Full-diversity Quasi-orthogonal Space-time Block Codes Research Articles

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.

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.

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.

High-rate full-diversity space-time block codes for three and four transmit antennas

The authors deal with the design of high-rate, full-diversity, low-maximum likelihood (ML) decoding complexity space-time block codes (STBCs) with code rates of 2 and 1.5 complex symbols per channel use for multiple-input multiple output (MIMO) systems employing three and four transmit antennas. The authors fill the empty slots of the existing STBCs from coordinate interleaved orthogonal designs (CIODs) in their transmission matrices by additional symbols and use the conditional ML decoding technique, which significantly reduces the ML decoding complexity of non-orthogonal STBCs while ensuring full-diversity and high coding gain. First, two new schemes with code rates of 2 and 1.5 are proposed for MIMO systems with four transmit antennas. The authors show that our low-complexity rate-2 STBC outperforms the corresponding best STBC recently proposed by Biglieri et al. (2008) for quadrature phase shift keying (QPSK), due to its superior coding gain while our rate-1.5 STBC outperforms the full-diversity quasi-orthogonal STBC (QOSTBC). Then, two STBCs with code rates of 2 and 1.5 are proposed for three transmit antennas, which are shown to outperform the corresponding full-diversity QOSTBC. The authors prove by an information-theoretic analysis that the capacities of new rate-2 STBCs for three and four transmit antennas are much closer to the actual MIMO channel capacity than the capacities of classical OSTBCs and CIODs.

High rate open-loop MIMO multi-user downlink transmission scheme based on blind precoding quasi-orthogonal space time block code

The authors first propose a new class of full-rate full-diversity quasi-orthogonal space time block code (QO-STBC), namely QO-STBC with blind precoding (BP-QO-STBC). Based on this code, a novel open-loop multiple-input multiple-output (MIMO) multi-user downlink transmission scheme is derived. Presuming M blocks of BP-QO-STBC (which could be of different code lengths) are transmitted from the access point simultaneously, thus achieving a multiplexing gain of M, we show that the multiplexed signal can be separated by any user with only mR≥M receive antennas, which is much smaller than that required by conventional linear schemes. The proposed scheme is extendable by simple iterative construction to an arbitrary number of transmit antennas. By exploiting the special structure of BP-QO-STBC, we derived two decoding algorithms with different levels of complexities, namely an optimal maximum likelihood decoder that achieves the lowest decoding complexity known for all full-rate full-diversity QO-STBC and a suboptimal linear decoder with even lower complexity. These two decoders combined with the simple construction method of BP-QO-STBC provide flexible tradeoffs between complexity and performance, as well as between diversity and multiplexing gains. A comparison between the proposed scheme and random beamforming in terms of bit error rate and achievable sum throughput is shown via simulation, and the results support our proposed scheme as a better practical candidate for high-speed wireless network.

High-Rate Space-Time Block Coding Schemes

A rate-6/4 full-diversity orthogonal space-time block code (STBC) is constructed for QPSK and 2 transmit antennas by applying constellation scaling and rotation to the set of quaternions used in Alamouti code. Also given is a rate-9/8 full-diversity quasi-orthogonal space-time block code (QOSTBC) for 4 transmit antennas. Lastly, a rate-10/8 code is presented for 4 transmit antennas. Simulation results indicate that these high-rate codes achieve better throughputs in the high signal-to-noise ratio region.

On the Relation of OSTBC and Code Rate One QSTBC: Average Rate, BER, and Coding Gain

Recently, the statistical properties of the equivalent channel representation of a multiple-input-multiple output (MIMO) system employing code rate one quasi-orthogonal space-time block codes (QSTBC), which are constructed by using orthogonal space-time block codes (OSTBC) as building elements, was characterized. Based on these characterizations we analyze the average rate (or mean mutual information), the bit-error-rate performance, and the coding gain achieved with QSTBC for any number of receive and nT=2n, n ges 2 transmit antennas. First, we study constellation rotation using a systematic approach in order to maximize the coding gain and to achieve full diversity QSTBC. Moreover, we present an upper bound on the coding gain. We derive a lower and upper bound on the BER-performance for QSTBC. Furthermore, we analyze the average rate achievable with QSTBC in case of an uninformed transmitter and also the case, in which the transmitter knows the mean channel matrix whereas the receiver has perfect CSI. Along with the analysis, we compare all the results of these performance measures with the results achieved with OSTBC, revealing important connections between OSTBC and QSTBC. For example, the coding gain of a QSTBC is upper bounded by the coding gain of the underlying OSTBC. Also, the BER of a QSTBC for nT transmit and nR receive antennas is tightly lower bounded by the BER of a full-diversity providing intersymbol-interference free system. In addition to that, we show that gains in terms of average rate by using a QSTBC (and, thus, with higher nT) instead of the underlying OSTBC are only attainable, if the available channel state information at the transmitter (CSIT) is utilized. Finally, we illustrate our theoretical results using numerical simulations.

Full-Rate Orthogonal Space-Time Block Code With Pulse-Shaped Offset QAM for Four Transmit Antennas

In this paper, we show, in both theory and simulation, that by transmitting two real orthogonal space-time block codes (O-STBC) on the I- and Q-channels with pulse-shaped offset QAM, we are able to achieve full rate transmit diversity for a 4 times 1 system with very simple "half-symbol" detection, i.e., the real I- and Q-symbols can be separately decoded. For this scheme, two families of pulse shapes of the offset QAM signal are considered: i) pulse shapes with zero inter-symbol interference (ISI) and ii) pulse shapes with controlled ISI between the I- and Q-channels. In the zero ISI case, the half-symbol decoding is optimum in the maximum likelihood sense and the system is able to achieve full transmit diversity. The associated bit error probability (BEP) performance is better than that of conventional full-rate, full-diversity quasi-orthogonal space-time block codes (QO-STBC), as well as rate-1/2 and rate-3/4 complex O-STBCs. To achieve good spectral confinement while maintaining decoding simplicity, we investigate pulse shape design techniques so that some performance gains can be traded off by introducing a controlled small amount of ISI at the sampling instants. We also extend the analysis to a 4 times 4 multiple-input multiple-output (MIMO) system, and derive the design criteria on how to construct the two real O-STBCs in order to minimize the performance degradation caused by the controlled ISI

General differential modulation scheme for quasi-orthogonal space–time block codes with partial or full transmit diversity

A general and simple differential modulation scheme that can be applied to both partial-diversity quasi-orthogonal space–time block codes and full-diversity quasi-orthogonal space–time block codes is reported. A new class of quasi-orthogonal coding structures is presented for various number of transmit antennas. Differential encoding and decoding can be simplified to differential Alamouti codes by grouping the signals in the transmitted matrix and decoupling the detection of data symbols, respectively. For the codes with partial transmit diversity, the new scheme can achieve constant amplitude of transmitted signals, and avoid signal constellation expansion; in addition, it has a linear signal detector with very low complexity. Simulation results show that these partial-diversity codes can provide very useful results at low signal-to-nose ratio for current communication systems. For codes with full transmit diversity achieved by constellation rotation, the proposed scheme has performance equal to the best full-rate quasi-orthogonal schemes previously described in the literature with the benefit of a simpler detector. Moreover, a simple linear detector is also presented for the case when two orthogonal ASK constellations are used. Extension to more than four transmit antennas is also considered.