ITU-R F 1111-1-1995 Improved Lincompex System for HF Radiotelephone Circuits《高频无线电话电路的增强型Lincompex系统》.pdf

1、 Rec. ITU-R F.1111-1 1 RECOMMENDATION ITU-R F.1111-1*IMPROVED LINCOMPEX SYSTEM FOR HF RADIOTELEPHONE CIRCUITS (Question ITU-R 146/9) (1994-1995) Rec. ITU-R F.1111-1 The ITU Radiocommunication Assembly, considering a) that, to maintain a satisfactory standard on international radiotelephone circuits

2、operating at frequencies below 30 MHz and connected to the national network, it is necessary to compensate, at the transmitting end, for most, if not all, of the variations in the subscribers speech volume and of the losses between the subscriber and the international exchange; b) that, as a result,

3、 the circuit often operates under a condition of overall gain (two-wire to two-wire) and it is necessary to use a singing-suppressor to maintain stability; c) that, the singing-suppressor markedly degrades the performance of the circuit, due to its switching action and its tendency to mis-operation

4、by noise or interference on the radio path; d) that the use of a singing-suppressor to maintain overall stability of the radiotelephone channel inhibits the interconnection, on a four-wire basis (see ITU-T Recommendation G.101), of radio circuits and long-distance cable or satellite circuits; e) tha

5、t, if HF radiotelephone circuits were operated at a nearly constant overall transmission loss, the singing-suppressor could be eliminated and a radio circuit could be integrated into an international chain; f) that, to maintain a constant overall loss, while catering for variations in subscribers sp

6、eech volume and line loss, it is necessary to insert, at the receiving end of the circuit, a loss equivalent to the gain inserted at the transmitting end; g) that the advantages of compandor operation, as used on some line transmission systems, are well established, but cannot be directly realized o

7、n a radio circuit subject to fading; h) that, on such a radio circuit, an alternative means of conveying information as to the state of the compressor is necessary to control the expander; j) that these alternative means enable advantage to be taken of a compression ratio in excess of that employed

8、in line compandors, which is generally 2/1 or 4/1; k) that the behaviour and advantages of a system employing a linked compressor and expander have been established as applicable to various communications environments; that for HF one administration has reported 22 dB average improvement across time

9、 for typical speech signals under varying propagation conditions with a maximum improvement of 47 dB; l) that these system behaviour and advantages are desired for use with radio circuits having only modest frequency stabilities and various voice channel bandwidths; m) that with such radio circuits

10、loss of voice naturalness can occur as a result of end-to-end frequency error, and that in many cases it is not practical or possible to eliminate the error; _ *This Recommendation should be brought to the attention of Radiocommunication Study Groups 8 and 10. 2 Rec. ITU-R F.1111-1n) that such end-t

11、o-end frequency error has an adverse effect on system behaviour and advantages;o) that the alternative means employed to convey compression information to the expander can also be used toeliminate the effect of end-to-end frequency errors and thereby provide system behaviour and advantages with voic

12、enaturalness;p) that the alternative means employed to convey compression information to the expander and the speechcompression band must both reside within available voice channel bandwidths;q) that it is highly desirable that this system be interoperable with non-equipped stations for applications

13、 innetworks handling mixed traffic;r) that for applications wherein all stations are equipped with the system and interoperability is not an issue, thesystem receive end should maintain silence when no Lincompex signals are being received;s) that with such an arrangement the two ends of a circuit wi

14、ll be complementary and the essential parameters ofthe system will have to be standardized,recommends1 that, wherever possible, HF radiotelephone circuits should be operated on the basis of a constant overalltransmission loss (two-wire to two-wire) and that the system is equally applicable to full-d

15、uplex and half-duplex(simplex) circuits;2 that a system comprising a compressor and expander linked by a control channel, which is separate from thespeech channel and is resistant to fading distortion, should be used to achieve this performance (such a system iscommonly known as Lincompex which is a

16、 convenient acronym for the phrase “linked compressor and expander”.Lincompex is neither a proprietary name nor does it refer to the manufacturer of a particular equipment); and that thecontrol channel should be utilized to correct baseband frequency errors due to radio circuit equipment so as to pr

17、ovidethe advantages of companding and natural voice for the majority of radio circuits;3 that the system should maintain optimum loading of the transmitter at all times despite variations insubscribers speech volumes and line losses;4 that the speech and control signals should both be contained with

18、in a single voice channel (the usable upperaudio frequency of a voice channel in existing equipments is known to vary from 3 kHz to less than 2 kHz depending onequipment design) so that the system is generally applicable to any transmission medium which outputs a usablebaseband signal;5 that such a

19、system should be in accordance with the description and parameters listed below:5.1 GeneralFor convenience, the performance requirements of this Recommendation are based on a system configuration (one end isshown in Fig. 1) which on the transmit side employs pre-compressor delay in conjunction with

20、a voice-signal amplitudeassessor. This does not preclude other configurations which meet the requirements. If desirable, a privacy device couldbe added within the circuit.Four sets of specifications are presented to accommodate the most common voice channel bandwidths found in userequipments. When s

21、pecifications differ between these sets, then each set is identified separately as (A), (B), (C), or (D).(A) provides interoperability with equipment conforming to Recommendation ITU-R F.455 (RF Series, Geneva, 1992).5.2 Transmit side (Fig. 1a)5.2.1 Speech channel5.2.1.1 Steady-state conditions (com

22、pression and overall characteristics)For input levels between + 5 dBm0 to 55 dBm0 (see Note 1 at the end of 5.8) the output should lie within the limitsshown in Fig. 2.Rec. ITU-R F.1111-1 32 700 Hz2 700 Hz3 000 Hz2 800 HzBCDEFHJLGKAMMFIGURE 1Schematic diagram of systemFrequency calibrate commanda) T

23、ransmit sideb) Receive sideHybrid transformerCompressorDelay networkExpanderNote The frequencies in a) and b) are for system (A). A: from landlineB: amplitude assessorC: frequency-modulated oscillatorD: frequency calibrate generatorE: to radio transmitterF: audio from radio receiverG: fading regulat

24、or (constant-volume amplifier)H: frequency calibrate detectorJ: frequency discriminator K: to landlineL: frequency shifterM: privacy deviceD01FIGURE 1/F.1111-1.D01 = 3 CM4 Rec. ITU-R F.1111-1 50 40 30 20 10 0 431 1 1105 5 10 15FIGURE 2Input/output characteristic of transmit sideRelativeoutputlevel(d

25、B)Input level (dBm0)D02FIGURE 2/F.1111-1.D02 = 3 CMThe overall amplitude/frequency response for the speech channel under both fixed-gain and assessor-controlledconditions at any level within the range + 5 dBm0 to 55 dBm0 should be in the range stated in Table 1.TABLE 1Amplitude/frequency responseSys

26、tem A B C DAttenuationAudio bandwidth (Hz) 250-2 500 250-2 380 250-2 000 250-1 575(dB)250-2 500 250-2 200 250-1 850 250-1 455 2Frequency response2 500-2 700 2 200-2 380 1 850-2 000 1 455-1 575 6(attenuation relative to themaximum response)2 800and above2 480and above2 100and above1 675and above 5525

27、0 and below 05.2.1.2 Transient response (overall, including amplitude assessor but excluding additional delay)Attack time, Fig. 3a) (see Note 2 at the end of 5.8) 07 2 msRecovery time, Fig. 3b) (see Note 2 at the end of 5.8) 20 5 msRec. ITU-R F.1111-1 5FIGURE 3Transient response of transmit sidea) A

28、ttack timeOutputAttack timeInputStep of 12 dBOutputRecovery timeInputStep of 12 dBb) Recovery timeV0V02.5 VsVs1.5 Vs0.75 VsVs1.5 VsD03FIGURE 3F/1111-1.D03 = 3 CM6 Rec. ITU-R F.1111-15.2.2 Control channelFrequencies of frequency-modulated oscillator (frequency controlled by amplitude assessor output)

29、 are shown inTable 2.TABLE 2Frequency of frequency-modulated oscillatorSystem A B C DCentre frequency (Hz) 2 900 12 580 12 200 11 775 1Oscillator frequency resulting froman input level of 0 dBm050 Hz lower than the aboveReference frequency deviation 60 HzChange of frequency for each 1 dB change of i

30、nput level (see Fig. 4) 2 HzInput level to transmit side to produce nominal centre frequency 25 dBm0Oscillator frequency increase beyond that 0 Hzcorresponding to 55 dBm0 when there is no input to the transmit side 0 Hzto the transmit side exceeds +5 dBm0 60 dB attenuationEnvelopetiming (ms)Control

31、tonefrequency (Hz)Speech levelControl toneEnvelope amplituderelative to testtone levelD05FIGURE 5/F.1111-1.D05 = 3 CM8 Rec. ITU-R F.1111-15.3 Receive side (Fig. 1b)5.3.1 Speech channel5.3.1.1 Steady-state conditionsThe relative overall amplitude frequency response of the speech channel under fixed a

32、nd controlled gain conditionsshould be in the range stated in Table 1.5.3.1.2 Fading regulator5.3.1.2.1 Steady-state conditionsFor input levels between + 7 dB and 35 dB, relative to the nominal design input level to the fading regulator, the outputshould be within the limits shown in Fig. 6. The nom

33、inal design input level which may vary between administrations isthe value measured at the input of the fading regulator, under steady-state conditions, when 0 dBm0 is applied to thetransmit side.1 6 5 105 8 10 15 16 18 207010 40 30 20 18 10FIGURE 6Input/output characteristic of fading regulatorRela

34、tiveoutputlevel(dB)Relative input level (dB)D06FIGURE 6/F.1111-1.D06 = 3 CM5.3.1.2.2 Transient responseAttack time: (Fig. 7a) 11 2 msRecovery time: (Fig. 7b) 32 6 ms5.3.1.3 Expander (controlled by the discriminator output)Effective dynamic range (dB) 60 dBRec. ITU-R F.1111-1 9FIGURE 7Transient respo

35、nse of fading regulatora) Attack timeb) Recovery time0.75 VsVs1.5 VsOutputAttack timeInput12 dB increaseOutputRecovery timeInput12 dB decreaseVsVsVsD07FIGURE 7/F.1111-1.D07 = 3 CM10 Rec. ITU-R F.1111-15.3.2 Control channel5.3.2.1 Amplitude/frequency and differential-delay characteristics of filterAt

36、tenuation within the band (nominal centre frequency 90 Hz)relative to that at nominal centre frequency. (Nominal centre frequenciesare defined in 5.2.2.) 1 to + 2 dBDifferential delay within the band (nominal centre frequency 60 to + 0 Hz) 55 dB5.3.2.2 Discriminator (Frequency/amplitude translator)C

37、haracteristic at nominal control tone level.Changes in the expander output with changes in the frequency of the control tone should lie within the limits shownin Fig. 8.10 60 540 50 56 30 20 40 10 460+ 40+ 20+ 60+ 80 20 40 60 80FIGURE 8Variation in output level at the receiver side with changein fre

38、quency of the control toneRelative output level (dB)Frequencyofcontroltone (Hz)NominalcentreD08FIGURE 8/F.1111-1.D08 = 3 CM5.3.2.3 Amplitude range of discriminatorThe performance quoted in 5.3.2.2 should be met for control tone input signal levels to the discriminators from 0 dB to30 dB relative to

39、the nominal input level; with control tone input levels between 30 dB and 50 dB relative tonominal, an additional tolerance of 1 dB could be added to the limits shown in Fig. 8. For transmission systems withdiscrete distortion products in the control tone band further reduced operation between 30 dB

40、 and 50 dB may beallowed.5.3.3 Overall attack and recovery time (a sudden change of 24 Hz in the frequency of the control tone is used tosimulate a 12 dB step)Attack time: (Fig. 9a) 20 5 msRecovery time: (Fig. 9b) 20 5 msRec. ITU-R F.1111-1 11FIGURE 9Transient response of receive sideVsAttack timeRe

41、duction in frequencyof 24 Hza) Attack time0.625 Vs0.25 VsRecovery timeIncrease in frequency of24 HzVs2.5 Vsb) Recovery time4VsD09FIGURE 9/F.1111-1.D09 = 3 CM5.3.4 Frequency calibrateWhen enabled, the calibrate detector shall detect the calibrate format defined by 5.2.3. The measurement of frequencye

42、rror shall be used to frequency shift the entire baseband in a direction to correct the error.The first 20 ms of the format is for receiver and transmitter settling and not for calibrate detection.The middle 256 ms of the format should be used for calibrate detection.The last 20 ms of the format is

43、used to determine the received control tone frequency. This presupposes a positivecalibrate detection. Frequency error is defined as the algebraic difference of the measured received control tonefrequency and the transmitted (known) nominal centre control tone frequency.Minimum error to be detected

44、and corrected 80 HzMinimum error design goal 100 HzMaximum post-correction baseband error 2 Hz5.3.5 Receive modesFor operation enhancement and for interoperability with non-Lincompex stations, the following selectable receive modesare defined: Automatic silence: The demodulator shall maintain silenc

45、e except in the presence of a received Lincompex signal.Frequency calibrate shall be selectable.12 Rec. ITU-R F.1111-1 Automatic bypass: The demodulator shall ascertain the presence and absence of usable Lincompex signals (seeNote 1).A usable Lincompex signal is defined as one which upon demodulatio

46、n provides aural advantages to thelistener. If a usable signal is present, Lincompex demodulation shall proceed. If a usable signal is not present, thefading regulator and expander shall be made linear. Speech filters shall remain in place. Frequency calibrate shall beselectable.NOTE 1 This determin

47、ation is subjective but also objective in that enhanced low S/N operation depends ondemodulation design techniques. Experience shows that adequate demodulation is possible for voice channel S/N inthe 0 dB to + 10 dB range. Bypass: The fading regulator and expander are made linear. Speech filters rem

48、ain in place. Frequency calibrate isselectable. Wideband: Same as bypass except that the speech bandwidth is 150 Hz to 3 400 Hz within 2 dB. Speech filters arebypassed. Frequency calibrate is selectable.5.4 Equalization (overall) of transmission timeTo ensure a reasonable transmission standard, in p

49、articular of tone pulses, such as would be used for ringing orsignalling, the overall transmission times of the speech and control channels should be equalized at the input to theexpander to within 4 ms.To ensure that this can be achieved with independent designs of equipment, the time equalization provided should bedivided equally between the transmit and receive sides of the equipment.5.5 Ringing and diallingCare should be taken to ens