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THz Communications
Nano Communication Networks 10 (2016) iv–v
Contents lists available at ScienceDirect
Nano Communication Networks journal homepage: www.elsevier.com/locate/nanocomnet
Editorial
THz Communications
Nano-scale devices can be organized in nanonetworks in order to perform complicated tasks, composed of multiple devices communicating and cooperating with each other. Electromagnetic (EM) communication has been suggested as one of the possible approaches for the communication among nano-devices. In particular, the THz band (0.1–10 THz) can be utilized for EM communication based on transceivers employing, for example, graphene-enabled plasmonic nano antennas. Furthermore, the THz band is also considered very attractive for traditional, macro-scale wireless communications since it provides an abundant bandwidth which might be used for ultra-fast short range communications, wireless backhauling, or transmission in femtocells, among others. This special issue is dedicated to wireless communication in the THz band on nano and macro scales. Special emphasis lies on channel characterization and modeling, modulation, human tissue properties at THz frequencies, and realization aspects of THz communications. After rigorous peer review conducted by expert reviewers, eight invited papers were selected for inclusion in the special issue. In the following, a brief summary of the contributions of these papers is provided. The first paper ‘‘Practical Considerations of Terahertz Communications for Short Distance Applications’’ by Tadao Nagatsuma, Kazuki Oogimoto, Yuki Inubushi, and Jiro Hirokawa investigates several practical issues related to the realization of THz communications for short-distance applications. It is shown that the effect of standing waves between transmitter and receiver arising in near-field communications can be combated via suitable carrier modulation and antenna array structures. Furthermore, the effect of beam misalignment on an indoor communication over a few meters is analyzed for both THz and free-space optics (FSO) communications, indicating the superiority of the THz scheme. Throughout the paper, theoretical calculations are supported by experimental results which demonstrate the practical feasibility of a transmission in the 120 GHz band with 3 Gbit/s. In the second paper ‘‘Review of Weather Impact on Outdoor Terahertz Wireless Communication Links’’ by John F. Federici, Jianjun Ma, and Lothar Moeller, the effects of atmospheric weather conditions on THz communications are studied. For several weather scenarios, THz and FSO links are compared. It turns out that under clear weather, FSO links exhibit a longer range compared to THz links since the latter ones are affected by water vapor, whereas there is no major impediment for the former ones. However, THz transmission is less affected by fog, dust, and air turbulence. In case of rain, the performance of both turns out to be comparable. In summary, THz schemes are generally more robust for a wide range of weather conditions, rendering them a promising candidate for outdoor communications. http://dx.doi.org/10.1016/S1878-7789(16)30071-0
The third paper ‘‘Chirality Effects on Channel Modeling for THzBand Wireless Communications in LoS/NLoS Propagation’’ by Anna Maria Vegni and Valeria Loscrì studies the electromagnetic wave propagation in the THz regime considering chirality effects caused by metamaterials. A corresponding full-wave propagation model is developed for both line-of-sight (LoS) and non-line-of-sight (NLOS) conditions. Biological and indoor application scenarios are taken into account, and an analysis of the path loss shows that chirality effects can be beneficial for LOS. For media with Giant Optical Activity (GOA), the path loss is shown to be flat within the whole THz frequency range for both LOS and NLOS. In the fourth paper ‘‘Modulation and Rate Adaptation Algorithms for Terahertz Channels’’ by Farnoosh Moshir and Suresh Singh, a pulse modulation technique is described for THz channels. Special emphasis lies on rate adaptation which is crucial for THz systems since the channel attenuation varies heavily with the transmission distance. Scheduling algorithms are reported for handling multiple users with different distances to an access point. The numerical results rely on a channel model which has been derived from measurements. It is shown that date rates in the order of Tbit/s can be achieved in highly directional channels. The fifth paper, titled ‘‘Terahertz Electromagnetic Field Propagation in Human Tissues: a Study on Communication Capabilities’’ and authored by Giuseppe Piro, Piero Bia, Gennaro Boggia, Diego Caratelli, Luigi Alfredo Grieco and Luciano Mescia, presents a novel study of the propagation of electromagnetic fields across human body tissues, including epidermis, dermis and fat, among others. In particular, tools from Finite-Difference Time-Domain dispersive modeling are utilized to compute path-loss, noise and ultimately capacity of the intra-body channel. The results show that absorption imposes the main bottleneck for THz waves propagation in the body and motivates the development of innovative communication solutions In the sixth paper, ‘‘Fibroblasts Cell Number Density based Human Skin Characterization at THz for In-body Nanonetworks’’ by Nishtha Chopra, Ke Yang, Jamie Upton, Qammer H. Abbasi, Khalid Qaraqe, Mike Philpott and Akram Alomainy, the refractive index and absorption coefficient for collagen under different hydration conditions are experimentally measured by means of a THz time-domain spectroscopy platform. Such characterization provides very useful information to better understand and validate existing models of propagation of THz waves in body tissues such as the dermis. The results emphasize the negative impact of water (higher hydration in this case) on signal propagation. Finally, the last two papers are focused on enabling device technologies for THz communication networks. In the seventh paper, titled ‘‘Graphene Terahertz Devices for Communication Applications’’ and authored by Berardi Sensale-Rodriguez, Mehdi
Editorial / Nano Communication Networks 10 (2016) iv–v
Hasan, Sara Arezoomandan, and Hugo Condori, an extensive survey on graphene-based signal sources, modulators and detectors for THz communications is presented. Beyond the state of the art, open challenges and future directions are highlighted for electronic and plasmonic devices in the THz band In the eighth and final paper, ‘‘Ultrashort Optical Pulse Source Using Mach-Zehnder-Modulator-Based Flat Comb Generator’’ by Isao Morashi, Takahide Sakamoto, Norihiko Sekine, Akifumi Kasamatsu and Iwao Hosako, a new pulsed THz source based on a Mach-Zehnder-modulator-based flat comb generator and a dispersion-flattened dispersion-decreasing fiber is proposed. Previously, it has been theoretically shown that pulse-based THz communication can provide very high data rates while supporting very large node densities. This paper proposes, fabricates and experimentally characterizes a source able to support this communication paradigm.
v
In the papers of the special issue, various aspects of THz band communications for different applications are investigated. As pointed out in these works, there are still a number of important open research issues in this area. Therefore, we hope that these papers will inspire the readers to work on these problems and further advance the field. We would like to thank Prof. Ian F. Akyildiz, Editor-in-Chief Emeritus and Founder of Nano Communication Networks, and Naveen Raja and Daniel Wang from Elsevier for supporting us to organize this special issue. We also thank all authors and reviewers. Their valuable contributions made this special issue possible.
Wolfgang Gerstacker Josep Miquel Jornet
Contents lists available at ScienceDirect
Nano Communication Networks journal homepage: www.elsevier.com/locate/nanocomnet
Editorial
THz Communications
Nano-scale devices can be organized in nanonetworks in order to perform complicated tasks, composed of multiple devices communicating and cooperating with each other. Electromagnetic (EM) communication has been suggested as one of the possible approaches for the communication among nano-devices. In particular, the THz band (0.1–10 THz) can be utilized for EM communication based on transceivers employing, for example, graphene-enabled plasmonic nano antennas. Furthermore, the THz band is also considered very attractive for traditional, macro-scale wireless communications since it provides an abundant bandwidth which might be used for ultra-fast short range communications, wireless backhauling, or transmission in femtocells, among others. This special issue is dedicated to wireless communication in the THz band on nano and macro scales. Special emphasis lies on channel characterization and modeling, modulation, human tissue properties at THz frequencies, and realization aspects of THz communications. After rigorous peer review conducted by expert reviewers, eight invited papers were selected for inclusion in the special issue. In the following, a brief summary of the contributions of these papers is provided. The first paper ‘‘Practical Considerations of Terahertz Communications for Short Distance Applications’’ by Tadao Nagatsuma, Kazuki Oogimoto, Yuki Inubushi, and Jiro Hirokawa investigates several practical issues related to the realization of THz communications for short-distance applications. It is shown that the effect of standing waves between transmitter and receiver arising in near-field communications can be combated via suitable carrier modulation and antenna array structures. Furthermore, the effect of beam misalignment on an indoor communication over a few meters is analyzed for both THz and free-space optics (FSO) communications, indicating the superiority of the THz scheme. Throughout the paper, theoretical calculations are supported by experimental results which demonstrate the practical feasibility of a transmission in the 120 GHz band with 3 Gbit/s. In the second paper ‘‘Review of Weather Impact on Outdoor Terahertz Wireless Communication Links’’ by John F. Federici, Jianjun Ma, and Lothar Moeller, the effects of atmospheric weather conditions on THz communications are studied. For several weather scenarios, THz and FSO links are compared. It turns out that under clear weather, FSO links exhibit a longer range compared to THz links since the latter ones are affected by water vapor, whereas there is no major impediment for the former ones. However, THz transmission is less affected by fog, dust, and air turbulence. In case of rain, the performance of both turns out to be comparable. In summary, THz schemes are generally more robust for a wide range of weather conditions, rendering them a promising candidate for outdoor communications. http://dx.doi.org/10.1016/S1878-7789(16)30071-0
The third paper ‘‘Chirality Effects on Channel Modeling for THzBand Wireless Communications in LoS/NLoS Propagation’’ by Anna Maria Vegni and Valeria Loscrì studies the electromagnetic wave propagation in the THz regime considering chirality effects caused by metamaterials. A corresponding full-wave propagation model is developed for both line-of-sight (LoS) and non-line-of-sight (NLOS) conditions. Biological and indoor application scenarios are taken into account, and an analysis of the path loss shows that chirality effects can be beneficial for LOS. For media with Giant Optical Activity (GOA), the path loss is shown to be flat within the whole THz frequency range for both LOS and NLOS. In the fourth paper ‘‘Modulation and Rate Adaptation Algorithms for Terahertz Channels’’ by Farnoosh Moshir and Suresh Singh, a pulse modulation technique is described for THz channels. Special emphasis lies on rate adaptation which is crucial for THz systems since the channel attenuation varies heavily with the transmission distance. Scheduling algorithms are reported for handling multiple users with different distances to an access point. The numerical results rely on a channel model which has been derived from measurements. It is shown that date rates in the order of Tbit/s can be achieved in highly directional channels. The fifth paper, titled ‘‘Terahertz Electromagnetic Field Propagation in Human Tissues: a Study on Communication Capabilities’’ and authored by Giuseppe Piro, Piero Bia, Gennaro Boggia, Diego Caratelli, Luigi Alfredo Grieco and Luciano Mescia, presents a novel study of the propagation of electromagnetic fields across human body tissues, including epidermis, dermis and fat, among others. In particular, tools from Finite-Difference Time-Domain dispersive modeling are utilized to compute path-loss, noise and ultimately capacity of the intra-body channel. The results show that absorption imposes the main bottleneck for THz waves propagation in the body and motivates the development of innovative communication solutions In the sixth paper, ‘‘Fibroblasts Cell Number Density based Human Skin Characterization at THz for In-body Nanonetworks’’ by Nishtha Chopra, Ke Yang, Jamie Upton, Qammer H. Abbasi, Khalid Qaraqe, Mike Philpott and Akram Alomainy, the refractive index and absorption coefficient for collagen under different hydration conditions are experimentally measured by means of a THz time-domain spectroscopy platform. Such characterization provides very useful information to better understand and validate existing models of propagation of THz waves in body tissues such as the dermis. The results emphasize the negative impact of water (higher hydration in this case) on signal propagation. Finally, the last two papers are focused on enabling device technologies for THz communication networks. In the seventh paper, titled ‘‘Graphene Terahertz Devices for Communication Applications’’ and authored by Berardi Sensale-Rodriguez, Mehdi
Editorial / Nano Communication Networks 10 (2016) iv–v
Hasan, Sara Arezoomandan, and Hugo Condori, an extensive survey on graphene-based signal sources, modulators and detectors for THz communications is presented. Beyond the state of the art, open challenges and future directions are highlighted for electronic and plasmonic devices in the THz band In the eighth and final paper, ‘‘Ultrashort Optical Pulse Source Using Mach-Zehnder-Modulator-Based Flat Comb Generator’’ by Isao Morashi, Takahide Sakamoto, Norihiko Sekine, Akifumi Kasamatsu and Iwao Hosako, a new pulsed THz source based on a Mach-Zehnder-modulator-based flat comb generator and a dispersion-flattened dispersion-decreasing fiber is proposed. Previously, it has been theoretically shown that pulse-based THz communication can provide very high data rates while supporting very large node densities. This paper proposes, fabricates and experimentally characterizes a source able to support this communication paradigm.
v
In the papers of the special issue, various aspects of THz band communications for different applications are investigated. As pointed out in these works, there are still a number of important open research issues in this area. Therefore, we hope that these papers will inspire the readers to work on these problems and further advance the field. We would like to thank Prof. Ian F. Akyildiz, Editor-in-Chief Emeritus and Founder of Nano Communication Networks, and Naveen Raja and Daniel Wang from Elsevier for supporting us to organize this special issue. We also thank all authors and reviewers. Their valuable contributions made this special issue possible.
Wolfgang Gerstacker Josep Miquel Jornet