Cross-layer Scheduling With Security Demands In OFDMA Networks

Due to the broadcast nature of wireless communication, the problem of securi-ty communication in wireless communication system catches great attention of re-searchers. Physical-layer security capacity stands for the physical security transmis-sion capability of wireless communication systems. So to Orthogonal Frequency Di-vision Multiple Accessing (OFDMA) networks, which are the next generation high-speed wireless communication technology, its physical-layer security problem is very essential. Besides, the stochastic processes in wireless communications, such as time-varying channel state, random arrival data and so on, bring huge challenges to the research of physical layer security in OFDMA networks.The objective in this work is to improve the physical-layer security capacity of OFDMA networks. Due to that OFDMA networks can individually control the trans-mission power and modulation scheme on every single subcarrier, we design cross-layer scheduling algorithms of several different transmission situations in OFDMA networks. The transmission situations include:1) A downlink situation where there are only security transmissions;2) A downlink situation where there are both open and security transmissions;3) OFDMA-based cognitive radio networks. So the major contributions of this paper are as follows.1) In a downlink situation where there are only security transmissions, every user has different security requirements on their secure transmissions. Firstly, in this pa-per, users’different security requirements are modeled as minimal security capacity constraints. Secondly, a cross-layer scheduling algorithm (FCRA) composed of flow control and resource allocation is designed in this paper. It utilizes dynamic queueing so that merely instantaneous state of the network is enough, which is advantageous for easier implementations. Thirdly, by the means of Lyapunov optimization, we prove our algorithm can obtain a performance of flow rate admission extremely close to the optimal, which is also proved by simulation results.2) An OFDMA downlink system with secure transmissions and delay constraints is investigated, in which a base station (BS) transmits both open data with delay limi-tations and private data with secrecy demands to each user. The proposed algorithm, FCRA-OP, uses current channel state information and queuing information (both ac-tual data queue and virtual queue) to make decisions to maximize the whole weighted throughput and subject to time-average power consumption limitation. Besides of the flow control and resource allocation algorithms, security control deciding the resource allocation between security transmission and open transmission is an important part of FCRA-OP.Besides, a tradeoff between the delay bound and the weighted throughput. While with some certain delay constraints, FCRA-OP can obtain a performance which can be extremely close to optimality and reduce operation complexity significantly.3) This paper investigates the scheduling and dynamic spectrum access of sec-ondary network in an OFDMA-based cognitive radio system. The primary and sec-ondary networks share the spectrum simultaneously in a full overlay mode, which is the optimal scheme when these two kinds of networks are far away from each other. An online cross-layer scheduling algorithm (COCA) is proposed in this paper to maximize the downlink throughput with time-average delay and power constraint of secondary network. Furthermore, COCA makes decisions based on current channel state infor-mation instead of channel statistics. In the end, it is proven by means of Lyapunov optimization technique that COCA’s performance would be close to optimality.