Lower Outage Probability Research Articles

Outage performance improvement with cooperative relaying in cognitive radio networks

In this paper, we investigate the outage probability in three different relay modes, namely Amplify-and-Forward (AF), Decode-and-Forward (DF), and Hybrid Decode-Amplify-Forward (HDAF). We derive the closed-form outage probability expressions for cooperative communication. Our aim is to ensure the quality of service (QoS) of the primary link while minimizing the outage probability of the cognitive radio user. The cooperation based spectrum access is investigated at the secondary network. The cognitive transmitter will allocate low power if the quality of service is very rigid. Firstly, it is beneficial that the cooperation is obtained at the cognitive user from the surrounding cognitive users to decrease outage probability. Secondly, we select the best relay that can provide the minimal outage probability for cooperation. Finally, we investigate the outage probability under the peak and average interference constraints. The results indicate that the average interference constraints has lower outage probability than the peak interference constraints, due to the power adaptation between the transmitter and relay. The comparison among three cooperation relay modes shows that the HDAF outperforms the AF and DF. At the same time, we can see that the performance gain of the HDAF cooperation is better than the other modes, and a lower outage probability can be acquired as the number of potential relays increases.

Higher Rank Interference Effect on Weak Beamforming or OSTBC Terminals

Spatial multiplexing is one of the multi-antenna techniques employed by current generation wireless systems. Based on existing research, spatial multiplexing is known to be susceptible to interference. However, it is not well known what the effect of spatial multiplexing on other transmissions is, i.e., how does user performance depend on whether a neighboring cochannel interferer applies a single (spatial) stream or a multi stream transmission. This work attempts to alleviate this shortcoming by analyzing the impact of interference rank (number of spatial streams) on a beamforming and orthogonal space-time block coded user transmission. We generalize existing analytical results on signal-to-interference-plus-noise-ratio distribution and outage probability under arbitrary number of unequal power interferers. Our results are in close form and include interference rank as a parameter, allowing for a thorough study of its impact. Analysis shows that higher rank interference causes lower outage probability, and can support higher outage threshold especially in the case of beamforming.

Ameliorated Resource Allocation in Two-Tier Femtocell–Macrocell Networks with Six Directional Antennas for Macrocells

Femtocells are deployed in the coverage area of traditional macrocell networks and can provide high data rates and good quality of service with low transmission power. In order to achieve the high spectral efficiency, allocated resources to the femtocells should be from the same licensed spectrum band of the macrocell network. Therefore, interference management is an important challenge in two-tier femtocell---macrocell networks. Previously, it was shown that cross-tier interference from macrocell to femtocell can be reduced by using directional antennas in macrocell tier. In this paper, we propose a new spectrum partitioning approach by dividing the spectrum to four sub-bands and then allocating them to different sectors of the macrocell with six directional antennas in a proper manner to reduce interferences. Therefore, first, we calculate the interference from the adjacent macrocells in different sectors. Then, based on the results of interference analysis, we propose a sub-band exchanging allocation strategy for improving the macrocells' and femtocells' performance. Moreover, we analyze the downlink outage probability of the two-tier femtocell---macrocell network based on the orthogonal-frequency-division-multiple-access. Finally, simulation and theoretical results demonstrate that the proposed cellular network achieves lower downlink outage probability of femtocell and macrocell in comparison with the previous cellular model and consequently, system throughput increases substantially.

Enhanced Cognitive Relaying for Providing Continuous Connections in Wireless Networks

Typically, when a target user moves from its own network, which is denoted Net1, into another one, which is denoted Net2, its services would be interrupted. In this case, the target user can be viewed as a secondary user (SU), whereas the user of Net2 is a primary user (PU). By taking the advantage of cognitive radios, we propose a two-phase cognitive relaying (TCR) protocol to provide continuous connections for Net1 while guaranteeing the quality-of-service (QoS) of Net2 in wireless networks. The interference cancelation and time optimization techniques are also employed in TCR to further improve the transmission performance of Net1. Under TCR, both the downlink and uplink transmissions of the target user are investigated. We derive the closed-form expressions of outage probabilities for traditional and proposed transmission protocols over Rayleigh fading channels, respectively. Simulation results demonstrate that, with a guaranteed QoS of Net2, TCR transmissions can not only ensure continuous connections for the target user but achieve lower outage probabilities than traditional cases as well. In addition, it is shown that the outage probabilities of TCR transmissions can be minimized by optimizing the transmission time allocation.

Resilient design of a cloud system over an optical backbone

Cloud computing enables users to receive infrastructure/platform/software as a Service (XaaS) via a shared pool of resources in a pay-as-you-go fashion. Data centers, as the hosts of physical servers, play a key role in the delivery of cloud services. Therefore, interconnection of data centers over a backbone network is one of the major challenges affecting the performance of the cloud system, as well as the operational expenditures of service providers. This article proposes resilient design of a cloud backbone through demand profile-based network virtualization where the data centers are located at the core nodes of an IP over elastic optical network. Three approaches, MOPIC, MRPIC, and RS-MOPIC, are proposed. MOPIC aims to design the cloud backbone with minimum outage probability per demand. MRPIC aims to minimize the usage of network resources while routing the cloud demands toward data centers. RS-MOPIC is a hybrid of both approaches aiming to reduce network resource usage while minimizing outage probability. Through simulations of a small-scale cloud scenario, we show that incorporation of manycast provisioning ensures significantly low outage probability on the order of 10–7. Furthermore, integration of a resource saving objective into MOPIC can make a compromise between network resource consumption and outage probability of the workloads submitted to the cloud.

An intelligent hybrid spread spectrum MAC for interference management in mobile ad hoc networks

This paper presents and analyses a fully distributive intelligent hybrid spread spectrum MAC for ad hoc networks. The IHSS MAC scheme has been developed with the aim to mitigate far field interference with the use of a robust DSSS physical layer, while managing near field interference with the use of intelligent slow frequency hopping. The IHSS design ensures a minimum required SINR threshold at active receivers, under low outage probability constraints. IHSS does not inhibit any nodes in space neither thins them out in time. A lower bound on transmission capacity for the case where the size of the frequency hopping zone is variable is derived in this paper. The mathematical model is validated through simulation. The simulation is based on a hopping sequence selection methodology that randomizes the available hopping sequences within a frequency hopping zone around each active receiver. The implementation utilises the RTS/CTS concept of the CSMA MAC, with a slight modification. The performance criterion used for analysis is transmission capacity normalized by the required bandwidth. It is observed that implementation of a suitable sized frequency hopping zone using the proposed IHSS MAC, shows superior performance over ALOHA and guard zone based MACs.

Evolving intuitionistic fuzzy priority classifier with bio-inspiration based scheduling scheme for WiMAX in vehicular ad-hoc networks

With the increase in user mobility the most challenging issues are data scheduling which premises its users high quality of service in the context of the interoperability for microwave access in WiMAX for vehicular ad-hoc network (VANET). There is no complete proof of existing techniques accessible to provide better quality as there is a starvation problem due to the uncertainty in decision process with imprecise data. In VANET for the sake of interest while vehicles started increasing more and more in network traffic this paper devised a two stage Optimized priority scheduling scheme known as Evolving Intuitionistic Fuzzy Priority Classifier with Bio-inspiration Based Scheduling Scheme. This work takes into account the hesitation degree of each factor for priority and the bio-inspiration based classification. Through our simulation, it is shown that the projected proposal can work to acclimatize and make competent to improve the existing VANET approaches in terms of high spectrum effectiveness and low outage probability.

SINR Estimation in Limited Feedback Coordinated Multipoint Systems

Coordinated multipoint (CoMP) transmission can provide high spectral efficiency for cellular systems if perfect channels are available. In limited feedback systems, except for channel direction, signal-to-noise-plus-interference ratio (SINR) is necessary to assist in user scheduling and adaptive transmission. When the methods to estimate SINR in single-cell systems is applied to CoMP systems, the performance will significantly degrade. In this paper, we estimate the SINR for downlink CoMP systems. We start by showing that the quantization error vector is no longer isotropic when quantizing CoMP channels. This implies that the vector has an inherent structure. We proceed to formulate an optimization problem to find the quantization error vector that maximizes the multiuser interference power under the structure constraint. This way, we can exploit the nonisotropic nature of the quantization error vector and avoid overestimating the SINR. Simulation results show that the proposed method provides high throughput and low outage probability with negligible extra feedback overhead.

Resource allocation in integrated femto–macrocell networks based on location awareness

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme, macrocell uses all resource blocks along with a portion of the spectrum allocated to femtocell while both networks operate simultaneously. Closed-form expressions for downlink throughput and outage probability of femtocells are also attained as well as the throughput of macrocell network. The results demonstrate that the proposed hierarchical cellular network achieves higher throughput and lower outage probability for femtocell when compared to other hierarchical macro–femto cellular networks.

Outage Performance Analysis of Incremental Relay Selection for STBC AF Cooperative Networks

In this paper, selection and incremental schemes are investigated for multi-input multi-output (MIMO) cooperative systems in which multiple amplify-and-forward relays and space---time block coding (STBC) are applied. In order to make an efficient use of the degrees of freedom of channel and provide full diversity order in the multi-relay STBC network, the selection and incremental protocols are employed by exploiting limited feedback from destination. Maximum ratio combination technique is applied at the destination. Outage probabilities of the both cooperative schemes are analytically derived at high signal to noise ratio regime. It is shown the incremental selection STBC scheme leads to a higher performance compared to the STBC selection relaying scheme and conventional STBC MIMO channels; so that the outage capacity provided by the incremental selection scheme is twice of the selection scheme at the low outage probabilities.

Probabilistic constrained multicast beamforming in cognitive relay systems

AbstractIn this paper, multicast beamforming in cognitive relay systems is investigated with the consideration of imperfect channel state information at the transmitter (CSIT). We focus at the design of the optimal signal forwarding matrix at the cognitive relay in both centralized relay mode (CRM) and distributed relay mode (DRM). The problem is formulated aiming at minimizing the total consumed power at the relay node with suitable QoS guarantee for secondary users and strict interference control for primary users. Due to the uncertainty of transmission channel gains, constraints for QoS guarantee and interference control cannot be expressed in closed forms, making it extremely difficult to solve the problem directly. To circumvent this, we first employ the Bernstein-type inequality to convert the probabilistic constraints into closed-form expressions and then present both the semi-definite relaxation (SDR) algorithm and the penalty function (PenFun) algorithm to accomplish the non-convex problem optimization. Simulation results show that CRM is more resource efficient than DRM, and the PenFun algorithm can achieve a much better solution than the SDR algorithm at the cost of complexity. Meanwhile, compared with existing schemes which do not consider the CSIT error, the proposed schemes can support a much lower outage probability and enjoy perfect interference control for primary users.

A two-hop equalize-and-forward relay scheme in OFDM-based wireless networks over multipath channels

Relay communications have attracted increasing research attentions as a cost-effective technique to improve spatial diversity, service coverage, and energy efficiency in wireless networks. However, existing relay schemes e.g., amplify-and-forward and decode-and-forward DF schemes still face several major challenges, particularly the accumulation of multipath channels effect in AF and long processing latency in DF. To address these issues, we propose a novel equalize-and-forward EF relay scheme to enhance the retransmission reliability while maintaining low processing delay at the relay node. In particular, the proposed EF relay estimates and equalizes the channel between source and relay to eliminate the channel accumulation effect without signal regeneration. To further reduce the relay processing time, the channel estimation and equalization in the proposed EF design are performed in parallel. The proposed equalization is realized by presetting the equalizer coefficients with the current channel response that is predicted in parallel using multiple past channel responses. Numerical results show that the proposed EF relay scheme can achieve comparable symbol error rate performance as the DF relay with much less relay latency. In addition, the EF relay exhibits low outage probability at the same data rate as compared with traditional amplify-and-forward and DF schemes. schemes. Copyright © 2015 John Wiley & Sons, Ltd

Network selection policy based on auction theory in heterogeneous wireless communication systems

A new network selection strategy based on auction theory is proposed to resolve the problem caused by the selectivity of the users. In switched network selection policy, each user selects only a single network. An optimal bid is obtained according to both quality function and interference quality function. Then the network allocates the resource to the user who gives the highest bid. In parallel network selection scheme, each user can access multiple networks; however the user who gives the higher bid will obtain more resources. Both the mathematical analysis and simulations show that the network selection strategy based on auction theory can achieve higher network throughput and lower outage probability.

Exact and Approximated Outage Probability Analyses for Decode-and-Forward Relaying System Allowing Intra-Link Errors

In this paper, we theoretically analyze the outage probability of decode-and-forward (DF) relaying system allowing intra-link errors (DF-IE), where the relay always forwards the decoder output to the destination regardless of whether errors are detected after decoding in the information part or not. The results apply to practical fading scenarios where all the links between the nodes suffer from independent block Rayleigh fading. The key idea of DF-IE system is that the data sequence forwarded by the relay is highly correlated with the original information sequence sent from the source, and hence with a proper joint decoding technique at the destination, the correlation knowledge can well be exploited to improve the system performance. We analyze this problem in the information theoretical framework of correlated source coding. Using the theorems for lossy source-channel separation and for source coding with side information, the exact outage probability is derived. It is then shown that the exact expression can be reduced to a simple, yet accurate approximation by replacing the theorem for source coding with side information by the Slepian-Wolf theorem. Compared with conventional DF relaying where relay keeps silent if errors are detected after decoding, DF-IE can achieve even lower outage probability. Moreover, by allowing intra-link errors, the optimal position of the relay is found to be exactly the midpoint between the source and destination. Results of the simulations are provided to verify the accuracy of the analytical results.

Network-Coding-Based Mutually Cooperative Transmission in Deep Space Communications

In deep space exploration, spacecrafts need to deliver large volume of time-insensitive scientific data to deep space station. However, power supply of spacecrafts is only from the solar energy and battery. That is to say, these spacecrafts are energy-limited. In order to reduce energy consumption, prolong the life of spacecrafts and send more data, the transmission protocol must be efficient and low-energy-waste. To achieve the aim, this paper proposes a network-coding-based mutually cooperative transmission protocol (NMCTP). Compared with the known protocols, i.e., COPE protocol and repeating transmission protocol, NMCTP can achieve higher diversity gain, and lower system outage probability.

Distributed Resource Allocation for Multi-Cell Relay-Aided OFDMA Systems

We propose an efficient resource allocation (RA) scheme for downlink of relay-aided orthogonal frequency division multiple access systems. To mitigate excessive computational complexity of the centralized RA where the base station (BS) is responsible for resource allocation of the entire cell, we take a distributed RA strategy with which each relay station (RS) and BS perform resource allocation for their respective receivers by themselves. The proposed RA scheme is composed of two parts, RS resource allocation (RS-RA) and BS resource allocation (BS-RA). Considering that multiple RSs compete for radio resource in a distributive manner, we design the RS-RA scheme according to noncooperative game framework. The proposed RS-RA scheme aims at allocating less resource to two-hop transmission via RS so that more resource can be used for one-hop (direct) transmission. This RA strategy greatly heightens the system performance. Simulation results show that the proposed RA scheme provides the high cell throughput and the low outage probability. In addition, we devise a heuristic RA scheme that can lower the computational complexity further with much smaller reporting overhead and also suggest an iterative algorithm that can easily implement the proposed RA scheme.

The Performance of Systems Featuring Dynamic Decode-and-Forward and Network Coding

We constructed a single-relay-station cooperative communications system, featuring integration between the dynamic decode-and-forward (DDF) protocol and network coding (NC) to examine the outage probabilities in the Rayleigh, Rician, and Nakagami fading channels. In addition, the diversity-multiplexing tradeoff of the system was analyzed to examine improvements for system performance through integrating these two technologies. Through simulations and analyses, we discovered that the systems featuring NC had lower outage probability and greater diversity gain, and consequently, greater system reliability compared to the ordinary system featuring only the DDF protocol. However, because we added a final phase for the transmission of network coded signals, the system showed lower multiplexing gain compared to the system featuring only the DDF. Users should adopt this system based on their needs. For example, in situations that have higher requirements for reliability and lower requirements for multiplexing gain, users can adopt a DDF-NC cooperative communications system.

Power optimization for dynamic spectrum access with convex optimization and intelligent algorithm

In dynamic spectrum access networks, relay transmission has been considered as a potential method to help cognitive users communicate by reducing their interferences to primary networks especially in the underlay mode. In this paper, we propose a power optimization algorithm for both regenerative and non-regenerative relay systems in condition of Rayleigh fading channels. Based on analyzing the features of dynamic spectrum access networks, a relevant interference model is first built. Then, we propose a combined power allocation strategy in order to minimize the outage probabilities in the cooperative transmission. For regenerative system, we give a closed-form expression for the power allocation by taking into account the characteristics of the fading channels. For non-regenerative system, we utilize pattern search algorithm to solve the optimization problem since the objective function is complex and uneasy to be figured out directly. A competitive strategy for initial point selection is also designed to guarantee a global optimal outcome for the proposed pattern search algorithm. Numerical results show that the system performances with optimum power allocation outperform those with uniform power allocation whereas lower outage probabilities can be obtained.

A Buffer-Aided Successive Opportunistic Relay Selection Scheme With Power Adaptation and Inter-Relay Interference Cancellation for Cooperative Diversity Systems

In this paper we consider a simple cooperative network consisting of a source, a destination and a cluster of decode-and-forward half-duplex relays. At each time-slot, the source and (possibly) one of the relays transmit a packet to another relay and the destination, respectively, resulting in inter-relay interference (IRI). In this work, with the aid of buffers at the relays, we mitigate the detrimental effect of IRI through interference cancellation. More specifically, we propose the min-power scheme that minimizes the total energy expenditure per time slot under an IRI cancellation scheme. Apart from minimizing the energy expenditure, the min-power selection scheme, also provides better throughput and lower outage probability than existing works in the literature. It is the first time that interference cancellation is combined with buffer-aided relays and power adaptation to mitigate the IRI and minimize the energy expenditure. The new relay selection policy is analyzed in terms of outage probability and diversity, by modeling the evolution of the relay buffers as a Markov Chain (MC). We construct the state transition matrix of the MC, and hence obtain the steady state with which we can characterize the outage probability. The proposed scheme outperforms relevant state-of-the-art relay selection schemes in terms of throughput, diversity and energy efficiency, as demonstrated via examples.

Space-Time Network Coding With Overhearing Relays

Space time network coding (STNC) is a recently proposed time-division multiple-access (TDMA)-based cooperative relaying scheme for multi-relay wireless systems, which can achieve full diversity order with low transmission delay by taking advantage of the concepts of network coding and distributed space time coding. However, STNC does not fully exploit the benefit of the broadcast nature of wireless channels, since it only allows relays to receive signals from the sources. To explore the potential capacity of STNC-based systems, in this paper, we propose a new cooperative relaying scheme, termed space-time network coding with overhearing relays (STNC-OR), by allowing each relay to collect the signals transmitted from not only the sources but also its previous relays. Then, we derive some explicit expressions for the outage probability and symbol error rate (SER) for STNC-OR with decode-and-forward relaying over independent non-identically distributed (i.n.i.d) Rayleigh fading channels. For comparison, we also derive the explicit expression of the outage probability for STNC. To further improve the performance of STNC-OR, we investigate the effect of relay ordering on the performance of STNC-OR and then present the optimal relay ordering algorithm. Further, a suboptimal relay ordering is also designed to reduce the complexity. Extensive simulation and numerical results are presented finally to validate our theoretical analysis. It is shown that the proposed STNC-OR achieves much lower outage probability and SER than STNC and traditional pure TDMA relaying schemes.