HK1089885A - Adaptive data rate determination for a reverse link in a communication system - Google Patents

Description

Adaptive data rate determination for reverse link in communication system

Technical Field

The present invention relates generally to the field of communications, and more particularly, to a system and method for improving data transfer performance in a wireless communication system.

Background

In a typical wireless voice/data communication system, base stations are associated with coverage areas. This area is called a sector. Mobile stations within a sector can transmit data to and receive data from the base station. In particular, within the scope of data communication, a base station may be referred to as an access network and a mobile station may be referred to as an access terminal. An access terminal may be able to communicate with more than one access network simultaneously, and as the access terminal moves, the set of access networks with which it communicates may change.

The parameters for communication between a particular access network and a particular access terminal are based in part on their relative locations and the quality and strength of the signals transmitted and received by them, respectively. For example, as the access terminal moves away from the access network, the strength of the signal received by the access terminal from the access network will decrease. And thus the error rate of the received data will increase. The access network may therefore typically compensate for the increased distance by reducing the rate at which it transmits data to the access terminal. This allows the access terminal to receive and decode the access network's signal with fewer errors. As the access terminal moves closer to the access network, the signal strength increases, thereby enabling the use of higher data rates to transmit data to the access terminal.

Similarly, as the access terminal moves away from the access network, the strength of the signal received by the access network from the access terminal may decrease, potentially resulting in a higher error rate. Similar to the access network, the access terminal may also typically compensate for the increased distance by reducing its data rate to allow the access network to receive the signal with fewer errors. The access terminal may also increase its power output to reduce the error rate if requested by the access network. In addition, stronger signals may support higher data rates as the access terminal moves closer to the access network.

In one system, an access terminal is responsible for determining the rate at which data may be transmitted from the access terminal to an access network. This rate is determined based on a number of factors. The main factors are the absolute maximum rate at which the access terminal and access network can communicate, the maximum rate based on the access terminal's allowed power output, the maximum rate adjusted by the amount of data the access terminal has in the queue, and the maximum rate allowed based on ramp-up (ramp-up) limits. In this system, each of these rates provides a hard limit that cannot be exceeded by the selected data rate. In other words, the selected data rate is not higher than the minimum of the four rates.

The first two of these rates (absolute and power-limited maximum rates) are caused by the physical limitations of the system and are outside the control of the access terminal. The third and fourth rates (the feasible data rate and the ramp-up-limited rate) are variable and are dynamically determined based on the particular prevailing conditions at the access terminal.

The data-justified rate is essentially the maximum rate that can be adjusted by the amount of data queued for transmission by the access terminal. For example, if the access terminal has 1000 bits in its transmit queue, a data rate of 38.4kbps (1024 bits/frame) may prove feasible, while a higher rate of 76.8(2048 bits/frame) may not prove feasible. The time frame may be defined as a unit of time, such as 26.666ms for a time frame in a cdma20001xEV-DO system as defined by the IS-856 standard. If there is no data in the access terminal's transmit queue, no transmission rate at all proves feasible.

The ramp-up-limited rate is the maximum rate allowed in view of the fact that a fast ramp-up may suddenly increase the interference experienced by other access terminals and degrade their performance. If the ramp-up of each access terminal is limited, the interference level caused by it may change more slowly and other access terminals can more easily adjust their operating data rates and transmit powers to accommodate the increased interference. It should be noted that the ramp-up limit rate is also calculated to control the ramp-down of the data rate. The overall effect is to minimize wide and/or rapid fluctuations in data rates to stabilize the overall operation of the access network and the access terminals in the system.

While the change in ramp-up-limited rate is controlled (with respect to increasing and decreasing data rates), the data-justified rate is not controlled. The data-justified rate may increase suddenly if the access terminal suddenly has enough data to justify a very high rate. The feasible data rate may suddenly drop to 0 if the access terminal finishes sending out data. Typically, because the ramp-up-limited rate is controlled, there is no problem with a sudden increase in the feasible data rate. Since the minimum of the four rates mentioned above sets the maximum value for the selected data rate, the ramp-up-limiting rate is controllable in this case. However, a sudden increase in the data rate feasible may result in a decrease in the actual data rate, since the data rate feasible is lower than the other rates and thus controllable (bearing in mind that the data rate selected for data transmission in the next frame is the minimum of the four rates).

In existing systems, if an access terminal has no data to transmit, no data is transmitted. This is of course intuitive and conventional thinking has been that useful bandwidth should not be wasted by transferring useless data. One of the problems caused by allowing the data rate to drop suddenly (e.g., to 0) is that it takes some time for the data rate to ramp back up, as explained above. Delays in the transmission of some data may be caused by a decrease in the data rate and a subsequent ramp up. This delay may occur particularly in the case of bursty or discrete arrival processes of data. One such type of data is real-time video that may include 500-1000 byte packets and arrive at the transmit queue at discrete intervals of 60-70 milliseconds. Real-time video is also a significant example of a type of data where transmission delays are particularly significant and unacceptable. Network gaming is another class of applications where data arrival is sporadic and data latency is a key performance metric. Therefore, there is a need to provide a method and apparatus for adaptive determination of data rates for fast ramping of data rates while minimizing undesirable effects in a communication system.

Disclosure of Invention

While the ramp-up limit rate is designed to prevent the access terminal from increasing its data rate, in a manner that causes excessive interference to other access terminals, there are cases where the additional interference is not too disruptive. A different aspect of the invention provides a method to detect whether few access terminals are active in a sector so that increasing the data rate is acceptable for a particular access terminal faster than the ramp-up-limited rate allows. Any ramp-up limitation imposed by the ramp-up limiting rate may reduce the overall performance of the system when there are few active access terminals in the sector. Thus, by qualitatively determining the impact of active access terminals in a sector by monitoring the reverse link activity bits and their historical values, the ramp-up-limited rate may be allowed to ramp up to a maximum value for a fast ramp-up of the data rate without substantially impacting the overall performance of the system, in accordance with various aspects of the invention.

The present invention generally comprises a system and method for improving data transmission performance in a wireless communication system by calculating a reverse link data transmission rate that allows for a fast ramp-up of the data rate for a burst data transmission. One embodiment of the present invention encompasses a wireless communication system in which an access terminal is configured to determine a rate at which data may be communicated on a reverse link to an access network. An access terminal includes a transmit subsystem for communicating data and a processor coupled to the transmit subsystem and configured to provide control information thereto. In particular, the processor is configured to determine a data rate at which the transmitting subsystem may transmit data on the reverse link. In one embodiment, the processor is configured to calculate a feasible data rate and a closed-loop resource allocation rate. The processor then selects the minimum of the feasible data rate, the closed-loop resource allocation rate, the absolute maximum rate, and the power-limited rate as the data transfer rate for the next transfer frame. The processor controls the closed-loop resource allocation rate to reach a maximum level when the statistics associated with the Reverse Activity Bit (RAB) meet a predetermined criterion. As such, the various aspects of the present invention allow communication on the reverse link to quickly begin the data rate for data transmission when the RAB meets predetermined criteria. This is achieved in one embodiment by maintaining statistics associated with the RAB in a digital filter in the processor.

One embodiment of the present invention encompasses a method for improving performance in data transmissions on a reverse link from an access terminal to an access network, wherein the method comprises calculating a first data transmission rate at which to transmit data on the reverse link, wherein the first data transmission rate is allowed to ramp up to a maximum level when the access terminal has received a RAB over a period of time that satisfies a predetermined statistical criterion and indicates that the wireless communication system is not busy. In one embodiment, the maximum level allowed may be limited by other rate determining parameters.

One embodiment of the present invention encompasses a wireless communication system in which an access terminal is configured to determine a rate at which data may be communicated to an access network on a reverse link. An access terminal includes a transmit subsystem for communicating data and a processor coupled to the transmit subsystem and configured to provide control information thereto. In particular, the processor is configured to calculate a first data transfer rate at which to transfer data on the reverse link, wherein the method includes calculating the first data transfer rate at which to transfer data on the return link, wherein the first data transfer rate is allowed to ramp up to a maximum level when the access terminal has received RABs that satisfy a predetermined statistical criterion and indicate that the wireless communication system is in a not-busy state for a period of time. In one embodiment, the maximum level allowed may be limited by other rate determining parameters.

A method and apparatus for determining a data rate for a reverse link communication of an access terminal includes receiving a Reverse Activity Bit (RAB) from an access point in the communication system and passing the RAB to a digital filter to produce a filtered RAB. In one embodiment, the reverse link data rate is determined based on a filtered value of the RAB. Further, a processor in the access terminal can determine whether the access terminal is in idle mode and pass a non-busy state value of the RAB to the digital filter when the access terminal is in idle mode. The filtered RAB may be compared to a threshold to determine the mode of reverse link data rate determination based thereon. The mode defines a set of criteria for how aggressively the reverse link communication data rate is increased or decreased. Thus, according to the determined mode, the processor determines the data rate based on the filtered reverse activity bits.

Another embodiment of the invention includes a software application. The software application is embodied in a computer readable medium or other data processor employed in an access terminal. The media may comprise floppy disks, hard drives, CD-ROMs, DVD-ROMs, RAMs, ROMs, and the like. The medium contains instructions configured to cause a computer or data processor to perform the method as described above. It should be noted that the computer-readable medium may comprise RAM or other memory that forms part of the access terminal. The processor of the access terminal is thereby capable of performing the method in accordance with the present disclosure.

Many additional embodiments are possible.

Drawings

Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a portion of a wireless communication system that is capable of operating in accordance with various aspects of the invention;

fig. 2 is a more detailed diagram illustrating an access network and an access terminal in two adjacent sectors of a wireless communication system, which can operate in accordance with various aspects of the invention;

FIG. 3 is a functional block diagram illustrating the architecture of an access terminal, which can operate in accordance with various aspects of the present invention;

FIG. 4 is a flow chart illustrating the manner in which a closed-loop resource allocation rate is determined in accordance with various aspects of the invention;

FIG. 5 is a flow chart illustrating a manner for determining different modes of reverse link data rate, where each mode has a particular aggressiveness for increasing or decreasing the data rate;

fig. 6 is a flow chart illustrating a manner for determining different modes of reverse link data rate, where each mode has a particular aggressiveness for increasing or decreasing the data rate.

In particular, the flow diagram includes an Access Terminal (AT) in an idle state.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. The disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

Detailed Description

Broadly, the present invention comprises systems and methods for improving data transmission performance in a wireless communication system by controlling increases and decreases in the data transmission rate of the reverse link.

Referring to fig. 1, a portion of a wireless communication system is shown according to one embodiment. In this embodiment, the system includes a plurality of access networks 12 and a plurality of access terminals 14. Each access network 12 communicates with access terminals 14 in the surrounding area. Access terminals may move within a sector, or they may move from a sector associated with one access network to a different sector associated with another access network. The coverage area is a sector 16. Although in practice these sectors may be somewhat irregular and may overlap with other sectors, they are depicted in the figure as being depicted by dotted lines. It should be noted that for clarity, only one of each access network, access terminal, and sector is indicated by a reference numeral.

Referring to fig. 2, a more detailed diagram illustrating an access network and an access terminal in two adjacent sectors of a wireless communication system in one embodiment is shown. In this system, sector 20 includes an access network 22 and a number of access terminals 24. Sector 30 includes an access network 32 and a single access terminal 34. Access networks 22 and 32 transmit data to access terminals 24 and 34 over what is referred to herein as a Forward Link (FL). Access terminals 24 and 34 communicate data to access networks 22 and 32 via a tunnel called a Reverse Link (RL).

Referring to fig. 3, a functional block diagram illustrating the structure of an access terminal in one embodiment is shown. In this embodiment, the access terminal includes a processor 42 connected to a transmit subsystem 44 and a receive subsystem 46. The transmit subsystem 44 and receive subsystem 46 are connected to a common antenna 48. Processor 42 receives data from receive subsystem 46, processes the data, and outputs the processed data via output device 50. The processor 42 also receives data from the data source 52 and processes the data for transmission. The processed data is then passed to transmit subsystem 44 for transmission over the reverse link. In addition to processing data from receive subsystem 46 and data source 52, processor 42 is configured to control the various subsystems of the access terminal. In particular, processor 42 controls transmit subsystem 44. The access terminal-based functions described below are implemented in the processor 42. A memory 54 is connected to the processor 42 for storing data used by the processor.

In one embodiment, the system is a cdma20001xEV-DO system. The main features of this system are defined by the commonly known IS-856 data communication standard. This standard IS based on the IS-95 family of Code Division Multiple Access (CDMA) standards. The designation "1 xEV-DO" refers to the evolution ("EV") with respect to the CDMA2000 family ("1 x") and standards for data optimized ("DO") operation. The 1xEV-DO system is optimized primarily for wireless internet access where high speed data throughput is desired over the forward link.

The 1xEV-DO system is designed to communicate data at one of 12 different predetermined data rates ranging from 38.4kbps to 2.4Mbps (except for the null rate) on the forward link. A corresponding data packet structure (specifying parameters such as packet period, modulation type, etc.) is defined for each of these predetermined rates. Communication on the reverse link occurs at one of five different data rates ranging from 9.6kbps to 153.6kbps (plus a zero rate). Further, a data packet structure is defined for each of these data rates.

The present invention relates generally to the reverse link. Therefore, the data rate for the reverse link is proposed as follows.

Rate of speed	Data rate
			Reference numerals	Kbps	Bits/frame
0	0	0
			1	9.6	256
2	19.2	512
			3	38.4	1024
4	76.8	2048
			5	153.6	4096

In the following discussion, for simplicity, the reverse link data rate will be referred to in terms of a rate label, rather than the number of bits per second or frame.

As indicated above, the 1xEV-DO based system is built based on CDMA standards. So that the data transmitted over the reverse link is code division multiplexed. That is, the data corresponding to each access terminal is distinguished by a corresponding code. Each code defines a communication channel. Thus, data from any or all access terminals can be transmitted at the same time, and the access network can distinguish between different data sources by using coding.

Code Division Multiple Access (CDMA) transmissions are interference limited. In other words, the amount of data that can be transmitted is limited by the amount of interference present in the environment. Although there is some amount of interference caused by background or thermal noise, the dominant source of interference with respect to access terminal transmissions is other access terminals in the area. If there are few other access terminals and they transmit little data, there will be little interference so it is possible to transmit data at a high data rate. On the other hand, if there are many other access terminals transmitting large total amounts of data, the interference level will be higher and only very low data rates for reverse link transmissions may be possible.

A mechanism must be provided for determining the appropriate data rate for each access terminal. A typical CDMA wireless communication system uses a small set of data rates for all access terminals. The set of two possible data rates IS typical in a system operating in accordance with the IS-95 standard. Some CDMA communication systems that provide for voice and data communications use some form of centralized control whereby the information needed to allocate the rates is centralized at a central location and then the rate allocations are communicated back to each access terminal. The centralized rate control algorithm is not necessarily defined by the process of assigning the same rate to all access terminals. The difficulties of centralized control are: 1) the computation of the optimal rate for all access terminals can be difficult and computationally intensive, 2) the communication cost for controlling signaling to and from the access terminals can be excessive, and 3) the effectiveness of the "optimal" rate allocation is unreliable once the delay and uncertainty regarding the network's future needs and its performance are taken into account.

One way in which the present system differs from typical systems is that the calculation of the data rate for an access terminal is responsible for each individual access terminal. In other words, it is distributed rather than centralized. The appropriate data rate for a particular access terminal is determined by the access terminal itself through the use of a reverse link Mac algorithm. ("Mac" is an industry term for multiple access communication.) the reverse link Mac algorithm is discussed further.

When a particular access terminal is calculating the data rate of its reverse link, it is apparent that it wants to select a rate that is as high as possible. However, there may be other access terminals in the sector. These other access terminals may also attempt to transmit their data at as high a transmission rate as possible. Since the power required to transmit data is roughly proportional to the data rate, increasing the data rate of each access terminal will increase the power at which they transmit. The transmissions of each access terminal will then cause an increased amount of interference to other access terminals. To some extent, so much interference will occur that no access terminals are able to transmit their data at an acceptable error rate.

It is therefore useful for an access terminal to have information about the interference levels present in the system. If the interference level is relatively low, the access terminals can increase their data rates to some extent without causing a significant adverse effect on the overall performance of the system. However, if the interference level is too high, the increase in the access terminal data rate can have a significant adverse effect.

The overall interference level is tracked by the access network in one embodiment. The access network is configured to simply determine whether the overall interference level is above or below a threshold. The access network sets a Reverse Activity Bit (RAB) to 0 if the interference level indicative of the activity level is below a threshold. The RAB is sometimes also referred to as a "busy bit". If the interference level, which represents the activity level, is above a threshold, the access network sets RAB to 1. The RAB is then communicated to each access terminal to inform them of the activity level/interference level in the system.

In one embodiment, the overall interference level is calculated by summing the power of each access terminal's reverse link transmission and dividing by the thermal noise level or background noise level in the environment. The sum is then compared to a threshold. If the sum is greater than the threshold, the interference level is considered high and RAB is set to 1. If the sum is less than the threshold, the interference level is considered low and RAB is set to 0.

Because the performance of reverse link data communications depends on the data rate and the interference level in the system, it is necessary to consider the interference level in calculating the appropriate data rate. Thus, as provided to the access terminal in the form of a RAB, the data rate calculation in the reverse link Mac algorithm takes into account the interference level in accordance with various aspects of the invention. The reverse link Mac algorithm also takes into account factors such as the needs of the access terminal and the physical limitations of the system. Based on these factors, the data rate for each access terminal is calculated once per frame.

The reverse link Mac algorithm is calculated substantially as follows.

R_new＝min(R₁，R₂，R₃，R₄)，

Wherein

R₁Is the maximum data rate of the system and,

R₂for the maximum data rate of the access terminal based on the maximum value of allowed transmit power,

R₃a data rate adjusted for data in a queue being transmitted, and

R₄rates are allocated for closed loop resources based on RAB according to various aspects of the present invention.

Each rate R₁-R₄To R_newA hard limit is set. In other words, the rate R selected by the reverse link Mac algorithm_newMust not exceed the rate R₁-R₄Any of the above.

Maximum rate R of the system₁Based on the design of the system including the access network and the access terminal. Data rate R₁Can be set by the access network but rarely changes and can be considered static. Thus the data rate R₁Is stored only at the access terminal for use in calculating R_new。

As noted above, the power of the reverse link data transmission is roughly proportional to the data transmission rate, so there is a maximum rate corresponding to the maximum power level and current channel conditions. Maximum data rate R based on power₂Based on the maximum power that the access terminal reverse link transmits, as a function of the access terminal design. Although the actual maximum transmission power P_maxIs static, R₂As P_maxAnd as a function of current channel conditions. R as seen at the access network₂Related to the signal-to-noise ratio (SINR) of the access terminal signal, which varies due to the channel gain and the current data rate of the terminal.

Rate R₃Is the data rate adjusted by the data waiting in the access terminal queue to be transmitted. R₃Is variable and is calculated once per frame. R₃The purpose of (a) is to reduce the reverse link data rate of access terminals when they have little or no data to transmit to reduce their interference to other access terminals. Conventionally, R₃Only the rate necessary to transmit the data in all queues with a single frame. Thus, if there are 1025 to 2048 bits of data in the queue, a rate of 76.8kbps will be selected. Referring to the table shown here with respect to the rate numbers, 2048 bits can be transmitted in one frame at rate number 4, transmitting data at 76.8 kbps. On the other hand, if there are 2049 bits of data in the queue, it is necessary to select a rate of 153.6kbps (4096 bits/frame) in order to transmit all the data in a single frame. If there is no data in the queue, the feasible rate is zero. Calculating R using this convention₃Corresponding to R₃Can range from rate index 0 to rate index 5 without considering the previous R₃The value of (c).

Closed Loop Resource Allocation (CLRA) rate R₄Is also calculated once per frame. R₄The objective is to prevent the data rate of each access terminal from increasing unnecessarily too fast and thereby creating more interference than is acceptable to other access terminals. The CLRA rate is based on the current rate and a set of predetermined probabilities that the rate varies up or down. The probabilities used in the calculation of the CLRA rate substantially control the rate to prevent it from changing too fast.

The CLRA rate R is calculated in the following manner₄. A corresponding flow chart is shown in fig. 4.

(1) Selecting a random number V, wherein V is more than or equal to 0 and less than or equal to 1,

(2) then the

(i) If the RAB is equal to 0,

if V < P_i，R₄＝R_old+1

Otherwise R₄＝R_old

(ii) If the RAB is equal to 1,

if V < P_i，R₄＝R_old-1

Otherwise R₄＝R_ola

Wherein

P_iIs the probability for the current state and RAB (see table below)

R_oldIs the current rate of the at least one channel,

R_old+1 is the next higher rate after the current rate, and

R_old-1 is the next lower rate after the current rate.

Probability P corresponding to different rate index and RAB values_iShown in the table below. When the access terminal begins to calculate a new data rate, it is transmitting at the current rate. The access terminal will also receive a current RAB from the access network with which it is communicating. Current rate determination probability P_iFrom which row it gets. Current RAB determination probability P_iFrom which column it is derived.

In one embodiment, the probabilities are fixed and preprogrammed into the access terminal. In another embodiment, the probability values may be calculated by the access network and then downloaded to the access terminal.

TABLE 1

Rate labeling	Probability of
			RAB＝0	RAB＝1
	0	1			0
1			P1	0
	2	P2			P5
3			P3	P6
	4	P4			P7
5			0	P8

Each value listed in the table represents the probability that an access terminal with a corresponding rate index and RAB value will change to the next rate index. The value in the column under "RAB 0" is the probability that the access terminal will increase to the next higher rate index when RAB 0. The value of 1 corresponding to rate index 0 and RAB-0 is because the access terminal is always allowed to rise from rate index 0 to rate index 1. To pairThe value of 0, which should be the case for rate index 5 and RAB-0, is because the access terminal cannot rise from rate index 5. Probability value P₁-P₄Varying from 0 to 1.

The values in the column below RAB 1 are the probability that the access terminal will decrease to the next lower rate index when RAB 1. The value of 0 corresponding to rate index 0 and RAB 1 is because the access terminal cannot drop from rate index 0. The value of 0 corresponding to rate index 1 and RAB ═ 1 is because the access terminal is never forced to fall from the lowest non-zero rate. Probability value P₅-P₈Varying from 0 to 1.

Calculating R in this way₄The effect of (a) is to allow R when the system is not busy (RAB 0)₄Increase in a controlled manner and force it to decrease in a controlled manner also when the system is busy (RAB 1). In other words, it results in R₄Ramp up, rather than simply rise abruptly, and cause it to ramp down rather than fall abruptly. The ramp up/down is controlled by the probabilities of table 1.

However, according to various aspects of the present invention, R₄The determination of (b) may take into account the filtered value of RAB as well as the current value of RAB. Even in relatively fully loaded sectors, the RAB may typically be reset (0) from time to time, and vice versa. In this case, the RAB is not set to 1 and is more likely to be reset (0) due to fluctuations in signal and interference levels. The relative time that the RAB is 1 versus the time that the RAB is 0 is an indication of sector loading and can be directly measured by each AT. The value of the filtered RAB reflects the sector load and is used in accordance with various aspects of the invention to determine the optimal rate. If RAB is reset, indicating not busy, and the sector is heavily loaded, R₄Should be conservative, preventing the transition of R₄A large probability and/or number of steps to transition from a low data rate to a high data rate. Although the access terminal cannot get any direct information about sector loading, according to various aspects of the invention, the indication of sector loading may be estimated by using the filtered RAB from previously received values. If only the current value of RAB is used, when the transition probability is set to 1, at R₄Is most likely in the rate determination algorithmThe allowed operation is a sudden jump from one rate to the next higher rate. However, in some applications, it may be necessary for an access terminal to increase its R in multiple stages in a frame₄Rate to reduce latency, thereby allowing R₄The "fast start" of the value. According to various aspects of the invention, the access terminal may "adapt" R as indicated by the filtered value of RAB₄The rate determination is aggressive to accommodate sector loading. According to various aspects of the invention, R₄May transition from a certain data rate to a higher data rate one or more times.

Rate R₁-R₄Is determined for each frame and then used for the data rate R of the next frame_newIs set to the minimum of these rates. Consider a video conferencing application that produces an average of 60kbps of data. The data comprises 500-1000 byte size packets that arrive at the transmit queue at 70-80 millisecond intervals. If there was no data in the queue (and the transmit data rate was 0) it would start to rise from rate index 0(0kbps) to rate index 1(9.6kbps) in one frame (approximately 27 milliseconds in one embodiment). Depending on the particular probability of access terminal usage, it may again use some frames to ramp up from rate index 1 to rate index 2(19.2kbps), and so on. Until the transmit data rate exceeds the arrival rate of 60kbps, data continues to accumulate in the queue.

Hypothesis for calculating R₄The probability of (d) allows the rate index to be increased by one step, on average, every two frames, requiring the expected six frames (160 milliseconds) to transmit the first 500 byte packet. At the same time, the data that has accumulated after this packet continues to be delayed. Although the data transfer rate will eventually catch up with the data arrival rate, there will be a significant delay in the transfer of at least a portion of the data. In applications such as video conferencing, these delays are unacceptable. It should also be noted that in this embodiment, the data transfer rate will eventually exceed the arrival rate and the amount of data in the queue will begin to drop. If the queue length drops to 0, R₃Will also drop to 0 and the ramp-up process will have to end, again resulting in a transmission delay.

In accordance with aspects of the present invention, to avoid the initial delay caused by a continuous increase in data rate and the subsequent need to ramp up the data rate, one embodiment of the present system uses a filtered RAB to allow a more aggressive or less aggressive determination of R₄The operation of (2). For determining R₄Some (N) threshold values T_iIs defined, where 1 ≦ i ≦ N, 0 < T₁＜T₂＜...＜T_NIs less than 1. N +1 for determining R corresponding to these thresholds₄The operating mode of (1). The difference between these modes is in the transition probability matrix and the determination of R₄Allowed maximum rate conversion step. May be based on the filtered RAB (f)_RAB) Selects the mode of operation. The value of RAB may be input to a digital filter having a fixed or variable time constant. The values of RAB received over a period of time corresponding to the filtering time constant are accumulated. For determining R₄Can be based on f_RABThe value of (c). If m is_iIndicating a mode of operation, which may be based on a threshold T_iComparative f_RABIs selected. For example, as shown in FIG. 5, according to various aspects of the present invention, for determining the calculated R₄The algorithm of the operation mode is displayed. As shown in fig. 3, the received RAB values are accumulated in a filter in the AT. The processor 42 may include a memory unit for implementing the filtering. The algorithm as shown in fig. 5 can be described as follows:

if 0. ltoreq. f_RAB＜T₁At m₁Selecting RLMac;

if T is_i-1≤f_RAB＜T_iAt m_iSelecting RLMac, wherein i is more than or equal to 2 and less than N;

if T is_N≤f_RAB< 1, in m_N+1RLMac is selected. More aggressive modes of operation may be used for f_RABLower values of (a). For example, mode m₁May be such that R is allowed₄The value is multilevel converted from one data rate to the most aggressive mode of another data rate between successive frames. In addition, for R₄Up data rate conversionA high probability may correspond to a lower f_RABValue, meaning that the AT can increase its transmission rate with a higher probability when the RAB is not set and enough data is available. The down-conversion probability may also be lower so that the AT reduces its transmission rate with less likelihood when the RAB is set.

In one embodiment, there may be a total of 2 thresholds (N ═ 2) and 3 modes. Modes 2 and 3 may allow rate up-conversion one stage at a time, and mode m₁The most aggressive of the three modes allows immediate up-conversion from the lowest rate to the specified rate. For example, if mode m is selected₁If the last RAB is not set (sector not busy) and enough data is available, the AT may be allowed to immediately transition the ramp-up rate from 0kbps to 38.4kbps or 19.2 kbps. In another embodiment, if mode m is selected₁The last RAB is not set (sector not busy) and enough data is available, the AT can be allowed to immediately ramp up the rate to either 76.8kbps or 153.6kbps from any rate.

In some applications, access terminals may run certain applications that only require them to send data sporadically and are idle (not sending any data) at other times. For these access terminals, it is desirable to have the rate transition quickly to a higher rate so that they can finish transmitting bursts of data and then remain idle until the next burst of data arrives. Thus, various aspects of the invention can be used with a variety of R₄A mode of rate determination, wherein the selected mode is based on the filtered value of the RAB. For access terminals that are in idle periods for long periods, the algorithm shown in fig. 6 may be used to select for R₄A mode of computation. The main difference between the algorithms shown in fig. 5 and 6 is the data bits input to the RAB filter. The RAB values received from the access point may be input to the filter if the access terminal is transmitting data. The RAB filter may be input with the RAB value set to "0" if the access terminal is not transmitting any data. The output of the filter is used to determine the mode of operation. In this case, an access terminal in idle mode may be allowed to have a means for calculating R once new data arrives₄The active mode of (2). In practice, this assumesThe sector is not loaded allowing the AT to be more aggressive in the ramp up of the rate as data becomes available. Since data arrival events at idle access terminals are generally uncorrelated, such sporadic aggressive operation can be controlled to maintain stable operation.

While the foregoing description has primarily been directed to embodiments of the invention that include various methods, it should be noted that other embodiments are possible. For example, one embodiment may include an access terminal configured to limit the drop in the feasible data rate, as described above. This embodiment may include a processor coupled to the transmit subsystem. The processor in one such embodiment is configured to calculate the data rate for the reverse link on a frame-by-frame basis using threshold values, probability data, fading factor data, and the like stored in a memory coupled thereto. The processor then provides control information including the calculated data rate to a transmit subsystem that transmits the queued data to the access network. It should be noted that the elements of the access terminal may vary from one embodiment to another.

Another embodiment may include an access terminal configured to cause a ramp-up limit rate to increase rapidly as described above. This embodiment may include a processor coupled to the transmit subsystem. The processor in one such embodiment is configured to calculate the data rate for the reverse link on a frame-by-frame basis using thresholds, probability data, historical data rate information, and similar parameters stored in a memory coupled thereto. The processor then provides control information including the calculated data rate to a transmit subsystem that transmits the queued data to the access network. Moreover, the elements of an access terminal may vary from one such embodiment to another.

Yet another embodiment may include a software application. The software application in this embodiment may be configured to receive information regarding the amount of queued data to be transmitted, the interference level in the system (e.g., via the RAB), threshold data, probability data, fading factor data, and various other data, and calculate a limited reduced data rate to be transmitted from the access terminal. In another embodiment, the software application may be configured to receive information regarding whether the communication system is busy, the probability that the data rate will increase or decrease, historical data rate information, and the like, and calculate a rapidly increasing data rate for data to be transmitted from the access terminal to the access network. The software application may be embodied on any computer-readable medium or other data processor, such as a floppy disk, hard drive, CD-ROM, DVD-ROM, RAM, or ROM, to name a few.

Benefits and advantages that may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. The terms "comprises," "comprising," or any other variation thereof, as used herein, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Thus, other embodiments, systems, or methods that include a set of elements are not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiments.

While the invention has been described with reference to specific embodiments, it should be understood that these embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. These variations, modifications, additions and improvements fall within the scope of the invention as described in the claims that follow.

Claims (11)

1. A method for determining a data rate for a reverse link communication of an access terminal, comprising:

receiving a reverse activity bit from an access point in a communication system;

passing the reverse activity bits to a digital filter to produce filtered reverse activity bits;

determining the data rate based on the filtered reverse activity bits.

2. The method of claim 1, further comprising:

comparing the filtered reverse activity bit to a threshold;

determining a mode of reverse link data rate determination based on the comparison, wherein the mode defines a set of criteria for increasing or decreasing the aggressiveness of the reverse link communication data rate;

correlating said filtered reverse activity bits to determine said data rate based on said pattern determined for a reverse link data rate.

3. The method of claim 1, further comprising:

determining whether the access terminal is in an idle mode;

passing a non-busy status value of the reverse activity bit to the digital filter when the access terminal is in the idle mode.

4. An apparatus for determining a data rate for a reverse link communication of an access terminal, comprising:

means for receiving a reverse activity bit from an access point in a communication system;

means for passing the reverse activity bits to a digital filter to produce filtered reverse activity bits;

means for determining the data rate based on the filtered reverse activity bits.

5. The apparatus of claim 4, further comprising:

means for comparing the filtered reverse activity bit to a threshold;

means for determining a mode of reverse link data rate determination based on the comparison, wherein the mode defines a set of criteria for how aggressively the reverse link communication data rate is to be increased or decreased;

means for correlating said filtered reverse activity bits to determine said data rate based on said pattern of reverse link data rate determinations.

6. The apparatus of claim 4, further comprising:

means for determining whether the access terminal is in an idle mode;

means for passing a non-busy status value of the reverse activity bit to the digital filter when the access terminal is in the idle mode.

7. An apparatus for determining a data rate for a reverse link communication of an access terminal, comprising:

a receiver for receiving reverse activity bits from an access point in a communication system;

a processor for passing the reverse activity bits to a digital filter to produce filtered reverse activity bits for determining the data rate based on the filtered reverse activity bits.

8. The apparatus of claim 7, further comprising:

the processor includes instructions for comparing the filtered reverse activity bits to a threshold, instructions for determining a pattern of reverse link data rate determinations based on the comparison, wherein the pattern defines a set of criteria for increasing or decreasing the aggressiveness of the reverse link communication data rate, and instructions for correlating the data rate determined based on the filtered reverse activity bits according to the pattern of reverse link data rate determinations.

9. The apparatus of claim 7, further comprising:

the processor includes instructions for determining whether the access terminal is in an idle mode;

the processor is further configured to pass a non-busy status value of the reverse activity bit to the digital filter when the access terminal is in the idle mode.

10. A method for determining a data rate for a reverse link communication of an access terminal, comprising:

receiving a reverse activity bit from an access point in a communication system;

passing the reverse activity bits to a digital filter to produce filtered reverse activity bits;

determining whether the access terminal is in an idle mode;

passing a non-busy status value of the reverse activity bit to the digital filter when the access terminal is in the idle mode;

comparing the filtered reverse activity bit to a threshold;

determining a mode of reverse link data rate determination based on the comparison, wherein the mode defines a set of criteria for increasing or decreasing the aggressiveness of the reverse link communication data rate;

determining the data rate based on the filtered reverse activity bits according to the mode determined by the reverse link data rate.

11. An apparatus for determining a data rate for a reverse link communication of an access terminal, comprising:

means for receiving a reverse activity bit from an access point in a communication system;

means for passing the reverse activity bits to a digital filter to produce filtered reverse activity bits;

means for determining whether the access terminal is in an idle mode;

means for passing a non-busy status value of the reverse activity bit to the digital filter when the access terminal is in the idle mode;

means for comparing the filtered reverse activity bit to a threshold;

means for determining a mode of reverse link data rate determination based on the comparison, wherein the mode defines a set of criteria for how aggressively the reverse link communication data rate is to be increased or decreased;

means for determining a reverse link data rate based on the filtered reverse activity bits according to the mode determined by the data rate.