Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1997-11-21
2002-06-11
Chin, Wellington (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S315000, C455S007000, C455S020000, C455S426100
Reexamination Certificate
active
06404775
ABSTRACT:
FIELD OF THE INVENTION
This application relates to wireless communications systems, and more particularly to repeaters for use in wireless telephone systems. Still more particularly, the application relates to repeaters for use with wireless telephone systems (or similar communications systems) having plural disparate radio interfaces differing in frequency band, format, or protocols, in which the repeater operates as a bridge to allow communication between components operating on such disparate interfaces.
BACKGROUND OF THE INVENTION
In 1983, conventional “analog” cellular telephone service became commercially available in several cities of the United States. This event marked the first time mobile telephone service was widely available to members of the general public. Although the concept of mobile telephony was not new, the systems which had been deployed previously in the United States were extremely limited in capacity. Prior to the advent of conventional cellular service, there were long waiting lists of persons desiring to subscribe to the existing systems, and service was very expensive. System capacity was so limited that subscribers desiring to make a call sometimes had to wait tens of minutes for a radio channel to become available.
“Cellular” systems (which term is used herein to refer to a family of mobile telephone services operating in the United States in the 824-849 MHz and 869-894 MHz frequency ranges) offer many advantages over prior mobile telephone systems. In particular, factors such as the large number of allocated radio channels, short RF path lengths, low subscriber terminal transmitter power requirements, and the ability of system operators to reuse channels within the system, combine to provide vastly greater system capacity and generally higher call quality. These factors also enable the use of hand-held telephones. In addition, service is available at relatively low cost. As a result, cellular telephone service has enjoyed great success, with consumer acceptance far exceeding what was expected by its original proponents.
Recently, the United States government has allocated radio spectrum in the 900 MHz range and in the 1.8 to 2.0 GHz range for construction of new communications systems referred to as “Personal Communications Services.” Systems operating in the new PCS bands at 1.8-2.0 GHz are being installed throughout the United States at a rapid rate. Although PCS service vendors may ultimately support a variety of portable and/or mobile wireless communications and data applications, PCS systems are initially being deployed and marketed primarily as wireless telephone services operating in competition with 800 MHz cellular telephone systems.
The positioning of PCS as a competitor to cellular systems presents special challenges to PCS system operators, particularly during the initial period of system deployment. Cellular systems are relatively mature, and subscribers have learned to expect service to be available nearly everywhere they go. In many areas of the country it is not economically feasible to install PCS base stations and related infrastructure equipment due to the relatively lower population densities involved. Since some PCS providers may compete directly with wireline cellular providers, it may be difficult and expensive to obtain carrier facilities from local telephone companies to connect base stations to switching offices. Nonetheless, there will be PCS subscribers who desire service in these areas on a roaming basis.
Even in regions of relatively high population density, in many locations it may not be economically feasible to install PCS infrastructure equipment of conventional architecture during the early stages of PCS system implementation when subscriber demand is low. Due to the greater path attenuation at the higher frequencies which PCS systems use (i.e., 1.9 GHz as compared to 800 MHz for conventional cellular systems), and to lower transmitter power available from PCS subscriber units, a PCS base station provides a substantially smaller coverage area (or cell size) compared to an otherwise-equivalent 800 MHz base station. Therefore, PCS base stations (or equivalent radio transmitting and receiving facilities) must be installed with much greater geographic frequency than in equivalent 800 MHz cellular systems.
At least one cellular equipment manufacturer has implemented PCS cell sites using standard 800 MHz cell site base station equipment augmented with conventional components (e.g. amplifiers and mixers) for shifting the operating frequency to the 1.9 GHz PCS band. This approach to implementing a PCS cell site may be attractive to the equipment manufacturer because only a small amount of new equipment need be developed, and even that equipment is more or less conventional. Accordingly, the manufacturer need not expend the resources that otherwise would be required to develop a PCS cell site from scratch.
However, this approach is only available if the “air protocol” to be used in the PCS system is identical (except for operating frequencies) to that implemented by the existing cellular base station equipment. The terms “air protocol” and “radio interface” are used interchangeably herein to refer to the fundamental characteristics of the radio communications medium used by terminals to communicate with other terminals and may include, for example, operating frequency bands, signal modulation methods, the format for encoding voice or data traffic, formats for call set-up messages and other signaling, and other aspects of the communication protocol. In general, if the air protocol of two systems are different, the systems are fundamentally incompatible, and terminals of one system cannot directly communicate with the terminals of the other system. In the context of cellular and PCS communications systems, the air protocol is the protocol or format which a cellular or PCS base station uses to communicate with a subscriber terminal (such as a portable telephone), and are typically defined by industry or government specifications.
Several “air protocols” are available for use in PCS systems; all employ digital transmission formats. Some PCS air protocols are identical (except for operating frequencies) to air protocols used in 800 MHz cellular systems. For example, the aforementioned PCS cell site equipment, and the existing 800 MHz cell site equipment upon which it was based, were both designed to implement the U.S. standard TDMA air protocol, which is used in both 800 MHz cellular and PCS systems. However, other air protocols, which traditionally have not been used in 800 MHz cellular systems, may be preferable for use in PCS systems, because they may afford improvements in channel density, audio quality, bandwidth, noise immunity, features, or other parameters. If the air protocols of the cellular base station equipment and the PCS system are not compatible, merely adding equipment to change the operating frequency of the cellular base station equipment will not allow that equipment to function as a base station in the PCS system.
Moreover, constructing a PCS base station using cellular base station components of existing design may be advantageous to an equipment manufacturer, but it does not resolve several problems faced by the PCS system operator (including those related to economic feasibility) in initially deploying a relatively large number of PCS base stations when subscriber density is low. Compared to mature cellular systems, PCS subscriber density will likely be low system-wide during an initial period after the system is constructed. Subscriber density may remain low in some areas due to lower population density or demographic factors. In addition, due to propagation factors and lower subscriber unit transmitter power, the effective communication range in a 1.9 GHz PCS system is shorter. Therefore, even if the subscriber density were comparable, a 1.9 GHz PCS system would require a larger number of lower-capacity base stations than an equivalent 800 MHz cellular system, and would require the base stations be
Bowen William A.
Goins Donnie L.
Leslie Samuel A.
Allen Telecom Inc.
Chin Wellington
Michael Best & Friedrich LLC
Tran Maikhanh
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