Abstract: A sender converts a non-compressed packet, which is to be transmitted, into a full-header packet including a full header or a header-compressed packet including a compressed header, and sends the converted packet to a receiver. The receiver receives the packet transmitted from the sender, and converts the received packet into a decompressed packet. In cases the full-header packet or header-compressed packet is lost between the sender and receiver, the receiver keeps header-compressed packers received during an interval from the packet loss to the next earliest reception of a full-header packet, and decompresses the compressed headers of the kept header-compressed packets on the basis of contents of the full header of the full-header packet.

Abstract: In a radio paging system wherein a user carrying a radio paging receiver is paged by means of radio waves, and the radio paging receiver sends back a response signal when it has received a paging signal addressed to itself, the response signal is sent back by means of direct sequence modulation using a code uniquely determined in accordance with the base station ID signal, which is different for each base station, and which has been inserted in the paging signal sequence transmitted from the base station, or in accordance with the order of each paging signal within the paging signal sequence. As a result, the response signal can be transmitted at low power from each radio paging receiver, and effective utilization can be made of frequency, regardless of an increase in the number of radio pagers.

Abstract: A data communication system in which a data communication address for a communication terminal can arbitrarily be changed whenever the communication terminal is used. This data communication system includes a database 60 for storing a corresponding relation between an identifier 41 of a communication terminal 40 and a plurality of data communication addresses used for the communication. The database 60 stores a corresponding relation between the identifier 41 of the communication terminal and the data communication addresses during a period of use thereof in accordance with instructions from the communication terminal 40. When incoming data is received that is directed to certain data communication address, a network switching device 50 obtains an identifier corresponding to the certain data communication address and transmits the data to the communication terminal with the identifier.

Abstract: Sampled signals SPS of a spread-spectrum received signal are fed to matched filters 12.sub.1, to 12.sub.4, wherein they are despread. A spreading code of a desired signal is used as a despreading code in the matched filter 12.sub.1, and a plurality of spreading codes which are orthogonal to the spreading code of the desired signal and orthogonal to one another are used for despreading in the matched filters 12.sub.2 to 12.sub.4. Outputs x.sub.1 to x.sub.4 from the filters 12.sub.1 to 12.sub.4 are multipled by weighting coefficients w.sub.1 to w.sub.4 ; the multiplied outputs are linearly combined into a combined signal DCS. A coefficient control part 37 is supplied with the signals x.sub.1 to X.sub.4 to be multiplied by the weighting coefficients w.sub.1 to w.sub.4 and the combined signal DCS and determines the weighting coefficients w.sub.1 to w.sub.4 by an algorithm that minimizes the average power of the combined signal DCS under a constraint on the weighting coefficients w.sub.1 to w.sub.4.

Abstract: The phase of a received signal is detected by a phase detector at symbol intervals T relative to the phase of a local signal. The detected phase is input to delay circuits that are connected in series and each of which has the delay interval T. Phases .PSI..sub.n (where n=0, 1, . . . , N) with delays of 1 to N symbols are output to a metric calculating portion. The sum of a partial sequence {.DELTA..phi..sub.i ; i=n+1-q, n+2-q, . . . , n} of a N-symbol phase difference sequence candidate {.DELTA..phi..sub.n ; n=0, 1, . . . , N} is added to a detected phase .PSI..sub.n-q at a time point (n-q)T (where q=1, 2, . . . , N) so as to obtain an estimated value of the received signal phase .PSI..sub.n. The v-th power value of the absolute value of a difference .mu..sub.n (q) between the estimated value and the received signal phase is defined as a branch metric of q-symbol differential phase detection. .SIGMA..vertline..mu..sub.n (q).vertline..sup.v =.lambda..sub.

Abstract: A determinant, which represents the relationship between a sequence of code division multiplexed transmission symbol vectors b(k) from L communicators and a sequence of despread output vectors y(k) of received signals taking into account the cross correlation between spreading code sequences of transmitted signals, is limited within the range of .+-.g symbol duration about symbol timing k, and despread outputs of received signals within the limited range are inputted into a 2g+1-stage shift register. On the other hand, partial correlation matrixes R.sup.k+h (1), R.sup.k+h (0) and R.sup.k+h (-1) for each symbol duration within the limited range are calculated by a partial correlation computing part with respect to h=-g, . . . , g, then a correlation matrix R.sup.k between the spreading code sequences corresponding to the L communicators is derived from the partial correlation matrixes in an inverse matrix computing part and an inverse correlation matrix R.sub.k.sup.-1 of the correlation matrix is calculated.