Multiple Input Multiple Output (MIMO) provides the potential for significant gains in channel capacity and spectral efficiency through its use of multiple element antenna systems and space-time coding. There are numerous published accounts of experimental MIMO communications links with high numbers of transmit and receive antennas, as well as commercial products exploiting MIMO with smaller antenna configurations. However, the use of MIMO as a modulation scheme for mobile ad hoc networking has so far only been explored as part of a theoretic or simulation exercise. In this paper we describe the design and implementation of a MAC protocol for a MIMO system which is designed to exploit the capability of 8x10 MIMO for ad hoc networks. This work is unique in that from the start our design considered the specific capabilities and parameters of an existing 8x10 MIMO physical layer, including nonnegligible decoding delays, variable array size and coding schemes, as well as fixed frame sizes. Furthermore, given the bandwidths and antenna array sizes available, the physical layer design could achieve hundreds of megabits in link capacity, and our MAC protocol therefore needed to be designed and implemented in such a way as to maximize this capacity, particularly in a network multi-hop environment. Our MIMO-MAC protocol provides this capability while supporting multi-hop ad hoc networks through novel schemes for channel access, segmentation/reassembly, ARQ and link adaptation. This paper discusses the challenges and tradeoffs involved in developing a MAC for real MIMO hardware, and briefly describes a subset of our solutions to them.
Multiple Input Multiple Output (MIMO) wireless communications vastly expand the capacity and connectivity of communications for forces operating in challenging environments such as urban or forested terrain. A MIMO architecture called BLAST (Bell Laboratories Layered Space-Time) has been formulated to realize these capacities. We have developed a packet version of BLAST, called PacketBLAST, specifically to support high mobility, ad-hoc, tactical communications on the move in challenging environments. PacketBLAST offers a number of benefits to tactical communications. We have implemented a first-ever, end-to-end mobile, ad-hoc network (MANET) of PacketBLAST nodes and have successfully tested it in a number of field demonstrations.
To demonstrate a real-time, mobile, peer-to-peer, ad-hoc networked MIMO system in a realistic tactical environment, the Defense Advanced Research Projects Agency (DARPA) has instituted a program, called Mobile Network MIMO (MNM). To assess the communication channel quality for ground level MIMO nodes, a comprehensive channel measurement and modeling effort was carried out to determine quantities such as spatial correlations, delay spread as well as propagation loss. It was found that median 8x10 MIMO capacity supported by the channel was about 8 times the corresponding 1x1 capacity, and 3.2 times the corresponding 1x10 capacity. Also
conducted were wideband soundings of such channels, where it was found that the median rms delay spreads were 0.6 μs. Reported are measurements and an empirical model of pathloss, spatial correlation scales, and crosspolarization properties of rural peer-to-peer channels.
Multiple Input - Multiple Output (MIMO) is a new communications paradigm which brings significant benefits to
future communication systems. In contrast to conventional wireless communication systems, MIMO systems exploit the
spatial diversity available in multipath propagation to create parallel channels within a common bandwidth. The
multiple channels can be used for capacity enhancement, coverage improvement, lower radiated power spectral density,
interference/jammer suppression, multi-beam communication and battery power savings.
Research, development and exploitation of MIMO technology for tactical communication systems is significantly
limited by lack of mobile, real-time MIMO testbeds to verify and validate extensive theoretical results. We report a 4x4
mobile, wideband, real-time MIMO-OFDM testbed designed and developed by the team of San Diego Research Center
(SDRC) and Brigham Young University (BYU). Using this testbed we have successfully demonstrated the feasibility of
peer-to-peer Mobile MIMO by closing 1000m links, at 50 mph speeds, at 12 bps/Hz spectral efficiency.
Multiple Input - Multiple Output (MIMO) systems use multiple antennas to exploit the multipath available in wireless channels and significantly improve communication performance. The use of multiple antennas open a multitude of dimensions to optimize performance based on application, mission and environments. Tactical networks impose additional challenges like mobility, jammers and distributed operation.
In this paper we present the design of a Media Access Control (MAC) protocol, called LiSL/M, which optimizes the performance of networked tactical MIMO systems. LiSL/M is an adaptive and opportunistic distributed protocol that schedules links dynamically based on interference, traffic and channel condition. We also discuss our experiments with interfacing accurate MIMO propagation and physical layer models implemented in MATLAB(R) with QualNet(R) network simulator. LiSL/M simulation results show significant 2-3 times better network performance in scenarios envisioned for Future Combat Systems (Lakehurst scenario).
Radio Frequency Identification (RFID) has recently attracted much attention in both the technical and business communities. It has found wide applications in, for example, toll collection, supply-chain management, access control, localization tracking, real-time monitoring, and object identification. Situations may arise where the movement directions of the tagged RFID items through a portal is of interest and must be determined. Doppler estimation may prove complicated or impractical to perform by RFID readers. Several alternative approaches, including the use of an array of sensors with arbitrary geometry, can be applied. In this paper, we consider direction-of-arrival (DOA) estimation techniques for application to near-field narrowband RFID problems. Particularly, we examine the use of a pair of RFID antennas to track moving RFID tagged items through a portal. With two antennas, the near-field DOA estimation problem can be simplified to a far-field problem, yielding a simple way for identifying the direction of the tag movement, where only one parameter, the angle, needs to be considered. In this case, tracking of the moving direction of the tag simply amounts to computing the spatial cross-correlation between the data samples received at the two antennas. It is pointed out that the radiation patterns of the reader and tag antennas, particularly their phase characteristics, have a significant effect on the performance of DOA estimation. Indoor experiments are conducted in the Radar Imaging and RFID Labs at Villanova University for validating the proposed technique for target movement direction estimations.
Recently, there has been considerable interest in the area of Radio Frequency Identification (RFID) and Radio
Frequency Tagging (RFTAG). This emerging area of interest can be applied for inventory control (commercial) as well
as friend/foe identification (military) to name but a few. The current technology can be broken down into two main
groups, namely passive and active RFID tags. Utilization of Space-Filling Curve (SFC) geometries, such as the Peano
and Hilbert curves, has been recently investigated for use in completely passive RFID applications [1, 2]. In this work,
we give an overview of our work on the space-filling curves and the potential for utilizing the electrically small,
resonant characteristics of these curves for use in RFID technologies with an emphasis on the challenging issues
involved when attempting to tag conductive objects. In particular, we investigate the possible use of these tags in
conjunction with high impedance ground-planes made of Hilbert or Peano curve inclusions [3, 4] to develop electrically
small RFID tags that may also radiate efficiently, within close proximity of large conductive objects .
Radio frequency identification (RFID) is poised for growth as businesses and governments explore applications implementing RFID. The RFID technology will continue to evolve to meet new demands for human and target location and tracking. In particular, there are increasing needs to find and track the positions of multiple RFID tagged items that are closely spaced. As a result, localization and tracking techniques with higher accuracy, yet low implementation complexity are required. This paper examines the applicability of
direction-of-arrival (DOA) estimation methods to the localization and tracking problems of passive RFID tags. Different scenarios of stationary and moving targets are considered. It is shown through performance analysis and simulations that simple DOA estimation
methods can be used to provide satisfactory localization performance.
Free Space Optical Communications through cloud-obscured channels suffer from severe degradations due to
multiscattering, which induces delay spread in the received signal. The delay spread of FSO channel can vary
considerably according to channel conditions, varying from nanoseconds to microseconds for clear and cloudy
channel, respectively. In this paper, we present the use of return-to-zero (RZ) modulation in conjunction with
multirate modulation schemes as viable means for minimizing the dispersive effects of the channels. We show that
multirate communications provide diversity against channel degradation and fluctuation, while RZ modulation is
more robust to dispersive channels than non return-to-zero (NRZ) modulation, thus providing an overall
improvement in system performance, reliability and availability.
The U.S. Army Research Laboratory, in support of network communications for a Horizontal Fusion program,
experimented with large-scale wireless LANs at the McKenna facility in Fort Benning, GA. In total, we deployed two
wireless LANs, one consisting of both the 802.11A and 802.11G protocols and the other consisting of only the 802.11G
protocol. In this paper, we will describe the deployment of wireless LAN access points and show the mapping of
wireless LAN signal strength reception in rooms of building B1 of McKenna village at Fort Benning, GA. We will also
describe our observations in using these wireless LANs.
Wireless sensor networks provide economical and viable solutions to many monitoring problems. The practical
deployment of sensor networks, however, introduces problems that traditional networks do not face. One such
problem is node compromise attack in which intruders physically capture sensor nodes and harm the network
by injecting false data. False data injection attacks may deceive the base station and deplete the limited energy
resources of relaying sensor nodes. Standard authentication schemes cannot prevent these attacks if there exists
more than one compromised node in the network. This paper proposes a collaborative data authentication
protocol that detects false data injection attacks. In the proposed protocol, false data injected by less than n
compromised nodes are detected and eliminated by constructing consecutive Merkle Hash Trees (MHT) between
the source node and the base station where the number of leaf nodes of each MHT is n. The performance analysis
shows that, considering the security it provides, the proposed protocol is efficient.
McQ has developed a family of low cost unattended ground sensors that utilize self-configured, mesh network communications for wireless sensing. Intended for use in an urban environment, the area monitored by the sensor system poses a communication challenge. A discussion into the sensor's communication performance and how it affects sensor installation and the operation of the system once deployed is presented.
Sensors have varied constraints, which makes the network challenging for communicating with its peers. In this
paper, an extension to the security of physical layer of a predictive sensor network model using the ant system is proposed.
The Denial of Service (DoS) attack on sensor networks not only diminishes the network performance but also
affects the reliability of the information making detection of a DoS threat is more crucial than recovering from the
attack. Hence, in this paper, a novel approach in detecting the DoS attack is introduced and analyzed for a variety of
scenarios. The DoS attack is dependent on the vulnerabilities in each layer, with the physical layer being the lowest
layer and the first to be attacked by jammers. In this paper, the physical layer DoS attack is analyzed and a defense
mechanism is proposed. Classification of the jammer under various attack scenarios is formulated to predict the
genunity of the DoS attacks on the sensor nodes using receiver operating characteristics (ROC). This novel approach
helps in achieving maximum reliability on DoS claims improving the Quality of Service (QoS) of WSN.
This paper presents a self-organizing MAC protocol framework for distributed sensor networks with arbitrary mesh
topologies. The novelty of the proposed ISOMAC (In-band Self-Organized MAC) protocol lies in its in-band control
mechanism for exchanging TDMA slot information while distributed MAC scheduling. A fixed length bitmap vector is
used in each packet header for exchanging relative slot timing information across immediate and up to 2-hop neighbors.
It is shown that by avoiding explicit timing information exchange, ISOMAC can work without network-wide time
synchronization which can be prohibitive for severely cost-constrained sensor nodes in very large networks. A slotclustering
effect, caused by in-band bitmap constraints, causes ISOMAC to offer better spatial channel reuse compared
to traditional distributed TDMA protocols. ISOMAC employs a partial node wake-up and header-only transmission
strategy to adjust energy expenditure based on the instantaneous nodal data rate. Both analytical and simulation models
have been developed for characterizing the proposed protocol. Results demonstrate that with in-band bitmap vectors of
moderate length, ISOMAC converges reasonably quickly - approximately within 4 to 8 TDMA frame duration. Also, if
the bitmap header duration is restricted within 10% of packet duration, the energy penalty of the in-band information is
quite negligible. It is also shown that ISOMAC can be implemented in the presence of network time synchronization,
although its performance without synchronization is just marginally worse than that with synchronization.
Localization is an important challenge in wireless sensor networks (WSN). Localization usually refers to the process of dynamically determining the position(s) of one or more node(s) in a larger network. The challenge lies in efficiently providing "acceptable" accuracy while conforming to the many constraints of WSNs. We propose a Cluster-based Partial Localization (CPL) to provide efficient localization, where the focus is on providing scalable partial localization suitable to a large and high-density network. CPL utilizes both a computationallyintensive localization technique (non-metric MDS) and a less intensive triangulation to achieve balance between complexity and performance. Clustering is utilized to select a subset of nodes to perform the non-metric MDS localization and then extend to the rest of the network. We show, with simulation results, that CPL will provide a considerable reduction in both computation and communication, while still yielding an acceptable accuracy.
Orthogonal Frequency Division Multiplexing (OFDM) is a widely used technique for data transmission on
multipath fading channels. The multipath component of these types of channels causes a phenomenon known
as frequency selective fading. This type of fading can severely degrade or completely eliminate the signal
energy of many of the OFDM tones producing an irreducible error rate, even when no noise is present. In the
early 1990's, researchers combined some of the characteristics of Code Division Multiple Access (CDMA)
and Spread Spectrum (SS) with OFDM in order to create a more robust modulation scheme capable of
surviving frequency selective fading without the need for forward error correction (FEC) techniques and thus
OFDM-CDMA was born. This paper will investigate how the code rate and channel estimation affect the
performance of coded OFDM and OFDM-CDMA waveforms on various HF multipath/fading channels.
In this paper, the effect of transmitter diversity on asynchronous
co-channel interference suppression and equalization is studied in
multi-user multiple input multiple output (MIMO) orthogonal
frequency division multiplexing (OFDM) systems. In an asynchronous
mode of data transmission, independent decoding without user
cooperation is a more appropriate approach. Thus, various
suboptimal transmitter diversity techniques such as space-time
block coding and beamforming are employed, and their performances
are evaluated. First, we develop space-time minimum mean squared
error (MMSE) receivers for both space-time block coded OFDM and
beamforming based MIMO OFDM. The average signal-to-interference
and noise ratio (SINR) resulting from MMSE combining indicates
that the bit-error rate (BER) performance of space-time block
coded (STBC) multi-user OFDM is highly dependent on the amount of
timing offset. Overall, simulation results demonstrate that
closed-loop MIMO systems need to be employed to obtain substantial
diversity gains in asynchronous multi-user OFDM channels with
random timing offset. Moreover, receiver diversity is an important
factor to the performance of a large system.
Inefficient use of network resources on the battlefield is a serious liability: if an asset communicates with the network command for data-a terrain map, for instance-it ties up the end-to-end network resources. When many such assets contend for data simultaneously, traffic is limited by the slowest link along the path from the network command to the asset. A better approach is for a local server, known as an infostation, to download data on an anticipated-need basis when the network load is low. The infostation can then dump data when needed to the assets over a high-speed wireless connection. The infostation serves the local assets over an OFDM-based wireless data link that has MIMO enhancements for high data rate and robustness. We aim for data rate in excess of 100 Mbps, spectral efficiency in excess of 5 bits/sec/Hz, and robustness to poor channel conditions and jammers. We propose an adaptive physical layer that determines power levels, modulation schemes, and the MIMO enhancements to use based on the channel state and the level of interference in the system. We also incorporate the idea of superuser: a user who is allowed preferential use of the high data rate link. We propose a MAC that allows for this priority-based bandwidth allocation scheme. The proposed infostation MAC is integrated tightly with the physical layer through a cross-layer design. We call the proposed infostation PHY, MAC, and network technology, collectively, as the Mobile Infostation Network Technology (MINT).
Coded space-time cooperation is an efficient approach in delivering information over a relay network. Multiple
cooperative terminals (nodes) form a distributed multiple-input-multiple-output (MIMO) systems, thus
providing high data rates and high diversity gains. However, unlike conventional co-located MIMO systems,
it is impractical for distributed MIMO networks to maintain perfect timing synchronization between different
transmit terminals. In particular, the presence of a fractional-symbol delay difference between the signals transmitted
from different terminals can cause erroneous sampling positions and yield highly dispersive channels even
at a memoryless channel environment. Existing methods solve such problem based on time-domain approaches
where adaptive equalization is required at the receivers for combining the information transmitted from distributed
sources. In this paper, we propose the use of OFDM-based approaches using distributed space-frequency
codes. The proposed schemes are insensitive to fractional-symbol delays and lead to higher data rate transmission
and simplified implementation. In addition, the proposed schemes permit the use of relatively simple
amplify-and-forward algorithm in multi-hop wireless networks without delay accumulations. The time delay in
each relaying hop by reconstructing the cyclic prefix and, as such, improve the spectral efficiency, while keeping
a simple relaying structure.
Orthogonal Frequency division multiplexing (OFDM) spread spectrum
technique, sometimes also called multi-carrier or discrete
multi-tone modulation, are used in bandwidth-efficient communication
systems in the presence of channel distortion. The benefits of OFDM
are high spectral efficiency, resiliency to RF interference, and
lower multi-path distortion. OFDM is the basis for the European
digital audio broadcasting (DAB) standard, the global asymmetric
digital subscriber line (ADSL) standard, in the IEEE 802.11 5.8 GHz
band standard, and ongoing development in wireless local area networks. The modulator and demodulator in an OFDM system can be
implemented by use of a parallel bank of filters based
on the discrete Fourier transform (DFT), in case the
number of subchannels is large (e.g. K > 25), the OFDM
system are efficiently implemented by use of the fast
Fourier transform (FFT) to compute the DFT. We have
developed a custom FPGA-based Altera NIOS system to
increase the performance, programmability, and low power
in mobil wireless systems.
The overall gain observed for a 1024-point FFT ranges depending on the multiplier used
by the NIOS processor between a factor of 3 and 16. A careful optimization described in the appendix
yield a performance gain of up to 77% when compared with
our preliminary results.
Mobile wireless networks of the future will be expected to function in highly diverse environments from dense
foliage to dense urban settings. Under these conditions, the phenomenon of multipath fading will be a problem Here we
describe a new technique to eliminate multipath fading in such wireless networks. Our technique is based on a free
parameter in the design of Fresnel zone plate antennas, a type of reference phase. The technique exploits our ability to
control relative phase between desired signals arriving in the antenna beam and of undesired multipath signals coming
from outside of the beam direction. By control over relative phase, we can reduce the degree of fading to arbitrarily
The use of Internet Protocol (IP) suite over satellite and space platforms is limited by the large propagation delays to
reach their earth-distant position and the wireless nature of channel errors. Before they can provide an effective and
commerciable service, IP protocols require proper augmentation and correction precisely due to long feedback loops,
large number of in-transit packets, transmission errors, possibly asymmetric links and intermittent connectivity. By a
careful collective look to current research literature, we identify that all IP problems in long delay wireless networks
either stem from network measurement inefficiency or can be better overcome if accurate measurements were available.
In this paper, we introduce a flexible middle-box IP performance enhancement solution that deals with the satellite
WAN optimization problem without changes to senders and receivers. It accomplished an IP steady state improvement
factor that corresponds to approximately optimal channel utilization by effectively changing TCP/IP parameters
according to innovative, accurate passive network measurements, suitable for the high bandwidth and delay wireless
environment. We believe that our approach can optimize not only protocols but also improve currently proposed
optimizations as those suggested in the SCPS transport. While this study is focusing on TCP, our concept can take on a
wide number of transport, security, multimedia, real-time and QoS performance enhancements tasks.
A novel routing scheme for mobile ad hoc networks (MANETs), which combines hybrid and multi-inter-routing path properties with a distributed topology discovery route mechanism using control agents is proposed in this paper. In recent years, a variety of hybrid routing protocols for Mobile Ad hoc wireless networks (MANETs) have been developed. Which is proactively maintains routing information for a local neighborhood, while reactively acquiring routes to destinations beyond the global. The hybrid protocol reduces routing discovery latency and the end-to-end delay by providing high connectivity without requiring much of the scarce network capacity. On the other side the hybrid routing protocols in MANETs likes Zone Routing Protocol still need route "re-discover" time when a route between zones link break. Sine the topology update information needs to be broadcast routing request on local zone. Due to this delay, the routing protocol may not be applicable for real-time data and multimedia communication. We utilize the advantages of a clustering organization and multi-routing path in routing protocol to achieve several goals at the same time. Firstly, IRP efficiently saves network bandwidth and reduces route reconstruction time when a routing path fails. The IRP protocol does not require global periodic routing advertisements, local control agents will automatically monitor and repair broke links. Secondly, it efficiently reduces congestion and traffic "bottlenecks" for ClusterHeads in clustering network. Thirdly, it reduces significant overheads associated with maintaining clusters. Fourthly, it improves clusters stability due to dynamic topology changing frequently. In this paper, we present the Intelligent Routing Protocol. First, we discuss the problem of routing in ad hoc networks and the motivation of IRP. We describe the hierarchical architecture of IRP. We describe the routing process and illustrate it with an example. Further, we describe the control manage mechanisms, which are used to control active route and reduce the traffic amount in the route discovery procedure. Finial, the numerical experiments are given to show the effectiveness of IRP routing protocol.
The demand for spontaneous setup of a wireless communication system has increased in recent years for areas like battlefield, disaster relief operations etc., where a pre-deployment of network infrastructure is difficult or unavailable. A mobile ad-hoc network (MANET) is a promising solution, but poses a lot of challenges for all the design layers, specifically medium access control (MAC) layer. Recent existing works have used the concepts of multi-channel and power control in designing MAC layer protocols. SU-MAC developed by the same authors, efficiently uses the 'available' data and control bandwidth to send control information and results in increased throughput via decreasing contention on the control channel. However, SU-MAC protocol was limited for static ad-hoc network and also faced the busy-receiver node problem. We present the Extended SU-MAC (ESU-MAC) protocol which works mobile nodes. Also, we significantly improve the scheme of control information exchange in ESU-MAC to overcome the busy-receiver node problem and thus, further avoid the blockage of control channel for longer periods of time. A power control scheme is used as before to reduce interference and to effectively re-use the available bandwidth. Simulation results show that ESU-MAC protocol is promising for mobile, ad-hoc network in terms of reduced contention at the control channel and improved throughput because of channel re-use. Results show a considerable increase in throughput compared to SU-MAC which could be attributed to increased accessibility of control channel and improved utilization of data channels due to superior control information exchange scheme.
A novel application-specific communications scheme for RF-based indoor wireless localization networks is proposed. In such a system wireless badges, attached to people or objects, report positions to wireless router units. Badges have very limited communication, energy, and processing capabilities. Routers are responsible for propagating collected badge information hop-by-hop toward one central unit of the system and are significantly less constrained by battery than the badges. Each unit can radiate a special sequence of bits at selected frequencies, so that any router in the wireless neighborhood can sense, store, aggregate and forward Received Signal Strength Indicator (RSSI) information. Once the central unit receives RSSI from routers, it calculates the overall relative position of each unit in the system. This new scheme has been developed based on the Chipcon CC1010 Evaluation Module with limited communication capabilities. The implemented protocol rules allow scalability of numerous system parameters. The feasibility of the proposed protocol is simulated on a typical floor: 2-dimensional topology where routers are deployed in a grid fashion. Results show that assuming normal operation and a maximum of thousand badges the system can periodically report about every five seconds. Different scenarios are compared, and the proposed scheme is demonstrated to meet strict reliability requirements while providing energy-efficient badges and an acceptable level of latency.
In this paper, we evaluate the packet latency performance of a new scheduler-based scheme that we have implemented
on top of the p-persistent 802.11 MAC layer. We extended Cali's dynamic p-persistent 802.11 protocol from single class
to multiple classes by means of a weighted fair queuing scheduler built on top of the MAC p-persistent layer. We used
the NS2 simulator in the implementation and testing of our multiple-class scheduler and incorporated the scheduler-based
architecture by modifying the NS2's 802.11 DCF implementation and the protocol stack of the wireless node. Our
tests showed that AEDCF cannot maintain the same throughput differentiation ratios among different traffic classes
under different loads. In contrast, the p-persistent Scheduler scheme maintains the desired differentiation ratios under
different loads, gives higher total network throughput and provides easier tuning. We present detailed performance
results of the scheduler-based architecture in terms of QoS differentiation and packet latency. All tests were
implemented in NS2. The paper concentrates on single hop wireless networks and compares the scheduler-based scheme
with AEDCF. The paper is concluded by a discussion on how to extend the evaluation to multi-hop wireless networks
and examine the role of the routing layer and the MAC layer.
This paper examines the problem of determining the degree of mixing of two independent and different types of traffic streams from observations of their statistically multiplexed stream. A common example of a pair of such different stream types in networks would be one conforming to the conventional Poisson model and the other obeying long-range dependence characterized by a heavy-tailed distribution. We provide an expression for the probability density function of the inter-arrival time of the mixed stream in terms of those of the input streams for the general case. An approach is provided to estimate input parameters from the first and second order statistics of the output traffic for the specific case of multiplexing Poisson and heavy-tailed processes.
Multipaths of the GPS signal reaching the GPS receiver lead to undesirable tracking errors and inaccurate ranging information. In this paper, we consider the multipath effect on noncoherent early-minus-late power discriminator. Analytical treatment of the effect of the carrier phase offset of the multipath relative to the direct path on the GPS receiver performance is provided. Compared with the well-known coherent discriminator, the noncoherent discriminator presents different tracking accuracy and sensitivity to multipath delay, magnitude, and phase. The paper considers the front-end precorrelation filter, which is typically applied to remove out-of-band interference and noise. Selections of suitable precorrelation filter bandwidth in conjunction with the early-late correlator spacing can aid in mitigating the multipath impeding effects on delay lock loop (DLL) and receiver discriminators. Computer simulations of the impact of a dominant multipath on the discriminator tracking performance are provided. It is assumed that the early and late correlations are performed within the same navigation symbol, and no symbol transitions are encountered over the correlation interval.
This paper deals with indoor source localization using multiple receivers. Unlike outdoor environment, indoor sources have restricted motion and move in partially or fully known indoor settings, including rooms and hallways. The source could be a robot or unmanned ground vehicle. The source could emit a wireless transmission of thermal, chemical or biological hazard event. In this paper, inequality geometric constraints are developed and applied to help improve localization estimates based on Trilateration for indoor environments. The constraints, which can be applied to outdoor environments as well, restrict the source position estimate from existing in certain regions that are labeled invalid and consistent with the building layout and blue prints. Simulations are conducted to demonstrate the advantage of subjecting the optimization problem to the developed constraints, which is particularly notable as the range error variance increases.
The output SINR achieved via Indirect Dominant Mode Rejection (IDMR) beamforming is substantially higher than the
achieved with other beamforming algorithms. IDMR is based on a parametric estimate of the covariance matrix which is
obtained using an estimate of the directions of the dominant sources and assuming that the array manifold is available. In
most applications the array manifold is not known precisely and performance of IDMR can be deteriorated. The focus of
this paper is to enable the IDMR beamformer to operate in a scenario of direction-independent steering vector mismatch. A
modified version of an algorithm introduced by Friedlander is employed to estimate the direction-independent mismatch.
Thereafter IDMR is implemented. Simulation analysis reveals that this technique enables IDMR to operate in a scenario
of direction-independent manifold mismatch.
Wireless sensors networks are currently being used in different engineering fields such as civil, mechanical and
aerospace engineering for damage detection. Each network contains approximately hundreds to thousands of MEMS
sensors that communicate to its base station. These sensors are placed in different environments and locations that create
changes in their output due to obstacles or interference between them and their base station. A research study was
conducted on wireless MEMS sensor nodes to evaluate the noise level and the effect of environmental interferences as
well as their maximum distance communication. In this paper, the effect of interference environments and obstacles
such as magnetic field created by electricity and cell phone communications, concrete and metal enclosures, and
outside/inside environments were evaluated. In addition, a neural network computer simulation was developed to learn
and teach the users what it takes to classify signals such as time, amount of samples and overtraining in order to obtain
the correct output instead of an unknown. By gathering all this information it helps to save money and time in any
application wireless MEMS sensors are used and idealized models and pictures of communication paths have been
created for easier evaluation of the MEMS sensor networks.
Both the military and consumer sectors are driving towards distributed networked sensors. A major
stumbling block to deployment of these sensors is the radio frequency (RF) propagation environment
within a few wavelengths of the earth. Increasing transmit power (battery consumption) is not the practical
solution to the problem. This paper will discuss some aspects of the near earth propagation (NEP) problem
and provide a few solutions. When radiating near the earth the communications link is subjected to a list of
physical impairments. On the list are the expected Fresnel region encroachment and multipath reflections
along with the intriguing radiation pattern changes and near earth boundary layer perturbations. A
significant amount of data has been collected on NEP. Disturbances in the NEP atmosphere have a time
varying attenuation related to the solar radiation (insolation). Solutions, or workarounds, to the near earth
propagation problem hinge on dynamic adaptive RF elements. Adaptive RF elements will allow the
distributed sensor to direct energy, beam form, impedance correct, increase communication efficiency, and
decrease battery consumption. Small electrically controllable elements are under development to enable
antenna impedance matching in a dynamic environment. Additionally, small dynamic beam forming
antennas will be developed to focus RF energy in the direction of need. By creating provisions for
decreasing the output RF power to the level required, battery consumption can be reduced. With the
addition of adaptive RF elements, distributed autonomous networked sensors can become a reality within a
few centimeters of the earth.