FI106280B - A method for allocating time slots for data transmission in a Multipoint Reverse TDMA Multipoint System - Google Patents

Abstract

According to this method, the time of origin (t''2) of the upgoing frames being, in every remote station, chosen in such a way that, in the central station, the time (t'2) of origin of these frames is separated from the time (t'1) of the end of the downgoing frames by a period less than To, where To denotes twice the time of propagation between this remote station and the central station, thus defining, in the said remote station, a region of so-called overlap between downgoing and upgoing frames, the said time slot assignment is effected so as to avoid any coincidence of assigned time slots, at any one remote station, in the upgoing and downgoing frames respectively, in the said region of overlap. <IMAGE>

Description

106280

The present invention relates to bidirectional transmission systems. The present invention relates to bidirectional transmission systems.

As is known, two-way transmission technology enables two-way transmission by a single transmission means 10, and according to this, each end station of such a transmission system is alternately transmitting and receiving.

Depending on the propagation speed of the signals transmitted by this transmission medium, the time of transmission of the signals may need to be taken into account, and the transmission format used may need to include time periods that take into account the time of transmission and cannot be used for information transmission. This is an obvious disadvantage because it limits the amount of information 20 that can be transmitted by these systems.

It is an object of the present invention to avoid this disadvantage in such two-way transmission systems where there are also multi-point (! 25) pixel types equipped with a central station and employing TDMA technology.

: T; The present invention can be used in flow * '···' directional transmission systems which are also a multiplex type with a central station in which data can be transmitted between the central station and remote stations on the other hand, and especially in systems where said central station • · *: *: j and a point called a hub. there is one time-divisional transfer medium for a plurality of remote • * * 35 stations, and between said hub and each point corresponding to a remote station is: a dedicated transmission device for each remote station, the length of which varies depending on these remote 106280 2 stations. position relative to the hub.

Further, the invention is particularly applicable to the case where the transmission medium is multiplexed by TDMA technology 5 (Time Division Multiple Access), i.e. using a transmission format with time slots assigned to remote stations in a predetermined manner.

The present invention is thus particularly applicable to distribution networks used in a terminal portion of a telecommunications network close to users, and particularly to distribution networks in which the transmission means are optical fibers and the hub is a passive optical switch.

The present invention is directed to a method of allocating time slots for transmission in a multicast TDMA multicore reverse link system, which allows communication between a central station on the one hand and remote stations on the other, wherein each remote station is allocated at least one slot for each transmission direction from the central station to the remote stations, grouped into the downlink frames, and the slots used for transmission from the remote 25 stations to the central station are grouped into the uplink frames, and the method is essentially characterized by selecting the beginning of the uplink frames at all remote stations such that the beginning of these frames is at the central station from the end of the frames 30 descending from the end 30 of the time To, where To means? guarantees twice the travel time between this remote station and the central station, and thus determines the distance. up and down in the station above. ··. interleaving zone, whereby time slots are allocated '·' 35 such that all coincidences of time slots allocated in the same remote station uplink and: .i .: downlink frames are avoided in said overlapping zone.

3, 106280

Other objects and features of the present invention will become apparent by reading the following description of embodiments related to the accompanying drawings, in which: - FIG. 1 is a diagram illustrating a transmission format used in prior art multipoint point-to-point TDMA multicast transmission systems; Fig. 2 is a diagram showing a transmission format used in a multipoint point-to-point multidirectional TDMA transmitting system according to the invention, 15 - Fig. 3 is a flow diagram showing various steps of the method according to the invention, - Figures 4 and 5 are diagrams a specific method for determining the travel time between the 20 remote stations and the central station in the case where the same transmission medium is used in both transmission directions and in the case where both transmission directions use different transmission means, The method a is preferably used in conjunction with the process of the invention.

In Fig. 1, the length of a frame transmitted by a central station OLT and received by a remote station ONT, also called a · · · 'downlink frame, is denoted Tx, a frame transmitted by a remote station and received by a central station also called ascending move the · · * to the forward frame, the length is denoted by T2 (whereby, for example, Tj * T2) and the aforementioned time slot which is not

. i «I

used to transfer information, length is denoted by T0.

\ 35 * * ·

In Fig. 2, the length of the downlink frame is denoted T1, whereby T1j> T1 #, the length of the uplink frame is 4106280 denoted T'2, where T'2> T2 (e.g. T'j ^ T'2) and the time slot , which is not used for information transfer, the length is denoted T'0, whereby T'0 <T0. In this example, the length T'0 is not zero, but the method of the invention does not exclude that T'0 is zero.

The method of the invention is based on the observation that since the transmission system, as mentioned above, is of the TDMA type, a remote station may be allowed to transmit while it is receiving information intended for another remote station.

The present invention assumes that the directional attenuation of the switch used to implement said hub in a multipoint system 15 with the central station under consideration is sufficiently large that the reflections to other remote stations caused by remote station transmissions can be considered negligible.

20

The present invention further assumes that the clock frequency regeneration that occurs at the reception at a remote station is capable of continuing said · '· *; assigning a clock frequency when the reception is interrupted to perform this transmission.

4 ·

In the exemplary embodiment described, the time period T0-T'0 which, due to the allocation method described herein, remains available for information transmission is divided evenly between the downlink frame and the uplink frame.

As mentioned above, the method is applicable to TDMA technology; kan transfer case, that is, where. ···. the transmission format is arranged in ascending or descending ^ 35 frames with different time intervals assigned to different remote stations • · · * · "'.

5, 106280

As illustrated schematically in Figure 2, the slot allocation method of the invention tends to allocate at least one slot in the downlink frame and 5 at least one slot in the uplink frame for transmission between a central station and a remote station, the number of slot slots being allocated there are several time slots, each of which is independently allocated according to the method of the invention, which implies that the different time slots are not necessarily consecutive.

The slots are now numbered according to a numbering which: 15 at the central station is continuously assigned starting from the start of the downlink frame and which numbering is common to the downlink frame and the uplink frame (of course 20 taking into account the time slot T'0 non-zero), - at a remote station: - - given to the descending frame continuously incrementally from the absolute starting point to the beginning of the descending 25 frame, ···. In the case of an ascending frame, the numbering includes a change in the starting point, and the numbering is given continuously from the relative starting point within the downward frame.

30 «·« ί · 'The beginning of the uplink frame t "2 is determined by the remote station · · · V · in fact such that the start time t'2 of this frame when viewed at the central station, that is, I · <. ···. taking into account the time between stations, coincides with • 1 • 35 the beginning of time slot T'2 As shown in Figure 2, this results in a certain overlap of the downlink frame and the uplink frame at the remote station .

106280 6

Assume that the ID is the number of the time slot within the descending frame which in this way coincides with the first time slot of the uplink frame. In the following representation, the overlapping zone, denoted by T ku-5 in column 2, refers to the downlink frame time slots having a number between ID (inclusive) and IU (inclusive), where IU represents the last slot of the downlink frame.

It should be noted that the number ID is different for each remote station because it depends on the travel time between the remote station and the exchange.

Assigning the number ID requires measuring the travel time δΤ between the remote station 15 and the central station, which may be performed according to a known method which is not described herein. The parameters t "2, t'2 and δΤ are in fact related to each other, according to the following relationship: 20 t" 2 + δΤ = t'2, which, when δΤ and t'2 are known to a given remote station, can obtain t "2 and thus the ID to this remote station.

In other words, the beginning of the uplink frames t "2" · at the remote station is located before the end of the downlink frames t "t and a sufficient time period to · · * · '' the transmission format at the central station is desirable, that is, to allow periods of time that cannot be used to transmit information to be reduced or even avoided.

* ♦ · «« · ·

Assume that Id and Iu are the number of slots in the downlink frame «· 35 and the slots in the uplink frame t, respectively, which are reserved for transmission between a central station and a designated ·: **: remote station, previously determined by 7106280 station.

In this example, it is assumed that the slot allocation method is performed at the central station. In addition, this example begins by entering the downlink frame time slot number Id.

The only condition that needs to be checked in the case of Id 10 is that it is a free slot number, i.e. it is not yet occupied and is smaller than IU. Any number meeting these conditions may form the desired number Id.

As shown in the flowchart of Fig. 3, the number Id can be searched, for example, by examining successively the different time slots of the descending frame from the first, i.e., the number 0 in the flowchart of Fig. 3, and checking in each case whether it is 20 free. In the case that the time slot is not free, the following is examined and if it is free, its number may be the number sought Id.

In the corresponding procedure, shown in the flow chart of • V, 25 in Fig. 3, an intermediate variable Ik is used, incrementing by one whenever the time interval is found to be 4 ·. In addition, detecting a number Ik greater than IU causes, as shown in the flow diagram of Figure 3, an error message.

30 n ·: *. · To reserve the slot number Iu in the ascending frame

II

5, then proceed as follows. Initially, ver,) ·, traverses the number Id thus assigned to the number ID defined above, to determine whether or not the time interval corresponding to Id is within the overlap area.

If this time slot is not in the overlap area, it is preferable to assign the number Iu 106280 8 so that the symmetry of the slot allocations in the downlink and uplink frames is retained, which, given the numbering used at the remote station, can be represented as:

Iu - ID + Id

However, the number Iu can remain a searched number Iu only if it is a free slot number. If it is not a number of 10 free slots, it is incremented, for example, by one, followed by the same free testing, and so on, until a free slot number is obtained, as shown in the flowchart of Figure 3.

If, on the other hand, the time slot corresponding to the number Id thus allocated is in the overlapping zone, then it must be checked that the selection of the time slot Iu does not cause a transmission and reception coincidence. Id.

· ;. The number Iu is determined, for example, by checking successively * · «the different time slots of the uplink frame starting with the first I. '25, that is, taking into account the distant

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the numbering used for the club, starting with the number 9 9 ID, and checking for each time interval that is free «* * • '. In case the slot is not free,

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5 .; Let's say the following, and if it is free, check 30 that the number of this time slot and the ones given earlier are not the same, so it is clear that if they are the same, then the next time interval is checked, and if they are *. not the same, this time slot number can be considered searchable ;;; see number Iu.

35 f:: In the corresponding process shown in the flow diagram of Fig. 3; ··; lys uses intermediate variable II, which increments with 9 106280 each time a busy time interval is detected.

The time slot allocation method described above can be performed either at the central station or at the remote stations, whereby it is clear that if performed at the remote stations, the results must be centralized at the central station and communication between the remote station and the central station is required.

A preferred embodiment of the present invention is included in the case where a time period having a length Τ'o defined in relation to FIG. 2 is used as a positioning window to determine the travel time between a remote station and a central station, especially when this window 15 is relatively small. according to a specific method of determining the travel time.

Initially, it is noted that the passage time between a remote station and a base station is usually determined by measuring the measured distance between the current remote station and the remote station taken as the reference station, and the reception time of the position f, V, The remote position of the 25 positioning signals has transmitted with respect to the reference reception of said information signals with a delay determined so that different positioning signals transmitted by different remote stations can be received within a predetermined positioning period, called: ', · As a dialog window and not assigned to receive information signal # »« *, J:.

9 • * f «I c, * · !, A relatively large positioning window must be used here, covering all of the positioning signals M, 'ki where the positioning signals« may be from the most distant position to the central station and 106280 from 10 central stations distant away. between the extreme positions corresponding to the position.

4 and 5, it is also possible to use a relatively narrow positioning window, also called a narrow window.

Suppose that T is the transmission period of the central station. In FIG. 4, 10, this transmission period includes a time period for transmission and a time period for reception.

Thus, in the first line of the diagram in FIG. 4, the reference symbol Te denotes a transmission period for a downlink, i.e., a remote transmission from a central station OLT "n" to eight remote stations in the example denoted 0NT1, ONT2. . ONT8. Figure 4 shows two consecutive transmission periods designated Tel and Te 2.

20

In the exemplary embodiments described, the downlink ·; · format contains at least one time slot reserved for transmission of specific information signals, called signaling signals, intended for all stations.

«F t · • • • • • • These signaling signals contain some" n "at a distance •« ·; position signal to trigger this remote position to send a position signal: * · *: 30 SW. In contrast to the other signaling signals discussed below, the address signals *. the transmission is not dependent on any condition, it is thus systematic · · · thematic and periodic, for example, by assigning <«'···'" n "the remote position alternately.

: 35 · t · ·; «·· The position reception signal measured by the central station relative to the base station transmission reference time 106280 enables the detection of the passage time between this remote station and the central station. The reference time t1 is, for example, the end of the transmission period Tel.

The remote station thus assigned transmits a position determination signal a delay after the reception time reference t2 of this remote station reception, which is, for example, the beginning of the reception period of the remote station, as shown in the four-to-10 square row of the diagram.

The delay may vary as a function of time from an initial value such that the corresponding positioning signal may not be received in the narrow positioning window Tf that occurs at the central station during the time period T-Te.

In the exemplary embodiments described, the signaling signals further include a signal indicating that the positioning signal has not been received in the positioning window.

• · · «· I« | • V. In the event that the positioning signal is not received in this window as indicated by the signal, which · ···, 25 la indicates that the positioning signal has not been received in the positioning window, the remote position under consideration transmits the following positioning position. a determination signal (triggered by an address signal, as above), from the previous delay such that the M ·: V 30 position determination signal is hit or at least approached by the position determination window. Delay time-. . ·. is obtained, for example, by incrementing the previous delay * · · *. <* t automatically with a predetermined value of the delay change scale.

'' .0 35 '! "! If the positioning signal is not received in the narrow positioning window with the initial delay value, the time intervals between 106280 12 so that the positioning signal is received with this initial value and any delay initial value and end value receiving the positioning signal in this window two separate transmission means or alternately the same transmission means), preferably a period of time not allocated to the central station for receiving the information signals to avoid the possibility of collision between the information signals received by the central station and the positioning signals.

Further, in the case of a two-way transmission in the same transmission medium, this ali-15 period is preferably a period of time allocated for transmission by the central station. The problems of collisions between the information signals transmitted by the central station and the positioning signals transmitted by the remote station can in fact be avoided by selecting the transmission-reception switching elements of the central station to be sufficiently powerful to respond to this station; the level of the received positioning signals does not affect the information signals transmitted by the station.

Further, as shown in Fig. 4, this time slot Te2 assigned to transmission to the central station is preferably a time interval T · V, followed by a narrow positioning window immediately preceding time period Te2.

• * ·: *: 30 • ♦

The initial delay Tri is then preferably selected, as shown in FIG. 4, equal to the length of the transmission period • · · ::: Τ. In this case, the positioning signal is not received at this initial value for any remote station:: 35, in the positioning window, and the delay is modified, as shown in Figure 4, by reducing it from this initial value to the final value Trf.

106280 13

It is also possible to select an initial delay value less than T, in which case the delay is changed by increasing it from this initial value.

A time period containing the respective reference time t1 could also be used for the transmission time period for which the positioning signal would hit the initial and intermediate values of the delay, whereby a narrow positioning window would follow immediately after this time period Tel 10, for example.

Thus, in the case considered, where reverse shifting using the same transmission means is used, the delay change step is preferably further selected to be equal to the width of the narrow positioning window.

In the case shown in Fig. 5, where bidirectional transmission using two separate transmission means is used, the transmission and reception times Te and Tr 20 of the central station shown in the first and second rows of Fig. 4 may extend over the entire ... transmission period T except for a narrow positioning window. nan width.

In addition, the width of the positioning window is preferably '/ ·: variable over time so that it has a first width Tfl during the first time period and a duration of 30 seconds during the second time period. the second width Tf2 being smaller than the first width, and the step of changing the delay, respectively, during the first time period has a first value, i »· '··', which is preferably equal to said first width and a second value during the second period. , which is . . '. Less than the first and preferably equal to said second width, wherein the procedure for each time period is similar to the one considered above for one of the 146280 and the first time period changes to a second time period when the positioning signal is received in the positioning window having said first width.

5

In all the examples thus considered, when a central station detects a positioning signal in a narrow window (or the narrowest window in the last viewed example), it is notified to that remote station 10 the next time it is addressed by a special signaling signal indicating the positioning signal detection. The remote station then sends the final value of the delay to the central station Trf. The exchange can then calculate the desired travel time δΤ, taking into account the selected reference moments, according to the following formula: 2 δΤ * Te + Te - Trf 20 where Te denotes the time received at the exchange after the above calculation and Te denotes the transmission period of the exchange. It will be appreciated that, irrespective of the selected reference times, for calculating the passage time, it is thus necessary according to this method: 25 - that the central station measures the time interval separating the reference time of transmission of the central station information signals. the positioning signal of the remote station • · φ: V 30 has sent a delay after the reference time of the information signals received by this remote station «« · '· /.: * ·., the delay being determined such that the positioning signal is received at that 0 35 - that the remote station determines the final delay value Trf at which the position signal is actually received in this window.

Since the travel time is calculated at the central station, the remote station transmits the value Trf to the central station. For example, the final delay time Trf can be transmitted by means of a special information signal, also called a signaling signal, which is used for uplink transmission.

In all of the examples discussed above, it is further advantageous to use a procedure in which the positioning signal level is changed from an extreme (minimum or maximum) to an intermediate value that varies depending on the remote location being considered and allows the central station to obtain substantially equal levels for all remote stations. .

The direction in which the remote station must change the level of the positioning signal to achieve this is determined, for example, at the central station and is transmitted to the remote station by means of a special level change control signal.

The actual control of the transmission of the positioning signal may be accomplished by any known method not described herein.

Note that the receiver at the central station is preferably selected so that its dynamics is maximized so that it can receive any remote station at any distance from the central station. sent level.

This receiver quality requirement may be higher if the transmission level is changed.

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by increasing the level from the minimum value as if lowering the level from the maximum value.

106280 16

In addition, it should be noted that the detection threshold of the receiver when selecting a positioning signal is advantageously selected to increase the probability of detecting this signal and, when the information signals are detected, relatively higher to optimize the reception conditions of the information signals.

It should also be noted that when the transmission level is changed by lowering the level from the maximum value, this change can be made after the positioning signal has been detected in a narrow (in the latter example narrowest) screening window.

15 It should further be noted that when the transmission level is changed by increasing the level from the minimum value, the level may need to be changed beyond the minimum value not only to achieve a substantially equal level at the central station for different remote stations, 20 but also to detect the positioning signal at the central station. in the narrowest example) in the positioning window. Thus, for a positioning signal to be detected in the • positioning window in question, two conditions must be satisfied <25, the first being that it has been transmitted with sufficient delay, as described above, and secondly, it must be sufficient level. For example, if Φ · · signaling that a positioning signal has not been received in a positioning window indicates that no signal has been detected with a given delay jV and a given level value, the whole or part of the level is systematically examined (e.g. - «· · t '* by incrementing the previous level with a specified value of level« r change step) before possible «, ή' 35 to the next delay value.

• «· I

Claims (5)

106280 1 II <«I * • · · I ·« • • • * I * I * l 4 • «i» I «l« • f • f * · · 1 * • «iw Iff ·« «••. m A method of allocating time slots for transmission in a multipoint point-to-point TDMA multicast system that allows data to be transmitted between a central station (OLT) on the one hand and remote stations (ONT) on the other hand, allocating at least one time slot to each the slots used for transmission from the central station to the remote stations are grouped into downlink frames and the slots used for the transmission from the remote stations to the central station are grouped into uplink frames, characterized in that the beginning of the uplink frames 15 (t "2) at the central station so that the start time (t'2) of these frames is at the central station from the end of the downlink frames (t'1) to To, where To represents twice the travel time between this remote station and the central station a 20 values and thus defines a downlink and a downlink interleave zone (T) at a remote station, whereby slots are allocated so that all coincidences of the slots allocated in the same remote station in the uplink * frame are avoided by said overlapping zone. . • I {• «f The method of claim 1, characterized in that the slots to be allocated to the remote station in the uplink and the downlink frames are allocated sequentially and. the latter being allocated a slot, in the event that the former allocated slot 9 is not within said overlap area, so as to obtain the symmetry of the charges in the uplink and the downlink frames. ; 35 f c c A method according to claim 1, characterized in that, in the uplink 18 106280 and downlink frames, the slots to be allocated are sequentially allocated and the latter to be allocated, provided that the formerly allocated slot is in said overlap area by searching for a slot in said frames. which has not been previously booked and which is different from said time slot in the overlap zone. A method according to claims 2 and 3, characterized in that, in said time slots, the one that is allocated earlier is allocated by looking in said frames for a time slot which is not previously allocated and which differs from said time slot in the overlapping zone. 15 A method according to claims 3 and 4, characterized in that the search is performed by sequentially examining different time slots of said frames. i · • · · t · «« Il 11 i «I I 4 < 4 A «t« f <<• c · «« «t * 106280 19