Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2002-09-03
2004-07-27
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S448000, C342S433000, C455S277200
Reexamination Certificate
active
06768457
ABSTRACT:
BACKGROUND
This invention relates to a diversity receiving system for digitally modulated terrestrial and/or satellite radio signals in the frequency range above 1 GHz for motor vehicles, with an antenna arrangement whose received signal is supplied to a radio receiver. In particular the OFDM method (orthogonal frequency division multiplex) and the MPSK method (phase shift keying with M phase conditions) are applied for the radio transmission of digital signals in the frequency range above 1 GHz. For the downlink of a satellite radio connection, the QPSK modulation (4 phase conditions) is frequently selected, and for terrestrial communication, the OFDM modulation is selected because the latter has a lower sensitivity with respect to traveling time differences between signals superimposing each other because of multi-way propagation. This also applies to the satellite radio system SDARS, which is designed for the area-covering mobile radio reception in the USA, and for terrestrial radio broadcasts which take place in heavily populated regions or overcrowded areas in addition to the radiation from 2 satellites.
The transmission disturbances occurring due to the multi-way propagation in connection with mobile reception have been successfully drastically reduced over the years with multi-antenna systems for transmitting analog transmitted signals such as, for example in connection with FM radio transmission. These systems are known from German patent P 3618452.7; P 4034548.3; and P 3926336.3. Because of the structure of OFDM or MPSK signals, these systems cannot be used with digital modulation. The present invention is based on European patent EP 1041736 A2. This patent describes and shows in
FIGS. 1 and 2
a
diversity receivers for OFDM signals as prior art, in which, in connection with the transmission of the OFDM burst, preamble signals are transmitted outside of the time slot provided for the data transmission for the synchronization, channel estimation and antenna selection according to a level criterion. This method has the drawback that the time slot for the preamble signal denoted in
FIG. 2
by reference numeral
11
has to be provided for, in the antenna selection in the transmitted burst signal. The most favorable antenna signal can be obtained exclusively depending on the occurrence of the burst signal, and not adapted to the necessity of updating, resulting from the driving movement in the multi-way scenario. This is of significance especially at carrier frequencies above 1 GHz. If, deeper level fading events are to be avoided, about ten updating events can be provided over a driving distance amounting to one half wavelength at 1 GHz. The updating then has to be repeated at a speed of 150 km/h at time intervals of 350 &mgr;s. For COFDM signals according to the DAB method (digital audio broadcasting) on the L-band (1.5 GHz), this would mean, in the reverse case, of having the unacceptable requirement that the speed of the vehicle be limited to 0.5 km/h.
Furthermore, defining a separate time slot for a preamble signal for the antenna election would lead to a reduction of the effective rate of transmittable data. The invention described in the EP document 1041736 A2 cited above, does not exclusively evaluate the signal level in view of the antenna selection, but provides, as a selection criteria for the antenna selected in connection with the subsequent data identification, additional signal errors that can be derived from a defined, known burst signal, such as, for example traveling time and phase effects. However, in this case, the updating of the antenna selection only takes place in response to the transmitted burst signal, and consequently at large time intervals.
Modern satellite radio systems, like those in use under the name “SDARS” reduce the high bit error rate caused by multipath propigation, shadowing effects, and changing reception conditions due to satellite movement by time-delayed multiple emission of the same signal content. Here QPSK-modulated signals are emitted in a time delayed manner by two satellites. There is also sent a terrestrial COFDM-modulated signal with information content in a time delayed manner, for support, especially in urban areas. In the receiver, the signals are transmitted in a frequency bandwidth of approximately 4 MHz respectively on different, but closely adjoining frequency bands. The signals are sent at approximately 2.33 Ghz and are received with a separate HF-ZF component, and the digital information is summarily evaluated by balancing the various time changes between channels. The system thus works based on the principle of frequency diversity, whereby the transmission paths make the decorrelated reception of different signals possible due to their diversity. However, it is necessary to support the system through a further diversity function, especially in areas that are urban, hilly or shaded by trees.
With the present invention, the signals can be received even if there is statistical interference via several reflected waves.
SUMMARY
One object of the invention is to create an efficient and inexpensive diversity system. Another object of the invention is to balance the cost of the device with sufficient and effective diversity efficiency.
Another object of the invention is to efficiently obtain an antenna diversity function that has an efficiency of &Dgr;n
ges
.
Thus to achieve these objects the invention relates to a diversity reception system for receiving digitally modified satellite signals and digitally modified terrestrial signals according to a SDARS or similar standard. In with this invention, one of the three reception channels p
d
=p
s
n
is considered for the probability for the shortfall of the necessary minimum reception level in diversity operation.
One of the three reception channels p
d
=p
s
n
is used to calculate the probability for the shortfall of the necessary minimum reception level in diversity operation. With this formula, p
s
signifies the probability for the shortfall of the necessary minimum reception level of a satellite or terrestrial reception signal with a single antenna in the respective reception channel. The diversity efficiency of the total system in relation to the overall effective diversity efficiency n
ges
present in the digital component of the receiver can be calculated taking into account the transmission paths n
sdars
=3. With this calculation, the resulting error probability of p
dges
−p
s
nges
with n
ges
=n
t
+n
s1
+n
s2
emerges for the assumed case of equal shortfall probabilities P
s
for all three signals. Here n
t
, n
s1
, n
n2
are the corresponding diversity efficiencies of the terrestrial or of the first and of the second satellite channel. The total diversity efficiency of the system therefore has the value n
ges
. The growth of the diversity efficiency of the total arrangement due to the diversity efficiency of the antenna system alone is thus calculated as &Dgr;n
ges
=n
ges
−n
SDARS
. This reference value is a description of the capacity of the diversity antenna system.
Differing evaluation criteria of the diversity efficiency result from the antenna diversity systems known until now from the special structure and the diversity of the high frequency channels. This same information respectively is however transmitted in a time delayed fashion. With the designs of all of these systems, the cost of the system is weighed against the effectiveness of the system to obtain the most efficient diversity system known.
SUMMARY OF THE INVENTION
Therefore, the present invention provides a diversity reception system, in which the received signal is updated in response to the selection of a more favorable received signal with the lowest possible bit error rate, at adequately short time intervals. Moreover, when the vehicle is driving at a high speed, and the data flow is being identified at the same time with a low cost cable link of the radio connection, the bit error rate is kept as low as possible, assuming that a use
Collard & Roe P.C.
FUBA Automotive GmbH & Co. KG
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