Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2001-03-14
2004-10-05
Tran, Cong Van (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S091000, C455S106000, C455S561000, C370S295000, C370S304000
Reexamination Certificate
active
06801791
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of telecommunications, and, more particularly, to cellular communications systems.
BACKGROUND OF THE INVENTION
Cellular communications systems typically include multiple base stations for communicating with mobile stations (e.g., a cellular telephone) in various geographical transmission areas. Each base station provides an interface between the mobile station and a telecommunications network which may include land lines, satellites, etc.
Many base stations use an array of antennas, rather than a single antenna, for transmitting signals to the mobile stations. The use of multiple antennas provides enhanced performance in a number of areas, including the ability to direct the transmit signals (i.e., “beam-steering”), enhanced security, and reduction in transmission power, for example. Yet, one problem associated with a multiple antenna transmission is that the transmit signal sent from each of the base station antennas is subject to an unknown fading factor which causes signal degradation. The fading factors are unique to each transmit signal because they are a function of the path of travel of the transmit signal.
To account for the fading factors, cellular systems typically provide some feedback from the mobile station to the base station regarding signal quality. Weighting factors may then be assigned to each of the transmit signals to improve the signal quality based upon this feedback. An example of such a system is disclosed in U.S. Pat. No. 6,037,898 to Parish et al. entitled “Method and Apparatus for Calibrating Radio Frequency Base Stations Using Antenna Arrays.” In this system a prescribed signal is transmitted from each antenna element using a transmit apparatus chain associated with the antenna element. The transmitted signal is received by receiver apparatus chains not associated with the antenna. Calibration factors for each antenna element are determined based upon the associated transmit apparatus chain and receiver apparatus chain transfer functions using the prescribed signal and each of the signals received during transmissions.
Such communications systems typically estimate the weighting factors at the mobile station based upon the assumption that there is no spatial fading between the various fading factors. That is, it is assumed that the fading factors are correlated and that the distortion seen along the various paths of travel of the antennas differs only by a simple phase rotation. Of course, this may not always be the case, and the fading factors may indeed be arbitrary with respect to one another. In such instances, this methodology may result in significant signal degradation, which in turn may lead to an increased bit error rate.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the invention to provide a cellular communications system including a base station with a plurality of antennas that reduces a bit error rate of signal transmission despite the presence of unknown and arbitrary fading factors associated with the signals transmitted from the antennas.
These and other objects, features, and advantages in accordance with the present invention are provided by a cellular communications system including a base station and at least one mobile station communicating therewith. The base station may include a plurality of antennas and a modulator for providing a transmit signal for each antenna. The modulator may estimate a weighting factor for each transmit signal based upon considering each transmit signal as having an unknown and arbitrary fading factor associated therewith and based upon considering the unknown and arbitrary fading factors to have a predetermined cross-correlation function.
More specifically, the modulator may consider the unknown and arbitrary weighting factors to be Gaussian random processes having the predetermined cross-correlation function. Further, a pilot signal may be broadcast on a first one of the plurality of antennas. The modulator may estimate a weighting factor a for the transmit signal broadcast on the first antenna according to the following equation:
α
=
1
-
∑
i
=
2
M
ω
i
2
,
where M is a number of the plurality of antennas and &ohgr;
i
are the weighting factors for each of the remaining antennas. Additionally, the modulator may estimate the weighting factors &ohgr;
i
for the transmit signals broadcast on each of the antennas except the first antenna according to the following equation:
ω
i
=
ρ
i
Γ
M
(
ρ
i
2
/
Γ
2
+
(
1
-
ρ
i
2
+
1
/
Γ
)
2
)
,
where &rgr;
i
is a magnitude value of the predetermined cross-correlation function and &Ggr; is a signal-to-noise ratio of the transmitted signals.
Furthermore, the modulator may estimate the weighting factors by considering a sum of squared absolute values of each weighting factor to be one. Also, the base station may further include a frequency synthesizer for assigning a carrier to the transmit signals. The mobile station may include at least one antenna for receiving the transmit signals and a receiver for demodulating the transmit signals.
A base station for communicating with at least one mobile station in a cellular communications system according to the invention includes a plurality of antennas and a modulator for providing a transmit signal for each antenna. The modulator may estimate a weighting factor for each transmit signal based upon considering each transmit signal as having an unknown and arbitrary fading factor associated therewith and based upon considering the unknown and arbitrary fading factors to have a predetermined cross-correlation function.
A method aspect of the invention is for transmitting communications signals using a cellular communications network and includes providing a transmit signal to each one of a plurality of antennas and estimating a weighting factor for each transmit signal. The estimation may be based upon considering each transmit signal as having an unknown and arbitrary fading factor associated therewith and based upon considering the unknown and arbitrary fading factors to have a predetermined cross-correlation function.
REFERENCES:
patent: 5504783 (1996-04-01), Tomisato et al.
patent: 6006110 (1999-12-01), Raleigh
patent: 6031877 (2000-02-01), Saunders
patent: 6037898 (2000-03-01), Parish et al.
patent: 6507629 (2003-01-01), Hatakeyama
patent: 6615024 (2003-09-01), Boros et al.
patent: 6665348 (2003-12-01), Feher
Buehrer R. Michael
Nicoloso Steven Peter
Soni Robert Atmaram
Uptegrove Dirck
Lucent Technologies - Inc.
Tran Cong Van
LandOfFree
Cellular communications system and related methods does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cellular communications system and related methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cellular communications system and related methods will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316196