Pulse or digital communications – Synchronizers
Patent
1996-01-24
1998-09-08
Bocure, Tesfaldet
Pulse or digital communications
Synchronizers
375372, 370252, 455 671, H04L 700
Patent
active
058056440
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a transmission timing measuring apparatus for measuring a transmission timing between channels in a digital communication system, e.g., a mobile communication system, in which a base station and a mobile station perform communication using different frequencies.
BACKGROUND ART
In recent years, in mobile communication systems which have rapidly spread, a PDC (Japanese digital mobile phone system), an NADC (U.S. digital mobile phone system), a GSM (European digital mobile phone system), a DMCA (Japanese digital MCA system), and the like are known as digital communication systems using TDM (Time-Division Multiplex) and TDMA (Time-Division Multi-Access).
In such a digital communication system, different transmission (carrier) frequencies are assigned to a base station serving as a fixed station and a mobile station serving as a movable station. Each frequency band is divided into a plurality of time slots, and data communication is performed using a corresponding time slot.
For example, as shown in FIG. 10, center frequencies F1 and F2 are respectively assigned to the base station and the mobile station, and each frequency band is divided into time slots 1 to 6 (indicated by Arabic numerals 1 to 6 in FIG. 10).
Each region defined by such frequency and time slot is called a channel.
FIG. 10 shows a case wherein data communication is performed by using time slot 2 (second channel), as indicated by the hatching.
The base station repeatedly transmits a signal to the mobile station at predetermined time intervals. Upon reception of each signal, the mobile station returns a burst-like signal (to be referred to as a burst signal hereinafter) which is kept ON for a predetermined period of time.
The signal transmitted from the base station is a continuous or burst signal.
Each of the signals transmitted from the base station and the mobile station is a signal obtained as follows. FIGS. 13A to 13C show signal formats based on the above NADC. As shown in FIG. 13A, one frame=1,944 bits (972 symbols) is constituted by slots 1 to 6, and 324-bit (162-symbol) data of each slot is subjected to digital modulation. The resultant data is then superimposed on a predetermined carrier signal, thus obtaining the above signal.
In the signal formats shown in FIGS. 13B and 13C, "G" represents a guard time; "R", a ramp time; "DATA", user information; "RSVD", reserved; "SACCH", a slow associated control channel; "CDVCC", a coded digital verification color code; and "SYNC", synchronization and training (to be referred to as a sync word hereinafter).
Note that each numeral value in the FIGS. 13B and 13C indicates the number of bits.
In such a digital communication system, if the mobile station side cannot transmit a burst signal within a specified channel alone, other channels are adversely affected.
More specifically, according to the digital communication scheme having slots 1 to 3 in FIG. 14, in channels other than a specified channel (to be referred to as a transmission channel hereinafter), signals from other mobile stations and the base station are transmitted. If, therefore, a burst signal deviates from the transmission channel, the signal causes radio interference with the signal in another channel.
FIG. 14 shows a case wherein the transmission timing of channel 2 deviates (broken line solid line) and causes radio interference with channel 1.
When such radio interference occurs, it is difficult for the reception side to receive only the signal in the transmission channel by separating it from the signal in another channel.
In order to prevent such a problem, in each system, as indicated by the hatching in FIG. 10, the transmission start time of a transmission channel (to be referred to as a reference channel), at which a base station (to be referred to as a reference station hereinafter) starts to transmit a carrier signal, is set as a reference time, and a difference To (to be referred to as a transmission timing hereinafter) between the transmission start time of a transmission
Anritsu Corporation
Bocure Tesfaldet
Webster Bryan
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