FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] ENCODING DEVICE, DECODING DEVICE, AND METHOD THEREOF; PANASONIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 5718501, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. Technical Field The present invention relates to a coding apparatus, a decoding apparatus and a method thereof used in a communication system for encoding and transmitting signals. Background Art When speech or sound signals are transmitted by a packet communication system typified by internet communication, a mobile communication system and so forth, compression and coding techniques are commonly used in order to improve t h e efficiency of transmission of speech or sound signals. In addition, in recent years, there is an increasing need for not only a technique to simply encode speech or sound signals at a low bit rate but also a technique to encode wider band speech or sound signals. To meet this need, various techniques for encoding wideband speech or sound signals without significantly increasing the amount of information after coding have been developed. For example, according to Patent Document I, spectral data is obtained by converting acoustic signals inputted in a certain period of time and the characteristic of a high frequency band of this spectral data is generated as auxiliary information and outputted with encoded information of a low frequency band. To be more specific. spectral data of a high frequency band is divided into a plurality of groups, and information to specify the low frequency band spectrum most similar to the spectrum of each group is provided as auxiliary information. In addition, according to Patent Document 2, discloses a technique for dividing a high frequency band signal into a plurality of subbands, determining the degree of similarity between a signal in each subband and a low frequency band signal and modifying, depending on the determination result, the content of information (the amplitude parameter in each subband, the position parameter of the similar low frequency band signal and the signal parameter of the difference between the high frequency band and the low frequency band. Patent Document I: Japanese Patent Application Laid-Open No.2003-140692 Patent Document 2; Japanese Patent Application Laid-Open No.2004-4530 Disclosure of Invention Problems to be Solved by the Invention However, according to the above-described Patent Document 1 and Patent Document 2. in order to generate a higher frequency band signal (spectral data of a higher frequency band), a lower frequency band signal similar to the higher frequency band signal is decided individually per subband (group) of the higher frequency band signal, and therefore the efficiency of coding is not sufficient. In particular, when auxiliary information is encoded at a low bit rate, the quality of decoded speech generated using calculated auxiliary information is not satisfactory and noise may occur depending on cases. It is therefore an object of the present invention to provide a coding apparatus, a decoding apparatus and a method of the same that make possible to efficiently encode spectral data of the higher frequency band based on spectral data of the lower frequency band of a broadband signal and improve the quality of a decoded signal. Means for Solving the Problem The coding apparatus according to the present invention adopts a configuration to include: a first coding section that encodes a low frequency band of an input signal equal to or lower than a predetermined frequency to generate first encoded information; a decoding section that decodes the first encoded information to generate a decoded signal; and a second coding section that generates second encoded information by dividing a high frequency band of the input signal higher than the predetermined frequency into a plurality of subbands and estimating each of the plurality of subbands based on the input signal or the decoded signal, using an estimation result from a neighboring subband. The decoding apparatus according to the present invention adopts a configuration to include: a receiving section that receives first encoded information generated in a coding apparatus and obtained by encoding a low frequency band of an input signal equal to or lower than a predetermined frequency and second encoded information obtained by dividing a high frequency band of the input signal higher than the predetermined frequency into a plurality of subbands and estimating each of the plurality of subbands based on the input signal or a first decoded signal obtained by decoding the first encoded information using an estimation result in a neighboring subband; a first decoding section that decodes the first encoded information to generate a second decoded signal; and a second decoding section that generates a third decoded signal by estimating the high frequency band of the input signal based on the second decoded signal using the decoded result in the neighboring subband obtained by using the second encoded information. The coding method of the present invention includes the steps of: encoding a low frequency band of an input signal equal to or lower than a predetermined frequency to generate first encoded information; decoding the first encoded information to generate a decoded signal; and generating second encoded information by dividing a high frequency band of the input signal higher than the predetermined frequency into a plurality of subbands and estimating each of the plurality of subbands using an estimation result in a neighboring subband. The decoding method of the present invention includes the steps of: receiving first encoded information that is generated in a coding apparatus and obtained by encoding a low frequency band of an input signal lower than a predetermined frequency and second encoded information that is obtained by dividing a high frequency band of the input signal higher than the predetermined frequency into a plurality of subbands and estimating each of the plurality of subbands based on the input signal or a first decoded signal obtained by decoding the first encoded information, using an estimation result in a neighboring subband; decoding the first encoded information to generate a second decoded signal; and generating a third decoded signal by estimating the high frequency band of the input signal based on the second decoded signal, using a decoded result in the neighboring subband obtained by using the second encoded information. Advantageous Effects of Invention According to the present invention, in order to generate spectra] data of a high frequency band of a signal to be encoded based on spectral data of a low frequency band, it is possible to efficiently encode spectral data of the high frequency band of a wideband signal and improve the quality of a decoded signal by performing coding based on the coding result in the neighboring subband, using correlation between high frequency subbands. Brief Description of Drawings FIG. 1 is a drawing explaining a summary of a search processing included in coding according to the present invention; FIG.2 is a block diagram showing a configuration of a communication system having a coding apparatus and a decoding apparatus according to Embodiment 1 of the present invention; FIG.3 is a block diagram showing primary parts in the coding apparatus shown in FIG.2; FIG.4 is a block diagram showing primary parts in the second layer coding section shown in FIG.3; FIG.5 is a drawing explaining in detail filtering processing in the filtering section shown in FIG.4; FIG.6 is a flowchart showing steps of searching for optimal pitch coefficient Tp! for subband SBP in a searching section shown in FIG.4; FIG.7 is a block diagram showing primary parts in the decoding apparatus shown in FIG.2; FJG.8 is a block diagram showing primary parts in the second layer decoding section shown in FIG.7; FIG.9 is a block diagram showing primary parts in a coding apparatus according to Embodiment 2 of the present invention; FIG.10 is a block diagram showing primary parts in a decoding apparatus according to Embodiment 2 of the present invention; FIG. 11 is a block diagram showing primary parts in a coding apparatus according to Embodiment 3 of the present invention; FIG. 12 is a block diagram showing primary parts in the second layer coding section shown in FIG. 11; FIG.13 is a block diagram showing primary parts in the decoding apparatus according to Embodiment 3 of the present invention; FIG.14 is a block diagram showing primary parts in a second layer coding section shown in FIG. 13; FIG.15 is a block diagram showing primary parts of a coding apparatus according to Embodiment 4 of the present invention; FIG.16 is a block diagram showing primary parts in the first layer coding section shown in FIG.15; FIG.17 is a block diagram showing primary parts in the second layer coding section shown in FIG.15; FIG.18 is a block diagram showing primary parts in a decoding apparatus according to Embodiment 4 of the present invention: FIG.19 is a block diagram showing primary parts in the first layer decoding section shown in FIG.18; FIG.20 is a block diagram showing primary parts in the second layer decoding section shown in FIG. 18; FIG.21 is block diagram showing primary parts in a second layer coding section according to Embodiment 5 of the present invention: FIG. 22 is block diagram showing primary parts in a second layer coding section according to Embodiment 6 of the present invention: and FIG.23 is block diagram showing primary parts in a second layer decoding section according to Embodiment 6 of the present invention. Best Mode for Carrying Out the Invention Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, the coding apparatus and decoding apparatus according to the present invention will1 be described using a speech coding apparatus and a speech decoding apparatus as examples. First, a summary of search processing included in coding according to the present invention will be described with reference to FIG.l. FIG.1(a) shows the spectrum of an input signal, and FIG.1(b) shows the spectrum (the first layer decoded spectrum) resulting from decoding encoded data of the low frequency band of an input signal. In addition, here, a case will be described as an example here signals in a frequency band for telephones (0 to 3.4 kHz) is extended to wideband signals (0 to 7 kHz). That is, the sampling frequency of an input signal is 16 kHz, and the sampling frequency of a decoded signal outputted from a low frequency band coding section is 8 kHz. Here, in order to encode the high frequency band of an input signal, the high frequency band of the input signal spectrum is divided into a plurality of subbands (composed of five subbands from 1st to 5th in FIG.l). and the part of the first layer decoded spectrum most similar to the spectrum of the high frequency band is searched per subband. In FIG.l, the first search range and the second search range indicate the ranges to search for parts (bands) of decoded low frequency band spectrums (the first layer decoded spectrums described later) similar to the first subband (1st) and a second subband (2nd). Here, the first search range is, for example, from Tmin (0 kHz) to Tmax. Frequency A indicates the beginning position of band 1st1, which is the part of the decoded low frequency band spectrum similar to the first subband and frequency B indicates the end of band 1st'. Next, when search with respect to the second subband (2nd) is performed, the result of search for the first subband (1st) having finished is used. To be more specific, in the range in the vicinity of the end position of part 1st' most similar to the first subband (1st), that is, in the second search range, part of the decoded low frequency band spectrum similar to the second subband (2nd) is searched. As a result of performing search for the second subband. for example, the beginning position of band 2nd', which is the part of the decoded low frequency band spectrum similar to the second subband is C and the end position is D. Search with respect to each of the third subband, fourth subband and fifth subband is performed in the same way using the result of search with respect to the previous neighboring subband. By this means, it is possible to efficiently search for similar parts using correlations between subbands, and therefore, it is possible to improve coding performance of the higher frequency band spectrum. Here, with FIG.l, although a case has been described as an example where the sampling frequency of an input signal is 16 ' kHz, the present invention is not limited to this and is equally applicable to cases in which the sampling frequency of an input signal is S kHz, 3 2 kHz and so forth. That is, the present invention is not limited depending on the sampling frequency of an input signal. (Embodiment I ) FJG.2 is a block diagram showing a configuration of a communication system having a coding apparatus and a decoding apparatus according to Embodiment 1 of the present invention. In FJG.2. the communication system has the coding apparatus and the decoding apparatus that are able to communicate with one another via a transmission channel. Here the coding apparatus and the decoding apparatus are usually mounted in a base station apparatus or a communication terminal apparatus and so forth and used, Coding apparatus 101 divides an input signal every N samples (N is a natural number) and encodes every one frame of N samples. Here, an input signal to be encoded is represented as x „ (n-0,..., N-t). rt represents n+11h signal element of an input signal divided every N samples. The encoded input information (encoded information) is transmitted to decoding apparatus 103 via transmission channel 102. Decoding apparatus 103 receives the encoded information transmitted from coding apparatus 101 via transmission channel 102 and decodes it to obtain an output signal. FIG.3 is a block diagram showing primary parts in coding apparatus 101 shown in FIG.2. If the sampling frequency of an input signal is S R i n P u t, downsampling processing section 201 dawnsamples the sampling frequency of the input signal from SRhip.it to SRhas<: (SRbase S E A R C H 2 will be described. Likewise, when pitch coefficient setting section 404 performs closed-loop search processing for fourth subband SB3, if the value of optimal pitch coefficient To; of first subband SBo is lower than predetermined threshold THP (pattern I), pitch coefficient setting section 404 sets pitch coefficient T by changing pitch coefficient T little by little in the search range calculated according to equation 29. based on optimal pitch coefficient T2' of previous neighboring third subband S B 2 • Meanwhile, when the value of optimal pitch coefficient To' of first subband SBo is equal to or higher than predetermined threshold THP (pattern 2). pitch coefficient setting section 404 sets pitch coefficient T by changing pitch coefficient T little by little in the search range calculated according to equation 30. In these cases, P is three (P = 3) in equation 29 and equation 30. Here, when the value of the range of pitch coefficient T set according to equation 27 to equation 30 is higher than the upper limit of the band of the first layer decoded spectrum, the range of pitch coefficient T is corrected as shown in equation 3! and equation 3 2 in the same way as in Embodiment 1. At this time. equation 3 1 corresponds to equation 2 7 and equation 30. and equation 32 corresponds to equation 28 and equation 29. Likewise, when the value of the range of pitch coefficient T set according to equation 27 to equation 3 0 is lower than the lower limit of the band of the First layer decoded spectrum, the range of pitch coefficient T is corrected as shown in equation 33 and equation 34 in the same way as in Embodiment ], At this time, equation 33 corresponds to equation 27 and equation 30, and equation 34 corresponds to equation 28 and equation 29. Thus, by correcting the range to search for pitch coefficient T, it is possible to perform efficient coding without reducing the number of entries in search for an optimal pitch coefficient. Pitch coefficient setting section 404 adaptively chnages the number of entries at the time of searching for the optimal pitch coefficients for the second subband and the fourth subband. That is, when optimal pitch coefficient To' of the first subband is lower than a preset threshold, pitch coefficient setting section 404 increases the number of entries at the time of searching for the optimal pitch coefficient for the second subband (pattern 1), and, when optimal pitch coefficient TO; of the first subband is equal to or higher than a preset threshold, decreases the number of entries at the time of searching for the optimal pitch coefficient for the second subband (pattern 2). In addition, pitch coefficient setting section 404 increases and decreases the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband in accordance with the pattern (pattern 1 or pattern 2) at the time of searching for the optimal pitch coefficient for the second subband. To be more specific, pitch coefficient setting section 404 decreases the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband in pattern 1, and increases the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband in pattern 2. At this time, the total number of the entries at the time of searching for the optimal pitch coefficient for the second subband and the entries at the time of searching for the optimal pitch coefficient for the fourth subband are the same between pattern ! and pattern 2, so that it is possible to more efficiently search for an optimal pitch coefficient while the bit rate is fixed. When an input signal is a speech signal and so forth, the first layer decoded spectrum is characterized in that its periodicity increases in the lower frequency band. Therefore, the effect due to an increase in the number of entries at the time of search is improved when the range to search for an optimal pitch coefficient is the lower frequency band. Therefore, as described above, when the value of the optimal pitch coefficient searched for the first subband is small, it is possible to more effectively search for the optimal pitch coefficient for the second subband by increasing the number of entries at the time of searching for the optimal pitch coefficient for the second subband. At this time, the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband is decreased. On the other hand, when the value of the optimal pitch coefficient searched for the first subband is large, an increase in the number of entries at the time of searching for the optimal pitch coefficient for the second subband provides little effect. Therefore, the number of entries at the time of searching for the optimal pitch coefficient for the second subband is decreased while the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband is increased. As described above, it is possible to more efficiently search for optima! pitch coefficients by adjusting the number of entries (bit allocation) at the time of searching for the optimal pitch coefficient between the second subband and the fourth subband in accordance with the value of the optimal pitch coefficient searched for the first subband, so that it is possible to generate a decoded signal with high quality. Primary parts in decoding apparatus 184 (not shown) according to the present embodiment are basically the same as in decoding apparatus 163 shown in FIG.18, so that descriptions will be omitted. As described above, according to the present embodiment. in coding/decoding to estimate the spectrum of the higher frequency band by performing band extension using the spectrum of the lower frequency band, the higher frequency band is divided into a plurality of subbands, and, in part of subbands (the first subband, the third subband and the fifth subband in the present embodiment), search is performed in the search range set for each subband. In addition, in the other subbands (the second subband and the fourth subband in the present embodiment), search is performed using the coding results of respective previous neighboring subbands. Here, when the optimal pitch coefficients are searched for the second subband and the fourth subband, respectively, the number of entries for search is adaptively switched based on the optimal pitch coefficient searched for the first subband. By this means, it is possible to use correlation between subbands and adaptively change the number of entries per subband. so that it is possible to more efficiently encode/decode the higher frequency band spectrum. As a result of this, it is possible to further improve the quality of a decoded signal. Here, with the present embodiment, a case has been described as an example where the total number of entries at the time of searching for the optimal pitch coefficients for the second subband and the fourth subband is the same. However, the present invention is not limited to this, and is applicable to a configuration in which the totaJ number of entries at the time of searching for the optimal pitch coefficients for the second subband and the fourth subband differs between patterns. In addition, with the present embodiment, although a case has been described as an example where the number of entries at the time of searching for the optimal pitch coefficients for the second subband and the fourth subband increases and decreases, the present invention is equally applicable to a case in which the search range covers all the low frequency bands by increasing the number of entries for search. In addition, with the present embodiment, as an example for a case in which the number of entries at the time of searching for the optimal pitch coefficients for the second subband and the fourth subband increases and decreases, a configuration has been explained where, when the value of optimal pitch coefficient To' of the first subband is lower than predetermined threshold THP (pattern 1), the number of entries at the time of searching for the optimal pitch coefficient for the second subband is increased (the search range is widened) and the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband is decreased (the search range is narrowed). Moreover, when the value of optimal pitch coefficient To' of the first subband is equal to or higher than predetermined threshold THP (pattern 2), the above-described configuration adopts a search range setting method opposite to the above-description. However, the present invention is not limited to the above-described configuration and equally applicable to a configuration to adopt a method of setting a search range for the first subband in the opposite way for each of pattern 1 and pattern 2. That is, the present invention is equally applicable to a configuration in which, when the value of optimal pitch coefficient To' of the first subband is lower than predetermined threshold THP (pattern I), the number of entries at the time of searching for the optimal pitch coefficient for the second subband is deceased (the search range is narrowed) and the number of entries at the time of searching for the optimal pitch coefficient for the fourth subband is increased (the search range is widened). Here, when the value of optimal pitch coefficient To' of the first subband is equal to or higher than predetermined threshold THP (pattern 2), the present configuration adopts a search range setting method opposite to the above-description. By this configuration, it is possible to efficiently encode an input signal having the spectral characteristics significantly different between a lower frequency subband and a higher frequency subband in the lower frequency band. To be more specific, experiments have ascertained that it is possible to efficiently quantize an input signal having characteristics that its spectrum is composed of a plurality of peak components and the density of peak components significantly varies between bands. (Embodiment 6) With Embodiment 6 of the present invention, a configuration will be described where the sampling frequency of an input signal is 3 2 kHz in the same way as in Embodiment 4 and the G.729.1 coding method standardized by ITU-T is applied as a coding method used in the first layer coding section. The communication system (not shown) according to Embodiment 6 of the present invention is basically the same as the communication system shown in FIG.2. but the configurations and operations of the coding apparatus and decoding apparatus differ only in part from those of coding apparatus 101 and decoding apparatus 103 in the communication system shown in FIG.2. Now. the coding apparatus and the decoding apparatus in the communication system according to the present embodiment will be assigned reference numerals "191" and "193," respectively, and explained. Coding apparatus 191 (not shown) according to the present embodiment is basically the same as coding apparatus 161 shown in FIG. 15 and composed mainly ofdownsampling processing section 201, first layer coding section 233, orthogonal transform processing section 215, second layer coding section 256 and encoded information multiplexing section 207. Here, parts except for second layer coding section 256 are the same as in Embodiment 4 and descriptions will be omitted. Second layer coding section 256 generates second layer encoded information using an input spectrum inputted from orthogonal transform processing section 2J5 and a first layer decoded spectrum inputted from first layer coding section 233 and outputs the generated second layer encoded information to encoded information multiplexing section 207. Here, second layer coding section 256 will be described in detail later. FIG.22 is a block diagram showing primary parts in second layer coding section 256 according to the present embodiment. Parts except for pitch coefficient setting section 414 in second layer coding section 256 are the same as in Embodiment A, so that descriptions will be omitted. In addition, in the same way as in Embodiment 4, a case will be described as an example where band dividing section 260 shown in FIG.22 divides the high frequency band (FL