JPH04179324A - Spread spectrum multiple access communication equipment - Google Patents

Abstract

PURPOSE:To reduce interference between channels and to improve frequency use efficiency by changing the phase of a spreading code to a phase relation where the correlation of plural spreading codes becomes a minimum or comparatively small, holding the phase relation and respectively transmitting plural pieces of information. CONSTITUTION:Data signals S1 and S2 are respectively transmitted from two transmitters 1 and 2 to which different spreading code systems PN1 and PN2 are allocated by using the same carrier frequency fB. A receiver 3 generates a timing signal from a timing signal generation circuit 40 at every specified timing in the spreading code systems PN1 and PN2 used for the transmission. The spreading code generators 10 and 16 of the transmitters 1 and 2 receive the timing signal and shift the generation timing of the self spreading code systems to a phase difference where the correlation of the spreading code systems PN1 and PN2 becomes the minimum and comparatively small. Thus, interference between the channels is reduced even if the common frequency band is used and transmitted, and frequency use efficiency can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a spread spectrum communication device that performs multiple access using code division multiplexing using a plurality of types of spreading code sequences. This improves frequency usage efficiency.

[Conventional technology]

Spread spectrum communication allows the data to be transmitted to
This is a method of widening the band of a data signal and transmitting it by modulating it with a spreading code sequence called a P N (Pseudo Noise) code.

In order to realize multiple access in spread spectrum communication, it is necessary to use spreading code sequences such that: ■ The autocorrelation function has a sharp peak at the phase difference -〇, and the absolute value is sufficiently small at other phase differences; ■ The mutual interaction between the spreading code sequences. A series with generally low correlation (preferred bear) is used. By employing such a spreading code sequence, it becomes possible to share the same frequency band and perform multiple access using code division multiplex communication.

Conventional code division multiplexing systems select and use spreading code strings (preferred bare) with generally small cross-correlation as spreading codes, but the cross-correlation for each phase difference between these spreading codes is I was doing multiplexing asynchronously without paying any attention to it.

[Problem to be solved by the invention]

Preferred bears generally have low cross-correlation, but
Even so, depending on the phase difference between spreading codes, the cross-correlation may become relatively large. For this reason, when multiplexing is performed asynchronously without paying attention to the cross-correlation for each phase difference as in the conventional device, inter-channel interference occurs when the cross-correlation becomes relatively large. For this reason, the number of channels that can be used for simultaneous communication is small, resulting in poor frequency utilization efficiency.

The present invention solves the problems in the conventional technology and reduces inter-channel interference when performing multiple access using code division multiplexing, increases the number of channels that can be simultaneously overused, and utilizes frequency. It is an object of the present invention to provide a spectrum multiple access communication device with improved efficiency.

[Means to solve the problem]

The present invention provides a spreading code generating means for generating a plurality of spreading code sequences in synchronization with each other and changing the mutual phase relationship, and a phase relationship in which the cross correlation of the plurality of spreading codes is minimized or relatively small. a phase changing means for changing and holding the phase of the spread code; a spread modulation means for spread-modulating and outputting a plurality of pieces of information using a plurality of spread codes changed to a specific phase relationship; and transmitting means for transmitting a plurality of pieces of information using a common frequency band.

[For production]

According to the present invention, the phase of the spreading codes is changed to a phase relationship in which the cross-correlation of the plurality of spreading codes is minimized or relatively small, and the phase relationship is maintained and the plurality of pieces of information are spread-modulated with each of these spreading codes. Therefore, even when transmitting using a common frequency band, interference between channels is reduced, the number of channels that can communicate simultaneously is increased, and frequency usage efficiency can be improved.

〔Example〕

Examples of this invention will be described below.

(Example 1) An example of the present invention is shown in FIG. This transmits data signals Sl from two transmitters 1.2 to which different spreading code sequences are assigned using the same carrier frequency fB.
, S2 are transmitted and received by one receiver 3.

In the transmitter 1, the data signal s1 is transmitted to the spreading code generator 1.
The spreading circuit 12 uses the spreading code PNI generated from 0.
is spread spectrum. This spectrum-spread signal is frequency-converted to a center frequency fB by a mixer 14 and then transmitted through an antenna 15.

In the transmitter 2, the data signal s2 is transmitted to the spreading code generator 1
The spreading circuit 18 uses the spreading code PN2 generated from 6.
is spread spectrum. This spectrum-spread signal is frequency-converted to the center frequency fB by the mixer 2o and then transmitted through the antenna 22.

The signal transmitted from the transmitter 1.2 is received by the receiver 3. The receiver 3 inputs the signal received by the antenna 24 to the receiving circuit 26 and tunes it to the signal of the center frequency fB.
A despreading circuit 30 performs despreading processing using the spreading code PNI or PN2 generated by the spreading code generator 28 to demodulate the data signal S1 or S2.

The despreading circuit 30 and the spreading code generator 28 are configured, for example, as a matched filter as shown in FIG. A received signal is input to the input terminal 34, and is passed through n-1 stages (
n; number of bits of spreading code series PN1゜PN2) delay circuits Di, D2 . .......

Dr+~1 is delayed by 1 bit at a clock frequency synchronized with the spreading code series PNI and PN2, and the human output of each stage is weighted by circuits Wl, W2, ..., Wn, and the output is By adding them in an adder 36, a despread output is obtained at an output terminal 38. Weighting is the circuit Wl
, W2 , . Set.

When a data signal using a spreading code sequence corresponding to the set weighting coefficient is input, a + or - peak is obtained at the output terminal 38 for each period of the spreading code sequence, and the data signal S1 Or S2 is demodulated. If a data signal using a spreading code sequence different from the set weighting coefficient is input manually, no peak will be obtained in the output of the adder 36, and the data will not be demodulated.

In FIG. 1, when the receiver 3 demodulates the data signal, it detects a peak at the output terminal 38 of the matched filter in FIG. A timing signal is generated from the timing signal generation circuit 40 and transmitted from the antenna 24 at each timing when . This timing signal also includes identification information of the spreading code sequence used in the data signal being received.

This timing signal is transmitted to the antennas 15. of the transmitters 1, 2.
22, respectively. The transmitter 1.2 detects this timing signal at a timing signal detection port, path 42, 44, when the power is on.

When the spreading code generator 10.16 receives this timing signal, if it contains the identification information of the same spreading code sequence assigned to itself, it directly generates the spreading code sequence. Furthermore, if it contains information about a spreading code sequence other than the one assigned to itself, the spreading code sequence PNI.

The generation timing of its own spreading code sequence is shifted to a phase difference where the cross-correlation of PN2 is minimized or relatively small (this phase difference is known in advance).

Thereby, even if the transmitters 1 and 2 simultaneously transmit, the receiver 3 can demodulate the desired data signal without causing inter-channel interference.

This timing adjustment is performed for each period or multiple periods of the spreading code sequence, and the above-mentioned phase relationship is maintained.

A specific example of the above phase difference control will be explained. Assume now that the spreading code sequences PNI and PN2 are given as 31-bit preferred bare code sequences as shown in FIG.

In a single connection in which transmission is performed only from transmitter 1 (or transmitter 2), only a signal modulated with the spreading code sequence PNI is transmitted, so communication can be performed without causing inter-channel interference. Therefore, the receiver 3 can obtain a correlation output (despread output) as shown in FIG. 4, and can perform good communication.

In a dual connection with simultaneous transmissions from transmitter 1.2, the spreading code sequence PNI of transmitter 1.2.

If the phase difference of PN2 is not adjusted, depending on the phase difference, cross-correlation may become large and inter-channel interference may occur. For example, the spreading code sequence PNI in FIG.
Transmission is performed simultaneously from the transmitter 1.2 in a phase relationship in which the timings of PN2 a and b match, and at this time, in the receiver 3, the matched filter for despreading uses the spreading code sequence PNI pattern (fixed). (see FIG. 5), the correlation output of the matched filter will be as shown in the lower part of FIG. 5, and the output will be output even at times other than the peak. Although this is a matched filter that optimally matches the transmission spreading code PNI, it is difficult to use other spreading codes (in this example, PN2
) shows some kind of reaction (output) to
The magnitude of this reaction becomes a problem when multiple connections are used.

That is, in the state shown in FIG. 5, the correlation output between the transmit spread code PN2 and the receive spread code PNI becomes +6 at the timing when the correlation output between the transmit spread code PNI and the receive spread code PNI peaks, so this peak is shifted by +6. For this reason, the peak on the plus side (when modulated with data "0") has a pulse height difference of 30, but the peak on the minus side (when modulated with data "1", that is, the spreading code is When the pulse is inverted), the pulse height difference is only 14. Therefore, the peak value cannot be detected well and the data signal cannot be demodulated.

In contrast, according to the present invention, for example, the spreading code sequences PNI and PN2 shown in FIG. 3 are controlled to a phase difference such that the timings of a and b' coincide. With such a phase difference, assuming that the matched filter of the receiver 3 is waiting for the spreading code sequence PNI (see FIG. 6), the output of the matched filter will be as shown in the lower part of FIG.

In other words, in the state shown in FIG. 6, at the timing when the correlation output between the transmission spreading code PN1 and the reception spreading code PNI peaks, the correlation output between the transmission spreading code PN2 and the reception spreading code PNI is as small as -1, so as shown in FIG. There is no large shift in the peak value, and both the pulse height difference between the positive side peak and the pulse height difference between the negative side peak is 22. Therefore, a good peak value that is not affected by cross-correlation can be obtained. As a result, good communication can be performed without inter-channel interference.

In the embodiment shown in FIG. 1, the case where there is only one receiver has been explained, but if there are multiple receivers each receiving different data signals, for example, spreading code sequences may be used. It is only necessary to prioritize the spreading code sequences in advance and adjust the phase differences of the other spreading code sequences in accordance with the timing of the spreading code sequence with the highest priority among the spreading code sequences used for transmission.

In addition, in the embodiment shown in FIG. 1, if there are two transmitters or three or more transmitters, there are three or more types of spreading code sequences, so all spreading code sequences are It is difficult to set a phase difference that results in a correlation. Therefore, in such a case, the phase difference is set so that all the spreading code sequences have a relatively small cross-correlation with each other.

Further, in the embodiment shown in FIG. 1, the transmitter 1
．． Although the timing between the spreading code sequences PNI and PN2 of 2 is taken, the timing between the spreading code sequences PNI and PN2 can also be determined by transmitting and receiving directly between the transmitters 1 and 2 without going through the receiver 3. can.

(Example 2) Another example of the present invention is shown in FIG. This is the spreading code sequence PNI from one transmitter 46.

Data signals Sl each spread-modulated by PN2.

S2 are simultaneously transmitted, each spreading code sequence PNI.

The receiver 48.50 to which PN2 is assigned receives the signal.

The transmitter 46 generates a spreading code sequence PNI using a common clock in spreading code generators 52,54.

Generates PN2. This spreading code sequence PNI.

PN2 is set by the timing circuit 56 to a phase difference (for example, the phase difference between a and b' in FIG. 3) that makes the cross-correlation minimum or relatively small.

The spreading circuits 58 and 60 are spread code series PNI.

Each data signal is spread modulated at PN2. The spread modulated signals are further frequency-converted to center frequency fB in mixers 62 and 64, added in adder 66, and transmitted from antenna 68.

The transmission signal from the transmitter 46 is received by the antenna 70.72 of the receiver 48.50, and the band of center frequency fB is tuned by the receiving circuit 74.76.

The receivers 48 and 50 then receive spreading code sequences PNI and PN2 generated from the spreading code generators 78 and 80, respectively.
The despreading circuits 82 and 84 perform despreading processing on the received signal using the despreading circuits 82 and 84. Thereby, each receiver 48, 50 can receive a signal using the spreading code sequences PNI and PN2 assigned to itself. In this case, the transmitter 46 sets the phase difference between the spreading code sequences PNI and PN2 so that the cross-correlation is the minimum or a relatively small value.
Can be received without inter-channel interference.

(Example 3) In the first and second embodiments, the spreading code sequence PNI.

Since the phase difference for which the PN2 cross-correlation is minimum or relatively small is known in advance, the setting is set to that phase difference, but even if the phase difference is not known in advance, the setting is automatically set to that phase difference. It can also be configured to be controlled.

FIG. 8 shows an example of a transmitter configured in this manner.

In the transmitter 86, spreading code generators 88.90 each generate a spreading code sequence PN1. Generates PN2. The phase changing means 92 uses a phase shift circuit 94 to convert the spreading code sequence PN2.
(or PNI) is sequentially shifted and a cross-correlation circuit 96 calculates the cross-correlation.

Then, after one cycle of shifting, the phase difference where the cross-correlation is minimum or relatively small is detected, and the phase difference is fixed to generate the spreading code sequences PNI and PN2.

The spreading circuits 98 and 100 spread the spreading code sequences PNI and PN2.
The data signals are each spread-modulated. The spread modulated signals are further frequency-converted to center frequency fB in mixers 102 and 104, added in adder 106, and transmitted from antenna 108.

This allows the receiver to receive signals without mutual interference.

[Example of change]

In the embodiment described above, the case where the despreading circuit is constituted by a matched filter is shown, but the present invention can also be applied to cases where various despreading circuits are used.

In the embodiments described above, the present invention is applied to one-way communication, but it can also be applied to two-way communication.

〔Effect of the invention〕

As explained above, according to the present invention, the phase of a plurality of spreading codes is changed to a phase relationship in which the cross-correlation between the plurality of spreading codes is minimized or relatively small, and the phase relationship is maintained and a plurality of pieces of information are respectively transmitted. Since these are spread-modulated and transmitted, even if they are transmitted using a common frequency band,
Inter-channel interference is reduced, the number of channels that can communicate simultaneously is increased, and frequency usage efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the invention. FIG. 2 is a block diagram showing an embodiment in which the spreading code generator 28 and the despreading circuit 30 of FIG. 1 are configured with matched filters. FIG. 3 shows the spreading code sequence PNI of FIG. It is a figure which shows an example of PN2. FIG. 4 is a time chart showing the operation when transmitting only from the transmitter l in FIG. 1. FIG. 5 shows the spreading code sequence PNI in FIG. 3 is a time chart showing the operation when transmitters 1 and 2 transmit simultaneously without considering the phase difference of PN2. FIG. 6 shows the spreading code sequence PNI in FIG. 12 is a time chart showing the operation when these phase differences are set so that the cross-correlation of PN2 is minimized. FIG. 7 is a block diagram showing a second embodiment of the invention. FIG. 8 is a block diagram showing a third embodiment of the invention. 10.16, 52, 54, 88.90... Spreading code generation means, 12, 18.58, 60, 98° 100...
Spreading circuit (spreading modulation means), 14,20°62.64
, 102, 104... mixer (communication means), 42.4
4...timing signal detection circuit (phase change means), 5
6...timing circuit (phase change means), 92...
Phase change means, PNI, PN2...spreading code sequence, S
l, S2...data signal (information). Applicant Yamaha Co., Ltd. Figure 7

Claims (1)

[Scope of Claims] Spreading code generating means for generating a plurality of spreading code sequences in synchronization with each other and changing their mutual phase relationship; and a phase at which the cross-correlation of the plurality of spreading codes is minimized or relatively small. a phase changing means for changing and maintaining the phase of the spreading code according to the specific phase relationship; a spreading modulating means for spread-modulating and outputting a plurality of pieces of information using a plurality of spreading codes changed to this specific phase relationship; and this spreading modulation. and transmitting means for transmitting a plurality of pieces of information using a common frequency band.