A practical approach to strengthen vulnerable downlinks using superposition coding

We propose and experimentally demonstrate a novel approach to improve the packet delivery efficiency on a vulnerable downlink (e.g., from a transmitter to a far-away receiver) using superposition coding, a multiuser transmission scheme that forgoes orthogonal transmission and deliberately introduces interference among signals at the transmitter. On a software radio platform that uses off-the-shelf point-to-point channel codes, we show that a transmitter serving multiple links can use simple two-user superposition codes to dramatically improve (compared to time division multiplexing) the packet delivery efficiency on its most vulnerable links. Interestingly, our results suggest that superposing signals of far-away users on to those of high-traffic users yields the maximum benefits - implying that the degrees-of-freedom gain in doing so can more than compensate for the increased interference from signal superposition.