Method and apparatus for controlling transmission power in CDMA cellular mobile telephone system

The present invention relates to a telephone system, in particular to a new and improved method and device for controlling transmission power in a code division multiple access (CDMA) cellular mobile telephone system.

The use of code division multiple access (CDMA) modulation technology is one of the communication technical means that facilitates the appearance of a large number of system users in communications. Although some other technologies are known, such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes, such as amplitude compression single sideband (ACSSB) technology, CDMA technology is much better than the other above technology. U.S. Patent Application No. 06/921261 discloses the use of CDMA technology in multiple access communication systems. The filing date of this application is October 17, 1986, with the title "Spread Spectrum Using Satellite or Terrestrial Repeaters". Multi-access communication system", the current U.S. Patent No. 4901307 is assigned to the assignee of the present invention, and the disclosure is incorporated by reference.

In the patent just mentioned, a multiple access technology is disclosed. There are a large number of mobile phone system users, and each user has a transceiver. It uses code division multiple access (CDMA) spread spectrum communication signals through satellites. Repeaters or terrestrial base stations (also known as cell sites or used as short cells) communicate. In the use of CDMA communication, the spectrum can be reused many times, which can increase the user capacity in the system. Using CDMA can obtain much more special benefits than using other multiple access technologies. In a CDMA system, by controlling the power of each mobile user's transmitter, the system capacity can be increased to reduce interference to other system users.

In the satellite application of CDMA communication technology, the transceiver of the mobile unit measures the power level of the signal received by the satellite repeater, uses the power measurement, and determines the downlink transmission power level of the satellite repeater and the sensitivity of the mobile unit receiver. In case, the mobile unit transceiver can estimate the channel loss of the channel between the mobile unit and the satellite. Then, according to the size of the channel attenuation measurement, the transmission data rate and the sensitivity of satellite reception, the mobile station transceiver determines the appropriate transmission power for signal transmission between the mobile unit and the satellite.

The signal sent by the mobile unit to the satellite is forwarded by the satellite to the ground station of the central control system. The central station measures the power of the received signal, which is the signal sent by each active mobile unit transceiver. The central station then determines the deviation between the received power level and the power level required to maintain the desired communication. Preferably, the desired power level is the lowest power level required to maintain communication quality in order to reduce system interference.

Then, the central station sends a power control command signal to each mobile user in order to adjust or "fine-tune" the transmit power of the mobile unit. The mobile unit uses the command signal to change the transmit power level to the lowest level required to maintain the desired communication. Because of the change in channel conditions, typically due to the movement of the mobile unit, the transmission power level is continuously readjusted according to the mobile unit receiver power measurement and the power control feedback from the master station in order to maintain an appropriate power level. The power control feedback from the central station is generally very slow, due to the round-trip delay of about 1/2 second propagation time through the satellite.

An important difference between satellite or terrestrial base station systems is the relative distance separating the mobile unit and the satellite or cell site. Another important difference between satellites and terrestrial systems is the type of attenuation that appears in these channels. Therefore, in the study of terrestrial system power control, these differences require very fine-grained.

In satellite/mobile unit channels, such as satellite channels, satellite repeaters are usually placed in geosynchronous earth orbits. Since all mobile units are close to the same distance from the satellite repeater, they experience almost the same propagation loss. Moreover, the satellite channel has such a propagation loss characteristic that it approximately follows the inverse square law, that is, the propagation loss is inversely proportional to the square of the distance between the mobile unit and the satellite repeater used. Therefore, the deviation of the satellite channel channel attenuation due to the distance change is typically about 1-2dB.

Compared with satellite channels, for terrestrial/mobile unit channels, that is, terrestrial channels, the distance between the mobile unit and the cell site can vary considerably. For example, one mobile unit may be placed at a distance of 5 miles from the cell station, while another mobile unit may be placed at a distance of several feet from the cell station. The distance can vary by more than one hundred to one. The propagation attenuation characteristics experienced by terrestrial channels are the same as satellite channels. However, the propagation attenuation characteristics in terrestrial channels are inversely proportional to the fourth power, that is, the attenuation of the channel is inversely proportional to the fourth power of the channel distance. Therefore, in a cell with a radius of 5 kilometers, the channel attenuation change may reach approximately more than 80dB.

The attenuation experienced by satellite channels typically exhibits Rician characteristics. Therefore, the received signal includes a direct component and the sum of multiple reflection components with Rayleigh fading statistics. The power ratio between the direct component and the reflected component is typically about 6-10 dB, which depends on the characteristics of the mobile unit and the environment around the mobile unit.

Satellite channels are compared with terrestrial channels, and the signal fading experienced by terrestrial channels typically includes Rayleigh fading components and no direct components. Therefore, the terrestrial channel presents a more severe fading environment than the satellite channel, and Risun fading in the satellite channel is a dominant fading characteristic.

The Rayleigh fading characteristics in terrestrial channel signals are caused by reflections from many different characteristics of the actual environment. Therefore, a signal from many directions, with different time delays, arrives at a mobile unit receiver almost at the same time. Generally, when the UHF frequency band is used for mobile radio communications, including those cellular mobile phone systems, signals propagating on different channels may have effective phase differences, and there is a possibility of signal destructive addition. Sometimes there is a deep decline.

The fading of the terrestrial channel is a strong function of the actual position of the mobile unit. A small change in the position of the mobile unit can change the actual delay of all signal propagation paths, and the change of its position further produces a different phase for each path. In this way, through the environment, the location of the mobile unit can produce a very rapid fading process. For example, in the 850MHz cellular radio frequency band, such fading can typically be as fast as one fade per hour per kilometer per second at the speed of a car. Fading of this magnitude can strongly damage the signal in the terrestrial channel, resulting in poor Communication quality. However, additional transmitter power can be used to overcome the fading problem.

Terrestrial cellular telephone systems typically require a full-duplex channel. In order to enable two-way telephone conversations to work at the same time, as in traditional wired telephone systems, this full-duplex wireless channel usually uses a frequency band as an out-of-bounds link. , That is, the transmission from the cell transmitter to the mobile unit receiver. For the inbound link, a different frequency band is used, that is, the transmission from the mobile unit transmitter to the cell receiver. Therefore, this frequency separation enables a mobile unit transmitter and receiver to work at the same time without feedback or interference from the transmitter to the receiver.

The important significance of using different frequency bands lies in the power control of the cell site and the mobile unit transmitter. Different frequency bands are used to produce multi-pass fading, and the incoming and outgoing channels are processed separately. The mobile unit cannot simply measure the channel attenuation of the outbound channel and assume that the inbound channel exhibits the same channel attenuation.

Therefore, the object of the present invention is to provide a new and improved method and device for controlling terrestrial channel transmitter power in order to overcome harmful fading without generating unnecessary system interference, because the interference adversely affects the overall system capacity .

In the terrestrial CDMA cellular telephone system, it is always desirable to control the transmitter power of the mobile unit in order to get the normal reception from each cell and each mobile unit transmitter working in the cell at the cell receiver. Signal power. The transmit power of all mobile unit transmitters in the cell coverage area should be controlled. Therefore, the total signal power received at the cell site should be equal to the mobile unit transmit signal multiplexed by a large number of mobile units transmitting in the cell. The normal receiver power. This power is also added to the noise power received at the cell from mobile units in adjacent cells.

The CDMA receivers of the cell sites work separately, transforming the wideband CDMA signal corresponding to one of the unit transmitters into narrowband digital information carrying the signal. At the same time, the other received CDMA signal is not selected, keeping its wideband noise signal. The bit error rate performance of the cell receiver is determined by using the ratio of the power of the desired signal to the power of the undesired signal received on the cell receiver, that is, by the selected mobile unit transmitter The ratio of the received signal power of the transmitted desired signal to the received signal power of the undesired signal transmitted by another mobile unit transmitter. Bandwidth reduction processing and correlation processing result in what is usually called "processing gain", which will increase the signal-to-noise-to-interference ratio, from a negative value to a positive value, so that it can work within an acceptable bit error rate .

In the terrestrial CDMA cellular mobile phone system, judging from the number of simultaneous phone calls, it is particularly desirable for the system to reach the maximum capacity. Phone calls refer to phone calls that can be handled within a given system bandwidth. If the power of each mobile unit transmitter is controlled so that the transmitted signal reaches the cell receiver with the smallest signal-to-noise-to-interference ratio (this ratio can allow acceptable data recovery), the system capacity can be maximized. If the signal sent by the mobile unit reaches the cell receiver at a power level that is too low, the bit error rate is too high to allow high-quality communication. On the other hand, if the signal transmitted by the mobile unit is received by the cell receiver at a power level that is too high, communication with that particular mobile unit will be acceptable. However, this high-power signal interferes with signals transmitted by other mobile units, and these signals share the same channel, that is, bandwidth. These interferences, in turn, may affect communications with other mobile units unless the total number of communicating mobile units is reduced.

In the UHF band of the cellular mobile phone channel, the channel attenuation of the signal can be characterized by two independent phenomena, the average channel attenuation and fading. The average channel attenuation can be statistically described by a lognormal distribution. Its average value is proportional to the reciprocal of the fourth square of the channel distance, and its standard deviation is approximately equal to 8dB. The second phenomenon is the fading process, which is produced by the multipath propagation of the signal, and it is characterized by the Rayleigh distribution. The average channel attenuation is a logarithmic distribution, and it can be considered that the out-of-bounds and inbound frequency bands are the same, which is the case for traditional cellular mobile phone systems. However, as mentioned above, Rayleigh fading is an independent phenomenon for the inbound and outbound link bands. The log-normal distribution of the average channel attenuation is a function of slow changes with respect to position, on the contrary, the Rayleigh distribution is a function of position, and its change is relatively fast.

In the present invention, on a cellular mobile phone system, a CDMA method is used to enable multiple users to access. In such a system, all cells in an area transmit a "pilot" signal of the same frequency and code. The use of pilot signals in CDMA systems is well known. In this particular application, the pilot signal used by the mobile unit is used for the initial synchronization of the mobile unit receiver. The pilot signal is also used as a phase, frequency and time reference for demodulating the digital voice signal transmitted by the cell site.

In the present invention, each mobile unit estimates the path loss of the signal sent from the cell site to the mobile unit. In order to obtain the signal path loss estimate, the power level of the signal transmitted by the cell site received by the mobile unit should be measured. In this way, the mobile unit measures the power of the pilot signal received from the cell site with which the mobile unit is communicating. The mobile unit also measures the sum of the power levels of all cell site transmission signals received at the mobile unit. The power level and measurement, as described in further detail below, need to deal with a situation where the mobile unit may temporarily obtain a better path, and the more distant cell is better than the nearest cell that is usually preferred.

The attenuation estimation of the out-of-bounds link is filtered by a nonlinear filter. The purpose of non-linearity in the estimation process is to allow rapid response to sudden improvements in the channel, while allowing a much slower response to sudden degradation of the channel. The mobile unit responds to a sudden improvement in the channel, which suddenly reduces the transmission power of the mobile unit transmitter. If the channel of a mobile unit suddenly improves, the signal received by the cell site from the mobile unit will suddenly increase in power. This sudden increase in power will cause additional interference to all signals sharing the same bandwidth channel. Quick response to sudden improvements will reduce system interference.

A typical example of sudden channel improvement occurs when a moving mobile unit passes through an area obscured by large buildings or other obstacles, and then moves out of the obscured area. The channel improvement can occur in about tens of milliseconds due to the movement of the car. As the mobile unit moves out of the sheltered area, the out-of-bounds link signal received by the mobile unit will suddenly increase in strength.

The out-of-bounds link path loss estimation at the mobile unit is for the mobile unit to adjust the mobile unit transmitter power. In this way, the stronger the received signal, the lower the power of the mobile unit transmitter will be. The strong signal received from the cell site indicates that the mobile unit is either close to the cell site or has a particularly good path to the cell site. The reception of strong signals means that a relatively small mobile unit transmitter power level is required for the normal received power of the mobile unit of the cell.

In the temporary situation, the channel has suddenly degraded, it is hoped that the mobile unit transmitter power can be allowed to increase slowly. This kind of slow increase of the mobile unit transmitter power is also desirable, so as to prevent the mobile unit transmitter power from being unnecessary. Increase rapidly, because this power increase will interfere with all other mobile units. Therefore, in order to avoid degradation of all mobile unit channels, temporary degradation of one mobile unit channel can be tolerated.

In the case of a sudden channel degradation, the non-linear filter prevents the mobile transmitter power from increasing at a high rate in response to the sudden decrease in the signal power of the signal received by the mobile unit. The rate of increase in the transmit power of the mobile unit transmitter must generally be limited to the rate at which closed-loop power adjustment commands are sent from the cell site, (as described below), the rate at which the transmit power of the mobile unit transmitter can be reduced. Utilizing cell sites that generate power adjustment commands will prevent the increased level from being significantly higher than the level required for communication, especially when there is a sudden channel degradation only in the outbound link path and not in the inbound link path .

It should be noted that it is not desirable to simply use slow response mobile unit transmitter power control in an attempt to separate fast Rayleigh fading from slow fading due to distance and terrain. The slow response in the power control of the mobile unit transmitter is undesirable because the possibility of sudden improvement and attenuation affects inbound and outbound channels equally. If the response improves suddenly, using a filter, it will slowly drop, and then, when the power of the mobile unit transmitter changes extremely and interferes with other mobile users, the above situation will occur frequently. Therefore, the present invention uses two time constants and a nonlinear method in estimating the channel attenuation.

In addition to measuring the received signal strength of the mobile unit, for the processor of the mobile unit, it is also desirable to know the power and antenna gain (EIRP) of the cell site transmitter, and the G/T (receiving antenna gain G of the cell site) Divided by the receiver noise level T), the antenna gain of the mobile unit and the number of effective calls with the cell site. This information allows the mobile unit processor to properly calculate the reference power level for the local power setting function. This calculation is done by calculating the power budget of the cell site to the mobile link, and solving the channel attenuation. Then, the path loss estimates the cell link budget equation used for mobile, and solves for the power transmitted by the mobile unit required to generate the desired signal level. This capability allows the system to have cell sites with different EIRP levels corresponding to the cell size. For example, a small radius cell does not need to transmit as high a power level as a large radius cell. However, when the mobile unit is a certain distance away from a low-power cell, it will receive a weaker signal than from a high-power cell. The mobile unit is more responsive to higher transmission power for the necessity of short distances. Therefore, the need for each cell to send information is precisely the characteristic of its power control.

The information sent by the cell site includes the EIRP of the cell site, G/T, and the number of effective calls to establish a channel in a cell. When the system synchronization is first obtained, the mobile unit receives this information, and continues to monitor the channel when a call from the public switched telephone network is intended to be paged by the mobile unit and is idle. The antenna gain of the mobile unit is stored in the memory of the mobile unit, and the mobile unit is installed in the car at this time.

As mentioned above, the power of the mobile unit transmitter is also controlled by the signal from the cell site. Each cell site receiver measures the signal strength received at the cell site from each mobile unit communicating with that cell. The measured signal strength is compared with the signal strength expected as a special mobile unit. A power adjustment command is generated, sent to the mobile unit via outbound link data or voice channel, and addressed to the corresponding mobile unit. In response to the cell site power adjustment command, the mobile unit increases or decreases the power of the mobile unit transmitter by a predetermined amount, usually 1 dB.

The cell transmitter transmits power adjustment commands at a relatively high rate, typically about 1 command per millisecond. The transmission rate of the power adjustment command must be high enough to allow tracking of the Rayleigh fading of the inbound link path. It is further hoped that the Rayleigh fading of the outbound link channel will be added to the tracked inbound link channel signal. 1 command per millisecond, for mobile communications in the 850MHz frequency band, vehicle speeds in the range of 25-50 miles per hour, tracking the fading process is appropriate. It is important to determine the waiting time of the power adjustment command and minimize its transmission so that the channel conditions will not change much before the mobile unit receives and responds to the signal.

In short, due to the independence of the two Rayleigh fading (inbound and outbound) paths, the mobile unit transmitter power is controlled by the power adjustment command from the cell site. Each cell receiver measures the signal strength received from each mobile unit. The measured signal strength is compared with the desired signal strength as a specific mobile unit, and a power adjustment signal is generated. The power adjustment signal is sent to the mobile unit in an out-of-bounds data or voice channel, and is addressed to the above-mentioned mobile unit. The power adjustment command is combined with the one-way estimation value of the mobile unit to obtain the final value of the transmitter power of the mobile unit.

Taking an embodiment as an example, a method of rewriting one or more user data bits every millisecond is used to transmit a power adjustment command signal. The modulation system used in the CDMA system can provide correction codes for user data bits. Rewrite with power adjustment command, deal with channel bit error or elimination, and correct with error correction, such as decoding in mobile unit receiver. Performing error correction encoding on the power adjustment command bit is not possible in many cases because it increases the waiting time during reception and responds to the power adjustment command. It is also conceivable that instead of rewriting user data channel symbols, time division multiplexing is used to transmit power adjustment command bits.

The cell controller or processor can be used to determine the desired signal strength, which is the signal transmitted by each mobile unit and received at the cell site. The desired signal strength level value is supplied to each cell receiver. The desired signal strength value is used to compare with the measured signal strength value to generate a power adjustment command.

A system controller is used to direct each cell processor to achieve the desired signal strength value used. The normal power level can be adjusted up and down to adapt to changes in average cell conditions. For example, a cell placed in an abnormal noise location or geographic area may be able to use a higher level than the normal inbound power level. However, this higher power level operating in the cell will produce a higher interference level, which will interfere with the cell closest to the cell. This kind of interference can be compensated for by allowing small adjacent cells to increase the power of the inbound link. In this way, the increased inbound power in adjacent cells will be less than the increased power in cell communication due to mobile users in a high-noise environment. It is further understood that the cell processor can monitor the average bit error rate. The system controller can use this data to direct the cell processor to establish an appropriate inbound link power level to ensure acceptable high-quality communications.

It is also desirable to provide a device for controlling the relative power used in each data signal transmitted by the cell in response to the control information sent by each mobile unit. The main reason for providing this control is to adapt to the reality that in certain locations, the outbound channel link from the cell to the mobile unit may be particularly flawed. If the power sent to the mobile unit is not increased, the communication quality may become unacceptable. An example of such a location is a location where the path loss to one or two adjacent cells is approximately the same as the path loss of the cell communicating with the mobile unit. In such a location, the total interference is three times greater than the interference generated by the mobile unit relatively close to its cell. In addition, the interference from these neighboring cells will not fade, consistent with the desired signal, as in the case of interference from the desired cell. This situation may require 3-4dB of additional signal power in order to obtain suitable performance.

In another case, the mobile unit may be placed where some strong multi-channel signals arrive, causing greater interference than normal interference. In this case, increasing the power of the desired signal relative to interference can allow acceptable performance. Normally, the mobile unit can be placed in a place with an unusually good signal/interference ratio. In this case, the cell site can use a lower power than the normal transmitter to transmit the desired signal in order to reduce interference with other signals transmitted by the system.

To achieve the above objectives, the preferred embodiment includes signal/interference measurement capabilities at the mobile unit receiver. This measurement is achieved by comparing the desired signal power with the total interference and noise power. If the measured ratio is lower than the predetermined value, the mobile unit sends a request to the cell station, requesting the cell station to send additional power. If the measured ratio exceeds the predetermined value, the mobile unit sends a request to reduce the transmission power.

The cell station receives the power adjustment request signal from each mobile unit, and responds with the adjusted power, that is, assigns a predetermined magnitude to the corresponding cell to transmit the signal. The adjustment amount is usually small, about 0.5dB, or 12%. The rate of power change may be slightly lower than the value used on the inbound link from the mobile unit to the cell. Approximately once per vocoder frame, or usually once every 15 milliseconds. The dynamic range of the adjustment is also limited to 4dB below the normal value to 6dB above the normal value.

The cell site must also consider the power requirements generated by all mobile units to decide whether to respond to any particular mobile unit's request. For example, if the capacity carried by the cell site can meet the request for additional power, but only 6% or less, instead of 12%. In this case, the request for power reduction should still be answered within the normal 12% change.

Through the following detailed description together with the accompanying drawings and the entire corresponding reference symbols, the features and advantages of the present invention will become more apparent, in which: Figure 1 is an overview schematic diagram of an exemplary mobile cellular phone system;

Figures 2A-2D show a set of graphs showing the signal strength received by the mobile unit and the transmitted power as a function of distance;

Figure 3 is a block diagram specifically related to a cell site having the power control features of the present invention;

Figure 4 is a block diagram of a mobile unit specifically related to the power control feature of the present invention;

Fig. 5 is a block diagram further illustrating the power control features of the mobile unit of Fig. 4; and Fig. 6 is a block diagram further illustrating the power control features of the cell site of Fig. 3 in further detail.

Figure 1 illustrates an exemplary cellular mobile telephone system incorporating the present invention. Figure 1 illustrates the system, which utilizes CDMA modulation technology for communication between mobile users and cells in the system. A cellular system in a large city may have thousands of cell sites serving hundreds of thousands of mobile phones. Using CDMA technology, in a system of the same size, compared with the current FM modulated cellular system, it is indeed convenient to increase user capacity.

In Figure 1, the system controller and switch 10 typically include appropriate interfaces and processing hardware for providing system control information to the cell site. The controller 10 controls the routing of telephone calls from the Public Switched Telephone Network (PSTN) to the appropriate cell site for transmission to the appropriate mobile unit. The controller 10 also controls the routing of calls from the mobile unit through a cell site to the PSTN. The controller 10 can direct calls between mobile users via a suitable cell site, because such mobile units typically cannot communicate directly with another mobile unit.

The controller 10 can be connected to the cell site via various devices such as dedicated telephone lines, optical fiber links or wireless frequency communication. In Figure 1, two exemplary cell sites 12 and 14 are illustrated, and two exemplary mobile units 16 and 18, which contain cellular telephones. Arrows 20a-20b and 22a-22b define possible communication links between the cell site 12 and the mobile units 16 and 18, respectively. Similarly, arrows 24a-24b and arrows 26a-26b define possible communication links between the cell site 14 and the mobile units 18 and 16, respectively. Cell sites 12 and 14 usually transmit at equal power.

The mobile unit 16 measures the total received power of the pilot signals transmitted by the cell sites 12 and 14 on the paths 20a and 26a. Likewise, the mobile unit 18 measures the total received power of the pilot signals transmitted by the cell sites 12 and 14 on the paths 22a and 24a. Each of the mobile units 16 and 18 measures the power of the pilot signal in the receiver, where the signal is a wideband signal. Therefore, the power measurement is performed before the correction of the received signal with the pseudo-noise spread spectrum signal.

When the mobile unit 16 is closer to the cell site 12, the received signal power will be controlled by the signal on the propagation path 20a. When the mobile unit 16 is closer to the cell site 14, the received signal power will be controlled by the signal on the propagation path 26a. Similarly, when the mobile unit 18 is closer to the cell site 14, the received signal power will be controlled by the signal on the propagation branch 24a. When the mobile unit 18 is closer to the cell site 12, the received signal power will be controlled by the signal on the propagation path 22a.

Each mobile unit of mobile units 16 and 18 uses the combined measurements, along with cell transmitter power and mobile unit antenna gain messages, to estimate the path loss to the nearest cell site. The estimated path loss, together with the mobile antenna gain and cell site G/T messages, is used to determine the normal transmitter power, which is required to obtain the desired carrier/noise ratio in the cell receiver . The message of the mobile unit and the cell parameters is either fixed in the memory or sent out by the cell information broadcast signal, and a channel is established to indicate the other nominal status of a particular cell station.

As a result of the determination of the normal transmission power of the mobile unit, there is no Rayleigh fading, and assuming the correct measurement, the signal transmitted by the mobile unit reaches the nearest cell with the exact desired carrier/noise ratio. In this way, the desired performance will be obtained with the minimum amount of mobile unit transmit power. Minimizing the transmission power of a mobile unit is important in a CDMA system, because the interference generated by each mobile unit will interfere with every other mobile unit in the system. In the system with the smallest mobile unit transmit power, the system interference will be at a minimum, thus allowing additional mobile users to share the frequency band. Therefore, the system capacity and special efficiency are maximized.

Figure 2A illustrates the Rayleigh fading as a function of distance and its influence on the strength of the cell transmit signal received by the mobile unit. The average channel attenuation is represented by a curve 30, and the attenuation is mainly determined by the fourth power of the distance between the cell site and the mobile unit and the shape of the terrain between them. As the distance between the mobile unit and the cell site increases, for fixed power transmission cell signals, the power of the signal received at the mobile unit decreases. For the two directions of the link, the average path loss is the same. Typically, the average path loss exhibits a log-normal distribution.

In addition to the slowly varying log-normal average channel loss, due to the existence of multi-channel signal propagation, there is a rise or fall around the rapid decline of the average channel loss. These signals arrive from these multiple channels with random phase and amplitude, and the result is a Rayleigh fading characteristic. The curve 32 shown in FIG. 2A represents the change in signal path attenuation due to Rayleigh fading. Rayleigh fading is typically independent of the two directions (ie, out-of-bounds and inbound) of the cell/mobile unit communication link. For example, when the outbound channel is fading, the inbound channel does not have to be fading at the same time.

Figure 2B shows that the power of the mobile unit transmitter is adjusted to correspond to the link channel signal strength of Figure 2A. The curve 34 in FIG. 2B represents the desired average transmission power corresponding to the average path attenuation of the curve 30 in FIG. 2A. Similarly, curve 36 is the corresponding mobile unit transmitter power in response to the Rayleigh fading represented by curve 32 in FIG. 2A. When the Rayleigh fading signal, as shown by the curve 32 in FIG. 2A, the signal strength decreases, the transmit power increases rapidly. This rapid upward shift in transmitter power has a detrimental effect on the performance of the entire system. Therefore, the present invention envisions using a non-linear filter to control the rapid upward shift or increase, and also control the power of the transmitter. The present invention also uses the closed-loop power adjustment feedback from the cell to adjust the transmitter power of the mobile unit.

Fig. 2C shows the transmitter power of the mobile unit corresponding to Fig. 2A without considering the closed-loop power adjustment feedback of the cell. In FIG. 2C, the desired average transmit power is represented by curve 34, which corresponds to the strength of the mobile unit received signal of curve 30 in FIG. 2A. Curve 38 represents the transmitter power using a non-linear filter in the power control of the present invention.

The transmitter power shifts upward rapidly, as shown by the dashed line in FIG. 2C, and the upward shift corresponding to the curve 36 of FIG. 2B is greatly reduced. In curve 38, by setting the ratio of transmitter power to a fixed value increase, the upward offset is greatly reduced. The change of transmitter power relative to the desired transmit power is limited by two factors: dynamic range and rate of change. This limitation allows the closed-loop power adjustment feedback process to be more easily implemented at a much lower control data rate, and more effective. The transmit power shown by curve 38 is allowed to decrease at a rate much greater than the rate of increase.

As the distance increases, the transmitter power from the marked points D1-D2 decreases slightly quickly, corresponding to the rapid improvement of the channel. The degradation of the channel between the D2-D3 distance of the marker point corresponds to an increase in transmitter power. The degradation change is not so effective because the maximum rate of the nonlinear filter limits the rate at which the transmitter power increases.

As the distance increases, from the distance marker D3-D4, the channel degradation will allow the transmitter power to increase much faster than the nonlinear filter. During this period, the transmitter power increases at the maximum rate allowed by the nonlinear filter. During the distance change indicated by the marks D4-D5, the channel starts to improve. However, as the channel quality improves, the transmitter power continues to increase at the maximum rate until the transmitter power is sufficient to meet the desired level as marked D5.

It is desirable to eliminate the upward shift in transmitter power, which may cause unnecessary system interference. If there is a better path to another cell site, it will cause unnecessary interference in the system, so the communication quality can be maintained by limiting the rate of transmitter power increase.

Fig. 2D is a graph illustrating the signal power received by the cell versus the transmission distance of the mobile unit. The mobile unit moves away from the cell site. Curve 40 represents the average received signal power desired to receive the signal transmitted from the mobile unit at the cell site. It is desirable that the average received signal power is a fixed level, and at least a high-quality communication link with a mobile unit must be guaranteed. Correction is carried out at the mobile unit to correct the Rayleigh fading in the signal transmitted by the cell.

The signal transmitted by the mobile unit undergoes Rayleigh fading before reaching the cell receiver. Therefore, the signal received at the cell is a signal with a fixed average received power level, but the Rayleigh fading of the inbound channel is still added to it. Curve 42 represents the Rayleigh fading that appears on the incoming signal.

In addition, there is a possibility that the mobile unit enters a rest state where there is no link fading, but the inbound link is severely fading. Such conditions will interrupt communication unless additional machines are used to compensate for the Rayleigh fading of the incoming channel. The use of closed-loop power adjustment command processing at the cell site is such a machine that is used to adjust the transmit power of the mobile unit to compensate for the Rayleigh fading of the inbound channel. In FIG. 2D, curve 44 represents the signal power transmitted by the mobile unit received at the cell site when the average branch attenuation and Rayleigh fading of the inbound and outbound channels are compensated. It can be seen from FIG. 2D that the curve 44 is very close to the curve 40 except for the severe fading that minimizes the fading process with closed-loop control.

In FIG. 3, the antenna 52 is used to receive signals transmitted by a plurality of mobile units, and then, the signals are supplied to an analog receiver 54 for amplification, frequency down conversion, and IF processing of the received RF signals. The analog signal output from the receiver 54 is supplied to a plurality of receiver modules to extract information signals for guiding users, generate power adjustment instructions and modulation of user input information signals for transmission. Such a module used in communication has a special mobile unit, such as mobile unit N, which is module 50. In this way, the output of the receiver 54 is supplied to a plurality of such modules including the module 50.

The module 50 includes a digital data receiver 56, a user digital baseband circuit 58, a received power measurement circuit 60, and a transmit modulator 62. The digital data receiver 56 receives the wideband spread spectrum signal for correction and despreading. The signal sent by the mobile unit N is a narrowband signal for transferring to a designated receiver communicating with the mobile unit N. The digital data receiver 56 provides the narrowband digital signal to the user digital baseband circuit 58. The digital data receiver 56 also provides a narrowband signal to the received power measurement circuit 60.

The received power measurement circuit 60 measures the signal level received from the mobile unit N. The received power measurement circuit 60 generates a power adjustment command in response to the measured power level, and the command is input to the transmitting modulator 62 for transmission to the mobile unit N. As described above, the data bits of the power adjustment command are used by the mobile unit N in adjusting the transmission power of the mobile unit.

When the received power measurement value is greater than the preset level provided by the cell site processor (not shown), an appropriate power adjustment command is generated. If the received power measurement value is lower than the preset level, a power adjustment command data bit is generated and indicates the mobile unit transmitter power that needs to be increased. Similarly, if the received measurement value is greater than the preset level, a power adjustment command is generated, which reduces the transmitter power of the mobile unit. Use power adjustment commands to maintain the normal received power level of the cell site.

The output signal from the digital data receiver 56 is supplied to the user's digital baseband circuit 58, which is an interface for connecting to a designated receiver via a system controller and a switch. Similarly, the baseband circuit 58 receives the user information signal designated as the mobile unit N and supplies it to the transmission modulator 62.

The transmit modulator 62 spread-spectrum modulation for transmitting to the mobile unit N a user-addressable information signal. The transmission modulator 62 also receives power adjustment instruction data bits from the received power measurement circuit 60. The power adjustment command data bits are also spread spectrum modulated by the transmit modulator 62 for transmission to the mobile unit N. The transmit modulator 62 provides the spread-spectrum modulated signal to the adder 64, which mixes the spread-spectrum signal with other module transmit modulators in the cell site.

The mixed spread spectrum signal is input to the adder 66, where the signal is mixed with the pilot signal provided by the pilot signal generator 68. Then, these mixed signals are supplied to a frequency up-conversion circuit (not shown) for changing the IF frequency band to the RF frequency band and amplified. Then, the RF signal is provided to the antenna 52 for transmission. Although not illustrated, transmit power control circuitry may be disposed added between the antenna 52 and the adder 66. The circuit responds to the power adjustment command signal transmitted by the mobile unit under the control of the cell processor. The signal is demodulated at the cell receiver and provided to the cell control processor, which is connected to the circuit.

In Figure 4, a mobile unit, such as mobile unit N, includes an antenna 70 for collecting signals transmitted by the cell site and radiating CDMA signals generated by the mobile unit. Mobile unit N uses antenna 70, analog receiver 72 and digital data. The receiver 74 receives the pilot signal and establishes the channel signal and the ground seeking signal of the mobile unit N. The receiver 72 amplifies and down-converts the received radio frequency CDMA signal into an IF signal and filters the intermediate frequency IF signal. The IF signal is output to the digital data receiver 74 for digital processing. The receiver 72 also includes a circuit for analog measurement of the mixed power of the received signal. The power measurement is used to generate a feedback signal, which is sent to the transmission power control circuit 76 for controlling the transmission power.

The digital data receiver 74 is used to de-spread and address the relevant received signal to the mobile unit N. The receiver 74 also separates the digital data from the power adjustment commands generated by the cell. The power adjustment instruction data bit is sent to the control processor 78. The processor 78 generates a transmission power control command in response to the power adjustment command data bit, and the command is supplied to the transmission power control circuit 80. The processor 78 also provides a level setting instruction to the transmission power control circuit 76. For further details about the interaction between the receiver 72, the transmit power controls 76 and 80, and the processor, refer to the further detailed description of FIG. 5.

The receiver 74 also provides, for example, digitally encoded voice data to the user's digital baseband circuit 82 for decoding and an interface with the user. The baseband circuit 82 includes interface hardware for connecting the receiver 74 and the transmitting modulator 84 to the user's mobile phone (not shown).

The transmitted data is provided through the baseband circuit 82, where it is encoded and sent to the transmit modulator 84. The data is spread-spectrum modulated by the transmission modulator 84 according to the designated spreading code. The spread spectrum signal is output from the transmission modulator 84 to the transmission power control circuit 80. According to the transmission power control instruction provided by the control processor 78, the power of the signal is adjusted. The power adjustment signal is supplied from the transmission power control circuit 80 to the transmission power control circuit 76, which adjusts the signal according to the analog measurement control signal. Although the figure shows two separate units for controlling the transmit power, the power level can be adjusted by a single variable gain amplifier. The amplifier has two input control signals, which are added to the variable gain amplifier. It was mixed before. However, in the illustrated embodiment, the two control functions are represented by separate elements.

In the operation of the power control circuit shown in FIG. 4, the receiver 72 measures the combined power levels of all signals received from all cell sites. These power level measurement results are used to control the power level, which is set by the transmission power control circuit 76. The transmission power control circuit 76 includes a circuit in which, as previously described, a non-linear filter is used to limit the rate at which the transmission power is increased. The set rate of increase should not be faster than the rate at which the transmit power control circuit 80 can respond to a series of down commands from the cell site to reverse the power drop, as processed by the receiver 74 and the processor 78.

Fig. 5 further shows in more detail the power control method of the mobile unit N discussed with reference to Fig. 4. In FIG. 5, the RF signal received from the antenna is supplied to a frequency down converter 90, which converts the received RF signal to an IF frequency. The IF frequency signal is connected to a band pass filter 92, which removes out-of-bounds frequency components from the signal.

The filtered signal is output from the filter 92 to a variable gain IF amplifier, which amplifies the signal. The amplified signal is output from the amplifier 94 to an analog/digital (A/D) converter (not shown), and a digital signal processing operation is performed on the signal. The output of amplifier 94 is also connected to an automatic gain control (AGC) detector circuit 96.

The AGC detector circuit 96 generates a gain control signal, which is connected to the gain control input of the amplifier 94. The gain control signal is used to control the gain of the amplifier 94 so as to maintain a fixed average power level as the output from the amplifier 94 to the A/D converter.

The AGC detector circuit 96 also provides an output to an input terminal of the comparator 98. The other input of the comparator 98 is provided by a level setting signal from the mobile unit processor (not shown). The level setting signal indicates the desired reference power level of the transmitter. These input signals are compared by a comparator 98, and the generated comparison signal is supplied to a non-linear filter circuit 100. The comparison signal corresponds to the deviation between the received power measurement and the desired mobile unit transmitter power level.

The filter 100 may be configured as a simple resistor-diode-capacitor circuit. For example, the input circuit is a common node shared by two resistors, and the other end of each resistor is connected to a diode. The diodes are connected in reverse in their connection with the resistance, and the other ends of each diode are connected together, with a common node as the output of the filter. A capacitor is connected between the common junction of the diode and ground. The designed filter circuit limits the rate of power increase to less than 1dB per millisecond. The rate of power drop is typically set to be approximately 10 times faster than the rate of power increase, that is, 10 dB per millisecond. The output of the filter 100 is input to the gain control input terminal of the variable gain IF amplifier 102 as a power level control signal.

The AGC detector circuit 96, the comparator 98 and the filter 100 estimate the received signal power of the mobile unit and the power correction required for the mobile unit transmitter. This correction is used to maintain the desired transmitter power level under the fading condition of the outbound channel, which is common to the inbound channel.

The transmit modulator circuit 84 of FIG. 4 provides a low-power IF frequency spread spectrum signal to an input of the variable gain IF amplifier 104, and the gain of the amplifier 104 is controlled by the power level control signal from the processor 78 (FIG. 4) . The power level control signal comes from the closed-loop power adjustment command signal, which is transmitted by the cell station and processed by the mobile unit, as described with reference to FIG. 4.

The power adjustment command signal includes a series of power increase and power reduction commands stored in the mobile unit processor. The mobile unit control processor starts by increasing the control level setting to reach a normal value. The gain control command value increased by each power up command corresponds to an increase of approximately 1dB in the amplifier gain. The gain control command value reduced by each power down command corresponds to approximately 1dB reduction in the amplifier gain. The gain control command is converted into an analog form by a digital/analog (D/A) converter (not shown) as a power level control signal before being applied to the amplifier 104.

The mobile unit reference power level can be stored in the memory of the control processor. In an alternative solution, the mobile unit reference power level can be included in the signal sent to the mobile unit, and the signal command data is separated by the digital data receiver and translated into the set level by the control processor. The signal provided from the control processor is converted by a digital/analog (D/A) converter (not shown) before being input to the comparator 98.

The output of amplifier 104 is provided to amplifier 102 as an input. As mentioned above, the amplifier 102 is also a variable gain IF amplifier with a gain determined according to the power level control signal from the filter 100. In this way, the signal for transmission is amplified according to the gain set by the power level control signal. The amplified signal output from the amplifier 102 is further amplified and the frequency is converted into a radio frequency for transmission. This radio frequency is then fed to the transmitting antenna.

Fig. 6 shows in more detail the power control principle diagram of the mesh shown in Fig. 3. In Figure 6, the cell receives the signal sent by the mobile unit. The received signal is processed by the cell analog receiver and the cell corresponding to the mobile unit N.

In the digital data receiver (receiver 56 in FIG. 3), the received analog signal is converted from analog to digital form by the A/D converter 110. The digital signal output from the A/D converter is provided to a pseudo-random noise (PN) correlator 112, in which the signal is correlated with a PN signal provided by the PN generator 114. The output of the PN correlator 112 is provided to a fast Hadamard transform digital filter 114 in which the signal is filtered. The output of the filter 114 is provided to a user data decoding circuit 116, which provides the user data to the user digital baseband circuit. The decoder 116 provides the largest transform filter symbols (Symbols) to the power averager circuit 118. The power averager circuit uses well-known digital techniques to average the maximum conversion output over an interval of one millisecond.

The indicator signal of each average power level is the output from the power averager 118, and the indicator signal is provided to the comparator 120. The comparator 120 also receives a power level setting signal indicating a desired received power level. The desired received power level is set by the control processor of the cell. The comparator 120 compares the two input signals and provides an output signal indicating the deviation of the average power level from the expected power level. This signal is output to the increase power/decrease power command generator 122. In response to the comparison result, the generator 122 generates a power increase or decrease power command. The power command generator 122 provides the power control command to the cell transmission modulator for transmission and control of the transmitter power of the mobile unit N.

If the power received at the cell is higher than the power expected by mobile unit N, then a power reduction command is generated and sent to mobile unit N. However, if the power received at the cell is too low, then a power increase command is generated and sent. Increase/decrease commands are transmitted at a high rate, in the embodiment, typically 1,000 commands per second. With one bit per command, the overhead of the power command is not important compared to the bit rate of a high-quality digital voice signal.

The power adjustment command feedback compensates for changes in the inbound channel, which is independent of the outbound channel. This independent inbound channel change cannot be measured in the outbound channel. Therefore, the path loss estimation based on the outbound channel and the corresponding transmitter power adjustment cannot reflect the change of the inbound channel. In this way, the power adjustment command feedback is used to compensate for the adjustment of the mobile unit transmitter power based on the inbound channel path loss, which does not exist in the outbound channel.

Before the situation changes significantly, it is best to use closed-loop control processing for commands to the mobile unit. The present invention provides a novel and unique power control circuit in the mesh for minimizing the delay and waiting time of measurement and transmission. The power control circuit (analog control and digital command response) in the mobile unit provides a greatly improved power control process in the cellular mobile phone system.

The above-mentioned preferred embodiments are provided to enable those skilled in the art to make and use the present invention. For those skilled in the art, the various improvements of the above-mentioned embodiments will not be difficult, and its general principles can be applied to other solutions without any creation. Therefore, the present invention is not limited by the embodiments shown here, but the present invention can be applied to a wider range without contradicting the principles and novel features disclosed herein.