In , a kind of distributed flexible channel assignment, called DFCA, is designed to assign the channel width and center frequency to each link based on the interfering relation among clients in the network. Some undesirable poll occurring will result in the wasting of bandwidth if the AP polls some clients without data to send or receive. However, our proposed algorithms can coordinate AP operating to reduce collisions and packet loss rate. Fundamentals of mobile communication - 8 - MCQs with answers Dynamic channel assignment Q1. By that, APs can judge whether the next polling client satisfies the conflict constraint, which can avoid the interference among the neighboring APs in the next polling. The idle APs in the next time slot query the set consisting of all adjacent APs and also query the polling list of all neighboring APs in the set . Average network throughput under various network densities. Workflow of clients and APs by centralized AC. Each client is associated with the AP which has the largest received signal strength indication (RSSI) and can obtain an optimal physical data rate according to the channel condition. In legacy IEEE802.11 standard, one bit field “more data” in “frame control” field is used to denote that more data will be transmitted from AP to some sleeping clients. The first one is the coloring algorithm given a graph and the number of colors , which seeks out a feasible color scheme with minimal number of colors. Although many optimal extensions of DCF are proposed, the competition among nodes cannot be eased and the transmission failure and retransmission increase sharply with the increase of the deployment density. In the basic channel assignment, part of APs may be idle in some time slots. Naturally, only one client in the same AP is allowed to transmit or receive data during a time slot. Simultaneously, to avoid transmission collisions, interfering clients from neighboring APs should be polled in different time slots. Sign up here as a reviewer to help fast-track new submissions. 2018, Article ID 6931765, 11 pages, 2018. https://doi.org/10.1155/2018/6931765, 1School of Computer Science and Technology, Chongqing University of Posts and Telecommunications, Chongqing 400065, China. Especially, in high density and multi-AP WLANs, high collision probability leads to low efficiency of channel access, and thus too much time is spent in dealing with collision for retransmission . In this section, we propose the CCA mechanism based on vertex coloring for cochannel channel assignment, which includes a basic channel assignment and an improved channel assignment strategy. In this paper, we present a network model and an interference model for multiple APs cochannel deployment and propose a channel assignment mechanism which formulates the channel assignment problem into a time slot allocation problem. The throughput of TMCA algorithm is slightly higher than that of our proposed algorithms when the number of clients is less than 20. Due to the global network state awareness of centralized data transmission, the AC gathers all necessary information from other components in this system. Research Article. Yet, these algorithms mainly concentrate on allocating nonoverlapping channels to APs while the coordination mechanism between APs is ignored. A similar channel assignment scheme is proposed in , where the expected transmission delay due to the interference from a neighboring BSS is regarded as the weight of the edge. By this procedure, an AP cannot poll any of its associating clients when one of its neighboring APs is receiving or transmitting data from or to its clients. The transmission delay refers to the average time from the sending time in source client to the reception time in target client, which is computed bywhere is the number of successfully transmitted data frames and and are the reception and transmission times of the th data frame, respectively. The clients in the polling list of AP are classified into three categories: (1) the clients with both uplink and downlink data, (2) the clients with uplink or downlink data, and (3) the clients without data needed to transmit. In , a client polling framework, named MiFi, is proposed for multi-AP deployment, in which CFPs (contention-free periods) at all APs are synchronized and divided into time slots. power control 1 Introduction Technological advances and rapid development of handheld wireless terminals have facilitated the rapid growth of wireless communications and mobile computing.
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