KR20000022540A - Method of controlling initial power ramp-up in cdma systems by using short codes - Google Patents

Abstract

PURPOSE: A method of controlling initial power ramp-up is provided to control transmission power during the establishment between CDMA subscriber units and stationary in CDMA system by using short codes. CONSTITUTION: A system and method of controlling transmission power during the establishment of a channel in a CDMA communication system utilize the transmission of a short code from a subscriber unit to a base station during initial power ramp-up. The subscriber unit quickly increases transmission power while repeatedly transmitting the short code until the signal is detected by the base station. The short code is a sequence for detection by the base station which has a much shorter period than a conventional spreading code. The use of short codes limits power overshoot and interference to other subscriber stations and permits the base station to quickly synchronize to the spreading code used by the subscriber unit. The ramp-up starts from a power level that is guaranteed to be lower than the required power level for detection by the base station. Once the base station detects the short code, it sends an indication to the subscriber unit to cease increasing transmission power.

Description

How to control initial power ramp-up in a CDM system using short codes

The use of wireless communication systems has grown significantly over the last decade as system reliability and capacity have improved. Wireless Communication Systems Terrestrial telecommunications systems have been used in a variety of applications that are either impractical or useable. Applications of such wireless communications include cellular phone communications, remote location communications, and temporary communications for disaster recovery. Wireless communication systems are economically valuable as replacements for old telephone lines and old telephone equipment.

The portion of the RF spectrum that can be used by the wireless communication system is an important resource. The RF spectrum must be shared by all commercial, governmental and military use. In order to increase system capacity, there has been a continuous demand for improving the efficiency of wireless communication systems.

Code Division Multiple Access (CDMA) wireless communication systems have shown particular improvements in this area. Although more traditional time division multiple access (TDMA) and frequency division multiple access (FDMA) systems have been improved using recent advances in technology, CDMA systems, particularly broadband code division multiple access (B-CDMA) systems, It has a clear advantage in comparison. This efficiency is due to improved coding and modulation density, interference rejection and multipath tolerance in B-CDMA systems, and the same spectral reuse in all communication cells. The format of the CDMA communication signal also makes it particularly difficult to intercept calls, thereby ensuring greater privacy for the caller and providing greater immunity to the fake.

In a CDMA system the same part of the frequency spectrum is used for communication by all subscribers. The base station data signal of each subscriber is multiplied by a code sequence called " spreading code " which has a much higher rate than the data. The spreading code ratio ratio to data symbol ratio is called " spreading factor " or " process gain ". Such coding results in a transmission spectrum that is much wider than the spectrum of the base station data signal, so this technique is called the "spread spectrum". The subscriber unit and their communication can be distinguished by assigning a unique spreading code to each communication link called a CDMA channel. Since all communications are transmitted on the same frequency band, each of the CDMA communications overlaps with communications from other subscriber units and noise-related signals in both frequency and time.

Using the same frequency spectrum by multiple subscriber units increases the efficiency of the system. However, as the number of users increases, it can cause a gradual decrease in system performance. Each subscriber unit detects a communication signal with a unique spreading code as a valid signal and all other signals are considered to be noise. The stronger the signal from the subscriber unit arrives at the base station, the greater the base station experiences interference when receiving and demodulating the signal from another subscriber unit. Ultimately, the power from one subscriber unit may be large enough to terminate the communication of the other subscriber unit. Therefore, it is extremely important to control the transmission power of all subscriber units in a wireless CDMA communication system. This can best be achieved by using a closed loop power control algorithm once the communication link is established.

Control of the transmit power is particularly important when a subscriber's unit starts communicating with the base station and when the power control loop has not yet been established. The transmit power required from the subscriber unit is continuously changed as a function of propagation loss, interference from other subscribers, channel noise, fading and other channel characteristics. Thus the subscriber unit does not know the power level at which it should start transmitting. If the subscriber unit starts transmitting at too high a power level, this may interfere with the communication of other subscriber units and may even terminate other subscriber unit communications. If the initial transmit power level is too low, the subscriber unit may not be detected by the base station and the communication link may not be established.

There are many ways to control transmit power in a CDMA communication system. For example, US Pat. No. 5,056,109 (Gilhousen et al.) Discloses a transmission power control system in which the transmission power of the subscriber unit is based on periodic signal measurements from both subscriber units and the base station. The base station transmits the pilot signal to all subscriber units analyzing the received pilot signal and evaluates the power loss in the transmitted signal and adjusts it accordingly. Each subscriber unit includes a nonlinear lossy output filter that prevents a sudden increase in power causing interference to other subscriber units. This method is so complex that it is not possible for the base station to acquire one subscriber unit quickly while excluding interference to other subscriber units. Also, the propagation loss, interference, and noise levels experienced on the forward link (transmission from base station to subscriber unit) are not the same as in reverse link (transmission from subscriber unit to base station). Reverse link power estimation based on forward link loss is not accurate.

Many other kinds of known transmission power control systems require the provision of complex control signals to control the transmission power between a communication unit or preselected transmission values. These power control techniques are inflexible and impractical to implement.

EP 0 565 507 A2 also discloses a system for minimizing interference between two wireless stations at the start of wireless communication. A mobile station initiates a low level access signal and gradually increases the transmit power level until the base station detects the signal. Once detected, the power level of the message remains at the detected level to avoid signal interference. EP 0 565 507 A2 also discloses a method for synchronizing random access communication despite the change in distance between them between the mobile station and the base station.

Thus, there is a need for an efficient method for controlling the initial ramp-up of transmit power by subscriber units in a wireless CDMA communication system.

The present invention relates to a CDMA communication system. In particular, the present invention is directed to a CDMA communication system that uses a short code transfer from a subscriber to a base station to reduce the time required at the base station to detect a signal from the subscriber. In this way, the improved detection time allows for faster ramp-up of the subscriber's initial transmit power while reducing unnecessary power overhead.

1 is a schematic diagram of a code division multiple access communication system in accordance with the present invention;

2 shows the operating range of a base station;

3 is a communication signal timing diagram between a base station and a subscriber unit.

4 is a flowchart for establishing a communication channel between a base station and a subscriber unit.

5 is a graph of transmit power output from a subscriber unit.

6A and 6B are flowcharts for establishing a communication channel between a base station and a subscriber unit according to a preferred embodiment of the present invention using a short code.

7 shows a graph of communication power output from a subscriber unit using a short code.

8 illustrates adaptive selection of short codes.

9 is a block diagram of a base station in accordance with the present invention.

10 is a block diagram of a subscriber unit in accordance with the present invention.

11A and 11B are flow charts of a ramp-up process implemented in accordance with the present invention.

12 is a diagram illustrating signal propagation between a base station and a plurality of subscriber units.

13 is a flow diagram of a preferred implementation of communication channel initialization between a subscriber unit and a base station using slow initial learning.

14 is a flow diagram of a preferred embodiment for resetting a communication channel between a base station and a subscriber unit using fast reacquisition.

15A is a diagram of communication between a base station and multiple subscriber units.

15B is a diagram of the base station and subscriber unit to be finally located;

16 is a schematic diagram of a plurality of subscriber units.

17 illustrates a subscriber unit made in accordance with the teachings of the present invention.

18 is a flow diagram of an optional embodiment for initializing a communication channel between a base station and a subscriber unit using slow initial learning.

19 is a flow diagram of an alternative embodiment of a communication channel reset between a base station and a subscriber unit using fast reacquisition.

20 is a flow chart of a second optional embodiment initializing a communication channel between a base station and a subscriber unit using slow initial learning.

The present invention includes a novel method of controlling the transmit power during channel establishment in a CDMA communication system by using a short code transfer from a subscriber unit to a base station during initial power ramp-up. The short code is one sequence for detection by the base station with a much shorter period than the conventional spreading code. The ramp-up starts from a power level as long as it is guaranteed by the base station to be below the required power level for detection. The subscriber unit rapidly increases the transmit power while repeatedly transmitting short codes until a signal is detected by the base station. Once the base station detects a short code, it sends an indication to the subscriber unit to stop increasing the transmit power. The use of short codes limits power overshoot, limits interference to other subscriber stations and allows the base station to quickly synchronize to the spreading code used by the subscriber unit.

It is therefore an object of the present invention to provide an improved technique for controlling power ramp-up during communication channel establishment between a CDMA subscriber unit and a base station.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the following description is given with reference to the drawings.

A communication network 10 using the present invention is shown in FIG. The communication network 10 consists of one or more base stations 14, each of which is in wireless communication with a plurality of subscriber units 16, fixed or mobile. Each of the subscriber units 16 communicates with either the nearest base station 14 or the base station 14 which provides the strongest communication signal. The base station 14 also communicates with a base station controller 20 that coordinates communication among the base stations 14. The communication network may also be connected to a public switched telephone network (PSTN) 22, which is also responsible for coordinating communication between the base station 14 and the PSTN 22. Each base station 14 preferably communicates with the base station controller 20 via a radio link, although a landline may be provided. The land line is particularly applicable when the base station 14 is in close proximity to the base station controller 20.

The base station controller 20 performs several functions. Firstly, the base station controller 20 is responsible for generating management and maintenance (OA & M) signals associated with establishing and maintaining all wireless communications between the subscriber unit 16, the base station 14, and the base station controller 20. Provides all the same behavior. The base station controller 20 also provides an interface between the wireless communication system 10 and the PSTN 22. Such an interface includes multiplexing and demultiplexing of communication signals entering and exiting system 10 through base station controller 20. Although a wireless communication system is shown using an antenna to transmit an RF signal, one of ordinary skill in the art will recognize that communication may be achieved through a microwave or satellite connection. In addition, the function of the base station controller 20 may be combined with the base station 14 to form a “master base station”.

In FIG. 2 the signal propagation between the base station 14 and the multiple subscriber units 16 is shown. The bidirectional communication channel (link) 18 is a signal 20 (Tx) transmitted from the base station 14 to the subscriber unit 16 and a signal 22 received by the base station 14 from the subscriber unit 16. (Rx). The Tx signal 20 is transmitted from the base station 14 and received by the subscriber unit 16 after propagation delay Δt. Similarly, Rx 22 signal is generated at subscriber unit 16 and another propagation delay Δt ends at base station 14 after t. Thus, the reciprocating trip propagation delay is 2Δt. In a preferred embodiment the base station 14 has an operating range of about 30 km. The reciprocating trip propagation delay 24 associated with the subscriber unit 16 in the maximum operating range is 200 microseconds.

The communication channel establishment between the base station and the subscriber unit is a complex procedure involving many tasks performed by the base station 14 and the subscriber unit 16 outside the scope of the present invention. The present invention is directed to initial power ramp-up and synchronization in setting up a communication channel.

In Figure 3 the signaling between the base station 14 and the subscriber unit 16 is shown. In accordance with the present invention, the base station 14 continues to transmit the pilot code 40 to all subscriber units 16 located within the transmission range of the base station 14. The pilot code 40 is a spreading code without any data bits. The pilot code 40 is used for subscriber unit 16 acquisition and synchronization and to determine the parameters of the adaptive match filter used at the receiver.

The subscriber unit 16 must obtain the pilot code 40 sent by the base station 14 before it receives or transmits any data. Acquisition refers to a process in which subscriber unit 16 aligns a locally generated spreading code with the received pilot code 40. The subscriber unit 16 examines all possible states of the received pilot code 40 until it detects the correct state (start of pilot code 40).

Subscriber unit 16 then synchronizes its transmit spreading code to the received pilot code 40 by aligning the beginning of its transmit spreading code with the beginning of the pilot code 40. The implied meaning of receive and transmit synchronization means that the subscriber unit 16 does not incur any additional delay as long as the spreading code state is related. Thus, as shown in FIG. 3, the relative delay between the pilot code 40 transmitted from the base station 14 and the transmission spreading code 42 of the subscriber unit received at the base station 14 is 2Δt, This is only due to the above reciprocating trip propagation delay.

In a preferred embodiment, the pilot code is 29,877,120 chips long and takes about 2 to 5 seconds to transmit depending on the spreading factor. The length of the pilot code 40 is chosen to be a plurality of data symbols no matter what kind of data rate or bandwidth is used. As will be appreciated by those skilled in the art, the longer pilot code 40 has better randomness characteristics and the frequency response of the pilot code 40 becomes more identical. Longer pilot code 40 also provides low channel cross correlation, thus increasing the capacity of system 10 to support more subscriber units 16 with less interference. The use of long pilot code 40 also supports a larger number of arbitrary short codes. For synchronization purposes the pilot code 40 is chosen to have the same period as all other spreading codes used by the system 10. Thus once subscriber unit 16 obtains pilot code 40 it is synchronized to all other signals transmitted from base station 14.

The subscriber unit 16 remains synchronized to the base station 14 by periodically reacquiring the pilot code 40 when no call is in progress during the idle period. This is necessary for the subscriber unit 16 to receive and demodulate a paging message indicating any downlink transmission, in particular an incoming call.

When a communication link is needed, the base station 14 must acquire the signal transmitted from the subscriber unit 16 before it can demodulate the data. The subscriber unit 16 must transmit an uplink signal for acquisition by the base station 14 to begin establishing a bidirectional communication link. One important parameter in this process is the transmit power level of the subscriber unit 16. Too high a transmission power level may damage communication in the entire service area, and a too low transmission power level may prevent the base station 14 from detecting an overlink signal.

In the first embodiment of the present invention, the subscriber unit 16 starts transmitting at a power level that is guaranteed to be lower than necessary and increases the transmit power output until the correct power level is achieved. This avoids the sudden occurrence of strong interference and thus improves the capacity of the system 10.

The establishment of a communication channel and the work performed by the base station 14 and the subscriber unit 16 according to the invention is shown in FIG. Although many subscriber units 16 may be located within the operating range of the base station 14, a single subscriber unit is referred to for simplicity in describing the operation of the present invention.

The base station 14 continues to transmit one periodic pilot code 40 to all subscriber units 16 located within the operating range of the base station 14 (step 100). When the base station 14 transmits the pilot code 40 (step 100), the base station 14 examines one " access code " sent by one subscriber unit 16 (step 101). . The access code 42 is a known spreading code sent from one subscriber unit 16 to the base station 14 during the start of communication and power ramp-up. The base station 14 must examine all possible states (time shifts) of the access code 42 sent from the subscriber unit 16 to find the correct state. This is called "acquisition" or "detection" processing (step 101). The longer the access code 42 is, the longer it takes for the base station 14 to examine the state and obtain the correct state.

As described above, the relative delay between the signal transmitted from the base station 14 and the signal received at the base station 14 corresponds to a round trip trip propagation delay 2Δt. The maximum delay occurs in the maximum operating range of the base station 14, known as cell boundary. The base station 14 must examine many code states in the maximum reciprocating trip propagation delay and the number is less than the code states present in one code period.

For data rate Rb and spreading code rate Rc, the ratio L = Rc / Rb is called spreading factor or process gain. In a preferred embodiment of the present invention, the cell boundary radius is 30 km, which corresponds to between 1000 and 2500 code states at the maximum round trip delay in accordance with the processing gain.

If the base station 14 does not detect the access code after examining the code state corresponding to the maximum round trip delay, the search is repeated starting from the state of the pilot code 40 corresponding to zero delay ( Step 102).

During the idle period, the pilot code 40 from the base station 14 is received at the subscriber unit 16 which periodically synchronizes its transmit spreading code generator (step 103). If synchronization with the pilot code 40 is lost, the subscriber unit 16 reacquires the pilot code 40 and synchronizes again (step 104).

When it is necessary to start the communication link, the subscriber unit 16 starts transmitting the access code 42 back to the base station 14 (step 106). The subscriber unit 16 retransmits the access code 42 until it receives a confirmation from the base station 14 (step 108) while continuing to increase the transmit power. The base station 14 detects the access code 42 in the correct state once the minimum power level for reception is achieved (step 110). The base station 14 subsequently transmits one access code detection acknowledgment signal to the subscriber unit 16 subsequently (step 112). Upon receiving the confirmation, the subscriber unit stops increasing the transmit power (step 114). When the power ramp-up is complete, closed loop power control and call setup signaling is performed to establish the bidirectional communication link (step 116).

Although this embodiment limits the subscriber unit 16 transmission power, in this way the acquisition of the subscriber unit 16 by the base station 14 will create unnecessary power overshoot from the subscriber unit 16 and thus This reduces the performance of the system 10.

The transmit power output profile of the subscriber unit 16 is shown in FIG. 5. At t0 the subscriber unit 16 starts transmitting at the starting transmit power level P ₀ , which is a power level that is guaranteed to be less than the power level required for detection by the base station 14. The subscriber unit 16 continues to increase the transmit power level until it receives a detection indication from the base station 14. In order for the base station 14 to properly detect the access code 42 from the subscriber unit 16, the access code 42 must be 1) received at a sufficient power level and 2) detected in an appropriate state. . Thus, in FIG. 5, the access code 42 is at a sufficient power level for detection by the base station 14 at t _P , but the base station 14 shows the correct state of the access code 42 generated at t _A. You have to keep looking.

The subscriber unit 16 continues to increase the output transmit power level until receiving a detection indication from the base station 14 so that the transmit power of the access code 42 is for detection by the base station 14. Exceed the required power level. This causes unnecessary interference to all other subscriber units 16. If the power overshoot is too large, interference to other subscriber units 16 may be so severe as to terminate the ongoing communication of other subscriber units 16.

The rate at which the subscriber unit 16 increases the transmit power to avoid overshoot can be reduced, but this will further lengthen the call setup time. One of ordinary skill in the art will understand that such an adaptive ramp-up ratio can be used but these ratios have disadvantages and will not completely eliminate power overshoot in all situations.

The preferred embodiment of the present invention uses a "short cord" and a two stage communication link installation to achieve fast power ramp-up without significant power overshoot. The spreading code sent by the subscriber unit 16 is much shorter than the rest of the spreading code (thus a short duration code) and the number of states is limited and the base station 14 can quickly find the code. have. The short code used for this purpose has no data.

The operations performed by the base station 14 and the subscriber unit 16 to establish a communication channel using a short code in accordance with a preferred embodiment of the present invention are shown in FIGS. 6A and 6B. During the idle period, the base station 14 periodically and continuously transmits the pilot code to all subscriber units 16 located within the operating range of the base station 14 (step 150). The base station 14 also continues to find the short code sent by the subscriber unit 16 (step 152). The subscriber unit 16 obtains a pilot code and synchronizes its transport spreading code generator to the pilot code. The subscriber unit 16 also periodically checks to see if it is synchronized. If synchronization is lost, the subscriber unit 16 reacquires the pilot signal sent by the base station (step 156).

When a communication link is required, the subscriber unit 16 starts transmitting a short code at the minimum power level P0 (step 158) and confirms that the short code has been detected by the base station 14 by the base station ( Resend the short code until it receives from 14) and continue to increase the transmit power level (step 160).

In the preferred embodiment, as described above, the access code is about 30 million chips long. But short code is much smaller. The short code can be chosen to be any length short enough to allow fast detection. There is one advantage to choosing a short code length that divides the access code cycle evenly. In the case of the access code described herein, the short code is preferably chosen such that its length is 32, 64 or 128 chips. Optionally, the short code may be as short as one symbol length as described in detail below.

Since the beginning of the short code and the beginning of the access code are synchronized, the base station 14 only needs to obtain the short code, so that the base station 14 has a corresponding state of the access code. Is an integer product of N chips, where N is the length of the short code. Thus, the base station 14 does not need to investigate all possible conditions corresponding to the maximum reciprocating trip propagation delay.

Using the short code, the calibration for detection by the base station 14 takes place much more frequently. The short code is detected quickly (step 162) when the maximum power level for reception is achieved and the transmit power overshoot is limited. The transmit power ramp-up ratio can be greatly increased without worrying about large power overshoot. In a preferred embodiment of the invention the power ramp-up ratio using the short cord is 1 dB per millisecond.

As soon as the base station 14 receives such an indication, it subsequently transmits a short code detection indication signal to the subscriber unit entering the second stage of the power ramp-up (step 164). In this step, the subscriber unit 16 stops transmitting the short code (step 166) and continues to transmit the periodic access code (step 166). The subscriber unit 16 continues to ramp up the transmit power while transmitting the access code. However, the ramp-up ratio is much slower than the previous ramp-up ratio used with the short cord (step 168). The ramp-up ratio with the access code is preferably 0.05 dB per millisecond. The slow ramp-up does not cause the base station 14 to lose synchronization with the small change in the channel propagation characteristics.

At this time the base station 14 has detected the short code at the appropriate state and power level (step 162). The base station 14 should now be synchronized to all other spreading codes and to access codes that are the same length as the spreading codes much longer than the short codes. Using the short code, the base station 14 can detect the proper state of the access code much faster. The base station 14 begins to check the access code proper state (step 170). However, since the start of the access code is synchronized with the start of the short code, the base station 14 is only required to examine all N chips, where N is the length of the short code. In summary, the base station 14 determines the proper state of the access code by 1) detecting the short code and 2) examining all N chips of the access code from the beginning of the short code to determine the appropriate state and power level. Obtain an access code quickly.

If the proper state of the access code is not detected after examining the number of states at the maximum round trip delay, the base station 14 resumes examining the access code by examining all chips instead of all N chips (step S). 172). When the appropriate state of the access code is detected (step 174), the base station 14 sends an access code detection acknowledgment to the subscriber unit 16 that stops increasing the transmit power upon receiving such confirmation (step 178). (Step 176). When the power ramp-up is complete, closed loop power control and call setup signaling is performed (step 180) to establish the bidirectional communication link.

In Fig. 7, although the starting power level P ₀ is the same as in the known embodiment, the subscriber unit 16 can ramp up the transmit power level at a much higher rate by using a short code. The short code is detected quickly after the transmit power level exceeds the minimum detection level, thus minimizing the amount of transmit power overshoot.

The same short code can be reused by the subscriber unit 16, but in the preferred embodiment of the present invention the short code is dynamically selected and dynamically selected and updated according to the following procedure. In FIG. 8, the period of the short code is equal to one symbol length and the beginning of each period is aligned to one symbol boundary. The short code is generated from a regular length spreading code. One symbol length portion from the beginning of the spreading code is stored and used as a short code for the next three milliseconds. Every 3 milliseconds, the new symbol length portion of the spreading code replaces the old short code. Since the spreading code period is an integer product of 3 milliseconds, the same short code is repeated once for each period of the spreading code. Periodic update of the short code allows to average the interference caused by the short code in the entire spectrum.

A block diagram of the base station 14 is shown in FIG. In brief, the base station 14 is composed of a receiver section 50, a transmitter section 52 and a deplexer 54. An RF receiver receives and converts the RF signal received from the deplexer 54. The received spreading code generator 58 outputs a spreading code to both the data receiver 60 and the code detector 62. In the data receiver 60 the spreading code is correlated with the base station signal to extract the data signal sent for further processing. The base station signal is also sent to a code detector 62 that adjusts the timing of the spreading code generator 58 to establish communication channel 18 and detects an access code or short code from the subscriber unit 16. .

In the transmitter section 52 of the base station 14, the transmit spreading code generator 64 outputs the spreading code to the data transmitter 66 and the pilot code transmitter 68. The pilot code transmitter 68 continues to transmit periodic pilot codes. The data transmitter 66 transmits a short code detection indication and a short code detection indication and an access code detection confirmation after the code detector 62 detects a short code or an access code, respectively. The data transmitter also transmits other message and data signals. Signals from the data transmitter 66 and pilot code transmitter 68 are combined and up-converted by the RF transmitter 70 for transmission to the subscriber unit 16.

A block diagram of the subscriber unit is shown in FIG. In brief, the subscriber unit 16 consists of a receiver section 72, a transmitter section 74 and a deplexer 84. An RF receiver 76 receives and downconverts the RF signal received from the deplexer 84. One pilot code detector 80 correlates the spreading code with the base station signal to obtain a pilot code sent by the base station 16. In this way, the pilot code detector 80 is kept synchronized with the pilot code. The receiver spreading code generator 82 generates and outputs a spreading code to the data receiver 78 and the pilot code detector 80. The data receiver 78 correlates the spreading code with the base station signal to process the short code detection indication and the access code detection confirmation sent by the base station 16.

The transmitter section 74 consists of a spreading code generator 86 for generating and outputting a spreading code to the data transmitter 88 and a short code and access code transmitter 90. The short code and access code transmitter 90 transmits these codes at different stages of the power ramp-up process as described so far. The signal output by the data transmitter 88 and short code and access code transmitter 90 is combined and upconverted by the RF transmitter 92 for transmission to the base station 14. The timing of the receiver spreading code generator 82 is adjusted by the pilot code detector 80 through a learning process. The receiver and transmitter spreading code generators 82 and 86 are also synchronized.

A description of the ramp-up process according to the invention is summarized in FIGS. 11A and 11B. The base station 14 transmits one pilot code while examining the short code (step 200). The subscriber unit 16 acquires the pilot code sent from the base station 14 (step 202) and starts transmitting a short code starting at the minimum power level P0 that is guaranteed to be lower than the required power. And rapidly increase the transmit power (step 204). Once at base station 14 the received power level reaches the minimum level needed to detect a short code (step 206), base station 14 acquires the correct state of the short code and sends an indication of such detection. And start the investigation of the private access code (step 208). Upon receiving the detection indication, the subscriber unit 16 stops transmitting the short code and starts transmitting the access code. The subscriber unit 16 starts a slow ramp-up of transmit power while transmitting the access code. The base station 14 checks the correct state of the access code by examining only one state from each of the short code length portions of the access code. If the base station 14 examines the state of the access code up to the maximum round trip delay and detects the correct state, such an investigation is repeated by examining every state (step 214). As soon as the base station 14 detects the correct state of the access code, the base station 14 sends a confirmation to the subscriber unit 16 (step 216). The receipt of the confirmation by the subscriber unit 16 concludes the ramp-up process. One closed loop power control is set and the subscriber unit 16 continues the call setup process by sending an associated call setup message (step 218).

One optional embodiment of the present invention in resetting the communication link will be described with reference to FIG. 12. The propagation of certain signals is shown in the establishment of one communication channel 318 between the base station 314 and the multiple subscriber units 316. The forward pilot signal 320 is transmitted from the base station 314 at time t ₀ and received by one subscriber unit 316 after a certain propagation delay Δt. The subscriber unit 316 transmits the access signal 322 received by the base station 314 after Δt of another propagation delay to be obtained by the base station 314. Therefore, the reciprocating trip propagation delay is 2Δt. The access signal 322 is transmitted and aligned with the forward pilot signal 320, which means that when transmitted the code state of the access signal 322 is the same as the code state of the received forward pilot signal 320. do.

The reciprocating trip propagation delay depends on the location of the subscriber unit 316 relative to the base station 314. Communication signals sent to subscriber unit 316 located closer to base station 314 will experience shorter propagation delays than at subscriber unit 316 further away from base station 314. Since the base station 314 must be able to acquire the subscriber unit 316 located at any location within the cell 330, the base station 314 is capable of acquiring all of the access signals corresponding to the full range of propagation delay of the cell 330. Code status should be examined.

In FIG. 13 the work associated with the initial acquisition of subscriber unit 316 by base station 314 is shown. The subscriber unit 316 does not have any knowledge of the two way propagation delay when the subscriber unit 316 wants to establish a channel 318 with the base station 314 which has never established a channel. Thus, the subscriber unit 316 inputs initial acquisition channel setting processing.

The subscriber unit 316 selects a low initial power level and zero code state delay (aligns the code state of the transmitted access signal 322 with the code state of the received forward pilot signal 320), and transmits the transmit power. Slowly ramping up (0.05-0.1 dB / msec) begins transmitting access signal 322 (step 400). While the subscriber unit 316 is waiting to receive an acknowledgment from the base station 314, it changes the code state delay at a predetermined stage from zero to a delay corresponding to the periphery of the cell 330 (maximum code Status delay) Allow sufficient time between steps for base station 314 to detect the approach signal 322 (step 402). If subscriber unit 316 reaches a code state delay corresponding to the periphery of cell 330, it repeats the process of changing the code state delay and continues the slow power ramp-up (step 402).

In order to acquire the subscriber unit 316 requiring access, the base station 314 continues to transmit the forward pilot signal 320 and detect the access signal 322 from the subscriber unit 316 (step 404). . As with the current system, the base station 314 only needs to check the code phase delay at the center of the periphery of the cell 330 without checking for the access signal 322 at every code state delay in the cell 330. have.

The base station 314 detects the access signal 322 when the subscriber unit 316 starts transmitting with sufficient power at a code state delay (step 406), which causes the subscriber unit 316 To appear in the periphery and thereby "seek" the subscriber unit 316 in the periphery of the cell 330. The base station 314 then confirms that the access signal 322 has been received (step 408) and sends a signal to the subscriber unit 316 to continue the channel setup process (step 410).

Once the subscriber unit 316 has received the acknowledgment signal (step 412) it stops ramping up the transmit power, stops changing the code state delay (step 414) and for subsequent reacquisition. The value of the code state delay is recorded (step 416). The subscriber unit 316 then continues with the channel establishment process including closed loop power transfer control (step 418).

If there is subsequent reacquisition when one subscriber unit 316 needs to establish one channel 318 with the base station 314, the subscriber unit 316 performs the reacquisition channel establishment process shown in FIG. Enter it. The subscriber unit 316 selects the low initial power level and code state delay recorded during the initial acquisition process and rapidly accesses the transmit power (shown in FIG. 13) (1 dB / msec) during the access signal. 322 continues to transmit (step 420). While varying the code state delay of the access signal 322 with the recorded code state delay while the subscriber unit 316 expects to receive an acknowledgment signal from the base station 314, changing the delay. Allow enough time for the base station 324 to detect the access signal 322 previously (step 422). The base station 314 as in FIG. 13 transmits one forward pilot signal 320 and delays the code state around the cell 330 in an attempt to acquire the subscriber unit 316 within its operating range. Only the test is made (step 424). The base station 314 detects the access signal 322 when the subscriber unit 316 transmits with sufficient power at the code state delay so that the subscriber unit 316 appears around the cell 330. (Step 426). The base station 314 transmits a signal to the subscriber unit 316 confirming that the access signal 322 has been received (step 428) and continues the channel establishment process (step 430).

When the subscriber unit 316 receives the confirmation signal (step 432) it stops power ramp-up, stops changing the code state delay (step 434) and the current value of the code state delay for subsequent reacquisition. Record (step 436). This code state delay is somewhat different from the code state delay initially used when starting the reacquisition process (step 422). The subscriber unit 316 then continues the channel establishment process at the current power level (step 438). If one subscriber unit 316 has not received one confirmation signal from the base station 314 after a certain time has elapsed, the subscriber unit 316 returns to the initial learning process described in FIG.

The effect of causing a code state delay in Tx 320 and Rx 322 communications between the base station 314 and the subscriber unit 316 is described with reference to FIGS. 15A and 15B. In FIG. 15A the base station 460 communicates with two subscriber units 462 and 464. The first subscriber unit 462 is located 30 km away from the base station 460, which is the maximum operating range. The second subscriber unit 464 is located 15 km away from the base station 460. The propagation delay of the Tx and Rx communications between the first subscriber unit 462 and the base station 460 will be twice the delay of the communication between the second subscriber unit 464 and the base station 460.

After the delay value 466 added in FIG. 15B is inserted into the Tx PN generator of the second subscriber unit 464, the communication propagation delay between the first subscriber unit 462 and the base station 460 is determined by the second subscriber unit. It will be equal to the communication propagation delay between 464 and base station 460. From the base station 460, the second subscriber unit 464 appears to be located in the virtual range 464 ′.

In FIG. 16, when a plurality of subscriber units S1-S7 are repositioned S1'-S7 'into the virtual range 475, the base station B should check only the code state delay at the center of the virtual range 475. To show.

Subscriber unit 316, which has achieved sufficient power levels using the present invention, will be obtained by the base station 314 in about 2 msec. The shorter acquisition time allows the subscriber unit 316 to ramp up at a much faster rate (about 1 dB / msec) and will not severely overshoot the desired power level. The same 20 dB power back-off would take about 20 msec for the subscriber unit 316 to reach a sufficient power level for detection by the base station 314. Therefore, the total duration of the reacquisition process of the present invention is about 22 msec, which is quite large in size from the known reacquisition method.

A subscriber unit 500 made in accordance with this embodiment of the present invention is shown in FIG. The subscriber unit 500 includes a receiver section 502 and a transmitter section 504. Antenna 506 receives a signal from base station 314 which is filtered by a bandpass filter 508 having a bandwidth equal to twice the chip rate and a center frequency equal to the bandwidth center frequency of the spread spectrum system. The output of the filter 508 is down-converted by the mixer 510 to a base station signal using a constant frequency (Fc) local oscillator. The output of mixer 510 is then spread spectral decoded by applying one PN order to one mixer 512 in PN Rx generator 514. The output of the mixer 512 is applied to a low pass filter 516 having a cutoff frequency at a data rate Fb of PCM data order. The output of the filter 516 is input to a coder / decoder (codec) 518, which is connected with the communication entity 520.

The base station signal from the communication entity 520 is a pulse code modulated by the codec 518. Preferably 32 kilobits are used per ADPCM. The PCM signal is applied to mixer 522 in PN Tx generator 524. The mixer 522 multiplies the PN order by the PCM data signal. The output of the mixer 522 is applied to a low pass filter 526 with a cutoff frequency equal to the system chip ratio. The output of the filter 526 is then appropriately upconverted as determined by the carrier frequency Fc applied to the mixer 528 and applied to the other terminal. The upconverted signal is then sent through a bandpass filter 530 to a wideband RF amplifier 532 which drives the antenna 534.

The microcontroller 536 controls the learning process as well as the Rx and Tx PN generators 514 and 524. The microprocessor 536 controls the code state delays added by the Rx and Tx PN generators 514 and 524 to obtain the forward pilot signal 520 and the subscriber unit 500 is obtained by the base station 314. And the microprocessor records the code state differences between these PN generators. For reacquisition the microprocessor 536 adds the delay recorded by the Tx PN generator 524.

The base station 314 uses a similar configuration as the subscriber unit 316 to detect the PN code signal from the subscriber unit 500. A microprocessor (not shown) in the base station 314 controls the Rx PN generator in a similar manner, so that the code state difference between the Rx PN generator and the Tx PN generator equal to the bidirectional propagation delay of the virtual location of the subscriber unit 316 Make it. Once the base station 314 only acquires the access signal 322 from the subscriber unit 316, all other signals (traffic, pilot, etc.) from the subscriber unit 316 to the base station 314 are processed for the acquisition. Use the same code state delay determined during the process.

Although the present invention has been described as a virtual location of subscriber unit 316 in the periphery of cell 330, the virtual location may be at any fixed distance from base station 314.

In FIG. 18 is shown the work associated with the initial acquisition of a "never-obtained" subscriber unit 316 by a base station 314 according to an optional embodiment of the present invention. The subscriber unit 316 continues to transmit one aligned access signal 322 to the base station 314 when setting up one channel 318 is required (step 600). The subscriber unit continues to increase the transmit power as the subscriber unit 316 continues to transmit the access signal 322 while waiting for the receipt of an acknowledgment signal from the base station 314 (step 602).

To detect a subscriber unit that has never been acquired, the base station 314 transmits a forward pilot signal 320 and sweeps the cell by examining all code states that cover the full range of propagation delay of the cell (step 604). ). The base station 314 also detects the aligned access signal 322 sent from subscriber unit 316 after the transmission achieves sufficient power for the detection (step 606). The base station 314 transmits a signal to the subscriber unit 316 as long as it confirms that the access signal 322 has been reached (step 608). The subscriber unit 316 receives the confirmation signal (step 610) and stops increasing the transmission power (step 612).

The base station 314 determines the required code state delay of the subscriber unit 316 by noting the difference between the Tx and Rx PN generators 524, 514 after acquiring the subscriber unit 316. The preferred code state delay value is sent to the subscriber unit 316 as an OA & M message that receives and stores the value for use during reacquisition (step 616) and continues channel setup processing (steps 622 and 624).

In Fig. 19, an optional method of fast reacquisition according to the present invention is shown. When the communication channel is to be reset between subscriber unit 316 and base station 314, the subscriber unit 316 transmits the access signal 322 with the necessary code state delay as in the preferred embodiment.

With all of the previously acquired subscriber units 316 in one virtual range, the base station 314 needs to examine the code state delay centered around the cell to obtain the access signal 322 of the subscriber unit 316. There is only (step 630). Subscriber unit 316 thus ramps up the power quickly to find more frequent acquisition opportunities. The subscriber unit 316 implements the delay in the same manner as in the preferred embodiment. The base station 314 then subsequently detects the subscriber unit 316 around the cell (step 636), sends a confirmation signal to the subscriber unit (step 637) and if necessary the code state delay value. Recalculate The recalculation (step 638) compensates for propagation path changes, oscillator drift and other communication variables. The subscriber unit 316 receives the confirmation signal from the base station 316 (step 639).

The base station 314 sends an updated necessary code state delay value to the subscriber unit 316 which receives and stores the updated value (step 642) (step 640). The subscriber unit 316 and the base station 314 then continue channel setting processing communication (steps 644 and 646).

The optional embodiment is based on examining both the code state delay in the periphery center of the cell to regain the previously acquired subscriber unit and the code state delay for the entire cell to acquire a subscriber unit that has never been acquired so far. I need a soup.

In FIG. 20 the work associated with the initial acquisition of the subscriber unit 316 which has not been obtained by the base station 314 according to the second alternative embodiment of the present invention is shown. The access signal 320 remains aligned with the forward pilot signal 320 when a subscriber unit 316 which has never been obtained in the embodiment shown in FIG. 18 is obtained. In such an embodiment, the base station 314 and the subscriber unit 316 change the code state alignment 322 of the access signal from the time of alignment to the delay (by means of code state delay) so that the subscriber unit 316 can read the code. Make it appear around the cell. This change is made at one specified time.

Steps 700-718 are the same as steps 600-618 shown in FIG. 18. However, after the base station 314 sends the necessary delay value to the subscriber unit 316 (step 716), the base station 314 sends a message to the subscriber unit 316 to sub-subscribe the forward pilot signal 320. Switch to the required delay value for the time referenced by the epipa (step 720). The subscriber unit 316 receives this message (step 722) and the two units 314, 316 wait until the switchover time is reached (steps 724, 730). At this time, the base station 314 adds the necessary delay value to its Rx PN operator (step 732) and the subscriber unit 316 adds the same necessary delay value to its Tx PN generator (step 726). The subscriber unit 316 and the base station 314 then continue with the channel setting processing communication (steps 728 and 734).

Claims (52)

Transmit a periodic signal from the subscriber unit at an initial predetermined power level, Continuously increasing the power level at a predetermined first ramp-up ratio, Detect the first periodic signal at the base station when sufficient power for detection has been achieved, Send a signal from the base station as long as confirming that the first periodic signal has been detected, Receiving the confirmation signal at the subscriber unit, and Suspending the predetermined first power level ramp-up ratio when the confirmation signal is received. 2. The method of claim 1, wherein the initial predetermined power level is lower than the power level required for detection by the base station. 3. The method of claim 2, further comprising continuing to increase the power level of the first periodic signal at a second predetermined rate after receiving the confirmation signal, wherein the second rate is lower than the first rate. How to. 4. The method of claim 3 wherein said first rate is about 1.0 dB / msec and said second rate is about 0.05 dB / msec. 4. The method of claim 3, further comprising transmitting a second periodic signal from the subscriber unit at the second power ramp-up ratio after the confirmation signal is received. 6. The method of claim 5, wherein the duration of the first periodic signal is shorter than the duration of the second periodic signal. 6. The method of claim 5, wherein the start of the second periodic signal is aligned with the start of the first periodic signal. 6. The method of claim 5, further comprising detecting by the base station the second periodic signal and examining the beginning of the second periodic signal. 9. The apparatus of claim 8, wherein the first and second periodic signals comprise a plurality of chips and the base station examines every Nth chip of the second periodic signal, where N is the number of chips in the first periodic signal. Characterized by the above. 10. The method of claim 9, further comprising stopping all Nth chip irradiation when the start of the second periodic signal is not determined after the predetermined duration. 11. The method of claim 10, wherein the predetermined duration corresponds to a round trip delay of a signal sent to the subscriber unit in the maximum operating range of the system. 11. The method of claim 10, further comprising examining all chips of the second periodic signal after the predetermined duration. 11. The method of claim 10, further comprising transmitting a confirmation signal from the base station when the start of the second periodic signal is detected by the base station. 12. The method of claim 11, further comprising stopping a continued increase in transmit power from said subscriber unit upon receipt of said confirmation signal by said subscriber unit. Includes a system for initial power control, The system consists of a subscriber unit and a base station, The subscriber unit Means for selectively transmitting the first periodic signal at a selected transmit power level, Means for detecting an acknowledgment signal from the base station, and Control means for changing the transmission power level in response to the detecting means, The control means continuously increases the transmit power at a first rate before receiving the acknowledgment signal and increases the transmit power level at a second rate after receiving the acknowledgment signal and the second rate is less than the first rate. And The base station Means for detecting the first periodic signal, and At least one base station having both means for transmitting a signal comprising means for transmitting a confirmation signal to said subscriber unit when said first periodic signal is detected in response to said detecting means; Network for communication between subscriber units. A communication network for performing a plurality of simultaneous communications using wireless transmission between a primary station and at least one secondary station, the network comprising a power control system for controlling initial transmission power, The power control system consists of a primary station and a first secondary station The primary station (i) means for transmitting a sync code, (ii) means for detecting an access code sent from the at least one secondary station, and (iii) means for generating an acknowledgment signal, said generating means having means for responding to said detecting means; The first secondary station (i) means for receiving synchronization information from the primary station, (ii) means for transmitting an access signal at the first transmission power level, and (iii) a communication network for performing a plurality of concurrent communications with means for increasing the transmit power level until the confirmation signal from the primary station is received. Transmit a periodic signal from the subscriber unit at a predetermined power level, The power level is low enough not to be detected by the base station, Gradually increase the power level of the signal at a predefined ramp-up ratio, Detecting the correct state of the periodic signal when the signal at the base station achieves sufficient power for detection by the base station, Transmitting a confirmation signal that the periodic signal has been detected from the base station, Receiving the confirmation signal at the subscriber unit, and A method for controlling transmit power ramp-up during communication establishment between a base station and at least one subscriber unit comprising stopping a predefined power level ramp-up ratio at the subscriber unit when the confirmation signal is received. . 18. The method of claim 17, further comprising increasing the power level of the signal at a second predefined ramp-up ratio, wherein the second ramp-up ratio is lower than the first ramp-up ratio. How to. 19. The method of claim 18, wherein the first ramp-up ratio is about 1.0 dB / sec and the second ramp-up ratio is about 0.05 dB / sec. 19. The method of claim 18, further comprising transmitting a second periodic signal from the subscriber unit at the second power ramp-up ratio when the confirmation signal is received. 21. The method of claim 20, wherein the duration of the second periodic signal is an even multiple of the first periodic signal. 22. The method of claim 21, wherein the start of the second periodic signal is aligned with the start of the first signal. 21. The method of claim 20, further comprising detecting by the base station the second periodic signal and examining the beginning of the signal. 24. The method of claim 23, wherein the base station examines every Nth chip of the second periodic signal and N is the length of the first periodic signal. 25. The system of claim 24, wherein after the predetermined duration is not determined the start of the second periodic signal is stopped by the base station examining all Nth chips of the second periodic signal. Characterized in that the round trip delay of the signal sent to one subscriber unit in the maximum operating range is equal to the predetermined duration. 26. The method of claim 25, further comprising examining all chips of the second periodic signal after the predetermined duration by the base station. 26. The method of claim 25, further comprising transmitting an acknowledgment signal from the base station to the subscriber unit when the second periodic signal is detected at the base station. 28. The method of claim 27, further comprising ceasing to increase transmit power from the subscriber unit when the confirmation signal is received at the subscriber unit. A communication system for communication between a base station and at least one subscriber unit, the communication system including one system for initial power control, The power control system consists of one subscriber unit, The subscriber unit Means for periodically transmitting a short access code having a predetermined length to the base station, the short access code being transmitted at a first power level, Means for increasing the power level by a first power ramp-up ratio, Means for detecting a transmission from the base station confirming receipt of the short access code at the base station, and Means for periodically transmitting a long access code that increases a power ramp-up ratio in response to the detecting means, wherein the long access code has a predetermined length that is an even product of the short access code and the second ramp-up ratio Means is less than the first rate of power growth, and The base station, Means for detecting communication from at least one said subscriber unit comprising said short and long access codes, and a transmission for sending an acknowledgment signal to said subscriber unit when said access code is detected in response to said detecting means; A communication system for communication between a base station and at least one subscriber unit, comprising means. A network for communication between a base station and at least one subscriber unit, the system comprising a system for reducing the reacquisition time of the subscriber unit by the base station, the system comprising a base station and a subscriber unit, wherein the base station comprises: Means for receiving a first communication from the subscriber unit, and means for sending a second communication to the subscriber unit in response to the first communication, and The subscriber unit, Means for transmitting the first communication to the base station, Means for receiving the second communication from the base station, Means for determining a duration between the transmission of the first communication and the reception of the second communication, and in response to the determining means calculates a difference between the determined duration and a desired duration, and by said calculated difference A network for communication between a base station and at least one subscriber unit comprising delay means for delaying a signal transmitted from the subscriber unit. 31. The system of claim 30, wherein said subscriber unit further comprises means for selectively changing the power level of said transmitting means. 32. The system of claim 31, wherein the base station receiving means further comprises means for analyzing a received communication in a plurality of code states. 33. The system of claim 32, wherein the base station transmitting means further comprises means for generating an acknowledgment signal for transmitting to the subscriber unit when a communication from the subscriber unit is detected. 34. The system of claim 33, wherein said subscriber unit delay means further comprises means for storing said calculated difference. 35. The system of claim 34, further comprising means for detecting an acknowledgment signal from said base station by said subscriber unit receiving means. 36. The system of claim 35, wherein said means for changing responds to said means for detecting to stop changing the transmit power level. 37. The system of claim 36, further comprising means for the base station to determine a duration between the transmission of the communication sent to the subscriber unit and the reception in response to the communication from the subscriber unit. 38. The system of claim 37, wherein the base station further comprises delay means responsive to the base station determining means for calculating a difference between the determined duration and the desired duration. 39. The system of claim 38, further comprising means for the base station to transmit a difference signal to the subscriber unit based on the calculated difference. 40. The system of claim 39, wherein the subscriber unit further comprises means for receiving the delay signal and the delay signal transmitted from the subscriber unit by the difference. A method for reducing the reacquisition time of a subscriber unit by a base station in a network for communication between one base station and at least one subscriber unit, the method comprising Transmit one access signal from one subscriber unit at a predetermined power transmission level, Increase the transmit power until an acknowledgment is received from the base station, The base station detects the approach signal when a sufficient power level is achieved, Send a confirmation signal from the base station when the access signal is detected, Receiving the confirmation signal at the subscriber unit, Stopping an increase in transmit power from the subscriber unit when the confirmation signal is received, Calculate a delay value between the access signal and the confirmation signal at the subscriber unit, and And storing the delay for subsequent reacquisition of the subscriber unit. 42. The method of claim 41 wherein the subscriber unit selectively increases the power level. 43. The method of claim 42, wherein the detecting at the base station further comprises analyzing the access signal in a plurality of code states. 44. The method of claim 43, further comprising generating an acknowledgment signal at the base station for transmission to the subscriber unit when a communication from the subscriber unit is detected. 45. The method of claim 44, further comprising detecting at the subscriber unit an acknowledgment signal from the base station. 46. The method of claim 45, further comprising determining at the base station a duration between transmission of a communication sent to the subscriber unit and reception in response to communication from the subscriber. 47. The method of claim 46, wherein the determining step further comprises calculating a difference between the determined duration and the desired duration. 48. The method of claim 47, further comprising transmitting a difference signal from the base station to the subscriber unit based on the calculated difference. 49. The method of claim 48, further comprising receiving at the subscriber unit the difference signal and the delay signal transmitted from the subscriber unit by the difference. A system for reducing the reacquisition time of a subscriber unit by the base station, wherein the system is Means for transmitting the first communication, Means for receiving a second communication in response to the first communication; Means for determining a duration between the transmission of the first communication and the reception of the second communication, and Means for calculating a difference between the determined duration and a desired duration to delay transmission of a subsequent communication by the difference. 51. The method of claim 50, further comprising means for selectively varying the power level of the transmission means. 53. The method of claim 51, wherein said delay means further comprises means for storing said calculated difference.