Abstract:
It is not uncommon for two or more wireless-enabled devices to spend most of their time in close proximity to one another. For example, a person may routinely carry a personal digital assistant (PDA) and a portable digital audio/video player, or a cellphone and a PDA, or a smartphone and a gaming device. When it is desirable to increase the memory storage capacity of a first such device, it may be possible to use memory on one or more of the other devices to temporarily store data from the first device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/382,151 filed May 8, 2006, entitled, “Sharing Memory Resources of Wireless Portable Electronic Devices”, which will issue on Nov. 9, 2010 as U.S. Pat. No. 7,831,786, and which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Limited memory resources pose a challenge with some portable electronic devices. Applications installed on a portable electronic device are stored in the device&#39;s memory, as are user data items that are used by the applications and system data used by the applications and the operating system of the device. For example, a device having several different applications will store in its memory contact information, e-mail messages, tasks, calendar entries, instant messages, audio files, image files and other forms of user data items. 
     In order not to waste the limited memory resources, data may be arranged and stored in an efficient manner, and techniques such as compression may be used. A user may also be able to add additional memory to the device, or to replace the existing memory of the device with memory having greater storage capacity. There are also portable memory units that can provide additional storage for the device. For example, if the portable electronic device has a universal serial bus (USB) port and supports the ability to transfer data to an external storage unit, a USB flash drive may be connected to the portable electronic device and the user may transfer data from the device to the drive. In another example, if the portable electronic device is a Bluetooth® (BT) device and supports the ability to transfer data to an external storage unit, then the user may select certain data and transfer the selected data from the device to a dedicated BT hard disk drive. 
     At some point in time the memory of a portable electronic device may have insufficient capacity to store data in addition to whatever is currently stored therein, or the unused storage capacity of the memory may have fallen below a predetermined threshold. The user of the device may then be prompted to erase some user data items in order to increase the unused storage capacity of the memory. The device may have a memory manager that automatically erases some of the user data items when activated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which: 
         FIG. 1  is a block diagram of an exemplary communications system, according to some embodiments; 
         FIG. 2  is a flowchart of an exemplary method for transferring data items or portions thereof to a wireless portable electronic device having unused storage capacity, according to some embodiments; 
         FIG. 3  is a flowchart of an exemplary method for retrieving data items or portions thereof from the wireless portable electronic device, according to some embodiments; and 
         FIG. 4  is a schematic illustration of an exemplary communications system, according to some embodiments. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments. However it will be understood by those of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the embodiments. 
     A person using a first wireless portable electronic device with limited memory resources may face a dilemma when the memory of the first device becomes too full. Should user data items be erased from the first device to make room for new data? Should additional memory for the first device be purchased? Should an external storage unit be purchased? 
     However, the person may also have in his or her possession a second wireless portable electronic device that is often within range of the first device. For example, it is not uncommon for a person to carry a personal digital assistant (PDA) and a portable digital audio/video player, or a cellphone and a PDA, or a smartphone and a gaming device. Some people even carry three or more wireless portable electronic devices. A non-exhaustive list of examples for the devices includes any of the following: personal digital assistants (PDAs), electronic organizers, handheld computers, cellular telephones, smart phones, gaming devices, digital audio players, digital video players, mobile managers, wireless smart card readers and the like. 
     The first device and the second device may be able to conduct secure wireless communications therebetween using cryptographic techniques and authentication algorithms. A non-exhaustive list of examples of wireless communication protocols with which the first device and the second device may be compatible includes Bluetooth® (BT), ZigBee™, ultra wideband (UWB), wireless USB, IEEE 802.11, radio frequency identification (RFID) protocols, and proprietary communication protocols. The first device and the second device may each have an address by which it can be addressed in the wireless communication protocol. For example, if the devices are BT devices, the first device has a unique BT address and the second device has a unique BT address. 
     If the second device has unused storage capacity, then data items or portions thereof from the first device may be transmitted via the secure wireless communications to the second device for storage therein. The first device will replace the data item or portion thereof with information that will be used to retrieve the data item or portion thereof from the second device when desired. Since the information occupies less memory than the data item or portion thereof itself, the unused storage capacity of the memory of the first device is increased. Although this description focuses on a first device and a second device, there may be in fact more than one “second device” to which data items are transmitted from the first device for storage therein. A centralized book-keeping application may be used to keep track of where all of the externally stored data items have been moved to. This provides a method for sorting data items by device. In the case where the user wishes to make one of the second devices obsolete, all of the data items stored on that device may be retrieved to the first device and/or re-stored in other locations. 
     The transfer of data items from the first device to the second device may be initiated by the user of the devices, or may occur automatically when the unused storage capacity of the first device&#39;s memory decreases below a threshold, or may occur automatically because a rule applies. 
     Rules may be applied automatically by the first device in order to determine which data items are transferred to the second device, and in order to determine when, if at all, to transfer the data items back to the first device. The rules may also be applied even if the unused storage capacity of the first device&#39;s memory is above the threshold, as a preventative measure. A non-exhaustive list of examples for such rules is given below. 
     The data items transmitted from the first device to the second device for storage therein could be user data items and/or large system data items that are used infrequently by the first device. 
       FIG. 1  is a block diagram of an exemplary communications system  100 , according to some embodiments. System  100  comprises a first wireless portable electronic device  102  and at least one second wireless portable electronic device  104 . 
     When within range of each other, devices  102  and  104  are able to communicate securely over a wireless communication link  106  using cryptographic techniques. 
     Device  102  comprises an antenna  110 , a wireless communication interface  112 , a processor  114  coupled to wireless communication interface  112 , and a memory  116  coupled to processor  114 . Memory  116  may be fixed in or removable from device  102 . Memory  116  may be embedded or partially embedded in processor  114 . Processor  114  and memory  116  may be part of the same integrated circuit or in separate integrated circuits. Wireless communication interface  112 , compatible with a short-range wireless communication protocol, comprises a radio  117  coupled to antenna  110 , and a processor  118  coupled to radio  117 . Radio  117  may be a software-defined radio. Wireless communication interface  112  and processor  114  may be part of the same integrated circuit or in separate integrated circuits. Device  102  also comprises a cache  119  coupled to processor  114 . Cache  119  may be internal or external to processor  114 . 
     Similarly, device  104  comprises an antenna  120 , a wireless communication interface  122 , a processor  124  coupled to wireless communication interface  122 , and a memory  126  coupled to processor  124 . Memory  126  may be fixed in or removable from device  104 . Memory  126  may be embedded or partially embedded in processor  124 . Processor  124  and memory  126  may be part of the same integrated circuit or in separate integrated circuits. Wireless communication interface  122 , compatible with the same short-range wireless communication protocol as wireless communication interface  112 , comprises a radio  127  coupled to antenna  120 , and a processor  128  coupled to radio  127 . Radio  127  may be a software-defined radio. Wireless communication interface  122  and processor  124  may be part of the same integrated circuit or in separate integrated circuits. 
     A non-exhaustive list of examples for antennae  110  and  120  includes dipole antennae, monopole antennae, multilayer ceramic antennae, planar inverted-F antennae, loop antennae, shot antennae, dual antennae, omnidirectional antennae and any other suitable antennae. 
     A non-exhaustive list of examples for processors  114 ,  118 ,  124  and  128  includes a central processing unit (CPU), a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set computer (CISC) and the like. Furthermore, processors  114 ,  118 ,  124  and  128  may be part of application specific integrated circuits (ASICs) or may be a part of application specific standard products (ASSPs). 
     A non-exhaustive list of examples for memories  116  and  126  includes any combination of the following: 
     a) semiconductor devices such as registers, latches, read only memory (ROM), mask ROM, electrically erasable programmable read only memory devices (EEPROM), flash memory devices, non-volatile random access memory devices (NVRAM), synchronous dynamic random access memory (SDRAM) devices, RAMBUS dynamic random access memory (RDRAM) devices, double data rate (DDR) memory devices, static random access memory (SRAM), universal serial bus (USB) removable memory, and the like; 
     b) optical devices, such as compact disk read only memory (CD ROM), and the like; and 
     c) magnetic devices, such as a hard disk, a floppy disk, a magnetic tape, and the like. 
     Device  102  may comprise a user input component  130  and a user output component  132 , both coupled to processor  114 . A non-exhaustive list of examples for user input component  130  includes a keyboard, a microphone, a thumbwheel, a trackball, a joystick, a touch sensitive display and the like. A non-exhaustive list of examples for user output component  132  includes a display, a speaker, and the like. 
     Memory  116  may store applications  133  and code  134  to be executed by processor  114 , rules  136  to be implemented by code  134 , information  138  about data items or portions thereof that have been stored in device  104 , and data items  135 . 
     Devices  102  and  104  may comprise additional components which are not shown in  FIG. 1  and which, for clarity, are not described herein. 
       FIG. 2  is a flowchart of an exemplary method for transferring data items or portions thereof to a wireless portable electronic device having unused storage capacity, according to some embodiments. Code  134  stored in memory  116  may implement the method of  FIG. 2  in device  102 . The method of  FIG. 2  may occur in the background. Alternatively, the user of device  102  may be prompted for permission to perform the method of  FIG. 2 . Alternatively, the user of device  102  may initiate performance of the method of  FIG. 2 . 
     At  200 , device  102  determines to transfer at least one data item  135  or portion thereof to another device. This determination may be initiated by the user of device  102 , or may occur automatically when the unused storage capacity of memory  116  decreases below a threshold, or may occur automatically because one or more of rules  136  apply. 
     At  202 , device  102  asks device  104  how much unused storage capacity is in memory  126 . At  204 , upon receiving the storage capacity information from device  104 , device  102  determines the maximum amount of data it can send to device  104  for storage in memory  126 . The request and reply may be sent over wireless communication link  106 , possibly securely. Alternatively, device  104  could send its unused storage capacity information to device  102  periodically or upon connection with device  102  over the wireless communication link  106 . 
     At  206 , device  102  determines which data items  135  or portions thereof that are currently stored in memory  116  to transmit to device  104 . For example, rules  136  stored in memory  116  may be applied automatically by code  134  in order to determine which data items  135  or portions thereof to transmit to device  104 . A non-exhaustive list of examples for such rules is given below. 
     At  208 , device  102  writes information  138  in memory  116 . Information  138  is to be used in the future to retrieve from device  104  each data item  135  or portion thereof to be transmitted. Information  138  may include, for example, an address or other indication of device  104 . For example, the address may be the media access control address of device  104  or the unique BT address of device  104 , if device  104  is a BT device. Information  138  may include, for example, a short summary of data item  135  or portion thereof. Information  138 , or a portion thereof, may be stored using a centralized book-keeping application in order to keep track of where all of the externally stored data items have been moved to. 
     At  210 , device  102  securely transmits data items  135  or portions thereof, as determined at  206 , to device  104  over wireless communication link  106  using cryptographic techniques and authentication algorithms. Upon receipt, device  104  stores data items  135  or portions thereof in memory  126 . Devices  102  and  104  may have similar file systems and store data items  135  or portions thereof in the same way. Alternatively, device  102  and  104  may have different file systems and store data items  135  or portions thereof in different ways. Since data items  135  or portions thereof are serialized prior to transmission over link  106 , the file systems of device  102  and device  104  need not be the same or similar. 
     At  212 , once device  102  has received confirmation from device  104  that data items  135  or portions thereof were successfully received, device  102  erases from memory  116  the data items  135  or portions thereof that were transmitted to device  104 . 
     Instead of asking device  104  how much unused storage capacity it has in memory  126 , device  102  may begin the method of  FIG. 2  at  206  and risk that device  104  will refuse to store all or some of the data items  135  or portions thereof that are transmitted at  210 . In this embodiment, device  102  only erases the data items  135  for which it receives a confirmation of successful receipt from device  104 . In this manner, the data items  135  that device  104  refuses to store will not be inadvertently erased from device  102 . 
       FIG. 3  is a flowchart of an exemplary method for retrieving data items or portions thereof from the wireless portable electronic device, according to some embodiments. Code  134  stored in memory  116  may implement the method of  FIG. 3  in device  102 . 
     At  302 , device  102  identifies a need to retrieve a particular data item  135  or portion thereof from device  104 . For example, this need may be identified from user input received via user input component  130 . In another example, user data items of applications  133  of device  102  may be synchronized with one or more applications on another device, for example, a personal computer (not shown). If a particular user data item or a portion thereof is stored on device  104 , and the synchronization application requests that particular user data item or portion thereof, then device  102  will identify a need to retrieve the particular user data item or portion thereof from device  104 . 
     At  304 , device  102  securely requests the particular data item  135  or portion thereof from device  104  over wireless communication link  106 . The request is based, at least in part, on the information  138  related to the particular data item  135  or portion thereof. If no wireless communication link is established with device  104 , or if the link is lost, for example, in the case where device  104  is out of the wireless communication range of device  102 , the operation of retrieving the data item fails, and an error message may be displayed on device  102 . 
     At  306 , device  102  securely receives the particular data item  135  or portion thereof from device  104  over wireless communication link  106 . 
     At  308 , device  102  may store the particular data item  135  or portion thereof in cache  119 . Applications  133  on device  102  may access the particular data item  135  or portion thereof until it is overwritten in cache  119 . Memory  116  retains information  138  related to the particular data item  135  or portion thereof and memory  126  retains its copy of the particular data item  135  or portion thereof. 
     Alternatively, device  102  may store at  310  the particular data item  135  or portion thereof in memory  116 , instruct device  104  at  312  to delete its copy of the particular data item  135  or portion thereof in memory  126 , and at  314 , erase from memory  116  information  138  related to the particular data item  135  or portion thereof. 
     The following is a non-exhaustive list of examples for rules that affect which data items or portions thereof are to be transmitted from the first device to the second device, and that affect when the first device identifies a need to retrieve a particular data item or portion thereof. 
     Rules for Messages 
     If the first device has at least one messaging application to handle e-mail messages, instant messages, peer-to-peer messages, and the like, then any or a combination of the following rules, presented below in no particular order, may apply. 
     (1) The first device may automatically store old messages on the second device. This may take effect periodically, or when a memory manager of the first device requires more memory. The received time, sender and subject may be retained on the first device, so that the user is able to identify the message in a list of messages on the first device, and the body of the message may be stored on the second device. When the user attempts to access the message on the first device, for example, by opening the message to view it or by searching for the message, the body of the message may be retrieved from the second device. 
     (2) The first device may retain a first portion of a message body, for example, of a predetermined size such as 2 Kb, and may store the remaining portion of the message body on the second device. The user may view the first portion of the message body on the first device, but as the user scrolls down past the first portion, the remaining portion or a next portion of the message will have to be retrieved from the second device in order for the user to view it. The first device will have stored information in its memory to enable the first device to retrieve the next portion or the remaining portion from the second device. The message displayed to the user, for example, via user output component  132 , may have an indication that there are additional portions of the message body. The messaging application may automatically retrieve the next portion or the remaining portion from the second device when the user scrolls to the indication. Alternatively, the messaging application may wait for the user to provide input, for example, via user input component  130 , that the user wants to have the next portion or the remaining portion of the message body retrieved from the second device. 
     (3) Messages may be marked with a timestamp indicating the time at which the message was last accessed by the user of the first device. Messages with a timestamp older than a predefined duration, for example, 30 days, may be automatically transmitted to the second device for storage therein. 
     (4) Message attachments may be automatically stored on the second device, rather than on the first device, and retrieved only when required, for example, when a message is being forwarded to another recipient. A threshold attachment size may be specified, wherein attachments larger than a threshold size may be automatically stored on the second device, and smaller attachments remain on the first device. 
     Rules for Calendar Appointments 
     If the first device has a calendar application, then any or a combination of the following rules, presented below in no particular order, may apply. Calendar appointments include calendar meetings. 
     (1) Calendar appointments for dates prior to a cut-off date may be automatically stored on the second device, since they are unlikely to be accessed frequently by the user. The cut-off date might be the current date, for example, such that all calendar appointments from past dates may be automatically stored. 
     (2) Calendar appointments for dates that are more than a predetermined time in the future, for example, more than 30 days, may be automatically stored on the second device. As the date of the calendar appointment approaches and is less than the predetermined time in the future, the calendar appointment may be automatically retrieved from the second device and stored solely on the first device. 
     (3) Notes of calendar appointments may be automatically stored on the second device, and retrieved from the second device only when the user attempts to access them. 
     Rules for Other User Data Items 
     Similar rules may be applied to user data items of other types. 
       FIG. 4  is an illustration of an exemplary communication system  400 , according to some embodiments. System  400  is similar to system  100  of  FIG. 1 , where device  102  is a mobile device  402 , and device  104  is a wireless smart card reader  404 . Mobile device  402  and smart card reader  404  are able to communicate securely over wireless communication link  106 . In the example shown in  FIG. 4 , wireless smart card reader  404  has a user input component that is an electro-mechanical device  406 , however, other and/or additional user input components are possible. Similarly, in the example shown in  FIG. 4 , mobile device  402  has user input components  130  that include a thumbwheel  430 , a keyboard  431  and a microphone  432 , and user output components  132  that include a display  441 , a speaker  442 , and a light emitting diode (LED)  443 . 
     A smart card  408  is shown inserted into smart card reader  404 . Smart cards are personalized security devices, defined by the ISO7816 standard and its derivatives, as published by the International Organization for Standardization. A smart card may have a form factor of a credit card and may include a semiconductor device. The semiconductor device may include a memory that can be programmed with security information (e.g., a private decryption key, a private signing key, biometrics, etc.) and may include a processor and/or dedicated logic, for example, dedicated decryption logic and/or dedicated signing logic. A smart card may include a connector for powering the semiconductor device and performing serial communication with an external device. Alternatively, smart card functionality may be embedded in a device having a different form factor and different communication protocol, for example a Universal Serial Bus (USB) device. The person whose security information is stored on smart card  408  may use smart card reader  404  for identification, to unlock mobile device  402 , and to digitally sign and/or decrypt messages sent by mobile device  402 . Smart card  408  may also include a random number generator. 
     For example, mobile device  402  may be able to send and receive e-mail messages via an e-mail server (not shown). If, for example, the Secure Multipurpose Internet Mail Extensions (S/MIME) protocol is used, e-mail messages received at mobile device  402  are encrypted using a symmetric algorithm with a random session key generated by the sender of the e-mail message. The e-mail message also includes the session key, encrypted using the public key of the recipient. Upon receipt of an encrypted e-mail message, mobile device  402  may extract the encrypted session key and send it to smart card reader  404  via communication link  106 . Smart card reader  404  may send the encrypted session key to smart card  408 , and the decryption engine of smart card  408  may decrypt the encrypted session key using the recipient&#39;s private decryption key, which is stored in smart card  408 . Smart card reader  404  may retrieve the decrypted session key from smart card  408  and forward it to mobile device  402  via communication link  106  so that mobile device  402  can decrypt the received e-mail message. The smart card  408  may prevent unauthorized use of the recipient&#39;s private decryption key by requiring that a password or personal identification number (PIN) be supplied before allowing the decryption operation to proceed. 
     Similarly, to add a digital signature to an e-mail message being sent by mobile device  402 , mobile device  402  may send a hash of the contents of the e-mail message to smart card reader  404  over communication link  106 . Smart card reader  404  may pass the hash to smart card  408 , which may produce a digital signature from the hash and the sender&#39;s private signing key, which is stored in smart card  408 . Smart card  408  may then pass the digital signature to smart card reader  404 , which may forward it to mobile device  402  via communication link  106  so that mobile device  402  can transmit it along with the e-mail message to the e-mail server. Again, smart card  408  may prevent unauthorized use of the recipient&#39;s private signing key by requiring that a password or PIN be supplied before allowing the signing operation to proceed. 
     The unencrypted message key should be sent securely over communication link  106  from smart card reader  404  to mobile device  402  to prevent a third party from retrieving the message key from communication link  106 . Similarly, the hash to be signed should be sent authentically over communication link  106  from smart card reader  404  to mobile device  402  to prevent a third party from modifying the hash and thereby causing smart card  408  to produce a signature using a hash different from the hash of the intended message. Therefore communication link  106  may need to be secured using cryptographic techniques. 
     To secure communication link  106 , smart card reader  404  may need to generate various cryptographic keys. For example, if smart card reader  404  and mobile device  102  are BT devices, then a relatively short (up to 16-digits) key may be used for a Pairing procedure. An additional layer of security for communication link  106  may involve encryption with one or more additional keys. These additional keys may be generated from a shared secret between smart card reader  404  and mobile device  402 , and one or more symmetric keys based on this shared secret may be generated using known Diffie-Hellman and simple password exponential key exchange (SPEKE) methods and variants thereof. Moreover, random session keys may be generated for each individual communication session over communication link  106 . 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.