Title of Invention	TRANSMISSION OF ETHERNET PACKETS VIA A CPRI INTERFACE
Abstract	The invention relates to a method for operating a base station, in which the base station comprises a first unit (REC) and a second unit (RE1, RE2, RE3); data are transmitted between the first unit (REC) and the second unit (RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a continuous synchronous data stream based on the CPRI interface, subsequently called CPRI data; the data stream is transmitted in packets as Ethernet packets, wherein antenna signals to be transmitted in the continuous synchronous data stream have exclusively received antenna signals or antenna signals which are to be sent.

Title of Invention

TRANSMISSION OF ETHERNET PACKETS VIA A CPRI INTERFACE

Abstract

The invention relates to a method for operating a base station, in which the base station comprises a first unit (REC) and a second unit (RE1, RE2, RE3); data are transmitted between the first unit (REC) and the second unit (RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a continuous synchronous data stream based on the CPRI interface, subsequently called CPRI data; the data stream is transmitted in packets as Ethernet packets, wherein antenna signals to be transmitted in the continuous synchronous data stream have exclusively received antenna signals or antenna signals which are to be sent.

Full Text	Transmission of Ethernet packets via a CPRI interface Description The invention relates to a method for operating a base station, in which the base station comprises a CPRI interface between a first unit and a second unit. The invention also relates to a base station for carrying out the method. In radio communication systems, messages, for example containing voice information, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data, are transmitted between a sending station and a receiving station via a radio interface using electromagnetic waves. Depending on the specific refinement of the radio communication system, these stations may be different kinds of subscriber radio stations or network base stations. In a mobile radio communication system, at least some of the subscriber radio stations are mobile radio stations. The electromagnetic waves are emitted at carrier frequencies which are in the frequency band provided for the respective system. Mobile radio communication systems are often in the form of cellular systems, e.g. based on the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standard, with a network infrastructure comprising, by way of example, base stations, devices for inspection and control of the base stations and other network devices. Apart from these expansively organized (supralocal) cellular, hierarchic radio networks, there are also wireless local area networks (WLANs) with a radio coverage area whose expanse is usually much more severely limited. Examples of different standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM. Base stations for radio communication systems contain, various units which are connected to one another by suitable interfaces. Base stations usually comprise units for baseband processing, with data for or from subscriber stations being processed in the devices for baseband processing. In addition, there are transmission and reception units which modulate baseband data delivered by the baseband processing onto carrier frequencies and send them to subscriber stations or convert data received from subscriber stations on the carrier frequencies to baseband and forward them to baseband processing. By way of example, the connection between a unit for baseband processing and a transmission and reception unit can be set up via an interface based on the CPRI standard (at present: CPRI Specification V2 . 0 (2004-10-01), Common Public Radio Interface (CPRI); Interface Specification, available at http://www.cpri.info/). It is the object of the invention to demonstrate an efficient method for operating a base station and to demonstrate exactly such a base station which involve the use of a CPRI interface. This object is achieved by a method having the features of claim 1 and by an apparatus having features from a coordinate claim. Advantageous refinements and developments are the subject matter of subclaims. The inventive method for Operating a base station involves data being transmitted between a first unit and a second unit in the base station via a CPRI interface. In line with the invention CPRI data are transmitted as Ethernet packets. There is a CPRI interface between the two units in the base station. Hence, the protocol stack of the two units contains layers which process data based on the CPRI standard. In line with the invention, these CPRI data arc packetized and transmitted in packets, the Ethernet standard "being used for the transmission in packets. Hence, information bits are transmitted between the first and second units not continuously but rather in packets, and transmission breaks may exist between the individual packets. The fact that Ethernet packets contain CPRI data means that both the first and the second unit process the CPRI data completely on the basis of the Ethernet protocol, i.e.. on the basis of the IEEE 8 02.3 standard. In particular, not just portions of this standard are used. In one development of the invention, the first unit and the second unit use the Ethernet protocol for processing the CPRI data on the bottommost protocol layer. In this context, the protocol layers are the protocol layers in the ISO/OSI layer model. On layers situated above the Ethernet layer, the first unit and the second unit process the data on the basis of the CPRI stipulations. In Line with one advantageous refinement of the invention, a line code added to the CPRI data at the transmitter end corresponds exclusively to the line code based on the Ethernet protocol. In this context, the transmitter may be the first or the second unit. In this case, the CPRI data have no line code bits added to them other than those which are used on the basis of the standard for transmitting Ethernet packets. In line with another refinement of the invention, the CPRI data contain exclusively manufacturer-independent information. This- refinement precludes the transmission of manufacturer-dependent information when CPRI data are transmitted as Ethernet packets. It is advantageous if the CPRI data contain no bits reserved for future expansions. Such bits increase the data rate, and it is therefore possible to dispense with them in order to reduce the data rate. The Ethernet packets therefore contain exclusively bits which are currently used for conveying information. in one development of the invention, the antenna signals which the CPR1 data contain have exclusively received antenna signals or antenna signals which are to be sent transmitted for them. Received antenna signals are signals which have been received by an antenna on the base station and then need to be transmitted between the first and the second unit in the base station. Antenna signals to be sent are signals which are transmitted between the first and the second unit in the base station and then need to be emitted by an antenna on the base station. In line with the development under consideration, only antenna signals which are used are transmitted via the CPRI interface. Filler bits for currently unused antenna signals are not transmitted. This results in a reduction in the data rate in comparison with the situation in which a particular number of antenna signals is transmitted via the CPRI interface, only a portion of which contains information to be emitted or received information, however. In line with one advantageous refinement of the invention, the CPRI data are transmitted between the first unit and a plurality of second units, the first unit being connected to an Ethernet switch and the Ethernet switch being connected to the plurality of second units in a star shape. In this case, the first unit may be connected to the Ethernet switch by means of an Ethernet line using an electrical or optical transmission method, such as by means of a Gbit or 100 Gbit Ethernet line, and each of the second units may be connected to the Ethernet switch by means of an Ethernet line using an electrical transmission method, such as by means of an Mbit or 100 Mbit Ethernet line. This configuration is particularly suitable for applications in buildings in which Mbit Ethernet lines have already been laid which can be used by the base station. In addition, the first unit may be connected to the Ethernet switch by means of an Ethernet line using an optical transmission method, such as by means of a Gbit or 100 Gbit Ethernet line, and each of the second units may be connected to the Ethernet switch by means of an Ethernet line using an electrical transmission method, such as by means of a Gbit or 100 Gbit Ethernet line. This configuration is particularly suitable for spanning large distances between the two units in the base station, on account of the use of the optical transmission method. In one refinement of the invention, the first unit and/or at least one of the second units are connected to the Ethernet switch by means of a plurality of Ethernet lines, with the Link Aggregation method being applied for the transmission via the plurality of Ethernet lines. It is particularly advantageous if the Ethernet packets are transmitted between the first unit and the second unit via one or more Ethernet fines, these Ethernet lines also being used for transmitting other data. In this case, Ethernet lines are used not exclusively for the CPRI interface, but rather CPRI data can share the transmission medium with packets from other applications. In this regard, it is advantageous if the CPRI interface's Ethernet packets are transmitted using VLAN (Virtual Local Area Network) technology. The inventive base station comprises a first and a second unit between which-data are transmitted via a CPRI interface. It has means for transmitting CPRI data as Ethernet packets. The invention is explained in more detail below using an exemplary embodiment. In this context: figure 1 shows a base station system based on the prior art, figure 2 shows a first base station system based on the invention, figure 3a shows a second base station, system based on the invention for indoor applications, figure 3b shows a third base station system based on the invention for metro applications. The base station system shown in figure 1 comprises the baseband processing device REC (Radio Equipment Controller) which is connected, to a radio network control device RNC (Radio Network Controller) via the interface called Iub in UMTS. The baseband processing device REC is connected to the transmission and reception units RE1, RE2 and RE3 (RE: Radio Equipment) via a respective CPRI interface CPRI. The transmission and reception units RE1, RE2 and RE3 emit subscriber station data to subscriber stations and receive such data from them. Figure 1 shows, by way of example, the subscriber station MS which is connected to the transmission and reception unit RE1 via the radio Interface called Uu in UMTS. Each transmission and reception unit RE1, RE2 and RE3 is responsible for emitting radio signals on a radio frequency or in a frequency band and/or to a sector. The CPRI interface is described in the currently valid standard version CPRI Specification V2.0, whose content is referred to here and which is part of the disclosure of the application. The CPRI interface uses an electrical and/or optical transmission method on the physical layer. The CPRI interface is used to transmit various data types, namely synchronization information, control information and useful data, using a time-division multiplex method. The CPRI standard defines layers 1 and 2 of the ISO/OSI protocol stack of the CPRI interface. In line with the prior art, the information transmitted via the CPRI interface is a continuous synchronous data stream which comprises the time-division multiplexed data types. Inline with the invention, the CPRI data, i.e. the information transmitted between the baseband processing device REC and the transmission and reception units RE1, RE2 and RE3 via the CPRI interface CPRI, are transmitted as Ethernet packets. As figure 2 shows, this is done by virtue of the baseband processing device REC being connected to an Ethernet switch ETHERNET SWITCH which is connected to the transmission and reception units REl, RE2 and RE3. This means that the Ethernet protocol ETHERNET is used for the CPRI data on the bottommost layer of the ISO/OSI protocol stack. In contrast to the prior art, a continuous synchronous data stream is not transmitted via the CPRI interface, but rather Ethernet packets. Above the Ethernet layer there are layers specified on the basis of CPRI for processing the CPRI data. In line with the current CPRI standard, the physical layer permits data rates of 614.4 Mbit/s, 1228.8 Mbit/s or 2457.6 Mbit/s. For transmission via Ethernet lines, data rates of 10 Mbit/s, 100 Mbit/s, 1 Gbit/s or 10 Gbit/s are possible. it Would therefore be necessary to use a 1 Gbit/s Ethernet line. for the 614.4 Mbit/s CPRI connection, two 1 Gbit/s Ethernet linos for the 1228.8 Mbit/s CPRI connection and three 1 Gbit/s lines for the 2457.6 Mbit/s CPRI connection. To reduce the number or bandwidth of the Ethernet lines required for transmitting CPRI data, and hence to be able to transmit the CPRI data efficiently as Ethernet packets, the following modifications are possible: Removal of the line code: For the CPRI line code, 8 respective bits are complemented by two bits of redundancy on the physical layer. If this line code is dispensed with, this reduces the CPRI data rate to 4 9.1. 520 Mbit/s, 983.040 Mbit/s or 1966.080 Mbit/s. The use of the Ethernet protocol on the physical layer adds a line code, which means that the CPRI data are transmitted in line- encoded form despite the disappearance of the CPRI line code. In line with the prior art, during the CPRI transmission, the receiver can identify from the line code what components of the CPRI data can. be found at what location within the continuous CPRI data stream. If the CPRI line code is dispensed with, an association should be provided between the structure of the CPRI data and the Ethernet packets which contain the CPRI data. By way of example, the Ethernet packets can have information fields added to them which indicate the start and end of the CPRI frame and the CPRI hyperframe. • Removal, of the manufacturer-specific information and/or of the-bits reserved for future expansions: The removal of the manufacturer-specific control information from the CPRI data results in a reduction in the CPRI data 16 192 rate by = 0.0039 or . = 0.047, depending on the use 16-256 16-256 of the pointer. The removal of the bits reserved for future expansions from the CPRI data results in a reduction in the CPRI data, rate by 52 -----=0.013. 16.256 • Removal of unused antenna signals: Depending on the form of the base station, a different number of antenna signals is required, an antenna signal being understood to mean the signal emitted or received by an antenna. Usually, a UMTS base station has six antennas, whereas a micro base station has just one antenna. The different number of antennas used means that it is possible that transmission resources which are provided and reserved for antenna signals are not used.in the case of CPRI. For unused antenna signals, zeros are transmitted between the baseband processing device REC and the transmission and reception units RE1, RE2 and RE3. Removing these unused resources from the CPRI data reduces the bandwidth required for transmitting CPRI data further. Using, the measures explained, it is possible to transmit a connection for CPRI data, which originally requires 1228.8 Mbit/s, via 1 Gbit/s Ethernet line, a 2457.6 Mbit/s CPRI connection via two 1 Gbit/s Ethernet lines and a 614.4 Mbit/s CPRI connection via a few 100 Mbit/s Ethernet lines. If the. CPRI data are transmitted . using Ethernet packets, existing Ethernet lines can be used to connect the baseband processing device REC to the transmission and" reception units RE1, RE2 and RE3. Figures 3a and 3b show examples of the use of existing Ethernet lines for the connection between the baseband processing device REC and the transmission and reception units REl, RE2 and RE3. The configuration shown in figure 3a is particularly suitable for indoor applications, i.e. for cases in which the transmission and reception units RE1, RE2 and RE3 are inside a building. The baseband processing device REC is connected to the Ethernet switch ETHERNET SWITCH by means of a gigabit Ethernet line GbE, whereas the transmission and reception units REl, RE2 and RE3 are respectively connected to the Ethernet switch ETHERNET SWITCH by means of two 100 Mbit Ethernet lines 100 MbE. It is naturally possible for the transrajssion and reception units RE1, RE2 and RE3 to be respectively connected to the Ethernet switch ETHERNET SWITCH by means of different numbers of Ethernet lines. An indoor base station usually provides coverage, for just one radio cell, a radio cell being understood to mean a particular sector in combination with a particular frequency band. An indoor base station Lherefore has no requirement for high data rates to be transmitted from and to the transmission and reception units RE1, RE2 and RE3, which means that the two 100 Mbit Ethernet lines 100 MbE are sufficient to supply one transmission and reception unit RE1, RE2 or RE3 each. In the case of 100 Mbit Ethernet lines, an electrical transmission method is used, and the range of these connections is several 100 meters at most. Many bulldings are wired with 100 Mbit Ethernet lines, which means that, already existing lines can be used for transmitting the CPRI data. The configuration shown in figure 3b is particularly suitable for metro applications, i.e. for instances in which the transmission and reception units RE1, RE2 and RE3 are distributed within an area which is approximately the size of a town. The baseband processing device REC is connected to the Ethernet switch ETHERNET SWITCH by means of a gigabit Ethernet line GbE. and the transmission and reception units RE1, RE2 and RE3 are also respectively connected to the Ethernet switch ETHERNET SWITCH by means of a gigabit Ethernet line GbE. For radio coverage, in an urban area, the transmission and receptidit units RE1, RE2 and R.E3 need to. cover a larger geographical area in comparison with the indoor scenario, and in this case a base station usually provides coverage for a plurality of radio cells. A larger volume of information is therefore sent to and received from subscriber stations by the transmission and reception units RE1, RE2 and RE3 than in the case of the indoor scenario, which means that it is appropriate to connect the transmission and reception units RE1, RE2 and RE3 by means of gigabit Ethernet lines GbE. For the gigabit Ethernet lines GbE, an optical transmission method is used, which means that the gigabit Ethernet lines can extend over several kilometers. Instead of the gigabit Ethernet lines GbE, it is also . possible to use 10 gigabit Ethernet lines. Transmit Ling CPRI data over gigabit Ethernet lines is advantageous because these connections are not expensive and arc increasingly being laid. It is advantageous if the Ethernet lines are used to transport not exclusively CPRI data but also other data. The Ethernet lines transmission resources can therefore be split between the CPRI application and other applications. Since the CPRI data need to be transmitted in real time, it is advantageous to use the VLAN (Virtual Local Area Network) technology known from Ethernet. This allows the CPRI data to be allocated a higher priority than the data of the other applications. VLAN is described by way of example in IEEE: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specification, IEEE Standards IEEE 802.3, 2002, part 1, particularly pages 42 and 43, and 802.1Q, IEEE Standards for Local and metropolitan area networks, Virtual Bridged Local Area Networks, May 7, 2003. If a plurality of parallel Ethernet lines are being used, as in figure 3a between the Ethernet switch ETHERNET SWITCH and the transmission and reception units RE1/-RE2 and RE3, for examples it is appropriate to use the Link Aggregation Method known from Ethernet, described by way of example in IEEE: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specification, IEEE Standards IEEE 802.3, 2002, part 2, particularly pages 269 ff. In this context, data are alternately passed to the plurality of lines. WE CLAIM : 1. Method for operating a base station, in which the base station comprises a first unit (REC) and a second unit (RE1, RE2, RE3); data are transmitted between the first unit (REC) and the second unit (RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a continuous synchronous data stream based on the CPRI interface, subsequently called CPRI data; characterized in that: the data stream is transmitted in packets as Ethernet packets, wherein antenna signals, to be transmitted in the continuous synchronous data stream have exclusively received antenna signals or antenna signals which are to be sent. 2. Method as claimed in Claim 1, wherein the first unit (REC) and the second unit (RE1, RE2, RE3) use the Ethernet protocol for processing the CPRI data on the bottommost protocol layer. 3. Method as claimed in one of Claims 1 and 2, wherein a line code added to the CPRI data at the transmitter end corresponds exclusively to the line code based on the Ethernet protocol. 4. Method as claimed in one of Claims 1 to 3, wherein the CPRI data contain exclusively manufacturer-in-dependent information. 5. Method as claimed in one of Claims 1 to 4, wherein the CPRI data contain no bits reserved for future expansions. 6. Method as claimed in one of Claims 1 to 5, wherein the CPRI data are transmitted between the first unit (REC) and a plurality of second units (RE1, RE2, RE3), the first unit (REC) being connected to an Ethernet switch (ETHERNET SWITCH) and the Ethernet switch (ETHERNET SWITCH) being connected to the plurality of second units (RE1, RE2, RE3) in a star shape. 7. Method as claimed in Claim 6, wherein the first unit (REC) is connected to the Ethernet switch (ETHERNET SWITCH) by means of an Ethernet line (GbE) using an electrical or optical transmission method, and each of the second units (RE1, RE2, RE3) is connected to the Ethernet switch (ETHERNET SWITCH) by means of and Ethernet line (100 MbE) using an electrical transmission method. 8. Method as claimed in Claim 6, wherein the first unit (REC) is connected to the Ethernet switch (ETHERNET SWITHC) by means of an Ethernet line (GbE) using an optical transmission method, and each of the second units (RE1, RE2, RE3) is connected to the Ethernet switch (ETHERNET SWITHC) by means of an Ethernet line (GbE) using an optical transmission method. 9. Method as claimed in one of Claims 6 to 8, wherein the first unit (REC) and/or at least one of the second units (RE1, RE2, RE3) are connected to the Ethernet switch (ETHERNET SWITHC) by means of a plurality of Ethernet lines (GbE, 100 MbE), with the Link Aggregation method being applied for the transmission via the plurality of Ethernet lines (GbE, 100 MbE). 10. Method as claimed in one of Claims 1 to 9, wherein the Ethernet packets are transmitted between the first unit (REC) and the second unit (RE1, RE2, RE3) via one or more Ethernet lines (GbE, 100 MbE), these Ethernet lines (GbE, 100 MbE) also being used for transmitting other data. 11. Method as claimed in Claim 10, wherein the Ethernet packets are transmitted using VLAN. 12. Base station having a first unit (REC) and a second unit (RE1, RE2, RE3) between which data are transmitted via a CPRI interface (CPRI), the data being a continuous synchronous data stream based on the CPRI interface, characterized by means for transmitting the data stream in packets as Ethernet packets, wherein antenna signals contained in the continuous synchronous data stream have exclusively received antenna signals or antenna signals which are to be sent. ABSTRACT TITLE "TRANSMISSION OF ETHERNET PACKETS VIA A CPRI INTERFACE" The invention relates to a method for operating a base station, in which the base station comprises a first unit (REC) and a second unit (RE1, RE2, RE3); data are transmitted between the first unit (REC) and the second unit (RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a continuous synchronous data stream based on the CPRI interface, subsequently called CPRI data; the data stream is transmitted in packets as Ethernet packets, wherein antenna signals to be transmitted in the continuous synchronous data stream have exclusively received antenna signals or antenna signals which are to be sent.

Full Text

Transmission of Ethernet packets via a CPRI interface
Description
The invention relates to a method for operating a base station,
in which the base station comprises a CPRI interface between a first unit and a second unit. The invention also relates to a
base station for carrying out the method.
In radio communication systems, messages, for example
containing voice information, image information, video
information, SMS (Short Message Service), MMS (Multimedia
Messaging Service) or other data, are transmitted between a
sending station and a receiving station via a radio interface
using electromagnetic waves. Depending on the specific
refinement of the radio communication system, these stations
may be different kinds of subscriber radio stations or network
base stations. In a mobile radio communication system, at least
some of the subscriber radio stations are mobile radio
stations. The electromagnetic waves are emitted at carrier
frequencies which are in the frequency band provided for the
respective system.
Mobile radio communication systems are often in the form of
cellular systems, e.g. based on the GSM (Global System for
Mobile Communication) or UMTS (Universal Mobile
Telecommunications System) standard, with a network
infrastructure comprising, by way of example, base stations,
devices for inspection and control of the base stations and
other network devices. Apart from these expansively organized
(supralocal) cellular, hierarchic radio networks, there are
also wireless local area networks (WLANs) with a radio coverage
area whose expanse is usually much more severely limited.
Examples of different standards for WLANs are HiperLAN, DECT,
IEEE 802.11, Bluetooth and WATM.

Base stations for radio communication systems contain, various
units which are connected to one another by suitable
interfaces. Base stations usually comprise units for baseband
processing, with data for or from subscriber stations being
processed in the devices for baseband processing. In addition,
there are transmission and reception units which modulate
baseband data delivered by the baseband processing onto carrier
frequencies and send them to subscriber stations or convert
data received from subscriber stations on the carrier
frequencies to baseband and forward them to baseband
processing. By way of example, the connection between a unit
for baseband processing and a transmission and reception unit
can be set up via an interface based on the CPRI standard (at
present: CPRI Specification V2 . 0 (2004-10-01), Common Public
Radio Interface (CPRI); Interface Specification, available at
http://www.cpri.info/).
It is the object of the invention to demonstrate an efficient
method for operating a base station and to demonstrate exactly
such a base station which involve the use of a CPRI interface.
This object is achieved by a method having the features of
claim 1 and by an apparatus having features from a coordinate
claim. Advantageous refinements and developments are the
subject matter of subclaims.
The inventive method for Operating a base station involves data
being transmitted between a first unit and a second unit in the
base station via a CPRI interface. In line with the invention
CPRI data are transmitted as Ethernet packets.
There is a CPRI interface between the two units in the base
station. Hence, the protocol stack of the two units contains
layers which process data based on the CPRI standard. In line
with the invention, these CPRI

data arc packetized and transmitted in packets, the Ethernet
standard "being used for the transmission in packets. Hence,
information bits are transmitted between the first and second
units not continuously but rather in packets, and transmission
breaks may exist between the individual packets. The fact that
Ethernet packets contain CPRI data means that both the first
and the second unit process the CPRI data completely on the
basis of the Ethernet protocol, i.e.. on the basis of the IEEE
8 02.3 standard. In particular, not just portions of this
standard are used.
In one development of the invention, the first unit and the
second unit use the Ethernet protocol for processing the CPRI
data on the bottommost protocol layer. In this context, the
protocol layers are the protocol layers in the ISO/OSI layer
model. On layers situated above the Ethernet layer, the first
unit and the second unit process the data on the basis of the
CPRI stipulations.
In Line with one advantageous refinement of the invention, a
line code added to the CPRI data at the transmitter end
corresponds exclusively to the line code based on the Ethernet protocol. In this context, the transmitter may be the first or
the second unit. In this case, the CPRI data have no line code
bits added to them other than those which are used on the basis
of the standard for transmitting Ethernet packets.
In line with another refinement of the invention, the CPRI data
contain exclusively manufacturer-independent information. This-
refinement precludes the transmission of manufacturer-dependent
information when CPRI data are transmitted as Ethernet packets.
It is advantageous if the CPRI data contain no bits reserved
for future expansions. Such bits

increase the data rate, and it is therefore possible to
dispense with them in order to reduce the data rate. The
Ethernet packets therefore contain exclusively bits which are
currently used for conveying information.
in one development of the invention, the antenna signals which the CPR1 data contain have exclusively received antenna signals
or antenna signals which are to be sent transmitted for them.
Received antenna signals are signals which have been received
by an antenna on the base station and then need to be
transmitted between the first and the second unit in the base
station. Antenna signals to be sent are signals which are
transmitted between the first and the second unit in the base
station and then need to be emitted by an antenna on the base
station. In line with the development under consideration, only
antenna signals which are used are transmitted via the CPRI
interface. Filler bits for currently unused antenna signals are
not transmitted. This results in a reduction in the data rate
in comparison with the situation in which a particular number
of antenna signals is transmitted via the CPRI interface, only
a portion of which contains information to be emitted or
received information, however.
In line with one advantageous refinement of the invention, the
CPRI data are transmitted between the first unit and a
plurality of second units, the first unit being connected to an
Ethernet switch and the Ethernet switch being connected to the
plurality of second units in a star shape. In this case, the
first unit may be connected to the Ethernet switch by means of
an Ethernet line using an electrical or optical transmission
method, such as by means of a Gbit or 100 Gbit Ethernet line,
and each of the second units may be connected to the Ethernet
switch by means of an Ethernet line using an electrical
transmission method, such as by means of an Mbit or 100 Mbit
Ethernet line. This configuration is particularly suitable for
applications in buildings in which Mbit Ethernet lines have

already been

laid which can be used by the base station. In addition, the
first unit may be connected to the Ethernet switch by means of
an Ethernet line using an optical transmission method, such as
by means of a Gbit or 100 Gbit Ethernet line, and each of the
second units may be connected to the Ethernet switch by means
of an Ethernet line using an electrical transmission method, such as by means of a Gbit or 100 Gbit Ethernet line. This
configuration is particularly suitable for spanning large
distances between the two units in the base station, on account
of the use of the optical transmission method.
In one refinement of the invention, the first unit and/or at
least one of the second units are connected to the Ethernet
switch by means of a plurality of Ethernet lines, with the Link
Aggregation method being applied for the transmission via the
plurality of Ethernet lines.
It is particularly advantageous if the Ethernet packets are
transmitted between the first unit and the second unit via one
or more Ethernet fines, these Ethernet lines also being used
for transmitting other data. In this case, Ethernet lines are
used not exclusively for the CPRI interface, but rather CPRI
data can share the transmission medium with packets from other
applications. In this regard, it is advantageous if the CPRI
interface's Ethernet packets are transmitted using VLAN
(Virtual Local Area Network) technology.
The inventive base station comprises a first and a second unit between which-data are transmitted via a CPRI interface. It has
means for transmitting CPRI data as Ethernet packets.
The invention is explained in more detail below using an
exemplary embodiment. In this context:

figure 1 shows a base station system based on the prior art,
figure 2 shows a first base station system based on the
invention,
figure 3a shows a second base station, system based on the
invention for indoor applications,
figure 3b shows a third base station system based on the
invention for metro applications.
The base station system shown in figure 1 comprises the
baseband processing device REC (Radio Equipment Controller)
which is connected, to a radio network control device RNC (Radio
Network Controller) via the interface called Iub in UMTS. The
baseband processing device REC is connected to the transmission
and reception units RE1, RE2 and RE3 (RE: Radio Equipment) via
a respective CPRI interface CPRI. The transmission and
reception units RE1, RE2 and RE3 emit subscriber station data
to subscriber stations and receive such data from them. Figure
1 shows, by way of example, the subscriber station MS which is
connected to the transmission and reception unit RE1 via the
radio Interface called Uu in UMTS. Each transmission and
reception unit RE1, RE2 and RE3 is responsible for emitting
radio signals on a radio frequency or in a frequency band
and/or to a sector.
The CPRI interface is described in the currently valid standard
version CPRI Specification V2.0, whose content is referred to
here and which is part of the disclosure of the application.
The CPRI interface uses an electrical and/or optical
transmission method on the physical layer. The CPRI interface
is used to transmit various data types, namely synchronization
information, control information and useful data, using

a time-division multiplex method. The CPRI standard defines
layers 1 and 2 of the ISO/OSI protocol stack of the CPRI
interface. In line with the prior art, the information
transmitted via the CPRI interface is a continuous synchronous
data stream which comprises the time-division multiplexed data
types.
Inline with the invention, the CPRI data, i.e. the information
transmitted between the baseband processing device REC and the
transmission and reception units RE1, RE2 and RE3 via the CPRI
interface CPRI, are transmitted as Ethernet packets. As figure
2 shows, this is done by virtue of the baseband processing
device REC being connected to an Ethernet switch ETHERNET
SWITCH which is connected to the transmission and reception
units REl, RE2 and RE3. This means that the Ethernet protocol
ETHERNET is used for the CPRI data on the bottommost layer of
the ISO/OSI protocol stack. In contrast to the prior art, a continuous synchronous data stream is not transmitted via the
CPRI interface, but rather Ethernet packets. Above the Ethernet
layer there are layers specified on the basis of CPRI for
processing the CPRI data.
In line with the current CPRI standard, the physical layer
permits data rates of 614.4 Mbit/s, 1228.8 Mbit/s or
2457.6 Mbit/s. For transmission via Ethernet lines, data rates
of 10 Mbit/s, 100 Mbit/s, 1 Gbit/s or 10 Gbit/s are possible.
it Would therefore be necessary to use a 1 Gbit/s Ethernet line.
for the 614.4 Mbit/s CPRI connection, two 1 Gbit/s Ethernet
linos for the 1228.8 Mbit/s CPRI connection and three 1 Gbit/s
lines for the 2457.6 Mbit/s CPRI connection. To reduce the number or bandwidth of the Ethernet lines required for
transmitting CPRI data, and hence to be able to transmit the
CPRI data efficiently as Ethernet packets, the following
modifications are possible:

Removal of the line code:
For the CPRI line code, 8 respective bits are complemented by
two bits of redundancy on the physical layer. If this line
code is dispensed with, this reduces the CPRI data rate to
4 9.1. 520 Mbit/s, 983.040 Mbit/s or 1966.080 Mbit/s. The use of
the Ethernet protocol on the physical layer adds a line code,
which means that the CPRI data are transmitted in line-
encoded form despite the disappearance of the CPRI line code.
In line with the prior art, during the CPRI transmission, the
receiver can identify from the line code what components of
the CPRI data can. be found at what location within the
continuous CPRI data stream. If the CPRI line code is
dispensed with, an association should be provided between the
structure of the CPRI data and the Ethernet packets which
contain the CPRI data. By way of example, the Ethernet
packets can have information fields added to them which
indicate the start and end of the CPRI frame and the CPRI
hyperframe.
• Removal, of the manufacturer-specific information and/or of
the-bits reserved for future expansions:
The removal of the manufacturer-specific control information
from the CPRI data results in a reduction in the CPRI data
16 192
rate by = 0.0039 or . = 0.047, depending on the use
16-256 16-256
of the pointer.
The removal of the bits reserved for future expansions from
the CPRI data results in a reduction in the CPRI data, rate by
52
-----=0.013.
16.256
• Removal of unused antenna signals:
Depending on the form of the base station, a different number
of antenna signals is

required, an antenna signal being understood to mean the
signal emitted or received by an antenna. Usually, a UMTS
base station has six antennas, whereas a micro base station
has just one antenna. The different number of antennas used
means that it is possible that transmission resources which
are provided and reserved for antenna signals are not used.in
the case of CPRI. For unused antenna signals, zeros are
transmitted between the baseband processing device REC and
the transmission and reception units RE1, RE2 and RE3.
Removing these unused resources from the CPRI data reduces
the bandwidth required for transmitting CPRI data further.
Using, the measures explained, it is possible to transmit a
connection for CPRI data, which originally requires
1228.8 Mbit/s, via 1 Gbit/s Ethernet line, a 2457.6 Mbit/s CPRI
connection via two 1 Gbit/s Ethernet lines and a 614.4 Mbit/s
CPRI connection via a few 100 Mbit/s Ethernet lines.
If the. CPRI data are transmitted . using Ethernet packets,
existing Ethernet lines can be used to connect the baseband
processing device REC to the transmission and" reception units
RE1, RE2 and RE3. Figures 3a and 3b show examples of the use of
existing Ethernet lines for the connection between the baseband
processing device REC and the transmission and reception units
REl, RE2 and RE3.
The configuration shown in figure 3a is particularly suitable
for indoor applications, i.e. for cases in which the
transmission and reception units RE1, RE2 and RE3 are inside a
building. The baseband processing device REC is connected to
the Ethernet switch ETHERNET SWITCH by means of a gigabit
Ethernet line GbE, whereas the transmission and reception units
REl, RE2 and RE3 are respectively connected to the

Ethernet switch ETHERNET SWITCH by means of two 100 Mbit
Ethernet lines 100 MbE. It is naturally possible for the
transrajssion and reception units RE1, RE2 and RE3 to be
respectively connected to the Ethernet switch ETHERNET SWITCH
by means of different numbers of Ethernet lines. An indoor base
station usually provides coverage, for just one radio cell, a
radio cell being understood to mean a particular sector in
combination with a particular frequency band. An indoor base
station Lherefore has no requirement for high data rates to be
transmitted from and to the transmission and reception units
RE1, RE2 and RE3, which means that the two 100 Mbit Ethernet
lines 100 MbE are sufficient to supply one transmission and
reception unit RE1, RE2 or RE3 each. In the case of 100 Mbit
Ethernet lines, an electrical transmission method is used, and
the range of these connections is several 100 meters at most.
Many bulldings are wired with 100 Mbit Ethernet lines, which
means that, already existing lines can be used for transmitting
the CPRI data.
The configuration shown in figure 3b is particularly suitable
for metro applications, i.e. for instances in which the
transmission and reception units RE1, RE2 and RE3 are
distributed within an area which is approximately the size of a
town. The baseband processing device REC is connected to the
Ethernet switch ETHERNET SWITCH by means of a gigabit Ethernet
line GbE. and the transmission and reception units RE1, RE2 and
RE3 are also respectively connected to the Ethernet switch
ETHERNET SWITCH by means of a gigabit Ethernet line GbE. For
radio coverage, in an urban area, the transmission and receptidit
units RE1, RE2 and R.E3 need to. cover a larger geographical area
in comparison with the indoor scenario, and in this case a base
station usually provides coverage for a plurality of radio
cells. A larger volume of information is therefore sent to and
received from subscriber stations by the transmission and
reception units RE1, RE2 and RE3 than in the case of the indoor

scenario, which means that it is appropriate to connect the
transmission and reception units RE1, RE2 and RE3

by means of gigabit Ethernet lines GbE. For the gigabit
Ethernet lines GbE, an optical transmission method is used,
which means that the gigabit Ethernet lines can extend over
several kilometers. Instead of the gigabit Ethernet lines GbE,
it is also . possible to use 10 gigabit Ethernet lines.
Transmit Ling CPRI data over gigabit Ethernet lines is
advantageous because these connections are not expensive and
arc increasingly being laid.
It is advantageous if the Ethernet lines are used to transport
not exclusively CPRI data but also other data. The Ethernet lines transmission resources can therefore be split between
the CPRI application and other applications. Since the CPRI
data need to be transmitted in real time, it is advantageous to
use the VLAN (Virtual Local Area Network) technology known from
Ethernet. This allows the CPRI data to be allocated a higher
priority than the data of the other applications. VLAN is
described by way of example in
IEEE: Carrier sense multiple access with collision
detection (CSMA/CD) access method and physical layer
specification, IEEE Standards IEEE 802.3, 2002, part 1,
particularly pages 42 and 43, and
802.1Q, IEEE Standards for Local and metropolitan area
networks, Virtual Bridged Local Area Networks, May 7,
2003.
If a plurality of parallel Ethernet lines are being used, as in
figure 3a between the Ethernet switch ETHERNET SWITCH and the
transmission and reception units RE1/-RE2 and RE3, for examples
it is appropriate to use the Link Aggregation Method known from
Ethernet, described by way of example in
IEEE: Carrier sense multiple access with collision
detection (CSMA/CD) access method and physical layer
specification, IEEE Standards IEEE 802.3, 2002, part 2,
particularly pages 269 ff.

In this context, data are alternately passed to the plurality
of lines.

WE CLAIM :
1. Method for operating a base station, in which the base station comprises a
first unit (REC) and a second unit (RE1, RE2, RE3);
data are transmitted between the first unit (REC) and the second unit
(RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a continuous
synchronous data stream based on the CPRI interface, subsequently
called CPRI data;
characterized in that:
the data stream is transmitted in packets as Ethernet packets, wherein
antenna signals, to be transmitted in the continuous synchronous data
stream have exclusively received antenna signals or antenna signals which
are to be sent.
2. Method as claimed in Claim 1, wherein the first unit (REC) and the second
unit (RE1, RE2, RE3) use the Ethernet protocol for processing the CPRI
data on the bottommost protocol layer.
3. Method as claimed in one of Claims 1 and 2, wherein a line code added to
the CPRI data at the transmitter end corresponds exclusively to the line
code based on the Ethernet protocol.
4. Method as claimed in one of Claims 1 to 3, wherein the CPRI data contain
exclusively manufacturer-in-dependent information.
5. Method as claimed in one of Claims 1 to 4, wherein the CPRI data contain
no bits reserved for future expansions.

6. Method as claimed in one of Claims 1 to 5, wherein the CPRI data are
transmitted between the first unit (REC) and a plurality of second units
(RE1, RE2, RE3), the first unit (REC) being connected to an Ethernet
switch (ETHERNET SWITCH) and the Ethernet switch (ETHERNET
SWITCH) being connected to the plurality of second units (RE1, RE2, RE3)
in a star shape.
7. Method as claimed in Claim 6, wherein the first unit (REC) is connected to
the Ethernet switch (ETHERNET SWITCH) by means of an Ethernet line
(GbE) using an electrical or optical transmission method, and each of the
second units (RE1, RE2, RE3) is connected to the Ethernet switch
(ETHERNET SWITCH) by means of and Ethernet line (100 MbE) using an
electrical transmission method.
8. Method as claimed in Claim 6, wherein the first unit (REC) is connected to
the Ethernet switch (ETHERNET SWITHC) by means of an Ethernet line
(GbE) using an optical transmission method, and each of the second units
(RE1, RE2, RE3) is connected to the Ethernet switch (ETHERNET SWITHC)
by means of an Ethernet line (GbE) using an optical transmission method.
9. Method as claimed in one of Claims 6 to 8, wherein the first unit (REC)
and/or at least one of the second units (RE1, RE2, RE3) are connected to
the Ethernet switch (ETHERNET SWITHC) by means of a plurality of
Ethernet lines (GbE, 100 MbE), with the Link Aggregation method being
applied for the transmission via the plurality of Ethernet lines (GbE, 100
MbE).

10. Method as claimed in one of Claims 1 to 9, wherein the Ethernet packets
are transmitted between the first unit (REC) and the second unit (RE1,
RE2, RE3) via one or more Ethernet lines (GbE, 100 MbE), these Ethernet
lines (GbE, 100 MbE) also being used for transmitting other data.
11. Method as claimed in Claim 10, wherein the Ethernet packets are
transmitted using VLAN.
12. Base station having a first unit (REC) and a second unit (RE1, RE2, RE3)
between which data are transmitted via a CPRI interface (CPRI), the data
being a continuous synchronous data stream based on the CPRI interface,
characterized by
means for transmitting the data stream in packets as Ethernet packets,
wherein antenna signals contained in the continuous synchronous data
stream have exclusively received antenna signals or antenna signals which
are to be sent.

ABSTRACT

TITLE "TRANSMISSION OF ETHERNET PACKETS VIA
A CPRI INTERFACE"
The invention relates to a method for operating a base station, in which
the base station comprises a first unit (REC) and a second unit (RE1, RE2,
RE3); data are transmitted between the first unit (REC) and the second
unit (RE1, RE2, RE3) via a CPRI interface (CPRI), the data being a
continuous synchronous data stream based on the CPRI interface,
subsequently called CPRI data; the data stream is transmitted in packets
as Ethernet packets, wherein antenna signals to be transmitted in the
continuous synchronous data stream have exclusively received antenna
signals or antenna signals which are to be sent.

TRANSMISSION OF ETHERNET PACKETS VIA A CPRI INTERFACE

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