FS-1052: Appendix C

FS-1052: Appendix C

APPENDIX C

SIXTEEN-TONE DIFFERENTIAL PHASE-SHIFT KEYING (DPSK) MODE

10. GENERAL

10.1 Scope. This appendix describes the sixteen-tone differential phase-shift keying (DPSK) mode.

10.2 Applicability. This appendix is a nonmandatory part of FED-STD-1052, however, when the optional 16-tone DPSK mode is used, it shall be implemented in accordance with this appendix.

20. APPLICABLE DOCUMENTS. See section 2.

30. DEFINITIONS. See section 3.

40. GENERAL REQUIREMENTS.

40.1 Introduction. The modulator accepts serial binary data signals at the input and converts this information into DPSK data tones transmitted at the modulator output. The input data signaling rate determines the type of modulation and the degree of in-band diversity that is used. The modulation rate of the modulator output signal is constant for all input signaling rates accepted by the modulator. The modulator-demodulator (modem) provides a means for synchronization and, if required, a separate tone for doppler correction. The demodulator accepts the DPSK data tones at the input and reconverts this information into serial binary data signals at the demodulator output.

40.2 Input/output data signaling rates. The modulator input shall accept, and the demodulator output shall deliver, a serial binary bit stream with standard data signaling rates ranging from 75 to 2400 bits per second (b/s).

50. DETAILED REQUIREMENTS

50.1 Modulator output signal. The modulator output signal shall contain 16 DPSK data tones (table XXXI). The 16 data tones shall be simultaneously keyed to produce a signal element interval of 13-1/3 milliseconds (ms) for each data tone. The composite modulator output signal shall have a constant modulation rate of 75 baud for all input data signaling rates from 75 to 2400 b/s. The modulator shall provide a separate tone combination to initiate synchronization and, if required, a separate tone for doppler correction.

TABLE XXXI. Data-tone frequencies and bit locations

Even and odd bit locations of serial binary bit stream, encoded and phase modulated on each data tone employing:
Quadrature-phase modulation Biphase modulation
Tone frequency (hz)

Function

2400 b/s

1200 b/s

 600 b/s

 300 b/s

 150 b/s

 75 b/s

   605

Continuous doppler tone In-band diversity (see par. 50.6)

   825*

Synchronization slot
   935 Data tone  1   1    2   1    2 1 1 1 1
  1045 Data tone  2   3    4   3    4 2 2 2 1
  1155 Data tone  3   5    6   5    6 3 3 1 1
  1265 Data tone  4   7    8   7    8 4 4 2 1
  1375 Data tone  5   9   10   9   10 5 1 1 1
  1485 Data tone  6  11   12  11   12 6 2 2 1
  1595 Data tone  7  13   14  13   14 7 3 1 1
  1705 Data tone  8  15   16  15   16 8 4 2 1
  1815 Data tone  9  17   18   1    2 1 1 1 1
  1925 Data tone 10  19   20   3    4 2 2 2 1
  2035 Data tone 11  21   22   5    6 3 3 1 1
  2145 Data tone 12  23   24   7    8 4 4 2 1
  2255 Data tone 13  25   26   9   10 5 1 1 1
  2365 Data tone 14  27   28  11   12 6 2 2 1
  2475 Data tone 15  29   30  13   14 7 3 1 1
  2585 Data tone 16  31   32  15   16 8 4 2 1
  * No tone is transmitted at this frequency (see par. 50.4).

50.2 Data tone frequencies. The frequency of each data tone shall be as listed in Table XXXII. The tone frequencies shall maintain an accuracy of ±0.1 hertz (Hz).

TABLE XXXII. Modulation characteristics

Input data signaling rate (b/s) Degree of in-band diversity combining Type of modulation Logic sense of dibits or bits in serial binary bit stream depending on: Phase (in degrees) of data tone signal element relative to phase of preceding signal element
Even bit locations Odd bit locations
2400
N/A
Four-phase MARK SPACE +45
SPACE SPACE +135
1200
2
SPACE MARK +225
MARK MARK +315
600
2
Two-phase

MARK*

+315

300
4
150
8

SPACE*

+135

75 16
* Regardless of even or odd bit locations.

50.3 Phase modulation and encoding. For data signaling rates of 75, 150, 300, or 600 b/s at the modulator input, each data tone signal element shall be two-phase (biphase) modulated as shown on Figure 19a. Each bit of the serial binary input signal shall be encoded, depending on the MARK or SPACE logic sense of the bit, into a phase change of the data tone signal element as listed in table XXXII. For data signaling rates of 1200 or 2400 b/s at the modulator input, each data tone signal element shall be four-phase (quadrature-phase) modulated as shown on Figure 19b. Each dibit of the serial binary input signal shall be encoded, depending on the MARK or SPACE logic sense and the even or odd bit location of each bit, into a phase change of the data tone signal element as listed in Table XXXII. The phase changes of the data tone signal elements specified in Table XXXII shall be relative to the phase of the immediately preceding signal element.

Figure 19. Phase modulation vectors for 16-tone DPSK data modem


50.4 Synchronization. Upon receipt of a transmit command, the modem shall initiate a synchronization preamble. The preamble shall consist of two tones with frequencies of 605 Hz and 1705 Hz, for a minimum duration of 66-2/3 ms, corresponding to a duration of 5 to 32 data tone signal elements. The 605 Hz tone shall unmodulated and used for doppler correction, if required. The 1705 Hz tone shall be phase shifted 180 degrees for each data tone signal element and shall be used to obtain proper modem synchronization by the demodulator. During the preamble, the transmitted level of the 605 Hz tone shall be 7 decibels (dB) (±1 dB) higher than the level of the 1705 Hz tone. The composite transmitted signal level of the 605 Hz and 1705 Hz tones during the preamble shall have a root-mean-square (rms) value within ±1 dB of the rms value of the modulator output signal level during data transmission when all 16 data tones plus doppler correction tone are transmitted. At the completion of the preamble, all data tones shall be transmitted for the duration of one signal element (13-1/3 ms) prior to the transmission of data to establish a phase reference. During data transmission, synchronization shall be maintained by sampling the signal energy in the 825 Hz synchronization slot. No tone shall be transmitted in the synchronization slot of 825 Hz.

50.5 Doppler correction. For those applications where a doppler correction capability is required, a tone with a frequency of 605 Hz shall be used. The level of the 605 Hz tone shall be 7 dB (±1 dB) higher than the normal level of any one of the subcarriers.

50.6 In-band diversity combining. In-band diversity combining shall be accomplished at data signaling rates from 75 b/s to 1200 b/s. The data tones shall be combined in accordance with table XXXI. The degree of diversity combining shall be as listed in Table XXXII.

50.7 Demodulator signal alarm. Provisions shall be made in the demodulator to activate an alarm when the incoming signal from the HF radio link decreases below a preset level.

NOTE: The specific techniques and levels to be used for the demodulator signal alarm are not standardized and should be defined in applicable modem specifications.