Sgr 2500-introduction
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software defined radio scenario simulator

software defined radio scenario simulator

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Sgr 2500-introduction Sgr 2500-introduction Document Transcript

  • SGR-2500
  • Contents 1. 2. 3. 4. Introduction..............................................................................................................................3 Software radio-techniques.......................................................................................................4 Equipment functionalities .......................................................................................................6 Equipment structure.................................................................................................................8 4.1. Baseband unit......................................................................................................................11 4.1.1. Digital Signal Processor (DSP) ..................................................................................11 4.1.2. Digital Modulator (DM) .............................................................................................11 4.2. Radio-frequency stage........................................................................................................12 4.2.1. Frequency Converter (FC) ..........................................................................................12 4.2.2. Frequency Extension (FE) ..........................................................................................12 4.3. Channel Controller (CC) ....................................................................................................13 4.4. Built-in Test Equipment (BITE) ........................................................................................13 5. Emitter unit configuration .....................................................................................................14 6. Operating and control software.............................................................................................15
  • 1. Introduction The equipment is developed on the basis of software radio technology that gained ground over the past years. In addition to applying cutting-edge digital processing techniques the equipment’s RF stages represent radio frequency and microwave technologic solutions of the highest standards. The Internet-based solution of external control and the object oriented graphic control program significantly contribute to the high standard of the product. The added value in the project is manifest in the development of system-technical principles, the engineering of applied hardware elements in terms of circuitries and mechanical solutions, the planning and implementation of embedded digital signal processing software, the development of control system and user programs as well as in the test and quality control and quality verification methods.
  • 2. Software radio-techniques An innovative solution of realising variable radio equipment is based on the concept of socalled “software defined radio”. In this the number of actual radio-frequency subunits (RF oscillators, amplifiers, up- and down-converters, filters designed for the highest bandwidth) is minimal and all signal processing operations (filtering, equalising, modulating, demodulating) are provided by digital processing by means of software. The programmability of still remaining high frequency stages, in addition to IF and BB signal processing, contributes to a great extent to achieving full re-configuration. Besides the programmability of high frequency stages the programming and remote control of actually emitting antenna systems is also feasible. Traditional radio sets are generally made for one type of modulation to realise one kind of communication standard (e.g. analogue FM radio-telephones, GSM terminals, GPS receivers etc.), they might occasionally use some different modes of modulations (e.g. communication receivers, equipment used in military applications). These equipment are built of nonprogrammable application specific integrated circuits (ASIC) mostly well suited for their tasks and which define equipment functionalities in an unalterable way. The family of software radio sets (Software Radio or Software Defined Radio, SDR) represents another approach that by means of programmable elements makes operations in various (possibly quite different) radio systems possible. Today the need for these are ever increasing, and shall increase, because worldwide there are similar purpose systems with different solutions, and it can also be foreseen – not exclusively due to technical aspects – that quite different systems propagate (e.g. the 3rd generation cellular telephony uses different air-interface in Europe, USE and even Japan). However, users require of their sets to be usable in the widest possible circles (e.g. roaming). On the other hand, the need is there to increase system inter-operability (e.g. there exist a number of wireless LAN standard and there are more under development). It would again be required of devices to support a number of standards and of terminals to be interoperable in heterogeneous environment as well. Similar aspects drive system developers as well as service providers; the introduction of new services would become faster and less expensive if there was no need to replace hardware elements but to simply provide for conditions to modify operating software. But complying with these requirements – first of all in the physical and data-link layers – would need high level programmability of applied components, and on the other hand would need very wide band and of high dynamic range devices, which was not a feature in the case of traditional ASIC-based radio sets. Application specific circuits have to be replaced by FPGA circuits excellently suitable of high speed signal processing and by programmable signal processing processors providing for the greatest flexibility. New devices can also perform at IF some part of signal processing tasks normally performed at baseband in traditional processors. The above principles first appeared in military applications. A military purpose radio set developed on the basis of software radio principles can operate on high variety of narrowand wideband modes of transmissions, and by means of adaptive antenna sets it improves the quality of links. It can adopt without any change in circuitry to features such as e.g. applied waveform or data-link protocol (spectrum extension, modulation, error correcting code, synchronization, interleaving, channel equalization, -framing etc.). Antenna characteristics (switch-over, adaptive antennae) as well as output power and operating frequency can be altered by software means.
  • Companies working on software radio technologies and those taking part in R&D and their applications have established an international forum, which co-ordinates work in the field. The homepage of Software Defined Radio Forum (SDRF) can be accessed at the [http://www.sdrforum.org] address. Almost all significant manufacturers are represented in this organisation. A feature of digital radio sets is the point where conversion between analogue and digital units is achieved. In structures applied today fully digitised baseband functions is a widely spread method. In this case (de)modulation method by processed baseband signals is implemented by means of analogue modulators. Since the quadrature principle provides for implementing arbitrary modulation process the circuits today in use apply IQ (de)modulators built for quadrature-components. The required signal processing performance makes the application of general DSPs possible for these functions. The next step of digitization is the application of digital IF signal processing. In this case both the generation of CW and the IQ (de)modulation is performed in digital domain. Units with this kind of functionality cannot be made of DSPs designed for fully general functions. Instead of these, special purpose processors specifically prepared for these functions with maximized performance can be used. These special purpose processors feature, in addition to (de)modulators, interpolation/decimation and filter functionalities. These have ports to receive baseband data and for configuration control ports as well as output interfaces. Figure: Conversion in digital radio sets Digital signal handling Digital baseband processing Digital IF processing Digital RF processing Conversion technologies available today offer ADC and interpolation DAC circuits between 75-300 Msps. Signal processing speed of special purpose processors match this and capable to perform at 75 Msps maximum sampling rate. Since these basic components only appeared on market during the last months, there is no significant supply in the market of signal processing units representing higher-level integration based on these basic components. This signal processing speed allows for direct applying lower IF bands (e.g. 21.4MHz, 30MHz), though the higher bands (e.g. 70MHz, 140MHz, 270MHz) can also be applied by means of various mirror-bands and on the cost of some decrease in dynamic ranges. The appearance of direct RF digitization in the commercial applications in frequency bands presently used for mobile information communications services still to be seen, and this solution cannot be expected in the near future.
  • 3. Equipment functionalities The Multi-Function Communication Simulator is a software radio emitter equipment producing real-time modulated radio-frequency signals as defined by a computer control software program. The equipment can be applied to simulate a complex, dynamically changing radio-electronic environment. By its means a virtual radio-electronic space can be generated, each important characteristics of which can be changed in a way according to a scenario predefined by control computer. The communication Simulator covers frequency ranges of 1 – 2500 MHz with 1Hz resolution and 90 dB dynamics, and can produce modulation modes applied in these ranges. Generated modulation modes extend from narrow band analogue modes (CW, SSB, ISB, AM, FM) to wide band, multi-state digital modulation modes (FSK, PSK, QAM). The equipment can generate frequency hopping and direct-sequence extended spread spectrum transmission-mode signals. It also has its source generator for modulators, in which simple sine wave, telegraphic and wire sources, analogue and digital human voice, modem and facsimile signals as well as digital signal trains and FDM and TDM multiplexed signals are also included. Figure: Characteristic modulation formats Any change in the equipment’s output characteristics can be achieved in less than 1 second. Since the equipment’s internal controller has its own TCP/IP stack the external computer control can be provided via a twisted twin-wire Ethernet link even through the Internet. The control software contains a control panel that can be used to downloading set-ups or to take direct control over the equipment. Another element of the control software is the scenario editor by means of which individual set-ups can be compiled in libraries and a control
  • scenario can be edited from saved set-ups. A scenario can store information for 24 hours in 1-second steps. Emitter sources of the virtual radio-frequency space can be place on platforms of which locations can be specified in the space. Disposition in space can also be displayed by means of a map-based visualization program. Modulators and sources are used for generating modulated radio-frequency signals. The Commsim generates all sources and modulator by means of digital signal processor. This, however, does not mean that analogue sources would not be used; only these are also digitally represented within the equipment. Different op modes can be created by interconnecting various sources and modulators. In cases of simpler op modes the notation is identical to that of the applied modulator. Major emitter parameters Frequency range Output power Modulation methods: 1 – 2500 MHz max. 0 dBm, min. - 90 dBm - AM, FM, PM analogue - ASK, FSK, PSK multi-state digital - QAM multi-state digital - FDM, TDM multi-channel multiplexing Applicable sources: - Single-channel and multiplexed analogue voice - Single-channel and multiplexed digital voice - Single-channel and multiplexed telegraph and wire - Analogue TV signal - Facsimile - Data-modem signal - Pulse - High data-rate digital data - White- and pink-noise sources Transmission security functions: - High bandwidth fast frequency hopping - High bandwidth direct-sequence spread spectrum
  • 4. Equipment structure The equipment is configured of a number of subunits. In order to functionally describe Commsim it is divided into three levels. The first one is the control computer platform, which is followed by the emitters then comes the output summer (combiner) unit. Figure: Functional model A: Audio in from tape recorder Control SW PC A Co A ntr ol B U S A #1 RF Channel RF #2 RF Channel Σ #16 RF Channel SPDT SUT Monitor output for calibration External RF Source External Noise Source Control computer RF channels Output stage A possible basic configuration consists of the following sub-units: • Control computer platform • Commsim CS-2500-E emitter unit • Commsim CS-2500-S summer unit The equipment’s mechanical design and the control program provides for extending the number of emitter units up to 16. This is made possible because the PC configuration running the control software can control more emitter units via Ethernet HUB, and the output of emitters can be applied to the output summer.
  • Figure: SGR-2500 configuration CS-2500-S summer EXT 1 IN 5- 8 IN 9-12 OUT1 EXT 2 IN 1- 4 OUT2 IN13-16 Control computer platform CS-2500-E emitter #1 IP adsress: 192.168. 2.101 POW ER AF INPUT CONTORL MENU < > ENTER BITE OUT RF OUT CS-2500-E CS-2500-E emitter #2 IP adsress: 192.168. 2.102 POW ER AF INPUT CONTORL MENU < > ENTER BITE OUT RF OUT CS-2500-E Ethernet HUB Figure: SGR-2500 configuration (photo) - -
  • An RF channel (emitter) unit implemented in Commsim equipment is made of a number of subunits. Fundamentally it consists of a baseband unit and a radio unit as well as a channel controller unit to provide for controlling the above two. Figure: Emitter’s functional description RF Channel unit Baseband Unit (BBU) Auta diope in re froco m rd er Co ntr ol B U S Signal Processor Unit (DSP) Digital Modulator Unit (DMU) Radio Frequency Unit (RFU) Frequency Frequency Conversion Extension Unit Unit (FCU) (FEU) Channel Controller Unit (CCU) Figure: (Photo of the equipment) RF ou t BI TE int erf ac e
  • 4.1. Baseband unit The Baseband Unit (BU) consists of two basic assemblies: a digital signal processor and a modulator assembly. Similarly, the Radio Unit (RU) is also divided into two parts. One assembly is a frequency converter of which output signal is fed to frequency extension assembly, where the output frequency is produced. 4.1.1. Digital Signal Processor (DSP) It is the Digital Signal Processor’s task to generate baseband signals of the various sources. Baseband signals of sources modulate the carrier wave in accordance with preset mode of modulation. In addition to generating baseband signals the DSP also produces quadrature components since the modulator applies general quadrature modulator. The generated signals are applied to modulator via wideband DMA. DSP also has digitising input that is needed to generating real-time sources’ signals. In this mode of operation the DSP receives real-time modulating signal by means of ADC chip and then processes it. (Figure: DSP – SC of DMU block diagram) Spreading and Converter of the Digital Modulator Unit Digital Signal Processor (DSP) ADC DMA REQ EXT DMA ACK RAM INT Address Baseband Modulation Generator I Data CTRL Q DMA REQ Serial port DMA ACK Address Data Spreading and Serial Converter Serial port Serial port Serial port Serial interface to up converters DSP EXT Paralel DMA based interface to DSP DSP Unit 4.1.2. Digital Modulator (DM) The function of DM is to perform quadrature modulation of baseband quadrature components generated by the DSP. The entire modulation process in achieved in digital domain and special digital up-converter and carrier generator circuitry are applied to the function. Digital up-converters perform the necessary interpolation and samples are produced on the sampling frequency of numerical controlled oscillator. DM’s output frequency is determined by the frequency of the programmable oscillator. Digitally produced modulated carrier wave is converted into analogue domain by means of digital-analogue converter located in the DM.
  • (Figure: Up-converter and CW gen – DM and summing block diagrams) Up Converter and Carrier generator of the Digital Modulator Unit DUC Unit S CLK DATA S DFS SCLK DATA SDFS SCLK DATA SDFS SCLK DATA SDFS Digital Modulator and Summing of the Digital Modulator Unit Modulator Units RAM Coefficient Filter (RCF) RAM Coefficient Filter (RCF) Cascaded Integrator Comb (CIC) Filter Cascaded Integrator Comb (CIC) Filter Serial port RAM Coefficient Filter (RCF) Cascaded Integrator Comb (CIC) Filter NCO O UT Serial port RAM Coefficient Filter (RCF) Cascaded Integrator Comb (CIC) Filter NCO O UT Serial port Serial port NCO Digital Summing O UT O UT MOD NCO O UT O UT MOD O UT MOD Digital Summing Unit DA C DIF OUT DAC O UT MOD 4.2. Radio-frequency stage 4.2.1. Frequency Converter (FC) FC transfers to higher frequency ranges the modulated IF signal produced by the modulator. It applies dual conversion to produce the upper IF. FC has an input attenuator (IF ATT) by means of which the level of digitally generated IF signal coming from modulator can be adjusted. The frequency of applied local oscillators can be programmed by coarse steps; the required fine resolution can be achieved by means of fine programming the carrier wave digitally produced by the modulator. Frequency hopping operation mode is also based upon the interoperation of frequency converter and the modulator. Fine frequency hopping is provided by means of the modulator and the wide band hopping by the frequency converter. Frequency converter also has its micro-controller. Microcontroller performs according to command from channel controller the adjustment of local oscillators and input attenuators. Frequency controller is connected to channel controller via a serial interface channel. 4.2.2. Frequency Extension (FE) FE provides for extending the modulated output signal over the entire frequency range. Desired output frequency is produced in FE by means of mixing the upper IF signal with the signal of a local oscillator programmable over wide range. In order to achieve desired output dynamics the FE has a digitally programmable power divider, by means of which the required output power level can be set. FE’s micro-controller provides for communicating with channel controller as well as for programming its oscillator and power divider.
  • (Figure: FC – FE block diagram) Frequency Conversion Unit -10dBm -10dBm Digital IF IF ATT input Frequency Extension Unit LIFM LIFB LIFL Control port HIFM HIFB AMP 0dBm -20dBm High I F output High IF input HIFL OM OLP AMP RF ATT RF output OL Control port MCU MCU 4.3. Channel Controller (CC) The function of CC is to control each unit of the RF channel in accordance with configuration commands coming from control computer. It has an Ethernet port to provide for interfacing with control computer, and four serial ports each connected to subunits of the RF channel unit. There is one more serial port on the CC for transferring the results of built-in test functions. In addition to providing for control the CC also manages the tests performed in RF channel by means of built-in test functions. Test can be performed from control computer or from front panel controls. (Figure: connections of CC – IP address settings) Connections of Channel Controller Unit IP cím beállítása Channel Control Control interface to PC Display Paralel port and function keys BITE interface Serial port Ethernet Serial port Channel Controller Unit FEU Serial port FCU Serial port MOD Serial port DSP 4.4. Built-in Test Equipment (BITE) Each functional unit of the emitter has its own built-in test feature. These tests can be run either from front panel controls or from control computer. Computer tests can be performed at the control level equipment constituted by devices applied in the system, or via a terminal or terminal software connected to the emitter. By means of self-tests any faulty emitter can be identified, and, provided that the system controller is well operational, a subassembly within a given emitter, which means the smallest non-factory replaceable entity of the system. In addition to information on operational performance the self-tests also provides operational characteristics such as e.g. the current consumption or temperature of individual assemblies.
  • 5. Emitter unit configuration In designing the emitter unit’s structure complying with environmental and mechanical durability standards are taken into consideration. Meeting any requirement is strictly verified by various tests. (Figure: SGR-2500 top view) Elılap (Figure: SGR-2500 bottom view)
  • 6. Operating and control software The operation of the equipment needs the control software running on computer hardware. Software system is basically divided up to a control window application and a scenario editor application that provides for tabular and graphic information display. The following figures show a characteristic display screen for each application.