Space-time Block Coding Scheme Research Articles

Full-Rate Complex Orthogonal Space-Time Block Code for Multiple Antennas

In this paper, full-rate and complex orthogonal space-time block code (STBC) schemes for multiple antennas are proposed, and turbo code is employed as channel coding to improve the proposed STBC schemes performance further. Compared with full-diversity multiple antennas STBC schemes, the proposed schemes can implement full data rate, partial diversity and a smaller complexity. On the condition of the same system throughput and concatenation of turbo code, the proposed schemes have lower bit error rate (BER) than those low-rate and full-diversity code schemes.

A two-stage partially adaptive linear receiver for CDMA MIMO systems with Alamouti's space–time block codes

The code-division multiple-access (CDMA) multiple-input multiple-output (MIMO) systems with Alamouti's space-time block codes (STBC) have been widely investigated for the great demand of capacities and transmission rates in the future wireless communication systems. The semi-blind Capon multiuser receiver is designed to achieve the goal by the usage of linearly constrained minimum variance (LCMV) filters. However, the Capon receiver suffers finite samples and signature vector errors. In this paper, we propose a novel two-stage receiver containing partially adaptive linear filters in parallel followed by the channel estimator and symbol detector. Two transformation schemes based on subspace techniques are designed in the partially adaptive linear filters. The channel estimation is executed after the partially adaptive linear filter where the computational complexity is saved considerably. A performance enhancement method is introduced by using the forward-backward averaging technique. According to the weighting analysis, we also present a simplified two-stage receiver with lower complexity. Furthermore, the diagonal-loading (DL) technique based on the worse-case performance optimization is often used to alleviate the drawbacks of Capon receiver. In the end, we apply the proposed the forward-backward averaging technique and the weighting analysis onto the DL-based Capon receivers. Computer simulations are given to demonstrate the effectiveness of the two-stage partially adaptive linear receivers for the CDMA MIMO systems with Alamouti's STBC schemes and the performance improvement of the DL-based Capon receivers with the forward-backward averaging technique and the weighting analysis.

Block-ordered layered detector for MIMO-STBC using joint eigen-beamformers and ad-hoc power discrimination scheme

Suitable for multi-input multi-output (MIMO) communications, the joint beamforming space-time block coding (JBSTBC) scheme is proposed for high-speed downlink transmission. The major functionality of the scheme entails space-time block encoder and joint transmit and receive eigen-beamformer (EBF) incorporating with block-ordered layered decoder (BOLD), and its operating principle is described in this paper. Within these functionalities, the joint EBFs will be utilized for decorrelating fading channels to cause an enhancement in the spatial diversity gain. Furthermore, to fortify the capability of layered successive interference cancellation (LSIC) in block-ordered layered decoding process, this paper will develop a simple ad-hoc transmit power discrimination scheme (TPDS) based on a particular power discrimination function (PDF). To confirm the superior behavior of the proposed JB-STBC scheme employing ad-hoc TPDS, computer simulations will be conducted under various channel conditions with the provision of detailed mathematical derivations for clarifying its functionality.

A general scheme for equalization of space-time block-coded systems with unknown CSI

Recently, space-time block codes (STBCs) have gained much attention as an effective transmit diversity technique to increase the capacity of wireless communication systems. In this paper, we consider a general technique for direct equalization of space-time block-coding systems with unknown channel state information (CSI). This technique is suitable for several existing hybrid STBC schemes, such as STBC/orthogonal-frequency-division multiplexing (STBC-OFDM) and STBC/code-division multiple access (STBC-CDMA). We show that by exploiting the redundancy in the structure of STBC, a zero-forcing equalizer can be constructed without channel estimation. The conditions for the identifiability of the zero-forcing equalizer are also derived to ensure correct equalization. To further improve the performance of the proposed method, a new iterative algorithm is developed by incorporating the finite alphabet property of information symbols. Simulation results show that the proposed algorithms can outperform comparative schemes in most simulation conditions.

Efficient spread space-time block coding scheme in multiple antenna systems

Space-time coding is an important technique that can improve transmission performance at fading environments in mobile communication systems. In this paper, we propose a novel diversity scheme using spread space-time block coding (SSTBC) in multiple antenna systems. At the transmitter, the primitive data are serial to parallel converted to multiple data streams, and each stream is rotated in constellation. Then Walsh codes are used to spread each symbol to all antenna space in a space-time block. The signals received from all receiver antennas are combined with the maximum ratio combining (MRC), equalized with linear equalizer to eliminate the inter-code interference and finally demodulated to recover to transmit data by using the one-symbol maximum likelihood detector. The proposed scheme does not sacrifice the spectrum efficiency meanwhile maintains the transceiver with low complexity. Owing to the transmission symbols of different transmit antennas passing through all the spatial subchannels between transceiver antenna pairs, the system obtains the partial additional space diversity gain of all spatial paths. It is also shown that the diversity gain is better than the previous space-time block coding (STBC) schemes with full transmission rate.

A unified capacity analysis for wireless systems with joint multiuser scheduling and antenna diversity in Nakagami fading channels

In this paper, we present a cross-layer analytical framework to jointly investigate antenna diversity and multiuser scheduling under the generalized Nakagami fading channels. We derive a unified capacity formula for the multiuser scheduling system with different multiple-input multiple-output antenna schemes, including: 1) selective transmission/selective combining (ST/SC); 2) maximum ratio transmission/maximum ratio combining (MRT/MRC); 3) ST/MRC; and 4) space-time block codes (STBC). Our analytical results lead to the following four observations regarding the interplay of multiuser scheduling and antenna diversity. First, the higher the Nakagami fading parameter, the lower the multiuser diversity gain for all the considered antenna schemes. Second, from the standpoint of multiuser scheduling, the multiple antennas with the ST/SC method can be viewed as virtual users to amplify multiuser diversity order. Third, the boosted array gain of the MRT/MRC scheme can compensate the detrimental impact of the reduced amount of fading gain on multiuser scheduling, thereby resulting in greater capacity than the ST/SC method. Last, employing the STBC scheme together with multiuser diversity may cause capacity loss due to the reduced amount of fading gain, but without the supplement of array gain.

Signal detection for orthogonal space-time block coding over time-selective fading channels: The H/sub i/ systems

One major assumption in all orthogonal space-time block coding (O-STBC) schemes is that the channel remains static over the length of the code word. However, time-selective fading channels do exist, and in such case conventional O-STBC detectors can suffer from a large error floor in the high signal-to-noise ratio (SNR) cases. As a sequel to the authors' previous papers on this subject, this paper aims to eliminate the error floor of the H/sub i/-coded O-STBC system (i = 3 and 4) by employing the techniques of: 1) zero forcing (ZF) and 2) parallel interference cancellation (PIC). It is. shown that for an H/sub i/-coded system the PIC is a much better choice than the ZF in terms of both performance and computational complexity. Compared with the, conventional H/sub i/ detector, the PIC detector incurs a moderately higher computational complexity, but this can well be justified by the enormous improvement.

Error prediction for adaptive modulation and coding in multiple-antenna OFDM systems

In this paper, the problem of packet error rate (PER) prediction is addressed in the multiple-antenna broadband OFDM context, and its impact on adaptive modulation and coding (AMC) is quantified. The analysis is based on a physical layer comprising various modulation and coding schemes, ranging from robust space–time block coding (STBC) modes to high bit rate spatial division multiplexing (SDM) modes, and also hybrid SDM–STBC schemes. For each mode the expression of several link quality metrics (LQM) enabling PER prediction in the broadband OFDM channel, such as instantaneous signal-to-noise ratio (SNR), capacity, or exponential effective SNR metrics are provided. Their advantages and limitations are investigated. Finally, their performance is benchmarked in the IEEE 802.11a/g/n context. It is shown that the choice of the LQM has a significant impact on the throughput performance of the AMC algorithm.

Decision feedback detection with error compensation for hybrid space-time block codes

Spatial division multiplexing (SDM) techniques increase the total throughput by transmitting independent information streams through multiple transmit antennas whereas space time coding (STC) techniques utilize diversity gain. Hybrid space-time block code (STBC) schemes proposed combine the above two techniques to maximize the link performance. We propose a decision feedback detection method to improve the performance of the hybrid STBC scheme for orthogonal frequency division multiplexing (OFDM). In this scheme, we take the error propagation effect into account to enhance the detection performance. Simulation results show that the proposed method outperforms the conventional hybrid STBC detection algorithm by more than 3dB at 1% frame error rate for frequency selective fading channels.

Closed-loop space time block coding techniques for OFDM based broadband wireless access systems

We propose a closed loop space time block coding technique using four antennae at the transmitter for the enhancement of link layer performance of orthogonal frequency division multiplexing (OFDM) based broadband wireless access systems such as wireless local area networks (WLANs) and wireless metropolitan area networks (WMANs). Since full code rate and complex valued space-time block codes (STBCs) do not exist for more than two transmit antennae, we propose two feedback based STBC schemes. In the first scheme, phases of certain symbols in each sub carrier are rotated according to the feedback from the receiver. In the second scheme, best two out of four antennae are activated for transmission based on the associated channel gains in each subcarrier. In both schemes, the channel perceived at the receiver becomes orthogonal and the transmit diversity gain is maximized. One of the major challenges associated with the closed loop STBC schemes in OFDM systems as compared to CDMA systems is the requirement for extensive channel state information feedback as channel orthogonalization is performed in each subcarrier. However, by exploiting the feedback correlation among subcarriers, we have proposed a group based quantization technique to reduce feedback overhead significantly, making this scheme very attractive to broadband wireless access systems.

STBC-Schemes With Nonvanishing Determinant for Certain Number of Transmit Antennas

A space-time block-code scheme (STBC-scheme) is a family of STBCs {C(SNR)}, indexed by the signal-to-noise ratio (SNR) such that the rate of each STBC scales with SNR. An STBC-scheme is said to have a nonvanishing determinant if the coding gain of every STBC in the scheme is lower-bounded by a fixed nonzero value. The nonvanishing determinant property is important from the perspective of the diversity multiplexing-gain (DM-G) tradeoff: a concept that characterizes the maximum diversity gain achievable by any STBC-scheme transmitting at a particular rate. This correspondence presents a systematic technique for constructing STBC-schemes with nonvanishing determinant, based on cyclic division algebras. Prior constructions of STBC-schemes from cyclic division algebra have either used transcendental elements, in which case the scheme may have vanishing determinant, or is available with nonvanishing determinant only for two, three, four, and six transmit antennas. In this correspondence, we construct STBC-schemes with nonvanishing determinant for the number of transmit antennas of the form 2/sup k/, 3/spl middot/2/sup k/, 2/spl middot/3/sup k/, and q/sup k/(q-1)/2, where q is any prime of the form 4s+3. For cyclic division algebra based STBC-schemes, in a recent work by Elia et al., the nonvanishing determinant property has been shown to be sufficient for achieving DM-G tradeoff. In particular, it has been shown that the class of STBC-schemes constructed in this correspondence achieve the optimal DM-G tradeoff. Moreover, the results presented in this correspondence have been used for constructing optimal STBC-schemes for arbitrary number of transmit antennas, by Elia et al.

Signal Detection for Orthogonal Space-Time Block Coding Over Time-Selective Fading Channels: A PIC Approach for the<tex>$ cal G_i$</tex>Systems

One major assumption in all orthogonal space-time block coding (O-STBC) schemes is that the channel remains static over the entire length of the codeword. However, time selective fading channels do exist, and in such case the conventional O-STBC detectors can suffer from a large error floor in the high signal-to-noise ratio (SNR) cases. This paper addresses such an issue by introducing a parallel interference cancellation (PIC) based detector for the G/sub i/ coded systems (i=3 and 4).

Upper Bounds on the BER Performance of MTCM-STBC Schemes over Shadowed Rician Fading Channels

Space-time block coding (STBC) provides substantial diversity advantages with a low decoding complexity. However, these codes are not designed to achieve coding gains. Outer codes should be concatenated with STBC to provide additional coding gain. In this paper, we analyze the performance of concatenated trellis-coded STBC schemes over shadowed Rician frequency-flat fading channels. We derive an exact pairwise error probability (PEP) expression that reveals the dominant factors affecting performance. Based on the derived PEP, in conjunction with the transfer function technique, we also present upper bounds on the bit error rate (BER), which are further shown to be tight through a Monte-Carlo simulation study.

Equalization Concepts for Alamouti's Space–Time Block Code

In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamouti's space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity, for which space-time coding had been originally developed. This restriction is circumvented by our approach. Here, the structural properties of the transmit signal of space-time block coding, which is shown to be improper (rotationally variant), are fully used. For this, equalizers with widely linear (WL) processing are designed, such as a WL equalizer, a decision-feedback equalizer with WL feedforward and feedback filtering, and a delayed decision-feedback sequence estimator with WL prefiltering. Simulation results demonstrate that the proposed concepts may be successfully employed in an enhanced data rates for GSM evolution (EDGE) receiver, especially for pure transmit diversity. Here, significant gains can be observed, compared with a conventional single-input single-output transmission.

A∕D clipping effects on STBC scheme in receivers employing direct conversion structure

The performance of the Alamouti space time block coding (STBC) technique and single-input single-output (SISO) system is compared in the presence of A/D clipping. Square clipping, imposed by a direct conversion receiver structure was considered. With the target symbol error rate of 10-3 it was shown that STB coded signals have higher clip floor, and sensitivity to noise, when compared to the SISO system.

Space–Time Block Coding for Channels with Intersymbol Interference

Stoica, P., and Lindskog, E., Space–Time Block Coding for Channels with Intersymbol Interference, Digital Signal Processing 12 (2002) 616–627 The downlink of many wireless communication systems can be a MISO channel. An important problem for a MISO channel is how to code across space and time to obtain the same ML receiver as for the corresponding SIMO channel. For flat fading channels, space–time block coding (STBC) is a recent breakthrough solution to this problem. In Lindskog and Paulraj (in Proceedings of ICC'2000, NewOrleans, LA, June 18–22, 2000), STBC has been generalized to channels with intersymbol interference (ISI) for the case of two transmit antennas and one receive antenna. In this paper we first revisit the generalized STBC scheme of Lindskog and Paulraj and show that it has the same appealing properties as the standard STBC for flat fading channels. Then we go on to present an extension of this scheme to ISI channels with any number of transmit and receive antennas.