Virtual Duplex: Scaling Dense WLANS and Eliminating Contention Asymmetry

In this paper, we propose "Virtual Duplex," a wireless architecture which, like Frequency Division Duplex (FDD), divides spectrum resources into two sub-bands. However, in contrast to FDD, both bands in Virtual Duplex are physically bidirectional, and transmissions are allocated to the bands according to whether they correspond to download or upload traffic. The "download data channel" carries data originating from the AP and that data\´s associated reversed-direction acknowledgements, and vice-versa for the "upload data channel." Thus, Virtual Duplex separates upload and download traffic at the link layer so that MAC layer Data-ACK handshakes are allocated into one of the two (physical) independent and asynchronous bi-directional channels. The spectrum division can be equal (as is typical with FDD) or weighted with a configurable bandwidth allocated to each channel to guarantee a spectrum share independent of client density. We show that the logical division and spectrum isolation between upload and download Data-ACK handshakes increases spectral efficiency, eliminates contention asymmetry and provides scalability to traffic asymmetry. Experimental and simulation results demonstrate that Virtual Duplex matches download vs. Upload throughput to demand ratio within 1% under any client density and traffic load. This matching capability offers unbounded download gains as congestion increases, minimizing and in some cases eliminating retransmissions and contention time.