Quasi-orthogonal Space-time Block Codes Research Articles

A simple asynchronous distributed STBC network scheme with full diversity

In this article, we propose a simple distributed space-time block code (STBC) network scheme for asynchronous relay network, where every two traditional relay nodes are combined to one node to amplify and forward the processed signals via the same transmission antenna. In the proposed distributed network scheme, we consider a wireless scenario with frequency selective fading channels. The orthogonal frequency division multiplexing (OFDM) symbols are broadcast from source to relay nodes in the first step, and in the second step, the received signals at the relay nodes are implemented with a simple operation and mixed partially and forwarded to destination. In this network scheme, the four by four quasi-orthogonal STBC (QO-STBC) is applied, and the orthogonal decoding algorithm can be used at the receiver because of the orthogonality of the re-constructed equivalent transmission matrix. Thus, the full rate and the full diversity are achieved at the transmitter and the receiver of the proposed distributed network scheme, respectively. Simulation result shows that the proposed distributed STBC network scheme has better performance than other network schemes.

A Rotated Quasi-Orthogonal Space-Time Block Code for Asynchronous Cooperative Diversity

The rotated quasi-orthogonal space-time block code (RQSTBC) for asynchronous cooperative diversity is proposed in this paper. The source selects half of the symbols from a signal constellation set and the other half of them from that constellation rotated with the optimum angle. Meanwhile, it constructs orthogonal frequency division multiplexing (OFDM) frames to counterbalance time delays of the signals. Then, relays create the frequency domain quasi-orthogonal space-time block transmitted signals matrix in such a way that its items are staggered to take on the Jafarkhani code structure or time-reversion of it. These three stages let the received signals at the destination take on RQSTBC structure with diversity order 4, which results in the fast symbol-pair-wise maximum likelihood (ML) decoder. Simulation results have shown that the proposed scheme outperforms the other asynchronous cooperative diversity schemes considered in this paper.

An Improved Full Rate Full Diversity QOSTBC with Linear Decoding in MIMO Systems

In this letter, we propose an improved Quasi-orthogonal space-time block code (QOSTBC) with full rate, full diversity, linear decoding and better peak-to-average power ratio (PAPR). Constellation rotation is used to the input symbol vector to ensure full diversity, and then the information symbol vector is interleaved in coordinates and pre-grouped by using a Given rotation matrix. The performance is evaluated by numerical experiments. The PAPR of our proposed QOSTBC is lower than that of CI-QOSTBC in Khan and Rajan (IEEE Trans Inf Theory 52(5):2062---2091, 2006). Meanwhile, the Bit-error-rate versus Signal-to-noise-ratio of our proposed QOSTBC is better than those of OSTBC (Tarokh et al. in IEEE Trans Inf Theory 45(5):1456---1467, 1999) QOSTBC (Jafarkhani in IEEE Trans Wirel Commun 49(1):1---4, 2001), G-QOSTBC (Park et al. in IEEE Commun Lett 12(12):868---870, 2008), slightly better that of the CI-QOSTBC, and as same as that of the recently proposed Minimum Decoding Complexity QOSTBCs (MDC-QOSTBC) in Yuen et al.(IEEE Trans Wirel Commun 4(5):2089---2098, 2005), Wang and Xia (IEEE Trans Inf Theory 55(3):1104---1130, 2009). Compared with MDC-QOSTBC, the proposed QOSTBC has simpler code construct and lower decoding complexity.

Efficient Decoding for Generalized Quasi-Orthogonal Space–Time Block Codes

Space–time coding can achieve transmit diversity and power gain over spatially uncoded systems without sacrificing bandwidth. There are various approaches in coding structures, including space–time block codes. A class of space–time block codes namely quasi-orthogonal space–time block codes can achieve the full rate, but the conventional decoders of these codes experience interference terms resulting from neighboring signals during signal detection. The presence of the interference terms causes an increase in the decoder complexity and a decrease in the performance gain. In this article, we propose a modification to the conventional coding/decoding scheme that will improve performance, reduce decoding complexity, and improve robustness against channel estimation errors as well.

BER Analysis Of Iterative Turbo Encoded MISO Wireless Communication System Under Implementation Of Q-OSTBC Scheme

In this paper, a comprehensive study has been made to evaluate the performance of a MISO wireless communication system. The 4-by-1 spatially multiplexed Turbo encoded system under investigation incorporates Quasi-orthogonal space-time block coding (Q-STBC) and ML signal detection schemes under QPSK, QAM, 16PSK and 16QAM digital modulations. The simulation results elucidate that a significant improvement of system performance is achieved in QAM modulation. The results are also indicative of noticeable system performance enhancement with increasing number of iterations in Turbo encoding/decoding scheme.

Performance improvement of QO-STBC over time-selective channel for wireless network

Signal detection for vehicle-to-vehicle and wireless network application has motivated new design for conditions in which channel is time-selective fading. Since the physical layer (PHY) forms the foundation of the communication protocol stack, the performance of this layer affects all high layers of the system stack. Quasi-orthogonal space-time block code (QO-STBC) can provide full rate transmission and partial diversity under low decoding complexity. Previous papers on QO-STBC assume that the channels are slow fading or remain static over the length of the codeword. However, time-selective channels do exist, and in this case, the decoder proposed in Jafarkhani (2001) cannot be used to achieve a proper error performance. In order to mitigate the severe performance degradation, the zero forcing (ZF) and minimum mean square error (MMSE) decoders are employed in this paper. We also propose a zero forcing interference cancellation decision-feedback equalizer (ZF-IC-DFE) and a minimum mean-square error interference cancellation decision-feedback equalizer (MMSE-IC-DFE) via Cholesky factorization of the channel Gram matrix after performing interference cancellation. By feeding back past decisions on previously detected symbols, DFE schemes can achieve an additional performance gain compared to their corresponding linear decoders.

Study on Quasi-Orthogonal Space Time Block Code Based on Amplify-and-Forward Relay Networks

A kind of quasi-orthogonal space time block code for amplify-and-forward relay networks is analyzed in this paper. At the source, 4 single-antenna users transmit the quasi-orthogonal space time block code matrix. At the relay node, fast maximum-likelihood decoding algorithm is adopted and the decoded symbols are then encoded into quasi-orthogonal code which is transmitted through transmit antenna. At the destination, pair-wise decoding algorithm is utilized. Finally we compare the performance of the quasi-orthogonal space time block code in relay networks with that of the quasi-orthogonal space time block code in traditional communication system. Simulation results show that at the given BER of 10-3, the new code can provide about gain of 4dB and 1 dB comparing with that for the traditional quasi-orthogonal code, respectively. And at the given BER of 10-5, the new code can provide about gain of 4.6dB and 2.6dB comparing with that for the old quasi-orthogonal code, respectively.

On Quasi-Orthogonal Space-Time Block Codes for Dual-Polarized MIMO Channels

As a space- and cost-efficient antenna configuration, dual-polarized antennas are widely deployed in real field MIMO wireless communication systems. The Quasi-Orthogonal Space-Time Block Code (QOSTBC), due to its advantages in the transmission rate and the decoding complexity, is an important transmit diversity scheme for more than 2 transmit antennas. In this paper, we investigate the performance of QOSTBC for dual-polarized MIMO channels. We show that when QOSTBC is used with dual-polarized antennas, we need to connect the power amplifiers (PAs) to the differently polarized antennas carefully, in order to avoid more than 1dB performance loss at high cross-polar discrimination (XPD). Also, we show that, if the QOSTBC with constellation rotations, which achieves full diversity in uni-polarized MIMO channels, is used, the performance loss due to the bad PA-to-antenna connections is mitigated. However, when the XPD is high, the QOSTBC without full diversity, if connected properly, can achieve better performance than the QOSTBC with full diversity when connected badly, which shows the importance of a proper connection at high XPD. So, to guarantee robust performance of QOSTBC at any XPD, besides designing codes to have full diversity and good diversity product, connecting the PAs and the antennas properly is also important.

Heterogeneous Constellation Based QOSTBC for Improving Detection Property of QRD-MLD

SUMMARY Orthogonal space-time block code (OSTBC) can achieve full diversity with a simple MLD, but OSTBC only achieves 3/ 4o f the maximum rate if more than two transmit antennas are used. To solve this problem, a quasi-orthogonal STBC (QOSTBC) scheme has been proposed. Even though a QOSTBC scheme can achieve the full rate, there are interference terms resulting from neighboring signals during detection. The existing QOSTBC using the pairs of transmitted symbols can be detected with two parallel MLD. Therefore, MLD based QOSTBC has higher complexity than OSTBC. To reduce the detection complexity, in this paper, we propose the heterogeneous constellation based QOSTBC for improving the detection property of QRD-MLD with maintaining a simple decoding

Quasi Orthogonal Space Time Block Codes Using Various Sub-Block Matrices

Space-time block codes (STBCs) from Orthogonal designs have attracted attention due to their fast maximum likelihood decoding and full diversity, but the maximum symbol transmission rate for complex signals is only ¾ for four transmit antennas so quasi orthogonal STBC was proposed, in this paper the structure and characteristics of some new type of a Quasi-orthogonal space time block codes (QOSTBC)is analyzed, The error performance for these codes for four transmitted antennas over uncorrelated and spatially correlated MIMO channels is investigated. A maximum likelihood (ML) decoding algorithm for the suggested code is also provided.

On Improving the Tradeoff between Symbol Rate and Diversity Gain Using Quasi-Orthogonal Space-Time Block Codes with Linear Receivers

On Improving the Tradeoff between Symbol Rate and Diversity Gain Using Quasi-Orthogonal Space-Time Block Codes with Linear Receivers

基于准正交空时分组编码的空间激光通信

基于准正交空时分组编码的空间激光通信

Performance Evaluation of Full Diversity QOSTBC MIMO Systems with Multiple Receive Antenna

Multipath fading is inherent in wireless communication systems. Diversity is the technique which takes advantage of multipath to mitigate the effect of fading and increase signal strength. Space Time Block codes (STBC) are used in MIMO systems to improve the performance by maximizing transmit and/or receive diversity. Among different schemes based on STBC, Quasi Orthogonal Space Time Block Code (QOSTBC) is able to achieve full rate transmission for more than two transmit antennas. Constellation Rotation QOSTBC (CR-QOSTBC) achieves full diversity and improves performance further along with full rate, to overcome the limitation of QOSTBC, which is unable to maintain orthogonality amongst the codes transmitted by different antennas. Higher diversity can be achieved by increasing uncorrelated paths between transmitter and receivers using higher number of receive antennas. This paper examines improvement in BER with reference to a number of receive antennas. Simulations were carried out under ideal as well as realistic environments, using least square technique with four antennas at transmitter side and variable receive antennas. Results of simulations presented in this paper indicate performance improvement of CR-QOSTBC over QOSTBC in flat fading channel environment. Simulation results also show performance degradation in BER when channel is estimated at the receiver.

A novel QO-STBC scheme with linear decoding

A new quasi-orthogonal space-time block code (QO-STBC) scheme, based on eigen value decomposition (EVD), is explored in this paper. The new scheme can significantly reduce the QO-STBC decoding complexity at receiver and achieves better bit-error rate (BER) performance as well. With EVD manipulations, the detection matrix and the channel matrix can be redefined to remove all interference terms which come from other antennas, and therefore the conventional maximum likelihood (ML) decoding method with less complexity can be applied. Moreover the new scheme improves the BER performance significantly. Theoretical analysis and simulation results are presented in this paper to show the validation of this new scheme.

Space-Time Coding Technique Based on Four-Antenna Transceiver System

Space-time block code, as one of the space-time codes, greatly improves the performance in the cooperative wireless communication systems by the use of space and time diversity. However, traditional STBC can’t enhance the overall transmission rate and there is no form of complex codes with the rate of 1 when the number of antenna is more than 2. In order to design codes with full-rate, we refer to quasi-orthogonal STBC whose generator matrix is orthogonal between its subspaces. In this paper, based on the combination of QO-STBC and Self-adaptation technology, we propose a new plan of space-time coding which dismisses the interference among symbols when decoding and advances the coding capabilities in the context of full-rate transmission, finally we justify the new plan through lots of computational simulations.

Quasi-Orthogonal Space-Time Block Coding Using Polynomial Phase Modulation

Recently, polynomial phase modulation (PPM) was shown to be a power- and bandwidth-efficient modulation format. These two characteristics are in high demand nowadays specially in mobile applications, where devices with size, weight, and power (SWaP) constraints are common. In this paper, we propose implementing a full-diversity quasiorthogonal space-time block code (QOSTBC) using polynomial phase signals as modulation format. QOSTBCs along with PPM are used in order to improve the power efficiency of communication systems with four transmit antennas. We obtain the optimal PPM constellations that ensure full diversity and maximize the QOSTBC's minimum coding gain distance. Simulation results show that by using QOSTBCs along with a properly selected PPM constellation, full diversity in flat fading channels and thus low BER at high signal-to-noise ratios (SNR) can be ensured. More importantly, it is also shown that QOSTBCs using PPM achieve a better error performance than those using conventional modulation formats.

Quasi-Orthogonal Space-Time Block Codes for Two Transmit Antennas and Three Time Slots

In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with two transmit antennas and three time slots, where the Alamouti code is not applicable due to the odd time slots. The proposed Q-STBC codes achieve rate one and full diversity with low complexity maximum likelihood decoding. The Q-STBC design also shows excellent properties in other practical aspects, such as the compatibility with the single antenna transmission mode, low power fluctuation, and low receiver decoding and transmitter encoding complexity.

Soft-decision-and-forward protocol for cooperative communication networks with multiple antennas

In this paper, a cooperative relaying protocol called soft-decision-and-forward (SDF) with multiple antennas in each node is introduced. SDF protocol exploits the soft decision source symbol values from the received signal at the relay node. For orthogonal transmission (OT), orthogonal codes including Alamouti code are used and for non-orthogonal transmission (NT), distributed space-time codes are designed by using a quasi-orthogonal space-time block code. The optimal maximum likelihood (ML) decoders for the proposed protocol with low de coding complexity are proposed. For OT, the ML decoders are derived as symbolwise decoders while for NT, the ML decoders are derived as pairwise decoders. It can be seen through simulations that SDF protocol outperforms AF protocol for both OT and NT.

Efficient Decoding for Extended Alamouti Space-Time Block code

Space-time coding can achieve transmit diversity and power gain over spatially uncoded systems without sacrificing the bandwidth. There are various approaches in coding structures, including space-time block codes. A class of space-time block codes namely quasi-orthogonal space-time block code can achieve the full rate, but there are also interference terms resulting from neighboring signals during signal detection. This causes an increase in decoding complexity and a decrease in performance gain. In this paper, we demonstrate an efficient method to reduce decoding complexity and improved performance.

MC‐CDMA MIMO systems with quasi‐orthogonal space–time block codes: Channel estimation and multiuser detection

SUMMARYThis paper investigates blind channel estimation and multiuser detection for quasi‐synchronous multi‐carrier code‐division multiple‐access (MC‐CDMA) multiple‐input multiple‐output (MIMO) systems with quasi‐orthogonal space–time block codes (QO‐STBC). Subspace‐based blind channel estimation is proposed by considering a QO‐STBC scheme that involves four transmit antennas and multiple receive antennas. Based on the first‐order perturbation theory, the mean square error of the channel estimation is derived. With the estimated channel coefficients, we employ minimum output energy and eigenspace receivers for symbol detection. Using the QO‐STBC coding property, the weight analyses are performed to reduce the computational complexity of the system. In addition, the forward–backward averaging technique is presented to enhance the performance of multiuser detection. Numerical simulations are given to demonstrate the superiority of the proposed channel estimation methods and symbol detection techniques. Copyright © 2011 John Wiley & Sons, Ltd.