Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1998-02-10
2001-08-07
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Interference or noise reduction
C455S059000, C455S059000
Reexamination Certificate
active
06272190
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of one and two-way wireless information transmission having a high rate of information transmission, a low error rate of transmission and transmission with low radiated power, transmitting circuitry for encoding and transmitting the information, receiving circuitry for receiving and decoding the information, a receiver and transceiver using the receiving circuitry, a transceiver using the transmitting circuitry, and a system including the transmitting and receiving circuitry.
BACKGROUND ART
A. One-Way Wireless Transmission
There is a movement in the wireless industry towards providing more than simple numeric telephone number messages. These alphanumeric messages are typically originated from personal and office computers and sent to the wireless transmitting system via a telephone network. These messages are received by the messaging system controller (paging terminal) and processed for transmission via a radio transmitting system.
E-mail services have gained tremendous popularity and it is predicted that the current more than 17 million electronic mail (E-mail) subscribers will grow to 53 million by 1995. The average E-mail message is approximately 450 characters in length and 5 to 8 messages are sent each working day.
Personal computers have become far more compact in size permitting them to “move” with the person verses remaining in a fixed location. It is predicted that within the next few years, the majority of the personal computers will be less than 8 pounds in weight making them extremely convenient as a “portable office”. This will make wireless communications a media of choice to accommodate portable office computers to receive information services and E-mail messages.
This places an extreme burden on the existing radio infrastructure that is allocated for messaging services. Currently, most metro area paging systems operating in the 150 and 450 MHz. radio bands are operating at or near full capacity accommodating current numeric paging subscribers. There is not adequate reserve air time available to accommodate alphanumeric information and E-mail services.
Nine hundred MHz. authorizations are currently available for local and regional paging implementation. However, at the current protocol speeds and the projected growth rates, the national channels will undoubtedly reach saturation within the next few years. Currently, one or more of the 900 MHz. nationwide paging channels are close to such a saturation. There is a pressing need to increase the air time efficiency of these radio paging systems.
Furthermore, U.S. Pat. Nos. 4,849,750, 4,851,830, 4,853,688, 4,857,915, 4,866,431, 4,868,562, 4,868,558, 4,868,860, 4,870,410, 4,875,039, 4,876,538, 4,878,051, 4,881,073, 4,928,100, 4,935,732, 4,978,944, 5,012,235, 5,039,984, 5,047,764, 5,045,850, 5,052,049, 5,077,834 and 5,121,115 disclose a frequency agile information transmission network and frequency agile data receivers. The above-referenced patents are incorporated herein by reference in their entirety.
U.S. patent application Ser. No. 07/702,939, now U.S. Pat. No. 5,436,960, filed May 20, 1991, entitled “Electronic Mail System with RF Communications to Mobile Processors”; U.S. Ser. No. 702,319, filed May 20, 1991, entitled “Electronic Mail System With RF Communications to Mobile Processors Originating From Outside of the Electronic Mail System” (now abandoned), U.S. Ser. No. 08/247,466, now U.S. Pat. No. 5,438,611 filed May 23, 1994, entitled “Electronic Mail System With RF Communications to Mobile Processors Originating From Outside of the Electronic Mail System and Method of Operation Thereof”; and U.S. Ser. No. 07/702,938, now U.S. Pat. No. 5,479,472, filed May 20, 1991, entitled “System for Interconnecting Electronic Mail Systems by RF Communications,” disclose a system for linking an electronic mail system to portable computers using one-way wireless transmissions which may use the network and receivers disclosed in the aforementioned patents. These applications are incorporated herein by reference in their entirety.
Collectively, the above improvements utilizing the existing 150 and 450 MHz. radio messaging infrastructure will produce a significant reduction in the message delivery cost to the wireless subscriber. The cost to deliver a 450 character message with the system described in the above-referenced patents has been projected to be approximately 65¢ versus $1.50 for a 50 character message the industry is currently offering subscribers. This significant cost reduction would further enhance the growth rate of the wireless information and E-mail service industry.
Furthermore, recently reallocated narrow band spectrum in the 220 MHz. radio messaging infrastructure is applicable to local and national data transmission for applications such as electronic mail. However, the narrow bandwidth of the channels in the 220 MHz. radio infrastructure does not support high data throughputs with prior art data protocols.
Adequate reserve radio spectrum is available in the 150 and 450 MHz. radio bands in the form of IMTS mobile channels that have been authorized for one- and two-way information transmission to transmit data and E-mail. However, a more reliable one-way messaging protocol is needed to accommodate the need for information and E-mail services. An additional requirement for a more air time efficient (faster) message protocol exists.
The POCSAG protocol was originally authored by the British Post office code Standardization Advisory Group. It was primarily developed for “tone only” or “semi-synchronous paging format”. Unlike a synchronous paging format that must be transmitted continually to maintain synchronization of all the paging receivers, the POCSAG protocol is somewhat asynchronous in the respect that it only needs to send a radio signal when messages are about to be delivered. However, a POCSAG protocol transmission is extremely sensitive to atmospheric fades which are discussed below. If a three bit error exists in a transmission of information to a POCSAG protocol receiver, the BCH error correction code of the frames may be ineffective to prevent the transmission synchronism between the transmitter and receiver clock from being lost which results in a failure to complete the transmission of the information to the receiver and the receiver reverting into a scanning mode to attempt to lock onto a new transmission containing its identification code. A three bit error is produced by a fade in reception level below the detection level of the receiver for a time interval such as 2 to 4 milliseconds for 1200 and 512 baud data rates respectively.
To gain insight as to the POCSAG protocol, reference is made to
FIG. 1
for the following explanation. A POCSAG protocol frame set consists of a PREAMBLE, a SYNC signal, and eight frames that are subdivided into two code words each. POCSAG protocol pagers are synchronous in the respect that once they detect the PREAMBLE and synchronize on the SYNC code word, they only then search for a message in their respective frame. If capcode ID numbers are consecutively assigned, the page is automatically assigned to a respective frame. Taking the binary equivalent of the last three digits of the ID of the pager, it is possible to determine in which one of the eight frames a respective pager would be located.
The POCSAG protocol pager is continually sampling the radio channel to look for its PREAMBLE. The PREAMBLE is typically 1.125 to 3 seconds in duration, and consists of an alternating string of ones and zeros sent digitally. When the pager samples the radio channel and determines the PREAMBLE string, it remains on and searches for the SYNC signal. The SYNC signal is actually a 62.5 millisecond code word that transmits a fictitious address to which the pagers respond. It is an unused address, and therefore does not cause falsing (erroneous turn on) of other pagers. Upon receiving the SYNC code word, the pager searches for a message in its respective frame group.
The POCSAG protocol has some inherent inefficienc
Antonelli Terry Stout & Kraus LLP
Chin Stephen
Ha Dac V.
NTP Incorporated
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