Base station for cordless telephone device, base station and handset for cordless telephone device, and telephone control device and base station for cordless telephone system

Abstract

To allow a handset to receive a beacon, which is a control signal, without being affected by interference by avoiding the occurrence of co-channel interference between adjacent base stations in a cordless telephone device using the DECT wireless communication system.SOLUTION: A base station 20 for a TDMA-TDD cordless telephone device includes: slot group information storage means 23 that stores slot group information that specifies a slot group to be used at the base station from among slot groups into which a plurality of slots used in wireless transmission are classified; blind slot information generation means 24 that identifies slots to be used at the base station from among all slots specified in the TDMA-TDD system based on the slot group information, and generates blind slot information, which is information on availability for each slot; and a DECT transmission / reception control unit 22 that broadcasts the blind slot information using a beacon and transmits and receives wireless transmission in a slot selected based on the blind slot information.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a base station for a cordless telephone device that utilizes a DECT wireless communication system suitable for application to digital cordless telephones, a base station and handset for a cordless telephone device, and a telephone control device and base station for a cordless telephone system. [Background technology]

[0002] In Japan, key telephone systems use not only key telephones that are directly connected to the main unit via a wired transmission line, but also digital cordless telephones (handsets) that are connected to the main unit via a wireless base station. These digital cordless telephones are highly valued as telephones that can be used anywhere, and are expected to have the same functionality as key telephones.

[0003] In Japan, digital cordless phones have used the second-generation cordless telephone system standard (RCR STD-28), but in 2011 a new standard for broadband digital cordless phones (ARIB STD-T101) was established, making it possible to realize digital cordless phones that comply with J-DECT. J-DECT is a DECT standard localized for Japan, and specifies six frequencies (F1 to F6) within the 1.9 GHz private band (1893.5 MHz to 1906.1 MHz).

[0004] In a key telephone system, the required number of telephone lines are connected to the main unit depending on the call volume (the number of communication lines occupied per unit time) in the user's installation environment, and these can be shared and used by each key telephone.

[0005] In such a system, if all or some of the key telephones are replaced with digital cordless telephones, the wireless base stations can be arranged so that the calling area of ​​one or more wireless base stations covers the entire service area (office). This is expressed as covering the entire service area (office) by expanding the base station zone, which is the calling area of ​​one base station, into an area.

[0006] As with key telephones, it is desirable for such digital cordless telephones (handsets) to be able to make and receive calls reliably at all times, except when the telephone lines are full. Even when traffic on the digital cordless telephones (handsets) becomes congested and the number of handsets making simultaneous calls increases, it is desirable for such digital cordless telephones (handsets) to be able to make and receive calls reliably at all times, except when the telephone lines are full.

[0007] Patent Document 1 discloses a technology for preventing co-channel interference in a TDMA-TDD digital cordless telephone device. When a call is being made on another nearby digital cordless telephone device, the timing of the slot in which transmission and reception are performed on the other digital cordless telephone device is detected, and a slot position that does not overlap in time with the detected slot position in which transmission and reception are performed is calculated, and transmission and reception are performed at this calculated slot position. By applying this technology, the effects of co-channel interference from surrounding base station zones can be reduced when base station zones are expanded to cover the entire service area.

[0008] Non-Patent Document 1 describes the carrier sense regulations for the J-DECT system. The J-DECT system defines two carrier sense levels (first level: -82 dBm, second level: -62 dBm) and two carrier groups (first carrier group: F1, F2, F5, F6, second carrier group: F3, F4), and specifies that before a base station or a mobile device starts transmission, carrier sense is performed in advance for two or more consecutive frames, and the channel to be used is selected in the following order of priority: First Priority: Channels in the first carrier group with an interference level below the first level Second Priority: Channels in the second carrier group with an interference level lower than the first level Third Priority: Channels in the first carrier group with an interference level below the second level 4th Priority: Channels in the 2nd carrier group with an interference level below the 2nd level - Transmission is not possible if there is no channel with an interference level below the second level

[0009] Furthermore, Non-Patent Document 1 also specifies the protection regulations for time division multiple access narrowband digital cordless telephones in the J-DECT system (hereinafter referred to as the private PHS protection regulations).The regulations state that a J-DECT base station determines whether or not there are radio waves at the frequencies of the two control channels of the private PHS system (1,899.072 MHz and 1,900.8 MHz), and if there are radio waves, it allows only the first carrier group to be used, and that when a DECT base station is idle, i.e., not communicating, it allows only F1 or F5 to be used as much as possible for transmitting dummy bearers.

[0010] The former provision was enacted because the radio waves of the second carrier group are in the same band as the control channel of privately operated PHS, and if interference occurs there is a risk that the privately operated PHS system will become uncontrollable.

[0011] On the other hand, the basic idea for the radio waves of the first carrier group is to share them with the private PHS system by detecting an available channel. However, the time interval for detecting an available channel in the private PHS system is often around 300 us, whereas the time length of the dummy bearer is 83.3 us, as shown in Figure 16 (details will be given later). This means that there is a possibility that interference that is not visible on the private PHS side will slip through the available channel detection, making it difficult to share the dummy bearer with the private PHS system by detecting an available channel.

[0012] Therefore, in order to avoid market disruptions, many privately operated PHS products have taken measures to avoid using the F1 and F5 channel bands, but they do use the F2 and F6 channel bands, and there is a risk of market disruptions occurring if J-DECT base stations transmit dummy bearers in these bands.As a result, the latter regulation was enacted, limiting the transmission of dummy bearers by J-DECT base stations to F1 or F5.

[0013] Figure 16 shows the frame format of a DECT frame, where (a) shows a short frame and (b) shows a long frame. As shown in Figure 16, DECT uses short frames with a time length of 83.3 us called dummy bearers and long frames with a time length of 368.1 us called traffic bearers.

[0014] The former is a downlink (base station → mobile device) transmission frame sent as a beacon by an idle (non-communicating) base station to inform the mobile device of base station identifier information, system information, paging information, etc. The latter is a bidirectional (base station ⇔ mobile device) frame used during one-to-one communication between the base station and mobile device, and can transmit 320 bits of information stored in the B-Field in both directions between the base station and mobile device.

[0015] In this way, when J-DECT base stations in the vicinity of a private PHS system transmit beacons, priority is given to using channels F1 or F5 with interference levels of level 1 or lower, but if no channels with interference levels of level 1 or lower exist, channels with level 2 or lower will also be used.

[0016] Non-Patent Document 2 describes that in a wireless LAN, the effect of reducing co-channel interference by increasing the interference distance by using different frequency channels between adjacent APs is evaluated by using throughput.

[0017] In addition, in mobile telephone systems, four-cell repeat arrangements, seven-cell repeat arrangements, etc. are used to spatially reuse the same frequency channel. In wireless systems with small zone configurations like this, it is a well-known technique to increase the interference distance and reduce co-channel interference by using different radio frequencies between adjacent base stations. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Application Publication No. 4-286431 [Non-patent literature]

[0019] [Non-Patent Document 1] Standard for Radio Equipment of Time Division Multiple Access Wideband Digital Cordless Telephone Stations (ARIB STD-T101) [Non-patent document 2] Dynamic Channel Allocation in Wireless LAN Systems, IEICE Technical Report. RCS, Wireless Communication Systems 97(266), 27-32, 1997-09-24 Summary of the Invention [Problem to be solved by the invention]

[0020] However, according to the carrier sense provision described in Non-Patent Document 1, while it is possible to reduce co-channel interference in systems with a small number of base stations or systems with low traffic, in systems with a large number of base stations or systems with high traffic during busy hours, there is a problem that channels at level 1 or lower are insufficient and it is necessary to use channels at level 2 or lower as well, which can result in co-channel interference. This problem will be explained below.

[0021] FIG. 17 is a diagram showing the relationship between the communication distance and the reception level of a DECT radio signal calculated based on the ITU-R P.1238-6 indoor propagation model, which is generally used as an indoor radio wave propagation model.

[0022] Generally, in indoor radio wave propagation, the reception level is affected by multipath fading and fluctuates by about 10 to 15 dB over time. Figure 17 shows the average reception level and the reception level when it drops due to fading, along with the carrier sense first level and carrier sense second level. The fading depth is set to 15 dB, assuming non-line-of-sight propagation.

[0023] Minimum receiver sensitivity of the DECT transceiver (for a given transmission quality, e.g., bit error rate 10 -3 In order to ensure that communication is possible within the base station zone even when there are drops due to fading, with a reception level required to achieve the following (required) of -86 dBm and a 20 dB margin for shielding effects due to human bodies, etc., it is clear from Fig. 17 that the base station zone radius must be 30 m or less. It can also be seen that the reception level is almost at or above Level 1 even at a communication distance of 120 m, which is four times the base station zone radius.

[0024] Figure 18 is a diagram illustrating the impact of co-channel interference when base station zones are deployed in an area using regular hexagonal zones. This diagram shows six adjacent base stations and 12 second-neighboring base stations relative to a centrally located base station. It can also be seen that if the base station zone radius is r, the distance between the centrally located base station and the adjacent base stations is 2r, and the distance between the centrally located base station and the second-neighboring base station is 4r. In this example of base station area deployment, there are approximately 20 base stations in an area four times the base station zone radius, including the second-neighboring base stations. Therefore, if carrier sensing is performed at the first level, approximately 20 base stations will share the channel.

[0025] Furthermore, if the distance between base stations in adjacent zones is 60 m, as shown in Figure 17, the range of fluctuation in the reception level of radio waves from adjacent base stations is -60 dBm to -75 dBm, and will probabilistically fall below the second level (-62 dBm). Therefore, if there are insufficient channels below the first level, adjacent base stations may transmit simultaneously, resulting in co-channel interference.

[0026] In a digital cordless telephone system using J-DECT, each base station transmits one or two beacons at 10 ms intervals. The reason for transmitting two beacons at 10 ms intervals is to ensure that if one beacon cannot be received due to co-channel interference, the other beacon can be received instead, and the two beacons broadcast the same information.

[0027] Another reason for transmitting two beacons at 10 ms intervals is that when a mobile device in a call moves between base station zones and performs a handover, it searches for a base station. Even if one of the beacons from the base station to which it is moving is transmitted in the same slot as the slot used by the mobile device for the call, it is possible to receive the other beacon from the base station that is transmitted in a different slot, thereby ensuring that the beacon from an adjacent base station can be received regardless of its transmission slot.

[0028] In this way, in a digital cordless telephone system capable of handover, it is desirable to transmit two beacons every 10 ms. However, as mentioned above, since the wireless channel is shared between neighboring base stations, if there are a large number of installed base stations, the number of channels used by the beacons increases, which increases the probability of co-channel interference. The following describes the issues with digital cordless telephone systems.

[0029] If the total number of base stations in a digital cordless telephone system is M (M is a natural number greater than or equal to 1), and the maximum number of simultaneous calls in the entire system is K (K is a natural number greater than or equal to 1), then a maximum of (M + K) or (2M + K) downstream channels can be used simultaneously.

[0030] Furthermore, as mentioned above, if a private PHS system exists near a digital cordless telephone system using DECT, the private PHS protection provisions of the ARIB standard (ARIB STD-T101) stipulate that the two frequency channels F1 and F5 must be used as much as possible for beacon transmission, effectively limiting the number of available channels to 24.

[0031] For example, in a digital cordless telephone system in which each base station transmits two beacons at 10 ms intervals, if there are 12 base stations, the beacons alone occupy 24 channels, and further calls must use channels at level 2 or lower, which can result in co-channel interference. Furthermore, if there are more than 12 base stations, beacons will be transmitted using channels at level 2 or lower, resulting in co-channel interference between beacons. Even if there are fewer than 12 base stations, if there are a large number of simultaneous calls during the busy hour, co-channel interference can occur, as channels at level 2 or lower will also be used.

[0032] A more detailed explanation will be given below using as an example a case where a regular hexagonal base station zone as shown in FIG. 18 is expanded to cover the entire service area.

[0033] As shown in Fig. 18, when regular hexagonal base station zones are deployed in an area to cover the entire service area, a maximum of six adjacent zones and 12 second-neighboring zones are generated. Therefore, with this area deployment of base station zones, even if only interference from adjacent zones is considered, for example, the central base station zone will receive a maximum of 14 beacons in a 10 ms cycle.

[0034] For this reason, for example, if more than 10 simultaneous calls are being made in the own base station zone or an adjacent base station zone, it becomes impossible to select a slot that does not overlap in time with slots where transmission and reception are already being performed. In such a case, the technology described in Patent Document 1 cannot be applied, and a base station in an adjacent base station zone may use the frequency channel and slot used for beacon transmission in the own base station zone for a call, which may result in a handset being unable to receive the beacon due to co-channel interference.

[0035] Incidentally, when a traffic bearer used during one-to-one communication between a base station and a mobile device is subjected to co-channel interference, the deterioration of communication quality can be used as a trigger to perform interference avoidance processing, such as frequency channel switching, slot switching, or handover.

[0036] On the other hand, the dummy bearer transmitted as a beacon by an idle base station is a notification channel transmitted by the base station, and no interference avoidance processing is performed. Therefore, a particular issue is that a handset that experiences same-channel interference near the base station zone boundary will be unable to receive the beacon.

[0037] Co-channel interference to beacons transmitted by base stations is discussed in more detail below.

[0038] In digital cordless telephone systems using DECT, 10-ms frame synchronization is typically performed between base stations to ensure sufficient communication capacity. The timing signal for this frame synchronization can be generated by the main unit and distributed to each base station via the base station transmission line. Each base station can also receive beacons broadcast from surrounding base stations when it starts up, and then synchronize wirelessly in sequence.

[0039] In this case, the downlink transmission period (base station → slave device) in the first half of the 10 ms frame and the uplink transmission period (slave device → base station) in the second half are synchronized between base stations, and in this case, only beacons from other adjacent base stations will interfere with the beacon transmitted by the base station.

[0040] In an area deployment using regular hexagonal base station zones, the distance between the base station in question and an adjacent base station is 2r, where r is the zone radius. According to Figure 17, the minimum reception level during fading fluctuations at a communication distance of 60 m, which corresponds to 2r, is -75 dBm, which is below the carrier sense level 2 of -62 dBm. Therefore, if there are no available channels below the carrier sense level 1, it is possible that the frequency and slot in which the beacon is being received will be used to transmit the beacon of the adjacent base station or the traffic bearer for the call.

[0041] Regarding the effects of co-channel interference from adjacent base stations, if the handset is located near the zone boundary with the adjacent base station, in the worst case scenario, the distance from the base station to the handset and the distance from the adjacent base station to the handset will be almost equal. As a result, the average reception level of the beacon from the base station and the average reception level of the interference wave will be almost equal, and there is a high probability that the beacon will not be received.

[0042] On the other hand, with regard to co-channel interference from the next-neighboring base station, in a planar deployment using a regular hexagonal base station zone, the distance between the base station and the next-neighboring base station is 4r, where r is the zone radius.

[0043] According to Figure 17, the average reception level during fading fluctuations at a communication distance of 120 m, which corresponds to 4r, is -68 dBm, which is below the second carrier sense level of -62 dBm. Therefore, the next-neighboring base station cannot detect the beacon from that base station and may transmit the beacon of the next-neighboring base station or a traffic bearer for a call using the same frequency and slot as the beacon.

[0044] However, in the example of area deployment using regular hexagonal base station zones shown in Figure 18, as shown in Figure 19, with regard to the impact of co-channel interference from the next-neighboring base station, even when the mobile device is near the zone boundary with the adjacent base station, the worst-case distance from the next-neighboring base station to the mobile device is three times the zone radius, and according to Figure 17, the average reception level of fading fluctuations at a communication distance of 90 m, which corresponds to 3r, is -66 dBm, which is 14 dB smaller than the average signal reception level of -52 dBm near the zone boundary, so it can be said that the beacon from the base station is hardly affected by co-channel interference from the next-neighboring base station.

[0045] As explained above, when area deployment is performed in a digital cordless telephone system using DECT, there is a risk that during times of traffic congestion, there will be a shortage of channels below the first carrier sense level, causing co-channel interference from adjacent base stations, which may result in some handset units being unable to receive beacons.

[0046] Non-patent document 2 describes that in a wireless LAN, the effect of reducing co-channel interference by increasing the interference distance by using different frequency channels between adjacent APs is evaluated using throughput. Also, in a mobile telephone system, a 4-cell repeat arrangement, a 7-cell repeat arrangement, etc. are used to spatially reuse the same frequency channel. In wireless systems with such a small zone configuration, the technology of increasing the interference distance and reducing co-channel interference by using different radio frequencies between adjacent base stations is generally known.

[0047] However, in a digital cordless telephone system using DECT, as mentioned above, when installed near a private PHS system, the only radio channels that can be used are essentially two, F1 and F5, and area expansion based on frequency channel allocation cannot reduce the interference distance.

[0048] The present invention aims to solve the above problems and to avoid the occurrence of co-channel interference between adjacent base stations in base stations of cordless telephone devices that use the DECT wireless communication system, base stations and handsets of cordless telephone devices, and telephone control devices and base stations of cordless telephone systems, and to reduce the effects of co-channel interference by increasing the interference distance, thereby enabling beacons, which are control signals, to be received without being affected by interference. [Means for solving the problem]

[0049] In order to solve the above problems, the present invention provides a base station for a TDMA-TDD cordless telephone device, which is configured by connecting one or more base stations, each capable of connecting a plurality of handset units, to a telephone control device connected to a wide area network, the base station comprising: slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used at the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in radio transmission are classified; blind slot information generation means for specifying a slot to be used at the base station from all slots specified by the TDMA-TDD system based on the slot group information, and generating blind slot information, which is information on whether each slot is available or not; and ,embedded in the MAC information of the DECT standard short page frame, or embedded in the proprietary information of the DECT standard system information frame, The device is characterized by including a DECT transmission / reception control unit that notifies by beacon and transmits and receives radio transmissions in slots selected based on the blind slot information.

[0052] The slot group information may be information for identifying the slot group used by the base station. Alternatively, the slot group information may be information on a slot group calculated in the cordless telephone device from identification information of the base station according to a predetermined rule, and the blind slot information generating means may generate blind information from the slot group information.

[0053] Furthermore, in order to calculate the slot group information from the base station identification information, the remainder obtained by dividing the base station identification information by L (L is a natural number of 3 or more) can be referenced.

[0054] The present invention also provides a base station and a handset for a cordless telephone device, which comprises one or more base stations connected to a telephone control device connected to a wide area network and a plurality of handset units connectable to the base stations, the base station comprising slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used by the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in radio transmission are classified; blind slot information generation means for specifying a slot to be used by the base station from all slots specified by the TDMA-TDD system based on the slot group information, and generating blind slot information, which is information on whether each slot is available or not; and ,embedded in the MAC information of the DECT standard short page frame, or embedded in the proprietary information of the DECT standard system information frame, a DECT transmission / reception control unit that notifies by a beacon and transmits / receives radio transmission in a slot selected based on the blind slot information, ,embedded in the MAC information of the DECT standard short page frame, or embedded in the proprietary information of the DECT standard system information frame, The slave unit is notified by a beacon and transmits and receives radio transmissions using a slot selected based on the blind slot information, and the slave unit is equipped with a slot group table storage means for generating a slot group table for each base station based on the base station search information and blind slot information acquired when searching for a base station and for storing the table, and slave unit control means for managing the slave unit state and state transition, for acquiring information on a slot group to be used at a base station with which a radio link is to be established by referring to the slot group table for each base station, and for controlling the establishment of a radio link and communication over the radio link by using a slot selected based on the slot group information.

[0055] Furthermore, the present invention provides a telephone control device and base station of a cordless telephone system configured such that one or more base stations to which a plurality of handset units can be connected are connected to a telephone control device connected to a wide area network, wherein a plurality of slots used in radio transmission are classified into L slot groups (L is a natural number of 3 or more), and the telephone control device comprises slot group information storage means for storing slot groups to which one or more slot groups to be used by each base station are assigned such that different slot groups are assigned to adjacent base stations, and the base station comprises slot group information storage means for storing slot group information of the base station that is acquired via a base station transmission path when the base station is started and stored in the slot group information storage means, blind slot information generation means for specifying a slot to be used by the base station from all slots specified in the TDMA-TDD system based on the slot group information and generating blind slot information which is information on whether each slot is available or not, and for storing the blind slot information ,embedded in the MAC information of the DECT standard short page frame, or embedded in the proprietary information of the DECT standard system information frame, The system is characterized by including a DECT transmission / reception control unit that notifies by beacon and transmits and receives radio transmissions in slots selected based on the blind slot information. [Effects of the Invention]

[0056] According to the present invention, in a digital cordless telephone system using the DECT wireless communication method, slots are classified into L slot groups (L is a natural number equal to or greater than 3), and adjacent base stations are assigned different slot groups. This makes it possible to avoid co-channel interference between downstream signals (base station → handset) from adjacent base stations, and the co-channel interference can be limited to interference from the next-neighboring base station, allowing the handset to receive beacons, which are downstream control signals from the base station, with almost no interference.

[0057] Furthermore, according to the present invention, available slots are classified into L slot groups (L is a natural number of 3 or more), adjacent base stations use different slot groups, and available slots at each base station are ,embedded in the MAC information of the DECT standard short page frame, or embedded in the proprietary information of the DECT standard system information frame,The slave device is notified by a beacon, and the slave device stores the received information on available slots for each base station. When establishing a link with a base station, an access request is sent in the available slot of that base station. This avoids the occurrence of co-channel interference between adjacent base stations, including traffic bearers, and by increasing the interference distance, the effects of co-channel interference are reduced, making it possible to receive the beacon, which is a downlink control signal, without being affected by interference.

[0058] Furthermore, according to the present invention, adjacent base stations use different slot groups, so that during handover, the beacon of the adjacent base station is always transmitted in a slot different from the slot used by the handset in question for the call. This makes it possible to limit the number of beacons transmitted every 10 ms at the base station to one, thereby significantly reducing co-channel interference. Even when traffic on digital cordless telephones (handsets) becomes congested and the number of handsets making simultaneous calls increases, calls can be made and received reliably at any time, except when there are no available telephone lines. [Brief explanation of the drawings]

[0059] [Figure 1] FIG. 10 is a diagram showing an example of classification of slot groups (when L=3) in the present invention. [Figure 2] FIG. 2 is a diagram showing an example of area expansion (when L=3) of base station zones for the slot groups of FIG. [Figure 3] FIG. 10 is a diagram showing another example of classification of slot groups in the present invention (when L=4). [Figure 4] FIG. 4 is a diagram showing an example of area expansion (when L=4) of base station zones for the slot groups of FIG. 3. [Figure 5] 1 is a block diagram showing the basic configuration of an embodiment of a digital cordless telephone system using the DECT wireless communication system according to the present invention; [Figure 6] 1 is a block diagram showing the basic configuration of an embodiment of a main device of a digital cordless telephone system using the DECT wireless communication system according to the present invention. [Figure 7] FIG. 1 is a diagram illustrating an example of a frame format for signal transmission in a TDD (ping-pong) system on a base station transmission line. [Figure 8] FIG. 10 is a diagram illustrating an example of transmission of common control data having a multi-frame configuration. [Figure 9] 1 is a block diagram showing the basic configuration of an embodiment of a base station in a digital cordless telephone system using the DECT wireless communication system according to the present invention. [Figure 10] FIG. 10 is a block diagram showing the basic configuration of another embodiment of a base station in a digital cordless telephone system that uses the DECT wireless communication system according to the present invention. [Figure 11] 1 is a block diagram showing the basic configuration of an embodiment of a handset in a digital cordless telephone system that uses the DECT wireless communication system according to the present invention. [Figure 12] FIG. 2 is a diagram illustrating an example of a slave device state and a state transition. [Figure 13] FIG. 10 is a diagram illustrating an example of a slot group table for each base station. [Figure 14] FIG. 10 is a diagram showing an example of a location registration sequence of a slave unit to a main unit. [Figure 15] 10A and 10B are diagrams illustrating an example of a call sequence when a key operation for making a call is performed on a handset. [Figure 16] 1A and 1B are diagrams showing the frame format of a DECT frame, where (a) shows a short frame and (b) shows a long frame. [Figure 17] FIG. 1 is a diagram showing the relationship between the communication distance and reception level of a DECT radio signal calculated based on the ITU-R P.1238-6 indoor propagation model, which is generally used as an indoor radio wave propagation model. [Figure 18] FIG. 10 is an explanatory diagram of the influence of co-channel interference when base station zones are deployed in a plane using regular hexagonal zones. [Figure 19] FIG. 10 is an explanatory diagram of the influence of co-channel interference when base station zones are deployed in a plane using regular hexagonal zones. [Figure 20] FIG. 1 is a diagram showing the arrangement of radio resources in J-DECT. [Figure 21] FIG. 1 is a diagram illustrating an example of a frame format of a DECT multiframe. [Figure 22] 10 is a diagram showing a frame format of base station ID information Nt that broadcasts base station ID information. FIG. [Figure 23] 10 is a diagram showing the frame format of system information Qt that notifies system information. FIG. [Figure 24] FIG. 10 is a diagram illustrating an example of the correspondence between a Qt header and system information. [Figure 25] 10 is a diagram showing a frame format of MAC control information Mt that broadcasts MAC control information. FIG. [Figure 26] FIG. 10 is a diagram illustrating an example of the correspondence between an Mt header and a message type. [Figure 27] FIG. 10 is a diagram illustrating an example of the correspondence between Mt commands and MAC control messages. [Figure 28] 10 is a diagram showing a frame format of paging information Pt that notifies paging information. FIG. [Figure 29] FIG. 10 is a diagram illustrating an example of the correspondence between a Pt header and Bs channel information. [Figure 30] 10 is a diagram showing an example of the correspondence between MAC information types and MAC information of a Pt short page. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0060] Since the present invention relates to the control operations of a digital cordless telephone system that uses the DECT wireless communication system, first, a brief description will be given of the DECT standard for control operations related to the present invention.

[0061] The DECT standard uses the TDMA-TDD method. Figure 20 shows the allocation of radio resources in J-DECT, which has a frame structure with a 10 ms period on the time axis, with 12 slots for downlink (base station → handset) and 12 slots for uplink (handset → base station).

[0062] Six waves (F1 to F6) are specified on the frequency axis. Although it shares the same frequency band as the privately operated second-generation cordless telephone (PHS) system, the PHS control channel is a fixed frequency, and interference with this could cause the PHS handset to become uncontrollable. Therefore, the ARIB STD-T101 Private PHS Protection Regulation stipulates that after powering on, J-DECT base stations check for the presence of radio waves on the PHS control channel before transmitting, and if they determine that radio waves are present, they will not use channels F3 and F4.

[0063] For channels other than F3 and F4, which overlap with the PHS control channel, the band is shared with PHS for free channel detection. However, the free channel detection time interval for PHS systems is often around 300 µs, which means that dummy bearers can slip through this time and cause invisible interference on the PHS side. Therefore, the ARIB STD-T101 PHS Protection Regulation stipulates that J-DECT base stations, after powering on, check for the presence of PHS control channel signals before transmitting. If signals are detected, they should avoid transmitting dummy bearers on F2 and F6 channels as much as possible. This is because many PHS products already have measures in place to avoid using the F1 and F5 channel bands to avoid market interference, but the F2 and F6 channel bands are in use, and transmitting dummy bearers on these bands by J-DECT base stations could cause market interference.

[0064] When transmitting wirelessly using DECT, the handset and base station detect available channels and select a channel (combination of frequency channel and slot) with a low reception (interference) level.

[0065] The dummy bearer transmitted as a beacon by an idle base station is a one-way broadcast channel for downlink only, and is transmitted using one or two downlink radio resources (channels) for each base station.

[0066] The traffic bearer used during one-to-one communication between the base station and the mobile station is a bidirectional channel, and a pair of slots (for example, slot 1 and slot 13) spaced 5 ms apart are used.

[0067] In addition, a base station in a communication state can transmit both a dummy bearer for a beacon and a traffic bearer, and can also transmit beacon information using the A-Field in the traffic bearer.

[0068] In a digital cordless telephone system using DECT, traffic bearers are transmitted for each point-to-point communication between a base station and a handset, and dummy bearers are transmitted up to the number of base stations or twice the number of base stations.

[0069] The transmission rights of both dummy bearers and traffic bearers are acquired in the same way through free channel detection. From the viewpoint of effective frequency utilization, the free channel detection level is set so that channels used by surrounding base stations and their slave devices can be reused and used. During traffic congestion, there is a possibility that some slave devices will not be able to receive dummy bearers due to co-channel interference from traffic bearers from surrounding base stations. For this reason, it is desirable to use traffic bearers to the minimum extent necessary.

[0070] FIG. 21 shows an example of a frame format of a DECT multiframe.

[0071] This multi-frame structure is used to broadcast tail data (40 bits) using beacons in DECT. One multi-frame has a time length of 160 ms and is made up of 16 frames (frame 0 to frame 15).

[0072] The tail data broadcast by the beacon is classified into base station ID information Nt, system information Qt, MAC control information Mt, paging information Pt, and upper layer control information Ct depending on its type. Such beacon type information is stored in the header information of the dummy bearer A-field.

[0073] FIG. 22 shows a frame format of base station ID information Nt that broadcasts base station ID information.

[0074] The base station ID information Nt includes a fixed access right code of "0001", an equipment manufacturer ID (EIC), a system ID (FPN), and a base station ID (RPN). Each user is assigned a different system ID, and the base station within the user's system is identified by the base station ID.

[0075] FIG. 23 shows a frame format of system information Qt that notifies system information, and FIG. 24 shows an example of the correspondence between the Qt header and system information.

[0076] The system information Qt includes basic information such as the carrier number information and slot number information of the Qt frame, as well as information on the number of available carriers, multiframe number information, transmission power information of the base station, and unique system information.

[0077] Fig. 25 shows the frame format of MAC control information Mt that broadcasts MAC control information, Fig. 26 shows an example of the correspondence between Mt headers and message types, and Fig. 27 shows an example of the correspondence between Mt commands and MAC control messages.

[0078] Fig. 28 shows a frame format of paging information Pt that broadcasts paging information, Fig. 29 shows an example of the correspondence between the Pt header and Bs channel information, and Fig. 30 shows an example of the correspondence between the information type of the Pt short page and MAC information.

[0079] The paging information Pt broadcasts data on the Bs channel (slow broadcast channel) and MAC information. The Bs channel can broadcast paging information and unique information to notify that there is downlink data addressed to a specific mobile station. MAC information includes blind slot information (unavailable slots of the base station), base station status (BUSY, etc.), and available frequency channel information, and the type of MAC information broadcast in the frame is stored in the information type of the dummy bearer A-field.

[0080] The paging information Pt frame includes a short page that broadcasts 20 bits of Bs channel data and MAC information, and a full page that broadcasts only 36 bits of Bs channel data. A long page can also be used, which broadcasts 36 × N bits of Bs channel data by concatenating multiple full pages. The frame type information of the paging information Pt is transmitted in the Pt header.

[0081] In the DECT standard, the frame number is specified as 28 bits, incremented by 1 for each frame, and goes through a cycle approximately once a month. The upper 24 bits are called the multi-frame number.

[0082] In a digital cordless telephone system using the DECT system, the frame numbers and multiframe numbers are generally synchronized between base stations.

[0083] Paging information Pt is transmitted in frame 0, and battery-powered, power-saving handset devices can receive only frame 0 discontinuously at 160 ms intervals. The DECT standard specifies that a base station must transmit the same beacon information in four consecutive multi-frames to enable discontinuous reception at 640 ms intervals. In other words, power-saving handset devices can receive only frame 0 discontinuously at 640 ms intervals.

[0084] If there are multiple pieces of paging information Pt, up to six pieces of paging information Pt can be transmitted within one multi-frame. The presence or absence of subsequent paging information Pt within the same multi-frame is indicated by the first bit of the Pt header, and the power-saving slave device transitions to a sleep state after receiving all of the paging information Pt.

[0085] Furthermore, if there is no particular paging information, the base station can transmit base station ID information Nt instead of paging information Pt. The base station ID information Nt is used by the mobile device when searching for a base station. Furthermore, system information Qt is always transmitted in frame 8, and base station ID information Nt is always transmitted in frame 14.

[0086] Furthermore, during one-to-one communication between a base station and a mobile device, even-numbered frames (frame 1, frame 3, ... frame 11) are used as upper layer control information Ct, a data link is established between the base station and the mobile device on the upper layer control information Ct, and low-speed control information can be transmitted in both directions using a bidirectional low-speed control channel Cs on the data link. Note that the upper layer control information Ct is a bidirectional channel, and the upper layer control information Ct is also transmitted using the A-Field for the uplink traffic bearer.

[0087] A traffic bearer is used for one-to-one communication between a base station and a handset, and the Cs channel is a low-speed channel that uses the tail (40 bits) of the A-field of the traffic bearer, but it is also possible to use the high-speed Cf channel that uses the B-field (320 bits) of the traffic bearer. For example, when a call is in progress, voice data is transmitted in the B-field, so control data is transmitted in the Cs channel in the A-field, and when there is no call, control data can be transmitted at high speed using the Cf channel in the B-field.

[0088] The even-numbered frames (frame 1, frame 3, etc.) are also used for bidirectional transmission of MAC control information Mt for MAC access control. When performing one-to-one communication between a base station and a mobile device, it is first necessary to establish a bearer (bidirectional data link) using the MAC control information Mt. The MAC control information Mt is also used in encryption procedures and handovers.

[0089] In the dummy bearer, if there is no MAC control information Mt, the base station ID information Nt can be transmitted in even-numbered frames (frame 1, frame 3, etc.) The base station ID information Nt is used when the mobile device searches for a base station.

[0090] Taking the above DECT standard into consideration, the present invention provides a digital cordless telephone system using the DECT wireless communication method, in which available slots are classified into L slot groups (L is a natural number equal to or greater than 3), adjacent base stations use different slot groups, and each base station notifies the handset of the available slots using a beacon. The handset stores the received information on the available slots for each base station, and when establishing a link with a base station, it transmits an access request using the available slot of that base station, thereby avoiding the occurrence of co-channel interference between adjacent base stations and reducing the effects of co-channel interference by increasing the interference distance, thereby enabling the beacon, which is a control signal, to be received without being affected by interference.

[0091] The present invention will now be described with reference to the drawings.

[0092] Figure 1 shows an example of slot group classification in the present invention (when L = 3), where each of the downlink slots (SL0 to SL11) and uplink slots (SL12 to SL23) in the radio resources of DECT is classified into three slot groups (slot groups SL0 to SL3 and SL12 to SL15, slot groups SL4 to SL7 and SL16 to SL19, and slot groups SL8 to SL11 and SL20 to SL23).

[0093] In Figure 1, consecutive slots are assigned to each slot group, but for example, every third slot may be assigned to the same slot group, and any slot group can be assigned as long as there is no overlap. Also, the number of slots assigned to each slot group does not necessarily have to be the same; for example, five or more slots may be assigned to a slot group of a base station where high traffic is expected, taking into account the traffic expected at each base station. As shown here, uplink and downlink paired slots belong to the same slot group.

[0094] Figure 2 shows an example of the area expansion of base station zones for the slot groups in Figure 1, where the slot groups used by each base station are shown in the same gray scale as in Figure 1. As shown here, by categorizing the slots as in Figure 1, it is possible to make the slot groups used by adjacent base stations different from each other. This makes it possible for the central white zone to be free from interference from adjacent base station zones (light gray or dark gray) and only to be subjected to interference from the next adjacent white zone, thereby increasing the interference distance and reducing the effects of co-channel interference.

[0095] Furthermore, when a mobile device in a call in the central white zone moves and performs a handover, the adjacent base station zone to which it moves is a light gray or dark gray zone, and because it uses a different slot group from the base station from which it moved, the slots used for the call and the beacon transmission slots of the destination base station are different, so it is guaranteed that the beacon of the destination base station will be found when searching for the base station in use during handover. This eliminates the need to transmit two beacons every 10 ms, and allows it to transmit one beacon every 10 ms, halving the channels used by idle base stations and reducing the effects of co-channel interference.

[0096] Figure 3 shows another example of slot group classification in the present invention (when L = 4), where each of the downlink slots (SL0 to SL11) and uplink slots (SL12 to SL23) in the DECT radio resources is classified into four slot groups (slot group SL0 to SL2, SL12 to SL14, slot group SL3 to SL5, SL15 to SL17, slot group SL6 to SL8, SL18 to SL20, and slot group SL9 to SL11, SL21 to SL23).

[0097] 3, consecutive slots are assigned to each slot group, but for example, every third slot may be assigned to the same slot group, and any slot group can be assigned as long as there is no overlap. Also, the number of slots assigned to each slot group does not necessarily have to be the same, and considering the traffic expected at each base station, for example, four or more slots may be assigned to a slot group of a base station where high traffic is expected.

[0098] FIG. 4 is a diagram showing an example of the area expansion of base station zones for the slot groups of FIG. 3, where the slot groups used by each base station are shown in the same gray scale as in FIG. 3. As shown here, by classifying the slots as in FIG. 3, it is possible to make the slot groups used by adjacent base stations different from each other. In addition, the number of slot group classifications L is arbitrary as long as it is 3 or more, but by making L larger, the interference distance can be made larger and the influence of co-channel interference can be further reduced.

[0099] FIG. 5 is a block diagram showing the basic configuration of an embodiment of a digital cordless telephone system using the DECT wireless communication system according to the present invention.

[0100] The digital cordless telephone system of this embodiment comprises a telephone control device (hereinafter referred to as a main device) 10, M (M is a natural number equal to or greater than 1) base stations 20, and N (N is a natural number equal to or greater than 1) handset units 30. One base station 20 and one handset unit 30 are selectively used from among the M base stations 20 and N handset units 30 to form the digital cordless telephone system.

[0101] P (P is a natural number greater than or equal to 1) telephone lines (office lines) are connected to the main unit 10, allowing simultaneous outgoing and incoming calls on up to P lines. M (M is a natural number greater than or equal to 1) base stations 20 are also connected to the main unit 10, allowing N (N is a natural number greater than or equal to 1) handset units 30 to make and receive calls via these.

[0102] After powering on, each handset 30 registers its location with one of the base stations 20 and becomes able to make and receive calls via this base station 20. This is expressed as the handset 30 connecting to the base station 20. In other words, each handset 30 becomes able to make and receive calls via the base station 20 to which it is connected.

[0103] As the handset 30 moves, it may be necessary to reconnect to a base station 20 that can provide better wireless communication. This is called roaming. Even during a call, as the handset 30 moves, it may be necessary to reconnect to a base station 20 that can provide better wireless communication. This is called handover.

[0104] The specific configurations of the main unit, base station, and slave unit will be described below.

[0105] 6 is a block diagram showing the basic configuration of one embodiment of a main unit of a digital cordless telephone system using the DECT wireless communication system according to the present invention. For simplicity of explanation, only the necessary components are shown here. This also applies to the following figures.

[0106] The main unit 10 of this embodiment includes a central office interface unit (central office I / F unit) 11, an internal interface unit (internal I / F unit) 12, a clock generating unit 13, a circuit switching unit 14, a control unit 15, and a slot group information storage unit 16 for each base station.

[0107] P (P is a natural number greater than or equal to 1) telephone lines (office lines) are connected to the office line I / F unit 11, and up to P lines can be used for outgoing and incoming calls simultaneously. M (M is a natural number greater than or equal to 1) base station transmission lines are connected to the extension line I / F unit 12, and up to M (M is a natural number greater than or equal to 1) base stations can be accommodated via these lines.

[0108] The audio data stored in the main unit 10 is, for example, an audio coded signal such as a PCM codec signal. The PCM codec signal is 64 kbps audio data that is obtained by quantizing an audio signal at 8 kHz (125 μs intervals) to 14 bits and then nonlinearly compressing the quantized signal to 8 bits.

[0109] The clock generating unit 13 generates a sufficiently high-speed voice multiplexing clock and a voice codec frame pulse with a 125 μs period in order to circuit-switch the voice signals of the telephone line and the extension line, and supplies these to the central office I / F unit 11 and the extension I / F unit 12, respectively. The multiplexed voice signal generated using these is applied to the line switching unit 14. The line switching unit 14 performs line switching in units of one sample based on the line switching control signals for outgoing and incoming calls on the outside line and the extension line given by the control unit 15.

[0110] Furthermore, the clock generating unit 13 generates an inter-base station synchronization timing pulse for DECT inter-base station synchronization. This inter-base station synchronization timing pulse is supplied to each base station via a base station transmission path, thereby performing inter-base station synchronization.

[0111] In addition, in digital cordless telephone systems that use the DECT wireless communication method, not only multi-frame synchronization between base stations but also frequency channel synchronization for detecting available channels is required, so timing synchronization with a period of 160 ms x (number of frequency channels) is required, and if the number of frequency channels is 6, timing information with a period of 960 ms is supplied.

[0112] The base station transmission path transmits two-way voice data with the handset connected to the base station for communication, two-way control data for all handset connected to the base station, and inter-base station synchronization timing pulses for DECT inter-base station synchronization.

[0113] FIG. 7 is a diagram showing an example of a frame format for signal transmission in a TDD (ping-pong transmission) system on a base station transmission line.

[0114] Here, downlink transmission and uplink transmission are provided, and a guard period is provided between the uplink transmission and the downlink transmission in consideration of the transmission delay time on the base station transmission path.

[0115] The TDD system's cycle (frame time length) is set to an integer multiple of 125 us to match the intervals between audio data segments. Downstream transmission data consists of a frame synchronization bit, a multi-frame synchronization bit, common control data, and one or more channels of audio data (not shown). The same applies to upstream transmission data.

[0116] Since the control data for the slave device is usually several bytes to several tens of bytes and a transmission delay of several hundred milliseconds is acceptable, multiple TDD frames may be concatenated to form a multiframe, and the control data may be transmitted in units of multiframes. In this case, a multiframe synchronization bit can be used. The time length of a multiframe is set to, for example, several tens of milliseconds.

[0117] FIG. 8 is a diagram showing an example of transmission of common control data having a multi-frame configuration.

[0118] Here, the multi-frame is configured with 50 bytes of control data per multi-frame.

[0119] Frame synchronization has a period of an integer multiple of 125 us, multi-frame synchronization has a period of about several tens of ms, and DECT inter-base station synchronization has a period of, for example, 960 ms. DECT inter-base station synchronization timing information may be transmitted using a frame synchronization bit pattern.

[0120] The control data is generated in the control unit 15. The two-way control data stores control commands for each control sequence between the main unit 10 and the base station. The control data can include ID information for identifying the handset to be controlled, and can also include information such as a call number assigned when making or receiving a call.

[0121] The control unit 15 manages the connected base station information, call status, whether or not ringing is specified, the office line key assignment, and the lamp status of the assigned office line key for all handset units in the system, and updates them accordingly. When the lamp status of the office line key of a handset unit changes, a line lamp display command is issued to that handset unit.

[0122] The base station slot group information storage unit 16 stores slot group information for each base station. The base station slot group information specifies, for example, for each base station identification information, a slot group that can be used by the base station.

[0123] The base station identification information may be, for example, a base station ID (RPN) of the base station ID information defined in the DECT standard shown in Fig. 22, or base station identification information defined on the system (main device) side, such as a base station number. Furthermore, the slot group information of the base station may be any L-number of numbers for identifying L slot groups (L is a natural number of 3 or more), or a remainder obtained by dividing the base station ID by L.

[0124] By deriving the slot group information of a base station using the base station ID, there is no need to store slot group information for each base station in the main unit, and there is an advantage that the slot group information of the base station can be obtained directly at the base station, as in another embodiment of the base station described later (Fig. 10). For example, the slot group information of the base station can be calculated from the base station ID information displayed on the back of the base station, and when a construction company installs a base station for a cordless telephone system, by appropriately setting the base station ID of adjacent base stations, it is possible to easily arrange the slot groups of adjacent base stations so that they are different from each other.

[0125] 9 is a block diagram showing the basic configuration of an embodiment of a base station in a digital cordless telephone system using the DECT wireless communication system according to the present invention. Here, only the basic configuration of base station 1 (20) is shown, but the other base stations also have the same basic configuration.

[0126] The base station 20 of this embodiment includes a base station transmission path termination unit 21, a DECT transmission / reception control unit 22, a slot group information storage unit 23, and a blind slot information generation unit 24.

[0127] The base station transmission path termination unit 21 decomposes and combines TDD frames transmitted over the base station transmission path. K (K is a natural number equal to or greater than 1) pieces of bidirectional audio data are transmitted over the base station transmission path, and these bidirectional audio data are serially transmitted to the DECT transmission / reception control unit 22 via, for example, a codec interface.

[0128] For the codec interface, a clock for the multiplexed audio codec and an audio codec frame pulse are also generated in the base station transmission path termination unit 21 and applied to the DECT transmission / reception control unit 22 .

[0129] Furthermore, predetermined timing information (inter-base station synchronization timing pulse) for DECT inter-base station synchronization, for example, with a period of 960 ms, is also output from the base station transmission path termination unit 21 and applied to the DECT transmission / reception control unit 22 .

[0130] The base station transmission path termination unit 21 also synthesizes or decomposes the bidirectional control data into handset control commands in multiframe units of the base station transmission path, and applies the commands to the DECT transmission / reception control unit 22 via a bidirectional serial interface, for example.

[0131] Conversely, the DECT transmission / reception control unit 22 applies the control information received from the handset via the wireless transmission path to the base station transmission path termination unit 21 as a handset control command, and the handset control command is notified to the main unit 10 via the base station transmission path.

[0132] In the control data exchange sequence with the main unit when the base station is started up, the slot group information storage unit 23 acquires the slot group information of the base station stored in the slot group information storage unit 16 for each base station of the main unit 10 and stores it in the slot group information storage unit 23.

[0133] Based on the relationship between the slot group information and the blind slot information, the blind slot information generator 24 generates blind slot information, which is information on whether each slot in the base station 20 is usable or not, and applies this information to the DECT transmission / reception controller 22. For example, if the first to fourth slots are usable and the fifth to twelfth slots are unusable, then the generated blind slot information is {1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0}.

[0134] When the DECT transmission / reception control unit 22 receives the blind slot information, it notifies all the slave units connected to the base station 20 of the blind slot information using a beacon.

[0135] The blind slot information can be notified by a beacon by storing it in the MAC information of the short page Pt, or can be notified as unique information of the system information Qt.

[0136] FIG. 10 is a block diagram showing the basic configuration of another embodiment of the base station 20 in a digital cordless telephone system using the DECT wireless communication system according to the present invention.

[0137] The base station 20 of this embodiment includes a base station transmission path termination unit 21, a DECT transmission / reception control unit 22, a base station number information storage unit 25, a slot group information generation unit 26, and a blind slot information generation unit 24. The difference from the base station 20 of Fig. 9 is that the slot group information is calculated from base station number information that is individually set and held in the base station 20, without acquiring slot group information from the main unit. Therefore, in the case of the base station 20 of this embodiment, the main unit does not need to include a per-base station slot group information storage unit.

[0138] The base station number information storage unit 25 holds the base station number, for example, as a base station ID, and the slot group information generation unit 26 calculates slot group information from the base station number by performing a predetermined process, for example, by calculating the remainder when the base station number is divided by L (L is a natural number greater than or equal to 3).Furthermore, the blind slot information generation unit 24 generates blind slot information, which is information on whether each slot in the base station is usable or not, from the relationship between the slot group information and the blind slot information, and applies this to the DECT transmission / reception control unit 22, which broadcasts the blind slot information as a beacon.

[0139] FIG. 11 is a block diagram showing the basic configuration of an embodiment of a handset in a digital cordless telephone system using the DECT wireless communication system according to the present invention.

[0140] The handset 30 of this embodiment includes a DECT transmission / reception control unit 31, a handset control unit 32, an audio codec 33, an office line key 34, a ringer 35, an LCD display unit 36, a microphone 37, a speaker 38, a numeric keypad 39, and a base station slot group table memory unit 40.

[0141] The DECT transmission / reception control unit 31 performs transmission and reception of DECT radio signals, GFSK or differential PSK modulation and demodulation, TDMA frame synthesis, TDMA frame decomposition, search processing when searching for a base station, radio state management, and the like.

[0142] The audio codec 33 transmits and receives audio codec signals to and from the DECT transmission / reception control unit 31, and also receives an audio codec clock and audio codec frames from the DECT transmission / reception control unit 31 to code / decode the audio. A microphone 37 and a speaker 38 are connected to the audio codec 33, and an audio signal uttered by the handset 30 is converted into an electrical signal by the microphone 37, sampled at a predetermined rate, for example, 8 kHz, by an AD converter provided in the audio codec 33, and the transmission band is further compressed by the audio codec 33. For example, a linear PCM signal that has been AD converted at 14 bits may be compressed to 8 bits by u-law PCM or A-law PCM, and then further compressed to 4 bits by ADPCM.

[0143] The DECT standard supports audio codecs such as 32 kbps ADPCM for narrowband audio and 64 kbps u-law PCM and 64 kbps G.722 for wideband audio. Narrowband audio uses one slot each for uplink and downlink, while wideband audio uses two slots each for uplink and downlink. Handset 30 may use either narrowband audio or wideband audio.

[0144] The voice signal uttered by the other party in the call is converted into an analog signal by a DA converter provided in the voice codec 33 and output from a speaker 38. An voice codec clock and a voice codec frame pulse indicating the starting point of one sampling of data are applied to the voice codec 33 from the DECT transmission / reception control unit 31, and bidirectional voice codec signals are transmitted between the voice codec 33 and the DECT transmission / reception control unit 31.

[0145] The handset control unit 32 is connected to an office line key 34, a ringer 35, an LCD display unit 36, a numeric keypad 39, etc., and in response to handset control signals, it displays the office line key lamps, sounds the ringer, and displays information on the LCD. Information on pressing the office line key 34 or the numeric keypad 39 is applied to the DECT transmission / reception control unit 31 as handset control signals and is processed within the control sequence.

[0146] The base station slot group table storage unit 40 stores a base station slot group table created based on base station search information and blind slot information acquired during base station search. This base station slot group table is updated as needed.

[0147] 12 is a diagram showing an example of the slave unit states and state transitions. The operation of the slave unit will be described below with reference to FIGS.

[0148] When each slave unit is powered on, it goes from an initial state to a base station search state, performs a base station search operation at regular time intervals, and acquires base station search information and blind slot information.

[0149] Specifically, the base station ID information Nt broadcast by each base station using a dummy bearer is received to obtain base station search information consisting of the base station ID information and beacon reception level information from that base station, and the base station system information Qt broadcast by each base station using a dummy bearer is received to obtain blind slot information from that base station. The blind slot information broadcast as system information Qt from the base station can also be received during base station search to obtain blind slot information and reception level information. When a mobile device searches for a base station, it may select a base station with which the number of location registration mobile devices has not reached the upper limit, and perform location registration.

[0150] Based on the acquired base station search information and blind slot information, a slot group table for each base station is created, and this information is stored in a slot group table storage unit for each base station 40 .

[0151] 13 is a diagram showing an example of a slot group table for each base station. This slot group table for each base station is composed of a list of base station ID information found during base station search, reception level information of beacons from each base station, and blind slot information of each base station.

[0152] The list of base station ID information can use all or part of the base station identification information included in the base station ID information Nt. For example, if the system ID information (FPN) included in the base station ID information Nt matches the system ID of the own system, the base station ID (RPN) and reception level information can be held.

[0153] Also, instead of the base station ID (RPN), base station identification information defined on the system (main unit) side, for example, a base station number, can be used, or this can be used in combination with the base station ID (RPN). Also, the base station identification information defined on the system (main unit) side can be broadcast as system information Qt, which can be received during base station search to acquire the base station identification information and reception level information.

[0154] As described with reference to FIG. 21, the base station ID information Nt, the system information Qt, and the paging information Pt are each broadcast using the same frequency channel and the same slot in one multi-frame.

[0155] As shown in Figures 23 and 24, the system information Qt includes RF carrier information, multiframe number information, unique system information, etc. in addition to basic system information, and the type of system information transmitted in the Qt frame is stored in the Qt header. Such different system information is broadcast using multiple multiframes, and the slave device can acquire these different system information by receiving multiple multiframes. The base station can add its own system information, such as base station identification information or blind slot information defined on the system (main device) side, to the system information Qt and broadcast it, and the slave device can acquire the base station identification information or blind slot information by receiving multiple multiframes.

[0156] As shown in Fig. 28, the paging information Pt includes short pages that include MAC information such as blind slot information, and full pages and long pages that do not include MAC information. Also, in short pages, as shown in Fig. 30, several different pieces of MAC information are broadcast using multiple multi-frames. The mobile device can also receive multiple multi-frames to acquire the blind slot information broadcast using the short page. As described above, by receiving multiple multi-frames in the same frequency channel and the same slot, it is possible to acquire base station search information and blind slot information.

[0157] The blind slot information of each base station can be acquired from the blind slot information, which is one piece of MAC information that is intermittently broadcast from the base station side using paging information Pt.

[0158] Next, the operation of the handset in the location registration sequence will be described in more detail.

[0159] FIG. 14 is a diagram showing an example of a location registration sequence of the handset 30 with the main unit.

[0160] In the location registration sequence, the mobile terminal first transmits an access request to the base station with which it is to register its location, in order to prepare a bearer (MAC layer) for establishing a link in the data link layer.

[0161] The slave device control unit 32 of the slave device in the base station search state references the slot group table per base station stored in the slot group table per base station storage unit 40, selects, for example, the base station with the highest reception level, and then acquires blind slot information of that base station from the slot group table per base station. Alternatively, the blind slot information may be acquired by intermittently receiving paging information Pt of that base station over multiple multi-frames.

[0162] The handset control unit 32 of the handset in the base station search state selects a base station to register its location with and acquires blind slot information of that base station. Based on the blind slot information, the handset control unit 32 generates a handset control signal for transmitting a MAC access request using an available slot in that base station and applies this to the DECT transmission / reception control unit 31. In response to this, the DECT transmission / reception control unit 31 transmits the MAC access request using an available slot in that base station.

[0163] Upon receiving the MAC access request, the base station transmits a MAC bearer confirmation message to the mobile station using a pair of slots. Here, a pair of slots refers to an uplink slot and a downlink slot that are spaced 5 ms apart on the same frequency channel, and both paired slots belong to the same slot group. In other words, the MAC bearer confirmation message is transmitted using a slot that belongs to the slot group available to the base station.

[0164] Thereafter, radio transmission is performed in accordance with the link establishment procedure and location registration procedure of the data link layer using the same pair of slots, i.e., using slots belonging to the slot group available for use by the base station, and location registration is performed.

[0165] When a mobile device registers its location with a base station, it enters an idle-locked state, which means that the mobile device is connected to a base station but only receives beacons and is not engaged in two-way communication with the base station.

[0166] When a mobile terminal in the idle lock state communicates with a base station, it must establish a link and transition to the communication lock state, in which two-way communication is performed with the base station using a traffic bearer.

[0167] FIG. 15 is a diagram showing an example of a call sequence when a key operation for making a call is performed on the handset.

[0168] When a key operation for making a call is performed on a handset in the idle-locked state, the handset control unit 32 detects this and generates a handset control signal for transmitting a MAC access request to the connected base station that has performed location registration, using a slot belonging to a slot group that is available at that base station, based on the blind slot information of that base station, and applies this signal to the DECT transmission / reception control unit 31. In response to this, the DECT transmission / reception control unit 31 transmits the MAC access request using a slot belonging to a slot group that is available at that base station.

[0169] Upon receiving the MAC access request, the base station transmits a MAC bearer confirmation message to the mobile station using the paired slot. Since both of the paired slots belong to the same slot group that is available for use by the base station, the MAC bearer confirmation message is transmitted using the paired slot.

[0170] Thereafter, wireless transmission of the link establishment procedure, call procedure and communication procedure of the data link layer is carried out using paired slots belonging to the same slot group, i.e., using slots belonging to the slot group that is enabled for use by the base station.

[0171] Even in a communication locked state, a pre-communication base station search can be performed when communication quality deteriorates or at predetermined time intervals, and if a new base station that allows better wireless communication is found, a link can be established with the new base station, and the communication can be transitioned to a communication locked state with the new base station, i.e., a handover can be performed.

[0172] When a handover is performed in a communication locked state, it is necessary to continue communication with the currently connected base station while simultaneously searching for a base station in use, using slots other than those currently being used for communication.

[0173] In conventional technology, when a handover is performed by moving between two base station zones while communicating, if the transmission slot of the beacon of the destination base station matches the slot currently being used for communication, the beacon of the destination base station cannot be found by searching for the base station currently in communication, and the destination base station must be selected from among base stations other than the destination base station whose beacon does not match the slot currently being used for communication.

[0174] It is fine if a suitable base station other than the destination base station can be found as a handover destination, but if no suitable base station can be found, even though there is actually a base station at the destination, the handover cannot be carried out because the base station cannot be found, resulting in a deterioration in communication quality, and in the worst case scenario, communication may be cut off.

[0175] To avoid this situation, two beacons are transmitted from each base station at 10 ms intervals to transmit the same information, but this occupies twice as many slots as the number of base stations, which makes congestion more likely to occur and increases the likelihood of co-channel interference.On the other hand, if each base station transmits one beacon at 10 ms intervals, as mentioned above, there is a possibility that the beacon from the destination base station cannot be received during handover.

[0176] In contrast, according to the present invention, different slot groups are assigned to adjacent base stations, so even if each base station transmits one beacon at a 10 ms cycle, the slots currently in use for communication and the slot group used by the destination base station are different, so there is no problem in that the beacon from the destination base station cannot be received during handover. Therefore, it is possible to use only one beacon at a 10 ms cycle, which is advantageous from the viewpoint of co-channel interference. [Explanation of symbols]

[0177] 10...Main device 11...Station line I / F section 12 Internal line I / F section 13. Clock generation unit 14 Circuit Switching Unit 15 Control section 16. Slot group information storage unit for each base station 20...Base station 21 Base station transmission line termination 22 DECT transmission / reception control unit 23 Slot group information storage unit 24. Blind slot information generator 25 Base station number information storage unit 26. Slot group information generation unit 30... Handset 31 DECT transmission / reception control unit 32 Child unit control section 33. Audio Codec 34 Local line key 35. Linga 36...LCD display section 37. Mike 38···Speaker 39. Numeric keypad 40...Base station slot group table storage unit

Claims

1. A base station for a TDMA-TDD cordless telephone device is configured by connecting one or more base stations, each capable of connecting a plurality of handset units, to a telephone control device connected to a wide area network, a slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used in the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in wireless transmission are classified; a blind slot information generating means for specifying slots to be used in the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use; A base station for a cordless telephone device, characterized in that the blind slot information is embedded in the MAC information of a short page frame of the DECT standard, or embedded in the unique information of a system information frame of the DECT standard, and is broadcast by a beacon, and is equipped with a DECT transmission / reception control unit that transmits and receives radio transmissions in a slot selected based on the blind slot information.

2. 2. The base station for a cordless telephone device according to claim 1, wherein said slot group information is information for identifying said slot group used by said base station.

3. The base station for a cordless telephone device according to claim 1 or 2, characterized in that the slot group information is information on a slot group calculated in the cordless telephone device from identification information of the base station in accordance with a predetermined rule, and the blind slot information generating means generates blind slot information from the slot group information.

4. The base station of the cordless telephone device according to claim 3, characterized in that in order to calculate the slot group information from the base station identification information, the remainder obtained by dividing the base station identification information by L (L is a natural number greater than or equal to 3) is referenced.

5. A base station and a handset of a cordless telephone device comprising one or more base stations connected to a telephone control device connected to a wide area network and a plurality of handset units connectable to the base stations, The base station a slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used in the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in wireless transmission are classified; a blind slot information generating means for specifying slots to be used in the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use; a DECT transmission / reception control unit that embeds the blind slot information in MAC information of a short page frame of the DECT standard or embeds the blind slot information in unique information of a system information frame of the DECT standard, and notifies the beacon, and performs transmission and reception of wireless transmissions in a slot selected based on the blind slot information; The blind slot information is embedded in MAC information of a short page frame of the DECT standard, or embedded in unique information of a system information frame of the DECT standard, and notified to a slave unit by a beacon, and wireless transmission is performed using a slot selected based on the blind slot information; The slave unit is a base station slot group table storage means for generating a base station slot group table based on base station search information and blind slot information acquired during base station search and storing the table; A base station and a handset of a cordless telephone device, characterized in that they comprise handset control means for managing handset states and state transitions, for obtaining information on slot groups to be used by a base station with which a radio link is to be established by referring to the slot group table for each base station, and for controlling the establishment of a radio link and communication over the radio link by using slots selected based on the slot group information.

6. A telephone control device and a base station of a cordless telephone system configured such that one or more base stations to which a plurality of handset units can be connected are connected to a telephone control device connected to a high-bandwidth network, A plurality of slots used in wireless transmission are classified into L slot groups (L is a natural number equal to or greater than 3), The telephone control device a slot group information storage means for storing slot groups to which one or more slot groups to be used by each base station are assigned, so that different slot groups are assigned to adjacent base stations; The base station slot group information storage means for storing slot group information of the base station, which is acquired via a base station transmission line when the base station is started and stored in said slot group information storage means for each base station; a blind slot information generating means for identifying slots to be used by the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use; A telephone control device and a base station for a cordless telephone system, characterized in that the blind slot information is embedded in the MAC information of a short page frame of the DECT standard, or in the unique information of a system information frame of the DECT standard, and is announced by a beacon, and the telephone control device and base station are provided with a DECT transmission / reception control unit that transmits and receives radio transmissions in a slot selected based on the blind slot information.

Images