GB2319928A

GB2319928A - Combined beacon and traffic channel transmission

Info

Publication number: GB2319928A
Application number: GB9622631A
Authority: GB
Inventors: John David Gass; Howard Peter Benn
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1996-10-30
Filing date: 1996-10-30
Publication date: 1998-06-03
Also published as: WO1998019485A2; GB9622631D0; AU5314698A; WO1998019485A3

Abstract

A base transceiver station for a time distributed (TDMA) cellular radio communication has a beacon channel transmitter for transmitting both beacon and traffic signals at a beacon frequency, and a traffic channel transmitter for transmitting traffic signals only at a traffic frequency. A data signal generator 101 produces conventional beacon channel signals in time slot 0 and traffic signals in time slots 1 to 7. These signals are converted into GSM format by modulator 102 before transmission by transmitters 103,104. In the absence of true traffic signals, artificial traffic signals are generated 105 and transmitted. The beacon channel transmits in all the time slots. A control link 106 activates traffic channel transmitter 104 during time slots 1 to 7 only. In an alternative embodiment a common intermediate frequency stage (201, fig.2) and a switch (204) between control signal generator (205) and traffic channel transmitter (104) are included after the modulator. The switch is closed by the control signal generator only in time slots when traffic signals are present, so that traffic signals only are transmitted by the traffic channel transmitter.

Description

COMBINED BEACON AND TRAFFIC CHANNEL TRANSMISSION Field of the Invention The present invention relates to time distributed digital radio communication systems, and, more specifically, to such systems in which the cells have a nominal radius of 100 metres, or less.

Background of the Invention Cellular radio communication systems have a number of fixed base transceiver stations each of which can communicate with one or more, usually mobile, and hereinafter referred to as such, subsidiary transceiver units within a limited area which constitutes a cell of the cellular radio communication system. Each base transceiver station operates in two ways, it produces continuously so-called beacon signals which are used by mobile stations to establish links between the base transceiver station, and mobile stations and it produces traffic signals when a link has been established between it and a mobile station. Corresponding signals are produced by the mobile station concerned. The beacon signals have a specific frequency which is assigned to the base transceiver station, and a mobile station operates on a frequency which is assigned to it when the link between it and the base station is established. In a time distributed cellular radio communication system, both the beacon and traffic signals are in the form of regular pulses, or bursts, each of which is divided into a series of intervals, known as time slots, which are separated by other intervals which are known as guard periods. The duration of each signal burst is known as a time frame. In time distributed digital cellular radio communication systems which conform with specifications laid down by a body known as Groupe Systeme Mobile (GSM systems) there are eight time slots, designated 0 to 7, in each time frame.

A proposed form of base transceiver station, or head unit, for use in connection with a GSM type picocell radio communication system incorporates two transceiver units one of which is the beacon channel transceiver and the other of which is the traffic channel transceiver. Each transceiver has an associated modulator adapted to produce artificial signals to be transmitted during time slots when there are no real data signals to be transmitted by the associated transmitter. The two transmitters operate independently. The beacon signal transmitter operates continuously on all time slots, as is necessary with GSM systems to enable mobile stations properly to perform cell selection and procedures, while the traffic signal transmitter transmits traffic signals on time slots 1 to 7 of each time frame only because the receiver of the beacon signal transceiver seeks channel access request signals from mobile stations during time slots 0 in each time frame.

The duplication of components in the above described head unit means that it is relatively complex and therefore costly to implement, and the simultaneous operation of both transceiver units is relatively inefficient.

Summary of the Invention It is an object of the present invention to provide a simpler form of base transceiver stations suitable for use as a head unit in a time distributed picocell radio communication system.

According to the present invention there is provided a base transceiver station for use in a time distributed digital cellular radio communication system, including means for producing beacon channel signals during designated time slots in each time frame, as hereinbefore defined, and traffic channel signals during other time slots in each time frame, a beacon channel transmitter arranged to transmit throughout a time frame both beacon and traffic channel signals at a beacon frequency. A traffic channel transmitter arranged to transmit traffic channel signals only during designated time slots in a time frame at a designated traffic channel frequency and means for producing and supplying to both transmitters artificial traffic signals in the absence of actual traffic data signals.

Preferably the base transceiver station is adapted for use as a head unit in a picocell radio communication system.

The artificial traffic signals are produced and supplied to each transmitter in a form appropriate to that transmitter.

Preferably the base transceiver station is adapted for use as a head unit in a picocell radio communication system. Also there is provided a method of operating a base transceiver station of a time distributed digital cellular radio communication systems including the operations of transmitting beacon and traffic signals throughout a time frame. As herein before defined at a beacon channel frequency and separately transmitting traffic signals only during designated time slots in a time frame.

Brief Description of the Drawings The invention will now be described by way of example, with reference to the accompanying drawings in which FIG. 1 is a block diagram of an embodiment of the invention, and FIG. 2 is a block circuit diagram of a second embodiment of the invention.

Detailed Description of a Preferred Embodiment Referring to FIG. 1 of the drawings, a data signal generator 101 produces conventional beacon channel data signals, during time slot 0 in a time frame, and traffic data signals during time slots 1 to 7 of the same time frame.

These data signals are applied to a modulator 102 where they are converted to a standard GSM format and thence to two radio transmitters 103 and 104, respectively. The transmitter 103 is adapted to transmit beacon channel signals and the transmitter 104 is adapted to transmit traffic channel signals, an artificial traffic signal generator 105 is arranged to produce artificial traffic data signals at the appropriate frequency and supply them to the transmitters 103 and 104. In the absence of any true traffic signals the transmitters 103 and 104 are adapted to transmit the artificial traffic signals in the relevant time slots. A control link 106 between the transmitter 103 and the transmitter 104 activates the transmitter 104 during time slots 1 to 7 only of a time frame whereas the transmitter 103 transmits in all time slots in a time frame.

Thus the beacon channel transmitter 103 transmits beacon channel signals during all time slots in a time frame, as is usual, and the traffic channel transmitter transmits traffic signals during time slots 1 to 7 only, in a time frame. If, however, additional paging channels are assigned to the beacon channel carrier frequency in time slots other then the 0 time slot, then the beacon channel transmitter 103 is adapted to disable the traffic channel transmitter 104 during those time slots.

FIG. 2 shows another embodiment of the invention in which certain stages of the transmitters 103 and 104 are common. Referring to FIG. 2 the output signals from the modulator 102 are applied to a common intermediate frequency IF, stage 201, the output signals, from which are applied via a switch 104 to the radio frequency stage 202 of the beacon channel transmitter 103 and the radio frequency stage 203 of the traffic channel transmitter 104. Control signals from a control signal generator 205 close the switch 204 during those designated time slots in a time frame in which traffic signals are present and isolates the RF stage of the traffic channel transmitter 104 during the remaining time slots in a the time frame. Any artificial traffic signals are applied directly to the RF stages of the transmitters 103 and 104.

Alternatively, the switch 204 can be normally closed and opened by the control signal, so as to isolate the RF stage of the transmitter 104 during the time slots when beacon channel signals are to be transmitted by the beacon channel transmitter 103 only.

Claims

1. A base transceiver station for use in a time distributed digital cellular radio communication system, including means for producing beacon channel signals during designated time slots in each time frame and traffic channel signals during other time slots in each time frame, a beacon channel transmitter arranged to transmit throughout a time frame both beacon and traffic channel signals at a beacon frequency; a traffic channel transmitter arranged to transmit traffic channel signals only during designated time slots in a time frame at a designated traffic channel frequency; and means for producing and supplying to both transmitters artificial traffic signals in the absence of actual traffic data signals.

2. A base transceiver station according to claim 1 wherein there is included means for activating the traffic channel transmitter only during these time slots in a time frame designated for the transmission of traffic signals.

3. A base transceiver station according to claim 2 wherein the beacon channel transmitter and the traffic channel transmitter have a common intermediate frequency stage and there is included a switch between the common intermediate frequency stage and a radio frequency stage of the traffic channel transmitter and means operative to operate the switch to provide a connection between the common intermediate stage and the radio frequency stage of the traffic channel transmitter only during those time slots in a time frame designated for such transmissions.

4. A base transceiver station according to claim 1, claim 2 or claim 3 wherein beacon channel signals are generated during time slot 0 of a time frame and traffic signals are generated during time slots 1 to 7 of the same time frame.

5. A base transceiver station according to any preceding claim adapted to act as a head unit for a picocell radio communication system.

6. A method of operating a base transceiver station of a time distributed digital cellular radio communication system including the operations of transmitting beacon and traffic signals throughout a time frame, as herein before defined, at a beacon channel frequency and separately transmitting traffic signals only during designated time slots in a time frame.

7. A base transceiver station for use in a time distributed cellular radio communication system substantially as herein before described and with reference to FIG. 1 or FIG. 2 of the accompanying drawings.

8. A method of operating a base transceiver station of a time distributed digital cellular radio communication system substantially as herein before described and with reference to FIG. 1 or FIG. 2 of the accompanying drawings.