Prototype: Enabling Commercial Off-the-Shelf LED Bulbs With Internet Protocol Connectivity Ming Che, Takeshi Kuboki, Kazutoshi Kato Graduate School of Information Science and Electrical Engineering, Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Email: [email protected] Abstract—With the commercial off-the-shelf (COTS) light IP emitting diode (LED) bulbs widely applied for illumination in MAC the consuming market, this potentially pushes forward the visible PHY light communication to promote a rapid development. It provided FTTH or LAN Ethernet a promising candidate for Internet access due to its larger license- Access Star Topology With Multiple Hops free bandwidths, a cost-optimized and hybrid Internet access IP scheme by augmenting the existing facilities. In this paper, a MAC PHY wireless Internet access prototype based on COTS LED bulb Router has been proposed. This system features integration with a full of TCP/IP protocol stack and software-based transceiver design, which has the advantage of cost-efficient, low-complexity, and high-flexibility. PLCC: Power Line Carrier Communication : Protocol Stack FTTH: Fiber To The Home : VLC (Wireless) Keywords— COTS; LED; VLC; Bulb; Illumination; PD; PoE: Power over Ethernet : Wire Beaglebone; ARM; PRU. I. INTRODUCTIONS Fig. 1. The star topological structure of Internet access point using VLC technique with multiple hops Since the high-efficiency and high-power much higher than a conventional light source, the light emitting diode (LED) has been widely used in consumer electronics, light bulbs, demonstrate the validation of this design. The paper also cars, display screens, indicators and signs. As a result, it is concludes this scheme in last section. possible to control light brightness at a higher frequency for illumination and communication simultaneously. This idea, II. PLATFORM AND ARCHITECTURE called visible light communication (VLC) or light fidelity The Beaglebone series of single board computer (SBC) (LiFi), has been proposed in 2003 and 2011 respectively [4, with a TI AM335X Sitara System-On-Chip contain two pro- 1]. As for increasing bandwidth needs for Internet access, this grammable real-time units (PRUs). When explore the high- technique is an available mean to solve ”last mile” bottleneck performance and low-power network devices, the primary 32- problem because of widely distribute existing infrastructure. bit ARM processor on the AM335X can provide high compute However, despite over the decade of development, there is no power (1 GHz) and rich ecosystem of extensions through the full solution for commercial off-the-shelf (COTS) LED-based Debian GNU/Linux operating system. The PRUs are intended network access with low cost. to targeted at real-time applications where predictable response As an Internet access point using VLC technology, fig. 1 is required. Thus, the Beaglebone Black (BBB) has been shows a framework with N hops in a star topology which has employed in this scheme for protype development. been established by the IEEE 802.15.7 VLC Task Group [5]. Fig. 2 shows the overall system architecture on this net- In this networking, the Internet access point use two or more worked access intermediate point based on VLC. To make wireless hops to stored-and-forward information with light use of higher-level network protocols which defined by open among other LED bulbs [2]. Thus, as for seamless handover systems interconnection (OSI) model, the media access control requirements in each bulb, it is critical for Internet access (MAC) layer and upper of VLC network access device is functions with full of protocol stack. Besides, it is very useful implemented by an ARM running a Linux Debian [10]. As for research and production. for physical layer’s (PHY’s) digital part, the PRUs are fast This paper describes a prototype realization of an Internet (32 bit, 200 MHz) processor with access to a number of the access device based on COTS LED Bulbs. The foundation general-purpose input/output (GPIO) port and internal memory is Linux network driver and a software-based firmware for and peripherals on the AM335x processor. They are capa- specified VLC transceiver circuits. The bulbs can provide ble of implementing things like pulse-width modulators, soft wireless Internet access and light illumination simultaneously. communication peripheral, digital codecs-machine and much In the following section, we gives an insight of this prototype’s more. Especially for physical layer implementation of OSI details. Then, in the next section we made some tests to model, using the two standalone micro-controller can achieve Published by Visible Light Communications Associated at ''2nd International Conference and Exhibition on Visible Light Communications 2018'' on March 16, 2018 in Yokohama, Japan. This is an open access article under a Creative Commons Attribution-NonComercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). This means that the work must be attributed to the auhtor (By clause), no one can use the work commercially (NC clause), and the work cannot be modified by anyone who re-uses it (ND clause). low price and high performance. In short, this layer-oriented SLIP does not provide error detection, being reliant on upper architecture is designed with the purpose of a balancing for layer protocols for this. It is however still useful for testing real-time and complexity. systems and easy to be substituted by another more suitable mechanism. Besides, It’s low complexity and no requirement OSI Model TI AM335x Implementation for excessive resource consumed when embedded this part into ARM Contex-A VLC APP Application Layer Shared (User Space) Linux driver code. Linux Memory Debian VLC Transport Layer Peripherals Network Device B. Software-based Baseband Controller Data SRAM Driver Internet Layer Cache (Kernel Space) The physical layer of OSI model deals with bit-level Data Link Layer L3 Interconnect (MAC) PRU 0 PRU 1 transmission between different devices. There are more real- L4 Interconnect VLC Inst. Data Inst. Data time needs when face to sampling and control tasks in PHY. RAM RAM RAM RAM Firmware Interconnect Peripherals GPIO (PRU, No OS) Although a lot of dedicated solutions available for this, such Share PRU INTC Physical Layer RAM I/O as standalone micro-controller connected via UART [7], the Tx Rx ADC DAC additional onchip PRUs belong to the BBB’s microprocessor VLC OTA TIA Analog Front-end can offer lower prices with higher integration and performance. LED PD Two build-in PRUs can be used as control unit of transmitter (Tx) and receiver (Rx) respectively. The Tx side provides Fig. 2. The system architecture of VLC Linux network access device based programmable channel coding and modulation functions, so on OSI layer-oriented as to flow-controlled services. The Rx side expects that when a frame is received it is immediately extracted from the circular A. Linux-based Network Driver buffer, and notice controller of the upper layer to transfer Network device drivers receive and transmit data packets frames from shared memory. The scheme based on build-in on hardware interface that connect to external systems and PRUs connected by inner bus as controller for Tx and Rx provide a uniform interface that network protocols can access. side can reduce the process delay, maximize the performance The Linux kernel has provided an implementation of TCP/IP of hardware with cost-efficiency, especially for software-based protocol and interfaces for network devices [8]. In fact, Linux modulation and data recovery technique. network drivers follow a fairly typical route in processing: 1) Softwared-based Coding and Modulation: Since the the kernel boots up, initializes data structures, sets up some non-coherent of LED bulbs used in illumination, the intensity interrupt routines, and tells the network card where to put IP modulation and direct detection (IM/DD) usually used in VLC packets when they are received. As shown in Fig. 3, when an systems in the optical domain. As for baseband modula- IP packet is actually received, the card (PRU firmware) signals tion schemes, this software-based PHY controller will easily the kernel causing it to do some processing and then cleans up support pulse amplitude modulation (PAM), pulse position some resources for next receive IP packet. As for transmitting modulation (PPM), pulse interval modulation (PIM), and so IP packet from upper layers, it will be processed according to on. The binary PAM, also popularly known as onoff keying MAC frame packing rule in sequence. (OOK), is implemented depending upon the method used to encode information into the optical carrier. 2) Data Recovery Based on Oversampling: In order to sim- VLC User Application plify the design of receiver’s clock and data recovery (CDR), insmod ifconfig send receive asynchronous serial communication (ASC) technique has been Socket Library employed in this scheme. It is a form of serial communication User Space in which the communicating endpoints’ interfaces are not Kernel Space Linux TCP/IP Protocol Stack continuously synchronized by a common clock signal. Instead ether_setup() netif_wake_que() netif_rx() of a generic synchronization signal, the data stream contains VLC Network Driver IP Packet synchronization information in form of start and stop signals, vlc_init() vlc_open() vlc_header() hard_start_xmit() recv_ISR() before and after each unit of transmission, respectively. The MAC Protocol Frame Driver start signal prepares the receiver for arrival of data and the Firmware Physical Layer Implementation stop signal resets its state to enable triggering of a new Octet (PRU, Analog Front-end) sequence. The sampling theorem introduces the concept of a sample rate that is sufficient for perfect fidelity for the original Fig. 3. The process of delivery-receiving IP packets for Linux VLC network driver signal. As show in Fig. 4, the oversampling clock recovery has been used as receive signal wave edge detection. Data is At present, No specific MAC Layer protocols for VLC are obtained by sampling data by multi-phase clock which at least already in place.