MIMO-OFDM

Multiple transmit and receive antennas can be used to form multiple-input multiple-output (MIMO) channels to increase the capacity by a factor of the minimum number of transmit and receive antennas. In this paper, orthogonal frequency division multiplexing (OFDM) for MIMO channels (MIMO-OFDM) is considered for wideband transmission to mitigate intersymbol interference and enhance system capacity. In this paper performance analysis of channel estimation through different algorithms for estimating channel using BPSK modulation scheme are investigated for different channel delay spread. The estimation of channel at pilot frequencies is based on Least Square, Minimum mean square channel estimation algorithm. We have compared the performances of these two channel estimation algorithm by measuring bit error rate Vs SNR. Minimum Mean Square estimation has been shown to perform much better than Least Square channel estimation algorithm.

This paper proposes an advanced MIMO-OFDM reconfigurable architecture along with companding transform. The reconfigurable architecture uses switching algorithm between MIMO diversity and special multiplexing which allows selecting the MIMO configuration and improves the BER. The major drawback of orthogonal frequency division multiplexing (OFDM) system is peak to average power ratio (PAPR). Many techniques were developed to reduce PAPR. Considering all available PAPR reduction techniques, companding transform is attractive technique for its simplicity. This paper put forward the comparison of two techniques namely exponential companding and nonlinear companding. In this paper evaluation of performance is shown in terms of bit error rate and peak to average power ratio.

Multi-user MIMO offers big advantages over conventional point-to-point MIMO: it works with cheap single-antenna terminals, a rich scattering environment is not required, and resource allocation is simplified because every active terminal utilizes all of the time-frequency bins. However, multi-user MIMO, as originally envisioned, with roughly equal numbers of service antennas and terminals and frequency-division duplex operation, is not a scalable technology. Massive MIMO (also known as large-scale antenna systems, very large MIMO, hyper MIMO, full-dimension MIMO, and ARGOS) makes a clean break with current practice through the use of a large excess of service antennas over active terminals and time-division duplex operation.

In this paper, we proposed a particle swarm optimization (PSO) based partial transmit sequence (PTS) technique in order to achieve the lowest Peak-to-Average Power Ratio(PAPR) in Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems. Our approach consist of applying the PSO based PTS on each antenna of the system in order to find the optimal phase factors, which is a straightforward method to get the minimum PAPR in such a system. The simulation results demonstrate that the PSO based PTS algorithm when applied to MIMO-OFDM systems with a wide range of phase factors, tends to give a high performance. In addition, there is no need to increase the number of particles of the PSO algorithm to enhance the performance of the system. As a result of this, the complexity of finding the minimum PAPR is kept at a reasonable level.

Advanced Communication Systems are wideband systems to support multiple applications such as audio, video and data so and so forth. These systems require high spectral efficiency and data rates. In addition, they should provide multipath fading and inter-symbol interference (ISI) free transmission. Multiple input multiple output orthogonal frequency division multiplexing (MIMO OFDM) meets these requirements Hence, MIMO-OFDM is the most preferable technique for long term evaluation advanced (LTE-A). The primary objective of this paper is to control bit error rate (BER) by proper channel coding, pilot carriers, adaptive filter channel estimation schemes and space time coding (STC). A combination of any of these schemes results in better BER performance over individual schemes. System performance is analyzed for various digital modulation schemes. In this paper, adaptive filter channel estimated MIMO OFDM system is proposed by integrating channel coding, adaptive filter channel estimation, digital modulation and space time coding. From the simulation results, channel estimated 2×2 MIMO OFDM system shows superior performance over individual schemes. 1. INTRODUCTION Advanced mobile systems aim on supporting high data rate services over multiple systems for multi-media applications involving voice, data, pictures and video. They should provide services without interruptions for private and public networks. These services require interference free transmission over frequency selective fading channels. OFDM is a promising technique for Long Term Evaluation-Advanced (LTE-A), Worldwide Interoperability for Microwave Access (Wi-MAX) systems, IEEE 802.11ac, and IEEE 802.15 [1]. A good channel estimation procedure is necessary in order to make reliable decisions and to coherently demodulate the received data. OFDM systems require effective and exact channel estimation for time-varying channels. The principal motto of this paper is to improve the OFDM system performance by proper channel coding, suitable digital modulation schemes, adaptive filter channel estimation techniques and multiple antennas at the transmitter and receiver. By using all these, an integrated OFDM system is proposed to enhance system performance [2-3]. Gosh [4] formulated a closed form expression for impulse noise performance in a multicarrier QAM system and showed that it is better than single carrier systems for moderate values of impulse power and probability. Dong et al. [5] determined the power and rate adaptation analytically with channel state information in the presence of carrier frequency offset (CFO) for an OFDM system. Sabbaghian et al. [6] developed a new code based on dual BCH code for reduction of PAPR in multi

In wireless communications, there is an endless quest for high channel capacity and improved quality.MIMO could increase the capacity of wireless communication system considerably compared to SISO.Fading causes poor performance in a communication because it can result in a signal power loss without reducing the noise power.OFDM could obtain good performances in multi-path frequency-selective fading channels.The closed form expressions of ergodic capacity of MIMO-OFDM systems is derived when transmitter has no channel state information(CSI) and the receiver has perfect CSI.In this paper, channel capacity of MIMO-OFDM system is estimated using Rayleigh fading channels under different system specifications like number of transmit and receive antennas and different power levels.

This work concerns of reducing the effect of a drawback of some wireless systems that were sensitiveto the peak power signals, namely peak-to-average power ratio (PAPR) problem. It is considered as a vitaldisadvantage of the Multiple-Input Multiple-Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM)-based wireless systems. The effect of a new proposition called special averaging adaptive wavelettransformation (SAAWT) will be studied over Sniffer Mobile Robot (SNFRbot) wireless system. This propositionwill check the SNFRbot performance and measure its capability of reducing the PAPR. Furthermore, two previously published works will be used to validate our proposition; Neural Network-based, special averagingtechnique-based. In addition, it compares the attained results with literature techniques such as selective mapping(SLM), Clipping technique, and partial transmit sequence technique (PTS). The SNFRbot based MIMO-OFDM performance is checked based on both of the Bit Error Rate (BER) and Complementary Cumulative DistributionFunction (CCDF) curves. This is true in the light of the limitation of bandwidth and channel behaviors constants.This will be attained by making use of two kinds of data; randomly generated data and practically collected datathat have been extracted from a funded project entitled energy consumption: efficiency and management (ECEM).As a result, the proposed work, namely special averaging adaptive wavelet transformation (SAAWT), shows promising results to enhance the SNFRbot performance. The SAAWT-based work is compared to five other worksand shows powerfulness in combatting the PAPR; the achieved enhancement falls in the range between 20% and83.89%. BER enhancements combat the channel effects, where it achieves a 65.5% over the SAT-Based work and42% over the NN-Based work. Furthermore, the enhancement of the SAAWT over literature work falls in the period between 46.3% and 55.1%

In this paper we suggest to use the ASTC (Algebraic Space Time Codes) as powerful coding technique for IEEE 802.11x OFDM standard combined with PAPR reduction scheme. ASTC with their very Algebraic-construction based on Quaternionic algebra, have a full rate, full diversity, non-vanishing constant minimum determinant for increasing spectral efficiency, uniform average transmitted energy per antenna and good shaping, readily lend themselves to high data rate situations. However, by their construction they require a nonselective flat fading channels belonging to narrow-band systems. In fact, such systems are not readily found in airs interfaces. In open air we have what are commonly called frequency-selective fading channels. As a matter of fact, it becomes extremely necessary to harness their power for wide-band systems.

This paper analyzes the impact of fading correlation, cross polarization coupling and channel degeneracy
alias keyhole condition on the error performance of V-BLAST MIMO system that employs detector
algorithms like ZF, MMSE and ML with ordering and successive cancellation. Deleterious impact of above
mentioned channel impairments on MIMO system capacity is studied. Simulation results show the BER
performance of these detectors for different modulation schemes. It is observed that lesser the channel
fading correlation and cross polarization coupling values better is the performance of these detectors.
Study is extended to see the effect of transmit and receive antenna correlation on Ergodic MIMO capacity.

A new work based-wavelet transform is designed to overcome one of the main drawbacks that found in the present new technologies. Orthogonal Frequency Division Multiplexing (OFDM)is proposed in the
literature to enhance the multimedia resolution. However, the high peak power (PAPR) values will obstruct such achievements. Therefore, a new proposition is found in this work, making use of the wavelet
transforms methods, and it is divided into three main stages; de-noising stage, thresholding stage and then the replacement stage.
In order to check the system stages validity; a mathematical model has been built and its checked after using a MATLAB simulation. A simulated bit error rate (BER) achievement will be compared with our
previously published work, where an enhancement from 8×10-1 to be 5×10-1 is achieved. Moreover, these results will be compared to the work found in the literature, where we have accomplished around 27%
PAPR extra reduction. As a result, the BER performance has been improved for the same bandwidth occupancy. Moreover and
due to the de-noise stage, the verification rate has been improved to reach 81%. This is in addition to the noise immunity enhancement.

Using the Channel State Information (CSI) at the transmitter is fundamental for the precoder design in Multiuser Multiple Input Single Output (MU-MISO-OFDM) systems. In Frequency Division Duplex (FDD) systems, CSI can be just available at the transmitter through a limited feedback channel [1], where we assume that each user quantizes its channel direction with a finite number of quantization bits. In this paper, we consider a scalar quantization (SQ) scheme of the Channel Direction Information (CDI). Although vector quantization (VQ) schemes [2], [3] still outperform this scalar scheme in terms of quantization error and Sum rate, the former scheme suffers from an exponential search complexity and high storage requirements at the receiver for high number of feedback bits.

The data rate for the Multiple-Input Multiple-
Output (MIMO) - Orthogonal Frequency Division Multiplexing
(OFDM) systems can be increased by spatial multiplexing which
uses Space-Time coding techniques. The spatial multiplexing
provides increased spectral (bandwidth) efficiency. In this
paper, vertical and horizontal encoding techniques of layered
Space-Time codes are implemented. Their performance is
analyzed by comparing the Bit Error Rate (BER) and Signal to
Noise Ratio (SNR). This technique performs better than
conventional methods. The powerful Forward Error Correction
(FEC) codes like Turbo codes and Rate-Compatible Punctured
Convolutional (RCPC) codes are compared. The Maximum
likelihood (ML) receiver is used for detection of transmitted
symbols. The simulation results show that Turbo codes gives
enhanced performance than RCPC and optimal detection
accuracy is given by ML receiver than others but with higher
complexity. This paper provides the possibilities of increasing
the data rate and data transmission with less error for MIMOOFDM
systems using spatial multiplexing and various FEC
codes with Maximum Likelihood receiver.

the conjunction of MIMO systems with OFDM has emerged as a promising technology in recent years. The use of multiple transmit and receive antennas forming MIMO-OFDM systems not only provide robustness against multipath fading impairments but also ensures significant increase in the rates over frequency selective channels. Furthermore this technology is now making possible to build high data rate communication systems with affordable receiver complexity. Because of these advancements, MIMO-OFDM has been widely adopted for different wireless standards all over the world and few names to mention are IEEE 802.11n (WLAN), IEEE 802.16e-2005(WiMAX), 3 rd Generation Partnership Project (3GPP) Long Term Evolution (LTE).

The main objective of this project is to design the full-rate Space-Time-Frequency Trellis code (STFTC), which is based on Quasi-Orthogonal designs for Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. The proposed Quasi-Orthogonal Space-Time-Frequency Trellis code combines set partitioning and the structure of quasi-orthogonal space-frequency designs in a systematic way. In addition to multipath diversity and transmit diversity, the proposed code provides receive diversity, array gain, and achieve high-coding gain over a frequency selective fading channel. As simulation results demonstrate, the code outperforms the existing Quasi-Orthogonal Space-Time-Frequency Trellis codes in terms of frame error rate performance.

In wireless communication systems, popularly known as MIMO (Multiple-Input Multiple-Output) technology, the use of multiple antennas at the transmitter and receiver has rapidly gained in popularity over the past decade due to its powerful performance-enhancing capabilities. This research incorporates a comprehensive BER simulation study undertaken on the effectiveness of a  Space-Time Trellis Coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) communication system. The STTC encoded MIMO-OFDM Communication system under present study has integrated two digital modulation schemes (QAM, QPSK) over fading (Rayleigh and Rician) and  Additive White Gaussian Noise (AWGN) channels for two transmitting  and two receiving antennas. Minimum Mean-Square-Error (MMSE) channel equalization algorithm has been implemented here. Computer simulations are performed with synthetically generated data from audio signal and the results on  bit error rate (BER) reveals that the MIMO-OFDM system with STTC coding under QAM modulation technique is highly effective to combat inherent interferences under Rayleigh, Rician fading and Additive White Gaussian Noise (AWGN) channels. It is projected from the study that the retrieving performance of the communication system degrades with the lowering of the signal to noise ratio (SNR).