Phase 2 Report Digital Radio for Underground Miners (DRUM)

Transcription

1 Phase 2 Report Digital Radio for Underground Miners (DRUM) Kutta, Inc. Contract W15P7T-06-C-K203 January 21, 2008 Overview The overall objective of this project is to develop a survivable wireless communications system for underground mines. Both analog and digital product lines are being developed analog for smaller mines, and digital for larger operations. Analog radios provide point-to-point voice communication, and digital radios form a networked communications system. Both systems will be capable of maintaining mine-wide operational integrity after an emergency situation such as a mine fire or explosion, assuming the radios are intact and the propagation mechanisms are still in place. The analog product line will be capable of a single hop, or a single conversion and transmission over one path, thus limiting the distance, and will support analog voice only. The digital product line will be capable of multiple hops by using digital mesh architecture, thus enabling transmission over paths cascaded together which effectively eliminates the distance limitations and allows mine-wide communications coverage. The digital product line will use compressed digital voice and be capable of transmitting voice as well as data such as text messaging. Kutta is developing two products in both the analog and digital product lines: portable radios and fixed repeaters. Analog Products The analog product line will be capable of a single hop, or a single conversion and transmission over one path, thus limiting the distance, and will support analog voice only. The portable analog radio (PAR) will be designed to talk from radio to radio or point to point and will support analog voice communications with the miner speaking directly into a microphone on the radio. The analog repeater is a dual or cross band radio. The analog repeater allows the miner to talk on a conventional UHF radio, while having the communications converted to medium frequency through the analog repeater. The analog repeater provides an interface to other analog UHF devices, such as handheld radios and leaky feeders. For example, in a mine with a leaky feeder installed, a miner can extend the range of the leaky feeder by placing one repeater at the end of the leaky feeder, and another repeater up to two miles away. As long as there is metallic infrastructure (power cord, phone line, pipes, etc.) to carry the MF signal between repeaters, the miner can use his UHF radio at the far repeater and still communicate on the leaky feeder. This concept of operations is shown in Figure 1 below. Figure 1. Operation of analog repeater as a leaky feeder extender

2 Digital Products The digital product line will be capable of multiple hops by using digital mesh architecture, thus enabling transmission over paths cascaded together which effectively eliminates the distance limitations and allows minewide communications coverage. The digital products will use compressed digital voice and be capable of transmitting voice and data. The digital portable radio, or mobile base station (MBS), is also a cross-band radio. A group of miners starting their shift can carry an MBS with them, place it near their work site, and use a UHF handheld radio (e.g. a Kenwood radio) to communicate on the digital MF network. The MBS also has a speaker microphone, as well as a screen and text entry to support text messaging. Digital repeaters are installed in strategic locations to create a mine-wide ad-hoc mobile network that is capable of supporting both voice communication and data traffic such as text messaging. Digital repeaters are also cross-band, and they also have speaker microphones. In an emergency, a miner can use a UHF handheld within range of the digital repeater, or the speaker microphone on the repeater itself, to communicate on the digital MF network. Deliverables The following table summarizes the hardware deliverables under the contract: Description Prototype Handheld Portable Analog Radio Analog Repeater Mobile Base Station Digital Repeater Hardware Summary Table Frequency of Operation Mode of Operation Production Category Qty Timeframe (contract month) MF Analog Prototype 2 7 MF Analog Production 4 13 MF/UHF Analog Production 3 13 MF/UHF Digital Production MF/UHF Digital Production 3 14 Table 1. Summary of hardware deliverables The completion of Phase 2 work included the following: Delivery of two analog prototype handheld radios. Testing to quantify parasitic propagation characteristics and coupling mechanisms in typical pre- and postdisaster underground mine scenarios. Characterization of the underground mining environment, interference sources, and determining the interoperability options with existing mine communications systems. Development of detailed product specifications for the portable analog radios and repeaters. Development of detailed radio system specification. Outstanding design issues. The following is a summary of the most significant Phase 2 results. The complete report may be viewed here. Analog Prototype Handheld Radios On Thursday, August 16, 2007, after several preceding days of successful testing along with NIOSH and mining industry personnel, the contractor delivered two prototype handheld MF radios like the one shown in Figure 2 to

3 NIOSH, to support further testing. The radios operate at 470 khz with a frequency modulated bandwidth of khz. The antennas are based on Kutta s patent pending compact omni-directional magnetic antenna design. Figure 2. Prototype MF Handheld Radio, Antenna, and Speaker/Microphone As a result of focus group discussions with miners and mine operators, it was decided that the handheld radio and associated antenna and batteries could not be made into a form factor that a miner could be expected to wear everyday. Thus the decision was made that for production purposes, a Portable analog radio (PAR) that could be worn as a small back-pack would be manufactured instead. Miners involved in every day mining operations will be able to use conventional radios that will be provided access to the medium frequency channel through the Kutta dual or cross band repeaters. Miners that were required to go into less-traveled areas of the mine could use the PAR as a redundant or primary communications device. Testing To Quantify Propagation Characteristics and Coupling Mechanisms Kutta has demonstrated its MF technology in underground environments on several occasions, beginning with demonstrations of technology being developed for the Army Subterranean Wireless Electronics Communication (SWEC) program in Testing and demonstrations specifically oriented toward application to the mining community are listed below. The table lists some testing dates performed before the beginning of the DRUM contract. The results demonstrate clearly that the medium frequency radios and UHF/VHF repeater designs could meet the functional requirements of the contract under a variety of conditions. Date Location Radio Gear * Comment/Results April 24-25, 2006 McElroy Mine Suitcase USRP (+Laptop) Voice comm. 2 mile range April 10, 2007 NIOSH PRL Test Mine inch USRP box (+Laptop) equipment check only April 13, 2007 Enlow Fork Mine inch USRP box (+Laptop) August 13, 2007 Loveridge Mine Camel Repeater August 14, 2007 Loveridge Mine Analog Handheld (Figure 2) Voice comm. 1.5 mile range, track entry Successful proof of concept of repeater design Voice comm. 2 mile range, escapeway test August 16, 2007 Rio Coalburg #2 Mine Analog Handheld (Figure 2) Voice comm. 2 mile range November 14, 2007 Newmont Gold Mine Analog Handheld (Figure 2) Voice comm. 1 mile range Table 2. Dates, locations, and results for in-mine testing of Kutta s technology Detailed Product Specifications Portable Analog Radio, Analog Repeater The following tables describe the current status of the analog system components. Complete data on the component documentation and estimated completion date is given in the full report.

4 GENERAL Portable Analog Radio Frequency Range 470 khz Number of Channels 1 Battery Voltage 12 V DC ± 20% Battery Life ( duty cycle) 10 hours Operating Temperature Range 0 to 70 C Frequency Stability 10 ppm Antenna Impedance 50 Ω Dimensions (W x H x D) 13 X 7 X 3 (estimate) Weight 7 lbs. (estimate) RECEIVER Sensitivity (12 db SINAD) 10 µv Selectivity db Intermodulation Distortion N/A Audio Output 1 W with < 10% distortion Spurious Rejection > 60 db TRANSMITTER RF Power Output 5 W Emission Designator 16K0F3E Spurious Emission < -60 db 3rd order IMD W Amplifier Type Class D Table 3. Portable Analog Radio Specifications GENERAL Analog Repeater MF VHF UHF Frequency Range 470 khz MHz MHz Number of Channels Battery Voltage 12 V DC ± 20% Battery Life ( duty cycle) 10 hours Operating Temperature Range 0 to 70 C Frequency Stability 10 ppm Antenna Impedance 50 Ω 50 Ω 50 Ω Dimensions (W x H x D) 12 x 9 x 3.5 (estimate) Weight 24.5 lbs. (estimate) RECEIVER MF VHF UHF 12 db SNR -124 dbm typical -78 dbm typical -78 dbm typical Selectivity db db db Spurious Rejection > 60 db > 60 db > 60 db Noise Figure 3 db typical 5 db typical 5 db typical Input IP3 (3rd order intercept) -23 dbm -9 dbm -9 dbm Input P1 db (1 db compression) -33 dbm -11 dbm -11 dbm TRANSMITTER MF VHF UHF RF Power Output 5 W 5 W 5 W Emission Designator 16K0F3E 16K0F3E 16K0F3E Spurious Emission < -60 db < -60 db < -60 db 3rd order IMD -31 5W -50 5W 5W Amplifier Type Class D Class AB Class AB Table 4. Analog Repeater Specifications

5 Detailed Radio System Specifications The Digital Radio for Underground Mines (DRUM) system will include a digital system implementation. A collection of portable radios and fixed repeaters will collaborate to transmit, receive and forward digital data between them using Medium Frequency (MF) wireless antennas, as shown in Figure 3. Figure 3. DRUM nodes creating a mesh network for multi-hop transmissions We call this collaborative system the DRUM network, and the radios and repeaters are DRUM nodes within this network. Initially, digitized voice and text message data will be the primary DRUM network payload; however, because the network is based on open standards, other types of data could be sent, dependent on network throughput availability. The DRUM network will be a form of mesh network, specifically closer to a Mobile Ad-hoc Network (MANet). This will allow nodes to transmit and receive digital data destined for themselves as well as route digital data packets to others. Additionally, being a mesh network implies the topology, or node layout within the network, is dynamic. Nodes can be added or removed from the network at anytime, and nodes can move. Each node will recalculate the optimum path of delivery dynamically. To implement the DRUM network, hardware within the nodes will contain a microprocessor and software. Tests performed of the DRUM system to date have focused on an analog implementation. This was necessary to prove the MF implementation s ability to transmit and receive data within and beyond the desired range. While the experiments showed that MF works as a data carrier, the analog implementation s data carrying abilities was limited to voice between two explicitly defined nodes, specifically two handheld radios. By shifting the implementation to a digital packet based network, the MF hardware s role will be altered to be more data general. Computers within each node will then take on the responsibility of encoding and decoding meaning (e.g. voice and text) into the digital packets. In addition, and unlike in the analog implementation, data packets will be routable and forwardable, i.e. they can be received by one node and then retransmitted to another node within the network and so on until packets reach their intended destination node. This has the advantage of allowing a node to communicate across much greater distances than the analog MF point-to-point communication distance. The detailed discussions of the network architecture, capabilities, area coverage are contained in the full Phase 2 report.

6 Characterization of the Underground Mining Environment For the DRUM system to operate correctly and reliably, the characteristics of the underground mining environment must be understood. This includes potential interference sources, ergonomic concerns, and environmental challenges. Data from US Bureau of Mines reports is being used to generate a noise model that is part of a system simulation. This model is used to develop the initial DRUM system design. Kutta intends to collect more data as testing progresses during program execution. Measurements will be taken at various locations, including candidate repeater installation sites and near heavy equipment that generates electromagnetic interference. Underground mines provide a challenging environment for electronic equipment. In a US Bureau of Mines report, the Collins Radio Company characterized the challenging environment in underground coal mines in the following paragraph: A mine presents a uniquely harsh environment in many areas. Equipment will receive harsh treatment when in operation. Rock dust and/or coal dust will pack in and around all exposed surfaces and crevices. High humidity and dripping water will erode surfaces. The moisture may be corrosive. The equipment must be designed to operate under all these conditions. MIL-STD-810 is a series of ruggedization standards produced by the US Army s Developmental Test Command. MIL-STD-810 specifies various environmental tests that are designed to show that equipment that passes these tests will survive in the field. Kutta will investigate the feasibility of formally qualifying DRUM system components as compliant with MIL-STD-810 standards. Ergonomic factors, or the relationship between coal miners and their working environment, must be considered for the DRUM system design. The following ergonomic considerations will be addressed in the final DRUM system design: Carrying portable units Both the Portable Analog Radio (PAR) and the Mobile Base Station (MBS) will have 1-piece polycarbonate XP enclosures, with the antenna assembly in the enclosure along with all other radio components. The radio will be either carried by hand (similar to a lunchbox) or like a backpack. When carried by hand, the operator has the ability to be as near or far from the conductive infrastructure as necessary without losing signal. If Kutta s in-mine testing is representative of product capabilities, a portable unit within feet of a repeater is likely to be required to be within 15 feet of a conductor, effectively providing entry-wide coverage. When signals are weaker, the unit should be mounted or located nearer to the conductive infrastructure. Mounting options The portable units (PAR, MBS) may include the ability to attach to a roof strap. This will allow an operator to place the radio near (within 1 foot of) a roof-mounted conductor without suffering fatigue. Recharging portable DRUM units Portable units will operate from internal, rechargeable batteries that are charged at the surface, once per shift. Fixed DRUM units Methods for rib-mounting to keep equipment off the floor and improve proximity to cabling are being pursued. Fixed units using large external battery packs may be mounted on the rib while the batteries remain at floor level, perhaps in a nearby crosscut. Text interface The digital DRUM units will support text messaging, and the user interface must be as basic and intuitive as possible. Audio interface DRUM radios may have ruggedized speaker/microphones that can be attached to a lapel for easy access. One option is a wireless speaker/microphone using Bluetooth. Mounting locations No technical reason for preferring roof-mounted, rib-mounted, floor-mounted, or buried wire has been identified. The PAR and MBS will both have features that allow for close coupling to a wire, regardless of where it is located, in order to provide flexibility to the mine operator for any conductor installation they wish or need. The PAR and MBS will have roof-mounting hardware in the form of hooks or clamps, they will stand upright when placed on the ground, and when carried by hand they will be in close proximity of a wire that is installed on a rib or as an escape line at waist height.

7 Outstanding Design Issues MSHA Permissibility The high-q oscillator circuits in Kutta s induction antenna make it very difficult to achieve intrinsic safety for any of the medium frequency transmitters under development. Under the desired 5 Watt transmit conditions, the applied voltage to the antenna is about 16 Volts RMS AC, drawing about 300 ma of current. However, the resonant elements in the antenna store the energy and create voltages we have measured to be as much as 200 Volts, and currents between 700 and 800 ma. MSHA s criteria for intrinsic safety in inductive circuits will not permit those levels of electrical energy to be exposed to the environment with a potentially explosive atmosphere. Kutta has evaluated three solutions for mitigating the electrical hazard and obtaining MSHA permissibility: Reducing transmit power, encapsulating components and using XP enclosures. Reducing transmit power to meet intrinsic safety requirements will result in too great a loss in performance while encapsulation will add substantially to the weight of portable components. As contractually specified, NIOSH has final approval of Kutta s approach to produce DRUM units that are MSHA permissible. Currently, that approach is to use XP enclosures, including novel polycarbonate designs for the portable devices. Battery Life Requirements A final decision is needed to specify the battery life for DRUM system components. Several battery life guidelines have been proposed. For example: For fixed installations: 96 hours, with provisions for power management For wearable devices: 10 hours For luggable devices: 24 hours These system issues will affect final system design and performance standards and will significantly affect Phase 3 Analog Radio Production and Digital Radio Design.