HK1066935B - Method and apparatus for link quality feedback in a wireless communication system - Google Patents

Description

Method and apparatus for link quality feedback in a wireless communication system

Background

FIELD

The present methods and apparatus relate generally to communications, and more particularly to providing link quality feedback in a wireless communication system.

Background

The increasing demand for wireless data transmission and the expansion of services available through wireless communication technologies has led to the development of systems capable of handling voice and data services. One Spread Spectrum system designed to handle the various requirements of these two services IS the Code Division Multiple Access (CDMA) system known as CDMA2000, which IS specified in "TIA/EIA/IS-2000 Standards for CDMA2000Spread Spectrum Systems". Advances in cdma2000 and alternative types of voice and data systems are also under development.

As the amount of data transmitted and the number of transmissions increases, the limited bandwidth of radio transmissions becomes a critical resource. Therefore, there is a need for an efficient and accurate method of transmitting information in a communication system that optimizes the use of available bandwidth.

SUMMARY

Embodiments disclosed herein address the above stated needs by providing a remote station apparatus having a quality measurement unit for iteratively measuring a link quality of a communication link, and a differential analyzer for determining variations in the measured link quality.

In one aspect, in a wireless communication system for handling voice communications and packet-switched communications, a transceiver comprising: a data rate control table for listing data rate control messages and related transmission information; a data rate calculation unit coupled to the data rate control table, the data rate calculation unit to select a data rate control message in response to a received signal at the transceiver; and a differential analyzer coupled to the data rate calculation unit for generating a differential indicator pointing to a next entry in the data rate control table.

In another aspect, in a wireless communication system, a method comprises: generating a quality message at a first frequency, the quality message providing information regarding a quality of a communication link; and generating a differential indicator at a second frequency, the differential indicator indicating a change in the quality of the communication link, wherein the second frequency is greater than the first frequency.

Brief Description of Drawings

FIG. 1 is a diagram of a wireless communication system;

fig. 2 is a diagram of a reverse channel structure in a wireless communication system;

FIG. 3A is a diagram of a remote station in a wireless communication system;

FIG. 3B is a flow chart of a method of generating link quality feedback from a remote station of a wireless system;

fig. 3C is a flow diagram of a method of processing link quality feedback at a base station of a wireless system;

fig. 3D is a timing diagram illustrating link quality feedback in a wireless system;

fig. 4A is a flow diagram of an alternative method of link quality feedback at a base station in a wireless communication system;

FIG. 4B is a timing diagram illustrating link quality feedback in a wireless system;

FIG. 4C is a table diagram of recorded variables during link quality feedback in a wireless system;

fig. 5 is a flow chart of a method of link quality feedback for a base station in a wireless communication system;

fig. 6 is a diagram of a reverse link structure in a wireless communication system;

fig. 7 is a timing diagram of link quality feedback in a wireless communication system;

FIG. 8 is a diagram of a data rate control table that may be used for packet-switched communications;

fig. 9 is a diagram of a portion of a remote station in a packet-switched communication system.

Detailed Description

The word "exemplary" is used exclusively herein to mean "serving as an example, instance, or illustration. Any "exemplary" embodiment described herein is not necessarily to be construed as preferred or advantageous over other embodiments.

In spread spectrum wireless communication systems, such as cdma2000 systems, multiple users transmit simultaneously to a transceiver, typically a base station, at the same bandwidth. A base station may be any data device that communicates through a wireless channel or through a wired channel, for example using fiber optic or coaxial cables. The user may be one of a variety of mobile and/or stationary devices, including but not limited to: PC card, mini-short, external or internal modem, or wireless or wireline phone. The user is also referred to as a remote station. Note that alternative spread spectrum systems include systems: a packet switched data service; wideband-CDMA (W-CDMA) systems, such as specified by the third generation partnership project 3 GPP; voice and data systems such as those specified by the third generation partnership project, two 3GPP 2.

The communication link through which a user transmits signals to the transceiver is called a reverse link RL. The communication link through which the transceiver sends signals to the users is called the forward link FL. As each user transmits to or receives from a base station, other users also communicate with the base station at the same time. Each user's transmission on the FL and/or RL causes interference to other users. In order to overcome the interference in the received signal, the demodulator tries to maintain a sufficient ratio E of bit energy to interfering power spectral density_b/N₀To demodulate the signal with an acceptable probability of error. The power control PC adjusts the transmitter power of one or both of the forward link FL and the reverse link RL to meet a given error criterion. Ideally, power control adjusts transmitter power to achieve a minimum required E at a given receiver_b/N₀The process of (1). Still further, it is desirable that no transmitter use be greater than minimum E_b/N₀E of (A)_b/N₀. This ensures that any benefit to the user achieved by the power control procedure is not obtained at an unnecessary cost to any other user.

Power control increases system capacity by ensuring that each transmitter causes only a minimal amount of interference to other users, thereby increasing processing gain. The processing gain is the ratio of the transmission bandwidth W to the data rate R. E_b/N₀The ratio to W/R corresponds to the signal-to-noise ratio SNR. The processing gain overcomes a limited amount of interference from other users, i.e., the total noise. Therefore, system capacity is proportional to processing gain and SNR. For data, feedback information is provided from the receiver to the transmitter as a link quality measure. The feedback is ideally a fast transmission with low delay.

Power control allows the system to adapt to changing conditions within the environment, including but not limited to geographical conditions and rates of movement. Since changing conditions affect the quality of the communication link, the transmission parameters are adjusted to match these changes. This process is called link adaptation. It is desirable that link adaptation tracks the condition of the system as accurately and quickly as possible.

According to one embodiment, link adaptation is controlled by the quality of the communication link, which value the SNR of the link provides a quality metric for evaluating the link. The SNR of the link may be measured as a function of the carrier-to-interference ratio C/I at the receiver. For voice communications, the quality metric C/I may be used to provide power control instructions instructing the transmitter to either increase or decrease power. For Packet Data communications, such as the HDR system specified in "TIA-856 cdma2000HighRate Packet Data Air Interface Specification" (3GPP and 3GPP2), Data communications are scheduled among multiple users, where only one user receives Data from an access network or base station at any given time. In a packet-switched data system, quality metric measurements such as SNR and/or C/I may provide valuable information to a base station or access network transmitter for use in determining the appropriate data rate, coding, modulation, and scheduling for data communication. Therefore, it is advantageous to efficiently provide the quality metrics from the remote station to the base station.

Fig. 1 illustrates an embodiment of a wireless communication system 20, wherein the system 20 is a spread spectrum CDMA system capable of voice and data transmission. The system 20 includes two parts: a wired subsystem and a wireless subsystem. The wired subsystems are the public switched telephone network PSTN 26 and the internet 22. The internet 22 portion of the wired subsystem interfaces with the wireless subsystem through an interworking function internet IWF 24. The increasing demand for data communications is generally associated with the internet and the ease of access to the data available therein. Advanced video and audio applications, however, increase the demand for transmission bandwidth.

The wired subsystem may include, but is not limited to, other modules such as a meter unit, a video unit, and the like. The radio subsystem comprises a base station subsystem comprising a mobile switching center MSC 38, a base station controller BSC 30, base transceiver stations BTS 32, 34, and mobile stations MS 36, 38. The MSC 38 is the interface between the wireless subsystem and the wired subsystem. Which is a switch that converses with a variety of wireless devices. The BSC 30 is the control and management system for one or more BTSs 32, 34. BSC 30 exchanges messages with BTSs 32, 34 and MSC 28. Each BTS 32, 34 is comprised of one or more transceivers placed at separate locations. Each BTS 32, 34 terminates one radio path on the network side. The BTSs 32, 34 may be co-located with the BSC 30, or may be independently located.

The system 20 includes radio air interface physical channels 40, 42 between the BTSs 32, 34 and the MSs 36, 38. The physical channels 40, 42 are communication paths described in terms of digital coding and RF characteristics.

As discussed above, the FL is defined as a communication link for conveying from one of the BTSs 32, 34 to one of the MSs 36, 38. An RL is defined as a communication link for communication from one of the MSs 36, 38 to one of the BTSs 32, 34. According to one embodiment, power control within system 20 includes controlling the transmit power of both the RL and FL. Various power control mechanisms are possible for the FL and RL within system 20, including reverse open-loop power control, reverse closed-loop power control, forward closed-loop power control, and so on. Reverse open loop power control adjusts the initial access channel transmit power of the MSs 36, 38 and compensates for changes in RL path loss attenuation. The RL uses two types of coded channels: traffic channels and access channels.

FIG. 2 illustrates a RL structure of the system 20 of FIG. 1, in accordance with one embodiment. The RL, i.e., the reverse channel, is composed of two types of logical channels: access and traffic. Each logical channel is a communication path within the protocol layers of either the BTS 32, 34 or the MS 36, 38. Information is composed onto logical channels according to criteria such as number of users, type of transmission, direction of transmission, etc. The information on the logical channels is eventually transferred to one or more physical channels. A mapping is defined between logical and physical channels. These mappings may be permanent or may be defined only for the duration of a given communication.

Note that for data services, a remote station may be referred to as an access terminal, AT, where an AT is a device that provides data connectivity for a user. The AT may be connected to a computing device, such as a portable personal computer, or may be a self-contained data device, such as a personal digital assistant. Furthermore, a base station may be referred to as AN access network, AN, where the AN is a network device providing data connectivity between a packet switched data network, such as the internet, and AT least one AT. The AT communicates with the AN using a reverse access channel when no traffic channel is allocated. In one embodiment, each sector of the AN has a separate reverse access channel.

Continuing with fig. 2, the traffic channel consists of three logical channels: a differential indicator, a link quality indicator, and data. The link quality indicator provides a quality measure of the FL pilot channel. One embodiment uses carrier-to-interference ratio, C/I, as the link quality metric, where the remote station measures the C/I of the FL pilot channel for a variety of conditions with predetermined periodicity. The link quality indicator is encoded for periodic transmission on the RL to the base station. The coding may include the application of coverage, where the particular coverage applied corresponds to the sector for which the pilot signal was measured. The encoded link quality indicator is referred to as a "quality message". Alternate embodiments may implement other means of determining a link quality indicator and may implement other metrics corresponding to link quality. Furthermore, the quality metric measurements may be applied to other received signals. The C/I measurement is typically expressed in dB units.

In an exemplary embodiment, the link quality message is determined and sent periodically with relatively low delay, thereby reducing any impact on the available bandwidth on the RL. In one embodiment, the quality message is sent every 20 milliseconds. Further, when the link quality indicator is not transmitted, the differential indicator is transmitted to the base station. In one embodiment, the differential indicator is sent every 1.25 milliseconds. As depicted in fig. 2, the traffic channel also includes a differential indicator subchannel. In contrast to the link quality indicator and the quality message, the differential indicator indicates a relative change in the quality of the FL pilot signal, which is transmitted more frequently. To determine the differential indicator, the continuous C/I measurements of the FL pilot signal are compared. The comparison result is sent as one or more bits indicating the direction of change. For example, according to an embodiment, the differential indicator is positive for an increase in consecutive C/I measurements and negative for a decrease in consecutive C/I measurements. The differential indicator is sent with little or no coding, thus providing a fast, efficient, low latency feedback method. The differential indicator effectively provides continuous fast feedback to the base station regarding FL status. The feedback is sent over the RL. Note that the quality message and differential indicator track the C/I measurement, as opposed to the power control command, which typically has the opposite polarity to the C/I measurement.

The use of differential indicators, which provide incremental comparisons for the final projected value, eliminates the need to transmit the entire C/I. The differential indicator according to an embodiment is an UP (+1dB) or DOWN (— 1dB) indicator. According to an alternative embodiment, consecutive steps in the same direction have increasing values, such as a first UP (+1dB), a second UP (+2dB), and so on. In yet another embodiment, the differential indicator includes a plurality of bits, wherein the bits have a valid bit identifying a direction and a variance. Since fading of the channel is a continuous process, C/I will be a continuous process and can therefore be tracked with this differential signaling technique. Since this differential message is much smaller than the complete C/I message, it not only takes less time to encode, transmit, and decode, but it also takes up less energy on the reverse link. This means that not only is FL performance improved, but RL loading is also reduced. The periodic transmission of the quality message prevents and/or corrects synchronization problems between the base station and the remote station. For example, consider a remote station with an initial quality message corresponding to a 0dB C/I measurement. The remote station continuously measures the link quality and continues to transmit three differential indicators, each corresponding to a 1dB increment. Thus, the remote station has calculated the planned C/I3 dB. The base station may decode both differential indicators correctly but with a decoding error on the third. Thus, the base station has calculated the planned C/I2 dB. At this point, the remote station and the base station are no longer synchronized. The next transmission of the encoded quality message is sent in a reliable manner and the synchronization inconsistency is corrected. In this way, the quality message resynchronizes the base station and the remote station. In one embodiment, the quality message is encoded with a very strong (5, 24) block code, interleaved, and sent in 20 milliseconds. Note that the quality message is used to correct any synchronization errors that may occur when feeding back the differential indicator, and therefore the quality message can tolerate a relatively large delay, such as 20 milliseconds.

The differential indicator is applicable in wireless communication systems using fast link adaptation techniques, which require the receiver to constantly feed back the latest channel state to the transmitter. While differential indicators may also be applied to feedback RL channel state on the FL, in data services, link adaptation typically occurs on the forward link, so the exemplary embodiment illustrates a remote station that feeds information about RL state to the base station using differential indicators on the RL. Ideally, link quality feedback occurs frequently, with minimal latency to optimize FL system performance. The use of differential indicators reduces the load on the RL, thereby increasing the capacity of the RL available for data traffic.

Fig. 3A illustrates a portion of a remote station 200 used in system 20. Remote station 200 includes receive circuitry 202, which includes but is not limited to an antenna, and pre-processing filtering. Receive circuitry 202 processes signals received at remote station 200 on the FL including, but not limited to, pilot signals. The receiving circuit 202 is coupled to a quality measurement unit 204 which determines a quality metric measurement of the pilot signal. In an exemplary embodiment, the quality measurement unit 204 measures the C/I of the received FL pilot signal. The quality metric measurement cur _ C _ I is provided to a differential analyzer 206. The differential analyzer 206 operates on a predetermined quality message period T_MESSAGEAnd (6) responding. During each quality message period, the differential analyzer 206 provides a planned C/I measurement projcjj as a link quality indicator for further processing to form a quality message. This further processing includes encoding the link quality indicator, including applying a cover to identify the transmitting sector of the measured pilot signal. For the remaining cycles, the quality measurement unit 204 provides successive C/I measurements to the differential analyzer 206.

Continuing with FIG. 3A, at each time periodT_MESSAGEDuring this time, the quality message is generated once, but a plurality of differential indicators are generated, the value of each generated differential indicator being referred to as a "DIFF". Note that the quality message and the differential indicator are generated at different rates. As illustrated in FIG. 3A, the differential analyzer 206 also receives an input signal T_DIFFFor controlling the rate of differential indicator generation.

Fig. 3B illustrates the operation of the remote intra-site differential analyzer 206, in accordance with one embodiment. According to one embodiment illustrated in fig. 3B, within the remote station, the differential analyzer 206 process begins by receiving a C/I measurement from the quality measurement unit 204, where cur _ C _ I is a link quality measurement of the received signal. In step 302, the process also stores the cur _ cj value as a planned measurement in the variable "proj _ cj". Step 302 is an initialization step that is performed only once per session. At this point, no historical C/I measurements are available for comparison.

In step 304, proj _ C _ I is sent as a quality message. In step 306, C/I is measured and stored as the current measurement in the variable "cur _ C _ I" to be used for the incremental differential comparison. In step 308, the differential analyzer 206 compares cur _ C _ I with proj _ C _ I and generates DIFF accordingly. In addition, in step 310, the variable proj _ C _ I is adjusted according to the comparison. The adjustment tracks changes in link quality, so if cur _ C _ I is greater than proj _ C _ I, the value proj _ C _ I is incremented, and vice versa. The differential indicator DIFF is sent at step 312 where DIFF has been determined by a comparison of cur _ C _ I and proj _ C _ I. Note that DIFF provides an indication of the direction of change within the link quality. In one embodiment, DIFF is a single bit, where a positive value corresponds to an increase and a negative value corresponds to a decrease. An alternative polarity scheme may also be implemented with a multi-bit representation of DIFF, which provides an indication of the amount of change in addition to the direction of change.

In step 314, the process determines whether the quality message time period has expired. One quality message is transmitted during each quality message time period, and a plurality of differential indicators are transmitted. When the quality message time period has expired, the process returns to step 304. Until the quality message time period expires, the process returns to step 306. Thus, the remote station provides a quality message with complete planned C/I information, i.e., proj _ C _ I, and a continuous differential indicator to record changes in planned C/I. Note that in one embodiment, it is assumed that each differential indicator corresponds to a predetermined stride. In an alternative embodiment, it is assumed that the differential indicator corresponds to one of several predetermined steps. In another embodiment, the magnitude of the differential indicator determines the stride. In another embodiment, the differential indicator comprises a plurality of information bits, wherein the bits have significance to select a direction and magnitude of a predetermined set of steps of the step. In yet another alternative embodiment, the stride may be dynamically varied.

Fig. 3C illustrates a method 350 for processing quality messages and differential indicators at a base station. At step 352, the variable "QUALITY 1" is initialized to a default value with the first reception QUALITY message. The default value may be based on the quality message initially received. The process then determines whether a quality message has been received at step 354. Upon receiving the QUALITY message, QUALITY1 is updated at step 360 according to the received QUALITY message. The process then returns to step 354. When no QUALITY message is received at step 356 and a DIFF is received, the process continues to step 358 where QUALITY1 is adjusted according to DIFF. The process then returns to step 354.

According to one embodiment, the quality message is sent on a gated channel, wherein each time period T_MESSAGEAnd is sent once. The differential indicator is transmitted on a continuous channel at a higher frequency. As shown in fig. 3D, the signal strength of the quality message and the differential indicator are plotted as a function of time. Quality message at time t₁、t₂、t₃Etc. where no quality messages are sent during the other times of each cycle TMESSAGE. The differential indicator is transmitted continuously. In an exemplary embodiment, for a predetermined duration T₁The quality message is sent internally. Differential indicator is lasted for time T₂And (4) separating.Ideally T₂Greater than T₁Wherein during the duration T of the transmission of the quality message₁No differential indicator is sent. Thus, the base station does not receive the differential indicator and the quality message at the same time. In practice, the base station uses the quality message if the differential indicator overlaps in time with the quality message.

The quality message and the differential indicator provide feedback to the base station. Although fig. 3D illustrates distinct and separate occurrences of the quality message and the differential indicator, the quality message may be sent over a longer time period, causing overlap between transmissions.

In one embodiment, the quality message may be encoded and transmitted, with the C/I message being processed very slowly. The quality message is then received and decoded at the base station later. The base station effectively streamlines the differential indicators and is able to exit the computation path and return to finding the planned measurements when the message is encoded and transmitted by the remote station. If the base station finds that the quality message shows an incorrect calculation, i.e. a result after applying the differential indicator, the result is adjusted according to the quality message. For example, where the projected measurement is less than +2dB, the current projected measurement may increase by 2 dB.

As discussed below, fig. 4B illustrates one scenario. Fig. 4A illustrates an alternative method 400 for processing a quality message and a differential indicator received at a base station, where overlap may occur between the quality message and the differential indicator. In step 402, two variables QUALITY1 and QUALITY2 are initialized with the first reception QUALITY message. During reception of the QUALITY message, the value stored in QUALITY1 at the mobile station at the beginning of the link QUALITY measurement remains unchanged until the QUALITY message is completely received. This allows any DIFF received during the quality message to be adjusted. In step 404, the process 400 determines whether reception of a link quality measurement is to begin. The base station knows the schedule of link quality measurements at the remote station in advance. If quality measurements have not started, the process continues to step 406 to determine if a DIFF has been received. If DIFF is not received, processing returns to step 404, otherwise QUALITY1 and QUALITY2 are adjusted in accordance with DIFF in step 408. Further in step 408, the QUALITY2 value is provided to the scheduler for use in effecting scheduling of transmissions. Beginning at step 404, if a quality message has started, step 410 determines if a DIFF is received during the quality message, i.e., the DIFF and quality message are received by the base station at the same time. If a DIFF is not received during the quality message, the process continues to step 414 to determine that the quality message is complete. If DIFF is received during the QUALITY message, QUALITY2 is adjusted in step 412 based on DIFF. Further in step 412, the QUALITY2 value is provided to the scheduler for use in effecting scheduling of transmissions. If the QUALITY message is not complete at step 414, processing returns to step 410, otherwise the difference between the received QUALITY message and QUALITY1 is set to DELTA, Δ at step 416. DELTA is used to correct the link quality calculation at the base station. Since the quality message is transmitted from the remote station prior to receiving the DIFF values during reception of the quality message at the base station, DELTA allows these DIFF values to be applied to the corrected values. DELTA adjustment QUALITY2 is used in step 418 to correct the results of processing DIFF received during QUALITY message reception. Further in step 418, the QUALITY2 value is provided to the scheduler for use in effecting scheduling of transmissions. In step 420, QUALITY1 is set equal to QUALITY2 and synchronization is complete. The process then returns to step 404. When a quality message is received in step 414, the method determines in step 415 whether an error has occurred within the quality message. If so, processing returns to step 404. If there are no errors in the received quality message, processing continues to step 416.

Fig. 4B and 4C illustrate reception of quality messages and DIFF at the base station in the form of timing diagrams. As shown, at time t₁Previously, the values QUALITY1 and QUALITY2 were equal to A. Quality message reception at time t₁And begins. Then, at time t₂To t₅A DIFF is received whose value is represented in the table of figure 4C. Note that for each received DIFF, the qualit 2 value is adjusted accordingly, while the qualit 1 value remains unchanged. At time t₇Here, the QUALITY message is complete and QUALITY1 is set equal to B. The value B is at time t₁At the moment or atTime t₁A quality message value previously sent from the remote station. Then, the variable QUALITY2 is adjusted according to the difference (B-A). The difference being at time t₈The value of QUALITY2 was added. Thus, the base station has a corrected value of QUALITY 2.

Fig. 5 illustrates a method 500 for processing feedback information at a base station in an embodiment. In step 602, the base station receives a quality message from the mobile station, wherein the quality message is related to the FL pilot signal strength. In step 604, the received quality message is stored in a memory device. In step 606, the base station provides the received quality message to the scheduler. For data communications, the scheduler is responsible for providing the base station with fair and proportional access from all access terminals that have data to transmit and/or receive. Scheduling of access terminals may be performed in any of a variety of ways. The scheduler then implements the scheduling in step 608. In addition to the quality message, the base station receives a differential indicator DIFF in step 610. In step 612, the base station applies the differential indicator to the stored quality message to track the quality of the FL channel. In this manner, an evaluation is made of the condition and quality of the FL channel seen by the base station at the access terminal receiver. In this way, the base station knows the condition and quality of the FL channel as seen at the access terminal receiver. In step 614, the process provides the quality message to the scheduler to implement the scheduling. In step 616, the process determines whether a quality message is received.

Continuing with FIG. 5, if the next quality message is not received, i.e., the system is currently at time t of FIG. 5₁And t₂Then processing returns to receive the next differential indicator at step 610. However, if a quality message is received at step 616, the process returns to step 604 to store the quality message in memory. The stored quality message is adjusted with each occurrence of the differential indicator. The stored quality message is replaced when the quality message occurs.

The link quality feedback method may be used in packet switched communication systems, such as data and voice systems. In packet-switched systems, data is transmitted in packets having a defined structure and length. These systems adjust the data rate and modulation scheme based on the link quality rather than adjusting the size of the transmission with power control. For example, in voice and data systems, the transmit power available for data transmission is not defined or controlled, but is dynamically calculated as the remaining power available after voice transmission is met. An exemplary system having the reverse link described in fig. 6 transmits the quality message and the differential indicator with a data rate control and an additional subchannel, respectively. As shown, the reverse link, i.e., the reverse channel, has two types of logical channels: access and traffic. The access channel includes subchannels of pilot and data, where the access channel is used when the traffic channel is inactive. The traffic channel includes subchannels for pilot, medium access control, MAC, acknowledgement, ACK, and data. The MAC further includes a subchannel for transmission of the reverse rate indicator and the data rate control DRC. The DRC information is calculated by the remote station or access terminal by measuring the quality of the FL and requesting corresponding data for receiving pending data transmissions. There are many ways to calculate the link quality and determine the corresponding data rate.

According to one embodiment, the differential indicator is continuously transmitted on the reverse rate indicator channel and the quality message is transmitted on the DRC channel. The corresponding data rate is typically determined by a table that identifies available and/or appropriate data rates, modulation and coding, packet structure, and retransmission policies. The DRC message is an index indicating an appropriate combination of specifications. An increase in the available data rate increases the index based on the link quality measurement. The reduction in available data rate reduces the index. The DRC message is encoded prior to transmission. The DRC cover is applied to identify the sector in which the FL signal, typically a pilot signal, is measured.

Fig. 7 illustrates various timing scenarios. In the first case, the DRC information is transmitted continuously, wherein one DRC message may be transmitted repeatedly in order to increase the reception accuracy. As shown, drc (i) is a four-slot message, where message drc (i) is sent in slot A, B, C and the D slot. Four slot messagesAt a duration T_DRCDuring which it is transmitted. The next message DRC (i +1) will be transmitted after slot D. In this case, the quality message is implicitly contained in the DRC message and is transmitted continuously. This situation wastes bandwidth and thereby reduces the capacity of the reverse link. In the second case, the DRC message is transmitted on a gated channel, a DRC channel, and at T_DRCOnce in a while. The differential indicator has a period T_diffAre transmitted on successive sub-channels. The differential indicator either increases or decreases the index of the DRC message. In this way, the access network is able to accurately and quickly track the available data rate, etc., since the differential indicator is an uncoded bit. Note that while the quality message and differential indicators have been described herein with respect to the FL, each differential indicator may also be applied to the RL.

FIG. 8 illustrates a data rate control table in accordance with one embodiment. As illustrated, the leftmost column lists DRC messages. The DRC message is preferably a code that identifies a combination of transmission parameters. The middle column corresponds to the data rate in kbps. The last column lists the packet length in slots. Each DRC message corresponds to a combination of these transmission parameters and may also include, but is not limited to: modulation technique, coding type, packet structure, and/or retransmission policy. Note that in the embodiment depicted in fig. 8, the first DRC message selects a zero data rate. The zero data rate is used in other processes within the system. Further, the several DRC messages correspond to unavailable or invalid sets of transmission parameters. These sets may be assigned to later developed systems or may be used for other operations within the system.

In an alternative embodiment, the quality message is included in the preamble of each transmission. The differential indicator is transmitted on consecutive subchannels. Differential indicators are provided at a frequency to help the transmitter accurately track the channel quality experienced by transmitted communications.

Fig. 9 illustrates one embodiment of a packet switching system using the DRC table of fig. 8. A portion 500 of the access terminal includes a DRC table 502 coupled with a DRC calculation unit 504. The DRC calculation unit 504 receives the FL signal in the packet-switched system. DRC computation unit 504 analyzes the received signal to determine a channel quality metric. The quality metric is a data rate. DRC calculation unit 504 selects a set of transmission parameters from DRC table 502, where the set corresponds to the calculated data rate available for the FL. The set is identified by the corresponding DRC message.

The DRC calculation unit 504 supplies the measured DRC to the differential analyzer 506. The differential analyzer 506 at each DRC time period T_DRCA planned DRC message is generated for a full transmission. According to T_DRCThe fully scheduled DRC message transmission is gated. In addition, differential analyzer 506 receives differential time period signal T_DIFFWhich is used to generate the differential indicator.

The successive current DRC values are compared to the planned DRC values with respect to the index within DRC table 502. The differential grouper 506 outputs a differential indicator based on the comparison. The differential indicator is an increment pointer to an adjacent entry within DRC table 502. If successive DRC messages increase in a given direction from the previous DRC message, the differential indicator points in that direction. Thus, the differential indicator tracks movement within DRC table 502. Thus, the FL transmitter receives continuous information of the FL channel quality, which can be used to estimate and/or adjust the transmission parameters. The feedback information may be used to schedule packet-switched communications within the system. Periodic DRC message transmission provides synchronization between the FL transmitter and receiver, generating error information from incorrectly received differential indicators.

Furthermore, the differential indicators within the packet switched system provide greater feedback than would be generated by the mobile station alone. The access network may use the feedback information to determine a scheduling policy and implement the policy for multiple users. In this way, the feedback information may be used to optimize the overall transmission system.

As discussed above, the periodic transmission of the quality message allows for synchronization of the remote station and the base station. In an alternative embodiment, the base station transmits the planned C/I calculated at the base station on the FL. The remote station receives the planned C/I from the base station and synchronizes with the base station. The transmission may be an encoded message or a signal transmitted at a predetermined power level. For example, the transmission may be a dedicated pilot or PC bit.

In addition to providing link quality feedback, the remote station may indicate the currently monitored sector by applying a cover or scrambling code to the quality message and/or differential indicator. The coverage identifies the sector for which the pilot signal has been measured. In one embodiment, each sector in the system is assigned a scrambling code. The scrambling code is a priori knowledge of the base station and the remote station.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application being used and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The implementation or execution of the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments described herein may be implemented or performed with: a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber unit. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

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 (13)

1. A remote station apparatus, comprising:

a receive circuit for receiving a signal on a forward link;

a quality measurement unit coupled to the receive circuit for iteratively measuring a link quality of a communication link and generating a quality metric; and

a differential analyzer for determining a change in the measured link quality and producing a differential quality metric, wherein the quality metric and the differential quality metric are to be transmitted to a base station to indicate link quality.

2. The remote station of claim 1, wherein the link quality is measured as a carrier-to-interference ratio of a received signal.

3. A remote station as defined in claim 2, wherein the remote station applies sector coverage to the quality metric.

4. In a wireless communication system, a method for link quality feedback, comprising:

receiving a signal on a communication link;

generating a quality message at a first frequency, the quality message providing information regarding a quality of a communication link; and

generating a differential indicator associated with the quality message indicating a change in the quality of the communication link at a second frequency, wherein the second frequency is greater than the first frequency.

5. The method of claim 4, wherein each quality message comprises a carrier-to-interference ratio of a received signal at the receiver.

6. The method of claim 5, wherein the received signal is a pilot signal.

7. The method of claim 4, wherein each differential indicator is at least one bit.

8. The method of claim 4, wherein the generating a differential indicator further comprises:

comparing the current link quality measurement to the planned link quality measurement;

when the current link quality measurement is less than the planned link quality measurement, the planned link quality measurement is decremented;

when the current link quality measurement is greater than the planned link quality measurement, the planned link quality measurement is incremented; and

the differential indicator is adjusted and transmitted based on a comparison of the current link quality measurement and the projected link quality measurement.

9. In a wireless communication system for handling voice communications and packet-switched communications, a base station comprising:

receiving circuitry for receiving a signal on a reverse link, including a quality message periodically providing a quality metric for a forward link and a differential indicator tracking the quality metric between successive quality messages;

a memory unit to store quality messages received on a reverse link, wherein the stored quality messages are adjusted with each occurrence of a differential indicator.

10. The base station of claim 9, further comprising:

a scheduler unit for scheduling packet switched communications within the system in accordance with the quality messages stored in the memory unit.

11. The base station of claim 10 wherein the quality metric is a data rate control message.

12. The base station of claim 11, wherein:

each data rate control message corresponds to an entry in a data rate control table; and

each differential indicator points to an adjacent entry in the data rate control table.

13. In a wireless communication system for handling voice communications and packet-switched communications, a transceiver comprising:

a data rate control table for listing data rate control messages and related transmission information;

a data rate calculation unit coupled to the data rate control table for selecting a data rate control message based on the received signal at the transceiver; and

a differential analyzer coupled to the data rate calculation unit for generating a differential indicator pointing to a next entry in the data rate control table, the differential indicator indicating a change in the quality of the communication link.