On adaptive frequency hopping to combat coexistence interference between bluetooth and IEEE 802.11b with practical resource constraints

In contrast to traditional frequency hopping techniques, Adaptive Frequency Hopping (AFH) is a low cost and low power solution to avoid interference dynamically. While each AFH algorithm proposed previously is shown to be efficient, a detailed performance analysis of various AFH mechanisms under realistic resource constraints is yet to be done. In particular, based on our performance study on Bluetooth systems presented in this paper, we have found that the AFH mechanism adopted by IEEE 802.15 Task Group 2 (TG2) is very sensitive to memory and power limitations. We then propose a novel Interference Source Oriented Adaptive Frequency Hopping (ISOAFH) approach based on a cross-layer design, in which the baseband layer of Bluetooth considers not only the instantaneous channels condition but also the physical layer transmission characteristics of potential interference sources in determining the hop sequence. In our simulations using detailed MATLAB Simulink modeling, we find that our proposed method is much more robust in that it is insensitive to memory and energy constraints. Indeed, our approach generally achieves a lower collision rate and higher ISM spectrum utilization.published_or_final_versio

Frequency hopping in wireless sensor networks

Wireless sensor networks (WSNs) are nowadays being used to collectively gather and spread information in different kinds of applications, for military, civilian, environmental as well as commercial purposes. Therefore the proper functioning of WSNs under different kinds of environmental conditions, especially hostile environments, is a must and a lot of research currently ongoing. The problems related to the initialization and deployment of WSNs under harsh and resource limited conditions are investigated in this thesis. Frequency hopping (FH) is a spread spectrum technique in which multiple channels are used, or hoped, for communications across the network. This mitigates the worst effects of interference with frequency agile communication systems rather than by brute force approaches. FH is a promising technique for achieving the coexistence of sensor networks with other currently existing wireless systems, and it is successful within the somewhat limited computational capabilities of the sensor nodes hardware radios. In this thesis, a FH scheme for WSNs is implemented for a pair of nodes on an application layer. The merits and demerits of the scheme are studied for different kinds of WSN environments. The implementation has been done using a Sensinode NanoStack, a communication stack for internet protocol (IP) based wireless sensor networks and a Sensinode Devkit, for an IPv6 over low power wireless personal area network (6LoWPAN). The measurements are taken from the developed test bed and channel simulator for different kinds of scenarios. The detailed analysis of the FH scheme is done to determine its usefulness against interference from other wireless systems, especially wireless local area networks (WLANs), and the robustness of the scheme to combat fading or frequency selective fading

Possibilities of Error Controls in Frequency hopping Stations

Doktorská práce se zabývá problematikou návrhu kódového zabezpečení pro stanice s kmitočtovým skákáním v pásmu s intenzivním rušením. U digitálních modulací dochází vlivem rušení k chybnému určení modulačního stavu na straně přijímače. Důsledkem jsou chybně přenesené symboly zprávy. Vzniklé chyby během přenosu je možné eliminovat za použití zabezpečovacích kódů. Zároveň je také možné těmto chybám předcházet pomocí algoritmů (technik) frekvenčního skákání, které provádí výběr vhodného komunikačního kanálu. Vhodným komunikačním kanálem se rozumí kanál s nižší pravděpodobností vzniku chybných symbolů ve zprávě. Hlavní přínos této práce spočívá v návrhu nové techniky frekvenčního skákání s předcházením kolizí (FH/CA). Stanice s technikou FH/CA provádí před každým skokem měření úrovně signálu v několika uvažovaných kanálech. Na základě provedených měření je pak vybrán nejvhodnější kanál, tj. kanál s nejnižší naměřenou hodnotou úrovně signálu. S vyšší pravděpodobností tak dochází ke skoku na kanál neobsazený nějakým přenosem. Pomocí matematického modelu byla porovnána výkonnost nově navržené techniky FH/CA se současně užívanými technikami FH a AFH. Porovnávacím kritériem byla pravděpodobnost kolize mezi komunikačním systémem FH/CA a statickými rušiči (zařízení vysílající nepřetržitě na stálém kmitočtu) nebo dynamickými rušiči (tj. jinými FH nebo AFH systémy). Porovnáním hodnot pravděpodobnosti rušeného přenosu byly zjištěny nesporné teoretické výhody nové techniky FH/CA oproti současně užívaným technikám FH a AFH. Technika FH/CA vždy dosahuje lepších nebo stejných výsledků v porovnání s technikou FH v případě rušení jak statickými tak i dynamickými rušiči. Technika FH/CA je většinově výhodnější než technika AFH v pásmu se statickými a dynamickými rušiči. Významný přínos techniky FH/CA je vidět zejména v oblasti dynamických rušičů. Naopak v oblasti statických rušičů je technika FH/CA oproti technice AFH v určitých situacích horší. Správnost matematických modelů byla ověřena simulačním modelem, který byl vytvořen v rámci řešení této doktorské práce v prostředí MATLAB. Na základě získaných dat z modelu byl následně proveden návrh kódového zabezpečení pro stanice s kmitočtovým skákáním s novou technikou frekvenčního skákání FH/CA, které jsou určeny pro přenos dat o malém objemu v pásmu s intenzivním rušením.The doctoral thesis deals with design of coding for frequency hopping stations in band with intensive jamming. In digital modulations erroneous determination of the modulation state occurs due to jam at the receiver side. The result is erroneously transferred symbols of the message. Errors created during the transmission can be eliminated by using error control systems. It is also possible to prevent these errors by using algorithms (techniques) of frequency hopping which select the appropriate channel. Appropriate communication channel is a channel with a lower probability of erroneous symbol in the message. The main contribution of this thesis is to design a new frequency hopping technique with collision avoidance (FH/CA). The station with FH/CA technique measures signal levels in the considered several channels before every jump. Based on the measurements the most appropriate channel with the lowest value of measured signal level is selected. Therefore, it is more probable that a jump to an unoccupied channel with a transmission will occur. Using a mathematical model, the performance of the newly proposed FH/CA technique is compared with the currently used techniques FH and AFH. Comparison criteria are the probability of a collision between an FH/CA communication system and a static (device transmitting continuously at a fixed frequency) or dynamic jammer (i.e. other FH or AFH systems). By comparing the values of the probability of jammed transmission, indisputable theoretical advantages of the new FH/CA technique were found, compared to the currently used FH and AFH techniques. The FH/CA technique always has better or equal results compared with the FH technique in the case of interference by static and dynamic jammers. The FH/CA technique in a band with static and dynamic jammers usually has better results than the AFH technique. A significant contribution of the FH/CA technique can be seen in the case of dynamic jammers. On the other hand, in the case of static jammers the FH/CA technique is in certain situations worse than the AFH technique. The accuracy of the mathematical models were successfully verified on a simulation model that was created as a part of this thesis in the MATLAB environment. Based on the obtained data from the model there was designed coding for frequency hopping stations with the new technique of frequency hopping FH/CA which is designed for small-volume data transfer in a band with intensive jamming.

A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals

Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility

Concurrent operation of Bluetooth low energy and ANT wireless protocols with an embedded controller

With the introduction of low-power wireless technologies, new applicationsin the healthcare, fitness and home entertainment markets emergethrough the use of ultra low-power sensors. These devices are designed torun for years on a single coin-cell battery.ANT and Bluetooth Low Energy are two low-power protocols that emergeas competitors in this market. The ability to combine these in a single systemnot only takes away the element of choice from the manufacturers, but alsoprovides compatibility between the two protocols. An ANT-enabled devicecan be coupled to a Bluetooth network, with the benefit of connecting tonon-ANT central devices, such as smartphones, tablets and laptops.In this thesis, the co-existence of these two protocols is discussed. Animplementation with two distinct radios for each protocol, controlled by asingle embedded microcontroller, is presented. The implementation is testedwith regards to packet loss with a simple test application. Test results showthat the obtained packet loss cannot be correlated to the co-existence of thetwo protocols

Air Force Institute of Technology Research Report 2014

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems Engineering and Management, Operational Sciences, Mathematics, Statistics and Engineering Physics

MedLAN: Compact mobile computing system for wireless information access in emergency hospital wards

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A&E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec

Spectrum control and iterative coding for high capacity multiband OFDM

The emergence of Multiband Orthogonal Frequency Division Modulation (MB-OFDM) as an ultra-wideband (UWB) technology injected new optimism in the market through realistic commercial implementation, while keeping promise of high data rates intact. However, it has also brought with it host of issues, some of which are addressed in this thesis. The thesis primarily focuses on the two issues of spectrum control and user capacity for the system currently proposed by the Multiband OFDM Alliance (MBOA). By showing that line spectra are still an issue for new modulation scheme (MB-OFDM), it proposes a mechanism of scrambling the data with an increased length linear feedback shift register (compared to the current proposal), a new set of seeds, and random phase reversion for the removal of line spectra. Following this, the thesis considers a technique for increasing the user capacity of the current MB-OFDM system to meet the needs of future wireless systems, through an adaptive multiuser synchronous coded transmission scheme. This involves real time iterative generation of user codes, which are generated over time and frequency leading to increased capacity. With the assumption of complete channel state information (CSI) at the receiver, an iterative MMSE algorithm is used which involves replacement of each users s signature with its normalized MMSE filter function allowing the overall Total Squared Correlation (TSC) of the system to decrease until the algorithm converges to a fixed set of signature vectors. This allows the system to be overloaded and user\u27s codes to be quasi-orthogonal. Simulation results show that for code of length nine (spread over three frequency bands and three time slots), ten users can be accommodated for a given QoS and with addition of single frequency sub-band which allows the code length to increase from nine to twelve (four frequency sub-bands and three time slots), fourteen users with nearly same QoS can be accommodated in the system. This communication is overlooked by a central controller with necessary functionalities to facilitate the process. The thesis essentially considers the uplink from transmitting devices to this central controller. Furthermore, analysis of this coded transmission in presence of interference is carried to display the robustness of this scheme through its adaptation by incorporating knowledge of existing Narrowband (NB) Interference for computing the codes. This allows operation of sub-band coexisting with NB interference without substantial degradation given reasonable interference energy (SIR=-l0dB and -5dB considered). Finally, the thesis looks at design implementation and convergence issues related to code vector generation whereby, use of Lanczos algorithm is considered for simpler design and faster convergence. The algorithm can be either used to simplify design implementation by providing simplified solution to Weiner Hopf equation (without requiring inverse of correlation matrix) over Krylov subspace or can be used to expedite convergence by updating the signature sequence with eigenvector corresponding to the least eigenvalue of the signature correlation matrix through reduced rank eigen subspace search

Enabling Techniques Design for QoS Provision in Wireless Communications

Guaranteeing Quality of Service (QoS) has become a recognized feature in the design of wireless communications. In this thesis, the problem of QoS provision is addressed from different prospectives in several modern communication systems. In the first part of the thesis, a wireless communication system with the base station (BS) associated by multiple subscribers (SS) is considered, where different subscribers require different QoS. Using the cross-layer approach, the conventional single queue finite state Markov chain system model is extended to multiple queues\u27 scenario by combining the MAC layer queue status with the physical layer channel states, modeled by finite state Markov channel (FSMC). To provide the diverse QoS to different subscribers, a priority-based rate allocation (PRA) algorithm is proposed to allocate the physical layer transmission rate to the multiple medium access control (MAC) layer queues, where different queues are assigned with different priorities, leading to their different QoS performance and thus, the diverse QoS are guaranteed. Then, the subcarrier allocation in multi-user OFDM (MU-OFDM) systems is stuied, constrained by the MAC layer diverse QoS requirements. A two-step cross-layer dynamic subcarrier allocation algorithm is proposed where the MAC layer queue status is firstly modeled by a finite state Markov chain, using which MAC layer diverse QoS constraints are transformed to the corresponding minimum physical layer data rate of each user. Then, with the purpose of maximizing the system capacity, the physical layer OFDM subcarriers are allocated to the multiple users to satisfy their minimum data rate requirements, which is derived by the MAC layer queue status model. Finally, the problem of channel assignment in IEEE 802.11 wireless local area networks (WLAN) is investigated, oriented by users\u27 QoS requirements. The number of users in the IEEE 802.11 channels is first determined through the number of different channel impulse responses (CIR) estimated at physical layer. This information is involved thereafter in the proposed channel assignment algorithm, which aims at maximum system throughput, where we explore the partially overlapped IEEE 802.11 channels to provide additional frequency resources. Moreover, the users\u27 QoS requirements are set to trigger the channel assignment process, such that the system can constantly maintain the required QoS