Random access communication method by CDMA and mobile station eq

Details Random access communication method by CDMA and mobile station eq Random access communication method by CDMA and mobile station eq

1994-10-25

1996-12-03

Olms, Douglas W.

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

375200, 375203, 375205, 375209, 375309, H04J 1300

Patent

active

055815472

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a CDMA (Code Division Multiple Access) random access communication method and mobile station equipment which enable a plurality of mobile stations and a base station to communicate using the same frequency and the same spreading code and permit random access to the base station from the mobile stations.
The service area of a mobile communication system called a cellular system is split into a number of cells, each of which is provided with a base station. Each cell is assigned at least one control channel, in the case of heavy traffic, two or more control channels, and a plurality of communication channels and each mobile station perform communication through the base station of the cell to which the mobile station currently belongs. Each mobile station under contract to receive services is assigned an identification number, and for example, in the case of sending a call originating signal to the base station over the control channel or sending a speech signal to the base station over the communication channel, the mobile station adds its identification number to the information to be sent.
The code division multiple access (CDMA) system that has been employed in the past is a communication system which multiplexes signals to be transmitted at the same frequency, by spectrum spreading them with spreading codes which differ with channels. The system configuration and capabilities of the conventional system are described in detail in a reference literature (R.C. Dixon, "Spread Spectrum Communication System," Jatec Shuppan). Now, a brief description will be given of a direct spreading CDMA system.
In FIG. 1 there is shown the configuration of a base station transmitting device in a typical CDMA communication system. N information sequences S1, S2, . . . , SN are provided to multipliers 41.sub.1, 41.sub.2, . . . , 41.sub.N, wherein they are spectrum spread by being multiplied by spreading codes C1, C2, . . . , CN from a spreading code generator 42 which differ with symbols in the information. These spread signals are combined by a combiner 43 at the same timing and the combined output is transmitted by a transmitter 44. At the receiving side, though not shown, the received signals are spectrum-despread by the same spreading codes C1, C2, . . . , CN as those used at the transmitting side, by which the N information sequences are extracted individually. In this case, pseudo-random noise codes of the same code length (chip number) (hereinafter referred to as PN codes) are used as the respective spreading codes.
As is well-known in the art, the PN codes can be generated by, for example, EXCLUSIVE ORing outputs from the last and a desired intermediate stage of a shift register composed of N delay stages, then inputting the EXCLUSIVE OR into the first stage of the shift register and driving it by a clock of a predetermined period (chip period) Tch. In this instance, a random code (an M-sequence code) of a fixed pattern which repeats with the longest (2.sup.n -1) chip period can be obtained according to the position of the intermediate state to be selected and the initial value to be set in the shift register. 1/Tch is called a chip rate and the period Tc of the M-sequence pattern that is generated is Tc=(2.sup.n -1)Tch.
In a digital mobile radio communication system, the transmitting timing of the mobile station is synchronized with a signal from the base station. That is, in one cell, each mobile station demodulates the signal sent from the same base station, then generates basic symbol timing for transmission which is synchronized with the symbol timing for transmission from the base station and transmits thereto a signal in synchronization with the basic symbol timing. The symbol mentioned herein is the minimum unit of information that is transmitted in the radio section.
The spreading codes that are needed to construct a large-capacity cellular CDMA system are code sequences which have excellent auto-correlation characteristics, that is, code sequences which, let

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