WO2002027984A2

WO2002027984A2 - Passive traffic channel and messaging testing for cdma systems

Info

Publication number: WO2002027984A2
Application number: PCT/US2001/026136
Authority: WO
Inventors: Cory R. Christensen; Jon Q. St. Clair
Original assignee: Motorola, Inc.
Priority date: 2000-09-27
Filing date: 2001-08-21
Publication date: 2002-04-04
Also published as: AU2001286595A1; WO2002027984A3

Abstract

The present invention is for testing channel elements in an RF communications system. After a channel element (24a - 24d) to be tested is identified, a communications node (26) and associated forward link signal (30) corresponding to the channel element (24a - 24d) to be tested are identified while the channel element (24a - 24d) to be tested is active during normal system operation. An RF diagnostic system (34) receives a sampled RF forward link signal (30) and associated forward link signal coding information, and decodes the forward link signal based on the coding information. Once the forward link signal (30) is decoded, the RF diagnostic system (34) tests and measures signal information such as subscriber messaging and sequence information to determine whether the channel element (24a - 24d) is functioning properly.

Description

PASSIVE TRAFFIC CHANNEL AND MESSAGING TESTING FOR CDMA

SYSTEMS

Background of the Invention Field of the Invention

The present invention relates generally to telecommunications networks, and more particularly to the testing of channel elements in a personal or cellular communications system using existing system call traffic.

Description of Related Art

In a conventional cellular communications system, a base transceiver site is not only responsible for establishing links between system communications nodes, such as mobile subscriber units, but also for ensuring that all system resources remain functional during system operation. Among the system resources, system channel elements, each of which is a finite and dedicated portion of processing necessary at the base transceiver site to support an individual communications node, are resources whose operation is critical to maintaining maximum system call load capacity. Therefore, periodic testing of the integrity of the channel elements is important in maintaining the operation of the channel elements at full or near-full capacity. Currently, channel elements may be tested using an RF diagnostic system in which a mobile test subscriber unit (TSU) such as a cellular phone is used to place a call on a designated channel element. Once the call is established, the TSU then measures and reports a frame error rate associated with the channel element. The call is then terminated, a new call is established on a subsequent channel element, and the TSU measures and reports frame error rates associated with the subsequent channel element. This pattern is repeated until all system channel elements have been tested.

While an RF diagnostic system such as the one discussed above enables all channel elements to be tested, such a diagnostic system has certain associated limitations. For example, testing each element with a single TSU is time-consuming and requires the use of other system resources to set up the test call. In addition, because each of the channel elements is only being tested by a single mobile TSU in a static environment, the accuracy of such testing is limited to only one variation of subscriber signatures. In addition, current RF diagnostic systems such as the one described above cannot monitor the low-level signaling of normal subscribers due to their inability to decode the user traffic signals.

Brief Description of the Drawings Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which:

FIG. 1 is a block diagram of a cellular or personal communications system including an RF diagnostic system of the type in which passive traffic channel and messaging testing in accordance with the present invention is implemented;

FIG. 2 is a block diagram showing the RF diagnostic system of FIG. 1 in more detail; and

FIG. 3 is a flow diagram of the methodology of the passive traffic channel and messaging testing in accordance with the present invention.

Detailed Description of the Preferred Embodiments Referring now to the drawings in which like numerals reference like parts, FIG.

1 shows the infrastructure of a communications system 10 such as a cellular or personal communications RF system. The system 10 includes a centralized base site controller 12 connected to a maintenance operator terminal 14 and a telecommunications network 16 via conventional network circuits 18. The centralized base site controller 12 is also connected to, and controls the operation of, all base transceiver sites (BTSs), such as the base transceiver site 20, within a predetermined geographical area through links such as a BTS control and subscriber traffic circuit 22.

The BTS 20 includes traffic channel elements, such as traffic channel elements 24a - 24d, used to established links with subscriber communications nodes, such as the mobile subscriber unit 26, through subscriber link signals, such as the subscriber forward link signal 30, transmitted by an RF section 31 over a BTS antenna 32. As used throughout this specification, the term "channel element" refers to a unit portion of resources, including integrated circuits and processing engines, dedicated to an individual system communications node, such as the mobile subscriber unit 26, to support that node during call set-up and call processing. Typically, a large pool of channel elements are implemented at a conventional BTS, with numerous elements integrated onto a single digital integrated circuit or into a custom processing engine, with each of the channel elements being randomly assigned to carry incoming call traffic. However, any number of channel elements can be implemented based on the particular communications protocol used and specific system parameters, such as expected call load.

The system 10 also includes an RF diagnostic subsystem (RFDS) 34, which preferably includes a diagnostic subscriber unit, connected to the antenna 32 through a link such as an RF coupler 36, and to the BTS 20 and a local maintenance terminal 38, which is typically brought to the site only for maintenance purposes, through control circuits 40, which may be RS232 cabling, Ethernet busses, firewire, or the like. The RFDS 34 is operative to test and measure the channel elements 24a - 24d in, and corresponding forward link signals transmitted from, the BTS 20 in a passive manner. The RFDS 34 performs this passive testing and measuring during normal BTS call processing by using information from the BTS 20 to decode a coded sampled forward link signal 30', corresponding to the forward link signal 30 and transmitted to the RFDS 34 through the RF coupler 36, on any active channel on the BTS forward link to measure both the signal frame error rate and signal power level. Because the RFDS 34 performs such passive testing and measuring during normal call processing rather than through use of a test call, all active channel elements can be rapidly tested without using system resources.

It should be noted that, for CDMA signals, the channel element information from the BTS 20 that must be received by the RFDS 34 includes both the Walsh code assigned to each channel and the channel long-code mask permutation used to further randomize user data for security purposes, as is well known in the art. Once the RFDS 34 has the channel element Walsh and long code information, it can decode the scrambled CDMA signal 30 ' and extract the user/communications node transmitted data necessary for testing and measurement purposes.

Referring to FIGs. 2 and 3, the RFDS 34 includes four main processing blocks: a control logic block 42, a rake receiver block 44, a message decoding block 46 and a test and measurement block 48. The control logic block 42 has a microprocessor

50 with memory, such as RAM and ROM-type memory, and is programmed with support and interface logic for all internal RFDS control functions. More specifically, the microprocessor 50 is programmed with antenna selection logic for generating and outputting antenna selection commands to an antenna selection switch 52 via an antenna selection line 54, frequency selection logic for outputting frequency selection commands to the rake receive block 44 via a frequency selection line 56, and pseudorandom noise (PN) offset and Walsh code selection logic for generating and outputting commands over a PN offset and Walsh code selection line 58 to a variable offset and code selection logic block 60 to generate codes used in signal detection. In addition, the control logic block 42 includes interface logic for external control and configuration functions that is downloaded from the local maintenance terminal 38 through the control circuit 40.

The rake receiver block 44 includes a quadrature RF downconverter 62 for downconverting the sampled forward link signal 30' based on signals received from one or more frequency-controlled local oscillators or synthesizers 64. One or more

RF baseband matched filters 66 then filter the downconverted forward link signal 30' and output the baseband I and Q signal components to a demodulator 68. The demodulator 68 demodulates the baseband I and Q signal components according to the specification type of signal modulation used, such as CDMA using short PN code and Walsh code generators 70, 72, respectively. One or more symbol detection and tracking loops each including a symbol detection and tracking block 74 lock to the filtered signal and feed back position information to the variable offset and code selection logic block 60 in the control logic block 50. A decimated long code de- scrambling block including a de-scrambler 76 and decimated long code generator 78 then descrambles the demodulated signals. The message decoder block 46 includes de-interleaver and convolutional decoder 80 to correct errors and re-assemble the decoded data back to the original ordering and sequence to decode higher level information found in trafficking and signaling messages within the sampled forward signal 30'. The test and measurement block 48 analyzes the decoded information from the message decoder block 46 to determine if the channel element being tested is functioning properly. Specifically, the test and measurement block tests for proper message formatting and sequences through a frame quality measurement block 82, tests for proper signal timing, and the like. Upon completing testing and measuring for a particular channel element, the test and measurement block then can transmit the test and measurement results back to the control logic block for transmission to the maintenance operator terminal 14, and can also transmit the test and measurement results to the local maintenance terminal 38 for more detailed analysis.

Referring now to FIG. 3, operation of the above-described RFDS 34 will now be described within the context of overall operation of the system 10. At 100, a channel element test request is entered at the maintenance operator terminal 14. At 102, in response to the channel element test request, the centralized base site controller 12 selects a target BTS, such as the BTS 20, as well as an active channel element, such as the channel element 24a, to test. At 104, the selected traffic channel element 24a is assigned to the mobile subscriber unit 26 via normal cyclic

BTS call processing methods to establish the forward link signal 30. At 106, the centralized base station controller 12, or a related process implemented in the BTS 20, identifies the mobile subscriber unit 26 by its mobile station long-code mask permutation that encodes the subscriber forward link signal 30. At 108, the centralized base station controller 12, or the related process implemented in the BTS

20, passes the sampled forward signal 30', including associated mobile subscriber unit Walsh and long-code information, over the RFDS control circuit 40 to the rake receiver 44 in the RFDS 34.

At 110, the rake receiver 44 begins decoding higher level information using the Walsh and long-code information associated with the sampled forward signal 30' before passing partially decoded higher information to the message decoder block 46 and the lower level signal information, such as preamble time, directly to the test and measurement block 48. The decoder block 46 then performs the remainder of decoding of the user traffic signal, and passes the decoded information to the test and measurement block 48. At 112, the test and measurement block 48 then analyzes the decoded lower and higher level information and determines if the channel element is working properly. At 114, upon completion of the testing of each channel element, or, alternatively, after all channel elements have been tested, the RFDS 34 transmits the test results to the maintenance operator terminal 14 via the control circuit 40, the BTS control and subscriber traffic circuit 22. Once the testing of the traffic channel element 24a is completed, at 116 the RFDS 34 determines if any additional active test elements are to be tested. If additional channel elements are to be selected by the centralized base controller 12 to be tested, operations at 102-114 above are repeated until all channel elements to be tested have been tested.

In view of the foregoing, it should be appreciated that an RFDS in accordance with the present invention is effective for passively measuring and testing channel elements based on forward signaling in a CDMA BTS. The RFDS is capable of passively measuring and testing the channel elements through use of BTS information to decode an active channel on the forward link designated to be tested to measure and report a frame error rate, power level and signaling verification associated with the channel. The RFDS can perform such measuring and testing passively during normal call processing and therefore does not need to place a special test call. Consequently, all active channel elements can be rapidly tested and in a variety of long-code patterns, as a variety of long-code masks associated with normal call processing will be associated with the active channels. In addition, because the RFDS is able to decode the user traffic signal, the RFDS can also facilitate verification of forward signaling and messages sent to a communications node by comparing same to known sequences and behaviors.

In addition to the above-described embodiment, the RFDS in accordance with the present invention can alternatively be used as a debugging tool in a laboratory environment to verify that a base station is correctly following given air interface standards and to verify that the actual physical signals being sent over the tested channel elements are correct. Also, the RFDS can alternatively be used to monitor forward signaling and messaging from system communications nodes to aid in diagnosing call processing problems, including layer 1 signaling, without compromising normal system operation, thereby providing another benefit over present diagnostic tools. Further, while the centralized base site controller typically designates a channel element to be tested and the RFDS then tests the channel element when the element is randomly assigned to a subscriber link during normal BTS call processing, the centralized base site controller can also be programmed to force a call to be routed to a designated channel element. While the above description is of the preferred embodiment of the present invention, it should be appreciated that the invention may be modified, altered, or varied without deviating from the scope and fair meaning of the following claims.

Claims

Claims What is claimed is:

1. A method of testing channel elements in an RF communications system, comprising: identifying a channel element to be tested;

5 identifying a communications node and forward link signal information corresponding to the channel element to be tested while the channel element to be tested is active; decoding the forward link signal information; and testing the decoded forward link signal information to determine whether the channel element is functioning properly. )

2. The method of claim 1, wherein the identifying of a communications node and forward link signal information comprises identifying the communications node by a corresponding mobile station long-code that encodes the forward link signal information.

5 3. The method of claim 1, wherein the identifying of a communications node and forward link signal information corresponding to the channel element to be tested while the channel element to be tested is active comprises identifying the communications node and the forward link signal information corresponding to the channel element to be tested while the channel element to be tested is active after being randomly assigned to the

) communications node during routine system operation.

4. The method of claim 1, further comprising forcing calls to be routed to the channel element to be tested prior to the identifying of a communications node and forward link signal information.

5. The method of claim 1, further comprising repeating the identifying of a channel element to be tested, the identifying of a communications node and forward link signal information, the decoding of the forward link signal information, and the testing of the decoded forward link signal information to systematically check a plurality of traffic channel ι elements within an identified base transceiver site.

6. An RF diagnostic apparatus for passively testing RF communications system channel elements, comprising: a receiver for receiving a sampled coded RF forward link signal supported by an active channel element during routine system operation, and for receiving coding information associated with the RF forward link signal; a decoder connected to the receiver for decoding the sampled coded RF forward link signal based on the coding information associated with the RF forward link signal; and a test and measurement device connected to the decoder for analyzing the decoded RF forward link signal to determine if the channel element is operating properly, and for generating resulting channel element test and measurement results.

7. The RF diagnostic apparatus of claim 6, wherein the controller is further for forcing a call to be routed to a designated channel element to be tested.

5 8. The RF diagnostic apparatus of claim 6, wherein the test and measurement device is for testing for proper message formatting and sequences in the decoded RF forward link signal to determine if the channel element is operating properly.

9. The RF diagnostic apparatus of claim 6, wherein the test and measurement device is ) for testing for proper signal timing in the decoded RF forward link signal to determine if the channel element is operating properly.

10. A method of passively testing channel elements in an RF communications system, comprising: i receiving both a communications node forward link signal and forward link signal information corresponding to a channel element to be tested while the channel element to be tested is active during normal system operation; decoding the forward link signal information; and testing the decoded forward link signal information to determine whether the channel l element is functiomng properly.