Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-02-10
2003-05-27
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S117000, C455S217000
Reexamination Certificate
active
06571110
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to base station receivers for communication applications and specifically to a receiver front end for base stations used in mobile radio systems.
BACKGROUND OF THE INVENTION
In terrestrial mobile radio systems of cellular, PCS or other type, geographical areas are subdivided into a number of cells. The communications traffic in each cell is supported by a base station and each base station has assigned to it a multiplicity of RF carriers. In such cellular mobile radio systems that operate at UHF and higher frequencies, the size of the cells is determined by terrain features (there can not be manor obstructions between the mobile station and the base station), network capacity requirements (the number of users the system needs to support), and the base station receiver sensitivity (limited by losses and noise generated in the base station receiver front end). In such cellular mobile radio systems, cells are called capacity cells when their size is determined by traffic requirements, and cells are called coverage cells when their size is determined by the base station receiver sensitivity and the terrain. Furthermore, a distinction is made between the forward link, which is the radio signal transmitted from the base station to the mobile station, and the reverse link, which is the radio signal transmitted from the mobile station to the base station.
In the reverse link, the mobile station typically transmits 10 to 100 times less power than the base station transmits in the forward link. Therefore,the received signal strength at the base station is much lower than the received signal strength at the mobile station. In situations where the base station range is limited by the reverse link signal strength, the base station is identified as reverse link limited. Likewise, in forward link limited cells the range is limited by the strength of the signal received at the mobile station.
Mobile radio networks are designed for balanced forward and reverse links, i.e., equal base station range in both directions. This balance is based on the assumption that all cells are at full capacity. However, many operational networks are not at full capacity. Under these conditions, the base station transmitter can be driven harder to provide an increased range for the forward link. The cell is then reverse link limited.
Specialized Mobile Radio (SMR) base stations and rural cellular base stations are typically reverse link limited. In particular, many existing cellular base stations are reverse link limited because they were designed for car phones transmitting at about 8Watts, while the majority of mobile stations today are battery operated hand-held phones, which transmit at much lower power levels (0.6 Watt in the U.S. and 2 Watts in Europe).
Reverse link limitations in specific existing cells due to terrain can be overcome. by increasing the antenna tower height at the base station. More general, construction of additional base stations or repeater sites is necessary. Both these approaches have major disadvantages: increasing the height of the receive antennas on the tower is typically not possible without replacing the entire tower and may violate zoning regulations. Building additional base stations or repeater sites is expensive and also requires a reassignment of the frequency reuse pattern of the network.
In capacity limited cellular networks, additional demand in the number of users can be met by adding new frequency channels to the existing cell sites if the additional channels are available. In networks where all channels are in use the only solution is splitting existing cells into smaller ones, and correspondingly, adding additional base stations and reassigning the frequency reuse pattern.
SUMMARY OF THE INVENTION
It is an objective of the present invention to disclose receiver front end circuitry that can provide significantly increased base station sensitivity for receiving reverse link signals from mobile stations. A related objective is to minimize the noise contributions from cable losses in the base station receive path which also increases the base station reverse link sensitivity compared to existing base stations.
Another objective is to reduce the number of base stations in coverage networks thereby reducing the installation and maintenance cost of such networks relative to existing cellular mobile radio systems.
Another related objective is to reduce the mobile station transmit power in coverage or capacity networks by increasing the base station receiver sensitivity.
It is a further objective to provide base station receiver front end circuitry with improved RF filter characteristics to reduce interference. This feature increases spectrum utilization providing increased capacity and revenue relative to existing base stations.
Yet another related objective is to operate said receiver front end circuitry in a thermally stable environment to avoid variations, degradation in performance, and failure due to ambient temperature fluctuations.
An additional objective relating to some digital cellular mobile radio systems is to increase network capacity. These and other objectives are achieved in the present invention which provides a receiver front end for a base station. The receiver front end includes: (1) a plurality of filtering means for spectrally filtering a plurality of RF signals to form a plurality of filtered RF signals; (2) a plurality of amplifying means, in communication with the plurality of filtering means, for amplifying the plurality of filtered RF signals; and (3) cooling means for cryogenically cooling the filtering means and the amplifying means. The cooling means is common to the plurality of filtering means and plurality of amplifying means and is substantially adjacent to the antenna to maintain the insertion loss along a transmission line extending between the antenna and amplifying means at or below a selected level. At least one of the plurality of filtering means and plurality of amplifying means comprises a superconducting material. In one embodiment, the receiver front end is mounted on a structure supporting the antenna. The cooling means can be a closed or open cycle refrigerator. The cooling means can maintain the filtering means and amplifying means at a stable temperature that is independent of the temperature of the environment external to the cooling means. The filtering means, amplifying means, and cooling means will hereinafter be referred to as the cryoelectronic receiver front end or the receiver front end. In one embodiment, the cryoelectronic receiver front end consists at a minimum of a spectral filter and a low noise amplifier, either or both of which can include a superconducting material for the passive components of the circuit.
To understand the performance advantages of the present invention, it is important to relate base station sensitivity with the base station noise figure. The sensitivity is described as the RF signal power level needed at the receive antenna port to detect a single telephone channel with a given signal quality. Frequently, in digital mobile radio systems, this signal quality is described by a frame error rate not exceeding one percent.
This error rate is a strong function of the signal to noise ratio as measured, for example, before the demodulator, and is thus strongly dependent on the noise power. The noise power in turn, is composed of noise received by the antenna and noise added by the RF receiver front end circuitry. The latter can be measured with standard techniques and is typically expressed as a noise figure value. The more noise added by the receiver, the larger the base station noise figure, the larger the total noise power at the demodulator, and the lower the sensitivity of the base station.
Cryogenic cooling significantly decreases RF losses in passive electronic circuits thereby reducing the thermal noise, also known as Johnson noise. As is also well known, Johnson noise generated in passive components is equal to the component lo
Arentz Robert F.
Koepf Gerhard A.
Martin Jerry Lynn
Patton David O.
Yandrofski Robert M.
Marshall Gerstein & Borun
Vo Nguyen T.
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