Lei Xie

A hybrid reservation-based MAC protocol for underwater acoustic sensor networks

Due to the characteristics of underwater acoustic channel, such as long propagation delay and low available bandwidth, media access control (MAC) protocol designed for the underwater acoustic sensor network (UWASN) is quite different from that for the terrestrial wireless sensor network. However, for the contention-based MAC protocols, the packet transmission time is long because of the long preamble in real acoustic modems, which increase the packet collisions. And the competition phase lasts for long time when many nodes are competing for the channel to access. For the schedule-based MAC protocols, the delay is too long, especially in a UWASN with low traffic load. In order to resolve these problems, a hybrid reservation-based MAC (HRMAC) protocol is proposed for UWASNs in this paper. In the proposed HRMAC protocol, the nodes reserve the channel by declaring and spectrum spreading technology is used to reduce the collision of the control packets. Many nodes with data packets to be transmitted can reserve the channel simultaneously, and nodes with reserved channel transmit their data in a given order. The performance analysis shows that the proposed HRMAC protocol can improve the channel efficiency greatly. Simulation results also show that the proposed HRMAC protocol achieves better performance, namely higher network throughput, lower packet drop ratio, smaller end-to-end delay, less overhead of control packets and lower energy overhead, compared to existing typical MAC protocols for the UWASNs.

Improved Decoding Algorithm of Bit-Interleaved Coded Modulation for LDPC Code

Bit-interleaved coded modulation (BICM), which has been proven to be powerful when applied in low-density parity-check (LDPC) sum-product algorithm (SPA) decoder, is a bandwidth efficient coding scheme. However, the BICM-SPA decoder does not take the statistical dependencies between bits from the same L-ary modulated symbol into account so that it cannot converge to the maximum a-posteriori (MAP) decoding algorithm. In this paper, an improved SPA decoding algorithm for the LDPC code, which combines decoding and demodulation, is proposed. The proposed decoding algorithm, referred to as the BICM-ISPA, is based on generalized distributive law and derived from the generalized symbol SPA under certain rational assumptions. And the BICM-ISPA can asymptotically converge to the MAP decoding solution algorithm. Simulation results show that the BICM-ISPA decoder jointly optimizes the decoding error performance and the computational complexity of the LDPC code over the additive white Gaussian noise channel. Compared with the BICM-SPA decoder, the advantage of the BICM-ISPA is quite significant with a large modulation size and in the scenario where Gray mapping cannot be used.

One-way hash chain-based self-healing group key distribution scheme with collusion resistance capability in wireless sensor networks

In order to resolve the collusion resistance problem in the one-way hash chain-based self-healing group key distribution schemes and improve the performance of previous self-healing group key distribution schemes, we propose a self-healing group key distribution scheme based on the revocation polynomial and a special one-way hash key chain for wireless sensor networks (WSNs) 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, a new method is addressed to provide the capability of resisting the collusion attack between revoked users and new joined users, and a special one-way hash chain utilization method and some new methods to construct the personal secret, the revocation polynomial and the key updating broadcast packet are presented. Compared with existing schemes under same conditions, our proposed scheme not only supports more revoked users and sessions, but also provides a stronger security. Moreover, our proposed scheme reduces the communication overhead, and is especially suited for a large scale WSN in bad environments where a strong collusion attack resistance capability is required and many users will be revoked.

Reputation-based collaborative spectrum sensing algorithm in Cognitive Radio networks

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.

Joint Spectrum Sensing and Resource Allocation Scheme in Cognitive Radio Networks with Spectrum Sensing Data Falsification Attack

Spectrum sensing and spectrum sharing are two fundamental issues in a cognitive radio network (CRN). The spectrum sensing data falsification (SSDF) attack imposes bad effects on both spectrum sensing and spectrum sharing. To deal with SSDF attacks and to incentivize secondary users (SUs) to behave well, a joint spectrum sensing and resource allocation (JSSRA) scheme in a CRN is proposed in this paper. The JSSRA problem is formulated as a weighted-proportional-fairness-based resource-allocation optimization problem under the constraint that the primary user (PU) network is sufficiently protected. The problem is decomposed into two subproblems, namely, the resource allocation subproblem and cooperative SU number decision subproblem, which are solved by the Lagrangian dual algorithm and the brute-force algorithm, respectively. Moreover, a user-selection method based on reinforcement learning is presented to select reliable SUs for cooperative spectrum sensing (CSS). In addition, the SUs trust degree is updated according to its behavior in CSS and is used in the sensed resource-allocation process. The key point of our proposed scheme is to make SUs improve the sensing reliability and prevent SUs from behaving maliciously by an incentive mechanism. Comprehensive performance evaluation is conducted by computer simulation. It is shown that the proposed JSSRA scheme deals with the SSDF attack well in cooperative sensing process to improve system robustness and achieves a significant system utility gain in resource allocation.

Access-polynomial-based self-healing group key distribution scheme for resource-constrained wireless networks

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

Improved One-Way Hash Chain and Revocation Polynomial-Based Self-Healing Group Key Distribution Schemes in Resource-Constrained Wireless Networks

Self-healing group key distribution (SGKD) aims to deal with the key distribution problem over an unreliable wireless network. In this paper, we investigate the SGKD issue in resource-constrained wireless networks. We propose two improved SGKD schemes using the one-way hash chain (OHC) and the revocation polynomial (RP), the OHC&RP-SGKD schemes. In the proposed OHC&RP-SGKD schemes, by introducing the unique session identifier and binding the joining time with the capability of recovering previous session keys, the problem of the collusion attack between revoked users and new joined users in existing hash chain-based SGKD schemes is resolved. Moreover, novel methods for utilizing the one-way hash chain and constructing the personal secret, the revocation polynomial and the key updating broadcast packet are presented. Hence, the proposed OHC&RP-SGKD schemes eliminate the limitation of the maximum allowed number of revoked users on the maximum allowed number of sessions, increase the maximum allowed number of revoked/colluding users, and reduce the redundancy in the key updating broadcast packet. Performance analysis and simulation results show that the proposed OHC&RP-SGKD schemes are practical for resource-constrained wireless networks in bad environments, where a strong collusion attack resistance is required and many users could be revoked.

A Handoff Decision Algorithm in Heterogeneous Wireless Networks with Parallel Transmission Capability

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.

Effective capacity region in a wireless multiuser OFDMA network

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.

Maximum-minimum eigenvalue detection-based method to mitigate the effect of the PUEA in cognitive radio networks

In cognitive radio (CR) networks, secure spectrum sensing is a very important issue. The primary user emulation attack (PUEA), a special attack of the spectrum sensing technology in CR Networks, reduces the spectrum utilization obviously. And our analysis reveals the undetected PUEA can prevent unlicensed users from accessing the space licensed spectrum effectively. In this paper, we propose the maximum-minimum eigenvalue detection-based method to mitigate the effect of the undetected PUEA in CR networks with correlated signals and spatially-correlated shadow fading. In our proposed method, the spatial correlation characteristic is used to select users attending the cooperation of the spectrum sensing. Simulation results show that our proposed method can effectively mitigate the effect of the PUEA.