METHOD AND SYSTEM TO SUPPLY DATA TO THE USERS OF A DECT SYSTEM

Abstract: Method for data transmission in a DECT system including at least one central unit (RFP) and at least one peripheral unit (PP), where the transmission of data between said units is organized in frames having pre-set duration in which a given number of time slots are allocated. The method foresees the low speed data transmission enabling only the field S and the field A of each time slot, disabling at the same time the field B provided for the transmission of data according to the conventional DECT standard. Disabling the above mentioned field B, it is possible to reduce by 70 % (seventy percent) approximately the power required to implement data transmission operations. Therefore, said method is particularly advantageous in whichever "data exchange/data collection" application foreseeing the use of the DECT standard and requiring fixed or mobile low power consumption peripheral stations with local battery supply.

Description: METHOD AND SYSTEM TO SUPPLY DATA TO THE USERS OF A DECT SYSTEM Field of the invention The present invention relates in general to a method for data low speed transmission in the DECT system, and more particularly relates to a method to offer data services to the users of the DECT system. As it is already known, the cordless system, called DECT (Digital Enhanced Cordless Telephone) includes a plurality of radio fixed transreceiver stations, distributed in order to cover the concerned areas and connected to a communication network of the private type (PABX), and portable user sets which connect via radio to the fixed parts and are therefore able to communicate between them and with other fixed users connected to the public network. Connections can be of the voice type or enable data exchange occupying the equivalent of one or more voice channels. A first structure of the DECT network is outlined as an e.iample in Figure 1. It includes groupings of k (in the example shown in the figure k = 4) radio fixed parts RFP preferably connected to branches (in tfcte example 3 branches) formed of connection or dorsal lines L through drop/insert devices DI. Without departing from the scope of the present invention, it results possible to star conriect each RFP station to the CCFP unit, thus eliminating the above mentioned dorsals lines and of course, also drop/insert DI devices. Each fixed part RFP can manage via radio a given number of PP (Portable Part) users, which are generally mobile ones. The branches revert to a transcoder battery TRAS, and this last is connected to the public network PSTN (Public Switching Telephone Network) through a central control fixed part CCFP (Common Control Fixed Part), associated to a switching network or peripheral advanced module MEP. The interface between the CCFP and the DECT network, as far as the voice signal is concerned, typically consists of 64 Kbit/s. The CCFP unit is associated to a battery of transcoders TRAS performing the conversion of the PCM coding on eight bits when used on the PSTN side, in ADPCM coding (Adaptive Differential Pulse Code Modulation), on four bits when used on DECT side. In this way, two 32 Kbit/s channels are grouped on each 64 Kbit s channel. The 2.048 Mbit/s (bi-directional) dorsal connecting the CCFP to the different radio fixed parts RFP supports therefore 48 voice channels plus a pre-set number of synchronization and signalling channels. The area covered by a fixed part or cell is generally rather reduced, reaching coverings even in the range of tenths or hundreds of metres of radius. Typical applications of cordless systems are encountered in industrial installations where they can substitute the laying of a cabled network, in commercial complexes or urban centres, where they can advantageously replace public telephone call boxes and others. The telecommunication network for personal calls is of the digital type. The radio access falls under the FDMA - TDMA - TDD class. The system is of the TDD (Time Division Duplex) type since transmission and receipt do not take place at the same time. More in detail, as shown referring to figure 2, the 10 millisecond basic frame is divided into two halves: in general, during the first 5 ms, the fixed part transmits and portable sets receive (TX DECT half frame for the fixed part, and RX DECT for the portable set), and during the subsequent 5 ms, the reverse operation takes place. Each half-frame consists of 12 time slots of the full type (the system is a TDMA one, due to this reason), each of them consisting of 420 (or 424, according to the case) bits. Time slots are transmitted or received using 10 (or more) different frequencies (the system is a FDMA one, due to this reason) totalling 120 (or more) slots available to the system, which are allocated time by time in order not to create interference problems. In the present description, the terms "data and data services" are referred to the transport of digital signals nor originated by voice, such as files, digital images, alphanumeric messages, video (moving digital images) or in general data suitable to supply multimedia services. Though the DECT system has been conceived also for data exchange between users, its present practical implementations are oriented to the transmission of voice services between the users. Background art For the supply of services offered to the users of the DECT System, solutions have been proposed not resulting satisfactory when the quantity of data to be transmitted is lower than a given extent, for instance in the range of 1-2 Kbit/sec. Works are currently in progress for analogue modems to be used on the DECT system, likewise what happens for the users of the traditional telephone network. This method enables very poor performances in terms of bit rate available to the user, and also the use of analogue modems involves useless analogue/digital conversions to carry a digital signal on a transmission system being already digital in itself. In practice, through said analogue modems, the signal to be transmitted by the user is converted into an analogue signal and sent as voice on the DECT system. This one, in its turn, converts the signal in the digital format to transfer the same, as it were a voice signal and sends it to the network. These useless conversions significantly deteriorate the performances which can be obtained from the system. Solutions have also been proposed, involving the modification of DECT access equipment, or of the Radio Fixed Parts (RFP). In practice, in the solution presently under evaluation, a protected air channel is used, identified as Ip channel, where for the voice application a non protected air channel is used, identified with In channel. The channel protection is referred herein to the errors due to air transmission. The use of the protected channel Ip appears impossible to be proposed, both in terms of efficiency and as for costs, for applications requiring a very low data flow, often mono-directional, and generally associated to a very reduced power consumption of the device generating the same. As said above, in fact, the DECT system has been structured for the exchange of voice signals on the In channel and for data exchange on the Ip channel. However, for applications of the type specified above, where a low speed data transmission is required, the use of the above mentioned Ip channel cannot be proposed in relation to the power budget related to the use of said channel, as it shall appear more clear hereafter, and in relation to efficiency problems considered above. In the Italian patent application no. MI96A 000784 in the name of the same applicant, it was also proposed the modification of the access profile (GAP) of the user terminal PP into a GAP++ profile capable to implement a data transmission on said unprotected In channel, usually provided for the transmission of voice signals. Even this solution, though requiring no modification of RFPs generally foreseen for the voice service to implement said data transmission, requires the installation of an additional server to establish calls to other users, therefore involving costs which do not appear to be justified when the flow of data to be transmitted has a rather poor speed and mainly for applications requiring a drastic limitation of power consumption. There are in fact, number of systems where a low speed data exchange is requested for which the power saving problem is rather stringent. Among these systems we mention for instance data exchange/data collection systems requiring fixed or mobile low power consumption peripheral stations, with local battery supply. The general structure of these systems foresees a given number of fixed or mobile peripheral stations, adapted to collect data through appropriate sensors, connected to a data collection station implementing the "data collection" operation, processing the same and taking possible adequate measures, such as for instance the operation of an alarm or the enabling of an actuator. Said known systems have different limits, among which the need of wire or "conventional" radio connection to the data collection station with high plant costs, mainly due to the laying of cabling or conventional radio infrastructures. Other limits of the known systems lie in the fact that they can be installed only in areas close to an electric power distribution network. This is due to the fact that data transmission equipment involve a power absorption such that their supply through local battery systems cannot be proposed. Objects of the Invention One object of this invention is to implement a method enabling the low speed data transmission on a DECT system. Another object is to implement a method enabling to considerably reduce the power consumption required to implement the above mentioned data transmission. Also, a particular object of the invention is to implement an effective "data exchange/data collection" system to be used where it is not recommended the laying of cables and power availability is very reduced. Summary of the invention The above mentioned objects are acheived trought the method of the present invention consisting in a method for low speed data transmission in a DECT system including at least one radio fixed part and at least one peripheral unit in which data transmission is organized in frames having pre-set duration in which a pre-set number of time slots are allocated, each of said time slots including: a first field containing useful data for the clock and phase recovery; a second field for the signal transmission, a third field for payload transmission, Said method is characterized in that it transmits in a connection oriented modality (c.f.r. ETS 300 175) data in said second field, disabling the third field at the same time. The invention consists also in a system for low speed data transmission on the DECT system of the type including at least one central unit and at least a peripheral unit in which data transmission is organized in frafties having pre-set duration in which a pre- set number of time slots is allocated, each of said time slots including: a first field containing useful data for the clock and phase recovery; a second field for the signal transmission, a third field for payload transmission said second field including in its turn the following sub-fields: a first sub-field consisting of an identification coding of the content of a second subsequent sub-field; a second sub-field where one out of a pre-set number of logic channels is allocated; a third sub-field containing bits for the cyclic redundancy code. Said system is characterized in that it transmits data in said second field, disabling at the same time said third field, after creation of a specific data profile relevant to a data transmission in the connection oriented modality, to which a specific coding allocated in said first sub-field is assigned. The invention finally consists in a "data exchange/data collection" system emitted by fixed or mobile peripheral units and for the enabling of pre-set functions in relation to the value of data emitted by peripheral units, characterized in that said data collection system includes at least a portable part and at least one radio fixed part of a DECT system. The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. Brief description of the drawings The invention, together with further objects and advantages thereof, may be understood with reference to the following description, taken in conjuction with the accompanying drawings, and. in wich: Fig. 1, already described, shows the general architecture of a DECT system; Fig. 2, already described, shows the frame architecture of the DECT system in fig. 1 as well as the detail of one of the 24 time slots of the full type; Fig. 3 outlines a geographical connection system on local scale, aimed at the bidirectional transport of data and voice calls between fixed of mobile peripheral units and at least one management and control central unit; Detailed description of a preferred embodiments. Making reference to Fig. 2, the structure of a DECT time slot shall be now recalled in brief. The time slot includes a field provided for the synchronization data transmission and a field D provided for general data transmission. The first field S is used in particular for the phase recovery and includes two words, in particular a first word formed of a sequence of bits having alternatively logic value one and logic value zero for the clock recovery, and a word characterized in that it has a maximum correlation capability. The data field includes in its turn a field A and a field B. The field A is used for signalling purposes, that is for the transmission of the signal aiming at constructing, maintaining and abating connections. The field B on the contrary is provided for the transmission of actual data, that is the so-called payload. As shown in Fig. 2 as well, the field A consists in its turn of three sub-fields, the first of which is identified by H and is provided for the transport of a header H, the second one identified T or "Tail" is provided for the transport of the data content and the third one is a sub-field useful for error determination, known as CRC or cyclic redundancy code. The header H contains a coding, expressed through three bits, identifying a respective logic channel which, in fact, is carried in the second sub-field T, that is to the sub-field relevant to the content. Finally, the CRC field has the function to highlight if the logic channel transmitted time by time is correct. Among the logic channel carried in the content sub-field T, we can mention for instance the Qt field relevant to system data, the Pt field relevant to paging data, etc. One of said logic channels is in particular the channel Cs which has 2 Kbit s transmission capacity. According to the DECT standard, said Cs channel is provided for the transmission of high level signals, that is third level signals or data. In conclusion, for the transmission of data, the conventional DECT standard foresees the presence of the following data profiles. I) For the transmission of data in connection oriented mode (c.f.r. ETS 300 175), the use of the field B is required, that is for instance the Ip channel, with a potential transmission capacity of 24.6 Kbit/s. II) For the transmission of data in connectionless mode (c.f.r. ETS 300 175), a field only is allowed, for instance for Cs channel transfer, with a potential transmission capacity of 2 Kbit/s. m) Furthermore, in the case of connection oriented data transmission the use of fields A+B is always required even when, following a basic set-up operation, transmision of data is made in field A and B field does not transport valid data. Referring to data profiles under points I) and III), the DECT system foresees a "basic set-up", characterized by the transmission of data on the field A and by the enabling of the whole slot, while another possible set-up form is the so-called "advanced set-up", characterized by data transmission on the field B and by the enabling of the whole slot. In particular the profile Hi) considered above for data transmission, though foreseeing an "idle" condition for the field B, results expensive as for power consumed. In fact, the radio power is essentially coinciding with power consumed when the field B is actually employed (and therefore contains data). Considering that monitoring systems of the type mentioned above making reference to figure 3 operate at best when the transmission is of the connection oriented mode, it is clear that the use of the connectionless mode cannot be proposed. Also data profiles I) and III) cannot be proposed for power-budget reasons. According to the method of the invention, data are transmitted in the above mentioned field A (that is enabling only the field S and the field A), reaching the target to reduce the power consumption required for the transmission of radiofrequency signals, disabling the field B which has no data content. In other words, the method according to the invention foresees the creation of a new data profile with a specific set-up definitely excluding the field B (that is without determining the enabling of radio equipment during the transmission of this field), but continuing to enjoy the benefits deriving from the protected transmission, thanks to the presence of the CRC sub-field of field A. The new set-up - called for instance "low speed set-up" is characterized by data transmission on field A, where only fields S+A are enabled (including the CRC field). In other words, the method according to the invention consists in assigning a specific coding to said "low speed set-up" which is allocated in the sub-field H of field A. The emission of a low speed set-up by the PP, may be considered as a request to the RFP station to which said PP is connected of a new type of set-up (that is presently not provided for by the DECT standard) showing given characteristics, that is request for a physical channel, characterized by the enabling of fields S and A only. The RFP, in response to the detection of said specific coding in said sub-field H of field A, establishes a communication with the portable part PP which transmits only in fields S and A (i.e. the transmitters are not activated during B field transmission). The method according to the invention enables to reduce the power required for the transmission by more than 70%. In fact, as shown always in fig. 2, a DECT time slot includes 32 bits in the field S, 64 bits in the field A and 324 bits in the field B, in addition to the above mentioned 4 additional bits in the CRC field. Not transmitting the 320 bits of the field B, that is not enabling the radio equipment during the transmission of the field B, a power save equal to 324/420, that is 77% approx. is obtained in power budget terms. The invention results therefore being highly advantageous in all the applications where the main constraint'is represented by the reduced availability of power. In addition to the above mentioned power saving, saving of the power related to the processing (at the PP and RFP) of data "potentially" present on the field B has to be considered, which as referred to above is enabled even in idle condition according to the known solutions of the DECT standard. In fact, since the field B foreseen by the standard to establish a data transmission in the connection oriented modality foresees the presence of no. 4 sub-fields and of a same quantity of CRC fields, also the use of a sole sub-field involves the processing of the four CRC fields. According to an additional embodiment (not shown in detail) power consumption can be more minimized, periodically enabling (for instance every 2 hours) the portable parts PP and perform a data transmission ending with the transmission, for instance, of a message indicating the fact that the transmission will be restarted after a pre-set time. In this way only a clock is supplied, while the remaining part of the circuitry is kept unsupplied. The output of the supply should be restarted only after the above mentioned pre-set time is elapsed. It is evident from the above how the invention enable to transform equipment complying with the DECT standard (not falling under the "low power" class) into low power like equipment maintaining the advantages related to a connection oriented data transmission. To give a range of magnitude we point out that low power consumption equipment are considered those characterized by a mono-directional transmission, such as for instance remote controls, etc. The invention is fully compatible with the common functions of the DECT system, that is with the transmission of voice signals as specified below, referring also to figure 3. In fact, when one wants to establish a telephone call through the DECT system, the concerned person will use a portable part PP suitable to emit a set-up request of the type generally foreseen to establish a voice communication. In other words in this case, in said sub-field H a specific coding shall be allocated, which translates into the request to the RFP station to which said PP is connected for a set-up showing the usual characteristics, that is a request for a physical channel characterized by the enabling of all the fields, that is of fields S, A, and B. In this way some portable parts PP can perform a low speed data transmission with the above mentioned advantages referring to the low power consumption, while other portable parts PP (connected or not to the same RFP) can be used to transmit voice signal in a completely conventional way. Fig. 3 outlines a "data exchange/data collection" system availing of the invention in order to establish a local geographical connection system, according to the DECT standard, aimed at bi-directional transport of data and voice communications between fixed peripheral units or mobile peripheral units and one (or more) Control/Supervision Centers. Field sizes (analogue and or digital) are detected through appropriate sensors; measurements made and conditions detected are acquired by a local Data Logger. A multiplexer takes care of the multiplexing of all data logged in a unique data flow launched through the PP unit in the DECT system scope of the invention. Through RFP and CCFP, and subsequently, possibly via switched telephone network, total data consisting of data and voice reach the Control/Supervision Center to enable the total management of the data exchange/data collection system. The bi-directionality of the connection enables also to re-launch data from the center to the periphery in order to perform control operations of the same, enabling for instance regulation elements through actuators. This system can find several applications, in particular where the control of fixed or mobile peripheral units is foreseen by a central unit on local geographical areas (for instance in the urban context, inside buildings, etc.) and in particular in the cases where the peripheral unit is local battery supplied, and therefore with very low power available. It is pointed out that the subject territorial telematic systems involve in general low speed type data transmissions, consistently with the basic method of the invention. The attention is drawn also on the fact that the data exchange/data collection system can integrate, besides connections for data transmission, also connections of PP units for telephone communications making reference to the compatibility of the low speed data transmission with the usual operation methods of the DECT. Therefore, while a particular embodiment of the present invention has been shown and described, it should be understood that the present invention is not limited thereto since other embodiments may be made by those skilled in the art without departing from the scope thereof. It is thus contemplated that the present invention encompasses any and all such embodiments covered by the following claims. In particular the present invention extends to cover any data exchange/data collection application foreseeing the use of the DECT standard and requiring fixed or mobile low power consumption peripheral stations and therefore with local battery supply.

Claims: CLAIMS 1.. Method for the low speed transmission of data in the connection oriented modality in a DECT system including at least one radio fixed part (RFP) and at least one portable part (PP) in which data transmission is organized in frames having pre-set duration in which a pre-set number of time slots are allocated, each of said time slots including: • a first field (S) including useful data for the clock and phase recovery; a second field (A) for the signalling transmission, a third field (B) for payload transmission, said second field (A) including in its turn the following sub-fields: a first sub-field (H) consisting of an identification coding of the content of a second subsequent sub-field (T); a second sub-field (T) where one of a pre-set number of logic channels is allocated; a third sub-field (CRC) containing bits for the cyclic redundancy code, said method being characterized in that it transmits data in said second field (A), disabling at the same time said third field (B); 2. Method according to claim 1, characterized in that it foresees the following steps: creating a new data profile relevant to a connection oriented data transmission adapted to enable said first field (S) and said second field(A) only; creating a specific set-up of said new profile and assigning it a specific coding to be allocated in said first sub-field (H) of the second field (A); supplying at said at least one portable part (PP) said specific coding assigned to said specific set-up; detection by said at least one radio fixed part (RFP) said, specific coding assigned to said specific set-up; establishing a data transmission between said at least one portable part and said at least one radio fixed part (RFP) enabling only said first (S) and second(A) field of each time slot. 3. Method according to the previous claims, characterized in that said data transmission terminates with the transmission of a message giving a command for the restart of transmission operations after a time interval of pre-set duration and in that a clock is associated to said at least one peripheral unit. 4. System for the low speed transmission of data in the connection oriented modality on the DECT system including at least one radio fixed part (RFP) and at least one portable part (PP) in which data transmission is organized in frames having pre-set duration in which a given number of time slots are allocated, each one of said time slots including: a first field (S) containing useful information for the recovery of the clock and of the phase; a second field (A) for the signalling transmission; a third field (B) for the payload transmission, said second field (A) including in its turn the following sub-fields: a first sub-field (H) consisting of an identification coding of the content of a second subsequent sub-field (T); a second sub-field (T) where one out of a pre-set number of logic channels is allocated; a third sub-field (CRC) containing bits for the cyclic redundancy code. said system being characterized in that it transmits data in said second field (A), disabling at the same time said third field (B). 5. System according to claim 4, characterized in that data are transmitted in said second field (A) after creation of a specific data profile relevant to a connection oriented data transmission, to which a specific coding allocated in said first sub-field (S) is assigned. 6. System according to claim 5, characterized in that said at least one portable part (PP) includes means suitable to emit said specific coding assigned to said specific data profile and in that said at least one radio fixed part (RFP) includes means suitable to detect 'said specific coding and enable radio equipment only during the transmission of said first and second fields (S and A) in response to said detection. 7. Data exchange/data collection system adapted to collect and to exchange data emitted by fixed or mobile peripheral units and for the enabling of pre-set functions in relation to the value of a code emitted by peripheral units, characterized in that said data exchange/data collection system includes at least a portable part (PP) and at least one radio fixed part (RFP) of a DECT system. 8. Data exchange data collection system according to claim 7, in which said DECT system includes also: - a transcoder battery (TRAS) to which said at least one radio fixed part (RFP) is connected; - a central control fixed part (CCFP) connected to a switching network, characterized in that said portable part (PP) includes at least a sensor suitable to supply data on one or more parameters and/or an actuator for the enabling of pre-set functions; a data collection unit (CONTROL/SUPERVISORY CENTER) is connected to said switching network. 9. Data exchange data collection system according to claim 8, characterized in that said data collection unit is a personal computer. 10. Data exchange/data collection system according to claims 7 to 9, in which the transmission of data between said portable part (PP) and said radio fixed part is organized in frames having pre-set duration in which a given number of time slots is allocated, each one of said time slots including: a first field (S) including information useful to the recovery of the clock and of the phase; a second field (A) for the signalling transmission; a third field (B) for the payload transmission, said second field (A) including in its rum the following sub-fields: a first sub-field (H) consisting of an identification coding of the content of a second subsequent sub-field (T); a second sub-field (T) where one out of a pre-set number of logic channels is allocated; a third sub-field (CRC) containing bits for the cyclic redundancy code. said data exchange/data collection system being characterized in that it transmits data in said second field (A), disabling at the same time said third field (B). 11. Data exchange/data collection system according to claim 10, characterized in that data are transmitted in said second field (A) after creation of a specific data profile relevant to a connection oriented data transmission, to which a specific coding allocated in said first sub-field (S) is assigned. 12. Data exchange/data collection system according to claim 11, characterized in that said at least one peripheral unit (PP) includes means suitable to emit said specific coding assigned to said specific data profile and in that said at least one radio fixed part (RFP) includes means suitable to detect said specific coding and to enable radio equipment only during the transmission of said first and second field (S and A) in response to the above mentioned detection.

Inventors: DE CAMILLI GIUSEPPE, PROSERPIO VITTORIO, ROSINA GIANCARLO, SALTINI GIORGIO, DE CAMILLI, GIUSEPPE, PROSERPIO, VITTORIO, ROSINA, GIANCARLO, SALTINI, GIORGIO
Applicants: ITALTEL SPA, ITALTEL S.P.A.
Application year: 1997
Main classification: H04B7
IPC codes: H04B7, H04W52, H04W72, H04W74, H04W99