Symbiotic Coding for High-Density Wireless LANs

Cochannel links in a Wireless LAN are separated across orthogonal time slots to avoid interference. With increasing density of links, time sharing the channel leads to severe capacity problems. In this paper, we identify a specific class of interference scenarios called asymmetric interference scenarios, where the nature of interference is different at the receivers of the concurrent signals. We show that, with appropriate handling, asymmetric interference allows each receiver to decode its intended reception successfully. We represent the signal combination at the receiver as a function fc and propose a solution called Symbiotic Coding (SC) such that f
_c
(E
₁
(d
₁
;d
₂
);E
₂
(d
₁
; d
₂
)) is equal to E
₁
(d
₁
;d
₂
), where d
₁
and d
₂
are the intended and interfering data symbol sequences and E
₁
is the encoder at sender 1 and E
₂
at sender 2, respectively. SC, thus, enables successful simultaneous cochannel transmissions even if they result in a collision. The performance of SC scales with the number of interfering links achieving median throughput improvements of 30 and 86 percent over time sharing with two and three interfering links, respectively. We address fundamental challenges in realizing SC including synchronization, coding algorithms, extensions to different modulations. We also implement SC on software defined radios and demonstrate its practical feasibility.