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.

Beam Pattern Scanning (BPS) versus Space-Time Block Coding (STBC) and Space-Time Trellis Coding (STTC)

In this paper, Beam Pattern Scanning (BPS), a transmit diversity technique, is compared with two well known transmit diversity techniques, space-time block coding (STBC) and space-time trellis coding (STTC). In BPS (also called beam pattern oscillation), controlled time varying weight vectors are applied to the antenna array elements mounted at the base station (BS). This creates a small movement in the antenna array pattern directed toward the desired user. In rich scattering environments, this small beam pattern movement creates an artificial fast fading channel. The receiver is designed to exploit time diversity benefits of the fast fading channel. Via the application of simple combining techniques, BPS improves the probability-of-error performance and network capacity with minimal cost and complexity. In this work, to highlight the potential of the BPS, we compare BPS and Space-Time Coding (i.e., STBC and STTC) schemes. The comparisons are in terms of their complexity, system physical dimension, network capacity, probability-of-error performance, and spectrum efficiency. It is shown that BPS leads to higher network capacity and performance with a smaller antenna dimension and complexity with minimal loss in spectrum efficiency. This identifies BPS as a promising scheme for future wireless communications with smart antennas.

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 Enhancement of Multiuser Passive Time Reversal Communication Based on Space-Time Block Coding

Reliable, with high data rate, acoustic communication in time-valTing, multipath shallow water environment is a hot research topic recently. Passive time reversal communication has shown promising results in improvement of the system performance. In multiuser environment, the system performance is significantly degraded due to the interference among different users. Passive time reversal can reduce such interference by minimizing the cross-correlated version of channel impulse response among users, which can be realized by the well-separated users in depth. But this method also has its shortcomings, even with the absence of relative motion, the minimization sometimes may be impossible because of the time-varying environment. Therefore in order to avoid the limitation of minimizing the cross-correlated channel function, an approach of passive time reversal based on space-time block coding （STBC） is presented in this paper. In addition, a single channel equalizer is used as a pest processing technique to reduce the residual symbol interference. Experimental results at 13 kHz with 2 kHz bandwidth demonstrate that this method has better performance to decrease bit error rate and improve signal to noise ratio, compared with passive time reversal alone or passive time reversal combined with equalization.

Non-Vanishing Space Time Block Code for Three Time Slots and Two Transmit Antennas

Recently, space time block codes (STBCs) are proposed for multi-input and multi-output (MIMO) antenna systems. Designing an STBC with both low decoding complexity and non-vanishing property for the Long Term Evolution Advanced (LTE-A) remains an open issue. In this paper, first our previously proposed STBC’s non-vanishing property will be completely described. The proposed STBC scheme has some interesting properties: 1) the scheme can achieve full rate and full diversity;2) its maximum likelihood (ML) decoding requires a joint detection of three real symbols;3) the minimum determinant values (MDVs) do not vanish by increasing signal constellation sizes;4) compatible with the single antenna transmission mode. The sentence has been dropped. Second, in order to improve BER performance, we propose a variant of proposed STBC. This scheme further decreases the detection complexity with a rate reduction of 33%;moreover, non-vanishing MDVs property is preserved. The simulation results show the second proposed STBC has better BER performance compared with other schemes.

Efficiency Improvement of Space Time Block Codes

Unlike most of the existing methods in Space Time coding (STC) system which focus on design of STC gaining full rate and/or maximum diversity, we propose an approach to improve spectral efficiency of the code. The proposed scheme carries more information symbols in each transmission block as compare to its counterpart code, and yet retains the property of simple decoding. Simulation results show that transmit diversity is retained with improvement of code efficiency. We mainly focus on Four transmit antenna scheme but it can be generalized for any number of transmit antennas.

An Iterative Power Allocation Algorithm for Group-wise Space-Time Block Coding Systems

An iterative transmit power allocation (PA) algorithm was proposed for group-wise space-time block coding (G-STBC) systems with group-wise successive interference cancellation (GSIC) receivers. Group-wise interference suppression (GIS) filters are employed to separate each group's transmit signals from other interferences and noise. While the total power on all transmit symbols is constrained, all transmit PA coefficients are updated jointly according to the channel information at each iteration. Through PA, each detection symbol has the same post-detection signal to interference-and-noise ratio (SINR). The simulation results verify that the proposed PA algorithm converges at the equilibrium quickly after few iterations, and it achieves much lower bit error rates than the previous single symbol SIC PA and the fixed ratio PA algorithms for G-STBC systems with GSIC receivers .

Linear Dispersion Orthogonal Space-Time Block Codes

A new architecture of space-time codes as a combination of orthogonal space-time block codes （OSTBC） and linear dispersion codes （LDC） is proposed in order to improve the bit error rate（BER） performance of OSTBC.The scheme proposed is named linear dispersion orthogonal space-time block codes （LDOSTBC）.In LDOSTBC scheme,firstly,the data is coded into LDC codewords.Then,the coded LDC substreams are coded into OSTBC codewords again.The decoding algorithm of LDOSTBC combines linear decoding of OSTBC and ML decoding or suboptimum detection algorithms of LDC.Compared with OSTBC scheme when the rate of LDC is MtR,the performance of LDOSTBC scheme can be improved without decreasing the data rate,where Mt is the number of transmit antennas and R is the spectral efficiency of the modulation constellation.If some rate penalty is allowed,when the rate of LDC is less than MtR the performance of LDOSTBC can be improved further.

Differential modulation based on space-time block codes

A differential modulation scheme using space-time block codes is put forward. Compared with other schemes, our scheme has lower computational complexity and has a simpler decoder. In the case of three or four transmitter antennas, our scheme has a higher rate a higher coding gain and a lower bit error rate for a given rate. Then we made simulations for space-time block codes as well as group codes in the case of two, three, four and five transmit antennas. The simulations prove that using two transmit antennas, one receive antenna and code rate of 4 bits/s/Hz, the differential STBC method outperform the differential group codes method by 4 dB. Useing three, four and five transmit antennas, one receive antenna, and code rate of 3 bits/s/Hz are adopted, the differential STBC method outperform the differential group codes method by 5 dB, 6. 5 dB and 7 dB, respectively. In other words, the differential modulation scheme based on space-time block code is better than the corresponding differential modulation scheme

A New Generalized Complex Orthogonal Space-Time Block Codes

Recent research challenges in the wireless communication include the usage of diversity and efficient coding to improve data transmission quality and spectral efficiency. Space diversity uses multiple transmitting and/or receiving antennas to create independent fading channels without penalty in bandwidth efficiency. Space-time block coding is an encoding scheme for communication over Rayleigh fading channels using multiple transmitting antennas. Space-time block codes from complex orthogonal designs exist only for two transmitting antennas. This paper generalizes a new complex orthogonal space-time block code for four transmitting antennas, whose decoding complexity is very low. Simulations show that the generalized complex orthogonal space-time block code has low bit error rate, full rate and possibly large diversity.

Analysis of Rate One Quasi-Orthogonal Space-Time Block Coding over Rayleigh Fading Channel

Full-rate is very important in any data transmission coding. For transmitting data at low bit rate than full-rate code, higher modulation scheme is required. But it is impossible to design full rate orthogonal designs with complex constellation for more than two transmit antennas. Only Alamouti code provides full-rate for two transmit antennas. In this paper, Bit Error Rate (BER) is calculated for Quasi-Orthogonal Space-time Block Coding (QOSTBC). Here we work with Rayleigh fading channel. We consider the codes which decodes pairs of symbols instead of simple separate decoding like Orthogonal Space-Time Block Coding. In Quasi-Orthogonal Space-time Block Code full-rate is achieved but full-diversity is sacrificed. Diversity is the most important techniques for providing reliable communication over fading channels. One of the diversity techniques that uses multiple transmit and/or receive antennas is space diversity. Multiple antenna technique provides a space diversity to struggle with the fading without necessarily sacrificing bandwidth resources, so the excellent solutions of removing the fading of the channel for broadband wireless communications is using space diversity. Then, with the constellation rotation of the symbol, rotated version of Quasi-Orthogonal Space-Time Block Code is generated. It provides full diversity. We simulate BER for QOSTBC, rotated QOSTBC, orthogonal STBC and for uncoded system. The simulation result shows that QOSTBC and rotated QOSTBC perform better than other systems. It shows that QOSTBC provides a full transmission rate but that rotated QOSTBC provides the full rate with the full diversity.

Joint channel estimation and symbol detection for space-time block code

The simplified joint channel estimation and symbol detection based on the EM (expectation-maximization) algorithm for space-time block code (STBC) are proposed. By assuming channel to be invariant within only one STBC word and utilizing the orthogonal structure of STBC, the computational complexity and cost of this algorithm are both very low, so it is very suitable to implementation in real systems.

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 spacetime 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.

Improved scheme with cooperative diversity based on distributed space-time block coding

An improved scheme with cooperative diversity based on distributed space-time block coding （WCD- DSTBC） is proposed, which effectively achieves diversity gains and improves the performance of the system by sharing some single-antenna users＇ antennas to form a virtual antenna array and combining with distributed spacetime block coding （DSTBC） mode. Then the relation between the system BER and the interuser BER for WCDDSTBC scheme is theoretically derived and the closed-form expression of BER for WCD-DSTBC system is obtained. The simulation results show that the proposed WCD-DSTBC scheme achieves distinct gains over the non-cooperative multi-carrier CDMA （MC-CDMA） system. When system BER is le-3 and interuser BER is le-3, about 2.5 dB gain can be gotten. When interuser channel state information （CSI） outgoes the users＇ individual CSI, about 3 dB gain is also achieved.

Closed Loop Space-Time Block Coding for Wireless Downlink Transmission

In order to improve the poor performance of Space-Time Block Coding (STBC) in a downlink correlated fading environment, a closed loop scheme is proposed. With the known channel fading statistics fed from the receiver, eigenbeamforming is utilized to improve the performance of STBC at the transmitter. The new system achieves the array and diversity gain simultaneously. Because reduced dimension processing is adopted, the proposed system has a relative simple structure compared with the traditional beamforming system. The validity of the scheme is verified in several situations by simulation experiments.

Partial Feedback Based Orthogonal Space-Time Block Coding With Flexible Feedback Bits

The conventional orthogonal space-time block code (OSTBC) with limited feedback has fixed p-1?feedback bits for the specific ntp?transmit antennas. A new partial feedback based OSTBC which provides flexible feedback bits is proposed in this paper. The proposed scheme inherits the properties of having a simple decoder and the full diversity of OSTBC, moreover, preserves full data rate. Simulation results show that for?ntp transmit antennas, the proposed scheme has the similar performance with the conventional one by using p-1?feedback bits, whereas has the better performance with more feedback bits.

禁飞区约束的CSTBC无人机中继通信系统航迹优化

中继无人机的飞行路径对无人机中继通信系统的链路传输可靠性具有重要影响。为提高无人机中继通信系统链路传输的可靠性,提出协作空时分组编码(CSTBC)无人机中继通信方案,并以链路中断概率最小化准则为基础,提出中继无人机的航迹优化方法;理论分析给出系统遍历容量和分集增益;为保障中继无人机飞行安全,并获取信道的分集增益,提出无人机禁飞区规避方法。结果表明:协作空时分组编码无人机中继通信系统可充分获取信道的分集增益,改善无人机中继通信系统链路传输的可靠性。

Comparative Study of Different Space-Time Coding Schemes for MC-CDMA Systems

In this paper, performance of space-time trellis-code (STTC), space-time block code (STBC), and space-time trellis-code concatenated with space-time block code (STTC-STBC) for multi-carrier code-division multiple-access (MC-CDMA) system are studied. These schemes are considered by employing different detection techniques with various multi input multi output (MIMO) antenna diversity for different number of states in multi-path fading channel. The corresponding bit error rate (BER) is obtained using simulation for minimum mean-square error (MMSE), maximum-ratio combining (MRC), and equal-gain combining (EGC) receivers employing Viterbi decoder. The simulation results show that the STTC-STBC MC-CDMA system perform better compared to other schemes considered in this paper using MMSE detection and it is also observed that the performance can also be enhanced by increasing diversity using more transmitter and receiver antennas. However, this improvement in performance comes at the cost of increased computational complexity, which is calculated for different transmitting and receiving antennas.