GB2329793A

GB2329793A - A Radio Communications Monitor

Info

Publication number: GB2329793A
Application number: GB9720382A
Authority: GB
Inventors: Timothy Simon Klein; Ken Jakobsen; Jean-Jacques Gras
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1997-09-26
Filing date: 1997-09-26
Publication date: 1999-03-31
Anticipated expiration: 2017-09-26
Also published as: GB2329793B; GB9720382D0

Abstract

In some communications systems such as the Terrestrial Trunked Radio (TETRA) system, it is not possible to use a standard receiver for monitoring the airwaves as the downlink channel needs to be demodulated and decoded to determine how the uplink channel is formatted with respect to interleaving, transmission slots encryption schemes and the like. The present monitor 36 therefore includes means 34 for receiving a downlink transmission and means for interpreting the received transmission to obtain the formatting information. This information can then be used to interpret uplink transmissions from the remote station 26.

Description

A RADIO COMMUNICATIONS MONITOR AND METHOD OF MONITORING RADIO COMMUNICATIONS Field of the Invention This invention relates to a radio communications monitor and a method of monitoring radio communications.

Background of the Invention In current radio communication systems, there is a need for monitoring the level and type of communications activity within the system. This information provides an insight into the operation of the system. Furthermore, such monitors can also be used for testing and maintenance purposes of the communications system.

A method for monitoring communications activity within a typical analogue communications system, such as an FM (frequency modulated) or FSK (frequency shift-keyed) system, is to use a standard receiver. The FM or FSK receiver is tuned to a particular frequency to monitor either the uplink or downlink activity. Typically it is irrelevant whether the uplink or downlink frequency channels are monitored as the type of communications can be determined from the signals received in the standard receiver.

However, with the development of digital communications systems, the signal transmissions are more complex than with previous analogue transmissions. In some communications systems, such as the Terrestrial Trunked Radio (TETRA) system, it is not possible to use a standard receiver for monitoring the air-waves, as the downlink channel needs to be demodulated and decoded to determine how the uplink channel is formatted with respect to interleaving, transmission slots, encryption schemes and the like.

This invention seeks to provide a monitoring arrangement and method of operation that mitigates at least some of the above mentioned disadvantages.

Summarv of the Invention According to a first aspect of the present invention there is provided a radio communications monitor as claimed in claim 1.

According to a second aspect of the invention there is provided a method of monitoring radio communications in accordance with claim 4.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings.

Brief Description of the Drawings FIG. 1 shows a communications system including a radio commmunications monitor in accordance with an embodiment of the invention; and FIG. 2 shows a timing diagram for employment in the communication system shown in Fig. 1.

FIG. 3 shows a flow chart of a method of monitoring radio communications in accordance with a second aspect of the invention.

Detailed Description of the Drawings With reference to Fig 1, a communications system 10 includes a base station 12 communicating on at least a downlink channel 24 and/or uplink channel 32 with a number of remote stations, at least remote stations 26, 28, 30. The downlink channel 24 is typically used for transmissions from the base station 12 to remote stations 26, 28, 30, whereas the uplink channel 24 is typically used for transmissions from the remote stations 26, 28, 30 to the base station 12. Base station 12 includes a microprocessor 14 operably coupled to a digital signal processor (DSP) 16 via a bi-directional line (or two independent lines).

The DSP 18 is operably coupled to an antenna 23 of the base station 12 via a transmitter section 20 and a receiver section 22. A tap 16 is positioned on the bi-directional line connection between the microprocessor 14 and the DSP 18, linking the line through an output port 34 of the base station, to a computer 36. The computer 36 contains a memory element 38.

In operation, in the preferred embodiment of the invention, the microprocessor 14 formats voice and/or data information into blocks, and transmits the information to the DSP 18. The formatted information is also transmitted to the computer 36 via the output port 34. The DSP 18 encodes the transmit information and passes the information to the transmitter section 20 for modulating, up-converting and amplifying the signal before radiating from the antenna 23. The information is transmitted to say, remote station 26 on a downlink channel 24 which receives, demodulates and decodes the information, particularly to determine how to transmit back to the base station 12.

The remote station 26 then formulates its information for transmission to the base station 12 and transmits the formulated information. The base station 12 receives the transmission from the remote station 26 at the receiver section 22 via the antenna 23. The receiver section 20 down-converts, amplifies and demodulates the received signal and passes the demodulated information to the DSP 18 where the remote station's transmission is decoded. The decoded information is then passed to the microprocessor 14 and the communication between the base station 12 and the remote station 26 continues.

However, the tap 16 also couples the decoded received information to the computer 36. The computer 36 then has both the formatted information transmitted from the base station 12 to interpret, understand and manipulate the information transmitted from the remote station 26. This information may be critical to determine aspects of the transmission such as channel type, burst type, scrambling code, interleaving rates, encryption information, etc. Without such knowledge of the format to be used by the remote station 26 for its uplink transmissions, as indicated by the microprocessor 14 in its downlink transmission, the computer would not be able to interpret, understand and manipulate the information transmitted from the remote station 26.

In the present arrangement, encryption is performed within the DSP 18. Hence, accessing the transmitted and received information before or after the DSP 18, depending upon transmit/receive operation, the analysis of the data can be made without additional encryption requirements within the monitoring arrangement.

Referring now to FIG. 2, a timing diagram according to the preferred embodiment of the invention is shown. The invention is described with respect to a time division multiple access (TDMA) system. However, it is within the contemplation of the invention that alternative access schemes, such as frequency division multiple access (FDMA) or code division multiple access (CDMA) would benefit from this invention.

In FIG. 2, a downlink channel 50 is shown. The downlink channel 50 includes four time slots 52, 54, 56, 58 per repeating frame.

This is consistent with the emerging TErrestrial Trunked RAdio system (TETRA) standard, as defined for trunked private and mobile communications particularly within Europe. The downlink channel 50 precedes in time the uplink channel 66. The uplink channel also has four time slots 68, 70, 72, 74 per repeating frame, corresponding to the downlink time slots. The time delay between the corresponding downlink and uplink time slots enables the receiving remote (or mobile) station to receive, demodulate and decode the full information content within the time slot, and prepare and transmit a response in the corresponding uplink time slot. Each time slot, for example downlink time slot 54 as shown, includes two portions of data 60, 64 that includes the voice and data transmissions to be sent to the remote station, and a central data portion 62, referred in TETRA as an associated assignment channel (AACH), or broadcast block. Approximately half of the AACH data dictates who can use the downlink channel 50 and the other half of the AACH data dictates the type of uplink channel 66 and who can use it.

Referring now to FIG. 3, a method of assessing communication activity in the communications system 10 is provided. The method includes the processor 14 in the base station 12 formatting the downlink blocks for encoding by the DSP 18, as shown in step 102. The downlink block sets the type of transmission to be used by the uplink channel, as in step 104. The processor 14 sends the formatted data to the DSP 16. A tap is provided on this communication link to also provide the formatted data to an external port 34, as shown in step 106. A channel analyser, typically a computer (PC or mainframe) 36 is connected to the external port 34 for receiving the downlink transmission and determining the format of the imminent uplink transmission, as in step 108. The DSP encodes the formatted data, as in step 110, and the base station 12 transmits the encoded (modulated, up-converted and amplified) information to the remote station, as shown in step 112.

The remote station receives the information transmitted from the base station 12 on the downlink channel, as in step 114, and demodulates and decodes the information to determine the dictated format for uplink transmissions, as shown in step 116. The remote station then encodes its information for transmission to the base station 12, as in step 118 and transmits the encoded information on the uplink channel, as shown in step 120. The base station 12 receives the transmission from the remote station, as in step 122, and demodulates and decodes the remote station's transmission in its DSP 18, as shown in step 124. The DSP 18 then transmits the decoded information from the remote station to the microprocessor 14. A tap is also provided on this communication link to provide the formatted data from the remote station to an external port 34, as shown in step 126. The channel analyser, having knowledge of the uplink format, as dictated in the earlier downlink transmission, can interpret the uplink transmission, as in step 108. This process then repeats itself for the next slot transmission within each respective frame.

In this manner, the channel analyser can determine the type and level of communication activity within the communications system.

Furthermore, the channel analyser can be arranged to perform multiprocessing of all transmissions between the base station and all of the remote stations, using this tap function. As such, all TDMA time slots can be parallel processed. Preferably the external port is a high bandwidth port to cope with the parallel nature of the time-slots and quantity of information.

A benefit of the present invention, over the prior art systemmonitoring arrangements, is that additional radio(s) are not required to determine the communications activity on the communications system.

Instead, access to a particular position in the information transfer process, as described with reference to FIG.'s 1 and 3, allows any computer (portable or mainframe) to make such a communications activity assessment.

A particular advantage of such a real-time access to the operation of the communications system is that maintenance of the system can be implemented. The maintenance engineer has a real-time access to the current operation of the system and can therefore de-bug any problems quickly and in a real time manner. Additionally, the success of solutions to such problems can be immediately quantified. As a memory element 38 is available in the computer 36, it is also possible to store the information on the communication activity of the system, to process and assess at a later time and location.

A significant advantage of the present invention is the ability to displace the communications link between the DSP 18 and the microprocessor 14 within the base station 12. This can be achieved by simulating transmissions from a number of remote units and inputting this correctly formatted information into the bi-directional link. This enables the system operator to simulate a particular operating condition or traffic loading of the system, to determine how the system copes with such operating conditions. With the immense complexity associated with such radio communications systems, particularly with the development of digital transmissions, producing ever more information to be transmitted in ever-decreasing resources, such a facility is invaluable. This allows a real-time manipulation of a "live" system with any condition the operator wishes to create. Such a facility can help determine, for example whether extra base sites or frequencies are required to be allocated to users; whether the existing resources can be better allocated; whether introducing power control of signals would be a benefit in optimally using the available resource, etc.

A yet further advantage of the aforementioned present invention occurs with systems such as TETRA. TETRA is a system designed for inter-operability between radios of various manufacturers. As such, a number of difficulties can arise in ensuring that the system is compatible with all such manufacturers. Having real-time access to the "live" system allows an assessment to be made on the usage of such varying radios and/or the ability to simulate their individual operations in the "live" system.

A still yet further advantage of the present invention is that the communications system allows for realtime analysis of the uplink signal quality, for example signal strength, vector error and transmission path delay.

The communication system according to the present invention provides a means and process for monitoring the transmissions in such a complex system, thereby mitigating at least some of the aforementioned problems associated with monitoring communication activity. Furthermore, the communication system according to the present invention provides a means of influencing and simulating transmissions in a real-time manner in a fully working system, thereby enabling both an opportunity of a real-time assessment of various operating conditions and an opportunity for real-time optimisation of system parameters.

Claims

Claims 1. A radio communications monitor comprising: a receiver for receiving uplink and downlink transmissions between a first and a second radio unit in a communications system; an interpreter for interpreting one of the received uplink or downlink transmissions to determine information about the other of the uplink or downlink transmissions.
2. A monitor as claimed in claim 1 wherein the receiver is operably coupled to the interpreter such that the information is used to enable the receiver to receive the other of the uplink or downlink transmissions.
3. A radio communications monitor substantially as hereinbefore described with reference to and or as illustrated by the drawings.
4. A method of monitoring radio communications comprising: receiving one of an uplink or downlink transmissions between a first and a second radio unit in a communications system; interpreting the received transmission in order to enable reception of the other of the uplink or downlink transmissions.
5. A method substantially as hereinbefore described with reference to and or as illustrated by the drawings.