1. A method for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said method comprising: finding a codevector in relation to at least one first wideband signal encoding parameter of said set; calculating a first factor representative of voicing in the wideband signal in response to at least one second wideband signal encoding parameter of said set; calculating a second factor representative of stability of said wideband signal in response to at least one third wideband signal encoding parameter of said set; calculating a smoothing gain in relation to said first and second factors; and amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

2. A gain-smoothed codevector producing method as claimed in claim 1 , wherein: finding a codevector comprises finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and the smoothing gain calculation comprises calculating the smoothing gain also in relation to an innovative codebook gain forming a fourth wideband signal encoding parameter of said set.

3. A gain-smoothed codevector producing method as claimed in claim 1 , wherein: finding a codevector comprises finding a codevector in a codebook in relation to said at least one first wideband signal encoding parameter; and said at least one first wideband signal encoding parameter comprises an innovative codebook index.

4. A gain-smoothed codevector producing method as claimed in claim 1 , wherein: finding a codevector comprises finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and said at least one second wideband signal encoding parameter comprises the following parameters: a pitch gain computed during encoding of the wideband signal; a pitch delay computed during encoding of the wideband signal; an index j of a low-pass filter selected during encoding of the wideband signal and applied to a pitch codevector computed during encoding of the wideband signal; and an innovative codebook index computed during encoding of the wideband signal.

5. A gain-smoothed codevector producing method as claimed in claim 1 , wherein said at least one third wideband signal encoding parameter comprises coefficients of a linear prediction filter calculated during encoding of the wideband signal.

6. A gain-smoothed codevector producing method as claimed in claim 1 , wherein: finding a codevector comprises finding an innovative codevector in an innovative codebook in relation to an index k of said innovative codebook, said index k forming said at least one first wideband signal encoding parameter; and calculating a first factor comprises computing a voicing factor rv by means of the following relation:', 'rv = (Ev - Ec) / (Ev + Ec)', 'where: - Ev is the energy of a scaled adaptive codevector bvT;', '- Ec is the energy of a scaled innovative codevector gck; b is a pitch gain computed during encoding of the wideband signal;', 'T is a pitch delay computed during encoding of the wideband signal;', '- vT is an adaptive codebook vector at pitch delay T; g is an innovative codebook gain computed during encoding of the wideband signal; k is an index of the innovative codebook computed during encoding of the wideband signal; and ck is the innovative codevector of said innovative codebook at index k.

7. A gain-smoothed codevector producing method as claimed in claim 6, wherein the voicing factor rv has a value located between -1 and 1 , wherein value 1 corresponds to a pure voiced signal and value -1 corresponds to a pure unvoiced signals.

8. A gain-smoothed codevector producing method as claimed in claim 7, wherein calculating a smooting gain comprises computing a factor λ using the following relation: λ = 0.5 (1 - rv).

9. A gain-smoothed codevector producing method as claimed in claim 6, wherein a factor λ=0 indicates a pure voiced signal and a factor λ=1 indicates a pure unvoiced signal

10. A gain-smoothed codevector producing method as claimed in claim 1 , wherein calculating a second factor comprises determining a distance measure giving a similarity between adjacent, successive linear prediction filters computed during encoding of the wideband signal

11. A gain-smoothed codevector producing method as claimed in claim 10, wherein: the wideband signal is sampled prior to encoding, and is processed by frames during encoding and decoding; and determining a distance measure comprises calculating an Immitance Spectral Pair distance measure between the Immitance Spectral Pairs in a present frame n of the wideband signal and the Immitance Spectral Pairs of a past frame n-1 of the wideband signal through the following relation:', 'D = âx88x91 (isp? - ispSUBi "0 f1=1', 'where p is the order of the linear prediction filters

12. A gain-smoothed codevector producing method as claimed in claim 11 , wherein calculating a second factor comprises mapping the Immitance Spectral Pair distance measure Ds to said second factor θ through the following relation: θ =1.25 - D / 400000.0', 'bounded by 0 âx89¤Î¸. <1

13. A gain-smoothed codevector producing method as claimed in claim 1 , wherein calculating a smoothing gain comprises calculating a gain smoothing factor Sm based on both the first λ and second θ factors through the following relation:14. A gain-smoothed codevector producing method as claimed in claim 13, wherein the factor Sm has a value approaching 1 for an unvoiced and stable wideband signal, and a value approaching 0 for a pure voiced wideband signal or an unstable wideband signal

15. A gain-smoothed codevector producing method as claimed in claim 1 , wherein: finding a codevector comprises finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; the wideband signal is sampled prior to encoding, and is processed by frames and subframes during encoding and decoding; and calculating a smoothing gain comprises computing an initial modified gain gO by comparing an innovative codebook gain g computed during encoding of the wideband signal to a threshold given by the initial modified gain from the past subframe g-1 as follows:', 'if g

18. A method for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said method comprising: finding a codevector in relation to at least one first wideband signal encoding parameter of said set; calculating a factor representative of voicing in the wideband signal in response to at least one second wideband signal encoding parameter of said set; calculating , in relation to said voicing representative factor, a smoothing gain using a non linear operation; and amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector

19. A method for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said method comprising: finding a codevector in relation to at least one first wideband signal encoding parameter of said set; calculating a factor representative of stability of said wideband signal in response to at least one second wideband signal encoding parameter of said set; calculating, in relation to said stability representative factor, a smoothing gain using a non linear operation; and amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

20. A device for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said device comprising: a codevector finder supplied with at least one first wideband signal encoding parameter of said set, and delivering a codevector found in relation to said at least one first wideband signal encoding parameter; a voicing factor calculator supplied with at least one second wideband signal encoding parameter of said set, and delivering a first factor representative of voicing in the wideband signal in response to said at least one second wideband signal encoding parameter; a stability factor calculator supplied with at least one third wideband signal encoding parameter of said set, and delivering a second factor representative of stability of said wideband signal in response to said at least one third wideband signal encoding parameter; a smoothing gain calculator supplied with the first and second factors, and delivering a smoothing gain in relation to said first and second factors; and an amplifier supplied with both the found codevector and the smoothing gain, and amplifying said found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

21. A device for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said device comprising: means for finding a codevector in relation to at least one first wideband signal encoding parameter of said set; means for calculating a first factor representative of voicing in the wideband signal in response to at least one second wideband signal encoding parameter of said set; means for calculating a second factor representative of stability of said wideband signal in response to at least one third wideband signal encoding parameter of said set; means for calculating a smoothing gain in relation to said first and second factors; and means for amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

22. A gain-smoothed codevector producing device as claimed in claim 21 , wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and the smoothing gain calculating means comprises means for calculating the smoothing gain also in relation to an innovative codebook gain forming a fourth wideband signal encoding parameter of said set.

23. A gain-smoothed codevector producing device as claimed in claim 21 , wherein: the means for finding a codevector comprises means for finding a codevector in a codebook in relation to said at least one first wideband signal encoding parameter; and said at least one first wideband signal encoding parameter comprises an innovative codebook index.

24. A gain-smoothed codevector producing device as claimed in claim 21 , wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and said at least one second wideband signal encoding parameter comprises the following parameters: a pitch gain computed during encoding of the wideband signal; a pitch delay computed during encoding of the wideband signal; an index j of a low-pass filter selected during encoding of the wideband signal and applied to a pitch codevector computed during encoding of the wideband signal; and an innovative codebook index computed during encoding of the wideband signal.

25. A gain-smoothed codevector producing device as claimed in claim 21 , wherein said at least one third wideband signal encoding parameter comprises coefficients of a linear prediction filter calculated during encoding of the wideband signal.

26. A gain-smoothed codevector producing device as claimed in claim 21 , wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to an index k of said innovative codebook, said index k forming said at least one first wideband signal encoding parameter; and the means for calculating a first factor comprises means for computing a voicing factor rv by means of the following relation:', 'rv = (Ev - Ec) / (Ev + Ec)', 'where:', 'Ev is the energy of a scaled adaptive codevector bvT; - Ec is the energy of a scaled innovative codevector gck; b is a pitch gain computed during encoding of the wideband signal;', '- T is a pitch delay computed during encoding of the wideband signal; - vT is an adaptive codebook vector at pitch delay T; g is an innovative codebook gain computed during encoding of the wideband signal;', '- âx96xa0 k is an index of the innovative codebook computed during encoding of the wideband signal; and - ck is the innovative codevector of said innovative codebook at index k.

27. A gain-smoothed codevector producing device as claimed in claim 26, wherein the voicing factor rv has a value located between -1 and 1 , wherein value 1 corresponds to a pure voiced signal and value -1 corresponds to a pure unvoiced signals.

28. A gain-smoothed codevector producing device as claimed in claim 27, wherein the means for calculating a smoothing gain comprises means for computing a factor λ using the following relation:', 'λ = 0.5 (1 - rv).

29. A gain-smoothed codevector producing device as claimed in claim 28, wherein a factor λ=0 indicates a pure voiced signal and a factor λ=1 indicates a pure unvoiced signal.

30. A gain-smoothed codevector producing device as claimed in claim 21 , wherein the means for calculating a second factor comprises means for determining a distance measure giving a similarity between adjacent, successive linear prediction filters computed during encoding of the wideband signal.

31. A gain-smoothed codevector producing device as claimed in claim 30, wherein: the wideband signal is sampled prior to encoding, and is processed by frames during encoding and decoding; and the means for determining a distance measure comprises means for calculating an Immitance Spectral Pair distance measure between the Immitance Spectral Pairs in a present frame n of the wideband signal and the Immitance Spectral Pairs of a past frame n-1 of the wideband signal through the following relation: D^ âx88x91 Osp^ - ispSUBt0)2 ι=l', 'where p is the order of the linear prediction filters.

32. A gain-smoothed codevector producing device as claimed in claim 31 , wherein the means for calculating a second factor comprises means for mapping the Immitance Spectral Pair distance measure Ds to said second factor θ through the following relation:', 'θ =1.25 - Ds / 400000.0', 'bounded by 0 âx89¤Î¸. <1.

33. A gain-smoothed codevector producing device as claimed in claim 21 , wherein the means for calculating a smoothing gain comprises means for calculating a gain smoothing factor Sm based on both the first λ and second θ factors through the following relation:', 'Sm = λθ

34. A gain-smoothed codevector producing device as claimed in claim 33, wherein the factor Sm has a value approaching 1 for an unvoiced and stable wideband signal, and a value approaching 0 for a pure voiced wideband signal or an unstable wideband signal.

35. A gain-smoothed codevector producing device as claimed in claim 21 , wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; the wideband signal is sampled prior to encoding, and is processed by frames and subframes during encoding and decoding; and the means for calculating a smoothing gain comprises means for computing an initial modified gain gO , said initial modified gain computing means comprising means for comparing an innovative codebook gain g computed during encoding of the wideband signal to a threshold given by the initial modified gain from the past subframe g-1 as follows:', 'if gg-1.

36. A gain-smoothed codevector producing method as claimed in claim 35, wherein the means for calculating a smoothing gain comprises means for determining said smoothing gain through the following relation:', '

37. A device for producing a gain-smoothed codevector during decoding of an encoded signal from a set of signal encoding parameters, said signal containing stationary background noise and said device comprising: means for finding a codevector in relation to at least one first signal encoding parameter of said set; means for calculating at least one factor representative of stationary background noise in the signal in response to at least one second wideband signal encoding parameter of said set; means for calculating, in relation to said noise representative factor, a smoothing gain using a non linear operation; and means for amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

38. A device for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said device comprising: means for finding a codevector in relation to at least one first wideband signal encoding parameter of said set; means for calculating a factor representative of voicing in the wideband signal in response to at least one second wideband signal encoding parameter of said set; means for calculating, in relation to said voicing representative factor, a smoothing gain using a non linear operation; and means for amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

39. A device for producing a gain-smoothed codevector during decoding of an encoded wideband signal from a set of wideband signal encoding parameters, said device comprising: means for finding a codevector in relation to at least one first wideband signal encoding parameter of said set; means for calculating a factor representative of stability of said wideband signal in response to at least one second wideband signal encoding parameter of said set; means for calculating, in relation to said stability representative factor, a smoothing gain using a non linear operation; and means for amplifying the found codevector with said smoothing gain to thereby produce said gain-smoothed codevector.

40. A cellular communication system for servicing a large geographical area divided into a plurality of cells, comprising: mobile transmitter/receiver units; cellular base stations respectively situated in said cells; means for controlling communication between the cellular base stations; a bidirectional wireless communication sub-system between each mobile unit situated in one cell and the cellular base station of said one cell, said bidirectional wireless communication sub-system comprising in both the mobile unit and the cellular base station (a) a transmitter including a decoder for encoding a wideband signal and means for transmitting the encoded wideband signal, and (b) a receiver including means for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal; wherein said decoder comprises means responsive to a set of wideband signal encoding parameters for decoding the received encoded wideband signal, and wherein said wideband signal decoding means comprises a device as recited in claim 21 , for producing a gain-smoothed codevector during decoding of the encoded wideband signal from said set of wideband signal encoding parameters.

41. The cellular communication system of claim 40, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and the smoothing gain calculating means comprises means for calculating the smoothing gain also in relation to an innovative codebook gain forming a fourth wideband signal encoding parameter of said set.

42. The cellular communication system of claim 40, wherein: the means for finding a codevector comprises means for finding a codevector in a codebook in relation to said at least one first wideband signal encoding parameter; and said at least one first wideband signal encoding parameter comprises an innovative codebook index.

43. The cellular communication system of claim 40, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and said at least one second wideband signal encoding parameter comprises the following parameters: a pitch gain computed during encoding of the wideband signal; a pitch delay computed during encoding of the wideband signal; an index j of a low-pass filter selected during encoding of the wideband signal and applied to a pitch codevector computed during encoding of the wideband signal; and an innovative codebook index computed during encoding of the wideband signal.

44. The cellular communication system of claim 40, wherein said at least one third wideband signal encoding parameter comprises coefficients of a linear prediction filter calculated during encoding of the wideband signal.

45. The cellular communication system of claim 40, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to an index k of said innovative codebook, said index k forming said at least one first wideband signal encoding parameter; and the means for calculating a first factor comprises means for computing a voicing factor rv by means of the following relation:', 'rv = (Ev - Ec) / (Ev + Ec)', 'where:', 'Ev is the energy of a scaled adaptive codevector bvT; Ec is the energy of a scaled innovative codevector gck;', '- b is a pitch gain computed during encoding of the wideband signal; - T is a pitch delay computed during encoding of the wideband signal; vT is an adaptive codebook vector at pitch delay T; g is an innovative codebook gain computed during encoding of the wideband signal; - k is an index of the innovative codebook computed during encoding of the wideband signal; and', '- ck is the innovative codevector of said innovative codebook at index k.

46. The cellular communication system of claim 45, wherein the voicing factor rv has a value located between -1 and 1 , wherein value 1 corresponds to a pure voiced signal and value -1 corresponds to a pure unvoiced signals.

47. The cellular communication system of claim 46, wherein the means for calculating a smoothing gain comprises means for computing a factor λ using the following relation:', 'λ = 0.5 (1 - rv).

48. The cellular communication system of claim 47, wherein a factor λ=0 indicates a pure voiced signal and a factor λ=1 indicates a pure unvoiced signal.

49. The cellular communication system of claim 40, wherein the means for calculating a second factor comprises means for determining a distance measure giving a similarity between adjacent, successive linear prediction filters computed during encoding of the wideband signal.

50. The cellular communication system of claim 49, wherein: the wideband signal is sampled prior to encoding, and is processed by frames during encoding and decoding; and the means for determining a distance measure comprises means for calculating an Immitance Spectral Pair distance measure between the Immitance Spectral Pairs in a present frame n of the wideband signal and the Immitance Spectral Pairs of a past frame n-1 of the wideband signal through the following relation:', 'Ds = __ (isp!° - ispSUBι*-!))2 ι=l', 'where p is the order of the linear prediction filters.

51. The cellular communication system of claim 50, wherein the means for calculating a second factor comprises means for mapping the Immitance Spectral Pair distance measure Ds to said second factor θ through the following relation:', 'θ =1.25 - D / 400000.0', 'bounded by 0 âx89¤Î¸ <1.

52. The cellular communication system of claim 40, wherein the means for calculating a smoothing gain comprises means for calculating a gain smoothing factor Sm based on both the first λ and second θ factors through the following relation:', '

53. The cellular communication system of claim 52, wherein the factor Sm has a value approaching 1 for an unvoiced and stable wideband signal, and a value approaching 0 for a pure voiced wideband signal or an unstable wideband signal.

54. The cellular communication system of claim 40, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; the wideband signal is sampled prior to encoding, and is processed by frames and subframes during encoding and decoding; and the means for calculating a smoothing gain comprises means for computing an initial modified gain gO , said initial modified gain computing means comprising means for comparing an innovative codebook gain g computed during encoding of the wideband signal to a threshold given by the initial modified gain from the past subframe g-1 as follows:', 'if g

55. The cellular communication system of claim 54, wherein the means for calculating a smoothing gain comprises means for determining said smoothing gain through the following relation:', '

56. A cellular network element comprising ( a) a transmitter including an encoder for encoding a wideband signal and means for transmitting the encoded wideband signal, and ( b) a receiver including means for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal; wherein said decoder comprises means responsive to a set of wideband signal encoding parameters for decoding the received encoded wideband signal, and wherein said wideband signal decoding means comprises a device as recited in claim 21 , for producing a gain-smoothed codevector during decoding of the encoded wideband signal from said set of wideband signal encoding parameters.

57. A cellular netword element as claimed in claim 56, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and the smoothing gain calculating means comprises means for calculating the smoothing gain also in relation to an innovative codebook gain forming a fourth wideband signal encoding parameter of said set.

58. A cellular network element as claimed in claim 56, wherein: the means for finding a codevector comprises means for finding a codevector in a codebook in relation to said at least one first wideband signal encoding parameter; and said at least one first wideband signal encoding parameter comprises an innovative codebook index.

59. A cellular network element as claimed in claim 56, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; and said at least one second wideband signal encoding parameter comprises the following parameters: a pitch gain computed during encoding of the wideband signal; a pitch delay computed during encoding of the wideband signal; an index j of a low-pass filter selected during encoding of the wideband signal and applied to a pitch codevector computed during encoding of the wideband signal; and an innovative codebook index computed during encoding of the wideband signal.

60. A cellular network element as claimed in claim 56, wherein said at least one third wideband signal encoding parameter comprises coefficients of a linear prediction filter calculated during encoding of the wideband signal.

61. A cellular network element as claimed in claim 56, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to an index k of said innovative codebook, said index k forming said at least one first wideband signal encoding parameter; and the means for calculating a first factor comprises means for computing a voicing factor rv by means of the following relation:', 'rv = (Ev - Ec) / (Ev + Ec)', 'where:', 'Ev is the energy of a scaled adaptive codevector bvT;', 'Ec is the energy of a scaled innovative codevector gck; - b is a pitch gain computed during encoding of the wideband signal;', 'T is a pitch delay computed during encoding of the wideband signal; vT is an adaptive codebook vector at pitch delay T; - g is an innovative codebook gain computed during encoding of the wideband signal; k is an index of the innovative codebook computed during encoding of the wideband signal; and ck is the innovative codevector of said innovative codebook at index k.

62. A cellular network element as claimed in claim 61 , wherein the voicing factor rv has a value located between -1 and 1 , wherein value 1 corresponds to a pure voiced signal and value -1 corresponds to a pure unvoiced signals.

63. A cellular network element as claimed in claim 62, wherein the means for calculating a smoothing gain comprises means for computing a factor λ using the following relation:', 'λ = 0.5 (1 - rv).

64. A cellular network element as claimed in claim 63, wherein a factor λ=0 indicates a pure voiced signal and a factor λ=1 indicates a pure unvoiced signal.

65. A cellular network element as claimed in claim 56, wherein the means for calculating a second factor comprises means for determining a distance measure giving a similarity between adjacent, successive linear prediction filters computed during encoding of the wideband signal.

66. A cellular network element as claimed in claim 65, wherein: the wideband signal is sampled prior to encoding, and is processed by frames during encoding and decoding; and the means for determining a distance measure comprises means for calculating an Immitance Spectral Pair distance measure between the Immitance Spectral Pairs in a present frame n of the wideband signal and the Immitance Spectral Pairs of a past frame n-1 of the wideband signal through the following relation:', 'p-i', 'D.s = âx88x91 (ispÏx8an) - isPSUBi("-l))2 i=l where p is the order of the linear prediction filters.

67. A cellular network element as claimed in claim 66, wherein the means for calculating a second factor comprises means for mapping the', 'Immitance Spectral Pair distance measure Ds to said second factor θ through the following relation:', 'θ =1.25 - D 400000.0', 'bounded by 0 âx89¤Î¸ <1.

68. A cellular network element as claimed in claim 56, wherein the means for calculating a smoothing gain comprises means for calculating a gain smoothing factor Sm based on both the first λ and second θ factors through the following relation:', 'λθ

69. A cellular network element as claimed in claim 68, wherein the factor Sm has a value approaching 1 for an unvoiced and stable wideband signal, and a value approaching 0 for a pure voiced wideband signal or an unstable wideband signal.

70. A cellular network element as claimed in claim 56, wherein: the means for finding a codevector comprises means for finding an innovative codevector in an innovative codebook in relation to said at least one first wideband signal encoding parameter; the wideband signal is sampled prior to encoding, and is proces