JP2005318090A - Spread spectrum communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spread spectrum communication apparatus capable of extracting a desired signal with high accuracy and realizing much further improvement of the throughput even when it is estimated that the same spread code is assigned to a plurality of terminals. <P>SOLUTION: The spread spectrum communication apparatus disclosed herein (transmitter 1-1 at a terminal) for utilizing the CDMA system to carry out random access control includes: a spread section 11-1 for generating e.g., a fundamental sequence with excellent correlation characteristics and spreading transmission data by using a spread code generated on the basis of the fundamental sequence to generate a spread signal; and a transmission timing control means 12-1 that controls a transmission timing of the spread signal in the unit of a chip on the basis of transmission timing information notified by a particular communication apparatus (receiver 2 of a base station) for accommodating a single or a plurality of spread spectrum communication apparatuses (transmitters 1-1 to 1-N at the terminal). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spread spectrum communication apparatus that performs random access control using a CDMA (Code Division Multiple Access) method, and in particular, a plurality of terminals communicate with a base station using the same spread code. The present invention relates to a spread spectrum communication apparatus used in a communication system assuming the above.

  Hereinafter, a random access control method in the conventional communication system will be described. For example, there is a slotted-ALOHA system as a basic random access control system in which a terminal randomly transmits a packet without assigning a radio channel to each terminal (mobile station) (Non-Patent Document). 1). In this slot aloha system, the time axis is divided into fixed time intervals called slots, and packets are transmitted using the slots. Since the time axis is slotted, each terminal needs to establish synchronization. In addition, the slot aloha method, like the most basic pure-ALOHA method, does not overlap the packets, either overlaps completely (collision) or does not overlap at all. It becomes.

  On the other hand, in a communication system in which a large number of terminals communicate with the same base station, for example, CDMA (Code Division Multiple Access) having excellent throughput performance is employed in order to increase the number of terminals that can be accommodated.

  Here, a conventional random access control method to which the CDMA method having a throughput characteristic superior to the slot Aloha method is applied will be briefly described. For example, each terminal on the transmission side spreads transmission data using a spread code assigned individually. Then, the spread signal is transmitted in synchronization with the slot time by the slot aloha method. On the other hand, the base station on the receiving side despreads the signal transmitted by the slot Aloha method with an individual spreading code, and extracts a desired signal. Thereby, since a desired signal can be extracted even at the time of a collision, packet retransmission is reduced, and as a result, throughput characteristics are improved.

IEICE Engineering Science DSP99-65, SST99-21, CS99-67 (1999-07)

  However, when the conventional random access control method in which the CDMA method is applied to the slot aloha method is applied to, for example, a system in which the same spreading code is assigned to a plurality of terminals, due to packet collision, There is a problem that a desired signal may not be extracted. In particular, the above-described conventional random access control method is applied to a satellite communication system (a system in which a plurality of terminals use the same spreading code) in which the distance to the satellite is almost equal between the terminals. In such a case, there is a problem that the probability that the reception timings of the slots coincide with each other becomes very high (there is no chip shift), so that a desired signal cannot be extracted.

  Furthermore, in the above conventional random access control scheme, for example, when a plurality of terminals use the same spreading code and the distance from the base station differs between terminals, and there is a chip shift, there is a difference between codes due to chip shift. There is a problem in that interference occurs, the ratio of signal power to interference power during random access increases, and throughput decreases.

  The present invention has been made in view of the above, and even when a situation where the same spreading code is assigned to a plurality of terminals is assumed, a desired signal can be accurately extracted, and further throughput can be improved. An object of the present invention is to obtain a spread spectrum communication apparatus capable of realizing the above.

  In order to solve the above-described problems and achieve the object, a spread spectrum communication apparatus according to the present invention is a spread spectrum communication apparatus that performs random access control using a CDMA (Code Division Multiple Access) system. A spreading means for generating a spread signal by generating a basic sequence having excellent correlation characteristics and spreading transmission data using a spreading code generated based on the basic sequence (a spreading section in an embodiment described later) 11-1, 11-2,..., 11-N) and transmission timing information notified from a specific communication device that accommodates a single or plural spread spectrum communication devices (including its own device). , Transmission timing control means (transmission timing control means 12-1, 12-2, ..., 12-N) for controlling the transmission timing of the spread signal in units of chips; Characterized in that it comprises.

  According to the present invention, for example, the base station notifies each terminal of the transmission timing information of the spread signal in units of chips, and each terminal controls the transmission timing of the spread signals in units of chips based on the transmission timing information. .

  According to the present invention, for example, in a system in which a situation is assumed in which the same spreading code is assigned to a plurality of terminals by the terminal controlling the transmission timing in units of chips based on the transmission timing information notified by the base station. Even when random access control is performed, there is an effect that it is possible to avoid the collision of slots, which has occurred in the prior art, and to further improve the throughput.

  Embodiments of a spread spectrum communication apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a wireless communication system including a spread spectrum communication apparatus according to the present invention. This communication system includes, for example, a transmitter 1-1 in a spread spectrum communication apparatus on the transmission side including a spreading unit 11-1 and a transmission timing control unit 12-1, a spreading unit 11-2, and a transmission timing control unit 12-. Transmitter 1-2 in the transmission-side spread spectrum communication apparatus including 2,..., Transmitter 1 -N in the transmission-side spread spectrum communication apparatus including the spreading unit 11 -N and the transmission timing control unit 12 -N And a receiver 2 in the spread spectrum communication apparatus on the reception side including the despreading units 13-1, 13-2,..., 13-N. Here, as an example, a wireless communication system is assumed in which the transmission-side spread spectrum communication apparatus is a terminal and the reception-side spread spectrum communication apparatus is a base station. 1-2,..., 1-N) transmit the spread signal by random access control (pure aloha system, slot aloha system, etc.), and the receiver 2 in the base station transmits transmission delays τ # 1, τ # 2,. , Τ # N will be described.

  FIG. 2 is a diagram showing a configuration example of the spreading code generation unit 21 that is a component of each of the spreading units (1-1, 1-2,..., 1-N). And a partial series generation unit 23. Further, FIG. 3 is a diagram illustrating a configuration example of a basic sequence generation unit 22 that generates an M sequence having excellent correlation characteristics as an example of a basic sequence, and includes delay units 31 to 34 and an adder 35 that configure a shift register. It has.

Here, the operation of the spread spectrum communication apparatus (transmitter in the terminal, receiver in the base station) of the present embodiment will be described in detail with reference to the drawings. In FIG. 1, individual transmission data S ₁ (t), S ₂ (t),..., S _N (t) are respectively transmitted to the transmitters 1-1, 1-2,. Hereinafter, the operation of the transmitter 1-1 will be described as an example.

  First, the basic sequence generation unit 22 in the spread code generation unit 21 in the transmitter 1-1 selects a code having excellent correlation characteristics and generates a basic sequence of spread codes. For example, an M-sequence is known as a code having excellent correlation characteristics. Here, as an example of the basic sequence, a basic sequence generation unit 22 configured by a combination of a shift register and an adder 35 shown in FIG. Then, an M sequence having a code length of 15 is generated.

  Next, the partial sequence addition unit 23 adds a predetermined partial sequence to the basic sequence generated by the basic sequence generation unit 22. Here, for the purpose of reducing the intersymbol interference generated between the spread signals of each terminal using the same spreading code, because the transmission timing of the spread signal by each terminal is shifted in units of chips, the above A partial series is added to the basic series.

  Here, the processing of the partial series adding unit 23 will be specifically described with reference to the drawings. FIG. 4A, FIG. 4B, and FIG. 4C are diagrams illustrating an example of a partial sequence addition method by the partial sequence addition unit 23. For example, in FIG. 4A, a predetermined end portion (a plurality of bits) in the basic sequence is added to the head of the basic sequence. Also, in FIG. 4B, a predetermined head portion (a plurality of bits) in the basic sequence is added to the end of the basic sequence. Further, in FIG. 4C, a tail part (a plurality of bits) defined in advance in the basic sequence is added to the head of the basic sequence so as to cope with a large shift in transmission timing in units of chips. Is added to the end of the basic sequence. Then, the spread code generated by adding the partial sequence by any one of the above methods is used for the spread processing described later.

In the transmitter 1-1, the spreading unit 11-1 spreads the transmission data S ₁ (t) using the spreading code generated by the spreading code generating unit 21 shown in FIG.

  Next, the transmission timing control unit 12-1 sets the transmission timing so that the reception timing from each terminal is not the same in the base station on the reception side. This transmission timing is notified from the base station to the terminal as transmission timing information, for example, in a slot provided to notify the transmission timing information. Also, the transmission timing is set at random by the transmission timing control unit 12-1 in the time range defined by the transmission timing information, for example. As a result, the ability to avoid slot collision can be improved.

  FIG. 5A is a diagram illustrating an example of a slot format in TDM (Time Division Multiplexing) in which the transmission timing information is inserted, and FIG. 5-2 is a CDM (Code Division Multiplexing) in which transmission timing information is inserted. 2 is a diagram showing an example of a slot format in FIG. When transmitting transmission timing information by TDM, a specific time zone or all of one slot is assigned as a time zone of transmission timing information. On the other hand, when transmitting transmission timing information by CDM, a specific channel (CH # 1 in FIG. 5-2) is assigned as a channel for transmission timing information.

  Thereafter, the transmission timing control unit 12-1 outputs the spread signal on the wireless transmission path at the transmission timing set above. This spreading code is added with a transmission delay in the wireless transmission path, and further becomes a signal in which transmission signals of other terminals are multiplexed (see FIG. 1), and reaches the base station.

Finally, in the receiver 2 of the base station, the despreading unit 13-1 performs despreading processing using the same basic sequence as that on the transmission side, and as a result, despread data Z ₁ (t) is obtained. In addition, in this Embodiment, although characteristic operation was demonstrated using the transmitter 1-1 and the de-spreading part 13-1 as an example, another transmitter (1-2-1-N) and reverse Similar processing is performed in the diffusion units (13-2 to 13-N).

  As described above, in the present embodiment, the base station notifies each terminal of the transmission timing information of the spread signal in units of chips, and each terminal controls the transmission timing in units of chips based on the transmission timing information. To do. As a result, when random access control is performed in a system in which the same spreading code is assigned to a plurality of terminals, it is possible to avoid a slot collision that has occurred in the prior art. Furthermore, in order to reduce the interference between spreading codes that occur with spreading signals of other terminals using the same spreading code, it is specified before, after, or before and after the basic sequence of spreading codes. Is generated, and a spread signal after spreading is transmitted using the spread code. Thereby, it is possible to improve throughput characteristics while reducing the influence of interference between spreading codes.

Embodiment 2. FIG.
Next, the operation of the spread spectrum communication apparatus according to the second embodiment will be described. Note that the configurations of the transmitter and the receiver included in the wireless communication system are the same as those in FIG. 1 of the first embodiment. Here, only a method for generating a basic sequence that is different from the processing in the first embodiment will be described.

  FIG. 6 is a diagram illustrating an example of a basic sequence generation method according to the present embodiment. In the first embodiment, the case where the M sequence is used as the basic sequence has been described as an example. However, in the M sequence, the number of 0s and 1s is not the same number (0 is less by 1), and the sequence length is an even code. Cannot be generated. Therefore, in this embodiment, for example, as shown in FIG. 6, since the number of 0s in the M sequence is one less than the number of 1, the number of 0s and 1s in the sequence is the same number and the sequence length is an even number. The leading 0 is added to the end so that

  In the example of FIG. 6, the number of 0s and 1s is made equal by adding the leading 0 in the sequence to the end, but it is not always necessary to add the leading 0 in the sequence to the end. For example, when the end of the sequence is 0, the end 0 may be added to the start position of the sequence, and the number of 0s and 1s in the sequence is the same number. If so, the added 0 may be the head or the tail.

  As described above, in the present embodiment, an even code sequence can be generated as a basic sequence. Thereby, a basic sequence having an arbitrary length can be generated without greatly degrading the correlation characteristics of the sequence.

Embodiment 3 FIG.
Next, the operation of the spread spectrum communication apparatus according to the third embodiment will be described. Note that the configurations of the transmitter and the receiver included in the wireless communication system are the same as those in FIG. 1 of the first embodiment. Here, only the processing of the spreading code generator having a different configuration from that of the first embodiment will be described.

  FIG. 7 is a diagram illustrating a configuration example of the spread code generation unit 21a in the present embodiment, and includes a basic sequence generation unit 22, an orthogonal code generation unit 24, and a partial sequence addition unit 23. First, basic sequence generation unit 22 generates a basic sequence having an even sequence length, as in the second embodiment. Next, the orthogonal code generation unit 24 selects an orthogonal code having the same number of sequence lengths as the basic sequence based on the orthogonal code selection signal, multiplies the basic sequence by the selected orthogonal code, and is orthogonal to the basic sequence. A code (sequence) is generated. There are as many orthogonal code selection signals as the number of orthogonal code sequences, and numbers assigned to the orthogonal codes in advance are used. Here, as an example, when the number of orthogonal codes when the number of orthogonal codes is M is # 0, # 1,..., # M−1, the orthogonal code selection signal is 0, 1,. 1, an arbitrary number is set at the time of data transmission inside the terminal, and the number is input to the orthogonal code generation unit by an orthogonal code selection signal. The orthogonal code generation unit 24 selects a Walsh code (Walsh) indicated by the orthogonal code selection signal and multiplies the output of the basic sequence generation unit 22. An example of the orthogonal code is a Walsh code.

  Then, the partial sequence addition unit 23 transmits the orthogonal code generation unit 24 to the orthogonal code generation unit 24 by the same method as in the first embodiment (see FIG. 4) or the same method as in the second embodiment (see FIG. 6). A spreading code is generated by adding a partial sequence to the generated sequence.

  As described above, in the present embodiment, a plurality of orthogonal codes for the basic sequence are generated by multiplying the basic sequence by the orthogonal code. This makes it possible to increase the number of available spreading codes. In addition, even when the reception timings of spread signals from a plurality of terminals are the same on a chip basis (at the time of a slot collision), if the orthogonal codes used between the terminals differ, Can be extracted.

  As described above, the spread spectrum communication apparatus according to the present invention is useful as a transmitter / receiver in the case of performing random access control using a CDMA system, and in particular, a plurality of terminals (transmitter side) have the same spreading code. It is suitable as a spread spectrum communication apparatus used in a communication system that is assumed to communicate with a base station (receiver side) using the.

It is a figure which shows the structural example of the radio | wireless communications system containing the spread spectrum communication apparatus concerning this invention. It is a figure which shows the structural example of the spreading code production | generation part which is a component of a spreading | diffusion part. It is a figure which shows the structural example of a basic series production | generation part. It is a figure which shows an example of the addition method of the partial series by a partial series addition part. It is a figure which shows an example of the addition method of the partial series by a partial series addition part. It is a figure which shows an example of the addition method of the partial series by a partial series addition part. It is a figure which shows an example of the slot format in TDM. It is a figure which shows an example of the slot format in CDM. It is a figure which shows an example of the production | generation method of a basic series. It is a figure which shows the structural example of a spreading code production | generation part.

Explanation of symbols

1-1, 1-2, 1-N transmitter 2 receiver 11-1, 11-1, 11-N spreading unit 12-1, 12-2, 12-N transmission timing control unit 13-1, 13- 2,13-N Despreading unit 21,21a Spreading code generation unit 22 Basic sequence generation unit 23 Partial sequence generation unit 24 Orthogonal code generation unit 31, 32, 33, 34 Delay unit 35 Adder

Claims (9)

In a spread spectrum communication apparatus that performs random access control using a CDMA (Code Division Multiple Access) system,
A spreading means for generating a spread signal by generating a basic sequence having excellent correlation characteristics and spreading transmission data using a spreading code generated based on the basic sequence;
A transmission timing control means for controlling the transmission timing of the spread signal in units of chips based on transmission timing information notified from a specific communication apparatus accommodating a single or a plurality of spread spectrum communication apparatuses (including its own apparatus). ,
A spread spectrum communication apparatus comprising:   2. The zero sequence is added to the beginning or end of the M sequence so that the same number of sequences can be generated as 0 and 1, and the generated sequence is used as a basic sequence used in the spreading means. Spread spectrum communication device. The diffusion means is
3. The spread spectrum communication apparatus according to claim 1, wherein a partial sequence at the end of the basic sequence is added to the head of the basic sequence, and the sequence after the addition is a spreading code. The diffusion means is
The spread spectrum communication apparatus according to claim 1 or 2, wherein a partial sequence at the beginning of the basic sequence is added to the end of the basic sequence, and the sequence after the addition is a spreading code. The diffusion means is
A partial sequence at the end of the basic sequence is added to the beginning of the basic sequence, and a partial sequence of the top portion of the basic sequence is added to the end of the basic sequence, The spread spectrum communication apparatus according to claim 1 or 2, wherein the spread code is a spread code. The diffusion means is
The spread spectrum communication apparatus according to claim 1 or 2, wherein the basic sequence is multiplied by a predetermined orthogonal code, and the spreading code is generated based on the sequence after the multiplication. The diffusion means is
7. The spread spectrum communication according to claim 6, wherein a partial sequence at the end of the sequence after the multiplication is added to the head of the sequence after the multiplication, and the sequence after the addition of the sequence is a spreading code. apparatus. The diffusion means is
7. The spread spectrum communication according to claim 6, wherein a part of the first part of the sequence after the multiplication is added to the end of the sequence after the multiplication, and the sequence after the addition is a spreading code. apparatus. The diffusion means is
A partial sequence at the end of the sequence after the multiplication is added to the beginning of the sequence after the multiplication, and a partial sequence at the top of the sequence after the multiplication is added to the end of the sequence after the multiplication. The spread spectrum communication apparatus according to claim 6, wherein the sequence after each sequence is added is a spreading code.

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