However, we can see that the restricted communications would not cause signal collisions and the temporal resources are wasted in case of Figure 1c.Įxample of co-channel interference in WLANs: ( a) data communication topology ( b) carrier sensing topology ( c) cases of CCI through neighboring AP and neighboring client station.Īs controlling the network topology and minimizing the overlapped signal zones is a straightforward way of reducing the CCIs in WLANs, many previous researches have focused on bringing effective environmental analysis schemes. Hence, CSMA/CA adapts a Request to Send (RTS)/Clear to Send (CTS) handshake protocol to avoid signal collisions from hidden terminals, where RTS for a transmission request and CTS for the response (if the channel is available at the moment), meanwhile any of communications from/to the source and destination’s neighbors would be restricted since they could sense RTS or CTS as well as hidden terminals. Figure 1c illustrates two instances of CCIs in overlapped areas, when a node pair is communicating and the destination has neighboring nodes in overlapped area, they would become hidden terminals to the source (if they have unreachable distance) which may potentially trigger signal collisions.
Figure 1b is the related carrier sensing topology, where all the node pairs with less than four hop distances (see Figure 1c) mutually trigger the CCI in same or overlapped channels. Figure 1 illustrates an example of CCIs among overlapped WLANs, where Figure 1a shows a topology of the wireless data networks formed by three BSSs. Therefore, in the high-density WLANs combining several overlapped basic station set (BSS) zones, neighboring APs would mutually generate large amounts of CCIs through APs and client stations in the overlapped areas, deteriorating the network quality of service (QoS).
In terms of the “listen before talk” policy of the CSMA/CA, when multiple wireless nodes share the same signal zone, there would be only one node per channel communicating with the access point (AP) at a time. The CCI of IEEE 802.11-based networks occurs when multiple networks overlap and trigger the carrier sensing mechanism known as carrier sense multiple access with collision avoidance (CSMA/CA), which is the most widely adapted distributed scheduling protocol in practice. With the growth of commercial and personal wireless local area networks (WLANs) deployments continuing unabated in recent years, we are witnessing an increasing level of mutual co-channel interference (CCI) among transmissions in public wireless environments, such as in airports, shopping malls, school campuses. With the queuing model, we perform simulations to see how the CCI influences the quality of service (QoS) in high-density WLANs. Most of the CCIs occur when multiple networks overlap and trigger channel contentions therefore, we use the ratio of signal-overlapped areas to signal coverage as a probabilistic factor to the queuing model to analyze the CCI impacts in highly overlapped WLANs. In this article, we present a novel CCI analysis approach based on the queuing theory, which considers the randomness of end users’ behavior and the irregularity and complexity of network traffic in high-density WLANs that adopts the M/M/c queuing model for CCI analysis. That means the CCI analysis is basic, but also crucial for an efficient resource management. CCI in IEEE 802.11-based networks is inevitable due to the nature of the carrier sensing mechanism however can be reduced by resource optimization approaches. Increased co-channel interference (CCI) in wireless local area networks (WLANs) is bringing serious resource constraints to today’s high-density wireless environments.
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