BACKGROUND OF THE INVENTION
1. Technical Field:
The present invention generally relates to mobik telecommunications, and in particular to a meAod and system for adaptively adjusting the downlink transmission rate to a mobile access tenninal. More particularly, the present invention relates to a method and system that compensates for channel fading by periodically adjusting fiie downlink transmission rate in accordance witfi on-going packet error rate analysis.
2. Description of the Related Art:
Mobile wireless access to the Internet and other communications networks is under rapid development. The development of mobile data communications capability is due to, and is modeled to some extent in light of, the success and advantages provided by the advent and development of mobile wireless telecommunications for voice communications. Several new air interface standards have been or are being developed to enable high speed wireless access to the Internet. These standards use fast feedback from a mobile tenninal regarding chamiel conditions, which enable the downlink data rate to be quickly changed to compensate for signal fading. The technology used in these standards is generally known as high data rate (HDR) technology. One of these standards is referred to as IxEV-DO, which has evolved into tfie industry standard IS-856.
HDR technology is typically implemented utilizing a combination of Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) technologies, In CDMA, all users transmit simultaneously over tiie entire allocated bandwidth utilizing speciaHzed spreading codes. In TDMA, users take
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turns accessing the channel utilizing multiple time slots that are allocated for transmission over a given channel bandwiddi. In this manner, TDMA enables a single frequency to support allocation of multiple, simultaneous data channels to access tenninals. As utilized herein, an access terminal is a mobile device such as a laptop computer, palm-pilot, etc., with the appropriate attachments that utilizes an air-interface to communicate with other terminals or network nodes via an access node, which is the aii-interface network poim-of-contact for any sending or receiving mobile terminal.
Existing HDR standards generally define two groups of channels, the forward channel (referred to hereinafter as the downlink channel) and the reverse channel (refened to hereinaflec as the uplink channel). The downlink clrannel, which communicates voice and data from the access node to mobile access tenninals, carries traffic, a pilot signal, and overhead information. The pilot and overhead channels establish system timing and station identity. The uplink channel, which communicates voice and data from the access terminal to the access node, carries both traffic and signaling.
Unlike voice or two-way multi-media sessions, "data" sessions (e.g. Internet file downloads) are highly asyrrmietrical, with the downlink (i.e. fte charmel information transmitted from the access node to the access terminal) capacity being a disproportionately critical parametei:. On the downlink of an HDR system, data may be transmitted in a time division multiplexed manner. The downlink capacity in HDR systems is measured, at least in part, in terms of the data rate allocated to the access terminal. In HDR implementations, interference caused by signals from other cells is a determinative factor in the allocation of a parhcular data rate to a given access temiinal. Excessive signal interference can cause a failure in decoding a packet delivered from the access node to the access terminal. Such a failure results in the need to re-transmit the packet, resulting in a diminished data transmission efficiency. Therefore, downlink data rate selection is a key parameter in maintaining the efficiency of a given HDR channel.

The various 3GPP and 3GPP2 HPR standards, which use time division multiplexing of the downlink (HSDPA and IxEV-DO, for example), require methods for determining the appropriate data rate allocated to an access terminal downlink. Generally, this requires that the access terminal perform a measuiement of tiie current chamiel conditions in terms of ftie signal-to-interference-plus-noise ratio (SINK), which is a ratio of the energy-per-chip interval (Ec) of the allocated channel to die outside spectral interference plus thermal noise (Nt). &i IxEV-DO, once the SINR is measured, the access terminal must update ttie access network with data rate control (DRC) requests fliat map to a set of data rates in bits-per-second (bps). It is the responsibility of the access terminal to select a data rate appropriate to tiie received SINR, such that the resultant packet error rate (PER) falls wifein certain limits specified in the applicable minimum performance standard. In IxEV-DO, the access node subsequently transmits data to the access terminal at the data rate specified by the DRC request Therefore, in IxEV-DO tiie data rate selection function typically resides in the access terminal. Once the access node has received the DRC request and determined that die access terminal should receive a packet, the access node transmits the packet over one or more time slots in accordance with the requested DRC rate.
Channel fading is a major source of channel signal strength fluctuations. So-called "slow fading" is caused by movement of the access terminal with respect to the access node (typically an RF transceiver station) resulting in mterference in the air interface pafli between the access terminal and Access node due to changing physical topology (buildings, power lines, ete.). "Fast fading" is a phenomenon associated with collisions of multiple versions of the transmitted signal that arrive at the receiver at slightly different times and is typically characterized in terms of Doppler Effect and Raylei^ fading factors. HDR technology may compensate for channel fading by adding a built-in constant error margin into the computation of the downlink DRC request such that the data rate requested is a product of a very conservative estimate. Implementation of a downhnk data rate based on such a conservative estimate results in wasted RF

resources and reduced throughput Alternatively, channel fading can be accounted for directly by modelii^ and predicting the chaniKl fading that will occur for a given nomadic access terminal. Companies that provide wireless mobile communications are adopting ray tracing and Doppler Effect tools that attempt to compute flie effects of channel fading in a complicated environment. Such methods present daunting computational objectives which require substantial and costly hardware and software overhead since ttiese meOiods directly or indirectly must account for access terminal speed, access terminal location within a given sector (with respect to an access node), and line-of-sight information betwe«i the access tenninal and flie access node.
It can ttierefore be appreciated ttiat a need exists for an improved approach to compensate for channel fading in the allocation of downlink chaiuiels in a mobile wireless environment. The present invention addresses such a need.

A method and system applicable within a mobile transmission system for adaptively allocating a downlink data rate to an access terminal to compensate for channel fading are disclosed herein. In accordance with the method of the present invention a downlink data rate is selected in accordance with a determined highest throu^put, wherein the downlink data rate is associated with a specified signal-to-noise threshold to achieve a specified packet error rate. Next, a packet is transmitted to an access «;nninal at the selected downlink data rate. In response to successfully decoding the packet at the access terminal, the signal-to-noise Qireshold specified for Qie selected downlmk data rate is decreased such that subsequent data rate selections are adaptively maximized. Responsive to a packet decoding error, the signal-to-noise threshold is abruptly increased to maintain the specified packet error rate. Such a method enables maximization of data throughput while observing a specified packet error rate.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description,

The novel features believed characteristic of flie invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, furrier objects ^nd advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
Figure 1 depicts an illustrative embodiment of a wireless communication network with which the method and system of the present invention may advantageously be utilized;
Figure 2 is s high-level block diagram of a mobile access terminal that may be utilized in implementing tiie present invention;
Figure 3 illustrates an exemplary data rate control table consisting of multiple data rate control sets that are selected and dynamically adjusted in accordance with the present invention; and
Figure 4 is a flow diagram depicting steps performed during adaptive allocation of a downlink data rate in accordance with a preferred embodiment of the present invention.

This invention is described in a preferred embodiment in the following description with reference to the figures. While this invention is described in terms of the best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the scope of the present invention. Although, the present invention will be described herein in terms of a particular system and particular components, one of ordinary skill in the art will readily recognize that fliis mefliod and system will operate effectively for other components in a data processing system.
Referring now to the drawings and in particular to Figure 1, there is depicted a high-level diagram of a wireless communication network 10 in which a preferred embodiment of the present invention may advantageously be implemented. Wireless communication network 10 preferably employs a mobile air-interface digital protocol such as IxEV-DO. As shown, wireless communication network 10 includes a packet data serving node (PDSN) 6 that supports various packet data session functions for a multiple-access technology such as IxEV-DO, as well as connectivity to a packet switched data network (PSDN) 5, an example of which in the Internet.
Coupled to PDSN 6 is a base station controller (BSC) 4 that generally comprises signal processing resources 7, which may be implemented as one or more mid-range computer systems, and a system parameters database 9. BSC 4 controls die operation of multiple base transceiver stations, referred to herein generically as access nodes 2a-2o distributed at various locations within wireless communication network 10 in accordance with the system parameters stored in system parameters database 9. Within the service area of wireless communication network 10, there are also several mobile stations (referred to hereinafter as mobile access terminals) such as mobile access terminals 8a, 8b, 8c, 8d and 8e, which transmit and receive calls, pages, data and control messages over-flie-air
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with access nodes 2a-2n. Although the present invention is described below with reference to mobile access terminals 8, those skilled in the art will appreciate from the following description that the present invention is also applicable to wireless local loop (WLL) implementations in which the subscriber units are generally fixed in a residence or business premises.
Referring to Figure 2, ibeie is illustrated a high-level block diagram of a mobile access terminal 8 or other subscriber unit tiiat may be utilized to implement the downlink data rate control mefliod of the present invention. Mobile access terminal 8 includes a controller 14 that generally includes a processor 16 and a memory 20. Processor 16 executes a control program stored within memory 20 to implement die subscriber unit side of the downlink data rate control method employed by wireless communication netwodc 10. Mobile access terminal 8 also has a keypad 18 by which the subscriber can enter keyed inputs, and a display 12 through which controller 14 can visually piesent alphanumeric and graphical ou^uts for viewing by the subscriber. Finally, mobile access terminal 8 includes a radio frequency transceiver 24 for sending (on an uplink chaimel) and receiving (on a downlink channel) wireless signals, including data messages, over-the-air.
Referring back to Figure 1, BSC 4, in conjunction with access nodes 2a-2n, allocates downlink channels, which communicate data from access nodes 2a-2n to mobile access terminals 8a, 8b, 8c, 8d and 8e. Such downlink charmels may carry ti^ffic, a pilot signal, and overhead information. The pilot and overhead channels establish system timing and station identity. Pilot chaimel bursts are ^ically utilized as a signal sOengOx reference that enables mobile access terminal 8 to estimate relevant channel conditions. In accordance with the embodiments depicted by the figures herein, a mobile access terminal may utilize flie pilot burst to resolve the multipath components into an estimate of the signal-to-interference-plus-noise ratio (SINK) in terms of the signal energy (Ec) to RF interference (N,).

Reverse, or "uplink" channels, are utilized to communicate data from mobile access tenninals 8a, 8b, 8c, 8d and 8e to access nodes 2a-2n, and, like the downlink channels, carry both traffic and signaling. After sampling a pilot channel burst from a base transceiver station, the mobile access terminal estimates the current SINR conditions and delivers channel state information in the form of a data rate request to the base transceiver station utilizing an uplink data rate control (DRC) channel.
A recently developed mobile data communications capability for use within mobile network environments, such as wireless communication network 10, is known as high data rate (HDR) service with time division multiplexing coding techniques such as TDMA. Current HDR implementations utilize selectable DRC sets that provide the mobile access terminal with a tabularized selection criteria by which a downlink data rate is selected. In a fading channel environment, the necessary SINR threshold increases (with respect to static Additive Wide Gaussian Noise conditions) to maintained a specilied PER. The present invention provides an efficient means by which a mobile access terminal can effectively map ttie received SINR measurement to a DRC rate option in a manner that maximizes allocated downlink bandwidtii while maintaining the requisite PER in a fading chaimel environment.
As explained in further detail with reference to Figures 3 and 4, the method and system of the present invention are applicable within mobile communication system 10 and mobile access terminal 8 to provide a means for efficiently allocating and dynamically adjusting a downlink data rate in view of periodic SINR estimates performed by mobile access terminal 8. In particular, the present invention is directed to improving downlink channel bandwidth allocation for high speed packet-based data transmission in a mobile environment such as that depicted in Figure 1.
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Wifli reference to Figure 3, there is illustrated an exemplary data rate control table consisting of multiple data rate control sets that are selected and dynamically adjusted in accordance with the present invention. Specifically, a DRC table 30 is depicted which includes twelve selectable DRC sets. As shown in Figure 3, each DRC set includes a specified data rate (in kbps) associated with a particular SINR, expressed as an Ec/Nt threshold, fliat is required to achieve a specified packet error rate (PER) of 1% for AWGN channel conditions. For example, ttie lowest selectable data rate (38.4 kbps) within DRC table 30 is associated with the lowest Ec/N, threshold (-13.5 dB) within a discrete DRC set 32 to meet the 1% PER requirement Modulation scheme and number of time slots are also included as metric guidelines and limitations within M«:h DRC set. The inclusion of time slot specification within DRC table 30 is a reflection of the nature of current HDR implementations in which the HDR downlink transmissions are time-multiplexed. Although the depicted DRC sets include slot number and modulation scheme metrics, it should be borne in mind that the present invention can be implemented in a much simpler tabular association between only selectable data rates and Ej/Ni thresholds. It should be further noted that the particular values depicted in DRC table 30 correspond to static AWGN channel conditions (as set in initializing a channel, for example). As explained in further detail herein below, the present invention enables optimum selection and adaptive adjustment of the direshold data sets within a DRC table such as DRC table 30.
DRC table 30 may be utilized in downlink data rate allocation as part of a standardized DRC mechanism. One such mechanism, IxEV-DO, is a newly developing wireless standard based on HDR technology and is optimized for wireless Internet services. In accordance with current HDR/DRC technology, an access terminal selects fi-om among the available data rates widiin DRC table 30 by comparing measured chaiuiel conditions to the Ec/N| flireshold values provided in DRC table 30 and selecting one of flie DRC sets accordingly. Alftiough DRC table 30 may typically be included witfiin memory 20 of mobile access terminal 8, it is possible to maintain the DRC table within access nodes 2a-2n or BSC 4, The
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methods by which the DRC sets are selected and dynamically adjusted are described in further detail with reference to Figures 4 below.
Wifli reference now to Figure 4, there is depicted a flow diagram illustrating steps performed by processor 16 contained within mobile access terminal 8 and/or signal processing resources 7, during adaptive allocation of a downlink data rate in accordance with a preferred embodiment of the present invention. The downlink data rate allocation process begins as shown at step 40, and proceeds to step 42 with a determination of whether a downlink traffic channel has been allocated by BSC 4 to mobile access terminal 8 via access node 2. After a traffic channel is allocated, initialization is preformed, setting default througl^ut and threshold values as depicted at step 43. As illustrated at steps 44 and 46, while a downlink traffic channel is allocated, a periodic SINR estimate is performed by mobile access terminal 8 at a specified interval, AtoRc. This estimate is followed by a DRC request that is formulated in accordance with the remaining steps in the process.
Although not expressly depicted in Figure 4, the values within each of the DRC sets within DRC table 30 are initialized to pre-specified values (static AWGN, for example). TTie data rate control mechanism described with lefercnce to Figure 4 enables a mobile access terminal to select among the DRC sets within a DRC table, and fiirthermore to adaptively adjust DRC set parameters to account for changing channel conditions such as channel fading wifliout unduly limiting the allocated downlink bandwidth.
Before explaining the process of a preferred embodiment as depicted in Figure 4, the concept of maximum throughput is discussed. On the forward link of IxEV-DO the throughput experienced by a smgle user can be expressed as:
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transmitted the process continues to step 44. Otherwise, the process advances to step 54.
During each DRC interval, packets are transmitted (determined at step 53) on the allocated downlink air-channel in accordance with the values specified in the selected DRC set as depicted at step 54. Afterwards, the k and / values for determining the throughput for the current DRC option are determined as illustrated at step 48. Following the determination of k and /, access terminal 8 updates the effective throughput as depicted at step 50. Hie effective ftroughput may he calculated as r = k/l. As illustrated at steps 56,58, and 60, in the case of an unsuccessful packet transmission (i.e. mobile access terminal 8 is unable to successfully decode the packet), the tfireshold for ttie current DRC option (Tj) is increased by the amount Aiocai and the threshold for all DRC data rates (Tj) is increased by the amount Agiotui. Conversely, as depicted at steps 56, 62, and 64, for each packet that is successfully transmitted to mobile access terminal 8, the SINR thresholds specified within DRC table 30 are decreased to maximize the available data rate bandwidth while maintaining the specified PER undet fading channel conditions. The threshold for the current DRC option (T,) is decreased by ttie amount PERjet * AIQ«I. and tiie threshold for all DRC data rates (Ti) is decreased by the amount PERjet * Agiobai-
The selection of a particular DRC set (performed in accordance with steps 44, 46, 48, 50, and 52), the transmission of packets (step 54), and the subsequent SINR threshold adjustments continue until the downlink traffic chaimet is deallocated at step 66, terminating the process as shown at step 68. It should be noted that although flie SINR thresholds are adjusted during a given data session, the initial values (such as those depicted in Figure 3) are maintained in memory and restored as initialization values upon a subsequent channel allocation to mobile access terminal 8.
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A method and system have been disclosed for adaptively selecting and adjusting date rate control parameters within a mobile data transfer system. Software written according to the present invention is to be stored in some fonn of computer-readable medium, such as memory, CD-ROM or transmitted over a network, and executed by a processor. Alternatively, some or all of the present invention could be implemented in hardware. Additionally, while the present invention has been described in conjunction with the IxEV-DO standard, it is equally applicable to the IxEV-DV and HSPDA standards. Further, one of ordinary skill in flie art will readily understand that the present invention may be implemented on an access node or access terminal.
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of die appended claims.
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WE CLAIM:
1. A method applicable within a mobile communication system for adaptively
allocating a downlink data rate to a mobile access terminal to compensate for
channel fading, said method comprising:
selecting, by the mobile access terminal, a downlink data rate in accordance with a determined signal-to-noise level, wherein said downlink data rate is associated with a specified signal-to-noise threshold value to achieve a specified packet error rate;
receiving a packet by the mobile access terminal at said selected downlink data rate; and
responsive to successfully decoding said packet, the mobile access terminal decreasing the signal-to-noise threshold value specified for said selected downlink data rate by:
computing an decreased signal-to-noise threshold value specified for
said selected downlink data rate in accordance with the relation:
T-Tj-(PER* A|o,,|)
wherein T represents the decreased signal-to-noise threshold value associated with the selected downlink data rate, Tj represents the current signal-to-noise threshold value associated with the selected downlink data rate. PER represents said specified packet error rate, and represents a local data rate
control delta value.
2. The method as claimed in claim 1, wherein said determined signal-to-noise
level at said mobile access terminal is a ratio of the signal strength of an allocated
access terminal channel to the combined external signal strength.
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3. The method as claimed in claim 1, wherein said selecting a downlink data rate is preceded by determining a signal-to-noise level at said mobile access terminal.
4. The method as claimed in claim 1, wherein said selecting a downlink data rate comprises:
comparing said determined signal-to-noise level with a plurality of signai-to-noise threshold values, wherein each of said plurality of signal-to-noise threshold values is associated with a downlink data rate; and
selecting a highest downlink data rate corresponding to one of said plurality of signal-to-noise threshold values that does not exceed said determined signal-to-noise level.
5. The method as claimed in claim 4, wherein said mobile communication
system comprises selectable data rate control sets in which each of said plurality
of signal-to-noise threshold values is associated with a corresponding downlink
data rate for said specified packet error rate, and wherein two or more of said
plurality of signal-to-noise threshold values that do not exceed said determined
signal-to-noise level are associated with said highest downlink data rate, said
method comprising:
comparing the relative values of said two or more signal-to-noise threshold values; and
selecting a data rate control set corresponding to the lowest among said two or more signal-to-noise threshold values.
6. The method as claimed in claim 1, comprising:
responsive to unsuccessfully decoding said packet, increasing the signal-to-noise threshold value specified for said selected downlink data rate.
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7. The method as claimed in claim 6, wherein said increasing the signal-lo-
noise threshold value specified for said selected downlink data rate comprises:
computing an increased signal-to-noise threshold value specified for said selected downlink data rate in accordance with the relation;
T = Tj - A local
wherein T represents the increased signal-to-noise threshold associated with the selected downlink data rate, Tj represents the current signal-to-noise threshold value associated with the selected downlink data rate, and Ai„cai represents a local data rate control deha value.
8. The method as claimed in claim 7, wherein said mobile communication
system comprises selectable data rate control sets in which each of a plurality of
signal-to-noise threshold values is associated with a corresponding downlink data
rate for said specified packet error rate, said method comprising:
responsive to unsuccessfully decoding said packet, increasing each of said plurality of signal-to-noise threshold values in accordance with the relation:
T ^ Tj - A global
wherein T represents the increased value for the i'** signal-to-noise threshold value among said plurality of signal-to-noise threshold values, Tj represents current value for the i'*" signal-to-noise threshold value among said plurality of signal-to-noise threshold values, PER represents said specified packet error rate, and A gjobai represents a global data rate control delta value.
9. The method as claimed in claim 1, wherein said mobile communicarion
system comprises selectable data rate control sets in which each of a plurality of
signal-to-noise threshold values is associated with a corresponding downlink data
rate for said specified packet error rate, said method comprising:
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responsive to successfijlly decoding said packet, decreasing each of said plurality of signal-to-noise threshold values in accordance with the relation:
T = Ti-(PER* Ag„bai)
wherein T represents the decreased signal-to-noise threshold, Tj represents the i^'' signal-to-noise threshold value among said plurality of signal-to-noise threshold values, PER represents said specified packet error rate, and Agiobai represents a global data rate control delta value.
10. A mobile communication system for adaptively allocating a downlink data rate to an access terminal to compensate for channel fading, said mobile communication system comprising:
processing means for selecting a downlink data rate in accordance with a determined signal-to-noise level, wherein said downlink data rate is associated with a specified signal-to-noise threshold value to achieve a specified packet error rate;
air-interface transmission means for transmitting a packet to an access terminal at said selected downlink data rate;
processing means responsive to successfiiUy decoding said packet for decreasing the signal-to-noise threshold value specified for said selected downlink data rate; and
processing means responsive to unsuccessfully decoding said packet for increasing the signal-to-noise threshold value specified for said selected downlink data rate, comprising;
means for computing an increased signal-to-noise threshold value specified for said selected downlink data rate in accordance with the relation:
T = Tj + A local
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wherein T represents the increased signal-to-noise threshold associated with the selected downlink data rate, Tj represents the current signal-to-noise threshold value associated with the selected downlink data rate, and Aiocai represents a local data rate control delta value.
11. The mobile communication system as claimed in claim 10, wherein said determined signal-to-noise level at said access terminal is a ratio of the signal strength of a pilot channel to the combined external signal strength.
12. The mobile communication system as claimed in claim 10 comprising signal detection and processing means for determining a signal-to-noise level at said access terminal.
13. The mobile communication system as claimed in claim 10, wherein said processing means for selecting a downlink data rate comprises:
processing means for comparing said determined signal-to-noise level with a plurality of signal-to-noise threshold values, wherein each of said plurality of signal-to-noise threshold values is associated with a downlink data rate; and
processing means for selecting a highest downlink data rate corresponding to one of said plurality of signal-to-noise threshold values that does not exceed said determined signal-to-noise level.
14. The mobile communication system as claimed in claim 13, comprising
memory containing selectable data rate control sets in which each of said plurality
of signal-to-noise threshold values is associated with a corresponding downlink
data rate for said specified packet error rate, and wherein two or more of said
plurality of signal-to-noise threshold values that do not exceed said determined
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signal-to-noise level are associated with said highest downlink data rate, said mobile communication system comprising:
processing means for comparing the relative values of said two or more signal-to-noise threshold values; and
processing means for selecting a data rate control set corresponding to the lowest among said two or more signal-to-noise threshold values.
15. The mobile communication system as claimed in claim 10, comprising
memory containing selectable data rate control sets in which each of a plurality of
signal-to-noise threshold values is associated with a corresponding downlink data
rate for said specified packet error rate, said mobile communication system
comprising
processing means for responsive to unsuccessfully decoding said packet for increasing each of said plurality of signal-to-noise threshold values in accordance with the relation:
T = Ti + A global
wherein T represents the increased value for the i signal-to-noise threshold value among said plurality of signal-to-noise threshold values, T] represents current value for the i* signal-to-noise threshold value among said plurality of signal-to-noise threshold values, PER represents said specified packet error rate, and A global represents a global data rate control deha value.
16. The mobile communication system as claimed in claim 10, wherein said
processing means for decreasing the signal-to-noise threshold value specified for
said selected downlink data rate comprises:
means for computing a decreased signal-to-noise threshold value specified for said selected downlink data rate in accordance with the relation:
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wherein T represents the decreased signal-to-noise threshold value associated with the selected downlink data rate, Tj represents the current signal-to-noise threshold value associated with the selected downlink data rate, PER represents said specified packet error rate, and represents a local data rate
control delta value.
17. The mobile communication system as claimed in claim 16, comprising memory for storing selectable data rate control sets in which each of a plurality of signal-to-noise threshold values is associated with a corresponding downUnk data rate for said specified packet error rate, said mobile communication system comprising:
processing means responsive to successfully decoding said packet for decreasing each of said plurality of signal-to-noise threshold values in accordance with the relation:
T-Tj -(PER* Ag„i,ai)
wherein T represents the decreased signal-to-noise threshold value associated with the selected downlink data rate, Tj represents the current signal-lo-noise threshold value associated with the selected downlink data rate, PER represents said specified packet error rate, and A global represents a local data rate control delta value.
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