concerning with mitigating multi-path fading distortion which appears in form of reducing BER level. In this paper three techniques have been combined in order to enhance mobile system performance in the presence of multipath fading channel. These techniques are, orthogonal frequency division multiplexing (OFDM), code division multiple access (CDMA), and modified space shift keying (SSK). The last technique is considered special case for MIMO technology. By the aid of MATLAB code, proposes system was simulated in order to display BER performance versus variation in the SNR at many various system condit...

2009

Recently some new multiple access schemes attracted much attention. Namely OFDM-CDMA and IDMA. So, this paper outlines the basic principals of OFDM-CDMA and IDMA. A comparative study of OFDM-CDMA and IDMA is given here on the basis of some attractive features like low-cost iterative multi-user detection, flexible data rate adaptation and modulation schemes.

2013

OFDM stands for Orthogonal Frequency Division Multiplexing. It is a special type of multicarrier modulation scheme. In it a high rate data stream is converted into a number of low rate data streams that are transmitted over parallel, narrowband channels that can be easily equalized and thus it is utilized for high data rate transmission in delay dispersive environments. It reduces the interference effects, distortion effects and multipath delay effects during data transmission and reception. Due to these advantages use of OFDM has become very popular in present day wireless technology. In this paper an OFDM system model has been used for transmission and reception of data in which M-ary Phase Shift Keying (MPSK) modulation technique is used. In Mary Phase Shift Keying (MPSK) modulation technique the carrier phase takes on one of the M possible values, here we have used M = 4, M = 8 and M =16 i.e. 4 PSK, 8 PSK and 16 PSK modulation techniques. MPSK modulation techniques are utilized ...

Communications on Applied Electronics, 2016

OFDM is a multicarrier technique for transmission, which divides the available spectrum into many carriers with each one of them being modulated by a data stream of low rate. OFDM is similar to FDMA in the sense that the multiple user access is achieved by further dividing the available bandwidth to multiple channels. These sub channels are then allocated to the users. But in OFDM, the spectrum is used much more efficiently by spacing the channels much close to one another. This is achieved by making all the carriers orthogonal to one another, preventing interference between these carriers. The digital data in serial form to be transmitted is split into different data streams, and each one of them is modulated by a separate carrier in the allotted bandwidth. The modulation done can be any one of the forms of modulation applied to digital data, but the most commonly used are quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM). When these modulators are used, their outputs are summed linearly, and the output signal is sent to the channel. In this paper we will analyze the performance of different modulation techniques in AWGN channel. We conclude that a different modulation scheme has different bit error rate.

Communications on Applied Electronics, 2015

Orthogonal frequency division multiplexing (OFDM) is a form of digital modulation used in a wide array of communication systems. This paper presents a comprehensive performance analysis of orthogonal frequency division multiplexing system. We investigate the basic principle of OFDM system and through computer simulation we present the Bit error rate(BER) and peak-to-average power ratio(PAPR) of OFDM system for different modulation techniques.

2013

this paper gives the effectiveness measures of OFDM as a modulation technique for wireless radio applications. OFDM is checked as a modulation technique for telephony communication system. A comparative study of COFDM a variant of OFDM is done with the CDMA technology for the same application. Various performance matrices like multipath delay spread, channel noise, distortion of the signal (clipping), and timing requirements are depicted. The study will provide bird eye view of COFDM and CDMA for communication engineering. It was found by study that OFDM performs extremely well, providing a very high tolerance to multipath delay spread, peak power clipping, and

2017

The communication in the past decades has made the revolution in the ICT techniques. It is only due to the recent advancement communication techniques, OFDM have opened the developed area for further Research. Many advantages of OFDM over single carrier scheme is ,its ability to cope with severe channel conditions such as attenuation of high frequency in a long copper wire .OFDM is a multi-carrier modulation technique with densely spaced subcarriers that has gained a lot of popularity among the broadband community in the last few years. OFDM has been shown to be an effective technique to combat multipath fading in wireless communications. OFDM has chosen as the standard for digital audio broadcasting and high-speed wireless local areas networks. Present Paper, explore the OFDM Modulation its advantages and demerits, and some applications of OFDM. OFDM Techniques for peak-to-average power ratio reduction (PAPR), time and frequency synchronization, and channel estimation will be discu...

Ninth International Conference on HF Radio Systems and Techniques, 2003

Output(MIMO) system. SC-FDMA is one of the most promising techniques aiming at solving the capacity problem of wireless communication systems and achieving higher spectral efficiency, depending on multiplexing signals based on their spatial signature. On the other hand most third generation mobile phone systems are using Code Division Multiple Access (CDMA) as their modulation technique. CDMA is not so complicated to implement as OFDM based systems. As CDMA has a wide bandwidth, it is difficult to equalize the overall spectrum -significant levels of processing would be needed for this as it consists of a continuous signal and not discrete carriers. Not as easy to aggregate spectrum as for OFDM. For this reason, CDMA is also investigating so that the performance of OFDM-SC-FDMA can be compared. Various OFDMA techniques are investigated including LTE or Long Term Evolution is the brand name given to the efforts of 3GPP 4th Generation technology development efforts mostly in Europe and UMB (Ultra-Mobile Broadband) is the brand name for similar efforts by 3GPP2, linear detection schemes, minimum mean square error, ordered successive cancellation, and maximum likelihood methods. Promising results are obtained to enhance spectral efficiency on the expense of computational complexity which needs to be addressed.

The actual and next communication schemes tend to use OFDM systems in order to provide high baud rates, less intercarrier interference, and less intersymbol interference. OFDM has become the core of most 4G communication systems as fixed Wi-Fi system (IEEE802.11a standard), mobile Wi-Fi system (IEEE802.11b standard), fixed WiMAX system (IEEE802.16a standard), mobile WiMAX system (IEEE802.16e standard), and Long Term Evolution (LTE) system. In this paper the detailed simulation of different OFDM systems with different constellation mapping schemes will be obtained using MATLAB-2011 program to study the effect of various design parameters on the system performance. Noise Ratio (SNR).