Delay Diversity Research Articles

Multiple-Input-Single-Output Based a Novel Pilot-Aided Channel Estimation for Cyclic Delay Diversity Orthogonal Frequency Division Multiplexing Frameworks

A low-complexity standard transmit diversity scheme for coded orthogonal frequency division multiplexing (OFDM) frameworks is cyclic delay diversity (CDD). As the cyclic delay esteem expands the diversity effect also increases. However, the channel estimation turns out to be more troublesome because of increased frequency selectivity as the increased cyclic delay value. In this paper we discussed about dissimilar channel estimation schemes and to conclude we proposed a novel pilot-aided channel estimation scheme for CDD to estimate the channel in an enhanced way. Our scheme estimates each channel separately and achieves significant performance improvement.

Secrecy Analysis of Distributed CDD-Based Cooperative Systems With Deliberate Interference

In this paper, a cooperative cyclic-prefixed single carrier (CP-SC) system is studied and a scheme to improve its physical layer security is proposed. In particular, a distributed cyclic delay diversity (dCDD) scheme is employed and a deliberate interfering method is introduced, which degrades the signal-to-interference-plus-noise ratio (SINR) over the channels from a group of remote radio heads (RRHs) to an eavesdropper, while minimizing the signal-to-noise ratio loss over the channels from the RRHs to an intended user. This is obtained by selecting one RRH that acts as an interfering RRH and transmits an interfering artificial noise sequence to the eavesdropper. Through the use of the dCDD scheme, a channel that minimizes the receive SINR at the eavesdropper is selected for the interfering RRH. This choice enhances the secrecy rate of the CP-SC system. The system performance is evaluated by considering the secrecy outage probability and the probability of non-zero achievable secrecy rate, which are formulated in closed-form analytical expressions for the case of identically and non-identically distributed frequency selective fading channels. Based on the proposed analytical framework, the diversity order of the system is studied. Monte Carlo simulations are employed to verify the analytical derivations for numerous system scenarios.

Cooperative communication system with multiple relays for performance improvement in wireless communication system

In a wireless communication system, a cooperative communication technique is a communication method for improving performance. In the conventional scheme, when a destination user is located in the cell boundary, one base station communicates with a destination user. At a same time, a destination user communicates with other base stations which cooperate with base station. If a distance between a base station and a destination user is far, the quality of communication is degraded by the effect of channel attenuation. Therefore, this paper proposes an enhanced cooperative transmission scheme using the orthogonal frequency multiplexing in the wireless communication system. The proposed scheme uses extra relays between a base station and a destination user. When the channel state of a destination user is bad, other base stations are used. In order to obtain better performance than the conventional scheme, the cooperative decode and forward (DF), and space time cyclic delay diversity (STCDD) and cyclic delay diversity (CDD) are applied in the extra relays. In simulation results, the proposed scheme has higher error and throughput performances than the conventional scheme for obtaining diversity gain when the used modulation scheme is increased. Also, the proposed scheme which uses cooperative DF has slightly better error and throughput performances than the proposed scheme which uses cooperative STCDD and CDD due to less error propagations and resultant higher diversity gain.

An Interference Cancellation Scheme for High Reliability Based on MIMO Systems

This article proposes a new interference cancellation scheme in a half-duplex based two-path relay system. In the conventional two-path relay system, inter-relay-interference (IRI) which severely degrades the error performances at a destination occurs because a source and a relay transmit signals simultaneously at a specific time. The proposed scheme removes the IRI at a relay for higher signal-to-interference plus noise ratio (SINR) to receive interference free signal at a destination, unlike the conventional relay system, which removes IRI at a destination. To handle the IRI, the proposed scheme uses multiple-input multiple-output (MIMO) signal detection at the relays and it makes low-complexity signal processing at a destination which is a usually mobile user. At the relays, the proposed scheme uses the low-complexity QR decomposition-M algorithm (QRD-M) to optimally remove the IRI. Also, for obtaining diversity gain, the proposed scheme uses cyclic delay diversity (CDD) to transmit the signals at a source and the relays. In simulation results, the error performance for the proposed scheme is better when the distance between one relay and another relay is low unlike the conventional scheme because the QRD-M detects received signal in order of higher post signal-to-noise ratio (SNR).

An enhanced channel estimation technique for CDD OFDM system over time varying channels

Cyclic delay diversity (CDD), employing multiple antennas provides increased frequency-selectivity and thereby achieves frequency diversity using forward error correction in orthogonal frequency division multiplexing (OFDM). However, channel estimation of CDD OFDM becomes crucial over frequency-selective fading channels. In this paper, we propose a low-complexity channel estimation technique for CDD OFDM systems over time-varying channels using basis expansion model. We first analyze the frequency correlation of CDD OFDM channels and then design scattered pilot structure for estimating the channel coefficients. In the proposed channel estimator, Slepian sequences are employed estimate the channel impulse response by exploiting the frequency correlation of CDD OFDM over time-varying channel. Simulation results demonstrated that the proposed channel estimator achieves better mean square error and bit-error-rate performance compared with that of existing methods over time-varying channels.

Performance Analysis of Distributed Single Carrier Systems With Distributed Cyclic Delay Diversity

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain.

Gold-MUSIC based DOA estimation using ULA antenna of DS-CDMA sources with propagation delay diversity

Direction of Arrival (DOA) estimation using gold-MUSIC is achieved for Uniform Linear Array (ULA) antenna based Direct-Sequence Code Division Multiple Access (DS-CDMA) sources having different Propagation Delay. The DOA is estimated by different MUSIC (Multiple Signal Classification) algorithms for M signal sources with Phase Shift Keying (PSK) transmission in presence of Additive White Gaussian Noise (AWGN). Spatial spectrum, computational efficiency and Root Mean Square Error (RMSE) of DOA estimation using gold-MUSIC over MUSIC and Root-MUSIC algorithms are studied meticulously. The effects of number of ULA elements, Data length and arrival angle on RMSE of DOA are also conferred here.

Full-Duplex Delay Diversity Relay Transmission Using Bit-Interleaved Coded OFDM

In this paper, a delay diversity orthogonal frequency-division multiplexing (DD OFDM) transmission scheme in amplify-and-forward (AF) full-duplex relay systems is investigated. One direct source-to-destination link, one relay forwarding link, and residual self-interference are considered in the system. The necessary cyclic prefix length is investigated and a suitable AF relay protocol in the full-duplex relay OFDM system is proposed. This paper demonstrates that the AF relay link and the direct source-to-destination link can be combined to provide spatial diversity. The key is that the DD OFDM scheme is used to transform the spatial diversity into increased channel frequency diversity that is further exploited by using the bit-interleaved coding. The bit error rate performance of the proposed system is verified by simulation results.

Cyclic Delay Diversity with Phase Shift in Low Rate SC-FDMA Uplink

This paper proposes a phase shift scheme in cyclic delay diversity (CDD) for single-carrier frequency division multiple access in Internet of Things (IoT) applications. The proposed scheme is assumed to be applied to the uplink of long term evolution (LTE) systems. Since the transmission rates of IoT applications are small, each uplink connection may occupy less than 12 subcarriers that corresponds to one resource block of the LTE. Since the length of the data sequence in time domain is short so that CDD may provide limited frequency diversity. The proposed scheme shifts the phases of the data symbols in time domain and spreads each subcarrier component over multiple subcarriers. Thus, more diversity gain can be realized with CDD. Numerical results obtained through computer simulation shows that the proposed scheme improves the performance by about 5–7 dB at the bit error rate of 10−4 for the data sequence length of 4. It is also shown that no increase of peak-to-average power ratio is observed with the proposed scheme.

Cooperative Transmission Scheme Using the Single Antenna in the Broadcasting and Cellular System

In this paper, the cellular system and broadcasting system use a cooperative transmission scheme. The conventional scheme is not consider the condition of a channel between a cellular base station (CBS) and a destination user. In this conventional scheme, two CBSs communicate with the user by the cooperative transmission scheme when the user is located in the cell edge. If CBS is distant from a user and the channel condition is poor, the performance of communication is degraded. The proposed scheme using the relay between CBS and the user located in the edge of CBSs improves the performance of the communication when the channel state between CBS and the user is bad. Also, space time block code and cyclic delay diversity scheme are used for the reliable transmission in the proposed scheme. The proposed scheme using the relay achieves good BER and throughput performance. Through the simulation, it is confirmed that the proposed scheme is better than the conventional scheme.

A Novel Optimized Approach for Underwater Acoustic (UWA) Cooperative Communication Systems to Achieve Delay Diversity

The communication through water is different scenario from the communication on the land, while transmission through the water the delays are frequently happens when the signals received from geographically separated nodes. Moreover, UWA communications enable high motion agility and flexibility of the nodes, and allow interactive system query and instantaneous system response. The UWA environment is commonly viewed as one of the most challenging environments for wireless communications and networking. It differs from the terrestrial radio environment in many different aspects. Although tremendous progress has been made in the past literature but still the synchronism issues is concerned area in the field of UWA communications. To resolve the issue of the synchronism issues usage of the OFDM communication system is employed and transmissions at the source node by preceding every OFDM block with an extremely long cyclic prefix (CP) which reduces the transmission rates dramatically. One may increase the OFDM block length accordingly to compensate for the rate loss which also degrades the performance due to the significantly time-varying nature of UWA channels. In this paper, we develop a new OFDM-based scheme to combat the asynchronism problem in cooperative UWA systems without adding a long CP (in the order of the long relative delays) at the transmitter. By adding a much more manageable (short) CP at the source, we obtain a delay diversity structure at the destination for effective processing and exploitation of spatial diversity by utilizing a low complexity Viterbi decoder at the destination, e.g., for a binary phase shift keying (BPSK) modulated system, we need a two-state Viterbi decoder. We provide pair wise error probability (PEP) analysis of the system for both time-invariant and block fading channels showing that the system achieves full spatial diversity. Finally the simulation results shows that performance of the proposed method is good over the conventional state of the art methods and extensive simulations that the proposed scheme offers a significantly improved error rate performance for time-varying channels (typical in UWA communications) compared to the existing approaches.

A Proposed H-STCDD Scheme in Cooperative Communication System

In this paper, the hierarchical space time cyclic delay diversity (H-STCDD) scheme is proposed. Proposed scheme uses hierarchical modulation and achieves approximately full rate. It also uses a cyclic delay diversity scheme, which improves the benefit of channel coding particularly in high SNR environment between source to relay and source to destination. According to simulation result, proposed scheme has up to 2.2 dB better BER performance than conventional cooperative scheme at BER of 10ź3 and has similar BER performance with the STCDD scheme particularly in high SNR environment between source to relay and source to destination. Throughput of the proposed scheme is better than those of other cooperative schemes. Therefore proposed scheme is more efficient than other cooperative scheme and can be efficiently used in high SNR environment between source to relay and source to destination.

Single-Carrier Frequency-Domain Equalizer with Multi-Antenna Transmit Diversity

Single-carrier (SC) block transmission with cyclic prefix (CP) is a method with several advantages that has been incorporated into standards. This paper has analyzed the performance of multi-antenna SC-FDE under Alamouti signaling and cyclic-delay diversity (CDD). Our analysis shows that the characteristic of diversity it is depends on data block length and data transmission rate as well as on the channel memory and antenna configuration. At higher rates their diversity diminishes and full diversity is available to both CDD and Alamouti signalling below a certain rate threshold. From our investigation we say that at high rates Alamouti signalling provides twice the diversity of SISO SC-FDE, while the diversity of the SISO SC-FDE under the CDD diversity degenerates. In this paper, we analyze the performance of SC-FDE in conjunction with either cyclic delay diversity (CDD) or Alamouti signaling, fully characterizing the diversity as a function of transmission-block length, number of antennas data rate and channel memory. In the process, we obtain a threshold rate (as a function of data-block length, channel memory, and number of antennas) below which the full spatial-temporal diversity is achieved, while at higher rates the diversity of both schemes diminishes. Our analysis shows that at high rates Alamouti signaling provides twice the diversity of SISO SCFDE, while the CDD diversity degenerates to the diversity of the SISO SC-FDE.

A low-power antenna selective synchronization method for IEEE 802.11ac WLAN systems

This paper proposes an antenna selective timing synchronization method for multiple-input multiple-output orthogonal frequency division multiplexing-based IEEE 802.11ac wireless local area network systems. IEEE 802.11ac systems support up to eight antenna elements for adopting an MIMO technique. The increase in the number of antennas results in high power consumption due to the very high computational complexity involved. In addition, cyclic delay diversity applied for each antenna causes timing synchronization difficulties due to the pseudo-multipath problems. In order to solve these problems, a method to reduce the computational complexity of the synchronization is proposed by utilizing selective antennas with higher received signal power. The timing synchronization method with the adaptive accumulation window is also proposed to enhance synchronization performance. The simulation and power estimation results show that the proposed timing synchronization method not only improves the performance, but also reduces the computation power considerably. The proposed method is very useful for IEEE 802.11ac wireless LAN systems, where not only synchronization performance but also computation power is one of the most important issues.

Enhancing the Performance of Multicarrier Delay Diversity Modulation Systems Using Alamouti Codes

This paper investigates the performance of multicarrier delay diversity modulation (MDDM) systems with both cyclic delay diversity and Alamouti space time code techniques and compare its performance with conventional MDDM systems. Deploying Alamouti space time code can allow cost efficient and flexible system deployment compared to classical MDDM system with multiple cyclic delays. In this paper, we propose MDDM system with both cyclic delay and Alamouti codes. The performance of the proposed MDDM system is mathematically illustrated and modeled. The received signals at MDDM receiver are mathematically derived and analyzed. The minimum mean square error (MMSE) and QR decomposition M-algorithm maximum likelihood detection (QRM-MLD) techniques for signal detection is mathematically analyzed and applied to the proposed MDDM system. The performance of the proposed MDDM system is evaluated by simulating the BER for a certain range of SNRs. The BER is calculated for the proposed and classical MDDM systems to investigate the effect of cyclic delay with Alamouti codes in MDDM techniques. Finally, simulation results demonstrate that the proposed MDDM system with QRM-MLD technique enhances the performance of classical MDDM system and gives low values of BER compared with the classical case.

Mimo Channel and Performance Analysis using OFDM System for Reduced Bit Error Rate

Multiple-input Multiple-output (MIMO) systems use multiple antennas at the transmitter and receiver end, are a key technology to meet the growing demand for high data rate wireless systems. The aim of this thesis is to investigate MIMO system capacity with the aim of achieving optimum Bit Error Rate (BER) while increasing the system capacity using multicarrier delay diversity modulation (MDDM), proposed for fifth generation systems. In principle, the capacity of MIMO system can increase linearly with the number of antennas. Multiple antennas at the transmitter and receiver provide diversity in a fading environment. Furthermore, the research work in this thesis consists of different investigations of the basic principle of MIMO, Multiple-input Single-output (MISO) and Single-input Single-output (SISO) wireless communication systems with Space Time Codes (STC). A MISO systems and MIMO systems are schematized using MDDM which incorporated with Orthogonal Frequency Division Multiplexing (OFDM). OFDM is chosen over a single-carrier solution due to lower complexity of equalizers for high delay spread channels or high data rates. The design is implemented with binary Phase Shift Keying (BPSK) and simulated using MATLAB, which is examined in associated Additive White Gaussian Noise (AWGN) channel. The receiver-design is included with the maximal ratio combiner (MRC) receiving technique with perfect wisdom of channel state information (CSI). The theoretical performance is derived for AWGN channels and compared with the simulated results as well as compared between each system to another.

Pattern selection in neuronal network driven by electric autapses with diversity in time delays

The electric activity of neuron and collective behaviors of neurons can be modulated by autapse, which can be described by self-feedback current in close loop with time delay being considered. Distribution of electric autapses in a local area can introduce heterogeneity in the network and thus traveling wave emits from this area. In this paper, diversity in time delay of electric autapse is considered and collision between emitting waves from different local areas driven by electric autapses under different time delays is observed. In the numerical studies, neurons in the square area with 15×15 (and/or 20×20) nodes are connected electric autapses with different time delays and target-like waves are induced and converted into, spiral waves after continuous collision between wave fronts. It is found that a group of spiral waves can emerge in the network, or coexist with target waves under appropriate coupling intensity due to time delay diversity in autapse and these waves can regulate the collective behaviors of neurons as continuous pacemakers.

A Distributed High-rate and Low-detection Complexity Cooperative Relay Transmission Scheme

Since the existing full-rate cooperative transmission schemes have a serious defect in low Bit Error Rate (BER) performance while the existing high-rate cooperative transmission schemes have a serious defect in low spectral efficiency, a distributed high-rate cooperative relay transmission scheme based on full-rate cooperative communication model is proposed in this paper, in which Cyclic Delay Diversity (CDD) technology and Linear Constellation Precoding (LCP) technology are employed. Moreover, the proposed scheme addresses the issue of obtaining maximum spatial and multipath diversity with low decoding complexity and high transmission reliability. The BER performance of the proposed scheme is contrasted to that of the full-rate transmission scheme where better performance is achieved, and is improved when the number of the multipath or the relay nodes increases.

Application of space–time Trellis codes for multicarrier delay diversity modulation systems

This study investigates the performance of multicarrier delay diversity modulation (MDDM) systems with both cyclic delay diversity and space–time Trellis code (STTC) techniques and compares its performance with conventional MDDM systems. Deploying STTCs can allow cost efficient and flexible system deployment compared with classical MDDM systems with multiple cyclic delays. In this study, the authors’ propose MDDM systems with both cyclic delay and STTCs. The MDDM system is modelled for two and four transmit antennas. In this study, they compare the performance of the proposed MDDM systems with quadrature phase shift keying (QPSK), 8 phase shift keying (8PSK) and 16 quadrature amplitude modulation (16QAM) STTCs and compare its results with conventional MDDM systems. The noise variance of the received signals at the MDDM receiver is mathematically derived. The minimum mean square error technique for channel estimation is applied to the proposed MDDM systems. Simulation results demonstrate that the proposed MDDM systems enhance the performance of classical MDDM systems and give large coding gains compared with the classical case.

On the Relation between Outage Probability and Effective Frequency Diversity Order

In this paper, the relation between the outage probability and the effective f requency diversity order will be investigated. If the number of nonzero elements in power delay profile (PDP) is two, there is one-to-one correspondence between the outage probability and the effective frequency diversity order. On the other hand, if the number of nonzero elements in PDP is greater than two, the effective frequency diversity order provides the upper and lower bounds on the outage probability rather than the exact outage probability. Also, the effective frequency diversity order and the outage probability of c yclic delay diversity (CDD) schemes will be discussed.