LenVDR10-Mp
PT Len Industri as one of the state-owned company engaged in the business line of defense, is developing a device for military communications radio. One of these products is LenVDR10-Mp. Radio is working on the VHF band 30 MHz - 88 MHz with FM modulation. Radio is designed as a tactical communications device with military standards, waterproof, vibration, durable and resistant to extreme temperatures.
Here are the technical specifications LenVDR10-Mp:
Frequency: 30-88MHz Tuning Step: 25 kHz Frequency Stability: 2ppm Capacity Channels: 100 channels Mode Modulation: FM Modulation Digital: BPSK Vocoder: CVSD FEC: Viterbi Encryption: AES 128 Output RF: 10Watt Maximum Sensitivity: -110 dBm for 10dB SINAD RF connection: 1.5m Whip, whip 3m & BNC 50R Power supply: LiPo battery 11.1VDC-12.6VDC, 10AH battery life: more than 14 hours with a ratio Tx: Rx: Stand by 1: 1: 8 temperature: -10C-50C IP Rating: IP67 Immersion: The depth of 1 meter Dimensions: 250mm (length) x 250mm (height) x 90mm (width)
LenVDR10-Mp platform was developed by implementing
Software Defined Radio (SDR). SDR itself is a technology in which the
software is run on a
hardware platform . The SDR technology which processes the signals digitally in a
chip DSP.
Speaking further about LenVDR10-Mp, there are two modes of communication that is the Analog (AFM) and Digital (DFM). In the AFM mode, the communication is done
plain without security, so that these radios can communicate with other radios on the same frequency. While in the digital mode, communication between the radio can only be made if the radio communication have the same mode.
Here is a graphic comparison of the quality of reception versus distance.
Figure: Comparison of Quality vs. Distance
From the graph above, it can be seen that the FM analog mode, the reception quality will decrease as the distance farther, in terms of loss of quality, sound is heard will be damaged. In Digital mode FM reception quality will remain good, until at a certain distance will be directly destroyed. The distance to the emission of waves is determined by many factors, such as
power output , antenna performance and terrain field. the greater the
power emitted, the greater
the gain antennanya, the farther away also the transmission range. Likewise, on the side of
the receiver , where the sensitivity of the
receiver that determines a range of communication that can be taken.
Signal processing
One technique algorithms
voice coding used to build digital communication is
a continuously variable slope Delta (CVSD). CVSD is one compression algorithm
sample data to encode 1 bit per
sample , that is to say, if there are 16 KHz audio sampling, it will be changed to 16 Kbit / s. This figure is the maximum speed (
datarate ) which can be reached to
transfer data. The following image is an example of an audio signal that is processed CVSD.
Image: Graph encode CVSD
Another example
of voice coding is used extensively for radio communication is
Mixed-Excitation Linear Prediction (MELP). The algorithm is ideal for use in communication with a narrow bandwidth, since MELP has a datarate 1200/2400 bps.
Next, the technique does is modulate data. No Binary modulation techniques such as Phase Shift Keying (BPSK), which is a technique that converts digital data into 2 type. Each record represents the phase of a wave. Similar to the BPSK, there are QPSK, which converts the digital data into a four phase data. etc. In contrast to the PSK, there is a technique called PAM or Pulse Amplitude Modulation, ie change the data in which each data represented the Amplitude of a wave.
Furthermore, the digital radio added
Forward Error Correction (FEC), which is an algorithm that allows to fix corrupted data received at the receiver. Some are
Viterbi ,
Reed Solomon , and others.
Secure Communication
Radio features one-Mp LenVDR10 are securing communications (
Comsec ) and transmission security (
transec ).
Comsec applied to the radio communications that are not easily intercepted. There are various methods of securing this, among others, by using the encryption key. LenVDR10-Mp using AES128 algorithm to scramble data and voice.
Advanced Encryption Standard (AES) is an encryption standard by the symmetric key. This standard consists of 3
blocks chipper , namely AES-128, AES-192 and AES-256. Each
chipper has a size of 128-bit key size respectively 128, 192 and 256 bits.
TRANSEC is security in the transmission signal. The method used to implement
transec are frequency
hopping and
spread spectrum . Frequency
hopping is a radio transmission method by varying the frequency of
the carrier that is used to quickly and randomly. Frequency hopping using a sequence
psedo-randomized controlled cryptographic algorithm with a key. Mode
Frequency Hopping meant that communications can not be intercepted or disturbed (by
jamming ). In LenVDR10-MP, changes in the frequency of
the carrier when
Hoppingchanging the moving speed of 100
hops / sec, with a resolution of 25kHz and the switching frequency of 3400 kHz frequency range around the frequency
channel is active. The following image is an illustration of frequency
hopping performed.
Image: Communication is hopping with interference
The illustration depicts if there is a process of communication between the radio, which at a certain frequency there is interference (
jamming ), then with frequency
hopping , the information will still be acceptable even though there is a decrease in signal quality.
Image: Communication is hopping with tapping
The illustration shows that in case of interception of information at a specific frequency, then just a little bit of information received by eavesdroppers.
Indeed radio frequency (RF) is a limited natural resource that has strategic value. Therefore, its use should be conducted in an orderly. It has been stipulated in government regulations that may apply in each country is different, but in essence, the radio frequency spectrum is set to be orderly, efficient and in accordance with its designation that does not cause harmful interference.