Asynchronous Cooperative Protocols for Inter-vehicle Communications

Currently, most of the research on inter-vehicle communication uses the same approach as research on general-purpose networks: protocols and algorithms are developed “bottom-up”, i.e., starting from medium access and addressing, proceeding upwards to the application layer. The set of applications is then evaluated through simulation or real-world experiments. In this paper we argue that, unlike general-purpose networks, inter-vehicle communication is about very specific goals defined by the application domain: preventing accidents and saving resources (e. g., travel time, fuel, road capacity). Inter-vehicle communication should therefore be tailored to achieve those specific goals. As a consequence, research in this area should follow a top-down approach, starting out with precise objectives. From these, applications and protocols should be derived - and not the other way around. Besides proposing the general concept of top-down research on inter-vehicle communication, we illustrate the process by means of a simple example, showing the relation between available information and road usage efficiency.

A novel approach to UWB data detection with symbol-level synchronization

Using OFDM and space-time coding to achieve asynchronous cooperative diversity has been proposed by Mei et. al. and Shin et al, where orthogonal space-time block codes, Alamouti code in particular, were used at relay nodes. This proposed space-time coding can not achieve the multipath diversity when the channels from nodes to nodes are frequency selective fading. In this paper, we also consider asynchronous cooperative communications where the channels are assumed to be frequency-selective fading. We design high rate distributed space-frequency codes to achieve both full asynchronous cooperative diversity and multipath diversities.

In this paper, we investigate cooperative OFDM communications using amplify-and-forward (AF) protocol at the relays, in the presence of imperfect timing synchronization. In most studies on cooperative communications, perfect time synchronization among cooperating nodes is assumed. In practice, however, due to imperfect time synchronization, orthogonality among the subcarriers of the different nodes' signals at the destination receiver can be lost, causing inter-symbol interference (ISI). In this paper, we derive analytical expressions for the average SINR at the DFT output at the destination as a function of timing offset in cooperative OFDM with AF protocol, and illustrate the SINR degradation as a function of the timing offset. We also present an interference canceling (IC) receiver to mitigate the effects of ISI when there is timing offset. We show that the proposed IC receiver achieves improved BER performance even when timing offsets are large.

In cooperative communications, due to the distributed nature, multiple different carrier frequency offsets (CFOs) may occur and make the channel time-varying. It is hard for the receiver to compensate multiple CFOs from multiple relay nodes simultaneously. Thus, the conventional space-time codes to collect cooperative diversity for co-located multi-input multi-output (MIMO) systems may not be applied directly. In this paper, we consider the cooperative transmission with multiple CFOs when the channels from relay nodes to destination node are flat (frequency-non-selective) fading. We approximate a flat fading channel with CFO as a block time-invariant intersymbol-interference (ISI) channel in the frequency domain. We then propose two distributed space-frequency codes (SFC) for such ISI channels in the frequency domain to achieve the cooperative full spatial diversity, where the space-frequency coding concept is different from the one in the literature and also has a different role. One is called frequency-reversal SFC and the other is called frequency-domain linear convolutive SFC. Furthermore, we show that, with only linear receivers, such as zero-forcing (ZF) and minimum mean square error (MMSE) receivers, our codes achieve the full cooperative diversity.

Cooperative communication has great potential to improve the wireless channel capacity by exploiting the antennas on wireless devices for spatial diversity. The performance in cooperative communication depends on careful resource allocation such as relay selection and power control. In this paper, the network is expanded and more than one source is used. What is proposed is a distributed buyer/seller game theoretic framework over multiuser cooperative communication networks in order to stimulate cooperation and improve the system performance. A two-level Stackelberg game is employed to jointly consider the benefits of the source node and the relay nodes in which the source node is modeled as a buyer and the relay nodes are modeled as sellers, respectively. In this work we proposed coded method in which relays amplify and code Source data and send it to destination at the same time and then signal detection occur in destination, but in the codeless network relays send source data separately to destination. So, here coded and codeless networks are compared and contrasted. The stimulation results revealed that the proposed coded method performed better than the codeless ones; furthermore, the research shows that relays near the sources can play a significant role in increasing source node's utility, so every source would like to buy more power from these preferred relays. Also, the proposed algorithm enforces truthful power demands.

Power Line Carrier (PLC) and micropower wireless are two mainstream local communication technologies for low-voltage electricity information acquisition system, the cooperation- and complementarity between which-represent the future development trend. Aiming at the high outage probability deficiency- of traditional PLC and micropower wireless cooperative communications and the insufficient utilization of channel diversity gains, an Adaptive Relay Selection (ARS) based PLC and wireless multi-channel cooperative communication method is proposed. When the quality of the PLC link between the source node and the destination node is poor, the data of the source node is first sent to the potential relay node through the micropower wireless channel. Then, based on the channel quality of the PLC link between the relay node and the destination node, as well as the channel capacity between the source node and the relay node, the relay node and relay mode can be confirmed. Thus, a virtual Multi-Input Multi-Output (MIMO) PLC array can be constructed between the relay node and the destination node, and the system reliability can be improved by using distributed space-timecoding scheme. Simulation results show that, compared with traditional methods, ARS can significantly reduce the outage probability of the relay system, and reduce the transmission error rate via transmission diversity gains of multiple relay nodes.

This paper proposes a simple orthogonal frequency-division multiplexing (OFDM) transmission scheme for asynchronous cooperative communications over frequency-selective fading channels. In this scheme, the relay nodes only implement very simple operations on their received signals, and no decoding, DFT or IDFT operation is needed. With our proposal, the received signals have the Alamouti code structure on each subcarrier, and thus, it has the fast symbol-wise ML decoding. The analysis and simulation results demonstrate that our simple scheme can achieve order-two spatial diversity gain for amplify-and-forward based cooperative communications over frequency-selective fading channels in the presence of asynchronization between relay nodes.

차량 애드혹 네트워크는 기반 시설의 도움 없이 차량간 무선통신을 통해 구성되는 임시 네트워크이다. 특히, 운전자의 안전과 관련된 교통 정보가 다루어지기 때문에 신속한 메시지 전파가 요구된다. 이를 위한 대표적인 메시지 전파 기법으로 거리 기반 브로트캐스트 기법이 있다. 이 기법은 소스노드로 부터의 거리를 기반으로 메시지 전파 노드를 선택한다. 그러나 각 메시지 전파 노드가 소스노드의 통신범위 가장자리에 위치하지 않을 경우 메시지 전파 지연시간이 증가하는 문제점을 가지고 있다. 특히, 노드의 밀도가 낮을 경우 메시지 전파 지연시간은 더욱 증가한다. 본 논문에서는 이러한 문제점을 개선하기 위해 시간창 예약 기반 릴레이 노드 선택기법을 사용한 브로드캐스트 프로토콜을 제안하였다. 제안한 기법은 각 노드가 주어진 시간창 내에서 임의의 메시지 전송 대기시간을 선택한다. 각 노드의 시간창은 릴레이 노드로부터의 거리에 따라 각기 다른 시간범위를 갖게 되며, 소스노드의 통신영역의 가장자리에 좀 더 가까이 위치한 노드가 다음 릴레이 노드로 선택될 수 있도록 주어진 시간창의 일부를 예약한다. 실험결과, 시간창 예약 기반 릴레이 노드 선정기법을 사용한 브로드캐스트 프로토콜이 거리 기반 브로드 캐스트보다 노드밀도의 변화에 상관없이 더 짧은 종단간 메시지 전파 지연시간을 보였다. 특히, 노드밀도가 낮을 경우 25.7% 짧은 종단간 메시지 전파 지연시간을 보였으며, 지연시간과 네트워크 부하의 합성성능은 제안한 기법이 46% 우수한 성능을 보였다. Vehicular ad-hoc networks is temporarily established through inter-vehicle communication without any additional infrastructure aids. It requires a immediate message propagation because it mainly deals with critical traffic information such as traffic accidents. The distance-based broadcast scheme is one of the representative broadcast schemes for vehicular ad-hoc network. In this scheme, a node to disseminate messages is selected based on a distance from a source node. However, a message propagation delay will be increased if the relay nodes are not placed at the border of transmission range of the source node. In particular, when the node density is low, the message propagation delay is getting longer. In this paper, we propose a time-window reservation based relay node selection scheme. A node receiving the alert message from the source node has its time-window and randomly selects its waiting time within the given time-window range. A proportional time period of the given time-window is reserved in order to reduce the message propagation delay. The experimental results show that the proposed scheme has shorter message propagation delay than the distance-based broadcast scheme irrespective of node density in VANET. In particular, when the node density is low, the proposed scheme shows about 26% shorter delay and about 46% better performance in terms of compound metric, which is a function of propagation latency and network traffic.

In this paper, we propose transmission strategies in multiple-input-single-output (MISO) cooperative communications with two relay nodes in cases when the relay nodes have different trust degrees, where the trust degrees represent how much the relay nodes can be trusted for cooperation. For the given trust degrees and channel conditions, we first derive a relay selection strategy that maximizes the expected achievable rate. We then propose a cooperative transmission strategy of relays with an optimal cooperative beamforming vector that maximizes the expected achievable rate, which is a linear combination of weighted channel vectors. Finally, we derive the optimal transmission strategy, which is a mixed strategy between the relay selection and cooperative transmission strategies with respect to the trust degrees. Our analysis and numerical results show that the proposed transmission strategies increase the expected achievable rate by exploiting the trust degrees of the relay nodes, along with the channel conditions.

Cooperative communication has been studied as a way to improve reliability of networks compared to conventional direct transmission scheme. We consider amplify-and-forward (AF) cooperative communication with multiple relays. In this system, there is a problem that which relay nodes should be selected and how much power should be allocated to the selected relay nodes. Most of conventional researches on this model have focused on only improving channel capacity or reliability, rather than saving power consumption in all over the network with maintaining such communication qualities. In this paper, we propose a new power allocation scheme for multiple relay nodes using game theory that focuses on transmission power efficiency. With computer simulation, we show that our proposed game theoretical approach has superiority to some conventional schemes from the viewpoint of transmission power efficiency.

Cooperative communication is a promising technique to mitigate channel impairment and improve spectrum efficiency. Due to the selfish nature of relay nodes, how to provide proper long-term incentives for relay nodes in dynamic communication environments is an essential issue. In this paper, a two-period dynamic contract is proposed under the dynamic asymmetric information scenario. Considering the relay nodes' types are independent in both periods with identical probability distribution, the contract-theoretic model for ability discrimination relay selection is formulated. And the necessary and sufficient conditions for the optimal contract are systematically characterized. To maximize the source's expected utility, a sequential optimization algorithm is proposed to obtain the optimal relay- reward strategy. Simulation results show that the optimal dynamic contract design scheme is effective in improving system performance for cooperative communication.

Wireless energy transfer cooperative communication systems are analyzed in this paper. In these systems, a source node can communicate with a destination node directly or via the selected relay nodes, while relay nodes harvest energy from radio frequency for forwarding the received signal. In addition, the decode and forward (DF) protocol is applied to relay nodes, and selection combination technique is employed at the destination in order to select the best relay node. The system performance is presented by outage probability expressions over independent and identically distributed (i.i.d) Nakagami-m channel model. The theoretical analysis and the close-form expression of outage probability are derived and compared with the Monte Carlo simulation. The perfect match of calculation and simulation results verifies our theoretical analysis.

A new cooperative communication algorithm for improving connectivity in the event of network failure in VANETs

On one hand, cooperative communication has been gaining more and more popularity since it has great potential to increase the capacity of wireless networks. On the other hand, the applications of cooperative communication technology are rarely seen in reality, even in some scenarios where the demands for bandwidth-hungry applications have pushed the system designers to develop innovative network solutions. A main obstacle lying between the potential capability of channel capacity improvement and the wide adoption of cooperative communication is the lack of incentives for the participating wireless nodes to serve as relay nodes. Hence, in this paper, we design TASC, an auction scheme for the cooperative communications, where wireless node can trade relay services. TASC makes an important contribution of maintaining truthfulness while fulfilling other design objectives. We show analytically that TASC is truthful and has polynomial time complexity. Extensive experiments show that TASC can achieve multiple economic properties without significant performance degradation compared with pure relay assignment algorithms.