International Journal of Wireless Information Networks, 2003
UWB has been the source of heated debate since the Federal Communications Commission made their f... more UWB has been the source of heated debate since the Federal Communications Commission made their first report and order in February, 2002. The promise of UWB was originally low cost, low power, high data rate, robust communications with the added benefit of location and tracking built in as a result of the inherent physical properties of the signal. What has emerged over the last 12 months has been a wealth of UWB concepts that offer only some of the benefits. The UWB world still has some distance to travel. Because of the huge bandwidth available, the capacity of UWB systems is potentially enormous. Quantifying this capacity in the rich multipath environment of the UWB channel is a challenging task. The capacity problem is addressed in this issue by examining the performance of a number of modulation schemes. Developing the signaling schemes to achieve this high capacity requires the development of novel approaches to modulation. Included in this issue is a paper examining the combination of pulse shape and pulse position modulation, which allows for increased data rates in UWB channels. The rich multipath environment also creates challenges for receiver design. Conventional RAKE structures need to be substantially revised to operate in an effective manner. This is addressed in this issue by considering simplified channel conditions that make analysis more tractable. One of the main concerns with UWB is the impact of interference on existing “victim” systems. This is addressed in one paper in this issue in which the impact of very high power UWB interference is examined for 802.11b systems. The results are very promising with noticeable interference under extremely heavy UWB interference conditions. The very low power permitted for UWB signals makes practical system implementation difficult. In particular the problem of signal acquisition poses specific problems for UWB systems. Signal acquisition is addressed in this issue with the examination of a hybrid acquisition scheme. The challenges to be overcome by researchers and engineers are substantial before the promise of UWB can be truly achieved. The efforts to date have shown that UWB is an extraordinary opportunity to redefine the way
VTT Technical Research Centre of Finland appointed its third Scientific Advisory Board (SAB) for ... more VTT Technical Research Centre of Finland appointed its third Scientific Advisory Board (SAB) for the period 2011-2012. The SAB held four thematic meetings during the period. The meeting themes were based on the VTT Research and Innovation Vision 2020. This final report describes the SAB's key findings regarding VTT´s research and scientific activities and competences within the selected thematic areas as well as its recommendations and proposals for the future.
Executive summary: main research challenges Vision: Trustworthy 6G. The challenges in creating a ... more Executive summary: main research challenges Vision: Trustworthy 6G. The challenges in creating a trustworthy 6G are multidisciplinary spanning technology, regulation, techno-economics, politics and ethics. A combination of the current regulation, economic incentives and technology are maintaining the current level of hacking, lack of trust, privacy and security on the Internet. In 6G, this will not suffice, because physical safety will more and more depend on information technology and the networks we use for communication. Therefore, we need trustworthy 6G. The roles of trust, security and privacy are somewhat interconnected, but different facets of next generation networks. This white paper addresses their fundamental research challenges. Research challenge 1: Inherited and novel threats in 6G scale. The diversity and volume of novel IoT devices and their control systems will continue to pose significant security and privacy risks and additional threat vectors as we move from 5G to beyond towards 6G system. The volume of new IoT devices introduced into 6G network will increase 10x from 10 billion scale of 5G networks to 100 billion scale in 6G. As a result of such deployment and use of 6G, the dependence of the economy and societies on IT and the networks will deepen. Safety will depend on IT and the networks. The development of AI blurs the line between reality and fake content and helps to create ever more intelligent attacks. The role of IT and the networks in national security keeps rising-a continuation of what we see in 5G. Research challenge 2: End-to-end trust in 6G. In current "open internet" regulation, the telco cloud can be used for trust services only equally for all users. 6G should position the future cellular network as a solution to the all issues of trustworthy or trust networking such that network based information technology can be trusted to provide expected outcomes even in the face of malicious actors trying to interfere. 6G network must support embedded trust such that the resulting level of information security in 6G and the packet data networks where 6G provides connectivity to is significantly better than in state-of-the art networks commonly used today. Trust modeling, trust policies and trust mechanisms need to be defined. Research challenge 3: Post-quantum cryptography and security architecture for 6G. The current 5G standard does not address the issue of quantum computing but relies on traditional cryptography. The development towards cloud and edge native infrastructures is expected to continue in 6G networks. While large-scale quantum computing can be expected to take longer, it is time to prepare for the shift to cryptography that is secure in the post-quantum world. According to current knowledge, contemporary symmetric cryptography remains secure for the most part even after the advent of quantum computing. Future of SIM cards and use of asymmetric cryptography will be interesting research questions. Research challenge 4: Machine-learning as tool and risk in softwarized 6G. As 6G moves toward THz spectrum with much higher bandwidth, more densification and cloudification for a hyper connected world by joining billions of devices and nodes with global reach for terrestrial, ocean and space, automated security utilizing the concepts of security function softwarization and virtualization, and machine learning will be inevitable. There are two facets: on the one hand, security algorithms can use machine learning to orchestrate attacks and respond to them in an optimal way. On the other hand, also the attacking algorithms can learn better how the network operates and create better attacks. Continuous deep learning is needed on a packet/byte level and applying machine learning to enforce policies, detect, contain, mitigate and prevent threats or active attacks. Research challenge 5: Physical layer security in 6G. Physical layer security techniques can represent efficient solutions for securing the most critical and less investigated network segments which are the ones between the body sensors and a sink or a hub node. Research questions include which are the most suitable physical layer features to be exploited for the definition of security algorithms in 6G challenging environment characterized by high network scalability, heterogeneous devices and different forms of malicious attacks, and should PhySec be a stand-alone security design or interactions with upper layers are mandatory in 6G networks. Research challenge 6: Privacy as exploited resource in 6G. The relevance specifically for 6G is that, 5G is still largely device / network specific, 6G envisages far more immersive engagement with the network. It is now the subject of ongoing discussion in the standards world. There is currently no way to unambiguously determine when linked, deidentified datasets cross the threshold to become personally identifiable. This is a major, unaddressed problem for many digital technologies in different sectors, such as in Smart Healthcare, Industrial Automation, and Smart Transportation. Courts in different parts of the world are making decisions about whether privacy is being infringed without formal measures of the level of personal information, while companies are seeking new ways to exploit private data to create new business revenues. As solution alternatives, we may consider blockchain, distributed ledger technologies and differential privacy approaches.
The Generative Adversarial Network (GAN) has recently been applied to generate synthetic images f... more The Generative Adversarial Network (GAN) has recently been applied to generate synthetic images from text. Despite significant advances, most current state-of-the-art algorithms are regular-grid region based; when attention is used, it is mainly applied between individual regular-grid regions and a word. These approaches are sufficient to generate images that contain a single object in its foreground, such as a "bird" or "flower". However, natural languages often involve complex foreground objects and the background may also constitute a variable portion of the generated image. Therefore, the regular-grid based image attention weights may not necessarily concentrate on the intended foreground region(s), which in turn, results in an unnatural looking image. Additionally, individual words such as "a", "blue" and "shirt" do not necessarily provide a full visual context unless they are applied together. For this reason, in our paper, we ...
Proceedings of GLOBECOM'96. 1996 IEEE Global Telecommunications Conference
This paper reports on a series of simulations designed to investigate the efficiency of a low mob... more This paper reports on a series of simulations designed to investigate the efficiency of a low mobility direct sequence, spread spectrum (DS-SS) cellular system operating over a 2.0 GHz wireless local loop (WLL). The WLL consists of a base station with omnidirectional antenna at roof-top height, or pole-mounted, transmitting to a receiver terminal which also uses an omnidirectional antenna. The receiver is always considered inside a building. The simulations and efficiency calculations were performed using wideband channel responses taken from experimental data at many locations worldwide representing both urban and suburban environments. The aim of the system is to provide data rates appropriate for voice communications for the maximum possible numbers of simultaneous users each with low mobility. The system modelled utilises a linear adaptive receiver structure to minimise the multiple access interference (MAI) experienced from other users. The performance of the system in terms of total efficiency is considered while maintaining a specific BER. The performance is compared to that of a similar system based on conventional matched filter DS-SS receiver. This paper will show that there is substantial gain to be achieved from using the adaptive receiver system in each of the propagation environments considered
This paper focuses on the performance analysis of the decorrelating multipath combining receiver ... more This paper focuses on the performance analysis of the decorrelating multipath combining receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER with channel uncertainty. The pilot-symbol aided linear minimum mean-square channel estimator is considered to obtain an accurate channel estimate and to obtain an expression for the variance of the channel estimation er...
Short-range low power radio frequency systems such as Bluetooth and UWB enable the deployment of ... more Short-range low power radio frequency systems such as Bluetooth and UWB enable the deployment of wireless personal area networks (WPAN). A WPAN can interface to larger networks to provide broader network access and Internet connectivity. We evaluate the performance of TCP over an integrated WLAN and WPAN system using a real network testbed. The end-to-end throughput is found to increase, when the window size is increased. However, for large window sizes, measurement results revealed that a wide range of round trip times (RTTs) is experienced. With small window sizes, the variability in the RTT is smaller. The measurements showed that in an integrated network long RTT delays and frequent duplicate acknowledgements lead to an increase in the number of packets transmitted unnecessarily. We study the effect of the number of active short-range devices (Bluetooth in this case) in a piconet. The results show that as the number of active slaves present in the WPAN increases, the bandwidth received by slaves exchanging data decreases. This behaviour is attributed to the Bluetooth scheduling mechanism which uses the round robin polling method. The main finding of our experiments is that for Bluetooth to be successful in enabling WPAN, the time slot allocation scheme should be efficient and fair. Finally, the issue of fair bandwidth allocation among multiple TCP streams is also investigated. The results show that for small number of TCP connections, the bandwidth is fairly distributed. However, as the number of simultaneous TCP connections increases, bandwidth distribution seems to become somewhat less fair.
... and Modeling 188 6.5.1 State of the Art 190 6.5.2 Channel Modeling Process 206 ... in the des... more ... and Modeling 188 6.5.1 State of the Art 190 6.5.2 Channel Modeling Process 206 ... in the design process (The self-fulfilling prophecy) 21 Figure 3.6 Full scenario development 26 Figure ... 92 Figure 4.12 The three concepts of OWL-S 99 Figure 4.13 Example ontology fragments for ...
This paper presents a study of a MC-CDMA system. Different diversity combining techniques in an u... more This paper presents a study of a MC-CDMA system. Different diversity combining techniques in an uplink and downlink channel; single and multiuser detection strategies; and an interference cancellation method have been considered. The performance of the system has been evaluated by simulations. F. Swarts et al. (eds.), CDMA Techniques for Third Generation Mobile Systems
Ultra-Wideband Wireless Communications and Networks, 2006
It is known that the ultra-wideband (UWB) developmental efforts are divided into two camps in ind... more It is known that the ultra-wideband (UWB) developmental efforts are divided into two camps in industry, that is, the Direct-Sequence (DS) UWB camp led by Motorola and Freescale (DS-UWB, http://www.uwbforum.org/), and the Multiband OFDM Alliance (MBOA) led by Intel, TI, and other companies (MBOA, http://www.wimedia.org/index. html). The physical layer and Medium Access Control (MAC) layer of these two camps are different. The readers may refer to [1] and [2] for the details of the PHY specifications of DS-UWB and MBOA, respectively. In this chapter, we would focus on the MAC layer. The DS-UWB camp still utilizes the IEEE 802.15.3 as the MAC support, which was originally designed for the high speed Wireless Personal Area Networks (WPAN) [3]; while the MBOA Special Interest Group (SIG) is defining its own MAC standard [4]. These two MAC specifications are rather different. Because the MBOA MAC has not been finalized, this chapter will mainly study the IEEE 802.15.3 MAC protocol. 8.1.1 Overview of IEEE 802.15.3 MAC A WPAN defined by the IEEE 802.15.3 is a wireless ad hoc data communication system that allows a number of independent devices (DEVs) to communicate with each other. Such a network is called a piconet, as shown in Figure 8.1(a). The DEV is designed to be low power and low cost. One DEV is required to perform the role of PNC (Piconet Coordinator), which provides the basic timing for the piconet as well as other piconet management functions, such as power management, Quality of Service (QoS) scheduling, security, and so on.
International Journal of Wireless Information Networks, 2003
This paper presents the results of a coexistence study investigating the impact of ultra-wideband... more This paper presents the results of a coexistence study investigating the impact of ultra-wideband (UWB) interference on IEEE 802.11b and Bluetooth networks. The results are based on the experimental test measurements made at the University of Oulu, Finland. Simple high-power UWB transmitters are used to interfere with victim networks. Preliminary results show that only under extreme interference conditions with thousands of equivalent Federal Communications Commission-(FCC)-compliant devices in close proximity, will the IEEE 802.11b and Bluetooth networks experience significant performance degradation. The impact of the UWB interference on the IEEE 802.11b network was insignificant if the distance to UWB transmitters was greater than 40 cm. The impact on Bluetooth was even less noticeable. In our study, several high-power UWB transmitters that greatly exceed the FCC radiation regulations have been used, and the measurement settings presents the worst case scenario because of the very short distance between the interferers and the victim system. Effectively our study approximates the use of thousands of FCC-complaint UWB devices in the same space.
The paper presents results of a coexistence measurement study between multiple ultra wideband (UW... more The paper presents results of a coexistence measurement study between multiple ultra wideband (UWB) transmitters and a Universal Mobile Telecommunications System (UMTS) mobile phone. Two environments were explored: an anechoic chamber with one operating UMTS link and a true operational UMTS network. A large number of FCC compatible UWB transmitters were used to generate interference for an active UMTS connection. In an anechoic chamber, only the voice service was studied between a radio communication analyser (used as a base station) and a mobile terminal. In the true commercial UMTS network case, both the voice and data services were investigated in a shelter having a low UMTS signal level. The results clearly show that UMTS and high pulse repetition rate UWB devices can co-exist at link level when a moderate number of simultaneously active UWB devices operate in close proximity of the UMTS 'victim' receiver. The results also show that the activity factor of the UWB transmitter disproportionately impacts the effective interference. When using low activity factors, even with high pulse repetition rates and very large numbers of UWB devices, it is difficult to detect UMTS link performance degradation. As the activity factors grow beyond 5%, the impact of the UWB interference becomes visible. However, this study covers only one active UMTS link in both environments but does not report on the UWB impact on the UMTS radio access network.
IEEE Transactions on Wireless Communications, 2006
ABSTRACT This letter focuses on the performance analysis of the decorrelating receiver in multipa... more ABSTRACT This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver
IEEE Transactions on Wireless Communications, 2005
ABSTRACT This letter investigates the performance analysis of a linearminimum mean square error r... more ABSTRACT This letter investigates the performance analysis of a linearminimum mean square error receiver forM-ary quadraticamplitude modulation in multipath fading channels. Both channel gain variances and instantaneous channel gains of the interferers are considered for receiver implementation. Approximate expressions for symbol and bit error rates are derived only when the receiver knows the channel gain variances of the interferers. In deriving the analytical expressions, we exploit large system analysis and results in single-user multipath combining. The receiver performance and the accuracy of the theoretical results are examined via simulations.
In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame c... more In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame collision survival (in the presence of simultaneous transmissions) on medium access control (MAC) protocols using impulse-radio-ultrawideband (IR-UWB) energy-collection noncoherent receivers. The MAC protocols that were considered are all IEEE 802.15.4 compatible, i.e., the IEEE 802.15.4a optional UWB clear-channel-assessment mode, the IEEE 802.15.4a ALOHA mode,
IEEE Transactions on Microwave Theory and Techniques, 2006
Impulse-radio (IR)-based ultra-wideband (UWB) technology is a strong candidate for short-range da... more Impulse-radio (IR)-based ultra-wideband (UWB) technology is a strong candidate for short-range data communication and positioning systems. This paper examines the performance of time-of-arrival (TOA) position estimation techniques as well as the simulated and measured performances of an IR-UWB noncoherent energy-collection receiver. The noncoherent IR-UWB transceiver has been designed for operation over the frequency range 3.1-4.1 GHz and implemented in 0.35-m SiGe BiCMOS technology. The performance of two different algorithms, namely, the threshold-crossing and the maximum selection (MAX) algorithms, are compared in terms of TOA estimation error in Saleh Valenzuela channel model 3 and channel model 4. The implemented structure of the TOA MAX algorithm suitable for IR-UWB-based noncoherent receivers is presented. A UWB testbed has been constructed in order to test and measure the transmitted waveform as well the receiver performances. The simulated receiver noise figure is 7.3 dB while the receiver gain is 34 dB. The TOA MAX algorithm can achieve 5-ns positioning accuracy for 95% of cases. Constant transconductance tuning circuits for improved TOA estimation reliability are also presented. Index Terms-Impulse-radio ultra-wideband (IR-UWB), noncoherent low-complexity transceiver architecture, RF front-end, SiGe BiCMOS, tag networks, time-of-arrival (TOA) estimation.
International Journal of Wireless Information Networks, 2003
UWB has been the source of heated debate since the Federal Communications Commission made their f... more UWB has been the source of heated debate since the Federal Communications Commission made their first report and order in February, 2002. The promise of UWB was originally low cost, low power, high data rate, robust communications with the added benefit of location and tracking built in as a result of the inherent physical properties of the signal. What has emerged over the last 12 months has been a wealth of UWB concepts that offer only some of the benefits. The UWB world still has some distance to travel. Because of the huge bandwidth available, the capacity of UWB systems is potentially enormous. Quantifying this capacity in the rich multipath environment of the UWB channel is a challenging task. The capacity problem is addressed in this issue by examining the performance of a number of modulation schemes. Developing the signaling schemes to achieve this high capacity requires the development of novel approaches to modulation. Included in this issue is a paper examining the combination of pulse shape and pulse position modulation, which allows for increased data rates in UWB channels. The rich multipath environment also creates challenges for receiver design. Conventional RAKE structures need to be substantially revised to operate in an effective manner. This is addressed in this issue by considering simplified channel conditions that make analysis more tractable. One of the main concerns with UWB is the impact of interference on existing “victim” systems. This is addressed in one paper in this issue in which the impact of very high power UWB interference is examined for 802.11b systems. The results are very promising with noticeable interference under extremely heavy UWB interference conditions. The very low power permitted for UWB signals makes practical system implementation difficult. In particular the problem of signal acquisition poses specific problems for UWB systems. Signal acquisition is addressed in this issue with the examination of a hybrid acquisition scheme. The challenges to be overcome by researchers and engineers are substantial before the promise of UWB can be truly achieved. The efforts to date have shown that UWB is an extraordinary opportunity to redefine the way
VTT Technical Research Centre of Finland appointed its third Scientific Advisory Board (SAB) for ... more VTT Technical Research Centre of Finland appointed its third Scientific Advisory Board (SAB) for the period 2011-2012. The SAB held four thematic meetings during the period. The meeting themes were based on the VTT Research and Innovation Vision 2020. This final report describes the SAB's key findings regarding VTT´s research and scientific activities and competences within the selected thematic areas as well as its recommendations and proposals for the future.
Executive summary: main research challenges Vision: Trustworthy 6G. The challenges in creating a ... more Executive summary: main research challenges Vision: Trustworthy 6G. The challenges in creating a trustworthy 6G are multidisciplinary spanning technology, regulation, techno-economics, politics and ethics. A combination of the current regulation, economic incentives and technology are maintaining the current level of hacking, lack of trust, privacy and security on the Internet. In 6G, this will not suffice, because physical safety will more and more depend on information technology and the networks we use for communication. Therefore, we need trustworthy 6G. The roles of trust, security and privacy are somewhat interconnected, but different facets of next generation networks. This white paper addresses their fundamental research challenges. Research challenge 1: Inherited and novel threats in 6G scale. The diversity and volume of novel IoT devices and their control systems will continue to pose significant security and privacy risks and additional threat vectors as we move from 5G to beyond towards 6G system. The volume of new IoT devices introduced into 6G network will increase 10x from 10 billion scale of 5G networks to 100 billion scale in 6G. As a result of such deployment and use of 6G, the dependence of the economy and societies on IT and the networks will deepen. Safety will depend on IT and the networks. The development of AI blurs the line between reality and fake content and helps to create ever more intelligent attacks. The role of IT and the networks in national security keeps rising-a continuation of what we see in 5G. Research challenge 2: End-to-end trust in 6G. In current "open internet" regulation, the telco cloud can be used for trust services only equally for all users. 6G should position the future cellular network as a solution to the all issues of trustworthy or trust networking such that network based information technology can be trusted to provide expected outcomes even in the face of malicious actors trying to interfere. 6G network must support embedded trust such that the resulting level of information security in 6G and the packet data networks where 6G provides connectivity to is significantly better than in state-of-the art networks commonly used today. Trust modeling, trust policies and trust mechanisms need to be defined. Research challenge 3: Post-quantum cryptography and security architecture for 6G. The current 5G standard does not address the issue of quantum computing but relies on traditional cryptography. The development towards cloud and edge native infrastructures is expected to continue in 6G networks. While large-scale quantum computing can be expected to take longer, it is time to prepare for the shift to cryptography that is secure in the post-quantum world. According to current knowledge, contemporary symmetric cryptography remains secure for the most part even after the advent of quantum computing. Future of SIM cards and use of asymmetric cryptography will be interesting research questions. Research challenge 4: Machine-learning as tool and risk in softwarized 6G. As 6G moves toward THz spectrum with much higher bandwidth, more densification and cloudification for a hyper connected world by joining billions of devices and nodes with global reach for terrestrial, ocean and space, automated security utilizing the concepts of security function softwarization and virtualization, and machine learning will be inevitable. There are two facets: on the one hand, security algorithms can use machine learning to orchestrate attacks and respond to them in an optimal way. On the other hand, also the attacking algorithms can learn better how the network operates and create better attacks. Continuous deep learning is needed on a packet/byte level and applying machine learning to enforce policies, detect, contain, mitigate and prevent threats or active attacks. Research challenge 5: Physical layer security in 6G. Physical layer security techniques can represent efficient solutions for securing the most critical and less investigated network segments which are the ones between the body sensors and a sink or a hub node. Research questions include which are the most suitable physical layer features to be exploited for the definition of security algorithms in 6G challenging environment characterized by high network scalability, heterogeneous devices and different forms of malicious attacks, and should PhySec be a stand-alone security design or interactions with upper layers are mandatory in 6G networks. Research challenge 6: Privacy as exploited resource in 6G. The relevance specifically for 6G is that, 5G is still largely device / network specific, 6G envisages far more immersive engagement with the network. It is now the subject of ongoing discussion in the standards world. There is currently no way to unambiguously determine when linked, deidentified datasets cross the threshold to become personally identifiable. This is a major, unaddressed problem for many digital technologies in different sectors, such as in Smart Healthcare, Industrial Automation, and Smart Transportation. Courts in different parts of the world are making decisions about whether privacy is being infringed without formal measures of the level of personal information, while companies are seeking new ways to exploit private data to create new business revenues. As solution alternatives, we may consider blockchain, distributed ledger technologies and differential privacy approaches.
The Generative Adversarial Network (GAN) has recently been applied to generate synthetic images f... more The Generative Adversarial Network (GAN) has recently been applied to generate synthetic images from text. Despite significant advances, most current state-of-the-art algorithms are regular-grid region based; when attention is used, it is mainly applied between individual regular-grid regions and a word. These approaches are sufficient to generate images that contain a single object in its foreground, such as a "bird" or "flower". However, natural languages often involve complex foreground objects and the background may also constitute a variable portion of the generated image. Therefore, the regular-grid based image attention weights may not necessarily concentrate on the intended foreground region(s), which in turn, results in an unnatural looking image. Additionally, individual words such as "a", "blue" and "shirt" do not necessarily provide a full visual context unless they are applied together. For this reason, in our paper, we ...
Proceedings of GLOBECOM'96. 1996 IEEE Global Telecommunications Conference
This paper reports on a series of simulations designed to investigate the efficiency of a low mob... more This paper reports on a series of simulations designed to investigate the efficiency of a low mobility direct sequence, spread spectrum (DS-SS) cellular system operating over a 2.0 GHz wireless local loop (WLL). The WLL consists of a base station with omnidirectional antenna at roof-top height, or pole-mounted, transmitting to a receiver terminal which also uses an omnidirectional antenna. The receiver is always considered inside a building. The simulations and efficiency calculations were performed using wideband channel responses taken from experimental data at many locations worldwide representing both urban and suburban environments. The aim of the system is to provide data rates appropriate for voice communications for the maximum possible numbers of simultaneous users each with low mobility. The system modelled utilises a linear adaptive receiver structure to minimise the multiple access interference (MAI) experienced from other users. The performance of the system in terms of total efficiency is considered while maintaining a specific BER. The performance is compared to that of a similar system based on conventional matched filter DS-SS receiver. This paper will show that there is substantial gain to be achieved from using the adaptive receiver system in each of the propagation environments considered
This paper focuses on the performance analysis of the decorrelating multipath combining receiver ... more This paper focuses on the performance analysis of the decorrelating multipath combining receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER with channel uncertainty. The pilot-symbol aided linear minimum mean-square channel estimator is considered to obtain an accurate channel estimate and to obtain an expression for the variance of the channel estimation er...
Short-range low power radio frequency systems such as Bluetooth and UWB enable the deployment of ... more Short-range low power radio frequency systems such as Bluetooth and UWB enable the deployment of wireless personal area networks (WPAN). A WPAN can interface to larger networks to provide broader network access and Internet connectivity. We evaluate the performance of TCP over an integrated WLAN and WPAN system using a real network testbed. The end-to-end throughput is found to increase, when the window size is increased. However, for large window sizes, measurement results revealed that a wide range of round trip times (RTTs) is experienced. With small window sizes, the variability in the RTT is smaller. The measurements showed that in an integrated network long RTT delays and frequent duplicate acknowledgements lead to an increase in the number of packets transmitted unnecessarily. We study the effect of the number of active short-range devices (Bluetooth in this case) in a piconet. The results show that as the number of active slaves present in the WPAN increases, the bandwidth received by slaves exchanging data decreases. This behaviour is attributed to the Bluetooth scheduling mechanism which uses the round robin polling method. The main finding of our experiments is that for Bluetooth to be successful in enabling WPAN, the time slot allocation scheme should be efficient and fair. Finally, the issue of fair bandwidth allocation among multiple TCP streams is also investigated. The results show that for small number of TCP connections, the bandwidth is fairly distributed. However, as the number of simultaneous TCP connections increases, bandwidth distribution seems to become somewhat less fair.
... and Modeling 188 6.5.1 State of the Art 190 6.5.2 Channel Modeling Process 206 ... in the des... more ... and Modeling 188 6.5.1 State of the Art 190 6.5.2 Channel Modeling Process 206 ... in the design process (The self-fulfilling prophecy) 21 Figure 3.6 Full scenario development 26 Figure ... 92 Figure 4.12 The three concepts of OWL-S 99 Figure 4.13 Example ontology fragments for ...
This paper presents a study of a MC-CDMA system. Different diversity combining techniques in an u... more This paper presents a study of a MC-CDMA system. Different diversity combining techniques in an uplink and downlink channel; single and multiuser detection strategies; and an interference cancellation method have been considered. The performance of the system has been evaluated by simulations. F. Swarts et al. (eds.), CDMA Techniques for Third Generation Mobile Systems
Ultra-Wideband Wireless Communications and Networks, 2006
It is known that the ultra-wideband (UWB) developmental efforts are divided into two camps in ind... more It is known that the ultra-wideband (UWB) developmental efforts are divided into two camps in industry, that is, the Direct-Sequence (DS) UWB camp led by Motorola and Freescale (DS-UWB, http://www.uwbforum.org/), and the Multiband OFDM Alliance (MBOA) led by Intel, TI, and other companies (MBOA, http://www.wimedia.org/index. html). The physical layer and Medium Access Control (MAC) layer of these two camps are different. The readers may refer to [1] and [2] for the details of the PHY specifications of DS-UWB and MBOA, respectively. In this chapter, we would focus on the MAC layer. The DS-UWB camp still utilizes the IEEE 802.15.3 as the MAC support, which was originally designed for the high speed Wireless Personal Area Networks (WPAN) [3]; while the MBOA Special Interest Group (SIG) is defining its own MAC standard [4]. These two MAC specifications are rather different. Because the MBOA MAC has not been finalized, this chapter will mainly study the IEEE 802.15.3 MAC protocol. 8.1.1 Overview of IEEE 802.15.3 MAC A WPAN defined by the IEEE 802.15.3 is a wireless ad hoc data communication system that allows a number of independent devices (DEVs) to communicate with each other. Such a network is called a piconet, as shown in Figure 8.1(a). The DEV is designed to be low power and low cost. One DEV is required to perform the role of PNC (Piconet Coordinator), which provides the basic timing for the piconet as well as other piconet management functions, such as power management, Quality of Service (QoS) scheduling, security, and so on.
International Journal of Wireless Information Networks, 2003
This paper presents the results of a coexistence study investigating the impact of ultra-wideband... more This paper presents the results of a coexistence study investigating the impact of ultra-wideband (UWB) interference on IEEE 802.11b and Bluetooth networks. The results are based on the experimental test measurements made at the University of Oulu, Finland. Simple high-power UWB transmitters are used to interfere with victim networks. Preliminary results show that only under extreme interference conditions with thousands of equivalent Federal Communications Commission-(FCC)-compliant devices in close proximity, will the IEEE 802.11b and Bluetooth networks experience significant performance degradation. The impact of the UWB interference on the IEEE 802.11b network was insignificant if the distance to UWB transmitters was greater than 40 cm. The impact on Bluetooth was even less noticeable. In our study, several high-power UWB transmitters that greatly exceed the FCC radiation regulations have been used, and the measurement settings presents the worst case scenario because of the very short distance between the interferers and the victim system. Effectively our study approximates the use of thousands of FCC-complaint UWB devices in the same space.
The paper presents results of a coexistence measurement study between multiple ultra wideband (UW... more The paper presents results of a coexistence measurement study between multiple ultra wideband (UWB) transmitters and a Universal Mobile Telecommunications System (UMTS) mobile phone. Two environments were explored: an anechoic chamber with one operating UMTS link and a true operational UMTS network. A large number of FCC compatible UWB transmitters were used to generate interference for an active UMTS connection. In an anechoic chamber, only the voice service was studied between a radio communication analyser (used as a base station) and a mobile terminal. In the true commercial UMTS network case, both the voice and data services were investigated in a shelter having a low UMTS signal level. The results clearly show that UMTS and high pulse repetition rate UWB devices can co-exist at link level when a moderate number of simultaneously active UWB devices operate in close proximity of the UMTS 'victim' receiver. The results also show that the activity factor of the UWB transmitter disproportionately impacts the effective interference. When using low activity factors, even with high pulse repetition rates and very large numbers of UWB devices, it is difficult to detect UMTS link performance degradation. As the activity factors grow beyond 5%, the impact of the UWB interference becomes visible. However, this study covers only one active UMTS link in both environments but does not report on the UWB impact on the UMTS radio access network.
IEEE Transactions on Wireless Communications, 2006
ABSTRACT This letter focuses on the performance analysis of the decorrelating receiver in multipa... more ABSTRACT This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver
IEEE Transactions on Wireless Communications, 2005
ABSTRACT This letter investigates the performance analysis of a linearminimum mean square error r... more ABSTRACT This letter investigates the performance analysis of a linearminimum mean square error receiver forM-ary quadraticamplitude modulation in multipath fading channels. Both channel gain variances and instantaneous channel gains of the interferers are considered for receiver implementation. Approximate expressions for symbol and bit error rates are derived only when the receiver knows the channel gain variances of the interferers. In deriving the analytical expressions, we exploit large system analysis and results in single-user multipath combining. The receiver performance and the accuracy of the theoretical results are examined via simulations.
In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame c... more In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame collision survival (in the presence of simultaneous transmissions) on medium access control (MAC) protocols using impulse-radio-ultrawideband (IR-UWB) energy-collection noncoherent receivers. The MAC protocols that were considered are all IEEE 802.15.4 compatible, i.e., the IEEE 802.15.4a optional UWB clear-channel-assessment mode, the IEEE 802.15.4a ALOHA mode,
IEEE Transactions on Microwave Theory and Techniques, 2006
Impulse-radio (IR)-based ultra-wideband (UWB) technology is a strong candidate for short-range da... more Impulse-radio (IR)-based ultra-wideband (UWB) technology is a strong candidate for short-range data communication and positioning systems. This paper examines the performance of time-of-arrival (TOA) position estimation techniques as well as the simulated and measured performances of an IR-UWB noncoherent energy-collection receiver. The noncoherent IR-UWB transceiver has been designed for operation over the frequency range 3.1-4.1 GHz and implemented in 0.35-m SiGe BiCMOS technology. The performance of two different algorithms, namely, the threshold-crossing and the maximum selection (MAX) algorithms, are compared in terms of TOA estimation error in Saleh Valenzuela channel model 3 and channel model 4. The implemented structure of the TOA MAX algorithm suitable for IR-UWB-based noncoherent receivers is presented. A UWB testbed has been constructed in order to test and measure the transmitted waveform as well the receiver performances. The simulated receiver noise figure is 7.3 dB while the receiver gain is 34 dB. The TOA MAX algorithm can achieve 5-ns positioning accuracy for 95% of cases. Constant transconductance tuning circuits for improved TOA estimation reliability are also presented. Index Terms-Impulse-radio ultra-wideband (IR-UWB), noncoherent low-complexity transceiver architecture, RF front-end, SiGe BiCMOS, tag networks, time-of-arrival (TOA) estimation.
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Papers by Ian Oppermann