Lin Xiaokang

A MAC Queue Aggregation Scheme for VoIP Transmission in WLAN

Current WLAN is still predominantly data centric, so it is not well equipped to meet the pressing voice capacity and quality of service (QoS) demands when transmitting VoIP traffic. One of the reasons is the large WLAN PHY/MAC overhead. This paper proposes and investigates a MAC queue aggregation scheme which aggregates multiple queuing MAC frames to reduce the overhead. The scheme will not incur any extra delay. Simulations in various scenarios show that the proposed scheme can improve the VoIP capacity by up to 65%.

An implementation of MAC in fixed BWA system

Broadband wireless access (BWA) is a novel access technology in broadband communications. The wireless structure, high access rates, and flexibility make it appropriate for telephone, videoconference, Ethernet, VoD and multimedia services. And it is promising among its competitors. The key technologies in MAC of a BWA system are discussed in this article. We also introduce the implementation of MAC in a 3.5 GHz BWA system. We apply the TDMA/TDM/FDD mode in MAC control.

Parallel positive justification in SDH C-4 mapping

Bit Rate Justification is a key technique in digital multiplexing. SDH adopts Positive Justification for C-4 mapping and PositivelZeroMegative Justification for other mappings. The mapping of C-4 has the highest system frequency in all Bit Rate Justifications of SDH. This demands highly on the technology and power consumption in the ASIC design. This paper puts forward a novel technique of Positive Justification with Parallel Processing and solves the problem caused by high speed. This method is very useful for implementing the C-4 mapping with CMOS Gate Array Technology. The design has been implemented with FPGAs of Xilinx Inc. The paper ends with the mapping jitter test results, which are quite satisfied. This paper is funded by the Project 863 of China.Bit rate justification is a key technique in digital multiplexing. SDH adopts positive justification for C-4 mapping and positive/zero/negative justification for other mappings. The mapping of C-4 has the highest system frequency in all bit rate justifications of SDH. This demands highly on the technology and power consumption in the ASIC design. This paper puts forward a novel technique of positive justification with parallel processing and solves the problem caused by high speed. This method is very useful for implementing the C-4 mapping with CMOS gate array technology. The design has been implemented with FPGAs of Xilinx Inc. The paper ends with the mapping jitter test results, which are quite satisfied.

An Innovative Time Synchronization Algorithm for Wireless HART Networks

Wireless HART is widely used in the field of industrial process control. The communication between the devices is performed using Time Division Multiple Access (TDMA) with time slots of 10ms. In addition, a series of actions must be completed in the slot unit of 10 ms, including the data reception, transmission and acknowledge, etc. Time synchronization is the most important premise to ensure the communication secure, reliable and conflict-free.

The MAC Mechanism with QoS Provision Based on Stream-Maintenance in Ad Hoc Networks

Because the signal of different nodes interferes with each other, the collision happens frequently in ad hoc networks. If only adopting contention-based MAC protocol, it is hard to guarantee quality of service (QoS) of multi-media services such as voice and video in ad hoc network. A series of periodical realtime service packages from the same source node can be regarded as a real-time data stream. By adopting the resource reserve mechanism to improve the IEEE 802.11 DCF, a new type of MAC mechanism including MAC-FM and MAC-FM (E) is brought forward in this paper. MAC-FM and MAC-FM (E) reserve dynamically the time slots for the real-time data stream in distributed mode to avoid the collision of real-time service packages. In addition, the networks performance including delay and throughput is analyzed in theory and validated via simulation. The result indicates that MAC-FM and MAC-FM (E) can decrease the delay greatly and increase the throughput of ad hoc networks

A neural network approach to blind-estimation of PN spreading sequence in lower SNR DS/SS signals

In this paper, an approach based on discrete Karhunen-Loeve transformation of the DS/SS signals is proposed to estimate PN sequence in lower SNR DS/SS signals. Characteristics of self-organization and principal components extraction of unsupervised neural networks are exploited adequately. Theoretical analysis and experimental results are provided to show that this approach can work well on the lower SNR input signals.

An Effective Way to Improve Actigraphic Algorithm by Using Tri-axial Accelerometer in Sleep Detection

This paper presents an effective method for improving the accuracy of sleep detection using actigraphic algorithm. We have collected 2 sets of comparative data, wrist movement acceleration and brain wave analysis. In the first mode, we use the acceleration on x-axis as the input of actigraphic algorithm, in imitation of uni-axial accelerometer used in former study. In the second mode, we calculate the vector magnitude of acceleration in 3 dimensions and use it as the input of algorithm. Two outputs are then compared with Zeo data that are collected simultaneously. The comparison of results between 2 modes exhibit fine improvement on sleep detection.

BER calculation of an OFDM system with phase nonlinearity

Orthogonal frequency division multiplexing (OFDM) is sensitive to the phase nonlinearity due to filter devices in both transmitter and receiver. In this paper, the bit error rate (BER) performance degradation of OFDM systems with phase nonlinearity is investigated in an additive white Gaussian noise (AWGN) channel. We consider the effects of BER both in parabolic and cubic phase nonlinearity. The theoretical approximate calculation method is also derived of BER for binary phase shift keying (BPSK) and quaternary phase shift keying (QPSK) modulation schemes in OFDM systems. In addition, the method of BER calculation is validated by simulations. In general, phase shift keying modulation schemes is easily affected by phase nonlinearity in transmitting channel. Especially in high data rate transmitting system, phase nonlinearity will make great degradation in BER.

Enhanced MAC Protocol for Voice Communication in IEEE 802.11 WLAN

Nowadays wireless LAN (WLAN) and voice over Internet protocol (IblP) become more and more pervasive. The combination of these two technologies, i.e. VoIP over WLAN attracted more and more attentions. However, voice capacity in current WLAN is quite low. This paper proposes an enhancement for legacy 802.11 MAC protocol which mitigates access point (AP) bottleneck effect and improves the VoIP transmission capacity. Simulations in various scenarios well verify the improvement achieved with increased voice capacity and decreased access delay.

Scaling issues of LDP protocol

This paper first introduces the label distribution protocol (LDP) in the MPLS network and then discusses and analyzes some key issues of the scaling capability of the LDP protocol in detail. Some deficiencies in the current LDP protocol and problems for further research have been pointed out.