HK1061757A - Method and apparatus for reducing transmission power in a high data rate system - Google Patents

Description

Method and system for reducing transmission power in high data rate systems

The present invention relates to wireless data communication. More particularly, the present invention relates to a novel method and apparatus for gating or reducing reverse link transmissions in a communication system supporting High Data Rate (HDR) services.

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

In the drawings:

fig. 1 is a diagram of an exemplary HDR communication system.

Fig. 2a is a diagram of gated or reduced reverse link transmissions using a carrier-to-interference ratio based access metric.

Fig. 2b is a diagram of gated or reduced reverse link transmissions using an average throughput-based access metric.

Fig. 3 is a flow chart of a method of determining when to gate or reduce reverse link transmissions.

Fig. 4 is a diagram of an access terminal apparatus.

Summary of The Invention

The present invention relates to a method and apparatus for periodically reducing reverse link transmissions in a High Data Rate (HDR) communication system. A typical HDR system is described in U.S. patent application 08/963,386, assigned to the assignee of the present invention, and entitled: "METHOD AND APPATUS FOR HIGH RATEPACKET DATA TRANSMISSION". This application is incorporated herein by reference and is hereinafter referred to simply as the "application' 386 which describes a system in which an HDR subscriber station transmits data on the reverse link using a CDMA waveform of multiple orthogonal channels. Each subscriber station transmits a reverse link signal containing Data Rate Control (DRC) information. Each base station transmits a forward link signal that is divided into a number of time slots. In each slot, each base station transmits data to the subscriber station according to the DRC information received from the subscriber station.

In an exemplary embodiment, the DRC message is a quantized value of the carrier-to-interference (C/I) ratio of the received forward link signal as measured by the subscriber station. In addition, the subscriber station may replace the DRC information with C/I information. The base station may transmit at exactly the data rate specified by the DRC or C/I information received from the subscriber station or may select the data rate based on additional information. If the base station does not comply with the subscriber station's specified data rate, the subscriber station may decode the rate indicator signal on the forward link or perform some form of blind rate detection.

Fig. 1 is a diagram of a typical HDR communication system. HDR subscriber stations, referred to herein as Access Terminals (ATs) 102, may be mobile or stationary, and each may communicate with one or more HDR base stations 104, referred to herein as Modem Pool Transceivers (MPTs). An access terminal 102 sends and receives data packets through one or more modem pool transceivers 104 to an HDR base station controller (referred to herein as a Modem Pool Controller (MPC), not shown). Modem pool transceivers and MPCs are part of a network called a visited network. The access network transmits data packets between a plurality of access terminals. The access network may be further connected to other networks than the access network, such as a company's intranet or the internet, and may thus transmit data packets between each access terminal and such outside networks. An access terminal that has established an active traffic channel connection with one or more modem pool transceivers is called an active access terminal and is said to be in a traffic state. An access terminal 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 access terminal may also be any of a variety of devices including, but not limited to, a PC card, compact flash, external or internal modem, or wireless or wireline phone. The communication link through which access terminal 102 sends signals to modem pool transceiver 104 is called a reverse link. The communication link through which modem pool transceiver 104 sends signals to access terminal 102 is called a forward link. The reverse link signal transmitted by an access terminal (e.g., 102a) may interfere with the reverse link signals transmitted by other access terminals (e.g., 102b and 102 c). This interference limits the reverse link capacity of the HDR system. Gating, as used herein, refers to turning off transmission, or transmitting a signal or signal component at near zero power.

To reduce interference caused by reverse link transmissions, an access terminal periodically gates or reduces its reverse link transmissions. The gating or reduced periods are designed so that they occur during periods that do not degrade forward link and reverse link throughput. For example, the access terminal evaluates parameters used by the access network to select the access terminal that is the destination of the forward link transmission. An example of such an access network selection algorithm is described in detail in U.S. patent application 09/317,298 entitled "TRANSMITTER DIRECTED, MULTIPLE RECEIVERSYSTEM USING PATH DIVERSITY TO equivalent maximum likelihood route right" assigned TO the assignee of the present invention and referred TO herein simply as "application' 298". The' 298 application includes an illustration of an algorithm that allocates forward link resources to maximize system throughput while ensuring that each user has fair access to the communication system.

The selection algorithm used by the access network typically selects an access terminal based on the throughput of data transmitted to all active access terminals and the DRC signals received from all active access terminals. Using the same or similar selection algorithm, the access terminal calculates the access metric and access metric threshold to predict when the modem pool transceiver will not select the access terminal to receive forward link data. Rather than transmitting a DRC rate that does not result in the access terminal being selected, the access terminal may transmit a partial reverse link signal with the DRC omitted, or may not transmit the reverse link signal at all. To avoid call loss, the access terminal limits the time to reduce reverse link signaling to a predetermined maximum transmitter off period. If the access terminal's access metric thus rises above the access metric threshold after reducing its reverse link transmission, or after a maximum transmitter off period, then the access terminal resumes transmitting the full reverse link signal.

Detailed Description

Fig. 2a illustrates a pattern of reverse link transmission gating or reduction 210 that occurs when an access terminal employs an algorithm based on a forward link carrier-to-interference (C/I) value 202. A typical forward link carrier-to-interference (C/I) curve 202 is shown as a function of time in a typical rayleigh fading environment. Because the access terminal moves in different areas covered by the modem pool transceiver, fading causes the C/I of the forward link signal received by the access terminal to exhibit rounded peaks 214 and sharp valleys 216.

In an exemplary embodiment, the access terminal performs a C/I low pass filtering or windowing operation to generate an average C/I value. For example, the access terminal may generate an average C/I value by calculating a non-weighted average of the C/I values for a predetermined number of the first time slots. Alternatively, the access terminal may generate an average C/I value by performing a weighted average of the previous C/I values. This averaged C/I value may be used to calculate a changed C/I threshold 204 that is used to compare with the C/I of the current time slot 202, or "current C/I". The C/I value and C/I threshold may be considered an "access metric" and an "access metric threshold," respectively, and used by the access terminal to predict when the access terminal will not be selected to receive forward link data.

At point 206, where the C/I value decreases below the C/I threshold, the access terminal stops transmitting reverse link signals. At point 208, where the C/I value subsequently rises above the C/I threshold, the access terminal begins transmitting the reverse link signal again, including the DRC information. In the exemplary diagram, gating pattern 210 illustrates a gating pattern of reverse link transmissions by an access terminal in relation to C/I curve 202 and C/I threshold 204. The gating pattern 210 is higher when the access terminal is transmitting a full reverse link signal, and the gating pattern 210 is lower when the access terminal gates or reduces reverse link transmissions.

The algorithm used to calculate the C/I threshold by averaging the C/I values may be constant or may change over time. For example, the C/I threshold may be calculated simply by multiplying the average C/I value by a constant k (k < 1). In another embodiment, k varies with the length of time 212 during which the access terminal has stopped transmitting (referred to as the transmitter off period). As the transmitter off period becomes larger, k increases. In an exemplary embodiment, k becomes 0 after a predetermined maximum transmitter off period, such as two seconds. Among other advantages, a significant advantage is that it mitigates the undesirable side effects of shutting down reverse link transmissions, such as termination of connections by modem pool transceivers or reduced effectiveness of reverse link power control mechanisms. In an exemplary embodiment, the access terminal ignores received reverse link power control commands that are associated with time slots that fall in the transmitter off period.

In another embodiment, rather than comparing the C/I threshold to the C/I value of the slot, the DRC rate is compared by the access terminal to a calculated selection estimate A. The access terminal selects a destination access terminal for forward link transmission according to the algorithm used by the access network, and the access terminal uses its own algorithm to compute the selection estimate a. In an exemplary embodiment, the selection estimate is computed based on an average forward link throughput associated with the access terminal. For example, the access terminal may calculate the average number of bytes of data received per second in the first 50 forward link slots (filtered using a finite impulse response or FIR filter). In addition, the average throughput may be calculated using a finite impulse response or FIR filter. This average value may be based on the data rate requested by the access terminal. In addition, if the protocol used by the access terminal and the access network provides for acknowledgement of the forward link data, the access terminal may calculate an average throughput based on the granted data rate. This selection estimate is corrupted for each access terminal that passes through each forward link slot without receiving data.

The selection algorithm used by the access network may be designed to balance the need to maximize forward link throughput and prevent any access terminal from starving of forward link data. The access network typically uses a selection algorithm based on information maintained for each active access terminal, such as historical forward link throughput and data present in the access terminal's forward link data queue. The access terminal may also be used to select whether data is present in the forward link data queue. The access network may also use DRC rate information received from the access terminal to select the target access terminal.

In one exemplary embodiment, the modem pool transceiver transmits forward link data to the access terminal in any particular data slot. The modem pool transceiver may also transmit forward link data to more than one access terminal in a time slot. The access terminal is only used to select whether there is forward link data that needs to be sent to the access terminal. The access network maintains a forward link data queue for each working access terminal. When there is no forward link data to send to the access terminal, the forward link data queue associated with the access terminal eventually becomes empty. In an exemplary embodiment, the selection of the target access terminal is based on the access network reserving access metrics for each access terminal and based on the state of the access terminal's forward link data queue. For each modem pool transceiver, an access terminal with a large (or in many cases, the largest) access metric value is selected from the access terminals with a non-empty forward link data queue to receive forward link transmissions.

Over time, if the number of active access terminals, channel conditions, and data rates remain constant, a steady state network threshold of access metric values will occur. The access terminal having an access metric value greater than the network threshold is immediately selected to receive forward link data. Any access terminal having an access metric value less than the network threshold will not be selected to receive forward link data.

Fig. 2b shows a reverse link transmission gating pattern using another algorithm. In an exemplary embodiment, the reverse link transmission gating or reduction is based on an access metric AM calculated as a function of the average throughput and a measured forward link channel state, such as a DRC value. Access terminal maintains a dynamically changing access metric threshold Th_AM. For each time slot, the access terminal calculates the current value of the access metric AM and compares it with an access metric threshold Th_AMA comparison is made. Based on the comparison, the access terminal determines whether to gateOr reduce the reverse link signal transmitted in the next reverse link time slot. In addition, the access terminal may gate or reduce a selected subset of the reverse link signal components, e.g., DRC signal components, based on the comparison.

In one exemplary embodiment, whenever AM is less than Th_AMThe access terminal reduces or gates its reverse link transmission. In another embodiment, as long as AM is less than S x Th_AMThe access terminal reduces or gates its reverse link transmission, where S is a scaling factor less than 1. The scaling factor S may be constant or may vary over time. In one exemplary embodiment, S is decreased such that it equals 0 for a predetermined maximum transmitter off period (e.g., two seconds later).

In an exemplary embodiment, the access terminal calculates the access metric AM according to the following formula:

AM＝ChC/T_AVGequation 1

Wherein:

ChC is a measured instantaneous channel state, e.g. DRC value,

T_AVGis an average throughput value calculated according to equation 2, an

AM is the access metric value for the current time slot.

In an exemplary embodiment, the average throughput T of the time slots_AVGIs calculated according to the following formula:

T_AVG(new)＝[(l-k)×T_AVG(previous)]+(k)×T_CUR]equation 2

Wherein:

k is a constant for the filtering to be performed,

T_AVG(new) is the new average throughput value,

T_AVG(previouS) is the original average throughput value, e.g. the average throughput calculated in the previouS slot, an

T_CURIs the current value of the data throughput, e.g., either 0 when the access terminal is not receiving data or the data rate when the access terminal is receiving data. As described above, the throughput may be a throughput requested by the access terminal or a throughput granted by the access network.

In the exemplary embodiment shown in fig. 2b, the DRC value is used to represent the instantaneous channel state ChC when calculating the access metric AM 250. In an exemplary embodiment, the DRC value is a data rate selected from a set of existing data rates based on a carrier-to-interference ratio (C/I) measured by the access terminal. Each DRC value is valid within a range of C/I values and is thus a quantized C/I. The average throughput is in one exemplary embodiment determined by using the average throughput T, as shown in equation 1_AVGDivided by the channel state ChC. Although C/I is continuous over time, the change in DRC rate value is stepped as C/I passes through a threshold from one DRC rate range to another. Therefore, when the DRC value changes, the access metric AM changes in value in a step 260.

When the access terminal is not receiving the forward link transmission, the average throughput of the access terminal decreases, and during the time slot in which the access terminal is receiving data, the average throughput of the access terminal increases. Thus, in period 254, the access metric AM increases when the access terminal is not receiving forward link data, while in period 252, the access metric AM decreases when the access terminal is receiving forward link data.

In an exemplary embodiment, the access network selects a target access terminal to receive data in forward link time slots. An access terminal is used only to select whether data is present in the forward link data queue. From the selectable access terminals, the access terminal having the greatest access metric value is selected. The access metric value of the access terminal selected by the visited network may vary depending on other factors such as the number of active access terminals and the DRC signal received. If the network state remains relatively constant (i.e., the number of active access terminals remains constant, the forward link channel state is stable, and all access terminals receive data such that their forward link data is never empty), the access metric for the access terminal selected for each time slot will stabilize to a relatively constant value. Access terminals with access metrics less than this stable value will not be selected. This stable value can be viewed as a network threshold that can be used to predict whether an access terminal with a particular access metric will be selected.

The access terminal may estimate the network threshold even if different factors affecting the network threshold are not stable over time. As described above, an access terminal is selected to receive forward link data only if its access metric value is greater than this network threshold. In an exemplary embodiment, the access terminal maintains an access metric threshold and uses it to predict whether it will be selected by the visited network. In an exemplary embodiment, the access metric threshold is an estimate of the network threshold.

The actual network threshold is a function of the number of active access terminals, the data present in the forward link data queue of each access terminal, and other varying parameters that are generally not present for a single access terminal. The access terminal can accurately predict whether it will be selected only when it can access the same parameters and use the same algorithm as that of the access network. Thus, the access terminal is typically unable to predict with complete accuracy whether it will be selected.

Even with incomplete estimates, the access terminal may increase the reverse link capacity of the network by selectively gating or reducing its reverse link signal. In an exemplary embodiment, the visited network provides some of this information to the access terminal to let it more accurately determine whether it will be selected by the visited network. For example, in one exemplary embodiment, the access network periodically transmits the number of active access terminals on the forward link.

Although the accuracy of the access terminal prediction is best when the access terminal and the access network both use the same algorithm, those skilled in the art will recognize that the algorithms need not be the same in order to increase reverse link capacity. In an exemplary embodiment, the access terminal uses an estimate of the network threshold as its access metric threshold. In other embodiments, the access terminal uses an access metric threshold that is not an estimate of the network threshold. Either way, the access terminal limits its transmission power when the access metric is less than the access metric threshold.

The access terminal compares its access metric value to an access metric threshold to predict whether it will be selected to receive forward link data. An access metric value less than the access metric threshold indicates that the access terminal is not at that time or is selected to receive forward link data in the next forward link time slot. If the access terminal determines that it is not selected and, at the same time, has no reverse link data to transmit, then the access terminal minimizes its contribution to reverse link interference by reducing the power of its reverse link signal. In an exemplary embodiment, the access terminal reduces the reverse transmit power by transmitting only a subset of the reverse link signal components, e.g., only the reverse link pilot signal. In another embodiment, the access terminal may choose not to transmit the reverse link signal at all for a period of time.

In fig. 2b is shown an access metric AM depicted as polyline 250, an access metric threshold depicted as dashed polyline 270, and a transmitter state depicted as polyline 272, according to an exemplary embodiment. The transmitter state 272 is higher when the access terminal is transmitting reverse link signals and lower when the access terminal gates on or reduces its reverse link signals. Also in fig. 2b, a broken line 274 shows whether the access terminal has been selected and is receiving forward link data from the access network. When polyline 274 is high, the access terminal is receiving forward link data. When polyline 274 is low, the access terminal is not receiving forward link data.

In fig. 2b, the access metric threshold 270 begins at a value 258a that is less than the access metric 250. While the access terminal is receiving forward link data, its access metric steadily decreases 252 a. At time T₁The channel state deteriorates, and thus the DRC value decreases. The channel conditions may deteriorate for a number of reasons, including rayleigh fading due to multipath interference, the presence of an object on the direct path between the access terminal and the modem pool transceiver, or an increase in the distance between the access terminal and the transmitting modem pool transceiver. The drop in DRC causes the access metric to be at time T₁Time drops below the access metric threshold 258 a. Thus, at time T, as shown in the transmitter state diagram 272₁The access terminal stops transmitting. During this time, the access terminal does not transmit the DRC signal and therefore does not receive the forward link data.

When the access terminal does not receive data, the access metric gradually increases as shown. At time T₂The DRC value changes to a larger value and the access metric is increased 260 b. At time T₂The access metric takes a value greater than the access metric threshold. Based on the comparison of the access metric and the access metric threshold, the access terminal resumes transmitting reverse link signals. In this example, the access terminal will not receive forward link data although the access metric is greater than the access metric threshold. This may mean either that the network has no forward link data to send to the access terminal, or that the actual network threshold is greater than the access metric threshold. When the access terminal is not receiving data, the access metric steadily increases 254 b.

At time T₃The DRC value is again increased, causing another step increase in the access metric 260 c. At the new access metric value, the visited network immediately begins transmitting forward link traffic to the visited terminal. In this example, the access terminal then adjusts its access metric threshold to be equal to that at the immediately preceding time T₃A maximum access threshold 258b reached in a period 254b prior to the DRC value jump. In another embodiment, access is providedThe terminal adjusts its access metric threshold to be the same as the maximum access metric value 258b, less than a predetermined warning value, such as 3 dB.

The access metric value steadily decreases 252b while the access terminal is receiving forward link data. At time T₄The access terminal stops receiving forward link data either because another access terminal is serviced by the modem pool transceiver or because there is no more forward link to send. The access metric steadily increases 254c when the access terminal is not receiving forward link data.

At time T₅The DRC value drops significantly causing a step decrease 260d in the access metric. The new access metric value is less than the access metric threshold and the access terminal stops transmitting reverse link signals. During this time, the access terminal does not transmit the DRC signal and therefore does not receive the forward link data. The access metric steadily increases 254d when the access terminal is not receiving forward link data.

As mentioned above, one does not expect an access terminal to turn off its transmitter too long. In this example, the access terminal turns on its transmitter after a maximum transmitter off period, even though the access metric is still less than the access metric threshold. In this example, the maximum transmitter off period ends at time T₆. At this point, the access terminal resumes transmitting reverse link signals even though the access metric is still less than the access metric threshold.

At time T₇The DRC value is raised again causing another step-wise rise in the access metric 260 e. Under the new access metric value, the access terminal immediately begins receiving forward link transmissions from the access network. In this example, the access terminal then adjusts its access metric threshold to be equal to that at the immediately preceding time T₇A maximum access threshold 258c reached in a period 254d before the transition of the upper DRC value. In another embodiment, the access terminal adjusts its access metric threshold to the same maximum access metric value 258c, which is less than a predetermined guard value, such as 3 dB.

When visiting the terminalWhile the peer is receiving forward link data, the access metric value is steadily decreased 252 c. At time T₈The access terminal stops receiving forward link data either because another access terminal is serviced by the modem pool transceiver or because there is no more forward link to send. The access metric computed in the access terminal steadily rises 254e when the access terminal is not receiving forward link data.

At time T₉The access network again begins transmitting forward link data to the access terminal. Because the start of the transmission and the sudden rise in the access metric do not coincide, the access terminal assumes that the network threshold is less than or equal to the current access metric value. The access terminal sets its access metric threshold to a value that is less than the current access metric value having the predetermined alert value. The access metric value steadily decreases 252d while the access terminal is receiving forward link data. At the same time, the access metric threshold is lowered 258d so that it remains less than the access metric value at the alert value.

As mentioned above, it is generally undesirable to avoid transmitting any reverse link signals for a longer period of time. One reason is that it can interfere with the reverse link power control algorithm. Another reason is that if the access network does not receive a reverse link signal from an access terminal, it may assume that it has lost the communication link with the access terminal. Thus, the access network will terminate the connection with the access terminal.

In one exemplary embodiment, when the access terminal is not transmitting reverse link signals, the access terminal ignores the associated reverse link power control commands from the access network. In another embodiment, the modem pool transceiver algorithm ignores frame errors on the reverse link if the modem pool transceiver determines that the access terminal has gated or reduced its reverse link transmission. This prevents the power control algorithm on the modem pool transceiver from erroneously raising its outer loop set point.

In an exemplary embodiment, the access terminal refrains from transmitting any reverse link signals during periods when its access metric is less than the access metric threshold. However, if this period is longer than a predetermined maximum transmitter off period, the access terminal turns its transmitter on again. The access terminal continues to transmit reverse link signals for at least a predetermined minimum transmitter recovery period (e.g., 5 milliseconds). The minimum transmitter recovery period is designed to ensure that the visited network does not terminate its contact with the visited terminal because the transmitter is turned off, and to allow the modem pool transceiver searcher to accurately track the reverse link multipath component.

In an exemplary embodiment where the access terminal refrains from transmitting any reverse link signals for a period of time, it may be desirable to resume transmission of certain signals after such a period of time, but before resuming transmission of other signals. For example, the access terminal may recover the transmitted pilot signal before recovering transmission of other reverse link signal components. This approach enables the pilot filter to be preloaded and multipath tracking to be performed in the modem pool transceiver.

In any of the above embodiments, an access terminal may determine its access metric threshold based on parameters applied to one or more other access terminals. In an exemplary embodiment, such parameters are received from the visited network on a timed basis. These parameters may include, but are not limited to, the number of active users served by the modem pool transceiver or the access network, or an access metric or previously selected average throughput value for the access terminal. Those skilled in the relevant art will appreciate that the specific other parameters received from the visited network may differ from those described above without departing from the methods described herein.

It will be appreciated by those skilled in the relevant art that the values described above, such as the maximum transmitter off period and the minimum transmitter recovery period, are for example only and may be varied without departing from the embodiments described herein. In addition, combinations that reduce various other reverse link signal components than those specifically described above should be considered within the scope of the embodiments described above.

Fig. 3 is a flow chart illustrating an access terminal method for determining when to reduce or completely shut down reverse link transmissions. For each forward link slot, the access terminal measures the forward link channel state at step 302. Parameters measured and used to determine the forward link channel state include such parameters as the carrier-to-interference (C/I) of the received signal and the received signal power. From the channel state measurements, the access terminal determines an access metric AM value in step 304. In an exemplary embodiment, the AM is calculated using a Data Rate Control (DRC) value and an average throughput value as described above.

In step 306, the access terminal compares the new AM value with the access metric threshold TH_AMTo determine whether to transmit the complete reverse link signal. If AM is greater than TH_AMThen the access terminal sends the complete reverse link signal in step 310. In one exemplary embodiment, the complete reverse link signal includes the pilot signal and DRC information. If AM is less than TH_AMThen the access terminal checks in step 307 if its reverse link transmission has been reduced in the previous reverse link slot. If the reverse link transmissions have been reduced, the access terminals determine how long they have been reduced. The reduced duration is compared to a maximum transmitter off period. If the reduced duration is greater than the maximum transmitter off period, the access terminal resumes transmitting the full reverse link signal at step 310.

In an exemplary embodiment, the access terminal also restricts when AM is less than TH_AMThe length of time it takes to transmit the complete reverse link signal. In step 307, the access terminal checks the timer to determine whether to reduce reverse link signaling in step 308 or to transmit a complete reverse link signal in step 310. For example, in AM remains less than TH_AMFor longer periods of time, the access terminal reduces its reverse link transmission during the maximum transmitter off period. After that, if AM is still less than TH within the minimum transmitter recovery period_AMThen the access terminal again decrements itReverse link transmission. This cycle of resuming full reverse link signaling after a maximum transmitter off period and reducing reverse link signaling after a minimum transmitter recovery period continues until AM is greater than TH_AM。

As described above, the access terminal may reduce its reverse link transmission in a different manner at step 308. In one exemplary embodiment, the access terminal gates on or stops transmitting all components of the complete reverse link signal. In another embodiment, the access terminal parameters transmit a complete reverse link signal lacking the DRC component. In other embodiments, the access terminal transmits some other subset of the reverse link signal components. In addition, the access terminal may transmit some or all of the reverse link signal components at a reduced power level, but not gate them entirely.

In one exemplary embodiment, the access terminal stops transmitting all components of the reverse link signal, but resumes transmitting the pilot signal before resuming other channels. This enables preloading of the signal filters within the modem pool transceiver.

Either the full reverse link signal is transmitted at step 310 or the reduced reverse link signal is transmitted at step 308, the access terminal processes any received forward link data at step 312 and updates T at step 314_AVGAnd TH_AM. The access terminal then begins processing the next slot again by measuring the forward link channel state at step 302.

The access network may continuously send reverse link power control commands to the access terminal regardless of whether the access terminal transmits a complete reverse link signal. If the access network bases reverse link power control commands on signal components that are gated or transmitted at reduced power, then these power control commands will not accurately reflect the state of the reverse link channel. In an exemplary embodiment, the access terminal ignores or specially processes any reverse link power control commands that are associated with periods when the access terminal is not transmitting a full reverse link signal.

Fig. 4 illustrates an exemplary access terminal apparatus. In the exemplary embodiment shown in the figure, the device, pilot signal, supplemental data, Data Rate Control (DRC), and base data signal are spread with walsh codes, gain controlled, and summed before being spread in a complex pseudo-noise (PN) spreader 410. Using pilot walsh code W in walsh spreader 410a_PThe pilot signal is multiplied and gain controlled in gain block 402 a. Walsh code W is used as supplemental data in Walsh spreader 401b_SThe complementary data signal is multiplied and gain controlled in the gain block 402 b. The DRC signal is multiplied by the DRC walsh code WD in the walsh spreader 401c and gain-controlled in the gain block 402 c. Walsh code W is used as base data in Walsh spreader 401d_FThe base data signal is multiplied and gain controlled in a gain block 402 d.

In an exemplary embodiment, walsh spreader 401 is implemented as a multiplier that multiplies the different walsh codes with the pilot signal, DRC, and supplemental and base data signals. The pilot signal, DRC, and supplemental and base data signals are converted to signal point mapping values, e.g., +1 and-1, prior to walsh spreading. In another embodiment, the signal point mapping occurs immediately prior to the gain control of the gain block 402. In such an embodiment, walsh spreader 401 employs an exclusive or (XOR) function that employs a walsh cover rather than a multiplication. In another embodiment, a "Walsh function zero" or W is used_OThe pilot signal is spread but not in fact fully spread. In such an alternative embodiment, walsh spreader 401a may be omitted.

The gain controlled signals produced by gain blocks 402a and 402b are added together to form the output of adder 408 a. The gain controlled signals generated by gain blocks 402c and 402d are added together to form the output of adder 408 b. The output of adder 408a provides the in-phase (I') or "real" component of the signal multiplied by the complex PN code in PN spreader 410. The output of adder 408b provides the quadrature-phase (Q') or "imaginary" component of the signal multiplied by the complex PN code in PN spreader 410. The output of the complex PN spreader 410 is a complex signal having I and Q components. Each of these components is filtered using baseband filters 412a and 412b before being upconverted in mixers 414a and 414 b. The up-conversion in mixers 414a and 414b is achieved by multiplying the sine and cosine signals with the outputs of baseband filters 412a and 412b as shown. The outputs of mixers 414 are then summed in summer 416 to form an upconverted reverse link signal that is amplified in amplifier 418 and transmitted via antenna 420.

The gain levels applied to the different signals by the gain block 402 are controlled by a control processor 424. The control processor 424 receives timing information, such as slot timing, from the system time processor 426. The control processor 424 then determines whether to gate or reduce reverse link transmissions according to one of the algorithms or embodiments described above. Control processor 424 then compares the access metric to an access metric threshold and gates or reduces the transmit power of the reverse link signal based on the comparison. In an exemplary embodiment, the control processor 424 uses parameters received from the access network and applied to one or more other access terminals to determine the access metric threshold.

In general, the control processor 424 gates or reduces reverse link transmissions during periods when the access metric is less than the access metric threshold. In an exemplary embodiment, the control processor 424 uses timing information from the system processor 426 to adjust the duration for which reverse link transmissions are gated or reduced. For example, if the time period is longer than a predetermined maximum transmitter-off time period, the control processor 424 causes the access terminal to resume transmitting the full reverse link signal. In one exemplary embodiment, control processor 424 causes the complete reverse link signal transmission so recovered to last for at least a predetermined minimum transmitter recovery period.

In an exemplary embodiment, the control processor 424 fully gates the reverse link transmission by having each gain block 402 apply a gain close to 0 to their respective input signals. Additionally, the control processor 424 may instead cause the amplifier 418 to stop transmitting or transmit at a power transmission close to 0. As described above, after the reverse link signal has been gated, the access terminal may recover the transmission pilot signal before recovering transmission of other reverse link signal components. Control processor 424 sets the gain in pilot gain block 402a to a value other than 0 by setting the gain in gain blocks 402b, 402c, and 402d to be close to 0 to cause control signal transmission to resume first. In another embodiment, the pilot gain block 402a is omitted such that only non-pilot signals are gated on or reduced.

In another embodiment, control processor 424 gates or reduces the gain of only a subset of the reverse link signal components according to one of the algorithms described above. In one exemplary embodiment, gain blocks 402b, 402c, and 402d are used to gate or transmit only non-pilot signals at reduced power to attenuate the signals.

In an exemplary embodiment, control processor 424 also executes a reverse link power control algorithm based on reverse link power control commands received from one or more modem pool transceivers. In accordance with the algorithm, the control processor 424 adjusts the reverse link power using the gain block 402 or the amplifier 418, or both, to vary the reverse link power. In an exemplary embodiment, the control processor 424 ignores or otherwise specially processes any reverse link power control commands that are associated with periods when the access terminal is not transmitting a full reverse link signal.

Those skilled in the relevant art will appreciate that the gain controlled channel signals may be combined in different ways before PN spreader 410 without departing from the embodiments described. For example, adder 408a may add the gain controlled outputs of gain blocks 402a and 402c instead of 402a and 402 b. In addition, some signals may be individually gain controlled and added to the real and imaginary components output by adders 408a and 408 b.

In an exemplary embodiment, PN spreader 410 sums the outputs of adders 408a and 408b with a component PN_IAnd PN_QThe complex PN code of (a) is complex multiplied according to the following formula:

I＝I′PN_I-Q′PN_Q

Q＝I′PN_Q+Q′PN_I

in another embodiment, PN spreader 410 multiplies the outputs of adders 408a and 408b by only one real PN sequence according to the following equation:

I＝I′PN

q ═ Q' PN in other embodiments, some other complex or real multiplication formula is used.

In an exemplary embodiment, the control processor 424 is a microprocessor, microcontroller, DSP, or similar device capable of executing a series of software instructions stored in an electronic medium. In an exemplary embodiment, the control processor 424 executes code stored in a memory, such as memory 422. Control processor 424 may also store temporary values, such as access metrics, access metric thresholds, and associated variables, in memory 422. In addition, control processor 424 may store temporary values, such as reverse power control parameters and timer values associated with a maximum transmitter off timer or a minimum transmitter recovery timer.

In the above embodiment, each access terminal transmits a reverse link signal to one or more modem pool transceivers. Each modem pool transceiver uses these signals to determine which access terminal will receive the forward link transmission in each forward link time slot. The modem pool transceiver also uses these reverse link signals to determine the maximum data rate at which forward link data can be transmitted to any access terminal. The reverse link signal may contain DRC information or C/I information, commonly referred to as data request information. Those skilled in the relevant art will appreciate that the data request information may take other forms without departing from the scope of the present invention. For example, the access terminal may transmit the error rate or Yamamoto metric of the received forward link signal as the data request information.

In one exemplary embodiment, each modem pool transceiver in the access network uses a data rate specific to the data request message received from the target access terminal, each time for forward link transmission to an access terminal. In such an embodiment, the access terminal demodulates the forward link at a data rate based only on the originally transmitted data request information. In addition, the access network may transmit forward link data at a rate different from the rate dedicated to the data request message received from the target access terminal. For example, each modem pool transceiver may transmit forward link data to more than one access terminal at a data rate selected by the access network. The target access terminal determines the rate at which the forward link signal is demodulated by performing blind rate detection or by decoding a separate rate indication signal received from the access network.

The components in the described apparatus embodiments are described in general terms to achieve the flexibility of the invention. Each of the described components may be implemented using one or a combination of a general purpose microprocessor, a Digital Signal Processor (DSP), a programmable logic device, an Application Specific Integrated Circuit (ASIC), or any other device capable of performing the functions described herein. Although illustrated with a wireless communication system, the embodiments and concepts described herein may be used in networks where network nodes communicate using other technologies, such as fiber, coaxial, or other wired technologies.

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 (41)

1. A method of receiving data transmitted from an access network to an access terminal, the method comprising:

measuring at least one parameter of a signal received from the visited network at the visited terminal;

determining an access metric value based on the measurements;

generating data request information based on the measurements;

comparing the access metric value to an access metric threshold;

estimating, based on the comparison, that sending data request information to the access network will not result in selection by the visited network for the access terminal; and

based on the estimate, power of a reverse link signal transmitted from the access terminal to the access network is reduced.

2. The method of claim 1, further comprising updating the access metric threshold based on the access metric value.

3. The method of claim 1, wherein the measuring further comprises low pass filtering the forward link data throughput values.

4. A method according to claim 3, characterized in that said low-pass filtering is performed using a finite impulse response filter.

5. A method according to claim 3, characterized in that said low-pass filtering is performed using an infinite impulse response filter.

6. The method of claim 3, wherein the forward link data throughput value is based on a data rate requested by the access terminal.

7. The method of claim 3, wherein the forward link data throughput value is based on a data rate granted by the access network.

8. The method of claim 3 further comprising updating said access metric threshold based on said forward link data throughput value.

9. The method of claim 1, further comprising:

receiving an access metric parameter from the visited network; and

the access metric threshold is updated according to the access metric parameter.

10. The method of claim 9, wherein the access metric parameters are access terminals receiving forward link data from a modem pool transceiver.

11. The method of claim 9 wherein the access metric parameter is an access network metric value associated with a previous forward link data transmission.

12. The method of claim 1, further comprising:

receiving a power control command from a visited network at a certain reception time;

comparing the reception time with the reduced time; and

processing the power control command in accordance with the comparison.

13. The method of claim 1, wherein the data request information includes a data rate control value.

14. The method of claim 1, wherein the data request information includes a carrier-to-interference ratio.

15. The method of claim 1 wherein said reducing further comprises gating a data request information signal based on said estimating, said reverse link signal comprising a plurality of signal components, and wherein said data request information signal is one of the plurality of signal components.

16. The method of claim 15 wherein said reducing further comprises gating an additional signal component of the plurality of signal components concurrently with said gating the data request information signal.

17. The method of claim 1 wherein said reverse link signal comprises a plurality of signal components, wherein said plurality of signal components comprises a pilot signal, and wherein said reducing further comprises gating all of said plurality of signal components concurrently with said gating of said data request information signal.

18. The method of claim 17, further comprising:

recovering transmission of the pilot signal; and

resuming transmission of at least one of the other of the plurality of signal components a predetermined period of time after said resuming transmission of the pilot signal.

19. The method of claim 1, further comprising:

monitoring a length of time that the reverse link signal is powered down in accordance with the reduction; and terminating the reducing when the length of time exceeds a predetermined maximum transmitter off period.

20. The method of claim 1 further comprising multiplying said reverse link signal by a PN code.

21. The method of claim 1 further comprising complex multiplying the reverse link signal with a complex PN code.

22. An access terminal apparatus, characterized in that the apparatus comprises:

a data request gain module configured to gain control the data request information signal according to a data request gain control signal to generate a gain-controlled data request information signal; and

a control processor configured to generate an estimate of whether transmitting a data request information signal will result in selection by the visited network for the access terminal, and to modify a gain control signal in dependence on the estimate;

a control processor configured to determine an access metric value based on measurements of at least one parameter of signals received from an access network, to generate data request information based on the measurements, to compare the access metric value to an access metric threshold, to estimate that sending data request information to the access network will not result in selection by the access terminal by the visited network, and to modify the gain control signal based on the estimation.

23. The apparatus of claim 22 further comprising a walsh spreader configured to spread the data request information signal using a walsh code.

24. The apparatus of claim 22 wherein the control processor is further configured to determine an average throughput value and to generate the estimate based on the average throughput value.

25. The apparatus of claim 22 wherein the control processor is further configured to determine an access metric value and an access metric threshold value and to generate the estimate based on a comparison of the access metric value and the access metric threshold value.

26. The apparatus of claim 25 wherein the control processor is further configured to update the average throughput value based on at least one access metric parameter received from an access network.

27. The apparatus of claim 25 wherein the control processor is further configured to update the average throughput value based on a value received from the access network, wherein the value corresponds to a number of access terminals receiving forward link data from the modem pool transceiver.

28. The apparatus of claim 25 wherein the control processor is further configured to update the average throughput value based on an access network access metric value received from an access network.

29. The apparatus of claim 22 further comprising a pilot gain module configured to gain control the pilot signal component based on a pilot gain control signal to produce a gain controlled pilot signal, wherein the control processor is further configured to alter the pilot gain control to gate the pilot signal based on the estimate.

30. The apparatus of claim 29 wherein the control processor is further configured to modify the pilot gain control to increase the gain of the pilot signal at a first time and to modify the data request gain control signal to increase the gain of the data request information signal at a second time, wherein the second time is a predetermined duration later than the first time.

31. The apparatus of claim 22 further comprising a PN spreader configured to multiply the data request information signal by a PN code.

32. The apparatus of claim 22 further comprising a complex PN spreader configured to complex multiply said data request information signal by a complex PN code.

33. An access terminal apparatus, characterized in that the apparatus comprises:

an amplifier configured to gate the upconverted signal according to a gate control signal; and a control processor configured to generate an estimate of whether transmitting a data request information signal will result in selection by the access terminal by the visited network, and to modify the gating control signal in dependence on the estimate.

34. The apparatus of claim 33 wherein the control processor is further configured to determine an average throughput value and to generate the estimate based on the average throughput value.

35. The apparatus of claim 33 wherein the control processor is further configured to determine an access metric value and an access metric threshold value and to generate the estimate based on a comparison of the access metric value and the access metric threshold value.

36. The apparatus of claim 35 wherein the control processor is further configured to update the average throughput value based on at least one access metric parameter received from the access network.

37. The apparatus of claim 35 wherein the control processor is further configured to update the average throughput value based on a value received from the access network, wherein the value corresponds to a number of access terminals receiving forward link data from the modem pool transceiver.

38. The apparatus of claim 35 wherein the control processor is further configured to update the average throughput value based on an access network access metric value received from the access network.

39. The apparatus of claim 33 further comprising a PN spreader configured to multiply the data request information signal by a PN code.

40. The apparatus of claim 33 further comprising a complex PN spreader configured to complex multiply said data request information signal by a complex PN code.

41. An access terminal apparatus, characterized in that the apparatus comprises:

means for generating an estimate of whether transmitting a data request information signal will result in selection by the visited network of the access terminal; and

means for reducing the power of the signal transmitted by the access terminal device based on the estimation.