OFDMA-based network-coded cooperation: design and implementation using software-defined radio nodes

Abstract

Benefits of network coding towards enhancing communication quality, both in terms of robustness or data transmission rates, make it a significant candidate as a future networking technology. Conventionally, network coding is mostly used in wired infrastructures, where transmission errors between nodes are negligible. Capturing the provided benefits of network coding via straightforward extension from wired networks to wireless networks is not trivial. In addition to the challenges introduced through the wireless channel impairments, we can also capture the spatial diversity gain provided by the broadcast nature of the wireless channels. In this work, we design and implement a network-coded cooperation (NCC) system that operates in real time through the use of software-defined radio (SDR) nodes for the first time in the literature. We specifically target wireless networks. Our system is based on orthogonal frequency division multiple access (OFDMA) that provides a practical means to enable high transmission rates through the use of narrowband subcarriers. The developed testbed is composed of three source nodes, a relay node and two destination nodes. The transmission of the proposed NCC-OFDMA system is completed in two phases; the broadcast and the relaying phases. Multiplexing of source nodes' signals is achieved through OFDMA technique. In the broadcast phase, an OFDMA signal is transmitted to relay and destination nodes. In the relaying phase, the relay node first detects the OFDMA signal, generates network-coded symbols, and then transmits these symbols to destination nodes. At the end of these two phases, the destination nodes determine the source nodes' signals by using network decoders. The destination nodes make use of both the uncoded and network-coded symbols, which are received in broadcast and relaying phases, respectively. Destination nodes then perform network decoding. Through real-time bit error rate and error vector magnitude measurements, we show that the NCC-OFDMA system can significantly improve the communication quality and robustness, while enabling data transmission between multiple users, as known from theoretical analyses. Some features of this implemented NCC-OFDMA system have the potential to be included in 5G standards, due to the improved radio resource usage efficiency.

RTWiFi‐Lab: A real‐time Wi‐Fi laboratory platform on USRP and LabVIEW for wireless communications education and research

“…In this module, real‐time information transmitted and received with the flexibility of changing the protocols, with two error correction codes implemented with three digital modulation techniques, with different pulse shaping filters. Gökceli et al implemented a six node network‐coded cooperation based OFDM system is implemented in real time using LabVIEW software, NI USRP 2921, and NI PXI hardware components. Their bit error rate and error vector magnitude measurement results show that the implemented system operates successfully in real time, outperforming point‐to‐point communication links.…”

Modeling and Analysis of Two-Way Relay Networks: A Joint Mechanism Using NOMA and Network Coding

“…Hence, the NC scheme brings performance gain in downlink two-way relaying system. However, conventional two-way relaying do not apply the NOMA scheme to the uplink [13], [14], which did not reach their full potential in improving system capacity.…”

Special issue on network coding

“…The most well-known PLNC protocols are amplify-andforward, where the relay just amplifies the received signal and forwards it; decode-and-forward, where the relay decodes the individual messages one-by-one by treating the other messages as noise and then forwards them; and the most recent one, compute-and-forward, where the relay computes (an approximation of ) a deterministic function of the messages (without decoding them first) and forwards the function. The authors of [11] went beyond the TWRC and developed a hardware testbed for a wireless network-coded cooperation system (with three source nodes, one relay, and two destination nodes) using orthogonal frequency division multiple access (OFDMA), in which different messages are assigned to the different subcarriers, allowing both the broadcast and the relaying phases to overlap in time, which is typical in PLNC relay networks. Noticeably, this approach differs from "pure" PLNC (which is a non-orthogonal multiple access scheme), given that OFDMA still guarantees orthogonality.…”