Heikki Karvonen

Coding for energy efficient wireless embedded networks

This paper studies the effect of coding on the energy consumption in wireless embedded networks. An analytical model of the radio energy consumption is developed to study how different DC balanced codes affect the energy consumption for the one-hop case. A Rayleigh fading channel is assumed. The analysis is extended to include multihop scenarios in order to study the tradeoff between coding overhead and energy consumption. The numerical results obtained show that energy efficiencies of the codes used in a multihop routing scenario are strongly dependent on the channel conditions and on the number of hops used.

Soft handover method for mobile wireless sensor networks based on 6LoWPAN

In many wireless sensor network applications the sensor nodes needs to be mobile. In order to support mobility, the management of several issues, such as routing, handover, security, addressing and auto-configuration of the network needs to be handled. In the past, the main focus of sensor network research has been on static sensor networks, therefore many mobility related problems remain unsolved. In this paper, the focus is on the management of handover and addressing in networks, where gateways and sensor nodes can be mobile. A novel approach, which eliminates unnecessary handovers in the case where multiple gateways are in the range of mobile sensor node, is introduced in this paper. The proposed soft handover method has been implemented and its functionality has been proven in a full-scale testbed. Furthermore, it has been evaluated that the soft handover method performs fairly well also in the sensor network where gateways are static. The proposed solution is designed for IEEE 802.15.4 standard based sensor networks which use 6LoWPAN technique, but it can be easily adapted also to other type of networks.

A cross-layer energy efficiency optimization model for WBAN using IR-UWB transceivers

An energy efficiency optimization model for the IEEE 802.15.6 standard based wireless body area network is described in this paper. Cross-layer approach has been used here by focusing on physical (PHY) and medium access control (MAC) layers taking into account relevant characteristics therein. Studied PHY is based on impulse radio ultra wideband (IR-UWB) signaling with mandatory on–off keying modulation and non-coherent energy detection receiver. The analyzed MAC protocol is slotted Aloha which is used in the contention based mode of the IEEE 802.15.6 std. using IR-UWB PHY. The proposed model can be used to compare the energy efficiency of uncoded and coded transmissions using different Bose–Chaudhuri–Hocquenghem code rates. The model enables joint code rate and packet length optimization in AWGN channel when using the path loss model for hospital scenario, defined by the IEEE P802.15 working group. Results clearly show the most energy efficient code rate and packet length as a function of distance.

A generic wake-up radio based MAC protocol for energy efficient short range communication

To avoid idle listening and to improve energy efficiency in short range communication networks, a generic wake-up radio (WUR) based medium access control (GWR-MAC) protocol is proposed. GWR-MAC is not restricted to a specific WUR technology or data radio technology, and therefore it is suitable for a variety of scenarios in wireless sensor and body area networks. GWR-MAC includes a bidirectional wake-up procedure and a transmission period for data communication. Two different options for the wake-up procedure are defined: source-initiated and sink-initiated. The data transmission period can be implemented by using different type of channel access methods, which enables scalability. This paper describes the GWR-MAC protocol and an analytical model which is used to explore the energy efficiency of the proposed GWR-MAC based network and conventional duty cycle MAC based network. The comparison is done as a function of number of events to enable the selection of a correct radio technology for different application scenarios. The results clearly illustrate the usefulness and energy efficiency of the proposed protocol especially in applications that have low event frequency and require a low delay wake-up procedure.

A Cross-Layer Optimization Approach for Lower Layers of the Protocol Stack in Sensor Networks

A cross-layer optimization approach for the physical and medium access control layers of wireless sensor networks is introduced in this article. This approach includes a Markov chain model, simulations, and analytical derivations that are applied to the analysis of sensor networks using impulse radio ultra-wideband signals with noncoherent energy detection. This type of communication system has low-power transmission requirements and noise like signal characteristics with low interference to other wireless systems. The energy efficiency of different Reed-Solomon code rates and uncoded case are studied in a star topology network, where slotted Aloha, as defined in the IEEE 802.15.4a standard, is used as the medium access protocol. Analytical and simulation results clearly show the potential energy gains that can be achieved with the proposed optimization approach that can be also used in the evaluation and optimization of other combinations of physical and medium access control protocols.

Cross-Layer Energy Efficiency of FEC Coding in UWB Sensor Networks

In this paper, energy efficiency of forward error correction (FEC) coding in ultra wideband (UWB) wireless sensor networks (WSNs) is studied taking into account the characteristics of the physical (PHY) and medium access control (MAC) layers. The underlying goal has been to develop a cross-layer framework that allows the design of energy efficient FEC coding in UWB WSNs. This study is carried out using analytical derivations and simulations. A cross-layer approach, such as the one described here, provides a deeper understanding of the various factors that affect the energy consumption in WSNs, and how FEC coding can improve it. Results clearly show that coding improves the energy efficiency in UWB transceivers. By using the framework introduced here, UWB network designers can analyze the network energy efficiency already in the design phase

Optimal code rate for wireless sensor networks using IR-UWB and non-coherent detection

In this paper, a cross-layer design approach has been used to evaluate the effect of forward error correction (FEC) on energy consumption of non-coherent energy detector receiver using impulse radio ultra-wideband in the context of wireless sensor networks. The proposed method captures relevant characteristics of the physical and medium access control (MAC) layers, while taking into account bit error probability (BEP) requirement of the application. A two-stage semi-analytical optimization model and code rate selection algorithm has been developed to find out the optimal code rate from the energy efficiency perspective. Firstly, a signal-to-noise ratio (SNR) gap analysis is used to select the code rates, which can provide the same target BEP as uncoded transmission, with lower received SNR. Secondly, an energy consumption model is used to explore which one of the selected code rates provide the highest energy saving, when compared to the uncoded case. In this work, the proposed algorithm has been executed for Reed-Solomon codes using Nakagami-m fading channel model and taking into account the channel access success probability of the Slotted Aloha MAC for different offered traffic loads. The results clearly illustrate the potential energy savings that can be achieved by using FEC and selecting the optimum code rate. The developed model is useful in the selection of code rate for particular communication distances and offered traffic load values.

Preliminary study of superregenerative wake-up receiver for WBANs

A superregenerative wake-up receiver with addressing capability (SR-WUR) for medical and wireless body area networks (WBAN) is proposed in this paper. The SR-WUR is based on a self-quenched superregenerative oscillator (SRO) which enables high sensitivity while maintaining low power consumption. Due to the high sensitivity, low transmit power can be used, which reduces the energy radiation towards a human body. In this work, the SRO is exploited in a novel manner. The SRO charges a voltage multiplier that is used to detect the transmitted bit. The SRO also generates the self-quench and provides a clock signal for a digital logic which processes the received bits. The SR-WUR design is scalable for different type of wireless network applications because the front-end configuration can be changed. Therefore, it can be easily integrated to different type of WBAN platforms. The SR-WUR performance is estimated by using simulations for the back-end components and mathematical analysis for an example front-end configuration. The example configuration includes a low noise amplifier that improves sensitivity of the receiver and it provides isolation between SRO and antenna. Results show that the SR-WUR sensitivity and average power consumption with the example front-end configuration are -84.8 dBm and 186 μW, respectively. Therefore, the proposed SR-WUR has potential to improve the overall energy efficiency, and to reduce the radiated power of wake-up signaling, which are important design goals in medical applications.

Loose synchronization method for low-power superregenerative wake-up receiver

The use of wake-up receivers (WURs) in wireless body area networks (WBAN) has remarkable potential to improve energy efficiency. During the recent years, multiple WUR designs and architectures have been therefore proposed for WBANs and wireless sensor networks (WSN). Superregenerative oscillator (SRO) based architecture is inherently sensitive, which makes it an attractive choice for a WUR. It is known that to improve the selectivity and to reduce the energy consumption the quench frequency should be the same or in the order of data rate. Therefore, synchronization is required. To achieve this with low-power consumption, pulse width modulation is used to encode transferred address information. The decoder measures the pulse widths and uses uncertainty interval that enables loose synchronization between the transmitter and the receiver. The decoder is implemented and its power consumption is measured. Decoder operation is verified with simulations using the hardware description language simulator.

Energy efficiency evaluation of ECC scheme utilizing decomposable codes in IEEE std 802.15.6 based WBANs

Recently, studies on medical and health monitoring systems using wireless communications have been actively conducted. In the field of health monitoring systems, wireless body area network (WBAN) is one of the key technologies and its standardization activities have also been extensively carried out. In previous work we proposed an optimal QoS control scheme employing a decomposable error control coding scheme. Furthermore, we extended the error correction capacity of our decomposable code and evaluated its bit error ratio and throughput performance in a multiple WBAN environment. In this paper, we evaluate the energy efficiency of the proposed scheme by computer simulations and compare it with energy efficiency of error control scheme defined in the IEEE Std. 802.15.6. Based on the results it can be stated that the proposed ECC method is more energy efficient especially in poor channel conditions.