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- Secure and efficient spectrum sharing and QoS analysis in OFDM-based heterogeneous wireless networks
- Alahmadi, Ahmed S.
- Electronic Theses & Dissertations
The Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the largemillimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require...
Show moreThe Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the largemillimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require line of sight (LOS) path and suffer from severe fading effects, leading to much smaller coverage area. For network design and management, this implies that: (i) MmWave band alone could not support the IoT networks, but has to be integrated with the existing lower band systems through secure and effective spectrum sharing, especially in the lower frequency bands; and (ii) The IoT networks will have very high density node distribution, which is a significant challenge in network design, especially with the scarce energy budget of IoT applications. Motivated by these observations, in this dissertation, we consider three problems: (1) How to achieve secure and effective spectrum sharing? (2) How to accommodate the energy limited IoT devices? (3) How to evaluate the Quality of Service (QoS) in the high density IoT networks? We aim to develop innovative techniques for the design, evaluation and management of future IoT networks under both benign and hostile environments. The maincontributions of this dissertation are outlined as follows.First, we develop a secure and efficient spectrum sharing scheme in single-carrier wireless networks. Cognitive radio (CR) is a key enabling technology for spectrum sharing, where the unoccupied spectrum is identified for secondary users (SUs), without interfering with the primary user (PU). A serious security threat to the CR networks is referred to as primary user emulation attack (PUEA), in which a malicious user (MU) emulates the signal characteristics of the PU, thereby causing the SUs to erroneously identify the attacker as the PU. Here, we consider full-band PUEA detection and propose a reliable AES-assisted DTV scheme, where an AES-encrypted reference signal is generated at the DTV transmitter and used as the sync bits of the DTV data frames. For PU detection, we investigate the cross-correlation between the received sequence and reference sequence. The MU detection can be performed by investigating the auto-correlation of the received sequence. We further develop a secure and efficient spectrum sharing scheme in multi-carrier wireless networks. We consider sub-band malicious user detection and propose a secure AES-based DTV scheme, where the existing reference sequence used to generate the pilot symbols in the DVB-T2 frames is encrypted using the AES algorithm. The resulted sequence is exploited for accurate detection of the authorized PU and the MU. Second, we develop an energy efficient transmission scheme in CR networks using energy harvesting. We propose a transmitting scheme for the SUs such that each SU can perform information reception and energy harvesting simultaneously. We perform sum-rate optimization for the SUs under PUEA. It is observed that the sum-rate of the SU network can be improved significantly with the energy harvesting technique. Potentially, the proposed scheme can be applied directly to the energy-constrained IoT networks.Finally, we investigate QoS performance analysis methodologies, which can provide insightful feedbacks to IoT network design and planning. Taking the spatial randomness of the IoT network into consideration, we investigate coverage probability (CP) and blocking probability (BP) in relay-assisted OFDMA networks using stochastic geometry. More specifically, we model the inter-cell interference from the neighboring cells at each typical node, and derive the CP in the downlink transmissions. Based on their data rate requirements, we classify the incoming users into different classes, and calculate the BP using the multi-dimensional loss model.
- Reliable 5G System Design and Networking
- Liang, Yuan
- Electronic Theses & Dissertations
The upcoming fifth generation (5G) system is expected to support a variety of different devices and applications, such as ultra-reliable and low latency communications, Internet of Things (IoT) and mobile cloud computing. Reliable and effective communications lie in the core of the 5G system design. This dissertation is focused on the design and evaluation of robust 5G systems under both benign and malicious environments, with considerations on both the physical layer and higher layers.For...
Show moreThe upcoming fifth generation (5G) system is expected to support a variety of different devices and applications, such as ultra-reliable and low latency communications, Internet of Things (IoT) and mobile cloud computing. Reliable and effective communications lie in the core of the 5G system design. This dissertation is focused on the design and evaluation of robust 5G systems under both benign and malicious environments, with considerations on both the physical layer and higher layers.For the physical layer, we study secure and efficient 5G transceiver under hostile jamming. We propose a securely precoded OFDM (SP-OFDM) system for efficient and reliable transmission under disguised jamming, a serious threat to 5G, where the jammer intentionally confuses the receiver by mimicking the characteristics of the authorized signal, and causes complete communication failure. We bring off a dynamic constellation by introducing secure randomness between the legitimate transmitter and receiver, and hence break the symmetricity between the authorized signal and the disguised jamming. It is shown that due to the secure randomness shared between the authorized transmitter and receiver, SP-OFDM can achieve a positive channel capacity under disguised jamming. The robustness of the proposed SP-OFDM scheme under disguised jamming is demonstrated through both theoretic and numerical analyses.We further address the problem of finding the worst jamming distribution in terms of channel capacity for the SP-OFDM system. We consider a practical communication scenario, where the transmitting symbols are uniformly distributed over a discrete and finite alphabet, and the jamming interference is subject to an average power constraint, but may or may not have a peak power constraint. Using tools in functional analysis and complex analysis, first, we prove the existence and uniqueness of the worst jamming distribution. Second, by analyzing the Kuhn-Tucker conditions for the worst jamming, we prove that the worst jamming distribution is discrete in amplitude with a finite number of mass points.For the higher layers, we start with the modeling of 5G high-density heterogeneous networks. We investigate the effect of relay randomness on the end-to-end throughput in multi-hop wireless networks using stochastic geometry. We model the nodes as Poisson Point Processes and calculate the spatial average of the throughput over all potential geometrical patterns of the nodes. More specifically, for problem tractability, we first consider the simple nearest neighbor (NN) routing protocol, and analyze the end-to-end throughput so as to obtain a performance benchmark. Next, note that the ideal equal-distance routing is generally not realizable due to the randomness in relay distribution, we propose a quasi-equal-distance (QED) routing protocol. We derive the range for the optimal hop distance, and analyze the end-to-end throughput both with and without intra-route resource reuse. It is shown that the proposed QED routing protocol achieves a significant performance gain over NN routing.Finally, we consider the malicious link detection in multi-hop wireless sensor networks (WSNs), which is an important application of 5G multi-hop wireless networks. Existing work on malicious link detection generally requires that the detection process being performed at the intermediate nodes, leading to considerable overhead in system design, as well as unstable detection accuracy due to limited resources and the uncertainty in the loyalty of the intermediate nodes themselves. We propose an efficient and robust malicious link detection scheme by exploiting the statistics of packet delivery rates only at the base stations. More specifically, first, we present a secure packet transmission protocol to ensure that except the base stations, any intermediate nodes on the route cannot access the contents and routing paths of the packets. Second, we design a malicious link detection algorithm that can effectively detect the irregular dropout at every hop (or link) along the routing path with guaranteed false alarm rate and low miss detection rate.