On the Cooperative Relaying Strategies for Multi-Core Wireless Network-on-Chip

Recently, hybrid wired-wireless Network-on-Chip (WiNoC) has been proposed as a suitable communication fabric to provide scalability and satisfy high performance demands of the exascale era of modern multi/many-core System-on-Chip (SoC) design. A well accepted low-latency wireless communication fabric for WiNoCs is millimeter wave (mm-Wave). However, the wireless channel of mm-Wave is lossy due to free space signal radiation with both dielectric propagation loss (DPL) and molecular absorption attenuation (MAA). This is exacerbated for edge situated cores and in macro-chips embodying thousands of cores. To this end, this article proposes efficient relaying techniques to improve the signal strength of the wireless channel in the WiNoCs using on-chip networking approaches under the realistic SoC channel conditions. First, we propose a realistic relay communication channel for the WiNoCs to characterise both MAA and DPL which have drastic effect on the performance. We then derive and show that the channel capacity for a single-relay WiNoC employing Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying protocols increases by up to 20% and 25%, respectively, compared to the conventional direct transmission. The AF protocol outperforms the DF mode for shorter transmissions between the relay and the destination cores, while the reverse is observed in other conditions. A hybrid protocol is then proposed to exploit the performance advantages of both relaying protocols to address the unbalanced distance between the cores, providing the maximal channel capacity close to the cutset bound. Finally, our approach is further validated in multi-relay WiNoCs where the communications of the remote cores is assisted by multiple intermediate cores along with the details of associated realistic channel model in emerging many-core SoCs.