Terahertz (THz) integrated sensing and communication (ISAC) systems promise ultra-high data rates and precise sensing capabilities, enabled by narrow and directional beams. However, such beams are susceptible to beam misalignment (BM) fading caused by platform instability. While statistical models for BM fading exist for communication links, their extension to sensing applications, especially in drone-to-drone (D2D) scenarios, remains unexplored. In D2D ISAC networks, misalignment effects from the aerial platforms impact both the forward and return paths. This paper presents closed-form statistical models for BM fading in THz ISAC, addressing both monostatic (co-located transceivers) and bistatic (separated transceivers) sensing configurations, and considering both the spot-filling regime (target larger than beam) and the spot-limited regime (target smaller than beam). The proposed models facilitate the extension of BM fading analysis to sensing in drone-to-drone THz ISAC systems and have been validated through Monte Carlo simulations.

Even though Terahertz (THz) band is promising for Drone-to-Drone (D2D) communication, there exists significant challenges, primarily high path loss and the sensitivity of directional links to mobility-induced beam misalignment. In this paper, we propose a novel adaptive beamwidth control system for THz D2D communication by activating rows of the designed 8×8 microstrip patch antenna array operating at 272.5 GHz. The proposed row-selective activation mechanism provides dynamic adjustment of the elevation beamwidth by activating different combinations of antenna rows (from 1×8 to 8×8 configurations). The proposed mechanism offers a flexible trade-off in its beam characteristics, utilizes narrow, high-gain beams to maximize performance in stable links, and dynamically switches to wider, more robust beams to ensure connectivity during drone maneuvers. The performance of the reconfigurable array is evaluated through real drone mobility traces. Simulation results reveal that during periods of misalignment, the adaptive beamwidth strategy maintains link capacity that is up to three orders of magnitude higher than fixed-beam configurations, promising a practical solution for resource-constrained THz D2D communication.

Enabled by Self-interference (SI) cancellation, In-Band Full-duplex (IBFD) communication is promising for wireless systems as it can double spectral efficiency. At high power levels, SI cancellation drops abruptly due to transceivers’ non-linearity, as estimation/cancellation of SI signal with non-linearity is particularly challenging in the presence of the linear SI channel. To resolve this problem, we propose switched IBFD radio architecture along with a frequency-domain non-linear estimation algorithm. In this architecture, during the training phase, proposed non-linear estimation is performed on the SI signal, isolated from linear SI channel. In the cancellation phase, the estimated non-linear signal is provided as a reference to linear SI estimation, followed by linear cancellation. Experiments on a software defined IBFD radio demonstrate that the proposed solution improves linear cancellation by up to 16 dB, existing non-linear cancellation algorithms by up to 13 dB, and SI is reduced to the noise level for almost all power levels. Since the non-linear model needs to be trained once, at power-up, our IBFD solution is not affected from changes in multi-path, while existing schemes require (re)optimization and (re)training of the model. With the same reasoning, proposed non-linear solution has no estimation overhead and complexity is only for non-linear reconstruction.

In this work, 0.75-10 THz band is explored for non-terrestrial communications, by leveraging the improved atmospheric conditions at various altitudes. A channel model for aerial communications at THz band is proposed to calculate the common flat bands for frequency-selective path gain and the colored noise spectrums, both of which are highly affected by the atmospheric conditions. With capacity computation based on common flat bands, we consider aerial vehicles at different altitudes and distances, under realistic weather and channel fading conditions, due to beam misalignment and also multi path fading. An extensive capacity analysis is presented, considering equal and water-filling power allocation. It is shown that, when there is no fading, capacity for aerial links is several orders of magnitude larger than the sea-level capacity. When ergodic capacity is computed for the fading scenarios, it is shown that the impact of fading vanishes with altitude. Sea-level ergodic capacity is increased by an order of magnitude for drone-to-drone communications, providing several Tbps at 10 m range, while 10s of Tbps is achievable among jet planes and UAVs, and several 100s of Tbps is possible for satellites/cubesats at 1 km under fading, suggesting that THz band is a promising alternative for aerial communications.

Orthogonal frequency division multiplexing (OFDM) is the pertinent waveform for current and next generation wireless systems, whose spectral efficiency can be potentially doubled by in-band full-duplex (IBFD) communication. However, in OFDM based IBFD systems, digital self-interference cancellation (DSIC) employed at baseband does not provide sufficient cancellation in the cyclic prefix (CP) region. When the propagation delay between two communicating radios is non-zero, the CP noise affects the data region of the desired signal. In this work, we propose CP noise reduction (CPNR) technique for OFDM based IBFD radios. We have evaluated CPNR with time and frequency domain DSIC schemes via both simulations and MATLAB and FPGA implementations on our Software Defined Radio based IBFD radio. In the laboratory tests, the total suppression of the IBFD radio is improved by 6 dB by employing CPNR in frequency-domain DSIC and EVM for bidirectional communication is improved by up to 5%, allowing realistic propagation delays. In addition to improving the total suppression and EVM performance, CPNR is also shown to enhance the multi-path resiliency of DSIC techniques.

Full duplex (FD) communication has attracted significant attention due to its potential for increasing the wireless link rate twofold without increasing the occupied bandwidth. For enabling FD communication, the self-interference (SI) signal at the transmitting radio should be suppressed down to the noise level. Despite SI cancellation applied at different stages via passive, analog and digital techniques, the current methods cannot sufficiently suppress SI at all power levels. Specifically at high power levels, the nonlinear behavior of the radio should be modeled within SI cancellation. In this paper, we propose a novel nonlinear digital cancellation approach by adapting support vector regression (SVR) for FD communication. The proposed SVR based nonlinear cancellation is integrated with linear cancellation and the digital SI cancellation algorithms are implemented and tested on a software defined radio set-up integrated with a monostatic antenna. With the proposed SVR based solution, up to 5 dB enhancement in total SI suppression is observed as compared to only linear digital cancellation, for the transmit power levels higher than 20 dBm. Moreover, for the same transmit power levels, up to 3 dB higher cancellation is achieved in comparison to the memory polynomial based nonlinear digital cancellation. Incorporating the proposed solution in the FD radio design only requires changes at the algorithmic level, which is implemented in software, hence there is no need for any hardware or circuitry modification. Additionally, the proposed nonlinear solution does not cause any extra communication overhead, since SVR models are to be learned only once for each transmit power level, then stored and re-used for the later transmissions.

In this paper, a joint power and beam-level beamwidth control scheme is proposed for full duplex (FD) millimeter wave (mmWave) indoor wireless systems. Energy efficiency of the proposed scheme is investigated considering various system parameters, such as maximum transmit power level, level of self-interference cancellation and pilot transmission overhead. With this analysis for a realistic indoor wireless communication scenario, the feasibility of FD is studied for mmWave links, considering their specific propagation characteristics, namely, narrow transmission and reception beam-level beamwidths and high absorption losses, as well as massive bandwidth which is much larger than the existing sub 6 GHz bands. We evaluate the performance of the proposed FD mmWave system for three power budget schemes (low, moderate and high) in terms of average total energy efficiency. Our simulation results show that, for currently available state-of-the-art self-interference cancellation levels, FD mmWave with proposed joint power and beam-level beamwidth control outperforms the smart half duplex (HD) mmWave with joint transmission slot and beam-level beamwidth control by a factor of up to four times and improves FD mmWave with only power control by up to 33.92 %. If higher (close to ideal) self-interference cancellation can be achieved, the net average total energy efficiency improvements over existing abovementioned schemes, are up to 4.8 times and 26.45 %, respectively. It is concluded that with the proposed joint power and beamwidth control, the current FD mmWave technology promises a good potential for indoor wireless networks.

In-band full-duplex (FD) communication provides a promising alternative to half-duplex (HD) for wireless systems, due to increased spectral efficiency and capacity. In this paper, HD and FD radio implementations of two way, two hop, and two way two hop communication are compared in terms of degrees of freedom (DoF) under a realistic residual self-interference (SI) model. DoF analysis is carried out for each communication scenario for HD, antenna conserved (AC), and RF chain conserved (RC) FD radio implementations. The DoF analysis indicates that for the two way channel, the achievable AC FD with imperfect SI cancellation performs strictly below HD, and RC FD DoF tradeoff is superior when the SI can be sufficiently cancelled. For the two hop channel, FD is better when the relay has a large number of antennas and enough SI cancellation. For the two way two hop channel, when both nodes require similar throughput, the achievable DoF pairs for FD do not outperform HD. FD still can achieve better DoF pairs than HD, provided the relay has sufficient number of antennas and SI suppression.

Underwater control applications, such as control of Autonomous Underwater Vehicles (AUV)s, have recently gained significant interest, and there is a growing demand for high-speed wireless communication between AUVs and base station. Acoustic communication provides low data rates and high propagation delays, both of which are not suitable for employing high control gains for the navigation of AUVs. On the other hand, Radio Frequency (RF) communication provides high data rate, but it is constrained by high attenuation due to high conductivity and permittivity of water resulting in a short working range. In this work, we propose an underwater networked control system with acoustic and RF hybrid communication, where an acoustic link is employed for long range communication and RF link is applied in close range. Our performance results indicate that the acoustic and RF hybrid communication system takes up to 38.5% less time to dock, up to 91% smaller steady state error and spends up to 39% lower communication energy as compared to the acoustic only system at the expense of up to 22.35% higher motive energy.

Recent works have demonstrated the feasibility and potential of full-duplex (FD) wireless systems to double the spectral efficiency of half-duplex (HD) systems. Self-interference (SI) cancellation is the key to FD communication and the residual SI is the major factor determining the performance of an FD radio. This paper presents a novel frequency domain based approach, for the reconstruction of SI signal in digital domain. Unlike the existing time domain reconstruction approach, which requires convolution, the proposed approach is simple and uses FFT processing for SI signal reconstruction. By means of computational complexity evaluation, it is shown that the proposed reconstruction approach offers 61% reduction in the floating point operations required to reconstruct SI signal. Furthermore, via detailed simulations on the performance of digital SI cancellation under fading channels, it is demonstrated that the SI suppression achieved with the proposed approach is not only comparable to existing approach, but with frequency domain SI channel estimates, it can offer 5-7 dB better cancellation under highly frequency selective fading conditions, suggesting its suitability for long range transmission.

With the emergence of self-interference cancellation techniques, wireless full-duplex communication at the same frequency channel and time slot has become possible. The gain of full-duplex communication over half-duplex depends on the success of self-interference cancellation or the amount of residual self-interference. In this paper, we propose a medium access control (MAC) protocol, named Synchronized Contention Window Full-Duplex (S-CW FD) protocol for enabling full duplex in wireless local area networks (WLANs) and we evaluate its performance under a realistic self-interference model and a realistic network model with hidden nodes. The proposed S-CW FD protocol can not only work both in ad hoc and infrastructure modes of IEEE 802.11 WLANs, but with the legacy nodes as well. Our performance analysis considering various network scenarios and different self-interference cancellation levels show that, when there are no hidden nodes in the network, the S-CW FD protocol can at most double the throughput of half-duplex IEEE 802.11. In the presence of hidden nodes, the advantages of full-duplex are further emphasized, as the throughput gain can get as high as an order of magnitude even for moderate SI cancellation levels.

Networked control systems offer significant advantages in terms of reliability, commissioning and maintenance, especially for complex systems. They must be able to withstand delays and data corruption caused by the underlying communication network. Existing results in networked control systems provide varying degrees of robustness. However, cost is also an important factor for real world implementations, which further restricts the bandwidth of the underlying network and complexity of the communication protocol. In this paper we introduce a networked control system method, WMBPNCS, that we have previously proposed, and implement a control system using IEEE 802.15.4 (ZigBee) as its communication protocol, in an attempt to overcome these problems. We find through simulations that performance of our implementation is acceptable even under large amounts of random network delay and data loss.

In wireless sensor networks (WSNs), multiple sources stream sensed data to the base station. As the base station is approached amount of streamed data becomes disproportionate to the number of forwarding nodes, causing excessive data forwarding at the nodes around the base station. We propose a packet forwarding framework to manage and reduce the energy dissipated at the nodes through partitioning the network into variable size regions. Our approach provides a means to control the transmission ranges of the nodes and the number of nodes serviced by a node as a forwarder. It is shown that the energy consumption in the network can be balanced through the optimal selection of the partition sizes. The proposed framework is shown to provide a simple solution to finding the optimum transmission ranges for balanced energy consumption in a densely deployed WSN, making it a practical forwarding strategy. The proposed framework does not require periodic message updates and it is suitable for implementation in dense networks.

A distributed cooperative forwarding framework based on randomized coding is proposed, where cooperative links are formed and packets are forwarded on the fly, without explicit relay selection, actuation or resource allocation. In this framework, a cooperative flooding method and two cooperative forwarding schemes that actuate the cooperative transmissions of the nodes within an optimally formed progress region are described. It is shown that by assuring packets' progress cooperatively through a region instead of a string of predetermined nodes, progress of the packets towards the final destination is guaranteed even in sparse networks, under severe fading and mobility conditions. The proposed forwarding schemes are shown to provide reductions in the total number of hops, while causing minimal spatial footprint on the network.

Owing to their distributed architecture, networked control systems (NCSs) are proven to be feasible in scenarios where a spatially distributed feedback control system is required. Traditionally, such NCSs operate over real-time wired networks. Recently, in order to achieve the utmost flexibility, scalability, ease of deployment, and maintainability, wireless networks such as IEEE 802.11 wireless local area networks (LANs) are being preferred over dedicated wired networks. However, conventional NCSs with event-triggered controllers and actuators cannot operate over such general purpose wireless networks since the stability of the system is compromised due to unbounded delays and unpredictable packet losses that are typical in the wireless medium. Approaching the wireless networked control problem from two perspectives, this work introduces a practical wireless NCS and an implementation of a cooperative medium access control protocol that work jointly to achieve decent control under severe impairments, such as unbounded delay, bursts of packet loss and ambient wireless traffic. The proposed system is evaluated on a dedicated test platform under numerous scenarios and significant performance gains are observed, making cooperative communications a strong candidate for improving the reliability of industrial wireless networks.

Abstract In wireless networks, opportunistic scheduling is used to increase system throughput by exploiting multi‐user diversity. Although recent advances have increased physical layer data rates supported in wireless local area networks (WLANs), actual throughput realized are significantly lower due to overhead. Accordingly, the frame aggregation concept is used in next generation WLANs to improve efficiency. However, with frame aggregation, traditional opportunistic schemes are no longer optimal. In this paper, we propose schedulers that take queue and channel conditions into account jointly, to maximize throughput observed at the users for next generation WLANs. We also extend this work to design two schedulers that perform block scheduling for maximizing network throughput over multiple transmission sequences. For these schedulers, which make decisions over long time durations, we model the system using queueing theory and determine users' temporal access proportions according to this model. Through detailed simulations, we show that all our proposed algorithms offer significant throughput improvement, better fairness, and much lower delay compared with traditional opportunistic schedulers, facilitating the practical use of the evolving standard for next generation wireless networks. Copyright © 2009 John Wiley & Sons, Ltd.

Cooperative transmissions emulate multi-antenna systems utilizing merely nodes equipped with single-antenna and the degree of performance enhancement is dependent upon the relay selection and actuation mechanism employed. An essential part in the realization of cooperative wireless networks is the design of efficient adaptive MAC protocols that empower distributed selection and actuation of the best relays in the network. In this paper, we propose and analyze a distributed relay selection and actuation scheme based on random access. Our method relies on slotted ALOHA based relay advertisements, and unlike the other protocols in the literature, it supports cooperation with multiple relays. We provide the analysis of the throughput gain provided by the proposed scheme and obtain the optimum channel access probability for the relays to announce their availability for cooperation. The proposed scheme renders simple distributed operation, which makes it suitable especially for densely deployed wireless sensor networks. Via simulations, we verify the validity of optimum cooperation probability solution and we show that the proposed actuation scheme can provide significant throughput enhancements and energy savings over direct transmission.

Cooperative communications is one of the promising techniques to enhance the performance of wireless networks. The extent of performance improvement needs to be carefully investigated, especially for wireless sensor networks, due to the overhead and energy costs involved with cooperation and the dependency on energy consumption models. In this paper, we propose a cooperative medium access control protocol, COMAC that enables cooperation in a realistic scenario using 802.11g based radios and leverages cooperative communications by making use of the overheard packets from neighboring nodes of a sender node. In an effort to determine the conditions under which cooperation is preferable, we evaluate COMAC's performance in comparison with standard 802.11 through detailed simulations, considering different physical layer data rates, varying transmission ranges, networks of different sizes and various energy consumption models. COMAC is shown to provide robustness to the wireless channel impairments, resulting in increased transmission range and improved packet success ratio in point-to- point scenarios. Throughput and energy efficiency performance is also quantified for multi-point-to-point scenarios with varying number of contending nodes. It is shown that cooperation with COMAC can provide significant enhancement in throughput, up to 23 times non-cooperative 802.11, together with energy savings of 50% even for high circuit energy consumption cases.

A major objective in wireless sensor networks is to find optimum routing strategies for energy efficient use of nodes. Routing decision and transmission power selection are intrinsically connected since the transmission power of a node is adjusted depending on the location of the next hop. In this paper, we propose a location-based routing framework to control the energy distribution in a network where transmission ranges, hence powers, of nodes are determined based on their locations. We show that the proposed framework is sufficiently general to investigate the minimum-energy and maximum-lifetime routing problems. It is shown that via the location based strategy the network lifetime can be improved by 70% and the total energy consumption can be decreased to three-fourths to one-third of the constant transmission range strategy depending on the propagation medium and the size of the network.

Opportunistic user access scheduling enhances the capacity of wireless networks by exploiting the multi user diversity. When frame aggregation is used, opportunistic schemes are no longer optimal, since users with high capacity links are frequently served, causing small queue sizes and low throughput. Recently, we have proposed schedulers that take queue and channel conditions into account jointly, to maximize the instantaneous throughput. In this paper, we extend this work to design a scheduler that performs block scheduling for maximizing network throughput over multiple transmission sequences. This scheduler makes use of the estimated evolution of the aggregation process by queueing theory and determines users' temporal access proportions using an approach based on the water-filling principle. Through detailed simulations, we show that our new algorithm with block scheduling offers further improvement in throughput over the previous schedulers, along with better fairness.

Wireless multimedia home servers are the next generation of home entertainment systems. From a single broadband connection entering home, the multimedia data is transmitted to TV and other peripherals by using only wireless links. Due to the high attenuation and multi-path fading environment caused by the walls as well as the contention of the channel by other users, the provision of service guarantees to time-critical services such as video streaming is extremely challenging. In our project, we use wireless mesh networks to combat with attenuation, and provide high end-to-end throughput to all users. We also use Enhanced Distributed Channel Access to combat with the channel contention for users with time critical services, e.g., video streaming. We use the latest video encoding standard H.264, which classifies the video packets according to their importance. In our prioritization technique, we use this classification in order to give a fair share of the channel to the ongoing data traffic, while providing a high quality video to the end users.

The multiuser diversity phenomenon is exploited via opportunistic scheduling for increasing system throughput in wireless networks. Another method to enhance system throughput is through frame aggregation, which increases MAC efficiency. We consider opportunistic scheduling jointly with frame aggregation. In this paper, we argue that existing opportunistic schemes are not optimal when frame aggregation is used. We propose new scheduling approaches that combine channel states with queue states. Through detailed simulations, we show that our new algorithms offer significant improvement in network throughput over non-opportunistic and greedy schedulers. Our algorithms also provide a good compromise between throughput and fairness.

This paper considers the problem of multiple video streaming over wireless local area networks. In particular, we propose video streaming techniques to improve the quality of video streams over the link from an access point to multiple wireless clients. The proposed video streaming techniques decide on clients to be served, packets to be (re)transmitted, and forward error correction (FEC) rates by considering video, channel, and network properties in a rate-distortion optimized manner. Multi-client rate distortion optimized video streaming is the first technique operated by an access point to jointly optimize client, packet, and FEC rate selection for video streaming. Second, we propose multi-client sub-optimal video streaming technique that optimizes packet and FEC rate, but not client. The client is selected by using the results of optimization to reduce the computational complexity. The simulation results show that the proposed video streaming techniques achieve signal-to-noise ratio (SNR) improvement up-to 5 dB as compared with time-division multiple access (TDMA) and packet adaptive TDMA.

We consider the downlink of a wireless network, where Tomlinson-Harashima precoding (THP) is applied as a MIMO spatial multiplexing method. THP facilitates a point-to-multipoint transmission strategy, in which a subset of mobile stations receives data packets over parallel subchannels formed by preceding. In this paper, we propose a low-complexity scheduling algorithm that determines the best subset of stations to maximize the system capacity. TH preceding is based on the QR factorization of the channel matrix H, and the proposed scheduling algorithm here makes use of incremental implementation for QR factorization with Gram-Schmidt algorithm. We show that significant reduction in complexity can be obtained over classical exhaustive search, while providing the same maximum capacity

In this paper, we investigate rate distortion optimized streaming of H.264 coded video sequences over time-varying wireless channels. Our main objective is to minimize average end-to-end distortion to satisfy a certain quality of service (QoS) by considering the media and channel characteristics such as packet importance, packet dependencies, decoding deadlines, channel state information and channel capacity. In particular, we propose a sender-driven optimized joint ARQ-FEC scheme that decides on packet transmissions, re-transmissions as well as the FEC rate used in each transmission. The optimized joint ARQ-FEC scheme along with packet scheduling aims to minimize a weighted sum of distortion and total transmission cost under capacity constraints. The other objective in this paper is to satisfy the QoS of the optimized joint ARQ-FEC scheme without minimizing end-to-end distortion. We improved two approximate algorithms that use the media and channel characteristics to transmit the best selected and FEC coded packet. The real-time simulation results with H.264 sequences demonstrate the efficacy of the all proposed algorithms over the classical error recovery scheme uses ARQ and FEC.

In this paper, we propose an automatic repeat request (ARQ) technique for enhancing the reliability and throughput of broadband wireless Internet access applications, and provide examples of its performance. ARQ is a method for making a link and flow more robust to errors. Other than enhancing link quality, ARQ provides early error recovery, so that the transport layer does not lower the data throughput. The cost of these enhancements is additional overhead. In this work, we have extensively analyzed our proposed ARQ scheme along with realistic wireless channel and protocol stack models. We have quantified the performance gains of our ARQ scheme as reduced end-to-end delay, increased throughput, SNR gain and fade margin, also providing the overhead costs. We have proposed and analyzed enhanced features namely, segmentation and reassembly (SAR) and bitmap compression. We showed that these features reduce the overhead, the extent of which depends on the nature of the errors.

Abstract Multi‐media support is an important feature of third generation (3G) wireless communication systems, and Quality of Service (QoS) is a crucial issue, as in any other networking environment. In this paper, the QoS issues in the wireless last‐mile is investigated for 3G systems based on Wideband‐Code division multiple access (W‐CDMA). Supporting multiple rates in the CDMA environment introduces the power assignment problem, which is coupled with the bandwidth and error QoS parameters. Also, multi‐media traffic flows should be classified and serviced in such a way to provision delay guarantees. In this paper, a new framework, namely dynamic resource scheduling (DRS), is described and extensively studied. In order to serve multi‐media services with different requirements, a family of nine algorithms has been developed within the DRS framework. These algorithms can be categorized with respect to single or prioritized queuing architectures, fixed or variable rate bandwidth and power allocation, and variable spreading gain or multi‐code spreading strategies. The paper presents the performance of the DRS algorithms in comparison with each other and with conventional scheduled‐CDMA (S‐CDMA) and proposed schemes in the W‐CDMA standard. The performance for error and throughput QoS provisioning and power control dynamics are explored; advantages, disadvantages and limitations of the algorithms are discussed. The DRS framework is concluded to be a promising QoS architecture, with a simple, flexible, scalable structure that can be configured according to a given traffic scenario. Copyright © 2004 John Wiley & Sons, Ltd.

W-CDMA is the strongest candidate as the air interface technology of the third generation mobile communication systems, which are expected to support multimedia services with QoS requirements. In this paper, we review the W-CDMA technology and consider the issues in multimedia support. We propose the dynamic resource scheduling mechanism for QoS provisioning in W-CDMA through optimal power assignment and code hopping. Our framework is able to carry variable QoS multimedia traffic, efficiently serving a wide range of classes with CBR, VBR, ABR and UBR characteristics. Dynamic resource scheduling improves capacity and throughput performance. Other advantages are power saving and faster convergence to the desired power level.