MXPA98006757A - An apparatus and method for sharing a signal channel - Google Patents

Abstract

The present invention relates to an apparatus and method for sharing a communication channel between two or more base stations connected to a base station controller via a common transmission line in a channelized format. The present invention allows each of the base stations to receive data transmitted in a communication channel shared from the base station controller, to determine whether the transmitted data from the base station controller is destined to the base station, and to insert its data within the communication channel without interfering with data transmitted by other base stations in the communication channel. In one embodiment, each of the base stations is bridged in the transmission facility in such a way that the signaling messages that are transmitted in a signaling channel could be received by all the base stations. The signaling messages have associated identifiers to specify particular base stations to which the signaling messages are intended. In another embodiment, each of the base stations can insert their signaling message into the data stream in the signaling channel without interfering with the signaling messages that are already in the data stream.

Description

AN APPARATUS AND METHOD FOR SHARING A SIGNALING CHANNEL FIELD OF THE INVENTION The present invention relates to a telecommunications system and, in particular, to a wireless communication system that uses a common transmission line to connect a plurality of base stations to a base station controller.

ANTECEDENTS OF RELATED ART Wireless communication systems generally use transmission lines that are configured in a piped format, such as IT or El facilities, to connect a set of base stations to a base station controller (BSC). FIG. 1 illustrates a wireless communication system 10 in which a BSC 12 is individually connected to the base stations 14 -i by the respective path of the IT facilities 16-i, where i = l, 2, ..., n.

Each of the TI facilities 16-i includes a downlink path 17 -i and an uplink path 19-i, as shown in FIG. 2, for the transmission of data to and from the base stations 14-i, respectively. Each of the trajectories 17 -i, 19-i is REF.:27998 configures in a channelized format - that is, the paths are divided into transmission time intervals. FIG. 3 illustrates a way to channel the trajectories 17-i, 19-i. Each of the trajectories 17-i, 19-i are divided into frames that have a frame time interval and twenty-four time slots DSOj, where j = l, 2, ..., 24 and each one of the intervals of DSO time have a bandwidth of 64 Kbps. Thus, the wireless communication system 10 has a number of 24'n time slots DSOj in the downlink direction and number of 24-n time slots DSOj in the direction of uplink.

The DSOj time slots are used to form communication channels, which include a signaling channel and a plurality of traffic channels. Each communication channel includes at least one time slot DSOj in the downlink path 17-i and the uplink path 19-i. For discussion purposes, a DSOj time slot should be considered in the following to refer to a DSOj time slot in the downlink path and a DSOj time slot in the uplink path, unless otherwise specified.

Each of the base stations 14-i uses x number of timeslots DSOj as a signaling channel for transmitting the control information between the base station 14-i and BSC 12, where x = 1. Each of the base stations 14-i can support enough user traffic to consume p number of traffic channels (to transmit user traffic between the base stations 14-i and the BSC 12 and a voice switch, not shown), wherein a traffic channel comprises and number of timeslots DSOj and y = 1. Thus, IT facilities 16-i should have at least one bandwidth including g number of time intervals DSOj, where g = y • p + x.

In general, each of the TI 16-i installations has a bandwidth that includes more than g numbers of timeslots DSOj- that is, the user traffic is supported by an individual base station (and the control information) does not consume the full bandwidth available in an IT facility (eg, g < n). Thus, the base station does not use some DSOj time slots that result in inefficient utilization of the IT installation.

To more efficiently use IT facilities and reduce the cost of a wireless communication system, one or more IT facilities could be shared by a plurality of base stations. FIG. 4 illustrates a wireless communication system 20 in which a daisy chain configuration is used to connect a number of base stations 22-i to a BSC 24 via a common facility 26. In contrast to the wireless communication system 10, the wireless communication system 20 has a total of 24 numbers of time slots DSOj (compared to 24 * n numbers of time slots in the wireless communication system 10). Similar to the base stations 14-i, each of the base stations 22-i has its own signaling channel comprising x number of timeslots DSOj - that is, n • x number of timeslots DSOj over the IT installation 26 are used as signaling channels. The remaining DSOj time slots in the TI 26 installation, eg, m-n • x, can be used as traffic channels. The number of remaining DSOj time slots should be at least equal to the total number of DSOj time slots required by the base stations 22-i to support user traffic, e.g. ex. , 24-n • x = y • p * n. Remember that n represents the total number of base stations, x represents the number of time slots DSOj that make up a signaling channel, and represents the number of time slots DSOj that make up a traffic channel, and p represents the number of channels of time. consumable traffic by user-per-base traffic.

In some cases, the total number of DSOj time slots required by the base stations to support user traffic is greater than the number of remaining DSOj time slots. In these cases, more DSOj time slots (or traffic channels) are required to support user traffic. For example, it is assumed that the wireless communication system 20 includes five base stations (eg, n = 5), each signaling channel and traffic channel comprises a DSOj time slot (eg, x = lyy = l), and the user traffic supported by each of the base stations 22-i consumes four traffic channels (eg, p = 4). If each base station 2-i has its own signaling channel (for a total of five DSOj time slots), then there would only be nineteen DSOj time slots available for use as traffic channels by the five base stations. Since each base station supports enough user traffic to consume four traffic channels, twenty DSOj time slots are needed by the wireless communication system for the traffic channels. Since the IT installation has only nineteen DSOj time slots available for use as traffic channels, the needs of the wireless communication system 20 would exceed the capacity of the IT installation.

One way to increase the number of DSOj time slots available for use as traffic channels is to use the additional IT facilities. Such a solution would undesirably increase the cost of the wireless communication system. Therefore, there is a need to increase the number of available DSOj time slots for use as traffic channels in an IT facility that connects two or more base stations to a base station controller.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an apparatus and method for increasing the number of available DSOj time slots for use as traffic channels in an IT installation or the one connecting two or more base stations to a base station controller for sharing a signaling channel between the base stations. The present invention is based on the concept that a simple base station does not use the amplitude of the entire band of the signaling channel for the transmission of signaling messages, e.g. eg, control information to manage resources in one or more base stations. The best use of the bandwidth of the signaling channel can be achieved if two or more base stations can share the same signaling channel which, in turn, results in making more DSOj time slots available for use as traffic channels. To share a signaling channel, the wireless communication system should be configured such that each of the base stations can receive their signaling on a downlink signaling channel, and transmit their signaling messages to the base station controller on an uplink signaling channel without interfering with signaling messages transmitted by other base stations in the uplink signaling channel.

In one embodiment, the base station controller transmits in the downlink signaling channel a downlink signaling message with an associated identifier specifying the base station to which the signaling message is intended. Each of the base stations bridges or drifts over the transmission facility to receive the message and downlink signaling identifier. This allows messages and downlink signaling identifiers to pass transparently through the receiving base station and to other base stations in the wireless communication system. The receiving base station examines the identifier to determine whether the associated downlink signaling messages are intended for the base station. If so, the base station executes instructions contained in the downlink signaling message. Otherwise, the downlink signaling message is ignored.

In another embodiment of the present invention each of the base stations transmits its uplink signaling message to the controller of the base station without interfering (eg, overwriting) with the uplink signaling messages transmitted by other stations. base. In this mode, the base station receives the uplink signaling messages (and associated identifiers) transmitted by other base stations in the uplink signaling channel to the controller of the base station. The receiving base station stores the received uplink signaling message in memory associated with the base station. Also stored in the same (or different) memory could be an uplink signaling message (and identifier) generated by the receiving base station for transmission to the base station controller. Any signaling message stored in the memory of the receiving base station is then transmitted to the controller of the base station at a "first-entry, first-exit" base on the uplink signaling channel. Therefore, signaling messages from all base stations in the wireless communication system are secured to be transmitted to the controller of the base station.

BRIEF DESCRIPTION OF THE DRAWINGS The features, aspects, and advantages of the present invention will be better understood with respect to the following description, appended claims, and accompanying drawings where: FIG. 1 represents a wireless communication system in which each of a plurality of base stations has an associated IT facility for connecting to a common base station controller; FIG. 2 represents an IT installation comprising an uplink path and a downlink path; FIG. 3 represents a way to channel an IT facility; FIG. 4 represents a wireless communication system in which a "chain of stations" configuration is used to connect a plurality of base stations to a base station controller via a common IT facility; FIG. 5 represents a wireless communication system comprising a plurality of base stations connected to a base station controller via a common IT facility in accordance with an embodiment of the present invention; FIG. 6 represents the data formats for transmissions in downlink and uplink paths of IT installations according to one embodiment of the present invention; Y FIG. 7 represents a downlink circuitry according to an embodiment of the present invention; Y FIG. 8 represents uplink circuitry according to an embodiment of the present invention.

DETAILED DESCRIPTION FIG. 5 shows a wireless communication system 30 comprising a plurality of base stations 32-i and a base station controller (BSC) 34 used in accordance with the present invention, where i = l, 2, ..., n. The base stations 32-i are connected to the BSC 34 in a chain-of-stations configuration using a common IT facility 36 configured in a channelized format. FIG. 6 illustrates the data formats for transmissions in the downlink and uplink paths 37,39 of the IT facility 36. In the downlink and uplink frame time slots, the transmissions include a predetermined sequence of bits (FIG. referred to here as frame bits). These framing bits provide a reference point to determine the start of a frame. In the DSOj time slots of the downlink and uplink signaling channel, the transmissions include additional dialing bits to indicate the start of the signaling channel and one of the following: a downlink or uplink signaling message with an identifier to specify a particular base station; or flag characters indicating the absence of signaling messages. In the downlink signaling channel, the identifier specifies a base station to which the associated downlink signaling message is intended. In the uplink signaling channel, the identifier specifies a base station from which the associated uplink signaling message was transmitted.

Similarly, in the DSOj time slots of the downlink and uplink traffic channel, the transmissions include additional frame bits to indicate the start of a particular traffic channel, downlink or uplink user traffic (e.g. ., voice or coded data), and a head indicating a mobile phone. In the downlink traffic channel, the head indicates a mobile telephone to which the voice or downlink encoded data is intended. In the uplink traffic channel, the head indicates a mobile telephone from which the voice or uplink data is transmitted.

The BSC 34 is a device for controlling the resources of the base stations 32-i and for establishing the replacement of user traffic between the 32-i base stations and a land-line network (such as a public switched telephone network connected to the BSC 34). via a mobile switching center), not shown. The BSC 34 includes control packet that executes in a processor 38 to process and generate uplink and downlink signaling message.

The 32-i base stations are devices for the interconnection between mobile telephones and a land-line network. Each of the base stations 32-i includes downlink circuitry 40 and uplink circuitry 42 for processing the data transmitted in the downlink or uplink signaling channels, respectively, as will be explained here. FIG. 7 is a simplified scheme of the downlink circuitry 40 according to an embodiment of the present invention. The downlink circuitry 40 includes a signal level compensator 50, a frame 52, and a time slot exchanger (TSI) 54, a synchronous-asynchronous universal transceiver (USART) receiver 56, a microprocessor 58 and a memory random access (RAM) 60. The signal level compensator 50 is connected to the downlink path 37 to reduce the load on the IT installation 36. The signal level compensator 50 allows the base station to establish a bridge or derivation in the downlink path without delaying or interrupting the current of the bit being transmitted in the downlink path. The downlink bit stream is passed through the level compensator 'of signal 50 to frame 52, which is a device having functionality to detect or find the start of a frame and / or a communication channel (e.g. eg, signaling channel or traffic channel) that uses the frame bits. In the detection of the start of a frame or a communication channel in the downlink bit stream, the frame 52 sends an indication to the TSI 54 that the start of a particular frame or communication channel has been detected.

The TSI 54 is a device for selectively terminating and repeating (or outputting) the data and is well known in the art. When the TSI 54 receives the indication, the TSI 54 will know that the next set of bits was transmitted at the beginning of the frame and / or in a particular communication channel. The TSI 54 is configured to pass the set of bits transmitted in the downlink signaling channel (eg, the downlink signaling channel bits) to the USART 56. The USART 56 is a device for examining the set of bits of the downlink signaling channel (or part thereof) for the presence of signaling messages, and is well known in the art. Specifically, USART 56 will look for flag characters indicating the absence of signaling messages. For example, it is assumed that the flag characters comprise a bit sequence "1000001". If the USART 56 does not detect flag characters (eg, 10000001), the USART passes to the bit set of the downlink signaling channel to the microprocessor 58 which, in turn, will store such a set of bits in the RAM 60. If USART 56 detects the flag characters, USART 56 discards the bit set of the downlink signaling channel and does not pass it to the microprocessor 58.

At any time the USART 56 detects the flag characters in a set of bits of the downlink signaling channel and a signaling message in a next set of bits of the downlink signaling channel, the USART 56 will transmit an interruption signal to the microprocessor 58 indicating that the next set of bits is the start of a signaling message. Also, at any time the USART 56 detects a signaling message in a set of downlink signaling channel bits and flag characters in a next set of the downlink signaling channel bits, the USART 56 will transmit a interrupt signal to the microprocessor 58 indicating that the former of the set of bits is the end of the signaling message. When a complete signaling message is in RAM 60, the microprocessor 58 examines the identifier associated with the stored signaling message to determine whether the signaling message is destined for its base station. If so, the microprocessor will process the signaling message. If not, the microprocessor discards the signaling message.

FIG. 8 is a simplified schematic of the uplink circuitry 42 according to an embodiment of the present invention. The uplink circuitry 42 includes signal level compensators 62, 64, a frame 66, a TSI 68, a USART 70, a microprocessor 72 and RAM 74. The level compensator of the signal 62 is connected to the path of the signal. uplink 39 to reduce the load in the IT installation 36. The uplink data is passed through the signal level compensator 62 to the framing 66, which searches for the start of a frame and / or a communication channel in the Uplink bit stream. In the detection of the start of a frame and / or a communication channel, the frame 66 sends an indication to the TSI 68 that the start of a frame and / or a communication channel has been detected.

The TSI 68 is configured to pass the set of bits transmitted in the uplink traffic channel in the uplink traffic channels via the level compensator of the signal 64, and to pass the set of bits transmitted in the signaling channel to USART 70. USART 70 will process the uplink signaling channel bits in the same way that USART 56 processes the downlink signaling channel bits. The signaling messages that passed through the USART 70 to the microprocessor 72 will be stored by means of the microprocessor 72 in RAM 74. It is noted that the signaling messages that passed through the USART 70 are signaling messages generated by other base stations in the system of wireless communication. In addition to these signaling messages, stored in the RAM 74 could also be a signaling message generated by the base station of which the microprocessor 72 is a part (eg, receiving or common base station). The signaling messages (generated by the common base station or other base stations) stored in the RAM 74 are passed before the USART 70 on a "first-in, first-out" basis. The USART 70, at the same time, will pass the signaling messages from the microprocessor 72 to the TSI 68. At any time the USART 70 does not receive a signaling message from the microprocessor to pass to the TSI 68, the USART 70 will pass the flag characters to the TSI 68. The TSI 68 will insert the passed bits of the USART 70 into the uplink signaling channel via the signal level compensator 64, thus transmitting all signaling messages to the base station controller.

It is noted that the present invention should not be limited to an apparatus and method for sharing a signaling channel. The present invention can also be used to share other communication channels. It is further noted that the present invention should not be limited to being used in a wireless communication system in which the base stations are connected in a chain-of-station configuration to a base station via a common IT facility. Other configurations are possible, such as parallel configurations, and other transmission facilities. Therefore, the spirit and scope of the present invention should not be limited to the description of the modalities contained herein.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, the content of the following is claimed as property.

Claims (10)

1. A method for sharing a communication channel in a wireless communication system having a plurality of base stations connected to each other via a transmission facility, the transmission facility having a plurality of time slots, the method , is characterized in that it comprises the steps of: receiving the data in a base station over the transmission facility, in at least a portion of the data received in a first communication channel having at least one time slot; Y examine at least a portion of the data received on the first communication channel to determine whether the data received in the first communication is destined for the receiving base station.

2. The method of claim 1, characterized in that the first communication channel is a signaling channel and the portion of data that was received in the signaling channel includes the data of the signaling channel, the data of the signaling channel having a message of signaling and an identifier to specify a particular base station to which the signaling message is intended.

3. The method of claim 2, characterized in that it comprises the additional step of: process the signaling message if the identifier specifies the receiving base station.

4. The method of claim 2, characterized in that it comprises the additional step of: emit the data of the signaling channel to another base station in the signaling channel.

5. The method of claim 1, characterized in that at least one other portion of the data is received in a second communication channel having at least one time slot.

6. A method for sharing a communication channel in a wireless communication system having a plurality of base stations connected to each other via a transmission facility, the transmission facility having a plurality of communication channels, the method is characterized in that it comprises the steps of: receiving in a base station a first set of bits in a communication channel; examining the first set of bits to determine whether the first set of bits includes flag characters indicating the absence of signaling messages; transmitting the base station a second set of bits in the communication channel, the second set of bits having at least the first set of bits if the first set of bits includes the flag characters.

7. The method of claim 6, characterized in that the second set of bits includes a third set of bits belonging to the receiving base station.

8. The method of claim 7, characterized in that the third set of bits includes a signaling message.

9. The method of claim 6, characterized in that the second set of bits includes the flag characters indicating the absence of the flag characters if the first set of bits does not include flag characters.

10. The method of claim 6, characterized in that the step of examining the first set of bits includes the step of: examine a subset of the first set of bits to determine whether the subset is flag characters indicating the absence of the flag characters.