Xiaofeng Zhong

Spatial modeling of the traffic density in cellular networks

Modeling and simulation of a cellular network typically assumes that the target area is divided into regular hexagonal cells and mobile stations (MSs) are uniformly scattered in each cell. This implies a statistically uniform distribution of traffic load over space, but in reality the spatial traffic distribution is highly non-uniform across different cells, which calls for actual spatial traffic models. In this article, we first present the analysis of traffic measurements collected from commercial cellular networks in China, and demonstrate that the spatial distribution of the traffic density (the traffic load per unit area) can be approximated by the log-normal or Weibull distribution depending on time and space. Then we propose a spatial traffic model which generates large-scale spatial traffic variations by a sum of sinusoids that captures the characteristics of log-normally distributed and spatially correlated cellular traffic. The proposed model can be directly used to generate realistic spatial traffic patterns for cellular network simulations, such as performance evaluations of network planning and load balancing.

An adaptive medium access control mechanism for cellular based Machine to Machine (M2M) communication

This paper discusses the realization of Adaptive Traffic Load slotted MACA in cellular based M2M communication. Based on the statistic information of the channels occupancy rate, the base station estimates the traffic load and calculates the RTS transmission probability and broadcast to the members. By using the ATL S-MACA we control the access of the terminals to the system for high arrival rates. Thus maintain its throughput at 70.4%. As no carry sensing module is needed, the implementation of this protocol is not very complex and only requires the continue measurement of the traffic load. ATL S-MACA protocol is qualified to be adopted in the system where no carrier sensing module is available, like the cellular based M2M modules.

A General Power Allocation Algorithm for OFDM-Based Cognitive Radio Systems

In OFDM-based cognitive radio systems, the interference power limits of the primary users (PUs) introduce subchannel transmit power constraints for the secondary user (SU). The power allocation among the subcarriers of SU should be subject to both the sum transmit power constraint as well as the transmit power constraint of each subchannel. Different from previous works, we deal with a more general case where the subcarrier sidelobes are specially considered. A general power allocation algorithm is proposed to obtain the optimal solution that maximizes the capacity while satisfying both the sum and subchannel transmit power constraints.

Connected Dominating Set in 3-dimensional Space for Ad Hoc Network

Connected dominating set (CBS) has been proposed as virtual backbone or spine of wireless ad hoc networks. Most literatures take the same assumption that the ad hoc network is distributed in a 2-dimensional plane. In this paper, the characters of CBS structure are deduced to 3-dimensional space, and a distributed approximation algorithm is analyzed for ad hoc network, whose performance ratio is proved to be 16 at most, in the case of 3-dimensions.

High Throughput Routing in Large-Scale Multi-Radio Wireless Mesh Networks

Routing in large-scale multi-radio wireless mesh networks (WMNs) is facing two challenges in achieving a high throughput. One is the long path between the source and the destination, and the other is the high routing overhead. We study the both aspects and develop our schemes accordingly. Firstly, a new routing metric for selecting multi-channel routes with maximum end-to-end capacity is presented. Secondly, a feedback based algorithm to maximize the control message broadcasting interval is proposed to minimize the routing overhead, offering more residual capacity for data traffic while keeping the routes reliable. Both the theoretic analysis and simulation experiments demonstrate the effectivity of our proposals.

Stable enhancement for AODV routing protocol

Routing algorithm has been the challenge in the wireless ad-hoc network for a long time because of the quick mutability of the network topology introduced by the mobility of nodes. AODV is appealing for ad hoc networks as an efficient on-demand routing protocol because of the low routing overhead and high performance. As an optimization for the current AODV, a novel stable adaptive enhancement for AODV routing protocol was proposed in this paper, which considers joint route hop count, node stability and route traffic load balance as the route selection criteria. Comparing with AODV protocol, the new algorithm has better performance as shown with the simulations results.

The analysis of the energy efficiency for the decode-and-forward two-way relay networks

In this paper, a two-way relay channel is considered, where two sources transmit information to each other with the help of a half-duplex decode-and-forward (DF) relay. We investigate the energy efficiency (EE) for the DF two-way relay transmission (TWRT). The EE expression is derived first and the properties of the EE are then analyzed. An novel algorithm is proposed to find the maximal EE under the relay power constraint for the DF-TWRT. Simulation results confirm the theoretical findings of the EE for the DF-TWRT.

Dynamic Spectrum Negotiation with Asymmetric Information

Spectrum scarcity is becoming a serious issue due to the rapid development of wireless communication technology. Dynamic spectrum sharing can effectively improve the spectrum usage by allowing secondary unlicensed users (SUs) to dynamically and opportunistically share the spectrum with primary licensed users (PUs). In this paper, we investigate a spectrum negotiation mechanism under incomplete information in a dynamic environment, where both the PU and the SU can obtain rate increases through cooperative communications. Specifically, an SU relays traffics for a PU in exchange for dedicated transmission time for the SU’s own communication needs. We model the bargaining process as dynamic Bayesian games and characterize the Perfect Bayesian Equilibria under different system model parameters. Analysis and numerical results indicate that both PU and SU obtain performance improvements compared with no cooperation, and thus achieve a win-win situation via the spectrum negotiation.

Sequential Bargaining in Cooperative Spectrum Sharing: Incomplete Information with Reputation Effect

Cooperative spectrum sharing can effectively improve spectrum usage by allowing secondary users (SUs) to dynamically share the licensed bands with primary users (PUs). Meanwhile, an SU can relay a PUs traffic to improve the PUs effective data rate. In this paper, we consider a sequential spectrum bargaining process to achieve cooperative spectrum sharing between one PU and one SU over multiple time slots. The SU may be a Low type or a High type, depending on its energy cost. Such information is private to the SU and is unknown to the PU. We model such a dynamic bargaining with incomplete information as a dynamic Bayesian game, and characterize several types of equilibria under different system parameters. In particular, we show that a Low type SU may maximize its total utility by utilizing the reputation effect, i.e., rejects profitable offers initially in order to create the reputation of a High type SU.

Content Aware Soft Real Time Media Broadcast (CASoRT)

Content aware soft real time media broadcast (CASoRT) system is a new solution of broadcasting systems and cellular systems converging. We are suffering the high price when enjoying the interaction multi-media services from new generation mobile communication systems like 3Gs and their enhanced. We are bound by the program parade when saving on payment from digital TV broadcasting systems. We propose the CASoRT system with a same customerpsilas experience of real time interaction as in cellular systems from consumerpsilas point of view and with a similar low operation cost to running broadcasting systems from carrierpsilas point of view.