KR987001196A - Roaming in Telecommunications Systems - Google Patents

Abstract

A communication system, such as a broadband digital calling system, includes a number of geographically separated primary stations (PS1, PS2, PS3), each defining a service area (CAR1, CAR2, CAR3), which are controlled by the system controller 10. To operate as a wide area network. Subscriber units SS1 and SS2 may move between service areas. In order to identify the channel to be used by the mobile subscriber units SS1 and SS2, the primary stations PS1, PS2 and PS3 often transmit system-wide announcement channels to provide details of the available channels. The subscriber unit has means for selecting one of these available channels.

Description

Roaming in Telecommunications Systems

Since this is an open matter, no full text was included.

In the case of a single operator, single frequency calling system, the wide radio service area is divided into multiple sub-areas and the subscriber selects the sub-areas to which he is to be called and billing is made for each sub-area. Thus, the subscriber must know in advance the sub-area accessible at the time of movement. When two or more independent operators use a single channel, the operator may include some form of operator identifier in the call signal and the subscribers registered with one operator to the subscriber units of similar addresses belonging to other systems and their It is necessary to be able to distinguish the call signal addressed to the terminal. Pagers can also send operator identifiers to distinguish multiple networks from each other, thereby preventing battery from receiving the wrong network signals.

In some countries, a frequency block (or channel block) is assigned to a call to assign one or more channels from this block to the competing operators. The terminal unit of the subscriber moving in the area should be able to detect the channel assigned to the operator and select the channel being applied to each area. In addition, when an extra channel is allocated to the operator, it is necessary that the terminal unit be able to acquire a channel whenever appropriate.

TECHNICAL FIELD The present invention relates to roaming in a communication system, and in particular to, but not limited to, a digital calling system.

1 is a schematic block diagram of an embodiment of a wide area digital calling system, FIG. 2 shows an example of a cycle structure, FIG. 3 shows an example of a placement zero marker, and FIG. 4 shows an example of a roaming address code word. 5 is a diagram showing an example of a sub-address code word, FIG. 6 is a diagram showing an example of a announcement channel message, FIG. 7 is a diagram showing an example of a four phase-offset region, and FIG. Table showing paging of three frequencies in a region, FIG. 9 shows an example of phase-offset setting on multiple regions, and FIG. 10 shows an example of 5 phase-offset region operating on four channels. 11 illustrates a frequency sequence used in FIG. 10.

It is an object of the present invention to facilitate the movement of subscribers within the service area of a communication system.

According to a feature of the invention, there is provided a communication system comprising a plurality of primary stations geographically separated and each defining a service area and operating as a network, and one or more movable secondary stations, Each primary station is adapted to transmit an announcement channel message containing information about radio channels available on its network, and the secondary station receives the announcement channel message and transmits one of the channels indicated in the message. A communication system is provided comprising means for selecting.

According to another aspect of the invention, in a secondary station for use in a communication system comprising a plurality of geographically separated primary stations acting as a network, each primary station is provided with information about radio channels available in its network. Wherein said secondary station is adapted to transmit an announcement channel message comprising: one or more signal storage means: means for storing details about a channel belonging to a network and one or more stored in said storage means in response to receiving said announcement channel message. A secondary station is provided comprising means for selecting details of a channel and adjusting the state of the secondary station accordingly. With reference to the accompanying drawings will be described the present invention as an embodiment.

Manner for practicing the present invention

The same reference numerals are used for corresponding features in the drawings.

The calling system shown in FIG. 1 includes a calling system controller (PSC: 10), which is connected to primary stations PS1, PS2, PS3 geographically separated by landline links. Each primary station includes a transmitter that defines respective service areas CAR1, CAR2, CAR3, which may overlap one or more peripheral areas. The PSC 10 may be one of several methods, for example, a single frequency quasisynchronous operation, a single frequency time-division cellular operation, or a multi-frequency operation. The operation of the station can be controlled. As will be clear from the description that follows, more than one network may serve the same area, each network having its own operator with a PSC and a geographically distributed primary station, where the service area by the primary station of one network is It is arranged differently from the service areas of other networks.

In Fig. 1, for example, a subscriber having secondary stations SS1, SS2, including a digital pager, moves within a given home area where the primary station can connect. However, for example, in order for the secondary station SS1 to operate in another service area, it is necessary to record it in the PSC 10. Moreover, the subscriber wants to be able to access other areas where the network of other operators is mainly serving. Each operator can assign one or more channels to the system and have their own operator identifier and area code. In addition, the modes of operation may be different between operators and each operator may provide different kinds of services, such as low speed standard service and high speed standard service.

The secondary station SS1 is shown in a schematic block. An antenna 12 is connected to the receiver stage 14, the output of which is provided to the decoder 16. The microcontroller 18 is connected to the decoder 16 via bidirectional links 19 and 20. The microcontroller 18 operates according to the software in the program storage 22. An address storage device 24 that stores the address sent to the secondary station is connected to the microcontroller 18. A RAM 26 for storing data messages received from the secondary station is connected to the microcontroller 18. One output of the microcontroller 18 is connected to the LCD driver 28, and the LCD driver 28 is connected to the LCD panel 30. Keypad 32 is connected to the microcontroller to provide a human / machine interface. A light emitter 35 such as an acoustic transducer 34 and an LED is connected to the microcontroller 18 to be used as an alarm device, and the light emitter 36 is also stored in the RAM 26 to optically output a message to a printer or a personal computer. do. The receiver 14 is operated by the microcontroller 18 in accordance with a battery saving protocol, and the battery saving stage 28 is connected between the microcontroller 18 and the receiver 14.

The additional memory 40, which may be part of the program memory 22, has a number of storage locations 42-52 for storing various data, which data has been recorded as part of the programming of the secondary station. The storage location 42 stores channel information. The storage location 44 stores a home identification code, which is an operator identification code and an area code. The secondary station can use this information to determine when it is in its service area, such as CAR1, and when it is visiting / moving in another service area, and an appropriate address mechanism can be used. The storage location 46 contains information related to the home channel, which is a preprogrammed channel. However, pagers moving within the same service area will have to dynamically select a channel. The storage location 48 includes an operator identifier and an area code associated with it, which information is valid at the secondary station while moving out of the home area. In some cases, the secondary station has one programmed operator identifier. However, the operator may want to use multiple operator identifiers to increase the addressing capacity. The storage location 50 stores data related to decoding the operator identification code and the area code included in a special code word such as a batch zero marker used for batch identification to be described later. Memory location 52 stores one or more channel scanning algorithms that can be used in different protocols.

The present invention will be described with reference to the calling protocol in which the transmission is made in cycle (CYC: FIG. 2). Each cycle includes a plurality of batches B0, B1, B2, each batch comprising a sync code word and a plurality of frames F0 through F27, each frame having a plurality of code word periods, i. 6, 8, 12, and 16 code words, depending on the rate). The first code word in each batch is the synchronization code word S, and the code word called batch zero marker BZM in the first batch B0 of the cycle is the first code word after this synchronization code word. By BZM, the secondary station is in cycle and batch synchronization.

3 shows the format of BZM, which is a 32-bit code word. Bit 1 contains a 1-bit flag with a value 0 indicating an address codeword. Bit 2 has a value of 0 for BZM as a BZM flag and a value of 1 for other address code words. Bits 3 through 15 are assigned to the operator identification code (AI) and area code (AC) of the calling network. Bit 16 is used to indicate whether it is in cycle mode or batch mode. Bit 17 indicates whether a batch zero message follows, with a value of 1 not followed by a batch zero message. The batch zero message is used for system-wide broadcast message transmission to all pagers on the network. Bits 18-21 of the BZM constitute a SUM field, which contains a 4-bit checksum for the information of the message code word. However, for BZM to which a batch zero message is not followed, the SUM field includes a 2-bit field indicating the number of cycle repetitions and a 2-bit field indicating the repetition number. The remaining 11 bits consist of 10 bits of CRC and 1 bit of parity bits.

In operation, the primary station PS transmits a message sequence formatted and encoded to conform to the format shown in FIG. Since the presently described system is a synchronous system, this transmission starts with a short preamble (P) followed by a first batch B0 of the first cycle.

The receiver stage 14 (FIG. 1) of the secondary station SS is activated to receive a preamble for bit synchronization. This preamble is followed by a first sync code word followed by a BZM. Assuming that the sync code word and BZM are received correctly, whether the operator identification code (A1), the area code (AC), and bits 3 to 15 of the BZM correspond to the home operator identification code and the home area code pre-programmed at the secondary station Review. In the corresponding case, the transmission is treated as a local transmission and the secondary station follows the prevailing battery saving protocol, which generally requires the receiver end 14 of the secondary station to be powered off until just before a given batch frame begins. It is. During the frame period, check the transmission from the primary station to see if the successfully received code word corresponds to the address assigned to the pager. If the message does not follow the address code word, if appropriate, the receiver stage 14 of the secondary station is turned off at the end of the frame period and the alarm device is activated. Otherwise, the receiver remains powered on until the end of the message is indicated, for example, by an address code word or a message termination code word, if appropriate, one or more alarm devices 34, 36 are activated. do.

On the other hand, when the operator identification code and the area code do not correspond to the home operator identification code and the home area code, it is determined that the secondary station is outside the home area. The primary station also determines that it is transmitting to the roaming secondary station and that it transmits a roaming address code word and subaddress code word in a given frame. 4 and 5 show examples of each type of code word, where the code word has a length of 32 bits. Considering the roaming address code word first, bit 1 is a flag with the value 0, which represents the address code word. Bits 2 through 7 are roaming flags, which indicate that roaming messages follow by setting all bits to 1. Bit 8 is reserved. Bits 9 through 21 are home operator identifiers and area codes that combine secondary stations. Bits 22 through 31 are CRCs and bit 32 is a parity bit.

The subaddress code word (FIG. 5) starts with a flag with a value of 1, indicating that it is a message code word. Bits 2 through 17 contain address bits corresponding to secondary station addresses. Bits 18-21 constitute the SUM field, which contains a 4-bit checksum for the information in the message code word. Bits 22 through 31 constitute a 10-bit CRC, and bit 32 is a parity check bit. The receiver stage 14 of the secondary station is started in a predetermined frame to check whether the home operator identification bit corresponds to the bit stored in the secondary station, and if so, the address of the subaddress code word is assigned to the address given to the secondary station. If it does, it keeps its activated state to receive subsequent messages, and if it does not, turns off the power at the end of the frame.

The description so far assumes that each network operates at the same frequency. However, multi-frequency (or multi-channel) is also possible by programming the secondary station in advance in the form of a channel number with frequency information relating to all available channels.

Calls to a single channel secondary station are sent over the preprogrammed channel of the pager. Calls from the home area of the secondary station to the multichannel secondary station are sent over the secondary channel's home channel.

In a call to a visiting multichannel secondary station, the channel selection method utilizes Announce Channels messages transmitted intermittently on each channel belonging to the operator.

6 shows the command parameters of the announcement channel message. This message begins with parameter A, which contains an operator identifier and area code corresponding to the same information given in BZM. Parameter B represents the name given to the service (or call) area. The parameter P is a single digit that defines the cycle phase as described below in a particular area. This number can have the following values and meanings:

0 phase T

1 phase T +

2 phase T ++

3 Undefined phase.

Parameter D relates to the transmission off interval, which is a number that defines the transmission interruption interval in a particular operator and region.

0 Unspecified interval.

The secondary station uses a pre-programmed value or the default value if there is no programmed value.

1 to 32 transmission off intervals.

The parameter Q is an integer that defines the number of radio channels that are operated in a particular calling area and identified in the following list. Finally, the parameters C ₀ -C _Q-1 each include a number defining a radio channel that is operated in a particular calling area.

The announcement channel message is typically sent in a batch zero message and informs the pager about the available wireless channels of a particular network in a particular calling area. Information is often given about the current and neighboring areas. This message contains a list of Q channels that the visiting pagers are currently available in that area, ie channels C ₀ , C ₁ ,..., C _Q-1 . The home secondary station and the visiting secondary station share the same channel. For the secondary station whose address code is Y, the channel is selected from the list of channel C _j (where j = Y MOD Q).

For ease of explanation, the following table shows an example of up to six channels in the calling area (Q = 1, 2, ...., 6).

Referring to the previous table, when a channel message (Q) with a announced channel message is transmitted, all secondary stations need to recalculate the channel number (j) and some secondary stations may need to retune to another channel.

In a simple example of an operator transmitting on two channels per region, the secondary station can be commanded to allow the secondary station to check the least significant bit so that one bit can tune to one channel and one bit to tune the second channel. .

The network uses the announcement channel message to provide information about the adjacent calling area to the secondary station. The secondary station can use this information to assist the channel scanning algorithm.

In operation, a roaming secondary station scans the channel as soon as it enters an area to find a channel that is available. The secondary station checks the BZM to determine whether the operator identification code and area code correspond to the operator identification code and area code stored in the storage location 48 (Fig. 1). If so, the secondary station remains active and receives the announcement channel message, then selects the appropriate channel according to the parameters of the message and follows the battery saving protocol for the standards propagated by the operator.

Depending on the network design and the level of roaming service that the operator wishes to provide to the subscriber, it may not be necessary to synchronize the cycle timing with the corresponding transmission on another channel. On the other hand, transmissions on different channels may be synchronized together to operate in phase-offset mode. To be flexible, multichannel secondary stations must be able to operate in non-phased and phased-offset networks.

In either case, the multichannel secondary station needs to have the ability to scan new channels if the signal quality of the current channel is degraded. One possible way to determine the signal quality is to check the bit error rate of the sync code word signal, for example, and start a channel search if the value exceeds the threshold.

In a network whose topology is not synchronized, a single channel or multichannel secondary station can move between networks or calling areas and synchronize back to the channel of each network or area to which it belongs. This mode of operation can be used in situations where the service area can maintain roaming or short calling times between networks or calling areas that are not adjacent to each other, and when it is clear which area the secondary station should communicate with. Suitable.

7 and 8 show an example of three frequency tuning in the phase-offset network and the adjacent region. The phase-offset network includes four areas AR1, AR2, AR3, AR4. The area AR1 transmits the primary station PAR1 on the phase T frequency F1, and the tuning of the cycle is as shown in the first line of FIG. Primary station PAR2 in area AR2 transmits on phase T + and frequency F2, with phase T + being one (1) relative to phase T as shown in the second line of FIG. It is offset by the batch period. The primary stations PAR3 and PAR4 of the two regions AR3 and AR4 that are not in contact with each other transmit on phase T ++ and frequency F3, with phase T ++ as shown in the third line of FIG. It is offset by (T) two (2) batch periods.

Tuning can result in soft handover between channels so that multichannel secondary stations can scan and synchronize on a new channel before releasing the current channel. In this way, the secondary station can move between the areas AR1 to AR4 and maintain communication continuously. To roam between networks, it is convenient to match the phase to an absolute time reference, for example by using a GPS system.

Even when a large network is configured as shown in FIG. 9, three phases are sufficient.

In order to inform the roanimg secondary station of the channel phase in the particular calling area, the parameter P of the announcement channel message is given an appropriate value as shown in the description of FIG.

When in the service area, the secondary station receives signals only from the local primary station and cannot receive signals from neighboring areas. In this case, the pager can monitor signals on different frequencies received from different areas using two other arrangements, arrangements B0 and B1.

The secondary station is not limited to monitoring two alternative frequencies. See, eg, FIG. 10. The secondary station can receive only the frequency F1 in the area AR5, but can scan the frequencies F2, F3, F4 as shown in FIG. If the secondary station moves west (Fig. 10) it will eventually receive the frequency F4. Upon receiving F4, the secondary station stops looking at another frequency of the same phase, namely the frequency F2 in this example.

Thus, the secondary station can cope with any number of frequencies while searching for an active frequency of a particular phase. If the secondary station finds an active frequency capable of carrying a call, only three (3) frequencies need to be monitored.

Only the example of FIG. 11, which selectively scans frequencies F2 and F4 to search for signal activity, is possible. In FIG. 11, the secondary station can search only one (1) frequency per batch period. In fact, the secondary station can search for signal activity on another frequency at any time when it is not receiving an assigned assignment on the active channel. In this way many frequencies can be scanned. The secondary station solves the problem of monitoring three frequencies in a three-phase structure only if activity is found on three effective frequencies.

By allowing channel selection from the announcement channel message (FIG. 6), the secondary station can change the network configuration, which benefits from this configuration change.

a. The secondary station is distributed almost evenly over the channels available in the calling area. From this the channel load is optimized and therefore the service assessment.

b. By changing the frequency of the area, for example, mutual interference can be overcome. (This does not apply when the home area frequency is preprogrammed with a secondary station in the home area. However, when the dynamic channel selection method is used in the home area. The same applies to the home area.)

c. New frequencies can be added to the calling area to cope with the increase in traffic load. If desired, call channels can be assigned to the busiest calling areas to meet traffic needs. (Dynamic channel assignment) In any case, the secondary station calculates a new channel from the announcement channel message.

d. You can set a new call area. Existing secondary stations in service can use this new area without having to preprogram information about the channel being used. In operation, the secondary station receives the announcement channel message, decodes it and stores its data. The next time the area is found, the secondary station can select the appropriate channel without first having to receive the announcement channel message. From the disclosure, other alternative embodiments will be apparent to those skilled in the art. Such modifications may relate to other features that are already known in the design, manufacture, and use of communications systems, devices, components, and that are used in addition to, or in addition to, features already described herein. While the scope of the patent specification is set forth in this application as specific combinations of features, the disclosure of this application includes new features or new combinations of features expressly and implicitly disclosed herein, which are currently described in the claims. Whether or not it is related to the same invention or whether to solve the same technical problem as in the present invention. Applicants of the present invention may add new claims for such features and / or combinations of features during the proceedings of the present application or other applications derived from the present application.

Wide area digital calling system and other forms of cellular communication system.

Claims (10)

A communication system comprising a plurality of primary stations geographically separated and each defining a service area and operating as a network, and at least one movable secondary station, wherein each primary station comprises: Apply to transmit a announcement channel message containing information about the available wireless channels on the network to which it belongs, and the secondary station receives the announcement channel message and selects one of the channels indicated in the message. And means for the communication. 2. The communication system of claim 1, wherein the secondary station has means for dynamically determining which wireless channel the secondary station will use in a network in response to receiving the announcement channel message. 2. The method of claim 1, wherein the number of channels in the network and / or the channel frequency of the network changes dynamically and which channel the secondary station will use among the plurality of wireless channels in the network in response to receiving the announcement channel message. And a means for dynamically determining. 4. The method of any one of claims 1 to 3, wherein the announcement channel message includes details of an operator identity and an area code, and wherein the secondary station has one or more operator icings. A communication system comprising a storage means preprogrammed using a sign. 5. The method according to any one of claims 1 to 4, wherein the secondary station is programmed using a home operator identity and a home area code, and the primary station is assigned an operator identification code and an area code. A communication system characterized in that the secondary station transmits a batch marking signal, including tuning the preprogrammed home channel in response to recognition of the home operator identification code and the home area code and not scanning another channel. . 6. The method of claim 5, wherein the secondary station is programmed using at least one other home operator identification code and a home area code, and in response to detection of the at least one other home operator identification code and a home area code, prior to channel selection. Waiting for receipt of an announcement channel message from each operator. The system of claim 1, wherein the system operates according to a protocol comprising a series of cycles, each cycle comprising a predetermined number of batches, each batch comprising a plurality of frames. Wherein each frame comprises a plurality of code words, and wherein the announcement channel message further comprises details of paging applied to each channel. 8. The method of claim 7, wherein adjacent regions of the same network operate at different frequencies, and the batch applied to each frequency is configured such that the corresponding identified batch is offset by one batch period. A communication system characterized by the ability to achieve soft handover between frequency channels without losing this data. 9. A communication system according to claim 8, wherein the channels of each service area are allocated to a predetermined phase of the plurality of phases so that no two channels have the same phase in successive areas overlapping each other. In a secondary station for use in a communication system comprising a plurality of geographically separated primary stations acting as a network, each primary station is adapted to transmit an announcement channel message containing information about radio channels available in its network. And the secondary station selects the details of one or more channels stored in the storage means in response to receiving the announcement channel message and means for storing the details of the signal receiving means and the channels belonging to the network and accordingly Means for adjusting the state of the secondary station. ※ Note: The disclosure is based on the initial application.