1. Space Division Multiplex for OBSS Interference Suppression
Date:
Authors:
Name
Affiliations
Address
Phone
Yongming Huang
Southeast University
Sipailou #2, Nanijng , P. R. China
(+86)
Ziquan Zhou
Baofeng Ji
Haiming Wang
Luxi Yang

2. Background
Users in OBSS will be affected strongly by communications of the adjacency BSS, the traditional solution includes:
1, FDMA: Adjacency BSS occupied with orthogonal frequency
2, TDMA: Set NAV by the RTS/CTS frame exchange to avoid sending simultaneously.
With the rapidly development of WLAN, however, the spectrum resource will be short of the FDMA solution.
And the efficiency of TDMA solution is low.

3. Interference Scene Figure 1
As in fig 1, STA1 stays in OBSS, AP1 and AP2 can not hear each other, STA1 is hidden node of STA2 and STA3.
For the traditional TDMA ways, if STA1 contends and occupies the channel and set the NAV of AP2. During the TXOP of STA1, AP2 can not communicate with STA2 or STA3. How can AP2 communicates to STA2/STA3?
The Space Division Multiplex interference suppression ways can solve this problem.

4. Space Division Multiplex interference suppression
Main Idea
1, STAs in OBSS can obtain the CSI from the adjacent AP and record it.
2, STAs in OBSS will send the above CSI, which can be used for interference suppression, to the adjacency AP by the CTS frames.
3, The adjacency AP can communicate with STAs belongings to its BSS in the non-interference spaces during the NAV duration set by the STAs in OBSS.
Modification
As in fig2, STA1 sets the B14 bit, which is reserved for CTS frame, in the frame control field in CTS frames when contends for the channel to signal to the adjacency AP that an Interference CSI feedback frame is followed.
The ICSI Frame contains the Address of adjacency AP and the CSI from AP2 to STA1
Figure 2

5. Space Division Multiplex interference suppression
advantages/disadvantages
Advantages
The solution can suppress the OBSS interference more efficiently than TDMA solution.
The concurrent sending of SDM can improve the frequency efficiency of the system.
Disadvantages
Increase little signal overheads. As 20Mhz, Ng=4(subcarrier group) with 18 bits each group , Total bits = 64/4*18=288bits. Use the lowest MCS0, duration= round(288/26)*4us=48us