Space-time-frequency Block Codes Research Articles

Peningkatkan QoS Layanan Video Call dengan Metode DASTFBC Sistem MIMO2x2 pada Jaringan LTE

ABSTRACT
 The DASTFBC (Diagonal Algebraic Space Time Frequency Block Code) method is a coding scheme that utilizes different diversity sources, namely space, time and frequency. This method is one method that can be used to improve video call services. The DASTFBC method uses a rotation matrix in the DAST code which is formed using algebraic number field theory. The code matrix structure consists of rotated information symbols, expanded using a square diagonal code matrix. This method is used to overcome signal power fluctuations at the receiver which cause the service quality to decrease (not comply with) BER video call standards. The DASTFBC method is applied to the LTE network MIMO system with 64 QAM modulation. This method will be simulated in the Matlab program to obtain results to improve video call services. The DASTFBC method simulation of BER was carried out for 4 user speed scenarios, namely 5km/hour, 40km/hour, 100km/hour, 120km/hour. Significant results of the DASTFBC method can already be seen when the user moves at 40km/ hour. With this method, a smaller BER value is obtained, namely 2x10-4, this shows that with the DASTFBC method the video call BER standard (10-3) can be met. The value of BER obtained when using DASTFBC with a speed of 120km/h is 8.5x10-3 this value almost exceeds the standard BER video call. So that the maximum speed of the user when using the DASTFBC method is 120km/h above that speed the standard value of the BER video call cannot be fulfilled.
 Keywords: video call, LTE network, MIMO, DASTFBC

Reduction of PAPR and improved BER using SLM technique

Abstract: With the introduction of 5G wireless technology, mankind has achieved a massive leap in data throughput of gigabits per second thanks to the combination of multiple input, multiple output, and orthogonal frequency division multiplexing technologies. Multiple (OFDM MIMO) can be achieved via frequency selective fading. PAPR (Peak-to-Average Power Ratio) is one of the most crucial performance concerns, since it makes OFDM particularly prone to harmonic distortion, reducing channel estimate accuracy and resulting in a lower bit error rate (BER). In the MIMO-OFDM system, we present a selective codeword shift mapping approach (SCS-SLM). It lowers the PAPR and forces the power amplifier to operate in the non-linear region, resulting in sub-carrier intermodulation, signal constellation, bit error rate distortion, and improved system performance. Additionally, using orthogonal frequency division multiplexing with space-time-frequency block code (STFBC OFDM) may increase BER performance. Selective Mapping is mentioned in this research as an effective approach for reducing PAPR. Furthermore, the bit error rate performance of this system is reviewed, as well as the process complexity as a result. A complete examination of the mutual independence of the alternative OFDM signals generated using this technique is also discussed, in addition to the previously mentioned analysis. Furthermore, the superfluous bits on the side of the transmitted OFDM signal are removed with this new technique. Keywords: (peak-average power ratio (PAPR), Multiple-input, multiple-output & orthogonal frequency-division multiplexing (MIMO-OFDM), space-time frequency block codes (STFBC), Selective Codeword Shift Selective mapping (SCS-SLM)

Coding advantage optimization of space-time-frequency block codes

In this article, we study the coding advantage of space-time-frequency block codes (STFBCs). Since in MIMO-OFDM coding there is the potential of exploiting space, time and frequency diversities and as the frequency tones of OFDM modulation are relatively substantial, the intricate structure of STFBCs makes it almost impossible to optimize the parameters of the code as the number of symbols increases in each block. Consequently, we investigate how to optimize the code parameters independently to reduce the computational complexity. Furthermore, code permutation is an important part of the STFBCs. However, due to elaborate structure of the STFBCs, it is very hard to calculate the optimum permutation. Therefore, we put forth a technique to decompose the coding advantage of the STFBCs. Using this technique, the permutation parameter can be easily introduced and optimized for STF-BCs. We then design a novel STFBC based on any given STBC and apply the proposed scheme on the proposed STFBC to illustrate the application of this technique by designing the optimum permutation for the code. Simulation results confirm that the proposed STFBC outperforms the best existing STFBCs in the literature.

Quasi‐orthogonal space–frequency and space–time–frequency block codes with modified performance and simplified decoder

Due to their superior performance and moderate computational complexity, quasi-orthogonal space–frequency block codes (QOSFBCs) and quasi-orthogonal space–time–frequency block codes (QOSTFBCs) are among prime candidates for implementation in multiple-input multiple-output communications systems. Originally, these codes were introduced for two transmit antennas and it is proved that they are full-diversity within channels with equal-power profile and integer delays. In this study, first, the authors generalise the construction of QOSFBCs and QOSTFBCs for arbitrary number of transmit antennas. Then, they provide the theoretical proof that these codes are full-diversity for any arbitrary number of transmit antennas and any arbitrary delay and power profiles. Furthermore, they prove that the coding advantage of these codes is decomposed into two distinct parts, one of which represents the effect of the channel and the other represents the effect of the precoder. By optimising these two parts, they propose a modified version of QOSFBCs and QOSTFBCs which outperforms the latest space–frequency block codes and space–time–frequency block codes in the literature according to the analytical results and support of simulation results. Finally, they propose a new suboptimum linear decoder for the QOSFBCs and the QOSTFBCs which could achieve almost the same performance as the maximum-likelihood decoder for large number of subcarriers.

IMPROVING STFBC MIMO OFDMA WITH CHANNEL ESTIMATION USING DFT AND DCT TECHNIQUE

Higher demand in rapid data transmission makes the wireless technology become more popular in this new modern era. However due to the many users that want to have access in the same time, it can cause congested traffic and affect the data rate. OFDMA modulation scheme with combination of MIMO will support high data signal and become one of the best solutions that can fulfil everybody’s dream. These MIMO OFDMA system is based on the diversity coding and appropriate channel estimation in order to achieve maximum diversity order for each user and minimize the interference that have been generated during the transmission. Thus, in this paper in order to boost the overall system performances, Space Time Frequency Block Code (STFBC) and channel estimation technique involving Discrete Fourier Transform (DFT) and Discrete Cosine Transform (DCT) are going to be tested to compare their performance. The result states that when using STF block code, it will gain better performance in MIMO OFDMA system by producing lower bit error rate compare to existence DCT and DFT.

Improving Space-Time-Frequency MIMO-OFDM with ICI Self-Cancellation Scheme using Least Square Error Estimator

Channel estimation techniques for Multiple-input Multiple-output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) based on comb type pilot arrangement with least-square error (LSE) estimator was investigated with space-time-frequency (STF) diversity implementation. The frequency offset in OFDM effected its performance. This was mitigated with the implementation of the presented inter-carrier interference self-cancellation (ICI-SC) techniques and different space-time subcarrier mapping. STF block coding in the system exploits the spatial, temporal and frequency diversity to improve performance. Estimated channel was fed into a decoder which combined the STF decoding together with the estimated channel coefficients using LSE estimator for equalization. The performance of the system was compared by measuring the symbol error rate with a PSK-16 and PSK-32. The results show that subcarrier mapping together with ICI-SC were able to increase the system performance. Introduction of channel estimation was also able to estimate the channel coefficient at only 5dB difference with a perfectly known channel.

On permutation of space‐time‐frequency block codings

Multi-input multi-output-orthogonal frequency-division multiplexing is the foundation of next generation of wireless communication systems and space-time-frequency block coding (STFBC) is considered one of the best schemes for implementing these systems. STFBCs have very complex structures and many parameters affect their performance. Studies have shown that permutation parameter plays a very important and sensitive role in the construction of STFBCs so much so that a small variation of this parameter could cause a significant change in the value of the coding advantage (CA) which alters the code's performance. In this study, first the authors explore how the permutation parameter affects STFBCs and demonstrate that existing permutation methods do not guarantee to attain the maximum possible CA. Next, they introduce a new structure for STFBCs permutation, which is the basis for the design of a modified model of one recently published STFBC. Comparison of the simulation results from the original and modified codes confirms the latter improves the performance by up to 3 dB. This is an achievement that is also verified by theoretical analysis.

Space–time–frequency coding over quasi-static frequency-selective channels with linear complexity for the ML receiver

The achievement of our previously proposed space–time coding algorithm entitled full-rate linear-receiver space–time block code (FRLR STBC) has motivated us to propose, in this paper, a new class of high-rate space–time–frequency block codes (STFBCs) over frequency-selective Rayleigh fading channels. We have called these codes FRLR STFBCs with interleaving (FRLR STFBCs-I). FRLR STFBCs-I could achieve a full-diversity property over quasi-static channels. Simulation results also verify that the proposed schemes exhibit proper performances in comparison with the recently proposed STFBCs. The most outstanding characteristic of the newly introduced high-rate codes is the linear complexity of the maximum likelihood (ML) receiver which makes possible a fast and economical decoding process.

Performance of MIMO-OFDM system using Linear Maximum Likelihood Alamouti Decoder

A MIMO-OFDM wireless communication system is a combination of MIMO and OFDM Technology. The combination of MIMO and OFDM produces a powerful technique for providing high data rates over frequency-selective fading channels. MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system.In this paper , the bit error rate (BER) performance using linear maximum likelihood alamouti combiner (LMLAC) decoding technique for space time frequency block codes(STFBC) MIMO-OFDM system with frequency offset (FO) is being evaluated to provide the system with low complexity and maximum diversity. The simulation results showed that the scheme has the ability to reduce ICI effectively with a low decoding complexity and maximum diversity in terms of bandwidth efficiency and also in the bit error rate (BER) performance especially at high signal to noise ratio.

Full-Diversity Space-Time-Frequency Coding with Very Low Complexity for the ML Decoder

Recently proposed full-diversity space-time-frequency block codes (STFBCs) generally suffer from very high computational complexity at the receiver side. In this paper, we introduce a new class of full-diversity STFBCs for quasi-static (QS) channels which features a comparatively low complexity at the receiver. We also demonstrate that our proposed algorithms could offer maximum coding advantage if the transmitter knows partial channel side information. Simulation results also verify that our coding schemes outperform other recently published STFBCs that were considered.

Blind Channel Shortening for Space-Time-Frequency Block Coded MIMO-OFDM Systems

This paper deals with multiple-input multiple-output (MIMO) broadband wireless communication systems, employing orthogonal frequency-division multiplexing (OFDM) with cyclic prefix (CP) in combination with space-time-frequency block coding (STFBC). In order to exploit the benefits of OFDM and STFBC in highly frequency-selective channels, without incurring in a significant increase of receiver complexity, a channel shortening prefilter is inserted at the receiver, aimed at reducing the length of the MIMO channel impulse response before CP removal. Two MIMO channel shorteners are proposed, both relying on linearly-constrained minimization of the mean-output-energy of the signal at the output of the channel shortener, where the linear constraints are optimally chosen so as to maximize the signal-to-noise ratio either at the output of the channel shortener or at the input of the STFBC maximum-likelihood decoder. Unlike other solutions proposed in the literature, these shortening designs are blind ones, i.e., a priori knowledge of the MIMO channel impulse response to be shortened is not required, and can be carried out in closed-form, i.e., iterative computation of the prefilter weights is not necessary. Numerical simulations show that, without a substantial increase in computational complexity, receivers equipped with the proposed blind channel shorteners pay only a negligible performance penalty with respect to non-blind channel shorteners, while being significantly more robust to finite sample-size effects.

Diversity technique for multiple input multiple output orthogonal frequency division multiplexing (MIMOOFDM) system using a new subcarrier mapping scheme

The objective of this research is to propose a new subcarrier mapping scheme intercarrier interference self cancellation intercarrier interference self cancellation (ICI-SC) technique using data allocation in space time frequency block codes (STFBC) multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system. It aims to achieve maximum diversity order and to compensate integrated effect of frequency offset (FO) for intercarrier interference (ICI) reduction in the system. Using theoretical derivation of the pairwise error probability (PEP), a simulation model is then being used to compare with adjacent and symmetric subcarrier mapping scheme with FO. The results show that the ICI contained in the received signals can be effectively reduced using a new subcarrier mapping scheme. Thus, the proposed method is using STFBC outperforms existing subcarrier mapping schemes by approximately reducing the ICI with maximum diversity order in MIMO-OFDM system.

Distributed space-time-frequency coding for cooperative OFDM systems

A distributed space-time-frequency (STF) coding scheme is proposed for cooperative OFDM (C-OFDM) systems with three terminals over quasi-static frequency-selective Rayleigh fading channels. The outage probability is derived and its tight closed-form lower bound is presented. Asymptotic analysis indicates that the proposed scheme can achieve both spatial and multipath (frequency) diversity. The theoretical analysis of the proposed STF coded scheme is further implemented by the distributed group STF block coding (D-GSTFBC) scheme based on the subcarrier grouping technique. Simulation results confirm the previously introduced theoretical analysis.

Single Carrier Frequency-Domain Equalization with Transmit Diversity over Mobile Multipath Channels

This paper discusses a cyclic prefixed single carrier frequency-domain equalization (SC-FDE) scheme with two types of transmit diversity. Firstly, we propose a SC-FDE system with space-frequency block coding (SFBC). The transmit sequence of the proposed system is designed to have spatial and frequency diversities, which is equivalent to the SFBC. The corresponding combining receiver is derived under a minimum mean square error (MMSE) criterion. It is shown that the proposed system significantly outperforms the SC-FDE system with space-time block coding (STBC) over fast fading channels, while providing lower computational complexity than orthogonal frequency division multiplexing (OFDM) combined with SFBC. We verify the performance of two-branch transmit diversity systems including the proposed one through bit error rate (BER) analysis. Secondly, as a scheme that combines STBC and SFBC, a space-time-frequency block code (STFBC) SC-FDE system is presented. Computer simulation results show that the proposed STFBC SC-FDE system has better immunity to the distortion caused by both fast fading and severe frequency selective fading, compared to the SC-FDE system with the STBC or the SFBC scheme. Complexity analysis is also conducted to compare their computational loads of the transceiver. It is shown that the proposed STFBC SC-FDE system has lower computational complexity than the STFBC OFDM system.

Rate-one space-frequency block codes with maximum diversity for MIMO-OFDM

We propose a novel rate-one (i.e., one symbol per transmission), space-frequency block code (SFBC) for an orthogonal frequency division multiplexing (OFDM) system with transmit (M), and receive (N) antennas that achieves the maximum diversity attainable over frequency-selective channels. Moreover, the space-frequency (SF) code design is shown to be robust to overestimation of the (true) channel order L at the price of increasing decoding complexity. Further, even if the channel order is underestimated (K<L), diversity order of MNK is achieved with commensurately reduced decoding complexity; this allows a natural mechanism for trading diversity for decoding complexity as desired. In addition, since the SF code symbol is transmitted in one OFDM block duration, it has a smaller processing delay than comparable space-time-frequency block codes (STFBC).

Improved Channel Estimation for OFDM Systems with Multiple Transmit Antennas over Time-Varying Multipath Fading Channels

By using multiple transmit antennas, wireless systems have a large capacity in time-varying multipath fading channels. Space-time block code (STBC), space-frequency block code (SFBC), and space-time-frequency (STF) block code are well-known techniques in transmitter diversity schemes. While the SFBC (or the STF block coded) system gives full diversity at frequency-nonselective channels, it breaks down when used in a frequency-selective environment. This is because the SFBC (or the STF block code) scheme disregards frequency selectivity of the channel by assuming that channel frequency responses (CFRs) at adjacent subcamers are the same. In this paper, we propose efficient channel estimation and symbol decoding methods, which consider the difference between CFRs at the adjacent subcamers of the SFBC (or the STF block coded) orthogonal frequency division multiplexing (OFDM) system in multipath fading channels. The proposed method gives initial channel information by designing a simple training symbol, and the CFRs at all the subcarriers and the differences between the CFRs are easily calculated by using an interpolation method or a discrete Fourier transform (DFT) operation.