CZ321592A3 - Access method in a group switching system, the group switching system and a distant unit for communication on said system - Google Patents

Abstract

A trunked communications system is provided which comprises a central station 11 and a remote unit 10 having means for communication over a TDMA link. Predetermined signalling slots (channel 1 Fig. 3) and predetermined traffic slots (channels 2-5 Fig. 3) are provided for transmission of signalling information and traffic information respectively from the central station to the remote unit and predetermined signalling slots and predetermined traffic slots for communication of signalling information and traffic information respectively from the remote unit to the central station during relatively heavy traffic. The invention provides for permitting the remote unit to transmit signalling information, e.g. an ALOHA access request, on a traffic slot (e.g. channel 5) during relatively light traffic and for receiving the signalling information at the central station during the traffic slot and treating the information as signalling information. <IMAGE>

Description

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BACKGROUND OF THE INVENTION Field of the Invention This invention relates to remote switching systems having a connection over a time division multiple access channel.

The prior art is known

Coupling systems are known to be arranged as follows. The user of the calling unit presses its push-to-talk (PTT) button or performs any other action to initiate a broadcast. The caller sends the ALOHA access request command at the beginning of the time period. The central unit claims and sends to the called unit a command AHOY is to check that the called position before attempting this step is not essential and is therefore called, the unit confirms this command by the start time period. The central unit 1 of the remote access unit for the signaling device receives it, the AHOY field. The purpose of the unit is to indicate a call, indicated by dashed lines, in the next signal to receive confirmation and in the next signaling time period;

sends a go to channel ”(GOTO CHANNEL.) command to the calling unit, specifying the traffic channel to be used. Thereafter, the calling unit transmits on said traffic channel.

Each time period is 15 milliseconds. The frame contains 6 slots and has a duration of 90 milliseconds. Between the inbound frame and the outbound frame there is a small offset, as is typical during operation.

These processes take place in a sequence which will be explained in more detail with a graphical timing of the time periods below with reference to the drawings demonstrating the prior art. The user presses his PTT button at point A. The next incoming signaling time period

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is in time Β. Within this time period, the calling unit Švftj sends an ALOHA request signal. The central unit acknowledges at time C, the called unit acknowledges at time D and z and n t r -a 1; , _ unit transmits go to channel \ time Ε. In the case where the channel is channel 2, the calling unit transmits an operating signal at time F. There is a total delay of 240 milliseconds between the PTT button being pressed and the start of transmission.

This delay in access is undesirable and is particularly difficult when traffic is weak. In low traffic, the user is more likely to expect immediate access to the channel. It is likely to be less patient than knowing or assuming traffic is strong.

SUMMARY OF THE INVENTION

The invention relates to a method of access in a grouped switching system comprising a central station and a remote unit having means for connection over a multi-access TDMA time-division channel, comprising creating predetermined signaling slots and predetermined operating slots of transmitting corresponding signaling information and traffic information from the central station to the remote unit during relatively heavy traffic, providing predetermined signaling time slots and predetermined traffic sections to transmit the corresponding signaling information and traffic information from the remote unit to the central station during relatively heavy traffic, and according to the invention it is allowed to allow the remote unit to transmit signaling information on the traffic slot during relatively low traffic and signaling information e is received at the central station during the operating time period and this information is treated as signaling information.

The invention also relates to a grouped connection system comprising a central station and at least one remote unit arranged to be connected over time access multiple access channel. The remote unit ob2i £ i

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Comprising means for transmitting signaling information at a signaling time point during relatively heavy traffic, and for transmitting signaling information selectively on one signaling period and traffic section during relatively low traffic, and the central unit is provided with means for receiving information during the operational phase; and for handling this information as signaling information, for example by sending acknowledgment and initializing granting access to the channel.

_r . “The central station may initialize granting access to the channel by signaling signaling slots. An advantage of the invention is that in low traffic, the remote unit does not have to wait for its nearest signaling time period before transmitting its channel access request.

Preferably, the remote unit has means for monitoring channel granting commands to other remote units and maintains a record of channel identifications allowed for access. In this way, the remote unit can transmit signaling information on an unallocated traffic channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained in the following description of embodiments with reference to the accompanying drawings, together with the foregoing a more detailed explanation of the problems of the known «art, and in these drawings shows a diagram of FIGs exchanges of commands between the remote unit and the central unit ¹ during the access to the channel · FIG. 2 is a schematic diagram of a typical splitting of downlink and uplink channels in a time division multiple access multiple link system; FIG. units according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It will first be explained in more detail with reference to Figs. 1 and 2 *.

the prior art, with its drawbacks.

A typical protocol for establishing a time division multiple access connection according to the prior art is shown in Fig. 1a. In Fig. 1, inbound transmissions from the calling remote unit (mobile or portable) to the central unit, the middle of the outgoing, are shown on the left. transmission to both the calling unit and the called unit from the called • unit button and on the right side of the incoming unit broadcast. The user of the calling unit presses his or her push-to-talk (PTT) call or performs any other action to initiate the transmission. The calling remote unit transmits the ALOHA Access request command on the signaling time slot. The central unit sends a command to the called unit

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AHOY. The purpose of the command ΑΚΟΥ is to check that the called unit is k ^; available before the call is attempted. This step is not essential and is therefore indicated by dashed lines. The called unit acknowledges this command in the next signaling time period. The central unit receives the acknowledgment and sends a go to channel (GOTO CHANNEL) command to the calling unit along with the indication of the traffic channel to be used in the next outgoing channel signaling time slot. Thereafter, the calling unit transmits on said traffic channel.

The letters on the right side of Figure 1 refer to the situation in Figure 2.

Fig. 2 shows the sequence of situations in the outgoing and incoming connection conditions performed at different frequencies and divided into periods of time. For purposes of illustration, there are five operating slots (channels) for each signaling slice (channel). The channels are numbered 1 to 6. Channel 1 is the signaling channel. Each time period is 15 milliseconds. The frame contains 6 slots and has a duration of 90 milliseconds. There is shown a small offset between the incoming frame and the outgoing frame, as is typical in operation.

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-5 V ^f y SSAX 'kW iťífcM ^ ^ ^ r.TMÍiw .uVjAsii-IR / sUživatel depresses their PTT button at point A. The next inbound signaling time slot is the time Β. In this time period the transmitting requests for access. The central unit acknowledges the called unit confirms in the send command go to the channel in the unit its signal ALOHA š at time C, ase D and the central unit at time E. In the case where the channel at the time press is channel 2, the calling unit sends an operating signal F.- There is a total delay of 240 milliseconds between the PTT buttons and the start of the broadcast.

This access delay is _; As already mentioned briefly in the introduction, it is undesirable and is especially a nuisance when traffic is weak. With a low probability, it expects that a high-traffic user will have immediate channel access. It is likely to be less or assumed * that traffic is heavy.

Figures 3 and 4 show an embodiment of the access method in a grouped connection system according to the invention.

FIG. 3 illustrates a TDMA time division multiple access protocol comprising two transmission links at two different frequencies, e.g., separated by 25 kHz. The outgoing link from the central unit to the remote units is illustrated by the sequence of time periods 30.

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segments 31. In each link ^e j time divided into frames containing time slots 6, the first time slot, the signaling section (channel) and sections 2-6 · the operating portions (channels). Each segment has a duration of 15 milliseconds. The 6-frame frame has a duration of 90 milliseconds.

According to a preferred embodiment of the invention, the connection is established as follows. The remote unit operator presses its PTT button to initiate a call (or performs an equivalent request to transmit) and the remote unit immediately transmits an ALOHA access command to the position (signaling or operation).

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The method by which the remote unit detects which signals are free is described below. This transmission of the ALOHA access command is represented by a gray-denoted traffic channel>

- 6 immediately following PTT. The central unit receives this ALOHA access command and, in the first available time (operating or signaling), the central unit transmits the acknowledgment command and the (C) ΑΓΙΟΥ command. In the example of Fig. 3, these are transmitted on the signaling channel (uplink channel 1).

The called unit transmits its acknowledgment in the first time slot (operation or signaling) available, which in the example shown is a signaling channel (incoming channel 1) The way the called unit knows which time slot is available is the same as for the calling unit and is described below.

The central unit sends a go to channel command. in the next available time slot, which in the example shown is on the uplink channel 3. The central unit instructs the called unit to switch to the selected channel, which, if all channels are free and subject to any additional requirements, may be the channel of the immediately following slot, i.e. the incoming channel 3.

The total time between pressing the PTT button and accessing the traffic channel in the example shown is 75 milliseconds. Although the rotation is the best case, it is a substantial reduction of the 240 milliseconds shown in the worst case of a typical prior art system.

Each remote unit records outgoing connections and receives and decodes commands addressed to other remote units. When the central unit transmits a GOTO CHANNEL command, the remote unit recognizes the command and records the channel that was allowed to access (even if the command is not intended for the remote unit in question). In this way, the remote unit can record the channels that have been allowed to access and the channels that remain free. A channel is recorded as a channel that becomes free, either by accepting a release channel command, or in a system where no such command exists, by recognizing a non-operating characteristic on the channel.

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in this case, channel gv - is registered as a channel that is free. The non-channel characteristic is an unmodulated carrier wave, an empty combination, or no carrier wave at all (depending on the transmitter configuration), but may be any non-operating characteristic; as known in the art.

As the overall traffic on the channel increases, the benefits of ¹¹ inventions decrease. ^When: and '^ tíúdÓů bsázěhýxčtýřl five traffic channels will be better labeled reduced.

Fig. 4 shows details of the remote unit 10. The remote unit comprises an antenna 40 connected to a duplexer 41 which itself is connected to a radio reception circuit assembly 42 and a radio transmission circuit assembly.

The receiving circuit assembly 42 is coupled to the analog-to-digital converter 44 and the transmitting circuit assembly 43 is coupled to the digital-to-analog converter 45. Converters 44 and 45 are the corresponding input and output of a digital signal processor that performs certain functions shown in the figure. Thus, a demodulator 46, a modulator 47, a channel formatter 48, a lookup table 49, a channel encoder 50 is used. errors and encoder 51 speech. The speech encoder 51 is connected to an analog-to-digital converter 52 for two-way connection to a handset. Of course, the speech encoder 51 and the converter 52 may be replaced in the data switching system.

The remote unit is in communication with the central unit 11. When the remote unit (mobile or ¹ portable transmitter and receiver) is energized, it begins to receive transmissions from the central station and synchronizes to pulse groups received from the central station. This is accomplished by a synchronization word received from the central station at the beginning of each time frame. These signals are received through the high-frequency receiving circuitry 42, demodulated in the demodulator 46 and identified in the channel formatter 43 using a synchronization algorithm, well known in the art. The unit remains idle

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active.

The unit receives, deroodulates, and decodes the signal information received from the central unit in signaling time slots. Channel enable commands for other field participants will be included in this information. For example, unit number 20 may be given a go to channel 2 instruction. This instruction is. is identified and in the lookup table 49 is a flag indicating that channel 2 has been granted access and is busy. Lookup table 49 has a flag. input, for each of the five operating channels. When traffic · xo ': v 7' Γ increases and other channels are allowed for access, the grant commands of these access channels are recorded in table49. Where no release channel command is used, i.e., where the channel is released only by stopping the transmission, the unit is determined that there is no other within said time slot; operation, the flag bit in table 49 is deleted. ;

Within a short period of power supply, the unit generates knowledge of channel operation and is stored in Table 49.

As an alternative to tracking, the unit can easily determine if it is to go to the channel if there is traffic on the individual channels. This ensures faster generation of information about existing traffic.

To create table 49, they can. different combinations of commands for channel access and channel release and traffic measurement can be used.

When the operator presses the PTT button (not shown), the formatter 48 examines table 49 to identify a free channel. The channel formatter 48 constructs a telegram for transmission to the central station that begins with the sync word including an access request ALOHA command. The channel formatter 48 releases this telegram to the modulator 47 at the beginning of the first unused slot of the traffic channel as shown in Table 4 9. The telegram is transmitted to the circuit 42 that is powered at the appropriate time and the telegram is transmitted by the antenna 40.

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The central station maintains similar

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, channel search table, and their allocation.

, _λα $ irtg ^ t.7.á ⁴ · the central station is as follows. Central Navenaip for Accepting an Application ⁴ o. ALOHA Approach in the Pole · When 'ALOHA' gets a request for access (assuming there is no collision, ie none).

do not transmit, the request for "ALOHA access simultaneously in the" Λ *? *: "·». "'* * *« "section) / receives so" as a consequence tefreframe ^ decodes from it the identity of the unit requesting access and * v the next immediately following signaling slot (slot JL in FIG. 3) transmits acknowledgment and AHOY message identifying the called unit.

The movable or portable unit receives acknowledgment and AHOY and transmits its acknowledgment for the next available time (operational or signaling). The procedure continues as described below.

When 'checks' increase traffic, units will rely more and more in advance ';' a defined signaling channel for signaling when the channels are saturated, no channels are ^{available for the} assignment and all other signaling information is overrun on the respective incoming and outgoing signaling channels.

Where two remote units simultaneously and interferingly transmit ALOHA access requests at the same time for the same time period and at a signal strength such that one or both signals cannot be regenerated, a collision occurs and one or both units they must retest. The system according to a preferred embodiment of the invention reduces the likelihood of collisions since the signaling transmissions are not all limited to the same signaling channel.

It will be appreciated that the remote unit according to the preferred embodiment of the invention may be in conjunction with another remote unit that performs all of its signaling on the signal.

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time, because the calling entity need not wait for the next, with _SK »/.?52S^^P ^{of manufacture herein} ^ P ^I / ^V; a certain proportion of) cases) will 'ρΈΓ be used ?; divided S® ^ ^ SpTÓvozního '^ channel broadcast its signal ALOHA application JPO ^ -. CT .včas access to the central unit has received a request and ^1' sent a confirmation and communication AHOY in the immediately following uplink time slot. This alone can lead to an exaggerated době-time of up to 150 ms in the example described?

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Γ / -λ Λ ^r in V ^r ~ 'r && ^ -, - k _t Ύ * Lid,! · - ··' * ' ^r ** "*";'' A system comprising a central station (11) and remote 'jed- ¹ Notka (10) having means for connection through a link with more ^^ ^ • ^ Nisoli ífaStupeiřW ^ aS ^ n díiéním' ·· TDMA containing '^ P ^'· ^ CH ^^ ignalizačíií časoyýchi ECI ^ ^ fl ^ f information and operating information

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Claims (4)

Wkwd »wwrt \ ^'u' i, and also signa1i AC nus * Central jjstanice ni / L ..vzdálenou .jednotku a relatively & -create previously learned signaling Ca- ^ Qvýchzúseků ávpředem intended operating portion for the i '"" - - 'i' - '< A corresponding signaling and operating information from a remote unit at a central station during relatively heavy traffic, characterized in that the remote unit is allowed to transmit signaling information over an operating period during relatively low traffic, and the signaling information is received at the central station during an operating time. This information is treated as signaling information. A grouped connection system comprising a central station (11) and at least one remote unit (10) arranged to be connected over a time division multiple access channel, characterized in that the remote unit comprises means for transmitting signaling information at the signaling time point during relatively strong traffic and for transmitting signaling information selectively to. one signaling slot and traffic slot during relatively low traffic, and the central unit is provided with means for receiving information during the slot and handling this information as signaling information. 3. The grouped connection system of claim 2, wherein the central station comprises means for transmitting acknowledgment and initiating granting access to the channel in response to receiving signaling information in the traffic. ζ / Ζ®7κ :: ίΖ _γ · _γ /:/.ζ:';required2Ζϊ;Λ/:λΖ.ϊ; In another name, the remote unit is arranged to connect a plurality of traffic channels and at least a network of a predetermined igniting channel, each channel. sequence -e ^ C ^ ^ gvých sections prokládanýcK časovýmrTúšéky kanálůT znařeriá ^^^ ^ ² in / É'é oKsáft ffJe ^ ^ ^^ řostFedel (49); j ^, ίϊΛϊ! The use of cannula is ^also possible. other remote units, for example. X signal to «operating nu * *. channel 1 u ^ mmb «SS ^ 0.K ^ :. φτ ' »» »* P ¹ ° ^{set off} h; - ,. ^roťtředek P ^ro P., ^y I / ^LAN / 4 = 43βΛ ·» ·%. ··· ^": ..' Λ n 4, and νχλί. · · »Zs« v4 ·% '{& »-» - * -'ΐκ1 £ ΑΛ ^ ττ »nvXottA ™ · nvnv'r> r? Λ Va fm r »n and Ί VAv5 r» <e 'ck etUnHiff 17 (99 ^1-occurring - * before the time slot' a predetermined traffic channel. · 8. A remote unit as claimed in claim 7, wherein the means for monitoring the use of the channels comprises means for identifying the &quot; grant access commands to other remote units &quot;. The remote / unit according to claim 7 or 8, characterized in that the means for. channel usage monitoring includes means for identifying channel release commands adre • Ί · - * «. t> '** V £ M **' * '* - * · - - * - - »V · ** -? * 4 * <f? and r045t *. · and mU MSlfcWr «Á jí jí))) C C. J j j. WMmv> - ~ s Hl λγ * ^ i »e« ό * 1 WiWiSr ^ -gjni tw ,. ·. · · ·. ™ ,,,, -............ 8g ^ S ^ 5 ^ £ ^ B? ^ «S« WfewS®S ^ SsaKO ^ Let ^S '7 T -. & R *, Z «57 v, * \ f 7 'i-ls: 3,' r'r ·, -4τ ^ ' 4 ‘J, .... \! - '«. ..TJll ........ ............. , ..... ,AND WSV, \ - · \ i Γ, U V '· -. $ & 1β ^ 4 7 ^ bZ 1/2 I .¼. o • o c rx rn N CALLING MOBILE CENTRAL STATION CALLED MOBILE PTT ALOHA ACCESS TRAFFIC | AND (B) - ACKNOWLEDGE Γ AHOY ~> W—> -. - --1 ACKNOWLEDGE i D