In this paper, the physical layer security is studied in a buffer-aided MIMO relaying system, which consists of a source, a destination, a multi-antenna relay and multiple eavesdroppers. The relay operates in either half-duplex mode or full-duplex mode, based on the channel state information (CSI) of legitimate links. The exact closed-form expressions for the secrecy throughput and the outage probability of the buffer-aided MIMO relaying system are derived. In this work, the transmission rates can be adjusted at the source and relay instead of the predetermined transmission rates in the existing work. The optimal transmission rates are obtained to maximize the average secrecy throughput under the intended secrecy outage probability constraint, where only statistical CSI is needed when the optimization problem is solved. Numerical results show that analytical results of the secrecy outage probability agree with simulation results well. Compared with the conventional bufferless relaying schemes, the proposed buffer-aided relaying scheme achieves a higher throughput, as well as preserving the secrecy performance.

In this study, the authors analyse the ergodic capacity of the downlink channel in a hybrid satellite–terrestrial cooperative system. The satellite link experiences shadowed Rician fading and the terrestrial link follows Rayleigh fading. Using the moment generating function‐based approach, they derived the formulae for the ergodic capacity with the amplify‐and‐forward protocol or the decode‐and‐forward protocol. Moreover, the asymptotic expression for the ergodic capacity at a high signal‐to‐noise ratio is derived, and the system multiplexing gain is also obtained. Using the asymptotic results, they propose a simple relay selection strategy, which only requires the knowledge of channel statistics. Monte Carlo simulations are provided to confirm the analytical results, and to illustrate the effect of different factors, in terms of the number of relays, channel conditions, and the cooperative protocol, on the ergodic capacity. Numerical results show that the analytical results are highly accurate in the single relay scenario and have low computational complexity in the multi‐relay scenario. In addition, the proposed relay selection strategy achieves low overhead in the price of a little performance degradation.

Cognitive radio is an effective technology to alleviate the spectrum resource scarcity problem by opportunistically allocating the spare spectrum to unauthorized users. However, a serious denial-of-service (DoS) attack, named the ‘primary user emulation attack (PUEA)’, exists in the network to deteriorate the system performance. In this paper, we propose a PUEA detection method that exploits the radio channel information to detect the PUEA in the cognitive radio network. In the proposed method, the uniqueness of the channel impulse response (CIR) between the secondary user (SU) and the signal source is used to determine whether the received signal is transmitted by the primary user (PU) or the primary user emulator (PUE). The closed-form expressions for the false-alarm probability and the detection probability of the proposed PUEA detection method are derived. In addition, a modified subspace-based blind channel estimation method is presented to estimate the CIR, in order for the proposed PUEA detection method to work in the scenario where the SU has no prior knowledge about the structure and content of the PU signal. Numerical results show that the proposed PUEA detection method performs well although the difference in channel characteristics between the PU and PUE is small.

In this paper, we address the challenging and important cooperative spectrum sensing (CSS) problem with M-ary quantized data under spectrum sensing data falsification (SSDF) attacks. We introduce a probabilistic SSDF attack model to characterize the attacks by a malicious secondary user (SU). We analyze the attack behavior and derive the condition to nullify the detection capability of the fusion center (FC). To defend against the SSDF attacks, we propose a novel attack-proof CSS scheme with M-ary quantized data, mainly including a malicious SU identification method and an adaptive linear combination rule. By using the malicious SU identification approach, FC identifies malicious SUs and removes them from the data fusion process. The adaptive linear combination rule adjusts the weighted coefficients with the distribution parameter sets of identified normal SUs estimated using a maximum likelihood-based estimator. FC performs the spectrum sensing process with M-ary quantized data from the identified normal SUs. Comprehensive evaluation is conducted. Evaluation results show that the proposed malicious SU identification method can remove malicious SUs successfully and the proposed CSS scheme with M-ary quantized data is robust against the SSDF attacks.

In this paper, the ergodic channel capacity is analyzed for a hybrid satellite-terrestrial single frequency network (SFN), which consists of a satellite (the source node), a mobile terminal (the destination node), and several gap fillers (the relay nodes) on the ground. The satellite-relay (S-R) link and the satellite-destination (S-D) link experience independent Rician fading, and the relay-destination (R-D) link experiences Nakagami-m fading. Based on the classical conclusions in multipath fading channels, the exact closed-form expression of the ergodic channel capacity for a hybrid satellite-terrestrial SFN with the decode-and-forward cooperative protocol is derived. The numerical results agree well with the simulation results. As the total transmit power of all nodes is assumed to be limited, the performance of hybrid satellite-terrestrial SFN is better than that of the no-relay system when the S-D link is in heavy-fading.

Recently, various medium access control (MAC) protocols have been proposed for underwater acoustic networks (UANs). These protocols have significantly improved the performance of MAC layer in theory. However, two critical characteristics, low transmission rates and long preambles, found in the commercial modem-based real systems, severely degrade the performance of existing MAC protocols in the real world. Thus, a new practical MAC design is demanded. Toward an efficient approach, this paper analyzes the impact of these two modem characteristics on the random access-based MAC and handshake-based MAC, which are two major categories of MAC protocols for UANs. We further develop the nodal throughput and collision probability models for representative solutions of these two MAC protocol categories. Based on the analyses, we believe time sharing-based MAC is very promising. Along this line, we propose a time sharing-based MAC and analyze its nodal throughput. Both analytical and simulation results show that the time sharing-based solution can achieve significantly better performance.

The rateless code is widely used as a forward error correction solution. This paper proposes a novel rateless coding scheme with a Gradually Incremental Degree (GID) which is based on Robust Soliton Distribution used in Luby Transform (LT) code. With the feedback information, the proposed scheme significantly reduces the average degree of encoding symbols, as well as maintains the performance of the rateless code. Moreover, a degree distribution of the proposed rateless coding scheme is addressed to reduce the computational complexity. Simulation results show that the proposed rateless coding scheme with GID achieves a lower average degree than that of the standard LT code under the same coding overhead.

We study the impact of the dynamics of the end-user playout buffer on the quality of experience (QoE) of the HTTP progressive video over wireless networks in this paper, especially the impact of the block size and the finite video length on the playback interruption during wireless video watching. The playout buffer at the end-user is formulated as a G/D/1 queue with arbitrary packet arrival and deterministic playback. An analytical framework is presented to investigate the impact of the playout buffer dynamics on the wireless HTTP progressive video QoE by analyzing the transient queue length of the buffer with the diffusion approximation method. The close-form expressions for the user-perceived video quality, in terms of the buffering delay, the playback duration and the playback interruption probability, are obtained. The results show that both the buffering delay and the interruption probability decrease as the average arrival rate increases for a given buffer threshold. The higher the video quality, the greater the impact of the dynamics of the arrival process on the buffering delay and interruption probability is. Moreover, a larger playback threshold leads to a more rapidly decreasing of the interruption probability along with the increase of the average packet arrival rate. The proposed analytical framework is validated by simulations.

Recently, various Medium Access Control (MAC) protocols have been proposed for underwater acoustic networks. These protocols have significantly improved the performance of MAC layer in theory. However, two critical characteristics, low transmission rates and long preambles, found in the commercial modem-based real systems, drastically degrade the performance of existing MAC protocols in the real world. A new practical MAC design is demanded. Toward a proper approach, this paper analyzes the impact of the two newly found modem characteristics on the random access-based MAC and handshakebased MAC, which are two major types of MAC protocols for underwater acoustic networks. We further develop the nodal throughput and collision probability models for representative solutions of these two MAC protocol types. Based on the analysis, we believe time sharing-based MAC is very promising. Along this line, we propose a time sharing-based MAC and analyze its nodal throughput. Both analytical and simulation results show that the time sharing-based solution can achieve significantly better performance.

Using differential transmission method, the space-time block codes (STBC) can be applied in a complicated communication environment without channel state information (CSI). However, since the differential calculation includes multiplications, additions and conjugations, differential space-time block codes (DSTBC) also cause constellation expansion and result in nonlinearity problems in a wireless transmitter. In this paper, we proposed a new double mapping method for the DSTBC. In our proposed scheme, the attribute of pre-transmitted data bits is analyzed, and one of two mappings is chosen to generate current transmitted signal block. The proposed scheme also takes the advantage of differential encoding, and then CSI is not needed at the transmit antennas or at the receive antennas. Furthermore, the proposed DSTBC scheme can achieve full code rate without constellation expansion. Simulation results show that the performance of our proposed DSTBC scheme is close to that of traditional DSTBC scheme at a high SNR environment. Among all of the exited codes without constellation expansion, our proposed DSTBC has the minimum mapping table size and the best performance.

The coexistence and integration of multiple radio access technologies (RATs) deployed by different network operators are fundamental for next-generation mobile communication systems. In heterogeneous wireless environments, the access network selection, which is to select the most suitable network(s) for a terminal equipped with multiple radio interfaces according to various selection strategies, is a very important issue resulting in the performance maximization. In this paper, we propose a terminal-controlled access network selection scheme with parallel transmission capability for heterogeneous wireless networks, in which the suitable network(s) is(are) selected to access according to the total utility of different access networks. And the utility of each RAT is calculated based on the user preference and multiple access network criteria. Furthermore, the terminal-controlled access network selection with parallel transmission is formulated as a multi-constraint Knapsack problem which is solved with the exhaustive method to an optimum combination of RATs. Our proposed scheme is user-preference-aware, cost-aware, power-aware, and QoS-oriented. Simulation results show that our proposed access network selection scheme with parallel transmission can greatly improve the achieved data transmission rate with only a little increment in the cost and power consumption.

Cooperative spectrum sensing is regarded as an efficient way to detect the spare spectrum in cognitive radio networks (CRNs), where malicious secondary users (SUs) can launch the spectrum sensing data falsification (SSDF) attack to interfere with the detection and threat the CRN. In order to defend against the SSDF attack, it is necessary for the fusion center to distinguish the trustworthiness of the reports from SUs. In this paper, we propose a cooperative spectrum sensing scheme based on the Bayesian reputation model for CRNs. The key idea is that the cooperation is viewed as a service-evaluation process, and SUs' reputation degrees reflect their service quality. In our proposed scheme, reputation degrees of SUs are updated based on the Bayesian reputation model, and the behaviors of malicious SUs can be tracked effectively. Simulation results show that our proposed scheme defends against various types of SSDF attack, especially the probability SSDF attack.

The wireless multiuser orthogonal frequency division multiple access (OFDMA) network in the fading channels with statistical quality of service (QoS) requirements is studied in this paper. Considering the statistical QoS requirement as a system performance metric, the concept of the effective capacity is introduced and the effective capacity region is characterized for a wireless multiuser OFDMA network. And then, we prove that the effective capacity region is convex. Moreover, the asymptotically optimal subcarrier and power allocation scheme which achieves the boundary points of the effective capacity region is proposed. Simulation results about the effective capacity region with two and three mobile stations under homogeneous and heterogeneous QoS constraints are given.

In this paper, we study primary user emulation attacks (PUEA) issue in a cognitive radio network. Most literatures about the PUEA discuss methods to deal with the attacks in a system model where the positions of the primary user and secondary users are fixed. Hence, we focus on the PUEA problem in a system model where the secondary users are motional. Based on the network model with motional secondary users, we discuss how the attacker emulates the primary user. Then, a hybrid PUEA defense strategy based on a combination of energy detection and variance detection is proposed. The performance of the hybrid PUEA defense strategy is analyzed on the premise that the system has particular performance requirements. Simulation results show that our proposed hybrid PUEA defense strategy always performs well. This is the first analytical treatment to study PUEA problem in the scenario with motional secondary users.

Linear combination-based collaborative spectrum sensing, in which a coefficient is used to weight each cognitive radio (CR) user's sensing result in the linear fusion process at the central controller, is an effective mechanism to solve the fading and hidden terminal problem in cognitive radio networks (CRNs). For a reliable scheme, it is important to distinguish whether the CR user is reliable or not. In this paper, we proposed a collaborative spectrum sensing scheme based on the ROCQ reputation management model for CRNs. In the proposed scheme, each CR user has a reputation degree used to calculate its coefficient in the linear fusion process, and the reputation degree is initialized and adjusted by the central controller according to each CR user's sensing result, sensing correctness and report consistency. Simulation results show that our proposed scheme alleviates the corrupted sensing problem resulting from the destructive channel conditions between the primary transmitter and CR users. Moreover, compared to the optimal linear fusion scheme, the detection performance of our proposed scheme is approximately same while it requires no instantaneous SNRs. And the convergence of the reputation degree adjusting method also performs well.

ABSTRACT The self‐healing group key distribution scheme with revocation can deal with the problem of distributing session keys for secure group communication over an unreliable wireless network, with the capability to resist packet loss and collusion attack. However, existing access‐polynomial‐based self‐healing key management schemes have some problems, such as the small number of active group members, much redundancy in the key updating broadcast packet, and limited collusion attack resistance capability. In order to increase the number of active group members and improve the performance of self‐healing group key distribution schemes, we propose a self‐healing group key distribution scheme based on the access polynomial and one‐way hash key chain for resource‐constrained wireless networks in this paper. In our proposed scheme, by binding the time at which the user joins the group with the capability of recovering previous group session keys, some novel methods to construct the personal secret, the access polynomial, and the session key updating broadcast packet are presented. Compared with existing schemes under same conditions, analysis and simulation results show that our proposed scheme not only supports much more group members and sessions, but also provides a stronger security, considering that it can deal with more colluding users. Moreover, our proposed scheme is especially suitable to resource‐constrained wireless networks in a very bad environment. Copyright © 2012 John Wiley & Sons, Ltd.

To provide the seamless mobility in heterogeneous wireless networks, the handoff decision strategy is regarded as a significant and challenging issue. In this paper, we propose a handoff decision algorithm with the parallel transmission characteristic of the mobile multimode terminal in heterogeneous wireless networks. In our algorithm, the model of Markov decision process is used to determine the optimal handoff policy in order to maximize the expected total reward during the transmission. Simulation results show that compared to some existing handoff decision algorithms, the proposed algorithm outperforms in terms of the expected total reward, the expected number of handoffs and the probability of connection dropping.

How to allocate rate to users with multiple services efficiently and fairly is an important issue in the wireless network. To ensure the quality of service required by multiple services of a user, efficient resource management becomes paramount. On the other hand, the fairness between users is also necessary. In this paper, we propose a bandwidth allocation scheme named as Efficiency and Inter-user Fairness (EIF). In the EIF scheme, the well-known game theoretic concept of Nash bargaining solution is deployed to allocate the total network bandwidth to users fairly and dispatch rate from user to services efficiently by maximizing the user's utility. We also propose a distributed algorithm for implementing the convex optimization problem in the EIF scheme. Simulation results show that the EIF scheme outperforms the compared schemes in that it considers both the system efficiency and the user's fairness, while other schemes only maximizes the total utility of all of the services or considers the user's fairness.

Due to the characteristics of the underwater acoustic channel, such as long propagation delay and low available bandwidth, the media access control (MAC) protocol designed for underwater acoustic sensor networks (UWASNs) is quite different from that for terrestrial wireless sensor networks. In this paper, we propose a MAC protocol for the UWASNs, named the funneling MAC (FMAC-U), which is a contention-based MAC protocol with a three-way handshake. The FMAC-U protocol uses an improved three-way handshake mechanism and code division multiple access (CDMA) based technology for request-to-send (RTS) signals transmitting to the sink in order that the sink can receive packets from multiple neighbors in a fixed order during each round of handshakes. The mechanism reduces the packet collisions and alleviates the funneling effect, especially alleviating the choke point of the UWASNs. Simulation results show that the proposed FMAC-U protocol achieves higher throughput, smaller packet drop ratio, lower end-to-end delay, and lower overhead of the control packet compared to the existing MAC protocols for UWASNs.

The 3780-point FFT is a main component of the time domain synchronous OFDM (TDS-OFDM) system and the key technology in the Chinese Digital Multimedia/TV Broadcasting-Terrestrial (DMB-T) national standard. Since 3780 is not a power of 2, the classical radix-2 or radix-4 FFT algorithm cannot be applied directly. Hence, the Winograd Fourier transform algorithm (WFTA) and the Good-Thomas prime factor algorithm (PFA) are used to implement the 3780-point FFT processor. However, the structure based on WFTA and PFA has a large computational complexity and requires many DSPs in hardware implementation. In this paper, a novel 3780-point FFT processor scheme is proposed, in which a 60×63 iterative WFTA architecture with different mapping methods is imported to replace the PFA architecture, and an optimized CoOrdinate Rotation DIgital Computer (CORDIC) module is used for the twiddle factor multiplications. Compared to the traditional scheme, our proposed 3780-point FFT processor scheme reduces the number of multiplications by 45% at the cost of 1% increase in the number of additions. All DSPs are replaced by the optimized CORDIC module and ROM. Simulation results show that the proposed 3780-point FFT processing scheme satisfies the requirement of the DMB-T standard, and is an efficient architecture for the TDS-OFDM system.

Spectrum sensing is a key component of cognitive radio networks. Compared with the single user spectrum sensing, cooperative spectrum sensing can detect the existence of the primary signal for improving the inference accuracy. However, cooperation induces additional communications overhead. In this paper, we propose a new cooperative spectrum sensing scheme with a light communication overhead caused by cooperation in cognitive radio networks. We also present two strategies for refreshing the confidence threshold. Simulation results show that compared with the traditional cooperative spectrum sensing scheme, our proposed scheme has a lower communication overhead as well as a nearly same detection performance.

Bandwidth allocation for multi-user sharing heterogeneous wireless access networks is one of the most important problems in the next generation wireless networks. In this paper, we propose a bandwidth allocation scheme named as Efficient and Fair Rate Allocation (EFRA), which is formulated as a convex optimization problem maximizing the user's utility as well as determining to split the total rate among multiple access networks fairly and efficiently. Compared with the scheme that minimizes the total expected distortion of all the video streams and other schemes that only consider either the system efficiency or the user fairness, the EFRA scheme considers both efficiency and fairness, and achieves utility fairness among all the users.

To provide reliable video stream transmission over wireless networks, we propose a cross-layer design model in this paper. In the proposed model, the adaptive modulation and coding parameters at the physical layer, the ARQ parameters at the data link layer and the application-layer forward error correction (A-FEC) parameters at the application layer are jointly designed. Our objective is to maximize the number of correctly decodable frames in a group of picture (GOP) according to the channel conditions and the GOP structure of the video stream. We also present a low-complexity bandwidth allocation algorithm for the A-FEC. The effectiveness of the proposed bandwidth allocation algorithm and the cross-layer design model was shown in the simulation results.

In this paper, retransmission strategies of the network-coding-based packet network are investigated. We propose two retransmission strategies, the packet-loss-edge-based retransmission strategy (PLERT) and the minimum retransmission strategy (MRT), which focus on optimizing the retransmission efficiency without the constraint on the encoding field size. We compared the performances of the proposed retransmission strategies with the traditional automatic repeat-request (ARQ) strategy and the random retransmission strategy. Simulation results showed that the PLERT strategy works well when the packet loss rate is small. Among these retransmission strategies, the performance of the MRT strategy is the best at the cost of the high complexity that is still polynomial. Furthermore, neither of the proposed strategies is sensitive to the encoding field size.

In order to resist the attack from malicious Cognitive Radio (CR) users, a reputation-based collaborative spectrum sensing model is proposed in this paper. In this model, each collaborative CR user has a reputation degree, which is set by the central controller and used to weight the sensing result from corresponding CR user in the fusion process at the central controller. We analyze and evaluate the performance of hard decision fusion and soft fusion with the proposed model. And simulation results show that our proposed model weakens the harmful influence caused by malicious CR users and has better detection performance than that of original model both in hard decision fusion and soft fusion.

Energy efficiency has been known as the most significant problem in all facets of the wireless sensor network operations. In this paper, we propose a meta-data-based data aggregation scheme in the clustering wireless sensor networks. For all sensor nodes in the sensing range of an event can detect the event and generate the sensing data, the cluster head will receive the sensing data packets about the same event, and there is likely to be some redundancy. In our scheme, only one of the sensor nodes within the sensing range of an event in a cluster is selected to transmit the sensing data to the cluster head via the meta data negotiation. We also evaluate this scheme with the LEACH protocol. The simulation results show that the cluster protocol with our data aggregation scheme is effective in prolonging the network lifetime and supporting scalable data aggregation.