Current generations of mobile phones are versatile devices capable of exchanging data such as short text messages or speech data. The short message service (SMS) facility provided by the GSM cellular system has proved popular, in particular with the younger end of the market. In some parts of the world, downloading of logos and ring tones to phones has also developed into big business.

Increasingly, these devices are required to carry out more complex operations.

Some current models are able to send one of a small number of predetermined images included in their text messages, e. g. Nokia 8210. These images are used to enhance communication between the two users. The most modern handsets allow the Multimedia Messaging Service (MMS). This allows images and sound to be transferred in a similar way to SMS, but not during a call. The next generation of mobile telephones will be capable of sending video and data at faster speeds. However, the changeover to 3rd generation mobile telephone technology will not be instantaneous and users of older generation mobile telephones should not be ignored.

In accordance with a first aspect of the present invention, a communication system comprises a first communication device and a second communication device; wherein each device comprises an input; a display and a processor for controlling operation of the device; wherein, in use, an expression is transmitted from the first user to the second user; wherein a reference value is allocated to the expression by the first device; wherein the reference value is transmitted to the second device ; and wherein the second device displays an image under control of the second processor dependent upon the reference value received by the second device.

In accordance with a second aspect of the present invention, a method of operating a communication system comprises allocating a reference value to an expression produced by a first user, transmitting the expression and the reference value to a second user and causing an image to be displayed to the second user; wherein the image to be displayed is chosen from one of a plurality of stored images in response to the reference value transmitted.

The present invention enables new functionality to be applied to existing communication systems, such as mobile telephones, whereby animated conversation is made possible in which each user is able to display an image representing e. g. emotion information determined by the other user during a call.

Although any stored image can be displayed, preferably, the or each stored image comprises a face representing an emotional state and a plurality of faces may be stored to represent different levels of each emotional state.

Two users are able to send e. g. happy faces, sad faces or jubilant faces to each other during a call and the method is flexible enough to allow the faces to be of the users'favourite celebrities, such as footballers or pop stars, or personal caricatures.

Preferably, the user can alter the level of an emotional state being displayed by depressing a key on the phone.

The invention is applicable to any system which implements the 3d Generation Partnership Project (3GPP) specification, but preferably, the communication system comprises a mobile phone and the expression is a spoken expression.

In one example, the reference value is allocated by pressing numbered keys on the telephone keypad of the transmitting telephone during a call, so that a picture is displayed on the receiving telephone-each of the numbered keys being assigned to a separate emotion, such as happiness or anger. The first user may choose to control the image displayed to the second user in this way, but preferably, the spoken expression is analysed by a processor in the first user's communication system and a reference value automatically allocated by comparing the tone of the spoken expression with the tone of stored expressions.

An example of a communication system and a method of operating the same according to the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram illustrating a communication system adapted to operate in accordance with the method of the present invention; Figure 2 illustrates an example of how the keypad and specific emotional states are mapped for use in the invention of Fig. 1; Figure 3 illustrates different levels for the emotional states of Fig. 2; and,

Figure 4 illustrates in more detail, three different levels of the emotional state of sadness.

Figure 1 illustrates a communication system comprising a pair of mobile phones adapted for operating the method of the present invention. The features of each phone are the same. A first mobile phone 1 communicates via a GSM interface 3 with a second mobile phone 2. A first user speaks into a microphone 4 in his phone 1 linked to a GSM messaging system 5 via a coder-decoder (codec) 6 which is responsible for coding the speech for transmission and decoding it on reception. The messaging system 5 transmits the spoken expression to the second mobile phone 2 and an animated conversation software program 7 stored on the phone, also causes the messaging system to transmit a signal to instruct the phone 2 of a second user to display an appropriate image on a display 12 of the second user. Optionally, a lip syncing facility 8 may be provided which will operate in the second user's phone to animate the lips of the image based on the speech received. Thus, the images which the software program 7 causes to be displayed on the second user's phone relate more directly to the spoken expression used by the first user.

Each phone 1,2 also has a keypad 9 and a selector 10 which allows manual or automatic operation to be selected. For manual operation each key will cause a specific image representing the first user to be displayed on the second user's phone. If a webcam image is to be provided there is an input 11 to receive a signal from the webcam. The webcam may be used to provide a direct representation of the user who is speaking or to generate a caricature. Pre-generated caricatures can be stored and appear on the receiving phone when a particular person's phone number is recognised as calling the receiving phone.

Operation between two users talking on a mobile telephone, requires a hands- free kit or a separate display. In manual mode, for example, UserA says something that UserB finds surprising. To reflect this, UserB expresses the emotion verbally, but at the same time presses a numbered key on his handset which has been allocated to the emotional state-surprise. Instantly, a picture of a surprised face is displayed on UserA's display. UserA then asks why UserB is surprised while, at the same time,

UserA presses the key corresponding to the emotional state-puzzlement on his handset. The entire conversation can continue in a similar fashion.

In automatic mode, the system may use voice processing software so that the spoken expression is analysed and a suitable image is displayed to reflect the expression of the user. Alternatively, the software may be adapted to produce in a caricature a particular facial response to vowel sounds, consonants and diphthongs and display this. This enhances the experience by providing a primitive form of lip- syncing.

The system must have at least one character set in memory 13. Assume that the user can choose to display emotions using either a male or female face-two sexes.

Assume also that there are seven possible emotions to convey and each emotion has three levels. The system must then store 42 images. Each image is a bitmap of size 50x101 bits, which is rounded up to be 632 octets. Therefore the 26,544 octets are needed to store the complete character set for a male and female.

The system may allow the character sets to be interchangeable so that personal caricatures, pop stars or other celebrity faces can be displayed. The system may also allow pictures from the webcam to be used so that the real user is reflected. The character sets can be downloaded to the device from a PC and the webcam picture will be converted to a suitable format before downloading via the input 11.

If several character sets are stored, then callerID information can be used to automatically display the correctly assigned character. The number of character sets that can be stored will be device dependant.

Figure 2 shows an example of how six different emotions, boredom, sadness, anger, surprise, excitement and happiness could be represented, and how they are mapped to the numbered key on the telephone keypad 9. For manual mode, the user has the option of selecting the same key up to three times during the call to display a more intense level of the chosen emotional state. A fourth press will display the first emotion again. In automatic mode, one key can be defined to change the level, although the actual emotional state will have been derived from the users voice tone by the voice processing software. A example of the emotions and the range of levels is given in Fig. 3, ranging from"slightly", through"fairly"to"very". Figure 4 shows for one emotional state-sadness-how the character changes to become increasingly sad

as the level is stepped up. The key"0"may be used to toggle the sex of the character displayed.

The exchange of information between the two phone handsets 1,2 is realised using the 3GPP User-to-User Signalling (UUS) supplementary service.

An animated conversation task running on the first mobile phone 1 would use the UUS supplementary service to transfer a small amount of information between itself and the second mobile phone 2. For a basic example of the system, there are 42 faces to choose from. When sending information between the phones 1, 2 only 6 bits of information need be transferred. However, there are a sufficient number of octets available in the User-User message to allow more information to be transferred. This means that the extended capability indicating facial response to vowels, diphthongs and consonants can easily be accommodated.

A summary of the UUS supplementary service is given below. Further information can be found in documents 3GPP TS 22.087 v 4.0. 0 (2001-2003), 3GPP TS 23.087 v. 4.0. 0 (2001-2003) and 3GPP TS 24.087 v. 4.0. 0 (2001-2003) available from ETSI, Mobile Competence Centre, 650 route des Lucioles, 06921 Sophia- Antipolis Cedex, Valbonne, France. This supplementary service allows a mobile subscriber to the service to send and receive a limited amount of information to and from another Public Land Mobile Network (PLMN) or Integrated Services Digital Network (ISDN) subscriber over the signalling channel during a call to the other subscriber.

The differences between the three services are as follows: i. UUS Service 1 allows the transfer of UUI embedded within the Call Control messages ii. UUS Service 2 allows the transfer of UUI after reception of address complete (dialled) and receiving the answer indication iii. UUS Service 3 allows the transfer of UUI during an active call The services may be used with other networks (PLMN/ISDN). However, these networks may support a maximum User-User Information element length of 35 octets.

The standard specifies a maximum user-user data length of 130 octets. IEI Information element Type/Reference Presence Format Length Call control Protocol discriminator M V 1/2 Protocol discriminator 10.2 Transaction identifier Transaction identifier M V 1/2 10.3. 2 User Information Message type M V 1 Message type 10. 4 User-user User-user M LV 3-130 10.5. 4.25 AO More data More data 0 T 1 10.5. 4.19

Table 1: GSM 04.08 : USER INFORMATION message content There are three possible scenarios for communication. The first is a call from a first user whose phone is capable of animated conversations (animated conversation capable-ACC) to a user whose phone is not capable of an animated conversation (animated conversation incapable-ACI). The second is from an ACI user to an ACC user and the third is between two ACC users.

In the first case UserA wishes to establish a call using his ACC mobile telephone to UserB with his ACI mobile telephone.

UserA dials UserB; A call is established (both parties talk); UserA presses an emotion key on his handset for the first time; MSA sends Message: "Facility (Invoke=UserUserService (UUS3, UUS not required))" MSB does not reply; MSA receives the message"Facility (Return Error) "with content"requested facility not implemented" ; UserA sees a message on the display that that the receiving device (UserB) is an ACI device and UserA's display does not show any animated conversation content.

Successive key presses have no effect and the call continues normally, including normal termination.

In the second case UserA wishes to establish a call using his ACI mobile telephone to UserB with his ACC mobile telephone.

UserA dials UserB ; Call established (both parties talk); UserB presses an emotion key on his handset for the first time;

MSB sends Message: "Facility (Invoke=UserUserService (UUS3, UUS not required))" MSA does not reply; MSB receives the message"Facility (Return Error) "with content"requested facility not implemented" ; UserB receives a message stating that the receiving device is ACI. UserB's display does not show any animated conversation content and successive key presses have no effect. The call continues normally, including normal termination.

In the third scenario UserA wishes to establish a call using his ACC mobile telephone to UserB with his ACC mobile telephone.

UserA dials UserB; UserB's display may show an image of UserA which has been stored as a character set in memory; The call is established (both parties talk); UserA presses an emotion key on his handset for the first time; MSA sends Message; "Facility (Invoke=UserUserService (UUS3, UUS not required))" ; MSB replies"Facility (Return Result)" ; MSA receives the message"Facility (Return Result)" ; UserA's display shows a face with neutral expression; UserB's display shows a face with expression corresponding to the key pressed by UserA.

Further key presses by either party display the corresponding image on the opposing handset. Call continues in a similar fashion, including normal termination In the third scenario, operating in automatic mode, the display will be of a face having an emotional state which has been determined by the voice processing software from the spoken expressions of the user and will change as the user's voice changes.

Alternatively, a small add-on component, similar to a web-cam, could be attached to the phone, which would be used in hands-free mode, to recognise the emotions expressed on the user's face automatically, rather than analysing the voice tones, and then to send the information as before. The add-on component houses the

necessary processing capability and is connected via an I/O connector through the input 11.

The same mechanism can be used for the real time transfer of data, such as sending an address during a call, or a telephone number, a diary appointment, serial numbers, business card, small amounts of encrypted data etc. and also for interactive games-such as chess, checkers, hangman, etc., by modifying the image displayed dependent upon the keys being depressed on both handsets. For example, the cartoon characters can be made to fight eachother if a suitable application is downloaded onto the phone. This can work in tv mode or a combination of tv and manual mode.

The size and scope of the service depends on the resources of the mobile telephone device. One particular model may only have enough free memory to store a single character set, whereas another may have enough free resources to store several character sets as well as additional processing for lip-syncing.

The invention is not limited to use with mobile phones, but is intended for systems that implement at least the GSM specification The system requires at least a simple display, a keypad and a processor to run the software and means to store the cartoon images. The images may be distributed and sold via the Internet or the communications carrier of the user. The PC application allows the user to generate his own set of cartoons from a standard webcam.