A Method for Improving Power Distribution Characteristics of Space Time Block Codes

Improving power distribution characteristics of space time block codes(STBCs),namely peak to average power ratio(PAPR),average to minimum power ratio(Ave/min),and probability of transmitting"zero"by antenna,makes easier their practical implementation.To this end,this study proposes to multiply full diversity STB C with a non-singular matrix in multiple input multiple output(MIMO)or multiple input single output(MISO)systems with linear or maximum likelihood(ML)receivers.It is proved that the obtained code achieves full diversity and the order of detection complexity does not change.The proposed method is applied to different types of STBCs.The bit error rate(BER)and power distribution characteristics of the new codes demonstrate the superiority of the introduced method.Further,lower and upper bounds on the BER of the obtained STBCs are derived for all receivers.The proposed method provides trade-off among PAPR,spectral efficiency,energy efficiency,and BER.

Performance of MIMO Systems Using Space Time Block Codes (STBC)

Digital Communications, in relation to wireless networks, have taken off in recent years due to the expanding need to communicate faster and more efficiently. A popular way to achieve this is by using wireless Multiple Input Multiple Output (MIMO) communication systems. MIMO systems utilize Space Time Block Codes (STBC) as one of the leading ways to obtain higher data rates with limited bandwidth and power. With several STBC methods currently available, this paper analyzes simulations using Orthogonal Space Time Block Codes (OSTBC) in Rayleigh fading channels to evaluate the performance of MIMO systems. The selection to use a Rayleigh fading channel as a model for a non-line-of-sight (nLOS) environment is selected to mimic installations where a large number of signal paths and reflections are expected. All simulations are coded, generated and plotted using MATLAB resulting in graphical data representing the bit-error rate (BER) to signal-to-noise ratio (Eb/N0) or SNR. Each simulation captures how different configurations of key variables including code rate, diversity and antenna count can impact system performance. Four modulation schemes (BPSK, QPSK, 16-QAM and 64-QAM) are included in each simulation. Conclusive evidence based upon these simulations suggests higher diversity gains were achieved with a greater number of antennas. The most significant factor for increasing system performance was using a lower count of transmit antennas with a higher count of receive antennas.

Performance and EXIT analysis of parallel concatenated space time trellis codes

Space time trellis coding （STTC） techniques have been proposed to achieve both diversity and coding gains in multiple input multiple output （MIMO） fading channels. But with more transmit antennas STTCs suffer from the design dificulty and complexity increasing. This paper proposes a scheme, named parallel concatenated space time trellis codes （PC-STTC）, to achieve the tradeoff between the performances and complexity of STTCs for a large number of transmit antennas. Simulation results and complexity comparison are provided to demonstrate the performance and superiority of the proposed scheme over conventional schemes in fast fading channels in low signal-to-noise ratio （SNR） regions. And an EXIT （extrinsic information transform） chart is given to analyze the iterative convergence of the proposed scheme. It shows that PC-STTC has better iterative convergence in low SNR regions.

Performance evaluation of MIMO-OFDM system based on time-switched transmit diversity

In this paper,a time-switched space-time(TSST) coded orthogonal frequency division multiplexing(OFDM) scheme against the time-varying channels is proposed.In the TSST-OFDM scheme,it is equipped with four transmit antennas,but only double of them are used for coding in every time slot.It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code.The analyses and simulations results validate that the proposed scheme not only gets timeswitched diversity and lower decoding complexity,but also suffers less time-varying impairments.Hence,it exhibits better performance than quasi-orthogonal space-time coded scheme.

Analysis for MIMO correlated frequency-selective channel in the presence of interference

The space time spreading, superimposed training sequences, and space-time coding are used to present a multiple input and multiple output （MIMO） systems model, and a closed-form of average error probability upper bound expression for MIMO correlated frequency-selective channel in the presence of interference （co-channel interference and jamming signals） is derived. Moreover, the correlation at both ends of the wireless link that can be incorporated equivalently into correlation at the transmit end is also derived, which is significant to analyze space-time link algorithm of MIMO systems.

Capacity analysis of high-rank line-of-sight MIMO channels

Matrix perturbation theory is utilized to investigate high-rank line of sight multiple input multiple output channels in a microwave relay system. The upper and lower bounds of channel capacity are derived based on space time block codes technique and singular values decomposition. A useful constraint for designing LOS MIMO channels is developed by the use of the condition number of the MIMO channel matrix. The theoretical analysis of channel capacity is confirmed by the simulation. The results show that the proposed method is able to give a physical explanation of the high-rank LOS MIMO channel matrix characteristics.

INTERFERENCE MITIGATION FOR ASYNCHRONOUS COOPERATIVE STBC-OFDM SYSTEMS

This paper addresses the problem of interference mitigation in cooperative Space Time Block Coded Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems in the presence of asyn-chronism. This scheme first preprocesses the received ST codewords to convert the equivalent fading matrix into a suboptimal ordering upper triangular form based on low complexity permutation QR decomposition, and then suppresses the InterCarrier Interference (ICI) and InterSymbol Interference (ISI) by exploiting Successive Interference Cancellation (SIC) technique. Simulation results show that the performance of the proposed algorithm slightly outmatches or asymptotically approaches to that of the existing Minimum Mean Square Error (MMSE) detector depending on the magnitude of the Carrier Frequency Offsets (CFOs) but with less complexity.

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.

New design of no-zero-entry single symbol ML decodable STBCs based on group precoding

In multiple-input multiple-output （MIMO） systems, space-time block codes （STBCs） from orthogonal designs （ODs） and coordinate interleaved orthogonal designs （CLOD） have been attracting wider attention due to their amenability for fast （single symbol） maximum-likelihood （ML） decoding, and full-rate with full-rank over quasi-static fading channels. However, most of these codes, for transmitting antennas more than 4, have large number of zero entries in their codeword matrix. Due to the zero entries in the design, the transmitting antennas need to be switched on and off imposing severe hardware constraints. To solve this problem, we propose a method to generate a new class of no-zero-entry single symbol maximum likelihood decodable STBCs （NZESSDCs）, which is based on coordinate interleaving and group precoding technique. The ability of the proposed group precoding based NZESSDCs （called G-NZESSDCs） on single symbol ML Decoding and full diversity are analyzed and derived. The performance evaluation is accomplished by numerical simulation and is compared with recently reported NZESSDCs （called C-NZESSDCs）. Compared with C-NZESSDCs, the proposed G-NZESSDCs have same bit-error-rate （BER） performance and better peak-to-average ratio （PAPR） performance.

Robust linear receivers for STBC systems with unknown co-channel interference

Focusing on space-time block code （STBC） systems with unknown co-channel interference, an oblique projection-based robust linear receiver is proposed in this paper.Based on the oblique projection, the desired signal subspace and interference-plus-noise subspace are first identified from the received signal.Then the matched filter receiver is used to decode the STBC encoded signals in the desired signal subspace.Simulation results show that the proposed linear receiver obtains significant performance improvement over conventional Capon-type receivers under finite sample-size situations and in the presence of channel estimation errors.