JP2000152332A - Mobile communication system employing cdma multiplexing technology - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a mobile terminal to retrieve a long spread code for decoding a signal channel at high-speed by using a 2nd perch channel, consisting of slots that are modulated by a short spread code to identify a start time of a long spread code transmitted from a base station, a short spread code for identifying a group of long spread codes and the long spread codes. SOLUTION: A short spread code C2 for slot synchronization and a short spread code C3 for classifying a long spread code group are transmitted through a 2nd perch channel that is used at a time rate of 10%. All slots of the new 2nd perch channel can be used, and the length of the spread code C3 can be extended because the short spread codes C2, C3 are transmitted through the 2nd perch channel. Thus, the choice items for long-spread codes D1 can be reduced to decrease a time required for the long-spread codes D1. Each slot of a 1st perch channel is specific to a mobile communication system as well as is made to code-modulate through duplicate spread of the short code C1 in common to each base station in the system and the long code D1 specific to each specific base station.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system using a CDMA multiplexing technique, and more particularly, to an interference generated between signals multiplexed by a CDMA system emitted from a base station. The present invention relates to a mobile communication system using a CDMA multiplexing technique capable of preventing a call control signal from being disturbed.

[0002]

2. Description of the Related Art In the CDMA system, a transmitting side modulates each radio channel with a unique spreading code and then multiplexes the data, and the receiving side performs a decoding operation called despreading using a code specific to each radio channel. This is a method of multiplexing / demultiplexing each channel. The above-described despreading operation on the receiving side requires that the receiving side previously know a spreading code specific to each channel, but as in a mobile communication system,
In the case of a system in which a different code is used for each call connection, it is necessary to provide a means for transmitting the spread code to be used to the receiving side in advance.

In the prior art of the mobile communication system using the CDMA system, for the above-mentioned purpose, an information channel called a perch channel is set in addition to a channel for transmitting user data for communication, and a reverse channel is set to this channel. It transmits code information for spreading. The perch channel itself is also code-modulated, but in general, the perch channel is decoded without transmitting a code for each call by using a predetermined code specific to the system. It becomes possible. However, a system that enables communication between an arbitrary mobile terminal and a base station for each call, such as a mobile communication system, or a system in which a plurality of base stations can be seen from one mobile terminal is called a base station. Each base station needs to have a unique code in order to separate the stations. For this reason, even if the mobile terminal decodes the above-mentioned perch channel by using a predetermined code unique to the system, it cannot distinguish the base station.

As a conventional technique for solving the above-mentioned problem, a perch channel is formed by a system-specific short common code C.
There is known a method of performing two-stage code modulation using two types of codes, i.e., 1 and a long individual code D1 unique to a base station.
In this case, the receiving side first performs despreading on the perch channel using the common code C1, and then performs despreading again using the individual code D1 unique to the base station. You can know the contents.

FIG. 5 is a diagram for explaining a perch channel signal system according to the above-mentioned prior art, which will be described below. In FIG. 5, A is one of the perch channels.
Slot B is one slot of the signal channel.

In the example shown in FIG. 5, a code for despreading used by a mobile terminal is transmitted by a perch channel as described above, and a user signal such as a speech signal and a data signal is carried on a signal channel. Can be Each slot A of the perch channel is double-spread and code-modulated by a short code C1 unique to the system and common to each base station in the system and a long code D1 unique to a specific base station.

A perch channel and an original signal channel (a plurality of signal channels are set for a plurality of mobile terminals) simultaneously transmitted from the base station are each transmitted to the same base station in order to avoid mutual interference. The spreading codes for modulating all the channels emitted from the station are determined to be orthogonal to each other. On the other hand, if the code D1 unique to the specific base station is made common to all signal channels emitted from the specific base station, the system configuration can be easily performed. Therefore, other signal channels other than the perch channel emitted from the same base station, that is,
Each slot B of the original signal channel is double-spread using another short code CN orthogonal to the short code C1 unique to the system used for the perch channel and a long code D1 unique to the specific base station. Code modulation is being performed. This makes it possible to ensure orthogonality between the perch channel and the signal channel.

However, in the above-described example, the mobile terminal does not know the code D1 unique to the base station in advance, and therefore, at the time of starting communication, the mobile terminal replaces all codes that can be considered in principle. You must try from one end to find the correct code. For this reason, if the types of the codes are enormous, it takes a lot of time to search for the codes.
Therefore, codes assigned to the base station are classified into some groups in advance, and the mobile terminal first detects which group a required code belongs to, and then searches for a code in the group. A method for compressing the search time by such a method is known.

Furthermore, in order to perform despreading using a long code D1 unique to the base station, it is necessary to know the time at which despreading is started from the code. However, in the example shown in FIG. 5, the start time of the code D1 cannot be known before the identity of the code D1 is known, and this must be solved.

FIG. 6 is a diagram for explaining another conventional perch channel signal system capable of solving the above-mentioned problems, which will be described below.

The example shown in FIG. 6 uses first and second types of perch channels as perch channels. Each slot of the first perch channel is defined by a short code C1 that is system-specific and common to each base station in the system and a long code D1 that is specific to a specific base station, as described with reference to FIG. It is composed of a region A1 which is heavily spread and code-modulated, and a region C.
In this area C, the spreading by the long spreading code D1 and the system-specific short spreading code C1 is interrupted, and instead the area C is spread using the short spreading code C2.

[0012] The spreading code C2 is used to clarify the transmission phase of the perch channel, and the mobile terminal can synchronize the slot of the perch channel by receiving the area C. That is, the mobile terminal can know from which time the long spreading code D1 was started. As the spreading code C2, a code predetermined by the system can be used similarly to the spreading code C1, but a special code with a small autocorrelation is used so that the mobile terminal can easily establish slot synchronization. Signs are used.

The second perch channel includes the first perch channel.
A region D is set at a time position synchronized with the region C of the perch channel. This area D is spread by a short spreading code C3 indicating to which classification (group) the long spreading code D1 unique to the base station belongs. A portion of the first perch channel between the regions D which is synchronized with the region A1 is left empty.

Conventional techniques relating to the mobile communication system using the CDMA multiplexing technique as described above include, for example, Kenichi Higuchi, Mamoru Sawahashi, Fumiyuki Adachi, "High-speed using long code mask in asynchronous cellular between DS-CDMA base stations. Cell Search Method ”IEICE TECHNICAL REPORT OF
IEICE DSP96-116, SAT96-111, RCS96-122 (1997-01)
And the like are known.

[0015]

In the prior art shown in FIG. 6, the long spreading code D1 is not used for spreading the first and second perch channels in the regions C and D. Also, the short spreading code is not necessarily a code orthogonal to C1. Therefore, the areas C and D do not have an orthogonal relationship with the original communication channels other than the perch channel. For this reason, in the above-described prior art, there is a possibility that the signals in the areas C and D of the first and second perch channels interfere with other original communication channels and cause the same interference as white noise. There is.

The above-mentioned interference causes partial noise to be mixed in the signal on the original signal channel. However, in general, sufficient interleaving in the signal channel does not cause partial error. It is not a big problem because it is averaged.

However, in a general signal channel, in addition to the original signal information, call control information for ring trip, handover, call termination control and the like are multiplexed. If it overlaps with the area of the call control information in time, it will seriously interfere with the call control information.

FIG. 7 is a diagram for explaining that the areas C and D interfere with call control information on a signal channel, which will be described below.

In FIG. 7, the first and second perch channels are configured as described with reference to FIG.
The signal channel for the original user signal transmits, in addition to the original signal information transmitted in the area E, the call control information used for ring trip, handover, call termination control, and the like in the area F. Region F is provided. Since the required bit rate of the call control information is lower than the original signal information, as shown in FIG. 7, the call control information is time-division multiplexed with the area E in which the signal information is transmitted as the area F having a relatively short time width. . The length of one slot by the region E and the region F of the signal channel is the same as the length of one slot by the region A1 and the region C of the first perch channel.

FIG. 7 shows the first,
Although the time positions of the second perch channel regions C and D and the signal channel region F are shown as being coincident with each other, each of a large number of signal channels provided for one set of perch channels is shown. The slot timings are disjoint, and therefore the area F in which the call control information of the signaling channel is transmitted does not necessarily overlap the areas C and D of the first and second perch channels in time. It often happens.

Therefore, according to the prior art described with reference to FIG. 6, as shown in FIG. 7, when the region C or the region D of the perch channel and the region F for transmitting the call control information overlap at the same time. This causes a problem that call control information is disturbed, which causes instability of call connection and drastic service deterioration. Since the time width of the area F in which the call control information is transmitted is short, the entire area is either the area C or the area D.
In this case, even if the information is interleaved, improvement of the error cannot be expected.

Further, the prior art described with reference to FIG. 6 speeds up the search for the long spreading code D1 by spreading the area D of the second perch channel with the short spreading code C3 indicating a group of long spreading codes. It is possible to do. However, searching for a long spreading code from many candidates requires a great deal of time. Therefore, in order to further shorten the search time, the short spreading code C3 is lengthened and the code C3 incorporates as much information as possible, that is, the long spreading code D1 is divided into as many groups as possible. Accordingly, it is effective to reduce the number of spreading code D1 candidates included in one group.

However, the prior art described with reference to FIG.
When the code C3 is lengthened, the time width of the region D of the second perch channel increases, and the time width of the region C of the first perch channel synchronized therewith must also be increased. However, as described above, there is a problem that the amount of interference with the signal channel increases and the signal channel becomes unpractical.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a region C and a long region C used to clarify the transmission phase of the perch channel in the first and second perch channels. An object of the present invention is to provide a mobile communication system using a CDMA multiplexing technique capable of preventing a region D indicating a group of spreading codes D1 from interfering with call control information on a signal channel.

Another object of the present invention is to provide a mobile communication system using a CDMA multiplexing technique which enables a mobile terminal to search a long spreading code for signal channel decoding at high speed.

[0026]

According to the present invention, the object is to provide a base station and a mobile terminal by a signal channel for transmitting user data and a perch channel for transmitting a spreading code used for demodulating the user data. CD that communicates between
In a mobile communication system using the MA multiplexing technique, a short spread code for identifying a start time of a long spread code transmitted from a base station and a short spread code for identifying a group of the long spread codes are modulated. This is achieved by providing two perch channels.

Further, the object is to prevent interference of the signal of the second perch channel with the signal channel.
The signal channel from the portion where the orthogonality of the spreading code with the signal channel provided in a part of the second perch channel is lost by eliminating by canceling with an interference canceller provided in the mobile terminal Is eliminated by canceling the interference with the interference by an interference canceller provided in the mobile terminal.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a mobile communication system using a CDMA multiplexing technique according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a CD according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration example of a perch channel and a signal channel of a mobile communication system using the MA multiplexing technology. FIG. 2 is a diagram showing a perch channel of a mobile communication system using a CDMA multiplexing technology according to a second embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration example of a signal channel.

In order to speed up the search for the long spreading code D1 used for demodulating the user data, the appearance frequency of the short spreading code C2 for detecting slot synchronization is increased, and the grouping of the long spreading code D1 is classified. It is effective to increase the code length of the short spreading code C3 to reduce the selection options of the long spreading code D1, and to reduce the time required for searching.

For this purpose, the area of the region C of the first perch channel is further expanded, or a short spreading code for slot synchronization is separately provided from the first perch channel coded with the long spreading code D1. It is desirable to newly construct a perch channel dedicated to C2 and a short spreading code C3 for discriminating a long spreading code group. But,
This channel is not orthogonal to the original signal channel.
For this reason, the above-mentioned method increases interference power in a cell and causes a large disturbance to a signal channel, thereby causing a great deterioration in system performance.

In the first and second embodiments of the present invention shown in FIGS. 1 and 2, even if the code length of the short spreading code C3 for grouping the long spreading code D1 is increased, the original signal channel is not Interference can be eliminated.

That is, in the first and second embodiments of the present invention shown in FIGS. 1 and 2, the short spreading code C2 for slot synchronization and the short spreading code C3 for long spreading code group discrimination are used. The second perch channel is transmitted using the second perch channel at a time rate of 100%. This new second perch channel can use all of the slots for the short spreading codes C2, C3, thus increasing the spreading code C3. For this reason, the first and second embodiments of the present invention can reduce the number of selections of the long spreading code D1 and shorten the time required for searching.

As a method of using the second perch channel in common by two codes, for example, a method such as time division multiplexing or double spreading can be considered. In the first embodiment of the present invention shown in FIG. 1, each slot H of the second perch channel is assigned a short spreading code C2 for slot synchronization,
In addition, two codes C2 and C3 are transmitted by double-spreading with a short spreading code C3 for classifying a long spreading code group. Further, the second embodiment of the present invention shown in FIG. 2 divides each slot H of the second perch channel into a region H1 and a region H2, and allocates a short spread code C2 for slot synchronization to the region H1. , Area H2
, A short spreading code C3 for classifying a long spreading code group is allocated and time-division multiplexed to transmit two codes C2 and C3.

In the first and second embodiments of the present invention, each slot of the first perch channel is system-specific and in-system, as in the case of the prior art described with reference to FIG. Is double-spread and code-modulated by a short code C1 common to each base station and a long code D1 unique to a specific base station. The spreading code C3, which is code-modulated to the second perch channel, may be the same for each slot. However, by repeatedly transmitting a slightly changed short code a plurality of times, the group is more reliably transmitted. Can be identified.

When information transmission from the base station is performed using the second perch channel having the above-described configuration, when viewed from the mobile terminal side, in the signal transmitted from the base station, However, since the second perch channel that is not orthogonal to the original signal channel is transmitted over the entire slot section, it causes large interference with the signal channel, and it is difficult to ensure sufficient transmission characteristics and communication capacity. Become.

For this reason, in the first and second embodiments of the present invention described above, a fixed interference canceller is provided on the mobile terminal side so as to eliminate interference from the second perch channel. That is, as described above, the signal content of the second perch channel in the first and second embodiments of the present invention does not change with time (the same signal is repeated every slot or every several slots). Therefore, it is possible to easily create a replica on the receiving side. Therefore, the receiving mobile terminal can cancel the signal from the second perch channel with extremely high accuracy, thereby achieving high-speed cell / sector without deteriorating system performance. A search, that is, a search for a long spreading code can be performed.

FIG. 3 is a block diagram illustrating a configuration example of the fixed interference canceller in the mobile terminal described above.
Hereinafter, this will be described. In FIG. 3, reference numeral 51 denotes a receiver dedicated to the second perch channel; 52, a main receiver;
3 is an AFC / level detection / frame synchronization unit, 54 is a replica generation unit, 55 and 521 are despreading units, 56 is a multiplier,
522 is a detector, 523 is a propagation path estimation unit, 524 is an absolute value conversion unit, and 525 is a subtractor.

The configuration example of the fixed type interference canceller shown in FIG. 3 constitutes a receiving section of a mobile terminal, and includes a second perch channel dedicated receiver 51, a main receiver 52,
It comprises an AFC / level detection / frame synchronization unit 53, a replica generation unit 54, a despreading unit 55, and a multiplier 56. The main receiver 52 includes a despreading unit 521, a detector 122, and a propagation path estimation unit 5 that generates a phase for detection.
23, an absolute value conversion unit 524, and a subtractor 525.

In the above, an input signal from the antenna of the mobile terminal is input to the second perch channel dedicated receiver 51 and the main receiver 52. The second perch channel dedicated receiver 51 can receive and demodulate the second perch channel described with reference to FIGS. 1 and 2 and reproduce the spreading codes C2 and C3 in the second perch channel. it can.

Based on the output signal from the dedicated receiver 51, the replica generation unit 54 converts the signal of the second perch channel mixed into the signal channel to cause interference.
Generate a replica signal for canceling from the signal channel. The replica signal is subjected to despreading with respect to the long spreading code D1 and short spreading code C1 which spreads the signal channel by the despreading unit 55 or the short spreading code for each signal channel orthogonal thereto, and then multiplication. Apparatus 56 is added. The reason why the replica signal is despread as described above is that the main receiver 52
This is because cancellation is performed after the signal channel is despread.

The second for receiving the spreading codes C2 and C3
If the signal power of the second perch channel is a sufficiently large value, the perch channel dedicated receiver 51 can obtain sufficient reception performance even with a relatively simple configuration. In this case, the carrier component, the clock component, and the like of the transmission signal that has been conventionally extracted from the first perch channel can be extracted from the receiver 51. In the example shown in FIG. 3, therefore, the AFC / level detection / frame synchronization unit 53 is connected to the output of the second perch channel dedicated receiver 51.

On the other hand, the first perch channel and the signal channel spread with the long spreading code D1 unique to the base station are received by the main receiver 52. That is, the signal of each channel input to the main receiver 52 is
After the despreading of the long spreading code D1 and the short spreading code C1 or the short spreading code for each signal channel orthogonal thereto is performed by the detector 21, the signal is reproduced by the detector 522. The detector 522 performs a detection process using an output of the propagation path estimation unit 523 that generates a phase for detection from an output signal of the despreading unit 521.

Since the signal of the second perch channel is mixed in the detected signal, it is necessary to remove this. For this reason, in the illustrated example, the propagation path estimation unit 523
From the output of the second perch channel to the signal of the second perch channel that would have been originally transmitted from the base station, as described above. Is added to the output of the despreading unit 55 for despreading the replica signal generated by
Multiply by 6. Thus, the level of the replica signal from the multiplier 56 becomes equal to the signal level of the second perch channel included in the output of the detector 122. The subtracter 525 can remove the signal of the second perch channel mixed into the signal channel received by the main receiver 52 by subtracting the output of the multiplier 56 from the output of the detector 122.

FIG. 4 is a block diagram for explaining another example of the configuration of the fixed interference canceller in the mobile terminal described above. This will be described below. 4 are the same as those in FIG.

The example described with reference to FIG. 3 has been described as removing the signal of the second perch channel mixed into the signal channel after detection (after despreading). The example shown in FIG. 4 is configured to cancel the interference of the signal of the tree channel before detection (before despreading).

The example shown in FIG. 4 has the same configuration as that of FIG. 3 except that the despreading unit 55 in FIG. 3 is eliminated to cancel the interference of the signal of the second perch channel mixed into the signal channel. , Performed before the despreading unit 521 of the main receiver 52. That is, the replica signal generated by the replica generation unit 54 is
Is multiplied by the value from the absolute value conversion unit 524, and the subtractor 525 placed on the input side of the despreading unit 521 of the main receiver 52
Is added to

As a result of the above, the subtractor 525 is connected to the main receiver 5
Before despreading by the second despreading unit 521, the signal of the second perch channel mixed into the signal channel can be canceled, and the despreading unit 521 and the detector 5
This means that the signal of the second perch channel is not mixed in the signal decoded through the signal 22.

By providing the fixed interference canceller described with reference to FIGS. 3 and 4 on the receiving side of the mobile terminal,
From the perch channel can be eliminated. For this reason, the code length of the short spreading code C3 for grouping the long spreading code D1 to be transmitted to the second perch channel can be increased, and high-speed cell transmission can be performed without deteriorating system performance. A sector search, that is, a search for a long spreading code can be performed.

In the embodiment described with reference to FIGS. 1 and 2, the short spreading code C of the second perch channel is used.
2. The portion modulated by C3 has been described as having a time rate of 100%. However, when the time rate is less than 100%, for example, as shown in FIG. 3 and 4 can be canceled by the canceller shown in FIG. 3 and FIG. 4 to prevent interference of the second perch channel with the signal channel. And stable communication can be performed.

[0051]

As described above, according to the present invention, a long spreading code for decoding a signal channel can be obtained on the mobile terminal side without or without the signal channel being interrupted by the perch channel. Can be searched at high speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a perch channel and a signal channel of a mobile communication system using a CDMA multiplexing technique according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a perch channel and a signal channel of a mobile communication system using a CDMA multiplexing technique according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration example of a fixed interference canceller in the mobile terminal described above.

FIG. 4 is a block diagram illustrating another configuration example of the fixed interference canceller in the mobile terminal described above.

FIG. 5 is a diagram illustrating a perch channel signal system according to the related art.

FIG. 6 is a diagram illustrating a perch channel signal system according to another related art.

FIG. 7 is a diagram illustrating that regions C and D on a perch channel interfere with call control information on a signal channel.

[Explanation of symbols]

 51 second perch channel dedicated receiver 52 main receiver 53 AFC / level detection / frame synchronization unit 54 replica generation unit 55, 521 despreading unit 56 multiplier 522 detector 523 propagation path estimation unit 524 absolute value conversion unit 525 Subtractor

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takaki Garaku 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. F-term in Hitachi Central Research Laboratory (reference) 5K022 EE02 EE11 EE21 EE35 5K067 AA03 CC10 DD19 EE02 EE10 EE64 EE71 EE72 JJ15

Claims (3)

[Claims] 1. A CDMA multiplexing technique for communicating between a base station and a mobile terminal using a signal channel for transmitting user data and a perch channel for transmitting a spreading code used for demodulating user data. In the mobile communication system, a second perch channel modulated by a short spreading code for identifying a start time of a long spreading code transmitted from a base station and a short spreading code for identifying a group of the long spreading codes is provided. A mobile communication system using a CDMA multiplexing technique. 2. The CDMA multiplexing technique according to claim 1, wherein interference to the signal channel due to the signal of the second perch channel is eliminated by canceling the interference by an interference canceller provided in a mobile terminal. Mobile communication system using. 3. An interference canceller provided in a mobile terminal cancels interference on the signal channel from a portion provided in a part of the second perch channel, where the orthogonality of a spreading code with the signal channel is lost. 2. The CDM according to claim 1, wherein the CDM is excluded.
A mobile communication system using A multiplexing technology.