Papers by Nozhan Hosseini
IEEE Communications Letters, 2021
Drones, unmanned aerial vehicles (UAVs), or unmanned aerial systems (UAS) are expected to be an i... more Drones, unmanned aerial vehicles (UAVs), or unmanned aerial systems (UAS) are expected to be an important component of 5G/beyond 5G (B5G) communications. This includes their use within cellular architectures (5G UAVs), in which they can facilitate both wireless broadcast and point-to-point transmissions, usually using small UAS (sUAS). Allowing UAS to operate within airspace along with commercial, cargo, and other piloted aircraft will likely require dedicated and protected aviation spectrum at least in the near term, while regulatory authorities adapt to their use. The command and control (C2), or control and non-payload communications (CNPC) link provides safety critical information for the control of the UAV both in terrestrial-based line of sight (LOS) conditions and in satellite communication links for so-called beyond LOS (BLOS) conditions. In this paper, we provide an overview of these CNPC links as they may be used in 5G and satellite systems by describing basic concepts and...
ArXiv, 2020
In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a co... more In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection in [1]. We derive the analytical bit error ratio (BER) expression for binary chirp spread spectrum (BCSS) in the presence of multiple access interference (MAI) caused by correlation with other user signals because of either asynchronism or Doppler shifts, or both, and validate with simulations. To achieve this we analyze the signal cross correlations, and compare traditional linear chirps with our recently-proposed nonlinear chirps introduced in [1] and with other nonlinear chirps from the literature. In doing so we illustrate the superior performance of our new nonlinear chirp designs in these practical conditions, for the noncoherent counterpart of [1].
2017 Cognitive Communications for Aerospace Applications Workshop (CCAA), 2017
Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to... more Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to the relatively weak satellite signal at the ground stations. This can cause connection failures or degradation in performance at the ground station, which could in some cases be significant or even catastrophic. The great flexibility of software defined radio (SDR) systems facilitates the implementation of cognitive relays as a complementary entity that can help reduce the effects of interference. In this paper, we describe a cognitive SDR testbed that has been developed based on the Universal Software Radio Peripheral (USRP) and the GNU radio software platform. One of our testbed's aims is to evaluate error performance improvements of satellite signal relays in the presence of interference. We report on performance evaluation in terms of bit error ratio (BER) as a function of carrier-to-noise ratio (CNR) and in the presence of interference, for our detect and relay algorithms in an...
In the near future, there will be a need for accommodating large populations of fast moving Unman... more In the near future, there will be a need for accommodating large populations of fast moving Unmanned Aerial Systems (UAS) operating in uncontrolled, very low level (VLL) (below 500 ft.) airspace. As is well-known, real-time knowledge of the wireless propagation channel is essential for the effective design and optimization of wireless communication systems. In this paper, we propose a software defined radio (SDR) based channel sounder employing a wideband linear frequency modulated continuous wave (FMCW) or chirp waveform technique for low altitude air-to-air (AA) links. This paper discusses both matched filter and heterodyne detector implementations in the receiver, and investigates advantages and disadvantages of both architectures for an SDR implementation in an AA scenario. We also discuss proper windowing techniques in the transmitter to improve sounding resolution. Some proof of concept measurement results using SDRs are presented for a simulated UAS scenario.
2020 Integrated Communications Navigation and Surveillance Conference (ICNS), 2020
MILCOM 2019 - 2019 IEEE Military Communications Conference (MILCOM), 2019
IEEE Transactions on Communications, 2021
Multi user orthogonal chirp spread spectrum (OCSS) improves the spectral inefficiency of CSS but ... more Multi user orthogonal chirp spread spectrum (OCSS) improves the spectral inefficiency of CSS but is only feasible with perfect synchronism and without any channel distortion. Either asynchronism or channel distortion causes multiple access interference (MAI), which degrades performance. Conditions with small timing offsets we term quasi-synchronous (QS) transmission. In this paper, we investigate CSS signaling in QS conditions. We do this for the classical linear chirp, for which cross correlations can be derived analytically, and also propose two sets of nonlinear chirps to improve CSS system performance. We numerically evaluate cross-correlation distributions, and show that with an FSK-based chirp modulation, our two new nonlinear chirp designs outperform the classical linear chirp and multiple existing nonlinear chirps from the literature, over the QS additive white Gaussian noise channel in both partially and fully-loaded systems. We also demonstrate our nonlinear CSS designs outperform the existing chirps in a realistic dispersive channel, via simulations using an empirical air-ground channel.
2019 IEEE Aerospace Conference, 2019
Drones, unmanned aerial vehicles (UAVs), or unmanned aerial systems (UAS) are expected to be an i... more Drones, unmanned aerial vehicles (UAVs), or unmanned aerial systems (UAS) are expected to be an important component of 5G/beyond 5G (B5G) communications. This includes their use within cellular architectures (5G UAVs), in which they can facilitate both wireless broadcast and point-topoint transmissions, usually using small UAS (sUAS). Allowing UAS to operate within airspace along with commercial, cargo, and other piloted aircraft will likely require dedicated and protected aviation spectrum-at least in the near term, while regulatory authorities adapt to their use. The command and control (C2), or control and non-payload communications (CNPC) link provides safety critical information for the control of the UAV both in terrestrial-based line of sight (LOS) conditions and in satellite communication links for so-called beyond LOS (BLOS) conditions. In this paper, we provide an overview of these CNPC links as they may be used in 5G and satellite systems by describing basic concepts and challenges. We review new entrant technologies that might be used for UAV C2 as well as for payload communication, such as millimeter wave (mmWave) systems, and also review navigation and surveillance challenges. A brief discussion of UAV-to-UAV communication and hardware issues are also provided.
IEEE Transactions on Communications, 2021
In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a co... more In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection in [1]. We derive the analytical bit error ratio (BER) expression for binary chirp spread spectrum (BCSS) in the presence of multiple access interference (MAI) caused by correlation with other user signals because of either asynchronism or Doppler shifts, or both, and validate with simulations. To achieve this we analyze the signal cross correlations, and compare traditional linear chirps with our recently-proposed nonlinear chirps introduced in [1] and with other nonlinear chirps from the literature. In doing so we illustrate the superior performance of our new nonlinear chirp designs in these practical conditions, for the noncoherent counterpart of [1]. I. INTRODUCTION Communication systems experience multiple impairments depending on their environment. These include multipath channel distortion, Doppler spreading, and interference. Nonlinear distortion due to equipment (e.g., high power amplifier) non-idealities are also present, and these are particularly challenging for commonly used multicarrier signals, and even for single-carrier signals that employ non-constant-envelope signaling, e.g., amplitude modulation such as in quadrature amplitude modulation (QAM). Thus other signal types are of interest, and frequency modulated signals such as chirps are one such signal type. Chirps have been investigated for multiple purposes, e.g., communications, radar and channel characterization [2]-[7]. Constant amplitude chirp signals exhibit a desirable low peak-to-average-power ratio (PAPR) which enables longer link range or use of less expensive amplifiers. Chirps also have a sharp This work was partially supported by NASA, under award number NNX17AJ94A.
First and foremost, I want to thank Professor David W. Matolak for his guidance, support and trus... more First and foremost, I want to thank Professor David W. Matolak for his guidance, support and trust he dedicated to me and patience throughout my entire research and study. His professionalism, thoroughness and expertise in the field inspired me to follow his sense of duty for the rest of my life. I also want to thank my committee members who were more than generous with their expertise and precious time. Thank you Dr. Alphan Sahin, Dr.
2021 IEEE/AIAA 40th Digital Avionics Systems Conference (DASC)
IEEE Antennas and Propagation Magazine
https://ieeexplore.ieee.org/document/9391731, 2020
In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a c... more In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection in [1]. We derive the analytical bit error ratio (BER) expression for binary chirp spread spectrum (BCSS) in the presence of multiple access interference (MAI) caused by correlation with other user signals because of either asynchronism or Doppler shifts, or both, and validate with simulations. To achieve this we analyze the signal cross correlations, and compare traditional linear chirps with our recently-proposed nonlinear chirps introduced in [1] and with other nonlinear chirps from the literature. In doing so we illustrate the superior performance of our new nonlinear chirp designs in these practical conditions, for the noncoherent counterpart of [1].
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[Citation]: https://ieeexplore.ieee.org/document/9391731
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IEEE Transaction on Communication
Multi user orthogonal chirp spread spectrum (OCSS) can improve the spectral inefficiency of chirp... more Multi user orthogonal chirp spread spectrum (OCSS) can improve the spectral inefficiency of chirp spread spectrum (CSS) but is only feasible with perfect synchronism and without any channel dispersion. Asynchronism, channel dispersion, or unexpectedly large Doppler shifts can cause multiple access interference (MAI), which degrades performance. Conditions with small timing offsets we term “quasi-synchronous” (QS). In this paper, we propose two new sets of nonlinear chirps to improve CSS system performance in QS conditions. We analytically and numerically evaluate cross-correlation distributions. We also derive the bit error probability for Binary CSS analytically and validate our theoretical result with both numerical and simulation results; our error probability expression is applicable to any binary time-frequency (TF) chirp waveform. Finally, we show that in QS conditions our two new nonlinear chirp designs outperform the classical linear chirp and all existing nonlinear chirps from the literature. To complete our analysis, we demonstrate that our nonlinear CSS designs outperform existing chirps in two realistic (empirically modeled) dispersive air to ground channels.
https://ieeexplore.ieee.org/document/9340403
IEEE milcom 2019, 2019
https://ieeexplore.ieee.org/document/9021056/
.................................................. more https://ieeexplore.ieee.org/document/9021056/
......................................................................................................................................................................In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multiuser chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multiuser chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.
IEEE ICNS, 2018
https://ieeexplore.ieee.org/document/8384840 ....................................................... more https://ieeexplore.ieee.org/document/8384840 ......................................................................
Citation: N. Hosseini and D. W. Matolak, "Wide band channel characterization for low altitude unmanned aerial system communication using software defined radios," 2018 Integrated Communications, Navigation, Surveillance Conference (ICNS), Herndon, VA, 2018, pp. 2C2-1-2C2-9.
In the near future, there will be a need for accommodating large populations of fast moving Unmanned Aerial Systems (UAS) operating in uncontrolled, very low level (VLL) (below 500 ft.) airspace. As is well-known, real-time knowledge of the wireless propagation channel is essential for the effective design and optimization of wireless communication systems. In this paper, we propose a software defined radio (SDR) based channel sounder employing a wideband linear frequency modulated continuous wave (FMCW) or chirp waveform technique for low altitude air-to-air (AA) links. This paper discusses both matched filter and heterodyne detector implementations in the receiver, and investigates advantages and disadvantages of both architectures for an SDR implementation in an AA scenario. We also discuss proper windowing techniques in the transmitter to improve sounding resolution. Some proof of concept measurement results using SDRs are presented for a simulated UAS scenario.
IEEE AEROSPACE CONFERENCE, 2019
https://ieeexplore.ieee.org/abstract/document/8741719 ............................................ more https://ieeexplore.ieee.org/abstract/document/8741719 ..........................................................................................................................Citation: N. Hosseini, H. Jamal, J. Haque, T. Magesacher and D. W. Matolak, "UAV Command and Control, Navigation and Surveillance: A Review of Potential 5G and Satellite Systems," 2019 IEEE Aerospace Conference, Big Sky, MT, USA, 2019, pp. 1-10.
Drones, unmanned aerial vehicles (UAVs), or
unmanned aerial systems (UAS) are expected to be an important
component of 5G/beyond 5G (B5G) communications. This
includes their use within cellular architectures (5G UAVs), in
which they can facilitate both wireless broadcast and point-topoint transmissions, usually using small UAS (sUAS). Allowing
UAS to operate within airspace along with commercial, cargo,
and other piloted aircraft will likely require dedicated and
protected aviation spectrum—at least in the near term, while
regulatory authorities adapt to their use. The command and
control (C2), or control and non-payload communications
(CNPC) link provides safety critical information for the control
of the UAV both in terrestrial-based line of sight (LOS)
conditions and in satellite communication links for so-called
beyond LOS (BLOS) conditions. In this paper, we provide an
overview of these CNPC links as they may be used in 5G and
satellite systems by describing basic concepts and challenges.
We review new entrant technologies that might be used for UAV
C2 as well as for payload communication, such as millimeter
wave (mmWave) systems, and also review navigation and
surveillance challenges. A brief discussion of UAV-to
IEEE CCAA, 2017
https://ieeexplore.ieee.org/document/8001874 .........................................
Citation... more https://ieeexplore.ieee.org/document/8001874 .........................................
Citation: N. Hosseini and D. W. Matolak, "Software defined radios as cognitive relays for satellite ground stations incurring terrestrial interference," 2017 Cognitive Communications for Aerospace Applications Workshop (CCAA), Cleveland, OH, 2017, pp. 1-4.
Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to the relatively weak satellite signal at the ground stations. This can cause connection failures or degradation in performance at the ground station, which could in some cases be significant or even catastrophic. The great flexibility of software defined radio (SDR) systems facilitates the implementation of cognitive relays as a complementary entity that can help reduce the effects of interference. In this paper, we describe a cognitive SDR testbed that has been developed based on the Universal Software Radio Peripheral (USRP) and the GNU radio software platform. One of our testbed's aims is to evaluate error performance improvements of satellite signal relays in the presence of interference. We report on performance evaluation in terms of bit error ratio (BER) as a function of carrier-to-noise ratio (CNR) and in the presence of interference, for our detect and relay algorithms in an example frequency band, using an emulated desired (satellite-relay-ground station) signal. Our testbed contains four separate segments: satellite (emulated), relay, interferer, and ground receiver. At each segment, we transmit and/or receive signals via SDRs or standard communication laboratory equipment. We consider two relaying protocols in our work, amplify-and-forward (AF), and decode-and-forward (DF). Initial experiments were indoors, although outdoor testing with small unmanned aircraft systems is planned for future work. Our experiments explore the effects of different relaying techniques, and provide some quantitative results on performance improvements via our software defined radio approach.
Thesis Chapters by Nozhan Hosseini
https://scholarcommons.sc.edu/etd/6032/
*********************************************************... more https://scholarcommons.sc.edu/etd/6032/
***********************************************************************Many wireless communication systems will need to accommodate a larger number of users in the future. One application in particular in which this is critical is low data rate, long range communication links with very large numbers of nodes, such as the internet of things (IoT), possibly the internet of flying things (IoFT), etc. These systems demand advanced multi-access techniques with minimal multiple access interference (MAI). They should also be robust to multiple impairments, including multipath channel distortions, Doppler spreading, and interference. Chirp waveforms are one type of waveform set that can satisfy future system demands in the presence of these impairments. When the constant amplitude variety of chirp is used, this exhibits a desirable very low peak to average power ratio (PAPR). The ridge-shaped ambiguity function of chirp signals can also be useful for radar and channel modeling (sounding) applications. Hence chirps are promising candidates for many such applications. Chirps are specified in the IEEE 802.15.4a standard as chirp spread spectrum (CSS). Another growing application area requiring advanced communications is aviation. In particular, unmanned aircraft systems (UAS), also known as unmanned aerial vehicles (UAVs), and “drones,” will in the future operate within airspace along with commercial, cargo, and other piloted aircraft. The command and control (C2), or control and non-payload communications (CNPC) link must provide highly reliable safety critical information for the control of the UAV both in terrestrial-based line of sight conditions and in satellite communication links. Chirp signaling features make chirp signal sets good candidates to meet CNPC link requirements.
In this dissertation, we investigate multi-user chirp signaling for future aviation communication and channel sensing systems. We describe the basics of chirp signaling, chirp sounding, and investigate via mathematical analysis, computer simulations, and some experiments, the effects of aviation channel-induced non-idealities such as Doppler and asynchronism on the chirp signaling schemes. We also describe a hybrid design where the system is not only a communication entity but also does channel estimation (sounding). We describe methods to increase spectral efficiency and how to avoid multiple access interference among users (and intersymbol interference for a given user). We also conducted experiments on chirp channel sounding using a small drone and software defined radios, and provide some channel characterization results.
The majority of this work, and our major contributions, pertain to detailed evaluation of performance of multi-user chirp spread spectrum systems under a variety of conditions. We find, analytically, new expressions for bit error rate performance of binary coherent and noncoherent chirp spread spectrum signals, and we compare and validate numerical and analytical results with simulations. These error probability expressions are general, and can be used for any multi-user chirp signaling set. We also design more practical sets of chirp signals that out-perform existing chirp signal sets when synchronization is imperfect, a condition we term quasi-synchronous. These new practical chirp designs employ nonlinear trajectories in the time-frequency plane. Our new chirp designs also outperform existing schemes in the presence of Doppler shifts. We provide examples of air to ground link performance with empirical channel models to illustrate the superior performance of our proposed designs.
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Papers by Nozhan Hosseini
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[Citation]: https://ieeexplore.ieee.org/document/9391731
*************
https://ieeexplore.ieee.org/document/9340403
......................................................................................................................................................................In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multiuser chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multiuser chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.
Citation: N. Hosseini and D. W. Matolak, "Wide band channel characterization for low altitude unmanned aerial system communication using software defined radios," 2018 Integrated Communications, Navigation, Surveillance Conference (ICNS), Herndon, VA, 2018, pp. 2C2-1-2C2-9.
In the near future, there will be a need for accommodating large populations of fast moving Unmanned Aerial Systems (UAS) operating in uncontrolled, very low level (VLL) (below 500 ft.) airspace. As is well-known, real-time knowledge of the wireless propagation channel is essential for the effective design and optimization of wireless communication systems. In this paper, we propose a software defined radio (SDR) based channel sounder employing a wideband linear frequency modulated continuous wave (FMCW) or chirp waveform technique for low altitude air-to-air (AA) links. This paper discusses both matched filter and heterodyne detector implementations in the receiver, and investigates advantages and disadvantages of both architectures for an SDR implementation in an AA scenario. We also discuss proper windowing techniques in the transmitter to improve sounding resolution. Some proof of concept measurement results using SDRs are presented for a simulated UAS scenario.
Drones, unmanned aerial vehicles (UAVs), or
unmanned aerial systems (UAS) are expected to be an important
component of 5G/beyond 5G (B5G) communications. This
includes their use within cellular architectures (5G UAVs), in
which they can facilitate both wireless broadcast and point-topoint transmissions, usually using small UAS (sUAS). Allowing
UAS to operate within airspace along with commercial, cargo,
and other piloted aircraft will likely require dedicated and
protected aviation spectrum—at least in the near term, while
regulatory authorities adapt to their use. The command and
control (C2), or control and non-payload communications
(CNPC) link provides safety critical information for the control
of the UAV both in terrestrial-based line of sight (LOS)
conditions and in satellite communication links for so-called
beyond LOS (BLOS) conditions. In this paper, we provide an
overview of these CNPC links as they may be used in 5G and
satellite systems by describing basic concepts and challenges.
We review new entrant technologies that might be used for UAV
C2 as well as for payload communication, such as millimeter
wave (mmWave) systems, and also review navigation and
surveillance challenges. A brief discussion of UAV-to
Citation: N. Hosseini and D. W. Matolak, "Software defined radios as cognitive relays for satellite ground stations incurring terrestrial interference," 2017 Cognitive Communications for Aerospace Applications Workshop (CCAA), Cleveland, OH, 2017, pp. 1-4.
Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to the relatively weak satellite signal at the ground stations. This can cause connection failures or degradation in performance at the ground station, which could in some cases be significant or even catastrophic. The great flexibility of software defined radio (SDR) systems facilitates the implementation of cognitive relays as a complementary entity that can help reduce the effects of interference. In this paper, we describe a cognitive SDR testbed that has been developed based on the Universal Software Radio Peripheral (USRP) and the GNU radio software platform. One of our testbed's aims is to evaluate error performance improvements of satellite signal relays in the presence of interference. We report on performance evaluation in terms of bit error ratio (BER) as a function of carrier-to-noise ratio (CNR) and in the presence of interference, for our detect and relay algorithms in an example frequency band, using an emulated desired (satellite-relay-ground station) signal. Our testbed contains four separate segments: satellite (emulated), relay, interferer, and ground receiver. At each segment, we transmit and/or receive signals via SDRs or standard communication laboratory equipment. We consider two relaying protocols in our work, amplify-and-forward (AF), and decode-and-forward (DF). Initial experiments were indoors, although outdoor testing with small unmanned aircraft systems is planned for future work. Our experiments explore the effects of different relaying techniques, and provide some quantitative results on performance improvements via our software defined radio approach.
Thesis Chapters by Nozhan Hosseini
***********************************************************************Many wireless communication systems will need to accommodate a larger number of users in the future. One application in particular in which this is critical is low data rate, long range communication links with very large numbers of nodes, such as the internet of things (IoT), possibly the internet of flying things (IoFT), etc. These systems demand advanced multi-access techniques with minimal multiple access interference (MAI). They should also be robust to multiple impairments, including multipath channel distortions, Doppler spreading, and interference. Chirp waveforms are one type of waveform set that can satisfy future system demands in the presence of these impairments. When the constant amplitude variety of chirp is used, this exhibits a desirable very low peak to average power ratio (PAPR). The ridge-shaped ambiguity function of chirp signals can also be useful for radar and channel modeling (sounding) applications. Hence chirps are promising candidates for many such applications. Chirps are specified in the IEEE 802.15.4a standard as chirp spread spectrum (CSS). Another growing application area requiring advanced communications is aviation. In particular, unmanned aircraft systems (UAS), also known as unmanned aerial vehicles (UAVs), and “drones,” will in the future operate within airspace along with commercial, cargo, and other piloted aircraft. The command and control (C2), or control and non-payload communications (CNPC) link must provide highly reliable safety critical information for the control of the UAV both in terrestrial-based line of sight conditions and in satellite communication links. Chirp signaling features make chirp signal sets good candidates to meet CNPC link requirements.
In this dissertation, we investigate multi-user chirp signaling for future aviation communication and channel sensing systems. We describe the basics of chirp signaling, chirp sounding, and investigate via mathematical analysis, computer simulations, and some experiments, the effects of aviation channel-induced non-idealities such as Doppler and asynchronism on the chirp signaling schemes. We also describe a hybrid design where the system is not only a communication entity but also does channel estimation (sounding). We describe methods to increase spectral efficiency and how to avoid multiple access interference among users (and intersymbol interference for a given user). We also conducted experiments on chirp channel sounding using a small drone and software defined radios, and provide some channel characterization results.
The majority of this work, and our major contributions, pertain to detailed evaluation of performance of multi-user chirp spread spectrum systems under a variety of conditions. We find, analytically, new expressions for bit error rate performance of binary coherent and noncoherent chirp spread spectrum signals, and we compare and validate numerical and analytical results with simulations. These error probability expressions are general, and can be used for any multi-user chirp signaling set. We also design more practical sets of chirp signals that out-perform existing chirp signal sets when synchronization is imperfect, a condition we term quasi-synchronous. These new practical chirp designs employ nonlinear trajectories in the time-frequency plane. Our new chirp designs also outperform existing schemes in the presence of Doppler shifts. We provide examples of air to ground link performance with empirical channel models to illustrate the superior performance of our proposed designs.
************
[Citation]: https://ieeexplore.ieee.org/document/9391731
*************
https://ieeexplore.ieee.org/document/9340403
......................................................................................................................................................................In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multiuser chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multiuser chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.
Citation: N. Hosseini and D. W. Matolak, "Wide band channel characterization for low altitude unmanned aerial system communication using software defined radios," 2018 Integrated Communications, Navigation, Surveillance Conference (ICNS), Herndon, VA, 2018, pp. 2C2-1-2C2-9.
In the near future, there will be a need for accommodating large populations of fast moving Unmanned Aerial Systems (UAS) operating in uncontrolled, very low level (VLL) (below 500 ft.) airspace. As is well-known, real-time knowledge of the wireless propagation channel is essential for the effective design and optimization of wireless communication systems. In this paper, we propose a software defined radio (SDR) based channel sounder employing a wideband linear frequency modulated continuous wave (FMCW) or chirp waveform technique for low altitude air-to-air (AA) links. This paper discusses both matched filter and heterodyne detector implementations in the receiver, and investigates advantages and disadvantages of both architectures for an SDR implementation in an AA scenario. We also discuss proper windowing techniques in the transmitter to improve sounding resolution. Some proof of concept measurement results using SDRs are presented for a simulated UAS scenario.
Drones, unmanned aerial vehicles (UAVs), or
unmanned aerial systems (UAS) are expected to be an important
component of 5G/beyond 5G (B5G) communications. This
includes their use within cellular architectures (5G UAVs), in
which they can facilitate both wireless broadcast and point-topoint transmissions, usually using small UAS (sUAS). Allowing
UAS to operate within airspace along with commercial, cargo,
and other piloted aircraft will likely require dedicated and
protected aviation spectrum—at least in the near term, while
regulatory authorities adapt to their use. The command and
control (C2), or control and non-payload communications
(CNPC) link provides safety critical information for the control
of the UAV both in terrestrial-based line of sight (LOS)
conditions and in satellite communication links for so-called
beyond LOS (BLOS) conditions. In this paper, we provide an
overview of these CNPC links as they may be used in 5G and
satellite systems by describing basic concepts and challenges.
We review new entrant technologies that might be used for UAV
C2 as well as for payload communication, such as millimeter
wave (mmWave) systems, and also review navigation and
surveillance challenges. A brief discussion of UAV-to
Citation: N. Hosseini and D. W. Matolak, "Software defined radios as cognitive relays for satellite ground stations incurring terrestrial interference," 2017 Cognitive Communications for Aerospace Applications Workshop (CCAA), Cleveland, OH, 2017, pp. 1-4.
Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to the relatively weak satellite signal at the ground stations. This can cause connection failures or degradation in performance at the ground station, which could in some cases be significant or even catastrophic. The great flexibility of software defined radio (SDR) systems facilitates the implementation of cognitive relays as a complementary entity that can help reduce the effects of interference. In this paper, we describe a cognitive SDR testbed that has been developed based on the Universal Software Radio Peripheral (USRP) and the GNU radio software platform. One of our testbed's aims is to evaluate error performance improvements of satellite signal relays in the presence of interference. We report on performance evaluation in terms of bit error ratio (BER) as a function of carrier-to-noise ratio (CNR) and in the presence of interference, for our detect and relay algorithms in an example frequency band, using an emulated desired (satellite-relay-ground station) signal. Our testbed contains four separate segments: satellite (emulated), relay, interferer, and ground receiver. At each segment, we transmit and/or receive signals via SDRs or standard communication laboratory equipment. We consider two relaying protocols in our work, amplify-and-forward (AF), and decode-and-forward (DF). Initial experiments were indoors, although outdoor testing with small unmanned aircraft systems is planned for future work. Our experiments explore the effects of different relaying techniques, and provide some quantitative results on performance improvements via our software defined radio approach.
***********************************************************************Many wireless communication systems will need to accommodate a larger number of users in the future. One application in particular in which this is critical is low data rate, long range communication links with very large numbers of nodes, such as the internet of things (IoT), possibly the internet of flying things (IoFT), etc. These systems demand advanced multi-access techniques with minimal multiple access interference (MAI). They should also be robust to multiple impairments, including multipath channel distortions, Doppler spreading, and interference. Chirp waveforms are one type of waveform set that can satisfy future system demands in the presence of these impairments. When the constant amplitude variety of chirp is used, this exhibits a desirable very low peak to average power ratio (PAPR). The ridge-shaped ambiguity function of chirp signals can also be useful for radar and channel modeling (sounding) applications. Hence chirps are promising candidates for many such applications. Chirps are specified in the IEEE 802.15.4a standard as chirp spread spectrum (CSS). Another growing application area requiring advanced communications is aviation. In particular, unmanned aircraft systems (UAS), also known as unmanned aerial vehicles (UAVs), and “drones,” will in the future operate within airspace along with commercial, cargo, and other piloted aircraft. The command and control (C2), or control and non-payload communications (CNPC) link must provide highly reliable safety critical information for the control of the UAV both in terrestrial-based line of sight conditions and in satellite communication links. Chirp signaling features make chirp signal sets good candidates to meet CNPC link requirements.
In this dissertation, we investigate multi-user chirp signaling for future aviation communication and channel sensing systems. We describe the basics of chirp signaling, chirp sounding, and investigate via mathematical analysis, computer simulations, and some experiments, the effects of aviation channel-induced non-idealities such as Doppler and asynchronism on the chirp signaling schemes. We also describe a hybrid design where the system is not only a communication entity but also does channel estimation (sounding). We describe methods to increase spectral efficiency and how to avoid multiple access interference among users (and intersymbol interference for a given user). We also conducted experiments on chirp channel sounding using a small drone and software defined radios, and provide some channel characterization results.
The majority of this work, and our major contributions, pertain to detailed evaluation of performance of multi-user chirp spread spectrum systems under a variety of conditions. We find, analytically, new expressions for bit error rate performance of binary coherent and noncoherent chirp spread spectrum signals, and we compare and validate numerical and analytical results with simulations. These error probability expressions are general, and can be used for any multi-user chirp signaling set. We also design more practical sets of chirp signals that out-perform existing chirp signal sets when synchronization is imperfect, a condition we term quasi-synchronous. These new practical chirp designs employ nonlinear trajectories in the time-frequency plane. Our new chirp designs also outperform existing schemes in the presence of Doppler shifts. We provide examples of air to ground link performance with empirical channel models to illustrate the superior performance of our proposed designs.