System Performance of Transmit Diversity Schemes for Interference-Limited Cellular Systems

For practical multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, it is important to develop transmit diversity schemes that are transparent to a receiver in that the receiver does not need to perform additional processing. In this paper, we examine one of the most widely-used receiver-transparent transmit diversity schemes - the cyclic delay diversity (CDD) scheme. It is shown that the CDD scheme effectively increases the delay spread of the channel and that the performance degrades under non-ideal channel estimation. As a remedy to the performance loss due to non-ideal channel estimation, a cluster-based transmit diversity scheme is proposed, which garners almost all the benefits of the CDD scheme without degrading the performance of a cluster- based channel estimation. The simulation results are provided in the realistic setting of IEEE 802.16e WiMAX systems.

The Alamouti Space Time Block Code (STBC) based Orthogonal Frequency Division Multiplexing (OFDM) is very attractive in frequency selective channel as the channels remain constant over Alamouti code period (two consecutive OFDM symbol block). But when the channel is fast fading, this assumption does not holds good and causes co-channel interference (CCI). Hence, the simple Alamouti detection method is not sufficient to recover the original transmitted signal from the mixed transmitted signals at the receiver side. To cancel the effects of CCI, several detection techniques are addressed namely SIC, DMLD, DZFD, DF and ML. The ML method has the optimum performance but the computational complexity is very high. Therefore, we propose a suboptimal MDF detection which provides comparable performance to that of ML with very less computational complexity. Finally, the performances of the above detection methods are compared in terms of symbol error rate (SER) and computational complexity for STBC OFDM system over doubly selective channel.

We present a space-frequency coding scheme using cyclic delay diversity (CDD) for an orthogonal frequency division multiplexing (OFDM)-based transmission system. CDD is a simple multiple transmit antenna approach for increasing the frequency selectivity of the channel seen at a single antenna receiver. This is due to the insertion of virtual echoes caused by antenna specific cyclic delays in the time domain at the transmitter. On each antenna a shifted version of the signal is sent, with these shifts being performed in the frequency domain. This allows the receiver to apply optimum demodulation, and thus exploit the diversity introduced by CDD. We optimize the selection of the time domain cyclic delays in the CDD so as to get full spatial diversity with the proposed space-frequency codes with CDD (SFC-CDDs) scheme. Moreover, we show simulation results for SFC-CDD, which confirm theoretical results with respect to the achieved spatial diversity, and present a comparison with the well-known Alamouti scheme implemented as SFC.

This paper considers the application of Monte-Carlo Simulation Method to quantify mean throughputs in interference-limited cellular systems along antenna pattern and frequency re-use factor. Firstly, we calculate the path loss between center cell to victim link receiver and all co-channel cells to victim link receiver to determine desired and undesired signals respectively. Next, AWGN and Shannon’s capacity have been used as a comparison to analyze the performance of throughputs in interference-limited cellular systems. The simulation results show that a re-use factor of N=1, directional antenna has improvement in the Shannon capacity by 242.2 % over Omnidirectional antennas whereas a frequency re-use factor of N=7 has increased to Shannon capacity by114% for N=7 over N=1.

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation scheme widely used in 4G. It is effective for reducing the effects of multipath delay in wireless communication. For OFDM system, total delay spread (Td) is less than symbol period (T); it can be combined with antenna arrays at transmitter and receiver (MIMO) to increase diversity gain called as MIMO-OFDM system. MIMO-OFDM improves system capacity on time-variant and frequency-selective channels. The quality of service provided by a system greatly depends upon the correct selection of modulation scheme. In this paper, analysis and simulation of OFDM-MIMO system with different digital modulation schemes like BPSK, 8-PSK, QPSK, and QAM is performed using Alamouti space–time block codes (STBC). STBC uses spatial and time dimensions for error control unlike traditional methods that uses only time dimension. A comparison study shows that for a given data rate and channel conditions, OFDM-MIMO using STBC with BPSK modulation is better compared with other digital modulation techniques in terms of error performance. OFDM-MIMO using STBC with BPSK modulation is further analyzed and simulated for various antenna configurations. It is observed that as numbers of antennas at transmitter and receiver side are increased, the system diversity increases and gives better performance in terms of BER.

In this paper, we consider the two-way relay channel (TWRC) over which communication is performed using space-time block codes (STBC) with physical-layer network coding (PNC) protocol. The three-node two-way relaying (TWR) model consists of two end nodes (sources) simultaneously communicating with each other over a relay node where each node is equipped with two antennas and uses Alamouti's STBC to provide diversity. We consider non-reciprocal channels where fading channel coefficients are independent for opposite directions of the same link. We first derive closed form expressions for the outage probability of the STBC-TWR system and uncoded TWRC assuming equal transmit power at each node and decode-and-forward (DF) strategy at the relay. We show that the STBC-TWR system significantly improves the uncoded TWRC outage performance. Then, to further improve the performance, we propose an optimal power allocation in TWR scheme employing Alamouti's STBC and PNC protocol. The optimal power allocation is obtained by maximizing the sum-rate under the total power constraint. We show that the optimal power allocation considerably improve the outage performance as well as the sum-rate compared to the equal-power case.

Space-time block code (STBC) based on orthogonal design is one of the space-time coding methods to achieve multi-input multi-output (MIMO) diversity gain. STBC can provide sufficient space diversity gain, but it can not provide coding gain. Polar codes based on channel polarization are the first class of provably capacity-achieving codes with low encoding and decoding complexity. In order to improve the bit error rate (BER) performance of STBC, a concatenated scheme with Polar codes and STBC, named Polar-STBC scheme, is proposed in this paper. The BER performance of Polar-STBC system is discussed by numerical simulation under different polar code length, different polar code rates, and different coding methods of STBC. The results show that the performance of Polar-STBC has a big improvement in comparison with that using STBC only. The coding gain of Polar-STBC system is about 5dB when the BER is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Meanwhile, the longer code length and the lower code rate Polar codes have, the better BER performance the Polar-STBC system has. In addition, the different STBC coding methods have influence on the Polar-STBC system. The Polar-STBC system with more receiving antennas has a better BER performance in comparison with those with the same sending antennas and less receiving antennas. The coding gain of Polar-STBC system with 2 receiving antenna is 6.5dB improvement to the system with 1 receiving antenna when BER is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and the code length is 1024.

This paper propose a new multiple-input multipleoutput (MIMO) signal processing scheme that combines optimum transmit and receive beamforming with the Alamouti space-time block code (STBC) transmission and modifies the decoding process. The scheme uses double antenna array groups to achieve stable performance regardless of direction of arrived (DOA) and angular spread (AS). In a multiuser MIMO communications scenario, the beamforming suppresses co-channel interference (CCI) by maximizing the uplink signal-to-noise-plus-interference-ratio (SINR) and suppress CCI independently while preserving orthogonality of the MIMO channel. It is shown that the beamforming process provides array gain by increasing the bit-error-rate (BER) performance and maximizes the available uplink channel capacity for each user in the presence of CCI.

A new MIMO transceiver is proposed for the downlink of high data rate multicarrier CDMA (MC-CDMA) systems over frequency-selective multipath channels. The design of the transceiver involves the following procedure. First, the data stream is demultiplexed into multiple substreams, which are then encoded by a set of space time block codes (STBC) for achieving spatial diversity. Second, the coded substreams are spread by a set of space-path spreading (SPS) codes which is designed to achieve path multiplexing by exploiting independent multipath channels and pre-suppress the multiple access interference (MAI) without the use of channel state information (CSI). These substreams are then transmitted simultaneously from multiple antennas. At each mobile station, a simple matched filter (MF) is used to despread the received data. Linearly combining the MF outputs with the aid of CSI and employing a multi-user detection scheme can then separate the mutually interfering signals from the multiple transmit antennas and restore the diversity gain due to SPS and STBC. An increased spectral efficiency and diversity gain can thus be achieved at the same time. Simulation results confirm that the proposed transceiver offers better performance than the conventional BLAST transceiver, and achieves nearly the performance of STBC and space-time spreading BLAST transceiver.

Two transmitter diversity techniques for turbo coded orthogonal frequency division multiplexing (OFDM) are presented: space-time block coding (STBC) and space-frequency block coding (SFBC). With different channel environment and block size, STBC and SFBC have different performance. Also, with the increase of interleaver size (equal to block size for BPSK), turbo has better performance. So the performance of STBC and SFBC with different transmission environment and block size is simulated and discussed. Some important conclusions about the transmitter diversity for turbo coded OFDM systems are achieved.

Alamouti空时块码与波束形成相结合的方案只使用了两个功率均分的波束,在很多情况下并非最优。该文提出了新的空时块码与波束形成相结合的方案,新方案能够根据信道互相关矩阵的特征值,展开不超过发射端天线数量的波束,在满足空时块码发射天线数量等于波束数量的条件下,与任意码率空时块码结合。该文还利用Gauss-Chebyshev积分对线性调制下新方案的误符号率进行了性能分析,得出了简单的数值计算表达式。新方案由于同时获得了分集增益和波束形成增益,显著提高了系统的性能。

Media-based modulation (MBM) is a new and promising transmission scheme that employs reconfigurable antennas to create different channel fade realizations and appears as an emerging index modulation (IM) application. In this paper, we present a novel multiple-input multiple-output (MIMO) transmission scheme called multidimensional media-based modulation (M-MBM) by redesigning the classical Alamouti's space-time block coding (STBC) scheme with MBM through the use of the additional dimension of channel states. The error performance of the proposed M-MBM scheme is theoretically analyzed for correlated and uncorrelated channel states and a union bound is obtained for the average bit error probability (ABEP). Moreover, through computer simulations, the superior error performance of the M-MBM scheme over the emerging IM techniques is demonstrated.

Wireless systems have rapidly moved toward becoming piece of regular day to day existence. Cell Phone systems, Remote LANs and individual region systems are only a couple of cases of largely utilized wireless communications. The Space Time Coding has advanced as a most dynamic research range in wireless communications. Spatial multiplexing builds categorize limit by division a soaring rate motion into several inferior rate streams and transmitting them through the diverse dissimilar antennas. In spatial multiplexing, the beneficiary can effectively interpret each stream given that the got signals have sufficient spatial symbols and that the receiver has sufficient antennas to isolate the streams. The outcome of utilizing these MIMO systems is higher information rate or longer transmit extend without requiring extra transfer speed or transmit control. This paper introduces full information of diversity coding for MIMO system. STBC (space-time block coding) plans including Alamouti's STBC used for 2 transmit antenna plus 2 recievier antanna are investigated. At last, these STBC systems are actualized and analyzed execution as indicated by their bit-error rates utilizing BPSK, QPSK, and 8-PSK modulation schemes.

In recent times, Chaos communication plays a significant role in addressing the security challenges that are more common in the regular communication systems. By exploiting the chaotic waveform properties, variety of chaos-based communication systems are proposed. Considering the aforementioned facets of communication, this research objective at merging the space-time block code (STBC) and orthogonal differential chaos shift keying (ODCSK) methods to improve the security aspects of multiple-input multiple-output (MIMO) based wireless system. Chaos signal is created by using the method called logistic mapping to achieve better secrecy. STBC method is used during the modulation stage for arranging the chaos signal. This system with different types of STBCs is aimed at analysing the differential chaos shift keying (DCSK) and orthogonal DCSK (ODCSK) modulation in AWGN channel. MATLAB software is used to simulate the Bit Error Rate [BER]. Initial simulation proves that the combination of orthogonal DCSK and Alamouti STBC with MIMO system gives better results for AWGN channel when compared to other combinations.KeywordsDifferential Chaos shift keyingSpace-time block codeMultiple-input multiple-output

A recent trend of research on the MIMO-OFDM system pays more attention to reduce complexity for implementation in design receiver structure. So in this paper, we propose differential space time block codes (STBC) MIMO-OFDM system with cyclic delay diversity (CDD) in a frequency selective fading channel. Differential modulation provides simplification of embodiment communication system because channel estimation block is not necessary. And also we apply proposed scheme to convolutional turbo codes (CTC) for playing an important part in MIMO-OFDM system as inner codes. This structure can provide a very close performance to that of the conventional diversity scheme with maximum likelihood (ML) detection without channel estimation block while the receiver structure is highly simplified. BER performance of the proposed system is analyzed and simulated for an AWGN channel by theoretical and simulated approaches. The results of this paper can be applicable to the 4G mobile multimedia communication systems.