4CH-VSG2000, Four Channel Phase Coherent Vector Signal Generator

Applications

• Electronic Warfare - Efficiently and quickly test designs of MIMO and other multi-channel electronic support, attack and countermeasure systems. Simultaneously transmit different waveforms or time/phase shifted versions of the same waveform to stress test receivers. Long duration spectral captures from battlefield conditions by the IQC-2110 provide an exact replica of wideband RF spectrum scenarios.
   
• Satellite Communications - Transmit across nearly an entire transponder utilizing the four signal generators, each operating at 110 MHz bandwidth and tuned to adjacent sub-bands. Easily test the compatibility of direct sequence or frequency hopped CDMA systems with other wideband access schemes using waveforms grouped in RF Editor and up-converted to IF by the 4CH-VSG2000.
   
• Spectrum Management - Shorten the time to design RF and IF circuits for multi-waveform devices and speed production testing through the use of concurrent waveform injection. Verify the performance of a single waveform device in the presence of multiple interfering signal types.
   
• Radar - Improve and test the effectiveness of active phased array antennas and associated waveforms.

Details

Functional Description and Block Diagram

A simplified block diagram of the X-COM 4CH-VSG2000 is shown above. It consists of four major functional sub-systems; waveform memory modules, the Memory Controller, Timing and Control Subsystem and the RF Signal Generators. Taken as a whole, the 4CH-VSG2000 provides four independent, arbitrary waveform, vector signal generators. The RF signal generators can act independently or be configured so that their outputs are time and phase synchronized.

Waveform Memory Modules (WMM)
Each RF channel is supplied with 1TB of removable, solid state disk drive capacity. If, for example a channel is utilizing its full 110 MHz channel bandwidth, playing back a spectrum record from the digital I & Q outputs of a high sample rate spectrum analyzer, the 1TB memory will provide 22 minutes of capacity. Lower signal bandwidths will require lower data rates with a commensurate increase in signal capacity from the SSD. Waveform segments for the 4CH-VSG2000 are stored in high dynamic range, interleaved 16 bit I and Q format.

Four SSD WMMs are housed in the 4CH-VSG2000 enclosure. They slide in from the front of the unit. To load waveform segments or sequences, they are removed from the 4CH-VSG2000 enclosure and inserted in the X-COM Datapack programmer which is attached to the X-COM SigAnalyst work station. Waveform segments can be any time length and of any span from 10 KHz to 110 MHz in occupied bandwidth but must be padded to a file size which is an integer multiple of 256KBytes.
Segments can be:

• Entire files, or time slices of recorded RF spectrum and stored in the .XIQ, .TIQ, .bin, .txt or .mat format
• Files created in digital signal processing software such as MATLAB® or RF Express®
• A combination of recorded and created waveforms that have been edited, concatenated and combined in RF Editor.

Waveform Memory Module File Format Definition
The 4CH-VSG2000 system has 4 Datapacks, 1 per channel. Each Datapack provides 1,024 GB of storage capacity. These Datapacks are built using four 1.8" 256 GB solid state hard drives configured as a Linux software RAID Level 0 array. The file system on the Datapacks is EXT2.

Waveform files can be loaded onto the Datapack using an MC-VSG Datapack Programmer. This programmer offers four External MiniSAS ports, 1 for each Datapack. These ports can be accessed using an LSI Logic Fusion MPT2-compatible Host Bus Adapter. All necessary hardware and software to perform this loading is part of the standard equipment list delivered with a 4CH-VSG2000.

The file extension for Waveforms is .DAT. The file format of the .DAT file is interleaved I/Q, whereby the first 16-bit I sample in time is followed by its corresponding 16-bit Q sample with subsequent I/Q samples following till the end of the file. An interleaver program is part of the 4CH-VSG2000 software suite. It can accept non-interleaved I & Q files in .XIQ format, interleave them and output the file as a .DAT format. Other non-interleaved file formats such as .TIQ or .bin can be converted to .XIQ using the X-COM Spectro-X software program.

In a .DAT file, the Least Significant Byte is stored first, followed by the Most Significant Byte within the file: I0[7:0]I0[15:8] Q0[7:0]Q0[15:8] I1[7:0]I1[15:8] Q1[7:0]Q1[15:8] … In[7:0]In[15:8] Qn[7:0]Qn[15:8] The I/Q samples are stored as binary, signed (ones complement) samples.

Waveform File Size Limitations
The following minimum file size limitations currently exist with the system:

• Minimum Unrepeated (single time playback) File Size: 256 KB
• Minimum Repeated (looped playback) File Size: 128 MB
• File Size Multiple: 256 KB
  Every file to be played back must be a multiple of 256 KB (262,144 bytes)

Memory Controller Module (MCM)
The MCM consists of; the 16 bit Digital to Analog converters (DAC) used to convert stored waveform files to analog I & Q waveforms prior to up-conversion, the single shared DAC timing source, and the time source divider circuits necessary to allow each channel to work under a different sample rate (span BW). The output of each DAC is low pass filtered for proper spectral reconstruction.

Waveform segments are stored on the WMM of each RF channel. Waveform sequencing tables are loaded in to the MCM which then controls the execution of the waveform playback sequence for each channel. Any combination of the four channels can be simultaneously playing a waveform segment or sequence, all under control of the MCM. A sequence consists of a series of waveform segments that can be played once or looped with specified time delays between loops prior to the playback of the next segment in the sequence. Once waveform segments have been stored in the WMM and a sequencing table stored in the MCM, the Memory Control Module works with the Timing and Control Subsystem to manage all the system disk resources to ensure seamless, zero delay waveform segment to segment transitions.

Timing and Control Subsystem (TCS)
The 4CH-VSG2000 can accept a high precision 10 MHz external time source to ensure precise synchronization between it and the other equipment in a typical development or automated test environment. The TCS also manages the external trigger input that can be used to initiate the starting or stopping of waveform playback across one or more of the four channels. I&Q channel slew settings/calibration and LO tuning for each channel are also controlled by the TCS.

RF Signal Generators (RSG)
Four independent RSGs use a single frequency reference source to ensure the phase coherency of their output so critical in MIMO test and development environments. Each can also be rapidly tuned to a different center frequency with excellent frequency settling times and amplitude flatness. RF amplitude levels can be set for each channel independently, along with center frequency for each RSG.

The maximum RF bandwidth of any RSG is 110 MHz and the RF center frequencies are independently tunable over the frequency range of 50 MHz to 2 GHz.

System Configurations and Control Software

Typical System Configuration

As shown in the figure above, the 4CH-VSG2000 is connected through a LAN switch to either a Windows 7 PC running the X-COM MC-VSG Control application or a SigAnalyst workstation. The advantage of using an X-COM SigAnalyst WS is its hardware configuration, specifically designed to accommodate multiple MiniSAS interfaces to X-COM IQC2110 Datapacks and up to 16TB of RAID5 waveform archive storage. The SigAnalyst WS also is equipped with an LSI Host Bus Adapter allowing direct MiniSAS connection to the X-COM Datapack Programmer. This is the device used for waveform segment programming of the four, removable 4CH-VSG2000 1TB Waveform Memory Modules (WMM).

A quad core processor and 24GB of RAM support the high speed execution of X-COM's Spectro –X and Spectro PDW analysis, search and waveform identification programs, and RF Editor for editing and customizing waveform segments. Other waveform development tools such as MATLAB®, Agilent's SignalStudio or RF Express from Tektronix can also reside and run on the SigAnalyst. In the case of RF Express, files can be exported in TIQ formats which are compatible with the X-COM software suite.

MCVSG Control Software
Full control of the 4CH-VSG2000 as well as the creation and editing of waveform sequence tables is provided through the graphical user interface of the MCVSG Control Software. The application is designed to run in a Windows 7 environment. The PC running the MCVSG program requires a LAN connection and can then work with any number of 4CH-VSG2000 as long as they each are assigned a unique IP address on the network. Each 4CH-VSG2000 is accessible through its own tab in the main GUI window as shown above.

The user has the option of setting up each channel to either use a waveform segment or waveform sequence as the I & Q modulation source. Then each of the WMMs is viewed and a segment or sequence is selected. Through the use of the Select Global option, the same waveform segment or sequence can be assigned to all four of the channels.

Next, the user sets the RF Parameters of the channel through the RF Parameter Modify window. Here, the user has control of each carrier's center frequency, amplitude and phase. In particular, the phase of any carrier can be adjusted relative to any other carrier in 3ps increments.

Each channel that has been assigned either a waveform segment or waveform sequence and had its RF Parameters set is now armed. Modulation of its RF carrier by the selected file is initiated either through the GUI or via receipt of an external, TTL leading edge trigger. The user has the option of selecting how each channel playback is begun.

From the Tools menu in the MCVSG GUI, the operator can open multiple copies of the Waveform Sequence Editor window. Similar in appearance, keywords and syntax to C or XML, the MCVSG scripting language enables the 4CH-VSG2000 operator to build, compile, save and load waveform sequences. A separate program called the X-COM JBOD loader is used to load the sequences, or individual waveform segments, on to the 4CH-VSG2000 WMMs.

Specifications

This section provides the specifications of the 4CH-VSG2000, multi-channel vector signal generator. Minimum or maximum specifications are warranted under the following conditions

• 30 minute warm-up time at ambient temperature
• Calibration cycles have been maintained
• Operating temperature of 10° C to 35° C

Specifications are subject to change without notice.

RF Performance, Single Output Channel Unless stated otherwise, RF performance specifications apply to all 4 channels independent of the number of active channels.
RF Output Frequency (RF Out)		Range: 50-2000 MHz Resolution (Step Size): 1Hz Stability, inclusive of temperature and aging¹: ±2 ppm RF Bandwidth (3dB) max.: 110 MHz Spectral purity¹ 10 Hz: -38 dBc / Hz½ 100 Hz: -43 dBc / Hz½ 1 kHz: -48 dBc / Hz½ 10 kHz: -78 dBc / Hz½ 100 kHz: -103 dBc / Hz½ 1 MHz: -123 dBc / Hz½ ¹Using internal 10 MHz reference clock
RF Output Amplitude (RF Out)		Output power, minimum, single-tone CW output, digital input signal = -3dB full scale: 0 dBm Output power attenuation: 0 to 25 dB Output power resolution (step size): 0.1 dB Uncertainty:² ±1 dB Repeatability: < 0.1 dBm Spurious Free Dynamic Range <10 kHz offset: -50 dBc >10 kHz offset: -60 dBc Harmonic suppression: < -30 dBc Signal-to-noise ratio, single tone: > 85 dB Image rejection, single tone: < -50 dBc LO leakage, single tone: < -60 dBm In-band ripple, measured from carrier < 100 MHz BW: ±2 dB Connector: SMA Impedance, Nominal: 50 ohms VSWR (max.): <1.8:1 Output ports: 1 Per channel ² At carrier frequency & into load VSWR of <1.1:1
Baseband I/Q Output (I/Q Out)		Connectors: SMA Impedance, Nominal: 50 ohms VSWR (max.): <1.8:1 Output bandwidth (3dB) max.: 110 MHz Output power, typical, single-tone CW output, digital input signal = -3dBc full scale: 5 dBm Output power attenuation range: fixed Output ports: 2 Per channel
Phase Coherency		Channel to channel phase tracking (RF output < 1GHz): < 1 deg Phase offset range: 300 psec Phase offset resolution: 3 psec
Modulation Signal		Format: I & Q baseband Resolution: 16 bits Supported Sample Rates: 150, 75, 50, 25, 12.5 MS/sec Source: Solid-State Drive Arrays
External Trigger		Modes: single, loop Source: external Type: Rising edge Level: 5 V Connector: BNC(F)
Reference, Storage and Communication
Internal Reference Oscillator (REF Out)		Frequency: 10 MHz Stability, temperature and aging inclusive: ±2 ppm Output Level (nominal): 3.3 Vp-p Output Waveform: Square wave (LVCMOS) Load: > 1000 ohms , < 15 pF> Connector: BNC (F)
Reference Oscillator Input Requirements (REF In)		Frequency: 10 MHz Uncertainty, max.: ±10 ppm Input Level (nominal): 0 to +13 dBm Input Impedance: 50 Ohms Connector: BNC (F)
Communication Interface		Ethernet 10BASE-T or 100BASE-TX (auto-sensing) Ethernet Version 2.0/IEEE 802.3 Protocols: TCP/IP Connector: RJ-45
Internal Waveform Storage		Capacity (per channel): 1024 Gb Playback time, max.3 150 MS/Sec (110 MHz BW): 22 Min. 75 MS/Sec (60 MHz BW): 44 Min. 50 MS/Sec (40 MHz BW): 66 Min. Data Rate (max.): 600 MB/sec Format: Linux software RAID level 0, ext2 file system ³ Overprovisioning and wear-leveling will reduce total capacity.
PC Requirements and Mechanical
Software Requirements		Windows 7 256 MB RAM & Pentium III or equivalent processor (512 MB RAM & Pentium 4/M or higher recommended) 800 x 600, 256 color display (1280 x 720, 16 bit or higher resolution recommended) 100 MB free disk space Mouse or pointing device CD-ROM Drive (for installation) Adobe Acrobat Reader (for Quick Start manual) Ethernet connection
Mechanical		Housing: Aluminum Buttons: Power On/Off – front panel Power Indicator: Green LED labeled "Power" (Front Panel) Connectors (Rear Panel) Power Input: 120/240 VAC, IEC inlet Voltage Range and Power Requirements: 84-264 VAC, 375 W peak Chassis grounding terminal: #10-32 x ¾" UNC Cooling method: Forced air, front panel intake Warm-Up: Specifications apply after a 30 minute warm-up period at ambient temperature. Operating Temperature: 10 to 35 °C Storage Temperature: –20 to +80 °C Humidity, Max: 80% non-condensing Altitude, Max: 4600m above sea level Weight, Max: 10 lbs. Dimensions, Max: 19" x 30" x 3.5" (2 RU)