MOBILE RADIO COMMUNICATION SYSTEM, COMMUNICATION APPARATUS FOR MOBILE RADIO COMMUNICATION SYSTEM, AND MOBILE RADIO COMMUNICATION METHOD

Abstract: In the mobile radio communication system where the UMTS and an another system coexist an idle slot for observing the frequency component of another system is inserted in one superframe of UMTS. The duration of this idle slot is at most half of the duration of one frame that form the superframe and it is inserted at an interval of a specified number of frames. Therefore, the frequency component of the another system can be observed securely from the UMTS. Further, deterioration of interleaving performance of the compressed mode frames during such observation can be suppressed.

Description: TECHNICAL FIELD The present invention relates to a mobile radio communication system in which UMTS (Universal Mobile Terrestrial communication System) and GSM (Group Specific Mobile) system coexist, communication apparatus applied in mobile radio communication system, and mobile radio communication method. More particularly this invention relates to a technology of observing the control channel of a GSM system that is another system in the mobile radio communication system by making use of an idle period. BACKGROUND ART In a CDMA cellular system, because the same carrier frequency is used repeatedly in every cell there is no need for handovers between frequencies within the same system. However, considering a case such as when existing systems are present together, there is a need for handovers between different carrier frequencies. Three points pertaining to detailed cases are described below. As a first point, in a cell where there is considerable traffic, a separate carrier frequency is used to accommodate the increased number of subscribers, and a handover may be performed between those cells. As a second point, when an umbrella cell constitution is used, different frequencies are allocated to large and small cells, and handovers are performed between the cells. Then, as a third point, there are cases of handovers between a third generation system, such as a W (Wideband)-CDMA system, and a second-generation system, such as a current mobile telephone system. When performing handovers in cases such as those mentioned above, it is necessary to detect the power of carriers at the different frequencies. To achieve this detection, the receiver need only have a structure capable of detecting two frequencies. However, this increases the size of the constitution of the receiver, or makes the constitution complicated. Furthermore, two types of handover method may be considered: a mobile assisted handover (MAHO) and a network assisted handover (NAHO). Comparing the MAHO and NAHO methods, NAHO reduces the burden of the mobile device. However, it is necessary to synchronize the mobile device and the base station, whereby the constitution of the base station and the network becomes complicated and large in order to be capable of tracking each dedicated mobile device. For such reasons, the realization of the MAHO method is more desirable, but to determine whether or not to handover, it is necessary to measure the strength of carriers of different frequencies at the mobile devices. However, a CDMA cellular system differs from a time division multiple access (TDMA) system used in a second generation, in that it uses ordinarily continuous transmission for both transmission/reception. In this continuous transmission/reception technique, unless receivers corresponding to two frequencies are prepared, it is necessary to stop the timing of the transmission or the reception and measure the other frequency. There has been disclosed a technique relating to a compressed mode method, for time-compressing the transmission data in the normal mode and transmitting it in a short time, thereby creating some spare time which can be utilized to measure the other frequency carrier. As an example of this, there is Japan Patent Application National Publication (Laid-Open) (JP-A) No. 8-500475 "Non-continuous Transmission for Seamless Handovers in DS-Mobile Radio Communications Systems". This application discloses a method of realizing a compressed mode, wherein the spreading factor of the spreading code used is lowered to compress the transmission timing. The method of realizing the compressed mode according to the above application will be explained below. FIG. 13 shows an example of transmissions in a normal mode and a compressed mode in a conventional CDMA system. In FIG. 13, the vertical axis represents transmission rate/transmission power, and the horizontal axis represents time. In the example of FIG. 13, the compressed mode transmission is inserted between normal transmission frames. In the transmission in the compressed mode, a non-transmission period is provided in the downlink frame, and can be set to a desired period of time (duration). This non-transmission period represents idle period during which the strength of the other frequency carrier is measured. In this way, slot transmission can be achieved by inserting the idle period between transmission of compressed mode frames. In this type of compressed mode transmission, transmission power is increased in accordance with the time ratio between the idle period and the frame (compressed mode frame) transmission duration. Therefore, as shown in FIG. 13, the compressed mode frame is transmitted at a higher transmission power than the frame in normal transmission. Consequently, transmission quality can be maintained even in frame transmission in compressed mode. Usually, between the GSM and GSM, different frequency component (control channel) is observed by using one observation period (no-transmission period) assigned in every one superframe. However, when a mobile radio communication system in which the UMTS and GSM systems coexist is considered, it requires operation for observing the frequency components between different systems, that is, from UMTS to GSM system. In this case, too, same as in the case of observation between GSM and GSM, an idle period for observing the frequency component of GSM is set in the superframe of the UMTS. That is, for one frame of superframe in the UMTS, it is necessary to assign the observation period composed of the same number of idle slots as in the case of GSM-GSM observation. However, in the existing technology, due to restrictions in the error correction code and spreading factor for frame transmission, it is difficult to insert all observation period in one frame, and there are many other problems. Therefore, a technology for observing the frequency component of GSM system from the UMTS is expected in the future. In TR 101 146; Universal Mobile Telecommunications System (UMTS); UMTS Terrestrial Radio Access (UTRA); Concept evaluation (UMTS 30.06 version 3.0.0)' EUROPEAN TELECOMMUNICATIONS STANDARD INSTITUTE (ETSI), December 1997 (1997-12), pages 48-50, XP002171845, an inter-frequency handover in a slotted downlink transmission is described, wherein the data transmitted in a frame is compressed in time and transmitted in the first half of the frame period thereby generating an idle period during the second half of the frame, which may be used for monitoring carrier frequencies in a different communication system. WO 96/23369 A also discloses an inter-frequency handover, wherein several slots for downlink transmission are provided in each frame. In Gustafsson M. et al.: 'Compressed Mode Techniques for Inter-Frequency Measurements in a Wide-band DS-CDMA System' WAVES OF THE YEAR 2000+ PIMRC. THE IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATION. TECHNICAL PROGRAM, XX, XX, vol. 1, 1 September 1997 (1997-09-01), pages 231-235, XP002127494, several compressed mode techniques for inter-frequency measurements are described, wherein the frame data are time compressed and transmitted during the first half of the frame period, the end of the frame period being used as idle period for the frequency measurement. It is an object of the present invention to solve the problems mentioned above by providing a mobile radio communication system, a receiver, a transmitter and corresponding mobile radio communication methods, capable of observing securely the frequency component of an another system from the UMTS even when the UMTS and the another system coexist, and suppressing deterioration of interleaving performance of compressed mode frame in such a case. This problem is solved by the system according to claim 1, the receiver according to claim 3, the transmitter according to claim 4 and the methods according to one of claims 5 - 7. Further improvements are provided in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a frame format applied in a GSM system, Fig. 1(a)is a diagram for explaining the frame format of dedicated traffic channel, and Fig. 1(b) is a diagram for explaining the frame format of common control channel; Fig. 2 is a diagram for explaining the observation period of GSM superframe applied in the GSM system; Fig. 3 shows an observation method of different frequency components between GSM and GSM, Fig. 3(a) is a diagram for explaining the frame format of common control channel, Fig. 3(b) is a diagram for explaining the frame format of dedicated traffic channel in relation to the common control channel, and Fig. 3(c) is a diagram for explaining the observation period inserted in every GSM superframe; Fig. 4 is a diagram for explaining an observation method in the GSM system; Fig. 5 show a frame format applied in the UMTS, Fig. 5(a) is a diagram for explaining the frame format of dedicated traffic channel applied in the GSM system, and Fig. 5(b) is a diagram for explaining the format of superframe of UMTS; Fig. 6 shows an observation method of different frequency components between GSM and UMTS, Fig. 6(a) is a diagram for explaining the frame format of common control channel applied in the GSM system, Fig. 6(b) is a diagram for explaining the relation of superframe between the UMTS and GSM systems, and Fig. 6(c) is a diagram for explaining the observation period inserted in every superframe in the UMTS; Fig. 7 is a diagram for explaining the frame transmission of downlink according to a first embodiment of the invention; Fig. 8 is a block diagram showing a mobile radio communication system according to the first embodiment of the invention; Fig. 9 is a flowchart for explaining the transmission operation in compressed mode according to the first embodiment of the invention; Fig. 10 is a flowchart for explaining the reception operation in compressed mode according to the first embodiment of the invention; Fig. 11 is a diagram for explaining the frame transmission of downlink according to a second embodiment of the invention; Fig. 12 is a diagram for explaining the frame transmission of downlink according to a third embodiment of the invention; and Fig. 13 is a diagram for explaining the frame transmission of downlink in a prior art. BEST MODE FOR CARRYING OUT THE INVENTION Referring now to the accompanying drawings, preferred embodiments of mobile radio communication system, communication apparatus applied in mobile radio communication system, and mobile radio communication method of the invention are described in detail below. First, the principle of a first embodiment of the invention is described. In the first embodiment of the invention, a mobile radio communication system in which UMTS and GSM systems coexist is presented as an example. To begin with, the existing system, GSM system, is explained. Fig. 1 shows a frame format applied in the GSM system. More specifically, Fig. 1(a) is a diagram for explaining the frame format of dedicated traffic channel, and Fig. 1(b) is a diagram for explaining the frame format of common control channel. In the GSM system, TACH (Traffic and Associated Channel) is defined as the dedicated traffic channel, and FCCH (Frequency Correction Channel) and SCH (Synchronization Channel) are defined as the common control channel. In the dedicated traffic channel TACH, as shown in Fig. 1(a), the period of transmitting the transmission unit of frame from #1 to #26 is designated as one GSM superframe. One frame has a duration of 8 BP (burst period). One BP is 0.577 ms. Therefore, one GSM superframe has a transmission period of 120 ms. In the common control channel FCCH/SCH, as shown in Fig. 1(b), the period of transmitting 8 BP frame from #1 to #51 is one FCCH/SCH superframe. The observation method of different frequency components between GSM and GSM is described next. Fig. 2 is a diagram for explaining the observation period of GSM superframe applied in the GSM system. Fig. 3 shows an observation method of different frequency components between GSM and GSM. More specifically, Fig. 3(a) is a diagram for explaining the frame format of common control channel. Fig. 3(b) is a diagram for explaining the frame format of dedicated traffic channel in relation to the common control channel. Fig. 3(c) is a diagram for explaining the observation period inserted in every GSM superframe. Fig. 4 is a diagram for explaining an observation example in the dedicated traffic channel of the GSM system. This Fig. 4 is disclosed in the publication "The GSM System for Mobile Communication" by Michel MOULY and Marie-Bernadette PAUTET (international standard book number 2-9507190-0-7). In the GSM system, the no-transmission period (idle period) assigned for one GSM superframe is 12BP (= 6.9 ms) as shown in Fig. 2. At the time of handover, different frequency component (control channel) of another GSM system is observed and detected by making use of this no-transmission period. The FCCH/SCH superframe is composed of 51 frames (see Fig. 3(a)). On the contrary, the GSM superframe (see Fig. 3(b)) has 52 frames in two periods. Comparing these two superframes, therefore, there is a difference of one frame. That is, the FCCH/SCH superframe is short of one frame. Since the observation period is once in one GSM superframe, in two GSM superframes, the frequency is observed and detected two times (see Fig. 3(c)). This observation and detection procedure is shown in Fig. 4. There is a difference of one frame between one FCCH/SCH superframe in common control channel and two GSM superframes in dedicated traffic. The position of the observation period assigned for one GSM superframe is fixed in the dedicated traffic channel TACH/F. Therefore, frequency is observed in a specified frame of every GSM superframe. When the FCCH/SCH superframe is composed of the same number of frames as the two GSM superframes, the same frame number is observed between GSM and GSM all the time. However, since there is a difference of one frame between FCCH/SCH superframe and two GSM superframes, observation is shifted by one frame each in every observation. Incidentally, one FCCH/SCH superframe corresponds to two periods of GSM superframe so that the frequency is observed and detected twice in every one FCCH/SCH superframe. That is, the time difference in this pair of observation periods is one GSM superframe, and the pair of observations progress in a form shifted by one period of one GSM superframe. Therefore, in a frequency handover between GSM and GSM, the frequency is observed and detected in such a manner that the timing of the observation and detection is shifted twice in every one period of FCCH/SCH superframe and by one frame each in every one period. The next-generation system, UMTS, is explained below. Fig. 5 shows a frame format applied in the UMTS. More specifically, Fig. 5(a) is a diagram for explaining the frame format of dedicated traffic channel applied in the GSM system. Fig. 5(b) is a diagram for explaining the format of superframe of UMTS. In the GSM system, in the dedicated traffic channel TACH mentioned above, as shown in Fig. 5(a), the period of transmitting the frames, which is the unit of transmission, from #1 to #26 is designated as one GSM superframe. One frame has duration of 8 BP (burst period). In the UMTS, on the other hand, the UMTS superframe is composed of the same period as in this GSM superframe. That is, in the UMTS, in all channels, as shown in Fig. 5 (b), the period of transmitting frames from #1 to #12, each having duration of 10 ms, is one UMTS superframe. The observation method of different frequency components between GSM and UMTS is described next. Fig. 6 shows the observation method of different frequency components between GSM and UMTS. More specifically, Fig. 6(a) is a diagram for explaining the frame format of common control channel applied in the GSM system. Fig. 6(b) is a diagram for explaining the relation of superframe between the UMTS and GSM systems. Fig. 6(c) is a diagram for explaining the observation period inserted in every superframe in the UMTS. As mentioned above, the FCCH/SCH superframe is composed of 51 frames (see Fig. 6(a)). On the contrary, the GSM superframe has 52 frames in two periods (see Fig. 3 (b)). The GSM superframe and UMTS superframe are equal in the duration of one period. Therefore, the relation between the FCCH/SCH superframe and the UMTS superframe coincides with the relation between the FCCH/SCH superframe and the GSM superframe explained above. That is, there is a difference of one frame in the FCCH/SCH superframe and two UMTS superframes (see Fig. 6 (b)). Herein, in frequency handover between UMTS and GSM, in order to obtain the same function as in frequency handover between GSM and GSM mentioned above, observation period of about 6.9 ms is required in one UMTS superframe. Accordingly, as shown in Fig. 6 (c), observation and detection is carried out twice in two UMTS superframes. Only when 12 BP = 6.9 ms, it is same as the handover between GSM and GSM. In this handover between UMTS and GSM, however, due to restrictions of error correction code and spreading factor, it is impossible to assign all necessary observation period for one frame in one superframe. That is, the operation for increasing the coding rate of the error correction code cannot be increased more than the number of information bits of the non-coding case. Further, in the UMTS, the frame length is 10 ms, and since the no-transmission period of about 6.9 ms for observation of different frequency components is more than half of the frame length, deterioration of interleaving performance is predicted. Further, in order to prepare the no-transmission period of about 6.9 ms in one frame, it is required to reduce the transmission period to about 3.1 ms. Therefore the transmission power in the compressed mode transmission should be increased. This results in a problem that the interference power on another channels is instantly increased. It may be hence considered to observe and detect different frequency components in one UMTS superframe by dividing in plural times. In this case, the time performance for compensating for control channel of GSM channel is same as when preparing an observation period once in every one UMTS superframe. Consequently, the number of idle slots for obtaining one observation period can be set smaller than in the case between GSM and GSM. The idle slots can be generated by using punctured code or higher coding rate of error correction coding. In the first embodiment, the frequency is observed and detected twice in every one UMTS superframe. Hence, in two UMTS superframes, the frequency is observed and detected four times. The observation and detection method is explained by referring to Fig. 7. Fig. 7 is a diagram for explaining the frame transmission of downlink in the first embodiment of the invention. In Fig. 7, the axis of ordinates denotes the transmission rate or transmission power, and the axis of abscissas represents the time. There is a difference of one frame between one FCCH/SCH superframe and two UMTS superframes in the common control channel. In the dedicated traffic channel TACH/F, the position of observation period assigned in one GSM superframe is fixed. Similarly, in the UMTS also the positions of two observation periods assigned in one UMTS superframe in the downlink traffic channel are fixed. Therefore, frequency is observed and detected in specified frames (two positions) of every UMTS superframe. Thus, since there is a difference of one frame between one FCCH/SCH superframe and two UMTS superframes, one frame is shifted each in each observation. Since one FCCH/SCH superframe corresponds to two periods of UMTS superframe, the frequency is observed and detected four times in one FCCH/SCH superframe. That is, the time difference in the pair of observation periods corresponds to one UMTS superframe in every UMTS superframe, and the pair of observations progress in a form shifted by one period of one FCCH/SCH superframe. Therefore, in frequency handover between UMTS and GSM, the frequency is observed and detected four times in every period of FCCH/SCH superframe, and while shifting by one frame each in every period of observation. The observation period, that is, the idle slot is set in the center of a specified frame. Hence, interleaving effect is obtained in the compressed mode frame transmission. Further, by increasing the coding rate in punctured coding or error correction coding, the redundancy is further decreased, and the idle period can be set longer proportionally. In this case, the quantity of information to be transmitted is decreased, the spreading factor can be kept unchanged. That is, the interference and noise resistant characteristic may be maintained. Incidentally, the characteristic deteriorates when transmitting compressed frames so that the transmission power must be slightly increased as compared to the normal transmission. A specific example of mobile communication system is discussed below. Fig. 8 is a block diagram showing a mobile radio communication system according to the first embodiment of the invention. The mobile radio communication system consists of a transmitter 1 and a receiver 2. Such a system is installed at both, a base station and a mobile station. In this mobile radio communication system, for example, W (wideband)-CDMA (code division multiple access) communication method is applied. The transmitter 1 comprises, as shown in Fig. 8, a controller 11, an error correction encoder 12, an interleaver 13, a framing/spreading unit 14, a radio frequency transmitter 15, etc. The controller 11 controls the operation of the interleaver 13, framing/spreading unit 14, and radio frequency transmitter 15 mainly through negotiation with the receiver 2. This controller 11 controls the operation suited to normal mode (non-compressed mode) and compressed mode by negotiation with the receiver 2. More specifically, the controller 11 instructs the transmission timing for transmitting the compressed mode frames, in compressed mode, to the framing/spreading unit 14. The controller 11 also instructs increase of average transmission power when transmitting compressed mode frames to the radio frequency transmitter 15. The error correction encoder 12 obtains coded data by error correction coding of transmission data stream. The interleaver 13 permutes the time sequence of (interleaves) the coded data in bit units in order to minimize the effects of transmission error in the event of, for example, loss of continuous bits of transmission signal due to fading during transmission. The interleaver 13 has a memory for interleaving one frame. The framing/spreading unit 14 spreads wider by using a spreading code of each user, depending on normal mode or compressed mode, and forms a frame depending on each mode. When transmission timing depending on the mode is instructed from the controller 11, this framing/spreading unit 14 sends out the frame to the radio frequency transmitter 15 at the transmission timing. The radio frequency transmitter 15 converts the transmission signal obtained from the framing/spreading unit 14 into radio frequency, and transmits. The radio frequency transmitter 15 increases the average transmission power in the compressed mode as compared with that of the normal mode according to the control of the controller 11, and outputs a transmission signal. The receiver 2 comprises, as shown in Fig. 8, a controller 21, an error correction decoder 22, a deinterleaver 23, a deframing/de-spreading unit 24, a radio frequency receiver 25, etc. The controller 21 controls the operation of the deinterleaver 23 and deframing/de-spreading unit 24 mainly through negotiation with the transmitter 1. This controller 21 controls the operation suited to the normal mode and compressed mode by negotiation with the transmitter 1. More specifically, the controller 21 instructs reception timing for receiving the compressed mode frames in the compressed mode to the deframing/de-spreading unit 24. The radio frequency receiver 25 demodulates the reception signal sent from an antenna not shown. The deframing/de-spreading unit 24 de-spreads using the spreading signal assigned to the user of the receiver 2 depending on the normal mode or compressed mode, and forms a frame suited to each mode. When reception timing depending on each mode is instructed from the controller 21, the deframing/de-spreading unit 24 receives the reception signal from the radio frequency receiver 25 at this reception timing. The deinterleaver 23 permutes the time sequence (de-interleaves) of the coded data in bit units in the reverse sequence of interleaving in the transmitter 1. The deinterleaver 23, like the interleaver 13, has a memory for interleaving one frame. The error correction decoder 22 decodes the de-interleaved signal, and obtains decoded data, that is, reception data stream. Explained next is the frame transmission including compressed mode. In this mobile radio communication system, in compressed mode, a period of transmitting intermittently by forming frames into slots is provided, and by making use of no-transmission period in this period, the intensity of different frequency carrier is measured. For this purpose, frames formed into slots must be compressed, but when interleaved same as in ordinary transmission, sufficient interleaving time is not available, and enough interleaving effect cannot be obtained. Accordingly, the transmission period of compressed frame in one frame is divided. One portion is assigned at the beginning of a frame area, and the other portion is set at the end of the same frame area, so that a required interleaving time may be obtained. That is, the idle slot corresponding to the observation period is placed in the center of a frame. In the receiver 2, this operation is reverse. Herein, the relation between the number of idle slots and the number of slots in the compressed mode frame is described. Supposing one frame to be composed of 16 slots, the number of slots in the first half to be A, the number of idle slots to be B, and the number of slots in the second half to be C, the following combinations can be considered. That is, (A, B, C) = (7, 1, 8)/(7, 2, 7)/(6, 3, 7)/ (6, 4, 6)/(5, 5, 6)/(5, 6, 5) According to these combinations, for example, supposing the number of slots in the first half and second half to be 7 slots and 8 slots respectively, one slot in the center of the frame is inserted as an idle slot. When a short idle slot such as one or two slots is assigned per frame, only punctured coding may be used. The position of the idle slot in principle should be in the frame center, but it may be deviated forward or backward. In such short idle slot, by properly determining the compressed mode frame of first half and second half and position of the idle slot, the same acquisition time as in the case of frequency handover between GSM and GSM may be obtained. In the first embodiment, the compressed mode frame is divided into first portion and second portion bounded by the idle slot within one frame. The following is to explain how to insert the observation period, that is, the idle slot in which frame in one UMTS superframe, and how to determine the inserting position. One UMTS superframe is composed of 12 frames. In the GSM, one GSM superframe is composed of 26 frames, and one frame is 8 BP long, and hence the total period is 208 BP. The idle slot equivalent to 8 BP is observed in two compressed mode operation, and hence one observation in compressed mode has an idle slot length equivalent to 4 BP. Thus, when a first frame is specified arbitrarily in one UMTS superframe, the equation between the position of the second frame and the first frame is as shown in equation (1). In the case shown in equation (1), it is assumed that the frame number of the first portion is even, and the frame number in the second portion is odd. This equation (1) is 4(2n+1) = K(208BP)/12 2n+1 = 13K/3. In equation (1), the position that can be observed in the compressed mode of the first half is the same, but since the observation period is 4 BP, half of 8 BP, and hence the equation shows the relation for observing the portion of 4 BP that can be observed in the compressed mode in the second half, equivalently to 4 BP corresponding to the second half of 8 BP missing in the first half. That is, 4(2n+1 denotes an odd-number multiple of 4 BP (when the first half is even, the second half is odd), and it suggests that the interval may be K times the UMTS frame length. When the UMTS frame length is expressed by BP, it is 208 BP (number of BP of UMTS superframe)/12 (number of UMTS frames included in UMTS superframe). Here, n is an arbitrary natural number. When combinations of K and n that satisfy equation (1), two kinds of combination can be obtained as shown in equation (2). That is, (K, n) = (3, 6)/(9,19) According to equation (2), the frame three frames after the first frame may be defined as the second frame, or the frame nine frames after the first frame may be defined as the second frame. In Fig. 7, for example, supposing frame #2 to be the first frame, frame #5 is the second frame. The compressed mode operation when observing and detecting from the UMTS to the GSM system is explained below. Herein, only the compressed mode is described. Fig. 9 is a flowchart for explaining the transmission operation in the compressed mode, and Fig. 10 is a flowchart for explaining the reception operation in the compressed mode. In the compressed mode of the transmitter 1 at the UMTS side (see Fig. 9), interleaving in one frame is instructed to the interleaver 13 (step S101), and the interleaver 13 interleaves in one frame. When the time reaches the timing of either first half or second half of the first frame timing or second frame timing to be observed (step S102), the transmission timing is instructed to the framing/spreading unit 14 (step S103). Further, increase of average transmission power is instructed to the radio frequency transmitter 15 (step S104), and the frames are transmitted at a higher power in the compressed mode than in the normal mode. Thus, the frequency is observed and detected twice in one UMTS superframe. In this compressed mode, the frames are transmitted intermittently (discontinuously). On the other hand, in the compressed mode of the receiver 2 at the UMTS side (see Fig. 10), when the time reaches the timing of either first portion or second portion of the first frame timing or second frame timing to be observed (step S111), the reception timing is instructed to the deframing/de-spreading unit 24 (step S112). After receiving the signal of the portion of one frame, deinterleaving by one frame is instructed to the deinterleaver 23 (step S113), and the deinterleaver 23 deinterleaves is one frame. Thus, in the compressed mode, the frames are received intermittently (discontinuously), and the signal of the GSM system is observed in an idle period. As explained herein, according to the first embodiment, where the UMTS and another system coexist, an idle period for observing the frequency component of the another system is inserted in the superframe of the UMTS. This idle period is at most half of one frame of the superframe of UMTS and is inserted at an interval of certain frames. Hence it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. As a result, even when the UMTS and an another system coexist, the frequency component of the another system can be securely observed from the UMTS, and deterioration of interleaving performance of the compressed mode frame can be suppressed at this time. Moreover, in one UMTS superframe, since the interval of the specified number of frames is determined by the difference in the transmission period between the UMTS and another system, different frequency components can be observed completely depending on the difference in the transmission period. Since the idle slot time is placed in the center of the frame that is the unit of superframe of UMTS, the interleaving effect can be obtained securely. In the superframe of UMTS, since plural idle periods are disposed separately in each frame, a necessary idle duration can be held in one superframe. The total of plural idle slot durations is set at about 6.9 ms equal to the case of GSM, so that the equal idle duration for the observation period of different frequencies of other systems can be held in one UMTS superframe. The frame in which the idle slot duration is inserted is compressed and transmitted intermittently, and therefore even when idle period is inserted in the duration of one frame, frame transmission of high decodability can be realized. Since the compressed frame is generated by increasing the coding rate the compression ratio is reduced, and the number of use of spreading codes of shorter code length can be suppressed. In the compressed mode, moreover, frames compressed at the same spreading factor as in normal mode are generated, and therefore the interference and noise resistant characteristic to the compressed frames can be assured. Since the average transmission power is increased when transmitting compressed mode frames, the characteristic deterioration can be suppressed to a minimum limit. In the foregoing first embodiment, at the time of frequency handover, the observation period (about 6.9 ms) is divided into two portions in one UMTS superframe for observing and detecting frequency. However, the invention is not limited to this embodiment alone. As a second embodiment explained below, the observation period may be divided in more than two portions. In the second embodiment, for example, the observation period is divided into four portions. The entire constitution in the second embodiment is same as in the first embodiment, and only the difference in operation is described below. The observation and detection method of the second embodiment is explained below. Fig. 11 is a diagram for explaining the frame transmission of downlink according to the embodiment of the invention. In Fig. 11, the axis of ordinates denotes the transmission rate or transmission power, and the axis of abscissas represents the time. In comparison between one FCCH/SCH superframe and two UMTS superframes in the common control channel, there is a difference of one frame. In the dedicated traffic channel TACH/F, the position of observation period assigned in one GSM superframe is fixed. Similarly in the UMTS, the positions of four observation periods assigned in one UMTS superframe in the downlink traffic channel are fixed. Therefore, the frequency is observed and detected in specified frames (four positions) of every UMTS superframe. Thus, since there is a difference of one frame between one FCCH/SCH superframe and two UMTS superframes, one frame is shifted each in each observation. Since one FCCH/SCH superframe corresponds to two periods of UMTS superframe, the frequency is observed and detected eight times in one FCCH/SCH superframe. That is, in every UMTS superframe, the difference in the pair of observation periods corresponds to one UMTS superframe, and the pair of observations progress in a form shifted by one period of one UMTS superframe. Therefore, in frequency handover between UMTS and GSM, the frequency is observed and detected eight times in every FCCH/SCH superframe, and while shifting by one frame each in every period of observation. In the second embodiment, same as in embodiment 1, the compressed mode frame is divided into first portion and second portion bounded by the idle slot within one frame. The following is to explain how to insert the observation period, that is, the idle slot in which frame of one UMTS superframe, and how to determine the inserting position. In the foregoing first embodiment, since one UMTS superframe is composed of 12 frames, the method of dividing the UMTS superframe by unit of a frame is employed. However, the UMTS superframe can be divided into a shorter time unit and a position for assigning the idle slot can be set. For example, since one frame in UMTS is composed of 16 slots, the UMTS superframe is divided by unit of a slot in the second embodiment. The case of four divisions is shown in equation (3). It requires first frame to fourth frame for assigning the each observation period in this case. Equation (3) shows a case in which the frame number of the first frame is even. Equation (3) is an equation for determining the second frame. In the same concept as in the first embodiment, this equation (3) is expressed as 2(4n+1) = K1(208BP)/12 × 16 4n+1 = 13K1/24. In equation (3), K1 shows the frame number of the second frame of UMTS superframe, and n is an arbitrary natural number. At the right side of equation (3), since one frame is composed of 16 slots, it is multiplied by 12 frames in the denominator. When combinations of K1 and n that satisfy equation (3) are calculated, two types of combination can be obtained as shown in equation (4). That is, (K1, n) = (24, 3)/(120, 16). In this case, since K1 = 24 indicates the number of slots, the second frame can be determined by dividing K1 by 16. In the case of K1 = 24, the solution is 1.5 frames, and when expressed by the frame number, the frame in which the second observation period is assigned is the frame 1.5 frames after the first frame. Equation (5) is for determining the third frame. This equation (5) is 2(4n+2) = K2(208BP)/12 × 16 2n+1 = 13K2/48. In equation (5), K2 denotes the frame number of the third frame of UMTS superframe, and n is an arbitrary natural number. When combinations of K2 and n that satisfy equation (5) are calculated, two types of combination are obtained as shown in equation (6). That is, (K2, n) = (48, 6)/(144, 19). In this case, since K = 48 indicates the number of slots, the third frame can be determined by dividing K by 16. In the case of K = 48, the solution is 3 frames, and when expressed by the frame number, the frame in which the third observation period is assigned is the frame 3 frames after the first frame. Equation (7) is for determining the fourth frame. This equation (7) is 2(4n+3) = K3(208BP)/12 × 16 2n+1 = 13K3/48. In equation (7), K3 denotes the frame number of the fourth frame of UMTS superframe, and n is an arbitrary natural number. When combinations of K3 and n that satisfy equation are calculated (7), two types of combination are obtained as shown in equation (8). That is, (K3, n) = (72, 9)/(168, 22). In this case, since K = 72 indicates the number of slots, the fourth frame can be determined by dividing K by 16. In the case of K = 72, the solution is 4.5 frames, and when expressed by the frame number, the frame in which the fourth observation period is assigned is the frame 4.5 frames after the first frame. As explained herein, the number of divisions of observation period in one UMTS superframe can be four, and the same effects as in the first embodiment are also obtained in this case. However, unlike the first embodiment, the division interval is not the specified number of frames interval, but is an interval of a specified number of slots. In the foregoing second embodiment, at the time of frequency handover, the observation period (about 6.9 ms) is divided into four portions in one UMTS superframe for observing and detecting frequency in four frames, but the invention is not limited to this embodiment alone. However, as a third embodiment explained below, the observation period can be divided in more than four portions. In the third embodiment, for example, it is divided into eight portions. The entire constitution in the third embodiment is same as in the first embodiment described above, and only the difference in operation is described below. The observation and detection method of the third embodiment is explained below. Fig. 12 is a diagram for explaining the frame transmission of downlink in the third embodiment of the invention. In Fig. 12, the axis of ordinates denotes the transmission rate or transmission power, and the axis of abscissas represents the time. As mentioned above, in comparison between one FCCH/SCH superframe and two UMTS superframes in the common control channel, there is a difference of one frame. In the dedicated traffic channel TACH/F the position of observation period assigned in one GSM superframe is fixed. Similarly, in the UMTS, the positions of eight observation periods assigned in one UMTS superframe in the downlink traffic channel are fixed. Therefore, the frequency is observed and detected in specified frames (four positions) of every UMTS superframe. Thus, since there is a difference of one frame between one FCCH/SCH superframe and two UMTS superframes, one frame is shifted each in each observation. Since one FCCH/SCH superframe corresponds to two periods of UMTS superframe, the frequency is observed and detected 16 times in one FCCH/SCH superframe. That is, in every UMTS superframe, the difference in the set of observation periods corresponds to one UMTS superframe, and the set of observations progress in a form shifted by one period of one UMTS superframe. Therefore, in frequency handover between UMTS and GSM, the frequency is observed and detected 16 times in every period of FCCH/SCH superframe, while shifting by one frame each in every period of observation. In the third embodiment, too, same as in the foregoing first and second embodiments, the compressed mode frame is divided into first portion and second portion bounded by the idle slot within one frame. The following is to explain how to insert the observation period, that is, the idle slot in which frame in one UMTS superframe, and how to determine the inserting position. In the third embodiment, same as in the foregoing second embodiment, the UMTS superframe is divided by the shorter time unit, and the position for placing the idle slot is set. Thus, in the third embodiment, the number of divisions of observation period in one UMTS superframe can be eight, and the same effects as in the first embodiment are also obtained in this case. However, unlike the first embodiment, the division interval is not the specified number of frames interval, but is an interval of a specified number of slots. In the foregoing first to third embodiments, the observation period is divided up to eight divisions, but the invention is not limited to these examples only. The number of divisions may be further increased as required on the basis of the smaller unit than the slot. The invention is thus described while referring to preferred embodiments, but the invention may be modified in various forms within the claimed scope, and such changes shall not be excluded from the scope of the invention. As described herein, in the case where the first communication system and second communication system coexist, since the idle period for observing the frequency component of the second communication system is inserted at most in 1/2 time of one frame duration for composing one superframe of first communication system, at intervals of a specified number of frames, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. In the case where the UMTS and another system coexist, since the idle period for observing the frequency component of the another system is inserted at most in 1/2 time of one frame duration for composing one superframe of UMTS, at intervals of a specified number of frames, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied, and therefore even when the UMTS and another system coexist, the frequency component of the another system can be securely observed from the UMTS, and deterioration of interleaving performance of the compressed mode frame can be suppressed at this time. Since the interval of a specified number of frames is determined by the difference in the transmission period between the UMTS and another system, the different frequency components can be observed completely depending on the difference in the transmission period. Since the idle period is placed in the center of the frame that is the unit of superframe of the UMTS, the interleaving effect is obtained securely. In the case where the first communication system and second communication system coexist, since the idle period for observing the frequency component of the second communication system is inserted at most in 1/2 time of one frame duration for composing one superframe of first communication system, at intervals of a specified number of slots, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. In the case where the UMTS and another system coexist, since the idle period for observing the frequency component of the another system is inserted at most in 1/2 time of one frame duration for composing one superframe of UMTS, at intervals of a specified number of slots, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied, and therefore even when the UMTS and another system coexist, the frequency component of the another system can be securely observed from the UMTS, and deterioration of interleaving performance of the compressed mode frame can be suppressed at this time. Since the interval of a specified number of slots is determined by the difference in the transmission period between the UMTS and another system, the different frequency components can be observed completely depending on the difference in the transmission period. Since the plural idle periods in the superframe of the UMTS are placed separately in each frame, the necessary idle duration is held in one superframe. Since the total of the plural idle periods is equal to the specified idle duration provided for observing the frequency component between the other systems, an idle period equal to the observation of different frequencies of other systems can be held in one superframe. Since the frame in which the specified time is inserted is compressed and transmitted intermittently, a frame transmission of a high decodability is realized even when an idle period is inserted in one frame period. Since the compressed frame is generated by increasing the coding rate, the compression rate is lowered, and the number of spreading codes of a shorter code length can be suppressed. Since the compressed frame is generated at a same spreading factor as another frame in which the specified idle duration is not inserted, the interference and noise resistant characteristic to the compressed frame is assured. In the case where the first communication system and second communication system coexist, since it is controlled so that the idle period for observing the frequency component of the second communication system is inserted at most in 1/2 time of one frame duration for composing superframe in the superframe of the first communication system, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. In the case where the UMTS and another system coexist, since the idle period for observing the frequency component of the another system is inserted at most in 1/2 time of one frame duration for composing one superframe of UMTS, at intervals of a specified number of frames, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the UMTS and another system coexist, the frequency component of the another system can be securely observed from the UMTS. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. Since the interval of a specified number of frames is determined by the difference in the transmission period between the UMTS and another system at the time of controlling, the different frequency components can be observed completely depending on the difference in the transmission period. Since the specified idle period is placed in the center of the frame which is the unit of superframe of the UMTS at the time of controlling, the interleaving effect may be obtained securely. In the case where the first communication system and second communication system coexist, since it is controlled so that the idle period for observing the frequency component of the second communication system is inserted at most in 1/2 time of one frame duration for composing superframe in the superframe of the first communication system and at an interval of a specified number of slots, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. In the case where the UMTS and another system coexist, since the idle period for observing the frequency component of the another system is inserted at most in 1/2 time of one frame duration for composing one superframe of first communication system, at intervals of a specified number of frames of UMTS, at intervals of a specified number of slots, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the UMTS and another system coexist, the frequency component of the another system can be securely observed from the UMTS. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. Since the interval of a specified number of slots is determined by the difference in the transmission period between the UMTS and another system at the time of controlling, different frequency components can be observed completely depending on the difference in the transmission period. Since plural idle periods are disposed in separate frames in the superframe of the UMTS at the time of controlling, a necessary idle duration can be held in one superframe. Since the total of the plural idle periods is set equal to the specified idle duration provided for observing the frequency component between the other systems at the time of controlling, an idle duration equal to observation of different frequencies between other systems can be held in one superframe. Since the compressed frame is generated by increasing the coding rate at the time of controlling, the compression rate is lowered, and the number of spreading codes of a shorter code length can be suppressed. Since the compressed frame is generated at a same spreading factor as another frame in which the specified idle duration is not inserted at the time of controlling, the interference and noise resistant characteristic to the compressed frame is assured. Since the average transmission power is increased in the compressed mode at the time of controlling, the characteristic deterioration may be suppressed to a minimum limit. By compressing the frames to be transmitted intermittently at the time of compressed mode, and inserting an idle period for observing the frequency component of the second communication system at most in 1/2 time of one frame duration for composing the superframe of the first communication system in the superframe of the first communication system and at an interval of a specified number of frames determined by the relation of the frame structure between the first communication system and second communication system, since the step for transmitting intermittently the compressed frames is set up, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. By compressing the frames to be transmitted intermittently at the time of compressed mode, and inserting an idle period for observing the frequency component of the second communication system at most in 1/2 time of one frame duration for composing the superframe of the first communication system in the superframe of the first communication system and at an interval of a specified number of slots determined by the relation of the frame structure between the first communication system and second communication system, since the step for transmitting intermittently the compressed frames is set up, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the first communication system and second communication system coexist, the frequency component of the second communication system can be securely observed from the first communication system. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. In particular, in the case where the UMTS and another system coexist, since the idle period for observing the frequency component of the another system is inserted at most in 1/2 time of one frame duration for composing one superframe of UMTS, at intervals of a specified number of frames or at an interval of a specified number of slots, it is not required to observe the frequency component by one observation in one superframe, and the restrictions in frame transmission such as error correction code and spreading factor can be satisfied. Therefore, even when the UMTS and another system coexist, the frequency component of the another system can be securely observed from the UMTS. Further, deterioration of interleaving performance of the compressed mode frame during such observation can be suppressed. Since the compressed frame is generated by increasing the coding rate at this step, the compression ratio is lowered, and the number of spreading codes of a shorter code length can be suppressed. Since the compressed frame is generated at a same spreading factor as another frame in which the specified idle period is not inserted at this step, the interference and noise resistant characteristic to the compressed frame is assured. Since the average transmission power is increased in the compressed mode at this step, the characteristic deterioration may be suppressed to a minimum limit. INDUSTRIAL APPLICABILITY As described herein, the mobile radio communication system, the communication apparatus applied in the mobile radio communication system, and the mobile radio communication method of the invention are useful for observing the control channel of another system by making use of idle period in the mobile radio communication system. In particular this invention can suitably used in the mobile radio communication system in which the UMTS (Universal Mobile Terrestrial communication System) and GSM (Group Specific Mobile) system coexist.

Claims: A mobile radio communication system employing a CDMA method, comprising a transmitter (1) transmitting a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode within a first frame transmission period, which is formed of plural frames and required to transmit a predetermined number of frames, and a receiver (2) receiving said frames and said compressed frames transmitted by said transmitter (1), said transmitter (1) comprises an interleaver (13) which performs interleaving of data in a frame in bit units; a spreading unit (14), in which a plurality of frames processed by said interleaver (13) are inputted, wherein said spreading unit (14) compresses frames within said first frame transmission period to produce compressed frames, and divides each of said compressed frames into two divided parts, and allocates one of said divided parts at the beginning of a frame period and the other one of said divided parts at the end of said frame period, and creates, into each of said compressed frames, an idle period whose length is half as much as that of each frame or less, in a compressed mode; and a radio frequency transmitter (15) which transmits said compressed frames processed by said spreading unit (14) in said compressed mode; and said receiver (2) comprises a radio frequency receiver which monitors, within said idle period in each of said compressed frames, a frequency component in a control channel, said control channel having a second frame transmission period and being employed in a different mobile radio communication system. The mobile radio communication system according to claim 1, wherein said different mobile radio communication system is GSM system. A receiver used in a mobile radio communication system employing a CDMA method, wherein a transmitter (1) of said mobile radio communication system transmits a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode during a first frame transmission period, which is formed of plural frames, performs interleaving of data to be transmitted in bit units, and said first frame transmission period is defined as a period required to transmit a predetermined number of frames, said receiver comprises: a radio frequency receiver (25), to which said compressed frames received by an antenna are inputted, for monitoring a frequency component in a control channel within an idle period in each of said compressed frames within said first frame transmission period, wherein said control channel has a second frame transmission period which is employed in a different mobile radio communication system, and each of said compressed frames has an idle period whose length is half as much as that of each frame or less, and each of said compressed frames is divided into two divided parts such that one of the divided parts is allocated at the beginning of a frame period and the other one of said divided parts is allocated at the end of said frame period. A transmitter used in a mobile radio communication system employing a CDMA method, wherein said transmitter (1) transmits a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode within a first frame transmission period, which is formed of plural frames, and said first frame transmission period is defined as a period required to transmit a predetermined number of frames, said transmitter (1) comprises: an interleaver (13) which performs interleaving of data in a frame in bit units; and a spreading unit (14), in which a plurality of frames processed by said interleaver (13) are inputted, wherein said spreading unit (14) compresses frames within said first frame transmission period to produce compressed frames, divides each of said compressed frames into two divided parts, allocates one of said divided parts at the beginning of a frame period and the other one of said divided parts at the end of said frame period, and creates, into each of said compressed frames, an idle period whose length is half as much as that of each frame or less, in a compressed mode; and a radio frequency transmitter (15) which transmits said compressed frames processed in said spreading unit (14) in said compressed mode. A mobile radio communication method used in a CDMA system, wherein said system includes a transmitter (1) which performs interleaving of data to be transmitted in bit units, and transmits a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode within a first frame transmission period, which is formed of plural frames, and a receiver (2) that receives said frames and said compressed frames transmitted by said transmitter (1), said first frame transmission period is defined as a period required to transmit a predetermined number of frames, said mobile radio communication method comprises: steps, executed by said transmitter (1), for compressing frames within said first frame transmission period; dividing each of said compressed frames into two divided parts for allocating one of said divided parts at the beginning of a frame period and the other one of said divided parts at the end of said frame period; allocating in each of said frames an idle period whose length is half as much as that of each frame or less; transmitting said frames with said idle period to said receiver (2); and a step, executed by said receiver (2) for monitoring frequency components in a control channel having a second frame transmission period within said idle period allocated in each of said compressed frames, wherein said second frame transmission period is employed in a different mobile radio communication system. A mobile radio communication method used in a receiver (2) for a CDMA system, wherein a transmitter (1) of said mobile radio communication system transmits a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode during a first frame transmission period, which is formed of plural frames, and said first frame transmission period is defined as a period required to transmit a predetermined number of frames, performs interleaving of data to be transmitted in bit units, said mobile radio communication method comprises: receiving said compressed frames within said first frame transmission period, each of said compressed frames having an idle period whose length is half as much as that of each frame or less and being divided into at least two parts such that one of said divided parts is allocated at the beginning of a frame period and the other one of said divided parts is allocated at the end of said frame period; and monitoring a frequency component in a control channel within said idle period in each of said compressed frames, wherein said control channel has a second frame transmission period which is employed in a different mobile radio communication system. A mobile radio communication method used in a transmitter (1) for a CDMA system, wherein said transmitter (1) transmits a plurality of frames in a normal mode and a plurality of compressed frames in a compressed mode within a first frame transmission period, which is formed of plural frames, and said first frame transmission period is defined as a period required to transmit a predetermined number of frames, said mobile radio communication method comprises: generating said compressed frames through processes of compressing a plurality of frames within said first frame transmission period, dividing each of said compressed frames into at least two parts for allocating one of said divided parts at the beginning of a frame period and the other one of said divided parts at the end of said frame period, and creating in each of said compressed frames an idle period whose length is half as much as that of each frame or less, and transmitting said compressed frames generated by said generating step.

Inventors: MURAI HIDESHI, VOYER NICOLAS, YANO YASUHIRO, MURAI, HIDESHI, VOYER, NICOLAS, YANO, YASUHIRO, Murai, Hideshi, Mitsubishi Denki Kabushiki Kaisha, VOYER, Nicolas, Mitsubishi Elec.Information Techn, YANO, Yasuhiro, Mitsubishi Denki Kabushiki Kaisha
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1999
Main classification: H04Q7
IPC codes: H04B7, H04W24, H04W72, H04W36