A Threshold-Free LLR-Based Scheme to Minimize the BER for Decode-and-Forward Relaying

In cooperative communications, the problem of error propagation has a detrimental effect on the diversity order of the wireless system. To mitigate such an effect, we present a relaying scheme that is based on the absolute value of the log-likelihood ratio (LLR) of the received message signals at both the relay node and the destination node. The calculated LLR values are then compared to each other and based on the result of the comparison, a decision is made on whether or not to activate the relay node. The proposed scheme does not rely on any threshold, and is thus simple in nature. A closed-form expression is derived for the bit-error-rate (BER) of the proposed scheme. The theoretical developments are validated by simulations. As a means for performance measurement, the proposed scheme is compared to its counterparts and is shown to provide a better BER performance at a much lower complexity. Furthermore, a closed-form expression of the outage probability is also derived.     

Simplified algorithms based on Haar transforms for signal recognition in protective relays

This letter presents the development of simplified algorithms based on Haar functions for signal extraction in relaying signals. These algorithms, being computationally simple, are better suited for microprocessor-based power system protection relaying. They provide accurate estimates of the signal amplitude and phase.     

两跳高斯线性中继信道：可达码率与最优设计

The relay node with linear relaying transmits the linear combination of its past received signals. The optimization of two-hop relay channel with linear relaying is discussed in this paper. The capacity for the two-hop Gaussian relay channel with linear relaying is derived, which can be formulated as an optimization problem over the relaying matrix and the covariance matrix of the signals transmitted at the source. It is proved that the solution to this optimization problem is equivalent to a “single-letter ”optimization problem. We also show that the solution to this “single-letter ”optimization problem has the same form as the expression of the rate achieved by Time-Sharing Amplify and Forward ( TSAF ). In order to solve this equivalent problem, we proposed an iterative algorithm. Simulation results show that if channel gain of one hop is relatively smaller, the achievable rate with TSAF is closer to the max-flow min-cut capacity bound, but at a lower complexity.     

Cooperative Decode-and-Forward Relaying for Secondary Spectrum Access

We propose a two-phase protocol based on cooperative decode-and-forward relaying for a secondary system to achieve spectrum access along with a primary system. The primary and secondary systems comprise of a transmitter-receiver pair, PT-PR and ST-SR, respectively. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST and SR, where it is decoded. At ST, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions alpha and (1 - alpha) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST in the second transmission phase. We show that as long as ST is located within a critical radius from PT, there exists a threshold value for alpha above which the outage probability of the primary system will be equal to or lower than the case without spectrum sharing. We also determine the outage probability achieved by the secondary system. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing scheme.     

Cooperative transmission based on decode-and-forward relaying with partial repetition coding

We propose a novel half-duplex decode-and-forward relaying scheme based on partial repetition coding at the relay. In the proposed scheme, if the relay decodes the received message successfully, it re-encodes the message using the same channel code as the one used at the source, but retransmits only a fraction of the codeword. We analyze the proposed scheme and optimize the cooperation level (i.e., the fraction of the message that the relay should transmit). We compare our scheme with conventional repetition in which the relay retransmits the entire decoded message, with parallel coding, and additionally with dynamic decode-and-forward (DDF). We provide a finite-SNR analysis for all the collaborative schemes. The analysis reveals that the proposed partial repetition method can provide a gain of several dB over conventional repetition. It also shows that in general, power allocation is less important provided that one optimally allocates bandwidth. Surprisingly, the proposed scheme is able to achieve the same performance as that of parallel coding for some relay network configurations, but at a much lower complexity.     

Additive mixing modulation for public key encryption based on distributed dynamics

We introduce a public key encryption scheme that is based on additive mixing of a message with chaotic nonlinear dynamics. A high-dimensional dissipative nonlinear dynamical system is distributed between transmitter and receiver. The transmitter dynamics is public (known to all) and the receiver dynamics is private (known only to the authorized receiver). Bidirectional signals that couple transmitter and receiver are transmitted over a public channel. Once the chaotic dynamics which is initialized with a random state converges to the attractor, a message is mixed with the chaotic dynamics at the transmitter. The authorized receiver who knows the entire dynamics can use a simple algorithm to decode the message. An unauthorized receiver does not know the receiver dynamics and needs to use computationally unfeasible algorithms in order to decode the message. Security is maintained by altering the private receiver dynamics during transmission. We show that using additive mixing modulation is more efficient than the attractor position modulation distributed dynamics encryption scheme. We demonstrate the concept of this new scheme by simulating a simple coupled map lattice.     

Relaying in mobile ad hoc networks: The Brownian motion mobility model

Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility. In these networks data transfer can be improved by using mobile nodes as relay nodes. As a result, transmission power and the movement pattern of the nodes have a key impact on the performance. In this work we focus on the impact of node mobility through the analysis of a simple one-dimensional ad hoc network topology. Nodes move in adjacent segments with reflecting boundaries according to Brownian motions. Communications (or relays) between nodes can occur only when they are within transmission range of each other. We determine the expected time to relay a message and compute the probability density function of relaying locations. We also provide an approximation formula for the expected relay time between any pair of mobiles.     

基于不同信道状态信息的MIMO中继系统收发信机设计

该文研究了在中继站已知完全信道信息或统计信道信息情况下的多输入多输出(MIMO)中继系统收发信机设计的问题。中继站利用获得的信道状态信息对接收信号进行滤波转发,接收节点采用线性最小均方误差接收机(MMSE)恢复出原始信号。仿真结果表明,所提中继转发策略性能优于传统的放大转发。在高信噪比条件下,基于部分信道状态信息反馈的设计方案可以获得与完全信道状态信息反馈接近的性能。     

Application of block pulse functions for signal recognition in power system relays

This letter presents the development of an algorithm based on block pulse functions for fundamental frequency component calculation in power system relaying signals. The proposed algorithm is computationally simple and can be used with any sampling frequency. The algorithm is better suited for microprocessor-based power system protective relays.     

RELAY ASSISTED TRANSMISSSION WITH BIT-INTERLEAVED CODED MODULATION

We investigate an adaptive cooperative protocol in a Two-Hop-Relay （THR） wireless system that combines the following： （1） adaptive relaying based on repetition coding; （2） single or two transmit antennas and one receive antenna configurations for all nodes, each using high order constellation; （3） Bit-Interleaved Coded Modulation （BICM）. We focus on a simple decoded relaying （i.e. no error correcting at a relay node） and simple signal quality thresholds for relaying. Then the impact of the two simple thresholds on the system performance is studied. Our results suggest that compared with the traditional scheme for direct transmission, the proposed scheme can increase average throughput in high spectral efficiency region with low implementation-cost at the relay.     

Applying informed coding and embedding to design a robust high-capacity watermark

We describe a new watermarking system based on the principles of informed coding and informed embedding. This system is capable of embedding 1380 bits of information in images with dimensions 240 x 368 pixels. Experiments on 2000 images indicate the watermarks are robust to significant valumetric distortions, including additive noise, low-pass filtering, changes in contrast, and lossy compression. Our system encodes watermark messages with a modified trellis code in which a given message may be represented by a variety of different signals, with the embedded signal selected according to the cover image. The signal is embedded by an iterative method that seeks to ensure the message will not be confused with other messages, even after addition of noise. Fidelity is improved by the incorporation of perceptual shaping into the embedding process. We show that each of these three components improves performance substantially.     

Single-Adversary Relaying Attack Defense Mechanism in Wireless Ad Hoc Networks

There have been many security protocols to provide authenticity and confidentiality in wireless ad hoc networks. However, they fail to defend networks against relaying attack in which attacker nodes simply broadcast received packets without compromising any legitimate nodes. Wormhole attack is a representative example of relaying attack, in which a pair of attacker nodes relay received packets to each other and selectively drop them. The wormhole attack is known to ruin routing and communication of a network considerably, however, is not very straightforward to be accomplished due to the pairwise nature. In this paper, we introduce two new types of relaying attack, called teleport and filtering attacks that require a single attacker node only for accomplishment. We describe their accomplishment conditions and impacts on the network performance in a formal manner. We then propose a countermeasure framework against these attacks called Single-Adversary Relaying Attack defense Mechanism (SARAM), which is composed of a bandwidth-efficient neighbor discovery customized for multi-hop environments and neighbor list management combined into an on-demand ad hoc routing protocol. SARAM does not require any special hardware such as location-aware equipments and tight synchronized clocks, thus is cost-efficient as well. We show via ns-2 simulation that the new relaying attacks deteriorate the network performance significantly and SARAM is effective and efficient in defending a network against these attacks.     

Clustered Local Decoding for Wyner-Type Cellular Models

We study the uplink of Wyner-type cellular models featuring short range inter-cell interference. We assume that the decoding of the message sent by a given transmitter is done locally, that is using only the signals received at the antennas in its vicinity. We derive upper and lower bounds on the achievable rate for a two-dimensional model and for a one-dimensional model with an attenuation parameter. The analysis of our cellular models will rely on rate splitting and genie-aided bounds, originally employed in the framework of the interference channel.      

MGF based performance analysis of dual-hop regenerative relaying IR-UWB systems

In this paper, a dual-hop regenerative cooperative relaying UWB communication system with detect-and-forward (DTF) and decode-and-forward (DF) in multipath channels is studied. The average system bit error rate (BER) and the system performance with DTF and DF relaying schemes are provided. The DF relaying with convolutional coding is employed in this cooperative relaying UWB system. Gaussian quadrature numerical method is used to obtain the moment-generating function (MGF) of the received energy. Our simulation results show the advantages of the DF based cooperative IR-UWB system over IEEE 802.15.3a channels.     

Multi-User Relaying of High-Rate Space–Time Code in Cooperative Networks

In this paper, we propose high-rate space–time coding for cooperative wireless networks to reduce the overall delay incurred in relaying signals to multiple receivers. The relay structure is optimized in order to achieve maximum SNR at the receiver nodes. The proposed scheme provides a significant reduction in the delay required for the relaying and transmission of the signals to the multiple receivers with a minute loss in performance. We have also shown by simulation that this loss in the performance could be recovered by selecting more number of relays. We propose two relaying strategies for high-rate space–time codes, which are very useful in providing high data-rate in wireless cooperative networks.     

Protocol design and data detection for two‐way relay networks with fractional asynchronous delays

In wireless two‐way relay systems, it is difficult to achieve perfect timing synchronization among different nodes. In this paper, we investigate relaying protocol design and data detect schemes for asynchronous two‐way relaying systems to combat the intersymbol interference caused by asynchronous transmission. We consider fractional asynchronous delays and two schemes are proposed based on cyclic prefixed single carrier block transmission, namely, the receiver frequency domain equalization scheme and relay synchronization and network coding (RSNC) scheme. In the receiver frequency domain equalization scheme, the relay simply amplifies the received signal and forwards to the two source nodes, and fractionally spaced frequency domain equalizer (FS‐FDE) is employed at the receiver to recover the transmit data. In the RSNC scheme, the asynchronous signals are resynchronized with an FS‐FDE at the relay node. The output signals of FS‐FDE are then demodulated and network coded before forwarding to the two source nodes. In this RSNC scheme, data detection at the source nodes is the same as that in synchronous networks because the asynchronous signals have already been synchronized at the relay node. Simulation results show that the performance of both schemes is almost the same as in the perfect synchronized two‐way relaying systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Exact analysis of the multihop multibranch hybrid AF/DF relaying networks

In this paper, the exact analysis of a multihop multibranch (MHMB) relaying network is investigated wherein each relay can operate in amplify‐and‐forward (AF) or decode‐and‐forward (DF) modes depending upon the decoding result of its received signal. If a relay decodes the received signal correctly, it works in DF mode; otherwise, the relay operates in AF mode. Therefore, we name such relaying network as hybrid amplify‐and‐forward and decode‐and‐forward (hybrid AF/DF) relaying network. We first investigate the signal transmission from source to destination node via n number of relays in a hybrid AF/DF MHMB mode. Then, we obtained the statistical features and analyze the end‐to‐end signal‐to‐noise ratio (SNR). Finally, a comprehensive performance analysis is conducted by using maximal ratio combining (MRC) scheme at the destination node. For comparison, we also obtained the results using selection combining (SC) scheme at the destination node. To the best of our knowledge, very few works in the literature have considered a general system model of MHMB relaying network wherein each relay can operate in AF or DF modes, that is, a hybrid AF/DF relaying network. Accordingly, the analysis of our system model is not only novel and exact, but also is comprehensive and can be employed in the future works.     

多接入中继信道中的单中继选择

研究表明,协作中继选择能提高无线中继网络的鲁棒性和能效。文中研究一个多接入中继信道,包含2个信源,N个中继和1个信宿。中继节点为半双工,对两个信源的信号采用非再生的网络编码。考虑直接链路,基于最佳最差信道、最佳信噪比和最佳调和平均选择,提出新的选择策略。仿真结果表明其在性能上优于原有策略。     

A New Full Rate Relaying Method for 4G OFDM Systems

In this paper, we introduce a new transmit architecture that employs a 2-Dimensional Fourier Transform and a 2-Dimensional Cyclic Prefix (2D-CP) at the base station. In addition, the proposed scheme incorporates relay nodes that forward the received signals with one OFDM symbol delay. The new method introduces artificial frequency, time and spatial diversity, and unlike previously proposed relaying communication systems, the proposed scheme requires only a single transmission phase. Extensive system simulation studies have shown impressive system throughput gain compared to a single hop and conventional 2-hop systems.     

Temporal Fade Reduction for Fixed Wireless Diversity Receivers with Unbalanced and Correlated Branches

Temporal correlation between diversity branches degrades the fade mitigation expected in a multi-antenna diversity receiver. We study the case when the receive power is unequal across the diversity array. We also include the effect of correlation among the received signals. The results are of particular interest when the diversity receiver is stationary because the antennas will be unbalanced since they experience a single instantiation of the spatial fade statistics. We present a simple analytical model applicable to fixed wireless links (FWLs). Experimental results illustrate the improvement in temporal link stability resulting from the use of an equal gain combiner (EGC)