Location-aware key management scheme for wireless sensor networks
Sensor networks are composed of a large number of low power sensor devices. For secure communication among sensors, secret keys must be established between them. Recently, several pairwise key schemes have been proposed for large distributed sensor networks. These schemes randomly select a set of keys from a key pool and install the keys in the memory of each sensor. After deployment, the sensors can set up keys by using the preinstalled keys. Due to lack of tamper-resistant hardware, the sensor networks are vulnerable to node capture attacks. The information gained from captured nodes can be used to compromise communication among uncompromised sensors. Du et al. , Liu and Ning  proposed to use the known deployment information to reduce the memory requirements and mitigate the consequences of node capture attack. Our analysis shows that the assumption of random capture of sensors is too <i>weak</i>. An <i>intelligent</i> attacker can selectively capture sensors to get more information with less efforts. In addition to selective node capture attack, all recent proposals are vulnerable to node fabrication attack, in which an attacker can fabricate new sensors by manipulating the compromised secret keys and then deploy the fabricated sensors into the sensor system. To counter these attacks, we propose a grid-group scheme which uses known deployment information. Unlike the pairwise key scheme using deployment information proposed by Du et al., we uniformly deploy sensors in a large area; instead of randomly distributing keys from a large key pool to each sensor, we systematically distribute secret keys to each sensor from a structured key pool. Our performance analysis shows that our scheme requires less number of keys preinstalled for each sensor and is resilient to selective node capture attack and node fabrication attack.

title: A key-chain-based keying scheme for many-to-many secure group communication
abstract: We propose a novel secure group keying scheme using hash chain for many-to-many secure group communication. This scheme requires a key predistribution center to generate multiple hash chains and allocates exactly one hash value from each chain to a group member. A group member can use its allocated hash values (secrets) to generate group and subgroup keys. Key distribution can be offline or online via the key distribution protocol. Once keys are distributed, this scheme enables a group member to communicate with any possible subgroups without the help of the key distribution center, and without having to leave the overall group, thus avoiding any setup delay. Our scheme is suitable for applications where the population of a system is stable, group size is moderate, subgroup formation is frequent, and the application is delay sensitive. Through analysis, we present effectiveness of our approach.

title: RINK-RKP: a scheme for key predistribution and shared-key discovery in sensor networks
abstract: Efficient schemes for key predistribution and shared-key discovery play a vital role in security and efficiency of pairwise key establishment in sensor networks. In this paper, we propose a scheme for key predistribution using hash-chain and subsequent shared-key discovery. We show potential active attacks on sensor networks due to key predistribution which can have severer consequences as compared to attacks described in existing proposals. We also show that as compared to the existing schemes, our scheme is more resilient to these active attacks.

title: Source routing based pairwise key establishment protocol for sensor networks
abstract: Sensor networks are composed of a large number of low power sensor devices. For secure communication among sensors, secret keys must be established between them. The establishment of secret keys after deployment of sensors requires wireless communication. Because of the energy constraints, an efficient key establishment scheme cannot be designed without considering the power consumption factor in wireless communication. In order to reduce the communication overhead, we propose a source routing based pairwise key establishment protocol for large-scale sensor networks. We then use a probability model proposed in [D. Huang et al., (2004)] to analyze the communication overhead, and security strength of the scheme.

title: Bit-interleaved time-frequency coded modulation for OFDM systems over time-varying channels
abstract: Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications, with its ability to transform a frequency-selective fading channel into multiple flat-fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM subcarriers, which was generally considered harmful to system performance. In this paper, we propose a bit-interleaved time-frequency coded modulation (BITFCM) scheme for OFDM to achieve both the time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme, and for relatively low maximum normalized Doppler frequency, a reduced-complexity maximum-likelihood decoding approach is proposed to achieve good performance with low complexity. For high maximum normalized Doppler frequency, the intercarrier interference (ICI) can be large, and an error floor will be induced. To solve this problem, we propose two ICI-mitigation schemes by taking advantage of the second-order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly.

title: An interference-cancellation scheme for carrier frequency offsets correction in OFDMA systems
abstract: Recently, orthogonal frequency-division multiplexing (OFDM), with clusters of subcarriers allocated to different subscribers (often referred to as OFDMA), has gained much attention for its ability in enabling multiple-access wireless multimedia communications. In such systems, carrier frequency offsets (CFOs) can destroy the orthogonality among subcarriers. As a result, multiuser interference (MUI) along with significant performance degradation can be induced. In this paper, we present a scheme to compensate for the CFOs at the base station of an OFDMA system. In the proposed scheme, circular convolutions are employed to generate the interference after the discrete Fourier transform processing, which is then removed from the original received signal to increase the signal-to-interference power ratio (SIR). Both SIR analysis and simulation results will show that the proposed scheme can significantly improve system performance.

title: A state-transition-based incremental protocol specification