In this paper, we demonstrate the suitability of the super-regenerative receiver in OFDM communication. The wellknown property of super-regenerative oscillators to preserve the amplitude and phase information is exploited to detect the OFDM symbols. A new super-regenerative architecture is presented that makes use of both an envelope detector and a phase detector connected at the output of the superregenerative oscillator. The peak-amplitude and phase samples of the generated RF pulses feed the digital processing blocks to extract the data. Through proof-of-concept simulations of a four-subcarrier QPSK OFDM modulation in the 2.4 GHz ISM band, we validate our proposed approach. This study paves the way to the use of low-power, low-cost super-regenerative receivers for widely-employed OFDM modulations.

3GPP standards organization is performing an impressive effort trying to reach sub-millisecond latencies for 5G. However, such efforts may become fruitless if exogenously generated delays at transport layer are not considered. Nowadays, Radio Access Networks (RANs) are deployed with large buffers to achieve full utilization and avoid squandering wireless resources. Unfortunately, and since the data path’s bottleneck resides on the radio link, RAN’s buffers are bloated by TCP’s congestion control algorithm. Thus, a flow with low-latency requirements that encounters a bloated buffer, suffers from inevitable large sojourn times associated with the buffer depletion time, severely downgrading its Quality of Service (QoS). This paper presents different solutions for efficiently multiplexing distinct traffic patterns that share buffers on the 5G stack. Bufferbloat is extensively studied within the actual 5G QoS scenario, which presents multiple challenges inherited from the dynamic radio link nature and the presence of multiple queues at different entities. We propose and extensively emulate different algorithms in order to avoid the exogenous delay caused by the bufferbloat phenomena. We use real cellular network traces with realistic delay-sensitive and background traffic patterns in different scenarios. The outcome presents valuable insights in the algorithms that will enable low-latency services to be delivered through the 5G network stack satisfying restrictive envisioned constraints.

Dense deployments of small cells (SCs) are key to fulfill the capacity requirements of future 5G networks. However, two roadblocks to the adoption of SCs are: 1) the limited availability and the cost of sites with wired backhaul resources and 2) the complexity to manage a dense deployment of wireless backhaul nodes. Towards these challenges we propose SODALITE, a novel system that applies software-defined networking (SDN) to a wireless backhaul network. We present, how SODALITE can be integrated to 3GPP's 4G and 5G architectures, and show the feasibility of SODALITE through LTE network testbed experiments. We substantiate the scalability of SODALITE through stochastic studies using real-life traffic traces from an LTE network and discuss the effects of cell densification and 5G system architecture on these studies. Further, a reliable backhauling solution for wireless links is introduced in SODALITE through SDN-enabled mechanisms that are capable of reconfiguring the data plane upon a link failure detection. Its reliability is shown through experiments on an LTE network testbed, and studied thoroughly via rigorous simulations and network emulator evaluations. As a result, we claim that SODALITE is a promising carrier-grade system to manage a wireless SC backhaul.

Due to the fast growing of data consumed in mobile devices through cellular networks, solutions that provide higher data rates are an important target for the mobile networking community. One such solution is the aggregation of mobile technologies (most commonly LTE) with wireless LAN solutions (most commonly Wi-Fi). Seeing its potential impact, 3GPP has devised the LTE/Wi-Fi Aggregation (LWA) specification, which defines a tight coupling between eNBs and Wi-Fi Access Points (APs). In this paper, we implement and evaluate an LWA solution, and compare its performance to the one for full offloading (only Wi-Fi) and no offloading (only LTE) through physical experimentation. The developed prototype LWA solution is based on open source and commodity hardware, which promises a low-cost and easily implementable LWA solution. Aggregation and offloading process are managed by the eNB, therefore, the core network remains intact without any modification. Physical experiments are done to detail the network performances for all these three policies for TCP and UDP traffic and both for uplink and downlink connections. In TCP transmissions with LWA policy, the different delays between Wi-Fi and LTE links causes the performance degradation because of the out-of-order arrivals of the segments. For this, we evaluate a solution where an artificial delay is added to reduce the number of out-of-order packets.

Mobility management is a critical component for any new wireless standard to be ubiquitous. While 4G-LTE and prior wireless standards utilized vendor specific hardware and software on which mobility management (MM) functionality was implemented, recent 5G architecture releases by 3GPP indicate a complete departure from the same. 3GPP in release 14 and the upcoming release 15 has stressed upon the utilization of Software Defined Networking (SDN) and Network Function Virtualization (NFV) as the drivers of 5G technology. Consequently, new challenges related to MM and specifically handover management will be encountered owing to the inter-working setup between the 5G Next-Gen Core (NGC) and the Evolved Packet System (EPS) core. In this paper, we exploit the SDN to enhance the signaling of the HO methods proposed by 3GPP. Although the proposed approach can be applied to any HO method, in this paper we specifically evaluate the scenario wherein a dedicated interface between the Mobility Management Entity (MME) in the EPC and the Access and Mobility management Function (AMF) in the 5G NGC, i.e., N26 as specified by 3GPP, is non-existent. Such a scenario is reasonable during the initial deployment phases of 5G networks. We show that the proposed mechanism is efficient as compared to the 3GPP handover strategy in terms of latency, transmission and processing costs.

The future wireless networks are expected to be extremely dense and heterogeneous, with the users experiencing multi-connectivity through the multiple available radio access technologies (RATs). These prevalent characteristics, along with the strict QoS requirements, renders the handover (HO) process optimization as a critical objective for future networks. Along side the evolving network characteristics and methodologies, an evolving network architecture needs to be considered as well. Such evolution should not only facilitate HO process enhancement, i.e., reduction in HO delay and signaling, but it should also allow for a smooth transition from current to future wireless networks. Hence, in this work we firstly present an evolutionary core network entity called the Integrated MME-SDN Controller and the associated network architecture. The proposed architecture provides a migratory path for the existing 3GPP cellular architectures towards the 5G networks. Next, we discuss the benefits and challenges of such an architectural approach, with one of the benefits being a manageable CAPEX for the network operators through its transitional nature. Subsequently, utilizing the aforementioned proposed architecture, we present the handover process enhancement for the current 3GPP defined HO processes. We quantify the improvements achieved in terms of latency, transmission and processing cost for the different 3GPP HO processes. We also show that the proposed HO mechanism leads to a significant reduction in latency and signaling for certain types of HOs which, as a consequence, will critically benefit any dense and heterogeneous wireless system, such as 5G.

Long Term Evolution (LTE) is projected to be the mostly used mobile technology before 2020, thanks to the high data rates, all IP-based and simplified architecture it brings compared to previous mobile network technologies. To address the exponential data requirements of the future, a targeted solution for LTE is network densification, i.e., deploying small cells (cells with reduced radius compared to macro cells), which will enable better frequency reuse. However, a challenge here is the backhauling of the evolved-NodeBs (eNBs) used for small cells, since the fiber-based backhauling is costly and is not always feasible given the physical environment. For this, a recent idea is to use LTE self-backhauling, where an eNB can relay its data to another eNB through the use of LTE technology. In this paper, we develop and evaluate an implementation of LTE Self-Backhauling building on an open-source software and commodity hardware (specifically, regular PCs and low-cost software-defined radios) for the LTE system. For this, we implement a self-backhauled eNodeB, which connects to another eNB through an LTE connection. Through physical experimentation using off-the-shelf user equipments (UEs), we show that the method proposed is viable and can improve the network coverage and the throughput of the network.

The Education Roaming (eduroam) is a widely spread federation of Wi-Fi networks that allows users to freely roam between providers. The key to eduroam's massive adoption has been the fact that a single global network identifier is used across all the federated Wi-Fi networks. However, when multiple eduroam networks are deployed in an overlapping geographical area, the current design may cause client devices to inadvertently roam between providers, hence potentially disrupting applications and hindering network planning. In this paper we study how virtual Access Points (vAPs) can be used to address the inter-domain mobility problem in eduroam. Our main contribution is a novel mechanism to steer clients across vAPs, which mitigates unintended handovers. The proposed extensions have been validated experimentally considering a wide range of commercial Wi-Fi clients available in the market.

The use of Visible Light Communication (VLC) in wake-up communication systems is a potential energy-efficient and low-cost solution for wireless communication of consumer electronics. In this paper, we go one step further and propose the use of visible light both for wake-up communication and energy harvesting purposes, with the final objective of an energy-autonomous wake-up receiver module. We first present the details and the design criteria of this novel system. We then present the results of evaluation of design criteria such as solar panel and capacitor type choices. To evaluate the performance of the developed wake-up system with energy-autonomous receiver system, we perform realistic indoor scenario tests, analyzing the effect of varying distances, angles, and light intensities as well as the effect of presence of interfering lights.

The demand for electrical power is growing tremendously, which poses grand challenges to modern energy systems. The telecommunications industry takes a significant part in the global power consumption. In this work we introduce the multi-beam zooming concept as a new perspective to the energy-efficient 5G network, where the multi-beam zooming technique incorporates the beam zooming and multi-beam beamforming methods. This approach enables multiple beams to be casted on different users with adjustable amplitudes of individual beams based on user locations obtained using PRS in LTE. We developed an LTE simulation framework to quantitatively evaluate the advantages of the multi-beam zooming approach in terms of the power savings. Using the realistic mobility traces, we analyze the effect of crucial system setting of antenna tapering method and its effect on the potential power savings achievable at the base stations.

Duty-cycled Medium Access Control (MAC) protocols certainly improve the energy efficiency of wireless networks. However, most of these protocols still suffer from severe degrees of overhearing and idle listening. These two issues prevent optimum energy usage, a crucial aspect in energy-constrained wireless networks such as wireless sensor networks (WSNs). Wake-up radio (WuR) systems drastically reduce these problems by completely switching off the nodes' microcontroller unit (MCU) and main radio transceiver until a secondary, extremely low-power receiver is triggered by a particular wireless transmission, the so called wake-up call. Unfortunately, most WuR studies focus on theoretical platforms and/or custom-built simulators. Both these factors reduce the associated usefulness of the obtained results. In this paper, we model and simulate a real, recent, and promising WuR hardware platform developed by the authors. The simulation model uses time and energy consumption values obtained in the laboratory and does not rely on custom-built simulation engines, but rather on the OMNET++ simulator. The performance of the WuR platform is compared to four of the most well-known and widely employed MAC protocols for WSN under three real-world network deployments. The paper demonstrates how the use of our WuR platform presents numerous benefits in several areas, from energy efficiency and latency to packet delivery ratio and applicability, and provides the essential information for serious consideration of switching duty-cycled MAC-based networks to WuR.

A passive wake-up radio in a wireless sensor network (WSN) has the advantage of increasing network lifetime by using a wake-up radio receiver (WuRx) to eliminate unnecessary idle listening. A sensor node equipped with a WuRx can operate in an ultra-low-power sleep mode, waiting for a trigger signal sent by the wake-up radio transmitter (WuTx). The passive WuRx is entirely powered by the energy harvested from radio transmissions sent by the WuTx. Therefore, it has the advantage of not consuming any energy locally, which would drain the sensor node's battery. Even so, the high amount of energy required to wake up a passive WuRx by a WuTx makes it difficult to build a multi-hop passive wake-up sensor network. In this paper, we describe and discuss our implementation of a battery-powered sensor node with multi-hop wake-up capability using passive WuRxs, called MH-REACH-Mote (Multi-hop-Range EnhAnCing energy Harvester-Mote). The MH-REACH-Mote is kept in an ultra-low-power sleep mode until it receives a wake-up trigger signal. Upon receipt, it wakes up and transmits a new trigger signal to power other passive WuRxs. We evaluate the wake-up range and power consumption of an MH-REACH-Mote through a series of field tests. Results show that the MH-REACH-Mote enables multi-hop wake-up capabilities for passive WuRxs with a wake-up range of 9.4m while requiring a reasonable power consumption for WuTx functionality. We also simulate WSN data collection scenarios with MH-REACH-Motes and compare the results with those of active wake-up sensor nodes as well as a low power listening approach. The results show that the MH-REACH-Mote enables a longer overall lifetime than the other two approaches when data is collected infrequently.

A wireless sensor network that employs passive radio wake-up of the sensor nodes can reduce the energy cost for unnecessary idle listening and communication overhead, extending the network lifetime. A passive wake-up radio is powered by the electromagnetic waves transmitted by a wake-up transmitter rather than a battery on the sensor node. However, this method of powering the wake-up radio results in a short wake-up range, which limits the performance of a passive wake-up radio sensor network. In this article, we describe our design of a passive wake-up radio sensor node—REACH 2 -Mote—using a high-efficiency, energy-harvesting module and a very low power wake-up circuit to achieve an extended wake-up range. We implemented REACH 2 -Mote in hardware and performed field tests to characterize its performance. The experimental results show that REACH 2 -Mote can achieve a wake-up range of 44 feet. We also modeled REACH 2 -Mote and evaluated its performance through simulations, comparing its performance to that of another passive wake-up radio approach, an active wake-up radio approach, and a conventional duty cycling approach. The simulation results show that REACH 2 -Mote can significantly extend the network lifetime while achieving high packet delivery rate and low latency.

The Constrained Application Protocol (CoAP) is a new Web protocol for the Internet of Things that allows to connect IoT devices directly to services hosted in the cloud. CoAP is based on UDP to better fit the requirements of constrained environments with resource-constrained nodes and low-power communication links. Being an Internet protocol, CoAP must still adhere to congestion control, primarily to keep the backbone network stable. Thus, the base specification uses conservative parameter values for the number of open requests, the retransmission timers, and the overall message rate. More powerful CoAP nodes, however, can use metrics to optimize these parameters to achieve a better quality of service. For this, the IETF CoRE working group is designing an advanced congestion control mechanism for CoAP called CoCoA. This paper presents first evaluation results for a mechanism that improves the communication between cloud services and resource-constrained IoT devices. We implement CoCoA for the Californium (Cf) CoAP framework and evaluate its performance on a wireless sensor network testbed that runs IPv6. Our results show that CoCoA can better utilize the available network capacity and can increase throughput by 19-112%.

One of the most promising energy-efficient communication methods is the use of wake-up receivers. In this paper, we propose and develop a novel wake-up communication system that uses Visible Light Communication (VLC) and an indoor solar panel as the receiver of the wake-up signal. After the reception of the wake-up signal, an interrupt generated by the wake-up receiver wakes up the wireless device attached. Through experiments we show the feasibility of the system and characterize its performances in terms of wake-up probabilities for different distances. We present two configuration options: an addressable and a broadcast-based wake-up configuration. We evaluate the effect of light interferences and show that the achieved wake-up distances under these conditions are reasonable for indoor scenarios.

Fundamental frequency (F0) is one of the essential features in many acoustic related applications. Although numerous F0detection algorithms have been developed, the detection accuracy in noisy environments still needs improvement. We present a hybrid noise resilient F0detection algorithm named BaNa that combines the approaches of harmonic ratios and Cepstrum analysis. A Viterbi algorithm with a cost function is used to identify the F0value among several F0candidates. Speech and music databases with eight different types of additive noise are used to evaluate the performance of the BaNa algorithm and several classic and state-of-the-art F0detection algorithms. Results show that for almost all types of noise and signal-to-noise ratio (SNR) values investigated, BaNa achieves the lowest Gross Pitch Error (GPE) rate among all the algorithms. Moreover, for the 0 dB SNR scenarios, the BaNa algorithm is shown to achieve 20% to 35% GPE rate for speech and 12% to 39% GPE rate for music. We also describe implementation issues that must be addressed to run the BaNa algorithm as a real-time application on a smartphone platform.

Passive RFID systems used for inventory management and asset tracking typically utilize contention-based MAC protocols, such as the standard C1G2 protocol. Although the C1G2 protocol has the advantage that it is easy to implement, it suffers from unfairness and relatively low throughput when the number of tags in the network increases. This paper proposes a token-based MAC protocol called Token-MAC for passive RFID systems, which aims a) to provide a fair chance for tags in the network to access the medium without requiring synchronization of the tags, b) to increase the overall throughput, i.e., the tag rate, and c) to enable a high number of tags to be read under limited tag read time availability, which is an especially important challenge for mobile applications. We implement Token-MAC as well as C1G2 and a TDMA-based protocol using Intel WISP passive RFID tags and perform experiments. Additionally, based on our experimental results, we develop energy harvesting and communication models for tags that we then use in simulations of the three protocols. Our experimental and simulation results all show that Token-MAC can achieve a higher tag rate and better fairness than C1G2, and it can provide better performance over a longer range compared with the TDMA-based protocol. It is also shown that Token-MAC achieves much lower tag detection delay, especially for high numbers of tags. Token-MAC is, therefore, a promising solution for passive RFID systems.

Use of a passive wake-up radio can drastically increase the network lifetime in a sensor network by reducing or even completely eliminating unnecessary idle listening. A sensor node with a wake-up radio receiver (WuRx) can operate in an extremely low power sleep mode until it receives a trigger signal sent by a wake-up radio transmitter (WuTx). After receiving the trigger signal, the attached WuRx wakes up the sensor node to start the data communication. In this paper, we implement and compare the performance of three passive wake-up radio-based sensor nodes: 1) WISP-Mote, which is a sensor mote that employs an Intel WISP passive RFID tag as the WuRx; 2) EH-WISP-Mote, which combines a novel energy harvester with the WISP-Mote; and 3) REACH-Mote, which uses the energy harvester circuit combined with an ultra-low-power pulse generator to trigger the wake-up of the mote. Experimental results show that the wake-up range and wake-up delay for the EH-WISP-Mote are improved compared with the WISP-Mote, while providing the ability to perform both broadcast-based and ID-based wake-ups. On the other hand, the REACH-Mote, which can only provide broadcast-based wake-up, can achieve a much longer wake-up range than any known passive wake-up radio to date, achieving feasible wake-up at a range of up to 37 ft.

The development of IPv6 stacks for wireless constrained devices that have limited hardware resources has paved the way for many new areas of applications and protocols. The Constrained Application Protocol (CoAP) has been designed by the IETF to enable the manipulation of resources for constrained devices that are capable of connecting to the Internet. Due to the limited radio channel capacities and hardware resources, congestion is a common phenomenon in networks of constrained devices. CoAP implements a basic congestion control mechanism for the transmission of reliable messages. Alternative CoAP congestion control approaches are a recent topic of interest in the IETF CoRE Working Group. New Internet-Drafts discuss the limitations of the default congestion control mechanisms and propose alternative ones, yet, there have been no studies in the literature that compare the original approach to the alternative ones. In this paper, we target this crucial study and perform evaluations that show how the default and alternative congestion control mechanisms compare to each other. We use the Cooja simulation environment, which is part of the Contiki development toolset, to simulate CoAP within a complete protocol stack that uses IETF protocols for constrained networks. Through simulations of different network topologies and varying traffic loads, we demonstrate how the advanced mechanisms proposed in the drafts perform relative to the basic congestion control mechanism.

The use of duty-cycling in Medium Access Control (MAC) protocols effectively helps improving the energy efficiency of wireless networks. However, while the benefits of these protocols are unquestionable, most of them still suffer from overhearing and idle listening, two issues that prevent duty-cycled systems from achieving optimum energy usage, which is a crucial aspect in specific types of wireless networks such as Wireless Sensor Networks (WSN).Wake-up Radio (WuR) systems have been employed recently to overcome these issues. Under this approach, the nodes' MicroController Unit (MCU) and main radio transceiver are completely switched off and only activated when a secondary, extremely low-power receiver in the node is triggered by a particular wireless transmission. Wake-up Radio systems allow for drastic energy savings since receiver nodes are only activated on-demand, maximizing their battery lifetimes. In this paper, we have modeled and simulated a real, recent and promising WuR hardware platform based on its time and energy consumption characterization. By comparing such WuR approach to B-MAC and IEEE 802.15.4, two well-known and widely employed MAC protocols, we show it effectively out-performs the conventional WSN MAC approaches in terms of energy efficiency. To the best of authors' knowledge, this is the first study to include a comparative analysis for multi-hop networks based on a real WuR platform, which shows WuR systems represent an energy-efficient solution that also provides a good tradeoff between latency, packet delivery ratio and applicability..

Energy-efficient operation is a challenge for wireless sensor networks (WSNs). A common method employed for this purpose is duty-cycled operation, which extends battery lifetime yet incurs several types of energy wastes and challenges. A promising alternative to duty-cycled operation is the use of wake-up radio (WuR), where the main microcontroller unit (MCU) and transceiver, that is, the two most energy-consuming elements, are kept in energy-saving mode until a special signal from another node is received by an attached, secondary, ultra-low power receiver. Next, this so-called wake-up receiver generates an interrupt to activate the receiver node's MCU and, consequently, the main radio. This article presents a complete wake-up radio design that targets simplicity in design for the monetary cost and flexibility concerns, along with a good operation range and very low power consumption. Both the transmitter (WuTx) and the receiver (WuRx) designs are presented with the accompanying physical experiments for several design alternatives. Detailed analysis of the end system is provided in terms of both operational distance (more than 10 m) and current consumption (less than 1 μA). As a reference, a commercial WuR system is analyzed and compared to the presented system by expressing the trade-offs and advantages of both systems.

Wireless image transmission is critical in many applications, such as surveillance and environment monitoring. In order to make the best use of the limited energy of the battery-operated cameras, while satisfying the application-level image quality constraints, cross-layer design is critical. In this paper, we develop an image transmission model that allows the application layer (e.g., the user) to specify an image quality constraint, and optimizes the lower layer parameters of transmit power and packet length, to minimize the energy dissipation in image transmission over a given distance. The effectiveness of this approach is evaluated by applying the proposed energy optimization to a reference ZigBee system and a WiFi system, and also by comparing to an energy optimization study that does not consider any image quality constraint. Evaluations show that our scheme outperforms the default settings of the investigated commercial devices and saves a significant amount of energy at middle-to-large transmission distances.

Emotion classification is essential for understanding human interactions and hence is a vital component of behavioral studies. Although numerous algorithms have been developed, the emotion classification accuracy is still short of what is desired for the algorithms to be used in real systems. In this paper, we evaluate an approach where basic acoustic features are extracted from speech samples, and the One-Against-All (OAA) Support Vector Machine (SVM) learning algorithm is used. We use a novel hybrid kernel, where we choose the optimal kernel functions for the individual OAA classifiers. Outputs from the OAA classifiers are normalized and combined using a thresholding fusion mechanism to finally classify the emotion. Samples with low `relative confidence' are left as `unclassified' to further improve the classification accuracy. Results show that the decision-level recall of our approach for six-class emotion classification is 80.5%, outperforming a state-of-the-art approach that uses the same dataset.

Wake-up radios present a promising alternative to traditional duty-cycle approaches, by reducing overhearing and by eliminating idle listening completely. However, energy-efficient operation of the wake-up mechanism is required for the success of such systems. In particular, addressing is an important component of the wake-up procedure that can consume a significant portion of the energy required. Hence, in this paper we propose a novel energy-efficient scheme for addressing. The proposed method is called Time-Knocking (TicK), since it utilizes the time duration of the MicroController Unit (MCU) sleeping to encode an address. In this paper, it is shown through mathematical analysis that TicK is much more energy efficient compared to the two common addressing mechanisms: MCU-decoding and correlator-based addressing. For realistic performance evaluations, physical measurements are performed to extract the parameter values of each method or the parameter values from well-documented off-the-shelf devices are used. TicK enables significant energy savings, especially in environments where false addressing initiations are frequent due to interference or where multiple nodes are addressed frequently.

Multicast routing protocols typically rely on the a priori creation of a multicast tree (or mesh), which requires the individual nodes to maintain state information. In dynamic networks with bursty traffic, where long periods of silence are expected between the bursts of data, this multicast state maintenance adds a large amount of communication, processing, and memory overhead for no benefit to the application. Thus, we have developed a stateless receiver-based multicast (RBMulticast) protocol that simply uses a list of the multicast members' (e.g., sinks') addresses, embedded in packet headers, to enable receivers to decide the best way to forward the multicast traffic. This protocol, called Receiver-Based Multicast, exploits the knowledge of the geographic locations of the nodes to remove the need for costly state maintenance (e.g., tree/mesh/neighbor table maintenance), making it ideally suited for multicasting in dynamic networks. RBMulticast was implemented in the OPNET simulator and tested using a sensor network implementation. Both simulation and experimental results confirm that RBMulticast provides high success rates and low delay without the burden of state maintenance.

Passive RFID systems typically utilize contention-based MAC protocols, such as the standard C1G2 protocol. While these protocols are easy to implement, they suffer from unfairness and low throughput. This paper proposes a token-based MAC protocol called Token-MAC for passive RFID systems. Token-MAC is designed to enable fair access to the medium for all tags without requiring a-priori knowledge of the tags or synchronization of the tags. We implement Token-MAC as well as a TDMA-based protocol and compare these approaches with the standard C1G2 protocol. Our experiments show that Token-MAC has a higher tag rate and better fairness than C1G2, and can achieve good performance over a longer range than the TDMA-based protocol. Token-MAC is therefore a viable solution for many passive RFID systems.

Motion sensors and cameras can be used together to build in-home video monitoring systems, where the cameras are only activated when the motion sensors detect motion. This saves both bandwidth (reduced video storage and/or transmission) as well as energy (if the cameras are battery-operated). However, motion sensors and cameras have different fields of view (FoV), and thus it is not clear that attaching motion sensors to cameras provides the most efficient system. Therefore, it is necessary to evaluate the performance of systems where the motion sensors are attached to the cameras (attached scenario) as well as where the motion sensors are detached from the cameras (detached scenario). We consider the motion sensor and camera placement problem under these two scenarios, with an additional hybrid scenario, and we formulate optimization problems to achieve the minimum energy consumption, longest network lifetime, or lowest cost. Simulation results show the tradeoffs between different objectives for all three scenarios.

It is increasingly common to see multiple wireless networks existing in the same environment, being accessed by devices of the individual networks as well as by "hybrid" devices capable of communicating on multiple networks. Typically these networks do not cooperate or share resources, resulting in sub-optimal network performances. The efficiency of such networks can be increased by exploiting hybrid nodes to enable network interactions that allow cross-network performance optimizations and cross-network information and service sharing. Such mutually beneficial interactions of the networks is referred to as symbiotic networking. In this paper, we investigate the potential performance gains of such interactions for the routing protocols and the effect of the network parameters on these potential gains. We use both simulation and mathematical frameworks that model the routing performances of both symbiotic and independent networking to quantify the routing benefits of symbiotic networking. Our results show that symbiotic networking can provide vital support to co-located networks, which is especially important in resource-constrained networks such as wireless sensor networks or mobile ad hoc networks.

Energy efficiency is one of the crucial design criteria for wireless sensor networks. Idle listening constitutes a major part of energy waste, and thus solutions such as duty cycling and the use of wake-up radios have been proposed to reduce idle listening and save energy. Compared to duty cycling, wake-up radios save more energy by reducing unnecessary wake-ups and collisions. In this paper, we investigate the feasibility and potential benefits of using passive RFID as a wake-up radio. We first introduce a physical implementation of sensor nodes with passive RFID wake-up radios and measure their energy cost and wake-up probability. Then, we compare the performance of our RFID wake-up sensor nodes with duty cycling in a Data MULE scenario through simulations with realistic application parameters. The results show that using a passive RFID wake-up radio offers significant energy efficiency benefits at the expense of delay and the additional low-cost RFID hardware, making RFID wake-up radios beneficial for many delay-tolerant sensor network applications.

Energy conservation is one of the primary goals of the majority of MAC protocols designed for wireless sensor networks. In Sensor-MAC (S-MAC), one of the first MAC protocols designed for sensor networks, nodes sleep and wake up periodically to save energy. MAC protocols such as Timeout-MAC (T-MAC) and Advertisement-MAC (ADV-MAC) improved upon S-MAC by introducing support for variable loads and providing further energy savings. In event-driven networks with sources generating bursty traffic or networks with period traffic, we can further reduce the energy consumption and increase node lifetime if we take into account the nature of the traffic. In this paper we propose Advertisement-based Time-division Multiple Access, or ATMA, a distributed TDMA-based MAC protocol for wireless sensor networks that utilizes the bursty or periodic nature of the traffic to prevent energy waste through advertisements and reservations for data slots. We provide detailed comparisons of the ATMA protocol with S-MAC, T-MAC and ADV-MAC through extensive simulations. The simulation results show that in bursty or periodic traffics, ATMA outperforms S-MAC, T-MAC and ADV-MAC in terms of energy consumption with reductions of up to 75%, while faring as well as T-MAC and ADV-MAC in terms of packet delivery ratio and latency.

Duty cycling is often used to reduce the energy consumption caused by idle listening in Wireless Sensor Networks (WSNs). Most studies on WSN protocols define a common duty cycle value throughout the network to achieve synchronization among the nodes. On the other hand, a few studies propose adaptation of the duty cycle according to uniform traffic conditions, which is beneficial assuming one-to-one traffic patterns that result in evenly distributed packet traffic. In this work, we consider the convergecast communication pattern commonly observed in WSNs. In convergecast communication, the packet traffic observed around the sink node is much higher than the traffic observed far from the sink, i.e., nodes with different distances to the sink node receive and must relay different amounts of traffic. Additionally, we utilize receiver-based protocols, which enable nodes to communicate with no synchronization or neighbor information, and hence do not require all nodes in the network to have the same duty cycle. In this paper, we model the expected energy consumption of nodes utilizing receiver-based protocols as a function of their duty cycle and their distance to the sink node. Using this analysis, we derive a closed-form formula for the duty cycle that minimizes the expected energy consumption at a given distance. Moreover, we propose an adaptation method for the derived distance-based duty cycle, based on local observed traffic. Performance evaluations of the two proposed duty cycle assignment methods show that they greatly improve the energy efficiency without sacrificing packet delivery ratio or delay significantly.

We consider optimal power allocation for wireless video sensors (WVSs), including the image sensor subsystem in the system analysis. By assigning a power-rate-distortion (P-R-D) characteristic for the image sensor, we build a comprehensive P-R-D optimization framework for WVSs. For a WVS node operating under a power budget, we propose power allocation among the image sensor, compression, and transmission modules, in order to minimize the distortion of the video reconstructed at the receiver. To demonstrate the proposed optimization method, we establish a P-R-D model for an image sensor based upon a pixel level sigma-delta (Σ∆) image sensor design that allows investigation of the tradeoff between the bit depth of the captured images and spatio-temporal characteristics of the video sequence under the power constraint. The optimization results obtained in this setting confirm that including the image sensor in the system optimization procedure can improve the overall video quality under power constraint and prolong the lifetime of the WVSs. In particular, when the available power budget for a WVS node falls below a threshold, adaptive sensing becomes necessary to ensure that the node communicates useful information about the video content while meeting its power budget.

In this paper, we propose a complete protocol stack framework called UPS (Unified Protocol Stack) as a solution for incorporating different protocols within WSNs through enabling the co-existence of multiple modules in same stack layer as well as providing unified access to cross-layer data.

In this abstract, we present Advertisement MAC (ADVMAC), an advertisement based MAC protocol for wireless sensor networks. Simulation results show that ADV-MAC provides a better way to conserve energy and at the same time to support variable traffic loads.

Several medium access control (MAC) protocols have been proposed for wireless sensor networks with the objective of minimizing energy consumption. For example, sensor-MAC (S-MAC) was proposed to reduce energy consumption by introducing a duty cycle. Under variable traffic load, the fixed duty cycle of S-MAC results in energy loss due to idle listening along with higher latency and lower throughput compared to an adaptive duty cycle. Timeout-MAC (T-MAC) introduced such an adaptive duty cycle to handle variable traffic loads. However, nodes that do not take part in data exchange waste energy because of continuous renewal of their timeout values. In this paper we propose advertisement MAC (ADV-MAC), a MAC protocol for wireless sensor networks that eliminates this energy waste by introducing the concept of advertising for data contention. ADV-MAC minimizes the energy lost in idle listening while maintaining an adaptive duty cycle to handle variable loads. Additionally, ADV-MAC enables energy efficient MAC-level multicasting. We provide detailed comparisons of the ADV-MAC protocol with S-MAC and T-MAC through extensive simulations. The simulation results show that ADV-MAC efficiently handles variable load situations and provides substantial gains over S-MAC and T-MAC in terms of energy (reduction of up to 45%) while faring as well as T-MAC in terms of throughput and latency.

Location area (LA) planning plays an important role in cellular networks because of the tradeoff caused by paging and registration signalling. The upper boundary for the size of an LA is the service area of a mobile services switching center (MSC). In that extreme case, the cost of paging is at its maximum but no registration is needed. On the other hand, if each cell is an LA, the paging cost is minimal but the cost of registration is the largest. Between these extremes lie one or more partitions of the MSC service area that minimize the total cost of paging and registration. In this paper, we seek to determine the location areas in an optimum fashion. Cell to switch assignments are also determined to achieve the minimization of the network cost. For that purpose, we use the available network information to formulate a realistic optimization problem, and propose an algorithm based on simulated annealing (SA) for its solution. Then, we investigate the quality of the SA-based technique by comparing it to greedy search, random generation methods, and a heuristic algorithm.

Location area (LA) planning plays an important role in cellular networks because of the trade-off caused by paging and registration signaling. The upper bound on the size of an LA is the service area of a mobile switching center (MSC). In that extreme case, the cost of paging is at its maximum, but no registration is needed. On the other hand, if each cell is an LA, the paging cost is minimal, but the registration cost is the largest. In general, the most important component of these costs is the load on the signaling resources. Between the extremes lie one or more partitions of the MSC service area that minimize the total cost of paging and registration. In this paper, we try to find an optimal method for determining the location areas. For that purpose, we use the available network information to formulate a realistic optimization problem. We propose an algorithm based on simulated annealing (SA) for the solution of the resulting problem. Then, we investigate the quality of the SA technique by comparing its results to greedy search and random generation methods.