The present invention relates to a microcellular mobile communication system using a Code Division Multiple Access (CDMA) scheme, more particularly the microcellular mobile communication system that provides subscribers with the high-speed mobile communication service more stably by providing the mobile communication service based on a microcell of a radius of several hundred meters, and improves frequency utility efficiency.
The microcellular mobile communication system may extend the life span of a mobile station because a cell radius is small, and is interesting as a structure to which a variety of services (i.e. data and image) are applicable. This microcellular mobile communication system needs a large number of base stations, which will increase the cost of initial facility investment and maintenance. A Base Station Transceiver System (BTS), in the conventional CDMA cellular mobile communication system, is connected with other equipments through E1/T1 or high-speed digital subscriber lines.
Accordingly, the BTS comprises a digital unit including the CDMA Channel Element Assembly (CCEA) for modulating and demodulating the signal of the CDMA scheme, a control processor including a Radio Frequency (RF) signal processing unit, a Base Station Controller (BSC) interface and an operation management interface, and the Global Positioning System (GPS) for synchronization between base stations and so on.
Such a BTS is not appropriate for a mobile communication system composed of a microcell type when taking weight or volume into account. Of course, there is an outdoor BTS of a small capacity structure, but it is difficult to install the BTS appropriate for various RF environments of metropolitan, in which it is needed, every several hundred meters and to extend capacity.
To solve the problems and the shadow areas, an antenna technique using the optical or the separate antenna has been used. However this technique, which transmits only an RF signal from the conventional BTS to a remote antenna through a coaxial cable or an optical fiber, is not appropriate for the mobile communication system of a large scale of microcell type in the future due to a synchronous problem between the conventional BTS and its antenna. That is, these can not perform various functions, needed for the microcell environment, which extend new cells, in order to increase the subscriber capacity, manage resources while maintaining the conventional service, or process a softer handover in more than three cells.
Accordingly, an object of the present invention is to provide a microcelluar mobile communication system that can perform various functions such as a centralized management of resources, a capacity increase, a Base Station Transceiver System (BTS) miniaturization, a synchronization between micro base stations, a dynamic resource management, a softer handover between cells, a grouping and ungrouping of base stations in accordance with a traffic distribution.
To achieve the above object, the present invention comprises a GPS receiver for generating a timing information and a reference clock signal to maintain synchronization of a system and a network; a micro base station controller for interfacing with a base station controller, performing a spreading modulation and demodulation, combining signals through a switching operation for dynamic channel allocation between cells and softer handover process, and up-converting the combined signal into at intermediate frequency so that said micro base station controller outputs the up-converted signal with a cable frequency if said micro base station controller transmits a signal to a plurality of micro base stations, and conversely down-converting a received cable frequency into the intermediate frequency so that said micro base station controller transmits a packetized message to said base station controller if said micro base station controller receives a signal from said plurality of micro base stations; a transferring means connected between said GPS receiver and said micro base station controller, for transferring the cable frequency signal in respond to a control signal; and said plurality of micro base stations for transmitting and receiving the cable frequency signal to and from said micro base station controller, respectively, through said transferring means, and for transmitting and receiving a radio frequency signal to and from a mobile station, respectively.
The present invention is divided into a digital hardware and an RF transceiver, the digital hardware and the RF transceiver are connected through optical fibers or hybrid fiber coaxial networks based on the Subcarrier Multiplexing (SCM) technique. The SCM means a transmission scheme that carries information on different frequencies from each other electrically in the transmission stage, combines the carried information, electrical-to-optical converts and transmits it through optical fibers, and optical-to-electrical converts and then recovers to an original signal through a band pass filtering.
The microcellular mobile communication of the present invention comprises a micro Base Station Controller (mBSC), which may manage resources in the center and supports a plurality of microcells, a Hybrid Fiber Radio (HFR) network based on the SCM technique and a plurality of micro Base Stations (mBSs) connected to the mBSC. Here the HFR, as a hybrid technique of the broad band nature of wire (optical fiber) and the mobility of radio, means that it transmits a Radio Frequency (RF) or an Intermediate Frequency (IF) through the optical fiber.
The micro Base Station (mBS) proposed in this invention, is installed within each microcell as an equipment only having an HFR network module, a simple control signal processor, a frequency up/down converter, an amplifier, a filter, a power source and so on. The mBSs are connected with the MBSC through the optical fiber or the hybrid fiber coaxial network. The MBSC performing the centralized control of the mBS comprises the digital hardware of the conventional Base Station Transceiver System (BTS), a Code Stream Switch (CSS) being capable of a dynamic resource allocation and the softer handover, an HFR network management module, the HFR network interface module and so on.
In addition, the mBSC performs the centralized-management of the mBS through the CSS, and minimizes an initial investment cost for constructing a microcell mobile communication system by allocating dynamically an intercell communication channel, and allows a cell design satisfying an optimum capacity. That is, the present invention as compared with the distributed control network of the conventional base station, permits the centralized control network, the dynamic channel allocation, and the base station grouping operation, and may process a handover between base stations with the softer handover.
Referring to a forward link, the mBSC converts a signal to be transmitted to each mBS into a cable frequency signal and then transmits the cable frequency signal through the HFR network. The mBS receives the cable frequency signal and then transmits the RF through an antenna after up-converting the cable frequency signal into the RF for personal communications system. On the other hand, the RF received from a mobile station is received in the mBS and then transmitted to the mBSC through a reverse link.
In particular, the present invention installs a GPS receiver in the mBSC without installing additionally the GPS receiver in the mBS, transmits a reference clock signal from the GPS receiver through the HFR network, and maintains the synchronization between mBSs. Thus the mBS installation cost is reduced, and the cell design may be applied to an indoor, a tunnel and so on that it is difficult for a GPS antenna to be installed. The communication system and network in accordance with the present invention interface with other communication network and are designed so that various radio communication services may be accommodated.