Sharif Digital Repository

Visible light communication (VLC) uses LED lights for simultaneous illumination and data transmission. The throughput of a VLC network is highly dependent on the location of VLC access points (AP). In this paper, we propose a novel optimization framework for approximately optimal VLC AP placement which takes into account the stationary distribution of users for the first time. This distribution is the result of the mobility pattern of users in an indoor environment. The proposed method is independent of the resource allocation algorithm and eliminates the need for exhaustive simulations to find the optimal location for VLC APs. Simulation results show a significant improvement in the... 

In this paper, we propose a data offloading algorithm in a network comprised of a macro base station and a few number of WiFi access points with overlapped coverage areas. The main goal of our algorithm is how to assign offloaded mobile stations (MSs) to access points (APs). Our approach in proposing the algorithm is based on mapping the problem onto finding a suitable matching algorithm, in order to minimize the average delay of the offloaded packets as one of the main QoS parameters on the one hand and to maximize the utility of the APs on the other hand. The utility of each AP is considered to be a combination of monetary benefit due to offloading service and the cost due to extra energy... 

In this paper, by making slight modifications in protocol stack of wireless access points, the proposed CICADA scheme aims at isolating problems related to wireless section of a TCP connection from its wired portion, using IP spoofing and Virtual Protocol Stack scheme. As the simulation results for an 802.11 based system show, the proposed scheme improves the overall network throughput while reducing the mean and variance of end-to-end delay for voice and video flows due to smarter bandwidth allocation to elastic and real-time traffic. In addition, the proposed scheme uses a centralized NAT structure that prevents undesired disconnections during handovers and achieves a smaller handoff delay... 

In this paper, by making slight modifications in protocol stack of wireless access points, the proposed CICADA scheme aims at isolating problems related to wireless section of a transmission control protocol (TCP) connection from its wired portion, using IP spoofing and virtual protocol stack scheme. As the simulation results for an 802.11 based system show, the proposed scheme improves the overall network throughput for both DCF and PCF scenarios, while reducing the mean and variance of end-to-end delay for voice and video flows due to smarter bandwidth allocation to elastic and real-time traffic. In addition, the proposed scheme uses a centralized network address translation (NAT)... 

Femtocell has appeared as a solution to increase both coverage and capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. In this paper, we deal with the problem of joint subband, rate, and power allocation in OFDMA based two-tier femtocell networks. It is assumed that for macrocell users, spectrum allocation is accomplished through Fractional Frequency Reuse (FFR). Our objective is to maximize the femtocell user's throughput while maintaining as little as possible reduction in the macrocell users' performance. Our proposed algorithm is decentralized, and needs to be done only when femtocell access point is... 

Frame aggregation (FA) mechanisms improve the throughput of WLANs. In this paper, the effect of the FA mechanism on the throughput of wireless local area networks (WLANs) has been investigated. To this end, we propose an analytical model in order to analyze an IEEE 802.11n network comprised of an access point (AP) and several conventional nodes (CNs), all in the coverage area of each other. With respect to the heavier download traffic compared to the upload one, in our scenario, only the AP uses an FA mechanism and the other nodes use the basic IEEE 802.11 standard. In our proposed analytical model, the maximum downlink (DL) throughput is derived. Regarding the asymmetry among nodes, our... 

In this paper, a new approach toward the optimization of Access Point (AP) placement in cellular Visible light Communication (VLC) networks is proposed based on the projected gradient algorithm. The objective of the optimal placement problem is to maximize the average throughput of the network subject to constraints on the minimum illumination level and the minimum rate of the users. This optimization framework gives the enhanced AP deployment in case of users with static, nomadic, or completely mobile behavior. Taking the distribution of users, the receiver's field of view, reflection from walls and interference from neighboring APs into account makes the deployment problem complicated. To... 

Vehicular ad hoc networks (VANets) are special cases of mobile ad hoc networks (MANets) in which the mobility pattern is very different. Actually, the topology of the network in VANets changes more often and the variance of speeds is high. Such characteristics lead to fairness problem in VANets, considered in this paper. In fact, vehicles with different speeds have their different limited time to communicate with an access point (AP). This attribute adversely affects the chance of a fast moving vehicle in communicating with the access point. We propose a modified 802.11 DCF channel access scheme as a solution to the problem. The proposed scheme adjusts the probability of transmission at a... 

Mobile Ad Hoc Networks (MANETs) are networks with selforganizing capabilities and without a fixed infrastructure. Wireless nodes communicate among themselves using multi-hop radio relaying, without requiring the packets to pass through a central access point or a base station. In a highly mobile and infrastructure-less scenario, pre-configuration of addresses is not possible. Therefore node addresses need to be configured dynamically with minimum delay and packet loss. Existing solutions for IP address auto-configuration do not address security issues. In this paper we propose a secure address autoconfiguration for Mobile Ad hoc Networks (MANET) based on Virtual Address Space Mapping [1]....