1. A method for contention resolution in a transmission system (1) having a primary station (2) and a plurality of secondary stations (3-1, . . . 3-n) coupled to the primary station (2), characterised in that Sign-On request messages are being sent by the primary station (2) marking starts of contention periods, numbered i0, 1, 2 . . . , and having period length Pi; that Ni denotes the number of secondary stations (3-1, . . . 3-n) participating at the start of contention period i; that each of a number Mi of the secondary stations (3-1, . . . 3-n) sends a Sign-On response message to the primary station (2) in contention period i, and, after sending, waits a feedback period of length Tfb for a response from the primary station (2); and that save for a possible constant factor an approximation for Mi is given by:
Ni. Pi1(Pi1Tfb) for i1, 2, . . . (1)
such that the respective period lengths Pi are determined based on said approximation for Mi.
2. The method according to claim 1, characterised in that for each i0, 1, 2 . . . , Pi has at least a minimum length Pmin.
3. The method according to claim 2, characterised in that the minimum length Pmin is not or not nearly a divisor of the feedback period Tfb.
4. The method according to claim 3, characterised in that the contention period length Pi, save for a possible constant factor, is defined as:
max Pmin, Ni*Pi1(R*(Pi1Tfb))
where R is the number of contention slots per time unit.
5. The method according to one of the claims 1-4, characterised in that if the number Ni of contending secondary stations (3-1, . . . 3-n) is not known, an a posteriori estimate of the expectation of empty slots within one or more contention periods is used to estimate Ni in equation (1).
6. The method according to claim 5, characterised in that if Ti1e denotes the number of empty slots in an inspection interval having length PiTfb time units, then an a posteriori estimation of the number Ni1 of secondary stations (3-1, . . . 3-n) that is participating at the start of contention period i1, save for a possible constant factor, is given by:
S ln (STi1e) with S(TfbPi1)*R
where R is the number of contention slots per time unit.
7. The method according to claim 6, characterised in that if Ti1e0 then it may be chosen that the a posteriori estimation of the number Ni1 of secondary stations (3-1, . . . 3-n) that is participating at the start of contention period i1 is a multiple A>1 of an earlier estimation, such as the a-posteriori estimation based on the previously inspected interval.
8. The method according to claim 7, characterised in that A2.
9. A transmission system (1) capable of resolving contention in a network by applying the method according to one of the claims 1-8, the network having a primary station (2) and a plurality of secondary stations (3-1, . . . 3-n) coupled to the primary station (2), characterised in that the primary station (2) is arranged for sending Sign-On request messages marking starts of contention periods, numbered i0, 1, 2 . . . , and having period length Pi; that Ni denotes the number of secondary stations (3-1, . . . 3-n) participating at the start of contention period i; that each of a number Mi of the secondary stations (3-1, . . . 3-n) sends a Sign-On response message to the primary station (2) in contention period i and, after sending, waits a feedback period indicated Tfb for a response from the primary station (2); and that save for a possible constant factor an approximation for Mi is given by:
Ni. Pi1(Pi1Tfb) for i1, 2, . . . (1)
such that the respective period lengths Pi are determined based on said approximation for Mi.
10. A primary station (2) for inclusion in the transmission system (1) according to claim 9, and arranged for executing the method according to one of the claims 1-8.
11. A secondary station (3-1, . . . 3-n) for inclusion in the transmission system (1) according to claim 9, and arranged for executing the method according to one of the claims 1-8.
12. Signals for use in the transmission system (1) according to claim 9 to execute the method according to one of the claims 1-8.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. A highly sensitive linear accelerometer for sensing acceleration in a predetermined direction, said accelerometer comprising:
a rigid housing;
a mass;
at least two elastic support members axially aligned in said predetermined direction and attached to opposite ends of said housing and further attached to said mass, said elastic support members suspending said mass within said housing; and
at least a portion of one of said elastic support members comprising a transducer capable of measuring a displacement of said mass within said housing in response to an acceleration along said predetermined direction.
2. The accelerometer of claim 1 further comprising:
a pair of fixed mandrels rigidly attached to opposite ends of said housing; and
wherein said mass comprises at least one floating mandrel and wherein said elastic support members comprise a wrap and wherein said elastic support members are disposed about one said fixed mandrel and said floating mandrel.
3. The accelerometer of claim 2 wherein said mass comprises a pair of floating mandrels and wherein each said elastic support member is disposed about one of said fixed mandrels and one of said floating mandrels.
4. The accelerometer of claim 2 wherein said mandrels and said mass comprise a toroidal shape.
5. The accelerometer of claim 1 wherein at least one of said elastic support members comprises an optical fiber coil.
6. The accelerometer of claim 5 wherein said and wherein said movement induces in said fiber a variation in length corresponding to said movement for interferometric measurement of said variation in length.
7. The accelerometer of claim 1 further comprising an axial alignment assembly attached to said mass limiting movement of said mass in a direction perpendicular to said predetermined direction.
8. The accelerometer of claim 7 wherein said axial alignment assembly comprises a flexure member attached to said mass and said housing allowing axial movement of said mass in said predetermined direction and limits non-axial movement of said mass.
9. The accelerometer of claim 7 wherein said flexure member comprises a diaphragm.
10. The accelerometer of claim 9 further comprising:
a pair of said axial alignment assemblies further comprising an alignment rod wherein said diaphragm is disposed on an end of said rod;
a bore positioned in each end of said housing; and
wherein said diaphragms are captured within said bore about the periphery of said diaphragms.
11. The accelerometer of claim 9 further comprising:
a pair of said axial alignment assemblies, wherein said axial alignment assemblies further comprise an alignment rod wherein said diaphragm is disposed on an end of said alignment rod;
a bore positioned in each end of said fixed mandrels; and
wherein said diaphragms are captured within said bore about an outer periphery of said diaphragms.
12. The accelerometer of claim 8 wherein said flexure member comprises a thin flexible plate wherein at least one pair of said flexure members are attached to said mass at a first end and to said housing at second end.
13. The accelerometer of claim 1 wherein said transducer comprises a strain sensing element.
14. The accelerometer of claim 13 wherein said strain sensing element comprises a fiber optic sensor, a piezo electric device, a PVDF material or a resistive strain gage.
15. The accelerometer of claim 1 further comprising an outer housing having end caps wherein said accelerometer is disposed within said outer housing.
16. A highly sensitive linear accelerometer for sensing acceleration in a predetermined direction, said accelerometer comprising:
a rigid housing;
a mass having an elongated body and a first and second rounded ends;
a first fixed mandrel and a second fixed mandrel, both rigidly attached to said housing a predetermined distance apart;
a first pair of elastic support members axially aligned in said predetermined direction and wrapped around said first fixed mandrel and said first rounded end in a continuous fashion;
a second pair elastic support members axially aligned in said predetermined direction and wrapped around said second fixed mandrel and said second rounded end in a continuous fashion;
at least a portion of one of said elastic support members comprising a transducer capable of measuring a displacement of said mass within said housing in response to an acceleration along said predetermined direction; and
a pair of axial alignment assemblies attached to said mass limiting movement of said mass in a direction perpendicular to said predetermined direction.
17. The accelerometer of claim 15 wherein said first and second fixed mandrels and said mass are comprised of a toroidal shape.
18. An apparatus for vertical seismic profiling of the earth having an x-direction, a y-direction and a z-direction orthogonal to each other, said apparatus comprising:
an optical fiber transmission cable; and
a plurality of linear accelerometers coupled to the earth and in optical communication with said optical fiber transmission cable and positioned in each of the three orthogonal directions, each said linear accelerometer comprising highly sensitive accelerometer for sensing acceleration in a predetermined one of said directions, said accelerometer comprising:
a rigid housing;
a mass; and
at least two elastic support members comprised of optical fiber axially aligned in said predetermined direction and attached to opposite ends of said housing and further attached to said mass, said elastic support members suspending said mass within said housing wherein at least a portion of one of said elastic support members comprises a transducer capable of measuring a displacement of said mass within said housing in response to an acceleration along said predetermined direction and providing a respective sensing light signal indicative of static and dynamic forces at a respective accelerometer location.
19. The apparatus of claim 18 further comprising an optical signal processor connected to said optical transmission cable providing seismic profile information based on said respective sensing light signal.
20. The apparatus of claim 18 further comprising an array of said linear accelerometers coupled to the earth at a plurality of predetermined positions.
21. The apparatus of claim 18 wherein the plurality of accelerometers are coupled to the earth via an oil well casing, a bore hole, or an oil production tube.