Transmitting and receiving devices in cellular system

Abstract

In a multi-carrier cellular system, a second synchronization code (a Walsh code or a GCL series code) mapped on a second synchronization channel is used as a signal for specifying in which cell of the base station a mobile station terminal device itself is. A signal transmitted from the base station to the mobile station terminal device is mapped in a radio frame having two-dimensional extension in frequency and time directions. When mapping a certain series number of the second code for specifying a cell or a cell group on the radio frame as the second synchronization channel, phase rotation or circular shift in which one radio frame is one cycle is applied to the second synchronization code. On the receiving side, the head timing of the radio frame is known by knowing the phase rotation angle or the amount of circular shift of the second synchronization code.

Claims

1. A transmitting device comprising: processor circuitry configured to map each of a plurality of codes on a respective one of a plurality of synchronization channels, the codes being given values of initial offsets of phase rotation, and being different from each other, each of the plurality of codes undergoing circular shifting in a frequency domain, the circular shifting occurring by a shift amount that depends on a position within a radio frame at which each of the plurality of codes is mapped on a respective one of the plurality of synchronization channels, wherein one frequency shift cycle is completed within one radio frame; and a transmitter that transmits a signal put in a radio frame in which the plurality of synchronization channels are multiplexed in a time direction.

2. The transmitting device according to claim 1, wherein each of the codes is circularly shifted by a given amount of a circular shift according to a position of each of the codes in the radio frame.

3. The transmitting device according to claim 1, wherein each of the codes is a different sequence generated by shifting a given code.

4. The transmitting device according to claim 1, wherein each of the codes is a combination of codes whose sequences are different.

5. The transmitting device according to claim 1, wherein each of the codes is a different sequence generated by a same processing circuit.

6. The transmitting device according to claim 1, wherein each of the codes is used to specify a cell or a cell group in a cellular system.

7. A communication system comprising: a receiving device; and a transmitting device that puts a signal in a radio frame in which a plurality of synchronization channels are multiplexed in a time direction and transmits to the receiving device, wherein the transmitting device includes, a transmitter configured to map each of a plurality of codes on a respective one of a plurality of synchronization channels, the codes being given values of initial offsets of phase rotation, and being different from each other, each of the plurality of codes undergoing circular shifting in a frequency domain, the circular shifting occurring by a shift amount that depends on a position within the radio frame at which each of the plurality of codes is mapped on a respective one of the plurality of synchronization channels, wherein one frequency shift cycle is completed within one radio frame and transmitting the codes.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A illustrates the multiplexing of SCHs (No. 1);

(2) FIG. 1B illustrates the multiplexing of SCHs (No. 2);

(3) FIG. 2 illustrates an example of the hopping code pattern;

(4) FIG. 3A explains the second example of the prior art (No. 1);

(5) FIG. 3B explains the second example of the prior art (No. 2);

(6) FIG. 4 explains the first preferred embodiment of the present invention (No. 1);

(7) FIG. 5 explains the first preferred embodiment of the present invention (No. 2);

(8) FIG. 6 explains the first preferred embodiment of the present invention (No. 3);

(9) FIG. 7 explains the second preferred embodiment of the present invention (No. 1);

(10) FIG. 8 explains the second preferred embodiment of the present invention (No. 2);

(11) FIG. 9 explains the third preferred embodiment of the present invention (No. 1);

(12) FIG. 10 explains the third preferred embodiment of the present invention (No. 2) and

(13) FIG. 11 explains the third preferred embodiment of the present invention (No. 3).

DESCRIPTION OF EMBODIMENTS

(14) In the preferred embodiment of the present invention, firstly, as the first solution, although the series number of a Walsh code to be multiplexed on each SCH symbol in a radio frame is the same, the phase of each Walsh code is rotated by certain amount according to its position in the radio frame. The phase rotation is closed in the cycle of one radio frame.

(15) Alternatively, as the second solution, although the series number of a GCL series code to be multiplexed on each SCH symbol in a radio frame is the same, the GCL series code is circularly shifted by certain amount according to its position in the radio frame. The circular shift is closed in the cycle of one radio frame.

(16) Preferred embodiments of the present invention will be explained in detail below. The following preferred embodiment expresses timing synchronization using a first synchronization channel and cell group identification using a second synchronization channel and is based on three-stage cell search using a pilot channel. However, the present invention is not limited to it. For example, even in the case of another piece of timing synchronization method (a guard interval correlation method in the case of OFDM) or when the second synchronization channel indicates a cell identifier, the present invention is applicable.

(17) The first preferred embodiment of the present invention will be explained below with reference to FIGS. 4 through 6.

(18) The first preferred embodiment is the most basic preferred embodiment of the first solution. FIG. 4 is an example configuration of a base station device. Data signals of a data channel, the first synchronization channel, the second synchronization channel whose phase is rotated by a phase rotation processing unit 10 are multiplexed in a channel multiplex unit 11 and are converted from serial to parallel in a serial/parallel conversion processing unit 12. After the data signal is converted to a parallel signal, inverse Fourier-transform is applied to it in an IFFT processing unit to generate a signal in the time domain. Then, a guard interval is attached to the data signal in a guard interval insertion unit 14 and the data signal is transmitted via a radio process unit 15 and an antenna 16.

(19) The pilot channel is a reference signal for data channel modulation. The first synchronization channel is a common inter-cell signal for timing synchronization. The second synchronization channel is a Walsh code indicating a cell group identifier (or a cell identifier). The Walsh code is a code used for an extended code in W-CDMA and the like and is an orthogonal code having nature that correlation between codes belonging to different identifiers is 0. The base station belonging to a cell group identifier g uses the g-th Walsh code W. The phase of the second synchronization channel is rotated according to its position in a radio frame by the channel rotation processing unit 10. More specifically, the phase of the Walsh code of the second synchronization channel multiplexed on the i-th (i=0, 1, 2, . . . , N.sub.sync1) (N.sub.sync is the number of SCHs in a radio frame) SCH symbol is rotated by exp{j2i/N.sub.sync}. Thus, the phase is rotated one cycle or the one cycle of the phase rotation becomes the length of one radio frame. Specifically, the length becomes as follows.

(20) $\begin{array}{cc}\left[\mathrm{Mathematical}\mathrm{expression}3\right]& \\ \exp \left(\mathrm{j2}\frac{}{N_{\mathrm{sync}}}\right)W_g& \left(2\right)\end{array}$
The channel multiplex unit 11 multiplexes respective channels. The serial/parallel conversion processing unit 12 maps a signal sequence inputted from the channel multiplex unit 11 on a sub-carrier. The IFFT processing unit 13 converts the signal in the frequency domain to a signal in the time domain and generates a valid symbol. The guard interval insertion unit 14 copies the later portion of the valid symbol and attaches it the head of the valid symbol. After a wireless process, such as up-conversion and the like, is applied to the signal in the radio process unit 15, the signal is transmitted from the antenna 16.

(21) FIG. 5 is an example of the radio frame structure. In the example of FIG. 5, the pilot channel and the synchronization channel are disposed at the head and tail symbols, respectively, of a sub-frame. The first and second synchronization channels are alternately frequency-multiplexed. FIG. 5 is only an example of the channel multiplex method and the method is not restrictive of the present invention. As to the mapping method of the second synchronization channel, many methods can be considered. For example, mapping can be performed in an absolute phase assuming coherent detection using the first synchronization channel as the reference signal. Alternatively, mapping can also be performed by differential encoding. At any rate, the method is not restrictive of the present invention.

(22) FIG. 6 is an example configuration of the cell search processing unit on a mobile station.

(23) In a first-stage processing unit 20, the correlation process between the replica signal of the first synchronization channel having a known pattern stored in a first synchronization channel replica signal storage unit 21 and a received signal is performed in the time domain by a correlation processing unit 22, the result is time-averaged by a time averaging unit 23 and timing of obtaining the maximum correlation value is detected as detected sub-frame timing and detected FFT timing by a sub-frame timing detection unit 24.

(24) In a second-stage processing unit 25, the guard interval is eliminated according to the FFT timing detected in the first-stage processing unit 20 by a guard interval elimination unit 26 and the signal is converted to a signal in the frequency domain by the FFT process of a FFT processing unit 27. Then, a second synchronization channel extraction unit 28 extracts the second synchronization channel. In this case, since radio frame timing is unknown, the phase of the extracted second synchronization channel is also unknown. However, since the amount of phase rotation pre-determined by the transmitting side is given to the Walsh code, the amount of phase rotation per SCH symbol is known. A phase rotation processing unit 29 applies phase rotation the reversal of applied on the transmitting side for each received SCH symbol and a time averaging unit 39 time-averages the result. In this case, although the amount of phase rotation given to the SCH on the transmitting side differs depending on its position in the radio frame of the SCH symbol, it is known that the unit amount of phase rotation is 2/N.sub.sync according to Expression 2. Therefore, this unit amount of reverse phase rotation is applied. Its correlation with a candidate Walsh code stored in a candidate code storage unit 32 is taken and in a second synchronization channel radio frame timing detection unit 33, the second synchronization channel and radio frame timing are detected by determining the maximum correlation value and its amount of phase rotation. Specifically, since the amount of phase rotation of the correlation value is 2(i1)/N.sub.sync, what is the order of SCH symbol in the radio frame can be known by calculating a value i indicating the order from the head of the SCH symbol in the radio frame. Since the position of the i-th SCH symbol in the radio frame is fixed, the position of the head of the radio frame is known.

(25) In a third-stage processing unit 35, a pilot channel extraction unit 36 extracts a pilot signal from the sub-carrier in which the pilot channel is multiplexed. The correlation between the extracted pilot signal and a candidate scramble code stored in a candidate scramble code storage unit 37 is taken by a correlation processing unit 38 and it is averaged by a time averaging unit 39. Then, a scramble code detection unit 40 detects a candidate scramble code having the maximum correlation value from its time averaged value as a detected scramble code.

(26) The second preferred embodiment of the present invention will be explained below with reference to FIGS. 7 and 8.

(27) In FIGS. 7 and 8, the same reference numerals are attached to the same components as in FIGS. 4 and 6.

(28) The second preferred embodiment is obtained by applying the first solution to a method for increasing the number of codes of the second synchronization channel explained with reference to Non-patent document 3.

(29) FIG. 7 is an example configuration of the base station. The configuration is the same as that of the base station in the first preferred embodiment except for that the second synchronization channel includes two codes (the second synchronization codes 1 and 2). A phase rotation process is independently applied to the second synchronization codes 1 and 2. Specifically, each of the second synchronization codes 1 and 2 multiplexed on the i-th (i=0, 1, 2, . . . , N.sub.sync1) (N.sub.sync is the number of SCHs in a radio frame) SCH symbol can be expresses as follows.

(30) $\begin{array}{cc}\exp \left(\mathrm{j2}\frac{}{N_{\mathrm{sync}}}\right)W_{1,g}\exp \left(\mathrm{j2}\frac{+d}{N_{\mathrm{sync}}}\right)W_{2,g}& \left[\mathrm{Mathematical}\mathrm{expression}4\right]\end{array}$
In the above expression, d (0, 1, . . . , N.sub.sync1) is the off-set of the phase rotation of the second synchronization code 2 against the phase rotation of the second synchronization code 1. By combining this off-set with the series numbers of the second synchronization code 1 and 2, the number of codes of the second synchronization channel becomes MMN.sub.sync and can be increased to N.sub.sync times as much as that of Non-patent document 3. However, M is the length of the second synchronization codes 1 and 2. In this way, a phase rotation processing units 10-1 and 10-2 perform the phase rotation of the second synchronization codes 1 and 2, respectively, and the channel multiplex unit 11 multiplexes them.

(31) FIG. 8 is an example configuration of the cell search processing unit in a mobile station.

(32) The first-stage processing unit 20 and the third-stage processing unit 35 are the same as those of the first preferred embodiment. The second-stage processing unit 25a includes a code separation unit 50 after the time averaging of the time averaging unit 30 and the process of a second synchronization channel radio frame timing detection unit differs from that of the first preferred embodiment. The code separation unit 50 separates the two second synchronization codes 1 and 2 multiplexed on the second synchronization channel. The correlation processing unit 31 performs the correlation operation between each received second synchronization code and a candidate Walsh code. The second synchronization channel radio frame timing detection unit 33 specifies the series number of each second synchronization code on the basis of the maximum correlation value, determines the amount of phase rotation of the correlation value of the second synchronization code 1, detects radio frame timing, detects the phase difference between the maximum correlation values of the second synchronization codes 1 and 2 and detects phase rotation off-set on the transmitting side.

(33) The third preferred embodiment of the present invention will be explained below with reference to FIGS. 9 through 11.

(34) In FIGS. 9 and 11, the same reference numerals are attached to the same components as in FIGS. 4 and 6.

(35) The third preferred embodiment is the preferred embodiment of the second solution.

(36) FIG. 9 is an example configuration of the base station device. For the second synchronization code, a GCL series code indicating a cell group identifier (or a cell identifier) is used. Since the GCL code has been explained in the paragraph of BACKGROUND, please refer to the explanation. The second synchronization code is circularly shifted according to its position in the radio frame by the circular shift processing unit 10a. More specifically, the second synchronization channel multiplexed on the i-th (i=0, 1, 2, . . . , N.sub.sync1) (N.sub.sync is the number of SCHs in a radio frame) SCH symbol in the radio frame is circularly shifted by id. The circular shift is designed to finish in one cycle of one radio frame. Specifically, the following relationship is established.

(37) [Mathematical Expression 5]
N.sub.syncd=L.sub.SSCH(3)
In the above expression, L.sub.SSCH is the length of the second synchronization code.

(38) However, although as illustrated in Expression 3, L.sub.SSCH is expressed in the form of the product of integers, it is necessary for the length of the GCL series code to be a prime number. Therefore, L.sub.SSCH and the length L.sub.GCL of a GCL series code used for the second synchronization code does not equal (L.sub.GCL is not a prime number according to Expression 3). Therefore, a method for shortening the GCL series code having the series length of the minimum prime number smaller than L.sub.SSCH or a method for filling up a GCL series code having the maximum prime number smaller than L.sub.SSCH with 0, a method for repeatedly using a part of a code or the like can be considered. Although the characteristic, such as an auto-correlation characteristic and the like, of a GCL series code is improved when its series length is a prime number, as described above, it has a characteristic sufficient to map it on an SCH and use it even when the series length is adjusted. Since the detection of the GCL series code, based on IDFT has no relation with the fact that the series length is a prime number, the use of a GCL series code (although it cannot be purely called a GCL series code since its series length is not a prime number) having length equal to L.sub.SSCH can be also considered.

(39) Furthermore, by attaching initial off-set (=0, 1, . . . , d1) to the circular shift, the initial off-set can be combined with a GCL system number used for the second synchronization code and the number of codes usable as the second synchronization codes can be increased.

(40) FIG. 10 is an example of the radio frame structure.

(41) In the example of FIG. 10, the pilot and synchronization channels are disposed at the head and tail symbols, respectively, of the sub-frame. The first and second synchronization channels are alternately frequency-multiplexed. FIG. 10 is only one example of the channel multiplex method and it is not restrictive of the present invention. As to the mapping method of the second synchronization channel too, many methods can be considered. For example, the second synchronization channel can be also mapped in an absolute phase assuming coherent detection using the first synchronization channel as the reference signal. Alternatively, it can also be mapped by differential encoding. At ant rate, the method is not restrictive of the present invention.

(42) As illustrated in FIG. 10, although in the 0-th SCH symbol of the second synchronization channel, non-circularly shifted GCL series codes (S.sub.0, S.sub.1, . . . , S.sub.L2 and S.sub.L1) are used, in the i-th SCH symbol, ones obtained by circularly shifting the same GCL series codes by id (S.sub.Lid, S.sub.Lid+1, . . . , S.sub.Lid2 and S.sub.Lid1) are used.

(43) FIG. 11 is an example configuration of the cell search processing unit in a mobile station.

(44) The first-stage processing unit 20 and the third-stage processing unit 35 are the same as those of the first preferred embodiment. In the second-stage processing unit 25b, the guard interval elimination unit 26 eliminates a guard interval according to the FFT timing detected by the first-stage processing unit 20 and the FFT processing unit 27 converts the signal to a signal in the frequency domain by its FFT process. Then, the GCL system mapped on the second synchronization channel is extracted. In this case, since radio frame timing is unknown, the starting position of the received GCL system (on what order SCH in the radio frame the GCL series code is mapped) is unknown. However, the unit amount of circular shift of an SCH symbol is known. Therefore, in the circular shift processing unit 29a, circular shift the reversal of the unit circular shift applied on the transmitting side for each received SCH symbol is applied on the receiving side and the result is time-averaged. The differential demodulation unit 55 differentially demodulates the received GCL system. The differential demodulation performs a process expressed by the following expression.

(45) [Mathematical Expression 6]
D(n)=R(n)R*(n+1)
In the above expression, R(n) indicates the n-th symbol in the received GCL system. The IDFT processing unit 56 applies an IDFT process to the differential demodulation output. The result of the IDFT process becomes as follows.

(46) $\begin{array}{cc}\left(k\right)=\underset{n=0}{\overset{n=L_{\mathrm{GCL}}-1}{.Math.}}D\left(n\right)\exp \left(\mathrm{j2}\frac{\mathrm{nk}}{L_{\mathrm{GCL}}}\right)& \left[\mathrm{Mathematical}\mathrm{expression}7\right]\end{array}$
An IDFT output peak detection unit 57 specifies k.sub.max in which the output power |(k)|.sup.2 of the IDFT processing unit 56 is a maximum as a detected GCL system number. The principle of detecting this GCL system number is the same as explained in the prior art. A circular shift correlation processing unit 59 reads the GCL system replica s(nd) of the detected GCL system number from a GCL system replica storage unit 60 and correlates circular shift d=0L.sub.GCL1 with the received GCL system.

(47) $\begin{array}{cc}\left(d\right)=\underset{n=0}{\overset{n=L_{\mathrm{GCL}}-1}{.Math.}}R\left(n\right)s*\left(n-d\right)& \left[\mathrm{Mathematical}\mathrm{expression}8\right]\end{array}$
The circular shift correlation output peak detection unit 60 detects and circularly shifts d.sub.max in which |(d)|.sup.2 becomes a maximum. Since d.sub.max indicates the amount of circular shift of the received GCL series code, it indicates on what order SCH in the radio frame the GCL series code is mapped. Since the time difference between the head of the radio frame and the SCH symbol is known in advance, by knowing d.sub.max, radio frame timing can be known.

(48) When radio frame timing is known, the position of the head of the radio frame is known. Therefore, data can be received.

(49) All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.