Telecommunications – Receiver or analog modulated signal frequency converter – Plural receivers
Reexamination Certificate
1998-09-30
2003-03-18
Vuong, Quochien (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Plural receivers
C455S273000, C455S561000
Reexamination Certificate
active
06535721
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to wireless receivers and receive paths in a base station. More specifically, the present invention relates to an improved receiver system architecture for wireless base stations which achieves enhanced dependability by separating diversity reception paths.
II. Description of the Related Art
In the field of wireless telecommunications, such as various cellular, Personal Communication Services (PCS), and Wireless Local Loop (WLL) communication systems, many different communication standards exist. For example, Code-Division Multiple Access (CDMA) digital communications may be governed by either Telecommunications Industry Association (TIA)/Electronics Industries Association (EIA) Interim Standard IS-95 (series) for cellular systems, or by ANSI J-STD-008 for PCS systems. Additionally, Time-Division Multiple Access (TDMA) digital communications may be governed by the TIA/EIA IS-54, or by the European standard Global System for Mobile Communications (GSM). Furthermore, analog FM-based communications systems may be governed by the Advanced Mobile Phone System (AMPS) standard or a related standard such as N-AMPS. Other wireless communication standards also exist for both digital and analog modulation.
According to any one of the above standards, wireless base stations communicate signals to one or more wireless mobile stations, such as cellular phones, PCS phones, or WLL phones. The wireless base stations primarily serve as the wireless “gateway” to the telephone system. In general, the wireless base station will be in communication with many mobile stations at one time.
The ability of the base station to operate when an internal software, hardware or other failure occurs is inherent to the base station architecture. The ability of the base station to continue to operate, either through “switching-in” additional backup or properly working components or by operating in a “reduced capacity” mode, is a measure of how well the base station architecture was designed.
For wireless communication systems, the system designer strives to design a base station architecture which is both cost-effective and highly reliable. One aspect of this is when a failure occurs at the base station, it does not result in loss of communications with the many mobile stations it may be serving. As a result, the system designer strives to connect the various base station components: front ends, receivers, demodulators, etc., in a manner which provides the best system reliability while still maintaining good performance, low cost, small size, low complexity, high degree of modularity, etc.
Wireless service providers who purchase and operate the base stations often specify a Mean Time Between Failure (MTBF) which represents the average amount of “downtime” that is tolerable. Often, this MTBF will be expressed as a total allowable downtime per year. “Downtime” is frequently defined as when the base station is unable to communicate at all with any mobile stations. Most service providers are keenly aware of this downtime because it results in a complete loss of revenues from that base station for the duration of the outage. As a result, a service provider will generally prefer that if a base station subsystem or component fails, that failure should affect the operation of the base station in the least significant way. Thus, reduced capacity modes of operation or partial degradations in service are strongly preferred over total loss of service.
A common base station architecture
100
which does not have optimum redundancy is shown in FIG.
1
. In
FIG. 1
, a pair of antennas
102
A,
102
B capture RF signals and provide them to RF front end
104
. Antennas
102
A,
102
B may be used for diversity reception, a well-known receiving technique in which the signal of interest is better received and processed by virtue of having two antennas receiving signals which can be compared and/or combined.
RF front end
104
typically comprises various bandpass filters and low-noise amplifiers which perform some initial frequency selection and signal amplification. RF front end
104
outputs two amplified signals
106
A,
106
B which correspond to antennas
102
A and
102
B, respectively. Receiver
108
receives, downconverts, and performs intermediate-frequency (IF) processing on the amplified signals
106
A,
106
B, and generates received signals
110
A and
110
B which correspond to antennas
102
A and
102
B, respectively. Demodulators
112
A-
112
N demodulate and perform IF and/or baseband processing on the signals
110
A,
110
B, thereby recovering the signal of interest from the RF signals received by antennas
102
A,
102
B. The architecture of
FIG. 1
may be generalized to multiple receive paths, one for each sector being served by the base station.
In the architecture of
FIG. 1
, the RF front end
104
and the receiver
108
are single points of failure. That is to say that when either RF front end
104
or receiver
108
fails for any reason, it breaks the receive path from antennas
102
A,
102
B to demodulators
112
A-
112
N. Thus, any failure of RF front end
104
or receiver
108
will result in total loss of service for the base station employing the architecture
100
of
FIG. 1. A
single failure path defined by RF front end
104
and receiver
108
exists whereby failure of any unit in the failure path will result in failure of the entire reception path. Namely, RF front end
104
and receiver
108
are both in the same diversity reception path and also in the same failure path.
A common improvement made to the base station architecture of
FIG. 1
is to provide a separate, redundant receive path which can be switched-in when the primary receive path fails. This is implemented by providing duplicate components such as a duplicate receiver
109
coupled by bypass switches
107
,
111
which connect RF front end
104
and demodulators
112
A-
112
N to the duplicate receiver
109
when the primary receiver
108
fails. This is often referred to as providing “N+1 redundancy” where there are N primary operating components and 1 duplicate component in standby that can be switched in to take the place of any one of the N primary operating components when there is a failure. Note also that bypass switch
107
could be placed before the RF front end
104
, and a redundant RF front end (not shown) could also be switched in.
In addition to the increased cost, size and complexity of providing duplicate components for the N+1 redundancy, the bypass switches
107
,
111
introduced in the receive path can introduce further undesirable signal level losses, thereby degrading the receive path performance. For example, a typical signal level loss incurred when introducing a switch matrix into the receive path is approximately 0.2 dB to 0.5 dB. This can be very significant when the receive path noise figure is typically in the 3 dB to 6 dB range. In addition, the control circuitry hardware and software (not shown) needed to detect a failure and control the switches also adds complexity, cost, size, and power dissipation to the base station. One can also call into question the reliability of the switches themselves.
What is needed is a base station architecture which improves the overall base station reliability without adding significant complexity or cost.
SUMMARY OF THE INVENTION
The present invention is a novel and improved base station and receiver system for use in a base station which achieves enhanced dependability by logically separating the diversity reception paths into different failure paths. In one embodiment, the receiver system includes a first diversity reception path for receiving a first radio signal and a second diversity reception path for receiving a second radio signal. The first and second radio signals may be amplitude and phase shifted versions of the same information signal according to well-known principles of diversity reception. At least one demodulator compares and/or combines the first and second radio si
Burke Joseph P.
Heidmann Peter D.
Edwards Christopher O
Miller Russell B.
Qualcomm Incorporated
Vuong Quochien
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