Lenan Wu

New scheme of MPPSK modem

The problems of m-ary Position Phase Shift Keying (MPPSK) signal demodulation and anti-interference were considered. A novel matched filtering scheme of the MPPSK demodulator which used output signal of the special impacting filter were proposed. The interference was filtered out by coherent processing and band-pass filtering, then the output waveform was put into the matched filter (MF) to decode. The simulation results of the MPPSK demodulator based on the MF, was compared with the traditional adaptive threshold integral discrimination demodulation scheme. The simulation results indicated that the demodulation with inter-symbol anti-interference performance was better than the existing mainstream demodulation schemes.

Efficient modulation and demodulation methods for multi-carrier communication

The modulation and demodulation problems for efficient multi-carrier communications are considered in this study. To maintain compact spectrum and realise dense multi-carrier transmission, a novel modulation method based on random hopping position, namely time hopping m-ary phase position shift keying (TH-MPPSK), is proposed to remove the discrete spectrum. Then, a multi-carrier scheme without guard interval among subcarriers is provided to reduce complexity in the practical communication systems. Moreover, a novel demodulation method is proposed to improve the efficient communication performance. Simulation results demonstrate that the TH-MPPSK can significantly remove the discrete spectrum and the proposed demodulation method can satisfactory performance.

The dual carrier ABSK system based on a FIR bandpass filter.

The special impacting filter (SIF) with IIR structure has been used to demodulate ABSK signals. The key points of SIF, including the resonance circuits high Q value and the “slope-phase discrimination” character of the filter sideband, are demonstrated in the paper. The FIR narrow-band bandpass filtering system, which can also provide the impact-filtering effect, is proposed. A dual carrier system of ABSK signals is designed with the proposed FIR filter as its receiver. The simulation results show that the FIR filter can work well. Moreover, compared to the traditional SIF, the proposed FIR filter can not only achieve higher spectral efficiency, but also give better demodulation performance.

A Simplified Mobile Ad Hoc Network Structure for Helicopter Communication

There are a number of volunteer and statutory organizations who are capable of conducting an emergency response using helicopters. Rescue operations require a rapidly deployable high bandwidth network to coordinate necessary relief efforts between rescue teams on the ground and helicopters. Due to massive destruction and loss of services, ordinary communication infrastructures may collapse in these situations. Consequently, information exchange becomes one of the major challenges in these circumstances. Helicopters can be also employed for providing many services in rugged environments, military applications, and aerial photography. Ad hoc network can be used to provide alternative communication link between a set of helicopters, particularly in case of significant amount of data required to be shared. This paper addresses the ability of using ad hoc networks to support the communication between a set of helicopters. A simplified network structure model is presented and extensively discussed. Furthermore, a streamlined routing algorithm is proposed. Comprehensive simulations are conducted to evaluate the proposed routing algorithm.

Design of a Multiorder OFDM Frequency Diversity Approach

Frequency diversity is used to reduce the effect of destructive fading, so as to improve the communication quality, by passing the information symbols through multiple independently faded paths, and ensure that reliable communication is possible as long as one of these paths is strong. In this paper a multiorder orthogonal frequency division multiplexing (OFDM) frequency diversity approach using properties of order theory and Hamming distance is proposed. The frequency diversity is obtained by specifying proper correlations among the transmitted symbols. As subchannels experience independent fading, at least one of the symbols may have robust signal, which can be used by the receiver to detect other symbols. Considering bit error rate (BER) performance, power consumption, bandwidth utilization, and practical implementation expense, simulation results show that the proposed approach outperforms other OFDM diversity techniques, such as Maximal Ratio Combination (MRC) and Space Frequency Block Coding (SFBC).

M-ary phase position shift keying with orthogonal signalling

An improved M-ary phase position shift keying (MPPSK) modulation, aiming to increase the spectral and energy efficiencies of existing MPPSK schemes while preserving their low demodulation complexity and error performance, is proposed in this study. Specifically, an improved MPPSK with orthogonal signals called OI-MPPSK is presented. For the proposed OI-MPPSK, the authors develop two demodulation schemes that employ a special impact filter (SIF): (i) the orthogonal SIF correlator (OSC) scheme, which consists of the orthogonal transmission, the SIF and a correlator; (ii) the orthogonal SIF position (OSP) scheme, which is the same as the OSC scheme except that the coherent demodulator is replaced by exploiting position-related information. As a result of exploiting the position-related information in the proposed OI-MPPSK scheme, the SER performance of the OSP-based demodulator is superior to that of the OSC-based demodulator.

Base station identification in single-frequency network positioning system under mixed line-of-sight/non-line-of-sight condition

A base station (BS) identification algorithm which does not modify the transmitter hardware and digital terrestrial television broadcasting signal framework is proposed for single-frequency networks positioning system. Similar to the outlier detection in multi-object tracking environments, the BS identification is formulated as a data validation problem which is solved with gate construction. Compared with traditional gate algorithm, an additional mode probability parameter is introduced to describe the wireless channel condition and overcome its drawback in non-stationary wireless channel environments by the interacting multiple model approach. In the proposed algorithm, two parallel innovation statistical distribution deduction modes with line-of-sight and non-line-of-sight condition are employed to estimate the corresponding parameters, respectively. Then a combination scheme is utilised to mix the two estimated statistical parameters by the predicted mode probabilities and obtains the final innovation distribution. At last, gate parameter is calculated like traditional gate algorithm and the BS identification is achieved. Simulation results demonstrate its robustness and high performance in different scenarios.

Exploiting the Randomness Inherent of the Channel for Secret Key Sharing in Vehicular Communications

Vehicular Ad Hoc networks (VANETs) have been employed in supporting several applications related to safety and comfort. VANET applications have strict security requirements, as they have direct impact on people comfort and safety. Although many ordinary networks security systems can be applied to provide security services in VANET, the key establishment between legitimate vehicles is the common challenge among all of these systems. This paper proposes a secret key establishment technique for vehicular communications exploiting the special properties and randomness inherent of the wireless channel. Our comprehensive simulations show that the proposed key extraction technique suits VANETs rather than other communication systems, owing to the multi environments operation of VANET which causes more randomness due to fading, noise multipath and velocity variation. The proposed approach can be tuned to extract low or high rate secret key with high entropy rate and less information exchange between legitimate vehicles. The extracted secret key can be employed to support providing security services in VANET.

Probabilistic data association detectors for multi-input multi-output relaying system

The authors investigate the performance of the probabilistic data association (PDA) detector in a cooperative system that consists of a source, a relay and a destination, which are all multiantenna nodes. Taking advantage of the soft information provided by the PDA detector at the relay, the authors present a relaying scheme in light of which the relay can just transmit signals to the destination under the condition of having high detection reliability. Characterised by the means on how to exploit the information provided by both the source and the relay at the destination, two detectors named as combing PDA (C-PDA) and iterative PDA (I-PDA) are developed, respectively. C-PDA adopts one PDA detector to retrieve the transmit signals by combining the received signals from the source and the relay. I-PDA employs two concatenated PDA detectors to perform detection with respect to the received signals from the source and the relay, respectively. Just as in turbo decoding, soft information is iteratively exchanged between these two concatenated PDA detectors to enhance the performance of I-PDA. Simulation results have shown that significant performance gains can be achieved by both C-PDA and I-PDA over the conventional zero-forcing detector.

On channel estimation in vehicular networks

In vehicular ad hoc network (VANET), the accuracy of the channel estimation plays a key role toward obtaining considerable improvement to the physical layer performance. In this study, least square (LS) and minimum mean square error (MMSE) estimation techniques are discussed and their performances in different VANET transmission scenarios are thoroughly investigated. Furthermore, a modified scheme of these techniques to improve the performance of the system and reduce the complexity in such a way that suits VANET communications is developed. Discreet Fourier transform and singular value decomposition techniques are companied with LS and MMSE to develop a channel estimation scheme which suits VANET channel conditions and ensures performance improvement and remarkable complexity reduction. Comprehensive simulations results show that the developed scheme greatly improves the performance of the system compared with LS and substantially reduces the complexity of MMSE.