Cooperative Diversity Techniques Research Articles

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.

Satellite component of NGN: Integrated and hybrid networks

AbstractFuture mobile networks are expected to involve systems that are based on different technologies, such as WiFi, WiMAX, 2G/3G/3G+, LTE, and satellite. To address this scenario, ITU has defined integrated and hybrid networks in the framework of Next‐Generation Networks. The interest is to exploit the cooperation of different wireless communication systems (segments) to provide service to mobile users in the most efficient way, taking into account signal quality (coverage), traffic congestion conditions, and cost issues. Integrated and hybrid networks have the potential to be an efficient and cost‐effective solution to employ satellite communications for mobile users. In the view of this, our paper focuses on the design of integrated/hybrid systems taking into account physical, MAC, and network layers issues. System examples and standards are described as well. Then, cooperative diversity techniques and traffic engineering issues for overflow traffic are discussed. This paper concludes identifying some possible future trends. Copyright © 2010 John Wiley & Sons, Ltd.

Cooperative FSO Systems: Performance Analysis and Optimal Power Allocation

In this paper, we investigate the cooperative diversity technique as a candidate solution for combating turbulence-induced fading over free-space optical (FSO) links. In particular, we propose a novel cooperation strategy that is suitable for quantum-limited FSO systems with any number of relays and we derive closed-form expressions for the error performance of this strategy. In scenarios where the channel-state-information (CSI) is available at the different nodes, we propose an optimal power allocation strategy that satisfies the Karush-Kuhn-Tucker (KKT) conditions and that further boosts the performance of FSO networks. It turned out that this closed-form optimal solution corresponds to transmitting the entire optical power along the “strongest link” between the source and the destination nodes. A simple procedure is proposed for selecting this link and for distributing the power among its different hops.

Cooperative Diversity for Free-Space Optical Communications: Transceiver Design and Performance Analysis

In this paper, we investigate the cooperative diversity technique as a candidate solution for combating turbulence-induced fading over Free-Space Optical (FSO) links. In particular, a one-relay cooperative diversity scheme is proposed and analyzed for non-coherent FSO communications with intensity modulation and direct detection (IM/DD). The error performance is derived in semi-analytical and closed-form expressions in the presence and absence of background radiation, respectively. Results show the enhanced diversity orders that can be achieved over both Rayleigh and lognormal fading models.

Multicarrier modulation and cooperative communication in multihop cognitive radio networks

For high-data-rate wireless communication systems, two major issues are the underutilization of limited available radio spectrum and the effect of channel fading. Using dynamic spectrum access, cognitive radio can improve spectrum utilization. Almost all proposed CR systems are based on multicarrier modulation since multiple users can access the MCM systems by allocating subcarriers. Generally, MCM mainly includes two different schemes, orthogonal frequency-division multiplexing and filtered multitone modulation. Considering mutual interference elimination, synchronization, and transmission efficiency, we conclude that FMT is better than OFDM in MCM-based CR systems. Additionally, cooperative diversity can reduce the fading effect since the space diversity gain can be obtained through the distributed antennas of each user. Hence, in this article, we combine CR with the cooperative diversity technique, and then construct three cooperative diversity cognitive models: the collaborative spectrum sensing model, the cooperative communication cognitive model, and the hybrid model. Additionally, radio resources can be extended from time-frequency dimensions to space-time-frequency dimensions in the proposed models, which effectively improves both spectrum utilization and MCM-CR system performance. Finally, extensive simulations are conducted to show the validity and effectiveness of the proposed models.

Spectral Efficient Cooperative Diversity Technique with Multi-Layered Modulation

This paper proposes a spectral efficient cooperative diversity technique with multi-layered modulation for high data rate transmissions. The proposed system transmits with different cyclic delay and phase rotation patterns, in order to achieve cooperative diversity gain for all transmit signals from the source. Since these patterns increase the interference between the layers, we derive optimal cyclic delay and phase rotation patterns to minimize mean square error. With the optimal patterns, the proposed system still suffers from inter-layer interference, especially in high-order modulations. To overcome this problem, multiple layers are separately interleaved by layer-specific interleavers and are mapped by hierarchical symbol mapping for the high data rate transmission with cooperative diversity. A destination structure with iterative equalization is also presented to separate each layer and extract diversity gain for high data rate transmissions. The proposed system can use reliable feedback from the layers and effectively remove the inter-layer interference. To estimate the performance of the proposed system, we develop a density evolution technique. It is shown that the predicted performances agree with simulated performances. Simulation results indicate that the proposed system achieves cooperative diversity and has better performance than conventional cooperative systems.

Energy-efficient quality-of-service-aware cooperation in wireless networks

Conventional cooperative diversity techniques consider a three-node setup, which involves a pair of source–destination nodes and a signal relay node. It is noted that the existing cooperation schemes are performed in a session-based manner in which the role of each node being a source or relay remains unchanged during each session. The radio resource allocation and the associated performance analysis are not jointly performed. As a result, resource utilisation is less efficient. In this paper, an energy-efficient quality-of-service (QoS)-aware cooperative transmission strategy based on joint resource allocation is proposed. Two source nodes with distinct destinations and QoS requirements are simultaneously considered in resource allocation to optimise the energy efficiency. The QoS outage probability is derived analytically and the attainable energy efficiency is investigated for the proposed scheme. Numerical results show that significant performance gain can be achieved for both node pairs with the proposed cooperation scheme.

Outage behavior of selective relaying schemes

Cooperative diversity techniques can improve the transmission rate and reliability of wireless networks. For systems employing such diversity techniques in slow-fading channels, outage probability and outage capacity are important performance measures. Existing studies have derived approximate expressions for these performance measures in different scenarios. In this paper, we derive the exact expressions for outage probabilities and outage capacities of three proactive cooperative diversity schemes that select a best relay from a set of relays to forward the information. The derived expressions are valid for arbitrary network topology and operating signal-to-noise ratio, and serve as a useful tool for network design.

Frequency offset mitigation of cooperative ofdm system in wireless digital broadcasting

Mobile digital broadcasting is expected to become a promising application in future wireless communication. To improve the system performance in limitation of size and cost, the OFDM and MIMO techniques are adopted. Recently, cooperative diversity techniques are developed to be a solution. In this paper, we propose the carrier frequency offset mitigation scheme in cooperative communication using multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), in which one cyclic prefix (CP) is used for multiple OFDM symbols. We use the FFT size-reduced MSE-OFDM system which can be used to reduce the peak-to-average power ratio (PAPR) and improve the robustness to carrier frequency offset. The cooperative communication uses not only direct path from source to destination but also indirect path via relay station. Each different relays require more precise frequency synchronization and lower PAPR, so we adopt the MSEOFDM to increase the system performance. The performance analysis of cooperative MSE-OFDM in multipath fading channels has been done and the effect of carrier frequency offset and PAPR have been studied.

A cooperative phase steering scheme in multi-relay node environments

We propose a decode-and-forward (DF) based cooperative phase steering scheme and analyze its outage probability. The cooperative phase steering scheme is to make the received signals from multiple relay nodes co-phased at a destination node by pre-adjusting the phase differences.With a reasonable amount of feedback information from a destination node, the cooperative phase steering scheme circumvents the drawbacks of conventional cooperative diversity techniques such as maximal ratio combining (MRC) reception, maximal ratio transmission (MRT), and opportunistic relay selection schemes. Our analytical and simulation results show that the cooperative phase steering scheme outperforms the opportunistic relay selection scheme and approaches the MRT scheme known as a theoretically optimal cooperative diversity technique. It is also shown that cooperative phase steering has sufficient robustness to phase incoherence.

Evaluation of Cooperative Diversity Techniques Using STC for Future S-DMB Services

This paper presents an evaluation of various cooperative diversity techniques applied to future satellite digital multimedia broadcasting (S-DMB) systems. The increasing importance of hybrid and/or integrated satellite and terrestrial networks is associated with the utilization of spatial diversity techniques such as antenna diversity using space-time coding. The space-time coding schemes can be expected to result in more diversity gain as the number of transmit antennas are increased. However, we cannot design a rate-1 scheme that achieves full diversity for more than two transmit antennas. To overcome this limitation, quasi-orthogonal schemes were proposed, at the expense of the decoder complexity and diversity gain. In this paper, we introduce an efficient quasi-orthogonal space time coding scheme, and evaluate various aspects associated with the application of the proposed scheme to satellite systems. The proposed scheme in this paper provides the full rate as well as maximum-likelihood decoding via simple linear detection.

Cooperative diversity technique for MIMO-OFDM uplink in wireless interactive broadcasting

OFDMA is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. Recently, to enhance the performance of OFDMA systems, MIMO techniques have been investigated, and the OFDMA systems have been extended to MIMO architectures. Although transmit diversity is clearly advantageous on OFDMA uplink system in interactive broadcasting, it may not be possible that practical OFDMA system of wireless interactive broadcasting have more than two antennas due to size, cost, or hardware limitations. Cooperative diversity techniques are proposed to overcome the limitations. Cooperative networks aim to utilize the available terminals as a collection of distributed antennas for the transmission of signals from one end of the network to the other. Therefore, this paper focuses on design and performance evaluation of MIMO-OFDMA uplink system with cooperative diversity for wireless interactive broadcasting. For high-rate and reliable transmission, efficient transmission codes are proposed for two transmission cases (one-sided transmission case and two-sided transmission case). And, we present our investigations of the effects of line-of-sight. In the wireless communication environment, line-of-sight is very important to improve the system performance. Under the condition of utilizing the line-of-sight of cooperative partner, the performance of a terminal without line-of-sight can be improved. Taking into account the effects of utilizing line-of sight of cooperative partner, the BER performance is investigated for a MIMO-OFDMA uplink scenario.

Recent and Emerging Topics in Wireless Industrial Communications: A Selection

In this paper we discuss a selection of promising and interesting research areas in the design of protocols and systems for wireless industrial communications. We have selected topics that have either emerged as hot topics in the industrial communications community in the last few years (like wireless sensor networks), or which could be worthwhile research topics in the next few years (for example cooperative diversity techniques for error control, cognitive radio/opportunistic spectrum access for mitigation of external interferences).

OFDM 시스템을 위한 순환 지연을 사용하는 협력 다이버시티 기법

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most promising technologies for high data rate wireless communications. OFDM has been adopted in wireless standards such as digital audio/video broadcasting. The combination of OFDM and cooperative diversity techniques can provide the diversity gain and/or increased capacity. In this paper, the cooperative coding using cyclic delay diversity (CDD) for multiuser OFDM systems is introduced. To improve the beneficial effects of relays`s cooperation, CDD is adopted in cooperative transmission of relays. Simulation results show the bit error rate (BER) for various consideration. The proposed scheme provides improved performance compared to delay.

A network coding approach to cooperative diversity

This paper proposes a network coding approach to cooperative diversity featuring the algebraic superposition of channel codes over a finite field. The scenario under consideration is one in which two ldquopartnersrdquo - node A and node B - cooperate in transmitting information to a single destination; each partner transmits both locally generated information and relayed information that originated at the other partner. A key observation is that node B already knows node A's relayed information (because it originated at node B) and can exploit that knowledge when decoding node A's local information. This leads to an encoding scheme in which each partner transmits the algebraic superposition of its local and relayed information, and the superimposed codeword is interpreted differently at the two receivers i.e., at the other partner and at the destination node, based on their different a priori knowledge. Decoding at the destination is then carried out by iterating between the codewords from the two partners. It is shown via simulation that the proposed scheme provides substantial coding gain over other cooperative diversity techniques, including those based on time multiplexing and signal (Euclidean space) superposition.

An efficient MAC protocol for cooperative diversity in mobile ad hoc networks

AbstractCooperative diversity is proposed to combat the detrimental effects of channel fading. In this paper, we investigate the effectiveness of cooperative diversity in interference limited ad hoc networks. The negative effects due to relay blocking on the network throughput are investigated. We show that the relay blocking problem is mainly dependent on the relay selection criterion. To overcome this problem, we propose a new cooperative diversity technique based on a modified IEEE 802.11 Medium Access Control (MAC) protocol. The throughput performance of the proposed MAC protocol is analyzed using a random structured network where nodes are assumed to be equipped with multiple antennas. In our simulations, we consider both single‐ and multiple‐relay scenarios over fading channels. Copyright © 2007 John Wiley & Sons, Ltd.

Cooperative-diversity slotted ALOHA

We propose a cooperative-diversity technique for ad hoc networks based on the decode-and-forward relaying strategy. We develop a MAC protocol based on slotted ALOHA that allows neighbors of a transmitter to act as relays and forward a packet toward its final destination when the transmission to the intended recipient fails. The proposed technique provides additional robustness against fading, packet collisions and radio mobility. Network simulations confirm that under heavy traffic conditions, in which every radio always has packets to send, the proposed cooperative-diversity slotted-ALOHA protocol can provide a higher one-hop and end-to-end throughput than the standard slotted-ALOHA protocol can. A similar advantage in end-to-end delay can be obtained when the traffic is light. As a result, the proposed cooperative-diversity ALOHA protocol can be used to improve these measures of Quality of Service (QoS) in ad hoc wireless networks.

Dual antenna cooperative diversity techniques

This paper presents the application of two spatial transmission techniques which can be used in a cooperative diversity wireless network, where each mobile terminal has two antenna elements. Initially the current body of work in single antenna cooperative diversity is expanded to include the effect of cooperative diversity upon the capacity of a link. This is to serve as a baseline model for comparison with the dual antenna methods. This paper then introduces two techniques which can be used for cooperative diversity where mobile terminals are each equipped with two antenna elements. Using the same metrics as the single antenna case, a comparison is made between the results from simulations of each technique. It is shown that dual antenna elements offer considerable advantage over the single antenna element case, and that two antenna element space-time transmit diversity (STTD) based cooperative diversity is preferred at low SNRs.