KR970000665B1 - Local radio communication system - Google Patents

Abstract

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Description

Local Radio Communications System

1 is a local wireless packet communication system according to the present invention.

2 is a block diagram showing the configuration of the mobile terminal of FIG.

3 is a block diagram showing the configuration of the base station of FIG.

4 is a diagram showing the configuration of a transmitter used in the mobile terminal and base station of FIG.

5 is a diagram showing the configuration of a receiver used in the mobile terminal and base station of FIG.

6 is a diagram illustrating a configuration of a base station that implements a multiple packet capture mechanism for capturing up to K packets according to the present invention.

7 is a diagram showing the form of packet data used for data transmission in a local wireless communication system according to the present invention.

8 shows an example of designing a time slot length, a packet length, a mini slot length, a transmission time randomization interval, and an example of packet reception in two consecutive slots by randomizing packet transmission.

* Explanation of symbols for main parts of the drawings

10: local wireless packet communication system 12: base station

14, 16, 18, 20, 22, 24: terminal 26, 36a, 80, 82: antenna

32,50,52,54: Transmitter 34,42,44,46: Receiver

36: transceiver 56,142: multiplexer

68: packet modulation circuit 78: RF defense circuit

90: RF demodulation circuit 92,118: automatic gain regulator

96,122: dual threshold detector 102: modulo-2 adder

110: IF demodulation circuit

The present invention relates to a wireless communication system, and more particularly, a base station (BS) and a plurality of base stations using a common spread spectrum code within a radius of about 60 to 600 meters outside and indoors. The present invention relates to a local radio communications system for enabling the simultaneous reception and processing of a plurality of packets between mobile terminals (MTs).

The remarkable growth of digital communications over the last four decades, driven by the ever-increasing data transfer and cost-competitive advances in digital integrated circuit technology, has resulted in packet switching-based packet wireless networks. The radio network allows multiple users to share frequency spectrum and information over large areas.

In order to use a wireless terminal as a transmission medium in a channel shared by a plurality of users, a method of providing multiple access processing capability for common use of communication resources among geographically dispersed terminals is required. do.

The existing wireless channel access method proposed to provide multiple access processing capability can be largely divided into a fixed channel access method and a random channel access method. A typical example of the fixed channel access method is time division multiple access (TDMA). ), And frequency division multiple access (FDMA), and random channel access includes an boiling / synchronous Aloha (ALOHA) method and a carrier sense mutiple access (CSMA) method.

Although the channel access method described above is mainly related to a system using a narrow band signal, the direct sequence spread spectrum (DS / SS) signaling method is an alternative to the narrow band signal method. It can also be used as a connection method.

A representative example is code division multiple access (CDMA).

The DS / SS signaling scheme has advantages such as narrowband interference signal cancellation, capture capability, multiple access capability, and the like.

Here, the capturing capability in a spread spectrum (SS) system refers to the ability of a receiver to keep track of one desired packet in synchronization and to exclude other packets that are received at the same time as noise.

In addition, the multiple access capability in spread spectrum refers to the ability of two or more packets to coexist in the same frequency and space-time with a level acceptable to the mutual interference level generated when multiple accesses.

The capture capability in the SS can be obtained when the wireless terminals in the wireless network use different orthogonal SS codes.

In this case, signal processing for code identification is required at the receiver of the base station.

However, when the number of wireless terminals subscribed to the wireless network increases, signal processing for finding its own code in the base station receiver becomes burdensome, and therefore, a large power consumption is caused. Therefore, in the local wireless communication system, it is required to design a simple and economical system of urgent low power consumption.

An object of the present invention is to enable a plurality of packet receptions and to design a simpler SS communication system while avoiding an increase in complexity and power consumption of a system caused by use of multiple orthogonal SS codes at a base station.

In one aspect, the present invention provides a DS / SS using one common spreading code, a synchronous ALOHA random channel access scheme, and uniform randomized randomization of packet transmission time based on mini-slot. In addition, the present invention provides a local wireless packet communication system using a mechanism that enables capture of a plurality of packets, and a base station having a plurality of receivers.

The use of the multi-packet capture system according to the present invention enables a remarkable increase in system capacity and a simpler structure than the existing CDMA system, thus enabling the implementation of an economical system capable of serving multiple subscribers in the region. .

Uniform discretization process for randomizing transmission time causes all wireless terminals to be randomly multiplied by an integer multiple of the mini slot unit within a window section allocated at the beginning of every time slot. By starting the packet transmission only at the time point, the packet collision rate due to the complete overlap between the packets received at the receiving end is greatly reduced, and sufficient orthogonality is maintained even between the same SS codes.

In CDMA cellular telephone systems, a special reference code, called a pilot, is implemented in a pseudo-noise (PN) sequence on the forwrd link (the BS to MT channel) (A. Salmasi, K. Gilhousen, On the system design aspects of code division mutiple acess (CDMA) applied to digital cellular and personal communication networks, Proc. Of IEEE Vehecular Technology Conference, pp. 57-62, May 1991).

Receiving this pilot signal at the receiver of all mobile terminals obtains information about the timing and frequency offset required for signal demodulation to facilitate synchronization and signal tracking.

However, under local or outdoor local wireless communication environments, the propagation delay time is so short that it can be negligible, so the mini slot timing between the transmitter and receiver can be easily synchronized.

In addition, by using a matched filter, synchronization time information for demodulating the SS signal can be obtained in a simpler manner.

The multiple packet capture system according to the present invention is similar to the conventional CDMA scheme in that one or more packets can be simultaneously received.

However, the multiple packet capture system according to the present invention uses a plurality of receivers in the base station as in the CDMA scheme, but uses only one spread spectrum code.

The present invention will now be described in detail with reference to the accompanying drawings.

1 illustrates a local wireless packet communication system 10 of the present invention for packet transmission using an electromagnetic carrier.

System 10 consists of one base station 12 and M terminals 14-24.

All terminals 14-24 are synchronized with the base station 12 in units of slots. Base station 12 is fixed but terminals 14-24 may move. Therefore, hereinafter, each of the terminals 14-24 is referred to as a 'mobile terminal'.

FIG. 2 shows the configuration of each of the mobile terminals 14-24 in FIG. 1. For convenience, the mobile terminal # 1 14 is shown in the drawing. In FIG. 2, 26 denotes an antenna for transmitting and receiving packet data, 28 denotes a directional coupler for combining an antenna transmission channel and a reception channel, and 30 denotes a signal processing and overall control of a signal related to packet transmission. A processor 36 represents a transceiver for transmitting and receiving a packet using given carrier frequencies, respectively.

As shown, the transceiver 36 includes a transmitter 32 for encoding packet data from the processor 30 into a single long PN code, and decoding the received PN code into packet data. And a receiver 32 provided to the processor 30.

In transmit mode, processor 30 provides packet data to transmitter 32, and an encoder (not shown) in transmitter 32 transmits packet data in a binary bit stream to a DS / SS chip stream. And modulate it into a carrier frequency and send it to the directional coupler 28.

The antenna 26 radiates and modulates the modulated RF spread signal in the form of electromagnetic waves.

Each terminal 14-24 enters the retransmission mode if the packet transmission fails and simply retransmits the packet until the packet transmission succeeds.

3 is a diagram illustrating a configuration of a base station 12. A transmission / reception system including K receivers 42-46 and transmitters 50-54 is provided to effectively receive a plurality of packets in a random channel access environment. Have

In the third, reference numeral 36a denotes an antenna, 38 denotes a directional coupler, 40 denotes a processor, 48 denotes a channel allocator, and 56 denotes a multiplexer.

The transceivers 42-46 and 50-54 of the base station 12 according to the present invention commonly use one spread spectrum code.

As such, it is by the multiple packet capture mechanism that the base station 12 can receive multiple packets while using the common spreading code.

The base station 12 includes K receivers 42-46, K transmitters 50-54, a processor 40 for controlling various functions in the base station 12, and a corresponding channel (transmitter) according to the address of a packet. It consists of a channel allocator 48 for allocating packets to the multiplexer, a multiplexer 56 for linearly summing packets of K channels, a directional coupler 38, and an antenna 36a.

The transmit and receive carrier frequencies are allocated differently, but all transceivers 42-46 and 50-54 use the same set of carrier frequencies.

In addition, while the carrier frequencies of the receivers 34, 42-46 and the transmitters 32, 50-54 of the base station 12 and the mobile terminals 14-24 are allocated differently for transmission and reception, the local wireless communication system 10 It is also conceivable to use a different set of carrier frequencies for all the mobile terminals 14-24 belonging to and to use all three sets of carrier frequencies in the base station 12.

Processor 40 of base station 12 is programmed to perform functions related to assembling and deassembling of packets.

The processor 40 writes the BS identification number and the MT identification number into the address field of the packet before transmitting each packet.

The processor 40 also performs error detection for the data portion and address and control region of the packet.

4 shows a configuration of a transmitter (eg, 32 or 50) used in the mobile terminal 14 or the base station 12. In Fig. 4, reference numeral 68 denotes a packet modulation circuit, and 78 denotes an RF modulation circuit.

The packet modulation circuit 68 is composed of an inter-transmitter randomizer 62, a pseudo noise (PN) generator 64, and a modulo-2 adder 66.

The RF modulation circuit 78 is composed of an IF local oscillator 70, an IF modulator 72, an RF-to-IF frequency converter 74, and an RF amplifier 76. Packet data is input to the packet modulation circuit 68 under the control of the processor 60. The input packet is first determined between the transmitters randomized by the inter-transmitter randomizer 62 driven by the processor 60 for each corresponding time slot.

In the randomization method of packet transmission, an integer multiple of the chip time is used as a unit to time offset for randomization of the transmission time, and a length of a preamble code is used as a unit. Therefore, there may be two methods of randomizing the transmission time by an integer multiple of the time by using an integer multiple of the preamble code length or a length larger than the preamble code length.

The latter method has some attenuation effect in terms of effective packet reception rate as the randomization interval Tr increases, but may be selectively used according to the signal environment because it will be a better method than the former for optimal packet reception performance.

In addition, numerical analysis shows that setting the length of the transmission time randomization interval to 15 mini-slot lengths can optimize the throughput of the effective packet, and therefore, use of 15 mini-slots is considered first.

As the number of mobile terminals to be serviced increases, the number of mini slots in the randomization interval can be adjusted to satisfy the capacity even though the effective packet throughput is slightly reduced.

Packet data having a random transmission time and a DS / SS code sequence output by the PN generator 64 are modulated into a spread spectrum chip sequence by a modulo-2 adder 66 and then input to the RF modulation circuit 78. do.

The input packet is first modulated into an IF carrier signal in the IF modulator 72 according to the IF frequency supplied by the IF local oscillator 70 driven by the processor 60.

At this time, the preamble code portion of the pseudo noise PN is not modulated by the spread spectrum chip string.

The IF carrier signal from the IF modulator 72 is up-modulated into the RF carrier signal by way of the IF-to-RF frequency converter 74, and this modulated signal is transmitted by the RF amplifier 76 to transmit power of the modulated signal. This is amplified and then radiated as an electromagnetic wave carrier through the antenna 980.

In the configuration of the transmitters 32 and 50 as described above, the configuration except for the transmission time randomizer 62 which performs transmission time randomization is the same as that of the conventional universal DS / SS encoding circuit.

As another embodiment of the transmitters 32 and 50, the transmission time randomizer 62 may be located in front of the IF-to-RF frequency converter 74 in the RF modulation circuit 78.

5 shows the configuration of the receivers 34 and 42 used in the mobile terminal 14 or the base station 12.

In FIG. 5, reference numeral 82 denotes an antenna, reference numeral 90 denotes an RF demodulation circuit, 92 an automatic gain controller (AGC), 94 a matched filter, 96 a double threshold A double threshold detector (DTD), 98 represents a processor and 110 represents an IF demodulation circuit.

The RF demodulation circuit 90 is composed of a bandpass filter (BPF) 84, an RF front end amplifier 86 and an RF-to-IF frequency converter 88.

IF demodulation circuit 110 includes PN generator 100, modulo-2 adder 102, IF local oscillator 104, IF demodulator 106 and A / D conversion and bit determiner 108. It is composed.

The spread spectrum signal transmitted from the transmitters 32 and 50 as the RF electromagnetic carrier signal is received by the antenna 82 and then input to the RF demodulation circuit 90.

The input packet first passes through a band pass filter 84 and then enters a low noise RF front-end amplifier 86.

The output of the RF frontal amplifier 86 is down-modulated into an IF carrier signal by the RF-to-IF frequency converter 88.

The down-modulated signal is normalized to a signal level at the IF automatic gain regulator (AGC) 92.

The output of AGC 92 is input to matched filter 94 controlled by processor 98, wherein the pseudonoise preamble portion of the input packet is the same as the impulse response sequence of matched filter 94. In the matching filter 94, an autocorrelation peak occurs at the input end point of the preamble sequence.

At this time, the center frequency of the matching filter 94 coincides with the IF carrier frequency.

If the output peak value of matched filter 94 crosses the threshold reference value, the dual threshold detector 96 is driven.

Here, the double threshold detector 96 determines the threshold at the chip rate used or higher.

The advantage of using the matched filter 94 is that it does not have to continuously find the input signal in time (G. R. Cooper and C. D. McGillem, Modern Communications and Spread Spectrum, New York: McGraw-Hill, 1986). Since the matched filter 94 will respond each time the target signal reaches the receiver, the positions and magnitudes of the autocorrelation peaks at the output of the matched filter 94 are determined by all packets received during the current slot duration. It indicates the exact time of arrival and the strength of the signals.

When the dual threshold detector 96 is driven, the processor 98 operates a decoder (not shown) to lock the current packet and then track it.

At this time, the processor 98 operates the PN generator 100 to initialize the chip synchronization mode in the IF demodulation circuit 10 and reversely spread the DS / SS sequence to recover message bits.

The processor 98 reverses the spread spectrum signal by inputting the output of the matched filter 94 to the modulo-2 adder 102 to perform modulo 2 addition with the output of the PN generator 100. To spread. The despread signal is converted from the IF demodulator 106 to the baseband signal by the IF local oscillator 104 and subjected to data modulation to the original binary bit string in the A / D conversion and bit determinator 108. Restore

In the configuration of the receivers 34 and 42 as described above, the configuration except for the double threshold detector 96 which is interlocked with the matching filter 94 is the same as that of the conventional universal DS / SS decoding circuit.

In the packet reception structure of the present invention, double threshold detection is required when the receiver threshold detection of the terminal 14-24 and the base station 12 is performed.

For example, when two packets are received at the same time, the power levels of the preamble portion of the received packet are doubled because all transmitters 32 and 50-54 share the same PN code as the preamble code of each packet. In the detector 96 of the receivers 34, 42-46, the preamble portion is amplified at twice the power level.

Therefore, when a single fixed threshold is used, the packet is detected because the autocorrelation peak of the matched filter 94 is sufficiently high.

However, in this case, when locking and tracking the address and the message portion of the received packet using the autocorrelation property of the PN code, since the composite data of the two packets is demodulated, correct signal demodulation is impossible.

Therefore, in order not to attempt false packet decoding due to false detetion of the detector 96, two fixed or adaptive threshold detection methods must be used to detect the preamble of the packet.

The principle of packet acquisition and decoding using the double threshold detector 6 can be described as follows.

First, let the output level, lower threshold, and upper threshold of the matched filter 94 be a, γ ₁ , γ ₂ , respectively.

As soon as the target signal arrives at the receiver, it will pass through matching filter 94 and an autocorrelation peak with level a will occur at the moment the end of the PN preamble code passes.

If a signal with level a is directed to double threshold detector 96, detector 96 tests whether level value a satisfies condition γ ₁ aγ ₂ . If this condition is satisfied, it is determined that it is legal to perform a capture or decoding process on the input signal, but if the condition is not satisfied, the next signal is continuously searched.

Once detector 96 is braked by threshold crossing, demodulation circuit 110 is driven to lock on the current input packet.

In this process, the initialization of the demodulation circuit 110, chip synchronization and tracking, carrier synchronization and tracking may be performed to demodulate the DS / SS sequence to recover message bits.

The exact timing of the tracking loop braking is set by the timing spikes generated by the detection circuit.

This timing can be accurately matched by calculating the starting point of the address and message parts from the point of autocorrelation peak since the packet structure is predetermined.

6 is a diagram showing the configuration of a base station 12 that implements the multiple packet capture mechanism of the present invention to capture up to K packets.

In FIG. 6, reference numeral 112 denotes an antenna and 114 and 116 denote an RF modulator and an RF demodulator, respectively.

Reference numeral 118 denotes an automatic gain regulator, 120 a matched filter, 122 a dual threshold detector, 124 a logic circuit, 126 a processor, 128-132 K demodulators, 134 a channel allocator, and 136-140 a K. Number of transmission circuits, 142, respectively.

Here, each of the K demodulators 28-132 corresponds to the IF demodulation circuit 110 in FIG.

The multiple packet reception system of the base station 12 can be regarded as a form in which demodulators (see 128-132), which are K simple DS / SS receivers, are connected in parallel under the multiple packet capture mechanism.

Each of these demodulators is operated under the control of the processor 126 and the logic circuit 124 and requires accurate information on different packet synchronization times for each input packet.

The basic structure and operation principle of each of the demodulators 128-132 and the transmission circuits 136-140 of the base station 12 are similar to those commonly known in the art.

The packet received at the antenna 112 is converted to an IF signal at the RF demodulators 90 and 116 and then reaches the AGC 118 as described above with reference to FIG. 5 to normalize its signal level.

Next, the output of the AGC 118 is input to the matched filter 120, wherein if the input signal has the same sequence as the impulse response sequence of the matched filter 120, the filter at the end of the input PN preamble It will output an autocorrelation peak.

At this time, the center frequency of the matched filter 120 corresponds to the IF carrier frequency. If the output peak value of the matched filter 120 crosses the threshold reference value, the double threshold detector 122 is driven.

When the threshold detector 122 is driven, the processor 126 determines that the packet currently being input is legitimate to capture and locks and tracks the current packet by operating the first demodulator 128. The processor 126 also operates the reference PN generator 100 to initialize the chip synchronization mode and despread the DS / SS sequence to recover the message bits.

Once the detector 122 is driven again, this time the second demodulator 130 is activated by the processor 126 to track the currently input packet. At this time, if the second packet arrives with a delay of at least one mini slot time than the first packet, the first packet is successfully received.

Likewise, once the detector 122 is driven again, tracking starts with the third demodulator waiting while the first and second packets are being successfully received.

In this way, when packet decoding starts up to the K-th demodulator 132, the processor 126 starts the demodulator 128 so that the first demodulator 128 can decode the next input packet again as soon as it finishes decoding and becomes idle. Prepare for operation.

Here, the processor 126 controls each demodulator 128-132 to start its decoding process only once per slot.

The packets decoded by each demodulator are allocated from the channel allocator 134 under the control of the processor 126 to the corresponding channel (transmitter circuit) 136-140 according to the address of the packet.

The channel allocator 134 allocates the packet to the corresponding channel according to the address of the input packet.

The transmitting circuits 136-140 of the base station 12 also spread and data modulate the packets to be transmitted in a predetermined PN sequence.

In the multiplexer 142, the IF signals of each channel are linearly added and then sent to the RF modulator 144 to be converted into an RF carrier signal.

Finally, the RF carrier signal is amplified to a transmission signal level via the RF amplifier 76 and then transmitted in the form of an electromagnetic carrier.

The receiver of the base station 12 also performs packet detection using the double threshold detector 122, and then performs packet decoding.

Therefore, as soon as the target signal arrives at the receiver, it will pass through the matching filter 120, and an autocorrelation peak having a level will be generated at the moment when the end of the PN preamble code passes.

When the signal having the level a is guided to the double threshold detector 122, the detector 122 tests whether the level value a satisfies the condition γ ₁ aγ ₂ , and captures an input signal when the condition is satisfied. If it is determined that the condition is not satisfied, the next signal is continuously searched.

For every slot, once detector 122 is first braked by threshold crossing, first demodulator 128 is driven to lock on the current input packet.

In this process, decoder initialization, chip synchronization and tracking, carrier synchronization and tracking are performed to demodulate DS / SS sequences to recover message bits.

The exact timing of the tracking loop braking is set by the timing spikes generated by the detector 122.

This timing can be accurately matched by calculating the starting point of the address and message parts from the point of autocorrelation peak since the packet structure is predetermined.

7 shows the form of packet data used by the base station 12 and terminals 14-24 for data transmission in the local wireless communication system 10 of the present invention.

The packet data according to the present invention, with reference to FIG. 7, takes advantage of a particular packet capture effect, in order to take advantage of one packet capture effect, a special PN preamble sequence portion 152 and a silence portion 154, a base station 12 and a terminal. A portion 156 having an address and control information of 14-24, a data portion 158, and a checksum portion 160 inserted at the end of every packet as a postamble.

A Barker code or a PN code may be used as the preamble sequence 152. The preamble code detects the arrival of a packet and provides reference time information for accurate packet synchronization in a despreading process for data demodulation of the decoder. Provide.

Successful packet acquisition and synchronization is made possible by using matched filters 94 and 120 with dual threshold detectors 96 and 122 inserted into the receiver as well as the use of the PN preamble sequence 152 inserted at the beginning of every packet.

The length of the silence portion 154 plus the time it takes to adjust the AGCs 92 and 118 before entering the steady state to compensate for the signal strength of the received packets and at least the time it takes the logic circuit 124 to generate the reference PN sequence. Place it as

The main purpose of the checksum portion 160 is to detect errors in the packet. If an error of a packet is detected, the packet is requested to be retransmitted.

8 is an illustration of packet reception in two consecutive slots by timing slot length, packet length, mini slot length, transmission time randomization interval design and randomization of packet transmission. Ts) shows a packet length Tq, a mini slot length Tm, and a randomization interval Tr for discrete randomization of transmission time.

The slot length is slightly extended to secure additional time for randomization of packet transmission time.

The actual slot length Ts is set as follows.

Ts = Tr + (Tp-Tm) = (N-1) Tm + Tp

Here, Tp denotes a packet length, Tm denotes a mini slot length, Tr denotes a packet transmission randomization interval, and N denotes the number of mini slots used in the packet transmission randomization interval Tr.

Numerical analysis shows that the length of the transmission time randomization interval can optimize throughput of valid packets when the length of 15 mini-slots is long.

As the number of mobile terminals to be serviced increases, the number of mini slots in the daughter randomization section may be increased to satisfy the required capacity.

The mini-slot length (Tm) is set to the minimum separation length between two adjacent packets that are input to the receiver so that two consecutive incoming packets can be safely separated.

In a real system, the mini-slot length (Tm) is several chip time units or longer for the use of AGC and the highest detectability of the PN preamble.

FIG. 8 also illustrates the case where ten packets arrive randomly at five receivers across two timeslots.

In this case, it may be noted that the packet 170 of the first terminal # 1 (12) arriving at the receiver and the packet 176 of the fourth terminal # 4 (20) arriving at the receiver completely overlap.

The first packet 170 arrived earlier by the time corresponding to one mini slot than the remaining nine packets 172-188 following it.

In this way, the fifth packet 178 arrives at the last packet transmitted in the first time slot with a delay of one mini slot length than the second packet 172.

A total of five packets 180-188 arrive at the second slot, such as the sixth packet 180 arriving four mini-slots from the start of the second slot.

In this case, the matched filters 94 and 120 sequentially output nine autocorrelation peaks.

If the base station 12 has only two decoders (when K = 2 in FIG. 3 or FIG. 6), the second packet 172 and the third packet 174 are received in the first slot. In the second slot, the sixth packet 180 and the seventh packet 182 are received.

In the receiving system of the base station 12, the first packet 170 and the fourth packet 176 are excluded from decoding by the double threshold detectors 96 and 122, since the system has only two decoders, the nth time The slot cannot decode the fifth packet 178, and the (n + 1) th time slot can decode the eighth packet 184, the ninth packet 186, and the tenth packet 188.

However, if base station 12 has five decoders (K = 5), then eight packets 172, 174, 178-188, except for the first packet 170 and the fourth packet 176, span two time slots. All are received.

As described in detail above, the present invention can be effectively used in various applications of indoor and outdoor wireless packet communication networks that communicate within a radius of about 60 to 600 meters in a reverse link (MT to BS direction). Can be.

Claims (20)

In the local wireless communication system consisting of a base station and a plurality of mobile terminals, the base station and the mobile terminal to send and receive packets to and from each other through their transceiver; The base station includes means for decoding packet data input from at least one of the plurality of mobile terminals, means for encoding packets to be delivered to the mobile terminals, and a base station identification signal for every packet sent to the mobile terminal. Means for writing a message, means for identifying a terminal number for every received packet, means for operating a plurality of receive channels for receiving a plurality of packets simultaneously, and a predetermined mini in a randomization interval for every time slot during packet transmission. Means for discrete randomizing the transmission time in slot units; All of the plurality of mobile terminals use the same pseudo-noise preamble sequence; Each of the plurality of mobile terminals includes means for decoding packet data from the base station, means for encoding a packet to be delivered to the base station, means for writing a terminal identification number for every packet transmitted, and for every received packet. Means for identifying a base station number, means for discrete randomizing transmission time in the predetermined mini slot unit in a randomization interval at every time slot during packet transmission, and performing packet detection and synchronization using the pseudonoise preamble sequence And a means for doing so. The system of claim 1, wherein the base station and each of the plurality of mobile terminals are synchronized with each other. 2. The local wireless communication system according to claim 1, wherein the channel operating means includes channel allocating means for allocating the demodulated packet of the decoded packet to the corresponding channel. 2. The local radio of claim 1, wherein the receiver of each of the base station and each of the plurality of mobile terminals includes a dual threshold detector of fixed and adaptive threshold detection methods, and detects the packet by the quasi threshold detector. Communication system. 2. The regional wireless communication system according to claim 1, wherein the channel operating means comprise a plurality of demodulators connected in parallel to each other and operated only once in each slot. 6. The apparatus of claim 5, further comprising: a matched filter for generating an autocorrelation pulse if the pseudonoise preamble sequence of the input packet matches the impulse response sequence and not generating the autocorrelation pulse if it does not match; And wherein said dual threshold detector performs packet detection and synchronization of signal locking and tracking in association with said matched filter. 2. The local wireless communication system of claim 1, wherein the transmitter of each of the base station and the plurality of mobile terminals comprises means for performing encoding for error detection. The local wireless communication system according to claim 1, wherein the base station and the receiver of each of the plurality of mobile terminals comprise means for detecting a code error occurring during data transmission in every received packet. The method of claim 1, wherein the carrier frequencies of the base station and the plurality of mobile terminals are respectively allocated differently to each other, and both the base station and the plurality of mobile terminals use the same set of carrier frequencies for transmission and reception. Local wireless communication system, characterized in that. The carrier of claim 1, wherein carrier frequencies of the transmitter and the receiver of each of the base station and the plurality of mobile terminals are allocated differently for transmission and reception, and the base station and the plurality of mobile terminals are different from each other. Local wireless communication system, using the frequency. 2. The local wireless communication system according to claim 1, wherein said encoding means of each of said base station and said plurality of mobile terminals comprises means for modulating packet data into an electromagnetic carrier signal. 12. The local wireless communication of claim 11, wherein the packet data includes a pseudonoise preamble sequence portion, a silence portion, a portion having an address and information of a mobile terminal, a message portion and a postamble portion for error detection. system. 12. The direct sequence area spreading packet of claim 11, wherein the encoding means of each of the base station and the plurality of mobile terminals spreads the packet data into the same pseudonoise sequence before converting the packet data into the electromagnetic carrier signal. And a means for converting the data into a local wireless communication system. The transmission time randomization means of claim 1, wherein Tp = Ts- (Tr-Tm), where Tp represents a packet length, Ts represents a time slot length, Tr represents a randomization interval, and Tm represents a mini slot length. Means for implementing packets, slots, randomization intervals, and mini-slots satisfying. 15. The local wireless communication system of claim 14, wherein the transmission time randomization interval is set to a length of a predetermined number of mini slots for optimizing throughput of valid packets. 16. The local wireless communication system according to claim 15, wherein the number of mobile slots is increased when the number of mobile terminals increases. 2. The local wireless communication system according to claim 1, wherein the transmission time randomization is performed before spread spectrum or before IF-to-RF frequency change. The method of claim 1, wherein the discrete randomization means of each of the base station and the plurality of mobile terminals is offset in time for the randomization of the transmission time by an integer multiple of this time in units of several chip times. Local wireless communication system. 19. The local wireless communication system according to claim 18, wherein the transmission time is randomized by an integer multiple of the preamble length based on the length of the preamble code selected by the discrete randomization means. 19. The local radio communication system according to claim 18, wherein the transmission time is randomized by an integer multiple of this time in units of a length larger than the length of the preamble code selected by the discrete randomization means.