Quantize-map-forward (QMF) relaying

Abstract

We present the design and experimental evaluation of a wireless system that exploits relaying in the context of WiFi. We opt for WiFi given its popularity and wide spread use for a number of applications, such as smart homes. Our testbed consists of three nodes, a source, a relay and a destination, that operate using the physical layer procedures of IEEE802.11. We deploy three main competing strategies that have been proposed for relaying, Decode-andForward (DF), Amplify-and-Forward (AF) and QuantizeMap-Forward (QMF). QMF is the most recently introduced of the three, and although it was shown in theory to approximately achieve the capacity of arbitrary wireless networks, its performance in practice had not been evaluated. We present in this work experimental results-to the best of our knowledge, the first ones-that compare QMF, AF and DF in a realistic indoor setting. We find that QMF is a competitive scheme to the other two, offering in some cases up to 12% throughput benefits and up to 60% improvement in frame error-rates over the next best scheme.

QUILT: A Decode/Quantize-Interleave-Transmit approach to cooperative relaying

“…This is supported from theoretical works that have proposed a number of relay cooperation schemes [1], verified by first experimental results [2] and recognized by the standards that are starting to include relaying mechanisms [3].…”

“…For this, the destination employs a graphical structure that captures the streams received in phases 1 and 2, and adapts to whether decoding or quantization were employed at the relay. The decoder for QUILT is an adaptation of the QIF decoder in [2][5], wherein the stochastic quantizer nodes become deterministic perfect connections if the relay decoding succeeds, and are the same as in [2] otherwise. The decision is guided by a 1-bit flag that the relay transmits, to inform the destination whether the relay-decoding succeeded.…”

“…In our recent work [2], we implemented the most promising state-of-the-art relaying schemes -Amplify-Forward (AF), Decode-Forward (DF) and Quantize-Map-Forward (QMF) on top of the WiFi physical layer. We found that our implementations of DF and QMF consistently outperformed AF, as is also the case in theory: the information-theoretical performance of both QMF and DF can achieve the capacity of the one-relay network within 1 bit/sec/Hz, which is not the case for AF.…”

“…First, we found that our choice of implementing QMF with interleaving, which was necessitated from practical considerations in [2], can in fact outperform the random mapping proposed in the original QMF scheme [4]. The original information-theoretical version of QMF asks the relay to quantize at the noise level, perform a random mapping and forward the resulting signal; these operations and the analysis assume infinite length and exponentially complex processing.…”

“…The original information-theoretical version of QMF asks the relay to quantize at the noise level, perform a random mapping and forward the resulting signal; these operations and the analysis assume infinite length and exponentially complex processing. We translated these insights to a practical system by using symbol-level quantization and interleaving of the resulting sequence in [2]. We opted for interleaving as it was the only (nontrivial) mapping we found that made decoding with low-complexity belief propagation algorithms possible, while maintaining a simple relay operation.…”