For Immediate Release
February 4, 1998
NTT's New PC Card Simultaneously Sends Voice and Images via PHS
Nippon Telegraph and Telephone Corporation (NTT) has developed a PC card for Personal Handyphone System (PHS), a mobile phone that enables voice to be transmitted simultaneously with data or moving color images between mobile communication devices.The card, designed for 32kbit/s multimedia communication, uses 8 kbit/s for voice and the remaining 24 kbit/s for data or image transmission. PHS telephones installed with the card can be connected to an integrated services digital network (ISDN) via a general PHS network and, with the addition of a portable personal computer, can be used to send and receive visual data while talking simultaneously.
NTT will provide prototype mobile terminal sets to the Nagano Olympic Committee for use during the Nagano Olympic Winter Games. The network will be provided by NTT Central Personal Communication Network Inc. Results of this field trial will be used to plan future product development and marketing.
Background
While multimedia terminals continue to shrink in size, the demand for such devices grows unabated and has prompted a race to develop 32 kbit/s multimedia communication devices for PHS phones. NTT's new 32 kbit/s card is the result of the corporation's focus on realizing simultaneous communication of multimedia.
Technology
PHS Multiple Media Transmission Method
Simultaneous transmission of multiple types of information, including voice, data and images, in a wireless environment requires that 1) voice transmission be real-time, even at the cost of some noise interference, and 2) data and image communication be accurate. Accordingly, voice is sent only once, while other data are checked for transmission accuracy and, if necessary, re-sent automatically.
NTT's new card minimizes over head by using frame timing, without using control flags to verify media type, which results in a simple, efficient method for multiple media transmission over wireless channels.
PHS Multimedia Communication Control LSI
PHS communication of voice, data and images without transmission
delays requires loading the communication card with a microprocessor for transmission and multiplex control, and separate interfaces for voice Coder and DECoder (CODEC), the PHS and a personal computer. Installing the interfaces in separate components results is unsatisfactory, however, because this increases both energy consumption and size. NTT's card solves this problem with an NTT-developed large-scale integrated circuit (LSI) that combines interfaces for voice CODEC, connection devices and memory.
CS-ACELP 8 kbit/s Voice Encoding System
Voice is transmitted with a sound-encoding system called Conjugate Structure and Algebraic Code-Excited Linear Prediction (CS-ACELP), an international standard. NTT played an important role in the development of CS-ACELP, which requires only 8 kbit/s to produce the same voice quality of 32 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM).
Moving Picture Through Continuous Encoding of Still Image Frames
When sending moving pictures, a personal computer encodes all frames to ensure transmission accuracy and then send a number of still frames every second. Fewer frames are sent in a given amount of time compared
to the H.263 international standard for moving image data transmission, where each frame is encoded consecutively for linkage with the next frame to condense information volume. Under the H.263 standard, however, if a unit of information does not reach the receiver, the moving image sequence fails. Since NTT's system encodes each frame individually, the moving image sequence still works even when "insignificant" components of information with only limited visual information do not reach the receiver.
In the case of the Olympics, the organizers have stressed that their main concern with image transmission is not in its speed but in its reliability, which is why this system is considered more suitable to the needs of the NAOC. In addition, the frames are sent with frame controls, which allows the recipient to adjust frame size.
Future Developments
NTT will evaluate prospects for commercializing its new communication card based on the results of the field test at the Olympics. NTT already plans to add security and other functions before commercially launching the card for mobile multimedia communications.
