On the Nanocommunications at THz Band in Graphene-Enabled Wireless Network-on-Chip
Quoc-Tuan Vien,1 Michael Opoku Agyeman,2 Tuan Anh Le,1 and TerrenceMak3
1Faculty of Science and Technology, Middlesex University, London NW4 4BT, UK
2Department of Computing and Immersive Technologies, University of Northampton, Northampton NN2 6JB, UK
3School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK
Correspondence should be addressed to Quoc-Tuan Vien
Received 15 March 2017; Revised 17 May 2017; Accepted 1 June 2017; Published 9 July 2017
Academic Editor: Vittorio Zampoli
Copyright © 2017 Quoc-Tuan Vien et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
One of the main challenges towards the growing computation-intensive applications with scalable bandwidth requirement is the deployment of a dense number of on-chip cores within a chip package. To this end, this paper investigates the Wireless Network-on-Chip (WiNoC), which is enabled by graphene-based nanoantennas (GNAs) in Terahertz frequency band. We first develop a channel model between the GNAs taking into account the practical issues of the propagation medium, such as transmission frequency, operating temperature, ambient pressure, and distance between the GNAs. In the Terahertz band, not only dielectric propagation loss but also molecular absorption attenuation (MAA) caused by various molecules and their isotopologues within the chip package constitutes the signal transmission loss. We further propose an optimal power allocation to achieve the channel capacity. The proposed channel model shows that the MAA significantly degrades the performance at certain frequency ranges compared to the conventional channel model, even when the GNAs are very closely located. More specifically, at transmission frequency of 1 THz, the channel capacity of the proposed model is shown to be much lower than that of the conventional model over the whole range of temperature and ambient pressure of up to 26.8% and 25%, respectively.
针对具有可扩展带宽要求的日益增长的计算密集型应用而言，其中一个主要挑战是在芯片封装内部署大量的片上内核。为此，本文研究了基于石墨烯纳米天线（GNAs）在太赫兹频段实现的无线片上网络（WiNoC）。我们首先考虑传播介质的实际问题，如传输频率，工作温度，环境压力和GNA之间的距离，在GNA之间建立信道模型。在太赫兹波段，不仅介质传播损耗，而且芯片封装内的各种分子及其同位素体引起的分子吸收衰减（MAA）也构成信号传输损耗。我们进一步提出一个最佳的功率分配来实现信道容量。所提出的信道模型表明，与常规信道模型相比，即使在GNA位置非常接近的情况下，MAA也在某些频率范围下显着降低性能。更具体地说，在1THz的传输频率下，所提出的模型的信道容量在整个温度范围和环境压力下分别显示为比常规模型低得多，分别高达26.8％和25％。
Wireless nanocommunication has attracted an extensive investigation of researchers in various fields, such as healthcare, environment, defense, and military services [1, 2]. Advances in nanotechnology with nanomaterials are promising to provide novel solutions for manufacturing various machines in the nanoscale from one to hundred nanometers [3]. However, the data communication between nanomachines over wireless medium via electromagnetic wave is challenging due to their size, complexity, and power consumption [4].
In order to overcome the limitation in wireless nanonetworks, graphene has recently emerged as a new nanomaterial to enable the production of nanoantennas for electromagnetic wave transmission in the THz band [5–7]. Specifically, graphene has been found as a favourable nanomaterial to enable the elaboration of transistors not only providing higher speed but also consuming lower energy compared to the conventional CMOS devices [8–10]. Therefore, graphene has been proposed to build graphene-based plasmonic miniaturized antennas, a.k.a. graphennas [6, 7], to facilitate the communication between nanomachines over wireless medium.
To meet the scalable bandwidth requirement for growing communication- and/or computation-intensive applications, such as emerging multimedia applications, Network-on-Chip (NoC) was initially proposed as an on-chip packet-switched micro-network of wireline routed interconnections [11]. However, the conventional metal based interconnections are insufficient to satisfy the needs of both low latency and high performance as the number of cores increases. Alternative fabrics and architectures, such as photonic NoC [12], nanophotonic NoC [13], three-dimensional (3D) NoC [14], Wireless NoC (WiNoC) [15–19], and hybrid WiNoC [20–23], have been then investigated.
Exploiting the properties of graphene-based nanoantennas (GNAs), WiNoC has adopted the GNAs for employing wireless nanocommunication between cores in the THz band [24–26]. The graphene-enabled WiNoC (GWiNoC) not only helps reduce the propagation delay of intrachip communication but also allows the flexibility and scalability in the chip design due to the inherent characteristics of wireless communications. Furthermore, the THz band can offer enough bandwidth to accommodate massive number of wireless cores in the GWiNoC for emerging System-on-Chip (SoC) design.
The propagation of electromagnetic waves was shown to have a significant effect on the performance of nanocommunications in the THz band [27]. The research challenges in the channel modeling for WiNoC were also discussed in [28]. Therefore, considering the deployment of GNAs in the practical WiNoC, it is crucial to investigate the effects of various propagation environment parameters inside a chip package on the performance of GWiNoC, such as operating temperature, ambient pressure, transmission frequency, and distance between the GNAs. To the best of the authors’ knowledge, these issues of the channel modeling in the GWiNoC had not been well investigated.
In this paper, we investigate the communications between GNAs within a GWiNoC environment at THz frequency band. The main contributions of this paper are summarised as follows:(i)We propose a channel model for GNAs within a GWiNoC environment. At THz frequency band, the total path loss of the signal transmission consists of both dielectric propagation loss (DPL) and molecular absorption attenuation (MAA). Specifically, a within-package reflection channel model is developed taking into account not only line-of-sight and reflected communications but also the transmission medium and built-in material inside a chip. The proposed channel model is regarded as an abstract model for theoretical analysis of various performance metrics allowing us to investigate the impact of the communication environment on the performance of data communication between GNAs.(ii)The path loss and channel capacity expressions of the proposed model are developed to investigate the impact of the communication environment on the performance of data communication between GNAs.(iii)We show that the total path loss does not monotonically increase as a function of the frequency but varies over certain frequency ranges, such as 1.21 THz, 1.28 THz, and 1.45 THz, depending on the molecules and their isotopologues within the chip package. Interestingly, the total path loss is shown to decrease over the system electronic noise temperature while it exponentially increases over the ambient pressure applied on the chip. The performance degradation caused by the distance between the GNAs is also shown to be higher than that of the conventional channel model over pure air. (The conventional model used as the baseline is a GWiNoC channel model based on a typical channel model where signals are transmitted over free-space without considering the impact of MAA.)(iv)We develop an optimal power allocation achieving the derived channel capacity subject to the total power transmission constraint at a GNA. The medium compositions, temperature, and pressure within the chip package are shown to have a significant effect on the total noise temperature and the channel capacity of the GWiNoC.(v)We show that MAA causes significant degradations in the performance of the nanocommunications within the GWiNoC in comparison with that of the conventional wireless channel model. Specifically, a performance degradation of up to 31.8% is caused by the MAA, even when the GNAs are very closely located of only 0.01 mm. At transmission frequency of 1 THz, the channel capacity of the proposed model is shown to be much lower than that of the conventional model over the whole range of temperature and ambient pressure of up to 26.8% and 25%, respectively. This performance degradation indicates the effectiveness of the proposed channel modeling in capturing the issues of the GNA deployment in the GWiNoC and thus can be regarded as a performance benchmark in the design of GWiNoCs.
The rest of this paper is organised as follows: Section 2 describes the system model of the nanocommunications between two cores in a typical GWiNoC. Section 3 presents the proposed channel model for the GWiNoC. The performance analysis of the proposed channel model is presented in Section 4 where the channel capacity of the GWiNoC is derived and the optimal power allocation is developed to achieve the channel capacity. Numerical results are presented in Section 5 to validate the findings. Finally, Section 6 draws the main conclusions from this paper.
