Title of Invention

A LONG RANGE RELAY BASE DECT SYSTEM

Abstract A long range DECT system comprising at least one fixed part (FP) and at least one portable or immobile subscriber terminal (ST) operating in blind-slot mode, characterized by means for modifying the internal transmit sub-frame timing by a predetermined value required for preventing the transmitted signal from ST to FP arriving late in the allotted time slot.
Full Text This invention relates to a long range relay base DECT (digital enhanced cordless telecommunication) system.
The -frequency band allotted to the known DECT system is 1880-1900 MHz band. There airs 10 -frequencies of operation in the 20 MHz with a spacing of 1.728 MHz. In each band the DECT standard employs Time Division Multiple Access (TDMA). The burst rate is 1.152 million bits per second, accommodating 24 slots in repeated -frames of 10 milliseconds each. The communication is Time-Division-Duplex (TDD). The 24 slots in a frame are divided into two groups of 12 slots each, one group for each direction of transmission. The frame duration is 10 milliseconds and a TDD slot-pair is separated by 5 milliseconds. Each subscriber"s terminal (ST), that is, the user"s telephone, transmits only one slot (one of slots 13-24) every frame and receives in a slot 12 slots away, also once for frame. Conversely, the DECT fixed part (FP) transmits to the ST in one of slots 1-12, and receives in a slot 12 slots away from ST. The FP communicates thus with multiple Sis in different slot-pairs.

In the known DECT system, the signal travelling at the speed o-f light will undergo a delay o-f 3.33 micro-second/km and the return delay (two way signal propagation) will therefore be 6.66 micro-second /km.
Guard bits are available -for absorbing the propagation
delay from ST; however, with only 39 bits of guard time to allow for late arrival of the signal at the FP from a distant ST, the maximum range that can be served is a little over 5 km.
In other words, the known DECT system can be used only for a range less than 5 km even if the signal strength is sufficiently high.
We have invented a long range DECT system, that is to say, a DECT system which can operate even when the distance between FP and ST is greater than that which can be handled by the known DECT system. This invention -23J.
is covered by our Patent Application No -ax┬╗/MAS/1997,
Briefly, our abovementioned invention pertains to a

long range DECT system comprising at least one fixed part (FP) and at least one portable or immobile subscriber terminal characterised by means for modifying the internal transmit sub-frame timing by a predetermined value required for preventing the transmitted signal from ST to FP arriving late in the allotted time slot.
The objective of the present invention, however, is to propose a system which can conveniently be rendered operative for longer distances. Thus, in accordance with this invention, a set of DECT fixed parts (FPs) could be located in a town and could serve subscribers in a radius of, say, 25 km or more. In order to have a sufficient signal strength at ST and FP, a line-of sight-link and antennas with sufficient gains are required
overcome this problem, it is advantageous to use a two-hop DECT link as proposed herein.
According to this invention, therefore, a relay base
station (RBS) is proposed and this would enable a two-
hop DECT link installation and provide a range of 25 km or
more in a cost effective manner.
Other objects and advantages of the long range relay base DECT system proposed herein will be apparent from the following further description.
The long range relay base DECT system, according to this invention, comprises a first set of at least one DECT fixed part (FPl) and at least one relay base station (RBS) having at least one fixed terminal (RBST) corresponding to a DECT subscribers" terminal operating in blind-slot mode; means for modifying the internal transmit sub-frame timing by a predetermined value required for preventing the transmitted signal from RBST to FPl arriving late with respect to the allotted time slot; a local base station (LBS) comprising a
-5-

second set of at least one DECT fixed part (FP2) located at the RBS, said FP2 being linked to the REST and also to" at least one portable or immobile subscriber terminal (ST).
In this specification (including the Claims herein) the means for modifying the internal transmit sub-frame timing by a predetermined value required for preventing the transmitted signal from RBST to FF"l arriving late with respect to the allotted time slot are the same means a have been defined and claimed in our Patent Application No355/MAS/1997.
This invention will now be described with reference to the accompanying drawings wherein the single Figure illustrates, schematically, by way of example, the layout of one of possible embodiments of the system proposed herein.
In the drawings, the system proposed herein is illustrated to depict a first set of multiple DECT fixed parts (FPl) and a relay base station (RBS)

having multiple -fixed terminals (RBST) corresponding to DECT subscribers" terminals. The RBST an.d FPl operate in -accordance with our invention covered by our above mentioned Patent Application.
The distance between FPl and RBST will be more than the possible range o-f the conventional DECT system (about 5 km) whereby the transmitted signal -from RBST to FPl does not arrive late with respect to the allotted time slot.
In the drawings a local base station (LBS) comprises a second DECT fixed part (FP2) located at the RBS, said FP2 being linked to the RBST by cable and also to at least one portable or immobile subscriber"s terminal (ST), by a DECT radio link. If FP2 is a standard DECT FP and ST is a standard DECT subscriber"s terminal, the radio range between FP2 and ST and the mode of operation will be the same as that in the known DECT system; however, the combined effect of the FPl, RBST, FP2 and ST will be to provide a long range relay base DECT system which is cost effective and advantageous.

1-f, however, the means for modifying the the internal transmit sub-frame timing, already referred to hereinabove, are included in FP2 and ST, the radio range can exceed 5 km as described in our Patent Application hereinbefore cited.
One of the salient advantages of the system proposed herein is that it will enable provision o-f inexpensive telephones in rural areas.
The terms and evipresaions in this specification are of description and not of limitation, there being no intention of excluding any equivalents of the features illustrated and described, but it is understood that various embodiments of the system proposed herein are possible without departing from the scope and ambit o-f this invention.


We Claim:
l.A long range relay base DECT system comprising a first six of at least one DECT fixed part (FPl) and at least one relay base station (RBS) having at least one fixed terminal (REST) corresponding to a DECT subscribers" terminal operating in blind-slot mode; means for modifying the internal transmit sub-frame timing by a predetermined value required for preventing the transmitted signal from REST to FPl arriving late with respect to the allotted time slot; a local base station (LBS) comprising a second set of at least one DECT fixed part (FP2) located at the RBS, said FP2 being linked to the RBST and also to at least one portable or immobile subscriber terminal 2.A long range relay base DECT system as claimed in Claim 1 wherein the said means for modifying the internal transmit sub-frame timing also comprise like means for preventing the transmitted signal from ST to FP2 arriving late with respect to the allotted time slot.

3. A long range relay base DECT system substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

Documents:

332-mas-1997 abstract duplicate.pdf

332-mas-1997 abstract.pdf

332-mas-1997 claims duplicate.pdf

332-mas-1997 claims.pdf

332-mas-1997 correspondence others.pdf

332-mas-1997 correspondence po.pdf

332-mas-1997 description (complete) duplicate.pdf

332-mas-1997 description (complete).pdf

332-mas-1997 drawing.pdf

332-mas-1997 form-1.pdf

332-mas-1997 form-26.pdf


Patent Number 198261
Indian Patent Application Number 332/MAS/1997
PG Journal Number 20/2006
Publication Date 19-May-2006
Grant Date 16-Jan-2006
Date of Filing 19-Feb-1997
Name of Patentee M/S. INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address IIT P.O MADRAS 600 036
Inventors:
# Inventor's Name Inventor's Address
1 DR. ASHOK JHUNJHUNWALA INDIAN INSTITUTE OF TECHNOLOGY, IIT P.O MADRAS 600 036
2 DR. BHASKAR RAMAMURTHI INDIAN INSTITUTE OF TECHNOLOGY, IIT P.O MADRAS 600 036
PCT International Classification Number H04J 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA