Performance of Orthogonal Frequency Division Multiplexing (OFDM) under the Effect of Wireless Transmission System Drawbacks (original) (raw)
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OFDM Technique For Wireless Communication
OFDM can be viewed as both modulation and multicarrier technique in which high rate serial data is split into parallel data streams which are orthogonal to each other. One of the main reason to use OFDM is to increase robustness against frequency-selective fading or narrowband interference .OFDM technique has found its wide applications in many scientific areas due to its high spectrum efficiency .In a single-carrier system, a single fade or interferer can cause the entire link to fail, but in a multi-carrier (MC) system, only a small percentage of the subcarriers (SCs) will be affected The difference between the conventional non-overlapping MC technique and overlapping MC technique is that we save almost 50% of the bandwidth in the latter case .To realize this, however, we need to reduce cross-talk between SCs, which means that we want orthogonality between the different modulated carriers.
2012
Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier modulation technique that provides high bandwidth efficiency because the carriers are orthogonal to each other and multiple carriers share the data among themselves. The main advantage of this transmission technique is its robustness to channel fading in wireless communication environment. This paper investigates the effectiveness of OFDM and assesses its suitability as a modulation technique in wireless communications. Several of the main factors affecting the performance of a typical OFDM system are considered and they include multipath delay spread, channel noise, distortion (clipping), and timing requirements. The core processing block and performance analysis of the system is modeled using Matlab.
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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...
SURVEY OF ANALYSIS AND PERFORMANCE OF OFDM SIGNALS IN TIME AND FREQUENCY DISPERSIVE CHANNELS
The increase in the number of wireless devices and the requirement for higher data rates places an increasing demand on bandwidth. This necessitates the need for communication systems with increased throughput and capacity. Multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) is one way to meet this need. OFDM is used in many wireless communication devices and offers high spectral efficiency and resilience to multipath channel effects. Though OFDM is sensitive to synchronization errors, it makes the task of channel equalization simple. MIMO makes use of multiple antennas to increase throughput without increasing transmitter power or bandwidth. Several modulation schemes are presented that are often used in conjunction with OFDM . Mathematical definitions and analysis of OFDM are given along with a discrete implementation common to modern communication systems. Synchronization errors are described mathematically, as well as techniques to estimate and correct those errors at the receiver.
OFDM – Orthogonal Frequency Division Multiplexing
wireless communication system, with the increase of data rate the distortion of the received signal caused by multipath fading channel become a major problem. OFDM (orthogonal frequency division multiple access) technique is a solution of this problem in wireless communication. OFDM provides much more bandwidth efficiency as compared to conventional multicarrier modulation schemes. Simulation results are based on MATLAB completely.
A Review on Orthogonal Frequency Division Multiplexing (OFDM
Orthogonal frequency division multiplexing (OFDM) is a special case of multicarrier transmission where a single DataStream is transmitted over a number of lower rate subcarriers. In July 1998, the IEEE standardization group decided to select OFDM as the basis for their new 5-GHz standard aiming a range of data stream from 6 up to 54 Mbps. This new standard is the first one to use OFDM in packet-based communications. In wireless communication, concept of parallel transmission of symbols is used to achieve high throughput and better transmission quality. Orthogonal Frequency Division Multiplexing (OFDM) is one of the techniques for parallel transmission. The idea of OFDM is to split the total transmission bandwidth into a number of orthogonal subcarriers in order to transmit the symbols using these subcarriers in parallel. In this paper we will discuss the basics of OFDM technique, role of OFDM in this era, its benefits and losses and also some of its application.
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
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Problem statement: Nowadays, the mobile telecommunications industry faces the problem of providing the technology that be able to support a wide variety of services ranging from voice communication with a bit rate of a few kbps to wireless multimedia in which bit rate up to 2 Mbps. Approach: This study introduced a new performance study to enhance the Orthogonal Frequency Division Multiplexing (OFDM) system based on both efficient iterative number of subcarrier estimation techniques and a tracking algorithm was proposed. Result: The performance of system degrades with increase of the mobile velocity or increase of the number of channel fingers. The noiseless received signal at the weakest subcarrier is estimated based on all the detected data symbols using a hard or soft decision. Due to the flexibility of the transform design, the analysis conducted is applicable for other common systems as well. Conclusion: Simulation results showed the proposed algorithm can track the velocity variation very well and perform channel estimation using the most efficient tracking mode.