Method and apparatus for alphanumeric data entry

[0002] The present invention relates to a user input device for entering alphanumeric data on a device having relatively few data entry keys, and more particularly to a keypad for entering alphanumeric data on a portable communication unit.

[0003] Portable electronic devices with text entry capabilities are increasing in usage. These devices are being built in smaller sizes each year. For many of these devices, such as cellular phones, models that are small in size are perceived as desirable by consumers. Cellular phone manufacturers have responded to this, and produce a variety of cellular phones that are small relative to earlier models, with some models being smaller than the size of a user's palm.

[0004] Cellular phones have a number of features that require a user to input alphanumeric characters. A user may, for example, enter alphanumeric text in the name field of a phone list maintained in the phone. A user may also use a cell phone to send text messages via short messaging service (SMS) technology. To do this, a user generally inputs alphanumeric characters into the phone. Typically, a numeric keypad is used to enter alphanumeric characters, where the number of alphanumeric characters exceeds the number of numeric input keys.

[0005] A technique generally used to enter alphanumeric characters into a phone uses a standard alphabetic arrangement illustrated in FIG. 1. In this method a cellular phone has two data entry modes, a numeric mode and an alphanumeric mode. In the numeric mode, activation of the data entry keys represents numeric digits. The numeric digits are determined from the correspondence between each data entry key and the numeric digit associated with that key. In a standard telephone, activation of data entry keys in numeric mode generates dual tone multifrequency (DTMF) signals in accordance with an industry standard.

[0006] When operating in the alphanumeric mode, single activation of a data entry key is interpreted as a user selection of the first letter in the sequence of letters that are assigned to the particular data entry key. Similarly, when a data entry key is activated twice by a user, this is interpreted as a selection of the second letter in the sequence of letters associated with that particular data entry key. A timeout threshold is used to determine when selection of a character is complete. If a period of time equal to the timeout threshold follows the activation of a key without a subsequent activation of a key, the selection of the character is considered to be completed. Also, if the user activates a first key followed by an activation of a different key, the activation of the second key is considered to be the beginning of the selection of a new character.

[0007] With this method, a user may activate a key one, two, three, or four times in order to select a particular letter of the alphabet. Multiple activations of keys increase the time required to enter text using the keypad.

[0008] In addition to use of the keys to enter alphanumeric data, letters on keys assist users in entering telephone numbers or other numeric data. Some telephone numbers are represented by mnemonic phone numbers, in which at least part of the phone number is specified by the use of letters, to assist in memorization of the number. For example, 1-800-ABCDEFG is equivalent to 1-800-2223334, when a user activates each key once for each number or letter in the mnemonic phone number.

[0009] Because entry of alphanumeric characters on a limited keypad is less efficient than on a full sized keyboard, a mechanism for improving the efficiency is desirable. Changes to increasing efficiency can be problematic because users are familiar with the standard key mapping. Also, the use of mnemonic telephone numbers is a further consideration.

[0010] The present invention provides an apparatus for data entry of a plurality of letters of an alphabet. In one aspect of the invention, the apparatus includes a plurality of data entry keys and a memory having a key mapping. The key mapping represents a correspondence between each of the data entry keys and a corresponding ordered set of letters based on an alphabetical ordering of the plurality of letters. The ordering of letters within each ordered set is based on a decreasing frequency of use of each character. The apparatus also includes a processor coupled to the memory and the data entry keys, the processor receiving signals representing activations of one of the data entry keys. The processor determines a selected character corresponding to the activations of the data entry key, based on the key mapping and the signals representing activation, wherein the number of activations corresponding to the selected character is based on the position of the selected character within its respective group.

[0011] In another aspect of the invention, the letters within each group of letters are adjacent to each other in the alphabet. Each letter within a group of letters precedes each letter within a group associated with a higher numbered data entry key.

[0012] In yet another aspect of the invention, at least one group of letters comprises an ordered set of letters in order of decreasing frequency of use and is not in alphabetical order. In an additional aspect of the invention, most of the groups of letters comprise an ordered set of letters in order of decreasing frequency of use and not in alphabetical order.

[0013] In yet another aspect of the invention, an indicia for each letter is located in physical association with a corresponding data entry key.

[0014] In still another aspect of the invention, each data entry key has a corresponding ordered set of letters, a selected letter is determined to be a first letter of the ordered set of letters if one activation of the data entry keys is detected, the selected letter is determined to be the second letter if two activations of the data entry keys are detected, and the selected letter is determined to be the third letter if three activations of the data entry keys are detected.

[0015] In yet still another aspect of the invention, the apparatus includes 8 data entry keys, each key having 3 or more letters in a corresponding ordered set of letters.

[0016] In a further aspect of the invention, the apparatus includes a transmitter that transmits a sequence of characters, wherein each character of the sequence of characters is determined by the processor in response to a sequence of activations of the data entry keys.

[0017] In a still further aspect of the invention, a device receives signals representing activations from a plurality of input keys, and a selected character is determined based on a key mapping. The key mapping maps each input key and each activation count to a letter corresponding to the input key. The letters are ordered on the input keys in decreasing order of frequency of use.

[0018] In yet another further aspect of the invention, the group of letters corresponding to each input key is compatible with a conventional telephone keypad. The groups are in an alphabetical order relative to each other.

[0019] In still yet another further aspect of the invention, a device is remote from the input keys and receives signals through a wireless transmission. The device can select from a number of key mappings, including a key mapping that is transmitted from a unit containing the input keys.

[0020] In yet another further aspect of the invention, the data entry keys have a numeric association and an ordered set of letters from the following group: (2—A, C, B), (3—E, D, F), (4—I, H, G), (5—L, K, J), (6—O, N, M), (7—S, R, P, Q), (8—T, U, V), and (9—Y, W, Z, X).

[0021] These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.

[0022] An embodiment of the present invention will now be fully described, by way of example, with reference to the drawings of which:

[0023] FIG. 1 illustrates a conventional portable communication device with a keypad;

[0024] FIG. 2 is a table showing the correspondence between data entry keys and activation counts in the conventional communication device of FIG. 1.

[0025] FIG. 3 illustrates a portable communication device with a keypad in accordance with the present invention;

[0026] FIG. 4 is a functional block diagram including the keypad in FIG. 3;

[0027] FIG. 5 is a flowchart detailing the operation related to the functional block diagram in FIG. 4;

[0028] FIG. 6 is a block diagram of an exemplary portable communication device incorporating the present invention.

[0029] The present invention provides a keypad and a key mapping for the entry of alphanumeric characters. Letters are assigned to data entry keys of a keypad in accordance with the frequency of occurrence of each letter. Hence, letters with a higher frequency of occurrence require less key activations than letters with a lower frequency of occurrence. This advantageously improves the efficiency of data entry as the frequently used letters are more easily selected by a user. Additionally, letters also correspond to numeric keys using a standard association, in order that phone numbers can be easily dialed using their mnemonic representation, and to take advantage of users' knowledge of alphabetical ordering when locating letters on the keypad.

[0030] In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention. However, the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0031] Reference throughout this specification to “one embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase “in one embodiment” are not necessarily all referring to the same embodiment, though they may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0032] FIG. 1 illustrates a cellular phone 100 with a conventional keypad 105 where the twenty-six letters, A to Z, are assigned to eight numeric keys having corresponding numbers two to nine. The keypad 105 provides a graphic display of the letters and numeric digits that are assigned to the keys. FIG. 2 depicts a key map 215 that illustrates required key activation, when operating in alphanumeric mode. Thus, for example, one activation of the input key corresponding to the number two results in a selection of the letter “A”, two activations of the input key corresponding to the number two results in a selection of the letter “B”, three activations of the input key corresponding to the number two results in a selection of the letter “C”, and four activations of the input key corresponding to the number two results in a selection of the digit “2”.

[0033] With reference to FIG. 3, in accordance with one embodiment of the present invention, a mobile electronic communication device, specifically a cellular telephone 300, includes a keypad 330 where the twenty-six letters of the alphabet, A to Z, are assigned to eight data entry keys that include the numeric keys “2” through “9” 302-309. The letters of the alphabet are arranged in groups, with one group of letters corresponding to each numeric key. As used herein, the term “group” refers to an unordered set of elements. For example, the group A, B, C is considered to be equivalent to the group A, C, B, while the “ordered set” A, B, C is not equivalent to the ordered set A, C, B. Also, as used herein, a “numeric” key is a key that corresponds to a numeric digit, and an “alphabetic” key is a key that corresponds to at least one letter. Numeric keys are referred to by their corresponding numeric digit. In FIG. 3, the numeric keys “two” through “nine” 302-309 are also alphabetic keys, while the numeric “zero” key 310 and “one” key 301 are not alphabetic keys.

[0034] As illustrated in FIG. 3, the letters of the alphabet are grouped and associated with each numeric key 302-309 in the following manner. The first three letters of the alphabet are associated with the “two” key 302. The next three letters of the alphabet are associated with the next numeric key in numeric order, specifically the “three” key 303. Each successive three letter grouping is associated with the next numeric key. Two variations to this procedure occur with respect to the “seven” key 307 and the “nine” key 309. Each of these keys has an associated group of 4 letters. In this manner, the group of letters corresponding to each numeric key is made up of consecutive letters of the alphabet and is equivalent to the illustrated group of letters corresponding to the corresponding numeric input key illustrated in FIG. 1. Therefore, the letter-to-key correspondence matches the standard letter-to-key correspondence illustrated in FIG. 1.

[0035] The ordering of the letters within each group, and therefore the positions of the 26 letters on each of the data entry keys 302-309 are assigned based on the frequency of occurrence of the letters. Within a group, letters with a higher frequency of use are positioned before letters with a lower frequency of use. Each of the eight alphabetic data entry keys 302-309 has multiple letters assigned in a predetermined activation sequence, where the first activation of a key selects the first letter in the sequence and a second subsequent activation, prior to a timeout, selects the second letter in the predetermined sequence, and likewise for the third and, where applicable, the fourth letter in the predetermined sequence. As used herein, frequency of occurrence, or frequency of use, refer to the frequency with which the letters occur within a representative corpus of usage.

[0036] Within each group of letters, the letter with the highest frequency of occurrence is assigned the first position in the predetermined sequence for each of the data entry keys. Remaining letters are assigned to a second, third, or fourth position based on their frequency of use relative to other letters within the same group. In particular, in one embodiment, the letters A, E, I, L, O, S, T and Y are assigned the first position within their respective groups, the letters C, D, H, K, N, R, U and W are assigned the second position, the letters B, F, G, J, M, P, V and Z are assigned the third position, and the letters Q and X the fourth position. More specifically, in one embodiment, as illustrated in FIG. 3, the following ordered sets of letters correspond to their respective numeric keys:

[0037] A, C, B—two key 302

[0038] E, D, F—three key 303

[0039] I, H, G—four key 304

[0040] L, K, J—five key 305

[0041] O, N, M—six key 306

[0042] S, R, P, Q—seven key 307

[0043] T, U, V—eight key 308

[0044] Y, W, Z, X—nine key 309

[0045] In one embodiment, the ordered set of letters corresponding to each data entry key is represented by indicia displayed on each respective data entry key, in a sequence that indicates the content of the ordered set. In one embodiment, an ordered set of characters corresponds to each data entry key, some of the characters are represented by indicia, and one or more characters within one or more ordered sets does not have a corresponding indicia. The characters without indicia are ones having a higher corresponding activation count.

[0046] FIG. 4 illustrates a functional block diagram corresponding to the keypad of FIG. 3. In FIG. 4, a controller 410 has a data entry mode selector module 425. The data entry mode selector module 425 contains program instructions executed by the controller 410 that detect a mode that the device is operating in. In one embodiment, the device can operate in either numeric mode or alphanumeric mode. In numeric mode, activation of each data entry key 301-312 is interpreted by the controller 410 as numeric input selections. This mode is associated with tasks such as entering a phone number to be dialed, or entering a phone number in a contact list maintained on the device. In one embodiment, when the device is operating in numeric mode, activation of each data entry key 301-312 causes a DTMF signal to be generated. Each data entry key 301-312 has a corresponding DTMF signal, unique among all data entry keys in the keypad 330, and in accordance with an industry standard for DTMF signals. In alphanumeric mode, activation of each alphabetic data entry key 302-309 is interpreted by the controller 410 as an alphanumeric input selection, as described in further detail below.

[0047] In one embodiment, data entry mode selector module 425 determines the selection between the numeric and alphanumeric modes by detecting a current task of the user. For example, when the user selects the task of generating an SMS message, the controller 410 detects the task selection, and in accordance with a pre-assigned data entry mode for this task, the data entry selector module 425 sets the controller to operate in alphanumeric data entry mode. Similarly, when the user wants to dial a telephone number or add a telephone number to a listing in the cell phone 300, and the user selects the appropriate task, for example via a selection on a displayed menu, the data entry selector module 425 sets the controller 410 to numeric data entry mode.

[0048] In one embodiment, the selection of alphanumeric mode or numeric mode is performed explicitly by a user, using a data entry mode activator, such as a button (not shown). A combination of the two mechanisms may be used, where the data entry mode selector 425 automatically selects a data entry mode based on the user task, and the user has the option of overriding the automatic selection and changing the data entry mode manually. This embodiment is useful, for example, where a user is entering a text message and wants to insert a phone number into the text. By selecting numeric mode while entering text, the entry of a phone number is made easier.

[0049] The keypad 330 has an output 407 coupled to the controller 410. When the controller 410 is operating in alphanumeric mode, the controller 410 detects each data entry key activation and the amount of time that has passed since the most recent data entry key activation, or the length of time between data entry key activations. A memory is coupled to the controller 410 and stores a key mapping 415, which includes the assignments between the physical data entry keys, the number of times a data entry key is activated, and the alphanumeric characters. The controller 410, then provides an output signal to an output 420, the output signal indicating the alphanumeric character selected by the user. In one embodiment, successive selected alphanumeric characters are stored in a memory and become a generated text string. The text string may be used to create a message, as data stored in a phone list, for notes, for entering text in a web browser, or for other uses of text strings.

[0050] In one embodiment, a display 317 is coupled to the controller 410. In one embodiment, the output signal from the controller causes the appropriate alphanumeric character to be displayed on the display 317. In one embodiment, as the user repeatedly activates an entry key and has not completed selection of a character, each successive activation causes a tentative character selection to overwrite the previous tentative character selection on the display 317.

[0051] In one embodiment, a shift selector, such as a button or switch, is provided on the device. The shift selector may be implemented in a variety of ways to allow a user to conveniently enter data in a combination of upper case and lower case. In one embodiment, activation of the shift selector specifies that the next single character selection is to be made from a set of upper case characters. Subsequent characters are selected from lower case characters, unless the shift selector is activated again. In one embodiment, activation of the shift selector specifies that the most recent previous character selection is to be converted to its corresponding upper case character. In one embodiment, upper case characters are selected by default, and the shift selector is used to specify that the next or previous character selection is a lower case character. In one embodiment, the shift mode is automatically determined based on a current activity of the user. For example, an activity may limit text input to upper case characters by automatically changing the device to upper case mode, and preventing changing of the mode. As used herein, unless explicit reference is made to an upper case character or a lower case character, specifications of a letter of the alphabet refer to the letter and to a corresponding character, which may be upper case or lower case. For example, a specification that the letter “E” is selected specifies either an upper case “E” or a lower case “e”, depending on the current shift mode. Designations of a letter “E” on a key or in a key map are to be interpreted as equivalent to a designation of “e” unless explicitly stated otherwise.

[0052] In one embodiment, the display 317 receives an indicator signal from the controller 410 that indicates the mode of data entry and whether the shift function has been activated. The indicator signal switches a shift mode indicator 325 accordingly to provide a visual indication to the user as to the status of the shift function. In one embodiment, the indicator signal switches a data entry mode indicator 320 to indicate whether the operational mode is alphanumeric or numeric.

[0053] In one embodiment, the controller 410 is physically located remotely from the communication device. The communication device transmits signals representing the activation of each input key. In one embodiment, the signals are DTMF signals. The controller receives signals representing the activation of each input key, and performs a process of determining corresponding alphanumeric characters, as described below. This embodiment is useful when the controller is part of, or communicates with, a server that communicates with the communication device. In one embodiment, a remote controller has more than one key mapping, and the communication device transmits data to the controller indicating a key mapping to use. In one embodiment, the communication device transmits the key mapping to the controller, allowing each communication device to have a key mapping that is not pre-programmed into the controller. In these embodiments, the remote controller determines alphanumeric characters from a number of communication devices using more than one key mapping.

[0054] In one embodiment, the key map 415 also includes a numeric digit corresponding to each alphanumeric key, where the numeric digit is the numeric digit corresponding to the data entry key. The numeric digit corresponds to an activation count that is one greater than the activation count corresponding to the last letter in the ordered set corresponding to each data entry key. For example, activating the “two” key four times results in a selection of the digit “2”. When numeric digits are included in the key map 415, their corresponding activation count is not based on frequency of use for the digit.

[0055] FIG. 5 illustrates a process 450 of determining a selected alphanumeric character using the present invention. The process 450 starts at a box 452. At a step 454, an activation count corresponding to the current character selection is initialized to zero. At a step 456, the controller 410 (FIG. 4) detects an alphanumeric input key activation has occurred. The controller saves an identifier designating the input key (302-309 in FIG. 3) that has been activated. Note that the processing of non-alphanumeric input keys is not illustrated in FIG. 5.

[0056] At a step 458, the controller 410 increments the activation count. At a step 460, a determination is made as to whether the input key activated and detected at the step 456 is the same or different from an input key activated during the alphanumeric character selection of the current process 450. The first time the determination 460 is made for a process 450 of selecting an alphanumeric character, the determination is always that a different key has not been activated, and control flow proceeds to a step 464, where a character corresponding to the combination of input key and activation count is displayed.

[0057] The character to display at step 464 is determined by using the key map 415 (FIG. 4) that associates each alphanumeric character with a corresponding combination of data input key (302-309) and activation count. In the key map, each character corresponds to a unique combination of data input key and activation count. For example, if the data input key 303, corresponding to the number three, has been activated one time, the alphanumeric letter “E” is displayed. Note that the letter “E” may be displayed in lower case or upper case, depending on the current shift mode.

[0058] After displaying a character at a step 464, a determination is made of whether a next input key activation is made prior to a predetermined timeout threshold elapsing between the prior key activation detection 456 and a next input key activation detection. If a period of time equal to or greater than the predetermined timeout threshold occurs, character selection is complete and flow proceeds to a step 468.

[0059] If a next input key activation is made prior to the timeout threshold occurring, flow control loops to the step 456. The steps as described above then repeat. On second and subsequent passes through the sequence of steps 456-466, at the step 460, the determination of whether a different input key has been activated may be positive. If this is true, flow control moves to a step 462, where the alphanumeric character selection is complete. In this situation, after the step 462 and associated processing of the character selection are completed, the process 450 starts again for the new character selection. The key activation detected at the step 456 for the new character is the different key that was detected at the step 460 for the processing of the previous character. The step 460 therefore allows only consecutive activations of an input key to be considered during the process 450 of determining a selected alphanumeric character.

[0060] In one embodiment, the key detection at step 456 only proceeds as illustrated when the key detected is one of a limited set of data entry keys. Activation of keys outside of the limited set are processed outside of the process 450, and flow returns to the step 456 when a key activation within the limited set is detected. In this embodiment, the detection of consecutive activations is therefore relative to the limited set of data entry keys.

[0061] At the step 464, the controller 410 accesses the key map 415 in the memory with an indication of the input key activated by the user and the number of times the key has been activated, and determines from the key map a tentative character selected by the user. This tentative character is displayed. Upon reaching the completion of the character selection (step 462 or 468), the tentative character becomes the actual character selection. The controller 410, then provides an output signal to an output 420, where the output signal indicates the character selected by the user.

[0062] In one embodiment, when the data entry mode is explicitly selected by a user, the controller detects the activation and toggles between numeric mode and alphanumeric mode. As discussed above, in one embodiment, a data entry mode actuator is not provided, and the mode of operation is determined based on the task that the user is performing. Dependent on the mode of operation of the controller 410, the activation of the data entry keys are interpreted by the controller 410 either as selection of numeric digits or selection of alphanumeric characters, by the user.

[0063] In numeric mode, the activation of a data entry key is interpreted as a numeric selection by the user. In numeric mode, an activation count is not kept, and each input key activation indicates the selection of one digit.

[0064] In the alphanumeric mode, the activation of the data entry keys and the number of times a particular data entry key is activated by a user are interpreted as alphanumeric selections by the user.

[0065] In alphanumeric data entry mode, the shift function is operational. Hence, when the controller 410 detects that the user has activated the shift function, by selection of a shift selector and the like, the controller 410 interprets data entry with respect to an alternate set of characters. The controller selects an upper case character or a lower case character corresponding to the selected letter, depending on the current shift mode.

[0066] In one embodiment, at the step 458, when the activation count becomes greater than the highest activation count corresponding to an alphanumeric character for the selected data entry key, the activation count is reset to one. In this way, the activation count wraps around, so that continuous activation of a single data entry key repeatedly cycles through the alphanumeric characters corresponding to the data entry key. In one embodiment, the key map 415 contains additional characters that may not be represented by indicia on the data entry keys 302-309. The additional characters correspond to activation counts greater than those for alphanumeric characters represented by indicia.

[0067] One advantage of the present invention is that mnemonic phone numbers, such as 1-800-ABCDEFG, and the like, can be entered in the same manner as with a conventional telephone because the correspondence between each letter and numeric key is compatible. The DTMF signal corresponding to each number is the same as for the standard phone of FIG. 1. Additionally, the DTMF signal corresponding to each letter is the same as for the phone of FIG. 1, even though the ordering of letters on each key, the key mapping, and the activation sequence is advantageously arranged, based on the frequency of use of letters, in accordance with the present invention.

[0068] Another advantage of the present invention is that, by maintaining compatibility between each letter and its corresponding numeric key, users can easily locate each letter, based on their knowledge of the alphabet and on conventional key mappings. Novice users quickly find the correct key to activate to select a desired letter without having to scan the keys as they might if the correspondence between letters and entry keys had not been maintained.

[0069] FIG. 6 illustrates one embodiment of a mobile electronic communication device 600 incorporating the present invention. The cellular phone 100 of FIG. 1 is one example of a mobile electronic communication device. Pagers, PDAs, and handheld messaging devices are additional examples of mobile electronic communications devices within which the present invention can be practiced. In this embodiment, the mobile electronic communication device 600 includes a transceiver 602, a display 603, a processor unit 604, a keypad 330, memory 610, a wireless interface unit 611, an audio speaker 612, a microphone 613, an operating system 615, and application software 616. In this exemplary embodiment, operating system 615 and application software 616 are stored in memory 610. In the embodiment illustrated in FIG. 6, memory 610 also stores the key map 415 (FIG. 4). As discussed above, a controller 410 (FIG. 4) is coupled to the memory 610 and employs the key map 415. In one embodiment, the controller 410 is implemented as instructions stored in memory 610 that are processed by processor unit 604. In one embodiment, controller 410 is implemented using a second processor and a second memory. Memory 110 may also be implemented as more than one memory component. Typically, memory 110 is implemented as a combination of a read-only memory component and a writable memory component.

[0070] In one embodiment, transceiver 602, display 603, keypad 330, memory 610, wireless interface unit 611, speaker 612, and microphone 613 are connected to processor unit 604. Processor unit 604 sends and receives commands from the operating system 615. The operating system 615 in conjunction with the processor unit 604 controls the application software 616. In one embodiment, keypad 330 is connected to the controller 410, which receives input signals when keys on the keypad are activated.

[0071] In operation, transceiver 602 is used to receive messages as in known mobile electronic communication devices, for example short message service (SMS), code division multiple access (CDMA), time division multiple access (TDMA), global system for mobile communications (GSM), and general packet radio service (GPRS). The wireless interface unit 611 operates in conjunction with the transceiver 602 to send and receive information. The audio speaker 612 converts the signals received from the transceiver 602 to sound. Display 603 is used to display text and/or images. In one embodiment, display 603 is an LCD. Processor unit 604 stores received message information in the memory 610. Processor unit 604 also controls display 603 to display the stored message information or other data from memory 610.

[0072] The present invention, as described, provides a keypad for efficient entry of letters, and combinations of letters and numeric digits. A single activation of the data entry keys selects letters that are more frequently used, and multiple activation of the data entry keys select letters that are less frequently used. The key mapping illustrated in FIGS. 3 and 4 is one embodiment of the present invention. In other embodiments, the precise ordering of alphanumeric characters on each input key may vary from the illustrated one, and still achieve benefits of the present invention, by generally placing more frequently used alphanumeric characters in positions that require less activations than those of less frequently used alphanumeric characters. Some devices may have one or more specific uses that vary the frequency of alphanumeric character uses. With these devices, the preferred order of characters on each input key may vary according to the frequency of their usage and the teachings of the present invention. Alternatively, on some devices, the exact key mapping may not be optimal for the particular usage of the device, but may vary in order to maintain a common key mapping with other devices in which the present invention is practiced.

[0073] For a given language, for example English, this is implemented by determining the frequency of use, sometimes referred to as the probability of occurrence, of each of the letters of the language. The letters are grouped in a manner compatible with standard telephone keypads, and the letters are ordered on each numeric key in order of decreasing frequency of use. Thus, the present invention, as described, advantageously makes user entry of the more frequently used letters more convenient and more efficient.

[0074] In one embodiment, the frequency of use of each letter is determined with respect to a corpus of usage representing general usage in a language. A table of probability of usage derived in this manner is included in “One-Gram Probability Distribution” from Alan G. Konheim's “Cryptography—A Primer,” John Wiley, 1981, p. 16. This work cites the letters of the English alphabet as the following, in decreasing order of frequency of use:

[0075] E, T, A, O, N, R, I, S, H, D, L, F, C, M, U, G, P, Y, W, B, V, K, X, J, Q, Z

[0076] In one embodiment, the above order of frequency of use is used to create the following ordered sets of letters corresponding to their respective numeric keys:

[0077] A, C, B—two key

[0078] E, D, F—three key

[0079] I, H, G—four key

[0080] L, K, J—five key

[0081] O, N, M—six key

[0082] R, S, P, Q—seven key

[0083] T, U, V—eight key

[0084] Y, W, X, Z—nine key

[0085] In variations of the embodiment illustrated in FIGS. 3 and 4, any one or more of the above ordered sets can be substituted for the ordered sets illustrated in these figures.

[0086] In one embodiment, the frequency of use of each letter is determined with respect to a corpus of usage of portable electronic devices that do not have a complete alphanumeric keyboard, a complete alphanumeric keyboard being one that allows each letter to have an input key distinct from each other letter. The frequency of use of letters on such devices varies from the frequency of use in the general language. For example, users of such devices often use abbreviations. They also use numbers to replace parts of words, such as using “SK8” in place of “SKATE.” Therefore, the present invention preferably employs frequencies based on this type of usage. In one evaluation of this corpus of usage, the frequency of use of letters within each group of letters on a standard keypad were compared with the frequency cited above. The following ordered pairs were found to differ from the above citation, where in each ordered pair the letter with the higher frequency appears first.

[0087] (S, R)

[0088] (Z, X)

[0089] From this data, the ordered sets corresponding to each key, as illustrated in FIGS. 3 and 4, were derived.

[0090] It will be appreciated that although only one particular embodiment of the invention has been described in detail, various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention. It will also be appreciated that the frequency of use of letters varies in situations where users predominately use languages other than English, or where geographical or cultural differences result in different corpuses of use. In these situations, ordered sets other than those explicitly described, and in accordance with the present invention, may be desirable.