Apparatus and method for a coding scheme selection

Field of the disclosure

0001This disclosure relates generally to wireless communication networks, and more particularly to a method and apparatus for coding scheme selection in a packet radio system.

Background

0002In wireless networks employing General Packet Radio Service (GPRS), a coding scheme for data message transmissions is selected by rules embedded in a fixed network and in a mobile station that are designed to result in the highest data throughput with the fewest possible retransmissions. GPRS is an extension of circuit-switched networks and data transmission services that uses packet radio transmissions to carry data messages using protocols such as Internet Protocol (IP) or X.25 information from mobiles to the network and visa versa, in data blocks, or packets. GPRS is an extension to the circuit-switched Global System for Mobile communications (GSM), having four different coding schemes with effective data rates of 9.05, 13.4, 15.6 and 21.4 kilobits per second (code rates 1/2, 2/3, 3/4 and 1) within the data blocks.

0003Some GPRS-enabled fixed networks can send a command to a mobile station, such as a cell phone, an Internet-enabled mobile phone or a personal digital assistant, to transmit data blocks using a selected one of the four coding scheme. The error rate of the selected coding scheme may rapidly degrade, however, with changing radio conditions or geographical movements of the mobile device. The mobile unit may have limitations in its coding capabilities and its ability to adapt to coding scheme commands. With the move toward third-generation network standards, there are even more possible problems with high-performance networks that use a wider variety of coding schemes. Mobile stations need to adapt their coding schemes rapidly during a data message when possible, and the fixed network needs to recognize mobile stations that are unable to use certain coding schemes, in order to use a best possible coding scheme and avoid undue retransmissions when a coding scheme is selected that cannot be accommodated by a mobile station.

0004Current GPRS fixed networks use dynamic link adaptation methods that monitor the quality of packet transfers and select one of the four presently defined channel coding schemes (also referred to herein simply as "coding schemes") based on changing radio conditions. As technologies and protocols emerge and evolve for wireless data transmissions, additional coding schemes will become available. For example, GSM networks incorporating Enhanced Data for Global Evolution (EDGE) with packet-switched enhancements for GPRS have nine additional coding schemes for increased performance. Other wireless network technologies such as GSM/EDGE Radio Access Network (GERAN) and Universal Mobile Telecommunications System (UMTS) provide enhanced coding schemes, requiring network algorithms that can determine the coding scheme adaptability of the mobile station and direct coding scheme commands to the mobile station based on the adaptability. When mobile stations do not respond to all of the defined set of four coding schemes, dynamic link adaptation methods in current use result in sub-optimal data throughput, and in some case, can result in no communication capability with certain mobile stations.

0005<patcit id="pcit0001" dnum="US6134230A"><text>US 6,134,230</text></patcit> discloses, an arrangement in which, in a communication system, a link protocol for a transparent data between a mobile station and a base station is selected by pre-selecting from all possible combinations of available link protocols a set of pre-selected combinations of link protocols based on a predefined service requirement and at least one basic capability of the mobile or base stations. Then, the link protocol is selected from the pre-selected combinations of link protocols based on measurements of one or more link quality parameters and at least one variable restriction caused by instantaneous conditions in the communication system.

0006<patcit id="pcit0002" dnum="US6363425B"><text>US 6,363,425</text></patcit> discloses a method and an arrangement for communicating packet information in a digital telecommunications system. A set of designated communication resources (chl-chn) is selected from an available amount of resources. Every packet (P) is forward error correction encoded into an encoded packet (Pci), via one of at least two different coding schemes (ci), prior to being transmitted to a receiving party, over the designated communication resources (chl-chn).

0007<patcit id="pcit0003" dnum="US6400928B"><text>US 6,400,928</text></patcit> discloses a method and system for blind detection of modulation in a wireless telecommunications network. A plurality of bursts are transmitted over an air interface to a receiving station using a first modulation scheme. Modulation detection statistics for the plurality of received bursts are calculated at the receiving station.

Summary of the Invention

0008In a first aspect of the invention, a method is for selecting a coding scheme for use on an uplink channel of a wireless packet data communication system. The coding scheme is one of a set of coding schemes that are useable on the uplink channel. In the method, each state in a set of states of support of a mobile station that correspond to the set of coding schemes is set to be either supported, unsupported, or unknown support. The mobile station is directed to transmit a portion of an uplink data transfer using a first coding scheme of the set of coding schemes. The state of support of the mobile station for the first coding scheme is set to unsupported when the portion of the uplink data transfer is not received having the first coding scheme. A second coding scheme is selected based upon the set of states of support.

0009In a second aspect of the invention, a method is for selecting a coding scheme for use on a downlink channel of a wireless packet data communication system. The coding scheme is one of a set of coding schemes that are useable on the downlink channel. In the method, each state in a set of states of support of a mobile station that correspond to the set of coding schemes is set to be either supported, unsupported, or unknown support. A portion of a downlink data transfer is transmitted to the mobile station using a first coding scheme of the set of coding schemes. The state of support of the mobile station for the first coding scheme is set to unsupported when no acknowledgment to the portion of the downlink data transfer is received. A second coding scheme is selected based upon the set of states of support.

0010In a third aspect of the invention, there is provided a base station subsystem apparatus that selects a coding scheme for use on an downlink channel of a wireless packet data communication system, the coding scheme being one of a set of coding schemes that are useable on the downlink channel, comprising: at least one processing unit controlled by a corresponding at least one set of program instructions that sets each of a set of states of support of a mobile station corresponding to each coding scheme of the set of coding schemes to one of a set of values including supported, unsupported, and unknown support; and at least one transmitter that transmits a portion of a downlink data transfer to the mobile station using a first coding scheme of the set of coding schemes, wherein the at least one processing unit sets the state of support of the mobile station for the first coding scheme to unsupported when no acknowledgment to the portion of the downlink data transfer is received; and selects a second coding scheme based upon the set of states of support.

Brief Description of the Drawings

0011The present invention is illustrated by way of example and not limitation in the accompanying figures, in which like references indicate similar elements, and in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a schematic diagram of one embodiment of a system for determining coding scheme adaptation capability of a mobile station, in accordance with the present invention;</li><li><figref idref="f0002">FIG. 2</figref> is a block diagram of one embodiment of a system for determining coding scheme adaptation capability of a mobile station, in accordance with the present invention;</li><li><figref idref="f0003 f0004 f0005">FIGS. 3-6</figref> are illustrations of four coding schemes used for GPRS, in accordance with the present invention;</li><li><figref idref="f0006">FIG. 7</figref> is a flowchart illustrating a method for selecting a coding scheme for use on an uplink channel of a wireless packet data communication system, in accordance with the present invention;</li><li><figref idref="f0007">FIG. 8</figref> is a flowchart illustrating a method for selecting a coding scheme for use on an uplink channel of a wireless packet data communication system, in accordance with the present invention; and</li><li><figref idref="f0008">FIG. 9</figref> is a flowchart illustrating a method for managing storage space in a wireless packet data communication system that has a set of coding schemes that are useable on the uplink and downlink channels.</li></ul>

0012Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

<u>Detailed Description of the Drawings</u>

0013The present invention provides a method for optimizing the selection of a coding scheme used for data messages to and from a mobile station in a system that includes mobile stations that do not support a subset of a defined set of coding schemes, thereby maximizing data throughput for all mobile stations connected to the network.

0014The method for selecting a coding scheme for a mobile station of the present invention maximizes data throughput for a mobile station connected within a GPRS network even when the mobile station is device that can respond only to lower data rate coding schemes. The invention helps insure that the throughput of data from a lower-performing mobile station is the highest possible.

0015It is anticipated that as third generation networking capacities supersede older two-generation (2G) or 2.5G network technologies, this invention will help the network to remain backward capable with older mobile stations and help optimize the performance of devices not employing the latest radio technologies and protocols. With this invention, throughput of these mobiles stations may be increased as much as 100 percent or more.

0016When the network sends the mobile station a command to change a coding scheme, the mobile station may behave in one of several ways. For example, the mobile station may transmit the next data blocks using the new configuration. It may continue to transmit blocks using the old configuration before blocks with the new configuration are transmitted. It may transmit using a coding scheme other than the one commanded, such as the one it was using.

0017The present invention rapidly determines an optimum coding scheme for a mobile station, even when the mobile station does not respond to a command to change to a coding scheme it does not support.

0018<figref idref="f0001"><b>FIG. 1</b></figref> shows a block diagram of one embodiment of a communication system <b>100,</b> in accordance with a preferred and alternative embodiments of the present invention. The communication system <b>100</b> includes one or more public-switched telephone networks (PSTN) <b>110,</b> an Internet <b>120,</b> one or more mobile switching centers (MSC) <b>130,</b> one or more general packet radio service support nodes (GSN) <b>140,</b> one or more base site controller and packet controller units (BSC/PCU) <b>150,</b> one or more radio tower or base transceiver stations (BTS) <b>160,</b> and one or more wireless mobile stations (MS) <b>180</b> such as a Internet-enabled cellular phone, a personal digital assistant or a laptop computer with wireless networking capabilities.

0019An exemplary network technology that may be used for network operations is Global System for Mobile (GSM) communications, a digital cellular standard used throughout the world. GSM data services include circuit-switched voice services, circuit-switched data, short message services (SMS), 2.5G and third-generation (3G) technologies that expand data-packet technologies and new multimedia types of wireless service. GSM uses three major frequency bands, including blocks of radio spectrum within the 900-, 1800-, and 1900-MHz bands. The 900- and 1800- MHz bands are the principal bands used in Europe and Asia, and the 1900-MHz band is used in North America.

0020With wireless networks employing General Packet Radio Service (GPRS), a mobile station is commanded to transmit data blocks at the optimal coding scheme that the network determines will result in the highest data throughput with the fewest possible retransmissions. For example, GPRS may offer transmissions via a GSM network within a range of 9.6 kilobits to 115 kilobits and allow users to make telephone calls and transmit data at the same time, the latter using an IP data transmission protocol.

0021Another embodiment of the wireless network may include Enhanced Data for Global Evolution (EDGE), which is moving toward wideband code division multiple access (WCDMA). EDGE may be used as a packet-switched enhancement for general packet radio service (GPRS), known as enhanced GPRS or EGPRS, and as a circuit-switched data enhancement called enhanced circuit-switched data (ECSD).

0022Public-switched telephone network (PSTN) <b>110</b> is a land-based telephone network. PSTN <b>110</b> may comprise one or more switched lines over one or a combination of wire, fiber, or wireless links. PSTN <b>110</b> is typically connected to Internet <b>120</b> and MSC <b>130.</b>

0023Internet <b>120</b> is a public data communication network, which may comprise one or more electronic, optical or wireless communication paths with associated hardware and software to connect PSTN <b>110</b> with one or more wireless data devices <b>180.</b>

0024Mobile switching center <b>130</b> may receive signals from and send signals to wireless data device <b>180</b> via a general packet radio service support node (GSN) <b>140,</b> base site controller and packet controller units (BSC/PCU) <b>150,</b> and BTS <b>160.</b> MSC <b>130</b> may contain suitable hardware and software for ensuring that transmissions between wireless data device <b>180</b> and BTS <b>160</b> are accurate and reliable. Accurate and reliable transmission of data packets (blocks) may require that certain data packets be retransmitted, or encoded in a manner such that the data packets are decoded at the receiver without requiring an additional transmission of the data packets. MSC <b>130</b> may communicate with PSTN <b>110.</b>

0025Mobile switching center <b>130</b> may be connected directly to Internet <b>120</b> via GSN <b>140</b> without requiring PSTN <b>110</b> as an intermediary. GSN <b>140</b> works with general packet radio service (GPRS), a packet-mode technique to transfer high-speed and low-speed data and to signal in an efficient manner over GSM radio networks. GPRS may employ GSN <b>140</b> to keep track of the location of wireless data device <b>180</b> and to perform security functions and access control. GSN <b>140,</b> which is at the same hierarchical level as MSC <b>130,</b> may be connected to the system of BTS <b>160</b> with frame relay. GSN <b>140</b> provides interworking with external packet-switched networks such as Internet <b>120,</b> and is connected with GSN <b>140</b> via the IP-based GPRS backbone network. GSN <b>140</b> can help MSC <b>130</b> with more efficient coordination of GPRS and non-GPRS services and functionality.

0026Base site controller and packet controller units (BSC/PCU) <b>150</b> may be connected to MSC <b>130,</b> GSN <b>140</b> and BTS <b>160.</b> The BSC/PCU 150 helps control BTS <b>160</b> in call set-up functions, coding schemes to use and use of radio channels, and various maintenance tasks.

0027Base transceiver station (BTS) <b>160</b> contains suitable electronic equipment for transmitting and receiving radio frequency signals. BTS <b>160</b> may transmit and receive radio signals and more particularly, digitally encoded signals from wireless data device <b>180.</b> Communications between BTS <b>160</b> and wireless data device <b>180</b> includes the transmission of data packets, which may be digitally encoded.

0028The data packets may be digitally encoded using a coding scheme (codes). The term scheme and code may be used interchangeably as appreciated by those skilled in the art. These schemes may be used in a variety of combinations with one or more received data packets. The transmission of data packets may use one or more modulation schemes, such as 16-QAM (quadrature amplitude modulation) or 8-PSK (phase shift keying). The modulation schemes and encoding schemes may be adaptively chosen based on factors such as requisite bit error rates (BER) or channel quality attributes. In accordance with the present invention, coding schemes are characterized in an ordinal relationship to each other, so that there are higher and lower coding schemes, with the higher coding schemes generally providing higher effective data throughput (i.e, the data rate not including error protection bits), and correspondingly requiring better environmental conditions to achieve sufficiently error free effective data throughput. Conversely, lower coding schemes generally employ either more redundant information or use slower modulation techniques to achieve effective data throughput that is similarly error free. Also, changing the coding scheme from a lower coding scheme to a higher coding scheme is referred to herein as raising the coding scheme, and conversely, a coding scheme can be lowered to a lower coding scheme. A successful transmission of multiple data packets comprising a data message may involve at least one additional transmission attempt (retransmission) of specific data packets whose contents were unsuccessfully decoded at the receiver. The retransmission may comprise a repeated transmission of the data packet that was corrupted in the channel. The retransmission may be sent at a lower coding scheme to improve the reliability of the data. The retransmission may also be sent using the same coding scheme, such as a repeated transmission. The retransmission may be sent at a higher coding scheme for faster data throughput. The coding scheme selection may be determined, for example, with feedback from wireless data device <b>180,</b> by a data scheme selected by the packet control unit (PCU) portion of the BSC/PCU <b>150</b> and communicated to the BTS <b>160.</b> A detailed description of some of the rules for selecting a coding scheme are described below with reference to <figref idref="f0006 f0007 f0008">FIGS. 7-9</figref>.

0029Wireless data device <b>180,</b> which may be a cellular phone, a laptop computer, a PDA or other wireless device, is equipped with suitable hardware and software for receiving and transmitting digital transmissions. Wireless data device <b>180</b> typically. transmits or receives data in a prescribed band of frequencies nominally at 900 MHz, 1900 MHz, or any other suitable band of frequencies prescribed for wireless communication. Wireless data device <b>180</b> may be carried by a human user, installed on mobile equipment, used in a fixed location such as on a desk or used in any other application where wireless communication services are desired.

0030<figref idref="f0002"><b>FIG. 2</b></figref> is a block diagram of one embodiment of a communication system <b>200</b> in, in accordance with the present invention. Components of communication system <b>200</b> include a public-switched telephone network (PSTN) <b>210,</b> a mobile switching center (MSC) <b>230,</b> base station subsystem (BSS) <b>250,</b> and a packet radio network <b>290.</b>

0031Public switch telephone network (PSTN) <b>210,</b> a land-based telephone network, is coupled to the MSC <b>230.</b> The packet radio network <b>290</b> comprises an Internet-protocol network <b>220</b> is coupled to, one or more GPRS support nodes (GSN) <b>240,</b> which are coupled to one or more packet controller units (PCU) <b>254</b>.One or more wireless data devices <b>280</b> form a portion of the packet radio network <b>290.</b>

0032GPRS support nodes (GSN) <b>240,</b> as payload-carrying and control devices, help the network to switch packet data, routing packets to and from the geographical area of packet radio-specific network <b>290</b> and interfacing with Internet-protocol network <b>220.</b> GSN <b>240</b> may be physically separate from the circuit-switched part of a cellular system core network, as shown in <figref idref="f0002">FIG.2</figref>, where it is coupled to the MSC 230, or may be integrated with the MSC 230. GSN <b>240</b> contains GPRS backbone network protocol (IP) routing functionality, and can be interconnected with IP routers.

0033Packet Controller Unit (PCU) <b>254</b> serves as an interface between BSS <b>250</b> and packet radio-specific network <b>290,</b> performing radio functions and general packet radio service (GPRS) network functions. In addition to PCU <b>254,</b> base site (or base station) controller (BSC) <b>252</b> and base transceiver station (BTS) <b>260</b> are components of BSS <b>250.</b> BSC <b>252</b> controls radio signals of multiple cell sites, thus reducing the load on MSC <b>230.</b> BSC <b>252</b> also performs radio signal management functions for BTS <b>260,</b> managing functions such as frequency assignment and handoff. BTS <b>260,</b> which may be equipped with antenna and radio equipment, is the central radio transmitter/receiver that maintains communications with mobile station <b>270</b> within its cell site or given range.

0034Mobile station <b>270</b> consists of mobile equipment such as a cellular phone and is used to communicate with the GSM network. Mobile station <b>270</b> may be coupled to or integrated with the wireless data device <b>280</b> such as a mobile personal digital assistant (PDA) or a wireless-capable laptop using over-the-air interface technologies such as those specified in IEEE 802.11. Mobile station <b>270</b> couples to base transceiver station <b>260</b> via air interface <b>262,</b> which is a preferably standard signalling system of a standard wireless network technology, preferably conforming to one of the GSM standards.

0035Other network topologies besides the network architecture described above are possible without departing from the essential characteristics of the present invention. Additional components to separate various functions of a piece of equipment or module may be included with departing from the nature of the present invention.

0036As previously mentioned, the PCU <b>254</b> manages, allocates, and schedules the packet data resources necessary to allow uplink and downlink packet data transmission between the BTS <b>260</b> and the MS <b>270</b> with its associated wireless data device <b>280.</b> Specifically, a packet resource manager (not shown) within the PCU <b>254</b> receives data, determines how to best "package" the data, and then instructs (via control instructions) the BTS <b>260</b> to package the data accordingly. Once received by the MS <b>270</b> from the BTS <b>260,</b> the data packages are "unpackaged" and reassembled, thereby completing the transmission of the data.

0037For example, layer 2 user data bits received by the PCU <b>254</b> from the IP internet <b>220</b> via the GSN <b>240</b> (resulting from a particular software application) are in the form of Logic Link Control (LLCs) frames. Upon receipt, the PCU <b>254</b> splits each of the LLCs into segments of bits and inserts additional bits (e.g., polling bits, data encoding instructions, etc.). The resulting blocks of bits, herein referred to as "segmented blocks," are forwarded to the BTS <b>260</b> for transmission as a downlink data message. Based on the data encoding instructions embedded in the segmented. blocks by the PCU <b>254,</b> the segmented blocks are encoded, or modulated, by the BTS <b>260</b> using the GPRS coding schemes, and the downlink data message is transmitted to the MS <b>270</b> as GPRS radio blocks. Similarly, a data message can be generated by the mobile data device <b>280</b> and transmitted from the MS <b>270</b> using the GPRS coding schemes. Current GPRS coding schemes selectable by the PCU <b>254</b> include Coding Scheme 1 (CS-1), CS-2, CS-3, or CS-4 (see, <figref idref="f0003 f0004 f0005">FIGS. 3-6</figref>) and Modulated Coding Scheme 1 (MCS-1), MCS-2, MCS-3, MCS-4, MCS-5, MCS-6, MCS-7, MCS-8, and MCS-9.

0038The particular GPRS coding scheme selected by the PCU <b>254</b> and MS <b>270</b> is based on whether the data is control data requiring maximum protection for transmitted bits, or maximum data integrity, requiring CS-1 coding, or whether the data is user data. If the data is user data, varying coding schemes (e.g., CS-1 through CS-4) are selected by the PCU <b>254,</b> generally based on channel quality factors and knowledge of the coding scheme capabilities of the MS <b>270,</b> as described in more detail with reference to <figref idref="f0006">FIGS. 7</figref> and <figref idref="f0007">8</figref> below.

0039The BTS <b>260</b> and the MS <b>270</b> encode the data into the GPRS radio blocks suitable for transmission over the Packet Data Traffic Channel between the BTS <b>260</b> and the MS <b>270.</b> For ease of discussion, the GPRS radio blocks carrying encoded data may be referred to herein as "GPRS data blocks".

0040<figref idref="f0003">FIG. 3</figref> is an illustration of coding scheme 1 (CS-1) <b>300</b> for maintaining maximum data integrity of GPRS radio blocks in a GPRS packet data transmission channel (PDTCH), in accordance with the preferred and alternative embodiments of the present invention. Referring to <figref idref="f0003">FIG. 3</figref>, for the CS-1 <b>300</b>, 181 Layer 2 bits resulting from applications (e.g., email, web browser, paging, etc.) as well additional information bits inserted by the PCU <b>254</b> are forwarded to the BTS <b>260</b> as a portion of a downlink data message (or possibly as a complete, short data message). (Of course, as is known, thousands of bits of layer 2 data may be received by the PCU <b>254</b> as a data message from a particular application). Based at least partially on the number of bits received and the information bits inserted by the PCU <b>254,</b> a predetermined number of uplink state flag (USF) bits <b>303</b> are added to the 181 Layer 2 bits <b>302</b> by the BTS <b>260.</b> The USF bits <b>303</b> are configured to notify a particular MS <b>270</b> that it has uplink transmission rights. Similarly, parity bits <b>304</b> and tail bits <b>306</b> are added to the 181 Layer 2 bits for error correction, herein referred to as a "block check sequence" (BCS). The addition of the USF bits <b>303,</b> the parity bits <b>304</b> and the tail bits <b>306</b> to the Layer 2 bits <b>302</b> results in 228 bits to be encoded. To maximize data integrity during transmission, each of the 228 bits of data is copied, resulting in 228 original bits and 228 copied bits for a total of 456 bits (i.e., a 1/2 code rate) to be transmitted from the BTS <b>260</b> to the MS <b>270.</b> As is known in the art, each group of 456 bits may be referred to a one GPRS data block. The 456 bits are distributed among four "bursts" containing approximately 114 bits/burst (i.e., one TDMA frame) shown in <figref idref="f0003">FIG. 3</figref> as bursts <b>308, 309, 310, 311.</b> Thus, two copies of each the original 181 Layer 2 bits <b>302</b> are transmitted from the BTS <b>260,</b> thereby increasing the odds that each of the original 181 Layer 2 bits <b>302</b> are received by the MS <b>270.</b> Typically, the four bursts <b>308-311</b> are transmitted with forty-four additional bursts <b>312</b> (representing eleven additional GPRS radio blocks), and four idle bursts (i.e., TDMA frames) in a "multiframe" configuration. As shown in <figref idref="f0003 f0004 f0005">FIGs. 3-6</figref>, a multiframe <b>320</b> is transmitted in approximately 240 milli-seconds. Upon receipt of the multiframe(s) <b>320,</b> using well-known methods, bits inserted in the bursts by the BTS <b>260</b> at the direction of the PCU <b>254</b> are used by the MS <b>270</b> to decode and reconstruct the data is a form suitable for receipt by an end user.

0041Of course, as will be appreciated by those of ordinary skill in the art, the "cost" of using the CS-1 scheme is high in terms of bandwidth resources; less than one data message bit is recovered for every 2 bits transmitted. The GPRS PDTCH coding schemes CH-2, CH-3, and CH-4 are constructed to more efficiently utilize bandwidth resources, depending on the quality or robustness of the communication channel <b>124.</b> More particularly, CH-2 and CH-3 utilizes controlled bit reduction, herein referred to as "bit puncturing" to reduce the amount of copied data bits transmitted. Moreover, CH-4 adds only USF and parity bits to the original layer 2 bits prior to transmission to the MS <b>270;</b> no copied bits are transmitted.

0042For example, <figref idref="f0004">FIG. 4</figref> is an illustration of the coding scheme 2 (CS-2) <b>330</b> where approximately 1/3 of the copied bits are punctured. Referring to <figref idref="f0004">FIG. 4</figref>, for CS-2, 268 Layer 2 bits <b>332</b> are transmitted from the PCU <b>254</b> to the BTS <b>260.</b> Similar to CS-1 <b>300</b>, 6 USF bits <b>333,</b> 16 parity bits <b>334</b> and 4 tail bits <b>336</b> are added to the 268 Layer 2 bits <b>332.</b> The addition of the USF bits <b>333,</b> the parity bits <b>334</b> and the tail bits <b>336</b> to the Layer 2 bits <b>302</b> results in 294 bits to be encoded. Each of the 294 bits of data is copied resulting in 294 original bits and 294 copied bits for a total of 588 bits. Of the 588 bits, however, only 456 bits are transmitted (i.e., a 2/3 code rate) from the BTS <b>260</b> to the MS <b>270.</b> The remaining 132 are selectively discarded based on known statistics. Thus, the original 268 Layer 2 bits <b>332</b> and approximately 2/3 of the copied 268 layer 2 bits are transmitted from the BTS <b>260</b> to the MS <b>270.</b>

0043<figref idref="f0004">FIG. 5</figref> is an illustration of the coding scheme 3 (CS-3) <b>340</b> where approximately 2/3 of the copied bits are punctured. Referring to <figref idref="f0004">FIG. 5</figref>, for CS-3, 312 Layer 2 bits <b>332</b> are transmitted from the PCU <b>254</b> to the BTS <b>260.</b> Like CS-2 <b>330</b>, 6 USF bits <b>343</b>, 16 parity bits <b>344</b> and 4 tail bits <b>346</b> are added to the 312 Layer 2 bits <b>342.</b> The addition of the USF bits <b>333,</b> the parity bits <b>334</b> and the tail bits <b>336</b> to the Layer 2 bits <b>302</b> results in 338 bits to be encoded. Each of the 338 bits of data is copied resulting in 338 original bits and 338 copied bits for a total of 676 bits. Of the 676 bits, however, only 456 bits are transmitted (i.e., a 3/4 code rate) from the BTS <b>260</b> to the MS <b>270.</b> The remaining 220 bits are selectively discarded based on known statistics. Thus, the original 312 Layer 2 bits <b>342</b> and approximately 1/3 of the copied 312 layer 2 bits are transmitted from the BTS <b>260</b> to the MS <b>270.</b>

0044<figref idref="f0005"><b>FIG.</b> 6</figref> is an illustration of a coding scheme 4 (CS-4) <b>350</b> where no copied bits are generated and no bits are punctured. Referring to <figref idref="f0005">FIG. 6</figref>, for CS-4, 428 Layer 2 bits <b>352</b> are transmitted from the PCU <b>254</b> to the BTS <b>260.</b> Unlike coding schemes CS-1, CS-2, and CS-3, only USF bits <b>353</b> and parity bits <b>354</b> are added to the Layer 2 bits. The addition of 12 USF bits <b>353</b> and 16 parity bits <b>354</b> to the 428 Layer 2 bits <b>352</b> results in exactly 456 bits. Thus, only the original 428 Layer 2 bits <b>352</b> are transmitted from the BTS <b>260</b> to the MS <b>270.</b>

0045When the MS <b>270</b> transmits a data burst to the BTS <b>260</b> in an uplink data message using one of the coding schemes CS-1, CS-2, CS-3, or CS-4, the data message bits and error control bits are arranged similarly to those in downlink data message bursts. However, the control bits that are included in an uplink burst have meanings different from those of the USF bits in a downlink burst and may be different in number than the USF bits of a downlink burst.

0046The CS-4 <b>350</b> provides the most efficient utilization of bandwidth resources and is therefore the coding scheme of choice when channel conditions of the communication channel <b>124</b> permits (i.e., optimum channel conditions) and the equipment (BTS <b>260</b> and MS <b>270)</b> is capable of such encoding scheme. Conversely, the CS-1 <b>300</b> provides the most reliable scheme to ensure data integrity of the GPRS radio blocks received or transmitted by the MS-1 and is therefore the coding scheme of choice when the communication channel <b>124</b> is adversely affected or when transmission of a control information message is required. The CS-2 <b>330</b> and the CS-3 <b>340</b> provide intermediate coding schemes.

0047As will be appreciated by those of ordinary skill in the art, coding schemes for GPRS PDTCH can be achieved using a number of coding schemes, for example modulation and coding schemes, MCS-1 to MCS-9 suitable for use with enhanced GPRS.

0048GSM specifications include requirements that mobile stations <b>270</b> that are designed for use in GPRS systems be capable of receiving and transmitting the four defined coding schemes CS-1, CS-2, CS-3, and CS-4. However, there are mobile stations <b>270</b> that have been distributed that do not conform to these requirements, and which support, for example, only CS-1 and CS-2, and make no response to a command to transmit using, for example, the CS-3 coding scheme. The present invention provides methods of selecting a coding scheme for use in transmitting uplink and downlink messages in an optimized manner in a system that includes such mobile stations, as well mobile stations that support all four GPRS coding schemes. It will be appreciated that the inventive methods described herein also apply to packet data communication systems that have other sets of coding schemes, of which the EDGE system is one example, and for which at least some mobile stations do not respond to a command to switch to particular coding schemes.

0049Referring to <figref idref="f0006">FIG. 7</figref>, a flow chart is shown that illustrates a method of selecting a coding scheme used to transmit downlink data blocks on a downlink channel, in accordance with the preferred embodiment and alternative embodiments of the present invention. At step <b>705,</b> an identification is made within the communication system <b>200</b> of a new downlink data message intended for a specific mobile station, identified as MS:Y in <figref idref="f0006">FIG. 7</figref>, and a specific base transceiver site (BTS) <b>260</b> is identified for transmitting the message. The PCU <b>254</b> creates a Properties Table for MS:Y when the Properties Table does not already exist, which can be the case when MS:Y has not been active in the communication system <b>200</b> for a predetermined time (for example, 30 minutes). The Properties Table for MS:Y includes such parameters associated with MS:Y as the mobile radio frequency band capabilities, call processing feature capabilities, and power control capabilities , which are conventional. The Properties Table for MS:Y also includes a unique set of downlink state of support indicators (or "downlink states of support" or "downlink indicators") for the set of coding schemes that might be used for downlink communication between the BTS <b>260</b> and MS:Y. The set of coding schemes preferably comprises the coding schemes expected to be used for downlink data packet communications in the communication system <b>200</b> for all mobile stations. In accordance with the preferred embodiment of the present invention, the downlink state of support for a mobile station corresponding to each coding scheme can have one of three values: Supported, Unsupported, and Unknown Support. These values indicate a determination by the PCU <b>254</b> of the availability of downlink communication between the BTS <b>260</b> and MS:Y. When a new Properties Table for MS:Y is created, the PCU <b>254</b> initializes the parameters, including the set of downlink states of support, and sets some downlink states of support for MS:Y to a state of Unknown Support. In the example being described herein, there are four downlink coding schemes (CS-1, CS-2, CS-3, CS-4), so the set of states of support has four members. In a first variation, all four coding schemes are set to the state of Unknown Support when a new Properties Table is created for any mobile station, including MS:Y. In a second variation, when a new Properties Table is created, two coding schemes, CS-3 and CS-4, are set to the state of Unknown Support, and two coding schemes, CS-1 and CS-2, are set to the state of Supported for any mobile station. In yet another variation, a function determines (for instance, by using a mobile identifier and another table) a class of mobile stations to which a mobile station belongs and from the class determines which coding schemes are set to a state of Supported, Unsupported, or Unknown Support.

0050When a new Properties Table for MS:Y is initialized at step <b>710,</b> a coding scheme parameter associated with MS:Y for transmitting a downlink message, described herein as DCS-X, is set at step <b>715</b> to an initial coding scheme, identified in <figref idref="f0006">FIG. 7</figref> as DCS-P. DCS-X is a parameter that identifies the coding scheme that is planned to be used for the next data transmission to MS:Y. When DCS-X is changed, a new downlink coding scheme is thereby selected. For example, in the first variation described above, DCS-P is preferably CS-2 and DCS-X is therefore set to CS-2. This coding scheme is selected in this example as the one for initial use because it provides reasonably good throughput but also provides a good probability of data blocks being received adequately error free on the first try. The PCU <b>254</b> then directs the BTS <b>260</b> to use DCS-X to transmit a predetermined number, M, of next unacknowledged blocks of the data message to MS:Y at step <b>720,</b> and requests an acknowledgement (ACK) back from MS:Y at step <b>725.</b> The PCU <b>254</b> determines at step <b>730</b> whether an ACK for the downlink data blocks (DL ACK) has been received from MS:Y. In accordance with the preferred embodiment of the present invention, a determination that the DL ACK is not received is made only when no blocks of DL ACKS are received sufficiently error free in response to one transmission and two re-transmissions of the next M unacknowledged blocks of data message within a standard time after having been transmitted or re-transmitted. This process provides confidence that MS:Y actually does not provide support for the coding scheme being used (DCS-X), rather than there simply existing a poor signaling environment. It will be appreciated that other numbers of missed acknowledgements could be used (e.g., 1 to 5), with an attendant tradeoff of certainty of the result versus the time needed to obtain it.

0051When the DL ACK has not been received at step <b>730,</b> the PCU <b>254</b> sets the downlink state of DCS-X (which is this example would be CS-2) in the Properties Table for MS:Y to Unsupported at step <b>775</b> (This is also described as marking DCS-X as Unsupported in the MS:Y Properties Table), and determines at step <b>777</b> whether DCS-X is at a lower limit, which is DCS-1 in accordance with the preferred embodiment of the present invention. When DCS-X is not at the lower limit, the PCU <b>254</b> decreases DCS-X to the next lower coding scheme at step <b>780,</b> which for the current example would change DCS-X to CS-1. When DCS-X is determined to be at the lower limit at step <b>777,</b> or when the PCU <b>254</b> decreases the DCS-X to the next lower coding scheme at step <b>780,</b> the PCU <b>254</b> then determines the state of support of DCS-X from the Properties Table for MS:Y, at step <b>785.</b>

0052When the downlink state of support is determined to be Unknown Support at step <b>785,</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>790</b> to retransmit to MS:Y the M unacknowledged blocks previously transmitted at step <b>720</b> using DCS-X, and requests an acknowledgement (ACK) back from MS:Y at step <b>725</b> and proceeds from step <b>725</b> as described above. When the downlink state of support is determined to be Unsupported at step <b>785,</b> the PCU <b>754</b> again determines whether DCS-X is at the lower limit at step <b>777</b> and proceeds from there as described above.

0053When the DL ACK has been received at step <b>730,</b> the PCU <b>254</b> sets the downlink state of support for DCS-X (which is this example would be CS-2) in the Properties Table for MS:Y to Supported at step <b>735.</b> (This is also described as marking DCS-X as Supported in the MS:Y Properties Table). The DL ACK being "received" is the inverse of the DL ACK being "not received" as described above, i.e., it is when any block of the DL ACK is received sufficiently error free in response to the transmission or two re-transmissions of the next M unacknowledged blocks of the data message within the standard time after transmission or re-transmission. The PCU <b>254</b> then directs the BTS <b>260</b> at step <b>740</b> to transmit a second predetermined number, N, of next unacknowledged blocks of the data message to MS:Y and to request an acknowledgment from MS:Y at step <b>740.</b> The PCU also directs the BTS <b>260</b> at step <b>740</b> to transmit a second predetermined number, N, of next unacknowledged blocks of the data message to MS:Y and to request an acknowledgment from MS:Y when the downlink state of support is determined to be Supported at step <b>785.</b> Channel parameters are measured by the BTS <b>260</b> during the receipt of an acknowledgment (if any) from the MS:Y at step <b>743</b> and sent to the PCU <b>254.</b> The channel quality parameters are conventional channel quality parameters, such as bit and block error rates absolute received signal strength (RSS) and RSS variation, or combinations thereof. At step <b>745,</b> the parameters are used to determine the channel quality relative to the coding scheme, DCS-X, used to transmit the N blocks of data. Levels used by the PCU <b>254</b> for the determination of channel quality made in step <b>745</b> are established at the time of equipment fabrication or system set-up for each coding scheme in a manner that optimizes the selection of the coding schemes used during the downlink data message.

0054When the channel quality is determined to be between a first level and a second level for coding scheme DCS-X at step <b>745,</b> the quality is acceptable and as a result, the PCU <b>254</b> directs the BTS <b>260</b> at step <b>740</b> to transmit the next N unacknowledged blocks of the data message to MS:Y and to request an acknowledgment from MS:Y, and proceeds from step <b>740</b> as described above. When the channel quality is above the second level for coding scheme DCS-X at step <b>745,</b> the quality is high and as a result the PCU <b>254</b> at step <b>750</b> seeks a next highest coding scheme at which the channel quality is at least acceptable and the coding scheme state is set to Supported or Unknown Support. The determination of the channel quality at each coding scheme is made using the same parameter measurements made in step <b>743,</b> but with levels associated with each coding scheme. For example, if DCS-X was at CS-2 at step <b>740,</b> the PCU <b>254</b> would determine the channel quality for CS-3 and if it was at least acceptable, the PCU <b>254</b> would determine whether the downlink state of support is Supported or Unknown Support for DCS-3. If the channel quality was at least acceptable for CS-3, but the downlink state was Unsupported for DCS-3, the PCU <b>254</b> would then determine if the channel quality for CS-4 was at least acceptable and whether the downlink state was Supported or Unknown Support for DCS-4. When the PCU <b>254</b> determines a coding scheme at which the channel quality is at least acceptable and the downlink state of support is Unknown Support at step <b>750,</b> the PCU <b>254</b> sets DCS-X to the determined coding scheme at step <b>755</b> and directs the BTS <b>260</b> at step <b>720</b> to use DCS-X to transmit the next unacknowledged M blocks of the data message to MS:Y, and proceeds from step <b>720</b> as described above. When the PCU <b>254</b> determines a coding scheme at which the channel quality is at least acceptable and the downlink state of support is Supported at step <b>750,</b> the PCU <b>254</b> sets DCS-X to the determined coding scheme at step <b>757</b> and directs the BTS <b>260</b> at step <b>740</b> to transmit the next unacknowledged N blocks of the data message to MS:Y and to request an acknowledgment from MS:Y, and proceeds from step <b>740</b> as described above. When the PCU <b>254</b> finds no coding scheme that is higher than the coding scheme most recently used at step <b>740</b> to transmit N blocks, and at which the channel quality is at least acceptable and the downlink state of support is set to Supported or Unknown Support at step <b>750,</b> the PCU <b>254</b> does not change the coding scheme most recently used to transmit N blocks, and directs the BTS <b>260</b> at step <b>740</b> to transmit the next unacknowledged N blocks of the data message to MS:Y and to request an acknowledgment from MS:Y, and proceeds from step <b>740</b> as described above.

0055When the channel quality is determined to be below the first level for coding scheme DCS-X at step <b>745,</b> the quality is low and as a result the PCU <b>254</b> at step <b>765</b> seeks a next lowest coding scheme at which the channel quality is at least acceptable and the coding scheme state is set to Supported or Unknown Support. The determination of the channel quality at each coding scheme is made using the same parameter measurements made in step <b>743,</b> but with different levels associated with each coding scheme. For example, if DCS-X was at CS-3 at step <b>740,</b> the PCU <b>254</b> would determine the channel quality for CS-2 and if it was at least acceptable, the PCU <b>254</b> would determine whether the downlink state of support is Supported or Unknown Support for DCS-2. If the channel quality was at least acceptable for CS-2, but the downlink state was Unsupported for DCS-2, the PCU <b>254</b> would then determine if the channel quality for CS-1 was at least acceptable and whether the downlink state was Supported or Unknown Support for DCS-1. When the PCU <b>254</b> determines a coding scheme at which the channel quality is at least acceptable and the downlink state of support is Unknown Support at step <b>765,</b> the PCU <b>254</b> sets DCS-X to the determined coding scheme at step <b>767</b> and directs the BTS <b>260</b> at step <b>720</b> to use DCS-X to transmit the next unacknowledged M blocks of the data message to MS:Y, and proceeds from step <b>720</b> as described above. When the PCU <b>254</b> determines a coding scheme at which the channel quality is at least acceptable and the downlink state of support is Supported at step <b>765,</b> the PCU <b>254</b> sets DCS-X to the determined coding scheme at step <b>769</b> and directs the BTS <b>260</b> at step <b>740</b> to transmit the next unacknowledged N blocks of the data message to MS:Y and to request an acknowledgment from MS:Y, and proceeds from step <b>740</b> as described above. When the PCU <b>254</b> finds no coding scheme that is lower than the coding scheme most recently used at step <b>740</b> to transmit N blocks, and at which the channel quality is at least acceptable and the downlink state of support is set to Supported or Unknown Support, the PCU <b>254</b> does not change the coding scheme most recently used at step <b>740</b> to transmit N blocks, and directs the BTS <b>260</b> at step <b>740</b> to transmit the next unacknowledged N blocks of the data message to MS:Y and to request an acknowledgment from MS:Y, and proceeds from step <b>740</b> as described above.

0056Using the procedures described with reference to <figref idref="f0006">FIG. 7</figref>, a best coding scheme for transmitting blocks of data messages downlink from the BTS <b>260</b> to MS:Y is rapidly determined, whether the signaling environmental conditions are stable or not and regardless of whether MS:Y is a mobile station that is enabled to transmit on all coding schemes defined for the communication system or MS:Y is a mobile station that does not respond to certain coding schemes. When the signaling conditions are stable, it will be appreciated that the procedure can loop between the functions described above with reference to steps <b>740, 743</b> and <b>745</b> for a large portion of a moderate length data message.

0057Referring to <figref idref="f0007"><b>FIG.</b> 8</figref>, a flow chart illustrates a method of selecting a coding scheme used to transmit uplink data blocks on an uplink channel, in accordance with the preferred and alternative embodiments of the present invention. At step <b>805,</b> a mobile station <b>270,</b> identified for this description as MS:Y, enters the communication system <b>200.</b> MS:Y is defined to enter the communication system <b>200</b> when MS:Y sends a request for uplink resources for transmitting an Uplink data message and no Properties Table for MS:Y exists for MS:Y in the BSS <b>250.</b> Other conditions may exist for which MS:Y is defined to have entered the system - for example, when a Properties Table exists for MS:Y but the Properties Table has a different BTS <b>260</b> identified than the one that has received the indicator of the Uplink data message. When MS:Y enters the communication system <b>200,</b> a new Properties Table is created at step <b>810</b> that includes the parameters described above with reference to <figref idref="f0006">FIG. 7</figref>, as well as a unique set of uplink state of support indicators (or "upnlink states of support" or "uplink indicators") for the set of coding schemes that might be used for downlink communication between the BTS <b>260</b> and MS:Y. The set of coding schemes preferably comprises the coding schemes expected to be used for downlink data packet communications in the communication system <b>200</b> for all mobile stations. In accordance with the preferred embodiment of the present invention, the uplink state of support of a mobile station corresponding to each coding scheme can have one of three values: Supported, Unsupported, and Unknown Support. These values indicate a determination by the PCU <b>254</b> of the availability of uplink communication between the BTS <b>260</b> and MS:Y. When a new Properties Table for MS:Y is created, the PCU <b>254</b> initializes the parameters, including the set of uplink states of support, and sets some uplink states of support of MS:Y to a state of Unknown Support. In the example being described herein, there are four uplink coding schemes (CS-1, CS-2, CS-3, CS-4) that are the same as the four downlink coding schemes, so the set has four members. As with the downlink method described above, a variety of combinations exist for initializing the uplink states of support. In the preferred embodiment of the present invention, all uplink states of support are set to "Unknown Support".

0058When a new Properties Table for MS:Y is initialized at step <b>810,</b> a coding scheme parameter associated with MS:Y for transmitting an uplink message, described herein as UCS-X, is set at step <b>815</b> to an initial coding scheme, identified in <figref idref="f0007">FIG. 8</figref> as UCS-P. UCS-X is a parameter that identifies the coding scheme that is planned to be used for the next data transmission from MS:Y. When UCS-X is changed, a new uplink coding scheme is thereby selected. For example, in the first variation described above, UCS-P is preferably CS-2 and DCS-X is therefore set to CS-2. This coding scheme is selected in this example as the one for initial use because it provides reasonably good throughput but also provides a good probability of data blocks being received adequately error free on the first try. At step <b>820,</b> the PCU <b>254</b> directs the BTS <b>260</b> to use CS-1 to transmit MS:Y a Packet Uplink Assignment message which directs MS:Y to use UCS-X (in this example, CS-2) to transmit subsequent blocks of the uplink data message, which are preferably some initial blocks of the data message that have not yet been transmitted.

0059When an uplink data block is received sufficiently error free at BTS <b>260</b> from MS:Y at step <b>825</b> that has been encoded using the UCS-X assigned at step <b>820,</b> the PCU <b>254</b> sets the state of support of MS:Y for UCS-X to Supported at step <b>830</b> (which is also described as marking UCS-X as Supported in the MS:Y Properties Table), and continues receiving data blocks of the uplink data message. When a selected quantity, Q, of block periods have expired after the beginning of the uplink data message (or after the end of a previous set of Q block periods within the same message) at step <b>835,</b> channel parameters measured by the BTS <b>260</b> during the receipt of the Q blocks of data are averaged by the BTS <b>260</b> and the averaged measurements are sent to the PCU <b>254</b> (in an alternative embodiment, the parameters are sent to the PCU <b>254</b> and averaged therein). The channel quality parameters are conventional channel quality parameters, such as bit and block error rates absolute received signal strength (RSS) and RSS variation, or combinations thereof. At step 840, the parameters are used to determine the channel quality relative to the coding scheme, UCS-X, used to transmit the N blocks of data. Levels used by the PCU <b>254</b> for the determination of channel quality made in step <b>835</b> are established at the time of equipment fabrication or system set-up for each coding scheme in a manner that optimizes the selection of the coding schemes used during the uplink data message, and are not necessarily the same as for the downlink coding schemes, particularly if they are different coding schemes.

0060When the channel quality is determined to be acceptable at step <b>840,</b> the PCU <b>254</b> again waits at step 835 for Q more block periods to have expired after the end of the previous set of Q block periods within the same message and averages the channel quality parameter measurements, and then proceeds from step <b>835</b> as described above.

0061When the channel quality is determined to be low at step <b>840,</b> the PCU <b>254</b> determines whether UCS-X is at a lower limit (e.g., CS-1) at step <b>853.</b> When it is not at the lower limit at step <b>853,</b> the PCU <b>254</b> decreases UCS-X to the next lower channel coding at step <b>855</b> and determines the state of uplink support of the lowered UCS-X at step <b>860.</b> When the PCU <b>254</b> determines UCS-X is at a lower limit (e.g., CS-1) at step <b>853,</b> the PCU <b>254</b> determines the state of uplink support of the lowered UCS-X at step <b>860.</b> When the uplink state of support is Unsupported at step <b>860,</b> the PCU <b>254</b> again determines whether UCS-X is at a lower limit at step <b>853</b> and proceeds from step <b>853</b> as described above. When the uplink state of support is Unknown Support at step <b>860,</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>880</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message (in <figref idref="f0007">FIG. 8</figref>, "Packet Uplink ACK/NAK") which directs MS:Y to use UCS-X to transmit subsequent blocks of the uplink data message, and waits a preset time at step <b>825</b> to determine whether an uplink data block is received at UCS-X. The method continues based on the determination made at step <b>825</b> as described elsewhere herein. In present day GSM systems, the subsequent blocks are blocks that have not yet been transmitted, but in other systems or future GSM systems they may include blocks for retransmission that were unacknowledged when transmitted using the previous coding scheme. When the uplink state of support is Supported at step <b>860</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>850</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use the decreased UCS-X for subsequent transmissions of blocks of uplink data, and waits at step <b>835</b> for Q more block periods to have expired after the end of the previous set of Q block periods within the same message and averages the channel quality parameter measurements, and then proceeds from step <b>835</b> as described above.

0062When the channel quality is determined to be high at step <b>840,</b> the PCU <b>254</b> determines whether UCS-X is at an upper limit (e.g., CS-4) at step <b>843</b> and when it is, the PCU <b>254</b> again waits at step <b>835</b> for Q more block periods to have expired after the end of the previous set of Q block periods within the same message, and proceeds from step <b>835</b> as described above. When UCS-X is not at the upper limit at step <b>843,</b> the PCU <b>254</b> increases UCS-X to the next higher channel coding at step <b>845</b> and determines the state of uplink support of the raised UCS-X at step <b>847.</b> When the uplink state of support is Unsupported at step <b>847,</b> the PCU <b>254</b> decreases the coding scheme at step <b>849</b> back to that used to determine the channel quality at step <b>840</b> and directs the BTS <b>260</b> at step <b>850</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use UCS-X for subsequent transmissions of blocks of uplink data, and waits at step <b>835</b> for Q more block periods to have expired after the end of the previous set of Q block periods within the same message and averages the channel quality parameter measurements, and then proceeds from step <b>835</b> as described above. When the uplink state of support is Unknown Support at step <b>847,</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>880</b> to use CS-1 to transmit MS:Y a Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use UCS-X to transmit subsequent blocks of the uplink data message, and waits a preset time at step <b>825</b> to determine whether an uplink data block is received at UCS-X. The method continues based on the determination made at step <b>825</b> as described elsewhere herein. When the uplink state of support is Supported at step <b>847</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>850</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use the increased UCS-X for subsequent transmissions of blocks of uplink data, and waits at step <b>835</b> for Q more block periods to have expired after the end of the previous set of Q block periods within the same message and averages the channel quality parameter measurements, and then proceeds from step <b>835</b> as described above.

0063When an uplink data block is not received at BTS <b>260</b> from MS:Y at step <b>825,</b> the PCU <b>254</b> sets the uplink support state for the coding scheme, UCS-X, that MS:Y was directed to use at step <b>820</b> to Unsupported at step <b>865</b> (also described as marking UCS-X as unsupported in the MS:Y Properties Table). "Not received" in this context means that no recoverable signal was received within an expected maximum time, or that a signal was received within the maximum expected time but it was encoded using a coding scheme other than UCS-X, or that it was received within the maximum expected time, but was not sufficiently error free. At step <b>867</b> the PCU <b>254</b> then checks whether UCS-X is at the lower limit (e.g., CS-1). When UCS-X is not at the lower limit at step <b>867,</b> the PCU <b>254</b> decreases UCS-X at step <b>870</b> and then determines whether the uplink state of UCS-X is Supported at step <b>875.</b> When UCS-X is at the lower limit at step <b>867,</b> the PCU <b>254</b> then determines whether the uplink state of UCS-X is Supported at step <b>875.</b> When the uplink state of UCS-X is Supported at step <b>875,</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>850</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use the increased UCS-X for subsequent transmissions of blocks of uplink data, and waits at step <b>835</b> for Q more block periods to have expired after the end of the previous set of Q block periods within the same message and averages the channel quality parameter measurements, and then proceeds from step <b>835</b> as described above. When the uplink state of UCS-X is Unsupported at step <b>875,</b> the PCU <b>254</b> determines whether UCS-X is at the lower limit at step <b>867</b> and proceeds from there as described above. When the state of UCS-X is determined to be Unknown Support at step <b>875,</b> the PCU <b>254</b> directs the BTS <b>260</b> at step <b>880</b> to use CS-1 to transmit MS:Y a Packet Uplink Acknowledgement/Negative Acknowledgement message which directs MS:Y to use UCS-X to transmit subsequent blocks of the uplink data message, and waits a preset time at step <b>825</b> to determine whether an uplink data block is received at UCS-X. Conventional mobile stations designed for GSM systems re-transmit the unacknowledged data blocks using the same coding scheme originally used for their initial transmission. The method continues based on the determination made at step <b>825</b> as described herein above. Using the procedures described with reference to <figref idref="f0007">FIG. 8</figref>, a best coding scheme for transmitting blocks of data messages uplink to the BTS <b>260</b> from MS:Y is rapidly determined, whether the signaling environmental conditions are stable or not and regardless of whether MS:Y is a mobile station that is enabled to transmit on all coding schemes defined for the communication system or MS:Y is a mobile station that does not respond to certain coding schemes. When the signaling conditions are stable, it will be appreciated that the procedure can loop between the functions described above with reference to steps <b>835</b> and <b>840</b> for a large portion of a moderate length data message.

0064In accordance with the preferred embodiment of the present invention, the same set of coding schemes are used in the uplink and downlink directions. Thus, any particular UCS_X equals the same particular DCS-X (both are CS-X). One Properties Table is maintained for any mobile station that is active in the communication system. The Properties Table includes a set of uplink states of support and a set of downlink states of support. Decisions for selecting an uplink coding schemes are based on both the uplink and downlink set of states of support. In particular, a coding scheme that has an uplink state of support of the mobile station for the coding scheme set to unknown support can only be selected for use on the uplink channel when the downlink state of support of the mobile station for the first coding scheme is set to supported. One method that the PCU <b>254</b> can use to accomplish is to check, after a determination is made at step <b>847, 860,</b> or <b>875</b> that the uplink state of support for the mobile station for UCS-X is set to unknown support, whether the downlink state of support for the mobile station for DCS-X is Supported, and if so, the PCU <b>254</b> uses UCS-X for the uplink data transfer. This improves the probability of selecting a good uplink coding scheme.

0065Referring to <figref idref="f0008">FIG. 9</figref>, a flow chart shows a method used in accordance with the preferred embodiment of the present invention. The steps <b>805</b> and <b>810</b> are as described above with reference to <figref idref="f0006">FIG. 7</figref>. Before step <b>915,</b> MS:Y has entered the communication system and is active in the system. At step <b>915,</b> the PCU <b>254</b> starts or restarts an activity timer at step <b>915</b> having a predetermined duration, D, whenever an uplink or downlink data transfer is completed. In this context, completed means the data transfer has been successfully made or the PCU <b>254</b> has abandoned the attempt to make the data transfer for any reason. Other restarting events could be used - for example the beginning of an uplink or downlink data transfer. One example of a duration for the activity timer is 5 minutes. When the duration expires at step <b>920,</b> the PCU <b>254</b> erases the Properties Table (or Tables, if there are separate uplink and downlink Properties Tables) at step <b>925.</b> After the MS:Y Properties Table is set up at step <b>810,</b> it is updated at step 917 whenever events such as those described with reference to steps <b>735</b> and <b>775</b> in <figref idref="f0006">FIG. 7</figref> and steps <b>830</b> and <b>865</b> in <figref idref="f0007">FIG. 8</figref> occur, until the MS:Y Properties Table is erased at step <b>925.</b> This method, which advantageously minimizes storage space in the PCU <b>254,</b> can also be described as including a function of erasing the Properties Table after a predetermined duration during which no uplink data transfer and no downlink data transfer is communicated with the mobile station.

0066In accordance with alternative embodiments of the present invention, an operator of the communication system <b>200</b> can set up a group of coding schemes or a plurality of groups of mutually exclusive groups of coding schemes, each of which comprises two or more of the coding schemes in the set or sets of coding schemes used in the communication system <b>200.</b> In one of the alternative embodiments, which is a modification of the preferred embodiment, there is one set of coding schemes used for both uplink and downlink data transfers. In another alternative embodiment, there is an uplink set of coding schemes and a downlink set of coding schemes. When the state of support of one of the coding schemes in a group is set to unsupported, the states of support of all other of the coding schemes in the group are set to unsupported. This method is useful when, for example, it is known by the operator that some mobile stations <b>270</b> that are expected to use the operator's communication system have coding schemes in a group or groups that are unsupported. For example, when the operator knows that some mobile station <b>270</b> do not support CS-3 and CS-4, then CS-3 and CS-4 can be advantageously grouped together. Having set up a group, when the PCU <b>254</b> sets the state of support of one of the coding schemes in the group to unsupported, the PCU <b>254</b> also sets the states of support of all other of the coding schemes in the group to unsupported. This improves the efficiency of selecting a good coding scheme.

0067In accordance with the preferred embodiment of the present invention, CS-1 is never set to a support state of Unsupported. This avoids infinite loop situations in the loops <b>777-780-785, 853-855-860,</b> and <b>867-870-875.</b> In alternative systems in which CS-1 could be Unsupported, a more complicated function such as the one described with reference to blocks <b>765, 767, 769</b> can be used to avoid the infinite loop situation.

0068It will be appreciated that there are a variety of ways to accomplish some of the same functions described herein. For example, steps <b>867</b> and <b>870</b> could be equivalently described in one step as "decrease UCS-X when it is not at the lower limit". Or, for example, having step <b>847</b> following directly after step <b>843,</b> inserting step <b>845</b> into the "unknown support" and "yes" result branches of step <b>847</b> and deleting step <b>849</b> from the "No" result Branch of step <b>847</b> would be equivalent to the approach described above.

0069For the methods described above with reference to <figref idref="f0006">FIGS. 7</figref> and <figref idref="f0007">8</figref>, some steps that may have been described elsewhere herein and some steps that are obvious to one of ordinary skill in the art may not be shown in the flow chart, but would be used in the method. The methods described with reference to <figref idref="f0006">FIGS. 7</figref> and <figref idref="f0007">8</figref> are performed in the BSS <b>250</b> of the communication system <b>200,</b> and are designed to require no hardware or programming changes to currently available mobile stations <b>270.</b> The methods described with reference to <figref idref="f0006">FIGS. 7</figref> and <figref idref="f0007">8</figref> are preferably embedded in the PCU <b>254</b> in the form of a novel set of program instructions executed by a conventional processor using conventional memory, but the methods could alternatively be embedded in, for example, the BSC <b>252</b> or the BTS <b>260,</b> as would be typical for a communication system <b>200</b> not having a PCU <b>254</b> as a separate identified piece of equipment

0070In summary, persons of ordinary skill in the art will readily appreciate that methods for selecting a more optimal channel coding scheme in a communication system that can include mobile stations having unsupported coding schemes have been provided. Systems using the example apparatus and methods described herein may benefit from reduced block error rate (resulting from poor coding scheme decisions), fewer retransmissions of user data blocks, and increased battery life of the mobile stations, increased spectral efficiency and higher user data throughput to an end user.

0071In the foregoing specification, the invention and its benefits and advantages have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims.

0072As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

0073The term "block" has been described herein primarily with reference to the GPRS data message scheme used in GSM systems, but should be understood to be a basic time duration used in any packet data signaling protocol. "Coding scheme" should be understood to mean any combination of error protection and correction and modulation speed and type, that results in a recovered data throughput rate that can be ranked in an ordinal manner with all other such combination within at least one direction (uplink or downlink) of a signaling protocol.

0074The terms "a" or "an", as used herein, are defined as one or more than one. The term "plurality", as used herein, is defined as two or more than two. The term "another", as used herein, is defined as at least a second or more. The terms "including" and/or "having", as used herein, are defined as comprising. The term "coupled", as used herein with reference to electro-optical technology, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term "program", as used herein, is defined as a sequence of instructions designed for execution on a computer system. A "program", or "computer program", may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system.