CN1189940A - Apparatus and method for synchronizing transmitters within a user terminal of a wireless telecommunication system - Google Patents

Abstract

The invention provides a method used to establish a down line communication path from the transmitter (200) of a central terminal (10) to the receiver of a user terminal (20). During configuring and operating a wireless telecommunication system (1), a down line signal (212) is transmitted from the transmitter (200) to the receiver (202). The down line signal (212) comprises an additional channel (224) with a code synchronization signal (234). The code synchronization signal can regulate the phase of a transmitter (204) arranged in the user terminal (20). A receiver (206) arranged in the central terminal (10) monitors an upper line signal (214) transmitted by the transmitter (204) arranged in the user terminal, and changes the code synchronization signal (234), thus synchronizing the transmitter (204) and the receiver (206). The synchronization of the transmitter (204) of the user terminal (20) with the receiver (206) arranged in the central terminal (10) facilitates the establishment of an upper line communication path from the user terminal (20) to the central terminal (10).

Description

Apparatus and method for synchronizing transmitters within a user terminal of a wireless telecommunication system

technical field

The present invention relates to telecommunication systems, and more particularly to an apparatus and method for synchronizing transmitters within user terminals of a wireless telecommunication network.

Background technique

Wireless telecommunications systems use transmitters and receivers in a network structure similar to telephones to send and receive information on radio frequency signals. A transmitter generally transmits a signal with one phase, and a receiver generally receives a signal with a different phase. The use of different phases in the system by transmitters and receivers can create problems in identifying information from multiple transmitter and receiver pairs. Furthermore, a receiver with one phase requires extensive circuitry and software to recognize information from a corresponding transmitter operating with a different phase. In addition, variations in the path delay between the transmitter and receiver may also cause phase differences between the receiver and transmitter. Accordingly, it is desirable to control the phase of transmitters and receivers in wireless telecommunications systems to provide improved radio frequency signal transmission.

Contents of the invention

It is an object of the present invention to provide an apparatus and method for synchronizing transmitters within a user terminal of a wireless telecommunication system, thereby substantially eliminating or reducing disadvantages and problems associated with conventional wireless telecommunication techniques.

According to one aspect of the present invention, there is provided a method of synchronizing a transmitter in a user terminal of a wireless telecommunication system, comprising the steps of: establishing a downlink communication path from the central terminal to the user terminal; transmitting a downlink signal; receiving the downlink signal at a receiver within the subscriber terminal; identifying a code synchronization signal within the downlink signal; adjusting the phase of the transmitter within the subscriber terminal in response to the code synchronization signal; responding to the communication with the central terminal The phase of the receiver is equal to the phase of the transmitter within the subscriber unit, establishing an uplink communication path.

According to another aspect of the present invention, there is provided a system for synchronizing communications within a wireless communication system, comprising: a transmitter within a central terminal operable to transmit a downlink signal including a code synchronization signal; a user terminal The receiver in the user terminal can be used to receive the downlink signal, the receiver in the user terminal can be used to extract the code synchronization signal from the downlink signal; the transmitter in the user terminal can be used to transmit the uplink signal, the transmitter in the user terminal It can be used to receive a code synchronization signal from a receiver in the user terminal, which can be used to adjust the phase of the uplink signal; a receiver in the central terminal can be used to receive the uplink signal, and the receiver in the user terminal can be used to adjust the phase of the uplink signal. Its receiver phase is compared with the phase of the uplink signal to determine whether the phase of the receiver matches the phase of the uplink signal. In order to match the phase of the uplink signal with the phase of the receiver, the receiver in the user terminal can The code sync signal sets a value.

According to another aspect of the present invention, a user terminal is provided in a wireless telecommunications system, comprising: a receiver operable to receive downlink signals, the downlink signals including code synchronization The code synchronization signal is extracted from the signal; the transmitter can be used to transmit the uplink signal, and the transmitter can be used to receive the code synchronization signal, and the code synchronization signal can be used to adjust the phase of the uplink signal.

According to one embodiment of the present invention, a method of synchronizing transmitters within a user terminal of a wireless communication system includes establishing a downlink communication path from a central terminal to the user terminal. Downlink signals are transmitted from transmitters within the central terminal and received by receivers at the subscriber terminals. The receiver of the user terminal extracts the code synchronization signal from the downlink signal. The code synchronization signal is used to adjust the phase of the uplink signal transmitted by the transmitter in the user terminal. In order to match the phase of the uplink signal to the phase at the central terminal receiver, the central terminal's receiver monitors the phase of the uplink signal and changes the code synchronization signal.

The present invention provides various technical advantages over conventional wireless communication techniques. For example, one technical advantage would be to remotely adjust the transmit phase of a transmitter within a user terminal. Another technical advantage is to obtain phase matching of transmitters in user terminals at the receiver at the central terminal. Yet another advantage is the insertion of the code synchronization signal into the downlink signal transmitted from the central terminal to incrementally adjust the transmit phase of the transmitter within the subscriber terminal. Yet another technical advantage is the continuous monitoring of the transmit phase of the transmitter in the user terminal to maintain a phase match with the receiver in the central terminal. Other technical advantages will become apparent to those skilled in the art from the following figures, description and claims.

Figure overview

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals are used for like features, wherein:

Figure 1 is a schematic diagram of an example of a wireless telecommunications system in which an example of the present invention is incorporated;

FIG. 2 is a schematic diagram of an example of a user terminal of the telecommunications system of FIG. 1;

Figure 3 is a schematic diagram of an example of a central terminal of the telecommunications system of Figure 1;

3A is a schematic diagram of a modem rack of a central terminal of the telecommunications system of FIG. 1;

Figure 4 is a diagram of an example of a frequency plan for the telecommunications system of Figure 1;

Figures 5A and 5B are schematic diagrams illustrating a possible structure of a cell of the telecommunication system of Figure 1;

6 is a schematic diagram depicting some aspects of a code division multiplexing system of the telecommunications system of FIG. 1;

Figure 7 is a schematic diagram depicting signal transmission processing stages of the telecommunications system of Figure 1;

FIG. 8 is a schematic diagram depicting signal reception processing stages of the telecommunications system of FIG. 1;

9 is a schematic diagram illustrating downlink and uplink communication paths of a wireless communication system;

Fig. 10 is a schematic diagram describing the structure of a downlink signal transmitted by a central terminal;

Fig. 11 is a graph describing the phase adjustment of the subordinate code sequence of the user terminal;

FIG. 12 is a graph of signal quality estimation by a receiver of a user terminal;

Fig. 13 is a schematic diagram describing the content of a frame information signal in a downlink signal;

Figure 14 is a tabular diagram depicting additional insertions made to the data stream of a downlink signal;

FIG. 15 is a list diagram of power control signals in an overhead channel of a downlink signal;

Fig. 16 is a list diagram of the code synchronization signal of the additional channel of the downlink signal;

Figure 17 is a graph of transmit power and transmit rate for each mode of operation of the wireless telecommunication system;

FIG. 18 is a schematic diagram describing the operation of a receiver and a transmitter of a user terminal.

Detailed description of the invention

Figure 1 is a schematic diagram of an embodiment of a wireless telecommunications system. The wireless telecommunications system comprises one or more service areas 12, 14 and 16, wherein each area is serviced by a respective central terminal (CT) 10 which establishes radio links with subscriber terminals (ST) 20 in the area concerned for service. The area covered by the central terminal 10 can vary. For example, in a rural area with a low user density, the service area 12 may cover an area with a radius of up to 15-20 Km. A service area 14 in an urban environment with a high density of user terminals 20 may only cover an area with a radius of the order of 100 m. In a suburban area with a moderate density of user terminals, the service area 16 may cover an area with a radius of the order of 1 km. It should be understood that the area covered by a particular central terminal 10 can be selected to meet desired local requirements or actual user density, local terrain conditions, etc., and is not limited to the embodiment shown in FIG. 1 . Furthermore, due to antenna design considerations, terrain considerations, buildings, etc., which will affect the distribution of the transmitted signal, the coverage area is not necessarily and generally is not circular.

The central terminals of the respective service areas 12, 14 and 16 are interconnected by means of links 13, 15 and 17 (for example, which interface with the public switched telephone network (PSTN) 18). Links can include traditional telecommunication technologies using copper wire, fiber optic cable, satellite, microwave, etc.

The wireless telecommunications system of Figure 1 is based on the provision of fixed microwave links between subscriber terminals 20 at fixed locations within a service area (e.g., 12, 14, 16) and a central terminal 10 for that service area . In the preferred embodiment, each user terminal 20 is provided with a permanently fixed access link to its central terminal 10 . However, in another embodiment, request-based access can be provided so that the number of users that can be served exceeds the number of telecommunications links available today.

FIG. 2 shows an embodiment of the structure of a user terminal 20 for the telecommunication system of FIG. 1 . FIG. 2 includes a schematic representation of a user premises 22 . A customer radio unit (CRU) 24 is installed on the customer's premises. The subscriber radio unit 24 includes a panel antenna or the like 23 . The subscriber radio unit is installed on the user's premises or at a position on a vertical pole, and in such an orientation that the panel antenna 23 in the subscriber radio unit 24 faces the center terminal 10 of the service area in which the subscriber radio unit 24 is arranged. Direction 26.

Via a drop line 28, the subscriber radio unit 24 is connected to a power supply unit (PSU) within the subscriber's premises. The power supply unit 30 is connected to a local power supply for supplying power to the subscriber radio unit 24 and the network termination unit (NTU) 32 . Via power supply unit 30, subscriber radio unit 24 is connected to network terminal unit 32, which in turn is connected to telecommunications equipment (eg, one or more telephones 34, facsimile 36 and computer 38) within the subscriber's premises. The telecommunications equipment shown is located within a single user's premises. However, this need not be the case, since a single subscriber terminal 20 may support two subscriber lines, since preferably a subscriber terminal 20 supports single or dual lines. It may also be arranged that the user terminal 20 supports analog and digital telecommunications, for example, analog communication at 16, 32 or 64Kbits/sec or digital communication according to the ISDN BRA standard.

FIG. 3 is a schematic diagram of an embodiment of a central terminal of the telecommunications system of FIG. 1 . The common equipment rack 40 includes a plurality of equipment racks 42, 44, 46 which are an RF combiner and power amplifier rack (RFC) 42, a power supply rack (PS) 44, and a plurality (four in this embodiment) of modems Rack (MS)46. The RF combiner rack 42 enables four modem racks 46 to operate in parallel. It combines and amplifies the power of the four transmitted signals (one from each of the four modem racks), and amplifies and splits the received signal four paths so that the separate signals can pass through each modem rack. A power shelf 44 is connected to a local power source and provides fuses for the various components in the common equipment rack 40 . A two-way connection extends between the RF combiner rack 42 and the main center terminal antenna 52 (typically an omnidirectional antenna mounted on the center terminal pole 50).

The central terminal 10 of this embodiment is connected by a point-to-point microwave link to a location forming an interface to the public switched telephone network 18 (shown in FIG. 1). As noted above, other types of connections (eg, copper wire or fiber optic cables) may be used to link the central terminal 10 with the public switched telephone network 18 . In this embodiment, the modem rack is connected to a microwave terminal (MT) 48 by line 47 . A microwave link 49 extends from a microwave terminal 48 to a point-to-point microwave antenna 54 mounted on a pole 50 for connection to the public switched telephone network 18 host.

Personal computers, workstations, etc. can be used as the site controller (SC) 56 to support the central terminal 10 . A site controller 56 may be connected to each modem rack of the central terminal 10 (eg, via RS232 connection 55). The site controller 56 may then provide support functions such as location of faults, alarms and status, and formation of the central terminal 10 . A network site controller 56 typically supports a single central terminal 10, although multiple site controllers 56 may be used to form a network to support multiple central terminals 10.

As an alternative to extending the RS232 connection 55 to the mesh point controller 56, a data connection such as an X.25 link 57 (in FIG. 3 is represented by a dash)) instead. The component manager 58 may support a plurality of distributed central terminals 10, the shown distributed central terminals 10 being connected to the switching nodes 60 by respective connections. The component manager 58 is capable of incorporating a potentially large number of central terminals 10 (eg, as large as 1000 or more) into the management network. The component manager 58 is built around a powerful workstation 62 and may include a number of computer terminals 64 for use by network engineers and control personnel.

FIG. 3A shows various parts of the modem rack 46 . A transmit/receive RF unit (RFU - eg implemented on a modem shelf card) 66 generates a modulated transmit RF signal at an intermediate power level and recovers and amplifies the baseband RF signal for the user terminal. The RF unit 66 is connected to an analog card (AN) 68 which performs A-D/D-A conversion, baseband filtering and vector summing of the 15 transmit signals from a modem shelf card (MC) 70 . The analog unit 68 is connected to a plurality (typically 1-8) of modem cards 70 . The modem card performs baseband signal processing for signals transmitted to or received from the user terminal 20 . This includes rate 1/2 convolutional encoding and CDMA code ×16 spreading for the transmitted signal, and synchronization recovery, despreading and error correction for the received signal. Each modem card 70 in this embodiment has two modems, and each modem card supports one user link (or two links) to the user terminal 20 . Then, with two modems per card and eight modems per modem shelf, each modem shelf can support 16 possible subscriber links. However, to include redundancy so that a modem shelf can be replaced in a subscriber's link in the event of a failure, one modem shelf 46 preferably supports 15 subscriber links. Thus, the 16th modem card is used as a spare to be plugged into the circuit should one of the other 15 modem racks fail. The modem card 70 is connected to a branch unit (TU) 74, which terminates the line at the host of the public switched telephone network 18 (e.g., via one of the lines 47) and handles up to 15 calls Signaling of telephony information for subscriber terminals (via 15 individual modems out of 16 modems).

Wireless telecommunications between the central terminal 10 and the user terminals 20 may operate at various frequencies. Figure 4 shows an example of available frequencies. In this embodiment, wireless telecommunications systems tend to operate within a 1.5-2.5 GHz bandwidth. In particular, the present embodiment tends to operate within the bandwidth specified by ITU-R (CCIR) standard F.701 (2025-2110 MHz, 2200-2290 MHz). FIG. 4 shows the frequencies used for the uplink from the subscriber terminal 20 to the central terminal 10 and for the downlink from the central terminal 10 to the subscriber terminal 20 . It should be noted that the 12 uplink and 12 downlink radio channels (each with a frequency of 3.5 MHz) are centered at 2155 MHz. The separation between the receive channel and the transmit channel exceeds the required minimum separation of 70 MHz.

In this embodiment, each modem shelf supports one frequency channel (ie, one uplink frequency plus a corresponding downlink frequency) as described above. As will be described later, a frequency channel can support up to 15 user links, so in this embodiment, each central terminal 10 can support 60 links, or 120 lines.

In general, radiotelephone service extends from a particular central terminal 10 into the area covered by nearby central terminals 10 . In order to avoid (or at least reduce) interference problems caused by adjacent areas, any given central terminal 10 only utilizes a limited number of available frequencies.

FIG. 5A shows a cellular layout of frequencies to mitigate interference problems between adjacent central terminals 10 . In the layout shown in FIG. 5A, the hatching of the cell 76 indicates the frequency setting (FS) of the cell. By selecting three frequency settings (for example, where: FS1 = F1, F4, F7, F10; FS2 = F2, F5, F8, F11; FS3 = F3, F6, F9, F12), and make the following arrangements, that is, contiguous Instead of cells having the same frequency set (see, for example, the layout shown in Figure 5A), an array of fixedly assigned omnidirectional cells can be provided, which avoids interference between neighboring cells. The transmitter power of each central terminal 10 is set so that the transmission does not exceed the nearest cell using the same frequency. The central terminal 10 can then use the four frequency pairs (for uplink and downlink respectively) within its cell, with each modem rack at the central terminal 10 connected to a respective RF channel (channel frequency pair).

Since each modem shelf supports one channel frequency (with 15 subscriber links to each channel frequency) and four modem shelves, each central terminal 10 supports 60 subscriber links (ie, 120 lines). Thus the 10 cell layout of Figure 5A supports up to 600 ISDN links or 1200 analog lines. FIG. 5B shows a cellular layout which employs partitioned cells to alleviate problems between adjacent central terminals 10 . The different types of hatching in Fig. 5B indicate different frequency settings compared to Fig. 5A. As shown in FIG. 5A, FIG. 5B shows three frequency settings (for example, where: FS1=F1, F4, F7, F10; FS2=F2, F5, F8, F11; FS3=F3, F6, F9, F12). However, in FIG. 5B, by employing a sectoral central terminal (SCT) 13 (which includes three central terminals 10, one for each sector S1, S2, and S3, and the transmission of each of the three central terminals 10 all point directly to the appropriate sector in S1, S2 and S3) to the cell sector. This triples the number of users per cell while still providing permanent fixed access to each user terminal 20 .

A seven cell repetition pattern is employed so that for a cell operating at a given frequency, a unique PN code is available for all six adjacent cells operating at the same frequency. This prevents neighboring cells from accidentally decoding data.

As mentioned above, each channel frequency can support 15 user links. In this embodiment, the above effects can be obtained by multiplexing signals using Code Division Multiple Access (CDMA) technology. FIG. 6 shows a schematic diagram of CDMA encoding and decoding.

In order to encode CDMA signals and baseband signals, for example, at 80-80N, the user signals on each user link are encoded into 160k symbols/second baseband signals, where each symbol represents 2 data bits (see, signal shown at 81). The signal is then spread by a factor of 16 by spreading functions 82-82N using respective Walsh pseudorandom noise (PN) codes to generate a signal with an effective subcode rate of 2.56 Msymbols/second at a frequency of 3.5 MHz. The signals on the various user links are then combined and converted to radio frequency (RF) to generate a plurality of user channel signals (eg, 85 ) for transmission from transmit antenna 86 .

During transmission, the transmitted signal passes through sources of interference 88, which include external interference 89 and interference 90 from other channels. Accordingly, by the time receive antenna 91 receives the CDMA signal, the multiple user channel signals are distorted, as shown at 93 .

To decode the signal for a given user link from the received multiple user channels, Walsh correlators 94-94N apply the same pseudorandom noise (PN) code (which is used for each user link signals) to extract signals for each of the received baseband signals 96-96N (eg, shown at 95). It should be noted that the received signal includes some residual noise. However, unwanted noise can be filtered out using a low-pass filter and signal processing.

The key of CDMA lies in the application of orthogonal codes, which enables multiple user signals to be transmitted and received at the same frequency at the same time. Once the Walsh codes are used to isolate the bit streams orthogonally, the signals on each user link will not interfere with each other.

Walsh codes are a set of mathematical sequences with the function of "orthogonalization". In other words, if any Walsh code is multiplied by any other Walsh code, the result will be zero.

FIG. 7 is a schematic diagram illustrating signal transmission processing stages constructed in a user terminal of the communication system of FIG. 1 . Construction is also made at the central terminal for equivalent signaling processing. In Fig. 7, the analog signal from one of a pair of telephones is sent to the mixed sound processing circuit 104 through the two-wire interface 102, and then a digital signal is generated through the codec 106, and the control information is included at 108 The additional channels of the digital signal are inserted. The resulting signal is processed by convolutional encoder 110 before passing through spreader 116, to which Rademacher-Walsh code and PN code are applied by RW code generator 112 and PN code generator 114, respectively. The obtained signal is passed through a digital-to-analog converter 118 . A digital-to-analog converter 118 shapes the digital samples into an analog waveform and provides a baseband power control stage. The signal is then modulated in modulator 122 after passing through low pass filter 120 . The modulated signal from the modulator 122 is mixed with a signal generated by a voltage controlled oscillator 126 which is responsive to a synthesizer 160 . The output of mixer 128 is then amplified in low noise amplifier 130 before passing through bandpass filter 132 . The output of the bandpass filter 132 is further amplified in another low noise amplifier 134 before being passed to the power control circuit. The output of the power control circuit is further amplified in a further low noise amplifier 138 before passing through another bandpass filter 140 and then transmitted from a transmit antenna 142 .

FIG. 8 is a schematic diagram illustrating signal reception processing stages constructed in a user terminal of the communication system of FIG. 1 . Construction is also made at the central terminal for equivalent signal reception processing. In FIG. 8 , the signal received at receive antenna 150 is passed through bandpass filter 152 before being amplified in low noise amplifier 154 . The output of amplifier 154 is then passed through a further bandpass filter 156 before being amplified by another low noise amplifier 158 . The output of the amplifier 158 is then passed to a mixer 164 where it is mixed with a signal generated by a voltage controlled oscillator 162 which is responsive to a synthesizer 160 . The output of the mixer is then passed through demodulator 166 and low pass filter 168 before being passed to analog-to-digital converter 170 . Then the digital output of A/D converter 170 is passed to correlator 178, respectively by RW code generator 172 (corresponding to RW code generator 112) and PN code generator 174 (corresponding to PN code generator 114) and The correlator 187 is applied to the same Rademacher-Walsh and PN codes used in transmission. The output of the correlator is applied to a Viterbi decoder 180. The output of the Viterbi decoder 180 is then sent to an additional extractor 182 for extracting additional channel information. The output of additional extractor 182 is then passed through codec 184 and hybrid circuit 188 to a two-wire interface 190 where the resulting analog signal is passed to a selected telephone 192.

At the user terminal 20, an automatic gain control stage is included at the IF stage. The control signal is derived from the output of a signal quality estimator (described below) for the digital part of the CDMA receiver.

FIG. 9 is a block diagram of the downlink and uplink communication paths between the central terminal 10 and the user terminals 20 . A downlink communication path is established from the transmitter 200 of the central terminal 10 to the receiver 202 of the user terminal 20 . An uplink communication path is established from the transmitter 204 of the user terminal 20 to the receiver 206 of the central terminal 10 . Once the downlink and uplink communication paths have been established in the wireless telecommunication system 1, it is possible to communicate between the first user 208 or the second user 210 of the user terminal 20 and the network serviced by the central terminal 10 via the downlink signal 212 and the uplink signal 214. Telephone communication between one user. The downlink signal 212 is transmitted by the transmitter 200 of the central terminal 10 and received by the receiver 202 of the user terminal 20 . Uplink signal 214 is transmitted by transmitter 204 of subscriber terminal 20 and received by receiver 206 of central terminal 10 . Downlink signal 212 and uplink signal 214 are transmitted as CDMA spread spectrum signals.

The receiver 206 and transmitter 200 in the central terminal 10 are mutually synchronized with respect to time and phase, and are aligned on message boundaries. To establish a downlink communication path, the receiver 202 of the subscriber terminal 20 should be synchronized with the transmitter 200 of the central terminal 10 . Synchronization occurs by performing the acquisition mode function and the tracking mode function on the downlink signal 212 . Initially, the transmitter 200 of the central terminal 10 transmits a downlink signal 212 . FIG. 10 shows the contents of the downlink signal 212 . The downlink signal 212 includes a coded sequence signal 216 for the central terminal 10 combined with a frame information signal 218 . The code sequence signal 216 is composed of a pseudorandom noise code signal 220 and a Rademacher-Walsh code signal 222 . Although FIG. 10 specifically refers to the composition of the downlink signal, the uplink signal has the same composition.

Each receiver 202 of each user terminal 20 served by a single central terminal 10 operates on the same but deviated pseudorandom noise code as the central terminal 10 . Each modem shelf 46 in the central terminal 10 supports one radio frequency channel and fifteen user terminals 20 each having a first user 208 and a second user 210 . Each modem shelf 46 selects one of sixteen Rademacher-Walsh code signals 222 , each Rademacher-Walsh code signal 222 corresponding to a unique subscriber terminal 20 . Thus, a particular subscriber terminal 20 will have the same code sequence signal 218 as the downlink signal 212 transmitted by the central terminal 10 and propagated to the particular subscriber terminal 20 .

Downlink signal 212 is received at receiver 202 of user terminal 20 . Receiver 202 compares its phase and code sequence with the phase and code sequence in code sequence signal 216 of downlink signal 212 . The central terminal is considered to have a master code sequence, while the user terminals are considered to have a slave code sequence. The receiver adjusts the phase of its secondary code sequence step by step to identify a match with the primary code sequence, and brings the receiver 202 of the user terminal 20 and the transmitter 200 of the central terminal 10 into phase. Due to the path delay between the central terminal 10 and the user terminal 20, the secondary code sequence of the receiver 202 is not initially synchronized with the primary code sequence of the transmitter 200 and the central terminal 10. This path delay is caused by the geographical separation between the user terminals 20 and the central terminal 10 and other environmental and technical factors affecting radio transmissions.

FIG. 11 depicts how the receiver 202 of the subscriber terminal 20 adjusts the secondary code sequence to match the primary code sequence of the transmitter 200 of the central terminal 10 . The receiver 202 increments the phase of the slave code sequence over the entire length of the master code sequence of the downlink signal 212 and measures the combined power of the slave code sequence and the master code sequence by making a measurement of the combined power of the slave code sequence and the master code sequence for each incremental change in the phase of the slave code sequence. A signal quality estimate is determined. According to the subcode period of 2.56 MHz, the length of the main code sequence is about 100 microseconds. During the acquisition phase, half a subcode period is used to adjust the phase of the secondary code sequence for each increment interval. When the receiver 202 identifies a correlation peak (where the combined power reaches a maximum value), the receiver 202 completes the first acquisition pass. The receiver 202 makes a second acquisition pass throughout the code sequence length to confirm the identification of the combined power maximum at the correlation peak. The approximate path delay between the user terminal 20 and the central terminal 10 is determined when identifying the correlation peak location in the acquisition mode.

Once the acquisition of the downlink signal is completed at the receiver 202, a fine adjustment of the phase of the slave code sequence is performed to keep the phase of the slave code sequence and the master code sequence matched in the tracking mode. Fine-tuning is performed by making incremental changes of one-sixteenth of a subcode period to the phase of the subordinate code sequence. Trimming can be done in the forward (positive) or reverse (negative) direction in response to the combined power measurements made by the receiver 202. The receiver 202 continuously monitors the master code sequence to ensure that the user terminal 20 is synchronized with the central terminal 10 for the downlink communication path.

Figure 12 is a graph of combined power measured by receiver 202 during acquisition mode and tracking mode. The maximum value of the combined power occurs at the associated peak 219 of the combined power curve. It should be noted that peak 219 is not as well-defined as in Figure 12, and its top may be flattened out, more like a mesa. This is the point at which the receiver 202 secondary code sequence is in phase and matches the transmitter 200 primary code sequence. Measurements that result in a combined power value (which occurs off peak 219) require incremental adjustments to the slave code sequence. A fine tuning window is established between the early correlator point 221 and the late correlator point 223 . Average power measurements are made at early correlator point 221 and late correlator point 223 . Since the early correlator point 221 and the late correlator point 223 are separated by a subcode period, an error signal is generated according to the average power difference between the early correlator point 221 and the late correlator point 223, and the error signal is used to control the slave Code phase fine-tuning.

To establish the downlink communication path, after the central terminal 10 primary code sequence acquisition and initial tracking of the coded sequence signal 216 in the downlink signal 212, the receiver 202 enters a frame alignment mode. The receiver 202 analyzes the frame information within the frame information signal 218 of the downlink signal 212 to identify the beginning of the frame location for the downlink signal 212 .

Since the receiver 202 does not know at which point in the data stream of the downlink signal 212 it receives the information, in order to be able to process the information received from the transmitter 200 of the central terminal 10, the receiver 202 must seek the beginning of the frame position . Once the receiver 202 identifies the start of yet another frame position, a downlink communication path is established from the transmitter 200 of the central terminal 10 to the receiver 202 of the user terminal 20 .

Figure 13 shows the general content of the frame information signal 218. Frame information signal 218 includes additional channel 224 , first user channel 226 , second user channel 228 , and signaling channel 230 for each frame of information conveyed via downlink signal 212 . Additional channels 224 carry control signals used to establish and maintain downlink and uplink communication paths. The first user channel 226 is used to communicate traffic information to the first user 208 . The second user channel 228 is used to deliver traffic information to the second user 210 . The signaling channel 230 provides signaling information to monitor the operation of the call function of the user terminal 20 . In an information frame, the additional channel 224 occupies 16 kilobits per second, the first user channel 226 occupies 64 kilobits per second, the second user channel 228 occupies 64 kilobits per second, and the signaling channel 230 occupies 16 kilobits per second. Second.

FIG. 14 shows how additional channels 224 are inserted into the data stream of the downlink signal 212. As shown in FIG. The data stream of the downlink signal 212 is divided into twenty bit subframes. Each twenty-bit subframe has two ten-bit segments. The first ten-bit segment includes one overhead bit, one signaling bit, and eight user bits. The second ten-bit segment includes one overhead bit, one signaling bit, and eight second user bits. This twenty bit subframe format is repeated throughout the four millisecond infoframe. Thus, in the data stream of the downlink signal 212, every tenth bit position of the frame information is occupied by an additional bit.

Additional channel 224 includes an eight-byte field (frame alignment word 232 ), code synchronization signal 234 , power control signal 236 , operation and maintenance channel signals 238 , and four reserved byte fields 242 . The frame alignment word 232 identifies the origin of the frame location for its corresponding frame of information. The encoded synchronization signal 234 provides information to control the synchronization of the transmitter 204 of the user terminal 20 and the receiver 206 of the central terminal 10 . The power control signal 236 provides information to control the transmit power of the transmitter 204 of the user terminal 20 . The operation and maintenance channel signal 238 provides status information with respect to the downlink and uplink communication paths and a path from the central terminal to the subscriber terminal on which communication between the modem shelf controller and the modem shelf is performed. The communication protocol has also been expanded.

Receiver 202 of subscriber terminal 20 searches ten possible bit positions of overhead channel 224 and frame alignment word 232 in the data stream of downlink signal 212 in order to identify the beginning of two consecutive frame positions. Receiver 202 initially extracts the first bit position for each ten-bit segment of frame information to determine whether additional channel 224 has been captured. If the frame alignment word 232 has not been recognized after a predetermined time interval from the extraction of the first bit position, the receiver 202 will repeat this process for the second bit position and subsequent bit positions of each ten-bit segment until the frame alignment word 232 is identified. Out frame alignment word 232. An example of a frame alignment word 232 that the receiver 202 looks for is 00010111 in binary. Once the correct bit position produces the frame alignment word 232, the receiver 202 wants to identify the beginning of two consecutive frame positions. Once the beginning of two consecutive frame positions has been successfully identified in response to the identification of successive frame alignment words 232 in the data stream of the downlink signal 212, a downlink communication path is established.

To identify subsequent frame alignment words 232 for subsequent information frames, the receiver 202 continuously monitors the appropriate bit positions. If the receiver 202 fails to recognize the frame alignment word 232 for three consecutive frames, the receiver will return to the search process and cycle through each bit position of the ten-bit segment until the frame alignment word 232 is identified by two consecutive frames. Word 232, two successive origins of frame positions are identified to re-establish frame alignment. Variations in the path delay between the central terminal 10 and the user terminal 20 may cause three consecutive frame alignment words 232 to be unrecognizable. After interrupting the downlink communication path from the transmitter 200 of the central terminal 10 to the receiver 202 of the user terminal 20, the receiver 202 will return to the search process.

After establishing the downlink communication path from the central terminal 10 to the subscriber terminal 20 by proper code sequence phase synchronization and frame alignment, the wireless telecommunications system 1 completes the communication from the transmitter 204 within the subscriber terminal 20 to the receiver within the central terminal 10. Step 206 of the uplink communication path. Initially, the transmitter 204 is powered down until a downlink communication path has been established to prevent the transmitter from interfering with the central terminal's communications with other user terminals. After establishing the downlink communication path, the transmit power of the transmitter 204 is set to a minimum value according to a command from the central terminal CT via the power control channel 236 of the additional channel 224 . The power control signal 236 controls the amount of transmit power generated by the transmitter 204 so that the central terminal 10 receives approximately the same value of transmit power from each user terminal 20 served by the central terminal 10 .

A power control signal 236 is transmitted by the transmitter 200 of the central terminal 10 in the supplemental channel 224 of the frame information signal 218 on the downlink signal 212 . Receiver 202 of user terminal 20 receives downlink signal 212 and extracts power control signal 236 therefrom. A power control signal 236 is provided to the transmitter 204 of the user terminal 20 and incrementally adjusts the transmit power of the transmitter 204 . The central terminal 10 continues to make incremental adjustments to the transmit power of the transmitter 204 until the transmit power falls within the desired threshold range determined by the receiver 206 . Initially, the transmit power is adjusted in a coarse mode with one decibel increments until the transmit power falls within the desired threshold range. When the transmitter 204 is turned on, the intensity of the transmission power is gradually increased by incremental adjustment, so as to prevent the communication between the central terminal and other user terminals from being interfered.

An example decoding scheme for the power control signal 236 is shown in FIG. 15 . After the transmit power of the transmitter 204 in the user terminal 20 reaches the desired threshold range, the receiver 206 in the central terminal 10 responds to any changes in power fluctuations obtained and changes in the path delay between the central terminal 10 and the user terminal 20, etc. The amount of transmit power from transmitter 204 continues to be monitored. If the transmit power falls below or exceeds the desired threshold range, the central terminal 10 will transmit appropriate control signals 236 to increase or decrease the transmit power of the transmitter 204 as desired. At this point, adjustments can be made in fine mode with 0.1 dB increments to return the transmit power to the desired threshold range. In the event of a downlink or uplink communication path interruption, the central terminal 10 can command the transmitter 204 to return to the previous transmit power value by restoring the parameters stored in the memory of the user terminal 20, so as to re-establish the appropriate communication path.

In order to fully establish the uplink communication path from the subscriber terminal 20 to the central terminal 10, the transmitter 204 in the subscriber terminal 20 should be synchronized with the receiver 206 in the central terminal 10. Central terminal 10 controls the synchronization of transmitter 204 via code synchronization signal 234 in overhead channel 224 of frame information signal 218 . The code synchronization signal 234 incrementally adjusts the phase of the transmitter 204 slave code sequence to match the phase of the receiver 206 master code sequence. Synchronization of the transmitter 204 is performed in substantially the same manner as synchronization of the receiver 202 .

On downlink signal 212 , transmitter 200 of central terminal 10 transmits code synchronization signal 234 on additional channel 224 of frame information signal 218 . Receiver 202 of subscriber terminal 20 receives downlink signal 212 and extracts code synchronization signal 234 therefrom. A code synchronization signal 234 is provided to the transmitter 204 to incrementally adjust the phase of the transmitter 204 slave code sequence. Central terminal 10 continues to make incremental adjustments to the phase of transmitter 204's secondary code sequence until receiver 206 confirms a code and phase match between transmitter 204's secondary code sequence and central terminal 10's primary code sequence.

Receiver 206 performs the same power measurement technique for synchronization of transmitter 204 as synchronization of receiver 202 in determining phase and code match. Initially, the phase of the secondary code sequence of the transmitter 204 is adjusted in a coarse mode with subcode rate increments of one-half until the receiver 206 confirms that the combined power of the primary code sequence and the secondary code sequence of the transmitter 204 maximum power position.

FIG. 16 shows an example decoding scheme for the code synchronization signal 234 . After identifying and verifying the phase and code match of the slave code sequence with the master code sequence, the receiver 206 proceeds The uplink signal is monitored 214 . If further adjustments to the phase of the secondary code sequence of the transmitter 204 are required, the central terminal 10 will transmit an appropriate code synchronization signal 234 to increase or decrease the phase of the secondary code sequence of the transmitter 204 as required. At this point, the phase of the transmitter 204's slave code sequence may be adjusted in a fine-tuning mode with subcode rate increments of one sixteenth. After a downlink or uplink interruption, the central terminal 10 can command the transmitter 204 to return to the previous slave code sequence phase value by restoring the parameters stored in the memory of the user terminal 20, so as to re-establish the appropriate communication path.

After synchronization of transmitter 204 is achieved, receiver 206 frames uplink signal 214 in the same manner as receiver 202 frames uplink signal 214 during establishment of the downlink communication path. Once the receiver 206 acknowledges two consecutive frame alignment words and obtains frame alignment, the uplink communication path has been established. When both the downlink communication path and the uplink communication path are established, the transfer of information between the first user 208 or the second user 210 of the user terminal 20 and the user coupled to the central terminal 10 may begin.

The wireless telecommunication system 1 can adjust the transmit power level and transmit rate to one of two settings for three different modes of system operation. The system operating modes are Capture, Stand and Talk. Adjustments to transmit power and transmit rate allow to reduce and minimize interference with other user terminals. Improvements in link setup time are also achieved. The transmit power value is decoded into a power control signal 236 and the transmit rate is decoded into a code synchronization signal 234 .

The transmit power for downlink signal 212 and uplink signal 214 may be set to a nominal high power value of 0 decibels or a reduced low power value of -12 decibels. The transmission rate of the downlink signal 212 and the uplink signal 214 can be set to a low rate of 10 kbits per second or a high rate of 160 kbits per second. When switching to the high rate of 160 kilobits per second, the user expands the traffic and additional information so that one information symbol can result in the transmission of 16 subcodes. The 16 subcodes are correlated, resulting in a processing gain of 12 dB. When switching to a low rate of 10 kilobits per second, only the additional information is extended, so that one additional symbol results in 256 subcodes being transmitted. The 256 subcodes are correlated, resulting in a processing gain of 24 dB.

Figure 17 shows the transmit power and transmit rate for the three system operating modes. The wireless telecommunications system 1 enters an acquisition mode upon power up or whenever a downlink or uplink communication path is lost. In acquisition mode, the downlink and uplink transmitter transmit power and correlator processing gain are maximized. This maximizes the signal-to-noise ratio at the output of the correlator, thereby increasing the magnitude of the correlation peak 219 for better identification and reducing the risk of false capture. Since only additional information is required in the acquisition mode, the transmission rate is at a low rate value of 10 kbits per second.

The wireless telecommunication system 1 enters a standby mode when downlink and uplink communication paths are acquired. In standby mode, the transmit power of the downlink and uplink transmitters is reduced by 12 dB. The reduction in transmit power reduces interference to other user terminals while still maintaining synchronization. Keeping the transmission rate at a low rate value allows control information to be exchanged between the central terminal 10 and the user terminals 20 on the additional channel 224 .

When an incoming or outgoing call is detected, a message is transmitted from the originating terminal to the destination terminal indicating the downlink and uplink communication paths required for transmitting subscriber call information. At this point, the wireless telecommunication system 1 enters a talk mode. In talk mode, the transmit power of both downlink and uplink communication paths is increased to a high power value and its transmit rate is also increased to a high rate value of 160 kilobits per second to facilitate information transfer between originating and destination terminals . Upon detection of call termination, a message is transmitted from the terminating terminal to the other terminals indicating that the downlink and uplink communication paths are no longer required. At this point, the wireless telecommunication system 1 re-enters the standby mode. Code synchronization and frame alignment tracking are performed in both standby mode and talk mode.

FIG. 18 is a detailed block diagram of the receiver 202 and transmitter 204 within the user terminal 20. Referring to FIG. Receiver 202 receives downlink signal 212 at RF receive interface 250 . The RF receive interface 250 separates the spread spectrum signal into I and Q signal components. The RF receive interface 250 bandpass filters each of the I and Q signal components by removing portions exceeding approximately half the bandwidth of the receiver 202 (3.5 MHz). The RF receive interface 250 low-pass filters the I and Q signal components to block image frequencies and prevent signal aliasing. The I and Q signal components are placed into digital format by an analog-to-digital converter 252 . The sampling frequency of the analog-to-digital converter 252 is four times the subcode period or 10.24 MHz, which has an eight-bit resolution.

The digital I and Q signal components are down-converted 254 to a rate of 5.12 MHz. Code generator and despreader 256 performs the synchronization acquisition and tracking functions described above to synchronize the phase of the Rademacher-Walsh and pseudorandom noise code sequences of receiver 202 to the phase of downlink signal 212 . Digital signal processor 258 controls the phase of the slave code sequence via code tracker 260 and carrier tracker 262 . The automatic gain control unit 264 generates an automatic gain control signal to control the gain of the RF receiving interface 250 . Code generator and despreader 256 generates 160 kilobytes per second of I and Q frame information for further synchronization by node synchronization interface 266 under control of node synchronization logic unit 268 . The node synchronization interface 266, through the node synchronization logic unit 268, determines whether the I and Q channels are to be swapped since they can be received in four different ways.

Viterbi decoder 270 provides forward error correction for the I and Q channels and produces an error corrected 160 kBps data signal after a 71 symbol delay. Error correction signals are processed by a frame locator, and an extractor 272 determines frame alignment and extracts power control signals 236, code synchronization 234, and operating and holding channel signals 238. The frame locator and extractor 272 also extracts the first user channel 226 and the second user channel 228 for call transmissions to the first user 208 and the second user 210, and is processed by the high-level data link controller 274 and microcontroller 276 The signaling channel 230. Frame locator and extractor 272 also provides alarms and error indications upon detection of frame locating failures. To facilitate link re-establishment in the event of a link loss, non-volatile random access memory 278 stores system parameter information for subsequent insertion by arbiter 180 . Arbiter 280 also provides an interface between digital signal processor 258 and microcontroller 276 .

Along the transmit direction, frame inserter 282 receives first user traffic and second user traffic from first user 208 and second user 210, signaling channel 230 information from advanced data link controller 274, and from microcontroller 276 operates and maintains channel 238 information. The frame interpolator generates a frame information signal 218 for the uplink signal 214 processed by the convolutional encoder 284 . Convolutional encoder 284 doubles the data rate of frame information signal 218 to provide forward error correction. Spreader 286 splits the 320 kbit/s convolutional encoder signal into two 160 kbit/s I and Q signals and is responsive to the system clock generated by clock generator 290 conditioned by code sync signal 234, A spreading sequence generated by code generator 288 XORs these I and Q signals. Code generator 288 generates one of sixteen Rademacher-Walsh functions that are XORed with a pseudo-random sequence of pattern length 256 and a subcode rate of 2.56 MHz. The pseudo-random sequence should match the central terminal 10, but the sequence can be adjusted under software control to reliably block signals from other frequency bands or other cells.

Expander 286 provides the I and Q signals to analog transmitter 290 . Analog transmitter 290 generates pulsed I and Q signals to RF transmit interface 292 . In response to the power control signal 236 extracted from the supplemental channel 224, transmit power is generated by first establishing a control voltage by a digital-to-analog converter. This control voltage is applied to the power control input of the analog transmitter 290 and the RF transmit interface 292 . 35 dB of power control is available in both the analog transmitter 290 and the RF transmit interface 292 . The RF transmit interface 292 includes stepped attenuators that provide 2 decibel attenuation steps in the 30 decibel range. This attenuator is used to switch between high and low power values. At power-up, maximum attenuation is selected to minimize transmitter 204 transmit power.

Thus, it will be apparent that according to the present invention there is provided an arrangement and a method for synchronizing transmitters within a user terminal of a wireless telecommunication system such that the above mentioned advantages are met. Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations could be made herein. For example, although downlink and uplink signals have been described with particular formats and rates, other formats and rates are implemented to provide similar transmission status, control and information. Thus, although particular embodiments have been described herein, it should be understood that the invention is not limited thereto and many modifications, additions and deletions may be made within the scope of the invention.

Claims (25)

1. one kind makes the synchronous method of transmitter in the radio telecommunications system user terminal, it is characterized in that may further comprise the steps:

The Down-Link Communications path of foundation from the central terminal to the user terminal;

Transmitter transmitting downstream line signal in the central terminal;

Receiver place in user terminal receives down link signal;

Code synchronization signal in the identification down link signal;

Regulate the phase place of transmitter in the user terminal in response to code synchronization signal;

Phase place in response to transmitter in the user terminal equates with the phase place of central terminal inner receiver, sets up the uplink communication path.

2. the method for claim 1 is characterized in that described code synchronization signal regulates the phase place of transmitter in the user terminal with the coarse mode with subcode cycles 1/2nd increment.

3. method as claimed in claim 2 is characterized in that the phase place of described code synchronization signal transmitter in regulating user terminal with 1/2nd increment forward directions or back.

4. the method for claim 1 is characterized in that further comprising the steps of:

Transmitter in user terminal is launched uplink signal;

Receiver place in central terminal receives uplink signal;

The phase place of uplink signal is compared with the phase place of central terminal inner receiver;

In response to central terminal in the unmatched uplink signal of phase place that receives and launch code synchronization signal, the value representation of described code synchronization signal will further be regulated the phase place of transmitter in the user terminal.

5. method as claimed in claim 4, it is characterized in that described comparison step comprise the combined power of the phase place of measuring uplink signal and central terminal inner receiver phase place and determine the phase place of expression uplink signal and the phase place of central terminal inner receiver between the greatest combined performance number of mating.

6. method as claimed in claim 5, the step that it is characterized in that measuring combined power are included between the PN code of uplink signal and the receiver reference signal carries out associative operation.

7. method as claimed in claim 5 is characterized in that further comprising the steps of:

The receiver place reception in central terminal and the uplink signal of the receiver homophase in the central terminal, receive and the uplink signal of the phase matched of central terminal inner receiver represents to determine phase delay between user terminal transmitter and the central terminal inner receiver, the uplink communication path from the user terminal to the central terminal has been set up in definite expression of phase delay; And

The emission code synchronization signal, the value representation of described code synchronization signal does not need further to regulate the phase place of transmitter in the user terminal.

8. method as claimed in claim 7 is characterized in that further comprising the steps of:

Continuously relatively from the phase place of the uplink signal of user terminal transmitter and the phase place of central terminal inner receiver;

The emission code synchronization signal, the value representation of described code synchronization signal will change in response to the path delay between transmitter in the user terminal and the central terminal inner receiver, and the transmitter phase in the user terminal is carried out slight readjusting.

9. method as claimed in claim 8, it is characterized in that described code synchronization signal in response to changing the path delay between transmitter in the user terminal and the central terminal inner receiver, regulates the phase place of transmitter in the user terminal with the fine tuning pattern with subcode cycles ten sixth increment.

10. method as claimed in claim 9 is characterized in that the phase place of code synchronization signal with increment forward direction or the back transmitter in regulating subscriber unit of ten sixths.

11. the method for claim 1 is characterized in that further comprising the steps of:

The uplink communication path of monitoring from the user terminal to the central terminal;

For the ease of rebuliding the uplink communication path,, the phase place of transmitter in the user terminal is reset to previous value in response to the interruption in the uplink communication path.

12. the method for claim 1 is characterized in that the additional channel of described code synchronization signal decoding becoming down link signal.

13. method as claimed in claim 12 is characterized in that overhead channel decoding becoming bit in per ten bit positions in the down link signal.

14. a system that makes the communication synchronization in the radio telecommunications system is characterized in that comprising:

The transmitter that is used for the transmitting downstream line signal in the central terminal, described down link signal comprises code synchronization signal;

Be used to receive the receiver of described down link signal in the user terminal, the receiver in the user terminal is used for extracting code synchronization signal from down link signal;

Be used to launch the transmitter of uplink signal in the user terminal, the transmitter in the user terminal is used to receive the code synchronization signal from the user terminal inner receiver, and code synchronization signal is used to regulate the phase place of uplink signal;

Be used to receive the receiver of uplink signal in the central terminal, receiver in the user terminal is used for its receiver phase is compared with the phase place of uplink signal, whether to mate between the phase place of determining receiver phase and uplink signal, receiver in the user terminal is used to set the value of code synchronization signal, so that the phase place of uplink signal and receiver phase are complementary.

15. system as claimed in claim 14 is characterized in that the additional channel of described code synchronization signal decoding becoming down link signal.

16. system as claimed in claim 15 is characterized in that overhead channel decoding is become a bit in per ten bit positions of down link signal.

17. system as claimed in claim 14 is characterized in that code synchronization signal carries out forward direction or back to incremental adjustments with the coarse mode with subcode cycles 1/2nd increment to the phase place of uplink signal.

18. system as claimed in claim 14, it is characterized in that the receiver in the central terminal compares the phase place of uplink signal and receiver phase continuously, receiver changes code synchronization signal in response to comparative result, with the phase place of maintenance uplink signal and the coupling between the receiver phase.

19. system as claimed in claim 18 is characterized in that code synchronization signal carries out forward direction or back to incremental adjustments with the fine tuning pattern with subcode cycles ten sixth to the phase place of uplink signal.

20. system as claimed in claim 14, the receiver that it is characterized in that central terminal is measured the phase place of uplink signal and the combined power of central terminal inner receiver phase place, receiver in the central terminal is determined the greatest combined performance number, and the phase place of the phase place of this value representation uplink signal and central terminal inner receiver is complementary.

21. a kind of user terminal in the radio telecommunications system is characterized in that comprising:

Be used to receive the receiver of down link signal, described down link signal comprises code synchronization signal, and described receiver is used for extracting code synchronization signal from down link signal;

Be used to launch the transmitter of uplink signal, described transmitter is used to receive code synchronization signal, and described code synchronization signal is used to regulate the phase place of uplink signal.

22. user terminal as claimed in claim 21 is characterized in that the additional channel of described code synchronization signal decoding becoming down link signal.

23. the system as claimed in claim 22 is characterized in that additional channel decoding is become a bit in per ten bit positions of down link signal.

24. system as claimed in claim 21 is characterized in that code synchronization signal carries out forward direction or back to incremental adjustments with the coarse mode with subcode cycles 1/2nd increment to the phase place of uplink signal.

25. system as claimed in claim 21 is characterized in that code synchronization signal carries out forward direction or back to incremental adjustments with the fine tuning pattern with subcode cycles ten sixth to the phase place of uplink signal.

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