Nippon Telegraph and Telephone Corporation

Hitoshi Takanashi

Hiroyuki Yamamoto

Hidetoshi Kayama

Takeo Ichikawa

Satoru Aikawa

Masahiro Morikura

Yoichi Saito

Hideo Matsuki

Yasuhisa Nakamura

A method of packet transfer is provided to resolve the problem of fraudulent access to user LANs through falsified source address so that only those pre-registered terminals are permitted to transfer packets with specific data networks. Each user LAN is assigned an identifier to identify respective user LAN beforehand. Packet network stores terminal information including terminal addresses, identifiers assigned to one and more user LANs that are permitted to communicate with each packet terminal and information necessary for terminal authentication beforehand. When the packet terminal starts a communication through a base station, the packet network authenticates the packet terminal, and if it is an unauthorized terminal, the packet network informs a denial for communication to the packet terminal. If an allowance for communication is obtained by authentication, the packet terminal encrypts data to be transmitted and sends a packet to the packet network with an attachment containing the encrypted data, identifiers for the selected user LAN among one and more user LANs, the destination address and the source address. Packet network receives the packet, and while decoding the encrypted data included in the received packet, detects tampering, and if tampering is detected, the received packet is discarded, but if there is no tampering, it checks whether the identity of source address and the identifier is registered in the terminal information, and if the identity is registered, the received packet is sent to the destination address, and if the identity is not registered, the received packet is discarded.

Method and base station for packet transfer

An SR (Selective Repeat) ARQ system with limited buffer memory is realized by modifying a part of a user data area. A transmitter side modifies a part of a user data area in a data frame so that it differs at least one bit from corresponding part of a frame with the same frame number as that of a current frame in a preceding modulo turn, and a receiver side compares said part of a user data area with corresponding part of a frame with the same frame number as that of a current frame in a preceding modulo turn. When they coincide, the receiver side disregards the received frame as it is re-transmitted frame which is already received correctly, and when they do not coincide, the receiver side takes the received frame. Preferably, said part of a user data area is the last word area in a user data area in a frame structure. When a user data has more words than capacity of a user data area in a frame structure, and when last word is completely equal to last word of a frame with the same frame number as that of a current frame in a preceding modulo turn, the last word in a user data area is transferred to a succeeding frame, and an area for that last word is filled with a data which differs at least one bit from a data in the last word in the corresponding frame having the same frame number as that of the current frame in a preceding modulo turn.

System for re-transmission in data communication

In Trellis coded modulation system in which an input digital signal in parallel form is encoded by a convolutional encoder which adds an additional bit to the input digital signal for error correction purpose, and a mapping circuit designated amplitude and phase for each symbol for QAM signal, the number of parallel bits at output of said convolutional encoder is the same as the number of parallel bits of an input digital signal. An input digital signal is first rate converted so that m+n bits in every T period is converted to m bits in every T' period, where T'=(m/(m+n)).T. The convolutional encoder adds n number of bits so that the total number of parallel bits is m+n, which is applied to the mapping circuit. In a receive side, a received signal having m+n bits in every T' period is decoded through an error correction decoder which provides m bits in every T' period, then, the decoded signal is rate converted to m+n bits in every T period. So, the number of parallel bits does not increase in spite of convolutional encoding, but a transmission rate is a little increased. The coding gain in the present invention is improved since the number of levels of the QAM signal is not increased although the bandwidth of the signal is a little increased because of the higher clock rate.

Coded modulation communication system

Growing community of inventors

Kanagawa, Japan

Hitoshi Takanashi