JPH05102943A - Spread spectrum transmission system - Google Patents

Abstract

PURPOSE:To make a transmission quality constant irrespective of a bit rate by varying a diffusion factor by the bit rate, and controlling transmitting power in inverse proportion to the diffusion coefficient. CONSTITUTION:Transmitting power of a transmitting power amplifier AMP is controlled by a control circuit CONT in inverse proportion to a value of a diffusion factor gamma inputted from a diffusion coefficient input terminal R. As for the diffusion factor gamma, it is also allowable to send it out to the CONT by deriving a ratio of a frequency (fb) of a clock timing signal to a frequency (fc) of a chip clock signal, in a clock timing generating circuit CLK. In such a way, transmitting energy per one bit becomes constant, and in a state that a transmission quality is maintained, a bit rate can be heightened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum transmission system having a variable transmission bit rate.

[0002]

2. Description of the Related Art A spread spectrum transmission system is known as a digital signal transmission system. This method forms a channel using a specific spreading code, and C
DMA (Code Division Multipl)
e Access) can be realized. CDMA is (i) F
There is no need for a synthesizer that generates multiple carriers like DMA, (ii) no need for burst synchronization like TDMA, and (iii) easy spreading and despreading by baseband waveform processing. Remarkable CMOS-
There are merits such as small size, low power consumption, low price equipment can be realized by IC technology.

A conventional transmitter in the spread spectrum transmission system is shown in FIG. In FIG. 2A, the code sequence of the bit rate f _b is input from the input terminal D to the spreading circuit SPR. On the other hand, the clock timing signal of frequency f _b is input from the clock terminal C to the clock generation circuit CLK,
It is converted into a chip timing signal of frequency f _c . Chip timing signal is synchronized with the clock timing signal, the spreading factor γ = f _c / f _b is an integer value. In the spreading circuit, a spread spectrum signal whose band has been expanded γ times by the specific code is output and radiated from the antenna ANT through the transmission power amplifier AMP.

A second example of the transmitter is shown in FIG. 2 (b). In this example, the code sequence from the input terminal D is input to the error correction circuit F.
It is converted into an error correction coded sequence by EC. The error correction coded sequence is spread by the same spreading circuit SPR as in FIG. In addition to the chip timing, the clock generation circuit also generates a timing signal of frequency f _e .

In the spread spectrum transmission system, different codes can be associated with different channels, so that the bit rate of the transmission code can be easily changed. For example, if the spreading factor γ = γ ₀ = f _c / f _b0 when transmitting at f _b = f _b0 , then when it is desired to transmit a code having a bit rate 2f _b0 that is twice that, the spreading factor is γ = γ _0. If you halve it like / 2 = f _c / 2f _b0 ,
A channel with double the bit rate can be formed without changing the transmission bandwidth. FIG. 2C shows a signal spectrum with a bit rate f _b0 and a spreading factor γ ₀ bandwidth B. FIG (d) shows the bit rate 2f _b0, spreading factor γ _0/2, a signal spectrum bandwidth B. Both have the same spectrum, but different spreading codes result in different channels. However, since the transmission amplifiers AMP having the same transmission power are used, the transmission powers represented by the shaded areas in FIGS. 2C and 2D are the same, so the transmission energy per bit is In some cases, it is half of that in (c).
However, the transmission quality, for example, the average bit error rate, is the ratio E _b / of the signal reception energy E _b per bit and the power spectrum density N ₀ of the sum of noise and despread interference.
Since it is given by N ₀ , there is a drawback that the transmission quality changes when the bit rate is made variable.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spread spectrum transmission system which solves the fluctuation of the transmission quality when the bit rate is made variable.

[0007]

The present invention is characterized in that, in a spread spectrum transmitter, the transmission power is controlled in inverse proportion to the spreading factor which changes depending on the bit rate.
It differs from the conventional technique in that transmission power control is performed according to the spreading factor.

[0008]

Since the spreading factor is variable according to the bit rate and the transmission power is controlled in inverse proportion to the spreading factor, the transmission power per bit, that is, the transmission quality becomes constant regardless of the bit rate, and the object of the invention is achieved. To be done.

[0009]

EXAMPLE An example of the present invention is shown in FIG. The spreading circuit SPR, the power amplifier AMP, the antenna ANT and the clock timing circuit CLK operate in the same way as shown in FIG. In addition to these circuits, the spreading factor input terminal R
The transmission power of the transmission power amplifier is controlled by the control circuit CONT according to the value of the spreading factor γ input from this terminal. Even if the diffusion rate γ is not input from the outside,
In the clock timing generation circuit CLK, f _b and f
A method of obtaining the ratio to _c and sending it to the control circuit CONT is also conceivable.

The operation of the control circuit is shown in FIGS. 1 (b) and 1 (c). When the bit rate is f _b0 , the output power spectral density of the transmission amplifier AMP is G ₀ as shown in FIG.
Is. The output power P is P = P ₀ = G ₀ B. Let E _b at this time be E _b0 = P ₀ / f _b0 . Bit rate is 2
When it is fold 2f _b0, since the spreading factor is halved it becomes γ = γ _0/2, power spectral density is controlled to be twice the 2G _0. At this time, the output power P is P = 2P ₀
= 2G ₀ B. This is shown in FIG. 1 (c). E _{b at} this time is E _b = P / f _b = P ₀ / f _b0 and is invariable. Therefore, since E _b / N ₀ is the same in both cases, the transmission characteristic is unchanged.

The above is the same when the error correction circuit FEC is provided. However, f _c / f _e is sufficiently large.

[0012]

As described above, by controlling the transmission power in inverse proportion to the spreading factor, the transmission characteristic can be made independent of the bit rate. Therefore, the bit rate can be increased while maintaining the transmission quality.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional spread spectrum transmission system.

[Explanation of symbols]

 SPR spreading circuit CLK clock generation circuit AMP transmission power amplifier ANT antenna FEC error correction circuit CONT transmission power control circuit

Claims (1)

[Claims] 1. A spread spectrum transmission system characterized in that a spreading factor is variable corresponding to a variable transmission bit rate, and transmission power is controlled in inverse proportion to the spreading factor.