IMPLEMENTATION OF ZIGBEE NETWORK TO WIRELESS TELECOMMAND AND TELEMETRY SYSTEM FOR SATELLITE COMMUNICATION NAVEEN H 1, CHETAN H 2 1 Asst Prof, MSEC, 2 Asst Prof,CMRIT E-mail: naveens.h.gowda@gmail.com, chetan.h.gowda@gmail.com Abstract: The Low Rate Wireless Personal Area Network (LRWPAN) /ZigBee standard is used for wireless command distribution to different subsystems in a spacecraft. The wireless TC system is designed to operate at 100Bps. In this paper we propose wireless TC-TM system for satellite communication and design, un-slotted CSMA/CA with non-beacon enabled network is used for wireless data transmission. It also presents wireless satellite architecture and highlights the usage of wireless technology in space application. It also highlights the advantage and difficulties in implementing the wireless system in satellite. Keywords- Wireless TC-TM, CSMA/CA, Zigbee I. INTRODUCTION The Telecommand and Telemetry subsystem [5] are vital systems of any spacecraft and requires interconnection between different subsystems in spacecraft. Traditionally all these on-board data communication requirements have been met by some combination of IEEE- standard. 1553 or RS-232 links. Presently, standards such as the CAN bus, Space wire based on IEEE-1335 and optical interconnection based on IEEE-1773 are also being used. It uses a customized bus for satellite subsystem integration as shown in fig.1. The custom built interface between subsystems has the unique, point-to-point interface for on-board data communication; it uses simple protocol, serial data and an authentication pulse for communication and testability. There are different types of command requirement to be transmitted to various subsystems in spacecraft. The types of commands to transmitted are data, pulse and level commands, Any spacecraft requires around 1000 of commands interface to other subsystems which are hard wired, carries huge harness mass from different subsystem to TC systems, which leads to the problems of interference, limited flexibility, testability and complexity of spacecraft and subsystem failure due to misinterpretation of interface specification by the subsystem designers and substantial time delay and overall it leads to spacecraft delay. The foremost advantages of wireless system is harness mass reduction, simpler integration, elimination of test connector, insertion or removal of payload at later stages of spacecraft integration, compatibility of communication, no interface related issues like in conventional design. It allows any subsystem to join and leave the network at any time. This would be extremely useful in spacecraft integration, as it would allow the incorporation of extra instruments later in the program with few changes. II. WIRELESS TECHNOLOGIES 1. ZigBee ZigBee is a low power, short-range point-tomultipoint data transfer system. It supports the data rate of 20-kbps/40 kbps/ 250 kbps. It operates in 2.4 GHz ISM band & covers a range of 10-50 meters. It supports star & mesh topology. It also has the characteristic of Self-healing i.e. it can detect, and recover from, fault appearing in either network nodes or communication links, without human intervention. ZigBee uses TDMA technique for accessing the network with GMSK/DSSS modulation. 2. Bluetooth Bluetooth is a short-range point-to-multipoint data transfer system based on a radio link operating in the ISM band about 2.4GHz. it can operate up to 723.2 kbps in asymmetric data transfer and 433.9 kbps in symmetric data transfer[2]. It has built in security & also omni directional in nature. III. SUITABILTY FOR SATELLITE Fig.1. Typical Wireless Subsystems In Satellite. Bluetooth and ZigBee can replace RS-232 links or conventional system. If power is criteria then ZigBee is better suited for wireless application, as the power 94
consumption is less then 25mW but range of operation is small, in case of Bluetooth it can go up to 1000mW. The implementation of ZigBee network is less complex then Bluetooth and also data rates are sufficient for telecommand & telemetry systems. The development of ZigBee based wireless system for satellite is easy as tools are available but in case of Bluetooth they are not available. We feel that for small satellite, and scientific mission, ZigBee standards are better suited for wireless Telecommand and Telemetry systems. In case of operational & big satellite possibility of using blue tooth has to be explored. IV. WIRELESS SATELLITE ARCHITECTURE In spacecraft application requirement, the star topology is selected, it is simple to implement and it has less complexity and it satisfies all the requirements of TC systems. The PAN coordinator and FFD s are wireless ZigBee devices and they are configured as star topology [1]. The demodulator, decoder and PAN coordinator is TC uplink part. Both transceiver and antenna is parts of RF system which is interfaced with TC systems. The TC uplink part is used for commanding and ranging the satellite. The PAN coordinator is interfaced with TC and. The FFD s are interfaced with other subsystems of the satellite. The figure 2 shows ZigBee based wireless Satellite architecture. constant interval and latched with set and reset D-flip flop. As soon as the TP pulse occurs D- flip flop is set, command is read from the port and stored in an array, TP reset pulse is generated to reset D-flip flop and enables command acquisition logic to keep ready for next command. Fig. 2. Zigbee Based Wireless Satellite Architecture In PAN coordinator, received command is converted into ZigBee format and it is broadcasted in wireless mode to all the FFD s in subsystems and intended FFD receives a wireless command in ZigBee format. It is decoded and converted as pulse or level or data command and it is executed in the subsystem end. Each FFD can execute any number of commands as required by the subsystems. In this fashion commands are distributed to subsystems through FFD s in wireless mode. V. IMPLEMENTATION OF TC SYSTEM 1. TC Command acquisition module The software modules of command reception and transmission are programmed in 8051F121 microcontroller of PAN coordinator [1]. Command transfer pulse (TP) is polled continuously with Fig.3. Command Acquisition module 2. TC Command transmission module In this module, network short address of an entity that has been added to the network is read, and PAN coordinator address is also read, using these addresses data received in command acquisition logic is transferred to ZigBee data frame[4] payload field and send data routine is called, where command transmission from PAN coordinator to FFD s is carried out 95
4. TM Data Transmission Module This module is similar to command transmission module here ZigBee data frame module is used for transferring TM data collected at different FFD s to PAN coordinator Fig.4. Command Transmission Module 3. TC Command validation and execution module The software modules of command reception and execution modules are programmed in 8051F121 microcontroller of FFD. In this module each received command bits are validated and Transferred to the local variable. The received command information is checked with the stored command information and address of the device, if they match, then checked for received command type, weather information received command is ON or OFF type and generate 64 msec pulse for ON command or OFF command and executes at subsystems end Fig 6. TM Data Transmission Module 5. TM data Acquisition module In this module the ZigBee data frame module is used to acquire TM data from FFD s to PAN coordinator. In PAN coordinator received TM data is converted as serial clock, serial data and mode pulse, these signals are given through telemetry transmission unit to downlink. Fig 5. Command Validation and Execution Module Fig 7. TM Data Acquisition Module 96
VI. TEST SETUP Implementation of Zigbee Network to Wireless Telecommand and Telemetry system for satellite communication The Wireless TC-TM system setup is shown in figure 4. bit), address (32 bit), Data ( 160 bit), and frame check (8 bit).total data frame is of 224 bit transmitted at 7 frames ( each frame of 32 bit). RTL Schematic for TC Transmitter Fig.8. Wireless TC system with satellite architecture Test Setup Fig 10. Internal Structure of TC Transmitter TC Receiver Simulation result in VHDL The PAN coordinator and FFD s consists of RF transceiver chip, micro controller and antenna and programmable interface devices. The wireless devices have been developed according to the current version of the standard specifications and works in low voltage, typically 3.3V. The Xilinx platform is used as TC command simulator. The Serial command, clock and authentic pulse called transfer pulse (TP) from Xilinx platform is interfaced with TC-TM glue logic card. In this card serial data is converted to parallel, level conversion and fast switching transitions are carried out. VII. TEST RESULT The test Result is simulated using Xilinx VHDL Code and resulting waveform for Telecommand and Telemetry system is shown below TC Transmitter simulation in VHDL Fig 11. Simulation result for Telecommand Reciever In Receiver command validation and execution takes place. From the waveform we can see that subsystem 1, 3, 5, and 8 are ON depending on the valid command input and respective address and subsystem 2, 4, 6, and 7 are made OFF with the corresponding command input. RTL Schematic for TC Receiver Fig 9. Simulation results for Telecommand Transmitter. From the Waveform we can see that final data frame consist of frame control (16 bit), Sequence number (8 Fig 12. Internal Structure of TC Receiver 97
TM Transmitter Simulation result in VHDL From the Waveform we can see that telemetry data, address of the Subsystem and sequence number are extracted from the Zigbee frame format. RTL Schematic for TM Receiver Fig 13. Simulation Result for Telemetry Transmitter From the waveform we can see that the telemetry data from subsystem along with sequence number are transmitted as Zigbee frame format. RTL Schematic for TM Transmitter Fig 14. Internal Structure of TM Transmitter TM Receiver Simulation result in VHDL Fig 16. Internal Structure of TM Receiver Timing Calculation The TC command distribution and TM health parameter acquisition have to be finished in stipulated time depending on up link and down link data rates. As ZigBee supports maximum data rate of 250 Kbps, a timing calculation for Telecommand and Telemetry data rate is explained. The following notation are used for timing calculation Fb = Data transmission rate Trf 1 = Maximum Physical Protocol Data Unit length Tar = TX-to-RX or RX-to-TX turnaround time Tb1 = PAN coordinator processor cycle time Tb2 = FFD processor cycle time TCcmd = TC command transmission from PAN to FFD TMdata = TM data acquisition from FFD to PAN TCTMtot= Total time required for TC command Transmission and TM data acquisition Where, 1) Fb = 250 KBPS, therefore, Tb = 1/ Fb = 4 usec 2) For Trf 1 =158 bytes =1264 bits* Tb =5.056 msec 3) Tar =12 symbol period *(4bits/symbol) = 48 bits* Tb=192 usec 4) Tb1 = Tb2 = 6 msec (processor cycle time required to carry out ZigBee functions) The duration of TC command transmission from PAN coordinator to FFD is calculated as follows TC cmd = Tar + Tb1 +Trf1 (1) = 192 usec+6 msec+5.05msec= 12 msec Fig 15. Simulation result For Telemetry receiver The duration of TM health parameter acquisition from FFD to PAN coordinator is calculated as follows TM data = Tar + Tb2 +Trf1 (2) 98
= 192 usec+6 msec+5.05musec= 12 msec The total time duration required for TC command transmission and TM heath parameter acquisition is TCTM tot = TC cmd +TM data (3) = 12 msec+12 msec=24 msec. Hence approximately TCTM tot requires 24 msec the ZigBee base TC-TM system working at 250 Kbps require a total time of 24 msec to complete the whole command transmission and heath parameter acquisition within the satellite, at present we can operate TC at 100 Bps and TM operates at 1Kbps which is well within the operational range of ZigBee standard. VIII. FUTURE IMPLEMENTATION In this Paper we acquired the Telecommand data and transmitted to different subsytem for excution of command,future implementation of this paper is to acquire the Telemmetry data from FFD to Pan coordinator in Zigbee data Format and send the acquired telemmetry data to Earth station. CONCLUSION Implementation of wireless technology in satellite has been dealt. A prototype model of wireless TC acquisition system functioning at 100 Bps using ZigBee Technology has been developed and demonstrated. The prototype model is tested for various command and health parameter reception. Before real time implementation of this technology in spacecraft, EMI/EMC interference has to be taken care and apart from these high data rate system using other wireless technologies like Bluetooth, WI-Fi, and WiMAX can be explored. REFERENCES Vasudevamurthy, H.S. Vanitha, M. Lakshminarsimhan, P. Digital Syst. Group, ISRO Satellite Center, and Bangalore, India this paper appears in: Advances in Recent Technologies in Communication and Computing, 2009. ARTCom '09. International Conference. [2]. SatishSharma,P.N.Ravichandran,Sunil,P.Lakshminarsimhan,Seshaiah, Wireless Telecommand and Telemetry System for Satellite IEEE sponsored, International conference on Recent Advance in Space Technologies (RAST), held at the Harbiye Military Museum, Istanbul, Turkey from 14-16 June-2007. [3]. M. A. M. Mohamed, A. Abou El-Azm and N. A. El- Fishawy, M. A. R. El-Tokhy, Optimization of Bluetooth frame format For efficient performance, Progress In Electromagnetics Research M, Vol. 1, 101 110, 2007 [4]. Stanislav safari, kresimir malaric, Zigbee Wireless Standard 48th International Symposium ELMAR-2006, 07-09 June 2006, Zadar, Croatia [5]. Johan Lönn, Jonas Olsson ZigBee for wireless networking March 2005. [6]. ZigBee Specification by ZigBee alliance, June 2005. [7]. Design of CAN bus Network for Telemetry & telecommand for On-Board Data handling Khurram, M.; Zaidi, S.M.Y, this paper appears in: Recent Advances in Space Technologies, 2005. RAST 2005. Proceedings of 2nd International Conference. [8]. Sinem Coleri Ergen ZigBee/IEEE 802.15.4 Summary September 10, 2004 [9]. Wireless Communication using the IrDA Standard Protocol, Microchip Technology Inc.Web Seminar January 21, 2004 [10]. IEEE 802.15.4 Standard-2003, "Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs)", IEEE-SA Standards Board, 2003. [11]. IEEE Standard for Information technology-802.15.4, 2003. [12]. Morrow, Robert "Bluetooth Operation and Use", Mcgraw- Hill, 2002. [1]. Wireless Telecommand and Telemetry Systems for Satellite Communication Using ZigBee Network Ravichandran, P.N. Kulkarni S. Sharma, S. [13]. MIL-STD-1553B: Digital Time Division Command/Response Multiplex Data Bus. United States Department of Defense, September 1978. 99