In [7], the authors propose a kind of global channel allocation method based on graph theory. The TMCA algorithm only has three nonoverlapped channels available, which can cause severe cochannel interference when more than three APs are deployed in the same overlap area. 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. In addition, an optimized CCA algorithm also is proposed by classifying the clients and optimizing the polling list to reduce empty polls. Fengjun Shang contributed to presenting the priority channel access strategy and guiding the evaluating experiments for the optimized CCA mechanism. important issue
hybrid allocation scheme
Hence, eliminating interference among APs under the limited number of channels has become an important issue. It is noted that only a trivial modification for the data frame of client is needed to adapt this mechanism. APs can obtain the load level in each channel and choose the channel in which the load is lighter and the interference is smaller. To utilize such idle time slots adequately and improve channel utilization, we propose an improved channel assignment mechanism that is called time slots reservation (TSR) scheme. The contributions of this paper are listed as follows. Review articles are excluded from this waiver policy. In [9], 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. To utilize such idle time slots adequately and improve channel utilization, we propose an improved channel assignment mechanism that is called time slots reservation (TSR) scheme. Figure 10 shows the packet loss rate for 5 and 9 APs’ deployment under various client densities. traffic condition
The authors of paper [12, 13] try to eliminate the interference by researching channel allocation and power control jointly. 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 [4]. In this paper, we propose a channel assignment algorithm based on PCF mechanism for multiple APs cochannel deployment scenario. Wireless Communications and Mobile Computing Volume 15, Issue 10 . published paper
Therefore, the overhead of both mechanisms is negligible compared with data traffic in the network. It includes two components. In the basic channel assignment, part of APs may be idle in some time slots. power control
Yet, these algorithms mainly concentrate on allocating nonoverlapping channels to APs while the coordination mechanism between APs is ignored. MAC Protocols – Wireless MAC Issues – Fixed Assignment Schemes – Random Assignment Schemes – Reservation Based Schemes. Figures 3, 4, and 8 and Table 1 are reprinted by permission from Springer Nature: Proceeding of the 6th Computer Science On-line Conference (CSOC2017) (A Novel Co-Channel Deployment Algorithm Based on PCF in Multiple APs and High Density WLANs, Jianjun Lei and Jianhua Jiang) copyright 2017.
M. Naghshineh, The College of Information Sciences and Technology. Lin, “Distributed flexible channel assignment in WLANs,” in, B. Kauffmann, F. Baccelli, A. Chaintreau, V. Mhatre, K. Papagiannaki, and C. Diot, “Measurement-based self organization of interfering 802.11 wireless access networks,” in, H. Zhang, H. Ji, and W. Ge, “Channel Assignment with Fairness for multi-AP WLAN based on Distributed Coordination,” in, D. Xu, Z. Feng, Y. Li, and P. Zhang, “Fair channel allocation and power control for uplink and downlink cognitive radio networks,” in, Y. Wu, Y. resource allocation
We present the network and interference model and formulate the problem of channel assignment into a vertex coloring problem. Therefore, two-class priority client polling mechanism based on queuing theory is proposed in some literatures [19–21]. Sun, Y. Ji, J. Mao, and Y. Liu, “A joint channel allocation and power control scheme for interference mitigation in high-density WLANs,” in, D. Gong, Y. Yang, and H. Li, “High-throughput collision-free client polling in multi-AP WLANs,” in, Y. Bejerano and R. S. Bhatia, “MiFi: A framework for fairness and QoS assurance for current IEEE 802.11 networks with multiple access points,”, H. Nishimura, R. Fujiwara, M. Miyazaki, and M. Katagishi, “Access point cooperation for collision-free polling between distributed real-time networks,” in, S. Gualandi and F. Malucelli, “Exact solution of graph coloring problems via constraint programming and column generation,”, Q. Wu and J. K. Hao, “Coloring large graphs based on independent set extraction,”, L.-Y.
However, our proposed algorithms can coordinate AP operating to reduce collisions and packet loss rate. The workflow is shown in Figure 2. In other words, allocating time slot to the corresponding AP in the network is equivalent to coloring a vertex in the graph.