Wireless LANs have expanded greatly and rapidly in recent years. The expansio¬¬¬¬¬n has caused many benefits to the end users but at the same time it has introduced problem of overlapping BSS (Basic Service Set) where BSS (i.e. WLAN cells) is fundamental block of IEEE 802.11 WLAN architecture. OBSS occurs due to two or more unrelated BSSs are used at the same place, at the same time and with the same frequency channel. With the expansion of channel bandwidth to 80 MHz (may be, 160 MHz) in upcoming standards, the OBSS problem is likely to be very severe in the future. This paper examines how OBSS can be harmful to the networks and how it can be avoided using beam forming, distributed coordination across different APs, and power management. At the end, this text explores the effectiveness of the proposed solutions.
Wireless Local Area Network (WLAN) is one of the most successful technologies in IEEE 802.XX standards family. WLAN provides free connectivity, mobility, and flexibility with a relatively low cost for users. The widespread use of WLAN technology in streaming videos and voice applications stimulated high bandwidth capacity for WLANs. Recently IEEE has announced latest WLAN standard 802.11ac. For 802.11ac to be effective, it requires minimum 80 MHz wide channel with optionally up to 160 MHz. The increase in bandwidth leads to problems like OBSS. OBSS problem occur when two or more BSSs operate in same channel and are close to hear each other. This is an undesirable situation where two or more BSSs compete for channel access and increase contention which ultimately degrades performance/efficiency of the WLAN system . The problem was not critical with 802.11a/b/g/n where the channel bandwidth was reasonable. OBSS problem will grow bigger with increase in channel bandwidth in latest standards, expansion of devices, and lack of available spectrum.
The objective of intentional OBSS is to facilitate sharing of the medium between BSSs so that they can hear each other’s beacons. But due to large channel bandwidths and lack of spectrum, many a times OBSS have to use the same channel as their neighbors. The problem becomes intense when there are many OBSS using the same channel. The wide range WLAN usage has caused “tragedy of commons” problem especially at public places. OBSS cause problems such as low efficiency, higher congestion and low data rate. OBSS is a problem for 802.11 when it is intended to use for applications which require QoS. EDCA does not solve this problem as it does not require other BSSs to coordinate. Admission control only solves bandwidth allocation problem within a single network and does not address OBSS .
A number of solutions have been recommended in the past up to today to reduce potential interference due to OBSS problem. Frequency channel assignment can be a solution where BSS, during initial setup, scans the area to avoid channels that are already being used at other...