TITLE OF THE INVENTION
Method for transmitting data between a user equipment and a base station in a
wireless radio network
FIELD OF THE INVENTION
The present invention relates to a method for transmitting data between a user
equipment and a base station in a wireless radio network. Especially, the present
invention relates to a method for transmitting data between a base station and a
user equipment comprising a plurality of antennas for transmitting radio frequency
signals according to a so called multiple-input and multiple-output (MIMO) technol
ogy or according to a so called diversity mode. The present invention relates fur¬
thermore to a base station and a user equipment which implement the method.
BACKGROUND OF THE INVENTION
For increasing data transmission performance and reliability, a so called multipleinput
and multiple-output technology (MIMO) may be used in wireless radio frequency
telecommunications for transmitting information between a base station
and a user equipment. The MIMO technology relates to the use of multiple send
and receive antennas for a wireless communication at a base station and/or at a
user equipment. The MIMO technology forms the basis for coding methods which
use the temporal as well as the spatial dimension for transmitting information and
enables therefore a space and time coding. Thus, a quality and data rate of the
wireless communication may be increased.
In a so called massive MIMO system, a plurality of user equipments may be a
ranged within a cell served by a base station having a plurality of antennas. In the
massive MIMO system, a configuration of individual antenna transceivers of the
base station may vary depending on the location of each of the user equipments
and transmission conditions in an environment of the base station and the user
equipment.
The massive MIMO system may be used in connection with a time division duplex
(TDD) system in which a transmission of an information stream between the base
station and a user equipment is split up in time slots. Different time slots for uplink
(UL) data communications and downlink (DL) data communications may be pro
vided for communicating information from the user equipment up to the base sta
tion and for communicating information from the base station down to the user
equipment. In the massive MIMO system, there is a need for an additional time slot
which may be called "header" for transmitting a training signal or training sequence
from the user equipment to the base station. Based on the received training signal,
the base station may configure the transceivers of its antenna array. Thus, high
antenna gain for the payload transmitted in the following time slots can be
achieved. The payload may be transmitted in a number of uplink and downlink time
slots. However, when the user equipment is moving, the channel quality may de
grade due to a change of the spatial arrangement of the base station and/or the
user equipment. Therefore, further training signals may be transmitted and the con¬
figuration of the transceivers updated.
Typically, massive MIMO systems are expected in buildings such as offices, shop
ping malls and so on. In this environment a large number of user equipments may
be expected. However, due to the space coding by an individual configuration of
the antenna parameters for each user equipment, even in this environment a high
data throughput and a high data reliability may be achieved with the MIMO tech¬
nology. For further enhancement, a so called 3D-MIMO system may be used in
which a plurality of base stations comprising each a plurality of antennas cooperate
for enabling an even more enhanced space coding of the transmitted information.
Many user equipments, for example handsets like mobile phones, provide two or
even more antennas for cellular communication. The antennas of the user equip¬
ment are typically arranged spaced apart from each other at or within the housing
of the user equipment, e.g. one antenna at a top and one at a bottom of the user
equipment. For example, two antennas may be used in two different modes for the
downlink (DL) communication, either in a diversity mode or in a MIMO mode. In the
diversity mode the base station sends a single radio frequency signal and both antennas
are supposed to receive it. If one of the antennas happens to be in a fading
dip or if the user covers the one antenna, the other antenna still may have contact
with the base station and the reception continues. The diversity mode is also called
rank 1 mode. In the diversity mode the second antenna may be seen as a backup
antenna. In the MIMO mode, which is also called rank 2 mode, the base station
sends two different space coded signals on the very same frequency channel.
Thus, the data rate may be up to two times higher. The two different radio f re
quency signals may be received at the two spatially separated antennas of the
user equipment. A beam forming or a focusing of radio frequency signals, such that
one of the two different signals may be received by a first of the two antennas of
the user equipment and the other of the two different signals may be received at
the same time by the other of the two antennas of the user equipment may be ac
complished by the multiple antennas of the base station or the base stations oper
ating according to the above-described massive MIMO or 3D-MIMO technology. As
described above, in scenarios with rich scattered environments or a lot of user
equipments, it is not possible to predict how to feed all the antennas of the base
station to provide the required focusing of the radio frequency energy. Therefore,
each user equipment needs to send a training sequence and then for example an
amplitude and a phase for each antenna of the base station may be determined
such that a radio frequency signal may be sent focused to the antenna of the user
equipment from which the training sequence has been sent.
The configuration parameters for the downlink communication may be achieved
based on the training sequence received in the uplink based on a channel reciproc
ity. With a rising transmission frequency and in rich environment scenarios with a
lot of reflections and no line of sight (LOS), e.g. in indoor offices, the focusing may
be very narrow, actually narrow enough to only cover one of the antennas of the
user equipment. For example, the focus may be only a tenth of the wavelength of
the transmission frequency. Therefore, for each antenna that needs to be covered
by a beam formed by the base station, there may be a need to transmit a training
sequence and therefore a transmitter for each antenna of the user equipment is
needed. However, in a typical user equipment with two antennas, for cost optimization
only a single transmitter may be provided, whereas two receivers are usually
foreseen to enable the above-described diversity mode. Therefore, there is a need
for a method enabling a transmission of data between the user equipment and the
base station according to the above-described MIMO technology in a massive
MIMO or 3D-MIMO system without increasing the complexity and cost of the user
equipment.
SUMMARY OF THE INVENTION
According to the present invention, this object is achieved by a method for transmitting
data between a user equipment and a base station in a wireless radio network
as defined in claim 1, a base station for a wireless radio network as defined in
claim 11, a user equipment for a wireless radio network as defined in claim 3, and
a method for transmitting data between a user equipment and a base station in a
wireless radio network as defined in claim 16. The dependent claims define preferred
and advantageous embodiments of the invention.
According to an aspect of the present invention, a method for transmitting data be¬
tween a user equipment and a base station in a wireless radio network is provided.
The user equipment comprises at least a first antenna and a second antenna for
transmitting radio frequency signals between the user equipment and the base sta
tion. The user equipment may have more than two antennas and in this case the
described method may be adapted accordingly to use the more than two antennas.
However, even if the user equipment has more than two antennas, the described
method may also be performed using only two of the antennas. The base station
comprises a plurality of antennas for transmitting radio frequency signals between
the base station and the user equipment. The terms "transmit", "transmitting", etc.
as used in the present description may relate to receiving information from the user
equipment at the base station as well as sending information from the base station
to the user equipment. Data transmitted from the base station to the user equip
ment will also be called downlink (DL) data or data sent in a downlink direction, and
data transmitted from the user equipment to the base station will also be called uplink
(UL) data or data sent in an uplink direction. According to the method, a first
training signal from the user equipment to the base station is transmitted via the
first antenna of the user equipment at a first time period. For each antenna of a
subset of the plurality of antennas of the base station a corresponding first conf igu
ration parameter is determined based on the first training signal received at the
corresponding antenna. Furthermore, a second training signal is transmitted from
the user equipment to the base station via the second antenna of the user equip
ment at a second time period. The second time period is different to the first time
period, for example the first time period may comprise a first time slot and the sec
ond time period may comprise a second time slot in a time division multiplex
transmission scheme. For each antenna of the subset of the plurality of antennas
of the base station a corresponding second configuration parameter is determined
based on the second training signal received at the corresponding antenna. The
first and second configuration parameters may be used for transmitting payload
information blocks between the base station and the user equipment. The subset
of the plurality of antennas may comprise those antennas of the plurality of anten
nas which are arranged to receive the first and second training signals from the
user equipment. For example, if the antennas of the base station are arranged cylindrically,
only a subset of the antennas may receive the training signals sent from
the user equipment, whereas some other antennas may not receive the training
signals. Furthermore, if a very large antenna array is used, only a part or a subset
of the array of antennas may be used for a specific user equipment. However, the
subset may also comprise all antennas of the plurality of antennas provided by the
base station. As an example, the base station may comprise for example an a n
tenna array of thirty to one hundred or even more antennas arranged for example
in a matrix or cylindrically. Likewise, the user equipment may comprise two or more
antennas, for example three or four antennas. In case the user equipment com
prises more than two antennas, the described method may be adapted to the more
antennas accordingly. Due to the configuration parameters determined for each
antenna of the subset of the plurality of antennas, the base station may be enabled
to communicate with each antenna of the user equipment according to the abovedescribed
MIMO technology. Therefore, according to the method, first downlink
data are transmitted from the base station to the user equipment using the deter
mined first configuration parameters for the antennas of the base station, and s i
multaneously second downlink data are transmitted from the base station to the
user equipment using the determined second configuration parameters for the a n
tennas of the base station. The first and second downlink data may be transmitted
at the same frequency. By using the first configuration parameters for transmitting
the first downlink data and by using the second configuration parameters for
transmitting the second downlink data, a spatial coding may be provided such that
the first downlink data may be received at a high quality at the first antenna of the
user equipment and the second downlink data may be received at a high quality at
the second antenna of the user equipment, although the first and second downlink
data are transmitted at the same time. A leakage between the antennas of the user
equipment may be handled by coding such that the user equipment is able to
separate the first and second data.
In a diversity mode, the first downlink data may comprise the same data as the
second downlink data, and the user equipment may select either the first downlink
data or the second downlink data for a further processing depending on which
downlink data provides the better reception quality. Additionally or as an alterna
tive, the signals of the first and second downlink data may also both be received
and then combined to provide the downlink data for the further processing. There
fore, in the diversity mode, a high transmission quality and reliability can be pro
vided, even if for example one or both of the antennas of the user equipment is/are
covered or has/have a degraded reception quality, for example due to a user hold
ing the user equipment and disturbing therefore the reception at the antenna(s). In
a MIMO mode, the first downlink data may be different from the second downlink
data and both data may be processed in the user equipment after reception.
Therefore, in the MIMO mode, a higher data rate, for example a data rate up to two
times higher via two antennas, may be achieved.
According to the method, a first signal quality parameter of the first downlink data
received at the user equipment is determined and a second signal quality parame
ter of the second downlink data received at the user equipment is determined.
Based on the determined first quality parameter and second quality parameter, one
antenna of the first and second antennas of the user equipment is selected for a
transmission of uplink data from the user equipment to the base station. In other
words, according to the above-described method, a downlink communication sup¬
porting either the MIMO mode or the diversity mode is enabled with accurately
adapted configuration parameters for the antennas of the base station to focus at a
plurality of antennas of the user equipment. Furthermore, in uplink direction a se
lection diversity or switched diversity may be realized. An uplink communication
from either one of the antennas of the user equipment is provided with a high qual
ity due to appropriate configuration of the antennas of the base station. Further
more, the above-described method may be realized with only one transmitter or
sending unit within the user equipment, as the first training signal and the second
training signal are sent at separate time periods. Therefore, the above-described
method may be realized at low cost in present user equipment designs.
According to an embodiment, the step of selecting an antenna of the user equip
ment for transmitting uplink data is performed by the user equipment. The base
station may listen on both channels for uplink data coming form the first antenna or
the second antenna of the user equipment. However, there will be only uplink data
from either the first antenna or the second antenna. Therefore, the base station will
receive uplink data on only one channel. Such an arrangement may be called an
open loop antenna selection, as the base station is not involved in or informed
about antenna selection for the uplink data. No additional protocol elements and
protocol overhead for synchronizing the user equipment and the base station are
needed.
According to another embodiment, the selection of an antenna of the first and sec¬
ond antennas of the user equipment for a transmission of uplink data is performed
by the user equipment, and the selected antenna is notified from the user equip¬
ment to the base station. As described above, the base station is not involved in
the selection process and therefore this embodiment represents also an open loop
process. However, by notifying the base station about the selection result, the re
ception of the uplink data may be realized more efficiently within the base station.
According to a further embodiment, for selecting an antenna of the user equipment
for transmission of uplink data, a preferred antenna of the first and second anten
nas of the user equipment for a transmission of uplink data is selected by the user
equipment based on the determined first and second signal quality parameters.
The preferred antenna is notified from the user equipment to the base station, and
the base station may acknowledge to the user equipment that the base station ex
cepts the preferred antenna of the user equipment to be used as the selected an
tenna for the transmission of uplink data from the user equipment to the base sta
tion. In other words, the user equipment requests at the base station an allowance
for selecting an antenna which should be used for the transmission of uplink data.
Upon acknowledgement from the base station, the user equipment may use the
selected antenna. Therefore, a closed communication loop is provided and both,
the base station and the user equipment, are involved in the selection process.
According to yet another embodiment, the first and second signal quality parame
ters are transmitted from the user equipment to the base station. In the base station,
an antenna of the first and second antennas of the user equipment is selected
based on the first and second signal quality parameters. The selected antenna is
notified from the base station to the user equipment. In other words, the base sta
tion controls which antenna of the user equipment is to be used. This enables the
base station to select an antenna taking additionally other conditions within a cell
served by the base station into account, for example communication channels to
other user equipments within the cell.
According to another embodiment, the user equipment comprises a sending unit
and a switch configured for selectively coupling either the first antenna or the sec
ond antenna to the sending unit. In case, the user equipment has more than two
antennas, the switch may be configured for selectively coupling the sending unit to
every single one of the more than two antennas. Furthermore, the user equipment
may comprise more than one sending units, but less sending units than antennas.
In this case, the switch may be configured for selectively coupling each of the a n
tennas to at least one of the sending units such that in a time multiplexed manner
each antenna may be coupled to a sending unit. However, this implies also that it
is not possible to couple all antennas at the same time to a corresponding sending
unit. According to this embodiment, for transmitting the first training signal from the
user equipment to the base station, the sending unit is coupled to the first antenna
via the switch during the first time period. Then, during the second time period, the
sending unit is coupled to the second antenna via the switch for transmitting the
second training signal. By coupling the sending unit in a time multiplexed manner
to the first and second antenna, or by coupling multiple sending units in a multi
plexed time manner to a plurality of antennas of the user equipment, a lower num
ber of sending units than antennas is needed to accomplish the above-described
method. Especially, only one sending unit may be needed to serve the first and
second antenna and even more antennas for transmitting corresponding training
signals.
The first and second quality parameters may comprise each for example a bit error
rate of the corresponding downlink data, a received signal strength indication of the
corresponding downlink data, or a signal to noise ratio of the corresponding
downlink data. The above-described quality parameters may be easily determined
within the user equipment and provide reliable information concerning the t rans
mission quality of the downlink data. Furthermore, the above-described quality pa
rameters may be transmitted in a commonly known way in corresponding protocol
data units to the base station for the above-described processing within the base
station.
According to an embodiment, the configuration parameter determined for each a n
tenna of the subset of the plurality of antennas of the base station may comprise
for example an amplitude information, a phase information, a parameter pair com
prising an amplitude information and associated phase information, a plurality of
these parameters, or a signal intensity information of a signal intensity received at
the corresponding antenna during receiving the corresponding training signal.
However, the above-listed types of configuration parameters are only examples
and the configuration parameters may comprise other or additional information for
configuring the antennas of the base station to enable a data transmission accord -
ing to the above-described MIMO transmission scheme. Furthermore, the phase
and the amplitude information may be used directly to determine the configuration
parameters of the antennas of the base station for receiving uplink data from the
user equipment, as the training sequence has been sent in the same uplink direc¬
tion. However, the configuration parameter for sending downlink data to the user
equipment may be determined based on a Hermitian transpose of the configuration
parameter for receiving uplink data. For example, if two uplink signal beams from
the user equipment are received at the base station with different delay (phase), for
sending downlink beams the phases need to be reversed as the beam with the
shorter path comes first and both beams need to be aligned at the user equipment
in the downlink direction.
According to another aspect of the present invention, a base station for a wireless
radio network is provided. The base station comprises a plurality of antennas for
transmitting radio frequency signals between the base station and a user equipment
which comprises at least a first antenna and a second antenna for transmit
ting radio frequency signals between the user equipment and the base station. The
base station comprises furthermore a processing device configured to receive a
first training signal which has been sent from the user equipment to the base sta
tion via the first antenna at a first time period. The processing device is configured
to determine for each antenna of a subset of the plurality of antennas of the base
station a corresponding first configuration parameter based on the first training sig
nal received at the corresponding antenna. Furthermore, the processing device is
configured to receive a second training signal which has been sent from the user
equipment to the base station via the second antenna at a second time period. The
first time period and the second time period are different, for example, the second
time period occurs after the first time period. The processing device determines for
each antenna of the subset of the plurality of the antennas of the base station a
corresponding second configuration parameter based on the second training signal
received at the corresponding antenna. Then, first and second downlink data are
transmitted from the base station to the user equipment simultaneously, i.e., there
is at least an overlap of the transmission of the first downlink data and the trans¬
mission of the second downlink data. The first downlink data is transmitted using
the determined first configuration parameters for the antennas of the base station.
The second downlink data is transmitted using the second configuration parame¬
ters for the antennas of the base station. Due to the usage of the first and second
configuration parameters for transmitting the first and second downlink data, a
space coding of the first and second downlink data may be provided such that the
first downlink data may be received with a high quality at the first antenna of the
user equipment and the second downlink data may be received with a high quality
at the second antenna of the user equipment. A signal processing for transmitting
the first and second downlink data using the first and second configuration data
(e.g. according a MIMO technology) may be performed in the analog or digital do¬
main or a combination thereof. Therefore, for example, a part of a transceiver func
tionality of each antenna may be implemented digitally, for example in a signal
processor or in the processing device, and the antennas and the remaining parts of
the transceivers may be passive components. The first and second downlink data
may comprise the same data in case the user equipment is operating in a diversity
mode, whereas the first and second downlink data may comprise different data in
case the user equipment is operating in a MIMO mode, thus increasing the data
rate, e.g. up to two times. The processing device is furthermore configured to re
ceive uplink data sent from the user equipment via either the first antenna or the
second antenna. For receiving the uplink data sent via the first antenna, the proc
essing device uses the first configuration parameters, and for receiving the uplink
data sent from the second antenna of the user equipment, the processing device
uses the second configuration parameter. However, the base station may be listen¬
ing to uplink data using the first configuration parameter as well as the second con
figuration parameter at the same time to be able to receive the uplink data in both
cases, i.e., in case the user equipment sends the uplink data via the first antenna
or in case the user equipment sends the uplink data via the second antenna.
According to an embodiment, the base station is furthermore configured to perform
any of the above-described methods and embodiments and comprises therefore
the above-described advantages.
According to another aspect of the present invention, a user equipment for a wire¬
less radio network is provided. The user equipment comprises at least a first an¬
tenna and a second antenna for transmitting radio frequency signals between the
user equipment and the base station. The base station comprises a plurality of antennas
for transmitting radio frequency signals between the base station and the
user equipment. The user equipment comprises furthermore a processing device
configured to send a first training signal to the base station via the first antenna at a
first time period, and to send a second training signal to the base station via the
second antenna at a second time period, which is different to the first time period.
To accomplish this, the user equipment may comprise a single sending unit and a
switch selectively coupling the sending unit to either the first antenna or the second
antenna. The processing device is furthermore configured to receive first downlink
data from the base station via the first antenna and to receive simultaneously sec
ond downlink data from the base station via the second antenna. Therefore, the
user equipment may comprise two receiving units, one for each antenna. Further
more, the processing device determines a first signal quality parameter of the re
ceived first downlink data and a second signal quality parameter of the received
second downlink data. Then, based on the determined first and second signal qual¬
ity parameters, the processing device sends uplink data via either the first antenna
or the second antenna to the base station. For sending the uplink data, the proc
essing device may configure the above-mentioned switch such that the single
sending unit of the user equipment is either coupled to the first antenna or to the
second antenna.
According to an embodiment, the user equipment is configured to perform the
above-described method and the above-described embodiments of the method
and comprises therefore the above-described advantages. The user equipment
may comprise for example a mobile telephone, a mobile computer, a personal digi
tal assistant or a tablet computer.
According to another embodiment, the base station may determine based on the
received first and second training signals the corresponding first and second qual
ity parameters and may select an antenna of the first and second antennas of the
user equipment for a transmission of uplink data from the user equipment to the
base station. Hence, the base station may determine which channel is the better by
comparing the received training signals and may then demand the user equipment
to use the corresponding antenna for coming uplink data.
Although specific features described in the above summary and the following de¬
tailed description are described in connection with specific embodiments and aspects
of the present invention, it should be understood that the features of the ex¬
emplary embodiments and aspects may be combined with each other unless spe¬
cifically noted otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in more detail with reference to the
accompanying drawings.
Fig. 1 shows schematically a base station and a user equipment according to embodiments
of the present invention.
Fig. 2 shows schematically a user equipment according to an embodiment of the
present invention in more detail.
Fig. 3 shows a flowchart comprising method steps for transmitting data between
the user equipment and the base station in a wireless radio network according to
an embodiment of the present invention.
Figs. 4-7 show schematically data transmissions between a user equipment and a
base station according to embodiments of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the following, exemplary embodiments of the present invention will be described
in more detail. It is to be understood that the features of the various exemplary embodiments
described herein may be combined with each other unless specifically
noted otherwise. Same reference signs in the various drawings refer to similar or
identical components. Any coupling between components or devices shown in the
figures may be a direct or an indirect coupling unless specifically noted otherwise.
Fig. 1 shows a user equipment 15 arranged in an environment 0 of a base station
11. The base station 11 comprises a plurality of antennas 12 and associated trans¬
ceivers 3. In Fig. 1 only six antennas 12 six transceivers 13 are shown for clarity
reasons. However, these are only exemplary numbers and the base station 11 may
comprise for example an array of 30 to 00 or even more antennas and associated
transceivers arranged for example in a matrix or cylindrically. The user equipment
15 comprises two antennas 16 and 7 . However, the user equipment 15 may com
prise even more antennas, for example three or four. The base station 1 com
prises furthermore a processing device (PD) 14 coupled to the transceivers 13 and
adapted to configure the transceivers 13 for transmitting radio frequency signals
between the base station 11 and the user equipment 15. The multiple antennas 12
and the transceivers 13 of the base station 11 may be used and configured such
that the above-described multiple-input and multiple-output (MIMO) technology
may be utilized for transmission of data between the base station and each of the
antennas 16 and 17 of the user equipment 15. In other words, the antennas 12 and
the transceivers 13 of the base station 11 may be configured such that they pro¬
vide two communication channels between the base station 11 and the user
equipment 15 separated by a space coding.
Fig. 2 shows the user equipment 15 in more detail. The user equipment 15 com
prises the two antennas 16 and 17 coupled via a switch 18 to a first receiver 19
and a transceiver 20 comprising a sender 2 1 and a second receiver 22. Furthermore,
the user equipment 15 comprises a processing device (PD) 23 coupled to
the switch 18 for controlling the switch. Under the control of the processing device
23, the switch 18 may couple for example the first antenna 16 to the first receiver
19 , the second antenna 17 to the second receiver 22, and selectively the sender
2 1 to either the first antenna 16 or the second antenna 17. Thus, the two receivers
19 and 22 may continuously receive signals via the antennas 16 and 17, whereas
only one antenna of the antennas 16 and 17 may be provided with a radio f re
quency signal from the sender or sending unit 2 1.
For setting up the above-described two communication channels between the base
station 11 and the user equipment 15, the transceivers 13 have to be configured to
provide a high quality transmission taking into account spatial information of the
antennas 16 and 17 of the user equipment 15 with respect to the base station .
For determining configuration parameter sets for the transceivers 13, a training
signal or a training sequence of radio frequency signals may be transmitted from
each of the antennas 16, 7 of the user equipment 15 to the base station 11.
Based on the received training signal, corresponding configuration parameters for
the transceivers 13 may be determined in the base station 11. However, when the
user equipment 15 is moving, the configuration of the transceivers 13 has to be
updated for the new position to avoid degradation of the transmission quality.
Therefore, the training signals from the antennas 16, 17 have to be transmitted in
regular terms, for example at beginning of each frame transmitted between the
base station 11 and the user equipment 15 .
A typical transmission frame used in wireless radio communication networks may
comprise a header, an uplink part for transmitting data from the user equipment 15
to the base station 11, and a downlink part for transmitting data from the base station
11 to the user equipment 15 . The above-described training signals may be
transmitted in separate time slots for each antenna 16, 17 of each user equipment
15 . To accomplish this with only one sending unit 2 1 of the user equipment 15, the
method 30 described in Fig. 3 may be utilized by the base station 11 and the user
equipment 15.
Fig. 3 shows method steps 3 1 to 38 of the method 30. In step 3 1 the processing
device 23 of the user equipment 15 configures the switch 18 such that the first a n
tenna 16 is coupled to the sending unit 2 1, and a first training signal is sent via the
first antenna 6 to the base station 11 at a first time period or time slot within for
example a header of a transmission frame. In step 32 the base station 11 deter
mines for each antenna 12 of the base station 11 a corresponding first conf igura
tion parameter based on the first training signal received at the corresponding an¬
tenna 12. Next, the processing device 23 configures the switch 18 such that the
sending unit 2 1 is coupled to the second antenna 17, and in step 33 a second
training signal is sent via the second antenna 17 to the base station 11. The proc¬
essing device 14 of the base station 11 determines for each antenna 12 of the
base station 11 a corresponding second configuration parameter based on the
second training signal received at the corresponding antenna (step 34). In step 35
the base station transmits downlink data via both channels to the user equipment
15. In other words, the base station 11 transmits first downlink data from the base
station 11 to the user equipment 15 using the first configuration parameters for the
antennas 12, and simultaneously the base station transmits second downlink
data to the user equipment 15 using the second configuration parameters. Due to
the space coding via the first configuration parameters and the second configuration
parameters, the first downlink data may be received at a high quality at the first
antenna 16 and the second downlink data may be received at the second antenna
17. In steps 36 and 37 the base station determines for each of the received
downlink data corresponding quality parameters indicating via a first quality pa¬
rameter a reception quality at the first antenna and via a second quality parameter
a reception quality of the second antenna. Based on the determined first and sec
ond signal quality parameters, either the first antenna 16 or the second antenna 17
is selected for a transmission of uplink data from the user equipment 15 to the base
station 1 (step 38).
As described above in the section relating to the background of the invention, the
user equipment 15 may operate in either the diversity mode which is also called
rank 1 mode, or in the MIMO mode, which is also called rank 2 mode. In the diver
sity mode, the base station transmits the same data as the first downlink data and
the second downlink data. In other words, the same data is transmitted via two
channels from the base station 11 to the user equipment 15 and received two
times at the user equipment 5 , via the first antenna 16 and via the second antenna
17. In case one of the channels is disturbed, for example due to a user cov¬
ering with the user's hand one of the antennas 16, 17, the downlink data can still
be received at the user equipment 15. In the MIMO mode, the base station 11
transmits different downlink data and therefore the amount of transmitted data may
be doubled.
The above-described data transmission between the user equipment 15 and the
base station will be described in more detail in exemplary embodiments in con¬
nection with Figs. 4-7 in the following. Especially, the above-described step 38 of
selecting an antenna for a transmission of uplink data, will be described in more
detail in the various exemplary embodiments.
In Fig. 4 a first embodiment is shown n which the selection of the antenna to be
used for the uplink data transmission is performed n the user equipment 15 , and
the base station 11 is notified about the selection. In Fig 4 two transmission frames
40 and 4 1 for each channel are shown. Each channel relates to a space coded
communication between the base station 11 and each of the antennas 16, 17 of
the user equipment 15 . Data transmissions in the first channel are identified with
the post fix "1" and data communications via the second channel are identified with
the post fix "2". Due to the space coding, a frame on the first channel may be
transmitted at the same time as a frame on the second channel. Therefore, in Fig.
4 the horizontal direction indicates the time, the first line of boxes relates to the first
channel, and the second line of boxes relates to the second channel.
The transmission starts with a transmission of a header information 50 on the first
channel and a header information 70 on the second channel. The headers of each
channel are synchronized such that time slots within the header may be separately
used by individual user equipments and individual antennas of the user equip¬
ments. Therefore, there is a dedicated time slot within the header 50 for the trans¬
mission of the first training signal from the first antenna 16, and a dedicated time
slot for transmitting the second training signal from the second antenna 17. As de¬
scribed above, the processing device 23 configures the switch 18 such that the
sending unit 2 1 is coupled to the first antenna 16 and the first training signal is sent
within the header 50 as indicated in Fig. 4 . Then, the processing device 23 config¬
ures the switch 18 such that the sending unit 2 1 is coupled to the second antenna
17 and the second training sequence is sent in the header 70 as indicated in Fig. 4 .
Next, the processing device 23 configures the switch 18 to couple the sending unit
2 1 with the first antenna 16 and first uplink data (UL1) 5 1 is transmitted from the
user equipment 15 to the base station 11. The first uplink data 5 1 comprises an
information informing the base station which antenna is to be used for the next
frame 4 1. In this case, for example, the user equipment 15 may have determined
based on a quality of previously received (not shown) downlink data to select the
second antenna 17 for the next transmission of uplink data. Next, the base station
11 transmits first and second downlink data (DL1 , DL2) 52, 72 via both channels in
a space coded manner to the user equipment 15. The first and second downlink
data may comprise the same data or different data depending on the used trans¬
mission mode, diversity mode or MIMO mode. The next frame 4 1 starts again with
headers 53 and 73 for each channel comprising first and second training signals to
update the first and second configuration parameters for the antennas 12. Then, as
notified before, the user equipment 15 couples the sending unit 2 1 to the second
antenna 17 and transmits uplink data (UL2) 74 via the second channel to the base
station. Again, the uplink data (UL2) 74 may contain an information for the base
station which channel will be used by the user equipment 15 in the next (not
shown) frame. The channel or antenna which will be used for the uplink data may
be selected based on quality parameters determined for the received first and sec¬
ond downlink data. For example, a first signal quality parameter of the first
downlink data 52 may be determined and a second signal quality parameter of the
second downlink data 72 may be determined. The first and second signal quality
parameters may be compared and the channel having the better quality may be
selected for transmitting next uplink data. After having communicated the selected
channel in uplink data 74, this channel may be used in a further (not shown) time
frame. Then, the base station 11 transmits simultaneously first and second
downlink data (DL1 , DL2) 55, 75 as described above, and the user equipment 15
may determine corresponding signal quality parameters for a future antenna reselection.
Fig. 5 shows a further embodiment of the method described in connection with Fig.
3. In the embodiment shown in Fig. 5, the user equipment 15 proposes one of the
antennas 16 or 17 for uplink data transmission, and the base station 11 may acknowledge
the request such that a closed communication loop for the antenna se
lection may be provided. As described in connection with Fig. 4 , in the headers 50
and 70 of the first frame 40 the first and second training signals are transmitted.
Based on quality parameters determined for downlink data received in a previous
(not shown) frame, the user equipment 15 may propose one of the antennas 16
and 7 to be used for a future uplink communication, for example, the user equip¬
ment 15 may propose to use the second antenna 17 in the future. This proposal is
communicated to the base station 11 via the uplink data (UL1) 5 1. Next, the base
station 11 transmits downlink data (DL1 , DL2) 52 and 72 on both channels to the
user equipment 15 which may be used for determining future antenna selections.
In the next frame 4 1 the user equipment still transmits uplink data (UL1) 54 via the
first antenna 16, as so far no acknowledgement for changing the sending antenna
has been received from the base station 11. In the downlink data (DL1 , DL2) 55,
75 of the frame 4 1 the base station 1 may acknowledge the proposed selection of
the second antenna 17 as the sending antenna. Therefore, in the next frame 42
after the headers 56 and 76 have been transmitted, the user equipment 15 sends
uplink data (UL 2) 77 via the second antenna 17 to the base station 11.
Fig. 6 shows a further embodiment for an antenna selection in which the user
equipment 15 may reselect the antenna for sending uplink data to the base station
without informing the base station 11. Therefore, the communication shown in Fig.
6 mainly corresponds to the communication shown in Fig. 4 . The only difference is
that the user equipment 15 does not notify in its uplink data (UL1 or UL2) 5 1 or 74
the next channel which will be used for the next uplink data. Therefore, the base
station 1 has to listen to both channels always and has to take the uplink data
from the channel at which it is provided. It is to be noticed that there will be data
only on one of the channels.
Fig. 7 shows a further embodiment for antenna selection in which the base station
11 performs the antenna selection and informs the user equipment 15 accordingly.
As described above, in frame 40 the first and second training signals are transmit¬
ted from the user equipment 15 in the headers 50, 70 to the base station 11. Next,
uplink data (UL1) 5 1 is transmitted from the user equipment 15 to the base station
via the first channel. Then, the base station transmits on both channels downlink
data (DL1 , DL2) 52, 72 to the user equipment 15. The user equipment 15 deter
mines a first signal quality parameter of the first downlink data (DL1) 52 and a sec¬
ond signal quality parameter of the second downlink data (DL2) 72. In the next
frame 4 1, after having transmitted the first and second training signals in the head¬
ers 53 and 73, the user equipment 15 transmits in the uplink data (UL1) 54 on the
first channel via the first antenna 16 the determined first and second signal quality
parameters to the base station 1 . The base station 1 transmits downlink data
(DL1 , DL2) 55 and 75 to the user equipment 15 which may be used by the user
equipment 15 to determine further signal quality parameters. In the next frame 42,
again training signals may be transmitted in the headers 56 and 76 and uplink data
(UL1) 57 may be transmitted via the first antenna 6 to the base station 11. Based
on the first and second quality parameters received in frame 4 1, the base station
1 has in the meantime determined which communication channel provides the
better performance and may therefore instruct the user equipment 5 to use the
second antenna 17 for sending uplink data in the future. This information may be
transmitted to the user equipment 15 in the downlink data (DL1 , DL2) 58, 78 of
frame 42. Therefore, in the next frame 43, after the first and second training signals
have been transmitted in the headers 59, 79, the user equipment 15 configures the
switch 18 to couple the sending unit 2 1 with the second antenna 17 and transmits
the uplink data (UL2) 80 via the second antenna 17 to the base station 11. Finally,
the base station 11 may transmit downlink data (DL1 , DL2) 6 1, 8 1 to the user
equipment 15 simultaneously via the two channels.

CLAIMS
1. A method for transmitting data between a user equipment and a base station in
a wireless radio network, wherein the user equipment (15) comprises at least a first
antenna (16) and a second antenna (17) for transmitting radio frequency signals
between the user equipment ( 5) and the base station ( 1 1), and wherein the base
station ( 1 1) comprises a plurality of antennas (12) for transmitting radio frequency
signals between the base station ( 1 1) and the user equipment ( 5), the method
comprising:
- transmitting a first training signal from the user equipment (15) to the base
station ( 1 1) via the first antenna (16) at a first time period,
determining for each antenna (12) of a subset of the plurality of the anten¬
nas (12) of the base station ( 11) a corresponding first configuration parameter
based on the first training signal received at the corresponding antenna (12),
- transmitting a second training signal from the user equipment ( 15) to the
base station ( 1 1) via the second antenna (17) at a second time period different to
the first time period,
determining for each antenna (12) of the subset of the plurality of the anten¬
nas (12) of the base station ( 1 1) a corresponding second configuration parameter
based on the second training signal received at the corresponding antenna (12),
transmitting first downlink data (DL1) from the base station ( 1) to the user
equipment ( 5) using the determined first configuration parameters for the anten¬
nas (12) of the base station ( 1 1), and simultaneously transmitting second downlink
data (DL2) from the base station ( ) to the user equipment ( 1 5) using the determined
second configuration parameters for the antennas (12) of the base station
( 1 1),
determining a first signal quality parameter of the first downlink data (DL1)
received at the user equipment (15),
determining a second signal quality parameter of the second downlink data
(DL2) received at the user equipment (15), and
selecting, based on the determined first and second signal quality parame
ters, an antenna of the first and second antennas (16, 17) of the user equipment
WO 2015/113684 PCT/EP2014/077153
( 15) for a transmission of uplink data (UL1 , UL2) from the user equipment ( 15) to
the base station ( 1 1).
2 . The method according to claim 1, wherein the step of selecting an antenna of
the user equipment ( 15) is performed by the user equipment ( 15).
3. The method according to claim 2 , further comprising:
notifying, from the user equipment ( 15) to the base station ( 1 1), the selected
antenna of the user equipment (1 5).
4 . The method according to claim 1, wherein the step of selecting an antenna of
the user equipment (15) comprises:
selecting by the user equipment ( 15), based on the determined first and sec
ond signal quality parameters, a preferred antenna of the first and second antennas
(16, 17) of the user equipment (15) for a transmission of uplink data (UL1 ,
UL2) from the user equipment ( 15) to the base station (1 1),
notifying, from the user equipment ( 15) to the base station ( 1 1) , the pre
ferred antenna of the user equipment ( 15), and
acknowledging, from the base station ( 1 1) to the user equipment ( 15), that
the base station ( 1 1) has accepted the preferred antenna of the user equipment
( 1 5) to be used as the selected antenna for the transmission of uplink data (UL1 ,
UL2) from the user equipment ( 5) to the base station ( 1 1).
5. The method according to claim 1, wherein the method further comprises:
- transmitting the first and second signal quality parameters from the user
equipment (15) to the base station ( 1 1), wherein the step of selecting an antenna
of the user equipment (15) is performed by the base station ( 1 1), and
notifying, from the base station ( 1 ) to the user equipment ( 15), the selected
antenna of the user equipment ( 15).
6 . The method according to any one of the preceding claims, wherein the first
downlink data (DL1) is the same as the second downlink data (DL2).
WO 2015/113684 PCT/EP2014/077153
7 . The method according to any one of claims 1-5, wherein the first downlink data
(DL1) is different from the second downlink data (DL2).
8. The method according to any one of the preceding claims, wherein the user
equipment (15) comprises a sending unit (21) and a switch ( 18) configured for se¬
lectively coupling either the first antenna (16) or the second antenna (17) to the
sending unit (21),
wherein the step of transmitting the first training signal comprises:
- coupling the sending unit (21) to the first antenna (16) via the switch ( 1 8),
and
wherein the step of transmitting the second training signal comprises:
coupling the sending unit (21) to the second antenna (17) via the switch
(18).
9. The method according to any one of the preceding claims,
wherein determining the first quality parameter comprises at least one of a group
consisting of:
determining a bit error rate of the first downlink data (DL1),
- determining a received signal strength indication of the first downlink data
(DL1), and
determining a signal to noise ratio of the first downlink data (DL1), and
wherein determining the second quality parameter comprises at least one of a
group consisting of:
- determining a bit error rate of the second downlink data (DL2),
determining a received signal strength indication of the second downlink
data (DL2), and
determining a signal to noise ratio of the second downlink data (DL2).
10. The method according to any one of the preceding claims, wherein the first
and/or second configuration parameter comprises at least one of a group consist
ing of.
WO 2015/113684 PCT/EP2014/077153
an amplitude information,
a phase information,
a parameter pair comprising an amplitude information and an associated
phase information, and
a plurality of the parameter pairs.
11. A base station for a wireless radio network, comprising:
a plurality of antennas (12) for transmitting radio frequency signals between
the base station ( 1 1) and a user equipment (15), wherein the user equipment ( 15)
comprises at least a first antenna (16) and a second antenna (17) for transmitting
radio frequency signals between the user equipment ( 15) and the base station
( 1 1), and
a processing device (14) configured to
receive a first training signal sent from the user equipment ( 5) to the base station
( 1 1) via the first antenna (16) at a first time period,
determine for each antenna (12) of a subset of the plurality of the antennas (12) of
the base station ( 11) a corresponding first configuration parameter based on the
first training signal received at the corresponding antenna (12),
receive a second training signal sent from the user equipment (15) to the base station
( 1 1) via the second antenna (17) at a second time period different to the first
time period,
determine for each antenna (12) of the subset of the plurality of the antennas (12)
of the base station ( 1) a corresponding second configuration parameter based on
the second training signal received at the corresponding antenna (12),
transmit first downlink data (DL1) from the base station ( 1 1) to the user equipment
( 15) using the determined first configuration parameters for the antennas (12) of
the base station ( 5), and simultaneously transmit second downlink data (DL2)
from the base station ( 1 1) to the user equipment ( 15) using the determined second
configuration parameters for the antennas (12) of the base station (1 1), and
either receive uplink data (UL1) sent from the user equipment (15) via the first an¬
tenna (16) using the first configuration parameter or receive uplink data (UL2) sent
WO 2015/113684 PCT/EP2014/077153
from the user equipment (15) via the second antenna (17) using the second con
figuration parameter.
12. The base station according to claim 1 , wherein the base station ( 1 1) is configured
to perform the method according to any one of the claims 1-1 0.
3. A user equipment for a wireless radio network, comprising:
at least a first antenna (16) and a second antenna (17) for transmitting radio
frequency signals between the user equipment ( 15) and a base station ( 1 1),
wherein the base station ( 1 1) comprises a plurality of antennas (12) for transmitting
radio frequency signals between the base station ( 1 1) and the user equipment
(15) , and
a processing device (23) configured to
send a first training signal to the base station ( 1 1) via the first antenna (16) at a first
time period,
send a second training signal to the base station ( 11) via the second antenna (17)
at a second time period different to the first time period,
receive first downlink data (DL1) from the base station (1 1) via the first antenna
(16) , and simultaneously receive second downlink data (DL2) from the base station
( 1 1) via the second antenna (17),
determine a first signal quality parameter of the received first downlink data (DL1),
determine a second signal quality parameter of the received second downlink data
(DL2), and
send, based on the determined first and second signal quality parameters, uplink
data (UL1 , UL2) via either the first antenna (16) or the second antenna (17) to the
base station ( 1 1).
14. The user equipment according to claim 13, wherein the user equipment (15) is
configured to perform the method according to any one of the claims 1-1 0 .
WO 2015/113684 PCT/EP2014/077153
15. The user equipment according to claim 13 or claim 14, wherein the user equip¬
ment (15) comprises at least one of a group consisting of a mobile telephone, a
mobile computer, a personal digital assistant, and a tablet computer.
16. A method for transmitting data between a user equipment and a base station in
a wireless radio network, wherein the user equipment (15) comprises at least a first
antenna (16) and a second antenna (17) for transmitting radio frequency signals
between the user equipment (15) and the base station ( 1), and wherein the base
station ( 1 1) comprises a plurality of antennas (12) for transmitting radio frequency
signals between the base station ( 11) and the user equipment (15), the method
comprising:
transmitting a first training signal from the user equipment ( 15) to the base
station ( 1 1) via the first antenna (16) at a first time period,
determining for each antenna (12) of a subset of the plurality of the antennas
(12) of the base station ( 1 1) a corresponding first configuration parameter
based on the first training signal received at the corresponding antenna (12),
transmitting a second training signal from the user equipment (15) to the
base station ( 1 1) via the second antenna (17) at a second time period different to
the first time period,
- determining for each antenna (12) of the subset of the plurality of the anten¬
nas (12) of the base station ( 1 1) a corresponding second configuration parameter
based on the second training signal received at the corresponding antenna (12),
determining a first signal quality parameter of the first training signal,
determining a second signal quality parameter of the second training signal,
and
selecting, based on the determined first and second signal quality parame¬
ters, an antenna of the first and second antennas (16, 17) of the user equipment
( 15) for a transmission of uplink data (UL1 , UL2) from the user equipment ( 15) to
the base station ( 11) .