JP3335777B2 - Spread spectrum communication equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication apparatus.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a conventional spread spectrum portable telephone base station apparatus. Each of the lines is incorporated into a transmission frame format with various control information and the like by a frame assembling circuit 501, and then the spreading circuit 5
02 is spread by the spreading code assigned to the line, and is combined into one system by the adding circuit 503. In this device example, since the quadrature modulation method such as QPSK is used, the output of the spreading circuit and the output of the adding circuit for each line are
It consists of two systems, I component and Q component. The output of the addition circuit 503 is converted into an analog signal by a D / A converter 504, mixed with a carrier signal from a carrier oscillation circuit 506 by a mixer 505, and converted into a modulation signal.
07 and transmitted from the transmitting antenna 508.

[0003]

However, in the above-mentioned conventional spread spectrum portable telephone base station apparatus, it is necessary to accurately reflect the amplitude information of a signal in which a plurality of channels are multiplexed on the transmission level, and the transmission There is a problem that the efficiency of the power amplifier circuit is low and the power consumption is large.
If the allowable dynamic range of the transmission power amplifier circuit cannot be sufficiently ensured for the multiplexed signal, there is a problem that out-of-band spurs increase in the large amplitude portion of the multiplexed signal. However, there is a problem that the small amplitude portion is lost, and as a result, the interference between the lines increases, and the error rate characteristic deteriorates remarkably.

[0004] The present invention solves such a conventional problem. Even if the dynamic range is set to be small, an excellent spectrum which can reduce the power consumption without adversely affecting the error rate or the like. An object of the present invention is to provide a communication system communication device.

[0005]

According to the present invention, there is provided a transmission power amplifier having a dynamic range smaller than a dynamic range of a signal obtained by code division multiplexing a plurality of channels on the same carrier. Before the power amplifier, the number of multiplexed lines must be reduced so that the effect of the lack of dynamic range of the transmission power amplifier is minimized.
An amplitude limiting circuit set to an optimum amplitude limiting level corresponding to the amplitude limiting circuit is provided.

[0006]

Therefore, according to the present invention, the required dynamic range of the base station power amplifier can be set small, and the power consumption and cost can be reduced without deteriorating the error rate.

[0007]

【Example】

(Embodiment 1) FIG. 1 shows a configuration of a transmitting section of a mobile phone base station apparatus using a direct spread spectrum system according to a first embodiment of the present invention. In FIG. 1, reference numeral 101 denotes a frame assembling circuit provided for each line, 102 denotes a spreading circuit that spreads a transmission signal assembled into a frame, 1
03 is an adder for integrating the outputs of the spreading circuits 102 into one system, 104 is an amplitude limiter that limits the amplitude of an optimum amplitude limit level according to the number of currently multiplexed lines, and 105 is an amplitude limiter 104. , A D / A converter for converting an amplitude-limited multiplexed signal into an analog signal, 107 a mixer, 108
Is a carrier oscillation circuit, 109 is a power amplifier circuit for amplifying the transmission signal mixed by the mixer 107, and 110 is a transmission antenna.

Next, the operation of the above embodiment will be described.
Each of the lines is incorporated into a transmission frame format with various control information and the like by the frame assembling circuit 101, and then spread by the spreading code assigned to the line by the spreading circuit 102. Outputs of the spreading circuit 102 for each line are combined into one system by an adding circuit 103 and sent to an amplitude limiting circuit 104. In this embodiment, QPSK
And so on, the spreading circuit 10 for each line is used.
The output of 2 and the output of the adder 103 are composed of two systems, an I component and a Q component. The amplitude limiting circuit 104 receives information on the number of currently multiplexed lines from the control device 105 and limits the amplitude to an optimum amplitude limit level according to the number of multiplexed lines. The amplitude-limited multiplexed signal is D
The signal is converted into an analog signal by the / A converter 106, mixed with the carrier signal from the carrier oscillation circuit 106 by the mixer 107, converted into a modulated signal, amplified by the power amplifier circuit 109, and transmitted from the transmission antenna 110.

Next, the amplitude limiting circuit 104 will be described. When a binary spreading code such as an M sequence or a Gold sequence is used as the spreading code, if the elements of the spreading code are +1 and −1, the signal obtained by multiplexing the N lines is −N, −N + 2,.
Take N + 1 values of N-2 and N. Therefore, in order to multiplex without deteriorating the cross-correlation characteristic of the spread code of each line, it is necessary to store N + 1 value amplitude information in the process from spreading to despreading. However, when the multiplex line N is large, the absolute value of the amplitude of the signal obtained by multiplexing the N lines is N
The probability of taking a value in the vicinity, that is, the probability that the spreading codes of all the lines are +1 or -1 at the same time is very small, and therefore, the deterioration of characteristics due to amplitude limitation is very small. Due to this property, when the allowable dynamic range of the transmission power amplifier cannot be sufficiently ensured for the multiplexed signal, the frequency of occurrence is lower than when the entire range of the possible amplitude of the multiplexed signal is input to the transmission power amplifier circuit. It is more advantageous in terms of error rate characteristics to discard the large amplitude part and input the small amplitude range to the transmission power amplifier circuit. Further, it has been confirmed by computer simulation that an optimum value exists for the level at which the amplitude is limited. In the present embodiment, an optimum amplitude limit level according to the number of multiplex lines is obtained in advance by computer simulation or the like, and stored in the amplitude limit circuit 104, so that the optimum amplitude limit for the current number of multiplex lines is performed.

Although the optimum value of the amplitude limit level varies depending on the number of multiplexed lines, generally, in the code division multiplexing method, when the number of multiplexed lines is small, the error rate characteristic has a margin, so that the amplitude limit level can be multiplexed. Even if the value is fixed to the optimum value for the maximum number of lines, the effect of limiting the amplitude can be obtained. In this case, there is no need to receive information on the number of currently multiplexed lines from the control device.

FIG. 2 shows an amplitude limiting circuit 10 according to this embodiment.
4 is shown. The input and output of the amplitude limiting circuit 104 are
Two orthogonal components (Iin 201 and Qin 202, I
out 203 and Qout 204). All of these components are represented by a digital signal having a width of several bits. A complex amplitude calculation circuit 205 in the amplitude limiting circuit 104 calculates a complex amplitude Zin of the inputs 201 and 202. The complex amplitude Zin is represented by equation (1).

Zin = (Iin ² + Qin ² ) ^1/2 (1) The calculated amplitude is input to the attenuation coefficient calculation circuit 206. The attenuation coefficient calculation circuit 206 calculates the following equation (2):
According to (3), the attenuation coefficient A according to the input amplitude is calculated. if Zin ≦ Zmax, A = 1 (2) if Zin> Zmax, A = Zmax / Zin (3) Finally, the input signals (Iin
201, Qin 202) by the attenuation coefficient A to obtain output signals (Iout 203, Qout 204). This allows
The output complex amplitude Zout is always equal to or less than the maximum amplitude Zmax. The complex amplitude Zout is represented by equation (4). ^{Zout = (Iout 2 + Qout 2} ) 1/2 = AZin ··· (4)

(Embodiment 2) FIG. 3 shows a configuration of a transmitting section of a portable telephone base station apparatus using a direct spread spectrum system according to a second embodiment of the present invention. In FIG. 3, reference numeral 301 denotes a frame assembly circuit provided for each line;
Reference numeral 302 denotes a spreading circuit that spreads a transmission signal assembled into a frame, 303 denotes an addition circuit that combines outputs of the spreading circuits 302 into one system, and 304 denotes an optimum amplitude limit according to the number of currently multiplexed lines. An amplitude limiting circuit for limiting the amplitude of a level; 305, a control device for providing line number information to the amplitude limiting circuit 304; 306, a D / A converter for converting a multiplexed signal with limited amplitude into an analog signal; 307, a mixer; Is a carrier wave oscillation circuit, and 309 is a mixer 30
7, a power amplifier circuit for amplifying the transmission signal mixed by 7,
310 is a transmitting antenna.

Next, the operation of the above embodiment will be described.
After each line is incorporated into a transmission frame format with various control information and the like attached by a frame assembling circuit 301, it is spread by a spreading code assigned to the line by a spreading circuit 302. The output of the spreading circuit 302 for each line is combined into one system by an adding circuit 303 and sent to an amplitude limiting circuit 304. In this embodiment, QPSK
And the like, the spreading circuit 30 for each line is used.
The output of 2 and the output of the adder circuit 303 are composed of two systems of an I component and a Q component. The amplitude limiting circuit 304 receives information on the number of currently multiplexed lines from the control device 305, and performs amplitude limitation at an optimum amplitude limiting level according to the number of multiplexed lines. The amplitude-limited multiplexed signal is D
The signal is converted into an analog signal by the / A converter 306, mixed with the carrier signal from the carrier oscillation circuit 306 by the mixer 307, converted into a modulated signal, amplified by the power amplifier circuit 309, and transmitted from the transmission antenna 310.

Next, the amplitude limiting circuit 304 will be described. The configuration of the amplitude limiting circuit 104 in the first embodiment includes a large number of operation LSIs such as digital multipliers and digital adders. Therefore, the circuit configuration is very complicated, and the cost and power consumption of the device are large. Therefore, in the present embodiment, as shown in FIG. 4, the amplitude limiting circuit 104 in the first embodiment is replaced with a ROM, and an output value corresponding to an input value is read from the ROM. An amplitude limiting circuit that requires a large number of arithmetic LSIs can be configured only with a ROM,
The size of the device can be reduced, and cost and power consumption can be reduced.

In FIG. 4, the amplitude limiting circuit 304
ROM 405 and 406. ROM-I4
The input signals Iin401 and Qin402 are connected to the address buses 05 and ROM-Q406. ROM-I405
And an output signal Iou from the data bus of the ROM-Q 406.
At t 403, Qout 404 is taken out. Iin401, Qin
402, Iout 403, and Qout 404 are digital signals represented by several bits. For example, if the signal is an N-bit signal, ROM-I405, ROM-Q40
For ROM 6, a ROM having 2N address buses and N data buses is used.

The value of the output Iout 403 corresponding to all possible combinations of the input signals Iin 401 and Qin 402 is calculated and stored in the ROM-I 405 in advance. The ROM-Q 406 has a possible input signal Iin4.
01 and the output Qout 404 corresponding to all combinations of Qin 402 are calculated and stored in advance. These output values are switched and output according to the line number information from the control device 305 in FIG.

The method of calculating the values of the outputs Iout 403 and Qout 404 corresponding to the input signals Iin 401 and Qin 402 will be described below. if Zin ≦ Zmax, Iout = Iin Qout = Qin if Zin> Zmax, Iout = AIin = Iin · Zmax / Zin Qout = AQin = Qin · Zmax / Zin (5) According to the above formula, Zin> Zmax When the amplitude is Z
The signal that is max is output.

With the above configuration, the output signals Iout 403 and Qout uniquely corresponding to an arbitrary input signal can be obtained simply by supplying the input signals Iin401 and Qin402 to the amplitude limiting circuit 304.
out404 can be obtained.

[0020]

As is apparent from the above embodiment, the present invention uses a transmission power amplifier having a dynamic range smaller than the dynamic range of a signal in which a plurality of channels are code-division multiplexed on the same carrier. In the pre-stage, the maximum number of multiplexed lines must be minimized to minimize the effect of the lack of dynamic range of the transmission power amplifier.
The provision of an amplitude limiting circuit set to an appropriate amplitude limiting level makes it possible to set the required dynamic range of the base station transmission power amplifier small, thereby reducing power consumption and cost without deteriorating the error rate. It becomes possible to plan.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a spread spectrum mobile phone base station apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an amplitude limiting circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a spread spectrum mobile phone base station apparatus according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an amplitude limiting circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional spread spectrum mobile phone base station apparatus.

[Explanation of symbols]

 101, 301 Frame assembling circuit 102, 302 Spreading circuit 103, 303 Addition circuit 104, 304 Amplitude control circuit 105, 305 Controller 106, 306 D / A converter 107, 307 Mixer 108, 308 Carrier oscillation circuit 109, 309 Power amplification Circuit 110, 310 Transmit antenna

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihiro Higashi 2-10-1 Toranomon, Minato-ku, Tokyo Inside NTT Mobile Communication Network Co., Ltd. (56) References JP-A-8-88588 ( JP, A) J. Kaihei 6-44255 (JP, U) Taku Nagase (2 others), Influence of dynamic range limitation of code division multiplexed signal, IEICE Autumn Meeting 1994-Society Pre-Convention-Lecture Shu, September 5, 1994, Communication 1, p. 311, B-311 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 13/00-13/06 H04B 1/69-1/713

Claims (3)

(57) [Claims] A transmission power amplifier having a smaller allowable dynamic range than a dynamic range of a signal in which a plurality of channels are code-division multiplexed, using a direct spread spectrum spread system as a digital signal transmission system,
In front of the transmission power amplifier, to reduce the influence of the lack of dynamic range of the transmit power amplifier, a multi
A spread spectrum communication apparatus, comprising: an amplitude limiting circuit set at an optimum amplitude limiting level according to the number of superposed lines . 2. The spread spectrum communication apparatus according to claim 1, wherein the amplitude limiting circuit includes a multiplication circuit for multiplying the input signal by the attenuation coefficient calculated by the complex amplitude calculation circuit and the attenuation coefficient calculation circuit. 3. The spread spectrum communication apparatus according to claim 1, wherein the amplitude limiting circuit includes a ROM storing an output value corresponding to a previously calculated input value.