Using Ofdm Transmitter And Receivers

Inter symbol interference (ISI) is avoided by assuming the duration of cyclic long enough and furthermore the channel is assumed to be stationary within one symbol period ( h(k)=hr ).

These sub-carriers are orthogonal to each other. It is very much popular scheme used in digital television, audio broadcasting and 4G communications. OFDM has the ability to deal with severe channel fading conditions without complex equalization filters. Due to the longer symbol period and the CP extension, OFDM is more robust against the effect of timing offset and delay spread in multipath fading channels. OFDM also gain higher spectral efficiency due to the overlapping of the subcarrier spectrum which are orthogonal to each other. The major drawback of OFDM is high

TDM advantage over FDM is that it offers bandwidth saving and there is low interference between the signals that are being multiplexed.

Shannon proved that data could be transmitted through a channel with speeds closing the channel’s capacity, with no transmission errors and low transmitting power by using the right code (Shannon, 1948). [2] For an Additive White Gaussian Noise (AWGN) channel the formula is R. In this paper, introducing Turbo codes they showed that it is possible to approach Shannon’s limit within 0,5 dB, for a bit error rate of 1:100000 (Berrou, Glavieux and Thitimajshima, 1993) [4]. Albeit Turbo codes were innovative, they actually used two previously known techniques; the concatenated coding and the iterative decoding, which will be briefly described below.

Various woks have been done on OFDM. In OFDM, as all the carriers are added using an IFFT operation, this may lead to a signal with large peaks and dynamic range in time domain. For an OFDM signal x (t),

Abstract- In multiple-input multiple-output (MIMO) systems, spatial demultiplexing at the receiver is a motivational task. Thus, several detection techniques are investigated in existing literature. There is a tradeoff between computational complexity and optimal performance in many detection techniques. The ordered successive interference cancellation (OSIC) with minimum mean square error (MMSE) is used to improve the error performance. However, maximum likelihood (ML) detection gives optimal performance at the higher complexity level whereas MMSE-OSIC detection is less complex. Therefore, MMSE-OSIC2 detection is suggested as a solution. In this paper, spatial multiplexed (SM) MIMO systems are considered to evaluate error performance with different detection techniques such as MMSE-OSIC, ML and MMSE-OSIC2 in a composite fading i.e. Weibull-gamma (WG) fading environment. In WG distribution, Weibull and gamma distribution represent multipath and shadowing effects respectively. It is shown by simulation results that the MMSE-OSIC2 detection technique gives the improved symbol error performance (SER) which is closely likely ML performance

One direct method for increasing the capacity of a system is to raise the transmission bandwidth per wavelength either optically or electronically. In optical communication, there are two broadly used techniques for increasing the capacity of the transmission. The first technique is to spread-out the bandwidth by adding numerous optical carriers. This technique has already been slow and deployed and it is known as Wavelength Division Multiplexing (WDM). Wavelength Division Multiplexing can benefit to extend the transmission bandwidth by adding various transceivers for the current optical fiber links deprived of the need to install other fiber links. WDM is considered as one of the most cost effective methods to raise the optical fiber link quantity. The second technique is to extend the electronic bandwidth per wavelength relying on the CMOS technology.

[1]S. M. Alamouti, describes a simple two-branch transmit diversity scheme. Using two transmit antenna and one receive antenna, the new transmit antenna provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit and two receive antennas. The scheme easily be generated to two transmit antenna and M receive antenna to provide a diversity order of 2M. This scheme does not require any bandwidth expansion any feedback from the receiver to the transmitter and its computation complexity is similar to MRRC. This also provide diversity improvement to all the remote units in a wireless system, using two transmit antennas at the base station instead of two receive antenna at all the remote terminals.

Rapid and exponential increases in data communications are continuing to drive the complexity of our computing, networking and sensing systems. Recently OAM has gained much interest in transmission efficiency and spectral efficiency in optical fiber communications with the ability of carrying independent data streams on orthogonal spatial modes. The key factor in the optical fiber communications using OAM is to design and fabrication of the fiber so as to support the the different modes of OAM.while the free space systems can theoretically use an unlimited number of OAM modes. However achieving the full potential of OAM multiplexing requires an efficient and rotation invariant multiplexer and demultiplexer which can be interfaced with single-mode optical components. Fiber based OAM generation and

OFDM is a great technique to handle impairments of wireless communication channels such as multipath propagation. Hence, OFDM is a practical candidate for future 4G wireless communications techniques [1]-[4]. On the other hand, one of the major drawbacks of the OFDM communication system is the drift in reference carrier. The offset present in received carrier will lose orthogonality among the carriers. Hence, the CFO causes a reduction of desired signal amplitude in the output decision variable and introduces ICI. Then it brings up an increase of BER. The effect caused by CFO for OFDM system was analyzed in [7]-[9]. In [7] BER upper bound of OFDM system is analyzed without ICI self-cancellation and BER of OFDM system is analyzed using self-cancellation, but this method is less accurate. In [9], it is indicated that CFO should be less than 2% of the bandwidth of the sub-channel to guarantee the signal to interference ratio to be higher than 30 dB. A critically sampled OFDM system/OQAM system is also not robust to CFO [9], even when optimal pulses are used as shaping filters. Thus, carrier frequency offset greatly degrades system performance. Therefore, practical OFDM systems need the CFO to be compensated with sufficient accuracy, and this has led to a whole lot of literature on CFO estimation algorithms. Most of the existing CFO estimators for OFDM are based on periodically transmitted pilot symbols. Yet, the pilot symbols transmission loses a significant bandwidth,

The principle goal of MIMO technology is to improve either the quality (BER) or the data rate of the communication by means of adequate signal processing techniques at both ends of the system. The capacity can increase linearly with the number of antennas when using MIMO system. MIMO can obtain both multiplexing gain and diversity gain thus significantly increasing the system capacity as well as improving the reliability of the wireless link. Having high spectral

Mr. R. K. Somani HOD(CE & IT) ITM,Bhilwara(Raj.)311001 Under the guidance of: Mr.Vijay Prakash Sharma Lecturer(CE)

The performance of spectrally efficient WDM system is analyzed in terms of Q-factor, BER and optical spectrum of the signal. Q-factor is given as:-

The growing need/use of satellite communications and constant technological evolvement proves the significance of this paper in modern day telecommunications.

In a single carrier system, single fade causes the whole data stream and undergo distortion i.e frequency selective fading. The Single carrier systems also suffer with heavy Inter Symbol Interference . In telecommunication Inter Symbol Interference was a form of distortion of signal in which one symbol interferes with the subsequent symbol. Thus it causes an unwanted phenomena as the previous symbols have similar effect as noise thus making communication less reliable . ISI occurs when the signal bandwidth is less than the coherence bandwidth or when the delay spread is greater than symbol duration. To combat the problem multicarrier techniques have been proposed for high data rate transmission. Multicarrier techniques divide the whole bandwidth into large number of narrow band orthogonal subcarriers [1, 2]. Thus the signal bandwidth becomes very less compared with coherence bandwidth ensuring no ISI in time domain and flat fading in frequency domain. Multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) and Multi Carrier Code Division Multiple Access (MC-CDMA) were considered to be the best technologies for 4G wireless communication [1, 2]. Fig. explains the spectrum of multicarrier and single carrier systems. In the single carrier system the information symbols are loaded into one of