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.

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.

Space-time cooperative diversity scheme using full feedback

This article proposes a new space-time cooperative diversity scheme called full feedback-based cooperative diversity scheme （FFBCD）. In contrast to the conventional adaptive space-time cooperative diversity schemes that utilize the feedback from only the destination node, the new scheme utilizes the feedback from both the destination node and the cooperation node. With the feedback from the destination node, the occasional successful reception of the destination node in the information distribution stage can be detected, thus avoiding unnecessary retransmissions in the information delivery stage. The feedback from the cooperation node indicates the receiving state of the cooperation node in the information distribution stage, and the source node and the cooperation node will not perform cooperative retransmission during the information delivery stage unless the cooperation node is received successfully in the information distribution stage. In this way the new scheme can reduce the number of transmission attempt and improve the channel utilization. The expressions of the average number of transmission attempt are given. Numerical approximations and simulation results both show that the new scheme performs better than the non-cooperative scheme and the conventional adaptive space-time cooperative diversity scheme.

A bandwidth efficient two-user cooperative diversity system with limited feedback

A two-user cooperative diversity system based on Alamouti signaling was proposed, which utilizes the orthogonal structure of Alamouti signaling to make cooperative users relay on the shared channel resources so that the spectral efficiency of the traditional cooperative system can be improved.When M -ary phase shift keying （M -PSK） modulation and an improved selection decode-and-forward （SDF） relaying protocol with limited feedback are used at the users and m（m 1） receive antennas are configured at the base station, the average bit-error-rate （BER） system performance for statistically similar uplink channels was derived and it was verified by simulations.Under various channel scenarios of interest, numerical and simulation results show that the diversity gain achieved and the BER performance of the proposed system increase with the interuser channel quality, and the full transmit diversity order of two can be obtained for sufficiently high interuser signal-to-noise ratios （SNRs）.

Performance analysis of cooperative diversity for two-way multi-relay system with channel estimation error

In this work, we consider an amplify-and-forward two-way multi-relay system for wireless communication and mvesngate me effect of channel estimation error on the error rate performance. With the derivation of effective signal-to-noise ratio at the transceiver and its probability density function, we can get approximate expression for average bit error rate. Simulation results are performed to verify the analytical results.

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.

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.

Pereformance and cooperative thresholds analysis for cooperative MIMO system

In this paper,the bit error rate(BER) performance of cooperative multiple input multiple output(MIMO) system is analyzed and two thresholds for decode-and-forward(DF) cooperative network are proposed.While the two thresholds are satisfied,the cooperative network may achieve a notable improvement of BER performance compared with the non-cooperative network.The analysis and simulation results show that the average BER of cooperation with the two thresholds is much lower than traditional cooperation,and the average BER of cooperation with only threshold one is almost the same as the former scheme and it is much easier to implement.

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.

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:

Asynchronous diversity receiving scheme and analysis on cooperative relay networks

The transmission antennas of cooperative systems are spatially distributed on multiple nodes, so the received signal can be asynchronous due to propagation delays. A receiving scheme for cooperative relay networks is proposed, multiple asynchronous signals are reconstructed at the receiver by forward and backward interference cancellation, which can obtain gains of cooperative transmission diversity with obvious delay and with no requiring timing synchronization or orthogonal channelization between relays. Analysis and simulation show that the bit error rate（BER） of the proposed scheme is similar to Alamouti code, and the scheme has the diversity order of orthogonal transmission scheme accompanied by minimal BER losses. It is demonstrated that the performance can be further improved by adding an error correcting code（ECC）.

A Beamforming Technique Using Rotman Lens Antenna for Wireless Relay Networks

Rotman lens,which is a radio frequency beam-former that consists of multiple input and multiple output beam ports,can be used in industrial,scientific,and medical applications as a beam steering device.The input ports collect the signals to be propagated through the lens cavity toward the output ports before being transmitted by the antenna arrays to the destination in order to enhance the error performance by optimizing the overall signal to noise ratio(SNR).In this article,a low-cost Rotman lens antenna is designed and deployed to enhance the overall performance of the conventional cooperative communication systems without needing any additional power,extra time or frequency slots.In the suggested system,the smart Rotman lens antennas generate a beam steering in the direction of the destination to maximize the received SNR at the destination by applying the proposed optimal beamforming technique.The suggested optimal beamforming technique enjoys high diversity,as well as,low encoding and decoding complexity.Furthermore,we proved the advantages of our suggested strategy through both theoretical results and simulations using Monte Carlo runs.The Monte Carlo simulations show that the suggested strategy enjoys better error performance compared to the current state-of-the-art distributed multiantenna strategies.In addition,the bit error rate(BER)curves drawn from the analytical results are closely matching to those drawn from our conducted Monte Carlo simulations.

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.

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.

一种基于网络编码协作的高能效无线传感器网络机制(英文)

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.

Detection time analysis for the multiple-user cooperative spectrum sensing scheme in cognitive radio networks

In this paper, a novel multiple-user cooperative spectrum sensing （MCSS） scheme is proposed to achieve the spatial diversity gains for cognitive radio （CR） networks, where only the best relay, selected among all the candidate relays in accordance with the quality of channel conditions, is utilized to cooperatively detect the primary user. Closed-form expressions of detection time for the traditional non-cooperative and the proposed MCSS schemes are derived over Rayleigh fading channels. In addition, numerical experimentations are conducted to make a performance comparison between the noncooperative sensing and our scheme. The result shows that by exploiting the multiple-user cooperation, the detection time is reduced greatly and moreover, diversity gains obtained by the MCSS scheme increase with a rise in the number of candidate relays.

Distributed space-time-frequency coding for cooperative OFDM systems

A distributed space-time-frequency （STF） coding scheme is proposed for cooperative OFDM （C-OFDM） systems with three terminals over quasi-static frequency-selective Rayleigh fading channels, The outage probability is derived and its tight closed-form lower bound is presented. Asymptotic analysis indicates that the proposed scheme can achieve both spatial and multipath （frequency） diversity. The theoretical analysis of the proposed STF coded scheme is further implemented by the distributed group STF block coding （D-GSTFBC） scheme based on the subcarrier grouping technique, Simulation results confirm the previously introduced theoretical analysis.

QoS-guaranteed multi-relay selection and power allocation optimization in cooperative systems

This paper investigates the relay selection and power allocation problem in multi-user based cooperative networks,where intermediate relay nodes help source forward information to destination using decode-and-forward （DF） relaying protocol. Specifically,we propose a novel multi-relay nodes selection strategy taking both instantaneous channel state information （I-CSI） and residual energy into consideration,by which ＇emergence＇ diversity gain can be achieved and the imbalance of resource utilization can be overcome. Besides,using Largangian dual-primal decomposition and subgradient projection approach,an optimal power allocation algorithm at source and cooperative relay nodes is presented with the constraints of each user＇s individual quality of service （QoS） requirements and system total transmit power. Theoretical analysis and simulation results demonstrate that the proposed scheme can significantly improve energy efficiency,while guaranteeing a good balance between achievable data rate and average network lifetime with relatively low implementation complexity.

Efficient detection for cooperative communication with two alternating relays

A two-path amplify-and-forward(AF)relaying scheme,which uses two relays to retransmit for the source alternately,was proposed by Rankov[Rankov et al.IEEE Journal on Selected Areas in Communications,2007,25(2):379–389].This scheme can avoid half-duplex loss in spectral efficiency,but it cannot work well when the interrelay channel gain is strong.An efficient detection scheme for two-path AF relaying system is proposed in this paper.In the proposed scheme,interference cancellation is first performed at the destination so that the received signal after interference cancellation is the superposition of two symbols with noise.Then,a low complexity soft maximum a posteriori(MAP)decoder and an iterative soft decoder are employed to extract the diversity of the two relay-destination links.The proposed detection scheme can efficiently improve the system performance compared to the detection scheme presented by Rankov(2007),especially when the inter-relay channel gain is strong.