Showing papers by "Jiandong Li published in 2004"

Maximum likelihood method for integer frequency offset estimation of OFDM systems

Abstract: A novel method for integer frequency offset estimation of OFDM systems is derived, which is based on the maximum likelihood (ML) technique and exploits the differential information between two consecutive blocks of OFDM data symbols in the frequency domain. The reason why the proposed ML method has better performance than the conventional method is analysed.

Performance analysis of IEEE 802.11 WLAN to support voice services

Abstract: This paper studies the performance of the IEEE 80211 standard MAC protocol for integrated data and voice transmission with the DCF (distributed coordination function) and the PCF (point coordination function) By simulation, we evaluate the network performance for various protocol parameters, especially, the delay jitter for voice traffic The main factor to influence delay jitter is given Numerical results show that it is important to choose appropriate parameters and compromise the number of voice stations and the data traffic throughput to get the enhanced performance of IEEE 80211 The performance of protocol in theory is derived and is verified by the simulation results

Functional networks based Internet end-to-end delay dynamics

Abstract: Nonstationarity and nonlinearity are found by the analysis of various delay series measured from different Internet links. The fact that different types of links have different degrees of self-similarity is also obtained. By constructing appropriate network architecture and neural functions, functional networks can be used to model the Internet end-to-end nonlinear delay time series. Furthermore, by using adaptive parameter studying algorithm, the nonstationarity can also be well modeled. The numerical results show that the provided functional network architecture and adaptive algorithm can precisely characterize the Internet end-to-end delay dynamics.

Performance evaluation of IEEE 802.11 WLAN - high speed packet wireless data network for supporting voice service

Abstract: The IEEE 802.11 standard MAC is a hybrid protocol of random access and polling when both DCF (distributed coordination function) and PCF (point coordination function) are used. This paper evaluates the performance of the MAC protocol for integrated data and voice transmission with the two access mechanisms. By simulation, we evaluate the network performance for various values of the protocol parameters. Especially, voice traffic is sensitive to delay jitter and here we point out the main factors to influence it. Numerical results show that it is important to choose appropriate parameters and we should compromise the number of the voice stations and the data traffic throughput to get the enhanced performance of IEEE 802.11. Finally, the performance of protocol in theory is derived and is verified by the simulation results.

Noncoherent reduced state differential sequence detection of continuous phase modulation

Abstract: A noncoherent reduced state differential sequence detection (RSDSD) for continuous phase modulation (CPM) is proposed in this paper. This method makes use of the reduced state trellis based on reduced state sequence detection (RSSD) and performs one-symbol differential Viterbi detection. The minimum Euclidean distance of the reduced state trellis is analyzed for full response CPM and partial response CPM. Bit error rates of RSSD and RSDSD are simulated for octal 2RC signal with h=1/8 in the AWGN channel and comparisons are made between the different RSSD schemes and between coherent RSSD and noncoherent RSDSD with Doppler frequency shifts. Although our proposed scheme is degraded by 2 dB at 10/sup -3/ bit error rate as compared with coherent detection, it is more appropriate and robust when the carrier recovery is difficult.

Self-adaptive transmission scheme of integrated services over an IEEE 802.11 WLAN

Abstract: A novel self-adaptive transmission scheme to support integrated data and voice transmission over an IEEE 802.11 WLAN is proposed. The simulation results show that the scheme can improve the data traffic performance and decrease efficiently the voice traffic delay jitter, and then increase the WLAN capacity. It is easy to realise as no change in the MAC protocol is required.

Maximum likelihood estimation of integer frequency offset for OFDM

Abstract: One of the principal disadvantages of orthogonal frequency division multiplexing (OFDM) is very sensitive to frequency offset. Carrier frequency offset can be divided into two parts: an integer one and a fractional one. The integer frequency offset has no effect on the orthogonality among the subcarriers, however causes a circular shift of the received data symbols, resulting in a BER of 0.5. The maximum likelihood (ML) estimation algorithm of the integer frequency offset is derived under the assumption that the channel impairments only consist of additive noise. Simulation results show that it can perform well even in a time-dispersive channel. Its performance is assessed and compared with the conventional method by computer simulations for the additive white Gaussian noise (AWGN) channel and a multipath fading channel.

A study of self-adaptive transmission for integrated voice and data services over an IEEE 802.11 WLAN

Abstract: The IEEE 802.11 standard MAC is a hybrid protocol of random access and polling when both DCF (distributed coordination function) and PCF (point coordination function) are used. On the base of the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self-adaptive transmission scheme to support multi-service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self-adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, the scheme is easy to be realized for no change in the MAC protocol is needed.

OWDM system based on ML algorithm and blind identification in multipath fading channel

Abstract: A novel OWDM system with blind identification based on the maximum likelihood (ML) algorithm is studied for the multipath fading channel. New OWDM structures based on the ML algorithm and blind identification and H matrix based on the ZF (zero forcing) algorithm are the two novel aspects of this system. The performance of the system under the multipath fading channel is analysed.

An efficient estimator for OFDM integer frequency offset synchronization

Abstract: An efficient estimator for integer frequency offset estimation of OFDM systems is derived, which is based on maximum likelihood (ML) technique and exploits the differential information between two consecutive blocks of OFDM data symbols in frequency domain. The reason why the proposed ML estimator has better performance than the conventional method is analyzed. How to select the differential sequence is also studied. By computer simulations, the effects of the various parameters such as length of cyclic prefix, value of integer frequency offset and differential PN sequence on the performances of the two estimators are evaluated, and the performance of the ML estimator is compared with that of the conventional method for the additive white Gaussian noise (AWGN) channel and a multipath fading channel. The simulation results are in good agreement with the analytical study.

A novel integer frequency offset estimator for OFDM

Abstract: A novel estimator for integer frequency offset estimation of OFDM systems is derived, which is based on maximum likelihood (ML) technique and exploits the differential information between two consecutive OFDM data symbols sequences in frequency domain. The reason why the ML estimator has better performance than the conventional method is analyzed. The effects of integer frequency offset, system parameters, and differential PN sequence on the performances of the two estimators are analyzed. How to select the differential sequence is also studied. By computer simulations, the performance of the ML estimator is compared with that of the conventional method for the additive white Gaussian noise (AWGN) channel and a multipath fading channel. The simulation results are in good agreement with the analytical study.

A user adaptive scheduling multiple access protocol

Abstract: A multiple access control (MAC) protocol - user adaptive scheduling multiple access (UASMA) protocol is proposed in this paper, which can perfectly schedule the packet transmission according to the exact number of active mobile terminals (MTs) determined by self-organizing algorithm, and adjust the number of packets sending by one node in one frame properly. UASMA protocol employs an especial frame structure, which makes it possible to allocate channel resource to uplink and downlink traffic according o their respective service requirements. And the concept of referenced-frame-length is proposed, which can ensure the frame length various in a certain range, and consequently increase the utilization of the channel greatly. Meanwhile, UASMA protocol uses an efficient collision resolution algorithm to guarantee that active MTs can access the channel rapidly. Finally, the performance of UASMA protocol is evaluated by simulation and compared with UPMA protocol, the simulation results show that the former has better performance than the latter.

Comparison of integer frequency offset estimators for OFDM systems

Abstract: In this paper, a new maximum likelihood (ML) estimator for the integer frequency offset estimation of OFDM systems is proposed and compared with the conventional SC estimator. Both estimators exploit the differential information between two consecutive blocks of OFDM data symbols in the frequency domain. The reason why the proposed ML estimator has better performance than the conventional SC method is analyzed. The mean and variance of the proposed and conventional estimators are discussed, and the estimation error probability is given. The computer simulation results are in good agreement with the analytical study.

A new interference cancellation arithmetic of space-time coding system

Abstract: Space-time code is a kind of antifading techniques discussed drastically in recent years. The paper focuses on the field of space-time block coding antiinterference technique. After introducing the fundamental concept of interference cancellation and the two-step interference cancellation method used usually, the paper submits a new arithmetic, which is unselective repeated feedback interference cancellation (URF-IC) arithmetic. The arithmetic can achieve the performance of two-step interference cancellation technique while its complexity of operation is lower.

Field emission properties of diamond-like carbon films annealled at different temperatures [annealled read as annealed]

Abstract: Diamond-like carbon (DLC) thin films have attracted much attention due to their unique properties (Robertson, 2002) for the application in the protective coating for magnetic recording disks and optical device. Recently, DLC films have been reported to have excellent field emission properties (Kiyota et al., 1999; Mammana et al., 2002) and the mechanism of field emission has been proposed (Ilie et al., 2000). The field emission properties of DCL films are mainly dependent on the variation of chemical structure bonding other than surface roughness and the doping. Although it is a fact that high temperature annealing can vary the chemical structure bonding of DLC films so that affect its field emission property, some controversies still existed in the relation between the chemical structure bonding states in the DLC films and its field emission properties. In this study, we report the effect of annealing inducing the chemical structural variations on the field emission properties of DCL films, and the possible mechanism is discussed.

ML-based estimator for integer frequency offset estimation of OFDM systems

Abstract: A novel estimator for integer frequency offset estimation of OFDM systems is derived, which is based on the maximum likelihood (ML) technique and exploits the differential information between two consecutive blocks of OFDM data symbols in the frequency domain. The reason why the ML estimator has better performance than the conventional method is analyzed. How to select the differential sequence is also studied. By computer simulations, the performance of the ML estimator is compared with that of the conventional method for the additive white Gaussian noise (AWGN) channel and the multipath fading channel. The simulation results are in good agreement with the analytical study.