FI104027B - The base station emulator - Google Patents

Description

104027 Station Emulator ν Current telephone systems tend to increasingly use radio technology for long distance calls, and in some cases have begun using 5 digital technologies; however, no existing system has been able to provide efficient and effective radiotelephone technology for local calls from individual subscribers to individual subscribers. Such technology has been described in various recent patents, e.g. the present application is jointly owned by the assignee of the present application, as, for example, in U.S. Patent Nos. 10,464,461 and 4,675,863. The technique described in these patents provides base stations that communicate with both a exchange and multiple subscriber stations using digital time division radio circuits associated with a particular subscriber.

The base stations 15 used in the aforementioned time-sharing system are relatively complex and expensive, but economically feasible in a large system serving a large number of subscribers; however, for relatively small systems serving a relatively small amount of Ti, they may not be economically feasible. In addition, such a system uses a frequency pair, one for transmission and one for reception, and given the limited number of channels available in the frequency band 20, it would be highly desirable if only one frequency could be used effectively.

It is therefore an object of the present invention to provide a base station which can be said to be simulated or emulated, which in certain situations can replace the actual base station.

; Another object is to provide a system that can be used for multiple subscribers, but can only be used on a single time frequency.

Other objects will be apparent from the following description and claims.

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claims.

The objects of the invention are achieved by a system which is characterized by what is stated in the independent claims. Preferred embodiments of the invention are apparent from the dependent claims.

The system of the present invention actually employs itself a · · I · modified subscriber station, which functions as a simulated, i.e., emulated, base station • I · 35, thereby substantially reducing the overall system cost and complexity. This emulated base station differs substantially from the subscriber station only in that it is able to initiate a synchronization procedure, whereas the subscriber unit only operates by erasing the rf signals transmitted by the emulated base station until it finds its assigned frequency and time slot. In periods between transmission of the rf signals, the emulated base station is arranged to receive 5 rf signals from the subscriber units. In this way, the subscriber unit can either talk to an emulated base station, which then acts as another subscriber station, or it can talk to another subscriber station synchronized to it by the emulated base station.

Fig. 1 is a block diagram showing a complete system of to-10 of the present invention;

Fig. 2 is a schematic representation of the RCC waveform used in a standard base station;

Figure 3 is a schematic representation of the RCC waveform used in the present invention.

Fig. 4 is a schematic representation showing the positive edges of the amplitude of a received signal used in synchronization of the present invention;

Fig. 5 is a block diagram of a circuit for providing synchronization of the present invention; Fig. 6 is a block diagram of a receive AGC circuit used in the present invention;

FIG. 7 is a block diagram showing a frequency generating circuit used in the present invention;

Figure 8 is a schematic representation of the structure of a radiotelephone system,. i. 25 which implements the present invention; · «« · *

Fig. 9 is a diagrammatic representation similar to Fig. 8, but * * * showing a two-subscriber system;

Fig. 10 is a schematic representation of the frame structure of the dual subscriber system of Fig. 9; Figure 11 is a schematic representation of the * · · frame structure of a set of two subscriber systems; Fig. 12 is a schematic representation of a system implementing the present invention used to monitor one or more operations; Fig. 13 is a schematic representation of an embodiment of the present invention; the repeater;

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Fig. 14 is a schematic representation of a system implementing the present invention using multiple repeaters; and FIG. 15 is a schematic representation of a system implementing the present invention using a single repeater to control a plurality of other repeaters and 5 subscriber units.

Generally, the internal operation of a system entity designated 10 is shown in block diagram form in Figure 1. In this system, during a call, a person speaks to a telephone 12 and the speech signal is transmitted to a local telephone interface unit 14. The signal is digitized by codec 16 and 10. ) for lower data rates. The compressed data is then supplied to the modem 20 via a cable 22 and a bipolar switch 24, whereby the modem functions to convert the frequency range of the data stream into an analog signal which efficiently utilizes. This analog signal is supplied to radio 15 via line 28. The radio converts the signal frequency to a higher frequency into a radio frequency (rf) signal and then transmits this rf signal through antenna 30.

At intervals of transmitting Rf signals, the unit is adapted to receive rf signals from the subscriber unit. Radio 26 converts all these RF signals 20 to a lower frequency into an intermediate frequency (if) signal and supplies this if signal to modem 20 via line 32. Modem 20 demodulates the if signal to form a digital signal which is then supplied to the speech processor via switch 24 and line 36. The speech processor then operates by expanding the signal to a digitized speech signal and this digitized signal is then supplied. 25 to a codec 16 which outputs an analog speech signal to a telephone 12 via a telephone interface 14.

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The data transfer operation is similar to that described above except that the pu-hel is replaced by a terminal or computer 38 and the telephone, codec and speech processor are bypassed by an alternate position of the switch 24 which is then connected to the terminal 38 via wires 40 and 42.

The modem 20 and radio 26 are both connected to the control unit 44.

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The control unit 44 is initially set for a predetermined time interval, for modulation; · and for the modem connection set-up mode, and for the radio's predetermined rf frequency and power level. However, these parameters can be adjusted by * * · 35 wide units in case they are not suitable for providing satisfactory reception at the subscriber station.

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In a system using an actual base station, such as the aforementioned U.S. Patent 4,675,863, the transmitted waveform is divided into several (i.e., 45) millisecond frames. Each frame is in turn divided into four 11.25 ms time slots. The base station transmits at all four time slots, producing a 100% modulated waveform, with the only exception being the radio control channel (RCC). The RCC time interval is slightly shorter than 11.25 ms and this causes a small gap in modulation at the beginning of each frame. This opening is known as the AM hole. The waveform diagram of the RCC channel in the actual base station format is shown in Figure 2. However, the system of the present invention does not transmit a 100% waveform. Instead, only one time slot is transmitted per frame (25% waveform) as shown in Figure 3.

This modified frame format requires changes in coarse sync, auto gain control (AGC) and frequency development. These changes are indicated in the following description.

coarse Anxiety

Since only 25% of the waveform is used in the present system, it monitors the amplitude of the received signal and looks for positive edges in the amplitude signal. These positive edges are illustrated in Fig. 4. The Ti-20 timing unit adjusts its frame timing so that it aligns with the occurrence of these positive edges.

The circuit providing the aforementioned coarse synchronization is shown in the form of a loh-i, diagram in Fig. 5, in which the received signal is amplified; a calculator 50 which produces a computer amplitude signal which:. 25, in turn, is applied to a comparator 52 to compare it with a predetermined threshold signal to generate a digital signal (1 = signal present, 0 = no signal). This digital signal is supplied to the edge detector 54 which at its output produces a signal pulse to indicate positive edge detection.

30 AGC

I I · * 25% modulation requires a specific type of receive AGC to avoid redirection in the absence of a signal. As a result, an AGC of slow rise and rapid decay is provided. This is illustrated in Fig. 6, in which the received signal is supplied to amplitude calculator 56, which may be in the form of a preprogrammed ROM, from which the resulting '··· [amplitude signal is supplied to comparator 58, where it in turn reduces • · * • • 5 5 104027 is set from a predetermined threshold to generate a difference signal. This difference signal is applied through one or two scaling multipliers shown in positions 60 and 62 to a low pass filter comprising an adder 64 and a delay member 66 coupled via loop 68. Either multiplier 5 is used, according to the sign of the difference signal. If the difference signal is positive, slow attenuation is applied to the AGC control signal. If the difference signal is negative, the AGC control signal applies a fast ascent. The output of the filter is a gain signal, which is then supplied to the gain control unit 44 shown in Figure 1.

10 Coarse frequency development

Since the 25% frame format does not require performing frequency generation in the inactive time (75% zero time), and since frame timing is not known when frequency generation is performed, a modified frequency generation circuit is provided as shown in Figure 7. 15, the received signal is supplied to a discrete Fourier Transform (DTF) calculator 70, which at its output produces higher frequency band energy (center frequency band energy) and lower frequency band energy (center frequency band band energy). The higher band energy output is subtracted from the lower band energy output in the summing 20 72 output to the mixer, i.e. the multiplier 74. The received rf signal is also applied to the output means 76 which removes the sign (negative or positive) of the signal, thereby determining only signal amplitude. The stripped signal is then applied to a filter 78 which smooths the signal s; with its average. The output of filter 78 is passed through amplifier 80 i i 25 to multiplier 74.

The main purpose of the circuit 76, 78, 80 is to prevent the effect of noise on the output signal, while at the same time emphasizing the actual signal. In this sense,. since noise generally has a small amplitude, it is effectively filtered out during the smoothing procedure. On the other hand, since the amplitude of the actual signal is relatively large, it is actually emphasized by adding a smoothed or filtered * · i · signal to the mixer 74.

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* · '' The scaled signal from mixer 74 is balanced for high and low energy frequencies, and this balanced signal proportional to the short-term average amplitude of the received signal,

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35 is provided to a low pass filter comprising an adder 82 and a delay member 84 connected through a loop 86. The delay member 84 causes the VCXO-I I · I · «

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The output signal 88 to control 104027 6 represents the output immediately preceding the output actually applied to the low pass filter. The VCXO control is used to adjust the frequency of the system's main oscillator.

After initial or coarse adjustment, the system is idle-5, but is fully ready for speech. If the handset at either end is lifted, the ring at the other end will ring until the ringing phone is answered or the phone that has switched on is closed.

The calls are connected with a speech code word (VCW) at the beginning of each call interval, which indicates lifting the handset at the starting station. When this occurs, the station acting as an emulating base station itself appears to the exchange (CO) to initiate a call, thereby establishing a connection to the exchange. The initiating subscriber then continues to dial by dialing the desired number. When the initiating subscriber closes the telephone, the emulated base station receives this information via the VCW and presents the closure to the exchange.

When the emulated base station detects a call signal from the exchange, the subscriber unit is made to ring by the corresponding VCW from the emulated base station. When the subscriber then closes, the emulated base station receives this information via the corresponding VCW and presents the closure to the exchange.

The structure of a radiotelephone system of the above type is illustrated by way of example in FIG. 8, wherein the subscriber unit 90 is shown to be in radio communication with base station 96 emulated by antennas 92 and 94.

: Two Subscriber System * «!.; The system described above may be implemented as a two-subscriber arrangement: as shown in FIG. 9. In this system, each channel can support two complete calls without requiring a splitter. In this sense, the two subscriber unit 102 is connected via wires 104 and 106 to the two telephone sets 108 and 110. The subscriber unit 102 is in radio communication with the dual base station 116 emulated by the antennas 112 and 114. The unit 116 is connected to ... 30 by cable 118 and 120.

l]. ' Both separate subscribers 108 and 110 use, for example, the time division arrangement shown in the aforementioned U.S. Patent 4,675,863, where each subscriber is assigned a separate time slot. The frame structure of this arrangement is shown in Fig. 10, which shows four time slots numbered 1, 2, 3 · · 35, and 4. The first two time slots are used for the emulated base station and the last two for both subscribers.

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Multiple two-subscriber systems can be operated on different channels without branchers, synchronizing the transmissions of all emulated base stations. This is illustrated by the frame structure shown in Fig. 11, in which channel 1 is shown above and channel n 0 'which indicates any number of channels 5 between them). For each channel, the first two time slots are for transmission and the last two for reception.

remote search service

One emulated base station can be used with many different subscribers, one at a time. In such an arrangement for reception, ti-10 broads continuously monitor radio control channel (RCC) transmissions, which are more fully described in the aforementioned U.S. Patent 4,675,863, until an emulated base station searches for a particular subscriber using a subscriber identity number (SID). Upon receipt of the paging request, the subscriber begins transmission back to the emulated base station using the synchronization procedure described above. To initiate a call, the subscriber transmits at the RCC using the synchronization procedure described above.

Monitoring Activities

The present system may be used to monitor one or more functions. To this end, using a computer as a control / data storage device, a periodic polling of multiple subscribers 20 may be conducted to report specific functions such as temperature, weather, security, water / flood warnings, fuel scarcity alarms, gas, electricity or water meters. , etc. This is illustrated in Figure 12, in which the emulated base station 122 is in radio communication

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a plurality of subscriber units designated 124, 126, and 128, respectively. 25 Unit 122 is connected by cable cable to both telephone 130 for voice communication and to computer or terminal 132 for data input. In a e-mail manner, each subscriber unit is connected both to a respective telephone 134, 136 or 138 for a voice connection and to a data device, as at 140, 142 and 144, respectively.

# ... f 30 Repeat System

An important use of the present system is as a repeater to expand the system's operating range. In this arrangement, the emulated base station can be used to overcome obstacles such as mountains or the like. FIG. 13 illustrates this function by indicating subscriber unit 146 in radio communication with an emulated · 35 base station base station 148. Unit 148 is also in radio communication with a conventional base station 150 connected to the exchange.

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104027

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The relative simplicity of the emulated base station and its relatively low cost make it a very affordable repeater unit. It can also be used as a repeater to extend the system's remote range regardless of the presence of obstacles. However, utilizing the slot arrangement, the repeater unit fits into the system as a whole without the use of splitters, yet remains transparent to both the conventional base station and the subscriber. Of course, it can also be placed between a subscriber and another emulated base station instead of a standard base station. This can be tracked in multiple steps from one emulated base station to another so that the range of the system is extended at a relatively low cost. This is illustrated in Fig. 14, where a set of repeater units 152 is disposed between subscriber 154 and base station 156.

In addition to expanding the range of the system, the repeater units function by refining the actual base station signal before transmitting it to the subscriber.

The repeater may also be used in a so-called repeater star system to control multiple repeaters and / or subscribers. This is illustrated in Fig. 15, where a separate repeater unit 158 is in radio communication with auxiliary repeaters 160 and 162 and one or more subscribers, as in 164. Auxiliary repeaters are also in turn radio communicated with subscribers such as in brochures 166, 168, 170, 172 and 174, auxiliary repeaters, such as a repeater in step 176. Any auxiliary repeater, such as auxiliary repeater 162, may be used as a terminal repeater which is in direct communication with the base station indicated by 178> i.

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: Multiple repeaters on different channels and can be placed in the same location

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·, · J 25 synchronized so that they are transmitted and received at the same time, thus avoiding the use of splitters. Such a structure uses a base station RCC channel to monitor the master repeater, which distributes monitoring information to different subscribers via the RCC emulated base stations. Such a structure m assigns to each subscriber a repeater channel when establishing a call.

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Claims (6)

104027 Patent Claims: A wireless digital communication system comprising at least two stations that are in radio communication with each other, characterized in that the primary station (122) initiates the timing of the RF signals and the secondary station (124, 126, 128) synchronizes its timing to the initiated timing, the synchronization means (70, 72, 76, 78, 80, 82, 84, 86) in the secondary station (124, 126, 128) including a frequency orienting circuit comprising 10 calculating means (70) separating the upper band and the lower band energy of the signal received from the primary station; frequencies, means (72) for reducing the high-band energy output from the lower-band energy output to obtain an output signal, means (76) for deriving the signal of the input signal only amplitude, means (78, 80) for pre-emphasizing the distorted signal, means (82, 84, 86) for stripping p to supply an ignal to a voltage-controlled crystal oscillator which provides secondary station timing. Communication system according to claim 1, characterized in that the RF signal comprises waveforms divided into a plurality of frames, each frame comprising a single time slot. .: A communication system according to claim 2, characterized by; they 11 u that: '': 25 it further comprises: · · · control means (44) at each station, amplitude control means (50, 52, 54) at each station controlled by the control means (44) for monitoring the amplitude of the signals of the other station and ... 4 to determine the position of the positive edges in the waveforms of these signals by comparing the amplitude of the signal at each other position to a predetermined • · 4 threshold signal, ft <·: · frame adjusting means (70, 72, 74, 76, 78, 80, 82 , 84, 86) at each station controlled by the control means (44) for adjusting frame timing at the station by aligning the frames with occurrences of positive edges, 35 primary stations (122) having means for initiating frame synchronization (70, 72, 74, 76, 78, 80); 84, 86) and the secondary station (124, 126, 128) 11104027 has frequency directing means (70, 72, 74, 76, 78, 80, 84, 86) received from the primary station (122). for synchronizing the timing of the new signals with the timing initiated by the pri (122), the system further includes a slowly rising, rapidly attenuating automatic gain control circuit (56, 58, 60, 62, 64, 66, 68), which refrains from tracking in the absence of the signal; an amplification control circuit comprising amplitude calculating means (56) to which the received signal is applied and outputting an amplitude signal, 10 comparator (58) for receiving and subtracting the amplitude signal from a predetermined threshold to generate a difference signal, and means (60, 62) a fast pitch optional application of the auto gain control signal; and means (64, 66, 68) for supplying the applied signal to the control means (44). The communication system according to claim 2, characterized in that the primary station (152) is a dual-mode subscriber station (152) and the secondary station (152) is a dual-mode base station (152), wherein each subscriber station is assigned within frame timing. custom time interval. The communication system of claim 1, characterized in that the secondary station (124, 126, 128) communicates with the central station (122). • · · The communication system according to claim 1, characterized by ·: ·. characterized in that it comprises a series of secondary stations (152, 154) and the last secondary station (154) of the series is wirelessly communicating with the primary station (152). • · «'' • · * * *» · # • · · · • # „104027