Vhf Data Link - Range

VHF Data Link The Park Air Systems PAE T6 Series MDR fully supports ICAO defined VHF data modes Future airspace management needs efficient air-ground data links. Park Air Systems has been at the forefront of VHF data link developments. The PAE T6 complies fully with international standards for ACARS, VDL Mode 2 and VDL Mode 3 data links. The Modes: ACARS - Airborne Communications Addressing and Reporting System

ACARS is used predominantly by data service providers to support airline operations, using a conventional analogue radio architecture to transmit and receive data at 2400 bit per second using MSK (Minimum frequency Shift Keying). The PAE T6 MDR is globally deployed for ACARS communications. VDL Mode 2

Provides a single high capacity air-ground data link, VDL mode 2 requires a DSP radio architecture with ultra-linear RF stages to transmit and receive data at 31,500 bits per second using modulation mode called Digital Eight Phase Shift Keying (D8PSK). VDL Mode 2 has been identified as a principal enabler for CPDLC (Controller Pilot Data Link Communications). The PAE T6 MDR is deployed for and supports VDL Mode 2 operations for the Eurocontrol datalink and the FAA CPDLC projects. The PAE T6 Series also supports the VDL based FIS-DL (Flight Information Services - Data Link). Using a VDL Mode 2 broadcast mode PAE T6 Series is widely deployed providing an uplink data service for airlines. VDL Mode 2 is defined in ETSI document EN301 841. VDL Mode 3 Using Time Division Multiple Access (TDMA), provides four discrete channels, each channel may be used for either digitised voice or data. VDL Mode 3 requires a DSP radio architecture with ultra-linear RF stages to transmit and receive data at 31,500 bits per second using modulation mode called Digital Eight Phase Shift Keying (D8PSK). The ITT/Park Air CAVU 2100 MDR Team using PAE T6 MDR technology has been awarded the FAA MDR programme and will provide VHF communications services at voice (25 and 8.33 kHz) and VDL-3. The programme will involve a complete upgrade of ground based radio facilities over the next ten years. Please refer to Park Air Systems News for more information. VDL Mode 4

Self Organising Time Division Multiple Access (STDMA) enables both air-to-ground and air-toair communications. VDL Mode 4 requires a DSP radio architecture with ultra-linear RF stages to transmit and receive data at 19,200 bits per second using modulation mode called GFSK (Gausian Filtered Frequency Shift Keying).

GFSK Differences & Advantages over FSK Modulation Original Post: Can anyone explain GFSK ?? (SIG Forum)

Date: 2000-05-03

The Bluetooth radio chip uses GFSK Modulation. It is natural to assume that GFSK is quite like FSK Modulation, however the differences between the 2 are substantial in implementation and results (output)

ChÝp radio cña Bluetooth sö dông ph¬ng ph¸p ®iÒu chÕ GFSK. GFSK chØ kh¸c FSK ë 2 ®iÓm, ®ã lµ sù bæ xung vµ kÕt qu¶ ra. Question 1 What are the physical Differences between an FSK & GFSK Modulator, and how do their results vary?

Sù kh¸c nhau gi÷a FSK&GFSK, t¹i sao l¹i cã kÕt qu¶ kh¸c nhau? Answer 1 An FSK Modulator is much the same as a GFSK Modulator ,but GFSK uses a Gaussian filter as well. In a GFSK modulator everything is the same as a FSK modulator except that before the baseband pulses (-1, 1) go into the FSK modulator, it is passed through a gaussian filter to make the pulse smoother so to limit its spectral width.

§iÒu chÕ FSK phÇn lín gièng víi GFSK, nhng GFSK l¹i sö dông bé läc Gaussian. Trong bé ®iÒu chÕ GFSK, tÊt c¶ ®Òu gièng FSK trõ mét ®iÓm lµ tríc khi c¸c xung tÝn hiÖu b¨ng c¬ b¶n (-1,1) ®i vµo FSK, nã ®îc ®i qua bé läc Gaussiaan ®Ó lµm cho xung nh½n h¬n vµ h¹n chÕ ®îc ®é réng phæ. Question 2 What is Gaussian Filtering?

Bé läc Gaussian lµ g×? Answer 2 Gaussian filtering is one of the very standard ways for reducing the spectral width, it is called Pulse Shaping. If we use -1 for fc-fd and 1 for fc+fd, once when we jump from -1 to 1 or 1 to -1, the modulated waveform changes rapidly, which introduces large out-of-band spectrum. If we change the pulse going from -1 to 1 as -1, -.98, -.93 ..... .96, .99, 1, and we use this smoother pulse to modulate the carrier, the out-of-band spectrum will be reduced.

Bé läc Gaussian lµ mét trong nh÷ng c¸ch chuÈn mùc ®Ó gi¶m ®é réng phæ, viÖc nµy gäi lµ t¹o h×nh xung. Question 3 So, why is GFSK implemented in Bluetooth Radios , and not FSK , is it cheaper?

Answer 3 The spectral width for FSK is unlimited, comparatively, there is a limitation on GFSK. fc "climbs slowly" to fd in GFSK, However, in the case of FSK, fc "jumps sharply" to fd, which greatly decreases spectral efficiency. GFSK is not implemented in the Bluetooth radio unit for cheaper chips (since you need to put an extra pulse-shaping filter in front of the modulator), but for spectral efficiency