JP2005269061A - Wireless communication system in which reception timing is controlled - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform good wireless communication by suppressing interference with other station in code division multiple access system. <P>SOLUTION: The wireless communication system includes a plurality of mobile stations and base stations utilizing a spread spectrum system and performs symbol semi-synchronization transmission for arranging the timing of the transmission symbol, of a transmission signal of each mobile transmission, arriving at the base station to a time sufficiently shorter than one symbol time for a reference symbol synchronization timing being provided at the base station when the plurality of mobile stations and base stations perform signal transmission. Timing difference between the reference symbol synchronization timing being set at the base station and the symbol timing of a signal being transmitted from the mobile station is measured at the base station and after data concerning that timing difference is transmitted to the mobile station through transmission from the base station to the mobile station, the mobile station regulates a symbol transmission timing provided in itself by an amount corresponding to the timing difference thus updating the symbol transmission timing which is employed in subsequent signal transmission. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to multiple access using spread spectrum technology in the field of wireless communications.

  Multiple access using spread spectrum technology is used in terminals and base stations of mobile phone systems, access points and terminals of wireless LAN systems, and the like. That is, the present invention can be applied to any wireless communication system that uses a code division multiple access method.

  Patent Document 1 is cited as a prior art for synchronization timing control in multiple access using spread spectrum technology. In the method described there, in the signal transmission (uplink) from the mobile station to the base station, "the maximum value of the round-trip propagation time between the base station and the mobile station" defines the upper limit of the synchronization timing error, The mobile station transmission SS (spread spectrum) signal spreading code timing is subordinately synchronized with the spreading code timing of the code division multiplexed signal received by the mobile station at the base station transmission ”,“ Code Division Multiple Access Signal Timing and Base Station Transmission Is established within the timing error range defined by the maximum value of the round-trip propagation time between the base station and the mobile station. The quasi-synchronized state is realized by finely adjusting the timing based on the transmission timing.

  Moreover, the thing of a nonpatent literature 1 is mentioned as a synchronous timing control technique. Here, a technique is shown in which the transmission timing of the mobile station is adjusted to control the timing at which the beginning of the frame arrives. In addition, a method is shown in which a timing shift is tracked by finely adjusting the time width of ¼ (1/8) chip for each “slot” which is a data block shorter than a frame.

  By the way, in the prior art, in order to allow a reception timing error (in other words, a signal is received at a quasi-synchronous timing), it is sufficient to take a margin of time for reciprocating between a base station and a mobile station at the maximum. FIG. 2 (1) schematically shows the reciprocation of the reference signal from the base station to the mobile station (1, N). The above-mentioned “sufficient margin for the time to reciprocate between the base station / mobile station” is the timing ((s) → (k) → (m), (m), ( s) → (l) → (n)), and each mobile station (1, N) transmits a signal.

However, in practice, in order to know the reception timing (at the mobile station) of the spread spectrum signal transmitted by the base station, it is necessary to despread (spread demodulation) the spread spectrum signal by some method. This requires a certain amount of time, generally at least a time (Tp) corresponding to one cycle of the spreading code. That is, the maximum synchronization timing error is as shown on the left of FIG.
Tp + [maximum round-trip propagation time]
It becomes.

  However, in the above, it is assumed that the time required for signal processing is zero, and that the reception timing can be reliably detected in one cycle time Tp of the spread code. As described above, a “guard section” is required to allow “reliable detection of the reception timing in one period of the spreading code”, and more than one period time of the spreading code is required in the guard section. Such a long guard interval leads to a decrease in data rate and a decrease in spreading gain due to the use of a shorter spreading code, and in any case leads to a significant deterioration in system performance.

For example, a micro cell with a radius of 300 m
・ Chip rate is 1 Mchip / s (seconds)
・ One symbol time (time including spreading code and guard interval) is 100 chips.
Assuming that the guard interval is about 0.2 ms, the data rate is only about 5 kbps when binary modulation is performed. Considering the expansion of the cell radius in mobile communication and the application to satellite communication, the data rate further decreases.
Japanese Patent No. 2653421 E. Hong, S .; Hwang, K .; Rim, and K.K. Whang, “Synchronous Transmission Technology for the Reverse Link in DS-CDMA Terrestrial Mobile Systems”, IEEE Trans. Commun. , Vol. 47, no. 11, pp. 1632-1635, Nov. 1999.

  An object of the present invention is to perform better radio communication with a code division multiple access system with low interference between other stations at a receiving station.

The present invention has been made to achieve the above object. The wireless communication system according to claim 1 of the present invention is
Multiple mobile stations and base stations are included, and multiple mobile stations and base stations use spread spectrum,
When a plurality of mobile stations and a base station perform signal transmission, the timing at which a transmission symbol of a transmission signal of each mobile station arrives at the base station is set to one symbol time with respect to a reference symbol synchronization timing provided in the base station. This is a wireless communication system that performs symbol quasi-synchronous transmission to match a sufficiently small time. In the wireless communication system,
The base station measures the timing time difference between the reference symbol synchronization timing set by the base station and the symbol timing of the signal transmitted by the mobile station,
After transmitting the data related to the timing time difference to the mobile station through the transmission from the base station to the mobile station, the mobile station adjusts the symbol transmission timing provided for itself by the timing time difference and updates the symbol transmission timing. It is used for signal transmission.

The wireless communication system according to claim 2 of the present invention is
The radio communication system according to claim 1, wherein the reference symbol synchronization timing is set to an integer multiple of the information symbol time in the base station.

A wireless communication system according to claim 3 of the present invention is
Multiple mobile stations and base stations are included, and multiple mobile stations and base stations use spread spectrum,
A base station transmits a reference signal for synchronization, and a mobile station that has received the signal immediately transmits a signal to the base station.
A radio communication system that performs symbol semi-synchronous transmission. In the wireless communication system,
By estimating the arrival time of the reference signal at the mobile station and transmitting the signal after an integral multiple of the information symbol time from the estimated time, the arrival time difference at the base station of the transmission symbol transmitted from each mobile station is symbolized It is characterized by being within a time sufficiently smaller than the time.

A wireless communication system according to claim 4 of the present invention is
As a reference signal transmitted by the base station, an impulse waveform generated by inputting a specific binary sequence into IDFT (Inverse Discrete Fourier Transform) is used.
In the mobile station, the circuit that measures the received power detects the most concentrated part of the impulse waveform and estimates the arrival time of the reference signal.
A wireless communication system according to claim 3.

The wireless communication system according to claim 5 of the present invention is
A wireless communication system in which a base station transmits a known signal waveform at a mobile station, and derives a symbol arrival timing based on a delay profile created by the mobile station from a received signal of the waveform,
A guard section is provided before and after the signal waveform, which is a no-signal section where no signal is transmitted. When an information signal is transmitted, the tail part and the head part of the signal circulate in the preceding and following guard sections, respectively. Inserted as
A wireless communication system according to claim 1 or claim 2.

  By utilizing the present invention, first, a quasi-synchronized state with higher accuracy than that of the prior art can be established. In addition, since the arrival time of the received signal can be easily estimated, it is easy to introduce an interference removal technique that requires complicated calculation.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

<< First Embodiment >>
In the code division multiple access scheme, interference between other stations can be suppressed to an extremely low level by using an appropriate spreading code and aligning the timing of signals arriving at the receiver. The first embodiment relates to a technique for aligning signal arrival timings in a receiver when a plurality of transmitting terminals transmit information signals to a receiving station (corresponding to a base station in a cellular system).

  FIG. 3 is a schematic block diagram of a mobile station (transmitting station) and a base station (receiving station) constituting the wireless communication system according to the first embodiment of the present invention. FIG. 1 shows an example of a procedure in which such a mobile station (transmitting station) and a base station (receiving station) cooperate to correct the transmission timing of the mobile station (transmitting station) to an appropriate one. It is a time chart figure. A first embodiment of the present invention will be described with reference to FIGS.

  First, the mobile station (transmitting station) performs signal transmission (FIG. 1 (a)). This signal arrives at the base station (receiving station) (FIG. 1 (b)). Here, the reception symbol timing measurement unit 16 in FIG. 3B measures the timing of the received signal. By this measurement, the synchronization timing error measuring unit 18 grasps (measures) a deviation from the reference symbol timing in the base station (receiving station), that is, the synchronization timing error Δτ, for the received signal.

  At the receiving station, the reference symbol timing is continuously issued. This reference symbol timing is (as a result) the timing at which the arrival timing of the received signal from the mobile station (transmitting station) is aligned in symbol units, and is recorded every predetermined time. In FIG. 3 (2), the reference symbol timing at the base station (receiving station) is generated by the reference symbol timing generation unit 20 and input to the synchronization timing error measurement unit 18.

  The data of the grasped synchronization timing error Δτ is added to the transmission signal (symbol) from the base station to the mobile station at the reference symbol timing (one of them, FIG. 1 (d)). 3 (2), the synchronization timing error Δτ is input to the information modulation unit 24, added to the input data series, and transmitted from the base station to the mobile station via the spread spectrum signal generation unit 26. .

  In order to reduce the amount of information, the synchronization timing error Δτ is preferably a value within one symbol time.

  The mobile station that has obtained the data of the synchronization timing error Δτ corrects the reference symbol timing (transmission timing) provided on the mobile station side based on the synchronization timing error Δτ (FIGS. 1E and 1F). Referring to FIG. 3A, the received symbol timing measurement unit 4 in the mobile station receives a signal from the base station and grasps the synchronization timing error Δτ. The reception symbol timing measurement unit 4 passes the synchronization timing error Δτ to the symbol transmission timing control unit 6. The symbol transmission timing control unit 6 corrects the transmission timing (standard symbol timing) of the transmission timing generation unit 8 based on the synchronization timing error Δτ.

  The corrected transmission timing of the transmission timing generator 8 (reference symbol timing on the mobile station side) is reflected in the transmission of the transmission signal. That is, an input data sequence that passes through the information modulation unit 10 is input to the spread spectrum signal generation unit 12, and is subjected to spread modulation (by the spread code adding unit 14) in the spread spectrum signal generation unit 12, and the symbol transmission timing. The transmission timing is adjusted by a signal from the control unit 6.

  As shown in FIG. 1, a signal is transmitted from the mobile station at the corrected transmission timing ((g ′)), and as a result, the arrival timing of the signal is aligned at the base station ((h)).

In FIG. 2 (2), the base station receives signals from the mobile station 1 and the mobile station 2, and the synchronization timing error (T ₁ , T ₂ ) information is received from the mobile station 1 and the mobile station 2 by downlink signals. The mobile station 1 and the mobile station 2 correct the inherent transmission timing (that is, the reference symbol timing), and thus show the timing until the arrival timings of the signals from the mobile stations in the base station are made uniform.

  Normally, control information such as power control is communicated from the receiver (at the receiving station) to the transmitter (at the transmitting station), so the receiving station uses the symbol timing error value of each transmitting station as a control signal. In addition to this, it can be transmitted to the transmitting station.

  In the prior art, the maximum distance between the base station / mobile station limits the cell size, the guard interval, the number of spreading codes, etc. in establishing the quasi-synchronization state. In the first embodiment, The quasi-synchronized state can be established regardless of the situation. Also, some conventional techniques have been controlled to align the signal arrival time from each mobile station. In the first embodiment, the arrival time of each information symbol is the reference symbol timing of the base station. Therefore, the degree of freedom of transmission timing that can be selected by the mobile station is very high. Furthermore, although the prior art can be applied only to a system using a direct spread spectrum spread system, it can be said that the first embodiment can also be applied to a system adopting a multicarrier transmission system.

<< Second Embodiment >>
In the wireless communication system of the prior art, the base station transmits a reference signal for synchronization, and a plurality of mobile stations that have received the signal immediately transmit signals to the base station, and the base station receives signals from the plurality of mobile stations. It is said that communication can be performed as long as the reply signal does not interfere. However, in this system, in practice, time for processing the reference signal for synchronization in the mobile station is indispensable.

  Then, even if the reference signal for synchronization is a symbol unit and the reference symbol timing is engraved in the base station, the arrival timing of the return signal to the base station is It becomes difficult to synchronize with the symbol timing.

  Therefore, in the process of the reference signal for synchronization in the mobile station of the wireless communication system according to the second embodiment, the arrival time of the reference signal is estimated. Then, a reply signal is transmitted after an integral multiple of the standard symbol time from the estimated time. In this way, the arrival time difference of the transmission symbols transmitted from each mobile station at the base station can be kept within a time sufficiently smaller than the reference symbol time.

  FIG. 4 is a schematic block diagram of (1) a base station and (2) a mobile station constituting the wireless communication system according to the second embodiment.

  First, (1) On the reference signal generation side (base station), an impulse waveform generated by inputting a specific binary sequence to IDFT (Inverse Discrete Fourier Transform) is used as a reference signal. That is, the impulse waveform generation input sequence is input to the discrete inverse Fourier transformer 30, and the reference symbol timing is given from the reference symbol timing generation unit 20 to the transmission signal.

  (2) On the reference signal receiving side (mobile station), the square wave detection circuit 32 detects the most concentrated portion of the impulse waveform for the impulse waveform. Based on the detection result of the square detection circuit 32, the symbol timing calculation unit 34 estimates the arrival time of the impulse waveform signal, and is an integer multiple of the reference symbol time from the estimated time (that is, the timing of the uplink signal). ) Is confirmed. In response to this, the transmission timing generator 8 forms a transmission timing.

  As shown in FIG. 4, the discrete inverse Fourier transformer 30 is used to generate the impulse waveform at the base station, and the square wave detection circuit 32 is used to detect the impulse waveform at the mobile station, so that the mobile station clearly transmits the waveform. Timing is formed.

<< Third Embodiment >>
The third embodiment is substantially the same as the first embodiment. Therefore, the difference between the two will be mainly described.

  In the first embodiment, the mobile station performs signal transmission, and the base station (receiving station) that receives this signal measures the synchronization timing error Δτ of the mobile station. The base station returns the result to the mobile station, and the mobile station corrects the transmission timing.

  In the third embodiment, first, the base station transmits a signal waveform known to the mobile station, for example, a direct spread spectrum spread signal having an M sequence as a spread code. Receiving it, the mobile station creates a delay profile from the received signal having the waveform. Further, the mobile station derives the symbol arrival timing based on the delay profile.

  FIG. 5 is a schematic block diagram of (1) a base station and (2) a mobile station configuring a wireless communication system according to the third embodiment. First, (1) the reference signal generation side (base station) generates and transmits a signal waveform known to the mobile station (for example, a direct spread spectrum spread signal having an M sequence as a spread code) in the spread spectrum signal generation unit 26. . The spreading code is given from the spreading code generator 36. The reference symbol timing generator 20 adjusts the transmission timing.

  (2) The reference signal receiving side (mobile station) that has received the above-mentioned known signal waveform of the mobile station creates a delay profile by the delay profile generator 38, and derives the symbol arrival timing by the symbol timing calculator 34. To do. The transmission timing (standard symbol timing) of the transmission timing generator 8 can also be adjusted by this symbol arrival timing.

  FIG. 6 shows the structure of a signal emitted from the base station for one symbol time.

  FIG. 6 (1) shows the configuration of a signal waveform (“pilot waveform”) that is known to the mobile station that is emitted from the base station. A guard interval is provided before and after the signal waveform (one cycle of the spreading code), and this is a no-signal interval where no signal is transmitted. FIG. 6B shows the configuration of the information signal (data symbol). When an information signal is sent, it is inserted so that the tail part and the head part of the signal (one cycle of the spreading code) circulate in the guard sections before and after FIG.

  By configuring as shown in FIG. 6, the delay profile of the pilot signal is accurately formed. Furthermore, data symbols can be transmitted more reliably.

<< Other embodiments >>
The above-described embodiment, particularly the first embodiment, can be used, for example, in mobile phone communication, but can also be used for various other purposes.

  For example, application to a cellular system is also conceivable. That is, it can be used to align the symbol arrival timings of signals between mobile stations in the cellular uplink. Further, it can be applied to a wireless LAN system.

  Furthermore, application to a packet communication system using a CDMA system is also conceivable. In this case, packet asynchronous / symbol semi-synchronous wireless access is possible. From the macro point of view, the packet seems to be sent at an arbitrary time, but the micro is not synchronized between symbols, but it is quasi-synchronized. The transmitter can be simplified and is suitable for a wireless LAN using a CDMA system.

FIG. 1 shows an example of a procedure in which such a mobile station (transmitting station) and a base station (receiving station) cooperate to correct the transmission timing of the mobile station (transmitting station) to an appropriate one. It is a time chart figure. (1) schematically shows the reciprocation of the reference signal from the base station to the mobile station (1, N). In (2), the base station receives signals from the mobile station 1 and the mobile station 2 and gives synchronization timing error information to the mobile station 1 and the mobile station 2 by a downlink signal. The station 2 corrects the inherent transmission timing, and thus shows the timing until the arrival timing of signals from each mobile station in the base station is made uniform. FIG. 2 is a schematic block diagram of a mobile station (transmitting station) and a base station (receiving station) constituting the wireless communication system according to the first embodiment of the present invention. It is a schematic block diagram of (1) base station and (2) mobile station which comprise the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram of (1) base station and (2) mobile station which comprise the radio | wireless communications system which concerns on 3rd Embodiment. (1) is a configuration of a signal waveform that is known to the mobile station that is emitted from the base station. (2) is a configuration of an information signal (data symbol).

Explanation of symbols

4 ... reception symbol timing measurement unit, 6 ... symbol transmission timing control unit, 8 ... transmission timing generation unit, 10 ... information modulation unit, 12 ... spread spectrum signal generation unit, 14 ... Spreading signal applying unit, 16: reception symbol timing measurement unit, 18 ... synchronization timing error measurement unit, 20 ... reference symbol timing generation unit, 24 ... information modulation unit, 26 ... spread spectrum Signal generation unit, 30 ... discrete inverse Fourier transformer, 32 ... square detection circuit, 34 ... symbol timing calculation unit, 38 ... delay profile generation unit.

Claims (5)

Multiple mobile stations and base stations are included, and multiple mobile stations and base stations use spread spectrum,
When a plurality of mobile stations and a base station perform signal transmission, the timing at which a transmission symbol of a transmission signal of each mobile station arrives at the base station is set to one symbol time with respect to a reference symbol synchronization timing provided in the base station. In a wireless communication system that performs symbol quasi-synchronous transmission to match a sufficiently small time,
The base station measures the timing time difference between the reference symbol synchronization timing set by the base station and the symbol timing of the signal transmitted by the mobile station,
After transmitting the data related to the timing time difference to the mobile station through the transmission from the base station to the mobile station, the mobile station adjusts the symbol transmission timing provided for itself by the timing time difference and updates the symbol transmission timing. It is used for signal transmission,
Wireless communication system.   The radio communication system according to claim 1, wherein the reference symbol synchronization timing is set to an integer multiple of the information symbol time in the base station. Multiple mobile stations and base stations are included, and multiple mobile stations and base stations use spread spectrum,
A base station transmits a reference signal for synchronization, and a mobile station that has received the signal immediately transmits a signal to the base station.
In a wireless communication system that performs symbol semi-synchronous transmission,
By estimating the arrival time of the reference signal at the mobile station and transmitting the signal after an integral multiple of the information symbol time from the estimated time, the arrival time difference at the base station of the transmission symbol transmitted from each mobile station is symbolized A wireless communication system characterized in that it is within a time sufficiently smaller than time. As a reference signal transmitted by the base station, an impulse waveform generated by inputting a specific binary sequence into IDFT (Inverse Discrete Fourier Transform) is used.
In the mobile station, the circuit that measures the received power detects the most concentrated part of the impulse waveform and estimates the arrival time of the reference signal.
The wireless communication system according to claim 3. A wireless communication system in which a base station transmits a known signal waveform at a mobile station, and derives a symbol arrival timing based on a delay profile created by the mobile station from a received signal of the waveform,
A guard section is provided before and after the signal waveform, which is a no-signal section where no signal is transmitted. When an information signal is transmitted, the tail part and the head part of the signal circulate in the preceding and following guard sections, respectively. Inserted as
The radio | wireless communications system of Claim 1 or Claim 2.

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