Antenna switching system

Abstract: An antenna switching system for handling high traffic sectors in a cellular radiotelephone system. The system switches the cell's base station transmitters (210) to sectors that have more mobile traffic than they can handle. The additional transmitters (210) increase the number of frequencies in the overloaded sector, thereby allowing a greater amount of mobile traffic to use the cell.

Description: TECHNICAL FIELD This invention relates generally to the switching of antennas. More particularly, this invention relates to the routing of radiotelephone transmissions from a transmitter to a particular antenna in a cellular radiotelephone system. BACKGROUND OF INVENTION Cellular radiotelephone cells typically consist of a number of transmitters that transmit, in either omnidirectional or directional antenna patterns, from the cell. The highest capacity cells use directional antennas, dividing the cell into sectors. A major metropolitan area can consist of a large number of these cells. The cells are linked to the land telephone line allowing mobile radiotelephone users to access the land telephone lines and vice versa. Using the cellular radiotelephone system, a mobile radiotelephone user can travel across a metropolitan area while keeping in contact with the land telephone lines. As a mobile user travels through an area, he may travel through more than one sector of a cell or, depending on the distance travelled, more than one cell. The cellular system takes care of handing off the user's call to another sector or cell. The mobility of the user means that the sectors within a cell could have widely varying demand at any given time. This variability could cause some sectors to become overloaded while other sectors may have excess capacity. Presently, when a sector has more users than it can handle, the users trying to communicate in that sector are either shifted to another sector or they must wait for a frequency to become free. Cellular base station receivers are diversity receivers which require 2 antenna inputs. In sector receive configurations, the 2 receive inputs come from one even and odd numbered sector that are adjacent. In order to route these two inputs from the odd or even antenna to the receiver, a configuration of passive splitters and matrix switches is used. The passive splitter splits the signal from the antenna into multiple signals to be handled by different receivers. The switch matrix switches the signals to the appropriate receivers. This configuration does not allow receivers to handle signals from any sector in the cell. Each receiver can only receive from the odd or even sector matrix to which it is assigned. Each sector of a cell typically has a single antenna for transmitting. In order to transmit on multiple frequencies in that sector, therefore, multiple transmitters must be combined on that single antenna. Fig. 1 illustrates the present method of combining transmitters onto an antenna. The transmitters (A) produce a signal that is amplified (B) and passed through a combiner (C). The combiner (C) merges the signals allowing a number of transmitters (A) to transmit on one antenna (E). The combiner (C) contains resonant cavities which each allow only one frequency at which the cavity is tuned to pass to the antenna (E). The cavities are manually tuned to a certain frequency which can only be changed by manually retuning the cavity. Therefore, only a limited number of fixed tuned frequencies can be transmitted from present sector cell configurations. In US-A-4 144 496 there is described a system where a set of transmitters can be assigned to one of the sector antennas of an antenna. A combination of signals is produced, which is then routed to a single desired antenna. GB-A-2 188 214 describes a series of transmitters which may be coupled, one at a time using a switch, to an antenna. Because mobile traffic is not distributed evenly, it is continuously changing in number and location, and present transmitter hardware is limited to a fixed number of frequencies within a sector, there exists a need to move underutilized transmitters and/or frequencies from sector to sector with varying traffic demands. SUMMARY OF THE INVENTION Accordingly, the present invention provides a dynamic frequency allocation system for allocating frequencies between sector antennas of a base station having a plurality of odd and even sector antennas, each odd sector antenna coupled to an odd sector switch matrix and each even sector antenna coupled to an even sector switch matrix, the system comprising: at least one signal transmission source for generating at least one signal; said system characterized by: a sector switching circuit, coupled to the at least one signal transmission source, for routing a first signal of the at least one signal from the signal transmission source to the odd sector switch matrix or the even sector switch matrix; a plurality of radio frequency signal combiners, a first radio frequency signal combiner of the plurality of radio frequency signal combiners coupled to either the odd or the even sector switch matrix; a plurality of linear power amplifiers, a first linear power amplifier coupled to the first radio frequency signal combiner; and a first odd or even sector antenna coupled to the first linear power amplifier. An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the prior art; FIG. 2 is a block diagram of one embodiment of the present invention with a single base station; FIG. 3 is a diagram of a cell site with 60° sectors; FIG. 4 is a block diagram of an alternate embodiment of the present invention with multiple base stations; and FIG. 5 is a block diagram of an alternate embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION The antenna switching system provides dynamic frequency allocation in a cell. In other words, a transmitter can be switched to other sectors in a cell on demand. This is accomplished by the use of a switch matrix similar to the matrix used in the receive portion of a cell. For proper operation, however, this transmit matrix is used in conjunction with a linear power amplifier and a signal combiner. Fig. 2 shows a single base station with the capability of switching between all odd and even sectors of a cell. The odd/even sector configuration of a cell is illustrated in Fig. 3. The odd/even sector switch (201) may be used when a mobile user (301) travels between sectors (303) of a cell (302). In this case, if the mobile user (301) travelled from sector 3 to sector 2, the sector switch would allow the base station (210) to follow the mobile user (301) from the odd to the even sector. This would also apply to a mobile user going from an even sector to an odd sector. The odd/even sector switch function may also be incorporated within the matrix switches (203). Once the odd or even sector is selected, the signal is switched by the switch matrix (203). The switch matrix (203) routes the signal to the appropriate broadband antenna combiner (204) that is within the sector the switch matrix (203) controls. Both the switch matrix (203) and the sector switch (201) have the task of isolating one antenna (220) from another. A broadband combiner (204) combines signals of different frequencies, from the switch matrices, to be transmitted on one antenna. The signals to be combined are, for example, in the ranges of 824.01 MHz to 848.97 MHz and 869.01 MHZ to 893.97 MHz. The broadband combiner (204) output may feed a linear power amplifier (205). The input to the linear power amplifier will be signals of multiple frequencies that will generate intermodulation products if the amplifier is non-linear. Therefore, the linear power amplifier (205) must have a very linear amplification for proper operation of the cell site. The linear power amplifier is only required for normal cell site coverage in a metropolitan area. If the antenna switching system is used in a building or other situations where high power is not needed, the linear power amplifier can be removed and the antenna switching system will still operate properly. A typical cell configuration uses a number of base stations for transmitting and receiving. A base station consists of a number of transmitters and receivers and typically has 8 to 10 frequencies for communication. Fig. 4 illustrates a multiple base station configuration, the typical configuration of a cell. As in the single base station configuration, the signal from the base station (401) is transmitted to the appropriate switch matrix (402). The switch matrix (402) switches the signal to the broadband combiner (403) feeding the appropriate antenna (404). The broadband combiners (403) illustrated in Fig. 4 are shown having unconnected inputs (405). This denotes that this embodiment can be expanded with additional switch matrices without departing from the present invention. Fig. 5 illustrates an alternate embodiment to interface the cavity combiner hardware presently used to the antenna switching system. Using this scheme, the cell will have some channels fixed in a sector and some reserved to accommodate changing traffic demands, thereby reducing the cost of upgrading a cell. The antenna switching system allows dynamic frequency allocation in a cell. This is a result of the ability to switch base station transmitters from sector to sector and because resonant cavity combiners are not needed. An overburdened sector in a cell can request a transmitter from another sector to assist in handling the traffic. The transmitters switched into the overburdened sector will be capable of transmitting on any frequency available in the system, thereby increasing the number of frequencies in that sector. If the system had control hardware/software to determine what frequency to assign to minimize interference between users, this invention would allow all the base stations in a cell to operate in one sector of the cell if needed.

Claims: A dynamic frequency allocation system for allocating frequencies between sector antennas (220) of a base station having a plurality of odd and even sector antennas, each odd sector antenna coupled to an odd sector switch matrix (203) and each even sector antenna coupled to an even sector switch matrix (203), the system comprising: at least one signal transmission source (210) for generating at least one signal; said system characterized by: a sector switching circuit (201), coupled to the at least one signal transmission source (210), for routing a first signal of the at least one signal from the signal transmission source to the odd sector switch matrix (203) or the even sector switch matrix (203); a plurality of radio frequency signal combiners (204), a first radio frequency signal combiner of the plurality of radio frequency signal combiners coupled to either the odd or the even sector switch matrix (203); a plurality of linear power amplifiers (205), a first linear power amplifier coupled to the first radio frequency signal combiner; and a first odd or even sector antenna (220) coupled to the first linear power amplifier (205).

Inventors: SCHULER JOSEPH J, SMITH JOHN M, SCHULER, JOSEPH J., SMITH, JOHN M.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1990
Main classification: H04Q7
IPC codes: H01Q3, H04W88