Multi-BSS with Universal Frequency Reuse

　

For IEEE 802.11 networks with multiple basic service sets (BSSs), most studies have focused on how to allocate different frequency sub-channels to BSSs for minimizing the co-channel interference. The frequency-division approach adopted in current IEEE 802.11 networks, nevertheless, may not be in line with the recent evolution of IEEE 802.11 standards, which tends to enlarge the bandwidth of each sub-channel to support the ever-increasing data rate, and the resulting number of sub-channels is greatly reduced. In the latest IEEE 802.11ac standard, for instance, each BSS could occupy a channel up to 160 MHz wide, leading to a data rate as high as 867 Mbps. However, as only one 160 MHz wide channel is provided in the 5 GHz band, BSSs longing for high data-rate transmissions would have to share the frequency band rather than operate at different sub-channels. Such a universal frequency reuse approach has in fact been widely adopted in cellular networks, and extensive studies have shown that compared to orthogonal frequency division among cells, it can achieve much higher spectral efficiency and provide more flexibility in cell planning. Different from cellular networks where centralized access is adopted in each cell, however, IEEE 802.11 DCF networks are based on random access. It is therefore of great theoretical and practical importance to characterize the performance of multi-BSS IEEE 802.11 DCF networks with universal frequency reuse.

In this paper, we focus on an uplink M-BSS IEEE 802.11 network where all the BSSs share the frequency band rather than operate at different sub-channels. By dividing the nodes in each BSS into multiple groups according to the set of access points (APs) they can be heard by, the steady-state points of M BSSs in saturated conditions are obtained as functions of the number of nodes in each group and the initial backoff window size of nodes of each BSS. The maximum network throughput is further characterized by optimally choosing the initial backoff window sizes of all the nodes, and shown to be closely dependent on the percentage of nodes that can be heard by multiple APs. The comparison to orthogonal frequency division reveals that although the maximum network throughput is degraded due to interference among BSSs, a higher network data rate can still be achieved by universal frequency reuse, which makes it a preferable option for multi-BSS IEEE 802.11 networks.