Method and device for radiotransmission

Description: TECHNICAL FIELD [Detailed description of the invention]

Description The present invention relates to methods and devices for effectively wirelessly transmitting data between a fixed station and at least one mobile station by one of a plurality of carrier frequencies, and these data are time division multiple access (TDMA). Is transmitted in Time Slots. The DECT standard was established in the early 1990s to replace various existing analog and digital standards in Europe. This DECT standard is the first common European standard for wireless telecommunications. The DECT network is a microcellular digital mobile wireless network for high subscriber density. It was conceived for use within the building in the first place. However, it is possible to use the DECT standard outdoors. The capacity of the DECT network with nearly 10,000 subscribers per square kilometer provides the ideal access technology for network providers by wireless standard. According to the DECT standard, both voice transmission and data signal transmission are possible. You can also build a wireless data network based on DECT. In the following, the DECT standard will be described in detail in relation to Figure 2. Under the name of DECT (Digital Enhanced Cordless Telecommunication), digital wireless remote communication systems for reachable distances smaller than 300 m have been standardized in Europe. This makes the system suitable for mobile phone traffic and data traffic in office buildings or commercial areas by connecting with the relay function of telecommunications equipment. The DECT function supplements the telecommunications device, which makes it a fixed station FS for wireless communication systems. Up to 120 channels establish, monitor, and control digital radio connections between fixed station feasibility studies and up to 120 mobile station MSs. Up to 10 different carrier frequencies (carriers) are transmitted in the frequency range of 1.88GHz to 1.9GHz. This frequency division multiplexing method is called FDMA (Frequency Division Multiple Access). Twelve channels are time-division multiple access TDMA (Time Division) before and after each of the twelve carrier frequencies. It is transmitted by Multiple Access). Therefore, for a wireless remote communication system based on the DECT standard, if there are 10 carrier frequencies and 12 channels for each carrier frequency, a total of 120 channels can be obtained. For example, since one channel is required for each voice connection, 120 connections to a maximum of 120 mobile station MSs can be obtained. Operates in Duplex mode (TDD) on the carrier. After 12 channels (channels 1-12) are transmitted, it is switched to reception and 12 channels (channels 13-24) are received in the opposite direction. Therefore, a time division multiplexing frame consists of 24 channels (see Figure 2). In this case, channels 1 to 12 are transmitted from the fixed station FS to the mobile station MS, while channels 13 to 24 are transmitted from the mobile station MS to the fixed station FS in the opposite direction. The frame duration is 10ms. The duration (time slot) of one channel is 417 μs. During this time, 320-bit information (eg voice) and 100-bit control data (synchronization, signaling and error checking) are transmitted. The effective bit rate for the subscriber (channel) is obtained from 320-bit information within 10 ms. Therefore, the effective bit rate for subscribers (channels) is 32 kilobits per second. An integrated module has been developed that switches the DECT function for fixed and mobile stations. In this case, the fixed station and the mobile station satisfy similar functions. One of these integrated modules described above is, in this case, an RF module, i.e., a module that performs the basic functions of reception and transmission in the RF domain. It is well known to use so-called fast-hopping RF modules. That is, it is an RF module capable of switching the carrier frequency from one time slot or channel to the next time slot or channel. However, this fast hopping RF module is very cumbersome and expensive. Therefore, in practice, the so-called slow hopping RF module is used in particular. That is, in this slow hopping RF module, a predetermined time is required for switching the carrier frequency. In practice, the time required by this slow hopping RF module to switch carrier frequencies is substantially equivalent to the time of one time slot. This means that each active time slot, i.e., a so-called inactive time slot (blind slot) in which data cannot be transmitted, must follow each slot in which data is transmitted. This means that: This means that in the case of the DECT standard, only 6 connections can actually be made instead of the 12 connections possible at one carrier frequency. The DECT channel is fixed by its time slot and its carrier frequency. Note that in this case, according to the DECT standard, the configuration of physical channel reuse is done by dynamic channel selection. This eliminates the tedious frequency planning of cellular systems. The signal levels of all channels are continuously measured for connection construction, and uninterrupted channels are managed in the channel list (channel map). During the connection, the signal level and reception quality of all channels are further monitored. This monitoring transmits the channel that is just being used at a carrier frequency, which is disrupted (eg by transmission from or to another fixed station at the same carrier frequency). If so, another carrier frequency is automatically selected for the next active time slot. Other carrier frequencies are carrier frequencies that are entered as uninterrupted in the channel list. Alternatively, a so-called frequency hopping method can be used. In this frequency hopping scheme, the carrier frequency is switched for a predetermined time, eg, after a transmission frame. In countries other than Europe, the DECT standard may change and must be adapted to local practice. For example, in the United States, transmission is not performed in the normal DECT region of 1.88 to 1.90 GHz, but rather the 2.4 GHz-ISM (Industrial, Scientific, Medical) band, which is generally accessible, is used. In addition, changes must be made to comply with national regulations, such as the US regulation "FCC part 15 (Federal Communications Commission)". The above US regulations describe the transmission schemes, transmission powers and bandwidths used for wireless interfaces. In the DECT standard, each time slot contains the above 320 information bits, as well as 104 bits required for signal transmission and 56 bits for the guard field. Therefore, each time slot contains a total of 480 bits. From this we get a data rate of (24x48 bits) / 10ms =) 115 2000 bits / s. A data rate of this magnitude is meaningless in the American ISM band. That's because each available channel would require too much bandwidth. An object of the present invention is therefore to provide a method and apparatus for digital wireless transmission of data that makes effective use of the bandwidth of a TDMA system. This method or device must enable, among other things, the cost-effective use of the slow hopping RF modules described above. According to the present invention, there is provided a method for digitally wirelessly transmitting data between a fixed station and at least one mobile station by one of a plurality of carrier frequencies. In this case, the data is transmitted in multiple time slots by time division multiplexing (TDMA). Switching from one carrier frequency to another requires a predetermined amount of time. Data is transmitted in the active time slot, which is followed by each inactive time slot, and no data is transmitted in this inactive time slot. Inactive time slots are shorter in the present invention than active time slots. The duration of an inactive time slot is half that of an active time slot. This time slot structure provides a relatively large number of active connections per time frame. This provides a relatively effective use of the bandwidth of the TDMA system. The time frame of transmission can include, among other things, four active time slots for transmission from a fixed station to a mobile station and four time slots for transmission from a mobile station to a fixed station. Transmission takes place in the 2.4 GHz band. In the present invention, a device for wireless transmission of data is further provided. The apparatus of the present invention has a fixed station and at least one mobile station, and data is transmitted between the fixed station and at least one mobile station in a plurality of time slots by time division multiplexing (TDMA) and in a frequency division multiplexing system. It can be transmitted at multiple carrier frequencies by the (FDMA) method. Each fixed station and at least one mobile station has an RF module that allows the carrier frequency to be selected for transmission between one of the time slots. The RF module in this case requires a predetermined amount of time, the size of one time slot, to switch from one carrier frequency to another. In the present invention, the transmission time frame has an active time slot, in which data is transmitted, the active time slot is followed by each inactive time slot, and this inactive time slot. No data is transmitted to. The duration of an inactive time slot is less than the duration of an active time slot. Especially advantageously, the duration of an inactive time slot is half that of an active time slot. Therefore, more active connections can be made during the time frame, thus ensuring that bandwidth is used effectively. The transmission time frame includes four active time slots for transmission from the fixed station to the mobile station and four time slots for transmission from the mobile station to the fixed station. The carrier frequency is in the 2.4 GHz band. RF modules can switch carrier frequencies, among other things, during inactive time slots. The present invention will be described in detail with reference to examples and drawings. FIG. 1 is an apparatus of the present invention for digital wireless transmission of data. FIG. 2 is a schematic diagram of a known DECT standard. FIG. 3 is a schematic diagram of channel use when a known DECT standard is applied to the American ISM band. Figure 4 shows the particularly advantageous use of DECT standard channels adapted to the ISM band according to the invention. In FIG. 1, a device for digital wireless transmission of data is provided. The fixed station 1 is connected to the fixed network by the terminal line 10 in this case. Fixed station 1 has RF module 4. Data can be transmitted or received by the antenna 6 by the RF module 4. This RF module 4 is a so-called slow hopping RF module in particular. That is, it is a module that is particularly advantageous in terms of cost. This RF module, however, requires a certain amount of time to switch from one carrier frequency to another. This time is the size of one time slot. That is, between approximately 100 μs and 1 ms, especially between approximately 300 μs and 500 μs. The time required for carrier switching may correspond to, for example, the time filled by a time division multiplexing (TDMA) time slot. The antenna 6 performs wireless transmission to the mobile station 2 via the wireless transmission section 8 or transmits to the mobile station (wireless telephone) 3 via the second wireless transmission section 9. All mobile stations illustrated in FIG. 1 have the same structure and therefore will be described in detail based solely on mobile station 2 illustrated herein. As can be clearly seen from FIG. 1, this mobile station 2 has an antenna 7 for transmitting and receiving data to or from a fixed station. The mobile station 2 is provided with an RF module 5. This RF module 5 substantially corresponds to the RF module 4 used in the fixed station 1. Therefore, the RF module 5 of the mobile station 2 is a so-called slow hopping RF module. With reference to Figure 2, we will explain how the known DECT standard fits into the American ISM band. As already mentioned earlier, the resulting data rate for the ISM band when maintaining the DECT standard is too high. As you can see from Figure 3, for this reason the number of time slots per frame has been halved. In other words, instead of the DECT standard 24 time slots (channels), only 12 time slots Z1 to Z12 are provided within 10 ms of one time slot, and 480 bits can be transmitted in each of these 12 time slots. By halving the number of time slots, the data rate is also halved to (12x480 bits) / 10ms = 576000 bits / s. This relatively low data rate results in acceptable bandwidth for the American ISM band. However, as can be clearly seen from FIG. 3, a so-called slow hopping RF module needs to be provided in order to realize the equipment required for wireless transmission in a cost-effective manner. This means that: That is, each active time slot in which data is transmitted must be followed by an inactive time slot (blind slot) in which no data is transmitted. Twelve time slots Z1 to Z12 (six time slots Z1 to Z6 are for transmission from mobile station to fixed station, and six time slots Z7 to Z12 are for transmission from fixed station to mobile station. In the case of), therefore only a maximum of 3 possible connections can be used. Therefore, when realized by the slow hopping RF module, which is advantageous in terms of cost, the available channel capacity by restricting to a maximum of three connections by the slow hopping RF module is not so large. Figure 3 shows the possible active time slots by hatching. For example, in time slot Z1, the carrier frequency f as shown.₂Transmission is performed from fixed station 1 to mobile stations 2 and 3 (RX1). This time slot Z1 is followed by time slot Z2, and if there is no data transmission in this time slot Z2 (inactive time slot, blind slot), the slow hopping RF module is also in this inactive time slot Z2. The duration is used to switch the carrier frequency. As illustrated in FIG. 3, the carrier frequency is, for example, the carrier frequency f.₂From carrier frequency f₁Can be switched to. Therefore, as illustrated in FIG. 3, in the time slot Z3, the transmission from the fixed station to the mobile station has a carrier frequency f.₁It is done in (RX2). Therefore, in the diagram shown in FIG. 3, the active time slot (shown in hatch) for a given time slot allocation has a predetermined carrier frequency (f).₁, f₂, ...) is characterized in that it can be operated by each of them. Recall that according to the DECT standard, the configuration of physical channel reuse is done by dynamic channel selection. In this case, the channel is defined by its carrier frequency and its time slot. Therefore, the troublesome frequency planning as in the case of the cellular system is not performed. For connection construction, the signal levels of all channels are continuously measured, and uninterrupted channels are managed in the channel list (channel map). During the connection, it also monitors the signal level and reception quality of all channels of all possible carrier frequencies. Carrier frequency f in time slot Z1 as illustrated in FIG.₂Carrier frequency f during transmission by (RX1)₁If it is detected that the reception or transmission status is more favorable, the carrier frequency f identified to be more favorable during the time slot Z2 where no data transmission occurs.₁Can be switched to. Transmission RX2 between time slots Z3 has been identified as more advantageous than this carrier frequency f₁It is done in. Alternatively, a so-called frequency hopping method can be used. In this frequency hopping method, the carrier frequency is switched after a predetermined time, for example, one frame of transmission. As described above, the usage diagram for the channel illustrated in FIG. 3 has the following drawbacks. That is, halving the number of time slots per time frame to 12 doubles the duration of the time slots to 833 μs, and the result is due to the need for inactive time slots after each active time slot. In contrast to the 6 possible connections according to the DECT standard, only 3 possible connections (3 connections from fixed station to mobile station and 3 connections from mobile station to fixed station) are given. It has the drawback of not being available. FIG. 4 illustrates the time slot structure. This timeslot structure can increase the maximum possible connections from 3 to 4 without compromising the flexible choice of carrier frequency from one active timeslot to the next. As can be seen from Figure 4, this increase in the maximum possible connection from 3 to 4 is essentially the duration of the inactive time slot with no data transmission and the duration of the active time slot. It is realized by shortening compared to. As shown in Figure 4, if one time frame has a total of 10 ms, the durations of the active time slots Z1, Z3, Z5, Z7, Z9, Z11, Z13 and Z15 of this time frame are respectively. It is 833 μs. The duration of the inactive time slots Z2, Z4, Z6, Z8, Z10, Z12, Z14 and Z16 is only 417 μs as illustrated in Figure 4, and thus effectively half the duration of the active time slot. Is. Slow hopping RF modules, well known from DECT technology, require at least one duration of 417 μs after the active time slot to perform frequency programming for the carrier frequency of subsequent time slots. Therefore, half the time slot of the DECT standard adapted for the ISM band with the time slot 833 μs / 2 = 417 μs is sufficient as an inactive time slot (blind throttle). As can be seen from FIG. 4, for example, the data transmission RX1 during the time slot Z1 has a carrier frequency f from a fixed station to a mobile station.₁It is done in. In order to carry out transmission with a small bandwidth, the duration of time slot Z1 in this case is twice the duration according to the DECT standard, or 833 μs. This time slot Z1 is followed by the inactive time slot Z2, which has a duration of only 417 μs. However, this duration of 417 μs is sufficient for the RF module of slow hopping technology to program the carrier frequency for the next active time slot Z3. So, for example, the carrier frequency f₃Is the carrier frequency f₁Carrier frequency f of time slot Z1 during the duration of time slot Z2 where no data transmission occurs if identified as providing better reception conditions.₁Carrier frequency f for time slot Z3₃Therefore, transmission from the fixed station to the mobile station occurs between the time slots Z3 (RX3). Carrier frequency f in the illustrated example_xIs illustrated in a case where is not switched between a fixed station and a predetermined mobile station due to transmission. Alternatively, of course, a so-called frequency hopping method can be used. In this frequency hopping method, the carrier frequency is switched after a predetermined time, for example, one frame of transmission. After eight time slots Z1 to Z8, which correspond to half of the time slots Z1 to Z16 in a 10 ms time frame, transmission from one or more mobile stations to a fixed station is performed by the duplex method (TDD). For example, during time slot Z9, transmission from mobile station to fixed station (TX1) is carried out at carrier frequency f.₁Do it with. The next inactive time slot Z10 following this active time slot Z9 has only half the duration of the active time slot Z9 (833 μs) in its duration, ie 417 μs. The duration of the inactive half time slot Z10 is sufficient for the RF module to perform frequency programming for the next active time slot Z11 for yet another transmission (TX2) from the mobile station to the fixed station. Is. Therefore, the structure of the time slot ZX of the present invention makes more effective use of the time frame of digital transmission of the TDMA system without compromising the flexibility of carrier frequency selection by the present invention. Reference code list 1 Fixed station 2 Mobile station (wireless phone) 3 mobile station 4 RF module fixed station 5 RF module mobile station 6 Antenna fixed station 7 Antenna mobile station 8 First wireless transmission section 9 Second wireless transmission section 10 terminal line Zx time slot fx carrier frequency