Shiying Han

Secure Transmission Against Pilot Spoofing Attack: A Two-Way Training-Based Scheme

The pilot spoofing attack is one kind of active eavesdropping activities conducted by a malicious user during the channel training phase. By transmitting the identical pilot (training) signals as those of the legal users, such an attack is able to manipulate the channel estimation outcome, which may result in a larger channel rate for the adversary but a smaller channel rate for the legitimate receiver. With the intention of detecting the pilot spoofing attack and minimizing its damages, we design a two-way training-based scheme. The effective detector exploits the intrusive component created by the adversary, followed by a secure beamforming-assisted data transmission. In addition to the solid detection performance, this scheme is also capable of obtaining the estimations of both legitimate and illegitimate channels, which allows the users to achieve secure communication in the presence of pilot spoofing attack. The detection probability is evaluated based on the derived test threshold at a given requirement on the probability of false alarming. The achievable secrecy rate is utilized to measure the security level of the data transmission. Our analysis shows that even without any pre-assumed knowledge of eavesdropper, the proposed scheme is still able to achieve the maximal secrecy rate in certain cases. Numerical results are provided to show that our scheme could achieve a high detection probability as well as secure transmission.

Licensed-Assisted Access for LTE in Unlicensed Spectrum: A MAC Protocol Design

Licensed-assisted access (LAA), which conveys control signal via licensed anchor carrier and data information via both licensed and unlicensed bands, is a promising solution to enhance the throughput of wireless communications. In view of the potential impact on the incumbent services in the unlicensed band, how to design the medium access control (MAC) protocol for LAA system to make fair and friendly coexistence with its neighboring incumbent users is one of the most critical and challenging issues. In this paper, a LAA using LTE (LAA-LTE) system in the WiFi unlicensed spectrum is investigated. The listen-before-talk (LBT) protocol is designed for the LAA-LTE system. By quantifying the WiFi throughput in the coexisting system, allowable LTE transmission time is determined by considering different targets of WiFi service protection. Then, the LTE transmission time is optimized for maximizing the overall normalized channel rate contributed by both LAA-LTE and WiFi system, with the protection to the WiFi system. Our work offers guidelines of designing the LAA-LTE system, paving the way to a controllable, not only harmonious, coexistence of LAA-LTE and WiFi systems in the unlicensed spectrum.

Spectrum Refarming: A New Paradigm of Spectrum Sharing for Cellular Networks

Spectrum refarming (SR) is a promising radio resource management technique which allows different generations of cellular networks to operate in the same radio spectrum. In this paper, an underlay SR model is proposed for an Orthogonal Frequency Division Multiple Access (OFDMA) system to refarm the spectrum assigned to a Code Division Multiple Access (CDMA) system through intelligently exploiting the interference margin provided by the CDMA system. We investigate the mutual effect of the two systems by evaluating the asymptotic signal-to-interference-plus-noise ratio (SINR) of CDMA users, based on which the interference margin tolerable by CDMA system is determined. With the interference margin together the transmit power constraints, the resource allocation problem of OFDMA system is formulated and solved through dual decomposition method. Simulation results have verified our theoretical analysis and validated the effectiveness of our proposed OFDMA resource allocation solution, as well as its protection to CDMA services.

Subcarrier allocation in multi-cell OFDMA wireless networks with non-coherent base station cooperation and controllable fairness

In this paper, a non-coherent base station cooperation (NC-BSC) scheme is examined for the downlink OFDMA wireless cellular networks. We formulate the resource allocation in the scheme as a subcarrier allocation optimization problem with equal power allocated on each subcarrier. To balance the tradeoff between system throughput and fairness, a multi-cell scenario controllable fairness is extended from single-cell scenario mentioned in [1], based on which the controllable global fairness (GF) scheme in the NC-BSC system is proposed. Two heuristic iterative algorithms are proposed to realize the subcarrier allocation in the NC-BSC system with and without the controllable fairness in a distributed manner. The performance is compared with traditional dynamic subcarrier allocation in noncooperative multi-cell networks. Simulation results show the performance enhancement through implementation of NC-BSC and the effectiveness of multi-cell controllable fairness in the NC-BSC system.

Spectrum refarming: A new paradigm of spectrum sharing for cellular networks

Spectrum refarming (SR) is a promising radio resource management technique which allows different generations of cellular networks to operate in the same radio spectrum. In this paper, an underlay SR model is proposed for an Orthogonal Frequency Division Multiple Access (OFDMA) system to refarm the spectrum assigned to a Code Division Multiple Access (CDMA) system through intelligently exploiting the interference margin provided by the CDMA system. We investigate the mutual effect of the two systems by evaluating the asymptotic signal-to-interference-plus-noise ratio (SINR) of CDMA users, based on which the interference margin tolerable by CDMA system is determined. With the interference margin together the transmit power constraints, the resource allocation problem of OFDMA system is formulated and solved through dual decomposition method. Simulation results have verified our theoretical analysis and validated the effectiveness of our proposed OFDMA resource allocation solution, as well as its protection to CDMA services.

Licensed-assisted access for LTE in unlicensed spectrum: A MAC protocol design

Licensed-assisted access (LAA), which conveys data information via both licensed and unlicensed bands through spectrum aggregation, becomes a promising solution to enhance the capacity of wireless systems. In view of the potential impact on the incumbent system operating in unlicensed bands, the medium access control (MAC) protocol design for LAA system to harmonically coexist with its neighboring incumbent users is one of the most critical and challenging issues. In this paper, we consider a long-term evolution-based LAA (LAA-LTE) system operating in the WiFi unlicensed spectrum, for which the listen-before-talk-based MAC protocol is carefully designed. By quantifying the WiFi throughput and packet delay in the coexisting system, we formulate the constraints of LAA-LTE transmission time to fairly maintain WiFi services. The conditions of known and unknown network size of incumbent WiFi system are each considered separately. Then, the feasible region of LAA-LTE transmission time is determined, and the LAA-LTE protocol is optimized for maximizing the LAA-LTE throughput or the overall throughput contributed by both LAA-LTE and WiFi system. The theoretical analysis is validated via simulation, which also illustrates important observations when LAA-LTE and WiFi systems coexist. This paper offers guidelines to design the LAA-LTE system, paving the way to a controllable, not only harmonious, coexistence of LAA-LTE and WiFi systems in the unlicensed spectrum.

Joint Resource Allocation in OFDMA/CDMA Spectrum Refarming System

Spectrum refarming (SR) is drawing a lot of attention nowadays for its capability to alleviate the spectrum scarcity problem by allowing different generations of cellular networks to operate in the same radio spectrum. In this paper, we propose a joint resource allocation scheme for the uplink OFDMA/CDMA SR system, by exploiting the tradeoff of the OFDMA throughput over the CDMA receive power. By investigating the convexity of the OFDMA throughput over the CDMA receive power, an algorithm, performed by the OFDMA system, is proposed to jointly optimize the OFDMA resource allocation and the CDMA receive power. Due to the existing CDMA uplink power control, when the OFDMA users transmit with the optimal allocated resource, the CDMA system will adjust its user transmission power to make the receive power be the optimal value, for guaranteeing the target signal-to-interference-plus-noise ratio. Simulation results are provided to verify the proposed scheme and algorithm.

Power Control Based on Subcarrier Exclusion to Mitigate Downlink Cross-Tier Interference in OFDMA Tiered Networks

In this letter, we propose a novel power control scheme based on subcarrier exclusion in OFDMA macro/femto two-tier networks implemented by femto base station (FBS). The FBS derives its optimal transmission power and radius of neighboring area (NA) according to its own location and the macro mobile station (MMS) distribution to maximize its ergodic capacity under the constraints of maximum FBS transmission power and MMS performance requirement. Moreover, the macro neighboring area is derived, within which the FBS avoids its deployment. Our simulation verifies the applicability and efficiency of the proposed scheme.

Robust Joint Resource Allocation for OFDMA-CDMA Spectrum Refarming System

In this paper, we investigate a spectrum refarming system where an OFDMA system shares the licensed band of a CDMA system. Both systems share the same cell site, but each has different base station (BS) antennas. Joint resource allocation problem is formulated to optimize the CDMA receive power, OFDMA transmit power, and subcarrier assignment. Conventional interference control to protect the primary CDMA system relies on the availability of cross-channel gains (CCGs) from each secondary OFDMA transmitter to the CDMA BS receiver. However, the CCGs are difficult to be obtained due to lack of intersystem cooperation. To address this problem, we first decouple the original problem into higher and lower-level problems via primal decomposition. Then, a robust lower-level resource allocation (R-LRA) scheme, which controls interference without using CCGs is proposed, with which CDMA users can be sufficiently protected. Thereafter, an enhanced R-LRA (ER-LRA) scheme is proposed to decrease the conservation of R-LRA scheme. Assisted by the CDMA inner power control and based on the ER-LRA, efficient algorithm is designed to solve the higher-level problem. Extensions of the ER-LRA for other scenarios are also studied. Simulation results are provided to validate the proposed schemes in facilitating and improving the spectrum sharing performance.

Spectrum refarming for OFDMA small cells overlaying CDMA cellular networks

In this paper, a novel spectrum refarming (SR) system is proposed in which the Orthogonal Frequency Division Multiple Access (OFDMA) small cells overlay the Code Division Multiple Access (CDMA) cellular networks in the same legacy CDMA spectrum. In order to predict and control the interferences from the OFDMA small cells to the CDMA macrocell, the OFDMA downlink transmissions in the small cells are arranged to be synchronous with the CDMA uplink transmission in the macrocell. We first analyze the interferences between the OFDMA small cells and CDMA macrocell, then formulate the OFDMA resource allocation problem for this proposed SR system. Through assigning the interference margins to each OFDMA small cell, a new resource allocation algorithm is proposed to solve the formulated problem efficiently. Simulation results are given to validate the effectiveness of the proposed algorithm and evaluate the performance of the proposed SR system.