Data transmission system utilizing spread spectrum codes, receiving device suitable for such a system and synchronization method for such a system

This data transmission system satisfies a specification of the type 3G TS 25.211 and, while using spread spectrum codes, is formed by at least a transmission part ( 10 ) for transmitting the data by using spread spectrum codes and at least a receiving part ( 20 ) for receiving said data. In this system first data are transmitted over the channel CPICH for a period of time that is relatively long, whereas second data are transmitted over the channel SCH for period of time that a relatively short. It is suggested that the second data be transmitted during the interruptions of the transmission of the first data, or also with an attenuation of this transmission.

In FIG. 1 is shown a system according to the invention. Reference 1 indicates a base station and the references 2 and 3 mobile stations. The base station comprises a transmission part of which a block 10 is shown in FIG. 1 . This block comprises a synchronizing data generator 12 . This generator produces the data for the channels CPICH and SCH defined in the specification cited above. These channels are transmitted by using spread spectrum codes CE(PI) for the channel CPICH for long periods of time and the code CE(S) for the channel SCH for rather short periods of time. These codes CE(PI) and CE(S) are multiplied by the multipliers 14 and 16 respectively, to the data streams of the channels CPICH and CE(S) produced by the generator 12 . As these codes CE(PI) and CE(S) are practically mutually orthogonal, it is possible to combine them on transmission, which is done in circuit 18 . The receiving part 20 of the mobile station 2 comprises a receiving circuit 22 which processes the signals received by the antenna 24 and produces a data stream which may be selected by using the decorrelators 26 and 28 and others for each of the transmitted channels. These decorrelators operate based on spreading codes assigned to each of these channels, notably the codes CE(PI) and CE(S) cited above. Other codes CE( . . . ) are used for the other channels. The data thus demultiplexed are fed to a processing circuit 29 for a normal use of the mobile. FIG. 2 explains the frame organization of the transmitted signals in accordance with the specification cited above. At A is represented the superframe of the channel CPICH which lasts: T super &equals;720 ms and which comprises 72 frames denoted Tr&num; 0 to Tr&num; 71 . At B is represented the structure of said frames which is in the form of time slots referred to as S 1 &num; 0 to S 1 &num; 14 each of which lasting T f &equals;10 ms. At C is shown the structure of these time slots which contain symbols, the symbols are combined with brief binary elements (chp) forming the spreading code (CE(PI)). These brief binary elements are better known by the English name of chip. At D is represented the transmission over the channel SCH of synchronization information. In accordance with the invention, when there is a transmission on the channel SCH, there is an attenuated transmission or this transmission is lost on the channel CPICH whose nominal value is A; this is indicated by &agr;×A at the line C. This duration is equal to a symbol or 256 chp. In FIG. 1 is represented by the switches 51 and 52 this transmission/no-transmission function. Thus the switch 51 is open for prohibiting any transmission on the channel CPICH when there is a transmission on the channel SCH, the switch 52 is thus closed. FIG. 3 shows the shape of the received signal transmitted by the channel SCH, without the measures recommended by the invention being applied. This signal is received by borrowing four main paths Ph 1 , Ph 2 , Ph 3 and Ph 4 . FIG. 4 shows the shape of this same received signal, transmitted by the channel SCH, by applying the measures recommended by the invention, while for the rest all matters are equal. The effect obtained by the invention is thus made obvious. The peaks relating to the various paths Ph 1 , Ph 2 , Ph 3 and Ph 4 are much more apparent than those obtained without implementing the invention.