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One approach to improve network capacity in future wireless networks is to deploy access points (APs) in a dense manner and employ a controller to manage these APs. Another innovation is to equip nodes with an in-band full-duplex (IBFD) radio, which allows them to transmit and receive simultaneously over the same frequency band. A key challenge, however, is interference. To this end, a link scheduler plays a critical role in ensuring the benefits of dense APs deployment and IBFD are not negated by severe interference. Henceforth, this paper proposes three centralized algorithms that aim to drain a given set of packets from links in minimum time. We have compared these algorithms against a schedule, where links transmit independently, and an algorithm that schedules links at slot boundaries. We studied the impact of varying node densities, transmission power, and signal-to-interference-plus-noise ratio thresholds on the link schedule. Our results show the overall completion time can be reduced by 68% as compared to scheduling links individually. Moreover, our algorithms reduce the completion time by 13% as compared to scheduling links on a slot-by-slot basis.

This paper considers the problem of deriving a time-division multiple-access (TDMA) schedule for multi-hop wireless networks that allow nodes to perform multiple transmissions/receptions to/from all of their neighbors simultaneously over the same frequency. To date, there are a number of link schedulers for the networks in question but they do not consider flow rate or any notion of fairness when deriving a TDMA schedule. Henceforth, we address this critical gap by proposing a link scheduler, called Algo-Fair, that, in addition to maximizing the number of links in each slot, also provides fairness among flows. In addition, it uses a novel augmentation step to distribute spare capacity fairly among flows. We believe this step is general and can be applied readily in other forms of wireless networks. Apart from that, Algo-Fair generates a schedule directly while yielding a fair rate allocation. This is different from existing methods that first use a flow contention graph to compute a fair share before deriving the corresponding schedule, which may not exist. Numerical results show Algo-Fair has higher fairness, minimum rate, and average total throughput than competing approaches, and low end-to-end delay.

Cube satellites, aka CubeSats, are a class of tiny satellites that have become popular for space programs. This is because they can be built relatively cheaply using commercial off-the-shelf components. Moreover, CubeSats can communicate with each other, and assemble into swarms to carry out different functions: e.g., wide area measurements and sensing. Swarms of CubeSats also have the effect of increasing the contact period with ground stations allowing for a longer communications window. These capabilities require CubeSats to be equipped with an efficient, high gain, small antenna to facilitate cross-link or inter-satellite communications. Henceforth, this paper presents a high gain coplanar waveguide (CPW)–fed slot antenna for CubeSats. A key feature is the use of a metasurface superstrate structure (MSS) to significantly improve gain and reduce back-lobe emissions. This also has the advantage of minimizing interference to components inside a CubeSat. We have comprehensively evaluated the antenna using the high-frequency simulator structure (HFSS) as well as a carrying out testing on a 3 U (10 × 10 × 30 cm3) CubeSat platform. We have studied the effect of MSS element sets and their position and the effect of a 3-U CubeSat body on the performance of the proposed antenna. The experimental results confirm that our antenna achieves a return loss of 21.5 dB and a fractional impedance bandwidth (BW) of 55.91% with S11 ≤ 10 dB and has a simulated and measured gains of 9.71 and 8.8 dBi respectively at the desired frequency of 2.45 GHz. In contrast, amongst all previous S-band planar antennas that are suitable for CubeSats, the best gain is only 5.96 dB at 2.45 GHz.

This paper studies the suitability of shorted patch and CPW-feed square slot antennas for CubeSat communications. To study the effect of the CubeSat body on the antennas performance, we have simulated both antennas in the High Frequency Structure Simulator (HFSS) with and without the CubeSat body. Compared to CPW- feed square slot antenna, the shorted patch antenna achieves higher gain and wider bandwidth. We have also re-dimensioned both antennas to shift their resonant frequencies to 2.45 GHz using Quasi Newton method in HFSS. This thus enables their use in the unlicensed ISM band. The repurposed shorted patch has smaller return loss; e.g., -27.5 dB (without CubeSat), higher gain; e.g., 5.3 dBi and wider bandwidth than the repurposed CPW-feed Square slot antenna. Lastly, further enhancement in the gain of re-dimensioned CPW-feed square slot antenna shows an increase of total gain from 2 to 2.52 dB.

The demand for bandwidth by multimedia applications remains unabated. This is particular critical given the growing number of devices with WiFi capability, and the ubiquity of Wireless Local Area Networks (WLANs). These trends have spurred researchers to develop low-cost and backward compatible solutions to increase the capacity of WLANs. One approach is to deploy additional Access Points (APs), and strategies to manage channel, user, and transmit power. As a result, stations are likely to be near one or more APs, and therefore are more likely to experience high data rates. In this paper, we take advantage of this fact to increase the capacity of a dense WLAN further by transmitting packets to a station via a neighboring AP if its associated AP is occupied by another station. Our approach is novel as prior works have not exploited the density and diversity of APs when scheduling downstream traffic. From extensive simulation studies, we show its viability in varying traffic scenarios, and in particular, WLANs with a high number of APs.s.

This paper considers the problem of deriving a Time Division Multiple Access (TDMA) link schedule for a single-channel, Multi-Transmit or Receive (MTR) Wireless Mesh Network (WMN). This problem is significant because a short schedule means the WMN has a higher network capacity. We first show that an existing solution, called Directed Edge Coloring (DEC), to channel assignment developed for WMNs with multiple transmit and receive capability is isomorphic to a TDMA schedule. This allows us to develop an efficient algorithm called DEC-MTR that derives a TDMA schedule or superframe for use in single-channel MTR WMNs. In addition, we propose a method to increase the number of links activated in each slot. We compare DEC-MTR against four state-of-the-art schedulers: DEC, Algo-1, HWF and MDF. Experiment results show that DEC-MTR produces equal superframe lengths with up to 23% higher capacity as compared to DEC, and up to 50% shorter superframe lengths as compared to Algo-1, HWF, and MDF with up to 58% higher capacity.

This paper addresses an NP-hard problem, called NTD-CB/R, whose solution is of importance to applications requiring one or more Quality of Service (QoS). Specifically, the problem calls for a network topology that meets two objectives, i.e., minimal cost and maximum bandwidth, subject to a predefined (s, t) reliability constraint. We approach the problem by converting it into one with a single objective. This is achieved via a ratio, called bc r , between network bandwidth and cost to measure the goodness of each topology, and by applying Lagrange relaxation. Then we propose a dynamic programming (DP) scheme, and propose a heuristic solution, called DPCB/R, to generate each topology using all of its n (s, t) paths. This paper also proposes three heuristic path orders that allow DPCB/R to generate and use only k≤n paths to reduce its time complexity while producing similar results. Extensive simulations using 125 benchmark networks with various sizes show the merits of the path-orders, and effectiveness of our approach. DPCB/R is able to generate 88% optimal results for the networks. Further, its non-optimal results have a bc r ratio, bandwidth, and cost of only up to 1.56%, 0.9%, and, 2.1% off from the optimal, respectively. Further, for a grid network that contains 299 paths it uses only 1.1−27% of the paths while producing a topology that is only 0.92% off from optimal, with respect to bc r metric.

The performance anomaly experienced by nodes in multi-rate wireless local area networks (WLANs) leads to low throughput and unfairness. To this end, we propose a distributed, token-based approach that allows applications to control nodes channel occupancy time via a single tuning knob. Our approach makes use of local information extensively and does not require any modifications to the IEEE 802.11 MAC nor require explicit signaling. Simulation results show our approach to be effective in ensuring fairness, and isolating high and low rate flows.

Dynamic framed slotted Aloha (DFSA) based tag reading protocols rely on a tag estimation function to calculate the best frame size to use for a given tag set. An inaccurate estimate results in high identification delays and unnecessary energy wastage. This is particularly serious when DFSA based tag reading protocols are used in RFID-enhanced wireless sensor networks (WSNs), where nodes are battery constrained. To this end, this paper presents qualitative and quantitative analysis of five tag estimation functions using Monte Carlo simulations. We iteratively estimate a given set of tags and evaluate the mean error, variability, skew and Kurtosis of each function's error distribution. Lastly, we compare and identify the most efficient tag estimation function that is suitable for RFID-enhanced WSNs.

This paper studies the characteristics of border gateway protocol (BGP) routes. In particular, it identifies autonomous systems (ASs) that appear frequently in path vectors. In addition, it analyzes path vector lengths. Finally, it investigates the prevalence of inflated paths, commonly used by ASs for traffic engineering purposes.

Multihop transmissions over wireless mesh networks present limited end-to-end (E2E) data rates, as every hop waits for an entire packet to arrive before starting retransmission. That is, the E2E data rate drops when every hop stores and then forwards packets, thus making such transmissions unsuitable for multimedia applications. In this work, in order to increase data rates, we present an ultra-wideband (UWB) radio transceiver capable of concurrently transmit and receive (cTxRx) packets. However, concurrently receiving and transmitting comes at the cost of a channel model with increased interference level. Herein, we explain a new interference model and propose a transceiver that compensates for it. We describe the transceiver mathematically and analyze its performance via simulations. Also, we demonstrate that the E2E data rate exceeds that of current multihop transmissions, thus allowing multimedia traffic to be transmitted over a multi-hop wireless mesh network.

This paper presents an analysis of MANET routing protocols' behavior in realistic channel fading scenarios. The motivation of this study was due to our previous testbed experimentations where we found that AODV and DSDV's performance did not match simulation results, primarily due to the use of a simple radio propagation model that did not take into account transient links caused by small-scale fading. Henceforth, we extended the ns-2 simulator with a realistic radio propagation model, that incorporated Rayleigh fading, to gain insights into the impact of transient links on AODV, DSR, and DSDVs behaviour. Our simulation studies explain each protocol's key behavior that leads to the following conclusions: (1) routing through stable routes is important, (2) hop count is the root cause of poor performance, (3) the 2-ray ground radio propagation model is inappropriate for simulating ad-hoc protocols in indoor environments, and (4) local recovery is important

Inverse Kinematics (IK) calculates internal joint angles for a kinematic chain given constraints on the end-effector. This study evaluates the advantages and limitations of algebraic, geometric, and iterative IK solutions reported in the literature. This analysis is used to develop a solution for animating arbitrary articulated structures such as robots and humans. For iterative solutions, various minimization and root finding algorithms described in the literature are compared through the analysis of experimental results. The minimization algorithm of Broyden et al. (1987) is shown to converge quickly using a small number of objective function evaluations, making it the best method for solving IK systems of those considered in this study. This observation has led to a generalized IK solution for actuators with N Degrees of Freedom, extending the work of Goldenberg and Lawrence (1985), Goldenberg et al. (1985), and Sasaki (1994) by considering additional minimization and root-finding algorithms. It is indicated that the new generalized IK solution will enhance the visual analysis of human joint range and ergonometric studies, provide the foundation for new interactive tools to teach functional anatomy, and enhance virtual environments which require realistic interactive human animation.

The IEEE 802.15.3 MAC enables high-rate communications between devices in a wireless personal area network and has good support for applications requiring quality of service (QoS). To meet applications' QoS requirements, such as delay and jitter, the channel time allocation (CTA) scheduler plays an important role in sizing and positioning CTAs within each super-frame. In this paper, we first present a novel CTA sharing protocol, called VBR-MCTA that enables the sharing of CTAs belonging to streams with the same group identity. This allows our protocol to exploit the statistical characteristics of variable bit rate (VBR) streams by giving unused time units to a How that requires peak rate allocation. We then present two optimizations to VBR-MCTA, namely VBR-Blind and VBR-TokenBus. The former, by giving ownership of a CTA in a round-robin manner without consideration to traffic profiles, does not consume any valuable "air-time" with signaling overheads. The latter allows a CTA to be shared by multiple devices that take turns owning unused "air-time" from CTAs. We have simulated VBR-MCTA and its optimizations in the ns-2 simulator over an implementation of the IEEE 802.15.3 MAC. Our results show that VBR-TokenBus has the best delay and jitter as it provides a one to six milliseconds reduction in both compared to standard CTA methods. VSR-Blind, although having performing poorer than MCTA-Token or VBR-MCTA, is still significantly better than traditional CTA methods at a reduced overhead.