SR-DCSK Cooperative Communication System with Code Index Modulation:A New Design for 6G New Radios

This paper proposes a high-throughput short reference differential chaos shift keying cooperative communication system with the aid of code index modulation,referred to as CIM-SR-DCSK-CC system.In the proposed CIM-SR-DCSK-CC system,the source transmits information bits to both the relay and destination in the first time slot,while the relay not only forwards the source information bits but also sends new information bits to the destination in the second time slot.To be specific,the relay employs an N-order Walsh code to carry additional log_(2)N information bits,which are superimposed onto the SRDCSK signal carrying the decoded source information bits.Subsequently,the superimposed signal carrying both the source and relay information bits is transmitted to the destination.Moreover,the theoretical bit error rate(BER)expressions of the proposed CIMSR-DCSK-CC system are derived over additive white Gaussian noise(AWGN)and multipath Rayleigh fading channels.Compared with the conventional DCSKCC system and SR-DCSK-CC system,the proposed CIM-SR-DCSK-CC system can significantly improve the throughput without deteriorating any BER performance.As a consequence,the proposed system is very promising for the applications of the 6G-enabled lowpower and high-rate communication.

Relay-Assisted Cooperative Communication Networks

To facilitate the demand for a higher spectrum and power efficiency arising from the next generation mobile communication system, the introduction of relay-aided cooperative communication into the existing cellular infrastructure is considered as the most practical improvement under high rate and coverage. In comparison with the legacy cellular network, relay-aided cooperative communication network enjoys relative advantages over coverage efficiency, operation cost and transmission capacity. Transmission in relay-aided cooperative system falls into three types: the three-terminal transmission model, two-hop multi-relay parallel transmission model, and multi-hop multi-relay transmission model. For the extensive perspective of relay-aided cooperative communication in application, a profound research has been carried out in communication standards such as Worldwide Interoperability for Microwave Access (WiMAX) and Wireless World Initiative New Radio (WINNER).

Degree distribution and robustness of cooperative communication network with scale-free model

With the requirements of users enhanced for wireless communication, the cooperative communication will become a development trend in future. In this paper, a model based on complex networks with both preferential attachment is researched to solve an actual network CCN （Cooperative Communication Network）. Firstly, the evolution of CCN is given by four steps with different probabilities. At the same time, the rate equations of nodes degree are presented to analyze the evolution of CCN. Secondly, the degree distribution is analyzed by calculating the rate equation and numerical simulation. Finally, the robustness of CCN is studied by numerical simulation with random attack and intentional attack to analyze the effects of degree distribution and average path length. The results of this paper are more significant for building CCN to programme the resource of communication.

Cooperative Communication and Cognitive Radio(3)

Cooperative communication and cognitive radio have become hot topics in recent research of communication networks, attracting a widespread attention. Cooperative communication technique can enhance the transmission capacity of a communication system, while cognitive radio technique can improve the spectrum utilization ratio. As a result, the combination of the two techniques will have a significant impact on the future wireless mobile communication system. This lecture comes in four parts. This part introduces the key technologies for cooperative communications, and the basic concept and key technologies of Cognitive Radio (CR).

THE STUDY ON DEGREE DISTRIBUTION PROPERTY OF COMPLEX NETWORK BASED ON COOPERATIVE COMMUNICATION

Complex networks have been widely studied. Recently,many results show that the degree distributions of some large networks follow the form of power-law and these networks possess better robustness against random nodes failure. As an effective technology on combating the channel fading,wireless cooperative communication is becoming one of the most important methods to improve the wireless communication performances. In this paper,the complex network models based on cooperative communication and non-cooperative communication are established; and the degree distribution properties for them are studied. The simulation results show that the degree distributions of these networks also follow the form of power-law,which means that the addition of cooperative communi-cation links will not change the property of degree distribution and then these networks will possess better robustness against random nodes failure as well.

Cooperative Communication and Cognitive Radio (2)

Cooperative communication and cognitive radio have become hot topics in recent research of communication networks, attracting a widespread attention. Cooperative communication technique can enhance the transmission capacity of a communication system, while cognitive radio technique can improve the spectrum utilization ratio. As a result, the combination of the two techniques will have a significant impact on the future wireless mobile communication system. This lecture comes in four parts. This part analyzes the impacts of cooperative communication technology on modern wireless communication systems.

Cooperative Communication and Cognitive Radio (1)

Cooperative communication and cognitive radio have become hot topics in recent researches of communication networks,attracting a widespread attention.Cooperative communication technique can enhance the transmission capacity of a communication system,while cognitive radio technique can improve the spectrum utilization ratio.As a result,the combination of the two techniques will have significant impact on the future wireless mobile communication system.This lecture comes in four parts.This part introduces the history of cooperative communication as well as several cooperation schemes.

Cooperative Communication and Cognitive Radio (4)

Cooperative communication and cognitive radio have become hot topics in recent research of communication networks, attracting a widespread attention. Cooperative communication technique can enhance the transmission capacity of a communication system, while cognitive radio technique can improve the spectrum utilization ratio. As a result, the combination of the two techniques will have a significant impact on the future wireless mobile communication system. This lecture comes in four parts. This part analyzes the impacts of cooperative communication technology on modern wireless communication systems.

Power Allocation for Cooperative Communications in Non-Orthogonal Cognitive Radio Vehicular Ad-Hoc Networks

To achieve the better system performance for cooperative communication in non-orthogonal cognitive radio vehicular adhoc networks(CR-VANETs),this paper investigates the power allocation considering the interference to the main system in a controllable range.We propose a three-slot one-way vehicle system model where the mobile vehicle nodes complete information interaction with the assistance of other independent nodes by borrowing the unused radio spectrum with the primary networks.The end-to-end SNR relationship in overlay and underlay cognitive communication system mode are analyzed by using two forwarding protocol,namely,decode-and-forward(DF)protocol and amplify-and-forward(AF)protocol,respectively.The system outage probability is derived and the optimal power allocation factor is obtained via seeking the minimum value of the approximation of system outage probability.The analytical results have been confirmed by means of Monte Carlo simulations.Simulation results show that the proposed system performance in terms of outage under the optimal power allocation is superior to that under the average power allocation,and is also better than that under other power allocation systems.

Genetic-optimization framework for SVC transmission based on partial cooperative communication

A genetic-optimization framework based on the partial cooperation communication protocol is proposed for scalable video coding (SVC) stream transmission under multi-relay amplify and forward cooperative networks. Unlike traditional cooperative transmission schemes, the transmission mode for each coded unit in this new protocol can be switched flexibly between direct transmission and cooperative transmission. Obviously, under this protocol, the bandwidth efficiency and transmission robustness can be balanced adaptively according to the priority level of coded units and wireless channel fading characteristics. Based on this, a well-known genetic optimization algorithm-differential evolution is exploited here to find the jointly optimal transmission modes, power allocation and unequal error protection (UEP) channel coding strategies to minimize the end to end reconstructed video distortion. Extensive simulation results show that, compared with classical optimal cooperative UEP transmission schemes, the proposed optimized transmission framework based on the partial cooperative protocol can bring significant peak-signal-to-noise-ratio (PSNR) gains for the reconstructed video in a variety of channel bandwidth, power budget and test sequences.

Relay Selection Strategy in the Secure Cooperative Communications System

With the low cost and low hardware complex considerations,cooperative systems are a tendency in the future communications.This work considers the secure cooperative communications systems.For a practical situation in the system,the scenario includes multiple source stations,multiple relay stations,multiple destination stations,and eavesdroppers.To analyze the optimal relay selection in the system,we begin with the performance analysis for a single source station and a single destination station.By applying two cooperative models,the amplify-andforward（AF） mode and decode-and-forward（DF）mode,the secrecy capacity is derived.Then,we apply the derived results to the considered environment to find the optimal relay assignment.By the way,the relay selection can be obtained by the exhaustive search algorithm.However,there are a lot of steps needed if the number of source stations is large.Hence,applying the characters of the cooperative modes in the relay selection,the pre-selection step is proposed with a mathematical derivation.It could be used for the practical situation without a long-time calculation.

Cooperative communications with hierarchical modulation in downlink OFDMA based cellular networks

Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes including relay selection and resource allocation using hierarchical modulation (HM) to fully exploit the radio resources in cellular networks where user equipments (UEs) relay for each other.The relay selection procedure considers both the channel conditions and the energies left in relays to make the cooperative communications behave better.To mitigate the spectrum efficiency loss due to the half-duplex mode,the bits of relayaided UE and its relay (which is also a UE) are transmitted simultaneously in one sub-channel using HM to improve the utilization efficiency of sub-channels.Besides,time resources are used effectively with the adaptively changed proportion of the two sub-frames divided for relay transmission.Simulation results show that the proposed schemes can improve the spectrum efficiency compared with the traditional schemes.

LLR-AWARE SMART LINK-ADAPTIVE STRATEGY FOR DECODE-AND-FORWARD COOPERATIVE COMMUNICATION

Error propagation seriously degenerate the diversity order of Decode-and-Forward (DF) cooperative communication. To address this problem, a novel Log Likelihood Ratio (LLR)-based Link Adaptive Relaying (LAR) is proposed to promote adaption accuracy at relay. The instantaneous Bit Error Probability (BEP) is calculated according to the LLR of the received signals firstly, then based on it, the equivalent Signal-to-Noise Ratio (SNR) is employed to operate dynamic power scaling by relay. It is theoretically proved that the full diversity order can be attained by the scheme. Besides, the power sensitivity is also analyzed. Simulation results show that the proposed scheme outperform the conventional LAR and can achieve full diversity order. Moreover, its strong adaptation to SNR fluctuation is validated.

BER-based relay selection strategy for cooperative communication

In this paper, a bit error ratio(BER)-based relay selection strategy is investigated under opportunistic relay selection.The challenging problem is to design the relay selection rule so that the relay is able to measure the performance of the cooperative system at the destination exactly with low computation costs.This paper derives a closed-form expression of the end-to-end bit error rate firstly. Then, an approximate BER expression based on the relationship between the instantaneous signal-to-noise ratio(SNR) of the relay-to-destination link and the probability of error propagation is derived. Finally, a simplified relay selection formula is proposed. Simulation results prove that the proposed relay selection rule can reflect the BER of each relay properly as well.

Cooperative Communication Protocols for Performance Improvement in Mobile Satellite Systems

A mobile satellite indoor signal is proposed to model perfor mance of cooperative communication protocols and maximal ra tio combining.Cooperative diversity can improve the reliability of satellite system and increase data speed or expand cell radi us by lessening the effects of fading.Performance is determined by measured bit error rates（BERs）in different types of coopera tive protocols and indoor systems（e.g.GSM and WCDMA net works）.The effect of performance on cooperative terminals lo cated at different distances from an indoor cellular system is al so discussed.The proposed schemes provide higher signal-tonoise ratio（SNR）-around 1.6 dB and 2.6 dB gap at BER 10-2for amplify-and-forward（AF）and decode-and-forward（DF）cooperative protocols,respectively,when the cooperative termi nal is located 10 m from the WCDMA indoor system.Coopera tive protocols improve effective power utilization and,hence,improve performance and cell coverage of the mobile satellite network.

Optimal power allocation to minimize SER for multinode amplify-and-forward cooperative communication systems

An optimal power allocation （OPA） method with mean channel gains is proposed for a multinode amplify-and-forward cooperative communication system. By making use of M-PSK modulation, a closed-form symbol-error-rate （SER） formulation and corresponding upper bound are first derived. Subsequently the OPA method is utilized to minimize the SER. Comparison of the SER of the proposed OPA method with that of the equal power allocation （EPA） method, shows that the SER of both methods, which is approximately optimal performance, is almost the same when relays are near the source. OPA outperforms the EPA when the relays are near the middle between the source and destination or near the destination. The proposed OPA method depends only on the ratio of mean channel gains of the source-to-relay to those of the relay-to-destination. Extensive simulations are performed to validate the theoretical results.

Optimal Relay Assignment and Power Allocation for Cooperative Communications

Cooperative communication for wireless networks has gained a lot of recent interest due to its ability to mitigate fading with exploration of spatial diversity. In this paper, we study a joint optimization problem of jointly considering transmission mode selection, relay assignment and power allocation to maximize the capacity of the network through cooperative wireless communications. This problem is much more challenging than relay assignment considered in literature work which simply targets to maximize the transmission capacity for a single transmission pair. We formulate the problem as a variation of the maximum weight matching problem where the weight is a function over power values which must meet power constraints （VMWMC）. Although VMWMC is a non-convex problem whose complexity increases exponentially with the number of relay nodes, we show that the duality gap of VMWMC is virtual zero. Based on this result, we propose a solution using Lagrange dual decomposition to reduce the computation complexity. We do simulations to evaluate the performance of the proposed solution. The results show that our solution can achieve maximum network capacity with much less computation time compared with exhaustive search, and our solution outperforms existing sub-optimal solutions that can only achieve much lower network capacity.

Relay selection in cooperative communication systems over continuous time-varying fading channel

In this paper, we study relay selection under outdated channel state information（CSI） in a decode-and-forward（DF） cooperative system. Unlike previous researches on cooperative communication under outdated CSI, we consider that the channel varies continuously over time, i.e., the channel not only changes between relay selection and data transmission but also changes during data transmission. Thus the level of accuracy of the CSI used in relay selection degrades with data transmission. We first evaluate the packet error rate（PER） of the cooperative system under continuous time-varying fading channel, and find that the PER performance deteriorates more seriously under continuous time-varying fading channel than when the channel is assumed to be constant during data transmission. Then, we propose a repeated relay selection（RRS） strategy to improve the PER performance, in which the forwarded data is divided into multiple segments and relay is reselected before the transmission of each segment based on the updated CSI. Finally, we propose a combined relay selection（CRS） strategy which takes advantage of three different relay selection strategies to further mitigate the impact of outdated CSI.

Hybrid Forwarding in Cooperative Communications

A cooperative communication scheme was developed in which the relay node performs hybrid forwarding, where the relay node will not forward data for a transmission pair unless the corresponding direct transmission fails, and the relay node will not forward data for a transmission pair unless the quality of the channel between the corresponding source and the relay is good. A performance analysis of the outage probability and the diversity-multiplexing tradeoff for the scheme shows that the forwarding mechanism efficiently reduces fading in wireless channels by achieving full diversity order of magnitude improvement. A considerable signal-to-noise ratio gain is provided by this scheme compared with existing cooperation schemes with fixed forwarding. This flexible forwarding mechanism enables the scheme to provide the optimal diversity-multiplexing tradeoff performance.

Research on improving the QoE of relay users in cooperative communication systems

Customers＇ satisfaction with services is reflected by quality of experience（QoE）.Insofar,most studies on cooperative communication have been focused on improving the QoE of source users.However,the improvement of a source user＇s QoE is obtained at cost of degradation of the relay user＇s QoE.On the other hand,cooperative communications can achieve performance similar to that of a conventional multiple-input multiple-output（MIMO） system by forming virtual MIMO arrays.Hence,to improve the QoE performance of relay users,this article proposes the concept of a belief threshold at the destination user and a new cooperative scheme based on the belief threshold destination（BTD） technique,while without decaying the BER performance of the communication system.