The demand for better and cheaper wireless telecommunication services and equipment continues to grow at a rapid pace. Much of this growth is spurred by the Federal Communication Commission's ("FCC") approval of certain frequency bands for the next generation of Personal Communication Service ("PCS") devices that provide voice telephone service as well as advanced voice and/or data message paging services. A relatively small portion of the available spectrum was set aside for narrowband PCS, which is more suited to advanced message paging services, to encourage efficient use of the available spectrum.
There are a number of well-known wireless communication techniques that attempt to maximize the efficiency with which the available spectrum is used. These methods include frequency division multiple access ("FDMA"), time division multiple access ("TDMA"), code division multiple access ("CDMA"), and the like. The term "multiple access" means that multiple, simultaneous users (or "subscribers") are supported in each of these systems.
In an FDMA system, for instance, the total available radio spectrum is divided into separate frequency bands (or "channels") of, for example, 25-30 KHz for those systems based on the "AMPS" or "TACS" standards, or 10 KHz for newer systems, such the narrowband PCS ("NPCS") advanced messaging systems. In FDMA, only one subscriber at a time is assigned to a channel. No other subscriber may access this channel until the transmission of the message sent by the first subscriber is completed.
In a TDMA system, the total available radio spectrum is again divided into separate frequency bands. Each band is then temporally subdivided into, for example, three time slots. Only one subscriber at a time is assigned to each channel, where a channel corresponds to a particular frequency band and a particular time slot for that band. No other subscriber may access this channel until the transmission of the message sent by the first subscriber is completed.
In a CDMA system, the total available radio spectrum is used by each subscriber. Each subscriber transmits a unique, pseudo-random noise ("PN") code sequence as a spread spectrum signal. The subscriber's transmitter and the receiving base station share the code, which is used to distinguish the subscriber from other subscribers in the system, who use different codes PN codes. Thus, a CDMA system uses codes rather than frequency and/or time slots to provide multiple access.
The total capacity of a multiple access system may be further improved by dividing a wireless system into cells and, in the case of FDMA and TDMA, using only different frequency channels in adjoining cells. The organization of message paging and cellular telephone systems into cells is widely known and understood. Division into cells is accomplished by limiting the transmission range of both the base stations and the mobile communication units. The frequencies used in one cell do not interfere with the different frequencies used in the adjoining cells and are not transmitted far enough to interfere with identical frequencies used in more remote, non-adjoining cells. Frequency "reuse" is therefore possible by dividing a TDMA or FDMA system into cells.
In the case of CDMA, division of the system into cells does not affect frequency allocation, since all subscribers use the same amount of spectrum. However, there are less subscribers per cell in smaller cells, so there is less interference to distort the signal transmitted by each subscriber. Thus, capacity is still improved for the overall system.
The structure of a message paging system is somewhat different than cellular telephone systems. In a message paging system, all of the base station transmitters throughout a wide coverage area are synchronized and simultaneously broadcast (i.e., simulcast) a paging message in a forward-channel to a subscriber's pager. This simulcast increases the likelihood that the paging message will reach the pager even through obstacles, such as buildings. The paging system does not assign the subscriber to a cell and transmit to the subscriber only in that cell, as in the case of a cellular telephone system.
However, even in a paging environment, there is a breakdown of the message paging system into cells. That is, due to the low power of a hand-held two-way pager, a message transmitted by a user in a reverse-channel has a very limited range compared to the base station transmitters. Therefore, a relatively large number of base station receivers must be deployed throughout the message paging system coverage area in order to ensure that the signal transmitted by any pager is received by a base station receiver. As a result, minimizing the number of receivers necessary to monitor the coverage area of a message paging system becomes an important consideration. Using less receivers lowers the infrastructure cost and, therefore, lowers the service cost to subscribers.
There exists a need in the art for an improved wireless communication system that minimizes the equipment cost necessary to operate the system. In particular, there is a need for an improved wireless messaging system that minimizes the number of base station receivers required to operate the system. There is a further need in the art for an improved narrowband messaging system capable of providing advanced two-way messaging services that maximizes frequency reuse and spectral efficiency with a minimum number of base station receivers.