Space-frequency Coding Research Articles

Space-Frequency Coded Quadrature Index Modulation With Linear Maximum Likelihood Detection

This paper focuses on the issue of achieving transmit diversity for the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system working with quadrature index modulation (QIM). Inspired by the ideas of quadrature spatial modulation (QSM) and quadrature space-frequency index modulation (QSF-IM), parts of the space-frequency resource units in each resource block (RB) of the MIMO-OFDM system are activated twice independently to send the in-phase and quadrature components of a space-frequency code, respectively, to achieve the second order transmit diversity. Thus the proposed scheme is called space-frequency coded QIM (SFC-QIM). The SFC-QIM scheme allows for a linear-complexity maximum likelihood (ML) receiver, which benefits from the orthogonality between the real and imaginary parts of the symbols in the SFC codewords. Owing to obtaining higher diversity order, simulation results of bit error rate (BER) performance demonstrate that the new SFC-QIM scheme outperforms some existing IM schemes in both independent and identically distributed (i.i.d.) and correlated Rayleigh fading channels.

Diversity-Achieving Quadrature Space-Frequency Index Modulation

Quadrature space-frequency index modulation (QSF-IM) is a recently developed space-frequency transmission scheme which generalizes the idea of quadrature spatial modulation into both spatial and frequency domains. However, QSF-IM lacks of transmit diversity. In this letter, by combining QSF-IM and space-frequency code designing, a novel diversity-achieving QSF-IM (DA-QSFIM) scheme which can achieve the second-order transmit diversity is proposed. In the proposed scheme, the real and imaginary parts of a symbol vector are respectively multiplied by two different precoding matrices and then they are placed into space-frequency resource block in diagonal or anti-diagonal form for transmission. Theoretical performance analysis and simulation results are presented to validate the superiority of DA-QSFIM over other existing schemes in terms of bit error rate (BER) performance under both Rayleigh and Rician channels.

Non-orthogonal space–frequency block codes from cyclic codes for wireless systems employing MIMO-OFDM with index modulation

Space–frequency codes (SFC) having error correcting structure can be used to enhance the bit error rate (BER) performance of modern wireless systems (5G and beyond) employing multiple-input multiple-output (MIMO) and multi-carrier communication. In this work, the construction of non-orthogonal space–frequency block codes (NSFBC) from (n,k) cyclic codes has been proposed. In which, n represents the number of symbols in the codeword and k represents the number of symbols in the information sequence. The performance of proposed codes has been evaluated in MIMO systems employing orthogonal frequency division multiplexing and index modulation (MIMO-OFDM-IM). We initially obtained (n,k) full rank cyclic codes for any 1<k<⌊nm⌋ using Galois field Fourier transform (GFFT) description of (n,k) cyclic codes over Fqm. Further, NSFBCs are obtained from full rank codes using Rank preserving maps. In a 2 × 2 system and a 10-path MIMO channel, the proposed full rank NSFBC with rank-preserving IM mapping (FR-NSFBC-IM), over F52, provides he similar BER performance when compared to MIMO-OFDM-IM system with Rate-1 Alamouti code and QPSK. Moreover, it provides an improvement in spectral efficiency of about 0.9 b/s/Hz. When compared to the MIMO-OFDM-IM with BPSK, FR-NSFBC-IM codes over F52 provide an asymptotic SNR gain of about 1 dB and also the spectral efficiency has been improved by about 0.6 b/s/Hz. In the 4 × 4 scenario, full rank NSFBCs over F54 with rank deficient IM mapping (RD-NSFBC-IM) provide an improvement in spectral efficiency of about 1.3 b/s/Hz. However, BER performance is similar to that of MIMO-OFDM-IM with BPSK.

Development of MIMO–OFDM system and forward error correction techniques since 2000s

The multi-input multi-output–orthogonal frequency division multiplexing (MIMO–OFDM) system serves as one of the most promising techniques that support high data rate and high performance in diverse fading channel conditions. The paper presents an overview of MIMO–OFDM wireless technology, covering advances in physical-layer design, various space–time codes, space–frequency codes and efficient concatenated forward error correction techniques, along with interleaving to yield reduced bit error rate performance (BER). Further, the paper presents the evolution of various performance metrics that are reported since the 2000s in the literature. The evolution outcome is examined using a quadratic nonlinear fitting function to assess the interesting performance metrics. Since BER versus SNR analysis is found as the interesting performance study of the MIMO–OFDM system, the current status of the achieved BER under varying SNR is reviewed and presented.

Efficient inter‐carrier interference cancellation transmissions for cooperative networks with frequency offsets

This study discusses new frequency reversal orthogonal frequency-division multiplexing schemes for cooperative networks in order to minimise the effect of multiple carrier frequency offsets. Theorem 1 proposed and proved in this study tells that zero-forcing (ZF) decoding is equivalent to maximum-likelihood (ML) decoding if the equivalent channel matrix is complex orthogonal. Frequency reversal Alamouti code for two-relay scenario and new space-frequency codes for more relay nodes scenario are designed under the guidance of Theorem 1. The reversal operations of these codes make the equivalent channel matrix between the relays and the destination complex orthogonalised. Thus, ZF decoding achieves the advantages of ML decoding, and simulation results also confirm that. Benefiting from the simplified ZF decoding method in Theorem 1, the decoding complexity becomes really low.

Space-Frequency Coded Index Modulation With Linear-Complexity Maximum Likelihood Receiver in the MIMO-OFDM System

In this letter, a new multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) scheme achieving diversity is proposed. It combines space-frequency code and MIMO-OFDM-IM to take advantage of both, and we call it as the space-frequency coded index modulation (SFC-IM) scheme. The proposed SFC-IM scheme can achieve the transmit diversity order of 2 by optimizing an angle parameter. A linear-complexity maximum likelihood receiver is given for the new scheme, which profits from the orthogonality between the real and imaginary parts of the symbols contained in the SFC-IM codewords. The simulation results show the performance advantage of the SFC-IM scheme over the MIMO-OFDM-IM scheme.

Signal Constellations of Quasi-Orthogonal Space–Time Codes for MIMO Systems

Orthogonal space---time codes (OSTCs) have recently captivated considerable attention due to their properties of full diversity and low implementation complexity. Quasi-orthogonal space---time codes (QOSTCs) provide full diversity and rate one, which enables simple pair wise decoding to be performed as well as better results to be obtained. In this paper, we derive effective OSTCs and QOSTCs for multi-input multi-output systems, which enable us to calculate coding gain of the OSTC. In addition, the fast maximum-likelihood (ML) decoding at the receiver can be performed separately. Since the QOSTC has a fast ML decoding, the symbol pairs can be decoded independently. With the constellation rotation of the symbol, rotated version of QOSTC is generated. OSTCs are designed to achieve the maximum diversity order for a given number of transmit and receive antennas subject to the constraint of having a simple decoding algorithm. This goal is achieved by properly choosing the signal constellations and comparing bit-error-rate (BER) to signal-to-noise ratio (SNR) for different quadrature pulse shift keying and quadrature-amplitude modulation techniques. The simulation results show that the QOSTC outperforms the OSTC at low SNR whereas it has higher complexity than the OSTC. From simulation result, we also compare the STC and space frequency code at BER versus SNR.

On the Diversity of Noncoherent Distributed Space–Frequency Coded Relay Systems With Relay Censoring

This paper considers a noncoherent distributed space-frequency coded (SFC) wireless relay system with multi- ple relays. Each relay adopts a censoring scheme to determine whether the relay will decode and forward the source's informa- tion toward the destination. We analytically obtain the achievable diversity for both cases of perfect and imperfect relay censoring. With perfect censoring, we show that the same diversity of a conventional noncoherent SFC MIMO-OFDM system is achiev- able in the considered noncoherent distributed SFC system with maximum-likelihood (ML) decoding, regardless of whether partial information of channel statistics and relay decoding status is avail- able at the destination. With imperfect censoring, we analytically investigate how censoring errors affect the achievability of the system's diversity. We show that the two types of censoring errors, which correspond to useless and harmful relays, respectively, can decrease the achievable diversity significantly. Our analytical insights and numerical simulations demonstrate that the nonco- herent distributed system can offer a comparable diversity as the conventional MIMO-OFDM system if relay censoring is carefully implemented.

Performance of Space–Time–Frequency Coding Over Indoor Power Line Channels

We present a multiple-input-multiple-output (MIMO) power line communication (PLC) system using coupled indoor differential mode ports, where 2 × 2 and 2 × 4 MIMO configurations are considered. In simulation, MIMO orthogonal frequency-division multiplexing (OFDM) PLC with the two OFDM symbol sequence reordering schemes, namely, Alamouti-scheme-based sequence reordering and circularly-shifted sequence reordering, is compared under the coupled channel conditions. For MIMO coding, we employ a maximum ratio combining scheme that is effective for both MIMO and single-input-single-output over indoor power line conditions. In simulation, we compare space-frequency coding (SFC), space-time coding (STC), and space-time-frequency coding (STFC) over statistical indoor power line channels, including fading, impulse noise, and crosstalk by coupling between ports. STFC and STC are more robust against crosstalk than SFC, and STFC, with some added complexity, outperforms the other coding schemes in terms of bit-error-rate performance. A least squares scheme for power line channel estimation is used, which is simple but has comparable performance to minimum mean square error. A decision-feedback-loop-based crosstalk cancellation scheme that effectively reduces the MIMO channel estimation error due to crosstalk is presented. Simulation results show that STFC is less sensitive to impulse noise than STC or SFC.

Quasi-Orthogonal Space-Frequency Coding in Non-Coherent Cooperative Broadband Networks

So far, complex valued orthogonal codes have been used differentially in cooperative broadband networks. These codes however achieve less than unitary code rate when utilized in cooperative networks with more than two relays. Therefore, the main challenge is how to construct unitary rate codes for non-coherent cooperative broadband networks with more than two relays while exploiting the achievable spatial and frequency diversity. In this paper, we extend full rate quasi-orthogonal codes to differential cooperative broadband networks where channel information is unavailable. From this, we propose a generalized differential distributed quasi-orthogonal space-frequency coding (DQSFC) protocol for cooperative broadband networks. Our proposed scheme is able to achieve full rate, and full spatial and frequency diversity in cooperative networks with any number of relays. Through pairwise error probability analysis we show that the diversity gain of our scheme can be improved by appropriate code construction and sub-carrier allocation. Based on this, we derive sufficient conditions for the proposed code structure at the source node and relay nodes to achieve full spatial and frequency diversity.

Space–Frequency Codes Based on the Space–Time Codes With Very Low Complexity for the Decoder

In this paper, we introduce a family of full-diversity space-frequency codes (SFCs) for the multi-input-multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. The most important feature of the proposed SFCs is that they can be swiftly decoded. More precisely, the decoding complexity on the order of O (M) or O(M2) can be attained for the proposed full-diversity SFCs, where M is the constellation size. Simulation results have also verified that the proposed SFCs display outstanding performance in comparison with the latest SFC model published in the literature.

Blind Joint Channel Estimation and Data Detection for Precoded Multi-Layered Space-Frequency MIMO Schemes

Due to the scarcity of the electromagnetic spectrum, multidimensional signaling schemes that take into account several signal dimensions such as space, time, frequency and constellation, are good candidates for increasing the data rate and/or improving the link reliability in future communication systems. This work addresses the problem of joint channel estimation and data detection in precoded multi-layered space-frequency codes (MLSFC) in multiple input multiple output (MIMO) systems based on orthogonal frequency division multiplexing (OFDM). First, we consider a modified (precoded) MLSFC transmit structure that consists in extending the constellation rotation across multiple OFDM symbols. By recasting the received signal as trilinear model, we propose a low-complexity blind receiver based on the least squares Khatri–Rao factorization (LSKRF). Our proposed LSKRF receiver is a closed-form solution and it outperforms the classical alternating least squares (ALS) receiver while being less complex since no iteration is need. Our results attest to the benefits of the proposed receiver in a variety of MLSFC schemes in comparison with the non-blind zero-forcing-based MLSFC receiver that assumes perfect channel knowledge.

Space-Frequency Codes for MIMO-OFDM Systems with Partial Interference Cancellation Group Decoding

Partial interference cancellation (PIC) group decoding is an attractive decoding alternative for multiple-input multiple-output (MIMO) wireless communications. It can well deal with the tradeoff among rate, diversity and decoding complexity of space-time block codes. In this paper, a design criterion of full-diversity space-frequency codes (SFC) is proposed for MIMO-OFDM systems with the PIC group decoding. Based on the criterion, a systematic design of full-diversity SFC is proposed that can achieve full diversity under the PIC group decoding. Simulation results of the newly proposed codes demonstrate the theory.

Space time frequency coding for dual polarization MIMO in hybrid mobile satellite system

The hybrid mobile satellite system operating in a single frequency network (SFN) mode is increasingly becoming attractive. The combination of satellite component (SC) and terrestrial component (TC) promises a better quality of service (QoS). Multimedia broadcast and multicast services (MBMS) are expected to be prevailed in this kind of system. Several space frequency (SF) or space time (ST) codes have been proposed to enhance the system performance due to the lack of reverse link and omni-directional transmission. However, they mostly consider the system with only one SC and one TC and fail to make full use of available diversities. This paper presents a novel way to realize the dual polarization multiple input multiple output (MIMO) transmission by using the space time frequency (STF) code. The theoretical analysis and simulations indicate that the application of STF code can improve the system performance dramatically. A higher diversity gain can be achieved due to the cooperative transmission of SC and TC, while the coding gain can be enhanced by the reusing of STF code between SCs or TCs. Even if some of the links are lost, it can still work properly and benefit from the STF code. The relative relay can result in a degradation up to 0.5 dB in the coding gain.

Modeling and performance evaluations of Alamouti technique in a single frequency network for DVB-T2

Abstract Alamouti space–frequency coding provides additional frequency diversity, especially in multipath propagation environments. This article addresses a new modeling of the Alamouti code multiple input single output (MISO) in a single frequency network(SFN) for two, three, and four transmitters, and different types of coding and modulations in the DVB-T2 (Digital Video Broadcasting Terrestrial second generation). Classical SFN, Alamouti MISO, and combined SFN with Alamouti MISO (called SFN-2x1 Alamouti MISO) are compared and analyzed. Performance evaluations are made for two, three, or four transmission antennas through 0-dB Echo profile, TU6 mobile channel, unbalanced received power and rotated constellation. The obtained results show clearly that the performance of an SFN network using 0-dB Echo profile with Alamouti MISO is only better than a pure SFN for two and three antennas. Moreover, an SFN based on four antennas (receiving from four antennas) has almost the same performance as SFN-2x1 Alamouti MISO.

단일 송신 안테나 및 OFDM을 이용하는 두 사용자의 저 복잡도 동시 전송 기법

A low-complexity dual-user multiplexing scheme is proposed for a pair of mobiles equipped with single antenna operating over frequency-selective fading channels. The proposed scheme employs OFDM transmission scheme with a modified version of a space-frequency code and a low-complexity PIC-SIC group detection is invoked at the corresponding receiver. The BER performances of the proposed scheme are studied using LTE-like parameters through simulations and are compared against those of conventional ZF and ML schemes.

Distributed Space-Frequency Coding for Cooperative Diversity Over Broadband Relay Channels With DF Relaying

Multipath fading is one of the main challenges in transmission over wireless broadband relay channels due to frequency selectivity, which may deteriorate the received signal. Exploiting the extra source of multipath diversity, aside from cooperative (user) diversity, is important when coping with these wireless channel limitations. In this correspondence, we propose a new distributed space-frequency code (SFC) for broadband fading relay channels that can exploit both the spatial and multipath diversities in a distributed fashion. An upper bound for pairwise error probability (PEP) is derived, and from this PEP bound, we show that the proposed code achieves a diversity of order <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NL</i> , where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> is the number of relay nodes, and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> is the channel memory length. The decode-and-forward (DF) protocol and erroneous decoding at the relay nodes are considered. Moreover, it is shown that the proposed code structure achieves the maximum coding gain among the linearly coded systems over channels with uniform power delay profiles.

Analysis of distributed interleave‐division‐multiplexing space–frequency codes

ABSTRACTThis paper investigates the application of interleave‐division multiplexing (IDM) to a relay network with orthogonal frequency‐division multiplexing (OFDM)‐based radio access. In the proposed scheme, the relay‐specific interleaving is performed on subcarriers in the frequency domain, which is called IDM space–frequency code (IDM‐SFC). It will be shown that IDM‐SFC in combination with OFDM radio access is well suited for distributed deployment of relays, as it is robust to multipath interference and it can achieve full spatial diversity with a constant rate of 1 on the relay–destination hop irrespective of the number of parallel relay nodes. It will be shown that IDM‐SFC outperforms other distributed diversity schemes like OFDM with cyclic delay diversity significantly in various scenarios. In addition to frame error rate analysis, also more theoretical considerations are carried out with the help of extrinsic information transfer charts and signal‐to‐noise power ratio distributions over the subcarrier to provide an insight into the behaviour of the two considered approaches. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Dual-Hop OSTBC Transmissions Over Fading Channels under Receiver Phase Noise for Regenerative Systems

Space-time coding for fading channels is a Communication technique that realizes the diversity benefits of multiple transmit antennas. Previous work in this area has focused on the narrowband flat fading case where spatial diversity only is available. In this paper, we investigate the use of space-time coding in OFDM based broadband systems where both spatial and frequency diversity are available. We consider a strategy which basically consists of coding across OFDM tones and will therefore be called space-frequency coding. For a spatial broadband channel model taking into account physical propagation parameters and antenna spacing, we derive the design criteria for space-frequency codes and we show that space-time codes designed to achieve full spatial diversity in the narrowband case will in general not achieve full space-frequency diversity. Specifically, we show that the Alamouti scheme across tones fails to exploit frequency diversity. For a given set of propagation parameters and given antenna spacing, we establish the maximum achievable diversity order. Finally, we provide simulation results studying the influence of delay spread, propagation parameters, and antenna spacing on the performance of Space-frequency codes.

Distributed Space-Time-Frequency Coding for Broadband Wireless Relay Networks

In this paper, a class of distributed space-time-frequency codes (DSTFCs) is proposed for broadband wireless relay networks. New DSTFCs employ subcarrier grouping and linear constellation precoding at the source node and distributed linear dispersion coding at the relay nodes, which can achieve both full spatial and multipath diversity. We further show that many existing coding constructions, including distributed space-time block coding (DSTBC), distributed space-frequency coding (DSFC), and distributed cyclic delay coding (DCDC), can be the special cases of our proposed DSTFCs. The simulation results are presented to verify the theoretical analysis.