Total System Throughput Research Articles

Adaptive SU/MU‐MIMO scheduling schemes for LTE‐A downlink transmission

We investigate multi-user (MU) multiple-input multiple-output (MIMO) scheduling under the practical constraints in long-term evolution advanced (LTE-A) downlink cellular networks. The authors first derive the received signal model in MU-MIMO systems when there exist both inter-stream interference (ISI) and inter-user interference (IUI) at each user device. Based on this, they formulate the optimisation problem as joint user pairing, precoding matrix indicator (PMI) selection, and resource block (RB) allocation to maximise the total system throughput. The authors then develop a codebook grouping technique for user pairing and PMI selection in MU-MIMO. With the help of codebook grouping, the authors propose some suboptimal and low-complexity scheduling algorithms to improve system throughput. From system-level simulation, the proposed algorithms can improve the network throughput significantly when exploiting only limited feedback designed for single-user (SU) MIMO in the LTE-A specification.

An inter-lighting interference cancellation scheme for MISO-VLC systems

ABSTRACTIn this paper, we propose an inter-lighting interference cancellation (ILIC) scheme to reduce the interference between adjacent light-emitting diodes (LEDs) and enhance the transmission capacity of multiple-input–single-output (MISO)-visible light communication (VLC) systems. In indoor environments, multiple LEDs have normally been used as lighting sources, allowing the design of MISO-VLC systems. To enhance the transmission capacity, different data should be simultaneously transmitted from each LED; however, that can lead to interference between adjacent LEDs. In that case, relatively low-received power signals are subjected to large interference because wireless optical systems generally use intensity modulation and direct detection. Thus, only the signal with the highest received power can be detected, while the other received signals cannot be detected. To solve this problem, we propose the ILIC scheme for MISO-VLC systems. The proposed scheme preferentially detects the highest received power signal, and this signal is referred as interference signal by an interference component generator. Then, relatively low-received power signal can be detected by cancelling the interference signal from the total received signals. Therefore, the performance of the proposed scheme can improve the total average bit error rate and throughput of a MISO-VLC system.

Performance Analysis of Cooperative Spectrum Sharing With Multiuser Two-Way Relaying Over Fading Channels

In this paper, we analyze the performance of an overlay multiuser two-way relay network with $N$ th-user selection by employing a three-phase cooperative spectrum sharing (3PCSS) scheme. Hereby, a one-end primary user (PU) communicates with the arbitrary (which may be the $N$ th best) selected other-end PUs with the cooperation of a secondary user (SU) in three transmission phases. By splitting up its available power, the SU assists in bidirectional primary transmissions and accesses the spectrum for its own transmission, based on satisfying the primary system outage constraint. Considering the involved $N$ th-order statistics with correlation, we derive the outage probability expressions for both primary and secondary systems over general fading channels. Based on these expressions, we compute the total system throughput of the 3PCSS scheme and compare it with other competitive schemes. We illustrate that the 3PCSS scheme can effectively realize spectrum sharing by harnessing additional cooperative diversity and achieving spectral efficiency at par with the primary two-phase direct transmission system. Numerical and simulation results substantiate our theoretical findings.

Joint Opportunistic Scheduling of Cellular and Device-to-Device Communications

The joint scheduling of cellular and D2D communications to share the same radio resource is a complex task. In one hand, D2D links provide very high throughputs. In the other hand, the intra-cell interference they cause impacts on the performance of cellular communications. Therefore, designing algorithms and mechanisms that allow an efficient reuse of resources by the D2D links with a reduced impact on cellular communications is a key problem. In general, traditional Radio Resource Management (RRM) schemes (D2D grouping and mode selection) focus on finding the most compatible D2D pair for an already scheduled cellular User Equipment (UE). However, such approach limits the number of possible combinations to form the group (composed by a cellular UE and a D2D pair) to be scheduled in the radio resource. To overcome that, in this work a unified Joint Opportunistic Scheduling (JOS) of cellular and D2D communications, which is able to improve the total system throughput by exploiting the spatial compatibility among cellular and D2D UEs, is proposed. But more complexity is brought to the scheduling problem. Thus, a low-complexity suboptimal heuristic Joint Opportunistic Assignment and Scheduling (JOAS) is also elaborated. Results show that it is possible to reduce the computational complexity but still improve the overall performance in terms of cellular fairness and total system throughput with less impact on cellular communications.

Balancing Interference and Delay in Heterogeneous Ad Hoc Networks With MIMO

Heterogeneous ad hoc networks with MIMO links can significantly improve transmission performance of the entire distributed wireless communication system. In this paper, we investigate how to increase total system throughput and decrease end-to-end delay with the help of heterogeneous characteristics of the ad hoc networks. Even if there are lots of references about distributed scheduling control considering multiple antennas, channel state, and so on, it still needs to be addressed how to guarantee destination to receive packets with a short delay. To resolve this issue, we first propose an interference-delay tradeoff method using convex optimization, which adjusts transmission rate and power to balance interference and delay. We then develop a speed power interference-based topology resource control algorithm with delay constraint to further adjust transmission power for reducing energy consumption. Simulation results show that the proposed algorithms can outperform the existing ones in terms of throughput, end-to-end delay, and power consumption.

A trophic model of the benthopelagic fauna distributed in the Santa Maria di Leuca cold-water coral province (Mediterranean Sea)

The benthopelagic fauna distributed in and around the Santa Maria di Leuca (SML) cold-water coral (CWC) province (Northern Ionian Sea–Central Mediterranean Sea) was analyzed through the development of a mass-balanced ecosystem model. A total of nine balanced simulations were provided taking into account the biomass data collected during several experimental bottom trawl surveys carried out from 2005 to 2010 in a depth range between 101 and 541 m. A total of 100 species were included in the analysis corresponding to 15 cephalopods, 25 crustaceans, 7 chondrichthyes and 54 osteichthyes. Simulations were developed maintaining the species-level detail. The total system throughput estimated in the SML CWC province trophic web resulted mainly due to consumption and about 80% of it was maintained by species with trophic level between 2 and 4. Results highlighted important features in terms of the structure and functioning of the system, such as the high level of activity maintained by intermediate trophic levels and the important role of top-down control in the faunal assemblage due to both vertebrate and invertebrate species.

A Fair Listen-Before-Talk Algorithm for Coexistence of LTE-U and WLAN

Recently, there has been an increasing interest in operating long-term evolution (LTE) in unlicensed bands (i.e., LTE-U). However, since LTE and wireless local area networks (WLANs) are designed to operate in different bands, they have no coexistence mechanism, which leads to significant performance degradation. In particular, since LTE does not sense channel vacancy prior to transmissions, the LTE interference severely affects the WLAN operation. To address this problem, we propose a fair listen-before-talk (F-LBT) algorithm for coexistence of LTE-U and WLAN in unlicensed bands. F-LBT jointly considers the total system throughput and the fairness between LTE-U and WLAN and then allocates an appropriate idle period for WLAN. Evaluation results demonstrate that F-LBT can improve the total system throughput while providing the fairness between LTE-U and WLAN.

A Space-Time Analysis of LTE and Wi-Fi Inter-Working

Cooperative inter-working of the long-term evolution (LTE) and the wireless fidelity (Wi-Fi) networks have drawn much attention recently, and several strategies have been proposed to enhance their network capacity. In this paper, we propose a new framework to analyze the network performance of several inter-working strategies for the LTE and the Wi-Fi. The proposed framework considers both the LTE and the Wi-Fi systems, both the downlink (DL) and the uplink (UL) transmissions, and the generated interference in both the time and the spatial domains. Based on such a framework, we theoretically analyze for the first time the performance of a Wi-Fi network, taking into account the intra-cell time efficiency and the signal and inter-cell interference with spatial randomness. Moreover, we study the performance of: 1) a coexisting architecture where Wi-Fi coexists with an ideal carrier sense multiple access (CSMA) duplex system, which represents an upper bound performance for the LTE Release 14 licensed assisted access network and 2) a brand-new architecture that allows UL on LTE and DL on Wi-Fi, referred to as the Boost architecture. We derive analytical results for both the DL and the UL network performances in terms of the signal quality distribution and the total area system throughput (AST) in these two architectures, and quantify their performance gain compared with the traditional disjoint LTE Wi-Fi architecture. Simulation results validate our analysis results, and show that, in a typical outdoor scenario, the coexisting architecture and the Boost architecture can, respectively, increase the total AST up to 11% and 25%, compared with the traditional disjoint LTE Wi-Fi.

Exploring the structural and functional properties of the Lake Victoria food web, and the role of fisheries, using a mass balance model

Human and environmental factors have greatly challenged Lake Victoria ecosystem, especially in the last four decades. However, the lake continues to support the World's largest freshwater fishery, currently producing ca. one million tons of fish per year and directly supporting livelihoods of ca. four million people in three riparian countries. We used the Ecopath component of Ecopath with Ecosim modelling software to re-parameterise two existing mass balance models to reflect ecosystem state of Winam Gulf in 1971–1972 and 1985–1986, and construct a new model for the whole lake to reflect ecosystem state in 2014. The aim was to understand the structural and functional properties of Lake Victoria food web and the role of fisheries on the ecosystem. We found a decrease over time in productivity in relation with biomass and respiration, and food web connectivity, and an increase in biomass cycling. The total system throughput, decreased fivefold between 1971 and 1972 and 1985–1986, but was slightly higher in 2014 with a moderate shift from herbivory to detritivory. The implication of these changes on system maturity and resilience are discussed. The trophic level of catches increased between 1971 and 1972 and 1985–1986 due addition of high trophic level catches from the introduced piscivorous Nile perch (Lates niloticus) i.e. “fishing up”. However, the decline in trophic level of catches between 1985 and 1986 and 2014 seems to have been due to sequential addition of low trophic level catches, especially from the native Silver cyprinid (Rastrineobola argentea), a phenomenon termed “fishing through”, as opposed to a decline of high trophic level catches (or “fishing down”). Currently, exploitation is unbalanced and skewed to the least productive species at higher trophic level, with significantly less fishing occurring at the most productive species at lower trophic level, and the causes are discussed.

Towards a sounder interpretation of entropy-based indicators in ecological network analysis

Various indicators rooted in the concepts of information and entropy have been proposed to be used for ecological network analysis. They are theoretically well grounded and widely used in the literature, but have always been difficult to interpret due to an apparent lack of strict relations with node and link weight. We generated several sets of 10,000 networks in order to explore such relations and work towards a sounder interpretation. The indices we explored are based on network composition (i.e., type and importance of network compartments), or network flows (i.e., type and importance of flows among compartments), including Structural Information (SI), Total System Throughput (TST), Average Mutual Information (AMI), Flow Diversity (H), and Ascendency (ASC). A correlation analysis revealed a lack of strict relationships among the responses of the investigated indicators within the simulated space of variability of the networks. However, fairly coherent patterns of response were revealed when networks were sorted by following a “bottom-up” criterion, i.e. by increasing the dominance of the large-sized top predator in the network. This ranking is reminiscent of ecosystem succession, along which the prominence of higher trophic level organisms progressively increases. In particular, the results show that a simple increase in organisms having large size and low consumption rates is potentially able to simultaneously lead to an increase of different types of information (as SI, H and AMI), thus also emphasizing the importance of bionomic traits related to body size in affecting information-related properties in a trophically connected community. The observed trends suffer from a certain dispersion of data, which was diminished by imposing specific and ecologically meaningful constraints, such as mass balancing and restriction to certain range of the ratio A/C, an index related to the viability of ecological networks. These results suggest that the identification of a set of effective constraints may help to identify improved conditions for applicability of the investigated flow-based indicators, and also provide indication on how to normalise them with respect to meaningful network properties or reference states. Thus, in order to increase confidence in the derived network metrics describing a particular ecosystem state, and thus increase their applicability, it is advisable to construct replicate networks by taking the variability of input data into account, and by applying uncertainty and sensitivity analyses.

Cognitive spectrum management in dynamic cellular environments: A case-based Q-learning approach

This paper examines how novel cellular system architectures and intelligent spectrum management techniques can be used to play a key role in accommodating the exponentially increasing demand for mobile data capacity in the near future. A significant challenge faced by the artificial intelligence methods applied to such flexible wireless communication systems is their dynamic nature, e.g. network topologies that change over time. This paper proposes an intelligent case-based Q-learning method for dynamic spectrum access (DSA) which improves and stabilises the performance of cognitive cellular systems with dynamic topologies. The proposed approach is the combination of classical distributed Q-learning and a novel implementation of case-based reasoning which aims to facilitate a number of learning processes running in parallel. Large scale simulations of a stadium small cell network show that the proposed case-based Q-learning approach achieves a consistent improvement in the system quality of service (QoS) under dynamic and asymmetric network topology and traffic load conditions. Simulations of a secondary spectrum sharing scenario show that the cognitive cellular system that employs the proposed case-based Q-learning DSA scheme is able to accommodate a 28-fold increase in the total primary and secondary system throughput, but with no need for additional spectrum and with no degradation in the primary user QoS.

Construction and analysis of the EWE model of the wetland ecosystem in lake buffering zone of Zhushan Bay, China.

Lake buffering zones play a special role in spatial arrangement of the lake watershed, and the wetland in buffering zones also is of great significance in basin ecological health and lake water environmental quality. Taking Zhushanhu wetland ecosystem in the area of lake buffering zone of Zhushan Bay, Lake Taihu as the research object, the biotic components were divided into 16 functional groups to construct the Ecopath with Ecosim (EWE) model, and the characteristics and state of the ecosystem and the interrelation between the functional groups were analyzed. The results showed that the range of effective trophic level in Zhushanhu wetland ecosystem was 1-3.72, tro-phic flows were mainly concentrated in the first 4 trophic levels, and most of the food chains started from submerged plants and detritus. The total energy conversion efficiency of the wetland ecosystem was 5.1%, being lower than the "1/10 law", indicating that the current energy conversion efficiency was low. The average transmission efficiency of material throughput in the ecosystem was 4.3%. The sum of all production in the ecosystem was 2496.66 t·km-2·a-1, and the total system throughput was 10145.2 t·km-2·a-1. The characteristic parameters of ecosystem showed that the current ecosystem was at the immature stage.

Optimal Channel and Relay Assignment in Ofdmbased Multi-Relay Multi-Pair Two-Way Communication Networks

The aim of the paper lies in maximizing the system total throughput by optimally coordinating the relay and subcarrier assignment among the multiple pairs of two-way users .In this Paper, consider an OFDM-based network where multiple relays help multiple pairs of source nodes to conduct Bidirectional communications.. The joint optimization problem of subcarrier pairing based subcarrier assignment and relay selection for multiple two-way users is considered as a combinatorial optimization problem. Hence graph based approach is implemented to establish the equivalence between the proposed problem and a maximum weighted bipartite matching (MWBM) problem. Then the problem is solved by the corresponding graph based algorithm optimally in polynomial time

A novel resource allocation algorithm based on downlink and uplink decouple access scheme in heterogeneous networks

Traditional cellular network requires that a user equipment (UE) should associate to the same base station (BS) in both the downlink (DL) and the uplink (UL). Based on dual connectivity (DC) introduced in LTE-Advanced R12, DL/UL decouple access scheme has been proposed, which is especially suitable for heterogeneous networks (HetNets). This paper is the pioneer to take the DL/UL decouple access scheme into consideration and develop a novel resource allocation algorithm in a two-tier HetNet to improve the total system throughput in the UL and ease the load imbalance between macro base stations (MBSs) and pico base stations (PBSs). A model is formulated as a nonlinear integer programming, and the proposed algorithm is a sub-optimal algorithm based on the graph theory. First, an undirected and weighted interference graph is obtained. Next, the users are grouped to let users with large mutual interferences to be assigned to different clusters. Then, the users in different clusters are allocated to different resource blocks (RBs) by using the Hungarian algorithm. Simulation results show that the proposed algorithm can provide great promotions for both the total system throughput and the average cell edge user throughput and successfully ease the load imbalance between MBSs and PBSs.

Assessment of long-term changes of ecosystem indexes in Tongoy Bay (SE Pacific coast): Based on trophic network analysis

Quantitative macroscopic's indexes have been used to compare three trophic models of the exploited benthic ecosystem of Tongoy Bay. In this system the primary productivity and benthic invertebrates are more important in the cycling of biomass. The models were built with a similar number of compartments for the years 1992, 2002 and 2012, using Ecopath with Ecosim (EwE). Odum and Ulanowicz's frameworks and ecological network analysis were then used to estimate the levels of maturity, growth and development of the system. Likewise, “keystoneness” indexes – at each time – were also estimated for the models. Our results show that Tongoy Bay exhibited an increase in maturity and development (“health”) in 2012 compared to past conditions, which was reflected by (1) an increase in the total system biomass, total system throughput, AMI, and absolute Ascendency, (2) higher flow and increased efficiency of transferred energy and its proportion at higher trophic levels, (3) an increase of recycling (FCI), (4) a reduction of NPP/R and NPP/B ratios of the system, and (5) an increase in the number of compartments trophically linked that comprise the keystone species complex. We argue that these results are a consequence of reduced fishing pressure on this benthic system in recent years. This study shows that the fishing would not only have a direct impact on exploited species, but would also affect the structure and functioning of the ecosystem. The information obtained could help to improve the management of fisheries resources, evaluating surveillance indicators that can show the putative changes of intervened ecosystems.

An Ecosystem Approach for understanding status and changes of Nador lagoon (Morocco): application of food web models and ecosystem indices

The work applies food web models to the Lagoon of Nador (Morocco) and subsequently estimates ecosystem indices. This effort supports the evaluation of the ecosystem status and the implementation of the Ecosystem Approach (EcAp), endorsed by the contracting parties of the Barcelona Convention for the Mediterranean Sea. The Lagoon of Nador, on the Mediterranean coast of Morocco, suffered from eutrophication during recent decades. We used indices derived from Ecological Network Analysis for investigating the most relevant features of ecosystem functioning in the decade 2000−2010 (present scenario), and comparing them with those of the 1980s (past scenario). As the Lagoon includes different habitats, the methodology was applied to each of them, in order to assess their contribution to the functioning of the whole ecosystem. Results highlighted an increase in Total System Throughput (TST) in the present scenario when compared with the past one, also associated to an increase of Total Respiration (TR) and of the ratio between Total Primary Production and Total Respiration (TPP/TR). Under the present scenario Nador lagoon shows a decreased cycling efficiency. The sensitivity analysis highlighted the capability of TST and Comprehensive Cycling Index (CCI) in detecting changes, in agreement with other recent studies on responses of food web functioning to eutrophication. The results are discussed in respect to three specific aspects, related with the application of food Web Models and Ecological Network Analysis in the EcAp context: i) data availability; ii) spatialization of indicators; iii) selected set of indicators. The results also highlight the important role of sensitivity/uncertainty analysis when implementing food web models in data-scarce systems.

Trophic models and short-term simulations for the coral reefs of Cayos Cochinos and Media Luna (Honduras): a comparative network analysis, ecosystem development, resilience, and fishery

We analyzed the trophic functioning of two Caribbean coral reefs with different disturbances, comparing their biomass flows, ecosystem development, and resilience. Cayos Cochinos is a protected reef impacted by tourism, artisanal fisheries, and continental river discharges, while Media Luna is an isolated reef located near to a lobster industrial fishery zone. Ecopath models were built to (1) estimate the ecosystem status-related properties; (2) evaluate the system recovery time; and (3) assess the fishery effects on species and functional groups. Our results indicate that the biomass of both systems is dominated by macroalgae (>75%), mainly at Cayos Cochinos that exhibit greater total system throughput. We show that the harvest of herbivores and coastal eutrophication causes increase in macroalgal biomass. The Media Luna ecosystem appears to be more mature and organized (Pp/R = 1.6, FCI = 6.95%), but is also less resistant to fishery impact (SRT = 10.79 and 21.72 years using bottom-up and top-down flow-control mechanisms, respectively) than Cayos Cochinos (SRT = 9.30 and 16.89). The benthic autotrophs, phytoplankton, and soft corals are the most important functional groups to the trophic functioning, resilience, and development of these ecosystems. However, fishery simulations also show that snappers and spiny lobster reduce the resilience of Cayos Cochinos and Media Luna, respectively.

Optimizing CMT performance by joint predictions of bandwidth and RTT

CMT uses the stream control transmission protocol's (SCTPs) multihoming feature to distribute data across multiple end-to-end paths in a multihomed SCTP association. As the disparity of multipaths, it is facing a great challenge to solve the disorder of the received data packets. To lighten the reordering degree and then to improve the throughput performance, we need to estimate the real-time paths' bandwidth and round trip time (RTT) as exactly as possible. In this paper, we use the extended vector (ext-vec) Kalman filter (KF) to predict the available bandwidth and RTT of each path simultaneously. Based on this, we propose a predictive path selection algorithm for CMT in SCTP. To simulate and compare the algorithms' performance, two kinds of scenarios, bandwidth sensitive scenario and time and bandwidth sensitive scenario, are built and NS-2 is used. The simulation results show that the path selection algorithm can lessen the data packets disordering by correctly predicting each path's bandwidth and RTT in real time. Comparing the existing algorithms, the algorithm can converge more quickly and can improve the system total throughput in a certain extent in bandwidth sensitive scenario. To time and bandwidth sensitive scenario, it can greatly improve the convergence speed and total throughput.

Bitcoin Market Return and Volatility Forecasting Using Transaction Network Flow Properties

Bitcoin, as the foundation for a secure electronic payment system, has drawn broad interests from researchers in recent years. In this paper, we analyze a comprehensive Bitcoin transaction dataset and investigate the interrelationship between the flow of Bitcoin transactions and its price movement. Using network theory, we examine a few complexity measures of the Bitcoin transaction flow networks, and we model the joint dynamic relationship between these complexity measures and Bitcoin market variables such as returns and volatility. We find that complexity of Bitcoin transaction network is significantly correlated with Bitcoin market volatility. More specifically we document that the popularity of Bitcoin gauged from total system throughput can significantly improve the predictability of Bitcoin market returns and volatility using network flow complexity measures.

Comparing trophic structure of a subtropical bay as estimated from mass-balance food web model and stable isotope analysis

The trophic structure of a subtropical bay in Taiwan Strait was analyzed by using two methods: mass balance modeling (Ecopath) and stable isotopic analysis (SIA). Trophic levels (TLs) of main functional groups estimated from the two methods were compared. The Ecopath model was built based on the fishery resource survey in Xiamen Bay in 2009. Specifically, data on species composition, biomass, mortality rates, diet composition and fisheries catches were obtained from the survey in and around the bay. The model consisted of 26 functional groups, including plankton, benthos, fish, cephalopods, shrimps, crabs and marine mammals. TLs of the main functional groups were estimated to be between 2.89 (cephalopods) and 3.94 (congers), with an average of 3.11. Trophic transfer efficiencies from levels II to V were 12.8%, 19.2%, 19.7% and 12.1%, respectively. Catfish (Tachysurus sinensis and Netuma thalassina) and the fisheries have major trophic impacts on most functional groups in the Xiamen Bay ecosystem. Total system throughput was estimated to be 411tkm−2year−1. TLs derived from isotopic analysis were highly correlated with those estimated from Ecopath (Linear regression: R2=0.696, n=23, p<0.001). On an average, Ecopath underestimated TLs of the functional groups by about 12.2% compared to those estimated from SIA, with TLs from Ecopath being slightly higher at low TLs and lower at high TLs. This studies support value of using both stable isotopes and Ecopath methods to analyze this food web.