MXPA00005819A - Base station transmit power control in a cdma cellular telephone system - Google Patents

Abstract

A power control method in accordance with the present invention synchronizes the transmit power levels at the base stations currently serving a mobile station and an initial transmit power level of a new target base station being added in a diversity handover situation. At the beginning of the handover, a radio network controller orders the serving base stations to measure their respective transmit powers to the mobile station. Each serving base station then measures its transmit power to the mobile station and reports the power level measurements to the radio network controller. An initial transmit power setting is determined for the target base station, and new transmit power settings are determinedfor the serving base stations synchronized for example to a particular time (i(t0)). At or about synchronizing time i(t0), the target base station transmits to the mobile station at the initial power setting, and at or about the same time, the serving base stations preferably also adjust their transmit powers toward the new values. Alternatively, the serving base stations transmit at their respective new values at or about time i(t0) . In a preferred embodiment of the present invention, the serving base station power adjustment is performed gradually.

Description

CONTROL OF TRANSMISSION POWER OF BASE STATION IN A CDMA CELLULAR TELEPHONE SYSTEM FIELD OF THE INVENTION The present invention relates to cellular telephone systems. More specifically, the present invention relates to the control of base station transmission power during transfer situations in a code division multiple access cellular telephony system. BACKGROUND AND COMPENDIUM OF THE INVENTION In a cellular communication system, mobile radio stations communicate through respective radio channels to a base station. Several base stations are connected to a switching node typically connected to a gate that connects the cellular communication system with other communication systems. A call made from an external network to a mobile station is directed towards the gate, and from the gateway through one or several switching nodes to the base station (s) serving the station. mobile call. A base station calls the mobile station called and establishes a radio communication channel. In a Code Division Multiple Access (CDMA) mobile communication system, the information transmitted between a base station and a mobile station is modulated by a mathematical code, sometimes known as an extension code in order to distinguish this information from the information associated with other mobile stations or base stations that are using the same radio frequency band. Accordingly, individual "channels" of radio are discriminated based on these codes. Several aspects of CDMA are presented in one or several books such as "Applications of CDMA and Wireless / Personal Communications", (Garfield, Vijay K et al., Prentice-Hall (1997). The extension spectrum communications allow the reception of mobile transmissions in two or more base stations ("diverse") and their simultaneous processing to generate a received signal. With these combined signal processing capabilities, it is possible to carry out a transfer from one base station to another, (or from one antenna sector to another sector in the same base station), without any perceptible disturbance as to voice or data communication. This type of transfer is typically referred to as "diversity transfer". During a diversity transfer, the signaling and voice information of several base stations are combined at a common point with decisions made as to the "quality" of the data received. Typically, this common point is located at the switching node connected to the base stations. In the opposite direction, voice and signaling information is transmitted from several base stations, and a mobile station combines the results. CDMA systems offer "soft" and "softer" diversity transfer. In a soft transfer, as the mobile station moves towards the edge of a cell, the adjacent cell base station assigns a transceiver to the call while the current base station continues to transfer the call. As a result, the call is transferred by both base stations on a do basis before interrupting. The soft diversity transfer occurs with both base stations handling the call until the mobile station has moved sufficiently close to one of the base stations which then handles the call exclusively. A smoother diversity transfer occurs when the mobile station is in transference between two different sectors in the same base station. Since all users in a CDMA communication system transmit information using the same frequency band at the same time, each user communication interferes with communications from other users. further, signals received by a base station from a mobile station near the base station are much stronger than signals received from other mobile stations located at the base station cell boundary. As a result, distant mobile communications are overcome and dominated by closer mobile stations, and it is the reason why this condition is sometimes referred to as the "proximity-distance effect". Therefore, to achieve increased capacity by decreasing unnecessary interference, all signals transmitted by mobiles must reach a base station with approximately the same average powers regardless of their distance from the base station.

Accordingly, a transmission power control (TPC) uplink (or reverse) of the mobile station to the base station is one of the most important factors to improve the performance and capacity of a CDMA system. In general, the mobile station tries to control its transmit power based on the strength of the signal to generate a signal-to-noise (SNR) value (or other suitable measurement) of signals received from a base station (control of open loop transmission power) and the base station sends transmission power control messages to the mobile station (closed-loop power control) for the ultimate purpose of controlling the power received at the base station within a relatively small tolerance, for example, IdB, for all transmissions of mobile stations received at this base station. The control of downlink (or forward) transmission power is also important for transmissions from the base station to the mobile station. Specifically, the base station varies its transmission power according to the messages or downlink transmission power control commands sent by the mobile station. There are many reasons to control the downlink power. One reason for controlling the downlink transmission power is to allow the fact that in certain coverage area locations the downlink channel from the base station a to the mobile station may be especially unsatisfactory, an example of such a location is a point at which the loss of trajectory towards one or two neighboring cells is almost the same as the loss of trajectory towards the base station communicating with the mobile station. In this location, the total interference is increased several times compared to the interference experienced by a mobile station at a point relatively close to the base station. An additional reason is that the interference of these neighboring cell sites does not vanish in unison with the desired signal. In addition, the mobile station can be located at a location where several strong multi-path signals arrive which results in relatively large interference. In other situations, the mobile station may be located in a location where the relationship between signal and interference is especially good. Another reason for controlling the downlink power is to minimize the interference of cells caused by unnecessarily high base station transmission power levels. By varying the downlink power level to the minimum value required to achieve a particular quality, unnecessary interference is avoided. If the downlink power level is set at a constant but high level to ensure a minimum quality in unsatisfactory conditions, a great part of the time the downlink power will be too high thus causing unnecessary interference. This interference reduces the capacity of the cell. In all these cases, it is advantageous for the base station to raise or lower its transmission power to ensure an acceptable quality but at the same time to reduce as much as possible the interference with other signals. Since control of the power in CDMA systems is important, transmission power control settings occur frequently, such as every 0.625 milliseconds. By adjusting the downlink transmission power, the mobile station is continuously measuring the transmission power level received from the base station and determines whether the average level is higher than a reference value. If this is the case, one or several transmission power control bits having a value are transmitted upwards from the mobile station to the base station to decrease the power transmitted by a predetermined increase., such as, for example, 1 dB up to a minimum transmission power value. On the other hand, when the measured value is less than the reference value, one or several transmission power control bits of opposite value are transmitted upwards to the base station in order to increase the transmission power by a predetermined increase. , such as 1 dB up to a maximum value. This transmission power control begins while uplink synchronization and downlink synchronization is being acquired and continues throughout the communication. A problem arises in the coordination of downlink transmission power levels between base stations in diversity transfer. One problem is that during a transfer, the transmit power command from the mobile station to the base stations involved in the transfer may be received erroneously at one or more of the base stations. Another is that a difference between the downlink transmission powers of the base stations involved in the soft transfer can be quite large. The difference refers to the difference between the transmission power level of one (or several) base stations that are currently providing service to the mobile station and the power level of a new base station that is carrying out a transfer of diversity with the mobile station. While a difference may or may not be desired for a particular application, it is difficult in any situation for the new base station to know the transmission power level of the old base station when the new base station begins transmitting. Since the. Transmission power adjusted as quickly as, for example, 16 settings every 10 milliseconds, when a transmission power level is determined and supplied to the new / white transfer base station based on a TPC command, the actual transmit power in one or several of the old service base stations that are already serving the mobile station may have changed significantly during this time delay. Let's consider the following scenario. At the beginning of a soft transfer, transmission power level measurements from a service base station and from a white base station to a mobile station are sent to a network node. The network node of these transmission power measurement reports periodically determines an appropriate power level for the white base station - either the same power or a power at a specific desired difference and sends the power level determined to the white base station. When the white base station receives the transmission power determined from the network node, it may have gone from 100 msec to one second. During this one second period, the service base station transmit power level may have changed 100 or up to 1000 times due to the speed at which the transmit power is adjusted, for example, every 0.625 milliseconds. Accordingly, the transmission power command determined for the white base station will probably be quite different from what the transmission power level should be at the time of actual receipt of the command and its implementation at the white base station, that is, after a significant time delay. What is required is a way in which this difference in unwanted base station transmission power at the time of transfer can be compensated for or eliminated. In addition, the solution to the problem identified above should preferably be a simple solution that allows the mobile station to transmit only a set of power control commands to all base stations involved in the transfer. It is an object of the present invention to overcome the problems identified above and in particular to offer a technique of coordination of base station transmission power that does not increase the complexity of the mobile station. It is another object of the invention to eliminate erroneous transmission power levels including transmission power levels of undesirable difference in base stations involved in a diversity transfer. It is a further object of the invention to compensate for the shift in transmission power levels between base stations involved in diversity transfer. For example, as a result of different error frequencies in the uplink control channels where the mobile station transmits the same downlink power control command to these base stations, each base station ends up transmitting power levels more or less different according to the respective frequencies of errors in the bits. A power control method according to the present invention synchronizes the transmit power levels in the base stations that are currently serving a mobile station and an initial transmit power level of a new white base station is added in a situation of diversity transfer. At the beginning of the transfer, a radio network controller gives commands to the service base stations to detect their respective transmission powers to the mobile station each service base station reports its transmit power (to the mobile station) to the radio network controller. The radio network controller determines an initial transmission power level for the white base station and new transmit power levels for the service base stations synchronized at a particular time (to) • The initial and new transmission powers and the synchronization time are provided to the respective base stations involved in the smooth transfer. The white base station transmits the initial power level to the mobile station and the service base stations adjust their transmission powers to the new values. In a preferred exemplary embodiment of the present invention, the service base station power adjustment is carried out gradually with the white base station transmitting at the initial power level and the service base stations by adjusting its transmission powers towards the new values at synchronization time t0.

In another exemplary embodiment, a future synchronization time may be employed and provided to all base stations to coordinate the transmit power levels such that they reach these desired values at this synchronization time. The invention can also be used to periodically correct shifting at previously coordinated base station transmission power levels. In addition, the invention can be used to control transmission power levels of different base station sectors involved in a smoother transfer. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following description of preferred embodiments in accordance with that illustrated in the accompanying drawings in which reference characters refer to the same parts in the drawings. several views, the drawings are not necessarily to scale, the illustration of the principles of the invention being emphasized. Figure 1 is a schematic overview of an exemplary mobile cellular communication system in which the present invention can be employed; Fig. 2 is a block diagram of functions showing in detail a radio network controller and a base station illustrated in Fig. 1; Figure 3 is a block diagram of function illustrating in greater detail a mobile station illustrated in Figure 1, as well as power control commands involving a mobile station, two base stations and a radio network controller; Fig. 4 is a diagram showing the transmission of messages between the radio network controller and the base stations to synchronize the transmit power of base station in soft handoff in accordance with an exemplary embodiment of the present invention; Figure 5 is a flow chart illustrating alternative methods for controlling the transmit power of the base station; Fig. 6 is a flowchart illustrating methods for adjusting base station power to newly received transmission power commands from the radio network controller in accordance with an exemplary preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS In the following description, for purposes of explanation and not limitation, specific details are presented, such as particular modalities, data flows, techniques, etc. for the purpose of offering a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention can be practiced in other embodiments that depart from these specific details. For example, while the present invention can be applied to other transfer situations, such as for example a "softer" diversity transfer between sectors of base station antennas, for explanation purposes only, the following description is offered in a scenario of soft transfer. In other cases, detailed descriptions of well-known methods, interfaces, devices and signaling techniques are omitted so as not to obscure the description of the present invention with unnecessary details. Figure 1 illustrates a mobile radio cellular communication system 10 which, in accordance with the preferred embodiment of the present invention, is a broadband CDMA or CDMA communication system. Radio network controllers (RNCs) 12 and 14 control various radio network functions including for example radio access bearer parameters, diversity transfer, etc. A radio network controller 12 is connected to a plurality of base stations 16, 18 and 20. A radio network controller 14 is connected to base stations 22, 24 and 26. Each base station serves a geographical area known as a cell, and a cell can be divided into several sectors. A base station 26 having six antenna sectors S1-S6 is shown. The base stations are connected to their corresponding radio network controller through various means, such as dedicated telephone lines, fiber optic links, microwave links, etc. Both radio network controllers 14 and 14 are connected to external networks such as Public Switched Telephone Network (PSTN), Internet, etc., through one or several mobile switching centers (MSCs) (not shown). The RNC directs mobile station calls through the appropriate base station (s). In Figure 1, two example mobile stations 28 and 30 are illustrated which communicate with several base stations. A mobile station 28 is communicating with the base stations 16, 18 and 20, and the mobile station 30 is communicating with the base stations 20 and 22. A control error between the radio network controllers 12 and 14 allows communications from diversity towards the mobile station 30 / from the mobile station 30 through the base stations 20 and 22. Each radio communication channel established between the. mobile station and a base station have an uplink component and a downlink component, as described above, since multiple communications employ the same radio frequencies in code division multiple access (CDMA) communication, Extension codes along with other well-known CDMA techniques are used to distinguish between communications from the various base stations and mobile stations. For the purpose of describing the exemplary embodiment, the term "channel" typically refers to a CDMA channel which, for any mobile station, is defined in terms of an RF frequency and a particular code sequence. Further details of a base station controller and radio network are now offered with the relation to Figure 2. Each radio network controller (RNC) includes a network interface 52 for interface communications with several base stations. Within the RNC, the network interface 52 is connected to a controller 50 and a diversity transfer unit (DHO) 54. The diversity transfer unit 54 performs numerous functions required to establish, maintain, and abandon connections of the network. diversity, such as diversity combination, diversity division, power control and other radio resource control algorithms related to links. Some of these DHO functions will be described in additional detail later. Each base station includes a corresponding network interface 60 for interfacing with the RNC. In addition, the base station includes a controller 62 connected to several transceivers (TRX) 64, 64, 68 and 70, as well as a transmission power controller 72. The controller 62 controls the overall operation of the base station as well as the establishment, maintenance, and release of radio connections. Representative transceivers 64-70 are assigned individually to specific communications with mobile stations. At least one transceiver is used as a common control channel in which the base station transmits a common signaling such as a pilot signal. The common channel is monitored by mobile stations in or near the base station cell, and has also been used to request a working channel (uplink) or to call a mobile station (downlink). The transmit power controller 72 performs the open loop and closed loop power control methods described in the background section above to control the transmit powers of all the mobile transmissions received by the base station, such as for example , so that they are approximately at the same power level considering that all mobile stations are using the same type of service. One of the advantages of CDMA communications is the use of diversity transfer (both soft and soft). Using a soft transfer as an exampleas a mobile station moves towards the edge of the current base station cell, the mobile station detects the power level of the common channel signaling (e.g. the pilot signal) and determines whether there is sufficient signal strength from of this common signal for this base station to be a white base station (BS2) for transfer. The mobile station sends a power measurement message to the service base station (BS1) which then sends a transfer request message to the RNC. The RNC accepts the transfer request and sends a transfer request message between base stations to the white base station. The white base station allocates a transceiver to the call that involves the mobile station while the service base station continues to handle the call. The RNC combines the connections coming from the two base stations in such a way that the transfer is carried out without interruption, ie a smooth transfer. This handling prior to call interruption by two or more base stations occurs until the mobile station has moved sufficiently close to one of the base stations or sufficiently far from one of the base stations to leave the base station. furthest base. As described in the background section, in the case of rapid power control, the transfer of diversity raises some coordination / synchronization problems of the transmission power levels of the base stations / sectors involved. Reference is made to Figure 3 to better understand the downlink power control synchronization problems that the present invention faces in soft handoff. Although multiple base stations may be involved in a diversity transfer and even more so than an RNC may be involved in a diversity transfer, as illustrated in Figure 1 in relation to communications between base stations 20 and 22 and mobile station 30 the following description is simplified for purposes of illustration only, to the scenario involving only two base stations BS1 and BS2 connected to the same RNC involved in the diversity transfer. As mentioned above, the present invention can also be applied to smoother transfer between base station sectors. If the sectors involved in the smoother transfer belong to the same base station, the RNC does not have to be involved in the downlink control coordination provided by the base station. The mobile station includes a controller 80 connected to a RAKE receiver 82, a transmit power controller 88, and a transmitter 90. A RAKE receiver 82 includes several receivers 84 and 85 (additional receivers may also be connected to several combiners 86. Transmissions from the two base stations BS1 and BS2 are received as multiple paths in the receivers 84 and 85, combined in the diversity combiner 86 and processed as a signal.The transmit power controller 88 detects the power level preferably as a signal / interference ratio Eb / I0 of the received diversity received signal The mobile station transmission power controller 88 also responds to transmission uplink power control commands from the base stations BSl and BS2 for adjust your uplink transmission power up or down with an appropriate increase in compliance ad with the received commands. Based on the power level measurement of the combined diversity signal, the controller 80 generates transmission power control commands (TPC) and transmits them through the transmitter 90 to both the BS1 service base station and the white base station BS2. In accordance with a preferred embodiment of the invention, the TPC commands include one or more bits indicating a desired increase in transmission power, a desired decrease in transmission power, or no change in transmission power. Obviously, any number of bits or bit allocations is possible and contemplated within the present invention. Based on the received TPC commands, BSl and BVS2 increase their transmission power by decreasing the corresponding increase, such as 0.5 or 1 dB. As mentioned above, there are substantial problems when attempting to coordinate the current transmission power level of the service base station BS1 when the initial power level of the new white base station is established in soft handoff. In essence, during the time during which RNC processes transmission power measurement messages from the service base stations BS1 to the mobile station, it formulates an initial power level for the base station BS2 and communicates this power level initial to the base station BS2, the BS1 service base station. will have adjusted its transmit power several times in response to a large number of "fast" TPC commands received during this time period. Accordingly, for the time at which the white base station BS2 begins to transmit, there is the possibility of a very important difference between the service base station power levels and the white base station. While the known power levels may differ according to a desired preset difference, in the preferred example mode, the white base station and service transmission powers are approximately at the same power level. An example of the above situation is when the mobile station is considerably closer to a first base station than to a second base station. Instead of the furthest base station transmitting at a very high power level in such a way that the levels measured at both base stations by the mobile station are equal, the interference is reduced and the capacity is increased while maintaining the highest level. lower than the power level of the first nearest base station. In many cases, it is preferable that the service base and target stations transmit at known power levels or at known differences in power levels, ie, the absolute power levels do not necessarily have to be known at any given time. The present invention accomplishes this desirable objective by the use of a transmission power synchronization method. In general, the power levels of all base stations involved in a diversity transfer are set at one or more predetermined levels at a specific time or during a specific time. The transmission power synchronization procedure can be divided into five phases including: (1) the determination of a transmission power synchronization time (to), when the white base station will start transmitting to the mobile station in the desired power level and the desired power levels for the base service and target stations based on the mobile station power reports; (2) reporting the new white base station in terms of a desired power level and in terms of the transmission power synchronization time (to); (3) informing the old service base station (s) and the white base station as to this desired power level and as to the transmission power synchronization time (to); (4) check the power level of the service base station (s) in the synchronization time (to); (5) adjust the transmission power of the service base station (s). Each service base station may as an option adjust its transmission power based on the difference between the desired power level for the new white base station and the actual power level of each service base station in the synchronization time of transmission power (to). A variation of the above procedure is to offer the synchronization time to all the base stations involved in the transfer. Each base station can adjust its respective transmission power in such a way that it is at the desired level at the synchronization time to. The above methods can also be used to resynchronize transmit power levels at the base stations periodically after the initial synchronization to compensate for any "shifts" in transmission power levels. In accordance with what has been described above, such shifts can occur due to the fact that errors in the bits that affect the transmission power level (TPL) command received by a base station will probably not be the same errors in the bits that affect the same TPL command sent to the second base station. This results in TPL commands received "different" and not the same TPL command which produces shift in the transmission power levels. Figure 4 illustrates exemplary procedures performed by the radio network controller and the base stations involved in the soft transfer example to achieve a station power synchronization in accordance with an exemplary preferred embodiment of the present invention. First, the radio network controller instructs each of the service base stations BS?, BS2 ..., BSn to measure their respective transmission power to the mobile stations Pi, P2 ..., Pn and that report the results measured at the RNC (block 100). Each of the service base stations measures their respective transmission powers Pi, P2 ..., Pn (perhaps in the form of Eb-Io values and reports their respective average transmission powers to the RNC (block 102). of these reports, the radio network controller determines the initial transmission power (Pnew) for the white base station BSnUeva to transmit at a transmission timing synchronization time in the future (t0) .The radio network controller it also determines new transmission power levels P, P ~ 2 ..., "Pn for service base stations BSi, BS2 ..., BSn at time (t0) (block 104) As already mentioned, in the preferred exemplary mode, the initial white power level and the new power levels for the service base stations are equal In the synchronization time (t0), the white base station BSnew transmits at the initial power level Pnew In addition, the stations is based on service BS?, BS2 ..., BSn adjust their transmission powers from the current values of transmission power P?, P2 ..., Pn in synchronization time (to) to the new levels of power commanded by RNC P ?, P2 ..., Pn in the synchronization time (block 106). Instead of the radio network controller performing the power control operations, these power control operations can be performed at the respective base stations. An alternative procedure is described below with reference to Figure 5. Instead of the base stations measuring their transmission powers towards the mobile station, the mobile station measures the received power level of each base station and sends the received power to the RNC. The RNC then determines a new transmission power PnUevo and synchronization time t0 for the new base station BSnuea as well as one or several controlled differences (the difference corresponds to BSi) between the new power Pnew and the old Pvieai power of each station of base BSi involved in soft transfer (block 110). The RNC then sends Pnew and t0 to the new base station BSnew and Pnew, t0 and the differential to each old base station BSi (block 112). At time t0, each old base station BSi detects its Pviejai transmission power and calculates an increment value? I = differential + Pv? E] a? (block 114). Each old base station then regulates its transmission power upwards or downwards by a value? I (block 116). While there are several ways through which the difference between the old and new power levels of the service base stations can be minimized or adjusted to a desired difference, this adjustment occurs preferably gradually (though not necessarily). The gradual adjustment is preferred when the power is increased, particularly when the transmission is carried out at a higher bit rate. This minimizes the interference with the rest of the system. A preferred methodology for adjusting the power of the service base stations explains as the Service Base Station Power Adjustment relationship (block 200) in the flow chart illustrated in the flowchart format in Figure 6. The current power in each service base station is represented by the variable P (to), and the new synchronization of transmission power in time (to) is represented by the variable P (to) - A variable a is defined as the absolute value of the difference in current and old power levels, that is, a = P "(to) -P (to) It is this difference that is ideally reduced to zero (or to a desired difference) in The time at which the service base and target stations are synchronized in the direction they are transmitting at approximately the same power level (or a desired difference) to the mobile station at the same time.The value of the parameter ß is set also n in block 102 in accordance with the speed with which it must reduce the difference. Two different values of ß can be used: ßascendente and ßdescendente.

A decision is made in block 204 as to whether the magnitude of power difference a is zero or approximately zero, ie, within a defined range. If this is the case, a determination is made in the sense that transmission power synchronization between the white base and service stations is achieved (block 202). Otherwise a decision is made in block 206 as to whether the current base transmission power at the synchronization time of (to) is greater than the desired power level at this time. If this is not the case, the transmission power of this base station is gradually increased. Instead of increasing the transmission power at each possible power adjustment opportunity, that is, upon receiving each fast TPC command, the power is increased only at some selected opportunities between these opportunities or periodically. Specifically, the power is increased only after ignoring the transmit power control commands a / ß. For increases in transmission power an exemplary value for a / ß is of the order of one dB. Alternatively, if the current transmission power is less than the desired power at this time, the transmit power of the base station to the mobile station is decreased by the appropriate power setting in each a / ß command (block 210). A suitable value for a / β in block 210 for the rate of power decrease is selected in such a way that the power decreases more rapidly than it is increased, for example, the power decrease is carried out in one step. The control returns it to decision block 204 from either 208 or 210 to determine if power synchronization has been achieved or to repeat the adjustment process presented above. Ignoring each a / b power adjustment command the present invention ensures a gradual increase or decrease in power while minimizing any unwanted power level difference at the same time. Accordingly, the present invention achieves base station power synchronization in diversity transfer without requiring additional complications from the mobile station. In addition, the mobile station only needs to transmit a set of power control commands to all base stations / sectors involved in the transfer. The invention can be applied at the initial power level of a new base station that becomes involved in a diversity transfer as well as periodically during the diversity transfer process to compensate for transmission power level shifts. By providing such dynamic and coordinated downlink power control, unnecessary interference caused by transmissions from high base stations is minimized while still retaining a minimum communication power. This improves the performance of the downlink system and optimizes capacity relative to relative transmission power levels in the downlink. Thus, while the present invention has been described in relation to what is now considered to be the most practical and preferred embodiment, it will be understood that the invention is not limited to the presented modality but on the contrary it has the purpose of encompassing several modifications and arrangements. equivalents included within the spirit and scope of the appended claims. As mentioned above, while the present invention has been discussed within the context of a soft transfer, the present invention could also be applied to other transfer situations including for example a smoother transfer.

Claims (36)

1. CLAIMS A method of power control for use in a mobile radio communication system that includes a controller connected to several base stations, each base station communicates with mobile stations located within or close to a geographic area associated with the base station , comprising the steps of: for a call involving the mobile station, the establishment of an initial communication between a mobile station and a first base station, with the first base station transmitting to the mobile station at a first power level; for the same call, establish a transfer communication between the mobile station and a second base station; determining a second initial power level for the second base station for transmissions from the second base station to the mobile station; and controlling the transmission power level of one of the first and second base stations for a desired transmission power difference. The method according to claim 1, wherein the desired difference is zero. The method according to claim 1, wherein the desired difference is not zero. The method according to claim 1, wherein signals received by the first and second base stations from the mobile station are combined by diversity in the controller and the signals received by the mobile station from the first base station and the second Base station are combined by diversity in a RAKE receiver in the mobile station. The method according to claim 1, the control step further comprising: the gradual change of the transmission power level of one of the first and second base stations to reduce the difference between them. The method according to claim 1, wherein the control step includes: adjusting the actual transmission power levels of the first and second base stations at the same power level. The method according to claim 1, wherein the termination step further includes: e.1 setting a predetermined time (to) associated with a desired transmission power level for the first base station and the initial power level of the second base station. The method according to claim 7, the control step further comprising: determining a difference between the actual transmission power level of the first base station at time t and the desired transmission power level of the first base station at time t0. The method according to claim 8, wherein if the difference exceeds a limit, the control step further comprises: comparing the actual and desired transmission power levels of the first base station; if the actual transmit power level exceeds the desired transmit power level of the first base station, decrease the actual power level; and if the actual transmit power level is less than or equal to the desired transmit power level of the first base station, increase the actual power level. The method according to claim 9, wherein the actual power of the first base station changes progressively with a first delay period between each progressive increase and a second delay period between each progressive decrease. The method according to claim 1, further comprising, following the transmission of the second base station: determining whether there is an undesired difference in transmission power level between the first base station and the second base station, and controlling the transmit power level of one of the first base station and second base station to reduce the unwanted difference in transmission power level. A mobile communication system, comprising: a mobile radio station; a first base station that establishes a communication with the mobile station, where the first base station transmits to the mobile station at a first power level; a second base station that establishes communication with the mobile station; and a base station controller, connected to the first base station and second base station, which establishes an initial power level for the second base station to transmit to the mobile station and adjust the transmit power level of the first base station to the mobile station in combination with the establishment of the initial power level of the second base station. The system according to claim 12, wherein the base station controller includes a diversity transfer unit for combining by diversity signals corresponding to a communication from a mobile station received from the first base station and the second station. of base. The system according to claim 12, wherein the transmit power level of the first base station is adjusted to the initial set power level of the second base station. The system according to claim 12, wherein the transmit power level of the first base station is adjusted to a desired difference from the initial set power level of the second base station. The system according to claim 12, wherein the first base station and the second base station each include a transmit power controller to vary the transmission power level of the base station to the mobile station. The system according to claim 16, wherein one of the first and second base station transmit power controllers varies its base transmit power in response to the transmission of a power level control signal from the base station controller. The system according to claim 12, wherein the mobile station includes: a RAKE receiver that combines by diversity the signals received by the mobile station from the first base station and the second base station to generate a combined received signal by diversity, and a mobile station controller measures a parameter of the received signal combined by diversity and transmits to the first base station and second base station a transmission power level control command to increase or decrease the transmission power with based on the measured parameter. The system according to claim 12, wherein the transmission power level of the first base station is adjusted to reduce a difference between the second level of initial transmission power and the first level of transmission power. The system according to claim 12, wherein the transmission power level of one of the first base station and second base station changes gradually. The system according to claim 12, wherein the base station controller establishes a predetermined synchronization time (to) associated with desired transmission power levels for the first base station and the second base station. 22. The system according to claim 21, wherein the first base station determines a difference between the actual transmit power level of the first base station at a synchronization time to and a desired transmission power level of the first station. of base in a synchronization time to and sets the first base station transmission power level to decrease the difference. 23. A method comprising the coordination of a transmission power level of a service base station transmitting to a mobile station with an initial transmission power level of a white base station transmitting to the mobile station in a transfer operation. The method according to claim 23, applied to a code division multiple access mobile communication (CDMA) system, wherein the transfer operation is a diversity transfer operation. The method according to claim 23, which includes the coordination of the respective transmission power levels of several service base stations with the initial transmission power level of the white base station. 26. The method according to claim 23, wherein a new transmission power level is determined for the service base station based on the initial power level of the white base station, and the transmission power levels. Initial and new are provided to the service base and target stations with a predetermined synchronization time. The method according to claim 26, further comprising adjusting the transmit power level in the service base station to reduce a difference between a transmit power level. real in the predetermined synchronization time and the new transmission power level. The method according to claim 27, wherein the reduction is carried out gradually. The method according to claim 26, further comprising adjusting the transmit power levels in one or both of the service base and target stations to reduce a difference between an actual transmit power level in the predetermined time and the new or initial transmission power level. A power control method for use in a mobile radio communication system that includes a controller connected to several base stations, each base station communicates with mobile stations located within or close to an associated geographic area • with the base station and having several sectors each having one or more antennas, comprising the steps of: for a call involving the mobile station, establishing an initial communication between a mobile station and a first sector with the first sector transmitting to the mobile station at a first power level; for the same call, establish a transfer communication between the mobile station and a second sector; determining a second initial power level for the second sector for transmissions from the second sector to the mobile station; and controlling the transmission power level of one of the first sector and second sector to achieve a desired difference in transmission power. . The method according to claim 30, wherein the desired difference is approximately zero. . The method according to claim 30, wherein the control step further comprises: gradually changing the transmission power level of one of the first sector and second sector to reduce the difference between them. 33. The method according to claim 30, wherein the control step includes: adjusting the actual transmission power levels of the first sector and second sector to the same power level. 34. The method according to claim 30, wherein the determination step further includes: setting a predetermined time (to) associated with a desired transmission power level for the first sector and the initial power level of the second sector. 35. The method according to claim 34, wherein the control step further comprises: determining a difference between the actual transmission power level of the first sector at time t0 and the desired transmission power level of the first sector in the time to 36. The method according to claim 35, wherein if the difference exceeds a threshold, the control step further comprises: comparing the real and desired transmission power levels of the first sector; if the actual transmission power level exceeds the desired transmission power level of the first sector, decrease the real power level of the first sector; and if the actual transmission power level is less than or equal to the desired transmission power level of the first sector, increase the real power level of the first sector. SUMMARY OF THE INVENTION A power control method in accordance with the present invention synchronizes the transmission power levels in the base stations that are currently serving a mobile station and an initial transmission power level of a new transmit station. white base that is being added in a situation of diversity transfer. At the beginning of the transfer, the radio network controller instructs the service base stations to measure their respective transmission powers to the mobile station Each service base station then measures its transmission power to the mobile station and reports the power level measurements to the radio network controller.An initial transmission power level is determined for the white base station and new transmission power levels are determined for the synchronized service base stations, for example, at a particular time (to). At the synchronization time to or approximately at that time, the white base station transmits to the mobile station at the initial power level, and at the same time or at about the same time, the stations The service base also preferentially adjusts its transmission powers to the new values, alternatively, the trans service stations they mitigate at their respective respective values at time t0 or approximately at that time. In a preferred embodiment of the present invention, the service base station power adjustment is carried out gradually.