Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-08-14
2004-05-11
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S431000, C455S448000, C455S012100, C343S705000, C343S835000
Reexamination Certificate
active
06735438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless communication system for use with aircraft. More particularly, the invention relates to a method and system for providing wireless communication service in an air-space communication system.
2. Background Technology
The growth of telecommunications and the desire for mobile connectivity has increased the demand for public telecommunication services while in flight. In an effort to satisfy the demand for in-flight telecommunications, commercial aircraft are often equipped with a special ground-to-air communication system in order to provide passengers with public phone and/or data service. However, in-flight public phone systems largely use air interface protocols that are not compatible with conventional mobile telecommunication systems. Furthermore, airline passengers are typically not permitted to use personal mobile telephones while in flight due to possible interference with aircraft systems and with the ground-based wireless systems.
In contrast to in-flight phone and/or data systems, conventional mobile telecommunications systems permit mobile subscribers to access the PSTN (Public System Telephone Network) or other network by using a cellular infrastructure system intended for communications on the earth's surface. Generally, mobile systems may be designed to maximize two equally important parameters. The first major parameter is coverage. Coverage provides an adequate radio communication link between the base station and the mobile user. The second major parameter is capacity. Capacity ensures that the system can handle the demand or load by mobile users collectively.
COVERAGE
The mobile coverage area of a system is generally based primarily on the type of terrain, the transceiver equipment performance requirements for a given telecommunications standard, and the level of RF interference. Coverage is primarily limited by two major factors: the strength of the signal and the quality of the signal. The strength of the signal is based on the propagation characteristics of the signal. The quality of the signal is based on impairments to a signal, primarily due to interference.
The propagation characteristics of radio waves in free-space are different from the propagation characteristics of radio waves along the earth's surface. Normally, radio waves propagate further in free space than along the surface of the earth. The free-space propagation of radio waves is characterized by the “Frenel zone,” which sets forth the spatial terrain requirements that will permit free-space propagation. As a result, communications between a base station and an aircraft may take place over greater distances than communications between a base station and a mobile unit located on the earth's surface.
Presently, if an aircraft in an air-to-ground system transmits on the same frequencies as a ground cellular system, the air-to-ground system will likely interfere with the ground cellular system. Due to the extensive free-space propagation, transmissions from an airplane are broadcast over a large area of the earth's surface, possibly interfering with one or more ground base stations. This is a primary reason why mobile subscribers are currently prohibited from operating mobile units, such as their personal telephones or other mobile communication devices, on aircraft.
For example, the propagation characteristics of radio waves in a typical suburban area at 800-900 MHz may be expressed as follows:
Received signal=−61.7 dBm−38.4 dB log radius (miles)
where the radius is the distance between the base station and the mobile station in miles, and the received signal is the signal strength in dBm at the receiver of the mobile station. William C. Y. Lee, “Mobile Communications Engineering”, McGraw-Hill, N.Y. 1982, pp 108. If the minimum receive signal at the receiver is −100 dBm, then the radius of a typical suburban cell site at 800-900 MHz is about 10 miles (16 Km). A ground base station cell radius may typically vary from approximately 0.5 kilometers to approximately 20 kilometers or more.
However, due to the extent of free space propagation, a similar base station adapted for in-flight communications may have a radius of up to 500 kilometers or more. The actual cell radius will depend on factors such as the power budget of the system, which takes into account transmit output power, path loss between the transmitter and the receiver, transmission line losses in, the transmit and receive paths, fade margin, and receiver sensitivity.
CAPACITY
System capacity, the second parameter to be maximized in a mobile system, is a function of the available spectral bandwidth and the RF interference rejection performance of the system equipment. Mobile telecommunications systems utilize large amounts of bandwidth to provide commercial grade telephony service to tens or thousands of mobile users in a service area. Lower interference levels, and thus greater system capacity, results from having a larger spectral bandwidth. The FCC (Federal Communications Commission), however, limits spectral bandwidth allocations. Consequently, in order to meet subscriber service demands, RF engineering techniques such as interference analysis and optimization (e.g., frequency re-use, and power control) may be used to optimize this limited available bandwidth. Some of these techniques, however, adversely affect interference levels. Frequency re-use in many systems for instance, is a principle generator of RF interference in a mobile system.
INTERFERENCE
Because system interference directly affects both capacity and coverage, characterizing such interference is desirable. Since most mobile systems are bi-directional interference may affect both a forward communication link and a reverse communication link. Communication from a base station to a mobile unit is known as the forward link. Communication from the mobile unit to the base station is known as the reverse link. Interference on the forward link exists when the mobile unit's receiver experiences interference from base stations other than the intended base station. Interference on the reverse link exists when the transmit carrier from the mobile unit to the base station is interfered with by other transmitting mobile units in the system. In both the forward and the reverse links, the intended transmit carrier may be referred to as carrier “C”, and interference created by other mobile unit transmitters may be referred to as interference “I”.
The mobile subscriber units and system infrastructure communication equipment operating in a mobile system are typically capable of tolerating a specified maximum ratio of RF carrier to interference known as a C/I (Carrier-to-Interference) ratio. The C/I ratio may, for example, be based on an applicable telecommunications standard (e.g., IS-95, IS-54, G3, etc.). So long as the ratio of the intended receive carrier signal to the system interference at the receiver meets or exceeds the specified C/I ratio, communications between the mobile user and the base station are able to function properly. However, if the ratio of the intended receive carrier signal to the system interference at the receiver does not meet or exceed the specified C/I ratio, then the mobile unit's receiver may not be able to reliably receive the signal, and communication may fail or be of poor quality. For example, a C/I ratio of 6 dB may be required for a CDMA (Code Division Multiple Access) air interface such as IS-95, while a C/I ratio of 18 dB may be required for an analog air interface standard such as AMPS (Advanced Mobile Phone Service).
Besides available spectral bandwidth, system interference is dependent upon the distribution of subscribers. For example, the maximum concentration of subscribers is significant, because, if subscriber concentration is high enough, then the C/I ratio may exceed a maximum allowable C/I ratio. If subscriber concentration is too high, then the air system may need to be reconfigured to
Miller Brandon
Sprint Spectrum L.P.
Trost William
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