JP3157199B2 - Wireless information communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication system for an information communication system for high-speed data transmission represented by a local area network.

[0002]

2. Description of the Related Art Wireless communication of various information communication devices, such as cordless telephones, is being promoted in various places, and a large market is being formed due to its convenience. In so-called local area networks (LANs), which connect various information communication devices with high-speed wired transmission lines on campuses such as offices, factories, and universities, there is a strong demand for wireless communication. In the United States in 1985, ISM (Indu
Wireless transmission of high-speed data has been approved in the strial, Scientific & Medical) bands on the premise of application of spread spectrum technology. With this, various wireless LANs have been commercialized and a new market has begun to be formed. All of these products have speeds from several 100 Kbps to about 2 Mbps, and are widely used as wired LANs.
03.3 Standard 10Mbps CSMA / CD (Carrie
r Sense Multiple Access With Collision Detection)
It was not compatible with the system.

[0003] In order to respond to the demand for compatibility, the study of the wireless LAN of the wired LAN was started as IEEE in 1987, and the study has been continued. On the other hand, the FCC in the United States has begun studying frequency allocation for personal communication due to the efforts of the IEEE and others. Against this background, the wireless LAN system is not necessarily restricted by existing access protocols such as the CSMA / CD system,
There is a demand for realizing throughput characteristics equivalent to those of ANs and ensuring compatibility with existing access protocols. If compatibility can be ensured, the software of various information communication devices can be used without any change, which brings great convenience to the user.

[0004]

As described above, the problem that a wireless LAN having compatibility with an existing wired LAN cannot be realized cannot be solved conventionally.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless information communication system capable of eliminating this problem and realizing a wireless LAN which is inexpensive and has a simple configuration and is compatible with existing wired LANs. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a radio information communication system in a radio transmission environment having frequency selective fading and delay spread when electromagnetic waves radiated in the air are reflected by various objects. Dividing at least a part of a data sequence into a plurality of bit strings so as to reduce deterioration of communication quality due to delay spread, performing primary modulation at a different carrier frequency for each bit string, and further performing secondary modulation by a spread spectrum method. It is characterized by.

[0007]

According to the present invention, at least a part of a data sequence is divided into a plurality of bit strings so as to reduce deterioration of communication quality due to frequency selective fading and delay spread, and primary modulation is performed at a different carrier frequency for each bit string. Further, by performing secondary modulation by the spread spectrum method, it is possible to surely reduce communication quality deterioration.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the points to be considered in realizing a wireless LAN will be summarized. The characteristics of wireless transmission media can be summarized as follows: (1) narrow frequency band (2) multipath (intersymbol interference) (3) frequency selective fading (4) portability (5) frequency sharing.

[0009] As seen in a cellular system such as an automobile communication, in a wireless system, a zone (cell or BS) having a radius of several tens of meters to several kilometers is generally used.
By providing a plurality of A (Basic Service Areas), the service area can be expanded while reducing transmission power and dispersing traffic. Wireless LAN
Although the service area is expanded based on the same idea, a method of providing a plurality of frequency bands and operating in different frequency bands for each zone has been considered in order to prevent mutual interference between zones. In order to suppress the mutual interference to a predetermined interference ratio or less, generally seven zones are required, and when a centralized station is provided and loopback is performed by the same station as seen in ordinary mobile communication, a total of 14 zones is required. Is required. For an information transmission rate of 10 Mbps, an error correction equivalent to the (43,31) BCH code used in mobile communication, for example, and performing QPSK modulation require a frequency band of 10 MHz per zone, a total of 140 MHz. Become. By the way, assuming that the antenna gain (directivity) is the same, the transmission power must be increased by the square of the frequency. However, in a portable information communication device such as a so-called laptop computer, the power that can be supplied from the device to the wireless unit is It is generally 500 mW or less, and therefore, operation in a band as low as possible, such as a quasi-microwave band, is essential. In the quasi-microwave band, radar (radio orientation) and mobile communication have already been used or planned, and it is not an exaggeration to say that it is impractical to secure a 140 MHz band in the same band. , 40M
It is considered that a band allocation of about Hz is realistic. 40M
Realization in a very narrow frequency band of about Hz is the first problem.

[0010] Next, in multipath, in a closed environment such as inside a building or in a city where buildings are forested, radio waves are reflected on walls and ceilings, various fixtures and buildings, etc., and have a delay through a plurality of paths. Is a phenomenon where multiple radio waves arrive,
270 ns maximum within the building as a range that could interfere with communication
It has been observed that ec delay spread (delay dispersion) exists. In other words, up to 270 nsec, a plurality of radio waves overlap and interfere with each other. Error correction and QP for the above 10 Mbps
One symbol time when SK modulation is performed is 144 ns
Since this is c, this effect (intersymbol interference) is directly received, and signal processing in a demodulation system such as waveform equalization is required.

On the other hand, frequency-selective fading is basically the same cause as multipath, but a phenomenon in which the signal level fluctuates by as much as 50 dB due to the phase relationship between radio waves arriving from different paths. It has been observed that even if the degradation of communication quality can be suppressed to some extent, fading occurs in the worst case in the range of 2 to 5 MHz, and communication may be disabled.

Portability is one of the effects of wireless communication. In addition to laptop computers, book-type computers have recently been widely used, and it has become possible to freely carry terminals. In such a use, the transfer function of the radio wave changes every moment, and it is difficult to suppress the above-described effects such as multipath or frequency fading due to waveform equalization or the like, and even if realized, it becomes extremely expensive.

The last frequency sharing is based on the above-mentioned ISM, especially in order to secure a wide band of 40 MHz in the quasi-microwave band.
The 2.4 GHz band, which is one of the bands, is considered to be a promising candidate, but since the band contains strong interference radio waves from microwave ovens and the like, reliable communication can be performed even with the interference radio waves. Required. Next, issues related to the wireless LAN architecture can be summarized as follows: (6) Equal distribution. This has the advantage that the required frequency bandwidth can be halved compared to the centralized system as described above, and also improves the reliability of the entire system and reduces the initial installation cost due to the absence of the centralized station. IEEE8
The two concepts of "high throughput", "fairness" and "no packet discarding" are regarded as important.

FIG. 1 shows an example of the configuration of a wireless LAN system. In a BSA (zone), equal distribution is possible, that is, communication can be directly performed between arbitrary wireless information communication stations (STNs) by radio waves. The BSAs are connected to a distribution system (DSM) via a station having a bridge or router function (STNbr), and can communicate between arbitrary user stations (STNus) across the BSAs. Each BSA has a size of, for example, a radius of about 20 to 50 m, and can also serve a larger area via a distribution system.

FIG. 2 shows four BSAs that do not interfere with each other.
(A) shows a two-dimensional array, (B) shows a one-dimensional array in the case where frequency reuse is performed, and (C) shows a vertical array. The sequence is shown. In a small area, the BSA is operated by itself, and in this case, the STNbr is unnecessary. For such applications, (7) another issue is to ensure reliable communication without interference between BSAs.

In realizing the 10 Mbps CSMA / CD system, the upper layer (for example, AUI: Attac) is used.
It is important to ensure the compatibility with the communication unit and the upper-layer communication software already implemented in the information communication device without any change. For this, CSM
Reliable and fair collision detection is required on the premise of equal dispersion, which is the point of the A / CD system. In contrast, a method of transmitting a predetermined number of pulses at random intervals before transmitting a packet and detecting a collision by assuming that a collision has occurred when more than a predetermined number of pulses exist on the wireless transmission medium. There is. (Japanese Patent Application No. 3-151876) FIG. 3 shows the principle of providing a collision detection window before transmitting transmission data and detecting collision. In realizing such a collision detection method, it is premised that (8) reliable transmission of a collision detection pulse under the characteristics of the wireless transmission medium described above is also one of the technical problems to which the present invention is directed. .

Further, as described above, there is no packet discarding which is an idea of IEEE802. (In IEEE802.11, the packet discard rate is set to 5 * E-
5 is set). For example, when a bit error or burst error that cannot be corrected by the error correction code is encountered and the address information is destroyed, it is determined to which station or to which station the address was sent. Since it becomes impossible to make a determination, the transmitting side must determine whether retransmission is necessary or not in an upper layer, resulting in extreme degradation of throughput at the station. In a station where traffic is concentrated, such as a host computer, such a situation has a great effect on the entire system. A further technical problem of the present invention is (9) If reliable transmission of address information can be realized, even if a large bit error or the like occurs in user information, a lower layer can promptly request retransmission to the transmitting side. And extreme degradation of throughput can be prevented. Also, communication may fail between specific stations due to the above-mentioned frequency selective fading, etc., but IEEE 802.11 states (10) reduction of communication outage rate (outage) as an issue. Has set a target of 0.1% or less per day in the service area.

The above is the main technical problem imposed on the wireless LAN. At present, however, no specific technical proposal has been made to solve these problems, and the present invention solves the problem.

FIG. 4 shows a carrier configuration example of four BSAs which do not interfere with each other in the multi-carrier frequency hopping (MCFH) system according to one embodiment of the present invention. In the figure, packet transmission in the BSA is divided into four bit strings and transmitted in parallel. When the information transmission rate is 10 Mbps, for example, if the above-mentioned (43,31) BCH equivalent is used as the error correction code,
The physical transmission speed of each bit string is 10 Mbps × (43/31) /4=3.47 Mbps. For example, when this is QPSK or quaternary FSK modulation, one symbol time is 577 nsec, which is sufficiently longer than the above-mentioned maximum delay spread: 270 nsec, and a highly reliable demodulation which is not affected by multipath on the receiving side. Will be possible. The frequency bandwidth of each carrier is 2.5 MHz when the roll-off coefficient is 0.45 when QPSK modulation is performed. Further, in the figure, the carrier frequencies of the four systems are arranged at intervals of 10 MHz, which is sufficiently wider than the aforementioned worst frequency selection fading width of 2 to 5 MHz, so that the probability that a plurality of carriers are simultaneously subjected to fading becomes extremely low,
At most, only one carrier will undergo fading. Accordingly, application of an error correction code assuming that a severe random or burst error occurs only in one bit string, that is, correction of a random or burst error bit string using other normal bit strings, specifically, for example, Packets can be transmitted with high reliability by dividing the data sequence into blocks, adding a correction code based on Reed-Solomon code thereto, and performing parallel transmission with interleaving at a depth of 4, for example. Also,
With the parallel transmission of four bit strings, it is assumed that bit synchronization is established between the bit strings. However, since the spatial propagation speed of the radio wave is constant regardless of the frequency, the bit strings are designed in the transmission system and the reception system. Bit synchronization can be easily achieved if care is taken so that the delay between them becomes constant.

Next, between BSAs, four B
In the case of the SA configuration, there are a total of 16 carriers, and the carriers are arranged at intervals of 2.5 MHz. Therefore, if the total bandwidth is 40 MHz, four BSAs can be supported. This bandwidth is, for example, 2.4 G of the quasi-microwave band as described above.
There is a possibility that the radio station can be allocated to the ISM band or the like in the Hz band. As a result, it is possible to realize a compact wireless station that has low transmission power for the reason described above, that is, can supply power to a wireless system from a laptop computer or the like.

As the frequency hopping method, hopping is performed at a low speed of, for example, 2 to 50 hops / second in units of 2.5 MHz. This increases the possibility that normal communication can be performed in the next hopping cycle, even if a certain station encounters intense fading with a plurality of bit strings and loses communication. This is, in a sense, due to the frequency diversity effect of the spread spectrum system, which makes it possible to use the station's portability at low cost without the application of advanced waveform equalization technology or multi-beam antennas, or to communicate with stations on high-speed moving objects. Communication is also possible.
Furthermore, the low-speed frequency hopping method does not require a wide band as in the direct spreading method and the like, and is effective in suppressing the required bandwidth to the above-mentioned 40 MHz. In addition, even with the above-mentioned interference wave from a microwave oven or the like, communication becomes possible in the next hopping cycle even if a specific bit string becomes uncommunicable due to the interference wave. As a more aggressive countermeasure against interference waves, high-quality communication can be provided by selecting a carrier frequency that avoids the frequency at which the interference waves are detected.

FIG. 5 shows an example of a packet configuration, in which only a collision detection window for transmitting the above-mentioned collision detection random pulse is provided before a standard packet subjected to an error correction code. As described above, in order to reduce the packet discard rate, reliable transmission of address information is necessary. However, as described above, by applying multi-carrier parallel transmission and applying an error correction code based on parallel transmission, Address information can be transmitted with high reliability, but when higher reliability is required, for example, all information of the preamble and the address information is transmitted (takes four times as long) on each of the four carriers. May be adopted.

FIG. 6 shows an example of a frequency hopping synchronization method and packet transmission control at a hopping point. Synchronization is performed between STNbrs connected to a DSM (distribution system).
Along with the A identification information, information such as a hopping synchronization signal and a hopping frequency (hereinafter collectively referred to as a hopping synchronization signal) is reported twice before and after the hopping point, that is, twice at different carrier frequencies. Each STNus detects the BSA identification information to which it belongs, changes the frequency synthesizer in the STNus to hop to a new frequency in synchronization with the hopping synchronization signal, and uses it as a local signal at the time of transmission or reception. . Also, to prevent packet transmission from overlapping with hopping,
As shown in the figure, hopping (F
H) A window may be provided, and within the window, the transmission of packets may be prohibited by activating the collision indication line defined as the AUI for the upper layer. As shown in the figure, the first half of the window needs to be set at least longer than the time for transmitting the maximum packet length. Also, the guard time provided near the hopping point is equal to each S of the hopping synchronization signal.
This is for absorbing the propagation time between the TNus and the STNbr, and is a time that can be ignored with respect to the hopping cycle. The hopping synchronization signal needs to be transmitted to all stations without fail. For this purpose, redundant transmission means using multicarriers may be used as described above.

By including the BSA identification information in the hopping synchronization signal, each station can determine which B
It is possible to determine whether the user belongs to the SA or to which BSA. That is, for example, the user selects the BSA to belong to by operating the BSA identification switch provided in the wireless unit or operating the software (remote instruction) from the station, or hopping synchronization signals from a plurality of STNbrs at each station. Are received in order, and the ST having the highest reception level among them is received.
It is possible to automatically select Nbr as the BSA to which the own station should belong, and notify the user of the BSA to which the station belongs.

Further, in the case of the BSA alone operation, if the FH synchronization detection / generation circuit in the STNus (see FIG. 7) autonomously generates and sends a hopping synchronization signal to another STNus in accordance with a predetermined rule. Good. Here, the predetermined rule is that, for example, when a hopping synchronization signal is not detected for a certain period of time, each STNus generates and sends out a hopping synchronization signal after a random time, and other STNus generates and sends a hopping synchronization signal after detecting the same hopping synchronization signal. Synchronize. The STNus which has transmitted the hopping synchronization signal first will transmit the hopping synchronization signal every predetermined period thereafter. STN
When a failure occurs in us and transmission of the hopping synchronization signal is stopped, a new STNus transmits a hopping synchronization signal in accordance with the above-described rule. By the above, BSA
Even in the case of stand-alone operation, it is possible to realize high reliability and reduction of initial introduction cost by equal distribution based on the idea of IEEE802.

In a large-scale system configuration for frequency reuse as shown in FIGS. 2B and 2C, a plurality of BSAs use the same carrier frequency. Unless you do, you will have some interference. For example, in the example shown in FIG. 3B, a station that receives interference with a worst interference (C / I) ratio of 6.5 dB exists in the two BSA-Bs. That is, frequency reuse is performed at substantially the same timing.
When a packet is transmitted by one BSA, a collision cannot be detected by the transmitting station, but a bit error due to mutual interference may occur in a specific receiving station. In response to this, for example, if the detection sensitivity of the collision detection pulse of the station is appropriately set, and the packet has been received for a predetermined time or longer despite the detection of the collision, the receiving station notifies the reception of the collision. By transmitting a random pulse as a signal for a certain period of time, the transmitting station may be informed of the collision, and may be prompted to retransmit the packet after a predetermined back-off process. In other words, in the present invention, other BSAs performing frequency reuse
If a slight decrease in throughput due to packet inflow from
A, or seven BSAs (required bandwidth 70 MH) which do not necessarily isolate
It is not necessary to prepare z).

FIG. 7 shows an example of the internal structure of the STNus. Transmission data 71 sent from an upper layer is temporarily stored in an interface / buffer memory 72, and this buffer memory 72 sends a packet to a collision detection circuit 88. Requests collision detection during transmission. Under the control of the circuit 88, a random pulse as a transmission pulse for collision detection is transmitted from the antenna 79 to the antenna 80 via a secondary modulator including primary modulators 75a to 75d, a mixer 76 and the like.
Radiated as On the other hand, in the receiving system, the primary demodulator 83a
A collision detection circuit 88 monitoring the output signal (collision detection reception pulse) from the signal .about.83d determines whether a pulse other than the pulse transmitted by itself has not been received. If no pulse has been received, there is no collision. The packet information accumulated in the buffer memory 72 is sent to the error correction encoder 73, and the error correction code is added by the error encoder 73, and the packet information is used for wireless transmission such as multi-carrier redundant transmission of address information. Convert to a suitable predetermined format. The output of the error correction encoder 73 is decomposed into four bit strings by a serial / parallel conversion circuit 74, and each bit string is primary-modulated by a primary modulator 75a to 75d such as QPSK so that each IF frequency is separated by 10 MHz. Modulation is applied. The frequency synthesizer 92 generates a hopping frequency under the control of an FH synchronization detection / generation circuit 91 which detects FH synchronization from packet information from the buffer memory 72, and the mixer 76 generates 1 based on the hopping frequency.
Secondary modulation for converting the output signal of the secondary modulator to a predetermined frequency is performed, and the signal is radiated into the air via an amplifier 77, a circulator 78, and an antenna 79. Note that the frequency synthesizer 92 requests the primary modulator and the primary demodulator to write the IF local oscillation signal at the time of data transmission / reception.

On the other hand, the antenna 79 and the circulator 78
Are demodulated by the mixer 82 into a predetermined IF frequency, and then input to the primary demodulators 83a to 83d to be demodulated into a predetermined bit string. Further, the signal is converted into a serial signal by a parallel / serial converter 84, subjected to predetermined error correction by an error correction decoder 85, and then converted into a predetermined format specified as AUI by an interface buffer circuit 86. After that, it is output to the upper layer as received data 87.

If it is determined that there is a collision as a result of the above collision detection, a collision indication signal 90 is activated to an upper layer via an interface 89 to notify that a collision has occurred. This collision detection is constantly monitored not only when the own station is in the transmission state, but also in the reception state.If the number of received random pulses is larger than a predetermined number, a collision occurs on the transmission path. And notifies the upper layer that a collision has occurred. The FH synchronization detection / generation circuit 91 always detects the hopping synchronization signal. When the hopping synchronization signal is detected, the FH window setting circuit 93 sets the hopping window and activates the collision detection line to the collision detection circuit 88. And requests the frequency synthesizer 92 to change to the next hopping frequency in the BSA to which it belongs in synchronization with the received hopping synchronization signal.

When the hopping synchronization signal is not received for a predetermined time by the FH synchronization detection / generation circuit,
After a random time, a self-generated hopping synchronization signal is generated and sent to another station via the above-described transmission system. Thereafter, hopping synchronization is performed at predetermined intervals until another station (for example, STNbr) transmits the same synchronization signal. Generate and transmit signals.

Next, another embodiment of the present invention will be described. The present invention is called a multi-carrier chirp (MCCP) system, and FIG. 8 shows an example of a carrier configuration in four BSAs that do not interfere with each other in the same system. In the figure, the packet transmission in the BSA is divided into four bit strings and transmitted in parallel as in the previous embodiment. The carrier frequencies of the four systems are arranged at intervals of 2.5 MHz, and the carrier frequencies are swept with a sweep width of 40 MHz at a low period of, for example, 20 to 500 msec. Therefore, the required bandwidth is 50 MHz.

Next, between BSAs, 4 BSA
, There will be a total of 16 carriers and B
Carriers between SAs are swept with a phase shift of 1/4 from the above-mentioned period, that is, at intervals of 10 MHz, and the required bandwidth is 50 M, which is the same as when operating with only one BSA.
Hz is sufficient.

The frequency diversity effect is the same in the spread spectrum system based on the chirp system, and the portability of the station or the communication with the station on a high-speed mobile unit can be inexpensively reduced without applying advanced waveform equalization technology or multibeam antennas. Enable. Further, the low-speed chirping method does not require a wide bandwidth like the low-speed frequency hopping method. Therefore, in the case of the 4BSA configuration, the low-speed chirp method is also effective in suppressing the required bandwidth to the above-mentioned 50 MHz. In addition, with respect to the above-mentioned interference waves from a microwave oven or the like, for example, by providing a window for prohibiting packet transmission in the vicinity of the interference wave frequency at a station that has detected the interference wave, a high-quality wireless communication environment is provided. And efficient use of frequency resources becomes possible.

FIG. 9 shows an example of a packet structure, in which a collision detection window for transmitting the above-mentioned collision detection random pulse is provided before a standard packet to which an error correction code has been applied. The address information is added to the last part of the packet in order to transmit redundantly at different carrier frequencies, so that the information can be transmitted more reliably.

FIG. 10 shows an example of the synchronization method of the sweep (chirp) signal and the packet transmission control at the sweep turning point. ST connected to DSM (Distribution System)
Synchronization is performed between Nbrs, and information such as a sweep synchronization signal and a phase (hereinafter, these are collectively referred to as a sweep synchronization signal) together with, for example, BSA identification information is transmitted to the STNus in the BSA before and after the turning point, that is, the maximum carrier frequency. And twice at the lowest carrier frequency. Each STNus detects the BSA identification information to which the STNus belongs and controls a frequency synthesizer (or a voltage controlled oscillator: VCO) in the STNus to sweep in synchronization with the sweep synchronization signal.
Used as a local oscillation signal at the time of transmission or reception. Also,
In order to prevent the packet transmission from overlapping with the turning point, a chirp window is provided before and after the turning point as shown in FIG. By activating the display line, transmission of a packet may be prohibited. As shown in the figure, the first half of the window needs to be set at least longer than the time for transmitting the maximum packet length. The guard time provided in the vicinity of the turning point is for absorbing the transmission delay time of the sweep synchronization signal between each STNus or STNbr, and is a time that is negligible with respect to the sweep cycle. .

In the case of the BSA alone operation, the sweep synchronization signal may be sent to another STNus from the sweep synchronization detection / generation circuit in the STNus in accordance with a predetermined rule as in the previous embodiment.

The configuration of the station in this embodiment is substantially the same as that of the previous embodiment, and therefore detailed description is omitted. However, the difference is that the FH synchronization detection / generation circuit is replaced with a sweep synchronization detection / generation circuit. is there.

Although the embodiments of the present invention have been described in detail with reference to the multi-carrier frequency hopping system and the multi-carrier chirp system, the direct spread system or the frequency hopping system faster than the present embodiment is used as the spread spectrum system. It is also possible to apply, it is possible to effectively utilize the frequency diversity effect and the like which is the object of the present invention, by only taking measures against the required bandwidth or mutual interference in each system, and further, only the synchronization system is different. is there. In the description so far, a plurality of bit strings are firstly subjected to primary modulation such as QPSK, and then subjected to secondary modulation by spectrum spreading. Q
It is clear from the principle of the spread spectrum method that the same effect can be obtained even when the secondary modulation is performed by PSK or the like.

Further, in the above description, when severe random or burst errors occur in a plurality of carriers, retransmission should be performed in the next hopping synchronization. This results in a high throughput degradation. Further, depending on the selection of the error correction code, it may not be possible to completely correct a severe random or burst error of one carrier. As a countermeasure, for example, a carrier having a burst error or a normal carrier (channel number) is notified from the receiving station to the transmitting station, and retransmission is performed from the transmitting side using a normal carrier or another empty carrier. Alternatively, measures such as strengthening the error correction code and retransmitting may be considered. If multiple packets are transmitted between the same stations and at the same hopping cycle, transmission using only normal carriers or transmission with enhanced error correction code as described above is continued, and the transmission is canceled after the next cycle. By doing so, the temporary decrease in throughput does not continue.

In the above description, the required bandwidth is set to about 40 MHz in consideration of the quasi-microwave band, and the number of BSAs that do not interfere with each other is set to four.
As the EE802 Standards Committee is working with frequency licensing agencies in various countries, if a wide band such as 70 MHz or 140 MHz is secured, more BSAs can be accommodated without interfering with each other. Absent.

In the above description, the number of multicarriers has been described as 4. However, by increasing the number of carriers, the ratio of uncommunicable carriers (channels) due to frequency selective fading can be reduced, and as a result, correction codes can be simplified. Or faster data transmission.

Further, in the present invention, equal dispersion, CSMA / C
Although specific embodiments have been described for the D system, baseband transmission speed: 10 Mbps, etc., the application to the centralized system as well as the token passing system, and even higher transmission speeds with completely different access protocols are attempted. The present invention can also be applied to information that does not need to be packetized and transmitted, such as audio and moving images. That is, the gist of the present invention resides in that high-speed data is divided into a plurality of bit strings and transmitted in parallel by a spread spectrum method, thereby causing a problem inherent to a wireless transmission medium caused by high-speed transmission such as multipath (delay spread). Many applications and modifications are conceivable along the above-mentioned gist, and these are also included in the present invention.

According to this embodiment to which the parallel transmission of a plurality of bit strings by the multi-carrier and the spread spectrum technique are applied, the former (multi-carrier transmission) allows one
Since the symbol length can be made longer than the maximum delay spread, problem (2) can be solved. Furthermore, as described above, due to the characteristics of frequency selective fading, the probability of a burst error occurring on a plurality of carriers is low, and therefore the quality is high by applying an error correction code for correcting a severe random or burst error of one bit string. Communication becomes possible. That is, the problem (3) can be solved. Also,
Since the collision detection random pulse can be transmitted redundantly on the multi-carrier, the problem (8), and eventually the problem (6), can be solved.In addition, all the address information can be transmitted on the multi-carrier without being divided into multiple bit strings. Problem (9) can be solved by transmitting redundantly. On the other hand, the latter (spread spectrum) enables a dynamic frequency diversity effect, and can solve the problems (3), (4), (5), and (10). Further, the problem (1) can be solved by applying a low-speed frequency hopping system or a chirp system as a spread spectrum system. Also,
When these schemes are applied, a large number of carriers are transmitted in the BSA and across a plurality of BSAs. However, the carrier frequencies are widely separated from the Nyquist bandwidth, that is, the intervals are set so as not to interfere with each other. By performing frequency multiplexing in the above, the problem (7) can be solved.

[0044]

As described above, according to the present invention, by applying a multi-carrier parallel transmission of a plurality of bit strings and a spread spectrum technique, it is possible to reduce the deterioration of communication quality and to have compatibility with an existing wired LAN. A wireless LAN can be realized at low cost and easily.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a peer-to-peer distribution-based wireless LAN system.

FIG. 2 is a diagram showing an example of application to an office building when four BSAs that do not interfere with each other are formed.

FIG. 3 is a diagram showing the principle of a random pulse transmission system.

FIG. 4 is a diagram illustrating a carrier configuration in four BSAs that do not interfere with each other in a multicarrier frequency hopping (MCFH) scheme according to an embodiment of the present invention.

FIG. 5: Multicarrier frequency hopping (MCFH)
The figure which shows the packet structure of a system.

FIG. 6: Multicarrier frequency hopping (MCFH)
The figure which shows the example of the window in a system.

FIG. 7: Multicarrier frequency hopping (MCFH)
Wireless station (S
FIG. 2 is a configuration diagram showing an embodiment of the present invention (TNus).

FIG. 8 is a diagram illustrating a carrier configuration of four BSAs that do not interfere with each other in a multi-carrier chirp (MCCP) system according to another embodiment of the present invention.

FIG. 9 is a diagram showing a packet configuration of a multicarrier chirp (MCCP) system.

FIG. 10 is a diagram showing an example of a window in a multi-carrier chirp (MCCP) system.

[Explanation of symbols]

 71 transmission data 72 interface / buffer memory 73 error correction encoder 74 serial / parallel conversion circuit 75a to 75d primary modulator 76, 82 mixer 77, 81 amplifier 78 circulator 79 antenna 80 antenna 83a to 83d primary demodulator 84 parallel / Serial converter 85 Error correction decoder 86 Interface buffer circuit 87 Received data 88 Collision detection circuit 89 Interface 90 Collision indication signal 91 FH synchronization detection / generation circuit 92 Frequency synthesizer

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Koichiro Kamura 70, Yanagimachi, Yuki-ku, Kawasaki-shi, Kanagawa Pref. Toshiba Corporation Yanagimachi Plant (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 12/28

Claims (17)

(57) [Claims] 1. An electromagnetic wave radiated in the air is reflected by various objects, and in a wireless information communication system in a wireless transmission environment having frequency-selective fading and delay spread, deterioration of communication quality due to frequency-selective fading and delay spread. Wireless information communication, wherein at least a part of a data sequence is divided into a plurality of bit strings so as to reduce noise, primary modulation is performed for each bit string at a different carrier frequency, and secondary modulation is performed by a spread spectrum method. method. 2. The wireless information communication system according to claim 1, wherein the modulation speed of the primary modulation is sufficiently reduced so as to reduce deterioration of communication quality due to delay spread. 3. The spread spectrum method of the secondary modulation,
The wireless information communication system according to claim 1, wherein the wireless information communication system is a frequency hopping system or a chirp system. 4. The wireless information communication system according to claim 1, wherein the data sequence has a packet form. 5. The wireless information communication system according to claim 4, wherein the hopping cycle in the frequency hopping scheme or the sweep cycle in the chirp scheme can accommodate a plurality of data sequences in the packet form. 6. The wireless information communication system according to claim 1, wherein a part of the data sequence is primary-modulated redundantly at different carrier frequencies. 7. The method of claim 1, wherein one of the different carrier frequencies is redundantly one.
The part of the data sequence to be modulated next includes a pulse for detecting the presence or absence of collision of the data sequence in the form of a packet in the wireless transmission environment. Wireless information communication system. 8. When a collision is detected at the time of receiving the data sequence in the packet form, if it is determined that the reception of the data series in the packet form has been continued for a predetermined time or more, a collision occurrence notification signal is transmitted from the receiving side. The wireless information communication system according to claim 4, wherein: 9. The system according to claim 8, wherein the collision occurrence notification signal is a random pulse signal that continues for a predetermined time.
Wireless information communication system described in 1. 10. The wireless information communication system according to claim 3, wherein a part or all of the synchronization signal related to the frequency hopping system or the chirp system is primary-modulated redundantly at different carrier frequencies. . 11. The wireless transmission environment is composed of a plurality of basic service areas, each of which is interconnected via a distribution system, and only a data sequence extending over the basic service area is transmitted via the distribution system. The wireless information communication system according to claim 1, wherein the wireless information communication system is transmitted between basic service areas. 12. The wireless information communication according to claim 5, wherein in the frequency hopping method or the chirp method, a window for inhibiting transmission of the data series is provided before and after frequency hopping or sweep return. method. 13. The wireless information communication according to claim 11, wherein the different carrier frequencies are separated by a predetermined frequency so as not to interfere with each other within a basic service area and between a plurality of basic service areas. method. 14. The synchronizing signal according to the frequency hopping system or the chirp system is generated at a station connected to the distribution system, and takes a predetermined mutual synchronization between the stations connected to the distribution system. The wireless information communication system according to claim 11, wherein the other stations in the basic service area are notified. 15. The method according to claim 1, wherein, when the synchronization signal related to the frequency hopping scheme or the chirp scheme is not detected for a predetermined time, a station autonomously generates the synchronization signal and notifies another station. The wireless information communication method according to claim 3. 16. The data sequence or the plurality of bit strings includes an error correction code capable of correcting the random or burst error from the bit string and another bit string when a random or burst error occurs in an arbitrary bit string. The wireless information communication system according to claim 1, wherein the wireless information communication system is applied. 17. An electromagnetic wave radiated in the air is reflected by various objects, and in a wireless information communication system under a wireless transmission environment having frequency selective fading and delay spread, a received wireless signal is spread by a spread spectrum method. A wireless information communication system characterized by performing a primary demodulation process on a predetermined bit sequence after performing a secondary demodulation process and reproducing a series of data sequences from each bit sequence.