MXPA99010987A - Transmit power control in a radio communication system - Google Patents

Abstract

Methods of controlling the power levels of transmitted signals in telecommunication systems are described. For example, a remote terminal measures the quality of a received signal, either by determining the frame error rate or the bit error rate, and reports its quality measurement to a network by sending a quality message. The network causes the signal transmitters to adjust their transmit power levels appropriately. Faster power control methods may be combined with slower power control methods for downlink (network to remote terminal) transmissions in various communications scenarios, such as soft hand-overs.

Description

"CONTROL OF POWER TRANSMISSION IN A RADIO COMMUNICATION SYSTEM" ; BACKGROUND This invention relates to the control of power levels of the signals transmitted in the telecommunication systems, in particular the dispersion spectrum multiple access systems. Good power transmission control methods can be important for communication systems that have many simultaneous transmitters because these methods reduce the mutual interference of these transmitters. For example, power transmission control is necessary to obtain high system capacity in communication systems that use code division multiple access (CDMA). This is important for the uplink, that is, for transmissions from a remote terminal to the network, e.g. a base station. Uplinks are also sometimes called reverse links. In a typical CDMA system, an information data stream to be transmitted is printed in a much higher bit rate data stream produced by a pseudorandom code generator.

The information signal and the pseudorandom signal are typically combined by multiplication in a process sometimes called encoding or dispersion of the information signal. Each information signal is assigned a unique dispersion code. A plurality of encoded information signals are transmitted as modulations of the radio frequency carrier waves and are received together with a composite signal in a receiver. Each of the coded signals overlaps all other coded signals, as well as signals related to noise, both in frequency and time. By correlating the composite signal with one of the singular scatter codes, the corresponding information signal can be isolated and decoded. The need for power transmission control in the uplink is recognized in current CDMA cellular systems, as can be seen from "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", TIA / EIA Interim TIA / EIA / IS-95 (July 1993) and its revision of TIA / EIA Interim Standard TIA / EIA / IS-95-A (May 1995). These standards that determine the particularities of the cellular communication systems of the United States are promulgated through the Telecommunications Industry - Association and the Electronic Industries Association, located in Arlington, Virginia. The control of the incoming link power, in accordance with the IS-95-A standard, is provided by a closed loop method, where a base station measures the strength of a signal received from a remote station and then transmits a bit of power control to the remote station every 1.25 milliseconds. Based on the power control bit, the remote station increases or decreases its transmit power (uplink) by a predetermined amount. In accordance with sections 6.1.2.3.2 and 7.1.3.1.7 of the standard, a power control bit of "zero" causes the remote station to increase its transmit power level by 1 dB and "a" bit of power control causes the remote station to decrease its transmit power level by 1 dB. The IS-95-A standard also focuses on uplink power control in other situations, such as when a remote station access system (before the closed circuit power control method is activated), but these do not are related to this request. The need for power transmission control for a downlink, i.e., for transmissions from the network to a remote station, has been considered less important in current cellular communication systems and other CDMA communication systems. Downlinks are sometimes also called forward links. This may be due in part to the fact that the interference of other transmitters is a smaller problem for the downlink than it is for the uplink because from a remote terminal point of view, the interference fades coherently with the downlink signal intended for it. The need for power transmission control in the downlink has also been misjudged because the signals from a base station are mutually orthogonal in a communication system that complies with the IS-95-A standard, and therefore thus, a large part of the mutual interference in a remote terminal is orthogonal with respect to the downlink signal intended for it. In addition, the IS-95-A standard that specifies a communication system that is intended to handle only speech, resulting in a symmetric load on the uplink and the downlink. Since it has usually been assumed that mutual interference in the uplink not the downlink limits the capacity of the system, the downlink transmission power control has been considered less important. In future communication systems, the services may not be symmetric in the uplink and the downlink and therefore, it is important to optimize both containers independently of one another. A trivial way of controlling the forward link power would be provided by a communication system in which the remote terminal measures its received downlink power level and simply reports the measurement to a base station, which can adjust its power of transmission in predetermined circumstances. This communication system is among those described in International Patent Publication Number WO 95/12297 by Gilhousen et al., Which also discloses a communication system wherein the level of downlink transmission power is reduced by a predetermined amount based on the measurements of the frame error rate, received uplink power levels or received downlink power levels. The downlink control in a system that complies with the IS-95-A standard is based on the frame error rate (FER) measurements by the remote station, which sends FER reports to the system. Sections 6.6.4.1.1 and 7.6.4.1.1 of the IS-95-A standard observe that these REF reports can be sent when a threshold has been crossed and / or periodically. (Typically, an FER report will be sent every 1 to 5 seconds). A problem with this method is that it may take a long time (several seconds) to accumulate the appropriate FER statistics. As a result, it is impossible to trace the Rayleigh fading and shadow fading. The method has shown that it is too slow and is usually hard attributed to any gain compared to the use of downlink power control. Some newer personal communications systems (PCS) also use CDMA. The particularities of the U.S. PCS are specified in "Personal Station-Base Station Compatibility Requeriments for 1.8 to 2.0 GHz Code Division Multiple Access (CDMA) Personal Communications Systems", ANSI J-STD-008 (August 1995), which is similar to the IS-95 standard cellular in many respects. Each operation with the regime set to 2, however, standard J-STD-008 requires the remote station to acknowledge the downlink box errors when they occur. This puts the network in complete control of the errors in the table, but it still takes a long period of time to accumulate the appropriate statistics, yielding only a slight improvement through the method of the IS-95-A standard. In another communication system, concepts such as CODIT, described in "Final Report on Radio Subsystem Functionality", R2020 / CSE / LC / DS / P / 047 / al, UMTS Code Division Testbed (CODIT), CSELT Centro Studi e Laboratori Telecomunicazioni SpA of (August 1995), the quality of the signal is determined by stimulating the untreated bit error (BER) regime instead of FER. Thus, good statistics can be obtained more quickly and a remote station sends BER reports to the network more frequently (typically 1 to 10 times per second). The operation of the system improves considerably compared to a system using de-linking power transmission control in accordance with IS-95-A, but the CODIT method is still too slow to handle Rayleigh fading. The uplink power transmission control method described in the IS-95-A standard for downlink transmission power control could be used. This is described in European Patent Publication Number 0 680 160 by Dohi et al. The remote terminal would then measure the downlink signal to interference ratio (SIR) and transmit an appropriate power control command in - the uplink. In accordance with IS-95-A, each power control command would be a single bit that would be decoded in order to minimize the overhead costs of sending signals. However, the communication system - to which European Patent Number 0 680 160 is addressed, has certain significant differences from the systems specified by the IS-95-A standard. For example, the European system has a frame length that is half of the IS-95-A, a bit rate of several hundred kilobits per second, a wider channel bandwidth of 5 MHz, and a scheme of CDMA chip of four million chips (integrated circuits) per second. This communication system would go to the track of the Rayleigh fading quite well and could work well when the remote terminal is not in a soft delivery mode, that is, when the remote terminal is not communicating with two or more base stations simultaneously. Soft delivery is described in U.S. Patent Nos. 5,109,528 issued to Uddenfeldt and U.S. 5,327,577 issued to Uddenfeldt, both of which are expressly incorporated herein by reference. When the remote terminal is not in soft delivery mode, the error rate of the uncoded power control commands would typically be - about one percent, which would not cause any big problems. However, the error rate of the uncoded downlink energy control knobs can be expected to increase significantly when the remote terminal is a smooth handling mode. In addition, errors in the commands received at different base stations involved in soft delivery will be almost independent. Since 1600 power control commands per second would be sent to the two base stations involved in a smooth delivery in accordance with the system described by Dohi and others, the power transmitter levels sent from the base stations can be expected to deviate with respect to each other up to levels that would be suboptimal from a system capacity point of view. The loss of capacity occurs because at least one of the base stations communicating with a remote station in soft delivery mode will transmit a power level that is too high.

COMPENDIUM These and other problems of the above communication systems are solved by the invention 1 of the applicants which provides in one aspect a method for controlling the power levels of the signals transmitted by the base stations, in a communication system having base stations and remote stations. The method includes the step of determining at a remote station whether the remote station is simultaneously receiving a first signal transmitted by a first base station and at least one second signal transmitted by, at least a second base station including essentially identical message information. The first base station transmits to the controller a first report of a power level of the first signal, and at least one second base station transmits to the controller at least a second report of a power level of at least one second signal. The controller, based on the first report and at least one second report, transmits to the first base station a first command to control the power level of the first signal and transmits to at least one second base station, so minus a second control to control the power level of at least one second signal. This method may further include the steps that when the first and at least one second signal does not include essentially identical message information, determine a signal to the interference ratio of the first received signal, transmitting from a remote station a report of the default signal to the interference ratio, and essentially controlling simultaneously the power level of the first signal based on the report that was received in the first base station. This method may also include the steps of, when only one of the first signal and at least one second signal is received at the remote station, to determine a signal to the interference ratio of the received signal, transmit from the remote station a report of the signal determined to the interference ratio and almost simultaneously controlling the power level of the signal based on the report as received at the respective base station. In these methods, the first and second controls may - cause the first and second base stations to adjust the power levels of their transmitted signals in such a way that the power levels have a predetermined relationship such as a considerable match to the arithmetic means of the power levels of the signals transmitted by the first and second base stations. Likewise, reports can be sent periodically or at the occurrence of a predetermined event.

- - In another aspect of the invention, a method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations includes the step of determining whether the remote station is receiving simultaneously a first signal transmitted by the first base station and at least one second signal transmitted by at least one second pass station including essentially identical message information. When the first and at least one second signal includes essentially identical message information, the remote station determines a quality of at least a first received signal and at least a second signal and transmits a report of the determined quality. The method further includes a step of controlling almost simultaneously the power level of the first signal and the power level of at least one second signal based on the report as received in the first base station and the report as received in at least one second base station. In a further aspect, the method may also include, when the first and at least one second signal does not include the essentially identical message information, the steps of determining a signal to the interference ratio of the first received signal, - transmitting from the remote station a report of the determined signal to the interference ratio and almost simultaneously controlling the power level of the first signal based on the report _tal and as received at the first base station. The method may also include when only one of the first signal or at least one second signal is received at the remote station, the steps of determining a signal to the interference ratio of the received signal, transmitting from the remote station a report of the signal determined to the interference ratio and almost simultaneously controlling the power level of the signal based on the report, as received at the respective base station. The determined quality may be a frame error rate and a bit error rate, and the reports may be sent periodically or upon occurrence - a predetermined event. In another aspect of the invention, a method for controlling the power levels and the signals transmitted by the base stations in a communication system having base stations and remote stations includes the step of determining whether the remote station is simultaneously receiving a first signal transmitted by a first base station and at least one second signal transmitted by at least one second base station that includes essentially identical message information. When the first signal and at least one second signal includes essentially identical message information, the remote station identifies the signal having a higher power level and transmits a report of the identified base station. The power levels of the first and at least the second control signals based on the report such that the power level of at least one second signal is essentially zero when the report indicates that the power level of the first signal is higher than the power level of at least one second signal. The control step includes determining a signal to the interference ratio of the first received signal, transmitting from the remote station a report of the determined signal to the interference ratio, and controlling the power level of the first signal based on the report as it was received in the first base station. This method may further include the steps of, when the first and second signals do not include essentially identical message information, determining the signal to the interference ratio of the first received signal, transmitting from the remote station the report of the determined signal to the interference ratio and controlling almost simultaneously the power level of the first signal based on the report, as received at the first base station. This method may also include the steps of, when only one of the first signal and at least one second signal is received at the remote station, determining a signal to the interference ratio of the received signal, transmitting from the remote station a report of the signal determined to the interference ratio and control almost simultaneously the power level of the signal based on the report that was received at the respective base station. Reports can be used periodically or when a predetermined event occurs. In another aspect of the invention, a method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations includes the step of determining whether the remote station is simultaneously receiving a first signal transmitted by the first base station and at least one second signal transmitted by, at least a second base station including essentially identical message information. When the first signal and so - minus a second signal includes essentially identical message information, the first base station calculates a signal to the inter-reference ratio of the first signal received at the remote station, and at least one second base station calculates a signal to the ratio of interference of at least one second signal received at the remote station. These calculations are transmitted to a controller that compares the respective reports, transmits to the first base station a first command to control the power level of the first signal, and transmits at least one second base station to at least one second command to control the power level of at least one second signal. At least one second command causes at least one second base station to reduce the power level of at least one second signal to essentially zero, when the controller determines that the signal calculated to the interference ratio of the first signal is greater than the signal calculated at the inter-reference ratio of at least one second signal. This method may further include the steps of, when the first signal and at least one second signal does not include essentially identical message information, determining a signal to the interference ratio of the first received signal, transmitting from the remote station 1 a report of the signal determined to the interference ratio and controlling almost simultaneously the power level of the first signal based on the report, as received at the first base station. This method may also include the steps of, only a first signal and at least one second signal is received at the remote station, to determine a signal to the interference ratio of the received signal, transmit from the remote station a report of the signal determined to the interference ratio and almost simultaneously controlling the power level of the signal based on the report, as received at the respective base station. Reports can be sent periodically or upon occurrence - a predetermined event.

BRIEF DESCRIPTION OF THE DRAWINGS The particularities and objects of the invention of the applicants will be understood by reading this description together with the drawings, in which: Figure 1 illustrates a method of controlling downlink transmission power; Figure 2 illustrates a smooth delivery involving a remote station and two base stations; Figure 3 illustrates a method of overcoming a problem of the remote control power control commands that are received with a signal level that is too low during the soft delivery mode; Figure 4 illustrates another method of overcoming the problem of the power control knobs of a remote station that are received by a signal level that is too low during the soft delivery mode; and Figures 5A, 5B and 5C illustrate the operation of the applicants' communication system in accordance with the invention.

DETAILED DESCRIPTION While this description is in the context of cellular communication systems involving portable or mobile radio telephones, it will be understood by those skilled in the art that the invention of the applicants can be applied to other communication applications. Furthermore, even though the invention can be used in the CDMA communication system, it can also be used in other types of communication systems. A rapid uplink power control method that involves the transmission of power control command consisting of individual uncoded bits, each 1.25 milliseconds, is specified by the IS-95-A standard. This method can be understood by referring to Figure 1, which is described in greater detail below. A remote RT station would measure the SIR of the downlink signal of a base station BS1 where the RT station is communicating and the remote station RT would transmit a measured SIR report or an uncoded power control command to "the base station, based on this report or command, the power level (and therefore, SIR) of the downlink signal would be appropriately controlled by the base station or by another component - of the network, such as the radio network controller RNC. This method can be used for downlink transmission power control and the European publication EP 0 680 160 cited above describes the use of this method for downlink control during soft delivery. Even though this simple downlink power control method using uncoded knobs can be used when the communication system is not in a soft delivery mode, this simple quick method does not work well during smooth delivery due to the possibility of errors reception and deviation of power level in the - Different base stations involved in smooth delivery. The independent errors in the downlink power control commands transmitted by a remote station and received by different downlink transmitters can be expected to cause the transmitted power levels of the downlink transmitters to bypass one with respect to the other. the other. When the intensities of the downlink signals of two or more transmitters received at a remote terminal in the soft delivery mode are more or less equal, the rate of deviation can be expected to be moderate. When the received downlink signal strengths are unequal, however, the transmit power levels of the downlink transmitters may deviate by rapidly separating causing large losses in system capacity. The disadvantages of using the fast power control method for the downlink are overcome by the invention of the applicants. One way to "solve the downlink transmission power control problem according to the applicants' invention is a method that makes frequent adjustments to the transmitted link power levels transmitted from the 1 - base stations involved in smooth delivery. These base stations send the last values of their downlink transmission power levels to a radio network controller, which compares those values and sends respective adjustment commands? Pi (tn) and? P2 (tn) back to the base stations. This scenario is illustrated in Figure 1 where the base station BS1 sends a message Pi (tn) indicating its downlink transmission power level P? (Tn) during time tn to the radio network controller RNC. In a cellular communication system, the RNC controller could be a base station controller or a mobile services switching center. In addition, a base station BS2 sends a message P2 (tn) indicating its downlink transmit power level P2 (tn) during it time tn to the controller RNC. In the second soft delivery mode shown in Figure 1, a remote station RT receives the signals from the base station BS1 and receives the signals having essentially the same message information from the base station BS2. The RNC controller sends respective adjustment commands? P? DL (tn) and? P2DL (tn) to the base stations which are based on the messages Pi (tn), P2 (tn). In other modalities that are described in greater detail to - Then, the controller may also determine the adjustment commands based on a report from the remote RT terminal identifying the base station receiving the remote terminal at a higher power level or with better SIR. The adjustment knobs cause the base stations to adjust their downlink transmit power levels so that the desired ratio between P? (Tn +?) And P2 (tn + i) is maintained (eg both levels can remain essentially the same). or as described in greater detail below, one of the power levels can be controlled to be essentially zero). It will be understood that the transmission power levels P? (Tn), P2 (tn) result from the above commands? Pi (tn -i) and? P2 (tn -i), as shown in Figure 1. The controller RNC can determine the adjustment controls in several ways. For example, the power levels P? (Tn) and P2 (tn) can be adjusted to their arithmetic mean value (P? (Tn) + P2 (tn)) / 2. As an alternative, power levels can be adjusted to their geometric mean value. As another alternative, which has the advantage of rapid response, the power levels can be adjusted in such a way that the largest power level e.g. to a level essentially equal to the lowest power level. As yet another alternative, the power levels can be adjusted in such a way that the lower power level is increased e.g. to a level essentially equal to the highest power level. As yet another alternative, the power levels can be adjusted in such a way that the lowest power level is controlled to make essentially zero. Power level adjustments would typically be made once per frame, maintaining the deviation between the downlink transmit power levels of the downlink transmitters involved in smooth delivery up to a low level eg, less than 1 dB on average . In order to minimize the delays between the measurement and power level settings, the in-band signals could be used to both send the messages Pi (tn), P2DL (tn) from the base stations BS1, BS2 to the RNC controller and send the adjustment knobs? P? DL (tn),? P2 (tn) from the RNC controller to the base stations. By "band signals" it is meant that the information is sent together with the user data and not as separate messages in a separate control channel. In the way that the independent errors in the remote station power control commands arrive, illustrated in greater detail in Figure 2, it demonstrates a remote RT terminal in communication with two base stations BSl, BS2 that remain under control of a radio network RNC controller. In a soft delivery mode shown in Figure 2, as in Figure 1, the remote RT station receives signals from the base station BSl with the power level Pi and receives signals that have essentially the same message information from the base station BS2 with a power level P2. The power control PC commands transmitted via the remote RT station are received by the base station BSl as PC commands and are received by the base station BS2 as PC 'controls. Due to errors that can arise from many sources, a PC control may not be the same as either or both of the PC, PC 'and PC commands may not be the same as the PC' command. The amplitude of the difference between a downlink power level and another downlink power level affects the capacity of the system because one of the transmissions from the base station looks similar to an interference with the other station of base. In addition, the rate at which each level of downlink power deviates is important, because faster regimes usually require that control commands be extracted more frequently. This increases the message load that must be carried out by the links between the base stations BS1, BS2 and the RNC controller. In a communication system operating in the manner described in section 6.6.6.2.7.2 of the IS-95-A standard, the transmission power of the remote terminal in the uplink to the base stations BSl, BS2 shall be mainly regulated , as ordered by the "nearest" base station BSl. As a result, the uplink transmission power level of the remote station will be too low from the point of view of the base station BS2"furthest away". It will be understood that a "nearer" transmitter does not necessarily remain geographically closer to a receiver but is nearer from a point of view of the received downlink power level, i.e., its downlink signal is received at a level of higher power for a given transmitted power level. Similarly, a "furthest" transmitter is further removed from the point of view of the received downlink power level, that is, its downlink signal is received at a lower power level for a transmitted power level. determined. Accordingly, the PC remote control power controls of the remote station will be received with too low a signal level in the base station BS2, causing more power control command errors at station BS2. These additional errors are the differences with the power control commands received in the base station BS1, ie, PC PC '. The difference between Pi and P2 can be large e.g. as much as 8 dB in some communication systems, and this large difference results in a plurality of PC? PC 'of approximately 10 percent. The downlink transmission power contact according to another aspect of the applicants' invention avoids these problems by using any of the downlink power control methods based on quality described above, such as the base methods. of FER specified in the IS-95-A or J-STD-008 standards or the BER-based method used in the CODIT_system when the remote terminal is in soft delivery mode. As described in more detail below, the remote RT terminal measures the quality of the downlink signal received either by determining the FER or the BER and then the remote RT terminal reports its quality measure to the network by sending a quality message appropriate to the base stations involved in the delivery. Each base station sends the quality message from the remote terminal (a Layer 3 message) to the RNC controller, which causes the - base stations appropriately adjust their downlink transmission powers. It is important to understand that quality messages from the remote terminal are more than just the forward link signal strength information, such as that described in International Publication Number WO 95/12297 cited above. The quality messages of the requesters are produced based on the downlink signals that have been decoded or demodulated instead of a single signal level or SIR determinations. The additional effort necessary to generate the quality messages is rewarded with the advantages of the invention of the applicants. The applicants method provides almost optimal CDMA communication system capacity for a very low cost in sending signals between the network's RNC controller and the base stations involved in soft delivery (eg BSl, BS2 stations in the Figure 2). It will be noted that the Layer 3 quality messages received by the network controller from a remote terminal through two or more base stations will generally be identical and therefore, the controller does not need to negotiate between message different quality from the same mobile station.

The gain obtained using the downlink power control method illustrated by Figure 1 compared to the use of one of the base power quality control methods (Figure 2) may be small during smooth delivery. Since the remote terminal in soft delivery mode is probably remote from the base stations, the remote terminal will possibly have good frequency diversity from each base station because of the multipath and the power fluctuations have a chance of being slow in Comparison with non-soft delivery mode. Therefore, the remote terminal can use signal strength from all the base stations with which it is connected during smooth delivery, reducing the fading effects and the remote terminal can use power control methods based on the quality of the "slow" signal is not needed "fast" methods. It will also be appreciated that the required quality reports can be obtained at low cost at the air interface and transport capacity. In another aspect of the Applicants' invention, the problem that the remote control power control PC commands are received at too low a signal level in a base station BS2"furthest away" during the soft delivery mode is exceeded by - - Several ways. A base station that is in a "soft delivery mode" is different from a base station that is not in a "soft delivery mode" due to the assignment of the first of the logical and physical resources eg, codec / decoders to different communication connections. For example, the remote RT station may either send periodic reports of its received downlink signal strength to the network or it may send a report of whether a signal from a new downlink transmitter is received at an intensity that is higher than any other downlink signal strength currently received. It will be understood that the IS-95-A standard does not require the remote station to send reports of its received downlink signal strength. In this communication system, the network controller RNC would respond to the signal strength reports of the remote station causing only the base station whose downlink signal is received with the highest intensity at the remote terminal RT to transmit. This scenario is illustrated in Figure 3 which shows that when the downlink power level Pi received at the remote terminal from the base station BSl is greater than the downlink energy level P2 received from the base station BS2, the downlink power level Pi transmitted by the base station BS1 is greater than zero and the downlink power level P2 transmitted by the base station BS2 is zero. (In practice, the level 'P2 of energy only needs to be considerably less than the level of energy Pi). The weaker base station BS2 would otherwise otherwise function in a soft delivery mode. The network informs the remote RT terminal when the system decides to change the transmitting base station to accommodate the differences of the base station such as different pseudo-noise signals, even though the different base stations usually have the same appearance from The point of view of the remote station in a soft delivery mode. The problem of deviation between the levels of downlink transmission power, ie, that the PC remote control power controls are received with too low a signal level in a base station BS2"further away" during the soft delivery mode, it can be overcome in a different way in a communication system in which the uplink SIR is measured for each frame in the base stations involved in a soft delivery and the SIR measurements are sent to the controller Communication. The communication controller processes the SIR values from the base stations involved in soft station delivery to only those base stations transmitting whose level of downlink power received at the remote terminal is higher. It will be understood that the signals received from the different transmitters e.g. the base stations different or received from a transmitter, e.g. a mobile station, in different receivers e.g. different base stations - they are advantageously processed by not dispersing each signal by combining the undispersed signals, e.g. using an equalizer, receiver or other equivalent device and then decoding the combination signal. This scenario is illustrated in Figure 4 which shows that the downlink power level P? (Tn +?) Transmitted by the base station BSl during the time tn + i is greater than zero and the downlink power level P2 (tn + i) transmitted by the base station BS2 during the time tn + i is zero. This condition occurs as a result of the respective adjusted downlink transmission power control knobs SetP? DL, SetP2DL sent by the radio network controller RNC to the base stations BS1, BS2 respectively. The network RNC control generates the power adjustment commands based on the respective determinations of the base stations and the reports of the uplink SIR values SIR (tn), SIR2 (tn) during the previous time tn. Therefore, sometimes when the uplink power received at the base station e.g. station BS1 is higher than the uplink power received at another base station, e.g. the station BS2, the controller RNC sends the messages to the base station BSl causing the station BSl to start transmitting towards the remote terminal RT to the base station BS2, causing the base station BS2 to stop transmitting to the terminal RT remote terminal and the remote RT terminal causing the RT terminal to listen only to the base station BSl and not the base station BS2 from a specific frame number forward. It is currently believed that the method illustrated in Figure 4 works best when the path losses in the uplink and downlink are highly correlated. This is possibly the case for a communication system such as that described in the aforementioned European Patent Publication Number 0 680 160 having a downlink / link bandwidth of 5 MHz. For that wide-channel bandwidth, the propagation of the multipath to and from the remote station is made possible by reducing the problems related to Rayleigh fading. Multipath propagation * is even more possible in a soft delivery mode where the remote terminal has the possibility of being placed on the border between the cells between the sectors of the cell. Thus, the correlation between the characteristics of the uplink channel and the downlink will usually be intense. For those cases in which this is not so, the operation of the method illustrated in Figure 4 to some degree will depend on the movement of the remote terminal and the length of the filter of the network controller. Applying either the method illustrated in Figure 3 and Figure 4, the remote station receives the downlink power only from the base station that is received most intensively. Therefore, the problem of loss of capacity due to the deviation of the downlink transmission power is eliminated without significantly increasing the message load through the transport interface between the base stations and the network controller. Another advantage of these methods is that the remote terminal remains synchronized to both base stations, while the system is in soft delivery mode, therefore, it is unnecessary to spend time and effort to re-synchronize the remote terminal, which it would be necessary if the system went out of soft delivery mode. A specific advantage of the method illustrated in Figure 4 is that it is independent of the way in which messages on its interface (the uplink and downlink between the remote terminal and the base stations) are specified; this is not the case for the method illustrated in Figure 3 which involves reports from the remote terminal of its received downlink power level. Figures 5A, 5B and 5C further illustrate the operation of a communication system in accordance with the invention of the applicants. (The method illustrated by these figures is also illustrated in Figure 1). In block 501, the base station BS1 receives the data and transmits power adjustment commands from a mobile RT station. The base station BS1 identifies and decodes an adjustment command received at a first moment in time that can conveniently have values of either +1 or -1, and correspondingly adjusts its "downlink" transmission power level during the next instant As indicated by block 503 in Figure 5A, for example, if the mobile station sends a setting edge PC = 1, then the transmit power level of the base station P? (tn +?) = +1 dB with respect to its previous transmission power level - P? (Tn). Similarly, if the mobile station sends an adjustment knob PC = 1, then the transmit power level of the base station P? (Tn +?) = -1 dB with respect to its previous transmission power level P ? (tn) In block 505, the message P? DL (tn) indicating the downlink transmission power level P? (Tn) during time tn is sent by base station BS.sub.1 to controller RNC. The base station preferably sends these messages not as frequently as the mobile station sends the power adjustment knobs in order to reduce the load of sending signals on the base station-controller connection. For example, the base station can count the number of adjustment knobs received n and send a message each adjustment knob N-th, where N is a factor a multiplied by the number n. The a factor can be an integer within the range of about 16 to about 1600 for some communication systems. In block 507, the base station BSl adjusts its downlink transmission power level to the amount of the command. As indicated by block 509 in Figure 5B, the controller receives the message Pi (tn) and possibly messages from other base stations involved in soft delivery, e.g. P2 (tn). The controller, which may include a specialized circuit or a programmable processor for the object, then determines the respective new adjustment commands? P? DL (tn + i) and? P2 (tn + i), which is indicated by block 503 in Figure 5B and can be based on the difference (block 511) between the downlink transmission power levels P? (tn), P2 (tn) of the base stations BS1, BS2. In the illustrated example P? DL (tn) > P2DL (tn), and therefore, the new adjustment knob? Pi (tn + i) corresponds to the previous power level of the first base station minus half of the difference between the power levels and the new command of setting? P2 (tn + i) corresponds to the second level of the previous power of the base station plus half of the same difference. If P2 (tn) > Pi (tn), essentially the same operations would be carried out, but the identities of the base stations would be exchanged. These commands are then communicated in any convenient manner with the respective base stations, as indicated by block 515. The operation of this kind of communication system is further illustrated by Figure 5C, where the adjustment knob? Pi from the RNC controller is received by the base station BSl, as indicated by the block 517. In response, the base station adjusts its transmit power level during the time tn + tm, as indicated by block 519, in - - where the interval tm is a convenient time interval such as a whole number of communication frames. It will be appreciated that similar operations would be carried out at the other base station (station BS2). Furthermore, if the power level of the weaker base station were to be sent to be essentially zero by the operations indicated by blocks 511-519, the weaker base station would advantageously be kept in soft delivery mode in all cases. the other respects, as described above. It will be understood that the invention of the applicants is not limited to the specific embodiments described above and that modifications can be made by persons skilled in the art. The scope of the invention of the applicants is determined by the following claims and any and all modifications that fall within the scope are intended to be included in it.

Claims (24)

R E I V I N D I C A C I O N S

1. A method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations, comprising the steps of: determining at a remote station whether the remote station is simultaneously receiving a first signal transmitted by the first base station, and at least one second signal transmitted by at least one second base station including essentially identical message information; transmitting to a controller from the first base station a first report of a power level of the first signal; transmitting to the controller from at least a second base station, at least a second report of a power level of at least one second signal; compare the controller of the first report and at least a second report; transmitting from the controller to the first base station a first command to control the power level of the first signal; and transmitting from the controller to at least a second base station, at least one second control to control the power level of at least one second signal.

The method of claim 1, further comprising the steps of, when the first signal and at least one second signal does not include essentially identical message information: determining a signal to the interference ratio of the first received signal; transmit from the remote station a report of the determined signal to interference ratio; and controlling almost simultaneously the power level of the first signal based on the report, as received at the first base station.

The method of claim 1, further comprising the steps of, when only a first signal and at least one second-signal is received at the remote station: determining a signal to the interference ratio of the received signal; transmit from the remote station a report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the signal based on the report, as received at the respective base station.

4. The method of claim 1, wherein the first and second knobs cause the first and second base stations to adjust the power levels of their signals transmitted in such a manner, so that the power levels have a predetermined relationship.

The method of claim 4, wherein the predetermined relation is considerable equality to an arithmetic means of the power levels of the signals transmitted by the first and second base stations.

6. The method of claim 1, wherein the reports are sent periodically.

The method of claim 1, wherein the report is sent when a predetermined event occurs.

8. A method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations, comprising in a remote station the steps of: determining whether the remote station is receiving simultaneously a first signal transmitted by the first base station and at least one second signal transmitted by at least a second base station including essentially identical message information; when the first and at least one second signal includes essentially identical message information, determining at the remote station a cavity of at least one first received signal, and at least one second signal; transmit a report of the determined quality from the remote station; and controlling almost simultaneously the power level of the first signal and the power level of at least one second signal based on the report, as received in the first base station and the report as received in at least a second base station.

The method of claim 8, further comprising the steps of, when a first signal and at least one second signal does not include essentially identical message information: determining a signal to the interference ratio of the first received signal; transmit from the remote station a report of the determined signal to the interference ratio; and to control almost simultaneously the power level of the first signal based on the report, as received at the first base station.

The method of claim 8, further comprising the steps of, when only one of the first signal and at least one second signal is received at the remote station: determining a signal to the interference ratio of the received signal; transmit from the remote station a report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the signal based on the report, as received at the respective base station.

The method of claim 8, wherein the determined output is a frame error rate.

12. The method of claim 8, wherein the determined quality is a bit error rate.

The method of claim 8, wherein the reports are sent periodically.

The method of claim 8, wherein a report is sent when a predetermined event occurs.

15. A method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations, comprising the steps of: determining whether the remote station is simultaneously receiving a first signal transmitted by the first base station, and at least one second signal transmitted by, at least one second base station including essentially identical message information; when the first signal, and at least one second signal includes essentially identical message information, identify at the remote station the signal having a higher power level; transmit from the remote station a report of the identified base station; and controlling a power level of the first signal and a power level of at least one second signal based on the report, such that the power level of at least one second signal is controlled to essentially make zero when the report indicates that the power level of the first signal is higher than the power level from at least one second signal; wherein the control step includes determining a signal to the interference ratio of the first received signal, transmitting from the remote station a report of the determined signal to the interference ratio and controlling the power level of the first signal based on the report as received at the first base station.

The method of claim 15, further comprising the steps of, when the first signal and at least one second signal does not include essentially identical message information: determining the signal to the interference ratio of the first received signal; transmit from the remote station the report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the first signal based on the report, as received at the first base station.

The method of claim 15, further comprising the steps of when the first signal and at least one second signal is received at the remote station: determining a signal to the interference ratio of the received signal; transmit from the remote station a report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the signal based on the report, as received at the respective base station.

18. The method of claim 15, wherein the reports are sent periodically.

19. The method of claim 15, wherein a message is sent upon the occurrence of a predetermined event.

20. A method for controlling the power levels of the signals transmitted by the base stations in a communication system having base stations and remote stations, comprising the steps of: determining whether the remote station is receiving simultaneously a first signal transmitted by the first base station, and at least one second signal transmitted by at least one second base station that includes essentially identical message information; when the first signal and at least one second signal include essentially identical message information, calculate in the first signal a signal to the interference ratio of the first signal received in the remote station; calculating in at least one second base station a signal to interference ratio of at least one second signal received at the remote station; transmitting to a controller from the first base station and from at least one second base station the respective reports of the calculated signal to the interference ratios; compare the respective reports in the controller; transmitting from the controller to the first base station a first command to control the power level of the first signal; and transmitting from the controller to at least one second base station, at least one second control to control the power level of at least one second signal; wherein at least one second command causes at least one second base station to reduce the power level of at least one second signal to essentially zero, when the controller determines that the signal calculated to the interference ratio of the first signal is larger than the signal calculated at the interference ratio of at least one second signal.

The method of claim 20, further comprising the steps of, when the first signal and at least one second signal does not include essentially identical message information: determining a signal to the interference ratio of the first received signal; transmit from the remote station a report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the first signal based on the report, as received at the first base station.

The method of claim 20, further comprising the steps of, when only the first signal and at least one second signal is received at the remote station: determining a signal to the interference ratio of the received signal; transmit from the remote station a report of the determined signal to the interference ratio; and controlling almost simultaneously the power level of the signal based on the report, as received at the respective base station.

23. The method of claim 20, wherein the reports are sent periodically.

24. The method of claim 20, wherein a report is sent upon the occurrence of a predetermined event.