WO1991006933A1

WO1991006933A1 - Satellite selective call signalling system

Info

Publication number: WO1991006933A1
Application number: PCT/US1990/005596
Authority: WO
Inventors: Robert John Schwendeman; Michael Joseph Deluca
Original assignee: Motorola, Inc.
Priority date: 1989-11-03
Filing date: 1990-10-04
Publication date: 1991-05-16
Also published as: AU6625890A

Abstract

A signalling system provides for efficient reception of message by a plurality of Earth based selective call receivers (30) such as pagers. The signals are transmitted from satellites (10) in orbit above the Earth. Each satellite (10) includes a multiple lobe antenna (14) capable of transmitting messages to a selected portion of the surface of the Earth. Methods for conserving satellite transmission power in the communication of message information are described. Furthermore, a signalling protocol transmitted by the satellite (10) provides for power conservation by Earth based selective call receivers (30). Additionally, a method enabling an area of the Earth to receive messages from multiple satellites is described.

Description

Satellite Selective Call Signalling System

Background of the Invention

This invention generally relates to the area of selective call signalling systems. More specifically, this invention relates to a signalling system of communicating from an orbiting satellite to a plurality of selective call paging receivers, and a method for conserving power at the satellite transmitter and the paging receiver.

With the advent of lower cost satellite transmitters and improvements in satellite technology, it is feasible to construct a system wherein selective call receivers such as pagers directly receive messages from satellite transmitters. In such a system, it is desirable for satellites transmitters to have a power conservation means in order to provide reliable service. Power is collected for satellite transmitters through solar cells and is used for transmitting signals . However, there are portions of the satellite orbit where the Earth shades the solar collectors. Thus power must be stored in batteries aboard the satellite during these intervals. It is desirable to make these batteries as small as possible, thus it is desirable to provide a method of transmitting selective call signals which conserves power. Additionally, paging receivers on the ground must be able to receive satellite signals. Pagers being small and portable also require battery saving methods to provide acceptable battery life. Summary of the Invention

It is therefore an object of the present invention to provide for the aforementioned desires.

It is an object of the present invention to provide a signalling transmitting system suited for a satellite paging system.

It is an object of the present invention to provide a selective call receiver capable of receiving paging signals transmitted in accordance with aforementioned transmitting system.

In accordance with the present invention, a transmitter transmits selective call signals to at least one of a plurality of geographic locations, the transmitter having an antenna having a plurality of lobes, each lobe for transmitting selective call signals within a corresponding geographic location, the transmitter comprising; means for selecting a lobe; and means for transmitting on the lobe selective call signals for the corresponding geographic location.

In accordance with the present invention, a selective call receiver is assigned to a predetermined group of selective call receivers, the receiver comprising: means for receiving a first signal indicative of the occurrence of a message signal having a group signal matching the predetermined group; and means for receiving the group signal at said occurrence.

In accordance with the present invention, a method of receiving a selective call signal by a selective call receiver having a predetermined group, the method comprises the steps of: (a) receiving a first signal indicative of the occurrence of a message signal having a group signal matching the predetermined group; and (b) receiving the group signal within the message signal in response to the first signal.

In accordance with the present invention, a method of transmitting selective call signals to a geographic location from a satellite in earth orbit above the geographic location, the satellite having an antenna for transmitting selective call signals, the antenna having a plurality of lobes each lobe for transmitting selective call signals within a portion of the geographic location, the method comprising the steps of; generating a periodic synchronization signal; transmitting said synchronization signal on a lobe; transmitting on the lobe said selective call signals after the synchronization signal.

In accordance with the present invention, a method of transmitting messages from a plurality of transmitters, each transmitter capable of selectively transmitting in at least one of a plurality of areas, the method comprising the steps of: selecting a first area for transmission by a first transmitter; selecting a second area different from the first area for transmission by a second transmitter; and simultaneously transmitting in the first and second selected area by the first and second transmitters respectively.

Description of the Drawings

Figure 1 shows an orbiting satellite selective call system operating in accordance with the present invention. Figure 2 shows satellite signals transmitted on three lobes and pager battery saving operations in response thereof.

Figure 3 shows the structure of signals transmitted by the satellite. Figure 4 shows a flowchart of a transmitter system including a satellite operating in accordance with the present invention.

Figure 5 shows a selective call receiver operating in accordance with the present invention.

Figure 6 shows a paging system having a plurality of satellites operating in accordance with the present invention.

Description of trie Invention

Figure 1 shows an orbiting satellite selective call system operating in accordance with the present invention. In orbit above the Earth 1, is a satellite 10 which has solar collectors 12 for collecting solar power and storing the resulting electrical energy in internal batteries (not shown) . The satellite receives signals from a ground based transmitter (not shown) and re-transmits the signals using a multi-lobe antenna 1 . The each lobe of the multi-lobe antenna radiates a portion of the Earth. Antenna 14 is shown to have a pattern 20 having nineteen lobes A through S. Alternate embodiments may have more or less lobes. There may exist a certain amount of radiation overlap between lobes. Each lobe of the antenna may be selectively activated. The entire power of the satellite transmitter may be directed on a single lobe or divided among any number of lobes . Each lobe may radiate a large portion of the earth. For example lobe may radiate the entire Baltimore-Washington vicinity.

Within lobe "L" is shown a selective call receiver 30 which receives satellite signals transmitted therein. The selective call receiver includes an antenna 32 and a receiver 34 tuned to receive radio frequency signals from the satellite. The received and demodulated signals are then processed by a decoder 36 which may include a microcomputer. Based on information within the received signals, battery saver 38 activates and deactivates the receiver in order to receive satellite signals and conserve battery power respectively. A description of a pager which battery saves in response to received signals is included within US Patent 4,860,003 to DeLuca et al. and assigned to the assignee of the present invention and is hereby incorporated by reference.

Figure 2 shows satellite signals transmitted on three lobes and pager battery saving operations in response thereof. Signals are divided into frames of equal time, 52, 54 and 56. Each frame potentially begins with a synchronization signal 58, 60 and 62. During the first frame shown in Figure 2, the signal on lobe A, shown by line 70, begins with a signal "SO", which indicates that a command signal "C" follows thereafter. The command signal includes a signal indicating the occurrence of various group signals Gl, G3 and G4 within the forthcoming frames. For the sake of explanation assume that each frame is divided into eight equal portions or blocks. The first portion or block being the synchronization signal and the subsequent seven blocks being data blocks. Thus the command signal occurs within the second block of the first frame. The Gl signal occurs beginning at the third block of the first frame 52 and a signal within the command signal indicates such. Furthermore G3 signals occur beginning at the fifth block of the second frame 54 and G4 signals occur beginning at the sixth block of the of the third frame 56, and signals within the command signal indicates such.

Lines 72,. 74, 76 and 78 indicate battery saving strobes for the groups of pagers which receive signals transmitted on lobe A. A "high" state indicates the receiver is active and the satellite signal is being processed, while a "low" state indicates that power is being conserved by not receiving and processing the satellite signal. Lines 72-78 show that all groups of pagers are receiving and processing the synchronization and control signals during the first frame 52. Gl pagers continue to receive and process the Gl signal after the command signal in response to information therein, while G2, G3 and G4 pagers battery save after the command signal. Within the Gl signal is a synchronization signal, a signal identifying Gl, and a signal indicative of the length of the following message information, in this case, four message blocks. Correspondingly, line 72 shows the Gl pagers receive and processes the message blocks within the first frame. During sync signal 60, Gl and G2 pagers perform receiving and processing operations during at least a portion of the expected sync signal. However, no signal is transmitted within lobe A, and upon detecting the absence of a sync signal, power is conserved. Since the command signal indicated no subsequent signals for Gl and G2 pagers, signal is searched for during interval 60. However, since the command signal indicated that G3 and G4 signals were in subsequent frames, lines 76 and 78 show that G3 and G4 pagers conserve power during interval 60. The command signal indicates that the occurrence of G3 signals begins with the fifth block of the second frame 54. Line 76 indicates that G3 pagers, in response to the command signal begin receiving and processing satellite signals at that time. The G3 signal begins with a synchronization signal followed by a G3 group ID signal and followed by a signal indicating that the next three blocks contain message information for G3 pagers. G3 pagers remaining actively receiving and processing message information during that interval as shown by line 76. During sync signal 62, Gl, G2, and G3 pagers receive and process during at least a portion of the expected sync signal. However, no signal is transmitted within lobe A, and upon detecting the absence of a sync signal, power is conserved. Since the command signal indicated no subsequent signals for Gl, G2, and G3 pagers, signal is searched for during interval 62. However, since the command signal indicated that a G4 signal is in a subsequent frame, line 78 shows that pagers conserve power during interval 62

The command signal indicates that the occurrence of G4 signals begins with the sixth block of the third frame 56. Line 78 indicates that G4 pagers, in response to the command signal begin receiving and processing satellite signals at that time. The G4 signal begins with a synchronization signal followed by a G4 group ID signal and followed by a signal indicating that the next block contains message information for G4 pagers. G4 pagers remaining actively receiving and processing message information during that interval as shown by line 78.

Lines 80 and 90 show satellite signals transmitted on lobes B and C of the satellite respectively and lines 82 and 92 show battery saver strobes of paging receivers receiving satellite signals on lobes B and C respectively. During sync signal 58, lobe B and lobe C pagers receive and process during at least a portion of the expected sync signal. Since the signal is transmitted only within lobe A, lobes B and C pagers receive no signal. Upon detecting the absence of a sync signal, power is conserved as shown by lines 82 and 92.

During sync signal 60, lobe B and lobe C pagers receive and process during at least a portion of the expected sync signal. Since the signal is transmitted within lobe B, lobe C pagers receive no signal. Upon detecting the absence of a sync signal, power is conserved as shown by line 92. However, lobe B pagers receive a SI signal which includes a synchronization signal and a signal indicating that all groups of pagers within the second lobe are to search the next three message blocks for message information. Battery saver strobe of line 82 further indicates that all groups of lobe 2 pagers remain active for the three message blocks in the second frame 54. During sync signal 62, lobe B and lobe C pagers receive and process during at least a portion of the expected sync signal. Since the signal is transmitted within lobe C, lobe B pagers receive no signal. Upon detecting the absence of a sync signal, power is conserved as shown by line 82. However, lobe C pagers receive a S2 signal which includes a synchronization signal and a signal indicating that no message information will be transmitted to lobe C pagers. Battery saver strobe of line 92 further indicates that all groups of lobe C pagers conserve power after interval 62. The S3 signal refreshes the synchronization of pagers during low activity periods. Figure 2 shows that the satellite transmitter transmits selectively on lobes in order to provide battery saving synchronization to pagers, and selectively send messages to all pagers within a lobe, or divide the pagers within a lobe into groups in order that pagers may conserve power while a large amount of information is being transmitted within a lobe. Another embodiment of the present invention could further inform groups of pagers of the frequency upon which group signals are modulated upon, in response to which, the group of pagers would received and processes on the designated frequency in coincidence with the designated occurrence. In varying embodiments of the invention, the relative size a synchronization signal may differ with respect to the size of command, group and message signals. Furthermore, message signals may consist of a number of interleaved data words. Additionally, in the example of the signal shown in the first frame 52 of lobe A, the Gl signal may be eliminated by incorporating necessary information for Gl pagers in the command signal.

The synchronization signals are shown consecutively transmitted in lobes A, B and C. In one embodiment, the synchronizations signals are consecutively transmitted on every lobe of the antenna shown in Figure 1. In such an embodiment, a satellite has a predetermined number of lobes, a pager may, in this example, expect a synchronization signal only every 19 frames. Thus the pager could further conserve power during the intervening 18 frame sync intervals. In yet another embodiment, the synchronization signals could be distributed between lobes as required. Thus a large city could be within a lobe and thus could have synchronization signals and subsequent traffic control signals more often transmitted therein. Pagers in this embodiment would search the beginning of every frame for a synchronization signal as shown by Figure 2. Pagers of either embodiment would attempt to re-acquire synchronization if a synchronization signal were not detected within a predetermined amount of time, wherein the predetermined amount of time may be varied from pager to pager or lobe to lobe and may be programmed into the codeplug of the pager.

In yet another embodiment, multiple lobes may be combined. In such a combination, the total power to the combined lobes would be limited to the transmit power of the satellite, thus the transmission power to a single lobe would be decreased. In order to compensate for the decrease in signal power, the data rate of the transmission may be decreased. Thus for example lobes A and B of Figures 1 and 2 could correspond to areas having large cities, each lobe being independently activated and signals transmitted at a first data rate of 4800 baud. However, lobes C, F, G and K of Figure 1 could correspond to an area having a low population. Thus these lobes could be treated as a single lobe having four times the area and having data transmitted at one fourth the data rate, 1200 baud in the example.

The selective use of antenna lobes by the satellite allows the satellite to conserve power. Only areas requiring messages are transmitted to. Thus the satellite does not expend power transmitting to areas where messages are not to be received by selective call receivers. The focusing of the power allows for less power to be consumed by the transmitter than if the satellite were to cover the entire area of lobes A-S as a single lobe. Furthermore, aside from periodic transmission of synchronization signals, if messages are not to be transmitted, the transmitter may be disabled, thereby conserving additional power at the satellite.

Figure 3 shows the structure of signals transmitted by the satellite. The synchronization signal "S (N) " 100 comprises a bit synchronization portion having a number of bit transitions at the data rate of the signal. The frame synchronization portion comprises a predetermined bit sequence which defines the boundary for the beginning of words within the signal, and a code word indicating the type of synchronization signal. A S(0) signal indicates that a command signal follows, while a S(l) indicates that a message information for all groups on the lobe follows, and a S(2) signal indicates that no message information follows.

The command signal "C" shown by 102, comprises a plurality of group signals followed by corresponding to location signals. In accordance with the embodiment of Figure 2 line 70, the LI signal would indicate that the Gl messages began in the third block after the SO command. The L3 signal would indicate that the G3 messages began in the thirteenth block after the SO signal, and the L3 signal would indicate that the G4 messages began in the twenty second block after the S(0) command. The L signals could alternately indicate the time of the occurrence, the number of bits or words before the occurrence or the portion of a frame of the occurrence of the corresponding group. Further note that the command signal may be extended in length to account for any number of groups by use of a continuation signal within the command signal, or a signal within the S(0) command indicating the length of the command signal.

The group signal "G(N)" 104 precedes each group of messages and includes bit and frame synchronization signals as well as a signal corresponding to the group. Furthermore, a "T" signal indicates the length of the group message transmission following the group signal. The "T" signal may indicate the length of the entire message transmission, the location of the address within the transmission, or the number of addresses within the transmission in an embodiment wherein the addresses are placed in the first portion of the message transmission. The synchronization signals within the group signal allow the groups to occur substantially far from the SO signal by providing a means for pager to re-acquire synchronization to the satellite signal.

The message signal "M" is shown to include two words having either message or address information. In alternate embodiments, any number of words may be contained within the message signal, and the message signal may be interleaved to prevent errors in reception caused by signal fading.

Figure 4 shows a flowchart of a transmitter system including a satellite operating in accordance with the present invention. In step 110 the system is initialized to transmit on the first lobe. Then step 112 determines messages to be transmitted on the selected lobe. Then step 114 determines if no messages are to be transmitted on the selected lobe, in response to which step 116 transmits a S2 signal at the beginning of the frame on the selected lobe. If step 114 is false, step 118 checks if messages within this lobe may be transmitted within the available frame capacity of the lobe. If true, step 120 transmits a SI signal and the messages for the lobe. If step 118 was false, step 122 divides the messages for the lobe into corresponding groups, locates the groups into the current and following frames (thereby reducing the available frame capacity checked in subsequent executions of step 118), generates a control signal indicating the occurrence of the located groups, transmits a SO synchronization signal followed by the control signal and then transmits the messages for the lobe. After completion of either step 116, 120, or 122, step 124 checks if messages for another lobe are to be transmitted in this frame. If true, this would correspond to execution of step 122 in a prior frame, and step 126 switches the antenna to transmit on the other lobe, then transmits the group signal at the occurrence corresponding to the prior control signal and then transmits the messages. Then from either step 124 or 126, step 128 checks if the frame has ended, if not step 126 may again be executed in order to transmit message information on yet another lobe. When the end of the frame is reached, step 130 selects the next lobe, being the lobe subsequent to the lobe selected in the previous execution of step 112, or the lobe requiring the most traffic in another embodiment.

Figure 5 shows a selective call receiver operating in accordance with the present invention. Beginning with step 150, synchronization is acquired using methods known in the art. Step 152 checks if sync has been found, if not step 154 checks if sync has been found in the last N frames, where N is a predetermined value. If not, the pager is out of sync and step 150 is returned to. If sync was not detected in this frame, and was detected less than N frames prior, step 156 is executed, wherein power is conserved until the beginning of the next frame where sync is again searched for in step 152. If sync is found in step 152, step 158 determines if S2 was detected. If true, no message signals follow and step 156 conserves power until the beginning of the next frame. If S2 was not found, step 160 checks for the detection of SI. If detected, step 162 decodes messages found in that frame. If false, SO is detected and the subsequent command signal is decoded. Step 166 checks if a group signal corresponding to a predetermined group signal assigned to the pager is found within the command signal. If not found, there are no messages for that group and step 156 is executed. If the group signal is found, step 168 conserves power until the occurrence of the group and then in step 170 power conservation stops, a signal is again searched for and synchronization is again performed. If synchronization was unsuccessful, step 156 is executed. If sync is acquired, step 172 checks if a group ID corresponding to the predetermined group assigned to the pager is again found. If not found step 156 is executed, if found, step 174 decodes messages after the group signal.

The re-synchronization executed in step 170 allows the group of messages to occur at a time substantially after the occurrence of the command signal. Re-synchronization allows for any data clock drift between the paging receiver and the transmitter to be compensated for. Thus a pager would begin to acquire synchronization prior to the expected occurrence of the synchronization signal in order to account for clock drift.

Figure 6 shows a paging system having a plurality of satellites in orbit above a planet 1, and operating in accordance with the present invention. Each satellite 200 and 300 has a plurality of lobes 210 and 310 correspondingly, and the lobes overlap. In such a system, pagers in one area may receive messages from either satellite, while conserving power in accordance with the prior description. In this embodiment a plurality of satellites transmit synchronization signals in substantial coincidence with each other and simultaneous transmissions do not occur in overlapping lobes of satellite antennas . Pagers begin searching for the synchronization signal for each frame substantially prior to the expected occurrence in order for provide for minor synchronization differences in the signals received from either satellite. An example embodiment includes satellites 200 and 300 which could sequentially transmit from lobes A through S (as shown by Figure 1) wherein satellite 200 transmits on lobe A while satellite 300 transmits on lobe J, thereby preventing the transmission in a common area at the same time by both satellites. In still another embodiment, a complex control system could ensure that both satellites do not transmit into the same area at the same time, thereby permitting satellites to concentrate in areas having a lot of traffic.

In yet another embodiment the overlap between satellites could be substantially less than the overlap shown by Figure 6 thereby allowing the satellites to cover a greater area. This embodiment further provides for continuous coverage of an area when the satellites are not in a geo-synchronous orbit. In this embodiment, an area on the Earth is covered by varying lobes as a satellite moves over the area. As a first satellite leaves the area, a second satellite moves in range of the area and transmits synchronization signals in sync with the first satellite and subsequent messages as previously described. In yet another embodiment, the number of lobes for each satellite may be varied thereby providing for future enhancements in antenna lobe and satellite transmission technology. It should be further appreciated that the invention provides for system having at least one satellite. More satellites may be added to the system, thus more information may be transmitted to each area of the planet, while providing an efficient battery saving means for the ground based receivers .

Examples of contemplated embodiments are illustrated below.

EXAMPLE 1

Assume: • SATELLITE IMPLEMENTATION

• Single Channel System, 20 Watts RF Available

• Preamble = 32 bit 1,0 pattern • Sync Word = 32,21 BCH code word.

• 32 Frame Numbers (#0-31) - can be represented by 5 bits within command • 64 Pager Groups (#0-65) - can be represented by 6 bits within command

• 32 antenna lobes

• In approximately 100 seconds one lobe is replaced by a second lobe.

• Effect of earth rotation is negligible for this example (polar orbit)

• Data Word = 32,21 BCH code word

^• • Interleave Depth = 16 ( Block = 512 Bits) • Bit Rate = 6000 BPS

• N = number of frames per lobe = 2

Therefore: • Block Length = 512 bits

• Frame duration ~ 100 secs/2+32 ~ 1.5625 sec or 9375 bits

• 18 blocks per frame (can be represented by 5 bits within command) of data accounts for 9216 bits after preamble/sync, leaving 159 bits, less 64 for sync, leaving 95 additional bits for more preamble, offset sync B sequences or other uses.

• Transmission time required per total cycle of frames under no traffic is due to preamble & sync only = 64 bits x 32 frames = 2048 bits = .34 sec out of 50 sec = 0.68%

• Avg. Power - no traffic = 0.68% x 20 = 0.136 watts for 50 sec cycle time

• Receiver Time (for 50 sec cycle time) = preamble + sync + uncertainty, wherein the uncertainty corresponds to the amount of time receiver activates prior to beginning of frame in order to account for clock skews and system sync inaccuracies.

=~ 85 bits x 32 = 2720 bits = .453 sec = 0.91% or about 11OX battery saving

• Note that Receiver looks for all frames to allow for movement to another area, shift to another coverage lobe and overlap of two satellite patterns. In many cases, receiver power can be saved by predicting which frames are of interest and only listening only to those frames.

•The other end of the power use spectrum is approximated by 100% Satellite Power with no traffic in 31 lobes, all traffic in one lobe. Then:

»Avg. Sat Power = -100% = ~20W

• Receiver on time approximately equals: 32 frames x 85 bits for preamble searches

+ 1 frame x 1024 bits for command reception + 64 bits + 3 blocks x 512 bits for preamble & sync B and addresses (assuming no more than 1/3 of data is pager addresses, rest being message information)

= 2720 + 1024 + 1600 = 5344 = .891 sec = 1.78% of 50 seconds or about 55X battery saver ratio.

• Traffic capability =~ 18 x 512 x 32 bits per 50 sec =~ 5898 bits/sec at 21 info bits per 32 bit word = 3870 info bits/sec.

EXAMPLE 2

Assume - As in example #1 except:

• 10 channel system - 2 watts each.

• Channels numbered 1 to 10 • Channel # 1 is control channel for system.

• 600 BPS per channel

• Interleave depth = 4

• N = 1

Therefore: • Frame duration =~ 100 sec + 32 = 3.125 sec = 1875 bits or 14 blocks of 128 bits each + 83 bits for preamble (32) + sync (32) + other )19) . • Under no traffic conditions, the transmission time is 64 bits x 32 frames

= 2048 bits = 3.4 sec out of 100 sec = 3.4%

• Average Power (no traffic)

= 3.4% x 2.0 - 0.068 watts (for 100 sec cycle time)

• Receiver Time (with no special prediction capability)

=~ 85 bits x 32 = 2720 bits = 4.53 sec = 4.5% or only = 20 battery saving ratio

• With only sync A satellite power in 31 lobes and all traffic in one lobe:

• Average Sat Power ~ 20 watts

• Receiver On time approximately equals (less actual pages)

32 x 85 bits for preambles + 1 x 1024 bits (or more) for commands + 64 + 2 x 128 bits for addresses = 2720 + 1029 + 320 = 4064 = 6.77 sec =

6.77% of 100 seconds or battery saving ratio =16

• Traffic capability =~ 14 x 128 x 32 bits x 10 channels/100 sec = 5734 bits/sec

In summary of the Satellite Examples 1 & 2, the 6000 bit single channel approach allows better response time and receiver battery saving at comparable total throughputs and transmitter powers than the 600 bit 10 channel approach. Both can use the same basic protocol.

Example # 3 Assume: Terrestrial Land Based Transmitting System

1 Frame number

64 Pager Groups

25 second period

N = 1

Bit Rate = 6000 BPS

Interleave Depth = 4

Transmitter Power & Time not of interest

Therefore: • In the no traffic case

• Receiver Time = preamble + sync + uncertainty

= 85 bits every 25 seconds = 0.0142 seconds per 25 seconds = 0.057% or Battery Saving Ratio = 1765 to 1

• In the full traffic case:

•Average Receiver On-Time = ~ 1 x 85 bits for preamble

+ ~1024 for commands

+ 6 x 128 for addresses

= 1877 bits per 25 sec

= .313 sec per 25 sec = -1.25% or Battery Saver Ratio = ~80

The invention has described by way of example, it is to be understood that numerous modifications may be made to the examples given herein while remaining within the scope of the invention which is defined by the following claims.

Claims

Claims :

1. A transmitter for transmitting selective call signals to at least one of a plurality of geographic locations, the transmitter comprising; means for selecting a geographic location from the plurality of geographic locations; and means for transmitting selective call signals to the selected geographic location.

2. The transmitter according to claim 1 wherein the transmitter is comprised within a satellite in orbit around a planet and the geographic locations correspond to areas substantially on the surface of the planet.

3. The transmitter according to claim 1 wherein said selecting means selects geographic locations in a predetermined sequence.

4. The transmitting means according to claim 1 wherein said selecting means selects the geographic location in response to the amount of selective call signals to be transmitted to each of the plurality of geographic locations .

5. The transmitter according to claim 1 further comprising: means for generating a periodic synchronization signal; wherein said transmitting means transmits one of said periodic synchronization signals to the selected geographic location and transmits the selective call signals substantially thereafter.

6. The transmitter according to claim 5 wherein after the transmission of the selective call signals, said selecting means selects a subsequent geographic location, and said transmitting means transmits a subsequent periodic synchronization signal to the subsequent geographic location.

7. The transmitter according to claim 1 further comprises an antenna having a plurality of lobes, wherein each lobe defines a geographic location, and wherein the selecting means selects a geographic location by selecting the corresponding lobe of said antenna.

8. The transmitter according to claim 1 further comprises a plurality of antennas, wherein each antenna defines a geographic location, and wherein the selecting means selects a geographic location by selecting the corresponding antenna.

9. The transmitter according to claim 8 further wherein at least one of said plurality of antennas is comprised within a satellite in orbit above a planet.

10. The transmitter according to claim 9 further wherein at least one of said plurality of antennas is positioned in substantial proximity with the surface of the planet.

11. A selective call receiver assigned to a predetermined group of selective call receivers, the receiver comprising: means for receiving a first signal indicative of the occurrence of a message signal having a group signal matching the predetermined group; and means for receiving the group signal in substantial coincidence with said occurrence.

12. The selective call receiver according to claim 11 wherein the first signal and the group signal are transmitted to a geographic area of a planet from a satellite in orbit above the planet, and the selective call receiver is located within the geographic area.

13. The selective call receiver according to claim 11 further comprising means for conserving power during an interval after the first signal and prior to the occurrence of the group signal.

14. The selective call receiver according to claim 11 further comprising a means for receiving message signals transmitted after the group signal, wherein the selective call receiver includes a unique predetermined address and said message receiving means detects an address in the message signals matching the predetermined address.

15. The selective call receiver according to claim 11 further wherein the first signal is preceded by a periodic synchronization signal and the selective call receiver further comprises: means for synchronizing to the synchronization signal; and said first signal receiving means receives the first signal in response to the synchronization signal.

16. The selective call receiver according to claim 15 further comprising a means for conserving power for a period corresponding to the period of the synchronizations signal if the synchronization signal is not received.

17. The selective call receiver according to claim 16 further comprising: means for detecting a third signal substantially following the synchronization signal; and means for conserving power for a period corresponding to the period of the synchronizations signal in response to the detection of the third signal.

18. The selective call receiver according to claim 11 further comprising: means for detecting a second signal indicative of a message signal for the selective call receiver substantially following the second signal; and means for receiving and processing the message signal for the selective call receiver substantially following the second signal.

19. The selective call receiver according to claim 11 wherein the first signal is received on a first receive frequency and the first signal further indicates a second receive frequency for receiving the message signal and wherein said receiving means further comprises a means for selecting and receiving the message signal on the second receive frequency in response to first signal.

20. A method of receiving a selective call signal by a selective call receiver being a member of a group of selective call receivers, the group being one of a plurality of groups of selective call receivers, the method comprising the steps of: receiving a first signal indicative of the occurrence of message signals for the group of selective call receivers; and receiving the message signals in response to the first signal.

21. The method according to claim 20 wherein the first signal is preceded by a synchronization signal and the method further comprises the step of receiving the synchronization signal.

22. The method according to claim 20 wherein the first signal occurs periodically and the first signal alternately indicates the absence of a message signal and the method further comprises the step of inhibiting receiving until the next occurrence of the first signal.

23. The method according to claim 22 wherein the selective call receiver consumes power during said steps of receiving and conserves electrical power during the step of inhibiting receiving.

24. The method according to claim 20 wherein the first signal alternately indicates the occurrence of a message signals for the plurality of groups of selective call receivers and the method further comprises the step of receiving the subsequent message signals in response to the first signal.

25. The method according to claim 20 wherein the selective call receiver consumes electrical power during said steps of receiving and further comprises the step of conserving electrical power by inhibiting receiving until the occurrence of the message signal.

26. The method according to claim 20 wherein the first signal may occur at predetermined periods and the method further comprises the step of inhibiting the reception of a subsequent first signal if the subsequent first signal occurs prior to the indicated occurrence of the message signal.

27. The method according to claim 20 wherein the message signal includes a synchronization signal preceding the group signal and the method further includes the step of synchronizing to the synchronization signal.

28. The method according to claim 20 wherein the selective call receiver includes a predetermined address and the message signal includes message information following the group signal and the message information includes an address signal, the method further comprising the steps of: receiving the message information in response to the group signal; determining if the address signal matches the predetermined address; and generating in response thereof, an indication perceivable by the user of the selective call receiver.

29. The method according to claim 20 wherein the first signal is received on a first receive frequency and the first signal further indicates a second receive frequency for the message signals and the method further comprises the step of receiving the message signals on the second receive frequency in response to the first signal.

30. The method according to claim 13 wherein the first signal includes a signal indicative of the baud rate of the message signals and the method further includes the step of receiving the message signals at the baud rate indicated by the first signal.

31. The method according to claim 30 wherein the first signal is transmitted at one of a plurality of predetermined baud rates and the baud rate of the first signal comprises the signal indicative of the baud rate of the message signals.

32. A method of transmitting selective call signals to a geographic location from a satellite in orbit above the geographic location, the satellite having an antenna for selectively transmitting selective call signals within a portion of the geographic location, the method comprising the steps off- generating a periodic synchronization signal; transmitting said synchronization signal and said selective call signals after the synchronization signal within the portion of the geographic location.

33. The method according to claim 32 further wherein the selective call signals are transmitted to a multiplicity of selective call receivers divided into a plurality of groups, the method further comprising the step off- transmitting within the portion of the geographic location, a command signal having a group signal identifying a group of selective call receivers, the group signal further indicating the occurrence of selective call signals for the group; and wherein said step of transmitting selective call signals further includes the step of transmitting at the occurrence indicated by the command signal, selective call signals associated with the group.

34. The method according to claim 33 wherein said step of transmitting selective call signals further includes the step of transmitting a synchronization signal and a group ID signal substantially prior to transmitting the selective call signals associated with the group.

35. The method according to claim 32 wherein the satellite includes an antenna having a plurality of lobes, each lobe for transmitting to a corresponding portion of the geographic location, the method further comprising the steps of: receiving a plurality of selective call signals for transmission in a plurality of geographic areas; determining a lobe corresponding to the area associated with each selective call signal; and wherein said steps transmitting transmit on the lobe associated with the location in response to said determination, and transmits selective call signals associated with the area.

36. The method according to claim 32 wherein said step of transmitting said synchronization signal further comprises the steps of transmitting a first synchronization signal a first portion of the geographic location and transmitting a subsequent synchronization signal on a subsequent portion of the geographic location, wherein the first synchronization signal is not transmitted in the subsequent portion.

37. The method according to claim 36 further wherein the selective call signals transmitted in the first portion of the geographic location are transmitted to a multiplicity of selective call receivers divided into a plurality of groups, the method further comprising the step of: transmitting in the first portion, a command signal having a plurality of group signals, each group signal identifying a group of selective call receivers, each group signal further indicating the occurrence of selective call signals for the group wherein the occurrence of at least one group occurs after said subsequent synchronization signal; and wherein said step of transmitting selective call signals further includes the step of transmitting in the first portion and at the occurrence indicated by the command signal, the selective call signals associated with the group.

38. A method of transmitting messages from a plurality of transmitters, each transmitter capable of selectively transmitting in at least one of a plurality of areas, the method comprising the steps of: selecting a first area for transmission by a first transmitter; selecting a second area different from the first area for transmission by a second transmitter; and simultaneously transmitting in the first and second selected areas by the first and second transmitters respectively.

39. The method according to claim 38 further comprising the step of: selecting the second area for transmission by the first transmitter; inhibiting transmission by the second transmitter; and transmitting in the second area by the first transmitter, wherein transmissions in the second area begin with a periodic synchronization signal transmitted by the corresponding transmitter wherein the synchronization signals of the first and second transmitters are synchronized, thereby producing a periodic synchronization signal in the second area regardless of the source of the transmission.

40. The method according to claim 38 wherein said first transmitter comprises a satellite in orbit above a planet and said first and second areas correspond to areas substantially on the surface of the planet.

41. The method according to claim 40 wherein said second transmitter comprises a transmitter located substantially on the surface of the planet.

42. A multiple area transmitter comprising: first means for transmitting a first information signal at a first data rate to a selective call receiver in a first area; second means for transmitting a second information signal at a second data rate to a selective call receiver in the first area and a selective call receiver in a second area different from the first area.

43. The multiple area transmitter according to claim 42 wherein the first and second signals are preceded by a synchronization signal and the synchronization signal includes a rate signal indicative of the data rate of the following information signal.

44. The multiple area transmitter according to claim 42 wherein the synchronization signal is transmitted at the data rate of the following information signal and wherein the rate signal corresponds to the data rate of the synchronization signal.

45. The multiple area transmitter according to claim 42 wherein the first message signal has an amount of information, said transmitter further comprising: means for determining the amount of information to be transmitted in the first area; and selecting means for selecting said first means if the amount of information for the first area is greater than a predetermined value, and for selecting said second means otherwise.

46. The multiple area transmitter according to claim 42 further comprising: first antenna element for transmitting to the first area; and second antenna element for transmitting to the second area, wherein the first signal is transmitted on the first antenna element and the second signal is simultaneously transmitted on the first and second antenna elements.

47. The multiple area transmitter according to claim 46 wherein the transmitter further includes an antenna having a plurality of lobes wherein the first antenna element corresponds to a first lobe and said second antenna element corresponds to a second lobe.

48. The multiple area transmitter according to claim 46 wherein the transmitter further includes an a plurality of satellites, each satellite having an antenna element, the satellites being in orbit above a planet wherein the first antenna element corresponds to an antenna element of a first satellite and said second antenna element corresponds to an antenna element of a second satellite.

49. The multiple area transmitter according to claim 42 wherein the first signal includes an address signal indicative of the a selective call receiver in the first area and the second signal includes the a first address signal indicative of the a selective call receiver in the first area and a second address signal indicative of a selective call receiver in the second area.