WO2002054620A1

WO2002054620A1 - Power controlling method with time slot specific power control command

Info

Publication number: WO2002054620A1
Application number: PCT/FI2001/001141
Authority: WO
Inventors: Petri Patronen; Otto-Aleksanteri Lehtinen; Kalle Passoja
Original assignee: Nokia Corporation
Priority date: 2000-12-28
Filing date: 2001-12-20
Publication date: 2002-07-11
Also published as: FI20002873A; FI20002873A0

Abstract

A method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots. The method comprises transmitting a signal on a downlink when transmission intended for one user uses more than one time slot of the same transmission frame, evaluating the quality of the signal received by the terminal in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part. If there is need for power control in at least one time slot used by the transmission intended for one user, a time slot specific power control command related at least to this time slot is transmitted.

Description

Power controlling method with time slot specific power control command

FIELD OF THE INVENTION

[0001] The invention relates to a method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal is code divisional (typically code division multiple access, CDMA) and consists of frames (typically time division multiple access, TDMA), which are divided into time slots.

BACKGROUND OF THE INVENTION [0002] Power control in a radio system refers to an opportunity of changing the transmission power of radio transmission within a certain range. Power control is primarily needed to minimize interference in the coverage area of base stations of the radio system and to optimize the power consumption of terminals while a sufficiently good quality of connection is guaranteed. [0003] CDMA systems, in particular, require rapid power control because the CDMA systems are interference limited, i.e. too high a transmission power causes capacity losses in the whole system. In the CDMA/TDMA system one time slot may have several users, and thus the connection of one user may consist of several different signals which are distinguished from one another by different codes. The connection of one user may also use several time slots. Furthermore, in a TDD system (time division multiplex) a subscriber terminal and a base station transmit alternately on the same frequency, i.e. a frame is divided into uplink time slots (UL, the subscriber terminal transmits to the base station) and into downlink time slots (DL, the base station transmits to the subscriber terminal). This means that in practice the power can be adjusted only once in a frame, as a result of which power control is slow in the TDD system compared to other CDMA systems, such as the FDD system of the UT- RAN.

[0004] The transmission power of both a base station in the radio network and a subscriber terminal within the coverage area of the base station can be changed. The transmission power can be changed e.g. according to the principles of a closed loop. The closed loop method is used e.g. on the downlink in the TDD (Time Division Duplex) mode in a UTRAN (Universal Terrestrial Radio Access Network) cellular radio system employing the code divi- sion multiple access CDMA, in which case the terminal uses a specific trans- mission power control TPC command to indicate the need for change of the transmission power it has received. In that case the terminal may, for example, inform the base station that the next transmission should be performed at a power level 1 dB higher than that of the received transmission. The problem is that in respect of one user the transmission power control TPC command is frame-specific, i.e. if several time slots are used for transmission to one user, all the time slots of the frame resented for this user receive the same transmission power control command regardless of the service used and the interference level of the time slot (caused either by the user's cell or a neighbouring cell). Furthermore, the transmission power control TCP command includes only a command to either increase or decrease the power of the frame. A radio network controller RNC collects information on the state of the radio network, which it uses for determining the size of the power step, which in the UTRAN TDD system is 1dB, 2 dB or 3 dB. The RNC changes the size of the power control step relatively seldom. Particularly in TDD systems, where the same frequency resource is divided into several time slots between different users, optimal power control usually requires power control that is more dynamic and can be adjusted better. Furthermore, the prior art power control is not optimal in a solution which is often required by fast data transmission connections and where several time slots are reserved for a data transmission connection of one user because the power of the time slots cannot be controlled separately.

BRIEF DESCRIPTION OF THE INVENTION

[0005] The object of the invention is to provide an improved method of controlling the transmission power when several time slots of the same transmission frame are reserved for one data transmission connection, and an arrangement where the method can be applied.

[0006] This is achieved with a method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots. The method comprises transmitting a signal on a downlink when transmission intended for one user uses several time slots of the same transmission frame, evaluating the quality of the signal received by the subscriber terminal in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part; if there is need for power control in at least one time slot used by the transmission intended for one user, a time slot specific power control command related to at least this time slot is transmitted.

[0007] The invention also relates to a method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots. A signal is transmitted on a downlink when transmission intended for one user uses several time slots of the same transmission frame, the quality of the signal received by the subscriber terminal is evaluated in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part; if necessary, a transmission frame specific power control command intended for one user is transmitted alternately with a time slot specific power control command related to at least one time slot used by the transmission intended for one user. [0008] The invention also relates to an arrangement implementing the method for controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots. A transmitter of the network part comprises means for transmitting a signal on a downlink when transmission intended for one user employs several time slots of the same transmission frame, the subscriber terminal comprises means for evaluating the quality of the signal it has received in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part, the subscriber terminal comprises means for transmitting a time slot specific power control command related to at least this time slot if there is need for power control in at least one time slot used by the transmission intended for one user, the network part comprises means for controlling the transmission power according to a command word.

[0009] The invention also relates to an arrangement implement- ing the method for controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots. A transmitter of the network part comprises means for transmitting a signal on a downlink when transmission intended for one user uses several time slots of the same transmission frame, the subscriber terminal comprises means for evaluating the quality of the signal it has received in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part, the subscriber terminal comprises means for transmitting, if necessary, a transmission frame specific power control command intended for one user alternately with a time slot spe- cific power control command related to at least one time slot used by the transmission intended for one user, the network part comprises means for controlling the transmission power according to a command word.

[0010] The preferred embodiments of the invention are disclosed in the dependent claims. [0011] The invention is based on the idea that the subscriber terminal transmits a power control command to the base station, the command being time slot specific or common to all time slots intended for this subscriber terminal and possibly also to codes. The command may also include determination of the size of the power control step. [0012] The method and system according to the invention provide several advantages. The method of the invention allows controlling of the power of each time slot or code of a base station transmission frame intended for one user regardless of other time slots or codes. Thus the location of each subscriber terminal can be taken into account in power control: is the sub- scriber terminal close to the base station or far away from it. The purpose for which the terminal is used can also be taken into account: is it used for transmitting speech or data. When several time slots of the same transmission frame are reserved for one data transmission connection, the method and the system of the invention can implement time slot specific and possibly also code specific power control, which saves power and reduces the interference caused to the system.

BRIEF DESCRIPTION OF THE FIGURES

[0013] The invention will be described in greater detail by means of preferred embodiments, with reference to the accompanying drawings, in which

Figure 1 shows an example of a telecommunications system,

Figure 2 shows another example of a telecommunications system,

Figure 3 shows an example of a radio system,

Figure 4 is a flow chart illustrating the method steps for time slot specific power control of downlink transmission, Figure 5 shows an example of how time slots are divided between different users,

Figure 6 is a block diagram showing an example of UE, i.e. a subscriber terminal, Figure 7 is a block diagram showing an example of a base station transceiver.

DETAILED DESCRIPTION OF THE INVENTION

[0014] In the following, preferred embodiments of the invention will be described in the UMTS system (Universal Mobile Telecommunication Ser- vices) without limiting the invention thereto. The invention can preferably be utilized in other radio systems, too, which employ a combination of time and code divisional multiple access methods (TDMA/CDMA). The description of the invention is based on the TDD mode of the terrestrial radio network UTRAN of the UMTS, where the downlink and the uplink utilize the same radio frequency but different time slots. The invention can also be applied in systems using the FDD, where different frequency bands are defined for the downlink and for the uplink.

[0015] The structure of a mobile communication system will be described by an example with reference to Figure 1. The main parts of the mobile communication network are a core network CN, a universal terrestrial radio access network UTRAN of the mobile communication system and user equipment UE. The interface between the CN and the UTRAN is called lu and the interface between the UTRAN and the UE Uu.

[0016] The UTRAN consists of radio network subsystems RNS. The interface between the RNSs is called lur. The RNS consists of radio network controllers RNC and one or more B nodes. The interface between the RNC and the B is known as lub. The coverage area of the B node, i.e. a cell, is marked with C in the figure.

[0017] The illustration in Figure 1 is rather general, but Figure 2 shows a more detailed example of a cellular radio system. Figure 2 comprises only the most essential blocks, but it is obvious to a person skilled in the art that a conventional cellular radio network also comprises other functions and structures that need not be described in greater detail here. The details of the cellular radio network may differ from those shown in Figure 2 but these differ- ences are not relevant to the invention. [0018] The cellular radio network typically comprises fixed network infrastructure 200 and subscriber terminals 202, which may be fixed, placed in a vehicle or portable, such as mobile stations or laptops which can communicate with a radio telecommunications system. The fixed network infrastructure 200 comprises network parts, such as base stations 204. The base station in turn corresponds to the B node of the preceding figure. Several base stations 204 are controlled centrally by a radio network controller 206 that communicates with them. A base station 204 comprises radio frequency parts 208 and a multiplexer unit 212. In the example of Figure 2 the radio frequency parts comprise both the transmitter parts and the receiver parts.

[0019] The base station 204 further comprises a control unit 210, which controls the function of the radio frequency parts 208 and the multiplexer 212. The multiplexer is 212 is used for arranging the traffic and control channels used by several radio frequency parts 208 on one transmission connec- tion 214. The transmission connection 214 forms an interface known as lub.

[0020] From the radio frequency parts 208 of the base station 204 there is a connection to an antenna unit 218, which establishes a radio connection 216 to the subscriber terminal 202. The structure of the frames to be transmitted on the radio connection 216 is defined according to the system and called a Uu interface.

[0021] The radio network controller 206 comprises a group switching field 220 and a control unit 222. The group switching field 220 is used for switching speech and data and for connecting signalling circuits. A radio network subsystem 224 formed by the base station 204 and the radio network controller 206 also includes a transcoder 226. The transcoder 226 is usually located as close to a mobile services switching centre 228 as possible because this saves transmission capacity when speech is transmitted in the format of cellular radio network between the transcoder 226 and the radio network controller 206. [0022] The transcoder 226 converts the different digital speech encoding formats used between the public switched telephone network and the radio telephone network into a compatible format, e.g. from the format of the fixed network into a format of the cellular radio network, and vice versa. The control unit 222 performs call controlling, mobility management, collection of statistics, signalling and controlling and management of resources. [0023] Figure 2 further illustrates a mobile services switching centre 228 and a gateway mobile services switching centre 230, which is responsible for the connections of the mobile communication system to an external network, which in this case is the public switched telephone network 232. [0024] Figure 3 is a simplified illustration of a mobile communication system, i.e. a cellular radio system, which comprises base stations 204A to 204D. The coverage areas of each base station, i.e. cells, are denoted by C1 to C4 in the figure. In practice the cells usually overlap, like in the example shown in the figure cell C2 partially overlaps with cells C1 and C3. One or more subscriber terminals 202A to 202F are shown in the area of each cell C1 to C4 in the figure. The subscriber terminals are mobile stations, for instance, but they may also be portable computers provided with a radio interface. In real-time cellular systems the shape of the cells usually differs from the regular ellipse shown in the figure due to geographical obstacles, for example. The cellular system may also comprise one or more 'umbrella cells' which are large radio cells provided with capacity for enhancing smaller cells.

[0025] Figure 3 shows a bi-directional radio connection 304A to 306A between the subscriber terminal 202A and the base station 204A in cell C1. Transmission from the base station 204A to the subscriber terminal 202A is called a downlink 306A. The radio connection in the other direction is called an uplink 304A. The power control of the radio transmission by the base stations 204A to 204D is implemented in the TDD mode of the UMTS using a closed loop on the downlink. In the example of the figure, power control of the closed loop on the downlink means that the terminal, such as 202A, transmits a power control command to a base station, such as 204A, and on the basis of the command the base station 204A typically adjusts its future transmission to the terminal 202A.

[0026] Figure 4 is a flow chart illustrating the method steps for time slot specific power control of downlink transmission. It should be noted that several time slots and, according to the CDMA system, also signals distinguished from one another by different codes can be used for transmission intended for the same subscriber terminal. The method starts in block 400. In block 402 a signal is transmitted on the downlink, e.g. the base station transmits a signal to the subscriber terminal and several time slots are reserved for the same user from the transmission frame. More than one time slot per frame can be assigned to one user e.g. when the user needs a lot of data transmis- sion capacity for a fast data transmission connection, such as the Internet. One application that requires a lot of transmission capacity is loading of pages containing images.

[0027] In block 404 the subscriber terminal evaluates the quality of the signal it has received in all time slots that it has received and that belong to the same transmission frame to determine the need for power control of the transmission by the network part, e.g. a base station. The subscriber terminal typically measures the signal it has received or determines the quality of the signal it has received by means of the bit error rate, for instance. The bit error rate describes the share of erroneous bits of all the bits that have been received. Furthermore, the subscriber terminal may measure the signal-to-noise ratio of the signal it has received, for example. There are also other methods for measuring the quality of a received signal, such as measuring the signal power. [0028] In block 406 a time slot specific power control command related to at least one time slot is transmitted if there is need for power control in the time slot used by the transmission intended for one user or, according to another embodiment, a transmission frame specific power control command intended for one user is transmitted, if necessary, and a time slot specific power control command related to the time slot used by the transmission intended for one user is transmitted alternately with the first mentioned command. The power control command may comprise only the direction of power control, i.e. increase or decrease of power, in which case the size of the power control step is determined in advance e.g. upon the design of the network or a network element defines it for certain periods. In addition to the direction of power control, the power control command may also comprise the size of the power control step, e.g. 1 or more decibels.

[0029] The time slot specific power control command is used for controlling the power e.g. by increasing the power of the time slots with too low power and decreasing the power of the other time slots. According to the second embodiment, when a time slot specific power control command and a frame specific power control command intended for one user are transmitted alternately, the power control command increases or decreases the power of a certain time slot whereas the power of the other time slots remains unchanged. It should be noted that the base station may also ignore a power control command given. [0030] The subscriber terminal decides on the need for power control of the transmission by the network part, such as a base station, e.g. by employing the total interference power indicated by the network part. In radio systems the network part also measures the power of the signals it has re- ceived and thus it can determine the total interference power of the network within certain limits set by the system. The subscriber terminal can also decide on the need for power control of the network part by means of the signal-to- noise ratio target set for the network and indicated by the network part, or the subscriber terminal decides on the need for power control by means of the bit error ratio it has determined from a signal it has received. The subscriber terminal can also decide on the need for power control of the network part by determining the propagation attenuation from the transmission power indicated by the network part and the power it has received. There are several methods of for making a decision but only some examples were given here. [0031] The subscriber terminal can give the power control command directly to the network part, e.g. to a base station, in which case the commands transmitted by different subscriber terminals are typically combined into one command word in the network part so that this command word includes all the power control commands that are related to one transmission frame. The net- work part can also forward the power control commands transmitted by the subscriber terminals to the radio network controller or to another network element, where different commands are combined into a command word.

[0032] Arrow 408 shows that the method is repeated at certain intervals, preferably the method is repeated frame by frame. It should be noted that the network part, e.g. the base station, can also ignore a power control command but typically the network part adjusts its transmission power according to the command it has been given. The method ends in block 410.

[0033] Next the use of a time slot specific power control command will be described by means of Figure 5. Figure 5 shows an example of a time slot frame of the base station 204A in accordance with the UMTS system. In one frame there are 15 time slots 500 to 528, of which one is reserved for a PCCPCH channel (Primary Common Control Physical Channel), and a synchronization channel SCH and PRACH (Physical Random Access Channel) use two time slots. Thus 12 time slots are left for speech and data. It should also be noted that when TDD transmission is used, the transmission in both directions (uplink and downlink) occurs on the same frequency and in the same time slot e.g. as follows: first 8 time slots are used for the transmission on the uplink and then 7 time slots for the transmission on the uplink or 4 for the downlink and 3 for the uplink. It is also possible to reserve more time slots for one direction, e.g. 12 for the downlink and 3 for the uplink, depending on the traffic situation.

[0034] According to the figure, the number of users varies in different time slots. More than one time slot may have been allocated to some user e.g. for a fast data transmission connection. Each terminal determines the power control need of the transmitter in the base station typically by measuring the power it has received and by comparing it with the set target power. In the determination of the need for power control the target set for the signal-to- noise ratio or the number of bit errors in detection, for example, can be taken into account. It should be born in mind that the number of users in a cell and the quality of required services vary as a function of time, which means that the network state changes constantly.

[0035] A time slot specific power control command can be used for determining a different power control direction for each time slot of the transmission frame in the base station, i.e. increase or decrease in power, and, if desired, the size of the power control step. This is illustrated by the following example: in the first time slot 500 there is first one user, the next time slot 502 is free, in the third time slot 504 there is one user who uses the whole time slot and the fourth time slot 506, too. In that case the user of the same physical channel uses two different time slots of a transmission frame. In this situation e.g. the following power control command could be given by combining the commands of different subscriber terminals: increase the power of the first and the third time slot and decrease the power of the fourth time slot, i.e. two power control commands are given to the same channel. In that case the command word could be e.g. 101000000000000.

[0036] Next we will describe other examples of feasible command words. If the frame consists of 15 operating time slots, command word of the following kind, for example, is used: the first bit indicates whether the command word is a frame specific command intended for one user or a time slot specific command, the next five bits indicate in the time slot specific command word to which time slots the command is directed, one bit indicates whether the power must be increased or decreased and the remaining bits indicate the size of the control step, preferably in decibels. The command word may also first indicate which time slot the command concerns and then the direction of power control or its direction and size.

[0037] The command word may also include only as many bits as is the number of time slots available to one user. In the example of Figure 5 the command word would be 110.

[0038] In the system it is also possible to transmit a prior art frame specific command word alternately with a time slot specific command word. In this case the frame specific command word and the time slot specific command word can be independent of each other or form together a pair of com- mand words, e.g. first a prior art frame specific command is given and after that a time slot specific command to the time slots the power of which does not need to be controlled at this point.

[0039] A command word can also be transmitted to one time slot used by one and the same user and the other time slots used by the same user can be controlled in the same direction but with a step of a different magnitude, or the command word can be transmitted to one time slot used by one and the same user and the other time slots of the same user can be controlled in different directions with a step of a different size. The size of the control step is typically determined in advance. Alternatively, the power control command can be transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in different directions as the control step remains unchanged.

[0040] Figure 6 illustrates in a simplified manner one terminal of a wireless communication system, such as a cellular radio system, where the method according to the invention can be applied. The terminal can be e.g. a mobile phone or a microcomputer, but the invention is not limited to these. The terminal described comprises an antenna 600 which is used both for transmitting and receiving signals via a duplex filter. The terminal also comprises the radio frequency parts, i.e. RF parts 602 (Radio Frequency), of the receiver, where the received signal is filtered, amplified and downconverted to a selected intermediate band or directly to the baseband. The power of the received signal can also be determined in the RF parts. The terminal further comprises an A D converter, which converts an analogue signal into a digital one by sampling and quantisizing a baseband signal. If the signal is a wide- band direct sequence signal, it is composed by multiplying it by a spread code sequence in block 610. The code generator of the receiver is synchronized with the received signal to provide it with the correct phase. The receiver also comprises a demodulator 614, which demodulates the received signal so that a data signal can be separated from the carrier wave. In addition, the receiver may comprise a counter-interleaver for de-interleaving the signal. [0041] The transmitter part of the terminal comprises a modulator

616, which modulates the carrier wave with a data signal comprising the desired information according to the modulation method selected. If a direct sequence spread spectrum system is concerned, the signal is multiplied by a spread code sequence in block 612. The purpose of spreading the signal over a wide band is to increase the system's resistance to interference and thus the capacity. A signal spread with a sufficiently long spread code resembles white Gaussian noise on the radio channel. The transmitter further comprises a D/A converter 608, which converts a digital signal into an analogue one, and RF parts 604, where the signal to be transmitted is upconverted to the transmis- sion frequency, amplified to achieve the sufficient transmission power and filtered, if necessary. The RF parts of the receiver and the transmitter can also be combined into one RF block.

[0042] The terminal further includes a control block 618, which comprises e.g. control and calculation means for controlling the function of the different terminal parts and means for processing the user's speech or the data generated by the user, such as a DSP processor (Digital Signal Processing), which comprises e.g. channel equalization functions, which compensate for the interference caused by the radio channel signal utilizing information obtained on the channel by means of a known training sequence, and encoding and decoding means which perform both channel coding and speech coding. In channel coding the systematic bit redundancy, typically parity bits, added to the signal is used for error detection and correction in the decoder. In speech coding, which is usually source coding, non-systematic redundancy is typically removed from source symbols to reduce the bit rate needed. Coding can also be used for encrypting the output or the information included in it. The control part 618 also comprises means for adjusting the signal to be transmitted and the signalling information to the air interface standard of the cellular radio system used.

[0043] The control part 618 further comprises means for determin- ing the need for transmission power control in the base station by means of the received signal and the reference information, such as the transmission power given by the base station, bit error ratios or other information received on the radio channel. The control part also generates a power control command based on the power control need, and the command is transmitted to the base station. [0044] The user interface of the terminal comprises a loudspeaker or an earpiece 622, a microphone 624, a display 620 and possibly also a keyboard, which are connected to the control part. The terminal also comprises various memory elements that are illustrated as one functional block 622. A memory element contains e.g. stored data, such as information on the state of the radio network and the transmission power of the base station. Some of the memory elements can also function as the memory buffer of the display. The memory element also includes a program which controls the operation of the terminal and sub-programs. The functions according to the invention in the terminal, such as determination of the need for power control in the base sta- tion and generation of a power control command, can typically be performed by means of software by including software comprising the necessary commands in the control unit of the terminal. The invention can also be implemented by hardware solutions that offer the necessary functionality, e.g. as ASIC (Application Specific Integrated Circuit) or utilizing logic components. [0045] Next the invention will be described with reference to Figure

7, which is a block diagram illustrating, for the sake of clarity, a simplified example of the transmitter of the base station by means of an embodiment. It is clear to a person skilled in the art that the transceiver also includes other parts than those described above in connection with Figure 7. [0046] Blocks 714 to 722 illustrate a transmitter and blocks 702 to

710 illustrate a receiver. In the example of Figure 7 the radio parts of the transmitter and the receiver are illustrated as separate parts but they can also be combined as shown in the example of Figure 2. The signal processing blocks 710 and 714 illustrate the parts of the base station that are needed to produce the user's speech or data in the transmitter. There may be only one signal processing block, or like in the example of the figure, one for the transmitter and one for the receiver. A signal, i.e. an information string consisting of symbols, i.e. one or more bits, is processed in the transmitter in various ways. Signal processing, which includes coding, is usually performed in a DSP proc- essor (Digital Signal Processing). If the transmission in the system consists of frames which consist of time slots, generation of the frames as well as inter- leaving of symbols are typically carried out in the DSP processor. In block 716 the signal is modulated by the desired modulation method. The purpose of signal coding and interleaving is to guarantee that the transmitted information can be restored in the receiver even though not all information bits could be re- ceived. Block 718 describes multiplication by a spread code which is performed on the information to be transmitted in the direct spread spectrum systems to spread a narrow band signal over a wide band. A signal is converted from the digital format into the analogue format in block 720. In the RF parts 722 the signal is upconverted to the selected transmission frequency, amplified and filtered, if necessary. In the example of the figure both the transmitter and the receiver have the same antenna 700, and thus a duplex filter is needed to separate the signal to be transmitted from the signal to be received. The antenna can be a single antenna or an array antenna consisting of several antenna elements. [0047] The receiver comprises RF parts 702 where the received signal is filtered, downconverted either directly to the baseband or to an intermediate band and amplified. In block 704 the signal is converted from the analogue format into the digital format by sampling and quantisizing. In block 706 the direct spread wideband signal is composed by multiplying it by a code se- quence generated by the code generator. In block 708 the influence of the carrier wave is eliminated from the signal by demodulating, and in block 710 the necessary signal processing is carried out, e.g. deinterleaving, decoding and decryption.

[0048] In a preferred embodiment the receiver, such as a RAKE- type multibranch receiver, comprises a delay estimator for estimating the delays of multipath propagated components. The delays of different RAKE branches are set to correspond to the delays of differently delayed signal components.

[0049] Furthermore, either the base station or the base station con- trailer comprises a control part 210, which in the solution according to the embodiment described here comprises combining power control commands transmitted by the subscriber terminals into one power control command. The power control command comprises power control of all transmissions of one frame either time slot by time slot or frame by frame in respect of one user. Examples of feasible command words were given above. It should be noted that the measures needed to implement power control, such as determination of the size of the power control step and setting or collecting the information indicating the state of the radio network can be performed in various ways in the base station, subscriber terminal or in the radio network controller RNC.

[0050] The invention is preferably implemented by software, in which case the base station 204A to 204D, for example, comprises a microprocessor where the functions of the method described are performed by software. It is clear to a person skilled in the art that the functions of the method can also be performed in a decentralized system where the method steps are carried out in one or more base stations and/or radio network controller. The invention can also be implemented e.g. by hardware solutions offering the necessary functionality, e.g. as ASIC (Application Specific Circuit) or utilizing separate logic components.

[0051] Even though the invention was described referring to the example according to the accompanying drawings, it is clear that the invention is not limited thereto but it may be modified in various ways within the inventive concept disclosed in the appended claims.

Claims

1. A method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots, characterized by

402 transmitting a signal on a downlink when transmission intended for one user uses more than one time slot of the same transmission frame,

404 evaluating the quality of the signal received by the subscriber terminal in all time slots received by the same subscriber terminal and belong- ing to the same transmission frame to determine the need for power control of the transmission by the network part,

406 if there is need for power control in at least one time slot used by the transmission intended for one user, transmitting a time slot specific power control command related at least to this time slot. 2. A method of controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots, characterized by

404 evaluating the quality of the signal received by the subscriber terminal in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part, 406 if necessary, transmitting a transmission frame specific power control command intended for one user alternately with a time slot specific power control command related to at least one time slot used by the transmission intended for one user.

3. A method according to claim 1 or 2, characterized in that the subscriber terminal decides on the need for power control utilizing the total interference power indicated by the network part.

4. A method according to claim 1 or 2, characterized in that the subscriber terminal decides on the need for power control by means of the signal-to-noise ratio target indicated by the network part.

5. A method according to claim 1 or 2, characterized in that the subscriber terminal decides on the need for power control by means of the bit error ratio estimate it has determined from a signal it has received.

6. A method according to claim 1 or 2, characterized in that the subscriber terminal determines propagation attenuation from the transmission power indicated by the network part and from the power it has received and decides on power control on the basis of propagation attenuation.

7. A method according to claim 1 or 2, characterized in that the power control command comprises the direction of power control.

8. A method according to claim 1 or 2, characterized in that the power control command comprises the direction of power control and the size of a power control step.

9. A method according to claim 1 or 2, characterized in that the power control command comprises only as many bits as is the number of time slots available to one user.

10. A method according to claim 1 or 2, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in the same direction but by a predetermined step of a different size.

11. A method according to claim 1 or 2, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in different directions and by a predetermined step of a different size.

12. A method according to claim 1 or 2, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in different directions but by a step of the same size.

13. A method according to claim 1 or 2, characterized in that the frame specific command word and the time slot specific command word are independent of each other.

14. A method according to claim 1 or 2, characterized in that the frame specific command word and the time slot specific command word form together a pair of command words.

15. A method according to claim 1 or 2, characterized in that the power control command comprises one bit for each time slot of the transmission frame.

16. A computer program according to claim 1 or 2, characterized in that it comprises routines for implementing the steps of the method.

17. A memory means according to claim 1 or 2, characterized in that it comprises a computer program according to claim 9.

18. An arrangement for controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots characterized in that a transmitter of the network part comprises means (700, 702) for transmitting a signal on a downlink when a transmission intended for one user uses several time slots of the same transmission frame, the subscriber terminal comprises means (600, 602, 618) for evaluating the quality of the signal it has received in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part, the subscriber terminal comprises means (600,604, 618) for transmitting a time slot specific power control command related to at least this time slot if there is need for power control in at least one time slot used by the transmission intended for one user, the network part comprises means (210, 722) for controlling the transmission power according to a command word.

19. An arrangement for controlling transmission power in a radio system where radio traffic between a network part and at least one subscriber terminal consists of frames, which consist of time slots characterized in that a transmitter of the network part comprises means (700, 702) for transmitting a signal on a downlink when a transmission intended for one user uses several time slots of the same transmission frame, the subscriber terminal comprises means (600, 602, 618) for evalu- ating the quality of the signal it has received in all time slots received by the same subscriber terminal and belonging to the same transmission frame to determine the need for power control of the transmission by the network part, the subscriber terminal comprises means (600, 604, 618) for transmitting, if necessary, a transmission frame specific power control command intended for one user alternately with a time slot specific power control com- mand related to at least one time slot used by the transmission intended for one user, the network part comprises means (210, 722) for controlling the transmission power according to a command word.

20. An arrangement according to claim 18 or 19, characterized in that the subscriber terminal decides on the need for power control utilizing the total interference power indicated by the network part.

21. An arrangement according to claim 18 or 19, characterized in that the subscriber terminal decides on the need for power control by means of the signal-to-noise ratio target indicated by the network part.

22. An arrangement according to claim 18 or 19, characterized in that the subscriber terminal decides on the need for power control by means of the bit error ratio estimate it has determined from a signal it has received.

23. An arrangement according to claim 18 or 19, characterized in that the subscriber terminal determines propagation attenuation from the transmission power indicated by the network part and from the power it has received and decides on power control on the basis of propagation attenuation.

24. An arrangement according to claim 18 or 19, characterized in that the power control command comprises the direction of power control.

25. An arrangement according to claim 18 or 19, characterized in that the power control command comprises the direction of power control and the size of a power control step.

26. An arrangement according to claim 18 or 19, characterized in that the power control command comprises only as many bits as is the number of time slots available to one user.

27. An arrangement according to claim 18 or 19, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in the same direction but by a predetermined step of a different size.

28. An arrangement according to claim 18 or 19, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in different directions and by a predetermined step of a different size.

29. An arrangement according to claim 18 or 19, characterized in that the power control command is transmitted to one time slot used by one and the same user and the other time slots of the same user are controlled in different directions but by a step of the same size.

30. An arrangement according to claim 18 or 19, characterized in that the frame specific command word and the time slot specific command word are independent of each other.

31. An arrangement according to claim 18 or 19, characterized in that the frame specific command word and the time slot specific command word form together a pair of command words.

32. An arrangement according to claim 16 or 17, characterized in that the power control command comprises one bit for each time slot of the transmission frame.