Network-Level Cooperation for a Multiple-Access Channel Via Dynamic Decode-and-Forward

This paper proposes a Markovian model of 1-persistent CSMA/CA protocols with K-Exponential backoff scheduling algorithm. The input buffer of each access node is modeled as a Geo/G/1 queue, and the service time distribution of each individual head-of-line packet is derived from the Markov chain of the underlying scheduling algorithm. From the queueing model, we derive the characteristic equation of network throughput and obtain the stable throughput and bounded delay regions with respect to the retransmission factor. Our results show that the stable throughput region of the exponential backoff scheme exists even for an infinite population. Moreover, we find that the bounded delay region of exponential backoff is only a sub-set of its stable throughput region due to the large variance of the service time of input packets caused by the capture effect. All analytical results presented in this paper are verified by simulations.

Energy harvesting (EH) is a promising technology for realizing energy-efficient wireless networks. In this paper, we utilize the ambient RF energy, particularly interference from neighboring transmissions, to replenish the batteries of the EH enabled nodes. However, RF energy harvesting imposes new challenges into the analysis of wireless networks. Our objective in this paper is to investigate the performance of a slotted Aloha random access wireless network consisting of two types of nodes, namely Type I, which has unlimited energy supply and Type II, which is solely powered by an RF energy harvesting circuit. The transmissions of a Type I node are recycled by a Type II node to replenish its battery. We characterize an inner bound on the stable throughput region under half-duplex and full-duplex energy harvesting paradigms as well as for the finite capacity battery case. Additionally, we analyze the case where RF energy harvesting serves as a backup for an unlimited energy source. We present numerical results that validate our analytical results, and demonstrate their utility for the analysis of the exact system.

In this paper, we investigate transmission techniques for a fundamental cooperative cognitive radio network, i.e., a radio system where a Secondary user may act as relay for messages sent by the Primary user, hence offering performance improvement of Primary user transmissions, while at the same time obtaining more transmission opportunities for its own transmissions. Specifically, we examine the possibility of improving the overall system performance by employing network coding techniques. The objective is to achieve this while affecting Primary user transmissions only positively, namely: 1) avoid network coding operations at the Primary transmitter in order avoid increase of its complexity and storage requirements, 2) keep the order of packets received by the Primary receiver the same as in the non cooperative case and 3) induce packet service times that are stochastically smaller than packet service times induced in the non-cooperative case. A network coding algorithm that operates without knowledge of channel and packet arrival rate statistics, is investigated in terms of achieved throughput region. It is shown that the proposed algorithm enlarges Secondary user throughput as compared to the case where the Secondary transmitter acts as a simple relay, while leaving the Primary user stability region unaffected.

In this paper, a cognitive multiple access channel with one primary node and M secondary nodes is considered, and the impact of the following techniques on the stability region of the system is investigated: (i) relaying by the secondary nodes of the primary traffic (cognitive relaying); (ii) opportunistic spectrum sensing at the secondary nodes. Specifically, inner bounds on the stability region of the system for the case of M =2 secondary nodes are derived by assuming cognitive relaying and both simultaneous and opportunistic spectrum sensing at the secondary nodes. The analysis is carried out by defining convenient systems which statistically dominate the original ones (dominant systems). Numerical results provide insight into the performance advantages of the different strategies in terms of stability region.

Maximizing the stable throughput of heterogeneous nodes under airtime fairness in a CSMA environment

Currently, most Landsat satellites are deployed in the low earth orbit (LEO) to obtain high resolution data of the Earth surface and atmosphere. However, the return channels of LEO satellites are unstable and discontinuous intrinsically resulting from the high orbital velocity, long revisit interval and limited ranges of ground-based radar receivers. Space-based information networks (SBIN), in which data can be delivered by the cooperative transmission of relay satellites, can greatly expand the spatial transport connection ranges of LEO satellites. While different types of these relay satellites deployed in orbits of different altitudes represent distinctive performances when they are participating in forwarding. In this chapter, we consider the cooperative mechanism of relay satellites deployed in the geosynchronous orbit (GEO) and LEO according to their different transport performances and orbital characteristics. To take full advantage of the transmission resource of different kinds of cooperative relays, we propose a multiple access and bandwidth resource allocation strategy for GEO relay, in which the relay can receive and transmit simultaneously according to channel characteristics of space-based systems. Moreover, a time slot allocation strategy which is based on the slotted time division multiple access is introduced for the system with LEO relays. Based on the queueing theoretic formulation, the stability of the proposed systems and protocols is analyzed and the maximum stable throughput region is derived as well, which provide the guidance for the design of the system optimal control. Simulation results exhibit multiple factors that affect the stable throughput and verify the theoretical analysis.KeywordsSpace-based Information NetworksCooperative CommunicationResource AllocationQueueing TheoryStability Analysis

In cooperative systems, users achieve spatial diversity and multihop gains by transmitting packets over multiple independent fading paths provided by their partners. Most previous works on cooperative communications focus on the physical layer aspects such as coding, modulation, and transceiver signal processing techniques. In this work, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit cooperative gains in random access networks. Based on the conventional slotted ALOHA protocol, we propose a simple cooperative transmission mechanism for a two-user cooperative pair. We derive the two-user stability region of the proposed system and show the improvements compared to noncooperative systems. The benefits can be attributed to both physical layer cooperation, where users with good channels may relay for those with bad channels, and MAC layer cooperation, where system parameters can be chosen to enhance cooperation and reduce competition. Then, we extend the proposed strategy to a finite-user system that consists of multiple cooperative pairs. By treating each pair as a single transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

Opportunistic scheduling has widely been used in wireless networks to send packet data over fading channels. In the literature, scheduling performance was usually analyzed by assuming a fixed number of active users and infinite packet buffers. However, the assumption may not be valid due to traffic dynamics in opportunistic packet transmissions. In this paper, we analyze opportunistic scheduling systems with varying number of users and burst packet arrivals. In particular, we define a stability region as the union of a set of convex polyhedral regions. We investigate the tradeoffs between throughput and fairness in terms of stability region. First, the maximal aggregated rate is derived under an optimal scheduling policy, which only depends on the quality-of-service (QoS) requirements without channel-state information (CSI). Second, the perfect fairness limit is defined such that the aggregated rate below the limit can equally be shared among users. Third, the fairness is optimized under a given overall throughput. As a metric to reflect the QoS requirements, we also derive a closed-form average delay for a symmetric system. Theoretical analysis and numerical results demonstrate the advantages of opportunistic scheduling.

This brief provides a novel criterion for the analysis of convergence of states of an infinite impulse response (IIR) digital filter to a bounded region under the influence of composite effects of quantization and overflow nonlinearities. The developed criterion is less conservative in its approach in terms of analyzing stability than conventional methods and can be employed for implementation of an IIR filter on comparatively smaller hardware word-length than existing methods. The conventional approaches consider asymptotic stability of a filter with respect to the quantization noise; however, quantization in digital filters can result into bounded oscillation and lead to infeasibility of the asymptotic stability. Therefore, a less conservative stability analysis together with estimation of steady-state region of convergence for an IIR filter is provided. In addition, the conventional approaches, analyzing stability, and steady-state region of convergence, may not guarantee an overflow oscillation-free realization of a filter. Consequently, a condition for estimating the steady-state region of convergence (along with the filter stability) with an additional constraint that the filter’s state should not overflow in the bounded region has been derived. A comparative analysis with conventional methods is provided in simulation results.

This paper presents the security in physical layer of cognitive cooperative radio network (CCRN). This network (i.e., CCRN) consists of a cognitive source (CS), a cognitive decode and forward relay (CDFR) with energy harvesting and a cognitive destination (CD). The CCRN uses the bandwidth of a primary network (PN) which contains a primary transmitter (PT) and a primary receiver (PR). The CS does not have a direct link with CD due to deep fading. An eavesdropper is present in the network which tries to decode the message of cognitive network. In this scenario, we have numerically investigated the secrecy performance by a metric named as conditional secrecy outage probability while meeting an outage constraint of PN. MATLAB based is carried out following our analytical development.

We determine a joint link activation and routing policy that maximizes the stable throughput region of time-varying wireless ad-hoc networks with multiple commodities. In practice, the state of the channel process from the time it is observed till the time a transmission actually takes place can be significantly different. With this in mind, we introduce a stationary policy that takes scheduling and routing decisions based on a possibly inaccurate estimate of the true channel state. We show optimality of this policy within a broad class of link activation processes under certain mild conditions. In particular, processes in this class may be induced almost by any policy, possibly non-stationary, even anticipative and aware of the entire sample paths of the arrival, estimated and true channel processes, provided that it has no knowledge on the current true channel state, besides that available through its estimate.

In this work, we consider an adaptive two-user random access scheme with multipacket reception (MPR) ca- pabilities. A user adapts its transmission characteristics based on the status of the other user. The users have external random traffic stored in their queues. We derive the stable throughput region of the system and the convexity conditions of this region. We derive analytically the queueing delay by formulating and solving a Riemann-Hilbert boundary value problem. Finally, we evaluate numerically the presented theoretical results.

In this paper, we consider a cognitive scenario where an energy harvesting secondary user shares the spectrum with a primary user. The secondary source helps the primary source in delivering its undelivered packets during periods of silence of the primary source. The primary source has a queue for storing its data packets, whereas the secondary source has two data queues: a queue for storing its own packets and the other for storing the fraction of the undelivered primary packets accepted for relaying. The secondary source is assumed to be a battery‐based node, which harvests energy packets from the environment. In addition to its data queues, the secondary user has an energy queue to store the harvested energy packets. The secondary energy packets are used for primary packets decoding and data packets transmission. More specifically, if the secondary energy queue is empty, the secondary source can neither help the primary source nor transmit a packet from the data queues. The energy queue is modeled as a discrete‐time queue with Markov arrival and service processes. Because of the interaction of the queues, we provide inner and outer bounds on the stability region of the proposed system. We investigate the impact of the energy arrival rate on the stability region. Numerical results show the significant gain of cooperation.Copyright © 2014 John Wiley & Sons, Ltd.

Drought stress is a major constraint to rice (Oryza sativa L.) production and yield stability in many rainfed regions of Asia, Africa, and South America. The genetic improvement of adaptation to drought is addressed through the conventional approach by selecting for yield and its stability over locations and years. Because of low heritability of yield under stress and inherent variation in the field, such selection programs are expensive and slow in attaining progress. The objective of this paper is to review the current knowledge in physiology and molecular genetics which have implications in breeding for drought resistance in rice. The ability of root systems to provide for evapotranspirational demand from deep soil moisture and capacity for osmotic adjustment are considered major drought resistance traits in rice. However, selection for these traits still entail extensive investments in field nurseries or greenhouse facilities and is prone to problems of repeatability because of environmental variability. Recent development of molecular linkage maps of rice and other advances in molecular biology offer new opportunities for drought resistance breeding. Molecular markers linked to root traits and osmotic adjustment are being identified, which should lead to marker‐assisted selection. Transgenic rice plants having tolerance to water deficit and osmotic stresses have been reported. Work on genetic engineering of osmoprotectants, such as proline and glycine betaine, into the rice plant for drought tolerance improvement is in progress. Close collaboration between molecular geneticists, plant physiologists, and breeders is needed to critically assess the contribution of specific genes and application of molecular genetics to breeding for drought resistance in rice and other crops.

In cluster-based cooperative cognitive radio networks (CCRNs), spectrum sensing and decision making processes to determine whether the primary user (PU) signal is present or absent in the network are very important and vital issues to the utilisation of the idle spectrum. The reporting time delay is a very important matter to make quick and effective global decisions for the fusion center (FC) in a cluster-based CCRNs. In this paper, we propose the concept of multiple reporting channels (MRC) for cluster-based CCRNs to better utilize the reporting time slot by extending the sensing time of secondary users (SUs). A multiple reporting channels concept is proposed based on frequency division multiple access to enhance the spectrum sensing performance and reduce the reporting time delay of all cluster heads (CHs). In this approach, we assign an individual reporting channel to each cluster for reporting purposes. All the SUs in each cluster sequentially pass their sensing results to the corresponding cluster head (CH) via the assigned single reporting channel, which extends the sensing time duration of SUs. Each CH uses the dedicated reporting channel to forward the cluster decision to the FC that makes a final decision by using the “K-out-of-N” rule to identify the presence of the PU signal. This approach significantly enhances the sensing time for all SUs than the non-sequential as well as minimize the reporting time delay of all CHs than sequential single channel reporting approach. These two features of our proposed approach increase the decision accuracy of the FC more than the conventional approach. Simulation results prove that our proposed approach significantly enhances the sensing accuracy and mitigate the reporting time delay of CH compared to the conventional approach.