Study of OFDM Performance over AWGN Channels. Under graduate Project Report (original) (raw)
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The next generation wireless communications systems need to be of a higher standard in order to provide the customers with the multitude of high quality services they demand. In recent years, Orthogonal Frequency Division Multiplexing (OFDM) has been successfully used in terrestrial digital video broadcasting and showed it is a strong candidate for the modulation technique of future wireless systems. This project is concerned with how well OFDM performs when transmitted over an Additive White Gaussian Noise (AWGN) channel only. In order to investigate this, a simulation model was created and implemented using MATLAB. The OFDM signal was transmitted over the AWGN channel for various signal-to-noise ratio (SNR) values. To evaluate the performance, for each SNR level, the received signal was demodulated and the received data was compared to the original information. The result of the simulation is shown in a plot of the symbol error rate versus SNR, which provides information about the system's performance. The plot shows that OFDM performance is good over this type of channel.
PERFORMANCE ANALYSIS OF OFDM-BASED SYSTEM FOR VARIOUS CHANNELS
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 0.20−0.20-0.20−1.30 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
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 in the near future. An Orthogonal Frequency Division Multiplexing (OFDM) scheme offers high spectral efficiency and better resistance to fading environments. In OFDM the data is modulated using multiple numbers of sub-carriers that are orthogonal to each other because of which the problems associated with other modulation schemes such as Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) is reduced. This paper deals with the analysis of OFDM System utilizing different modulation techniques over Rayleigh, Rician and Additive White Gaussian Noise (AWGN) fading environments with the use of pilot aided arrangement and finally the results are conveyed. The aim of this thesis is to provide practical solutions for OFDM communication system by showing its better performance on different channel using different modulation technique. We applied different channel like AWGN, Rayleigh and Rician over OFDM system. We analyzed the performance of OFDM system regarding different channel. We analyzed the performance and showed the most suitable channel for OFDM communication system. Moreover, we also applied different modulation scheme over OFDM system to show which modulation technique is more efficient for OFDM system. Here we used BPSK, QPSK, 16-QAM and 64-QAM modulation technique. From our experiment we found that, among AWGN & the fading channels (Rayleigh & Rician), AWGN channel has less BER and P(e) than others. So we can say that, for OFDM system, AWGN channel is most suitable. We also found that, in all environments BPSK shows better performance than QPSK, 16QAM & 64QAM. When modulation level increased, corresponding BER & Probability of error P(e) also increased.
Study Of Performance Parameters Effects On OFDM Systems
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).
Performance Evaluation of OFDM System-A Simulation Study
2013
OFDM is a combination of modulation, multiplexing and wireless technology. OFDM involves a broadband multicarrier modulation method that offers superior performance and benefits over older, more traditional single-carrier modulation methods because it is better fit with today"s high-speed data requirements and operation in the UHF and microwave spectrum. In recent years, OFDM has come up with successful use in terrestrial DVB and has proved its strong candidature as a modulation technique for future wireless systems.It completely fulfills today"s increased need of high speed data transmission. In this paper the channel capacity for different channels has been studied. Also the bit error rate has been reduced and SNR has been improved so as to find out that which channel is better for OFDM transmission and under which modulation scheme.
Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction PAPR, intercarrier interference (ICI) and multiple-input–multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.
IAETSD-EVALUATION: OFDMA & SC-OFDMA PERFORMANCE ON WIRELESS COMMUNICATION
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.