Lianfeng Shen

Modeling and Performance Analysis of Periodic Broadcast in Vehicular Ad Hoc Networks

This paper proposes a Markov model for analyzing the performance of periodic broadcast in vehicular ad hoc networks (VANETs). Since there is no packet retransmission in broadcast, we only consider a one-dimensional Markov model. In the proposed model, we assume that the traffic condition is unsaturated and introduce a state to represent the situation when there is no packet waiting for transmission in the buffer of a node. Meanwhile, the state of a backoff counter changes only when the channel is sensed idle. When the channel is busy, the state of the backoff counter does not change. Moreover, we use a discrete time D/M/1 queue to model the periodic broadcast of each node. Based on this model, we also show numerical results to analyze the performance of the periodic broadcast in VANETs in terms of packet collision probability and average packet delay.

Stable throughput and delay performance in cognitive cooperative systems

The cognitive cooperative system with coexisting scenario of multiple primary users and one secondary capable of relaying is considered in this study. The primary users transmit packets in orthogonal subchannels. According to the cognitive principle, the secondary activity cannot interfere with the primary performance. Therefore in this study, the secondary user makes use of the spectrum when sensed idle. Based on the proposed media access control (MAC) protocol, the authors derive the stable throughput and delay slots expressions of each primary user with secondary relaying. They also achieve the stable network constraints of relaying probability e, the feasible range of primary arrival rates and the maximum allowed secondary transmitting power which is to make a tradeoff between the stable throughput of the primary and secondary user. Simulation results show that secondary relaying can increase the primary and secondary throughput and also reduce the delay slots when designing an appropriate e.

Stable Throughput Analysis of Multi-User Cognitive Cooperative Systems

The cognitive cooperative system with coexisting scenario of multiple primary users and one secondary capable of relaying is considered. The primary users transmit packets in orthogonal sub-channels. According to the cognitive principle, the secondary activity cannot interfere with the primary performance. Therefore, in this paper, the secondary user makes use of the spectrum when sensed idle. Based on the proposed MAC protocol, we derive the stable throughput expressions of each primary user with secondary relaying. We also achieve the stable network constraints of relaying probability ε, the feasible range of primary arrival rates and the maximum allowed secondary transmitting power which is to make a tradeoff between the stable throughput of the primary and secondary user. Numerical simulations show that secondary relaying can increase the primary and secondary throughput when designing an appropriate ε.

Capacity of hybrid cognitive network with outage constraints

The concept of cognitive radio is to exploit efficiently the spectrum resources by allowing the coexistence of the primary and secondary users in the same bandwidth without interfering the performance of primary users. Three coexisting models (overlay, underlay and interleave) were presented in recent literature. In this study, the authors propose a hybrid cognitive network model with overlay and underlay models, whereby a primary link leases its fractions of transmission time to the secondary users for their cooperation (i.e. these nodes form as a virtual multiple input multiple output (VMIMO) group) under the outage constraints of the primary and secondary systems. A new cooperative protocol between primary and secondary users is presented. The authors attempt to achieve the maximum transmission capacity of the secondary users under the primary and secondary outage constraints, which depend on the secondary density in the cognitive network. This study gives the upper bound density of the secondary transmitters that are modelled as a homogeneous marked Poisson point process. The maximum density is achieved by computing an optimal set of system parameters such as power control factor of the secondary user and the dirty paper coding (DPC) parameter. Simulation results illustrate that the maximum secondary density obtained using VMIMO is superior to that obtained by direct primary transmission.

Optimal Cluster Number Determination for Clustered Wireless Sensor Networks

A method to determine the optimal clusterhead number in a clustered wireless sensor network is proposed to improve the energy efficiency of clustering schemes. The wireless sensor network is modeled as points locating randomly on the plane according to a homogeneous spatial Poisson process. This leads to derive the means of some typical cluster parameters accordingly. After that, the total energy cost consumed in the system is calculated based on a practical radio model. As a result, the optimal probability of becoming a clusterhead for each node is deduced via minimizing the system energy cost. Ultimately, the total energy costs are compared in the scenarios that the networks employ the same clustering algorithm with a range of values for the probability of becoming a clusterhead. Simulation results show that the optimal probability we obtained has indeed minimized energy dissipation in the system and is applicable to other clustering algorithms directly.

Interference analysis of 3G/ad hoc integrated network

A C3G-A network integrating the 3G network and the ad hoc network is proposed. In such C3G-A network, 3G and ad hoc networks adopt the same frequency bands, which result in additional interference for each other. In this study, an interference model of the C3G-A network is presented. Based on this model, the effects of the interference on network capacity are analysed. Meanwhile, the corresponding formulae of network capacity are deduced. It is observed from extensive simulation and numerical analysis that network capacity is seriously affected by the additional interference. In order to suppress the effects of the additional interference, an algorithm based on distance (ABD) is proposed so as to decrease the additional interference and maximise network capacity. The simulation results show that the ABD algorithm can effectively overcome the effects of the additional interference and approximate network capacity in the 3G network and the ad hoc network with different frequency bands.

A preset threshold based cross-tier handover algorithm for uplink co-channel interference mitigation in two-tier femtocell networks

This paper considers the co-channel interference mitigation problem and proposes a preset threshold based cross-tier handover algorithm for uplink co-channel interference mitigation in two-tier femtocell networks. The proposed cross-tier handover algorithm introduces a preset threshold cross-tier handover policy, which takes into account both the time-to-stay (TTS) of a macrocell user equipment (MUE)/femtocell user equipment (FUE) in a femtocell/the macrocell, and the received signal to interference plus noise ratio (SINR) at a femtocell access point (FAP)/the macrocell base station (MBS) in making a cross-tier handover decision for an MUE/FUE. A cross-tier handover decision is made by comparing the TTS of an MUE/FUE in a femtocells/the macrocell and the SINR at a FAP/the MBS with a preset TTS threshold and different SINR thresholds. The objective of the preset threshold based cross-tier handover algorithm is to increase the received SINR at the MBS/FAPs and thus improve the network performance. The performance of the proposed cross-tier handover algorithm with the minimum power transmission and the optimal power transmission is analyzed, respectively. Numerical results show that the proposed preset threshold based cross-tier handover algorithm can significantly improve the network performance in terms of the outage probability, user sum rate, and network capacity.

Relativity-based access strategy for frequency hopping system

In this study, two relativity-based access strategies are proposed for frequency hopping system with cognitive ability (C-FH). Sensing module is added in the receiver to perform real-time measurement of channel states. The first access strategy is studied in consideration of partial relative FH pattern. The spectrum band is divided into several groups and each C-FH user can only jump over the channel group authorised by the active user. In the second access strategy, the C-FH user will adaptively choose an active user as the scheduler to apply for access. The application users may be rejected because of lack of resources or accepted to access the available channels in order of arranged sequence. The chosen scheduler will accept applications according to number of available channels and the spectrum resource will be shared in condition of being temporally correlated. With relativity-based strategies, FH patterns of users have the minimum Hamming correlation, even to zero. Markov chains are built to model the access processes. The performance analysis and the simulation results show that the relativity-based access strategy brings lower collision probability, higher bandwidth utilisation and higher normalised average throughput.

Access Policies for Frequency Hopping System Based on Frequency Relativity in ISM Band

We try to achieve quick and accurate channel access in background of coexistence between Bluetooth system (BT) and frequency hopping system with cognitive ability (C-FH) in ISM band. In this paper, access policies based on frequency relativity (FRA) are proposed. The C-FH user could use frequency relativity (FR) to make fuzzy prediction and access the available sub-channels. With channel states variation Markov models, the performance of new schemes could be verified. Compared with access control without FR, the FRA policies are revealed to get lower collision probability and higher bandwidth utilization in ISM band.