Microcell including radio channel units controlled by a remote macrocell radio control complex

Abstract: A microcell unit (e.g.108), in a cellular telephone system using digital signal processing Bss (104), is digitally connected to a macrocell (104), via a metallic link (128), such as a twisted pair. The microcell (108) includes a plurality of radio channel units (RCU), (149), to provide voice connectivity to mobile subscribers (MS), which are under control of a radio control complex (RCC) located in the macrocell (104). Several time slots of the macrocell TDM bus (124), through which the RCC exerts control of the RCUs, are remoted (at 138) to the microcell (108) thereby enabling control of the RCUs at the microcell location by the RCC of the macrocell. This remoting action is achieved, via a remote time division multiplex (TDM) circuit pack (135) which enables the RCC to communicate with the RCUs as if they were located within the macrocell (104).

Description: This invention relates to microcell stations. Cellular communication systems are divided into a plurality of contiguous specific geographical coverage areas called cells. Access, via mobile subscriber (MS) radiotelephones, to the telephone network is through a cell site or macrocellular base station (BS) located in each cell, (i.e. equipment which includes antennas, radio transceivers and control equipment operative to facilitate radio air interconnection between a MS and the BS assigned to cover the geographical area where the MS is located). The BS is connected to a mobile switching center (MSC) which is in turn connected to the public switched land telephone network (PSTN). A detailed description of the cellular telecommunications system may be found in "The Cellular Concept" by V.H. MacDonald in The Bell System Technical Journal, January 1979, vol. 58 no. 1, pages 15 - 42. Coverage in the geographical area of a cell by a single BS is typically uneven. Due to topographical features and building structures and highway passageways, dead or weak spots exist within the cell's geographical area. Coverage of an MS within these dead or weak spots is either substandard or non-existent. MSs may fail to connect, may be suddenly disconnected or may experience a fading of transmission signals. Coverage of a cell area may be readily enhanced by the utilization of microcells distributed among the dead or weak spots or in places needing enhanced capacity to handle MSs. Microcell units typically act as satellites or repeaters and are used to illuminate or radiate the dead or weak spots. The typical microcell includes amplifiers and radiation antennas. All other signal processing is performed at the BS. They are typically connected to the cell site or BS, via a high capacity link such as light fiber. BSs operate with analog signal processing at present. The light fiber link is hence used to transmit analog signals between the BS and the microcell. These light fiber lines are frequently provided by a public utility whose tariff is based on a digital bit rate use. Hence transmitting analog signals becomes prohibitively expensive. According to this invention there is provided a microcell station as claimed in claim 1. Brief Description of the Drawing In the Drawing: Fig. 1 is a block schematic of a cellular radio telephone system employing microcell access stations embodying the invention; Fig. 2 is a block schematic of a macrocell BS and a microcell access station and their corresponding bus interconnection arrangement; and Fig. 3 is a block schematic of an interface circuit used to couple a bus of the macrocell BS with a bus in the microcell station. Detailed Description In the cellular radiotelephone system of FIG. 1 the public switched telephone network (PSTN)(101) is connected by a T1 carrier twisted wire pair link (102) to a mobile switching center (MSC) (103). The MSC (103) interconnects the PSTN (101) to a plurality of digital macrocell base stations (BS) (104) and (105), each operating as a macrocell site serving a particular geographical service area (106 -107). Since a central BS may not provide adequate coverage of its assigned area, microcell stations (108 - 111) each under control of one of the BSs are located within the assigned service area to provide service in sub areas not adequately serviced by the BS. This deficiency in service is often the result of failure of the centralized BS to satisfactorily radiate that sub area. The service area (106) is shown as containing one BS (104) and two microcell stations (108) and (109). Within the service area (106) the macrocell BS (104) has a radiating antenna (114). The two microcell access stations (108) and (109) also have radiating antennas (118) and (119) to provide radiant signal energy to sub areas not properly radiated by the macrocell BS (104). The microcell stations (108) and (109) are each connected to the macrocell BS (104) by metallic twisted pair wires (128) and (129), respectively. These wires are typically operated as a T1 carrier link. The macrocell BS (104) is a digital BS which includes a digital time division multiplex bus (124) connecting a plurality of radio channel units (144) to a digital facilities control (125) connected to the MSC by a T1 carrier line (121). The TDM bus (124) is also connected to interface circuits (126), and (116) which are connected, via T1 carrier links (129) and (128), to the interface circuits (136) and (135) located in the microcell access stations (109) and (108) respectively. The electrical interconnection through the interface circuits (136) and (135) integrates the remote TDM busses (138) and (139) as an integral part of the local TDM bus (124). Radio channel units (RCUs) (149) and (140) in each of the microcell access stations (108) and (109) are connected to the remote TDM busses (138) and (139). Due to the interface circuit interconnection and the metallic connection these RCUs (140) and (149) are effectively controlled, by the BS (104) in the same manner as are the RCU's (144) physically co-located with the local TDM bus within the macrocell BS (104). Hence the remote TDM busses (138) and (139) are effectively operative as a part of a single common bus (124) which controls the RCUs distributed among the macrocell BSs and the microcell access stations. The multiplex bus (124) is, as shown in FIG. 2, a time division multiplex (TDM) bus in the illustrative embodiment. This TDM bus (124) is under the control of a radio control complex (RCC) (290) and is operative, under the control of the core computer processors (260) and (280) to connect circuitry, included within the RCC (290), to the RCUs (144) and through the local TDM interface circuits (126) to the RCUs (148) located at the microcell access station (108). The circuitry of the RCC includes an active control system and a parallel connected backup control system. The active control system includes a network control interface (NCI) (261) to synchronize control channel messages between the bus (124) and processor (260). A communications processor interface (CPI) (265) provides control channels for communicating with the MSC, via T1 carrier link (121), (shown in FIG. 1). A memory circuit (MEM) (269) is included to store call processing information. An alarm facility interface (AFI) (267) provides for alarm signaling. A backup core processor (280) is connected to the active processor (260) by an update data communication bus (270). It's stored memory is continuously updated by the processor (260), via the update bus (270). The NCI (281), CPI (285), MEM (286), and AFI (287) connected to processor (280), all function in the same manner as their duplexed counterparts connected to processor (260). Their function is to assume bus and system control should processor (260) fail. The macrocell BS (104) includes a plurality of RCUs (144) connected to the TDM bus (124). These RCUs are transceiver circuits connected to a combiner/splitter circuit (255) which splits outgoing signals into parallel paths connected to a plurality of paralleled linear amplifiers and filters (256). The plurality of linear amplifiers are operated in parallel to reduce the signal power level that any single amplifier must accommodate. The combiner/splitter (255) receives incoming signals from paralleled amplifiers and combines them and applies them to the RCUs (144). The amplifiers (256) are connected to the antennas (114). An RF switch control (257) is used to control connection of the amplifiers to selected antennas (114) of the macrocell BS (104). A local TDM interface circuit (126) is connected to the TDM bus (124) and is connected, via the T1 carrier metallic wire, to a corresponding remote TDM interface circuit (135) located at the microcell station (108). This remote TDM interface (135) is connected to the remote TDM bus (138) (TDM). The local and remote TDM interfaces (126) and (135) are operative to condition signals for their transmission over the T1 carrier wire (128) and incorporate the remote TDM bus (138) as an integral part of the local TDM bus (124) at the BS (104) connected to other remote TDM bus (138) are a plurality of RCUs (148) which are also connected to a combiner/splitter (251)..... The combiner/splitter (251) is connected to a power amplifier array (252) which is in turn connected to antennas (118). Coupling of RCUs (148) and antennas (118) is under control of a RF switch control (253). The microcell's RCUs (148) provide for two way voice connection to the mobile radiotelephone subscribers in a sub area radiated by the microcell access station. They modulate and control voice and control information transmitted over the air interface. The combiner/splitter (251) applies a combined signal of a plurality of channels to the amplifier (252) which amplifies the signal to a level appropriate for providing service to the area covered by the microcell. The structure of both the local and remote TDM bus interfaces (126) and (135) are shown in detail in the block diagram of FIG. 3. The local and remote bus interfaces communicate with each other over a T1 carrier link (128) interconnecting the macrocell BS and the microcell access station. Interfacing to the T1 carrier link is provided by a T1 link interface (321), which includes the Digital interface facility (310) and the framing controller circuitry (309). The T1 carrier link (128) is connected to a DS1 digital interface facility (310). The T1 link interface (321) provides framing, signaling and data link access to the T1 carrier link. The typical DS 1 format is 24 digital voice communication channels in slots of 64 K bits/sec serial data packaged in the proper framing format for transmission over a T1 link at 1.544 Mbit/sec. The digital interface facility includes circuitry to permit interfaces with CEPT lines (a European Standard). Control of the bus interface circuitry is directed by a board control unit (323) including a microcontroller (305) and an associated memory unit (306). The memory unit includes RAM and ROM memory to store data and provide stored program instructions for controlling operation of the interface unit. Within the bus interface (321) and DS 1 digital interface facility (310) is connected to a framing and controller circuit (309). This circuit packages the digital signal frame for transmission over the T1 carrier link and provides the proper framing format. The TDM bus interface (322) plugs into a normal RCU TDM bus slot with lead (311). The bus interface (322) includes a TDM buffer circuit (301) which is connected to a TDM bus slot of either the BS or microcell access station depending on the location of the TDM bus interface at either the BS or microcell access station. The TDM buffer is connected to the TDM multi-address control logic circuit (302). A manually switched group address control (303) is connected to an input of the control logic circuit (302) to provide manual addressing control. A dual port memory (314) is connected to a bus coupling the controller (323) to the protocol controller (313). The protocol controller (313), connected to the dual port memory operates to provide data retransmission to the T1 link interface (321) and provide formatting functions such as CRC checking and framing. A network processing circuit (308) provides information transfer, including a serial to parallel conversion, between the T1 link interface (321) and the TDM buffer (310). Overall TDM interface circuit protection is provided by a TDM bus sanity an control interface circuit (304).

Claims: A microcell station (108) operative in a cellular radiotelephone system having primary service area coverage provided by digital processing base stations (BS) as part of a macrocell station (104) and the microcell station being operative for enhancing service coverage in a selected portion of the primary service area; the BS including a radio control complex (RCC) (290) having a multiplex bus (126) and a plurality of radio channel units (RCU) (144) connected to the multiplex bus and responsive to control of the RCC; CHARACTERIZED BY: the microcell station (108) including: a remote multiplex bus extension (138) included in the microcell station; a plurality of remote radio channel units (RRCU) (148) each connected to the remote multiplex bus extension; a remote interface circuit (135) connected to the remote multiplex bus extension at the the microcell station and a local interface circuit (126) connected to the multiplex bus at the BS; and a metallic wire (128) interconnecting the remote interface circuit and the local interface circuit, the metallic wire in combination with the the remote interface circuit and the local interface circuit, enabling the remote bus extension to be functionally equivalent to being an integral part of the multiplex bus and under control of the RCC. A microcell station as claimed in claim 1, wherein the metallic wire is a twisted pair operating as a T1 carrier link. A microcell station as claimed in claim 1, wherein the local and remote interface circuit each include a T1 link interface (321) for interconnecting to the T1 carrier link; a bus interface (301) for connecting to the multiplex bus; a message processor connected to receive and utilize control signals from the RCC to control RCUs connected to the bus; and a protocol control (313) for formatting data transmission.

Inventors: ABBASI SALMAN YOUSEF, GERSZBERG IRWIN, KENDIG EUGENE THOMAS, MARTIN JEFFREY STEPHEN, OPLINGER THOMAS MARK, ABBASI, SALMAN YOUSEF, GERSZBERG, IRWIN, KENDIG, EUGENE THOMAS, MARTIN, JEFFREY STEPHEN, OPLINGER, THOMAS MARK
Applicants: AT & T CORP, AT&T CORP.
Application year: 1993
Main classification: H04Q7
IPC codes: H04W88