The packet error rate (PER) performance of multi-hop STBC based cooperative and diversity relaying systems are studied. These systems consist of a source, a destination, and two relay stations in each hop. From in-lab experiments, it is confirmed that the cooperative relaying system has better PER performance than the diversity relaying system with highly correlated channels.

The smart grid is expected to be the next generation electricity grid. It is beneficial for communication systems to improve energy efficiency and reduce carbon emissions. In this paper, we propose a distributed game theoretical framework for decode-and-forward (DF) cooperative relay networks with smart grid. A relay selection and power allocation strategy based on the buyer-seller game is proposed that processes the statistic channel-state information (CSI) available. The user is modeled as a buyer who selects the optimal relay and determines the optimal amount of power to be bought from the relay by the maximum utility criterion. The relay powered by the smart grid is modeled as a seller who determines the price of the power to achieve the maximum profit with its own cost. The equilibrium conditions of the game between the two sides are analyzed. The simulation results verify the existence of a Nash equilibrium point and illustrate that the proposed strategy may guarantee the utility of the source, the relay and the network and increase the energy efficiency.

The end-to-end packet error rate (PER) performance of a multi-hop cooperative relaying system is discussed in this paper. In this system, the end-to-end PER performance improves with the number of hops under certain conditions. The PER performance of multi-hop cooperative networks is analyzed with the state transition technique. The theoretical analysis reveals that the PER performance can be kept almost constant, or even improved, as the number of hops is increased. Computer simulation results agree closely with the analysis results. Moreover, to confirm this performance characteristic in an actual setup, an in-lab experiment using a fading emulator was conducted. The experimental results confirm the theoretical end-to-end PER performance of this system.

This paper proposes an application of splitting source-node power for a two-phase cooperative relaying system where the transmit powers of the source and the relay node are individually constrained. In the proposed usage, the limited source power is divided into two parts that are used in the first and the second phase. Unlike conventional relaying methods, in the second phase the source retransmits its signal with the split power and, at the same time, the relay forwards the signal received at the first phase, which causes interference between the signals. In order to avoid the intervention, so-called a co-phasing weight for aligning the phases of the two signals is used at at the source before the second transmission. The forwarding operation at the relay however is exactly the same as the conventional techniques. Optimal power-splitting as well as the co-phasing weight is provided in this paper. With numerical investigation, the proposed power-splitting is shown to significantly improve the achievable throughput as well as reduce the outage probability compared with the conventional individual power allocation.

An incremental relaying protocol is a promising scheme for preventing the inefficient use of resources in half-duplex cooperative relay networks. In particular, the incremental selection amplify-and-forward (ISAF) relaying scheme is a well-designed protocol under the condition that the source-to-destination (SD) link is static during the two transmission phases. However, from a practical viewpoint, the SD link is not static but varies with time, and thus the ISAF relaying scheme may not work well in the field. In this work, we first show that the outage performance of the ISAF relaying scheme may decrease when the SD link is not static during the two transmission phases. We then propose a modified version of the ISAF relaying scheme which overcomes such a limitation of the ISAF relaying scheme under time-varying environments. Finally, numerical and simulation results are provided to support our findings.

In this paper we establish a secure communication model where eavesdropper and intended receiver have multiple antennas. We use cooperation and jamming to achieve physical layer security. First, we study how to allocate power between the information bearing signal and the jamming signal. Second, based on this model, we also jointly optimize both the information bearing signal weights and the jamming signal weights to improve physical layer security. The optimal power allocation and the weights are obtained via an iteration algorithm to maximize the secrecy rate. Comparing with equal power allocation and some other different methods, it shows that using cooperative relaying and jamming can significantly improve the physical layer security from the simulation results.

We consider wireless secure communications between a source and a destination aided by a multi-antenna relay, in the presence of an eavesdropper. In particular, two cooperation schemes of the relay are explored: cooperative relaying (CR) and cooperative jamming (CJ). We first investigate the transmit weight optimization of CR and CJ, for both cases with and without the eavesdropper's channel state information (ECSI). Then, for the case with ECSI, we derive the conditions under which CR achieves a higher secrecy rate than CJ; for the case without ECSI, we compare the secrecy rates of CR and CJ in high transmit power regimes. Building on this, we propose a novel hybrid scheme in which the relay utilizes both CR and CJ, and study the power allocation of the relay between CR and CJ for maximizing the secrecy rate under individual power constraints. Further, we study the case with imperfect channel state information (CSI) for both CR and CJ. At last, extensive numerical results are provided.

Orthogonal frequency and code division multiplexing (OFCDM) is available as orthogonal frequency and code division multiple access (OFCDMA) by allocating subcarrier to users. OFCDMA is an efficient transmission method assigning the subcarrier and the channel code according to channel state or many different environments. However, OFCDMA is hard to apply many frequency spreading codes when it is compared with OFCDM because of the restrictive subcarriers. This problem leads to decrease the frequency diversity. Therefore we propose system that combines cyclic delay diversity (CDD) with cooperative relaying system based on OFCDMA. This system complements this restrict by spatial diversity. In addition to that, the proposed system obtains diversity gain without loss of the throughput when direct-path condition is not good.

With the purpose of improving the performance of next generation wireless networks, cooperative relaying (CoR) and network coding (NC) are promising techniques. The number of time slots required for NC in bidirectional transmission is less than that required for CoR, and hence, NC can achieve higher throughput performance than CoR. However, the disadvantage of NC is that asymmetric traffic ratio conditions might cause a significant decrease in the bidirectional throughput. In contrast, CoR is robust to asymmetric traffic ratio conditions. In this paper, in order to improve the throughput of NC even under asymmetric traffic ratio conditions, we propose an opportunistic scheduling scheme for hybrid NC and CoR. In the proposed scheduling scheme, the transmission protocol with best throughput performance can be adaptively selected based on instantaneous channel state information. Computer simulation results reveal that the proposed scheduling scheme not only achieve higher throughput than the conventional scheduling scheme but is also robust against asymmetric traffic ratio conditions. By adjusting the scheduler's parameter, the proposed scheduling scheme can provide a tradeoff between the throughput and the traffic ratio. Moreover, in certain cases, maximizing the throughput of NC and guaranteeing the offered traffic ratio can be achieved at the same time.

Multihop network is an approach utilizing distributed wireless stations for relaying. In this system, area size, coverage and total transmit power efficiency can be improved. It is shown by computer simulations that the cooperative relaying scheme provides transmit diversity effect, and can offer much better performance compared with that of non-cooperation case. To confirm this superior performance in actual environments, field trials using real time communication equipments are now being planned. This paper reports the design and the performance of wireless equipments for field trials.

Cooperative relaying (CR) is a promising technique to provide spatial diversity by combining multiple signals from source and relay stations. In the present paper, the impact and use of the asymmetric property in bi-directional CR under asymmetric traffic conditions are discussed assuming that CR involves one communication pair and one relay station in a time division duplex (TDD) system. The asymmetric property means that the average communication quality differs for each transmission direction because of the difference in signal power between the combined signals for each direction. First, numerical results show the asymmetric property of bi-directional CR. Next, in order to evaluate the impact of the asymmetric property, the optimal relay position and resource allocation are compared to those in simple multi-hop relaying, which does not have the asymmetric property. Numerical results show that, in order to maximize the overall quality of bi-directional communication, the optimal relay position in CR depends on the offered traffic ratio, which is defined as the traffic ratio of each transmission direction, while the offered traffic ratio does not affect the optimal relay position in multi-hop relaying. Finally, the asymmetric property is used to enhance the overall quality. Specifically, a high overall quality can be achieved by, for example, opportunistically switching to the transmission direction with higher quality. Under asymmetric traffic conditions, weighted proportionally fair scheduling (WPFS), which is proposed in the context of downlink scheduling in a cellular network, is applied to transmission direction switching. Numerical results reveal that WPFS provides a high overall quality and that the quality ratio is similar to the offered traffic ratio.

A cooperative relaying system with transmission scheduling is investigated. Cooperative relaying is composed of multiple links because the source sends the data to more than one receiver, and the destination receives multiple data transmitted by more than one transmitter. Therefore, if the source can transmit the data when the channel gains of the links are high, it is not clear which channel gains should be high in order to achieve high spectral efficiency. In the present letter, the spectral efficiency of a cooperative relaying system is theoretically derived under the assumption that the source transmits the data only when the channel gains of links are above certain threshold values. Numerical results reveal that a high spectral efficiency can be achieved by assuring a high channel gain for the link with the highest average received power among links to the destination.

In the present paper, the performance of cooperative relaying networks with adaptive relaying scheme selection is analyzed. Cooperative relaying is a new technique to achieve spatial diversity gain by using neighboring stations. However, when multiple stations transmit simultaneously, the number of interference signals increases. Therefore, the introduction of cooperative relaying in radio communication systems does not always increase the network capacity due to the co-channel interference. Therefore, in order to achieve high spectral efficiency, it is necessary to select cooperative relaying or non-cooperative relaying adaptively. Assuming both centralized and decentralized adaptive controls, the spectrum efficiency is evaluated. The performance under decentralized control is evaluated using a game-theoretic approach. Simulation results show that the introduction of cooperative relaying with centralized control always increases the spectral efficiency. On the other hand, Simulation results also show that, when each source selects a relaying scheme independently and selfishly to maximize its own spectral efficiency, the introduction of the cooperative relaying may reduce the spectral efficiency due to the increase in the number of interference signals.

We propose the use of an invertible code in cooperative multi-hop relaying networks. The effect of the code on the probability that an information block is undelivered to the destination is analyzed at the link level with a simple network topology. Numerical results indicate that significant improvement is feasible by an incorporation of an invertible code, since an information block can be reproduced by correcting channel errors in the received blocks at a relaying node.

The spectral efficiency of cooperative relaying in interference-limited environments in which a given channel is spatially reused is investigated. Cooperative relaying is a promising technique that uses neighboring stations to forward the data toward the destination in order to achieve spatial diversity gain. It has been reported that by introducing cooperative relaying into communication between an isolated source-destination pair, the error rate or spectral efficiency is generally improved. However, it is not intuitively clear whether cooperative relaying can improve the performance in interference-limited environments because the simultaneous transmission of multiple stations increases the number of interference signals. Assuming the most fundamental cooperative relaying arrangement, which consists of only one relay station, numerical results reveal that cooperative relaying is not always superior to non-cooperative single-hop and two-hop transmissions in terms of spectral efficiency.

The cooperative relaying technique enables a terminal to get space-diversity through the support of other terminals. However, existing cooperative relaying techniques for code division multiple access (CDMA) system decrease the total system transmission rate. In this letter, a new relaying technique is presented which supplies lossless transmission-rate using 2 spreading codes per terminal. We verify the performance of the proposed technique through a bit error rate (BER) simulation for a direct-sequence ultra wideband (DS-UWB) system. It is also shown that forward error correction (FEC) coding provides a better environment for the cooperative relaying.

In this paper, we evaluate the effect of space-time coded cooperative relaying technique in multihop inter-vehicle communication (IVC) networks. The IVC systems have an issue that communication links are often blocked by obstacles such as heavy vehicles. The breakage of a radio link in multihop connections may significantly decrease the system throughput in multihop IVC networks. It is demonstrated through system-level evaluations that the cooperative relaying can offer remarkable capacity enhancement by exploiting multi-route diversity and overcoming accidental link breakage resulting from frequent topological changes.