EP0832538A4 - Dual channel dual speed fm subcarrier paging system - Google Patents
Dual channel dual speed fm subcarrier paging systemInfo
- Publication number
- EP0832538A4 EP0832538A4 EP96917201A EP96917201A EP0832538A4 EP 0832538 A4 EP0832538 A4 EP 0832538A4 EP 96917201 A EP96917201 A EP 96917201A EP 96917201 A EP96917201 A EP 96917201A EP 0832538 A4 EP0832538 A4 EP 0832538A4
- Authority
- EP
- European Patent Office
- Prior art keywords
- data rate
- subcarrier
- messages
- transmission
- transmission data
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/02—Terminal devices
- H04W88/022—Selective call receivers
- H04W88/025—Selective call decoders
- H04W88/026—Selective call decoders using digital address codes
Definitions
- This invention relates generally to wireless paging systems and more particularly to a system that effectively varies transmission coverage in different regions by varying the transmitted data rate.
- Patents 4,713,808 and 4,897,835 both by Gaskill
- Patent 5,187,470 King
- pending application serial number 08/046,112 filed 04/03/93 show systems where digital data is transmitted on an FM subcarrier and modulated on a FM baseband. The data is transmitted to a pager receiver that filters the subcarrier from the rest of the FM baseband and then decodes the data on the subcarrier into digitally encoded messages.
- FIG. 1 is a diagram showing two different geographical regions identified as region 12 (city A) and region 16 (city B).
- FM transmitters 14 in both region 12 and region 16 send digitally encoded messages on an FM baseband to portable pagers.
- the transmitters 14 in region 12 are spaced relatively close together in relation to the transmitters in region 16 and therefore, provide denser transmission coverage than the transmitters in region 16.
- each transmitter 14 in regions 12 and 16 has an associated transmission range 18.
- the transmission range is based on a given transmission data rate, transmission power, transmitter height, geographic surroundings, etc.
- the letters "R" represent receivers (e.g., pager receivers) positioned at different locations within regions 12 and 16.
- receiver "R” When receiver "R” is located within range 18 of a transmitter 14, messages can be successfully received from the transmitter. In other words, within range 18 the strength of the transmission signal is sufficient for the receiver to successfully receive messages.
- the transmission range for transmitters 14 extend over substantially the entire area in region 12 (i.e., dense transmission coverage). Thus, the receiver “R” can successfully receive paging messages from almost any location in region 12.
- the transmission range for transmitters 14 in region 16 extend over only a small portion of the region (i.e., sparse transmission coverage). Thus, there are many locations in region 16 where receiver “R” will not be able to successfully receive messages. For example, no transmitter in region 16 has a range 18 that extends to locations 20, 22 or 24. Thus, receiver "R" cannot successfully receive messages in these locations.
- the transmission range 18 can be increased by increasing broadcast power.
- digital messages as described above, are often transmitted on a subcarrier of an FM broadcast channel. Because, the broadcast power for FM stations is often restricted, it is not always possible to increase transmission coverage by increasing the transmitter output power.
- the range within which a receiver can successfully receive signals from a transmitter is varied by changing the transmission data rate.
- the effective transmission range for transmitters is increased in regions with normally sparse transmission coverage to increase the number of locations in the region where signals can be successfully received.
- the transmission data rate is lowered in regions with sparse transmitter coverage lowering the minimal signal strength required by the receiver to successfully receive messages.
- the effective sensitivity of the receiver is increased increasing the maximum transmission range of the transmitter.
- a high data rate is maintained in regions with dense transmitter coverage.
- data can be transmitted at a faster rate allowing for more data capacity.
- the information identifying the different transmission data rates is communicated to the receiver by several different methods.
- the subcarrier frequency and the transmission data rate for different transmitters are transmitted in control packets.
- the receiver decodes subsequent transmitted signals from the identified transmitter at the pre-defined data rate.
- the receiver demodulator contains clock extraction circuitry that automatically locks onto signals at the transmitted data rate.
- the same message is transmitted on two different subcarriers in the same FM channel.
- a first subcarrier carries the message at a relatively high data rate and the second subcarrier carries the message at a relatively low data rate.
- the receiver then demodulates the appropriate subcarrier according to transmission coverage in the given region.
- only one subcarrier on each FM channel carries digital messages while the other subcarrier, if present, may carry non-paging digital data.
- Messages on the single subcarrier are transmitted at either the high or low data rate again according to transmission cover in the region.
- the receiver then demodulates the subcarrier at the transmitted data rate appropriate for the given area.
- different FM channels in the same region contain messages transmitted at different data rates.
- a local list sent by each transmitter indicates the transmission frequencies and data rates at which messages are transmitted from each transmitter in the region.
- the receiver automatically searches for messages at the transmitter frequencies and data rates identified in the local list.
- This invention is particularly useful in a communication system designed to (a) operate on a large number of broadcast stations in a large number of geographical regions and (b) which is designed to transmit information to receivers that can receive signals on either one or two channels of the baseband.
- FIG. 1 is a prior art diagram showing two separate coverage regions of a wireless communication system.
- FIG. 2 is a diagram showing a transmitter having an effective variable transmission range according to the invention.
- FIG. 3 is a diagram showing the system of FIG. 2 in the two coverage regions previously shown in FIG. 1.
- FIG. 4 is a diagram of an FM baseband transmitted from an FM broadcast station including a first subcarrier carrying digital data either at a fast or slow data rate according to the invention.
- FIG. 5 is a diagram of the FM baseband shown in FIG. 4 including an additional subcarrier containing messages transmitted at a second data rate according to another embodiment of the invention.
- FIG. 6 is a diagram showing the possible transmission data rates for messages sent from two different FM stations.
- FIG. 7 is a diagram showing the format for messages transmitted at 19,000 bits per second and 7,000 bits per second.
- FIG. 8 is a detailed diagram of the format for messages transmitted by the system shown in FIG. 7.
- FIG. 9 is a schematic diagram of a transmitter circuit that transmits messages at two different data rates according to the invention.
- FIG. 10 is a schematic diagram of a receiver that decodes messages at two different data rates according to the invention.
- FIG. 2 is a diagram of a system with a variable transmission range that changes according to the transmission data rate.
- the signals 31 are transmitted at a fast data rate of nineteen thousand bits per second (19 kbps).
- Signals 30 are transmitted at a slow data rate of 7 kbps.
- transmitter 28 At a given broadcast power, transmitter height, etc. and at a data rate of 19 kbps, transmitter 28 has a maximum range 18. Thus, receiver 26 must be within range 18 to successfully receive signals from transmitter 28. As described above in FIG. 1 , range 18 may be too small to reliably receive messages in regions with sparse transmission coverage (FIG. 1 , region 16).
- Signal 30 is transmitted at a slower data rate (7 kbps) so that receiver 26 can reliably receive messages over a larger transmission range 32.
- the slower 7 kbps transmission data rate is used to increase transmission coverage in sparce transmission coverage regions.
- Data Rate L low transmitted data rate
- Data Rate H high transmitted data rate
- gain increase in gain attributed to using slower data rate.
- the receiver gain or sensitivity increases by approximately 4.3 decibels. This increased sensitivity allows the transmitter 28 to transmit messages over a larger transmission range 32.
- FIG. 3 shows the effect of varying the transmission data rate according to regional transmission coverage.
- the number of transmitters, the transmitter output power and other physical characteristics for each transmitter in regions 12 and 16 are the same as previously shown in FIG. 1. As described above, there is sufficient coverage in region 12 for the transmitters 14 to operate within the smaller transmission range 18 associated with a 19 kbps transmission data rate.
- the transmitters 28 transmit messages at the slower data rate of 7 kbps providing an increased transmission range 32.
- the increased transmission range 32 allows the receiver “R” to move into almost any location in region 16 and still successfully receive messages from at least one transmitter 28.
- the receiver “R” is now within the transmission range 32 of at least one transmitter 28 when positioned at any of locations 20, 22 or 24.
- the transmission data rate is increased back to 19 kbps.
- the effective transmission range of the receiver then automatically returns back to range 18.
- the receiver then processes data at the faster data rate when increased transmission range is not required.
- FIG. 4 is a diagram showing the spectral components of FM signals used in transmissions of both analog radio station broadcasts and digital pager messages according to the invention.
- Most FM radio stations use the baseband frequencies from 50 hertz (Hz) to 53 kilohertz (kHz) to transmit stereo program material.
- a first channel 38 transmits left plus right channel audio material.
- a channel 40 then transmits left minus right channel audio material.
- the remaining baseband frequencies from 53 kHz up to the legal maximum are typically available for transmission of other data.
- information is transmitted at frequencies up to 100 kHz.
- FM stations are only transmitted at frequencies up to 75 kHz.
- Subcarrier 42 contains a time division multiplexed (TDM) digital message that is transmitted to one or more target receivers.
- Subcarrier 42 has a center frequency at 66.5 kHz and contains data transmitted at a rate of either 19 kbps or 7 kbps.
- the transmitter 28 has a transmission range 18 when messages are transmitted at 19 kbps.
- the signal on subcarrier 42 is transmitted at a slower transmission data rate of 7 kbps.
- the effective transmission range is varied according to transmission coverage in a given region to increase reception reliability.
- data on subcarrier 42 is transmitted to a one-way wireless pager receiver.
- the invention can be utilized in any system used to transmit wireless digital information.
- FIG. 5 shows another embodiment of the invention where the FM baseband previously shown in FIG. 4 contains two subcarriers 42 and 44.
- One of the subcarriers 42 or 44 contains messages transmitted at 19 kbps.
- the other subcarrier contains the same messages transmitted at a slower data rate of 7 kbps.
- the receiver 26 demodulates either subcarrier 42 or 44 according to the transmission coverage in the region where the receiver is currently located. For example, when the receiver is located in region 12 of FIG. 3 (dense transmission coverage), the receiver demodulates the subcarrier carrying the message transmitted at the faster data rate of 19 kbps. When the receiver moves into region 16 of FIG. 3 (sparse transmission coverage), the receiver demodulates the subcarrier containing messages transmitted at the lower data rate of 7 kbps.
- Different transmitters in a given region may also transmit the same message at different data rates. For example, a first transmitter in a given region may transmit messages at a high transmission data rate. A second transmitter located in a more remote part of the same region may broadcast the same message at a slow transmission data rate.
- FIG. 6 shows two FM transmitters 46 and 48.
- the transmitter 46 has a broadcast frequency of 106.5 megahertz (mHz).
- the transmitter 48 has a broadcast frequency at 90.2 mHz.
- the FM baseband for transmitters 46 and 48 each include a subcarrier containing digitally encoded messages 50-56.
- both transmitters 46 and 48 may transmit messages at the fast bit rate as represented by message 50.
- transmitter 46 may have a fast transmission data rate and transmitter 48 may have a slow transmission data rate as shown by message 52 or visa vera by message 54.
- Transmitting messages at both a fast and slow transmission data rate allow faster data communications when the receiver 26 is within a relatively close range of the transmitter. However, when the transmitter is outside of range 18 (FIG. 2), the receiver 26 can still successfully receive messages at the slower data rate. For regions with extremely sparse transmitter coverage, both transmitter 46 and 48 transmit messages 56 at the slow data rate.
- FIG. 7 is a diagram showing the format of the digital messages for both fast and slow transmission data rates.
- a system for encoding and transmitting digital data into control packets, data packets, subframes and master frames at a single date rate is described in Gaskill and is, therefore, not explained in detail.
- Subframe 64 shows the time required to send messages at 19 kbps and subframe 66 shows the time required to send messages at 7 kbps.
- Each bit in subframe 64 extends for a time of approximately 52 microseconds (ms).
- Each bit in subframe 66 extends for a time of approximately 143 ms.
- the packet and subframe format remains the same for messages sent at either high or low data rates.
- present transmitter and receiver systems can be easily adapted to transmit and receive messages at dual data rates.
- the specific transmission data rate can vary according to the transmitter coverage in a given region and varying system requirements.
- FIG. 8 shows one method for identifying different transmission data rates to a receiver.
- Each subframe includes multiple control packets (CTL 0-2) and data packets (DATA 0-1023).
- Multiple subframes are encoded together into a master frame and transmitted on one of the subcarriers 42 or 44 shown in FIGS 4 and 5. Master frames carrying the same data are sent from different transmitters at different time offsets.
- the control packets CTL0-CTL2 for each subframe contain transmitter protocol information 62 that direct the receiver to demodulate messages at the transmission data rate associated with the transmitter.
- the control packets CTL0-CTL2 contain information regarding the subcarrier frequencies and associated transmission data rates for messages transmitted in the data packets DATA 0-1023.
- the receiver decodes messages according to the identified subcarrier frequency and transmission data rate.
- Control packets CTL0-CTL2 also carry a local list 60 containing transmission data rates for other transmitters in the same region.
- the local list 60 contains the broadcast frequency of adjacent transmitters carrying digitally encoded messages, a time offset which indicates the time delay between transmission of master frames, and the subcarrier frequency and data rate at which the message is transmitted by other transmitters.
- the local list notifies the receiver that the current region may have sparce transmission coverage.
- the receiver can locate messages transmitted at the slower transmission data rate to effectively increase transmission coverage.
- FIG. 9 is a detailed schematic diagram of the transmitter 28 shown in FIG. 2.
- Data 75 is first input into a bit rate controller that generates a bit stream at either a fast or slow bit rate according to the required transmission coverage in the region.
- the bit rate controller 77 communicates the bit rate to a control circuit 76.
- a first bit stream 68 having either a fast or slow bit rate is fed into a square wave generator 69.
- a second bit stream 82 having either a fast or slow bit rate is fed into a square wave generator 84.
- the square wave generators 69 and 84 transform the bit streams into a series of square waves that are input into shaping filters 70 and 86.
- Control circuit 76 selects stored filter coefficients 78 for a slow bit rate (e.g., 7 kbps) or stored filter coefficients 80 for a fast bit rate (e.g., 19 kbps).
- the filter coefficients 78 and 80 are selected by the control circuit .76 according to the rate of the bit streams 68 and 82 received from bit rate controller 77.
- Filter 70 is coupled to multiplier 74 and filter 86 is coupled to multiplier 88.
- Multiplier 74 moves the data signal onto a first subcarrier frequency at 66.5 kHz.
- Multiplier 88 moves the data signal from filter 86 onto a subcarrier frequency at 85.5 kHz.
- Square wave generator 69, shaping filter 70 and multiplier 74 are defined as a first transmitter channel.
- Square wave generator 84, shaping filter 86 and multiplier 88 are defined as a second transmitter channel.
- transmitter 28 can transmit messages at either a fast or slow data rate on either the 66.5 kHz subcarrier or the 85.5 kHz subcarrier.
- the transmitter has the flexibility to adapt to different FM baseband constraints in different regions. For example, if the transmitter region has both the 66.5 and 85.5 kHz subcarriers available in the FM baseband, the transmitter can transmit the message at both the fast and slow data rates at the same time or selectively on either subcarrier.
- the transmitter sends messages on a single subcarrier at either the fast data rate or the slow data rate according to regional transmission coverage.
- Information identifying the subcarrier transmission frequency and transmission data rate can be contained in control packets as described above in FIG. 8.
- the receiver contains a clock extraction circuit that identifies the transmission data rate.
- FIG. 10 is a detailed schematic diagram of the receiver 26 (FIG. 2) used for receiving messages at dual transmission data rates.
- the receiver includes a tunable FM receiver circuit 100 that selectively tunes to different FM broadcast frequencies.
- the signal at the tuned frequency is fed into FM decoder 102 extracting the FM baseband shown in FIGS. 4 and 5.
- a finite impulse response (FIR) filter 106 filters the 66.5 Khz subcarrier from the FM baseband and FIR 120 filters the 85.5 kHz subcarrier from the FM baseband.
- Data demodulators 108 and 118 selectively demodulate the signals on the 66.5 Khz subcarrier and 85.5 Khz subcarrier, respectively, at either the low or high bit rate.
- a control circuit 114 decodes information in the control packets that may identify the subcarrier frequency and the associated transmission data rate.
- the control circuit 114 accordingly connects either oscillator 110 or oscillator 112 to demodulators 108 and 118.
- Oscillator 110 is used for demodulating the subcarriers at the low bit rate and frequency oscillator 118 is used for demodulating the subcarriers at the high bit rate.
- the demodulators 108 and 118 contain a clock extraction circuit that identifies the transmission data rate for messages on the two subcarriers. The demodulators then automatically demodulate the subcarriers at the transmitted data rate. By using a clock extraction circuit, the receiver is not required to extract the transmission data rate from the control packets.
- Flag detect circuit 116 decodes the subframes to identify messages directed to receiver 26. Accordingly, receiver 26 decodes the message packets and appropriately displays or processes the data.
- the flag detection circuitry and additional control circuitry is well known and, therefore, not explained in detail.
- the system described above increases communication reliability in regions having different transmitter coverage by automatically varying the transmission data rate. Varying transmission data rate accordingly changes the range in which a receiver can successfully receive messages from a given transmitter.
- the invention can be used in existing digital message formats with minimal changes to the transmitter and receiver circuitry. Thus, the invention is easily incorporated into existing wireless communication systems.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US47715095A | 1995-06-07 | 1995-06-07 | |
US477150 | 1995-06-07 | ||
PCT/US1996/008951 WO1996041489A1 (en) | 1995-06-07 | 1996-06-04 | Dual channel dual speed fm subcarrier paging system |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0832538A1 EP0832538A1 (en) | 1998-04-01 |
EP0832538A4 true EP0832538A4 (en) | 2000-05-10 |
Family
ID=23894730
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP96917201A Withdrawn EP0832538A4 (en) | 1995-06-07 | 1996-06-04 | Dual channel dual speed fm subcarrier paging system |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0832538A4 (en) |
JP (1) | JP3805369B2 (en) |
AU (1) | AU5986096A (en) |
CA (1) | CA2219215C (en) |
WO (1) | WO1996041489A1 (en) |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4646290A (en) * | 1984-08-03 | 1987-02-24 | National Information Utilities Corp. | Data transmission method and apparatus |
US4713808A (en) * | 1985-11-27 | 1987-12-15 | A T & E Corporation | Watch pager system and communication protocol |
EP0327533B1 (en) * | 1986-10-21 | 1993-07-07 | Motorola, Inc. | Radio communication receiver with apparatus for altering bit rate of the receiver |
US4918437A (en) * | 1988-10-13 | 1990-04-17 | Motorola, Inc. | High data rate simulcast communication system |
US5170487A (en) * | 1989-01-19 | 1992-12-08 | Seiko Corp. | Paging system with multiple frequencies and multiple protocols |
US5146612A (en) * | 1989-04-17 | 1992-09-08 | Spingarn James L | Technique for using a subcarrier frequency of a radio station to transmit, receive and display a message together with audio reproduction of the radio program |
US5142692A (en) * | 1989-06-16 | 1992-08-25 | Seiko Corp. | Transmitting information with cut and flip spectrum |
US5262769A (en) * | 1990-04-23 | 1993-11-16 | Reach Electronics, Inc. | Programmed scanning pager receiver |
-
1996
- 1996-06-04 JP JP50139497A patent/JP3805369B2/en not_active Expired - Lifetime
- 1996-06-04 EP EP96917201A patent/EP0832538A4/en not_active Withdrawn
- 1996-06-04 AU AU59860/96A patent/AU5986096A/en not_active Abandoned
- 1996-06-04 CA CA002219215A patent/CA2219215C/en not_active Expired - Fee Related
- 1996-06-04 WO PCT/US1996/008951 patent/WO1996041489A1/en not_active Application Discontinuation
Non-Patent Citations (1)
Title |
---|
ANDERSON H R ET AL: "A TECHNIQUE FOR DIGITAL INFORMATION BROADCASTING USING SCA CHANNELS", IEEE TRANSACTIONS ON BROADCASTING,US,IEEE INC. NEW YORK, vol. BC-27, no. 4, December 1981 (1981-12-01), pages 65 - 70, XP000762733, ISSN: 0018-9316 * |
Also Published As
Publication number | Publication date |
---|---|
AU5986096A (en) | 1996-12-30 |
WO1996041489A1 (en) | 1996-12-19 |
JP3805369B2 (en) | 2006-08-02 |
CA2219215C (en) | 2007-09-25 |
EP0832538A1 (en) | 1998-04-01 |
JPH11507187A (en) | 1999-06-22 |
CA2219215A1 (en) | 1996-12-19 |
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