This invention relates generally to the field of cable television systems and, more particularly, to a system for reporting back to a centrally located office, the viewing of certain premium programming for which a subscriber is billed in addition to his regular monthly subscription fee. This practice is popularly referred to as "pay-per-view" (PPV). More specifically, the subject invention relates to the most desirable type of PPV, known as "impulse pay-per-view" (IPPV). An IPPV system allows a subscriber to order a program at the last minute.
Early PPV systems worked with one way addressable set-top terminals (STT). A subscriber who wished to order a PPV event did so by calling an operator and orally placing his order. The operator entered the order into a computer, which then transmitted authorization to the subscriber's set-top terminal.
This system suffers from the requirement of using the telephone and a human operator. This increases the cost of handling PPV requests, and effectively eliminates IPPV as a viable service since only a limited number of people are able to call in during the last minutes before a program begins. Therefore, the majority of people desiring to view a program must order it long before it begins.
Some prior art systems exist which purport to solve the IPPV problem. One such system employs a two-way cable television (CATV) plant, in which the set-top terminal may be equipped for transmitting a signal back to the headend ("upstream transmission") on a suitable frequency, such as between 5 MHz and 30 MHz. The terminal transmits information as to what programs are being or have been viewed to a computer at the headend. This system suffers from the fact that no protocols have been developed which operate efficiently in an enviroment of an exceedingly large number of set-top terminals who "speak" very little, but who must be serviced quickly when they do speak. Further, two-way CATV plants have proved difficult to maintain with adequate integrity to permit reliable return transmission, and the cost of the plant is excessive compared to the revenues to be gained from IPPV.
Another system uses credits downloaded to the terminal, and then makes deductions against the credits when a program is viewed. At the end of the month, certain alpha-numeric characters are displayed, indicating programs viewed. The subscriber writes these characters on a card which is mailed to the CATV operator. This system suffers from excessive delay in reporting programs watched, a limited number of programs which can be viewed (due to the limited number of characters a subscriber can be expected to write down), and the possibility of unrecoverable errors in transcription.
A similar system is disclosed in U.S. Pat. No. 4,484,217 to Block. In this system, credits are downloaded to the terminal and deductions are made when programs are viewed. An indicator informs the subscriber that the stored credit has expired or is low. The headend office, upon receipt of payment, will add credits to the subscriber's terminal and the indicator will be extinguished. In this system the subscriber must pay in advance and may miss programs due to delay in crediting his account.
An impulse pay-per-view system is disclosed in commonly assigned U.S. Pat. No. 4,792,848, herein incorporated by reference.