REAL EFFECTS & DIVERSITY TO BE STRESSED IN INTERNATIONAL COOPERATION

In recent years, the Shanghai Institute of Organic Chemistry under the CAS has freed itself from the stereotyped rut of conventional forms in its external intercourse while still sticking fast to upholding its strategic goal of disciplinary development. Our stress in this aspect has shifted to the pursuit of real effects and diversified forms in international S&T exchange. Our exploration features the following four characteristics:

An Energy-Efficient Network Coded Cooperation Scheme in Wireless Sensor Networks

Energy-efficient communications is crucial for wireless sensor networks(WSN) where energy consumption is constrained. The transmission and reception energy can be saved by applying network coding to many wireless communications systems. In this paper,we present a coded cooperation scheme which employs network coding to WSN. In the scheme,the partner node forwards the combination of the source data and its own data instead of sending the source data alone. Afterward,both of the system block error rates(BLERs) and energy performance are evaluated. Experiment results show that the proposed scheme has higher energy efficiency. When Noise power spectral density is-171dBm/Hz,the energy consumption of the coded cooperation scheme is 81.1% lower than that of the single-path scheme,43.9% lower than that of the cooperation scheme to reach the target average BLER of 10-2. When the channel condition is getting worse,the energy saving effect is more obvious.

Achieving fairness by aggregate power allocation in opportunistic cooperation networks

Within a wireless opportunistic network,one of the lucky users gets an opportunity to utilize thewhole radio resource.However some of the unlucky users keep silent during an unexpected period result-ing from severe wireless environment and imperfect scheduling algorithms .An opportunistic cooperationprotocol is proposed that can achieve equivalent performance measured in terms of outage probability,inwhich scheme the opportunistic user helps to relay what need retransmitting indicated by the destinationand selects the appropriate power allocation to pursue fairness.The proposed scheme deploys superposi-tion coding and successive interference cancellation at relay and destination,respectively .To improve thespectral efficiency,the modified cooperation architecture involves two opportunistic users which work inturn.The simulation results demonstrate that the protocol obtains better performance compared with theconventional methods.

Cooperative diversity based on rotation code

In order to obtain coding gain along with diversity gain,rotation code was applied to cooperative diversity employing decoded-and-forward cooperative protocol.Different from the same two symbols transmitted in conventional repetition-coded scheme,two different symbols were transmitted separately in two successive timeslots in the proposed rotation-coded cooperative diversity.In this way,constellation spread in the available two-dimensional signal space rather than on a single-dimensional line in repetition-coded scheme,which was supposed to be responsible for the additional coding gain.Under the proposed cooperative transmission model,upper bounds for the symbol-error-rate(SER)of cooperative diversity based on repetition code and rotation code were derived respectively.Both analytical and simulated results show that cooperative diversity based on rotation code can obtain an improved coding gain(by about 2 dB)than repetition-coded scheme without the expense of power or bandwidth.

Resource allocation for cooperative diversity systems based on quadrature modulation

To improve the error performance and the resource utilization of cooperative systems, the optimum resource allocation, i.e., power allocation and partner choice, for an adaptive decode-and-forward （DF） cooperative diversity system based on quadrature modulation is investigated. The closed-form expression of the bit error rate （BER） system performance is derived and an optimal power allocation （OPA） algorithm is proposed to optimize the power allocation between the local and relayed signals under the minimum BER criterion. Based on the OPA algorithm, a partner choice strategy is proposed to determine the partner locations specified by various cooperation gains. Simulation results show that the proposed resource optimization algorithms are superior to the unoptimized algorithms by significantly reducing the BER and improving the cooperative gain, which is useful to simplify the practical partner choice process.

A CROSS-LAYER STRATEGY FOR COOPERATIVE DIVERSITY IN WIRELESS SENSOR NETWORKS

We investigate the problem of how to minimize the energy consumption in multi-hop Wireless Sensor Network (WSN),under the constraint of end-to-end reliability Quality of Seervice (QoS) requirement.Based on the investigation,we jointly consider the routing,relay selection and power allocation algorithm,and present a novel distributed cross-layer strategy using opportunistic relaying scheme for cooperative communication.The results show that under the same QoS requirement,the proposed cross-layer strategy performs better than other cross-layer cooperative communication algorithms in energy efficiency.We also investigated the impact of several parameters on the energy efficiency of the cooperative communication in WSNs,thus can be used to provide guidelines to decide when and how to apply cooperation for a given setup.

Enhanced quadrature signaling-based cooperative transmission with full rate and full diversity

Quadrature signaling-based cooperative transmission is an efficient and simple scheme to obtain spatial diversity.However,this scheme causes date rate loss compared with direct transmission.In this work,our focus is on recovering from the data rate loss while simultaneously achieving spatial diversity.Particularly,an enhanced quadrature signaling-based cooperative scheme was designed,which can realize full-rate transmission by using the signal space diversity(SSD)technique.Then,accurate bit error rate(BER)expression for the full-rate scheme was derived over independent and non-identically distributed(INID)Rayleigh fading channels.Specifically,a closed-form BER expression is obtained,which is quite tight over the whole SNR range,and thus allows for rapid and efficient evaluation of system performance under various channel conditions.Moreover,an asymptotic approximation of the BER was derived to show that the full-rate scheme can achieve full diversity.Simulation results verify the tightness of the analysis and show that the full-rate scheme significantly outperforms the traditional quadrature signaling-based scheme by about 2 dB with the same complexity order.

Enhanced cooperative packet retransmission employing joint cooperative diversity and symbol mapping diversity

A joint cooperation diversity and symbol mapping diversity (SMD) strategy is proposed for cooperative packet retransmission system with high-order modulation such as 16QAM. Substantial SER/BER (symbol error rate/bit error rate) gains result from multiple packet transmissions over independent paths and distinct bit-to-symbol mappings for each packet transmis-sion. The SER/BER performance of relay assisted retransmission system is analyzed. Simulation results show that the joint-diversity strategy can provide more BER gains than other relaying strategies (i.e., decode-and-forward and constellation rearrangement relaying strategies) when no relay makes a decision error; but if some relays make decision errors, the joint-di-versity strategy outperforms other relaying strategies only when the relays are closer to the source than to the destination.

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.

Performance analysis of amplify-and-forward cooperative diversity with multiple-antenna nodes via analog network coding

Network coding (NC), which works in the network layer, is an effective technology to improve the network throughput, by allowing the relay to encode the information from different users and ensuring the destination to retrieve the desired information. Employing network coding technique in a cooperative network can improve the network performance further. In this paper, we introduce analog network coding (ANC) to a simple two-user cooperative diversity network, which adopts amplify-and-forward (AF) mode and all nodes use multiple antennas. The impact of the number of antenna on the system achievable rate is investigated. And the bit error rate (BER) performances of the traditional relay cooperative network and the cooperative network based on analog network coding under different propagation conditions are discussed. The simulation results show that the performance of the traditional cooperative network has improved significantly due to the employ of network coding.

Outage Performance and Diversity Analysis for Multi-antenna Multi-relay Networks

The performance of multi-antenna multi-relay cooperative system is investigated in this paper. Two relaying strategies, i.e., reactive and proactive strategies are analyzed with the Amplifyand-Forward (AF) and Decode-and-Forward (DF) protocols. We derive the Cumulative Distribution Function (CDF) of the received Signal-to-Noise Ratio (SNR) at the destination, which is used to calculate the exact outage probability, for both AF and DF protocols. According to these results, we conclude that a cooperative network which composes K relays each equipped with nr antennas can achieve maximal order-(2nrK+1) diversity gain, by proper processing at relays and destination. Furthermore, the performance comparison is given, in terms of outage probability. These two strategies outperform each other in different scenarios in AF protocol, whilst proactive strategy is always better than its counterpart in DF protocol. According to these results, the optimal power allocation schemes among relay nodes are also presented, with reasonable power constraint.

THE THEORETICAL BER PERFORMANCE ANALYSIS OF A COOPERATIVE DIVERSITY SCHEME IN FREQUENCY SELECTIVE FADING CHANNEL

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.

Single carrier frequency domain equalization and diversity combining for cooperative systems

A low-complexity single carrier frequency-domain equalizer （SC/FDE） and diversity combining method for cooperative systems with demodulate-and-forward relaying over frequency-selective channels is proposed. At the relay nodes, linear SC/FDE is adopted and normalized correlation coefficlent is mtrodueed to derive an equivalent source-to-relay-destination （S-R-D） channel that is highlighted in this study. At the destination, a joint SC/FDE and diversity combining receiver is proposed by utilizing the equivalent S-R-D channel. Simulation results demonstrate the superiority of the proposed SC/FDE scheme over the straightforward SC/FDE which ignores the decisions errors at the intermediate relay nodes.

A Novel Beamforming Emulating Photonic Nanojets for Wireless Relay Networks

In this article,a low-cost electromagnetic structure emulating photonic nanojets is utilized to improve the efficiency of wireless relay networks.The spectral element method,due to its high accuracy,is used to verify the efficiency of the proposed structure by solving the associate field distribution.The application of optimal single-relay selection method shows that full diversity gain with low complexity can be achieved.In this paper,the proposed technique using smart relays combines the aforementioned two methods to attain the benefits of both methods by achieving the highest coding and diversity gain and enhances the overall network performance in terms of bit error rate(BER).Moreover,we analytically prove the advantage of using the proposed technique.In our simulations,it can be shown that the proposed technique outperforms the best known state-of-the-art single relay selection technique.Furthermore,the BER expressions obtained from the theoretical analysis are perfectly matched to those obtained from the conducted simulations.

Improved Bi-Directional Three-Phase Single-Relay Selection Technique for Cooperative Wireless Communications

Single-relay selection techniques based on themax-min criterion can achieve the highest bit error rate(BER)performance with full diversity gain as compared to the state-of-the-art single-relay selection techniques.Therefore,in this work,we propose a modified max-min criterion by considering the differences among the close value channels of all relays while selecting the best relay node.The proposed criterion not only enjoys full diversity gain but also offers a significant improvement in the achievable coding gain as compared to the conventional one.Basically,in this article,an improved bi-directional three-phase single-relay selection technique using the decodeand-forward protocol for wireless cooperative communication networks that enhances the overall network performance in terms of BER is proposed and its performance is proved analytically and through Monte-Carlo simulations.More specifically,the proposed criterion is first used to select the best relaynode.After that the selected relay-node forwards the information symbols of the communicating terminals after performing a digital network coding to minimize power consumptions.In our simulations,we show that our proposed technique outperforms the best-known single relay selection techniques.Furthermore,we prove that the BER results obtained from our conducted simulations perfectly match those obtained from the theoretical analysis.

Optimal joint relay selection and resource allocation with QoS constraints in multiuser OFDM-based cellular networks

This paper investigates the relay selection and resource allocation problem in multiuser orthogonal frequency division multiplexing （OFDM） based cooperative cellular networks, in which user nodes could relay information for each other using the decode-and-forward （DF） protocol to achieve spatial diversity gain. Specifically, the paper proposes an optimal joint relay selection and resource allocation （0RSRA） algorithm whose objective is to maximize system total achievable data rate with the constraints of each user＇ s individual quality of service （QoS） requirement and transmission power. Due to being a mixed binary integer programming （MBIP） problem, a novel two-level Lagrangian dual-primal decomposition and subgradient projection approach is proposed to not only select the appropriate cooperative relay nodes, but also allocate subcarries and power optimally. Simulation re- suits demonstrate that our proposed scheme can efficiently enhance overall system data rate and guarantee each user＇ s QoS requirement. Meanwhile, the fairness among users can be improved dramatically.

Performance analysis and threshold selection for cooperative multiple packet reception based on NDMA

To accurately assess the performance of cooperative multiple packet reception （MPR） based on network-assisted diversity multiple access （NDMA）, non-ideal collision detection is introduced in ALLIANCES （ALLow improved access in the network via cooperation and energy savings）. To provide a unified anatysis frame- work, the length of cooperative transmission epoch is fixed to the detected collision order. The mathematical analysis of potential throughput （PTP） and potential packet loss rate （PPLR） are given under a pessimistic assumption and an optimistic assumption. According to the analysis of PTP and PPLR, threshold selection is done to optimize system performances, e.g. the optimal threshold should guarantee PTP to be maximum or guarantee PPLR to be minimum. In simulations, the thresholds are selected according to PTP under the pessimistic assumption. Simulation results show that the proposed cooperative MPR scheme can achieve higher throughput than NDMA and slotted ALOHA schemes.

Two-Phase Bidirectional Dual-Relay Selection Strategy for Wireless Relay Networks

In this article,we introduce a new bi-directional dual-relay selection strategy with its bit error rate(BER)performance analysis.During the first step of the proposed strategy,two relays out of a set of N relay-nodes are selected in a way to optimize the system performance in terms of BER,based on the suggested algorithm which checks if the selected relays using the maxmin criterion are the best ones.In the second step,the chosen relay-nodes perform an orthogonal space-time coding scheme using the two-phase relaying protocol to establish a bi-directional communication between the communicating terminals,leading to a significant improvement in the achievable coding and diversity gain.To further improve the overall system performance,the selected relay-nodes apply also a digital network coding scheme.Furthermore,this paper discusses the analytical approximation of the BER performance of the proposed strategy,where we prove that the analytical results match almost perfectly the simulated ones.Finally,our simulation results show that the proposed strategy outperforms the current state-of-the-art ones.

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 implementa-tion-cost at the relay.

Selfish behavior detection of cooperative relay

A selfish behavior detection technique is investigated to assist secure cooperative trans- mission at the physical layer. The detection technique calculates the correlation ratio between signals received from the diversity branches to determine the relay＇ s behavior in amplify and forward coop- eration strategy. The correlation ratio is considerably reduced because the relay＇ s selfish behavior makes the correlation between the received signals in the diversity branch degraded. Simulation re- sults show that the proposed mechanism can effectively detect selfish nodes and performance will be improved significantly with the destination＇ s detection technique.