Guixia Kang

Resource Allocation in a New Random Access for M2M Communications

To increase the number of successful accesses for machine-to-machine (M2M) communication, we propose a new random access (RA) procedure. The proposed RA procedure allows evolved NodeB (eNB) to know the preamble collisions in the first step by attaching user equipment (UE) identity information in physical random access channel (PRACH). This improvement prevents eNB from scheduling physical uplink shared channel (PUSCH) to the collided preambles, which improves the resource efficiency. Based on the enhanced RA procedure, a resource allocation scheme is proposed. By estimating the number of successful preamble, the proposed scheme achieves a reasonable resource tradeoff between PRACH and PUSCH. Simulation results show that the proposed RA procedure significantly improves the number of successful accesses as well as the resource efficiency.

Pilot Design for Inter-Cell Interference Mitigation in MIMO OFDM Systems

In this letter, the design of pilots aiming at mitigating the inter-cell interference in MIMO OFDM systems is addressed. It is shown that if an ideal channel between interferer and receiver is assumed, pilots resulting in a variation coefficient of zero, and therefore best performance on system level, can be designed. The properties of these pilots are described, and numerical calculations as well as simulation results are presented to verify the theoretical analysis.

Energy-Efficient Spectrum Sensing Strategy in Cognitive Radio Networks

In this letter, a novel metric is proposed to evaluate the average sensing energy-efficiency of cognitive radio (CR) networks. A theorem as well as the related closed-form expression for determining the optimum number of cooperative sensing cognitive terminals is provided to optimize the proposed metric. According to the theorem, we propose an efficient terminal-assignment strategy for coordinated spectrum sensing. Simulation results show that the proposed strategy can significantly improve the overall average sensing energy efficiency of the CR system.

Outage Performance of Cognitive-Radio Relay System Based on the Spectrum-Sharing Environment

In the spectrum sharing systems, an unlicensed (secondary) user may share a frequency band with its licensed (primary) user as long as its transmission does not interfere with the primary users communications. For the cognitive wireless relay networks, this interference regulation from the primary user may affect its cooperative scheme. In this paper, we investigate the outage performance of cognitive wireless relay networks in a spectrum sharing environment, in which the secondary users including the source and relays may take advantage of a frequency band of the primary user to transmit data to the receiver while not interfering with the primary users communication. In particular, we quantify the relation between the outage performance of the secondary relay link and the interference inflicted on the primary user.

A monitoring system for type 2 diabetes mellitus

This paper presents a novel type 2 diabetes mellitus (T2DM) monitoring system. Decisions on the statuses of diabetes control and predictions of future blood glucose of an individual made by the system depend both on the original medical data collected by medical sensors and some contexts either are entered manually or generated automatically. When dealing with the data, first we clean and transform data and contexts, then build data mining models using several mining algorithms. After the mining process, we analyze and assess the accuracy and sensitivity of the models, and find out the appropriate models for decision making and predicting in diabetes control. Our study is of certain significance to help prevent and treat T2DM.

Linear Precoding Design in Multi-User Cognitive MIMO Systems with Cooperative Feedback

In this letter, we present a linear precoder design scheme for a cognitive (CR) multi-input multi-output (MIMO) system, where a secondary broadcast channel uses the same spectrum with multiple primary users (PUs). Considering both cooperative feedback from the PUs and local feedback from the secondary users (SUs) to the secondary transmitter (ST), the ST can obtain the quantized information regarding the direction of the channels. The proposed scheme is based on the minimum mean square error (MMSE) criteria and is robust to the channel uncertainties caused by quantization error. The derivation is given under two different levels of interference constraints respectively. Simulation results show the effectiveness of the proposed precoder design scheme.

Range-Free Distance Estimate Methods Using Neighbor Information in Wireless Sensor Networks

Distributed localization algorithm continues to be an important and challenging topic in todays wireless sensor networks (WSNs). The accurate estimations of distances among nodes are premises for the accurate estimations of node po- sitions. In this paper, we propose some schemes towards the DV-Hop algorithm to improve the distance estimations. These improvements are based on accurate analysis of hop information of neighbor nodes in a WSN with randomly deployed sensors. It is demonstrated that our proposals ensure better distances estimations and hence improve the localization accuracy with low communication overheads. In addition, we discuss the de- ployment, communication cost and computing complexity of the novel algorithms. Simulations are performed and the results are observed to be in good agreement with the analysis.

Pilot Sequence Design Scheme for MIMO OFDM Systems under Time-Varying Channels

Orthogonal frequency division multiplexing (OFDM) systems encounter performance degradations due to the time varying (TV) channels in wireless environments. As delay spread increases, symbol duration should also increase, and then OFDM systems become more susceptible to time-variations. Time-variations introduce inter-carrier interference (ICI), which must be mitigated to improve the performance in high delay and Doppler spread environments. In this paper, a pilot design scheme for multiple input multiple output (MIMO) OFDM system is proposed under TV channels. The properties of these pilots are described, and the simulation results are presented.

An Advanced Semi-Markov Process Model for Performance Analysis of Wireless LANs

During the last decades, there are numerous researches in the field of wireless local area networks (WLANs). A large number of these researches focus on performance analysis of IEEE 802.11 Medium Access Control (MAC) protocols. And the most representative model for MAC mechanism in WLANs is the two-dimensional Markov model, which has been proven to be an accurate model to analyze the performance of WLANs, in the assumption of finite number of terminals and ideal channel conditions. But this two-dimensional Markov model is rather complex, as far as computation and analysis are concerned. Recently, a novel semi-Markov process model for IEEE 802.11 MAC protocols has been put forward to mitigate the complexity of analyzing the performance of WLANs. However, this semi-Markov model has some defects, such as not taking maximum retransmission number into account. In this paper, we propose an advanced semi-Markov process (ASMP) model, which not only withholds the merits of semi-Markov chain model, but also eliminates its shortcomings, thus more accurately calculating the network parameters of WLANs. Simulation results show that our proposed model achieves accurate results with less complexity, and is suitable for evaluating the performance of the MAC protocols.

Further Investigation on Pilot Design for MIMO OFDM Systems in Multi-Cell Environment

In this paper, the pilot design aiming at mitigating the inter-cell interference in MIMO OFDM systems is addressed. We first compute the mean square error of the frequency domain LS joint channel estimation with the consideration of interfering cell. We then overview the optimal pilot sequences within a cell, which can cancel the intra-cell multiple access interference. Based on the mean square error and variation coefficient, we propose two conditions for the pilot design to mitigate the inter- cell interference. It is shown that if an ideal channel between interferer and receiver is assumed, we can obtain the pilots resulting in a smaller value of mean square error based on the variation coefficient of zero, which make the power of inter-cell interference distribute at all paths of the channel more uniformly and less, therefore, the performance on system level would be improved. A further discussion about proposed guidelines in practical system is made, and numerical calculations as well as simulation results are presented to verify the theoretical analysis. Index Terms—pilot design, inter-cell interference, MIMO, OFDM.