Orthogonal Space Time Block Code (OSTBC)

In this paper, we present a low-complexity algorithm for detection in high-rate, non-orthogonal space-time block coded (STBC) large-multiple-input multiple-output (MIMO) systems that achieve high spectral efficiencies of the order of tens of bps/Hz. We also present a training-based iterative detection/channel estimation scheme for such large STBC MIMO systems. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed multistage likelihood ascent search ( -LAS) detector in conjunction with the proposed iterative detection/channel estimation scheme at low complexities. The fact that we could show such good results for large STBCs like 16 16 and 32 32 STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot based training for channel estimation and turbo coding) establishes the effectiveness of the proposed detector and channel estimator. We decode perfect codes of large dimensions using the proposed detector. With the feasibility of such a low-complexity detection/channel estimation scheme, large-MIMO systems with tens of antennas operating at several tens of bps/Hz spectral efficiencies can become practical, enabling interesting high data rate wireless applications.

We consider large MIMO systems, where by 'large' we mean number of transmit and receive antennas of the order of tens to hundreds. Such large MIMO systems will be of immense interest because of the very high spectral efficiencies possible in such systems. We present a low-complexity detector which achieves uncoded near-exponential diversity performance for hundreds of antennas in V-BLAST (i.e., achieves near SISO AWGN performance in a large MIMO fading environment) with an average per-bit complexity of just O(NtNr), where Nt and Nr denote the number of transmit and receive antennas, respectively. With an outer turbo code, the proposed detector achieves good coded bit error performance as well. For example, in a 600 transmit and 600 receive antennas V-BLAST system with a high spectral efficiency of 200 bps/Hz (using BPSK and rate-1/3 turbo code), our simulation results show that the proposed detector performs close to within about 4.6 dB of the theoretical capacity. We also adopt the proposed detector for the low-complexity decoding of high-rate non-orthogonal spacetime block codes (STBC) from division algebras (DA). We have decoded the 16 × 16 full-rate STBC from DA using the proposed detector and show that it performs close to within about 5.5 dB of the capacity using 4-QAM and rate-3/4 turbo code at a spectral efficiency of 24 bps/Hz. The practical feasibility of the proposed high-performance low-complexity detector could trigger wide interest in the implementation of large MIMO systems.

In this paper, we study a wireless multiple-input multiple-output system in a Rayleigh flat-fading environment with correlation among the transmit antennas. We assume that the receiver has perfect CSI and the transmitter only knows the correlation matrix. The transmitter employs a quasi-orthogonal space-time block code in combination with a linear precoder; the receiver uses a linear MMSE detector. We analyze the optimal transmit precoding strategy that minimizes the average sum MSE at the receiver. We show that, as expected, the optimal precoding directions coincide with the eigenvectors of the transmit correlation matrix. The optimal power allocation, however, only supports at most 2 directions at all SNRs independent of the number of transmit antennas, which correspond to the 2 largest eigenvalues of the transmit correlation matrix. We characterize this optimal power allocation by the necessary and sufficient optimality conditions. At high SNRs, the optimal allocation approaches equal power on the two supported modes. At low SNRs, the weaker mode is dropped and the precoding matrix becomes single-mode beamforming. We provide a closed-form expression characterizing this low-SNR range. Numerical simulations confirm our theoretical analysis.

This paper considers a downlink multiple-input multipleoutput (MIMO) multi-carrier code division multiple access (MC-CDMA) system with pilot aided channel estimation (PACE) and iterative channel estimation (ICE) in the receiver. Exploiting orthogonal space-time block coding (STBC), we investigate ICE schemes as a simple extension of PACE using estimated data chips as additional pilots. Due to the superposition of different users' spread data signals, zero-valued chips can occur after spreading, which can cause noise enhancement when using data estimates as reference signals in ICE. Hence, we propose MIMO channel estimation methods to overcome the above problem. Simulations with a realistic outdoor MIMO channel model, over a wide range of data rates and speeds, show that ICE can outperform PACE at the cost of increased complexity.

This paper considers a downlink multiple-input multipleoutput (MIMO) multi-carrier code division multiple access (MC-CDMA) system with pilot aided channel estimation (PACE) and iterative channel estimation (ICE) in the receiver. Exploiting orthogonal space-time block coding (STBC), we investigate ICE schemes as a simple extension of PACE using estimated data chips as additional pilots. Due to the superposition of different users' spread data signals, zero-valued chips can occur after spreading, which can cause noise enhancement when using data estimates as reference signals in ICE. Hence, we propose MIMO channel estimation methods to overcome the above problem. Simulations with a realistic outdoor MIMO channel model, over a wide range of data rates and speeds, show that ICE can outperform PACE at the cost of increased complexity.

We study the performance of differential orthogonal space-time block codes over independent and semi-identically distributed Rayleigh fading channels. In this semi-identically distributed fading model, the channel gains from different transmit antennas to a common receive antenna are identically distributed, but the gains associated with different receive antennas are non-identically distributed. Arbitrary fluctuation rates of the fading processes from one transmission block to another are considered. We first derive the optimal symbolby-symbol differential detector, and show that the conventional differential detector is suboptimal. We then derive expressions of exact bit error probabilities (BEP) for both the optimal and suboptimal detectors. The results are applicable for any number of receive antennas and any number of transmit antennas for which orthogonal space-time block codes exist. For two transmit antennas, explicit and closed-form BEP expressions are obtained. A Chernoff bound on the BEP of optimal detection for any number of transmit antennas is also derived.

Recently, several linear receiver algorithms have been developed for space-time block-coded multiaccess multiple-input multiple-output (MIMO) wireless communication systems. All these techniques are based on the assumption that the channel state information (CSI) at the receiver side is perfect. However, in practical situations, the available CSI may be imperfect because of channel estimation errors and/or outdated training. In this paper, we develop new robust linear receiver techniques for joint space-time decoding and interference rejection in multiaccess MIMO systems that use orthogonal space-time block codes and erroneous CSI. The proposed receivers are based on worstcase performance optimization. They are shown to provide a substantially improved robustness against CSI mismatches as compared with the existing linear multiaccess MIMO receivers.

Constructions of square, maximum rate complex orthogonal space-time block codes (CO STBCs) are well known, however codes constructed via the known methods include numerous zeros, which impede their practical implementation. By modifying the Williamson and Wallis-Whiteman arrays to apply to complex matrices, we propose two methods of construction of square, order-4n CO STBCs from square, order-n codes which satisfy certain properties. Applying the proposed methods, we construct square, maximum rate, order-8 CO STBCs with no zeros, such that the transmitted symbols are equally dispersed through transmit antennas. Those codes, referred to as the improved square CO STBCs, have the advantages that the power is equally transmitted via each transmit antenna during every symbol time slot and that a lower peak-to-average power ratio (PAPR) is required to achieve the same bit error rates as the conventional CO STBCs with zeros. C OMPLEX orthogonal space-time block codes (CO STBCs) have been intensively examined, as they provide large transmit diversity and increase the capacity of wireless channels, while requiring a very simple maximum likelihood (ML) decoding method [3]- . A CO STBC over variables is corresponding to transmit (Tx) antennas, decoding delay (or memory length) of , rate and is denoted as CO STBC. Given and , the goal is to minimize the decoding delay . Hence, square CO STBCs are particularly interesting because they require the minimum Manuscript

We analyze the outage probability for the orthogonal space-time block code based multiple-input multiple-output (MIMO) relay networks, composed of one source, one relay, and a single destination. The relay forwards the decoded and interleaved information sequence even though the information part may contain error(s), according to the lossy forward strategy. In spatially independent MIMO channels, we find that the diversity order of the relay network can be interpreted and formulated by the well-known max-flow min-cut theorem. Moreover, we extend the analysis to the case of spatially correlated MIMO channels. Approximated explicit expressions for the outage probabilities are obtained in high signal-to-noise ratio regime.

This paper investigates a new approach to the adaptation of the HiperLAN/2 transceiver with multiple antennas based multiwavelet, replaced DFT-OFDM by multiwavelets OFDM on HiperLAN/2 physical layer .The new transceiver proposed achieved, further reduce the level of interference and increase spectral efficiency than conventional HiperLAN/2 Transceiver. In MATLAB/ Simulink modeling simulation proved that the performance of proposed HiperLAN/2 baseband transceiver has a significant degradation in the packet (PDU or PSDU) error rate (PER) compared to conventional HiperLAN/2 baseband transceiver due to the considerable channel models.

Ultrawideband (UWB) systems show excellent potential benefits when used in the design of high-speed digital wireless home networks. The constantly-increasing demand for higher data transmission rates can be satisfied by exploiting both multipath-and spatial-diversity, using multiple-input multiple-output (MIMO) together with proper modulation and coding techniques. Unlike conventional MIMO OFDM systems, the performance of MIMO MB-OFDM UWB systems does not depend on the temporal correlation of the propagation channel although narrowband interference (NBI) is still a problem. In this paper we put forward a technique for suppressing NBI by the use of adaptive narrowband filtering. The method is compared experimentally with other algorithms for the identification and cancellation/suppression of complex NBI in OFDM single-band and multiband (MB) UWB systems. The study shows that the different schemes offer slightly differing performances, depending on the parameters of the MIMO UWB system. The proposed complex adaptive narrowband filtering technique is an optimal solution which offers a good balance between NBI suppression efficiency and computational complexity.

To improve the bit rate, the effectiveness of wireless transmission systems and limit the effects of fading transmission channel, an increased attention have recently been paid to MIMO systems. In fact, Alamouti's space-time block code is introduced in various wireless standards and systems. This manuscript deals with the problem of presence identification as well as blind separation of Orthogonal Space-Time Block Code (OSTBC) in the context of non data aided. KEY WORD: MIMO channel, OSTBC, ICA, Alamouti's code, BSS of underdetermined mixture.