JPH0235497B2 - MUSENSOSHINDENRYOKUSEIGYOSOCHI - Google Patents

Description

[Detailed description of the invention] (Technical field to which the invention pertains) The present invention is directed to frequency division multiplexing (hereinafter referred to as FDM).
The present invention relates to an improvement in a wireless transmission power control device installed in a narrowband wireless communication system to reduce radio wave interference inside and outside the system.

(Prior Art) In an FDM narrowband wireless communication system, the frequency pitch between adjacent channels is 12.5 kHz or less, and measures are required to prevent interference with adjacent channels. Particularly in the field of mobile communication systems, a so-called small zone method is often adopted in which the same frequency is repeatedly used spatially in order to increase the capacity of communication traffic and make effective use of frequencies, and to reduce the frequency of radio wave interference. It is necessary to dynamically optimize transmission power.

In order to control such wireless transmission power, conventional devices provide a reference voltage level corresponding to the target transmission power by rectangular variation, detect the output level from the transmission power amplification section, and detect the output level. By configuring a negative feedback loop that amplifies the difference signal between the output and the reference voltage with high gain and returns it to the power control terminal of the transmission power amplification section through a loop filter (low frequency filter), the difference signal between the output and the reference voltage is adjusted to the reference voltage. Obtaining transmit power to follow.

In this negative feedback loop configuration, a first-order lag filter is generally used as the loop filter, but the envelope waveform at the rise and fall of the transmission output is an exponential complement waveform [1-exp(-t/τ)]. Become.
However, the above configuration has the following problems. In other words, it is well known that instantaneous spread of the spectrum occurs at the rise and fall points of the transmission output, but in general, the envelope waveform of the transmission output can be differentiated over time until a discontinuous function appears. When is n times and f is the relative frequency with respect to the transmission center frequency, the instantaneous spread of the transmission power spectrum (envelope of the power spectrum)
is proportional to 1/f ²⁽ⁿ⁺¹⁾ . Therefore, in the exponential complement function, n=1, and the spread of the transmission power spectrum is proportional to 1/f ⁴ .

Figure 1 shows an example of the simulation result of the interference wave level to the adjacent channel in this case.The receiving station of the adjacent channel is located 12.5kHz away from the transmission frequency due to the spread of the spectrum at the start of transmission in the conventional equipment. shows the time waveform of the interference wave received by The horizontal axis of the figure is time in ms, and the vertical axis is the relative interference reception level (in dB) based on the required reception level. As a parameter, the time constant of the exponential complement function τ ₁ = 70 μs (90% rising point is
160μs), the receiving filter is a 15th-order TBT (Tievisiev-Butterworth characteristic) bandpass filter, (m
=0.4) Bandwidth is 8kHz.

The simulation results show values that are almost the same as the actual measurements, with the worst interference wave level reaching -250 dB. This value is extremely undesirable considering that the required wave level itself varies by several tens of dB. In order to improve this, it is possible to increase the order of the loop filter, but if the order of the loop filter is increased, the transient response of negative feedback will become unstable, and the absolute values of the rise and fall times will increase. There is a drawback.

(Specific Object of the Invention) The present invention has been made to eliminate the above-mentioned drawbacks.
It is characterized by suppressing the instantaneous spread of the spectrum without extending the rise and fall times of the transmission power, and reducing the interference level of adjacent channels.

(Configuration and Operation of the Invention) FIG. 2 is a block diagram of an example configuration of a wireless transmission power control device embodying the present invention. Symbol 1 in this diagram
is the reference voltage waveform R that smoothly follows the target level signal (binary value) L _A corresponding to the target transmission power.
T is a timing signal that provides a target value, 2 is a differentiator that outputs a difference signal between two inputs, and the output R of 1 is connected to one input (positive electrode) of 2. The output of the differentiator 2 is the transfer function F
(S) is input to the loop filter 3. 4 is a level amplifier that amplifies the output of 3 with an amplification gain of K,
Its output becomes a control signal C that controls transmission power. 5 is a variable gain power amplifier, which transmits a carrier wave signal.
It inputs TXIN, power amplifies it with a gain corresponding to control signal C, and outputs a transmission output signal TXOUT. 6 is a monitor coupler that is roughly coupled to this HXOUT to obtain a monitor signal M attenuated from the transmission output level, and 7 is a rectifier circuit that amplifies and rectifies the monitor signal M to provide a DC voltage feedback signal F that is proportional to the transmission level. is sent to the other input (negative electrode) of the differentiator 2.

In this way, the circuit composed of 2 to 7 is
A negative feedback loop that follows the reference voltage waveform output R is configured. The closed loop transfer function H(S) that defines the response of the transmission output level to R is given by the following equation by simple consideration of FIG. 2, where B is the feedback gain due to 6 and 7.

H(S)∝KF(S)/1+KB·F(S)...(1) ∝ indicates a proportional relationship, and K is the gain of the level amplifier 4. In addition, the steady state (DC) characteristic is S=
0, and H(0)∝K/1+KB...(2) However, in order to maintain the follow-up ability due to the negative feedback loop, it is generally set so that KB≫1, H(0) is proportional to 1/B, and the deviation from 1/B becomes a steady error, which becomes smaller as K increases. Note that here, the closed loop transfer function H
The loop time constant of (S) is set to be sufficiently smaller than the change time of the output of the smooth waveform generator 1.

Next, FIG. 3 is a diagram showing an example of the circuit configuration of the smoothing waveform generator 1 in FIG. 2. Numeral 11 in the figure is a follow value counter, whose count output L _B (in this example, 9 bits in binary) uses the target signal level L _A (in this example, 3 bits in binary) as the upper bit and the lower bit. +1 or - until equal to 0 added to
A step of 1 is executed in synchronization with the rise of the timing signal T. To configure the additional value counter 11 with the above-mentioned functions, a value obtained by adding 0 to L _A and a value L _B
Using a comparator and an up-down (reversible) counter to determine the polarity of the step (+1 or -1), a flip-flop captures the rising edge of the timing signal T and up-downs a predetermined clock (several MHz). This can be easily realized with a simple configuration such as inputting to a counter.

12 and 13 are registers that store the upper bits of L _A and L _B , respectively, in synchronization with the rising edge of the timing signal T, and their outputs L' _A and L' _B are stored in accordance with the timing signal T.
Regarding L' _B , there is a relationship where L' B is delayed by one trigger time from L' _A. Reference numeral 14 denotes a read-only memory (ROM, whose capacity is 32K bytes in this example), and inputs L' _A and L' _B as the upper bits of the address signal to specify the desired section of the memory space. , the output L _B of the additional value counter 11 is inputted as the lower bit of the address signal, and the stored value D is output while sequentially scanning the memory space in accordance with the increment of L _B.

15 is a D/A converter which converts the stored value D into an analog value. 16 is a low frequency device and a follow value counter 11
The scanning clock frequency component of the ROM 14 is removed, and the output becomes the reference voltage waveform R for the closed loop in FIG.

Next, the operation of the apparatus of the present invention shown in FIGS. 2 and 3 will be explained using FIGS. 4 and 5. Figure 4 is a time chart of an example of control operations for starting, increasing, and stopping transmission power, and the upper part of the figure shows changes in the binary values of L' _A , L' _B , and L' _B explained in Figure 3. is plotted on the vertical axis, and the passage of time is plotted on the horizontal axis. Among these, L _B is the step output of the follow value counter 11, which is actually a step waveform, but its change due to analog approximation is shown by a broken line. L′ _A and L′ _B are shown by solid lines and dashed-dotted lines, respectively. In addition, the lower part of Figure 4 shows the change in the output R of the LPF 16 in Figure 3 in the same manner as the upper part, and L' _A1 , L _B1 ,
Symbols such as L′ _B1 , R ₁ , etc. represent constant values in each time interval.

Now, suppose that the value of L' _A changes from 0 to L' _A1 due to the rise of the timing signal T that gives the target value of power at time t ₁ in Fig. 4, then L' _B becomes L' _B1 (=0).
Since it is held in ROM14, L′ _A =
The memory section of L′ _A1 , L′ _B = L′ _B1 (=0) is specified,
Also, L _B advances by +1 as it moves from 0 to L _A1 ,
The rising operation continues until the value of L′ _A1 is reached at time t′ ₁ . Here, in the corresponding memory section of the ROM 14, a value that increases smoothly and monotonically from lower address 0 to L' _A1 from 0 to _R1 is written in advance (however, smooth means that the differential of the change is continuous). ), then the value of R ₁ exhibits a smooth upward change, for example, in the interval from time t ₁ to t' ₁ in the lower part of Figure 4, and from time t' ₁ to t ₂ .
Since L _B does not change, R remains at ₁ .

Next, at time t ₂ , the value of L′ _A further increases from L′ _A1 .
When it rises to L′ _A2 , L′ _B changes to L′ _B2 (=L′ _A1 ),
Since L _B starts a similar step from L' _A1 to L' _A2 , in this case as well, L' _A = L' _A2 , L' _B = L' _B2 (=
L′ _A1 ) specifies another memory section of ROM14,
Assuming that the series of write data from lower address L′ _A1 to L′ _A2 is the same as in the interval from time t ₁ to t′ ₁ ,
The change in R is also similar, resulting in a smooth upward curve from R ₁ to R ₂ .

Next, at time t ₃ , the value of L′ _A changes from L′ _A2 to L′ _A3 (=
0), L′ _B changes to L′ _B3 (=L′ _A2 ),
Since L _B starts stepping by -1 from L' _A2 to L' _A3 (=0), it continues its downward movement until it reaches 0 at time t' ₃ . In this case, L′ _A =L′ _A3 (=0),
L' _B = L' _B3 (= L' _A2 ) specifies a memory section of the ROM 14 that is different from the above, and it smoothly monotonically decreases from lower address L' _A2 to L' _A3 (=0). If the value has been written, the value of R will be changed from time t ₃ to t′ ₃
There is a smooth downward change like in the section.

As explained above, the smooth change in the value of R is sufficiently slow compared to the loop time constant of the closed-loop transfer function shown in Figure 2, so from equation (1), the output of the variable gain amplifier is approximately The value of R changes accurately in proportion to the value of R, and the value of R is a constant value (between times 0 and _t1 , between _t'1 and _t2 , between _t'2 and _t3 , and between t'3 and _t'3 in Fig. 4). It is clear that in the case of the above section), additional value control is similarly performed to a constant target value. The effect of reducing the level of interference to adjacent channels by the transmission output that follows the smooth change in R will be described below with reference to FIG.

Figure 5 is 12.5k lower than the transmission frequency as in Figure 1.
Said, cosine is the time waveform of an interference wave received by a receiving station on an adjacent channel Hz apart, and is an example of a function in which changes in R and transmission output level are smooth.
This is an example of a simulation when the waveform is 1/2 (1-cosπt/2τ ₂ ), and the scales of the vertical and horizontal axes and the receiving system parameters are the same as in FIG. 1. However, the 50% rise or fall time τ ₂ is 125 μs. According to FIG. 5, the worst interference wave level is about -44 dB, and it can be seen that the interference reduction effect is about 19 dB compared to the case of FIG. On the other hand, the 90% rise (fall) time of the transmission output in Figures 1 and 5 is 160 μs.
and 200μs, there is no big difference.

Next, the performance required for the ROM 14 in the block diagram of the smooth waveform generator 1 shown in FIG. 3 will be further examined. First, the target value of the transmission level that can be set is L _A
is 3 binary bits and has 2 ³ =8 levels. This corresponds to a dynamic range of 40 dB when the difference between levels is 5 dB, and is suitable for practical use.

Since L _B is 9 binary bits, the maximum number of quantization steps for the next generated waveform is 2 ⁹ = 512 steps.
The minimum change due to the remaining 6 bits excluding the upper 3 bits is 2 ⁶ =64 steps, which is a sufficient number of steps to approximate a smooth waveform. From the above
The capacity of the ROM14 is L' _A + L' _B + L _B = 15-bit address space, and 32 Kbytes is sufficient.
A commercially available 32K byte 1-chip ROM can be used.

In addition, the waveform generation speed is 250/512 = 250/512 to generate the maximum 512 steps in 250 μs as in the example in
The access time is sufficient to be within 0.49 μs/step (the clock of the additional value counter 11 is approximately 2 MHz), and is fast enough to be used even with a low power consumption CMOS ROM.

(Effects of the Invention) As described above, according to the wireless transmission power control device of the present invention, in variable power control having a plurality of transmission power target values, a transition from one transmission output level to another transmission output level is possible. Since the change in the output follows the time waveform generated by the sequence of smoothly monotonically increasing or decreasing numerical values written in advance in the ROM, the instantaneous spread of the spectrum when the transmitting output changes is reduced. It is possible to reduce interference with other channels including adjacent channels, and to obtain stable negative feedback control power similar to the conventional one in a time period in which the transmission power does not change. Furthermore, since ROM is used, there is a high degree of freedom in selecting smooth waveforms, which has the advantage of being applicable to correction of deviations from the ideal value of the closed-loop step response.

[Brief explanation of drawings]

FIG. 1 is an example of the time waveform of the interference wave level to the adjacent channel at the time of the rise of transmission in a conventional device.
FIG. 2 is an example circuit diagram of a wireless transmission power control device embodying the present invention, FIG. 3 is an example circuit diagram of a smooth waveform generator in FIG. 2, and FIG.
FIG. 5 is a time chart showing an example of rising and stopping operation, and is a time waveform example of the adjacent channel interference wave level at the time of rising of transmission by the apparatus of the present invention. DESCRIPTION OF SYMBOLS 1...Smooth waveform generator, 2...Differentiator, 3...Loop filter, 4...Level amplifier, 5...Variable power amplifier, 6...Rough combiner, 7...Rectifier circuit, 11...Additional value counter, 12, 13...Register , 14...ROM,
15...D/A converter, 16...Low frequency device, L _A ...
Target level signal, L′ _A ...signal sampled from L _A ,
L _B ...Count value output of the follow-up counter 11, L' _B ...
Signal obtained by sampling the upper 3 bits of L _B , C...control signal, D...memory value of ROM14, F...feedback signal, M...monitor signal, R...reference voltage waveform, T...timing signal that provides target value, TXIN... Transmission carrier signal, TXOUT...transmission output signal, t...time.

Claims (1)

[Claims] 1. In order to generate a reference voltage level for the target transmission output in order to control the transmission signal output of a wireless transmitter, one reference voltage value is changed from one reference voltage value to another by a smooth change whose time derivative is continuous. A smoothing waveform generator that generates a waveform that transitions to a reference voltage value, a two-signal differentiator that inputs the output to the positive side, a loop filter that extracts low frequency components from the output of the differentiator, and a loop filter that extracts the low frequency component from the output of the differentiator. a level amplifier for amplification, a variable gain power amplifier for outputting a transmission output proportional to the output level of the level amplifier from an input from an input terminal, and a signal output that is loosely coupled to the output of the power amplifier to take out a signal output proportional to the output. A negative feedback loop circuit constituted by a coupler and a rectifier circuit that rectifies the signal from the coupler and inputs a DC voltage proportional to the transmission output level to the negative electrode side of the differentiator, and generates the smooth waveform. 1. A wireless transmission power control device, characterized in that the output of the variable gain power amplifier is used as a reference voltage, and the transmission signal output of the variable gain power amplifier is changed to follow changes in the reference voltage.