Abstract-Channel emulators are valuable tools for controllable and repeatable wireless experimentation. Often, however, the high cost of such emulators preclude their widespread usage, especially in large-scale wireless networks. Moreover, existing channel emulators offer either very realistic channels for simplistic topologies or complex topologies with highly-abstracted, lowfidelity channels. To bridge the gap in offering a low-cost channel emulation solution which can scale to a large network size, in this paper, we study the tradeoff in channel emulation fidelity versus the hardware resources consumed using both analytical modeling and FPGA-based implementation. To reduce the memory footprint of our design, we optimize our channel emulation using an iterative structure to generate the Rayleigh fading channel. In addition, the channel update rate and word length selection are also evaluated in the paper which greatly improve the efficiency of implementation. We then extend our analysis of a single channel to understand how the implementation scales for the emulation of a large-scale wireless network, showing that up to 24 vehicular channels can be emulated in real-time on a single Virtex-4 FPGA.

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In this paper, an advanced duplex scheme called cross-division duplex (XDD) is proposed to enhance uplink (UL) coverage in time division duplex (TDD) carriers by utilizing self-interference cancellation (SIC) capability at a base station. With XDD, it is possible to combine TDD's ability to efficiently handle asymmetric UL and downlink (DL) traffic with frequency division duplex's coverage advantage. To do so, XDD simultaneously operates UL and DL on the same TDD carrier but on different frequency resources. Such operation leads to severe interference on the received UL signal at the base station which requires two levels of SIC implementation; antenna and digital SIC. More than 50 dB of interference is removed through the antenna SIC using electromagnetic barriers between the transmitting and receiving antennas. The remaining interference is removed by the digital SIC based on estimating the non-linear channel of the circuit at the receiver baseband. It is verified by simulation and analysis that with the proposed XDD, the UL coverage can be improved by up to 2.37 times that of TDD. To check the feasibility of XDD, a Proof-of-Concept was developed where it was observed that the benefits of XDD can indeed be realized using the proposed SIC techniques.

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