Quasi-Orthogonal Space-Frequency and Space-Time-Frequency Block Codes for MIMO OFDM Channels

Fazel, Farhad; Jafarkhani, Hamid

doi:10.1109/twc.2008.060420

Cited by 53 publications

(71 citation statements)

References 27 publications

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“…For instance, if there are four different time slot codewords then there must be four independent OFDM modulators, one for each. For maximum diversity gains, it is required that number of OFDM subcarriers be more than or equal to the number of independent delay paths, L [11]. Now, if C is the independent codeword resulting in the discrete b j [n]-term after OFDM modulation, then the received message will be:…”

Section: B Channel Modelmentioning

confidence: 99%

“…The code structure adopted has been discussed in [8] following the QO-STBC method of code construction discussed in [6]. An interference free QO-STBC system achieves full diversity (see [11]) and the decoding matrix should be of the Equation 15 form [2,13]. Equation 14 can be obtained as in [2,8] by formulating: …”

Section: Free-interference Qo-stbc With Full Diversitymentioning

confidence: 99%

“…The combination of QO-STBC scheme with OFDM drives the system towards achieving maximum diversity gain since in achieving maximum diversity gain, the number of subcarriers, N, must be larger than or equal to the number of independent delay paths, L, [11]. …”

Section: Vmentioning

confidence: 99%

See 2 more Smart Citations

Improved QO-STBC OFDM System Using Null Interference Elimination

Anoh¹,

Abd‐Alhameed²,

Dama³

et al. 2013

IJACSA

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Abstract-The quasi-orthogonal space time block coding (QO-STBC) over orthogonal frequency division multiplexing (OFDM) is investigated. Traditionally, QO-STBC does not achieve full diversity since the detection matrix of QO-STBC scheme is not a diagonal matrix. In STBC, the decoding matrix is a diagonal matrix which enables linear decoding whereas the decoding matrix in traditional QO-STBC does not enable linear decoding. In this paper it is shown that there are some interfering terms in terms of non-diagonal elements that result from the decoding process which limit the linear decoding. As a result, interference from the application of the QO-STBC decoding matrix depletes the performance of the scheme such that full diversity is not attained. A method of eliminating this interference in QO-STBC is investigated by nulling the interfering terms towards full diversity for an OFDM system. It was found that the interference reduction technique permits circa 2dB BER performance gain in QO-STBC. The theoretical and simulation results are presented, for both traditional QO-STBC and interference-free QO-STBC applying OFDM.

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Section: B Channel Modelmentioning

confidence: 99%

Section: Free-interference Qo-stbc With Full Diversitymentioning

confidence: 99%

See 1 more Smart Citation

Improved QO-STBC OFDM System Using Null Interference Elimination

Anoh¹,

Abd‐Alhameed²,

Dama³

et al. 2013

IJACSA

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show abstract

“…For instance, the minimum distance between different codewords may reduce the likelihood of correctly decoding the right code. Hence, it is discussed that by properly choosing the constellations, the minimum distance between the STBC codewords is increased, then the QO-STBC performance can be improved towards full diversity [6,7,10]. Some other common methods by which full diversity can be attained by interference reduction have been shown in [3,8,9].…”

Section: Introductionmentioning

confidence: 99%

A Simplified Improvement on the Design of QO-STBC Based on Hadamard Matrices

Anoh¹,

Dama²,

Abd‐Alhameed³

et al. 2014

IJCNS

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In this paper, a simplified approach for implementing QO-STBC is proposed and evaluated with improved performance. It is based on the Hadamard matrix, in which the scheme exploits the Hadamard matrix property to attain full diversity. Hadamard matrix has the characteristic that diagonalizes a quasi-cyclic matrix and consequently, a decoding matrix so that a diagonal matrix which permits linear decoding is achieved. Using quasicyclic matrices in designing QO-STBC systems requires that the codes should be rotated to reasonably separate one code from another such that error floor in the design can be minimized. It will be shown that, orthogonalizing the secondary codes and then imposing the Hadamard criteria of the scheme can be well diagonalized. The results of this simplified approach demonstrate full diversity and better performance than the interference-free QO-STBC. Results show about 4 dB gain with respect to the interference-free QO-STBC scheme and it performs alike with the earlier Hadamard based QO-STBC designed with rotation. These results achieve the consequent mathematical proposition of the Hadamard matrix and its property is also shown in this study.

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“…Thus, space-time-frequency (STF) and spacefrequency (SF) coding were developed to deed the maximum diversity provided by MIMO frequency selective channels [4]. In ST coding, the diversity is equal to the product of the number of transmit and receive antennas .In STF coding, diversity is given by the product of the number of its transmit antennas, the number of its receive antennas, and the number of independent channels taps [5]. Liu , Xin and Giannakis [6] introduced STF coding across multiple OFDM block for multiple transmit antenna.…”

mentioning

confidence: 99%

Combined Beamforming with Space Time Frequency Coding for Mimo-OFDM Systems

Selvi¹

2017

IJRASET

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Multiple antennas can be used in wireless systems to attain good quality of service and high data rate communication. Recently, efficient space-time-frequency (STF) codes have been developed to improve the diversity gain. Performance of multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system using STF Coding and random beamforming is analysed. Combined beamforming with STF code offers improved performance over STF in term of bit error rates (BER) when compared to existing combined space-time block code (STBC) with beamforming Keywords: space-time -frequency code,MIMO-OFDM,beamforming,diversity order. I. INTRODUCTIONDiversity is an real technique to combat fading and increase the transmission reliability over wireless channels since it provides multiple independent replica of the trans-mitted signal at the receiver. MIMO systems have achieved a focus of attention because it can significantly increase the spectral efficiency by exploiting the spatial degrees of freedom created by multiple antennas [1]. In wireless communications, where the channel involves frequency selectivity, called frequency diversity, can be exploited by taking advantage of the frequency-selectivity characteristics of the channel. Both transmit diversity and orthogonal frequency-division multiplexing (OFDM) have been receiving a lot of attention and have shown great potential for the next generation wireless communication systems [2] due to its toughness to multi path fading, high spectral efficiency, and high flexibility in resource allocation. Space-time (ST) coding deeds the spatial diversity provided by the number of transmit antennas [3]. However, frequency selective channels provide an extra diversity dimension: frequency diversity. Thus, space-time-frequency (STF) and spacefrequency (SF) coding were developed to deed the maximum diversity provided by MIMO frequency selective channels [4]. In ST coding, the diversity is equal to the product of the number of transmit and receive antennas .In STF coding, diversity is given by the product of the number of its transmit antennas, the number of its receive antennas, and the number of independent channels taps [5]. Liu , Xin and Giannakis [6] introduced STF coding across multiple OFDM block for multiple transmit antenna. Gong and Letaief [2] introduced STF coding method over MIMO-OFDM channels. In [4],authors presented a STF coding method that expand the idea of frequency spreading and show how the symbols spread across several OFDM block transmission to perfectly isolate them at the receiver. In [7], authors use exponential correlation model and offer the BER by combining beamforming with space time block code (STBC) scheme. STF and beamforming techniques are two developing technologies that can be working at the base station (BS) with multiple antennas to deliver transmit diversity and beamforming gain to increase SNR of the downlink. This paper objects at performance analysis of multiple-input multiple-output orthogonal frequency-division multi...

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Quasi-Orthogonal Space-Frequency and Space-Time-Frequency Block Codes for MIMO OFDM Channels

Cited by 53 publications

References 27 publications

Improved QO-STBC OFDM System Using Null Interference Elimination

Improved QO-STBC OFDM System Using Null Interference Elimination

A Simplified Improvement on the Design of QO-STBC Based on Hadamard Matrices

Combined Beamforming with Space Time Frequency Coding for Mimo-OFDM Systems

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