YD/T 3695-2020Vehicle Emergency Alarm System Based on Public Telecommunication Network Wireless Data Transmission Technology Requirements (English PDF)

3.1 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1.6 MSD data frame

It includes the uplink signal transmission time of one MSD data (after synchronization is established). The duration is 1320 ms. This is equivalent to a total of 10560 samples at 8kHz sampling rate (if a fast modulator is used) or 18560 samples (if a reliable modulator is used).

3.1.7 modulation frame

Symbol transmission time. The duration is 2 ms, equivalent to 16 samples at 8kHz sampling rate (if a fast modulator is used), or 4 ms, equivalent to 32 samples at 8kHz sampling rate (if a reliable modulator is used).

3.1.8 synchronization frame

It includes the signal transmission time of synchronization information. The duration is

260 ms. This is equivalent to 2080 samples at a sampling rate of 8 kHz.

3.2 Abbreviations

The following abbreviations apply to this document.

4.1 Overview of eCall system

Figure 1 gives an overall description of the eCall system.

4.3 eCall in-band modulation architecture

4.3.1 General

The eCall in-band modulation scheme specified in this Standard consists of an IVS data modem and a PSAP data modem. The signal design used allows the signal to pass through the voice vocoder with only moderate distortion and provide sufficient data rate to meet the requirements of transmitting MSD as quickly as possible.

4.3.2 IVS data modem working principle

Figure 3 shows the basic components of an IVS data modem. The MSD information input to the IVS transmitter is first added with CRC check information, and then all bits are input to the HARQ encoder. FEC coding is used to combat transmission errors.

5.1 IVS transmitter

5.1.1 General

The IVS transmitter is used to modulate the MSD data so that it is suitable for in-band transmission over the voice channel to the PSAP. The components of the IVS transmitter are shown in Figure 5.

5.1.3 CRC check code

Each MSD message is preceded by a 28-bit CRC checksum before HARQ FEC encoding.

5.1.4 HARQ FEC encoder

5.1.4.1 Bit scrambling

Bit scrambling is performed on the MSD information after the CRC check is added (before Turbo encoding).

5.1.4.2 Turbo coding

The Turbo encoder scheme used in eCall intra-band modulation consists of two identical 8-state parallel-concatenated convolutional coding (PCCC) sub-encoders and a Turbo code intra-interleaver. The transfer function of the sub-encoder is.

Table 2 -- MSD data frame format

5.1.7 Synchronization signal and frame format

The synchronization frame is composed of the following two parts in series.

5.2.6 Message processing

This function activates the corresponding function of the IVS modem according to the received message. After synchronization lock, once a START message is received, the

IVS transmitter is activated for MSD transmission.

6.1 PSAP transmitter

6.1.1 General

The PSAP transmitter generates downlink transmission signals. These downlink signals are used to control the transmission of uplink MSD. The PSAP transmitter is shown in

Figure 15.

6.1.2 Message encoding

According to the design, the PSAP transmitter can send a total of 16 different link layer messages to the IVS. The following three are currently used.

6.1.3 BCH coding

The link layer feedback uses a truncated (60, 4) BCH block code. This code is generated from the (63, 7) BCH block code. See Table 4 for different messages and their encoding methods.

6.1.5.2 High-level confirmation feedback message

The feedback frame in the high-level feedback message (see 5.1.7) needs to be inverted (i.e. all samples are multiplied by -1). Its frame structure contains two DL-Data fields and a silent interval.

6.1.5.3 Downlink message processing

Before detecting the uplink synchronization frame, the PSAP transmitter sends/retransmits the START message multiple times.

6.1.6 Synchronization

The PSAP synchronization signal is similar to that described in 5.1.7, except that the

PN sequence pulse amplitude is increased by 5000, that is, its pulse amplitude is 25000 and -15000, and the original zero is replaced by a sample with an amplitude of 12000.

For high-level confirmation messages, the above synchronization frame needs to be inverted, that is, each sample is multiplied by -1.

6.2 PSAP receiver

6.2.1 General

The PSAP receiver demodulates the MSD message from the IVS and checks the integrity of the received MSD through CRC check. The block diagram of the PSAP receiver is shown in Figure 17.

7.1 Normal operation

The previous sections describe the eCall data transmission operation under normal circumstances.

7.2 Abnormal operation

This section describes some abnormal situations that occur due to severe signal distortion caused by the transmission channel. These situations need to be handled by the overall transmission protocol to avoid deadlock situations. It shall be noted that the abnormal situations described here are not mutually exclusive.

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