WO1998032242A1

WO1998032242A1 - Method and apparatus for directed simulcast delivery of a data stream in a radio communication system

Info

Publication number: WO1998032242A1
Application number: PCT/US1997/022256
Authority: WO
Inventors: Steven Jeffrey Goldberg; Thomas Casey Hill
Original assignee: Motorola Inc.
Priority date: 1997-01-21
Filing date: 1997-12-02
Publication date: 1998-07-23

Abstract

A method and apparatus locates (404) a subscriber unit (102) for which a message is intended, and adjusts (408) a launch time of a data stream from at least two geographically disparate base sites such that symbols of the data stream will arrive simultaneously at the subscriber unit. The method and apparatus then simulcasts (412) the data stream from the at least two geographically disparate base sites.

Description

METHOD AND APPARATUS FOR DIRECTED SIMULCAST DELIVERY OF A DATA STREAM IN A RADIO COMMUNICATION SYSTEM

Field of the Invention

This invention relates in general to radio communication systems, and more specifically to a method and apparatus for directed simulcast delivery of a data stream in a radio communication system.

Background of the Invention

Prior art paging systems have utilized simulcast transmission for delivery of messages to portable subscriber units. Simulcast transmission produces improved delivery reliability because of directional diversity and a power summation effect that occurs in areas of signal overlap. The recently developed two-way messaging systems generally have not used simulcast transmission for message delivery. Instead, such systems track the location of a subscriber unit operating therein and send a message via a transmitter serving the location. This provides the advantage of frequency reuse in the system, which increases capacity compared to that of a simulcast system. A disadvantage, however, is that without simulcast there is no power summation effect and no directional diversity, and delivery reliability can be compromised.

Thus, what is needed is a method and apparatus that can regain the delivery reliability associated with .simulcast transmission, while retaining the frequency reuse capability of two-way messaging systems. Preferably, the method and apparatus will be cost effective, making use of existing infrastructure without requiring additional transmitters. Summary of the Invention

An aspect of the present invention is a method for directed simulcast delivery of information in a radio communication system. The method comprises the steps of locating a subscriber unit for which the information is intended, and adjusting a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit. The method further comprises the step of simulcasting the information from the at least two geographically disparate base sites.

Another aspect of the present invention is a controller for directed simulcast delivery of information in a radio communication system. The controller comprises an input interface for receiving the information, and a processing system coupled to the input interface for processing the information. The controller further comprises an output interface coupled to the processing system for controlling at least two transmitters to transmit the information. The processing system is programmed to locate a subscriber unit for which the information is intended, and to adjust a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit. The processing system is further programmed to control the at least two transmitters to simulcast the information from the at least two geographically disparate base sites.

Another aspect of the present invention is an apparatus for directed simulcast delivery of information in a radio communication system. The apparatus comprises an input element for receiving the information, and a processing element coupled to the input element for processing the information. The apparatus further comprises an output element coupled to the processing element for controlling at least two transmitters to transmit the information. The processing element is programmed to locate a subscriber unit for which the information is intended, and to adjust a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit. The processing element is further programmed to control the at least two transmitters to simulcast the information from the at least two geographically disparate base sites. Brief Description of the Drawings

FIG. 1 is an electrical block diagram of a radio communication system in accordance with the present invention.

FIG. 2 is an electrical block diagram of a controller in accordance with the present invention.

FIG. 3 is a radio coverage diagram depicting directed simulcast in accordance with the present invention. FIG. 4 is a flow chart depicting operation of the radio communication system in accordance with the present invention.

Detailed Description of the Drawings

Referring to FIG. 1, an electrical block diagram of a two-way messaging system in accordance with the present invention comprises a plurality of subscriber units 102, which communicate by radio with a fixed portion of the radio system, comprising a plurality of base stations 104 and a plurality of output controllers 110. The base stations 104 are coupled via communication links 106 to the plurality of output controllers 110 for control by and communication with the plurality of output controllers 110 utilizing well-known techniques. The base stations 104 can comprise collocated transmitters and receivers, transmitters only, or additional base station receivers only, as necessary to meet system radio frequency (RF) coverage requirements. An example of a receiver-only base station is the base station 105. The output controllers 110 are coupled to a plurality of home controllers 120 via communication links 122, 124, and via a conventional communication network 108 for receiving selective call messages from the home controllers 120. The home controllers 120 and the output controllers 110 preferably communicate by utilizing a well-known protocol, e.g., the Telocator Network Paging Protocol (TNPP), the Wireless Messaging transfer Protocol (WMtp™), or the InterPaging Networking Protocol (IPNP). It will be appreciated that, alternatively, ones of the home controllers 120 and ones of the output controllers 110 can be collocated. The home controllers 120 are preferably coupled via telephone links 126 to a public switched telephone network (PSTN) 112 for receiving the messages from message originators utilizing, for example, a telephone 114 or a personal computer 116 to originate the messages. It will be appreciated that, alternatively, other types of communication networks, e.g., packet switched networks, local area networks, and the Internet can be utilized as well for transporting originated messages to the home controllers 120. The hardware of the home controllers 120 is preferably similar to the Wireless Messaging Gateway (WMG™) Administrator! paging terminal, while the hardware of the output controllers 110 is preferably similar to that of the RF-Conductor!™ message distributor, both manufactured by Motorola, Inc. of Schaumburg, IL. The hardware of the base stations 104 is preferably similar to that of the Nucleus® Orchestra! transmitter and the RF-Audience!™ inbound base receiver manufactured by Motorola, Inc. It will be appreciated that other similar hardware can be utilized as well for the home controllers 120, the output controllers 110, and the base stations 104.

The protocol utilized for transmitting the messages between the base stations 104 and the subscriber units 102 is preferably similar to Motorola's well-known FLEX™ family of digital selective call signaling protocols. These protocols utilize well-known error detection and error correction techniques and are therefore tolerant to bit errors occurring during transmission, provided that the bit errors are not too numerous in any one code word. It will be appreciated that other similar messaging protocols can be used as well. Referring to FIG. 2, an electrical block diagram depicts the output controller 110 in accordance with the present invention, comprising a conventional input interface 202 for receiving information through the home controller 120 and the communication network 108. The output controller 110 further comprises a processing system 204 coupled to the input interface 202 for processing the information. The output controller 110 also includes a conventional output interface 206 coupled to the processing system 204 for controlling at least two transmitters of the base stations 104 to transmit the information using well-known techniques for transmitter control. The processing system 204 comprises a conventional processor 208 and a conventional memory 210 programmed with software elements for controlling the processing system 204 in accordance with the present invention. The software elements include a message processing element 212 for processing the information, and a location database 214 for storing the locations of semi-fixed subscriber units. Semifixed subscriber units include, for example, units residing in a single building all day long. The software elements further comprise a subscriber unit tracking element 216 for programming the processor 208 to track mobile subscribers as they move about the system. Tracking can be done by a number of conventional techniques, including subscriber unit zone registration and transmitter color code reporting. In addition, the software elements include a delay adjustment element 218 for adjusting a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the targeted subscriber unit 102. The software elements further comprise a power equalizing element 224 for programming the processor 208 to adjust the transmitted power from the at least two transmitters such that substantially equal signal power is received from each transmitter by the subscriber unit. The software elements also include an antenna aiming element 220 for programming the processor 208 to aim the beams of at least two adjustable beam antennas at the targeted subscriber unit 102 so that the message can be simulcast to the subscriber unit 102. It will be appreciated that, alternatively, the functions of some of the software elements, e.g., the location database 214 and the subscriber unit tracking element 216, can be performed by the home controller 120 as well. It will be further appreciated that it is not necessary to use all of the software elements to obtain an improvement. For example, a system that has omnidirectional antennas can still obtain beneficial results by adjusting the differential delay of the signals representing the information from the at least two geographically disparate base sites such that the signals will arrive in synchronism at the targeted subscriber unit 102. Referring to FIG. 3, a radio coverage diagram 300 depicts directed simulcast in accordance with the present invention. First and second transmitters 302, 304 located at geographically disparate base sites are coupled to adjustable beam antennas having their beams 308, 310 aimed at a targeted subscriber unit 306. In addition, the transmitted power of the transmitter 302 has been reduced so that the two transmitters 302, 304 deliver substantially equal power to the targeted subscriber unit 306. This arrangement advantageously produces a more reliable signal at the targeted subscriber unit 306 than would be produced by a single transmitter operating with an omnidirectional antenna. Preferably, the adjustable beam antennas are similar to the switch-beam antennas described in "The Capacity Enhancement of the DCS network by the use of Switch-beam Antennas", Fehri Benhamida and Jean-Franςois Sante, 1996 5th IEEE International Conference on Universal Personal Communications, pp. 463-467, USA.

Referring to FIG. 4, a flow chart 400 depicts operation of the radio communication system in accordance with the present invention. The flow chart 400 begins with information being received 402 for one of the subscriber units 102. In response, the system determines 404 the location of the subscriber unit 102, using the appropriate one of the location database 214 and the subscriber unit tracking element 216. The system then determines 406 the base sites that can reach the subscriber unit 102. The processing system 204 then accesses the delay adjustment element 218 to adjust 408 the differential delay to synchronize the signals from the base sites at the subscriber unit 102. In a store-and-forward data communication system, for example, the differential delay can be easily adjusted by controlling the launch time for beginning transmission from each base site. The processing system 204 also preferably accesses the power equalizing element 224 to adjust 409 through well-known techniques the output power transmitted from each of the base sites to equalize the power received from each by the subscriber unit 102. The processing system 204 then preferably accesses the antenna aiming element 220 to aim 410 the beams of the base site antennas at the subscriber unit 102. The message is then simulcast 412 from the base sites, thereby advantageously improving the delivery reliability.

A similar technique is used to improve the reliability of reception of a response from the subscriber unit 102. To better receive 414 the response from the subscriber unit 102, the beams of the base site receiver antennas are aimed at the subscriber unit 102. The received signals are then adjusted 416 by the processing system 204 to equalize the transmission delays between the subscriber unit 102 and the base sites. The adjusted received signals are then combined 418 using well-known techniques to derive the response. A simple way of combining the signals is to decode the signals at the base sites and then use conventional error detection and correction techniques to determine which data to keep and which to discard. Alternatively, the received analog signals can be returned to a central location where they are combined and then decoded to derive the data.

While by way of example the foregoing has described a store-and- forward data embodiment, it will be appreciated that the present invention can be applied as well to a real-time or isochronous system such as a two-way voice communication system. For such systems the differential delay can be controlled by conventional adjustable delay elements. It should be clear by now that the present invention provides a method and apparatus that can regain the delivery reliability associated with simulcast transmission, while retaining the frequency reuse capability of two-way messaging systems. The method and apparatus are cost effective, making use of existing infrastructure without requiring additional transmitters. It will be appreciated that the present invention can significantly reduce simulcast differential delay, thereby advantageously enabling use of a faster data rate than would otherwise be possible with simulcast. In addition, the present invention can achieve coverage at somewhat lower power levels than required for single- transmitter directed transmission. Lower power produces lower interference, and thus enables increased density of frequency reuse.

While the foregoing has disclosed by way of example an embodiment in accordance with the present invention, it will be appreciated that many alternative embodiments in accordance with the present invention may occur to one of ordinary skill in the art, given the teachings of this disclosure. Consequently, the scope of the invention is delimited only according to the following claims.

What is claimed is:

Claims

1. A method for directed simulcast delivery of information in a radio communication system, comprising the steps of: locating a subscriber unit for which the information is intended; adjusting a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit; and simulcasting the information from the at least two geographically disparate base sites.

2. The method of claim 1, further comprising the step of adjusting transmitted power from the at least two geographically disparate base sites such that substantially equal signal power is received from each base site by the subscriber unit.

3. The method of claim 1, further comprising the step of aiming at least two antenna beams at the subscriber unit, the at least two antenna beams originating from the at least two geographically disparate base sites.

4. The method of claim 1, wherein the subscriber unit has a semi-fixed location, and wherein the locating step comprises the step of locating the subscriber unit through information programmed into a database.

5. The method of claim 1, wherein the subscriber unit is mobile, and wherein the locating step comprises the step of locating the subscriber unit through information determined dynamically as the subscriber unit moves about the radio communication system.

6. The method of claim 1, further comprising the steps of: receiving a response from the subscriber unit at at least two geographically disparate receivers; and combining signals received at the at least two geographically disparate receivers to derive the response.

7. The method of claim 6, wherein the combining step comprises the step of adjusting the signals received to equalize transmission delays encountered in receiving the response.

8. A controller for directed simulcast delivery of information in a radio communication system, the controller comprising: an input interface for receiving the information; a processing system coupled to the input interface for processing the information; and an output interface coupled to the processing system for controlling at least two transmitters to transmit the information, wherein the processing system is programmed to: locate a subscriber unit for which the information is intended; adjust a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit; and control the at least two transmitters to simulcast the information from the at least two geographically disparate base sites.

9. The controller of claim 8, wherein the processing system is further programmed to adjust transmitted power from the at least two geographically disparate base sites such that substantially equal signal power is received from each base site by the subscriber unit.

10. The controller of claim 8, wherein the processing system is further programmed to aim at least two antenna beams at the subscriber unit, the at least two antenna beams originating from the at least two geographically disparate base sites.

11. The controller of claim 8, wherein the subscriber unit has a semi-fixed location, and wherein the processing system is further programmed to locate the subscriber unit through information programmed into a database.

12. The controller of claim 8, wherein the subscriber unit is mobile, and wherein the processing system is further programmed to locate the subscriber unit through information determined dynamically as the subscriber unit moves about the radio communication system.

13. The controller of claim 8, wherein the processing system is further programmed to: receive a response from the subscriber unit at at least two geographically disparate receivers; and combine signals received at the at least two geographically disparate receivers to derive the response.

14. The controller of claim 13, wherein the processing system is further programmed to adjust the signals received to equalize transmission delays encountered in receiving the response.

15. An apparatus for directed simulcast delivery of information in a radio communication system, the apparatus comprising: input means for receiving the information; processing means coupled to the input means for processing the information; and output means coupled to the processing means for controlling at least two transmitters to transmit the information, wherein the processing means is programmed to: locate a subscriber unit for which the information is intended; adjust a differential delay of signals representing the information from at least two geographically disparate base sites such that the signals will arrive in synchronism at the subscriber unit; and control the at least two transmitters to simulcast the information from the at least two geographically disparate base sites.

16. The apparatus of claim 15, wherein the processing means is further programmed to adjust transmitted power from the at least two geographically disparate base sites such that substantially equal signal power is received from each base site by the subscriber unit.

17. The apparatus of claim 15, wherein the processing means is further programmed to aim at least two antenna beams at the subscriber unit, the at least two antenna beams originating from the at least two geographically disparate base sites.

18. The apparatus of claim 15, wherein the subscriber unit has a semi-fixed location, and wherein the processing means is further programmed to locate the subscriber unit through information programmed into a database.

19. The apparatus of claim 15, wherein the subscriber unit is mobile, and wherein the processing means is further programmed to locate the subscriber unit through information determined dynamically as the subscriber unit moves about the radio communication system.

20. The apparatus of claim 15, wherein the processing means is further programmed to: receive a response from the subscriber unit at at least two geographically disparate receivers; and combine signals received at the at least two geographically disparate receivers to derive the response.

21. The apparatus of claim 20, wherein the processing means is further programmed to adjust the . signals received to equalize transmission delays encountered in receiving the response.