Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 1938

d) transmitter decay. Note.— The definitions of the stages are given in Sections 6.9.5.2.3.1 to 6.9.5.2.3.4. 6.9.5.1.4.3 Automatic transmitter shutdown. A VDL Mode 4 station shall automatically shut-down power to any final stage amplifier in the event that output power from that amplifier exceeds –30 dBm for more than 1 second. Reset to an operational mode for the affected amplifier shall require a manual operation. Note.— This is intended to protect the shared channel resource against so-called “stuck transmitters”. 6.9.5.1.5 NOTIFICATION SERVICES 6.9.5.1.5.1 Signal quality. The operational parameters of the equipment shall be monitored at the physical layer. Signal quality analysis shall be performed in the demodulator process and in the receive process. Note.— Processes that may be evaluated in the demodulator include bit error rate (BER), signal to noise ratio (SNR), and timing jitter. Processes that may be evaluated in the receiver include received signal level and group delay. 6.9.5.1.5.2 Arrival time. The arrival time of each received transmission shall be measured with a two-sigma error of 5 microseconds. 6.9.5.1.5.3 Recommendation.— The receiver should be capable of measuring the arrival time within a two-sigma error of 1 microsecond. 6.9.5.2 PROTOCOL DEFINITION FOR GFSK 6.9.5.2.1 Modulation scheme. The modulation scheme shall be GFSK. The first bit transmitted (in the training sequence) shall be a high tone and the transmitted tone shall be toggled before transmitting a 0 (i.e. non-return to zero inverted encoding). 6.9.5.2.2 Modulation rate. Binary ones and binary zeros shall be generated with a modulation index of 0.25 ± 0.03 and a BT product of 0.28 ± 0.03, producing data transmission at a bit rate of 19 200 bits/s ± 50 ppm. 6.9.5.2.3 STAGES OF TRANSMISSION 6.9.5.2.3.1 Transmitter power stabilization. The first segment of the training sequence is the transmitter power stabilization, which shall have a duration of 16 symbol periods. The transmitter power level shall be no less than 90 per cent of the steady state power level at the end of the transmitter power stabilization segment. 6.9.5.2.3.2 Bit synchronization. The second segment of the training sequence shall be the 24-bit binary sequence 0101 0101 0101 0101 0101 0101, transmitted from left to right immediately before the start of the data segment. 6.9.5.2.3.3 Ambiguity resolution and data transmission. The transmission of the first bit of data shall start 40 bit intervals (approximately 2 083.3 microseconds) ± 1 microsecond after the nominal start of transmission. Note 1.— This is referenced to emissions at the output of the antenna. Note 2.— Ambiguity resolution is performed by the link layer. Part I Annex 10 — Aeronautical Communications I-6-23 22/11/07 6.9.5.2.3.4 Transmitter decay. The transmitted power level shall decay at least by 20 dB within 300 microseconds after completing a transmission. The transmitter power level shall be less than -90 dBm within 832 microseconds after completing a transmission. 6.9.5.3 CHANNEL SENSING 6.9.5.3.1 Estimation of noise floor. A VDL Mode 4 station shall estimate the noise floor based on power measurements of the channel whenever a valid training sequence has not been detected. 6.9.5.3.2 The algorithm used to estimate the noise floor shall be such that the estimated noise floor shall be lower than the maximum power value measured on the channel over the last minute when the channel is regarded as idle. Note.— The VDL Mode 4 receiver uses an energy sensing algorithm as one of the means to determine the state of the channel (idle or busy). One algorithm that can be used to estimate the noise floor is described in the Manual on VDL Mode 4 Technical Specifications. 6.9.5.3.3 Channel idle to busy detection. A VDL Mode 4 station shall employ the following means to determine the channel idle to busy transition at the physical layer. 6.9.5.3.3.1 Detection of a training sequence. The channel shall be declared busy if a VDL Mode 4 station detects a valid training sequence followed by a frame flag. 6.9.5.3.3.2 Measurement of channel power. Regardless of the ability of the demodulator to detect a valid training sequence, a VDL Mode 4 station shall consider the channel busy with at least a 95 per cent probability within 1 ms after onchannel power rises to the equivalent of at least four times the estimated noise floor for at least 0.5 milliseconds. 6.9.5.3.4 CHANNEL BUSY TO IDLE DETECTION 6.9.5.3.4.1 A VDL Mode 4 station shall employ the following means to determine the channel busy to idle transition. 6.9.5.3.4.2 Measurement of transmission length. When the training sequence has been detected, the channel busy state shall be held for a period of time at least equal to 5 milliseconds, and subsequently allowed to transition to the idle state based on measurement of channel power. 6.9.5.3.4.3 Measurement of channel power. When not otherwise held in the channel busy state, a VDL Mode 4 station shall consider the channel idle with at least a 95 per cent probability if on-channel power falls below the equivalent of twice the estimated noise floor for at least 0.9 milliseconds. 6.9.5.4 RECEIVER/TRANSMITTER INTERACTION 6.9.5.4.1 Receiver to transmitter turnaround time. A VDL Mode 4 station shall be capable of beginning the transmission of the transmitter power stabilization sequence within 16 microseconds after terminating the receiver function. 6.9.5.4.2 Frequency change during transmission. The phase acceleration of the carrier from the start of the synchronization sequence to the data end flag shall be less than 300 Hz per second. 6.9.5.4.3 Transmitter to receiver turnaround time. A VDL Mode 4 station shall be capable of receiving and demodulating with nominal performance an incoming signal within 1 ms after completing a transmission. Note.— Nominal performance is defined as a bit error rate (BER) of 10–4. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-6-24 6.9.5.5 PHYSICAL LAYER SYSTEM PARAMETERS 6.9.5.5.1 PARAMETER P1 (MINIMUM TRANSMISSION LENGTH) 6.9.5.5.1.1 A receiver shall be capable of demodulating a transmission of minimum length P1 without degradation of BER. 6.9.5.5.1.2 The value of P1 shall be 19 200 bits. 6.9.5.5.2 PARAMETER P2 (NOMINAL CO-CHANNEL INTERFERENCE PERFORMANCE) 6.9.5.5.2.1 The parameter P2 shall be the nominal co-channel interference at which a receiver shall be capable of demodulating without degradation in BER. 6.9.5.5.2.2 The value of P2 shall be 12 dB. 6.9.5.6 FM BROADCAST INTERFERENCE IMMUNITY PERFORMANCE FOR VDL MODE 4 RECEIVING SYSTEMS 6.9.5.6.1 A VDL Mode 4 station shall conform to the requirements defined in section 6.3.5.4 when operating in the band 117.975–137 MHz. 6.9.5.6.2 A VDL Mode 4 station shall conform to the requirements defined below when operating in the band 108-117.975 MHz. 6.9.5.6.2.1 The VDL Mode 4 receiving system shall meet the requirements specified in 6.3.5.1 in the presence of twosignal, third-order intermodulation products caused by VHF FM broadcast signals having levels in accordance with the following: 2N1 + N2 + 72 ≤ 0 for VHF FM sound broadcasting signals in the range 107.7–108.0 MHz and 3 24 20 log 0.4 Δ ⎧ ⎫ + + − ≤ ⎨ ⎬ ⎩ ⎭ f N N for VHF FM sound broadcasting signals below 107.7 MHz, where the frequencies of the two VHF FM sound broadcasting signals produce, within the receiver, a two-signal, third-order intermodulation product on the desired VDL Mode 4 frequency. N1 and N2 are the levels (dBm) of the two VHF FM sound broadcasting signals at the VDL Mode 4 receiver input. Neither level shall exceed the desensitization criteria set forth in 6.9.5.6.2.2. Δf = 108.1 – f1, where f1 is the frequency of N1, the VHF FM sound broadcasting signal closer to 108.1 MHz. Note.— The FM intermodulation immunity requirements are not applied to a VDL Mode 4 channel operating below 108.1 MHz, and hence frequencies below 108.1 MHz are not intended for general assignments. Part I Annex 10 — Aeronautical Communications I-6-25 22/11/07 6.9.5.6.2.2 The VDL Mode 4 receiving system shall not be desensitized in the presence of VHF FM broadcast signals having levels in accordance with Tables 6-5 and 6-6. 6.9.6 Link layer Note.— Details on link layer functions are contained in the Manual on VDL Mode 4 Technical Specifications. 6.9.7 Subnetwork layer and SNDCF Note.— Details on subnetwork layer functions and SNDCF are contained in the Manual on VDL Mode 4 Technical Specifications. 6.9.8 ADS-B applications Note.— Details on ADS-B application functions are contained in the Manual on VDL Mode 4 Technical Specifications. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-6-26 TABLES FOR CHAPTER 6 Table 6-1. Modes 2 and 3 data encoding Xk Yk Zk Δφk 0 π / 4 1 π / 4 2 π / 4 3 π / 4 4 π / 4 5 π / 4 6 π / 4 7 π / 4 Table 6-2. Modes 2 and 3 modulation stability VDL Mode Aircraft Modulation Stability Ground Modulation Stability Mode 2 ± 0.0050 per cent ± 0.0050 per cent Mode 3 ± 0.0005 per cent ± 0.0002 per cent Table 6-3. Scrambler functions Function Data in Data out scrambling clean data scrambled data descrambling scrambled data clean data Table 6-4. Physical services system parameters Symbol Parameter name Mode 2 value P1 Minimum transmission length 131071 bits Part I Annex 10 — Aeronautical Communications I-6-27 22/11/07 Table 6-5. VDL Mode 4 operating on frequencies between 108.0–111.975 MHz Frequency (MHz) Maximum level of unwanted signal at receiver input (dBm) 88–102 +15 +10 +5 107.9 –10 Table 6-6. VDL Mode 4 operating on frequencies between 112.0–117.975 MHz Frequency (MHz) Maximum level of unwanted signal at receiver input (dBm) 88–104 +15 +10 +5 107.9 Note.— The relationship is linear between adjacent points designated by the above frequencies. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-6-28 FIGURES FOR CHAPTER 6 Figure 6-1. Transmitter power stabilization Figure 6-2. PN-generator for bit scrambling sequence Centre of first symbol of unique word Major divisions are symbol periods Power at 90 per cent by t = 3- -3 -4 -5 -5.5 -2 -1 Data in Data out T

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