Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND ARRANGEMENT FOR TRANSMITTING PAYLOAD DATA IN
A RADIOCOMMUNICATION SYSTEM
The invention relates to a method and an arrangement for transmitting payload
data in
a radiocommunication system, particularly a mobile radio system.
In communication systems, messages (for instance voice, image information or
other
data) are transmitted via transmission channels; in radiocommunication systems
this is
l0 accomplished with the aid of electromagnetic waves via a radio interface.
The
electromagnetic waves are emitted with carrier frequencies lying in the
frequency
band that is provided for the respective system. In the GSM mobile
radiotelephone
system (Global System for Mobile Communication), the carrier frequencies are
in the
region of 900 Mhz. For future radiocommunication systems, for instance UMTS
(Universal Mobile Telecommunication System) or other systems of the 3'd
generation,
frequencies in the frequency band of ca. 2000 Mhz are provided.
DE 195 49 158 teaches a radiocommunication system that uses a CDMA subscriber
separation (CDMA: Code Division Multiple Access), whereby the radio interface
2 0 additionally comprises a time division multiplex separation (TDMA). In the
base
stations a joint detection method is used at the receiving side to guarantee a
better
detection of the transmitted payload data given knowledge of the CDMA codes of
several subscribers, since the intracellular interference within a radio
coverage area
can be almost completely eliminated. It is known that several transmission
channels
2 5 can also be allocated to a communication connection via the radio
interface, it being
possible to distinguish each transmission channel by an individual CDMA code.
By contrast, in mobile radio stations a detection of the transmitted payload
data is
performed at the receiving side only on the basis of the allocated CDMA code,
since
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only this is known in the mobile radio station a priori. The CDMA codes of the
other
subscribers are not known and thus cannot be integrated into the detection as
in a joint
detection method. The transmitted payload data of the communication
connections to
the other mobile radio stations are treated as noise, as in the known method
of DS
CDMA subscriber separation (DS: Direct Sequence).
WO 97/05707 teaches a method for reducing common channel interference in
receiving equipment of base and subscriber stations of a cellular radio
system. In the
radio cells, radio channels with the same frequency are used, whereby a signal
transmission is accomplished in accordance with a known JD CDMA method (JD:
Joint Detection). The decoding in the respective receiving equipment in one
radio cell
entails the use, at least in part, of spread codes that are used in at least
one other radio
cell which uses the same frequency band.
It is the object of the invention to set forth a method and an arrangement
that improve
the detection capabilities of a mobile radio station. This object is
inventively achieved
by the method according to the features claimed in patent claim 1, and by the
arrangement according to the features claimed in patent claim 12. Advantageous
developments of the invention emerge from the subclaims.
In the method for transmitting payload data in a radiocommunication system,
payload
data of a communication connection is inventively transmitted from/to a first
and a
second radio station, which are respectively located in a radio coverage area
of a first
base station. At least one frequency channel having several CDMA codes is
allocated
2 5 to the radio coverage area of the first base station. An allocation of a
first or second
CDMA code, respectively, is signaled to the first and second radio stations.
In
addition, the allocation of the second CDMA code to the second radio station
is
signaled to the first radio station, whereupon the first and second CDMA codes
are
used by the first radio station for detecting the transmitted payload data.
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By this inventive method, the first radio station can additionally use the
second
CDMA code for detecting the payload data transmitted to the first radio
station,
whereby the intracellular interference in the first radio station is almost
totally
eliminated, and the reception quality is increased due to an improved
signal/noise
ratio (SNR).
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In a first development of the invention, the payload data are additionally
transmitted
within a TDMA subscriber separation method. Here, each radio channel is
subdivided
into time slots. This subscriber separation method has the advantage that the
payload
data transmission from and to the radio stations can be accomplished in one
frequency
channel, a specific number of time slots being used for the upstream
direction, and a
specific number being used for the downstream direction.
In a further development of the invention, the payload data are detected in
the first
radio station according to a known joint detection method. By this method, the
interference at the location of the first radio station can be almost
completely
eliminated.
According to another development of the invention, the allocation of the CDMA
codes to the first or second radio station, respectively, can occur at the
network side
and can be signaled by the first base station, or alternatively in that the
first and
second radio stations select the first or second CDMA code, respectively, and
the
selection is respectively signaled to the first base station. It is possible
to perform a
flexible and dynamic allocation of CDMA codes in this way. Furthermore, given
allocation at the network side, the CDMA codes can be allocated base-station-
wide,
2 o whereby the quality of reception is increased when different CDMA codes
are used in
neighboring radio coverage areas, due to a lower intercellular interference.
In an advantageous development of the invention, the allocation of additional
CDMA
codes to additional radio stations is also signaled to the first radio
station, which codes
2 5 are additionally used by the first radio station for detecting the payload
data
transmitted thereto. The additional radio stations are located in the same
radio
coverage area and/or in a neighboring area, and payload data are respectively
transmitted from/to to [sic] the additional radio stations in a common
frequency
channel and/or in a common time slot.
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The signaling of the allocation of additional CDMA codes in the neighboring
radio
coverage areas results in an elevated signal load; however, it makes it
possible to
further increase the noise margin, and thus to improve the reception quality.
In a further development of the preceding development, only the allocation of
the
simultaneously active CDMA codes to the additional radio stations is signaled
to the
first radio station. In this way, it is possible to save computing power in
the detection
via the joint detection algorithm, to enlarge the noise margin, and to achieve
an
optimal reception quality given minimal signal processing.
The allocation, or respectively, the signaling of the allocation, to the first
radio station
can alternatively ensue by a transmission of the respective CDMA codes or by a
transmission of code indexes that are allocated to a CDMA code, respectively.
According to a first development, the transmitted CDMA codes are stored in a
storage
device of the first radio station; or respectively, according to a second
development,
the corresponding CDMA codes are detected by the first radio station with the
aid of
the code indexes and are stored in a storage device. Since the costs of
realizing the
storage device in the first radio station are all but negligible, the
signaling load can
advantageously be significantly reduced by this simple measure.
According to another development of the invention, the allocation of a
respective
additional CDMA code is signaled to the first radio station when a connection
is set
up from/to an additional radio station, the payload data of the communication
connection from/to the additional radio station being transmitted only upon
the
2 5 successful completion of the signaling to the first radio station. In this
way it is
advantageously ensured that at all times the first radio station has knowledge
of all
simultaneously active CDMA codes as soon as these are allocated, and even
before
they are used by the additional radio stations, thus guaranteeing a constantly
high
reception quality for the communication connection to the first radio station.
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Furthermore, changes of the allocation of the CDMA
codes are advantageously signaled to the first radio station
when an additional communication connection to an additional
radio station is set up or cleared, respectively; when a higher
5 or lower transmission capacity is required for the additional
communication connection, respectively; or when a connection
takeover is required given the crossing of the additional radio
station into a neighboring radio coverage area of another base
station. Any modification of the allocation and use of CDMA
codes is thereby advantageously signaled to the first radio
station.
In accordance with one aspect of this invention,
there is provided a method for transmitting payload data in a
radiocommunication system comprising a first base station
(BTS1) and at least a first radio station (MS1) and a second
radio station (MS2), which are located in a radio coverage area
of the first base station (BTS1), respectively, in which method
at least one frequency channel having several CDMA codes (CC1,
CC2, CC3,...) is allocated to the radio coverage area of the
first base station (BTS1), payload data of communication
connections (V1, V2) are transmitted from/to the first radio
station (MS1) and the second radio station (MS2) according to
the CDMA subscriber method, a first CDMA code (CC1), which is
allocated to the first radio station (MS1), is signaled to the
first radio station (MS1) and a second CDMA code (CC2), which
is allocated to the second radio station (MS2), is signaled to
the second radio station (MS2), for purposes of detecting the
respective payload data, the allocation of the second CDMA code
(CC2) to the second radio station (MS2) is also signaled to the
first radio station (MS1), and the first CDMA code (CCl) is
used by the first radio station (MS1) to detect the payload
data, and the second CDMA code (CC2) is used by the first radio
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station (MS1) to improve the reception quality of the payload
data.
In accordance with another aspect of this invention,
there is provided a radiocommunication system for transmitting
payload data, comprising a first base station (BTS1) and at
least a first (MS1) and a second (MS2) radio station, which are
located in a radio coverage area of the first base station
(BTS1); whereby, at least one frequency channel having several
CDMA codes (CC1, CC2, CC3...) is allocated to the radio coverage
area of the first base station (BTS1), and payload data of
communication connections (v1, V2) are transmitted from/to the
first radio station (MS1) and the second radio station (MS2)
according to a CDMA subscriber separation method, characterized
in that the first base station (BTS1) comprises means for
allocating a first CDMA code (CC1) to the first radio station
(MS1) and a second CDMA code (CC2) to the second radio station
(MS2), respectively, for purposes of detecting the respective
payload data; the first base station (BTS1) comprises means for
signaling the allocation of the first CDMA code (CC1) to the
first radio station (MS1) and of the second CDMA code (CC2) to
the second radio station (MS2), respectively, and for
additionally signaling to the first radio station (MS1) the
allocation of the second CDMA code (CC2) to the second radio
station (MS2), and the first radio station (MS1) comprises
means for detecting the payload data transmitted thereto with
the aid of the first (CC1) and second (CC2) CDMA codes.
Exemplifying embodiments of the invention are
detailed below with the aid of the enclosed drawings.
Shown are:
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Figure 1 a block circuit diagram of a
radiocommunication system, particularly a mobile radiotelephone
system,
Figure 2 a schematic illustration of the general
structure of the radio interface,
Figure 3 a schematic illustration of the construction
of a radio block,
Figure 4 a block circuit diagram of the receiver of a
radio station,
Figure 5 a signaling flowchart of a connection set-up
to an additional radio station.
The radiocommunication system illustrated in Figure 1
corresponds in its structure to a known GSM mobile
radiotelephone network that consists of a plurality of mobile
switching centers MSC which are interlinked, or respectively,
which provided access to a stationary network PSTN.
Furthermore, these mobile switching centers MSC are
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connected to at least one device for allocating radio resources RNM. In turn,
each of
these devices RNM makes it possible to connect to at least one base station
BTS, in
this case to a first BTS 1 and a second base station BTS2. These base stations
BTS 1
and BTS2 are radio stations that can set up communication connections to
additional
radio stations via a radio interface, in this case to mobile radio stations MS
1 to MS4.
Figure 1 exemplarily depicts three communication connections V1,V2 and V3 for
transmitting payload data and signaling information between the mobile
stations
MS1,MS2,MS3 and the first base station BTSI, whereby a respective C:DMA code
CC1,CC2 or CC3 is allocated to each mobile radio station MS1,MS2,MS3 for
purposes of detecting the payload data in the respective communication
connection
V 1,V2,V3. A fourth communication connection V4 for transmitting payload data
and
signaling information between the fourth mobile radio station MS4 and the
second
base station BTS2 is also illustrated. The CDMA code CC4 is allocated to this
fourth
mobile radio station MS4 for detecting the payload data.
The functionality of this structure is used by the radiocommnuciatoin system
according to the invention; however, it can also be transferred to other
radiocommunication systems, such as wireless subscriber access networks, in
which
2 0 the invention can be applied, as it were.
The base stations BTS 1 and BTS2 are respectively connected to antenna
equipment,
which consists of three individual radiators, for example. Each of the
individual
radiators radiates directionally into a sector of the radio cell that is
covered by the
2 5 respective base station BTS 1 or BTS2. But a greater number of individual
radiators
(according to adaptive antennas) can alternatively be used, so that a spatial
subscriber
separation according to a CDMA method (Space Division Multiple Access) can
also
be used.
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The general structure of the radio interface can be seen in Figure 2. In
accordance
with a TDMA component, a splitting of a broadband frequency range, for
instance the
bandwidth B=1.6 MHz, into several time slots ts, for instance 8 time slots tsl
to ts8, is
provided. Each time slot is in the frequency region B constitutes a frequency
channel.
Within the frequency channels which are provided for payload transmission,
information of several connections is transmitted in radio blocks. In
accordance with
an FDMA component, several frequency regions B are allocated to the
radiocommunication system.
According to Figure 3, these radio blocks for payload data transmission
consist of data
parts dt with data symbols d, in which segments are embedded having Mittambels
m
that are known at the receiving side. The data d are spread in a connection-
specific
manner with a fine structure ( a spread code (CDMA code)), so that, for
instance, K
data channels DK1,DK2,DK3,..,DKK can be separated by this CDMA component at
the receiving side. A specific energy E is allocated to each of these data
channels
DK1,DK2,DK3,..,DKK per symbol at the transmitting side.
The spreading of individual symbols of the data d with Q chips has the effect
that,
within the symbol duration Ts, Q subsegments of duration Tc are transmitted.
The Q
2 o chips form the individual CDMA code. The Mittambel m consists of L chips,
also of
duration Tc. Furthermore, a protection time GUARD of duration Tg is provided
in
the time slot is for purposes of compensating varying signal transit times of
the
connections of consecutive time slots ts.
2 5 Within a broadband frequency region B, the consecutive time slots is are
organized
according to a general structure. Eight time slots is are thus combined into
one frame,
whereby one particular time slot of the frame forms a frequency channel for
transmitting the payload data and is used recurrently by a group of
connections.
Additional frequency channels, for instance for frequency or time
synchronization of
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the mobile radio stations, are not inserted into every frame, but rather at
definite times
within a multiframe. The spacings between these frequency channels determine
the
capacity made available by the radiocommunication system for this purpose.
The parameters of the radio interface are as follows, for example:
Duration of a radio block 577 ~s
Number of chips per Mittambel m 243
Protection time Tg 32 ps
Data symbols per data part N 33
Symbol duration Ts 6.46 ~s
Chips per symbol Q 14
Chip duration Tc 6/13 ~s
In the upstream (MS->BTS) and downstream (BTS -> MS) directions, the
parameters
can also be set differently.
Figure 4 exemplarily details the reception path in a joint detection receiver.
The
receiver relates to radio stations, which can be base stations as well as
mobile radio
stations. Figure 4 only illustrates the signal processing for one exemplary
2 0 communication connection V 1.
In the submodule E 1 the reception signals are converted from the transmission
frequency band into the low-pass region and are split into a real and an
imaginary
component. In the submodule E2 an analogous low-pass filtering ensues; and
lastly,
2 5 in submodule E3 a two-fold oversampling of the reception signal with 13/3
MHz and
a word width of 12 bits ensues.
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In submodule E4 a digital low-pass filtering occurs using a filter of the
bandwidth
13/6 MHz with optimally high edge steepness for channel separation. The twice
oversampled signal then undergoes a 2:1 reduction in the submodule E4.
The resulting reception signal a consists essentially of two parts; namely, a
portion
em for channel estimation, and the portions a l and e2 for data estimation. In
the
submodule ES all channel impulse responses h~k~ are estimated with the aid of
a known
Mittambel base code m of all the data channels transmitted in the respective
time slot.
In the submodule E6 parameters b«~ for matched filters for each data channel
are
determined using the CDMA codes c~k~. In submodule E7 interferences in the
reception blocks a 1 /2 that are used for data estimation, which are caused by
the
Mittambels m ~k~, are eliminated. This is possible based on the knowledge of
h~k~ and
m~k>,
In submodule E8 the cross-correlation matrix A'TA is calculated. Since A'TA
has a
Toplitz structure, it is only necessary here to calculate a small part of the
matrix,
which can then be used to expand to the complete size. In submodule E9 there
occurs
a Cholesky factorization of A'T A into H'T H, whereby H is an upper triangular
2 0 matrix. Because of the Toplitz structure of A'TA, H also approximately has
a Toplitz
structure and need not be calculated entirely. A vector s represents the
reciprocals of
the diagonal elements of H, which can be advantageously used in the equation
system
solvers.
2 5 In the submodule E 10 there occurs a matched filtering of the reception
symbol series
e1/2 with b~k~. Submodule E11 realizes the equation system solver 1 for
H'T*zl/2=ell2, and submodule E12 realizes the equation system solver 2 for
H*dl/2=zl/2. In submodule E13 the estimated data d1/2 are demodulated,
descrambled, and finally convolution-decoded by means of Viterbi decoders. The
CA 02301682 2000-02-28
decoded data blocks e~k~El3 are selectively fed to a first data sink Dl or via
the source
decoder E 14 to a second data sink D2. The source decoding is necessary in
data
blocks that were transmitted via signalling channels SACCH or FACCH.
5 According to the inventive subject matter, this receiver is also employed in
the first
mobile radio station MS1, for example; whereby, besides the allocated first
CDMA
code CCI, the second CDMA code CC2, which was allocated to the second mobile
radio station MS2, is also used in the submodule E6. In Figure 5, a time
characteristic
of a signaling of an allocation of a CDMA code to the third mobile radio
station MS3
l0 is exemplarily illustrated below.
Figure 5 depicts a signaling flowchart with a connection set-up that is
initiated by the
third mobile radio station MS3, and with a signaling of the allocation of a
CDMA
code to the third mobile radio station MS3 and a signaling of this allocation
to the first
mobile radio station MSI, said signaling being performed by the first base
station
BTS 1.
The management of the radio resources in the radio coverage area of the first
base
station BTS l, particularly of the CDMA codes, exemplarily occurs in the
equipment
2 0 known from Figure 1 for allocating radio resources RNM that is connected
to the first
base station BTS 1. The equipment for allocating radio resources RNM thus also
has
at its disposal information about the allocation of CDMA codes in the
neighboring
radio coverage region of a second base station BTS2 and can perform an optimal
allocation in order to minimize the intercellular interference between the
neighboring
2 5 radio coverage areas.
The illustrated signaling is based on generally known and standardized GSM
signaling, whereby a few signaling messages are enhanced for the inventive
method in
order to create the additional signaling of the allocation of CDMA codes. In
addition
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to the known GSM signaling, a signaling message "signaling allocation" (CDMA
code update) is used for signaling the allocation of a CDMA code to a further
mobile
radio station, in this case to the third mobile radio station MS3.
In the example of Figure 5, the third mobile radio station MS3, which is
located in the
radio coverage area of the first base station BTS1 according to Figure 1,
initiates a
"connection set-up attempt" (random access) on a transmission channel RACH
(Random Access Channel) that is reserved for this purpose. An acknowledgment
of
this "connection set-up attempt" is delivered to the third mobile radio
station MS3 by
the first base station BTS 1 by means of an "access acknowledgment" (access
grant).
The signaling of the "access acknowledgment" further contains the allocation
of a
CDMA code CC3 that the third mobile radio station MS3 is to use for detecting
additional signaling data. Furthermore, the allocation of the other active
CDMA
codes - for instance the CDMA code CC 1 that is allocated to the first mobile
radio
station MS l, and the second CDMA code CC2 that is allocated to the second
mobile
radio station MS2 - as well as a starting point to defining the starting time
for using
the third CDMA code CC3 can also be transmitted in the signaling message
"access
acknowledgment" .
2 0 All active mobile radio stations that are located in the radio coverage
area of the first
base station BTS 1 and that transmit payload data in the same frequency
channel and
time slot as the third mobile station MS3 are informed about the newly
allocated third
CDMA code CC3 via the first base station BTS 1. The signaling of the
allocation of
the other CDMA code CC3 to the other active mobile radio stations ensues via a
2 5 "signaling allocation" (CDMA code update), whereby the example illustrated
in
Figure S is limited to the signaling of the allocation of the new third CDMA
code CC3
to the first mobile radio station MS 1. In addition, the starting time to for
using the
third CDMA code CC3 is also transmitted in the signaling messages "signalling
allocation" and "access acknowledgment" to the first mobile radio station MS 1
and to
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the third mobile radio station MS3, respectively. With the aid of this
signaling, it is
possible for the first mobile radio station MS 1 to to [sic] detect the
payload data of the
communication connection V 1 subsequent to the starting time to using is own
allocated first CDMA code CC1, the additional active CDMA codes that are
active in
the radio coverage area, and the newly allocated third CDMA code CC3.
Once the starting time to has been reached, it is also possible for the third
mobile
station MS3 to use the allocated third CDMA code CC3 on the signaling channel,
whereupon it signals the connection set-up and the number K of desired
transmission
l0 channels which are characterized by different codes CDMA to the first base
station
BTS 1 via the signaling message "connection set-up" (SETUP). Given a possible
set-
up of a connection, the first base station BTS 1 then signals a "set-up
acknowledgment" (SETUP ACK), an allocation of new CDMA codes of the desired
number K, and a starting time t, for using the new CDMA codes, to the third
mobile
radio station MS3. As described above, the first base station BTS 1 in turn
signals the
allocation of the new CDMA codes, the dismantling of the third CDMA code, and
the
defined starting time t~ to the first mobile station MS 1. When the starting
time t, has
been attained, the third mobile radio station MS3 can begin the transmission
of the
payload data to the first base station BTS 1 using the K allocated CDMA codes.
At
2 0 the same time, the first mobile radio station MS 1 can use the new
allocated CDMA
codes for the detection of the payload data on the communication connection V
l, for
instance by the joint detection method.
