Diversified Adaptive Frequency Rolling to Mitigate Self and Static Interferences

Increase in the number of coexisting networks in license free Industrial, Scientific and Medical (ISM) band causes interferences for industrial automation, e.g., shop floors of manufacturing facilities. In order to ensure the reliability for automation networks, interference avoidance schemes are required. This paper proposes a novel Predefined Hopping Pattern (PHP) technique for frequency hopping in ISM band, which mitigates self-interferences and static interferers as well. This technique generates optimized frequency hopping sequences which ensure sufficient frequency diversity and frequency offset among the coexisting Bluetooth piconets and exploits transmission experiences for a particular frequency in eliminating interference. Simulation studies have shown that PHP has better collision avoidance rate than well known adaptive frequency hopping (AFH) and adaptive frequency rolling (AFR) schemes.

In this paper, an adaptive and self-organizing spectrum allocation policy for ad hoc femtocells in two-tier networks based on usage of random frequency hopping is presented. As femto- and macrocells normally share the same frequency resources, the proposed approach is able to minimize InterCell Interference (ICI) in an adaptive manner. Each femto- and macrocell user chooses random carrier frequencies for transmission corresponding to a given probability density function (pdf). If the level of interference reaches a certain limit, which is typically the case for femtocell edge users, the probability density function of the carrier frequencies is changed in a way that it is quasi-orthogonal to the one of the macrocell users nearby. The changeover point between different probability density functions is realized in a self-organizing manner regarding the detected level of interference. Hence, the approach is able to adjust the trade-off between spectral efficiency and introduced interference during operation. We present analytical models for the Signal-to-Interference-and-Noise-Ratio (SINR), the Bit Error Ratio (BER) and the required transmission power of Orthogonal Frequency Division Multiple Access (OFDMA) femtocells applying adaptive random frequency hopping. The mobile radio channel is characterized by non-frequency selective Rayleigh fading and all results are verified by simulations implemented in MATLAB. In order to evaluate the improvements, the results are compared to systems using centralized orthogonal planning, systems using neither centralized nor distributed planning, and systems using static random frequency hopping. The comparison shows that adaptive random frequency hopping is capable of reducing the BER by a factor of 15 and the transmission power of femtocells by 17 dBm compared to systems where the macrocell user transmits in the same subbands as the femtocell user.

In this paper we present the multi-frequency wireless communication protocol and adaptive frequency hopping algorithm that are designed specifically with the goal of increasing the reliability of the physiological data transmissions by medical body area networks (MBAN). We discuss the protocol structure and compare adaptive and non-adaptive frequency hopping algorithms used within the MAC protocol. We introduce the comprehensive simulation framework and provide the simulation results which clearly show the advantage of using adaptive frequency hopping in realistic hospital scenarios, dominated with inter-MBAN and Wi-Fi interferes.

Wireless systems based on WLAN (802.11), ZigBee (802.15.4) and Bluetooth (802.15.1) are continuously deployed in new applications covering consumer, industry or medical fields. Especially, Bluetooth is recommended by the Health-Care-Organization for medical applications as frequency hopping is considered as a robust scheme. However dealing with frequency-dynamic sources of interference in the 2.4GHz ISM band is important due to the increase of wireless devices. Adaptive frequency hopping (AFH) suggested by the Bluetooth standard and implemented in many of todays products identifies and avoids using bad channels. It is a good and established coexistence mechanism in the presence of frequency-static sources of interference such as WLANs when the 2.4GHz band is not crowded. However, AFH is facing problems in a crowded 2.4GHz band, especially when the interference is dynamic. We developed a cross-layer algorithm SAFH (Smooth Adaptive Frequency Hopping) that is inspired by entropy maximization and the conventional Bluetooth AFH. SAFH assigns usage probabilities to all channels based on an exponential smoothing filter for frame error rates to estimate and predict the channel conditions. The application layer can adapt SAFH by parameter settings in a cross-layer approach. SAFH achieves low average frame error rate and responds fast to changing channel conditions if required from the application. Simulative Evaluation in the presence of different types of interference (802.11b, 802.15.4 and 802.15.1) shows that our algorithm outperforms conventional frequency hopping and AFH. Additionally, SAFH works smoothly and stable exploiting frequency diversity compared to previous approaches like entropy-maximization based adaptive frequency hopping and Utility Based Adaptive Frequency Hopping (UBAFH).

A wide band, dual radiator Multiple input multiple output (MIMO) antenna resonating at 2.4 GHz Industrial Scientific and Medical (ISM) band is designed and analysed for the body-centric wireless communication. Defected ground structure (DGS) is used to reduce the antenna size and to achieve wide bandwidth. Moreover, a decoupling slot is also etched in the ground plane to improve the port isolation. Proposed 2 × 1 array MIMO structure has occupied the volume of 90 × 40 × 0.8 mm3. Rectangular and cylindrical shaped multi-layered tissue models are used for simulation and pork tissue is used for the measurement of antenna performance. Broad 10-dB bandwidth of 1250/900 MHz, port isolation of 21/20 dB, gain of 5.53/5.07 dBi with, SAR value of 0.628/0.627 W/kg is achieved for the flat/deformed state of antenna. Results show that the proposed DGS-based antenna is reliable to operate on different tissue environment for body area network.

In May, 1985, the Federal Communications Commission (FCC) allowed the unlicensed use of spread spectrum (SS) in the Industrial, Scientific and Medical (ISM) band for commercial transmission without the need for a license as long as the user follows certain guideline in terms of transmission power level. The scarcity of communication bandwidth has lead researchers to investigate algorithms to identify busy channels over the airwave so they can be avoided and not add to communication degradation. This is very salient in the over used ISM band. In the ISM band the solution lies in developing efficient algorithms to detect which parts of the band are being used and utilize an agile communication system to hop to the available parts which support good communication. In addition, a solution of this nature can find application in electronic warfare, where fire fighters in the field would like to identify enemy attacks on their frequency hop spread spectrum (FHSS) channels and take appropriate measures to protect their communication channels from a jammer's interference. This paper is based on a scaled down version of the Bluetooth FHSS channel model. It proposes the use a polyphase channelizer to identify an active channel.

The authors propose an adaptive frequency hopping (AFH) algorithm, entitled robust adaptive frequency hopping (RAFH), for providing increased reliability of a wireless medical telemetry system (WMTS) under coexistence environment with non-medical devices. The conventional AFH scheme classifies channels into `good` or `bad` according to the threshold-based on`off decision by packet error rate (PER) measurement, and only uses good channels with a uniform hop probability. Unlike the conventional AFH scheme, RAFH is a novel technique, which solves a constrained entropy maximisation problem and assigns every channel a different hop probability as a decreasing function of the measured PER. The key novelty of RAFH over existing AFH schemes is that it reflects the relative channel condition by assigning non-uniform hop probabilities. By adopting constrained entropy maximisation, RAFH not only improves the average PER, but also reduces the PER fluctuation over time under a dynamic interference environment, both of which increase the reliability of WMTS. Through extensive simulation, we show that RAFH outperforms basic frequency hopping (FH) and the conventional AFH with respect to the PER under various scenarios of dynamic interference.

The main objective of this contribution is to introduce novel techniques for reducing the time taken from the reader to identify the frequency coded chipless radio frequency identification tags existed in the reader's interrogation region, system latency. The frequency scanning methodology, number of averaging for clutter removal, and hop duration are the 3 main parameters that significantly affect the overall system latency. Consequently, the adaptive frequency hopping (AFH) and adaptive sliding window (ASW) methodologies are proposed and proofed to be efficient for the chipless radio frequency identification systems from the latency and accuracy perspectives. Likewise, the performance of the designed AFH and ASW techniques are compared with the classical fixed frequency hopping methodology with a fine frequency step to validate the accuracy of the proposed methods. Moreover, 4 different coded frequency coded chipless tags are manufactured and used in the measurements. A real‐world testbed is designed including a software‐defined radio platform by which the proposed adaptive algorithms and traditional fixed frequency hopping methodology are implemented. All the measurements are performed in an indoor realized scenario, including the environmental effects. The experiments show that the proposed AFH combined with ASW algorithms significantly reduce the system latency by 58%.

As the popularity of wireless communication increases rapidly, the unlicensed Industrial Scientific and Medical (ISM) band becomes crowded. Interference avoidance thus becomes an important issue when designing wireless communication in the unlicensed ISM band. As shown in related works, channel hopping with blacklisting is a promising mechanism addressing interference in 802.15.4e time slotted channel hopping (TSCH) networks. However, the blacklisting mechanism changes the number of channels used, and thus requiring the frequency hopping sequence (FHS) be regenerated. A time-random channel selection mechanism avoids regeneration overhead; however, it breaks close-to-optimality property of the default FHSs, which in turns leads to high probability of interference. In this paper, we propose a new algorithm that generates FHSs in presence of interference without regeneration overhead, and at the same time maintains the optimality property. With the new proposed mechanism, we can generate FHSs with one designed original sequence. Analysis and simulation results show that optimal/near optimal properties are achieved by these new FHSs.

A ultra miniaturized implantable antenna operating on Industrial, Scientific and Medical (ISM) band of 902–928 MHz is proposed in this paper. This antenna is designed on bio-compatible Rogers ULTRA-LAM 3850HT (ε <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> = 2.9, tanδ = 0.0025) dielectric with a thickness of 0.1 mm for substrate and super-strate. Shorting pin has been introduced to miniature the antenna geometry with a volume of 8 mm×8 mm×0.2 mm making it flexible for monitoring. This antenna is preferable in terms of size and performance with a maximum gain of −28.2 dBi having a bandwidth of 178.6 MHz at a single Industrial, Scientific and Medical (ISM) band of 902–928 MHz. This antenna provides better bandwidth and gain on this frequency with these dimensions proving itself beneficial for monitoring the gastrointestinal tract of the patient.

In this paper, we propose a slotted adaptive frequency hopping and rolling (SAFHR) scheme to realize the dynamic spectrum access for cognitive radio (CR). First, based on the CR spectrum sensing result and the quadratic prime code, an adaptive frequency hopping scheme is designed to avoid the frequency static interference due to primary user (PU). Secondly, adaptive frequency rolling scheme is incorporated to combat the frequency dynamic interference in the presence of multiple CR nets. As a whole, the SAFHR algorithm aims to maximize the frequency spectrum utilization and frequency diversity for each CR user, and to accommodate as many CR users as possible. By employing a so called Instruments-in-MATLAB software defined radio (IM-SDR) platform, experimental results of the SAFHR scheme is demonstrated under the scenario with two CR nets, five CR nodes, and one PU.

Wireless systems using low-power wireless communication protocol are rapidly gain popularity in the license-free industrial scientific, and medical (ISM) frequency bands. One such emerging trend in ISM frequency bands is home automation. Historically, all the home devices were once unconnected, today are now being connected either by a wired or wireless connection. The low-power wireless communication protocols enable integration of all the digital home devices into a single system and enhance end user product experience. The rapid prototyping of these end user product using programmable radio system such as software-defined radio (SDR) has been the game-changer in the field of home automation. In this article, we present an overview of popular ISM bands in different regions of the world. Furthermore, we analyze the signals from the wireless electric switch using a software-defined radio in 433 MHz ISM band.

The proposed implantable CPW fed monopole slot antenna for industrial scientific and medical (ISM) band biomedical applications of dimension 25mm × 16mm × 0.5mm at ISM band (2.4 – 2.48 GHz) and short distance communication band (Electronic Communications Committee approved the frequency band 688 MHz). The antenna is placed on human tissues like skin, fat, muscle, etc and it is made compatible for implantation by embedding it on FR4 substrate. These Implantable CPW fed monopole slot antennas are significantly used in implantable biomedical devices due to the merits such as flexibility in design, conformability, size, safety and low power consumption.

This paper presents a 12-lead electrocardiogram (ECG) wireless medical system (WMS) aimed to provide continuous patient monitoring. The WMS consists of three sections: end device (ED), base station (BS) and graphical user interface (GUI). The ED and BS communicate through an RF link that operates in the industrial, scientific and medical (ISM) band at 2.45 GHz. The ED is based on commercially-available ultra-low power integrated circuits, including an 8 channel analog front-end (AFE) intended for biopotential monitoring, a microcontroller unit and an ISM radio transceiver. Details on the 12-lead ECG WMS operation including the low-power oriented control algorithm of the ED and the detection algorithm embedded in the GUI are presented. Measurements of the WMS using a 10 electrode ECG signal generator show successful communication up to 35m line of sight. The ED average current consumption is 33mA (including RF transmission) in continuous operation. This allows the ED to operate up to 88 hours.

The 2.4 GHz industrial, scientific and medical (ISM) band is a shared electromagnetic resource where many wireless communications technologies such as wireless local area networks, Bluetooth, ZigBee, cordless phones, amongst others, coexist. Due to the large amount of users of different technologies that might utilize the band at the same time and geographical region, it is reasonable to assume that the band is very busy all the time. In this paper, however, a spectrum measurement campaign is carried out to determine the actual spectrum occupancy of the ISM band in an environment with high density of users. Although many wireless technologies share this frequency band, results show its low spectrum utilization. Indeed, it is shown that the spectral occupation of the band ranges between 7% and 34% of a normal working day, and it is moderate even during busy hours. Therefore, the use of a more sophisticated approach is essential to exploit the unlicensed access to this band, for which cognitive radio is well suited. This is valid despite the fact that, formally speaking, there are no licensed (or primary) users in the ISM band. Nevertheless, ISM users could be treated as pseudo-primary. Thus, cognitive radio techniques can be implemented to improve the spectrum utilization.