Method and apparatus for controlling gain level of a communication channel in a cdma communication system

The present invention generally relates to the field of communication, and in particular to communication in cellular communication systems.

In code division multiple access (CDMA) communication systems, excessive transmission by a user can cause interference with other users in addition to reducing system capacity. Thus, the power level and / or data rate of the communication channels transmitted by the various users of the system will maintain the proper system capacity to control the interference level while still receiving the right quality at the receiving end. Controlled to do. The power level and / or data rate of the communication channel can establish the gain level of the communication channel. Communication services may include wireless transmission of digitized voice, mood or video, text messages and other forms of data. Such communication services can be required with different levels of quality and different levels of mobility.

For this purpose as well as others, there is a need for efficient control of the power level and / or data rate of communication channels at various levels of mobility in communication systems.

[Overview] The methods and associated devices in a code division multiple access communication system provide control of the gain level of a communication channel at various levels of mobility. According to various aspects of the invention, the rate of change in carrier-to-interference ratio (C / I) of the communication channel received by the receiver is determined. The rate of change in C / I can be directly related to the mobility level experienced by the communication channel. As such, according to embodiments, the gain level of the communication channel may be based on the rate of change in the C / I of the communication channel. Therefore, communication services are provided at varying levels of mobility and at efficient channel data rates and / or power levels.

The features, objectives, and advantages of the present invention will become more apparent from the detailed description described below when similar reference characters are incorporated with the correspondingly identifying drawings throughout.

Various embodiments of the present invention are for wireless communication in accordance with code division multiple access (CDMA) techniques disclosed and described in various standards published by the Telecommunications Industry Association (TIA). It may be incorporated into the system. Such standards include the TIA / EIA-95 standard, the TIA / EIA-IS-2000 standard, the IMT-2000 standard and the WCDMA standard, all of which are incorporated as references therein. The systems for data communication described in the document entitled "TIA / EIA / IS-856 cdma High Rate Packet Data Atmospheric Interface Specification" incorporated herein by reference are particularly various of the present invention. It is possible to incorporate the embodiment of. For a copy of the standard, connect to the World Wide Web at http://www.3gpp2.org, or the United States, VA22201, Arlington, Wilson Odori 2500, Ministry of Standards and Technology, TIA (TIA, Standards and Technology Department, 2500 Wilson It can be obtained by writing to Boulevard, Arlington, VA 22201, United States of America). Standards commonly identified as WCDMA standards and incorporated as references within them are Valbonne-France, Lucior-Sophia Antipolis Road 650, 3GPP Support Office, 650 Route des Lucioles-Sophia Antipolis. , Valbonne-France).

Generally speaking, new and improved methods and accompanying devices provide efficient control of power levels and / or data rates of communication channels at various levels of mobility in CDMA communication systems. One or more exemplary embodiments described herein are described in the context of digital wireless data communication systems. Although its use in this context has advantages, various embodiments of the invention may be incorporated into different environments or configurations. In general, the various systems described herein may be formed using software controlled processors, integrated circuits, or individual logic circuits. Data, procedures, instructions, information, signals, symbols, and chips that may be referenced throughout the field of application are voltages, currents, electromagnetic waves, magnetic fields or particles, light fields or light particles. Optical fields or particles), or a combination thereof, is favorably represented. Further, the blocks shown in each block diagram may represent hardware or method steps.

FIG. 1 is a general block diagram of a communication system 100 capable of operating according to any code division multiple access (CDMA) communication system standard while incorporating various embodiments of the present invention. Communication system 100 may be for voice, data, or both communication. In general, the communication system 100 includes a base station 101 that provides a communication link between a large number of mobile stations, such as mobile stations 102-104, and between mobile stations 102-104 and the public switched telephone and data network 105. Base station 101 may include a number of components such as mobile station controllers, base station controllers and radio frequency transceivers. For simplicity, such components are not shown. Base station 101 may also communicate with other base stations (not shown). Base station 101 communicates with each mobile station 102-104 via a forward link. The forward link can be maintained by a forward link signal transmitted from base station 101. Forward link signals targeting mobile stations 102-104 may be summed to form forward link signal 106. Each of the mobile stations 102-104 that receives the forward link signal 106 decodes the forward link signal 106 in order to extract information targeted at that user.

Mobile stations 102-104 communicate with base station 101 via the corresponding reverse links. Each reverse link is maintained for mobile stations 102-104 by a reverse link signal, such as reverse link signal 107-109. Each of the mobile stations 102-104 may transmit a pilot channel to base station 101. The pilot channel transmitted from the mobile station may be used to demodulate the information carried by the reverse link signal transmitted from the same mobile station. The uses and operations of pilot channels are well known. Transmitters and receivers for communicating over forward and reverse links are included in each mobile station 102-104 and base station 101. Various block diagrams for transmitters are shown and described in IS-95, IS-2000, IMT-2000, WCDMA and IS-856 standards.

FIG. 2 illustrates a forward channel structure 200 according to an embodiment that can be used for communication over forward links. The forward channel structure 200 may include pilot channel 201, medium access channel (MAC) 202, traffic channel 203 and control channel 204. MAC channel 202 may include reverse activity channel 206 and reverse power control channel 207. Reverse activity channel 206 is used to display the activity level on the reverse link. Reverse power control channel 207 is used at that power level to control the power level at which the mobile station can transmit over the reverse link.

FIG. 3 illustrates a reverse channel structure 300 that may be used for communication on a reverse link according to an embodiment. The reverse channel structure 300 includes a connection channel 350 and a traffic channel 301. The connection channel 350 includes a pilot channel 351 and a data channel 353. Traffic channel 301 includes pilot channel 304, MAC channel 303, acknowledgment (ACK) channel 340 and data channel 302. MAC channel 303 includes reverse link data rate indicator channel 306 and data rate control channel 305. The ACK channel 340 is used to convey whether a packet of data has been successfully decrypted by the mobile station. The reverse rate indicator channel 306 is used to display the rate currently being transmitted by the mobile station at that rate. The data rate control channel 305 displays the data rate requested by the mobile station and / or received on the forward link.

FIG. 4 illustrates a block diagram of a receiver 400 used to process a CDMA signal. The receiver 400 demodulates the received signal in order to extract the information carried by the received signal. The received (Rx) sample may be stored in RAM404. Received samples are generated by radio frequency / intermediate frequency (RF / IF) system 490 and antenna system 492. The antenna system 492 receives the RF signal and hands the RF signal to the RF / IF system 490. The RF / IF system 490 may be any conventional RF / IF receiver. The received RF signal is filtered, down-converted and digitized to form an RX sample at baseband frequency. The sample is fed to the demultiplexer (demux) 402. The output of demux402 is supplied to the searcher unit 406 and the finger element 408. The control unit 410 is coupled to them. The combiner 412 combines the decoder 414 with the finger element 408. The control unit 410 may be a software-controlled microprocessor, or may be installed on the same integrated circuit or on separate integrated circuits. The decoding function in the decoder 414 may follow a soft output Viterbi algorithm with or without connection with feedback.

During operation, the received sample is fed to demux402. The Demux 402 feeds the sample to the searcher unit 406 and the finger element 408. The control unit 410 forms the finger element 408 to demodulate the signals received at various time offsets based on the search results from the searcher unit 406. The result of the demodulation is combined and handed to the decoder 414. The decoder 414 decodes the data and outputs the decoded data. Channel despreading is by multiplying the received sample with the complex conjugate of the PN sequence and the assigned Walsh function in a single timing hypothesis, and often the integrate and dump accumulator circuit. ) (Not shown) is used to digitally filter the resulting specimen. Such techniques are usually technically well known. Receiver 400 may be used to decode information on reverse and forward link signals.

Each time the interrelationship process is initiated, the searcher 406 and finger element 408 may be initiated again to determine the demodulation of the pilot channel for testing the timing hypothesis and phase offset. The searcher 406 or finger element 408 or the combined searcher 406 and finger element 408 may determine the carrier-to-interference ratio (C / I) for each received signal. The ratio Eb / I can be synonymous with the ratio C / I. The ratio Eb / I is a unit of data symbol or a unit of measure of carrier energy over interference per data bit. Therefore, C / I and Eb / I may be interchangeable in some respects. Interference may generally be defined as the power spectral density and thermal noise of the interference.

The system controls the gain level of each transmitted channel from each source in order to control interference and maintain adequate system capacitance while allowing proper reception at the receiving end. The gain level of each channel may be adjusted by adjusting the channel data rate or power level or both the data rate and the power level. The gain level of a channel is based on the data rate of the encoded information at the transmitter and the power level at which the channel is transmitted over the signal at that power level. In general, channels at higher data rates require higher power levels to overcome interference. Channels at lower data rates require less power to overcome the same level of interference. Therefore, the gain of the channel may be adjusted by adjusting the power level, the data rate or both the power level and the data rate.

Various power control methods for controlling the power level of a signal and various methods for controlling the data rate of a channel are well known. The various standards incorporated herein by reference provide one or more methods for controlling the power level of a signal and the data rate of a channel. The power level of the channel may be controlled by two independent power control loops, namely open loop and closed loop. Open-loop power control is based on the receiver's requirements to maintain a proper communication link with the transmitter. The data rate adjustment is generally to allow reception quality at the receiving end and to control interference in the coverage area. When the feedback quality measurement indicates poor reception, the data rate may be reduced while keeping the power level constant in order to improve the quality of reception and to overcome the effects of interference. The data rate may be reduced in order to allow other users to receive communications at a higher data rate.

According to at least one CDMA spread spectrum system standard incorporated herein by reference, the mobile station may adjust the output power level according to the nature of the code channel. The mobile station may maintain a power level ratio between the sign channel power level and the reverse pilot channel power level. The ratio may be set according to the data rate used for the code channel. In general, the table applies that value to that ratio at various data rates. The ratio generally increases in search of higher data rates. Ratios of 1 or less are also possible. At a ratio equal to 1, the power level of the pilot channel is equal to the power level of the code channel as set by the power control loop. While transmitting data on the traffic channel, the data rate and traffic channel power level can be adjusted. Once an acceptable data rate is selected, the corresponding channel power with respect to the reverse link pilot power level is used to set the traffic channel power level.

In data mode, the base station may provide communication links to a large number of mobile stations at various data rates. For example, one mobile station connected to a forward link may be receiving data at a low data rate and the other mobile station may be receiving data at a high data rate. On the reverse link, the base station may receive a large number of reverse link signals from various mobile stations. Based on independent forward link measurements, the mobile station may request the desired data rate from the base station. The desired forward link data rate can be transmitted to the base station via the data rate control (DRC) channel 305. The data rate may also be selected by the base station based on explicit weighing. The metric may include the transmit power level of the power control subchannel and / or the transmit power level of one or more forward traffic channels. The base station attempts to provide forward link data transfer at the requested data rate.

The gain level of the channel may be based on the C / I level of the signal received at the receiving end as set by the transmitter through adjustment of the channel power level and data rate. The receiver 400 may measure the C / I level of each received signal, as described. The receiver notifies the transmitter of the C / I measurement value. The transmitter compares the notified C / I to the target C / I threshold and then adjusts the channel gain level of the channel to maintain the target C / I at the receiver. The signal between the transmitter and receiver can propagate through the channel with various fading conditions before being received by the receiver. The C / I level can change from one level to the next without interruption. The control loop used to control the gain level of the channel may use a C / I target threshold level such that the frame error rate is maintained at an appropriate level. The C / I target threshold is the appropriate frame error rate for at least some period after the notification of the channel C / I state to explain the variation in the channel during the notification time and the actual transmission time of the signal. To maintain, the tuned channel gain can be selected and maintained to be above the minimum required level. As such, the channel gain is maintained at the lowest level plus margin.

There can be a delay between the time when the C / I level is measured and notified, and the time when the channel gain level is subsequently selected and transmitted from the transmitter. As such, by pushing the channel gain above the lowest level in the fading channel state, the frame error rate is almost always maintained at the appropriate level in a predictive way. Excessive gain margins cause communication to go to lower data rates, higher power levels, or both with respect to the lowest gain level. Communication at low data rates requires less power than communication at high data rates. Therefore, in order to add the gain margin by varying the data rate, the data rate may be reduced while keeping the power level constant. If the data rate is kept at the same level, the channel gain can be increased by increasing the power level. The power level and data rate may be varied to achieve a higher channel gain corresponding to the gain margin.

Referring to FIG. 5, the graph 500 shows the minimum required channel with respect to channel C / I state 502 and time. An example of gain) 501 is depicted. The minimum required channel gain 501 is sufficient, for example, for channel C / I state 502 at the receiver to maintain a proper communication link between the transmitter and receiver. The channel gain is at the peak level when the channel C / I state is at the bottom point. At time 591, the gain of the channel for transmission to the receiver may be set to gain level 504. At time 591, an excessive margin of 590 between the lowest gain level 501 and the selected gain level 504 causes communication over the channel to have an appropriate frame error rate under the highest fading conditions, at least for a period of time. By accepting an excessive gain margin, the selected gain level 504 is sufficient to maintain proper communication between the transmitter and receiver, for example, for at least a period of time 550. Excessive margin provides protection if the channel C / I state drops during period 550. If the channel C / I state improves during period 550, thus requiring a lower gain level, the effective excess margin is substantially higher than the selected excess gain margin 504. As such, the receiver is capable of receiving at an appropriate frame error rate under the highest channel conditions.

At time 592, the excessive margin 590 provides protection against changes in channel state over a period of 551. The period 551 is shorter than the period 550 due to the rate at which the channel state is changing. The channel state is changing during period 550 at a rate slower than period 551. At time 593, an excessive margin of 590 provides protection against any changes in the channel state over a much longer period of time. The corresponding C / I channel state at time 593 is thus improved to require lower channel gain at the actual transmit time. The rate at which the channel C / I state changes has a direct correlation with the rate at which the transmitter and receiver are separated from each other and / or the rate at which the propagation channel is changing.

Generally speaking, various aspects of the invention provide for efficient gain control of communications in different states. In the code division multiple access communication system 100, the rate of change in the carrier-to-interference ratio (C / I) of the communication channel received by the receiver 400 is determined. According to embodiments, the gain level of the communication channel at the transmitter may be based on the rate of change in the C / I of the communication channel. As shown in FIG. 5, for example, the rate of change in C / I at time 591 is different from the rate of change at times 592 and 593. If the rate of change in C / I is positive, the gain margin is subtracted from the gain level of the communication channel to form the final gain level for transmission of the communication channel, according to embodiments. When the rate of change in C / I is positive, the channel state is improving. For example, the rate of change in C / I is positive at time 593. C / I increased at time 593. Therefore, at time 593, according to the embodiment, the gain margin is subtracted from the gain level of the communication channel to form the final gain level for transmission of the communication channel.

The magnitude of the gain margin may correspond proportionally to the magnitude of the rate of change in C / I, depending on the embodiment. If the rate of positive change in C / I is high, the channel state is improving at a faster rate than when the rate of positive change in C / I is low. Therefore, in a predictive way, the channel state requires a final gain level that is much smaller than that estimated in the channel with the rate of large positive changes in C / I. As such, the magnitude of the gain margin can be greater in the channel state associated with the rate of positive change in C / I than in the channel state associated with the rate of positive change in C / I. For this effect of subtracting the gain margin, the data rate of the communication channel can be increased according to embodiments. The data rate can be increased when the rate of change in C / I is positive, as the channel state is improving. Therefore, in a predictive way, the channel can maintain a communication link at a higher data rate. The power level of the communication channel may be reduced according to embodiments for the purpose of subtracting the gain margin. The power level can be reduced when the rate of change in C / I is positive, as the channel state is improving. According to embodiments, the power level can be reduced and the data rate can be increased at the same time, for the purpose of subtracting the gain margin. Therefore, in a predictive way, the channel can maintain a communication link at the same data rate and at a lower power level.

If the rate of change in C / I is negative, the gain margin is added to the gain level of the communication channel to form the final gain level for transmission of the communication channel, according to embodiments. When the rate of change in C / I is negative, the channel state is degraded. For example, the rate of change in C / I is negative at times 591 and 592. C / I decreased at times 591 and 592. Therefore, according to embodiments, the gain margin is added to the gain level of the communication channel at times 591 and 592 to form the final gain level for transmission of the communication channel.

The magnitude of the gain margin can correspond proportionally to the magnitude of the rate of change in C / I according to the embodiment. If the rate of negative change in C / I is high, the channel state is deteriorating at a faster rate than when the rate of negative change in C / I is low. Therefore, in a predictive way, the channel state requires a final gain level that is much higher than that estimated in the channel with the rate of large negative changes in C / I. As such, the magnitude of the gain margin can be greater in the channel state with a large negative change rate of C / I than in the channel state with a small negative change rate of C / I. The rate of negative change at time 591 is less than the rate of negative change at time 592. Therefore, the size of the gain margin at time 591 is smaller than the size of the gain margin at time 592 according to the embodiment.

The data rate of the communication channel can be reduced according to the embodiment for the purpose of adding the gain margin. When the rate of change in C / I is negative, the data rate can be reduced because the channel state is degraded. Thus, in a predictive way, a channel can maintain a communication link at a lower data rate while avoiding frame erasure. Further, the power level of the communication channel can be increased according to the embodiment for the purpose of adding the gain margin. When the rate of change in C / I is negative, the channel state is degraded and the power level can be increased. The data rate can be reduced and the power level can be reduced at the same time for the purpose of the effect of adding the gain margin. Therefore, in a predictive way, the channel can maintain a communication link at the same data rate and at a higher power level.

The channel state between the transmitter and receiver can be dynamic. The fast fading state may be referred to as a high mobility state, and the slow fading state may be referred to as a low mobility state. Reference to FIG. 6 shows an example of the C / I state of the channel. For example, at time zone 610, the channel may be in a fast fading state, and at time zone 620, the channel may be in a slow fading state. The average C / I 601 is the average C / I of the channel over a period of time. The C / I602 at the moment of the channel intersects the average C / I601 at various times. The number of times the instantaneous C / I 602 intersects the average C / I 601 is higher in the fast fading state corresponding to time zone 610 than in the slow fading state corresponding to time zone 620. The number of times the instantaneous C / I 602 intersects the average C / I 601 can be proportional to the mobility level of the communication channel in communication system 100. Thus, the mobility level of receiver 400 can be determined by determining the number of times the instantaneous C / I 602 intersects the average C / I 601.

According to embodiments, the mobility level of a communication channel in communication system 100 can be determined by determining the number of times the instantaneous C / I of the channel intersects the average C / I 601 of the channel. The mobility level can be compared to the mobility threshold. The mobility threshold can correspond to a low mobility level. If the mobility level meets the low mobility threshold, the gain level of the communication channel between the transmitter and receiver 400 in communication system 100 can be based on the rate of change in C / I, according to embodiments. .. If the mobility level is below the low mobility threshold, the channel state corresponds to the low mobility state. In the low mobility state, the channel state can change slowly, thus, according to embodiments, in a predictive way, the gain level of the channel is based on the rate of change in C / I.

With reference to FIG. 7, flow diagram 700 can be followed to carry out various aspects of the invention. At step 701, the mobility level of the receiver may be determined. The mobility level is compared to the low mobility threshold in step 702. The low mobility threshold can correspond to a low mobility level state. If the mobility level is less than the low mobility threshold, the rate at which the channel C / I is changing is determined in step 703. At step 704, a controller such as control system 410 at receiver 400 may determine whether the rate of change in C / I is positive or negative. At step 705, if the rate of change is positive, the gain margin is subtracted from the lowest gain of the channel according to the embodiment. In step 706, if the rate of change is negative, the gain margin is added to the lowest gain of the channel according to the embodiment. Channels can be transmitted with adjusted gain levels.

For those who are technically proficient, the various exemplary logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein are electronic hardware, computer software, or. It is more justified that it can be implemented as a combination of both. To clearly illustrate this hardware and software compatibility, various exemplary components, blocks, modules, circuits, and steps have generally been previously described in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and design constraints imposed on the overall system. A skilled technician may perform the functionality described in various ways for each particular scope of application, but such practice decisions are to be construed as occurring outside the scope of the invention. Should not be.

The various exemplary logic blocks, modules, and circuits described in connection with the embodiments disclosed herein are general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), and field programs. With possible gate arrays (FPGAs) or other programmable logic devices, individual gate or transistor logic circuits, individual hardware components, or any combination thereof designed to perform the functions described therein. Can be carried out or can be carried out. The general purpose processor may be a microprocessor, but as an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be a combination of arithmetic units, such as a combination of DSP and microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration.

The steps of methods or algorithms described in connection with the embodiments described herein can be embodied directly in hardware, in software modules executed by a processor, or in combination thereof. The software module may be present in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known technically. Good. An exemplary storage medium is coupled to a processor such that the processor can read information from the storage medium and write the information to the storage medium. Alternatively, the storage medium may be built into the processor. The processor and storage medium may reside in the ASIC. The ASIC may be present at the user terminal. Alternatively, the processor and storage medium may be present as individual components in the user terminal.

The description of the preferred embodiments above is provided so that any person who is technically proficient can commercialize or use the present invention. The various changes to these embodiments are immediately apparent to those who are technically proficient, and the inclusive principles set forth therein are other without the use of creative abilities. Can be applied to embodiments. As such, the invention is not intended to be confined to the embodiments presented herein, and is consistent with the broadest scope consistent with the principles and novel features disclosed herein. It is a thing.

<figref num="1">FIG. 1 illustrates a communication system capable of operating according to various embodiments of the present invention.</figref><figref num="2">FIG. 2 illustrates an exemplary forward link channel structure.</figref><figref num="3">FIG. 3 illustrates an exemplary reverse link channel structure.</figref><figref num="4">FIG. 4 illustrates a communication system receiver for operating in mobile and base stations that can operate according to various embodiments of the present invention.</figref><figref num="5">FIG. 5 illustrates exemplary channel C / I states and associated channel gain levels.</figref><figref num="6">FIG. 6 illustrates exemplary channel mean C / I states and instantaneous channel C / I levels over a period of time at various mobility levels.</figref><figref num="7">FIG. 7 illustrates a flow diagram for controlling the gain level of a communication channel according to various embodiments.</figref>