MXPA97004019A - Method and apparatus to test a digi communication channel - Google Patents

Abstract

The present invention relates to a communication system in which the digital information is transmitted at variable speeds on a communication channel, a method for measuring an execution of the communication channel comprising the steps of: transmitting a test sequence of digital data frames at one or more of a plurality of selectable speeds on the communication channel, wherein the speed of each of the frames is selected according to a human voice model, receive the test sequence of the digital data transmitted over the communication channel, generate a replica of the digital data test sequence, and compare the replica of the digital data test sequence with the test sequence of the data received on the communication channel, to determine the execution of the transmission of data on the communication channel

Description

METHOD AND APPLIANCE TO TEST LTN DIGITAL COMMUNICATION CHANNEL BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to communication systems using digital signals and, more particularly, to a novel and improved method and apparatus for evaluating transmission quality in digital communication channels.

II. Description of Related Art Communications systems have been developed to allow the transmission of information signals from a source location or place to a physically different user destination. Both methods, analogue and digital, have been used to transmit these information signals on the communication channels that link to the locations and source and user places. Digital methods tend to provide various advantages over analog techniques, including, for example, improved immunity to noise and interference in the channel, an increase in capacity and an improvement in the security of communication through the use of of the encryption. By transmitting an information signal from a place or source location on a communication channel, the information signal first becomes a suitable form for efficient transmission on the channel. The conversion or modulation of the information signal includes varying a carrier wave parameter based on the information signal, such that the spectrum of the resulting modulated carrier is confined within the channel bandwidth . In the user's place, the original message signal is replicated from a modulated carrier version received subsequent to the propagation in the channel. This replication is usually achieved using the inverse of the modulation process employed by the source transmitter. Modulation also facilitates multiple access, that is, the simultaneous transmission of various signals on a common channel. Multiple access communication systems will often include a plurality of remote subscriber units that require intermittent service of a relatively short duration, instead of continuous access to the communication channel. Systems designed to enable communication over short periods of time with a set of subscriber units have been called multiple access communication systems. A particular type of a multiple access communication system is known as an extended spectrum system. In extended spectrum systems, the modulation technique used results in the dispersion of the signal transmitted over a wide frequency band within the communication channel. One type of multiple-access extended spectrum system is a code division multiple access modulation (CDMA) system. Other techniques of the multiple access communication system, such as time division multiple access modulation (TDMA) schemes, frequency division multiple access (FDMA) and AM demodulation are known in the art, such as simple lateral band of compacted amplitude (compressed-expanded). However, the extended spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is presented in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned by the assignee of the present invention, which it is mentioned as a reference in the present.

In the aforementioned United States Patent No. 4,901,307, a multiple access technique is presented, wherein a large number of users of the mobile telephone system each have a transceiver that communicates through satellite repeaters or through through terrestrial base stations using the extended spectrum communication signals CDMA. When using CDMA communications, the frequency spectrum can be reused multiple times, thus allowing an increase in the capacity of system users. The use of CDMA results in a much higher spectral efficiency than can be achieved using other multiple access techniques. A further example of a CDMA communication system is presented in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL AVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", also assigned to the assignee of the present invention, which is he mentions in the present as a reference. More particularly, communication in a CDMA system between a pair of locations is achieved by dispersing each transmitted signal over the channel bandwidth, using a unique dispersion code for the user. The specific signals transmitted are extracted from the communication channel by dispersing the energy of the composite signal in the communication channel, with the dispersion code of the user associated with the transmitted signal that will be extracted. The transmitted signal is divided into several "frames", each of which includes a specified number of information bits. It is generally possible to transmit the information bits within each frame to any of the various predetermined data rates. The implementation of extended spectrum, for example, CDMA, cellular systems capable of providing the appropriate service to a particular geographic region, generally includes the consideration of several factors that impede or that affect the performance of the system. For example, it is generally necessary to consider the degree or measure of the available frequency spectrum, as well as the potential for coordination with other nearby communication systems. In addition, the limitations or restrictions imposed by the thermal noise and the interference generated by the various subscriber units need to be taken into consideration. The interference estimates are of particular interest within the CDMA systems, since the energy is transmitted by the subscriber units over the same bandwidth without considering the location within the cellular coverage area.

Interference on the communication channels linking to a particular base station and the subscriber units within a given cell may originate when the neighboring cells use the same 5 CDMA radio channels or one adjacent one as those used within the given cell. In order to evaluate the performance of the system under real conditions, a selected number of subscriber units can be deployed at various distances from multiple base stations, such as a means to estimate the various levels of channel interference. During the deployment of the system, the quality of the transmission signal can be determined at various distances from the base station, based on the qualitative characterization of the signal received by the users of the subscribing units. The various parameters of the system can then be adjusted (for example, the level of power or energy transmitted) in order to improve the quality of the communication. However, it is anticipated that the measurement Quantitative of the capacity of a digital communication channel to carry particular types of information (for example, variable speed or fixed speed data) would allow a more accurate evaluation of the performance of the system. That is, the measurements Quantitative performance of the system would allow the accumulation of more accurate performance data than the subjective characterizations of the quality of the received signal requested from the current subscribing users. For example, subjective evaluations of signal quality do not allow the determination of transmission statistics (for example, the rate or frame error rate at various data rates). In addition, the qualitative estimation of the quality of the signal does not allow the detection in real time of the degradation of the channel, giving rise to rates or error regimes in bits that exceed a predetermined threshold. This capability would facilitate, for example, the identification of particular digital data frames that are so "altered" that they are useless if a desired level of precision is to be maintained. In accordance with the foregoing, an object of the invention is to provide a system for quantitatively evaluating the quality of communication channels within a digital communication system.

SUMMARY OF THE INVENTION The present invention provides a system and method for testing the transmission quality of the signal within a digital communication system. In an exemplary embodiment, the present invention can be incorporated into a digital cellular communication system in which the information is exchanged in the extended spectrum communication channels, between a plurality of mobile users, by means of at least one cellular site. The present invention contemplates testing a digital communication channel by transmitting a digital data test frequency in the communication channel. The test sequence of the digital data transmitted on the communication channel is received at a receiving station, within which a replica of the test sequence of the digital data is also generated. The accuracy of the transmission in the communication channel is then determined by comparing the replication of the test sequence of the digital data with the test sequence of the data received in the communication channel. The present invention allows the test sequence of digital data to be transmitted to one of a set of known data rates, in which the receiving station is positioned to identify the data rate associated with each digital data test sequence . To simulate the transmission of, for example, voice data, the system can be configured in such a way that each test sequence of digital data is generated in accordance with a pseudorandom process.

In a preferred transmission implementation of the test sequence is included generating a first plurality of data packets, which collectively comprise the digital data test sequence. Each data packet is assigned to one of a multiplicity of data rates in accordance with a first pseudo-random process and is then transmitted at the data rate assigned thereto. In an exemplary implementation, the bit sequences within each data packet are generated based on a second pseudo-random process.

BRIEF DESCRIPTION OF THE DRAWINGS The particularities, objectives and advantages of the present invention will be more evident from the following detailed description set forth below, when taken together with the drawings, in which the reference characters are constant throughout the description and, where: Figure 1 shows an exemplary cellular subscriber digital communication system, within which the communication channel test technique of the present invention can be employed; Figure 2A illustrates a preferred implementation of a mobile unit transmission modulator within which a transmission portion of the digital communication test system of the invention is incorporated; Figure 2B shows a block diagram of a cell site receiver that operates to receive transmissions from mobile units deployed within a sector or associated cell.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES I. System Overview In Figure 1 an exemplary digital subscriber digital communication system is illustrated, within which the communication channel test technique of the present invention can be used. The system of Figure 1 may use, for example, the extended spectrum technique or other modulation techniques familiar to those skilled in the art, in order to facilitate communication between users of mobile units (e.g., mobile phones) and, cell cycles. In Figure 1, the controller and switch 10 of the system typically includes the interface and the processing circuitry to provide control of the system to the cellular sites. When the system of Figure 1 is configured to process telephone calls, the controller 10 operates to route or direct telephone calls from the public switched telephone network (PSTN) to the appropriate cellular site for transmission to the appropriate mobile unit. In this case, the controller 10 also functions to route or direct calls from the mobile units, by means of at least one cellular site to the PSTN. The controller 10 can connect calls between mobile users through the appropriate cellular sites since the mobile units do not normally communicate directly with each other. The controller 10 can be coupled to the cellular sites by various means, such as dedicated or dedicated telephone lines, fiber optic links or microwave communication links. In Figure 1, two of these exemplary cell sites 12 and 14 are illustrated, along with mobile units 16 and 18. Cell sites 12 and 14, as discussed herein and illustrated in the drawings, are considered to serve to an entire cell. However, it must be understood that the cell can be divided geographically into sectors and, each sector treated as a different coverage area. In accordance with the above, transfers are made between sectors of the same cell as described herein for multiple cells, while diversity between sectors can also be achieved as for the cells. In Figure 1, the arrow lines 2a-20b and 22a-22b define respectively the possible communication links between the cell site 12 and the mobile unit 16 and 18. Similarly, the arrow lines 24a-24b and 26a-26b respectively define the possible communication links between the cellular site 14 and the mobile units 16 and 18. The cellular sites 12 and 14 nominally transmit using the same power. The cell site service areas or cells are designed in geometric forms, such that the mobile unit will normally be closer to a cell site and, within a sector of the cell, if the cell will be divided into sectors. When the mobile unit is unoccupied, ie there are no calls in progress, the mobile unit constantly monitors the transmissions of the pilot signal from each nearby cell site and, if applicable, from a single cell site in which the cell is sectorized . As illustrated in Figure 1, the pilot signals are respectively transmitted to the mobile unit 16 via the cellular sites 12 and 14 on the forward or forward communication links 20a and 26a. The mobile unit 16 can determine which cell it is in by comparing the signal strength in pilot signals transmitted from cell sites 12 and 14.

The voice transmission for each mobile unit is initiated by providing the analog voice signal of the mobile user to a digital vocoder. Then and sequentially, the output of the vocoder is encoded by convolutional forward error correction (FEC), is coded in 64-ary orthogonal sequence and modulated in a PN carrier signal. The 64-ary orthogonal sequence is generated by a Walsh function encoder. The encoder is controlled by collecting six successive binary symbol outputs from the convolutional FEC encoder. The six binary symbol outputs collectively determine which of the 64 possible Walsh sequences will be transmitted. The Walsh sequence is 64 bits long. In this way, the Walsh "chip" speed should be 9600 * 3 »(1/6)« 64 = 307200 Hz for a data transmission rate of 9600 bps (9.6 kbps). In the mobile-to-cell link (ie, the "inverse" link) a common short PN sequence is used for all voice bearers in the system, while the encoding of the user's address is performed using the sequence generator PN of the user. The user PN sequence is uniquely assigned to the mobile for at least the duration of each call. The user PN sequence is subjected to a 0-exclusive operation with the common PN sequences, which are maximum linear displacement register sequences increased, with length 32768. The resulting binary signals that then biphasically modulate each quadrature carrier are summed to form a composite signal, they are filtered in band pass and are transposed to an IF frequency output. In the exemplary embodiment, a portion of the filtering process is actually effected by the operation of the digital finite impulse response (FIR) filter at the binary sequence output. The output of the modulator is then controlled in power by the signals from the digital control processor and the analog receiver, converted to the RF operating frequency, by mixing them with a frequency synthesizer that tunes the signal to the appropriate output frequency and then amplifies to the final output level. The transmission signal then passes to a duplexer and an antenna. Although the present invention can be incorporated into an extended spectrum communication system, the principles of the invention are described with reference to the generalized representation of a digital communication system, as represented in Figures 2A and 2B.

II. Transmission of Test Data and Information Data Figure 2A illustrates a preferred implementation of a mobile unit transmission modulator 30, in which a transmission portion of the digital communication test system of the invention is incorporated. During normal operation, the transmit modulator processes the digital information data, for example, the voice information from a vocoder to the multiplexer 32. As described below, the multiplexer 32 allows the control messages and the like to be transmitted together with test data during an "attenuation and burst" phase of the operation in test mode.

During operation in test mode, a test mode selection switch 34 is operated in response to instructions received from a control processor (not shown), such that the transmit modulator 30 operates on a pseudorandom data test sequence provided by a test data generation circuit 33. Referring again to Figure 2A, during the normal operation of the mobile unit, the test mode selection switch 34 is adjusted such that only the input line 31 is connected to the coder / interleaver 35, as a multiplexer 32. During both the normal and the test modes of operation, the coder / interleaver 35 performs a block interleaving operation. During operation in normal mode, the interleaving interval will preferably be performed over a range equivalent to the duration of a single "frame" of data received from, for example, a vocoder, through the input line 31. An exemplary frame structure is described in, for example , copending patent application of the United States of America Serial No. 08 / 117,279 entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION", assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference . Additional details of an exemplary frame structure can be found in the TIA / EIA Interim Standard publication "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", TIA / EIA / IS-95, July 1993. Accompanying to each frame of the vocoder, there is a cyclic redundancy check (CRC) code of the familiar type for those skilled in the art. The CRC code is used in a decoding process (described below) to identify bit errors that occur during transmission over the communication channel. As described below, the test technique of the communication channel contemplated by the invention can be used concurrently with conventional error detection techniques, in order to allow a more thorough evaluation of the channel accuracy to be made. Again with reference to Figure 2A, during the operation in test mode, the coder / interleaver 35 operates on the interleaving interval identical to that used during normal mode operation. However, during the test mode, the coder / interleaver 35 processes a single "packet" of test data, instead of a vocoder data frame. In an exemplary embodiment, each test data packet, provided by the test generation circuit 33, comprises a pseudorandom bit sequence of predetermined length. After the encoding of the pseudorandom test data and the subsequent transmission in the communication channel to a receiving station, the received test data is compared with a replica thereof generated synchronously within the receiving station. According to the invention, the integrity of the data transmission on the communication channel can then be evaluated based on this comparison between the received and locally generated versions of the test data. Considering now the operation of the encoder / interleaver 35 in greater detail in a specific embodiment, the encoder / interleaver 35 is arranged or arranged to generate an output code sequence using a 64-ary orthogonal signaling technique. During the 64-ary orthogonal signaling, for the coding of the data a set of 64 possible characters is available, each character will be coded in a 64-length sequence containing 64 binary bits or "chips". The number of code symbols produced in an exemplary interleaving period of 20 msec, assuming a data rate of 9.6 kbps and a code rate r = l / 3, is 576. Code symbols are written or recorded in the memory arrangement of the interleaver in lines and they are read in columns. Repetition of code can be supported to support four different data rates produced by the vocoder based on a 20 msec frame. However, repeated code symbols are not transmitted to the air at lower energy levels, rather, only one code symbol of a repeating group is transmitted at the power or nominal power level. That is, the repetition of code in the exemplary mode is used only as a resource to adjust the variable data rate schema in the interleaving and modulation structure. Referring again to Figure 2A, during operation in both normal and test mode, the encoded data of the encoder 35 is supplied to a transmission modulator 37. The modulator circuit 37 operates on the digital output of the encoder 35 using a modulation format consisting of, for example, 64-ary orthogonal signaling. In other words, the interleaved code symbols are grouped into groups of six to select one out of 64 orthogonal waveforms. In an exemplary implementation, the data modulation time interval is equal to 208.33 μsec, and is referred to as a Walsh symbol interval. At 9.6 kbps, 208.33 μsec correspond to 2 bits of information and, equivalently to 6 code symbols at a code symbol speed equal to 28800 sps. The Walsh symbol interval is subdivided into 64 intervals with equal length of time, referred to as Walsh chips, each with a duration of 208.33 / 64 = 3.25 μsec. The Walsh chip speed is then 1 / 3.25 μsec = 307.2 kHz. For a specific PN dispersion rate of 1.2288 MHz, there are exactly 4 PN chips per Walsh chip. As indicated by Figure 2A, the transmit modulator 36 also includes a transmitter 38 coupled to the modulator circuit 37. A carrier signal generated within the transmitter 38 is modulated by the digital frequency output of the modulator circuit 37. The resulting modulated carrier is it then transmits via antenna 39 to a cell site receiving station 40 (Figure 2B). In an exemplary embodiment, the digital test packet associated with each frame is extracted from the signal received at the cell site and compared to a replica of the locally generated test packet. In a preferred embodiment, the results of this comparison are then used by a cell site control processor for calculating error statistics related to data accuracy, on the communication channel linking to the mobile unit and the station of the cell site. A particularity of the present invention is that the "forward or forward link" from the cellular site to the mobile unit can be tested independently of the "inverse" or "mobile-to-cell" link. Specifically when it is desired to evaluate the accuracy of the reverse link, the reverse link test packets are transmitted from the mobile unit and evaluated at the cell site. When the forward link is tested, the test packets transmitted from the cell site are received and analyzed in the mobile unit.

III. Receiving the Test Data and the Information Data Referring to Figure 2B, a block diagram of a cellular site receiver 40 operating to receive transmissions from the mobile units deployed within an associated cell or sector is shown. Both during the operation in normal mode and in test mode, the signals transmitted by the mobile units and received in the antenna 41, are provided to the analog receiver 42. Within the receiver 42, the signals received from the antenna 41 are amplified, sub -convert to an intermediate frequency, they are filtered in band pass and sampled by an analog to digital converter. In an exemplary CDMA implementation of the receiver 40, the timing or synchronization of the received signal is tracked using, for example, the well-known technique of correlating the received signal by a slightly anticipated local reference PN code and correlating the received signal with a PN code of local reference slightly delayed. The difference between these two correlations will average zero if there is no synchrony error. Conversely, if there is a synchronization error then this difference will indicate the magnitude and sign of the error and the synchrony of the receiver will be adjusted accordingly. It is noted that the digitized output of the receiver 42 will be supplied to the demodulator 44. The digital code sequences generated within the demodulator 44 in response to the energy of the received signal are provided to a decoder / deinterleaver 45 which operates to identify the code sequences orthogonal transmitted by a particular mobile unit. That is, the decoder / deinterleaver 45 retrieves the digital input data transmitted by the transmission modulator 30 (FIG. 2A) and provides the result to a demultiplexer 47. When the two information, the control message and the test message, have been transmitted during an "attenuation and burst" phase of the operation in test mode, the demultiplexer 47 identifies the first bit of each concatenated frame of the test / message data. The composite bit sequence comprising each concatenated frame is then bifurcated into received control message data sequences and into a received packet of digital test data. As indicated by Figure 2B, the received control message data is output by the demultiplexer 47 to the cell site control processor during "dither and burst" test mode operation.

The demultiplexer 47 supplies the received test and message data to a test mode selection switch 48, during operation in test mode and normal mode, respectively. The operation of switches 32 and 48 is synchronized, such that during operation in normal mode, the test mode selection switch 48 is set to route or direct the digital signal data output retrieved by the decoder / deinterleaver. 45 to the cell site control processor. During the operation in test mode, the switch 48 effectively links the decoder / deinterleaver output 45 with a digital comparator 49. As indicated by FIG. 2B, the digital comparator 49 also receives a locally generated replica of the received test packet from a circuit 50 for replication of test data. In the preferred implementation, the cell site control processor adjusts the timing of the test data replication circuit 50, so as to establish synchronization with the test data generation circuit 33. The digital bit sequences comprising the received test packet and the replicated test packet associated with a given frame are then compared within the comparator 49.

As indicated by Figure 2B, the results of each of these comparisons are stored within the frame error memory 52. The frame error memory 52 will preferably be capable of storing the number of "bit errors" that exist between the corresponding bits of the received and replicated test data sequences., associated with a particular picture. As described below, the information within the frame error memory 52 can then be used by the cell site control processor to calculate a desired set of frame error statistics.

IV. Generation of the Test Package As will be discussed below, the present invention allows, advantageously, that the test be carried out without modifying the existing signaling formats. That is, the conventional frame category indications accompanying the test sequences are provided and generated for transmission over the communication link during operation in test mode. In addition, the ability of the present invention to provide variable speed test packets allows evaluation of the ability of a communication channel to carry voice data and the like.

As mentioned above, during the operation in test mode, the test data generation circuit 33 can provide any fixed speed or variable speed data. In an exemplary implementation, the data generation and replication circuits 33 and 50 are capable of generating digital data test packets at a set of predetermined rates (e.g., 9.6 kbps, 4.8 kbps, 2.4 kbps or 1.2 kbps). In the following, a data rate of 9.6 kbps will be considered as "full or full speed" data (ie speed 1), a data rate of 4.8 kbps will be "half speed" data (ie, speed), a data rate of 2.4 kbps will be considered as "quarter-speed" data (ie, M speed), and a data rate of 1.2 kbps will be considered data at "one-eighth speed" ( that is, speed 1/8 speed). With the exception of the "dimming and burst" operation in which the control messages are combined within the multiplexer 32 together with a lower or full speed test sequence, during the fixed-speed test, the bit sequences that comprise each test packet will be transmitted normally at the same speed. In accordance with one aspect of the invention, voice communication is simulated, by selecting the speed at which consecutive packets of test data will be transmitted based on a second-order, four-state Markov process, in which the "state "Markov present is a function of the data rates of the two preceding test packets. However, it will be understood that in alternative embodiments, Markov processes of different order and / or state may be used. In the case of a second-order Markov process, an equivalent representation can be used that uses a Markov chain of first order and sixteenth status. Each state within the model is defined by voice speeds (for example, full speed, half speed, quarter speed or one eighth speed) associated with a preceding pair of consecutive voice frames. For example, in the following, the state "0" corresponds to a preceding pair of consecutive frames characterized by a voice activity at full speed. TABLE I below sets out the pair of preceding speech velocities that define each of these Markov states.

TABLE I In accordance with the foregoing, during the test designed to approximate the voice communication, the data rate of each test packet is selected in accordance with the pseudo-random process represented by TABLE I. As will be explained below, the bit sequences Within the data packages used in both the fixed speed and variable speed tests are also generated using a specified pseudorandom process. The synchronization of the bit sequence generation processes performed using the data generation and replication circuits 33 and 50, allows an exact replica of each transmitted data packet to be produced within the cell site. Referring now to FIGURE II, the number of bits included within the sequences comprising a set of exemplary data packets transmitted at various data rates is listed. For example, in the embodiment represented by TABLE II, a speed packet 1 includes a sequence of 171 bit bits transmitted at full speed (eg, 9.6 kbps). A packet at 1/2 speed is transmitted at half the full speed (for example, 4.8 kbps), a packet at 1/4 speed is transmitted at one quarter of the full speed (for example, 2.4 kbps), a packet at 1/8 speed is transmitted au eighth of all the speed (for example, 1.2 kbps). The encoder / interleaver 35 is programmed to repeat code symbols for data rates less than full speed. Each symbol will be issued 1, 2, 4 or 8 times for full, average, quarter or one-eighth speed packets of the test data, respectively. In accordance with the foregoing, the number of bits included within each packet (i.e., the packet size) of the test data varies in the manner indicated in TABLE II, so that the product of the speed of data and the package size remains constant. In this way, an equivalent number of code symbols per frame is established and, the appropriate repetition of the code symbol occurs for frames in which the data rate is less than the full speed.

TABLE II As noted above, during "attenuation and burst" test data transmission, the multiplexer 32 combines a control message with the test bits comprising a data packet with speed less than full (i.e. 2 Speed, 1/4 Speed or 1/8 Speed). In an exemplary embodiment, during the "attenuation and burst" mode of operation, the control message and the concatenated test data of each frame are transmitted at full speed. For example, when a 1/8 speed test packet (i.e., 16 bits of test data) is generated for the transmission of a relatively long packet of control message data (i.e. 152 bits of message data) control) are combined in the box. Thus, the number of bits transmitted tests are "attenuated" in order to provide a "burst" of information control message that will be communicated during the testing process. Under certain circumstances it may be desired to transmit a control message that has a length encompassing a complete frame. In this case, a box "empty and burst" including only control message information (ie, 0 bits of test data) is transmitted by the mobile unit. In an exemplary embodiment, a flag (in the form of compensation bits) is set to specify the size of the packet and the control message data transmitted during a phase of "attenuation and burst" of the operation. Similarly, "vacuum and burst" transmissions are also identified by placing a flag within an auxiliary transmitted field (ie, compensation bits). Details on the flag in the frame structure can be found in the technical standard TIA / EIA / IS-95 and in the aforementioned pending application Serial No. 08 / 117.279.

V. Replication of the Test Package Within the cellular site receiver 40, the bit rate of each received data packet is determined by the decoder 45. In an exemplary embodiment, the decoder 45 operates or functions to implement a Viterbi decoding algorithm. wherein the most probable decoding sequence is determined with respect to each packet received from test data. Since the decoder 45 is not provided with a priori knowledge of the degree of symbol repetition associated with each received frame code decoding attempt is necessary at each possible data rate. An exemplary Viterbi decoder is disclosed in co-pending United States of America Patent Application Serial No. 08 / 126,477, entitled "MULTIRATE SERIAL VITERBI DECODER FOR CDMA SYSTEM APPLICATIONS", assigned to the assignee of the present invention and which is mentioned in the present as a reference. After the identification of the data rate associated with a particular received frame, the circuit 50 of test data replication provides a locally generated test data packet of the appropriate type to the digital comparator 49. Specifically, a category of indicative frame either of a speed 1, 1/2 Speed, 1/4 Speed or 1/8 Speed, vacuum, speed 1 with bit error or with insufficient frame quality is provided by circuit 50 to comparator 49. In addition, TABLE III lists the number of bits within the test package of a given frame category provided to comparator 49 in the absence of attenuation and burst transmission or of vacuum and burst transmission. The first five types of locally generated packages listed in TABLE III correspond to the five types of packets transmitted, listed in TABLE II. For example, a packet of speed 1 to the comparator 49 by the circuit 50 is supplied replication when determined that a full rate frame test data was received without CRC error detected. Again, during the decoding of each received frame, the CRC code information received therewith is processed using conventional techniques in order to identify the bit errors that arise during transmission. Similarly, the replication circuit 50 provides packets of 1/2 Speed, 1/4 Speed and 1/8 Speed to the comparator 49, when it is determined that in the absence of CRC error frames of a medium have been received. speed, a quarter of speed and an eighth of speed, respectively. A blank or empty packet is supplied to the comparator 49 when it is determined that the "empty and burst" flag of a received frame has been placed. If the detected CRC error is such that the received frame quality is considered sufficient to allow accurate speed determination, the test data replication circuit 50 provides a blanking frame. The deletion box contains no bits, as shown.

TABLE III The test packet generated by the test data replication circuit 50 is in accordance with the data packet generation algorithm discussed below. As noted above, during the "attenuation and burst" mode of operation a flag was placed which is indicative of the size of the test packet and which accompanies the data of the control message. This allows the digital comparator 49 to be supplied with a test pack of the appropriate size, subsequent to the demultiplexing of the control message from the received test sequence.

SAW . Generation of Data Packs In a preferred embodiment, the test and replication data generation circuits 33 and 50 function to create the bit sequences within each test data packet, generating identical pseudo-random sequences of predetermined length. In particular, circuits 33 and 50 are arranged or arranged to generate a pseudo-random 31-bit number for each data packet in accordance with the following linear congruence generator: xn = (a) • (xn-?) (Od m ) where xn-? And xn denote the successive whole exits of the generators. In a preferred implementation, the parameters "a" and "m" are selected in such a way that a = 75 = 16807 y, m = 231-l = 2147483647. During the test of the reverse link channel between the transmitter 30 of the mobile unit and the receiver 40 of the cell site, the identical random number generators within the circuits 33 and 50 are reinitialized each time the least significant 9 bits of the result of a predefined exclusive OR operation becomes equivalent to the least significant 9 bits of a 32-bit electronic serial number (ESN), which uniquely identifies a particular mobile unit. Specifically, the re-initialization of the random number generation occurs each time the nine least significant bits of a unique 0 bit by bit of the frame number (ie, # of frames transmitted since the last initialization) with a predefined mask sequence ( for example '0101 0101 0101 0101 0101 0101 0101 0101') becomes identical to the 9 least significant bits of the ESN. Different seeds are used to reinitialize the random number generators for the direct traffic channel and for the reverse traffic channel. The initial value of the "seed" of x0 is selected on the basis that it is equivalent to the result of the exclusive 0, bit by bit, of the frame number 32 -bits in the reinitialization with a mask of "seeds" of reverse link (for example '0101 0101 0101 0101 0101 0101 0101 0101'). During each reset, the random number generators are iterated three times before producing a value (ie, x3) used as the first, or for the 1/8 speed packets used as the only one, of a string or string of one or more randomized concatenated numbers included within a first frame. These multiple iterations ensure that the test sequences generated in neighboring mobile stations using identical processes will correlate appropriately. During the variable speed test, the first random number produced (i.e., x3) is also used for the data rate selection of the first frame in the manner described below. These three initial iterations are performed as follows: x0 = seed, xx = a «Xo mod-m, x2 = a« X? mod m, and x3 = a * x2 mod m. Each value of xn can be transformed into a corresponding pseudo-random number of 24-bits and n, taking the 24 most significant bits of xn. That is, yn is the integer part of xn / l28. The nth of this 24-bit number and n, can be expressed in binary form as follows: Yn, 23 vn, 22 Vn, 21 vn, 20"" 'Yn, 3 Yn, 2 vn, l Yn, 0 where yn, 23 denotes the most significant bit of yn. Again, with respect to the variable speed test for speed frames 1, the random number generator is iterated six more times after the production of the term x3, in order to provide the remaining bits included within the sequence of the test packet. The speed packet 1 is comprised of the 24 bit values from y3 to y10 in addition to the three predetermined bits, preferably all "0" to fill the 171 bit test packet. For the 1/2 speed packets, the random number generator is iterated three additional times after the production of the term x3, in order to provide the remaining bits included within the sequence of the test packet. The 1/2 speed packet is comprised of the 24-bit values of y3 to y and the 8 most significant bits of the y5 value to fill the 80-bit test pack. For 1/4 speed packets, the random number generator iterates once again after the production of the term x3, in order to provide the remaining bits included within the sequence of the test packet. The 1/4 speed packet is comprised of the 24-bit values of y3 to y5 and the 16 most significant bits of the value y5 to fill the 40-bit test pack. And for the 1/8 speed data frames, the 16 most significant bits of the random number y3 corresponding to the initial value x3 comprise the entire sequence of the test pack. It should be noted that when a speed packet l is selected and that control message data exists, for example, secondary signaling or traffic data, which will be sent in an "attenuation and burst" phase of the operation in test mode, a speed test packet l is generated, as described above, but multiplexer 32 is provided with a packet of 1/2. In addition, when there is control message data that will be sent in a "white and burst" phase of the operation in test mode, a speed test packet 1 is generated, but a white packet is provided (i.e. 0 test data bits). During the test at fixed speed, a test packet of the same speed is generated for all the frames during the test at the selected fixed speed. For example, at 9.6 kbps, 4.8 kbps, 2.4 kbps, or 1.2 kbps, the random number generator is iterated seven times for the speed of 1, four times for the speed of 1/2, twice for the speed of 1 / 4 and once for the speed of 1/8, respectively, as discussed above in order to provide the required number of test bits. In alternate embodiments, the direct communication link between the cell site station and the mobile station may be tested concurrently with the reverse communication link between the mobile station and the cellular site or instead of the latter. When the forward link is tested, a transmitter substantially identical to the transmitter 30 (FIG. 2A) is included within the cellular site and, a receiver substantially identical to the receiver 40 (FIG. 2B) is located within the mobile unit. In a preferred implementation, the process of generating the random number used during the direct link test is reinitialized with the least significant 9 bits of the result of the exclusive O-operation, bit by bit, of the frame number with a direct link mask (for example '0010 1010 1010 1010 1010 1010 1010 1010') which becomes equivalent to the least significant 9 bits of the ESN of the mobile station. In accordance with the above, although the reinitialization of the processes generating the random number of the direct and inverse link will occur at different times or times, each process will be reinitialized once every 512 frames.

VII: Selection of Frame Rate Referring again to FIGURE I, in an exemplary embodiment, a series of test packages designed to simulate speech are generated at selected rates in accordance with the first order Markov chain of 16 states . The state of the Markov chain is defined by the data rates associated with the two preceding test packets, as indicated by TABLE I. As can be seen from TABLE I, each state is capable of transitioning to one of at most four states, at the end or conclusion of a particular picture. For example, since the "state 0" exists when the speeds of the N-th box (that is, the current or present) and the speed of the frames (N-l) -th are one, the speed of the frame (Nl) -th of any state to which state 0 transitions must also be 1. Hence, state 0 can make a transition only to states 0, 1, 2, and 3, - and state 1 can only make a transition to states 4, 5, 6 and 7. In general, the state "M" can make a transition towards the most states (4 «M) module 16, (4» M + 1) module 16, (4 «M + 2) module 16 y, (4 * M + 3) module 16. Referring now to TABLE IV, a set of cumulative probabilities indicative of the probability of a speech box (N + l) is vented -th are of a particular velocity, as a function of the existing Markov state in the nth voice box. Each of the cumulative probabilities in BOX IV are scaled to fall within the range of 0 to 32,768. That is, an input of 32,768 corresponds to a probability of unity, an entry of 0 corresponds to a cumulative probability of 0, and so on. For example, assuming that the Markov state of the nth chart is 0, TABLE IV specifies that there is a probability of 0 that the data rate of the (N + l) -th chart is either 1/8 speed or speed 1/4. Similarly, there is a probability of 2916 / 32,768 that the table (N + l) -th is of speed of 1/2 y, a probability of (32, 768-2916) / 32, 768 that the table (N + l) -th is full speed. The entries in the TABLE IV are representative of an exemplary set of parameters of two derivatives in empirical form, it will be understood that the values of these inputs could be modified to modulate other variable speed processes.

TABLE IV The pseudo-random number of 24-bits and n which, as indicated above, comprises all or part of the sequence of the test packet of a given frame, can also be used to facilitate the random selection of the data rate of each successive frame. In particular, a pseudo-random number zr is formed from the least significant 15 bits of the random number of 24-bits and n, associated with the Nth table and from here, it varies from 0 to 32,768. The data rate of the box. (N + l) -th is determined by comparing the value of zr with the entries in the row of TABLE IV that corresponds to the Markov state of the nth chart. In general, a speed R is chosen if the value of zr is greater than or equal to the input of the column "i-1" and, it is smaller than the entry of the "i-th" column. As an example, TABLE IV indicates that if the Markov state of the nth table is 6 and zr is less than 21856, then the data rate of the (N + l) -th chart is selected to be 1 / 8 speed. That is, a 1/8 speed test packet is generated within the test generation and replication circuits during the (N + 1) -th chart. Considering again the case of the Markov state of the nth table is 6, when zr is greater than or equal to 21856, but less than 25887, the data rate of the (N + l) -th chart is selected to be 1/4 speed and a 1/4 speed test package is generated. Similarly, if zr is greater than or equal to 25887 but less than 27099, the data rate of the (N + l) -th chart is selected to be 1/2 speed and a test packet of 1/2 speed. Finally, if zr is greater than or equal to 27099, the data rate of the (N + l) -th chart is selected to be speed 1 and a velocity packet of 1 is generated.

In an exemplary mode, the chain of Markov is set or put into a state of 15 with the initialization of the test data generation circuits 33 and 50. With the subsequent reinitialization of the random number generators within the circuits 33 and 50, the state of the string of Markov readjusts again in state 15.

VIII. Accumulation of Box Error Statistics Referring now to BOX V, a set of accumulated transmitted box counters is listed within a memory of the control processor (not shown) of the mobile unit. The notation RTn used within BOX V denotes the data rate associated with the nth frame transmitted by the mobile unit subsequent to the initialization of the test. For each frame transmitted after the initialization of the test, the control processor of the mobile unit increases to the appropriate counter of the counters included within FIGURE V. Similarly, within FIGURE VI, an illustrative set of received frame statistics accumulated within the memory of the control processor (not shown) of the base station. The annotation RRn used within TABLE VI denotes the data rate associated with the nth frame received by the base station subsequent to the initialization of the test. In addition, the term "CRC error" refers to the CRC errors detected during the decoding process. Similarly, the phrase "error of the test sequence" indicates that one or more bit errors were detected by the digital comparator 49 during a bit-by-bit comparison of a received test packet sequence and its corresponding packet sequence. replicated test. For each frame received after the initialization of the test, the control processor of the base station increases to the appropriate counter of the counters included in TABLE VI. The counters in BOX VI are increased based on the results of up to several speed determination operations. These operations may include, for example, a Viterbi decoding process, CRC error checking and various energy measurement techniques. In an exemplary embodiment, a first rate determination method is implemented using the aforementioned Viterbi decoding process, performed by the decoder 45. Bit errors not detected during the Viterbi decoding but subsequently detected during the comparison of test data, performed within digital comparator 49, are also recorded within BOX V. In a particular implementation, the contents of BOX V may be replicated within the memory of the control processor of the base station and the contents of BOX VI replicated within of the control memory of the mobile station.

TABLE V TABLE VI MS02 R31 Number of packets with speed of 1/4 received in the absence of "attenuation and burst" given that RRp was 1/8 MS02 R32 Number of packets with correct 1/8 speed received given that RR? was 1/8 MS02 R33 Number of packets with "attenuation and burst" received given that RRn was 1/2 MS02 R34 Number of packets with a speed of 1 received with detected test sequence errors given that RRn was 1/8 MS02 R35 Number of packets received with insufficient frame quality given that RRn was 1/8 MS02 R36 Number of packets with speed of 1/8 received with detected test sequence errors given that RRn was 1/8 MS02 R37 Number of packets with correct "m" speed since RRn was "m", therefore: (MS02_R37 = MS02_R1 + MS02_R13 + MS02 R23 MS02 R37 + MS02 R33) MS02 R38 Number of packets with a speed of 1 received in error, for Therefore: (MS02_R38 = MS02_R4 + MS02_R5 + S02_R6 + MS02_R7 + MS02 R8) MS02 R39 Number of total bad frames, therefore: (MS02 R39 = MS02 R14 + MS02 R15 + MS02 R16 + MS02 R17 + MS02 R18 + MS02 R19 + MS02 R22 + MS02 R24 + MS02 R25 + MS02 R26 + MS02 R28 + MS02 R31 + MS02 R32 + MS02 R34 + MS02 R35 + MS02 R38) IX. Calculation of Frame Error Rate Frame transmission and error statistics compiled in FIGURES V and VI can be used to calculate a set of frame error rates associated with transmission at various frame rates. An exemplary set of frame error rates (FERs) for full-speed transmissions, at 1/2 speed, at 1/4 speed and at 1/8 speed at the reverse link between mobile and cell-site stations can be determined in accordance with the following expressions: FERPlena speed = 1 MS02_Rlc / MS02_Tlm, FER? / 2 speed = 1 MS02_R13c / MS02_T2m, FER1 / 4 speed = 1 MS02_R23c / MS02_T3m, and FER1 / 8 speed = 1 MS02_R33c / MS02_T4m, wherein the counters that were increased within the mobile station are identified by the subscript "m" and, where the counters that were increased within the cell site station are denoted by the subscript "c". It will be noted that the illustrative set of frame error rate expressions, set forth above, is independent of the frame number with attenuation and burst and of frames with blank and burst transmitted in a particular test range. Similarly, the frame transmission and error statistics compiled within TABLES V and VI can be used in the calculation of a set of frame error rates associated with the forward link transmission at various frame rates. An exemplary set of frame error rates (FERs) for full speed transmissions, 1/2 speed, 1/4 speed and 1/8 speed in the direct link from the cell site station to the unit mobile can be determined according to the following expressions: FERplen speed = 1 MS02_Rlm / MS02_Tlc, ER1 / 2 speed = 1 MS02_R13m / MS02_T2c, FERl / 4 speed = 1 MS02_R23m / MS02_T3c, and FERl / 8 speed = 1 MS02_R33m / MS02_T4c, wherein the counters that were incremented within the mobile station again are identified by the subscript "m" and, where the counters that were incremented within the cell site station are denoted by the subscript "c". This exemplary set of the forward link frame error rate expressions are also independent of the number of frames with transmitted attenuation and bursts and of transmitted frames with blank and burst. It will be noted that the values of the counters of the cell site station MS02_T1C, MS02_T2C, MS02_T3C, and MS02_T4C, can be estimated by adding the values of the corresponding counters of the mobile station. Similarly, the values of the mobile station MS02_Tlm, MS02_T2m, MS02_T3m, and MS02__T4m can be estimated by adding the values of the corresponding counters of the base station.

The above description of the preferred embodiment is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, it is not intended that the present invention be limited to the modalities shown therein but the broader scope consistent with the principles and novel features set forth herein will be agreed upon.

Claims (29)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. In a communications system in which digital information is transmitted at variable speeds on a communication channel, a method for testing the communication channel comprising the steps of: transmitting a test sequence of digital data to one or more of a plurality of selectable speeds on the communication channel, - receiving the test sequence of the digital data transmitted on the communication channel; generate a replica of the digital data test sequence; and comparing the replica of the digital data test sequence with the test sequence of the data received on the communication channel, to determine the accuracy of the transmission of data on the communication channel. The method according to claim 1, wherein the step of transmitting includes the step of transmitting the digital data test sequence to a first rate of one or more selectable data rates and, the receiving step includes the step of identifying the first data speed. The method according to claim 1, wherein the digital data test sequence is generated in accordance with a pseudorandom process. The method according to claim 1, wherein the step of transmitting includes the steps of: generating a first plurality of data packets comprising the digital data test sequence, - allocating one of a multiplicity of data rates to each of the data packets according to a first pseudorandom process; and transmitting each of the first plurality of data packets at a speed of the multiplicity of data rates assigned thereto. The method according to claim 4, wherein the step of generating the replica of the digital data test sequence includes the step of generating a second plurality of data packets substantially identical to the first sequence of data packets. The method according to claim 4, wherein the step of generating the first plurality of data packets includes the step of generating bit sequences within each of the first plurality of data packets, in accordance with a second pseudorandom process . 7. In a digital communication system in which digital data frames are transmitted at the selected speeds over a communication channel, between a remote terminal and a base station, a method for testing the communication channel, comprising the steps of : transmitting, from the remote terminal to the base station, on the communication channel, a first frame of the digital data frames, the first digital data frame includes a first packet of digital test data; receiving, at the base station, the first digital data frame, - generating, at the base station,. a replica of the first digital test data packet, - and compare the replica of the first digital test data packet with the first inherent digital test packet within the first digital data frame received at the base station, to determine the accuracy of the transmission of data on the communication channel. 8. The method according to claim 7, further including the step of receiving each of the digital data frames in the base station, determining a data rate associated with each of the received frames of digital information. The method according to claim 8, further including the step of generating the replica of the first digital test data packet, in accordance with the data rate associated with the first digital information frame. The method according to claim 9, further including the step of generating a bit sequence within the first packet of digital test data in accordance with a pseudorandom process. 11. The method according to claim 7, wherein the step of transmitting the first digital data frame on the communication channel includes the step of modulating the first digital data frame using an extended spectrum modulation signal. The method according to claim 7, wherein the step of transmitting the first digital data frame on the communication channel includes the step of modulating the first digital data frame using a pseudonoise (PN) signal, corresponding to a sequence default PN binary.Fo. 13. The method according to claim 7, further comprising the step of transmitting a plurality of digital data frames on the communication channel, wherein each of the plurality of frames includes a packet of digital test data generated in accordance with a process pseudo-random The method according to claim 7, wherein the step of comparing includes the step of comparing bit sequences comprising the replication of the first digital test data packet with a corresponding bit sequence within the first data packet. of digital tests, in order to accumulate a cumulative bit error account. The method according to claim 14, further including the steps of: counting the digital information frames received at the base station, to determine an account of received frames, - and calculating the frame error statistics based on the account of cumulative bit error and the count of received frames. 16. In a digital communication system in which digital information frames are transmitted at selected rates over a communication channel from a base station to a remote terminal, a method for testing the communication channel, comprising the steps of: transmitting, from the base station to the remote terminal, a packet of digital test data within each of the digital information frames; receiving, in the remote terminal, the digital information frames transmitted from the base station, - generating, in the remote terminal, replicas of each of the digital test data packets within the digital information boxes received in the base station , - and compare the replicas of the digital test data packets with the received digital test data packets, to determine the accuracy of the data transmission on the communication channel. The method according to claim 16, wherein the step of comparing includes the step of comparing bit sequences comprising the replicas of the digital test data packets with the corresponding sequences of bit sequences comprising the packets received from digital test data, in order to accumulate a cumulative bit error account. The method according to claim 17, further including the steps of: counting the digital information frames received in the remote terminal to determine an account of received frames; and calculate the frame error statistics based on the cumulative bit error account and the received frames count. 19. In a communication system in which the digital information is transmitted at selected rates over a communication channel, a system for testing the communication channel comprising: a transmitter for transmitting a test sequence of digital data to one or more selectable speeds on the communication channel; a receiver for receiving the test sequence of the digital data transmitted on the communication channel, the receiver includes a means for generating a replica of the test sequence of the digital data; and a digital comparator circuit for comparing the replica of the digital data test sequence with the test sequence of data received on the communication channel, to determine the accuracy of data transmission on the communication channel. 20. The system according to claim 19, wherein the transmitter includes a means for transmitting the digital data test sequence to a first one of one or more selectable speeds and the receiver includes a means for identifying the first data rate. The system according to claim 19, further including a means for selecting the digital data test sequence from a pseudorandom data sequence set. The system according to claim 19, wherein the transmitter further includes: means for generating a first plurality of data packets comprising the digital data test sequence; means for assigning one of a multiplicity of data rates to each of the data packets, in accordance with a first pseudorandom process; and a means for transmitting each of the first plurality of data packets at a speed of the multiplicity of data rates assigned thereto. The system according to claim 22, wherein the means for generating the replica of the digital data test sequence includes a means for generating a second plurality of data packets substantially identical to the first data packet sequence. The system according to claim 23, wherein the means for generating the first plurality of data packets includes a means for generating bit sequences within each of the first plurality of data packets, in accordance with a second pseudorandom process . 25. In a digital communication system in which the digital data frames are transmitted at selected rates on a communication channel between a remote terminal and a base station, a system for testing the communication channel comprises: a transmitter, arranged or located in the remote terminal to complete a packet of digital test data within each of the digital information boxes; a receiver, located in the remote terminal, to receive the digital information frames transmitted from the base station, - a means for generating replicas of each of the digital test data packets within the digital information frames received in the base station, - and a means to compare replicas of '-. the digital test data packets with the received packets of digital test data, to determine the accuracy of the data transmission on the communication channel. . 26. The system according to claim 25, wherein the receiver includes a means for determining a data rate associated with each of the digital information frames. The system according to claim 26, further providing a means for generating each of the replicas of the digital test data packets based on the data rate associated with one of the digital information frames. The system according to claim 27, further including a means for generating bit sequences within each of the digital test data packets in accordance with a pseudorandom process. 29. The system according to claim 25, wherein the comparing means includes means for comparing bit sequences, comprising replicas of the digital test data packets, with the corresponding bit sequences, comprising the received packets. of digital test data, in order to accumulate a cumulative bit error account.