HK1067466B - Method and apparatus for controlling transmit power of a supplemental channel in a reverse link - Google Patents

Description

Method and apparatus for controlling transmit power of supplemental channels in reverse link

Background

FIELD

The present invention relates generally to data communications, and more particularly to a novel and improved reverse link architecture for a wireless communication system.

Background

Wireless communication systems are commonly employed to provide different types of communications including voice and packet data services. These systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or some other modulation technique. CDMA systems may provide some characteristics that include increased system capacity over other systems.

In a wireless communication system, a user communicates with another user through transmissions on forward and reverse links through one or more base stations using a remote terminal (e.g., a cellular telephone). The forward link (i.e., downlink) refers to transmission from the base station to the user terminal, and the reverse link (i.e., uplink) refers to transmission from the user terminal to the base station. The forward and reverse links are typically allocated different frequencies using a Frequency Division Multiplexing (FDM) method.

Packet data on the forward and reverse links typically has very different characteristics. On the forward link, the base station typically knows whether there is data to send, the amount of data, and the identity of the receiving remote terminal. It is also possible to provide the base station with an "efficiency" achieved by each receiving remote terminal, which can be represented by the amount of transmit power required per bit. Based on the known information, the base station can efficiently schedule data transmissions to the remote terminal at selected times and rates to achieve desired performance.

On the reverse link, the base station typically does not know in advance which remote terminals have packet data to transmit and the amount of data to transmit. The base station generally knows the efficiency of each receiving remote terminal, which can be quantified by the ratio of energy per bit to total noise plus interference, Ec/(No + Io), required at the base station to correctly receive the data transmission. The base station may allocate resources to the remote terminal when requested and available.

The use of the reverse link may fluctuate significantly due to uncertainty in user demand. If many remote terminals transmit at the same time, large interference can be generated at the base station. The transmit power from the remote terminal needs to be increased to maintain the target Ec/(No + Io), which results in a greater interference level. If the transmit power is increased further in this manner, it eventually results in "blocking" and transmissions from all or most of the terminals may not be received correctly. This is because the remote terminal cannot transmit with sufficient power to close the link to the base station.

In a CDMA system, the channel loading on the reverse link is often described by a "hot-rise". The thermal rise is the ratio of the total received power at the base station receiver to the thermal noise power. Theoretical curves show that the thermal rise increases with increasing load, based on theoretical capacity calculations for the CDMA reverse link. The load where the heat rises infinitely is often referred to as the "pole". A load with a 3dB thermal rise corresponds to 50% of the load supported at the pole or half the number of users supported at the pole. As the number of users rises and the user data rate increases, the load becomes greater. Accordingly, as the load increases, the amount of power that the remote terminal must transmit increases. The thermal rise and channel load are measured by a.j. viterbi in "CDMA: further detailed in Principles of Spread Spectrum communications, Addison-Wesley Wireless communications series, May 1995, ISBN: 0201633744, herein incorporated by reference.

The reference to Viterbi provides a classical equation showing the relationship between the thermal rise, the number of users and the user data rate. The equation also shows that there will be a higher capacity (bits per second) if there are a few users transmitting at a higher rate than a large number of users. This is due to interference between transmitting users.

In a typical CDMA system, the data rate of many users is continuously varied. For example, in IS-95 or cdma2000 systems, voice users typically transmit at one of four RATEs corresponding to voice activity at the remote terminal, as described in U.S. patent nos. 5657420 and 5778338, entitled "voice mobile voice decoder," and U.S. patent No. 5742734 entitled "ENCODING RATE SELECTION information voice decoder," and similarly, many data users vary their data RATEs continuously. This causes a significant change in the amount of data transmitted simultaneously and hence a significant change in the thermal rise.

In view of the above, there is a need in the art for a reverse link channel structure that achieves better performance for packet data transmission, taking into account the data transmission characteristics of the reverse link.

SUMMARY

An aspect of the present invention provides a method of controlling a transmit power of a supplemental channel in a reverse link of a wireless communication system, comprising: receiving a first power control stream for controlling transmit power of a supplemental channel along with at least one other reverse link channel; receiving a second power control stream that controls the transmit characteristics of the secondary channel; and adjusting the transmit power and characteristics of the supplemental channel in accordance with the first and second power control streams.

Another aspect of the present invention provides a remote terminal in a wireless communication system, comprising: a transmit data processor for processing and transmitting: data and signaling on a reverse fundamental channel, packet data on an assigned reverse supplemental channel, signaling on a reverse control channel, and information related to packet data transmission on a reverse indicator channel; a receive data processor for receiving a plurality of power control streams on a forward power control channel; and a controller coupled to the transmit and receive data processors and configured to control transmit characteristics of the one or more reverse supplemental channels in accordance with the plurality of power control flows.

Yet another aspect of the present invention provides a method of supporting data transmission on a reverse link of a wireless communication system, comprising: transmitting data and signaling on a reverse link of a reverse fundamental channel; transmitting packet data on a reverse link of a reverse supplemental channel; transmitting signaling on a reverse link of a reverse control channel; and transmitting first and second power control streams for a reverse link of a particular remote terminal on a forward power control channel, wherein the first power control stream is used to control the transmit power of the reverse supplemental channel along with at least one other reverse link channel, and the second power control stream is used to control the transmit characteristics of a group of remote terminals.

Aspects of the present invention provide mechanisms that support efficient and effective reverse link resource allocation and use. In an aspect, mechanisms are provided to quickly allocate resources (e.g., secondary channels) as needed, and to quickly de-allocate resources when not needed or to maintain system stability. Reverse link resources may be rapidly allocated and deallocated via short messages exchanged over control channels on the forward and reverse links. In another aspect, mechanisms are provided to facilitate efficient and reliable data transfer. In particular, a reliable acknowledgement/negative acknowledgement scheme and an efficient retransmission scheme are provided. In another aspect, mechanisms are also provided to control the transmit power and/or data rate of the remote terminal to achieve high performance and avoid instability. Another aspect of the present invention provides a channel structure that implements the features described above. These and other aspects will be described in further detail below.

The disclosed embodiments further provide methods, channel structures, and apparatuses that implement various aspects, embodiments, and features of the invention, as described in further detail below.

Brief description of the drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 is a diagram of a wireless communication system supporting a number of users;

FIG. 2 is a simplified block diagram of an embodiment of a base station and a remote terminal;

FIGS. 3A and 3B are diagrams of corresponding reverse and forward channels;

FIG. 4 is a diagram illustrating communication between a remote terminal and a base station for assigning a reverse link supplemental channel (R-SCH);

FIGS. 5A and 5B are diagrams illustrating data transmission on the reverse link and Ack/Nak message transmission for two different cases;

FIGS. 6A and 6B are diagrams illustrating acknowledgment sequences with corresponding short or long acknowledgment delays;

FIG. 7 is a diagram illustrating variable rate data transmission on R-SCH with fast congestion control, according to an embodiment of the invention; and

FIG. 8 is a graph illustrating the improvement that is possible with R-SCH fast control.

Detailed Description

Fig. 1 is a diagram of a wireless communication system 100 that supports a number of users and is capable of implementing various aspects of the invention. System 100 provides communication for a number of cells, each of which is serviced by a corresponding base station 104. The base stations may also be generally referred to as Base Transceiver Systems (BTSs). Various remote terminals 106 are dispersed throughout the system. Each remote terminal 106 may communicate with one or more base stations 104 on the forward and reverse links at any particular moment, depending on whether the remote terminal is active and whether it is in soft handoff. The forward link refers to transmissions from the base station 104 to the remote terminal 106, and the reverse link refers to transmissions from the remote terminal 106 to the base station 104. As shown in fig. 1, base station 104a communicates with remote terminals 106a, 106b, 106c, and 106d, and base station 104b communicates with remote terminals 106d, 106e, and 106 f. Remote terminal 106d is in soft handoff and is communicating with both base stations 104a and 104 b.

Within the system 100, a Base Station Controller (BSC)102 is coupled to a base station 104 and may further be coupled to a Public Switched Telephone Network (PSTN). The coupling to the PSTN is typically accomplished through a Mobile Switching Center (MSC), which is not shown in fig. 1 for simplicity. The BSC may also be coupled to a packet network, typically implemented by a Packet Data Serving Node (PDSN), not shown in fig. 1. BSC 102 provides coordination and control for the base stations coupled to it. BSC 102 further controls the routing of telephone calls between remote terminals 106 and users coupled to the PSTN (e.g., conventional telephones) and packet networks through base stations 104.

The System 100 IS also used to support one or more CDMA standards, such as (1) the "TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wireless spread Spectrum Cellular System" (the IS-95 Standard), (2) the "TIA/EIA-98-D communicated Minimum Standard for Dual-Mode Wireless spread Spectrum Cellular Station" (the IS-98 Standard), (3) the "3-communication Standard^rdThe Generation Partnership Project "(3 GPP) alliance provides documents embodied in a set of documents including document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS25.214(the W-CDMA standard), (4) by the name" 3G TS 25.211^rdThe Generation PartnershipProject 2 "(3 GPP2) alliance provides documents and is embodied in a set of documents including document numbers C.S0002-A, C.S0005A, C.S0010-A, C.S0011-A, C.S0024, and C.S0026(the cdma2000 standard), (5), and some other standards. Within the 3GPP and 3GPP2 documents, there is a conversion from worldwide standards (e.g., TIA, ETSI, ARIB, TTA, and CWTS) to regional standards and from International Telecommunications Union (ITU) to international standards. These standards are incorporated herein by reference.

Fig. 2 is a simplified block diagram of an embodiment of a base station 104 and a remote terminal 106, which are capable of implementing various aspects of the present invention. For a particular communication, voice data, packet data, and/or messages can be exchanged between base station 104 and remote terminal 106. Different types of messages may be transmitted, such as messages used to establish a communication session between the base station and the remote terminal and messages used to control data transmission (e.g., power control, data rate information, acknowledgements, etc.). Some of these message types will be detailed below.

For the reverse link, at the remote terminal 106, voice and/or packet data (e.g., from a data source 210) and messages (e.g., from a controller 230) are provided to a Transmit (TX) data processor 212, which formats and encodes the data and messages with one or more coding schemes to generate coded data. Each coding scheme may include any combination of Cyclic Redundancy Check (CRC), convolutional, Turbo, block, and other coding or no coding. Typically, voice data, packet data, and messages are encoded using different schemes, and different types of messages can also be encoded differently.

The encoded data is then provided to a Modulator (MOD)214 and further processed (e.g., covered, spread with short PN sequences, and scrambled with a long PN sequence assigned to the user terminal). The modulated data is then provided to a transmitter unit (TMTR)216 and conditioned (e.g., converted to one or more analog signals, amplified, filtered, and quadrature modulated) to generate a reverse link signal. The reverse link signal is transmitted through a transceiver converter (D)218 and through an antenna 220 to the base station 104.

At base station 104, the reverse link signal is received by an antenna 250 and routed through a duplexer 252 to a receiver unit (RCVR) 254. Receiver unit 254 conditions (filters, amplifies, frequency downconverts, and digitizes) the received signal and provides samples. A demodulator (DEMOD)256 receives and processes (despreads, decovers, and pilot demodulates) the samples to provide recovered symbols. Demodulator 256 may implement a rake receiver function that processes multiple samples of the received signal and generates combined symbols. A Receive (RX) data processor 258 then decodes the symbols to recover the data and messages transmitted on the reverse link. The recovered voice/packet data is provided to a data acceptor 260 and the recovered messages may be provided to a controller 270. The processing by demodulator 256 and RX data processor 258 are complementary to that performed at remote terminal 106. Demodulator 256 and RX data processor 258 may process multiple transmissions received via multiple channels, e.g., a reverse fundamental channel (R-FCH) and a reverse supplemental channel (R-SCH). Also, transmissions may be received from multiple remote terminals simultaneously, each transmitting on a reverse fundamental channel, a reverse supplemental channel, or both.

On the forward link, at base station 104, voice and/or packet data (e.g., from a data source 262) and messages (e.g., from controller 270) are processed (e.g., formatted and encoded) by a Transmit (TX) data processor 264, further processed (e.g., covered and spread) by a Modulator (MOD)266, and conditioned (e.g., converted to analog signals, amplified, filtered, and quadrature modulated) by a transmitter unit (TMTR)268 to generate a forward link signal. The forward link signal is routed through the transceive switch 252 and transmitted through the antenna 250 to the remote terminal 106.

At the remote terminal 106, the forward link signal is received by an antenna 220, routed through a duplexer 218, and provided to a receiver unit 222. Receiver unit 222 conditions (down converts, filters, amplifies, quadrature demodulates, and digitizes) the received signal and provides samples. The samples are processed (e.g., despreaded, decovered, and pilot demodulated) by a demodulator 224 to provide symbols, and the symbols are further processed (e.g., decoded and examined) by a receive data processor 226 to recover the data and messages transmitted on the forward link. The recovered data is provided to a data receiver 228 and a recovery message may be provided to a controller 230.

The reverse link has characteristics that are very different from those of the forward link. In particular, data transmission characteristics, soft handover behavior, and fading phenomena are typically very different on the forward and reverse links.

As described above, on the reverse link, the base station typically does not know in advance which remote terminals have packet data to transmit, nor does it know the amount of data. Thus, the base station may allocate resources to the remote terminal when requested and available. The use of the reverse link fluctuates greatly due to uncertainty in user demand.

In accordance with aspects of the present invention, mechanisms are provided to efficiently and effectively allocate and utilize reverse link resources. In an aspect, mechanisms are provided to quickly allocate resources as needed, and to quickly de-allocate resources when not needed or to maintain system stability. Reverse link resources may be allocated through supplemental channels for packet data transmissions. In another aspect, mechanisms are provided to facilitate efficient and reliable data transfer. In particular, a reliable acknowledgement scheme and an efficient retransmission scheme are provided. In another aspect, mechanisms are also provided to control transmit power to achieve high performance and avoid instability. These and other aspects will be described in more detail below.

Fig. 3A is a diagram of an embodiment of a reverse channel structure implementing various aspects of the invention. In this embodiment, the reverse channel structure includes a reverse access channel, an enhanced access channel, a reverse pilot channel (R-PICH), a reverse common control channel (R-CCCH), a reverse dedicated control channel (R-DCCH), a reverse fundamental channel (R-FCH), a reverse supplemental channel (R-SCH), and a reverse rate indicator subchannel (R-RICH). Different, fewer, and/or additional channels may also be supported within the scope of the present invention. These channels may be implemented in a similar standard as defined by the cdma2000 standard. The characteristics of some of these channels will be described below.

The particular set of channels used for each communication (i.e., each call) and its configuration is defined by one of a number of radio frequency configurations (RCs). Each RC defines a particular transport format that is specified by different physical layer parameters such as, for example, transmission rate, modulation characteristics, spreading rate, etc., radio frequency configuration may be similar to that defined by the cdma2000 standard.

A reverse dedicated control channel (R-DCCH) is used to transmit user and signaling information, e.g., control information, to a base station upon communication. The R-DCCH may be implemented similar to the R-DCCH defined in the cdma2000 standard.

The reverse fundamental channel (R-FCH) is used to transmit user and signaling messages (e.g., voice data) to the base station during communication. The R-FCH may be implemented in a similar manner to the R-FCH defined in the cdma2000 standard.

A reverse supplemental channel (R-SCH) is used to transmit user information (e.g., packet data) to a base station at the time of communication. The R-SCH is supported by some radio frequency configurations (e.g., RC3 through RC11) and is assigned to a remote terminal when needed and available. In an embodiment, zero, one, or two supplemental channels (i.e., R-SCH1 and R-SCH2) may be assigned to the remote terminal at any time. In an embodiment, the R-SCH supports retransmission at the physical layer, and different coding schemes may be used for retransmission. For example, the retransmission may use the code rate of 1/2 that was originally sent. The retransmission may repeat the same rate 1/2 code symbols. In another embodiment, the priority code may be a rate 1/4 code. The original transmission may use 1/2 of the symbols and the retransmission may use the other half of the symbols. If a third retransmission is completed, one of the symbol groups, a portion of each group, a subset of any group, and other possible symbol combinations may be repeated.

R-SCH2 may be used in conjunction with R-SCH1 (e.g., RC 11). In particular, the R-SCH2 may be used to provide different quality of service (QoS). Also, type II and III hybrid ARQ schemes may be used in conjunction with the R-SCH. The hybrid ARQ scheme is generally described by s.b. wicker in "Error Control System for digital Communication and Storage", prentic-Hall, 1995, chapter 15, which is incorporated herein by reference. The hybrid ARQ scheme is described in the cdma2000 standard.

The reverse rate indication channel (R-RICH) is used by the remote terminal to provide information pertaining to the (packet) transmission rate on one or more reverse supplemental channels. Table 1 lists fields of the specific format of R-RICH. In one embodiment, for each data frame transmitted on the R-SCH, the remote terminal transmits a Reverse Rate Indicator (RRI) symbol that indicates the data rate of the data frame. The remote terminal also transmits the SEQUENCE number of the data frame being transmitted (SEQUENCE _ NUM) and whether the data frame (RETRAN _ NUM) is transmitted for the first time or retransmitted. It is also within the scope of the invention to use different, fewer, and/or additional fields for the R-RICH. The information in table 1 is sent by the remote terminal for each data frame transmitted on the supplemental channel (e.g., every 20 msec).

TABLE 1

Field(s)	Length of
		RRI	3
SEQUENCE_NUM	2
		RETRAN_NUM	2

If there are multiple reverse supplemental channels (e.g., R-SCH1 and R-SCH2), there may be multiple R-RICH channels (e.g., R-RICH1 and R-RICH2), each with RRI, SEQUENCE _ NUM, and RETRAN _ NUM fields. In addition, the fields of multiple reverse supplemental channels may be combined into a single R-RICH channel. In particular embodiments, blind rate determination is achieved using a fixed transmission rate or base station without the RRI field, where the base station determines the transmission rate from the data. Blind RATE determination may be achieved by the means described in U.S. patent No. 6175590 entitled "METHOD AND APPARATUS FOR DERTERMINING THE RATE OF RECEIVED DATAIN A VARIABLE RATE COMMUNICATION SYSTEM", filed on 12.5.1998, assigned to the assignee OF the present invention AND incorporated herein by reference.

Fig. 3B is a diagram of an embodiment of a forward channel structure that supports various aspects of the present invention. In the present embodiment, the forward channel structure includes a common channel, a pilot channel, and a dedicated channel. Common channels include a control broadcast channel (F-BCCH), a quick paging channel (F-QPCH), a common control channel (F-CCCH), and a common power control channel (F-CPCCH). The pilot channels include a primary pilot channel and a secondary pilot channel. The dedicated channels include a fundamental channel (F-FCH), a supplemental channel (F-SCH), a dedicated supplemental channel (F-APICH), a dedicated control channel (F-DCCH), and a dedicated packet control channel (F-CPDCCH). Likewise, different, fewer, and/or additional channels may also be supported within the scope of the present invention. These channels may be implemented similar to those defined by the cdma2000 standard. The characteristics of some of the channels will be described below.

The forward common power control channel (F-CPCCH) is used by the base station to transmit power control subchannels (e.g., one bit per subchannel) for power control of the R-PICH, R-FCH, R-DCCH, and R-SCH. In one embodiment, the remote terminal is assigned a reverse link power control subchannel from one of the three sources, F-DCCH, F-SCH and F-CPCCH, at the time of channel assignment. The F-CPCCH may be allocated if the F-DCCH or F-SCH does not provide a reverse link power control subchannel.

In one embodiment, the available bits within the F-CPCCH may be used to form one or more power control sub-channels, which may be allocated for different uses. For example, a number of power control sub-channels may be defined and used for power control of a number of reverse link channels. POWER CONTROL of multiple channels according to multiple POWER CONTROL sub-channels is accomplished as described in U.S. patent No. 5991284 entitled "POWER CONTROL," filed on 23.11.1999, assigned to the assignee of the present invention and incorporated herein by reference.

In one particular implementation, the 800bps power control subchannel controls the power of the reverse pilot channel (R-PICH). All reverse traffic channels (e.g., R-FCH, R-DCCH, and R-SCH) have their power levels related to the R-PICH in a known relationship, e.g., as described in C.S 0002. The ratio of these two channels is commonly referred to as the traffic-to-pilot ratio. The traffic-to-pilot ratio (i.e., the power level of the reverse traffic channel relative to the R-PICH) can be adjusted via a message from the base station. However, this message is very slow, so it is possible to define a 100 bit per second (bps) power control subchannel and for power control of the R-SCH. In one embodiment, the R-SCH power control subchannel controls the R-SCH associated with the R-PICH. In another embodiment, the R-SCH power control subchannel controls the absolute transmission power of the R-SCH.

In one aspect of the invention, a "congestion" control subchannel may be defined for control of the R-SCH and may be implemented in accordance with the R-SCH power control subchannel or other subchannels.

Power control for the reverse link will be described in detail below.

A forward dedicated packet control channel (F-DPCCH) is used to transmit user and signaling information to a particular remote terminal during communication. The F-DPCCH may be used to control reverse link packet data transmissions. In an embodiment, the F-DPCCH is encoded and interleaved to enhance reliability, and may be implemented like the F-DCCH defined by the cdma2000 standard.

Table 2 lists fields for the F-DPCCH specific format. In one embodiment, the F-DPCCH has a 48-bit size frame, with 16 bits for CRC, 8 bits for code tail, and 24 bits for data and messages. In one embodiment, the default transmission rate for the F-DPCCH is 9600bps, where 48-bit frames can be transmitted within 5 msec. In one embodiment, each transmission (i.e., each F-DPCCH frame) is covered with a common long code for the receiving remote terminal that is to receive the frame. This avoids the use of explicit addresses (hence, the channel is referred to as a "dedicated" channel). However, since many remote terminals in dedicated channel mode may continuously monitor the channel, the F-DPCCH is also "common". The CRC is checked if the message is directed to a particular remote terminal and received correctly.

TABLE 2

Field(s)	Number of bits per frame
		Information	24
Frame quality indication	16
		Code tail	8

The F-DPCCH may be used to transmit short messages, such as defined by the cdma2000 standard. For example, the F-DPCCH may be used to transmit a reverse supplemental channel assignment short message (RSCAMM) for granting the F-SCH to the remote terminal.

The forward common packet Ack/Nak channel (F-CPANCH) is used by the base station to transmit (1) acknowledgement (Ack) and negative acknowledgement (Nak) for reverse link packet data transmissions and (2) other control information. In one embodiment, the acknowledgments and negative acknowledgments are transmitted as n-bit Ack/Nak messages, each of which is associated with a corresponding data frame transmitted on the reverse link. In one embodiment, each Ack/Nak message may include 1, 2, 3, or 4 bits (or possibly more), with the number of bits in the message depending on the number of reverse link channels in the service configuration. The n-bit Ack/Nak message may be block coded to increase reliability or clear transmission.

In one aspect, to increase reliability, Ack/Nak messages for a particular data frame are retransmitted (e.g., after 20msec) within successive frames to provide time diversity of the messages. Time diversity provides additional reliability or may maintain the same reliability while reducing the power used to transmit Ack/Nak. The Ack/Nak message may use error correction coding as is known in the art. For retransmissions, the Ack/Nak message may repeat exactly the same codeword or may use increased redundancy. The transmission and retransmission of Ack/Nak will be described in detail below.

Several types of control are used to control the reverse link on the forward link. These include control of supplemental channel requests and grants, Ack/Nak for reverse link data transmissions, power control for data transmissions, and other possibilities.

The reverse link may be used to maintain a relatively constant level of thermal rise at the base station when there is reverse link data to transmit. The transmission on the R-SCH may have different assignments, two of which are described below:

● by infinite allocation. This method is used for real-time traffic that cannot have much delay. Allowing the remote terminal to transmit immediately at a certain assigned data rate.

● by dispatch. The remote terminal sends an estimate of its buffer size. The base station determines when the remote terminal is allowed to transmit. The method is used for available bit rate traffic. The goal of the scheduler is to limit the number of simultaneous transmissions so that the number of remote terminals transmitting simultaneously is limited, thus reducing interference between remote terminals.

Since the channel loading may vary relatively widely, a fast control mechanism, as described below, may be used to control the transmit power of the R-SCH (e.g., relative to the reverse pilot channel).

Communication between a remote terminal and a base station to establish a connection may be obtained as follows. Initially, the remote terminal is in a sleep mode or monitors the common channel with an active slotted timer (i.e., the remote terminal monitors each slot). At a particular time, the remote terminal expects a data transmission and sends a short message to the base station requesting reconnection of the link. In response, the base station may send message-specific parameters for communication and configuration of different channels. This information may be sent via an Extended Channel Assignment Message (ECAM), a specially defined message, or some other message. The message may specify the following:

● each active set or each number of subsets of the active set for each remote terminal. The MAC _ ID is later used for addressing on the forward link.

● whether R-DCCH or R-FCH is used for the reverse link.

● for F-CPANCH, the spreading (e.g., Walsh) code to be used and the active set. This may be accomplished by (1) transmitting the spreading code within the ECAM or (2) transmitting the spreading code within a broadcast message received by the remote terminal. The spreading codes of the neighboring cells may need to be included. Only a single spreading code may need to be transmitted if the same spreading code can be used for the neighboring cells.

● for the F-CPCCH, the active set, the channel identity and the bit position. In an embodiment, the MAC _ ID may be hashed to the F-CPCCH bit positions to avoid the need to send the actual bit positions or subchannel IDs to the remote terminal. The hash permutation is a pseudo-random method to map the MAC _ ID onto a sub-channel on the F-CPCCH. Since different synchronized remote terminals are assigned different MAC IDs, the hashing may enable the mapping of these MAC IDs onto different F-CPCCH sub-channels. For example, if there are K possible bit positions and N possible MAC _ IDs, then K ═ N × ((40503 × KEY) mod 2¹⁶)/2¹⁶Where KEY is a number fixed in this example. There are many other hash functions available and discussion of this can be found in many textbooks relating to computer algorithms.

In an embodiment, a message from the base station (e.g., ECAM) is provided with a specific field USE _ OLD _ SERV _ CONFIG for indicating whether the parameters of the last connection setup are used for reconnection. This field may be used to avoid sending service connection messages when reconnecting, which may reduce latency when reestablishing connections.

Once the remote terminal has initialized the dedicated channel, it will proceed as described in, for example, the cdma2000 standard.

As described above, it is possible to better utilize reverse link resources if the resources can be allocated quickly as needed and if available. In a wireless (especially mobile) environment, where link conditions are continuously floating, long delays in allocating resources may result in inaccurate allocations and/or usage. Thus, in accordance with an aspect of the present invention, mechanisms are provided to quickly allocate and deallocate the supplemental channels.

Fig. 4 is a diagram illustrating communication between a remote terminal and a base station to allocate and deallocate a reverse link supplemental channel (R-SCH), according to one embodiment. The R-SCH may be allocated or deallocated as quickly as necessary. When the remote terminal has packet data to transmit that requires the use of the R-SCH, it requests the R-SCH by sending a supplemental channel request short message (SCRMM) to the base station (step 412). SCRMM is a 5msec message that may be sent on R-DCCH or R-FCH. The base station receives the message and forwards it to the BSC (step 414). The request may be authorized or may be denied. If the request is authorized, the base station receives the authorization (step 416) and transmits the R-SCH grant using a reverse supplemental channel assignment short message (RSCAMM) (step 418). RSCAMM is also a 5msec message that may be sent on the F-FCH or F-DCCH (if allocated to the remote terminal) or on the F-DPCCH (otherwise). Once assigned, the remote terminal may thereafter transmit on the R-SCH (step 420).

Table 3 lists fields of the RSCAMM specific format. In this embodiment, the RSCAMM includes 8 bits of the layer 2 field (i.e., MSG _ TYPE, ACK _ SEQ, MSG _ SEQ, and ACK _ requirent fields), 14 bits of the layer 3 field, and two reserved bits for padding as described in c.s0004 and c.s 0005. Layer 3 (i.e., the signaling layer) may be as defined by the cdma2000 standard.

TABLE 3

Field(s)	Length (bit)
		MSG_TYPE	3
ACK_SEQUENCE	2
		MSG_SEQUENCE	2
ACK_REQUIREMENT	1
		REV_SCH_ID	1
REV_SCH_DURATION	4
		REV_SCH_START_TIME	5
REV_SCH_NUM_BITS_IDX	4
		RESERVED	2

When the remote terminal no longer has data to send on the R-SCH, it sends a resource release request short message (RRRMM) to the base station. The base station responds with an extended release short message (erm) if no additional signaling is required between the remote terminal and the base station. RRRMM and erm may also be used on the same channel to transmit 5msec messages for transmitting requests and grants, respectively.

There are many scheduling algorithms that may be used to schedule reverse link transmissions for remote terminals. These algorithms may trade off between rate, capacity, delay, error rate and fairness (giving the minimum level of service for all users) to indicate some major criteria. In addition, the reverse link is constrained by the power limitations of the remote terminal. In a single cell environment, there will be maximum capacity when a minimum number of remote terminals are allowed to transmit at the highest rate that the remote terminals can support-while at capacity and the ability to provide sufficient power. However, in a multi-cell environment, it is desirable to have remote terminals near the boundary of another cell transmit at a lower rate. Since their transmissions cause interference to multiple cells rather than just one. Another aspect of maximizing reverse link capacity is high heat-up operation for the base station, which indicates high load on the reverse link. For this reason some aspects of the invention use scheduling techniques. Scheduling attempts to allow a small number of remote terminals to transmit synchronously, those capable of transmitting are allowed to transmit at the highest rate they support.

However, a high thermal rise tends to cause a decrease in stability because the system is more sensitive to small changes in load. For this reason, fast scheduling and control is important. Fast scheduling is important since channel conditions vary very rapidly. For example, fading and shadowing processes may cause a signal that is weakly received at a base station to suddenly become very strong at the base station. The remote terminal automatically changes the transmission rate for voice or certain data activities. Although the scheduler may take these factors into account, the scheduler may not be able to react to this quickly enough. For this reason, aspects of the present invention provide fast power control techniques, which will be described in detail below.

One aspect of the present invention provides a reliable acknowledgement/negative acknowledgement scheme to facilitate efficient and reliable data transmission. As described above, an acknowledgement (Ack) and a negative acknowledgement (Nak) are transmitted by the base station for data transmission on the R-SCH. The Ack/Nak may be transmitted by using F-CPACNH.

Table 4 shows a specific format of the Ack/Nak message. In this particular embodiment, the Ack/Nak message includes 4 bits allocated to four reverse link channels-R-FCH, R-DCCH, R-SCH1, and R-SCH 2. In one embodiment, acknowledgement is represented by a bit value of zero ("0") and negative acknowledgement is represented by a bit value of one ("1"). Other Ack/Nak message formats may also be used within the scope of the invention.

TABLE 4

Description of the invention	All used channel Number _ Type (binary)	R-FCH, R-DCCH and R-SCH1Number _ Type used	R-FCH and R-DCCHNumber _ Type (binary) are used
				ACK_R-FCH	xxx0	xxx0	xx00
NAK_R-FCH	xxx1	xxx1	xx11
				ACK_R-DCCH	xx0x	xx0x	-
NAK_R-DCCH	xx1x	xx1x	-
				ACK_R-SCH1	x0xx	00xx	00xx
NAK_R-SCH1	x1xx	11xx	11xx
				ACK_R-SCH2	0xxx	-	-
NAK_R-SCH2	1xxx	-	-

In one embodiment, the Ack/Nak message is sent in block coding but without the use of CRC check errors. This keeps the Ack/Nak message short and allows the message to be sent with less energy. However, no other coding can be used for the Ack/Nak message, or a CRC may be appended to the message, and these variations are within the scope of the invention. In one embodiment, the base station transmits one Ack/Nak message per frame, wherein the remote terminal grants permission to transmit on the R-SCH, and does not transmit the Ack/Nak message during periods when the remote terminal is not granted a frame to permit transmission.

During packet data transmission, the remote terminal monitors the F-CPACNH for Ack/Nak messages indicating the transmission result. The Ack/Nak message may be transmitted by any number of base stations in the active set of any remote terminal (e.g., one or all base stations in the active set). The remote terminal implements different actions depending on the received Ack/Nak message. Some of which are described below.

If an Ack is received by the remote terminal, the data frame corresponding to the Ack may be removed from the physical layer transmission buffer of the remote terminal (e.g., data source 210 in fig. 2) since the data frame was previously correctly received by the base station.

If the Nak is received by the remote terminal, the data frame corresponding to the Nak may be retransmitted by the remote terminal if it is still within the transmit buffer of the physical layer. In one embodiment, there is a one-to-one correspondence between the forward link Ack/Nak message and the transmitted reverse link data frames. The remote terminal can thus identify the sequence number of the data frame that was not correctly received by the base station based on the frame in which the Nak was received. If the data frame is not dropped by the remote terminal, it may be retransmitted in the next available slot, which is typically the next frame.

If no Ack or Nak is received, the remote terminal has several possible next actions. One possible action is that the data frame is retained in the physical layer transmit buffer and retransmitted. The base station transmits an Ack if the retransmitted data frame is then correctly received at the base station. Upon correct reception of the Ack, the remote terminal discards the data frame. This may be the best approach if the base station is not receiving reverse link transmissions.

Another possible action for the remote terminal is to drop the data frame if neither Ack nor Nak are received. This is the best solution if the base station receives a data frame and the transmission of the Ack is not experienced by the remote terminal. However, the remote terminal does not know what is happening and needs to select a policy. A policy is an action to guarantee the likelihood of two occurrences and to achieve maximum system throughput.

In one embodiment, each Ack/Nak message is retransmitted after a certain time (e.g., at the next frame) to improve the reliability of the Ack/Nak. Thus, if no Ack or Nak is received, the remote terminal combines the retransmitted Ack/Nak with the original Ack/Nak. Thus, the remote terminal may process as described above. And if the combined Ack/Nak still fails to produce a valid Ack or Nak, the remote terminal may drop the data frame and continue transmitting the next data frame in the sequence. The second transmission of Ack/Nak may be at the same or a lower power level relative to the power level of the first transmission.

If the base station does not actually receive the data frame after retransmission, a higher signaling layer at the base station may generate a message (e.g., an RLP NAK) that may result in retransmission of the entire sequence of data frames including the erased frame.

Fig. 5A is a diagram illustrating data transmission on the reverse link (e.g., R-SCH) and Ack/Nak transmission on the forward link. The remote terminal begins transmitting data frames in frame k in the reverse link (step 512). The base station receives and processes the data frame and provides the demodulated frame to the BSC (step 514). The BSC may also receive demodulated frames of the remote terminal from other base stations if the remote terminal is in a soft handoff state.

Based on the received demodulated frame, the BSC generates an Ack or Nak for the data frame. The BSC then sends the Ack/Nak to the base station (step 516), which then sends the Ack/Nak to the remote terminal in frame k +1 (step 518). The Ack/Nak is transmitted from one base station (e.g., the best base station) or from multiple base stations within the active set of the remote terminal. The remote terminal receives Ack/Nak in frame k + 1. If Nak is received, the remote terminal retransmits the erased frame, in this case frame k +2, within the next available transmission time (step 520). Otherwise, the remote terminal transmits the next frame in the sequence.

Fig. 5B is a diagram illustrating data transmission on the reverse link and a second transmission of an Ack/Nak message. The remote terminal initially transmits a data frame in frame k on the reverse link (step 532). The base station receives and processes the data frame and provides the demodulated frame to the BSC (step 534). Likewise, for soft handoff situations, the BSC may receive demodulated frames for the remote terminal from other base stations.

Based on the received demodulated frame, the BSC generates an Ack or Nak for the frame. The BSC then sends the Ack/Nak to the base station (step 526), which sends the Ack/Nak to the remote terminal during frame k +1 (step 538). In this example, the remote terminal does not receive the Ack/Nak transmitted during frame k + 1. However, the Ack/Nak for the data frame transmitted in frame k is sent a second time during frame k +2 and received by the remote terminal (step 540). If Nak is received, the remote terminal will retransmit the erased frame, in this case frame k +3, in the next available transmission time (step 542). Otherwise, the remote terminal will transmit the next data frame in the sequence. As shown in fig. 5B, the second transmission of Ack/Nak improves the reliability of the feedback and can result in improved performance of the reverse link.

In another embodiment, the data frame is not sent back from the base station to the BSC, and the Ack/Nak is generated from the base station.

Fig. 6A is a diagram illustrating acknowledgments ordered by short acknowledgment latency. The remote terminal initially transmits a data frame with a zero sequence number in frame k on the reverse link (step 612). For the present example, the data frame is received with an error at the base station, which then transmits Nak during frame k +1 (step 614). The remote terminal also monitors the F-CPANCH for Ack/Nak messages for each data frame transmitted on the reverse link. The remote terminal continues to transmit data frames with sequence number one in frame k + 1.

Upon receiving the Nak in frame k +1, the remote terminal retransmits the erased frame with sequence number zero in frame k +2 (step 618). The data frame transmitted in frame k +1 is received correctly and the remote terminal transmits a data frame with sequence number two in frame k +3 as indicated by the Ack received during frame k +2 (step 620). Similarly, the data frame transmitted in frame k +2 is correctly received, and the remote terminal transmits a data frame with sequence number three in frame k +4 as indicated by the Ack received in frame k +3 (step 622). The data frame with sequence number 3 is received and acknowledged by an ACK signal in a frame with k being 5. Within frame k +5, the remote terminal transmits a data frame of sequence number zero for the new packet (step 624).

Fig. 6B is a flow diagram illustrating acknowledgments ordered by long acknowledgment delay, such as when a remote terminal demodulates Ack/Nak transmissions according to Ack/Nak retransmissions as described above. The remote terminal initially transmits a data frame with sequence number zero in frame k on the reverse link (step 632). The data frame is received in error at the base station, which then transmits Nak (step 634). For this example, the Nak for frame k is transmitted during frame k +2 due to the longer processing delay. The remote terminal continues to transmit data frames with sequence number one in frame k +1 (step 636) and sequence number two in frame k +2 (step 638).

For this example, the remote terminal receives Nak in frame k +2, but cannot retransmit the erased frame in the next transmission interval. However, the remote terminal transmits a data frame with sequence number three within frame k +3 (step 640). In frame k +4, the remote terminal retransmits the frame with sequence number zero as the deleted frame is still in the physical layer buffer (step 642). At frame k +4, the base station transmits an ACK signal corresponding to correct reception of data within the k +2 frame. Further, in frame k +5, the base station transmits an ACK signal corresponding to correct reception of data in frame k + 3. Alternatively, it may be retransmitted within frame k + 3. And since the data frame transmitted in frame k +1 was correctly received, as indicated by the Ack received in frame k +3, the remote terminal transmits a data frame with a sequence number of zero for the new packet (step 644).

As shown in fig. 6B, the erased frame may be retransmitted at any time as long as it is still in the buffer and there is no ambiguity as to which higher layer packet the data frame belongs to. The longer delay for retransmission may be due to a number of reasons such as (1) processing and transmitting the longer delay for Nak, (2) not detecting the first transmission of Nak, (3) retransmitting the longer delay for erased frames, and others.

An efficient and reliable Ack/Nak scheme can improve utilization of the reverse link. A reliable Ack/Nak scheme may also enable data frames to be transmitted at a lower transmit power. For example, without retransmission, the data frame needs to be at a higher power level (P)₁) To obtain a one percent frame error rate (1% FER). If retransmission is used and is reliable, the data frame may be at a lower power level (P)₂) Is transmitted to reach a FER of 10%. 10% of the erased frames may be retransmitted to obtain an FER of 1% of the transmission overall. In general, 1.1P₂＜P₁And less transmit power is used in the transmission using the retransmission scheme. Also, the retransmission provides time diversity, which may improve performance. The retransmitted frame may be combined with the frame of the first transmission at the base station and the combined power of the two transmissions may also improve performance. The recombination may cause the erased frames to be retransmitted at a lower power level.

An aspect of the present invention provides different reverse link power control schemes. In an embodiment, reverse link power control of R-FCH, R-SCH, and R-DCCH is supported. This can be achieved by a power control channel (e.g., 800bps), which can be divided into a number of power control sub-channels. For example, a 100bps power control subchannel may be defined and used for the R-SCH. The F-CPCCH may be used to transmit power control bits to the remote terminal if the remote terminal is not assigned the F-FCH or F-DCCH.

In one implementation, a (e.g., 800bps) power control channel is used to adjust the transmit power of the reverse link pilot. The transmit power of the other channels (e.g., R-FCH) is set relative to the transmit power of the pilot (i.e., by a particular delta). Thus, the transmit power of all reverse link channels may be adjusted along with the pilot. The delta for each non-pilot channel may be adjusted by signaling. This implementation does not provide the flexibility to quickly adjust the transmit power of different channels.

In an embodiment, a forward common power control channel (F-CPCCH) may be used to form one or more power control sub-channels for different purposes. Each power control subchannel may be defined using a number of bits available within the F-CPCCH (e.g., the mth bit within each frame). For example, some of the available bits within the F-CPCCH may be allocated for the 100bps power control subchannel of the R-SCH. The R-SCH power control subchannel may be assigned to the remote terminal during channel allocation. The R-SCH power control subchannel may be used to (more quickly) adjust the transmit power of the designated R-SCH, e.g., with respect to the transmit power of the pilot channel. For a remote terminal in soft handoff, the R-SCH power control may be based on a reduced-OR-of-the-downs rule that reduces transmit power if any base station in the active set of the remote terminal tends to reduce transmit power. Since power control is maintained at the base station, this enables the base station to adjust the transmitted power and then the load on the channel with minimal delay.

The R-SCH power control subchannel may be used in different ways to control transmission on the R-SCH. In one embodiment, the R-SCH power control subchannel may be used to direct the remote terminal to adjust the transmit power on the R-SCH by a certain amount (e.g., 1dB, 2dB, or some other value). In another embodiment, the sub-channel may be used to direct the remote terminal to decrease or increase the transmit power by some step amount (e.g., 3dB or possibly more). In both embodiments, the adjustment of the transmit power may be related to the pilot transmit power. In another embodiment, the sub-channels may be directed to adjust the data rate allocated to the remote terminal (e.g., to a higher or lower data rate). In another embodiment, the sub-channel may be used to direct the remote terminal to temporarily stop transmitting. In another embodiment, the remote terminal may apply different processing (e.g., different interleaving intervals, different coding, etc.) based on the power control instructions. The R-SCH power control subchannel may be divided into a number of "sub-subchannels," each of which may be used in one of the various manners described above. The sub-channels may have the same or different bit rates. The remote terminal may apply power control immediately upon receiving the instruction, or apply the instruction at the next frame boundary.

The ability to reduce the R-SCH transmit power by a large margin (up to zero) and not terminate the communication session is particularly important for better use of the reverse link. Temporary reductions or suspension of packet data transmissions can generally be tolerated by the remote terminal. These power control schemes can be better used to reduce interference from high rate remote terminals.

Power control of the R-SCH may be obtained in different ways. In one embodiment, the base station monitors the received power from the remote terminal with a power meter. The base station may also be able to determine the amount of power received from each channel (e.g., R-FCH, R-DCCH, R-SCH, etc.). The base station can also determine interference, some of which may be from other remote terminals not served by the base station. Based on the collected information, the base station may adjust the transmit power of some or all of the remote terminals based on different factors. For example, power control may be based on the type of service, recent performance, recent throughput, etc. of the remote terminal. The method of power control is done to achieve the most desirable system goals.

There are various ways to implement power control. Examples of implementations are described IN U.S. Pat. No. 5485486 entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMACELLULAR MOBILE TELEPHONE SYSTEM", filed 1/16 1996, U.S. Pat. No. 5822318 entitled "METHOD AND APPARATUS FOR CONTROLLING POWER IN A VARIABLE APPARATUS MUNCATION SYSTEM", filed 10/13 1998, AND U.S. Pat. No. 6137840 entitled "METHOD AND APPARATUS FOR PERFORM METHOD FOR PERFORM FAST POWER CONTROL MOBILE COMMUNICATION SYSTEM", filed 24/10 2000, all of which are assigned to the assignee of the present invention AND incorporated herein by reference.

In a power control method generally used for controlling the level of an R-PICH channel, a base station measures the level of the R-PICH, compares it with a threshold, and then determines whether to increase or decrease the power of a remote terminal. The base station transmits a bit to the remote terminal instructing the remote terminal to increase or decrease its output power. If the bit is received in error, the remote terminal may transmit at the wrong power. In the next measurement of the R-PICH level received by the base station, the base station may determine that the received level is not at the desired level and send one bit to the remote terminal to change its transmit power. Thus, bit errors do not accumulate and the loop controlling the remote terminal transmit power stabilizes to the correct value.

Bit errors in the traffic-to-pilot ratio transmitted to the remote terminal to control congestion power control may cause the traffic-to-pilot ratio to be undesirable. However, the base station generally monitors the level of the R-PICH for reverse power control or channel estimation. The base station can also monitor the level of the received R-SCH. By changing the R-SCH to the R-PICH level, the base station can estimate the traffic-to-pilot ratio used by the remote terminal. If the traffic-to-pilot ratio is not desired, the base station can set the bits controlling the traffic-to-pilot ratio to correct the difference. Thus, there is automatic correction of bit errors.

Once the remote terminal receives the grant for the R-SCH, the remote terminal typically transmits at the granted rate for the granted period (or at a lower rate if it does not have sufficient data to transmit or sufficient power). The channel loading from other remote terminals may be rapidly changing due to fading or the like. As such, it may be difficult for the base station to accurately estimate the load in advance.

In one embodiment, a "congested" power control subchannel may be provided to control a group of remote terminals in the same manner. In this example, rather than a single remote terminal monitoring the power control subchannel to control the R-SCH, a group of remote terminals monitor the control subchannel. The power control subchannel may be at 100bps or at any other transmission rate. In an embodiment, the congestion control subchannel is implemented with a power control subchannel for the R-SCH. In other embodiments, the congestion control subchannel is implemented as a "subchannel" of the R-SCH power control subchannel. In another embodiment, the congestion control subchannel is implemented as a different subchannel than the R-SCH power control subchannel. Other implementations of congestion control sub-channels are also contemplated within the scope of the invention.

Remote terminals within a group may have the same class of service (e.g., remote terminals with low priority available bit rate services) and may be assigned a single power control bit per base station. Group control according to a single power control flow enables similar operation for a single remote terminal to provide congestion control on the reverse link. In the case of capacity overload, the base station may direct the group of remote terminals to reduce their transmit power or their data rate, or suspend transmission according to a single control instruction. The reduction in the R-SCH transmit power in response to the congestion control command may be a large step down relative to the transmit power of the pilot channel.

An advantage of power control flow to a group of remote terminals rather than one remote terminal is that less overhead power is required on the forward link to support the power control flow. It is noted that the transmit power of the bits within the power control stream may be equal to the power of the normal power control stream used to control the pilot channel of the remote terminal requiring the maximum power. That is, the base station can determine the remote terminal within the group that requires the most power within the normal power control flow and use that power to transmit power control bits for congestion control.

Fig. 7 illustrates variable rate data transmission on the R-SCH with fast congestion control in accordance with an embodiment of the present invention. During transmission on the R-SCH, the remote terminal transmits according to the data rate granted in a reverse supplemental channel assignment short message (RSAMM). If variable rate operation is allowed on the R-SCH, the remote terminal may transmit at any of the allowed data rates.

If the remote terminal's R-SCH has been assigned to the congestion control subchannel, then in one embodiment, the remote terminal adjusts the traffic-to-pilot ratio based on the bits received in the congestion control subchannel. If variable rate operation is allowed on the R-SCH, the remote terminal checks the current traffic-to-pilot ratio. If it is below the level of the lower data rate, the remote terminal reduces its transmission rate to the lower rate. If it is at or above the level of the higher data rate, the remote terminal increases its transmission rate to a higher rate if it has enough data to transmit.

Before the beginning of each frame, the remote terminal determines the rate to be used to transmit the next data frame. Initially, at step 712, the remote terminal determines whether the R-SCH traffic-to-pilot ratio is below the next lower rate ratio plus a margin Δ_low. If so, it is determined whether the service configuration allows for a reduction in data rate at step 714. If so, the data rate is decreased and the same traffic-to-pilot ratio is used at step 716. And if the service configuration does not allow for rate reduction, then certain embodiments may allow the remote terminal to temporarily stop transmitting at step 722.

Returning to step 712, if the R-SCH traffic-to-pilot ratio is not at the next lower data rate plus a margin Δ_lowAbove, then a determination is made in step 718 whether the R-SCH traffic-to-pilot ratio is greater than the next higher data rate traffic-to-pilot ratio minus a margin Δ_low. If so, a determination is made at step 720 as to whether the service configuration allows for an increase in data rate. If so, the transmission rate is increased and the same traffic-to-pilot ratio is used at step 722. And if the service configuration does not allow a rate increase, the remote terminal transmits at the current rate at step 724.

FIG. 8 is a graph illustrating the possible improvement of R-SCH fast control. Without rapid control of the R-SCH within the left hand frame, the thermal rise at the base station varies more, in some instances substantially beyond the expected thermal rise value (which may result in performance degradation of data transmission from the remote terminal), and in other instances substantially below the expected thermal rise value (resulting in under-utilization of reverse link resources). In contrast, the frame on the right carries the R-SCH fast control, and the thermal rise at the base station is maintained closer to the expected thermal rise value, which improves reverse link utilization and performance.

In one embodiment, the base station may schedule more than one remote terminal to transmit (via SCAM or ESCAM) in response to multiple requests (via SCRM or SCRMM) received from different remote terminals. An authorized remote terminal may then transmit on the R-SCH. If overload is detected at the base station, a "fast" reduction of the bit stream may be used to shut down (i.e., disable) a group of remote terminals (e.g., all but one remote terminal). Alternatively, a fast reduction in the bit stream may be used to reduce the data rate of the remote terminal (e.g., by half). Temporarily disabling or reducing the data rate on the R-SCH for multiple remote terminals may be used for congestion control, as will be described in more detail below. The fast reduction capability can also be used to reduce scheduling latency.

When the remote terminal is not in soft handoff with other base stations, a decision can be made at the BTS as to which remote terminal is located to be most beneficial (efficient) in utilizing the reverse link capacity. The most efficient remote terminal may then be allowed to transmit while others are temporarily disabled. An active remote terminal may be changed quickly if the remote terminal signals the end of its available data, or when some other remote terminal becomes more efficient. These schemes may increase the throughput of the reverse link.

In contrast, for a typical setup in a cdma2000 system, R-SCH transmission can only be started or stopped by layer 3 messaging, which may require several frames to decode from the constituent frames transmitted to the remote terminal. This longer delay results in the scheduler (e.g., at the base station or BSC) working with (1) a less reliable but long-term prediction of the remote terminal's channel conditions (e.g., reverse link target pilot Ec/(No + Io) or set point), or (2) a gap in reverse link utilization when the remote terminal informs the base station of its end of data (which often occurs because the remote terminal often declares itself that there is a large amount of data to send when requesting the R-SCH).

Referring back to fig. 2, elements of remote terminal 106 and base station 104 may be used to implement various aspects of the present invention, as described above. Elements of the remote terminal or base station may be implemented using a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a processor, a microprocessor, a controller, a microcontroller, a Field Programmable Gate Array (FPGA), a programmable logic device, other electronic units, or any combination of the preceding. Some of the functions and processes described herein can also be implemented in software executing on a processor, such as controller 230 or 270.

Headings are used herein to generally indicate the materials disclosed and are not intended to limit the scope of the invention.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. A method of controlling transmit power of a supplemental channel in a reverse link of a wireless communication system, the wireless communication system including a remote terminal and a base station, comprising:

transmitting, by the remote terminal, data and signaling on a reverse link of a reverse fundamental channel;

transmitting, by the remote terminal, packet data on a reverse link of a reverse supplemental channel;

transmitting, by the remote terminal, signaling on a reverse link of a reverse control channel;

transmitting, by the base station, signaling on a forward acknowledgment channel indicating a receipt status of the packet data transmission on the reverse link;

transmitting, by the base station, an acknowledgement or negative acknowledgement for each transmitted data frame on the reverse supplemental channel;

receiving, by a remote terminal, a first power control stream for controlling transmit power of a reverse supplemental channel along with at least one other reverse link channel;

receiving, by the remote terminal, a second power control stream for controlling transmission characteristics of a secondary channel, the transmission characteristics of the secondary channel comprising: a ratio of a transmit power of the supplemental channel to a transmit power of a designated reverse link channel, a data rate of the supplemental channel, and an activation and deactivation of transmissions on the supplemental channel; and

the transmit power and characteristics of the supplemental channel are adjusted by the remote terminal according to the first and second power control streams.

2. The method of claim 1 wherein the step size of the adjustment of the transmit power of the supplemental channel in response to the second power control stream is greater than the step size of the adjustment thereof in response to the first power control stream.

3. The method of claim 1 wherein the second power control flow is distributed to a plurality of remote terminals.

4. The method of claim 3, wherein the supplemental channels for the plurality of remote terminals are controlled by a second power control flow.

5. The method of claim 1, wherein the acknowledgement or negative acknowledgement for each transmitted data frame is transmitted multiple times on a forward acknowledgement channel.

6. The method of claim 1, further comprising:

signaling for allocating and deallocating the reverse supplemental channel is transmitted by the remote terminal on the reverse control channel.

7. The method of claim 1, further comprising:

information associated with packet data transmissions is transmitted by a remote terminal on a reverse rate indicator channel.

8. A remote terminal in a wireless communication system, comprising:

a transmit data processor for processing and transmitting:

data and signaling on the reverse fundamental channel,

packet data on the assigned reverse supplemental channel,

the signaling on the reverse control channel is performed,

information related to packet data transmission on a reverse rate indicator channel;

a receive data processor for receiving:

signaling on the forward acknowledgment channel indicating the receipt status of packet data transmissions on the reverse link,

an acknowledgement or negative acknowledgement for each transmitted data frame of the reverse supplemental channel, an

First and second power control streams on a forward power control channel; and

a controller coupled to the transmit and receive data processors and configured to control transmit characteristics of one or more reverse supplemental channels in accordance with first and second power control streams, wherein the first power control stream is configured to control transmit power of the reverse supplemental channel along with at least one other reverse link channel, and the second power control stream is configured to control transmit characteristics of the supplemental channel, the transmit characteristics of the supplemental channel comprising: the ratio of the transmit power of the reverse supplemental channel to the transmit power of the designated reverse link channel, the data rate of the reverse supplemental channel, and the activation and deactivation of transmissions on the reverse supplemental channel.