MXPA97001756A - A method to adapt a sync transmission - Google Patents

Abstract

A method for adapting synchronous transmission to the rules that apply to asynchronous transmission in a radio medium. In asynchronous transmission, it is decreed that the transmitter / receiver operate in the supervision mode for a certain short period of time (tm), in order to establish whether the transmission will be carried out or not carried out. Synchronous transmission is, for example, a TDMA transmission for an active personal telephone system over short distances (from 10 to 200 meters). According to the proposed method, the radio means is monitored by a synchronous transmitter (PT) over a short period of time (G) between two time intervals (T1, T2) and the energy or power (Pm) received. it is measured and compared with a given signal threshold power (Pt) according to the asynchronous rules. The permission to transmit can be provided based on the result of this comparison

Description

"A METHOD TO ADAPT A SYNCHRONOUS TRANSMISSION" TECHNICAL FIELD The present invention relates to a method related to synchronous radio transmission. More specifically, the invention relates to a method for synchronous transmission through a frequency band where synchronous transmission rules are applied. The synchronous radio system can be a DECT-type system, that is, a relatively short-range wireless personal communication system, which will be adapted to comply with the rules for asynchronous transmission, for example, a so-called data transmission by switching package, with retained synchronism.

DESCRIPTION OF THE BACKGROUND OF THE TECHNIQUE In radiocommunication technology it is common to distinguish between asynchronous and synchronous transmission. Traditionally, radio communication has been developed for circuit-switched synchronous services, such as mobile telephones and cordless telephones for conversation communication and ISDN services. A common characteristic of these types of system is that the information is transmitted to a specific receiver within specific time points determined in a system divided in time or through a certain radiofrequency, a system divided in frequency. An example of time-divided systems are the so-called TDMA systems (Time Division Multiple Access) where the information is transmitted in time intervals with periodic time separation determined for each channel. Radiosistems using asynchronous transmission usually use so-called packet switching through some radio frequency even when these packets are transmitted and received totally randomly from one transmitter-receiver to another transmitter-receiver. An example of asynchronous systems is found in so-called local area data networks, which use data packet switching over a radio instead of through circuit-switched radio means. A certain frequency spectrum has been reserved for asynchronous radio transmission (eg, a frequency spectrum from 1910 to 1920 MHz assigned by the Federal Commission, FCC in the United States of America). This allows short access times for transmission per asynchronous packet to be obtained.

In asynchronous transmission, several users share the same aspect of frequency thus avoiding the need for frequency planning. A crash occurs during times that result in network congestion between two users, even when the proposed data packet is retransmitted. The re-transmission of the data packets at certain time points after transmitting an asynchronous data packet is already known in the art; see for example the exposures made in Patent Number SE-A-9302067-5. Synchronous or periodic transmission involves sending and receiving information at predetermined time points and / or through certain determined frequencies, such as in the case of the TDMA systems mentioned in the introduction. In the case of the previous example of American standards that have a frequency band between 1910 and 1920 MHz in the case of an asynchronous transmission, a band between 1920 and 1930 MHz is intended for synchronous transmission. These two bands will therefore be used separately from each other.

COMPENDIUM OF THE INVENTION One incovenience of asynchronous transmission is that it is not appropriate for use in the same system or in the same environment as those services offered in synchronous radio networks, due to the risk of interference and disturbances from asynchronous transmission. In particular, asynchronous transmission is not appropriate for easy inclusion in a digital integrated services ISDN network. It is already known how to sustain the synchronous services in an asynchronous medium with the help of the so-called ATM (Asynchronous Transmission Mode). In this application, the data asynchronously recycled is collected for a period of time in a buffer on the receiving side, after which the data collected in this memory is transmitted under the control of a synchronous clock. This period of time must have sufficient duration to allow any of the retransmissions that will have to be made due to the shocks before the reconstructed bitstream can be synchronously clocked. This allows asynchronous transmission to transmit synchronous services. Even when the known method works well, a delay is caused by the memory function. An excessively long delay can not be tolerated in the case of transmission of conversations. In order to maintain a short delay (approximately 10 milliseconds), a very high bandwidth is required in the case of radio transmission, generally greater than 40 MHz, when a plurality of users coexist in one and the same frequency spectrum. On the other hand, it is appropriate to use one and the same radio system for both synchronous and asynchronous services, using a half service (1920-1930 MHz) of the assigned frequency band and using the other service the other half (1920-1930 ) of the same band. However, this has the advantage of unnecessarily limiting the capacity of synchronous transmission, because it only uses half of the allocated band through the whole system (as a whole). This in turn means that the density of the base station should be increased in the radio system with more compact re-transmission of the access channels. Therefore, it is desirable to use the full band for synchronous transmission. The present invention provides a method for adapting the synchronous transmission of services to the rules for asynchronous radio transmission. The novel method does not cause exaggerated delays even when the allocated spectrum is small (5-20 MHz). In this way, the object of the present invention is to provide a method for synchronous radio transmission over short distances that satisfies the asynchronous transmission rules within an assigned frequency band. The synchronous radio transmission has a certain periodicity for the transmission of information. For example, in the case of a DECT-type system, information is transmitted in frames in accordance with the TDMA principle, where a given frame contains a number of time slots for transmission from a number of users, and the same number of time intervals to receive the information in the respective users. Then follow the following table. A normalized protection time is included between two mutually sequential time slots in the table for different users. In accordance with the present invention, this protection time is used to secure and the transmission in the following time interval may or may not be carried out in accordance with the asynchronous rules. The invention is characterized by the characteristics indicated in the following claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail with reference to the accompanying drawings, in which Figure 1 is a functional diagram illustrating a known radio system that includes both synchronous and asynchronous radio transmission within one and the same geographical area; Figure 2 schematically illustrates a frequency spectrum assigned to a radio system in accordance with Figure 1; Figure 3 illustrates an example of a timing diagram related to the previously known synchronous radio transmission, for transmitting and receiving; Figure 4 similarly illustrates the known asynchronous radio transmission, but only in the transmission mode; Figure 5 is a time diagram similar to those shown in Figures 2 and 3, and is intended to explain the method of the invention; and Figure 6 is a simplified functional diagram analogous to Figure 1 illustrating only the synchronous transmission adapted in accordance with the invention.

BEST WAYS TO CARRY OUT THE INVENTION Figure 1 is a simplified functional diagram illustrating a system for synchronous and asynchronous radio transmission. In the illustrated case, the radio systems include two base stations BS1 and BS2 communicating with two mobile subscribers, of which one is a portable telephone PT device and the other is a mobile data terminal DT. The two terminals PT and DT are placed in proximity to each other geographically, and therefore, have the possibility of interfering with one another. For example, the two devices / terminals can be installed in one and the same place in an office building. It can also be placed close to each other within the same building. Both terminals are placed a short distance from the base stations BS1 and BS2. By the term "short distance" is meant in this respect, a distance of 10 to 200 meters, that is, a distance much shorter than the maximum distance at which a mobile subscriber in a cellular system will probably be located from a base station (up to 30 kilometers). A Trl transmission is synchronous and is used by the portable PT telephone. This telephone transmits to base station BS1 which operates synchronously and receives radio signals from the base station within a given frequency band and divided in time according to the TDMA principle. Therefore, in addition to a given frequency spectrum that is reserved for synchronous transmission, a given time interval in each frame is also reserved for transmitting from the PT terminal and a time interval for receiving a certain period of time after transmit in the same box (see Figure 3). The base station BS1 is able to communicate synchronously with other portable telephone sets, not illustrated. The other transmission Tr2 is an asynchronous transmission using the DT data terminal. This terminal transmits to the asynchronous operating base station BS2 and receives radio signals from this base station within a certain frequency band, but at random time, instead of periodically as in the case of the PT terminal. As with the base station BS1, the radio signals are transmitted and received by the base station BS2 within a given frequency band. The transmission Tr2 can be a packet switched data transmission, for example. The base stations BS1 and BS2 can be located inside or outside the building and are physically connected to a private or public switched network (not illustrated) by means of telephone wires.

Figure 2 is a schematic illustration of two frequency bands for synchronous and asynchronous Trl, Tr2 transmission. Only the asynchronous Tr2 transmission occurs between the band limits Bl, B2, and only synchronous Trl transmission occurs between the band limits B2-B3. In the United States of America, these band limits have been specified at 1910-1920 MHz and 1920-1930 MHz, respectively. The inconvenience with this division is that only half of the total bandwidth B1-B3 is accessible for respective synchronous and asynchronous transmissions, as mentioned above. Figure 3 illustrates the known principle of tranmsmitting radio signals in accordance with the TDMA techniques being this periodic or synchronous transmission. In this case, the transmission of TDMA in a DECT system for personal radiocommunication (standardized by ETSI) is shown by way of example. According to this norm, the transmission is carried out in a frame of a length of 10 microseconds and the reception is made during the following frame through a duration of 10 milliseconds. According to this norm, each square will contain twelve time intervals, even though only four time intervals have been shown in the transmission and reception tables in Figure 3, for reasons of simplification. An essential feature of the method of the invention is the provision of a protection space between two following time intervals in sequence, in accordance with the standard, ie a short protection time of 30 microseconds is included in order to prevent a burst in a time interval between a following time interval as a result of mutually different propagation times of the two bursts, among other things. Figure 4 is a time diagram related to the asynchronous transmission in a packet data system, for example the base station BS2 and the data terminal DT in Figure 1. The data packets Pl, P2 and P3 which contain information and directed to a certain receiver are sent at certain time points. In accordance with the asynchronous transmission rules, a short time period tm during which monitoring is carried out is included before each data packet, for example, before the packets Pl. During this monitoring period, the transmitter measures the strength of the signal in the proposed channel to establish whether or not the channel is free of other transmissions, which can be ensured by measuring the power or energy in the receiver. If it is found that the energy is less than a certain level, specified by the aforementioned rules, the channel is considered as being free for a certain limited period of time (10 milliseconds) immediately after the measurement period tm. Therefore, the transmission is carried out during this period or as part of this period, on the frequency of the proposed channel within the frequency band Bl. In accordance with the present invention, the brief protection time G between two transmission time intervals in the synchronous Trl transmission is used to satisfy the fundamental rule in the asynchronous transmission which decrees that before each transmission, a period of short time before transmitting a limited time packet within the transmission period. The short time period is usually much shorter than a time interval in a synchronous system. Figure 5 is a time diagram illustrating the principles of the method, and Figure 6 illustrates a single PT terminal of synchronous transmission that even when similar to the PT terminal in Figure 1 is adapted to the asynchronous rules in accordance with the method of the invention. The upper part of Figure 5 illustrates the synchronous transmission in accordance with Figure 3, with four transmission time slots mutually in sequence from one and the same transmitter. The time intervals are separated by a distance corresponding to 10 milliseconds, within which spaces the remaining transmission time intervals and an equal number of reception time intervals are accommodated. For a particular transmitter / receiver that transmits during a certain transmission time interval TX, e.g., TI in Figure 3, and re-transmit in the next TX time interval, a silent period is included during the transmission time slots T2-T4 and the reception time slots R1-R4 and the corresponding protection times G in Figure 3. In the illustration of Figure 5, it is assumed that the synchronous transmission is started with the transmission in the time interval TX assigned to time t. Prior to this, the corresponding protection time Go has been used during the brief monitoring period to measure the power or energy emanating from the prevailing interference created by some other system, such as the power or power received in the receiving part of the terminal Synchronous PT shown in Figure 6. As shown in Figure 5, the asynchronous transmission is assumed to be performed during the time periods TY. This transmission interferes with the synchronous TX transmission, during time periods II, 12 and 13. The asynchronous transmission is monitored during the protection time G immediately preceding a given assigned transmission time TX interval, v. g., the time interval TI of the illustration of Figure 3. Therefore, the power or power of the asynchronous TI transmission is measured during the protection time Gl as it is received in the receiving part of the synchronous terminal P2 shown in Figure 1. The PT terminal shown in Figure 1 therefore measures the interference I supplied thereto from the data terminal DT, by measuring the power or energy of the radio signal from the DT terminal and all the time Gl of protection, or during part of it. In the case of the example, Figure 5, no interference is observed when measured during the protection time Gl, and consequently, the transmission is carried out during the next TX interval of transmission time starting during time ti. An additional measure is taken during protection time G2, before the time interval starting during time t2. In the case of the illustrated example, this additional measurement indicates that the asynchronous transmission is running but because the measurement process is running for a short period through the protection time G2, the synchronous transmission is unable to determine the length of the asynchronous transmission. The synchronous transmission is inhibited due to interference 12 from the transmission TY, which also appears during the protection time G2. Another measure is still taken during the protection time G3 before the time interval starting during time T3. In the case of the illustrated example, it is established that no asynchronous transmission is in progress. It is assumed that the asynchronous transmission will not start until later, even though during a part of the time interval starting during time T3, which can not of course be established when measured during protection time G3. Accordingly, the synchronous transmission is carried out even when it is subjected to interference for a short period of time, in accordance with Figure 5. A new measurement is taken during the protection time G4 before the time interval starting during the time t4. In the case of the illustrated example, it is ensured that no asynchronous transmission is running and consequently the transmission is carried out in the same way as during the time ti. It is not possible to use a period of time longer than the protection time G during the still period between two transmission time slots mutually in sequence, because the synchronous transmission may be running for another time interval, for example, the time interval T2 according to Figure 3, from another synchronous transmitter. This other synchronous channel has been shown in broken lines in Figure 6 and is referred to as ST. Thus, the monitoring and measuring of possible interference transmissions in the synchronous channel can only be carried out during the protection time G between two transmission time intervals. If the time G is not sufficient to satisfy a specific asynchronous norm, an alternative procedure is that the synchronous system is prevented from transmitting during certain time intervals, for example, during each alternate time interval, and the protection time G can be made as long as a time interval. Avoiding transmission during certain time intervals, it is a solution to the case when the asynchronous rules require a separation between two bursts from one and the same transmitter to have a smaller time interval, for example, a number that is selected at random from 50 and 400 microseconds. After measuring the interference radio signal from the asynchronous transmission in the synchronous receiver, the power or energy of the interference radio signal is compared in the receiver with a threshold value related to this power and stored in the receiver. receiver and that has been determined in accordance with the rules for asynchronous transmission, see the example given below. If the measured power of the interferendum signal is Pm and the threshold power (called the access threshold) is Pt, then the transmission in the next time interval is inhibited when Pm >; Pt, and the transmission in the next time interval is allowed when Pm < Pt. The result of the adapted synchronous transmission is shown in the bottom of Figure 5. The measurement of the power of the interference signal during the protection times Go and G2 and the comparisons made in the synchronous receiver showed the condition Pm > Pt and consequently no synchronous transmission was carried out in the corresponding time intervals. Transmission takes place only in those time intervals that start at you, t3 and t4. The following numerical values are provided as an example for a transmission with 10 MHz assignment: Transmission bandwidth: less than 10 MHz Transmission power: less than 100 MHz - l Supervision time before transmission: at least 30 microseconds Supervised power level for allowed transmission: Less than -90 dBm Maximum burst transmission length: 10 milliseconds It will be understood that the method of the invention is not limited to exemplary mode previously described. For example, it is not necessary to transmit in the time TX interval immediately following the monitoring and measuring process carried out during, eg, the protection time Gl in accordance with Figure 5, even when the result of the measurement allows it. Instead of this, it is possible to jump through the table and carry out a new supervision process during the corresponding protection time Gl in the following table or in a certain following table. This alternative will ensure an even more positive interference-free synchronous transmission. Nor is it necessary to precisely measure the power from the transmission of interference in the synchronous channel, since it is also possible to measure, instead of this, v.gr, the so-called C / I ratio, where C is the value of the signal in the synchronous channel and I is the value of the interference signal from the asynchronous transmission in the synchronous channel. Naturally, this assumes that synchronous rules have defined C / I by measuring instead of this, as an alternative to measuring power thresholds. The method of the invention solves the problem of transmitting synchronous services, for example conversation with a short delay, using a frequency band with the rules for asynchronous transmission. Since these synchronous services become sensitive to interference from a purely asynchronous system in the same frequency band, the main area in which the invention is applied is in offices or buildings that are controlled by an owner or owner. This means that only one type of system will be installed in each building, or on each floor of a building.

Claims (5)

CLAIMS;

1. A method for the synchronous transmission of radio signals through a frequency band (B1-B2) within which the rules for asynchronous transmission are applied and that is performed through only short distances and periodically within periods of certain active time (TX), wherein a period (G) of determined inactive time is reserved between two mutually active time periods in sequence where the transmission is not effected, characterized by monitoring the state of a radio channel assigned for transmission within the frequency band (B1-B2) in accordance with the asynchronous transmission during period (G) of inactive time, where permission is given for transmission within the active time period (TX) that follows the period (G) ) of inactive time, in accordance with the determined asynchronous transmission criterion. A method according to claim 1, characterized by monitoring the state of the radio channel allocated for transmission within the frequency band (B1-B2), measuring the power of the signal in the proposed synchronous transmission channel, and comparing the value of the measurement power (Pm) with a predetermined threshold value (Pt) in accordance with the asynchronous transmission criterion, where permission is given to transmit in the proposed channel when the measured value is smaller than the threshold value by a certain amount. 3. A method according to claim 1, characterized in that no transmission is effected in the active time period (TX) that immediately follows the period (G) of inactive time during which the monitoring process is performed, but rather in the next closest time period in which permission has been given to transmit with respect to this last active time period. 4. A method according to claim 3, characterized by measuring the power during the main part of the inactive time period (G). 5. A method according to claims 1 to 3, characterized by measuring the power periodically in each of the short periods of time (G) that precedes the periodic transmission in the synchronous transmission in that frequency band.