JP4186212B2 - Method and apparatus for variable rate communication at high transmission rate - Google Patents

Description

  The present invention relates to a transmission / reception apparatus in a mobile communication system such as a cellular phone system using a code division multiple access (CDMA) system, and more particularly to an uplink transmission apparatus.

  In the CDMA communication system, when a large number of terminals are connected to one base station, the communication quality of a plurality of terminals reaching the base station is made the same (preventing interference), thereby making it possible for one base station. The terminal usage number has been acquired. That is, between the base station and the terminal, the base station performs fine power control of the terminal so as to keep the uplink communication quality constant.

  In addition, from the relationship between the transmission rate and the transmission power, conventionally, in order to keep the communication quality of the transmission data constant, by reducing the transmission power and devising error correction processing, etc., For the purpose of maintaining communication quality, various techniques have been proposed, such as changing an optimal communication method from among a plurality of communication methods.

  For example, in Patent Document 1, a mobile station is provided with means for obtaining a distance between a mobile station and a base station, and a plurality of mobile stations reaching the base station are controlled by controlling transmission power of the mobile station according to the distance. The communication quality from the network is made uniform to prevent interference.

  In Patent Document 2, the transmission rate is determined and thereby the transmission power and the constrained encoder constraint length are made variable. When the transmission rate is lowered, the convolutional encoder constraint length is reduced instead of reducing the transmission power. Thus, the error correction gain on the receiving side is increased to compensate for the decrease in transmission power.

  In Patent Document 3, the silence time of intermittent transmission information signals is detected, and during this silence time, the transmission power of the pilot signal is reduced, thereby reducing the interference without reducing the transmission quality, and the data signal communication Techniques for increasing speed are described.

  In Patent Document 4, in a wireless communication system having a plurality of systems including a CDMA-FDD system and a CDMA-TDD system, a mobile station selects a system that desires a desired connection from the CDMA-FDD system and the CDMA-TDD system. By communicating with the selected system, the transmission rate (throughput) is prevented from decreasing at the edge of the cover area in a system including a line with a high transmission rate.

JP 2000-232682 A Japanese Patent Laid-Open No. 11-17650 JP 2000-315977 A JP 2001-346265 A

  When performing power control according to the prior art, the operation when the terminal is away from the base station is controlled from the base station in the direction of increasing the transmission power in order to ensure communication quality, but the terminal can transmit Since there is a limit on the maximum transmission power, communication quality is maintained by lowering the transmission rate. In other words, when the terminal is far from the base station and the transmission power is high, it is impossible to add a multicode or change the transmission rate to be high.

  For example, there is W-CDMA (Wideband-Code Division Multiple Access), which is currently being specified by IMT-2000 (International Mobile Telecommunications 2000). In this specification, the transmission power limit (MAX) is determined by the device capability of the terminal, and the transmission power ratio varies depending on the selection of a format (TFC: Transport Format Combination) for transmitting transmission data. ing. This means that the TFC is changed to add a transmission channel or change a transmission rate according to a service requested by the user.

  Furthermore, when the terminal is moving, the radio wave environment to be used is constantly changing, so the transmission power is always maintained by the close loop operation (TPC operation: Transmit Power Control) instructed by the reception capability of the base station. Fluctuating.

  Especially when the terminal is away from the base station or when the radio wave environment is bad, the transmission power is high due to the TPC operation, but if you try to increase the transmission rate with a request from the user under such conditions, The terminal becomes the limit of transmission power, and even if the transmission power ratio of DPCCH / DPDCH is the same, the power of each physical channel will decrease, so the terminal device must transmit at the maximum transmittable power (attached to the maximum transmission). become.

  On the other hand, since the base station performs an operation for maintaining the communication quality, the control works in the direction of increasing the transmission power by the operation by the TPC, but the communication quality cannot be improved any more due to the limitation of the power that can be transmitted by the terminal. Therefore, the transmission rate is lowered to maintain the communication quality, and the terminal is forced to select the low-rate transmission in order to maintain the communication quality at a place far away from the base station.

  As described above, in the conventional technology, in order to maintain the set communication quality, the current transmission data is determined by looking at the current transmission level so as not to set the transmission rate so as to reach the limit of the transmission power of the terminal. The amount is adjusted (Change of TFC), but this means that the transmission power resources used are not used up to the limit.

  The above problem will be further described with reference to FIG. In FIG. 2, the horizontal axis represents the distance between the base station and the terminal, and the vertical axis represents the transmission power of the terminal. Since the initial transmission power of the terminal is specified by the DPCCH power at the antenna end, the total transmission power of the terminal is DPCCH + DPDCH, which is increased by the amount indicated by a with respect to the DPCCH power. When the distance between the terminal and the base station increases, the radio wave is generally attenuated by the square of the distance, so that the transmission power of the terminal is controlled to be increased accordingly.

  If the distance between the terminal and the base station enters the section indicated by b, the total transmission power of DPCCH + DPDCH should be added as shown by the dotted line c, but it is above the transmission power limit of the terminal. Therefore, the transmission power cannot be increased any further, and the reception quality at the base station cannot be maintained.

  In CDMA communication, the spreading factor (SF) varies depending on the transmission rate. When the rate is low, the spreading factor is high (SF = 256). When the rate is high, the spreading factor is low (SF = 4). That is, when the rate is high, the spreading gain becomes small. The transmission power must be increased.

For example, the transmission rates of DPDCH and DPCCH are respectively
DPDCH: Transmission rate 240 ksps (k-symbol / sec)
DPCCH: Transmission rate 15ksps
In this case, the weights βc and βd of DPCCH and DPDCH are set to βc = 4 and βd = 15, respectively, so that more power is allocated to the high rate DPDCH, so that both DPDCH and DPCCH have the same communication quality.

  Therefore, in this case, the power of the DPDCH must be increased by 11.78 dB (= 10 × log ((βd ^ 2 + βc ^ 2) / βc ^ 2)) with respect to the DPCCH, and the terminal is away from the base station. For example, when the current transmission power is high, transmission with a high rate cannot be performed.

  In view of the above problems, an object of the present invention is to provide means capable of maintaining transmission of user data at a high transmission rate as much as possible even when the transmission power limit of the terminal is exceeded.

  The variable rate communication method of the present invention comprises DPDCH (Dedicated Physical Data Channel) and DPCCH (Dedicated Physical Control Channel), and multiplexes signals of these channels from a terminal to a base station by a CDMA (Code Division Multiple Access) system. In the transmission method, when the current transmission power required for transmission to the base station exceeds the maximum transmission output possible with the device capability of the terminal, the DPCCH symbol rate is changed, or the DPCCH pilot information is changed. Transmission is performed in a burst manner, and control is performed to maintain transmission of a high transmission rate of user data as much as possible by changing the power distribution of the DPCCH and the DPDCH.

  That is, the present invention has a mechanism for controlling the total transmission power by judging the current transmission power and the relative power ratio of DPDCH and DPCCH, and changing the transmission rate or timing of DPCCH, and finely controls the DPCCH power control. Realized by implementing the algorithm to set.

  That is, when the total power of the DPCCH and DPDCH exceeds the transmission power limit of the terminal, as shown in FIG. 2d, the power distribution to the DPCCH is reduced and transmission of a high transmission rate of user data is possible as much as possible. It is characterized by controlling to maintain.

  According to the present invention, for example, by changing the slot format of the DPCCH when away from the base station, reducing the number of bits for the pilot, and doubling the length of other control information bits, the actual rate of the DPCCH Therefore, the DPCCH power can be lowered accordingly (corresponding to the dotted line d in the section b in FIG. 2). For this reason, it is possible to obtain the effect of not reducing the DPDCH transmission rate even in the section b of FIG.

  In addition, since the terminal has already established communication with the base station and is transmitting, it is already synchronized, and therefore the terminal does not always need to transmit the pilot information in the DPCCH, so the transmission rate of the DPCCH is lowered. It is possible to allocate transmission power to the DPDCH accordingly.

  In the case of the first and second embodiments, since the pilot information of the DPCCH is reduced, the synchronization with the base station may be lost depending on the environment used by the terminal. In that case, by transmitting the transmission rate of the DPCCH to Burst, it is possible to periodically supplement the synchronization at the base station and continue the effect while preventing loss of synchronization.

  As described above, in the present invention, it is possible to continue or increase the transmission rate compared to the prior art even at a distance from the base station (it is possible to reduce the communication amount of user data as much as possible). Even if the transmission power is the same, a high transmission rate can be maintained.

  FIG. 1 is a block diagram showing a first embodiment of the present invention. In the present embodiment, the power distribution to the DPCCH is reduced by changing the DPCCH symbol rate from the current transmission power state.

  In this embodiment, a transmission signal sequence input terminal 101 to which transmission data to be transmitted is input, a convolutional coding unit 102, a transmission power instruction unit 103, a data format generation unit 104, a primary modulation unit 105, a spreading processing unit 106, a digital It comprises a D / A conversion unit 107 that converts data into an analog signal, a transmission radio unit 108, a transmission antenna 109, and a TPC code sequence input terminal 110 set from the reception (base station) side.

  FIG. 3 shows a transmission signal format in the present embodiment, where DPDCH and DPCCH are multiplexed by Channelization Codes and transmitted as a total signal. 4 is a diagram showing an outline of DPDCH and DPCCH processing in primary modulation section 105 and spreading processing section 106 in FIG. 1 (in an actual apparatus, there are a plurality of DPDCHs).

  Table 1 shows an example of the number of bits in the DPCCH format used in the present embodiment. In the present embodiment, Slot Format # i-A1, Slot having a lower transmission rate than Slot Format #i. Format # i-A2 is prepared, and when the total power of DPCCH and DPDCH exceeds the transmission power limit of the terminal, DPCCH is changed from Slot Format #i to Slot Format # i-A1, Slot Format # i-A2 as appropriate. Switch to.

  FIG. 5 is a flowchart showing the operation of the present embodiment. Hereinafter, the operation of the present embodiment will be described with reference to FIGS. 1 to 5 and Table 1. FIG.

  First, the flow of transmission data will be described. When a transmission data sequence is input to the transmission signal sequence input terminal, it is transmitted to the convolutional coding unit 102. Here, the necessary parameters are obtained from the upper level, and the convolutional coding process for performing error correction at the base station is performed. The encoded transmission data is sent to the data format generation unit 104. Here, transmission data is assigned to DPDCH (Dedicated Physical Data Channel), and control data is assigned to DPCCH (Dedicated Physical Control Channel).

  The generated signal sequence of DPDCH and DPCCH is multiplied by codes Cd and Cc (Channelization Codes) generated according to the spreading factor SF, respectively, by the next primary modulation section 105, thereby being spread-modulated according to the spreading factor. Is converted to a CDMA signal. At this time, the power of the signal sequence of DPDCH and DPCCH is adjusted by the β ratio which is weighting.

  The CDMA signal spread by the primary modulation unit 105 and mapped on the IQ plane is multiplied by a scrambling code by the spread modulation unit 106. In this scrambling, (1) transmission data is concealed with respect to a transmission CDMA signal, (2) the base station performs individual identification of the terminal by a scrambling code, and (3) orthogonal control with other terminals. It is implemented for the purpose of creating a signal and eliminating interference with other terminals.

  The spread-modulated CDMA signal is input to the D / A conversion unit 107, and the D / A conversion unit 107 converts the digital signal into an analog signal. The signal converted into the analog signal is subjected to transmission power control by the transmission radio unit 108, converted into a radio frequency signal, and transmitted from the transmission antenna 109.

  In addition, transmission power instruction section 103 calculates DPCCH and DPDCH weightings based on transmission rate information from convolution coding section 102 and a transmission power control signal from a base station input from TPC code sequence terminal 110. The result is notified to the data format generation unit 104 as weighting information β. Further, it is determined whether to increase or decrease the current transmission power value based on the TPC code notified from the base station, and a GCA (Gain Control AMP) in the transmission radio section 108 is controlled every time transmission power is determined.

  Next, operations related to power control will be described using the flowchart of FIG.

  First, the transmission power instruction unit 103 calculates the current transmission power (S301). Based on the initial transmission power specified by the base station and the amount of data to be transmitted, the transmission power serving as the DPCCH reference can be calculated. Further, the current transmission power is always calculated based on the power control information input at a certain period from the TPC code sequence terminal.

  Next, it is determined whether or not the transmission power of DPCCH + DPDCH is equal to or higher than the MAX power (transmission power limit value) of this terminal (S302). If the power of DPDCH + DPCCH does not exceed the threshold value (S302, No), the operation is performed by the normal operation TPC control. If it has exceeded (S302, Yes), the process proceeds to transmission data format change (S303).

  Here, the format of DPCCH is changed from slot format # 0 to # 0-A1 (see Table 1). When the slot format is changed, the data format generation unit 104 is notified and the generation of the DPCCH format is changed. Further, since the weighting of DPDCH and DPCCH is changed, the control value is updated to primary modulation section 105, and TXAGC control value is also updated to transmission radio section 108.

  In other words, since the pilot information is synchronized with the base station once, there is no need to send it constantly, so the information amount is reduced from 6 bits to 2 bits. Instead, the information amount of TFCI and TPC As is, the length is doubled and integrated on the receiving side so that it can be received. For example, if the TPC in slot format # 0 that can be normally transmitted is “01”, and enters the section b in FIG. 2 and is changed from slot format # 0 to # 0-A1, the TPC is “ 0011 "and so on.

  For this reason, an effect equivalent to the fact that the transmission rate of the DPCCH is substantially reduced occurs, and the error rate of the DPCCH can be improved. Therefore, the transmission output of the DPCCH can be lowered correspondingly, and the transmission output of the DPCCH can be reduced. The β ratio on the DPDCH side is adjusted so that the decrease is sent to the transmission output of the DPDCH, and control is performed so as to maintain the quality and high rate of the DPDCH.

  According to the present embodiment, when the transmission power of DPCCH + DPDCH is equal to or higher than the MAX power (transmission limit value) of this terminal, the DPCCH transmission power by reducing the symbol rate of DPCCH or performing equivalent processing Therefore, it is possible to maintain the high transmission rate even if the transmission power is the same as in the prior art.

  FIG. 6 is a block diagram showing a second embodiment of the present invention. In the present embodiment, a position detection unit 301 is added to the first embodiment, and other configurations are the same as those in the first embodiment.

  In the present embodiment, the position detection unit 301 obtains position information such as the distance and the positional relationship between the base station and the terminal station, and notifies the transmission power instruction unit 103 of the position information. The transmission power instruction unit 103 uses this position information as a criterion for control of the data format generation unit 104, the primary modulation unit 105, and the transmission radio unit 108. The position information is calculated by the position detection unit 301 based on the positional relationship between the position information of the mobile station calculated by the GPS circuit or the like and the base station.

  Functions of the position detection unit 301 include (a) distance information between the base station and the terminal, (b) a function of providing information on a specific area, and the like. This specific area information means that if a place where radio waves are difficult to reach due to the influence of a building or the like is known in advance, the information is recorded in a ROM or the like, and if the terminal is in that specific area, the DPCCH Control to reduce the transmission rate. In this way, the same effect can be obtained as a flow for changing the transmission data format according to the distance information between the base station and the terminal or information on a specific area.

  FIG. 7 shows a transmission signal format according to the third embodiment of the present invention. In the first and second embodiments, the DPCCH transmission rate is changed according to a certain transmission power and a specific area, whereas in this embodiment, the DPCCH pilot information is not always output. , And Burst transmission, and power distribution is performed with intermittent timing synchronization by burst transmission of DPCCH.

  Normally, when transmitting transmission data, the convolutional encoding unit 102 processes the data in a certain unit of time. This is called TTI (Transmission Timing Interval). Since the terminal establishes communication once with the base station and transmits, the terminal is synchronized. Therefore, the terminal does not always need to transmit the pilot information in the DPCCH. Therefore, the transmission rate of the DPCCH is changed by repeating the frame in which the DPCCH Pilot is transmitted and the frame in which the transmission is not performed in accordance with the processing timing of the convolutional coding unit 102.

  In the frame of Type A in FIG. 7, the normal slot format # 0 (see Table 1) is selected. In the Type B frame, the slot information # 0-A2 in which the DPCCH pilot information is eliminated and the DPCCH transmission rate is reduced is selected. Thereafter, transmission is repeated in units of TTI. FIG. 7 shows an example in the case of TTI = 4.

It is a transmission side block block diagram which shows embodiment of this invention. It is a figure which shows the transmission power relationship at the time of leaving | separating from a base station. It is a figure which shows the transmission signal format in this embodiment. FIG. 2 is a diagram showing an outline of DPDCH and DPCCH processing in primary modulation section 105 and spreading processing section 106 in FIG. 1. It is a flowchart which shows operation | movement of this embodiment. It is a block diagram which shows the 2nd Embodiment of this invention. It is explanatory drawing at the time of setting the pilot information of DPCCH to burst transmission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Transmission signal sequence input terminal 102 Convolution encoding part 103 Transmission power instruction | indication part 104 Data format production | generation part 105 Primary modulation part 106 Spreading modulation part 107 D / A conversion part 108 Transmission radio | wireless part 109 Antenna 110 TPC code series input terminal 301 Position detection Part

Claims (7)

In a method that consists of DPDCH (Dedicated Physical Data Channel) and DPCCH (Dedicated Physical Control Channel), multiplexes signals of these channels and transmits them from a terminal to a base station by a CDMA (Code Division Multiple Access) method.
High transmission of user data by changing the power distribution of the DPCCH and the DPDCH when the current transmission power required for transmission to the base station exceeds the maximum transmission power possible with the device capability of the terminal A variable rate communication method characterized by controlling transmission of a rate as much as possible.   The variable rate communication method according to claim 1, wherein power distribution between the DPCCH and the DPDCH is changed by changing a symbol rate of the DPCCH.   2. The variable rate communication method according to claim 1, wherein power distribution between the DPCCH and the DPDCH is changed by Burst transmission of pilot information of the DPCCH. In a wireless portable terminal having a function of multiplexing signals of DPDCH (Dedicated Physical Data Channel) and DPCCH (Dedicated Physical Control Channel) and transmitting them to a base station by a CDMA (Code Division Multiple Access) system,
Transmission power calculation means for calculating the current transmission power required for transmission to the base station, and when the calculation result by the transmission power calculation means exceeds the maximum transmission output possible by the device capability of the terminal, the DPCCH A wireless portable terminal comprising DPCCH transmission rate changing means for switching a transmission rate to a lower transmission rate.   The wireless portable terminal according to claim 4, wherein the DPCCH transmission rate changing means is configured by means for changing the DPCCH transmission rate by changing a symbol rate of the DPCCH.   5. The wireless portable terminal according to claim 4, wherein the DPCCH transmission rate changing means is configured by means for changing the transmission rate of the DPCCH by transmitting the DPCCH pilot information in a Burst manner.   The wireless portable terminal includes position detection means for detecting the position of the terminal, and the transmission power calculation means is a current transmission power required for transmission to the base station based on information of the previous position detection means. The wireless portable terminal according to claim 4, wherein the wireless portable terminal is calculated.

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