Telecommunications – Radiotelephone system
Reexamination Certificate
2001-05-21
2004-07-27
Trost, William (Department: 2684)
Telecommunications
Radiotelephone system
C455S410000, C455S411000, C455S422100, C455S517000, C380S247000, C380S248000, C380S249000, C380S250000, C380S033000, C380S034000
Reexamination Certificate
active
06768903
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of radiocommunications, and in particular to the ciphering techniques used in cellular networks.
The invention finds application in particular in third-generation cellular networks of the UMTS type (“Universal Mobile Telecommunication System”) using code division multiple access (CDMA) techniques.
The invention is described hereinbelow in its application to a UMTS network, of which
FIG. 1
shows the architecture.
The switches of the mobile service
10
, belonging to a core network (CN), are linked on the one hand to one or more fixed networks
11
and on the other hand, by means of a so-called Iu interface, to control equipment
12
or RNCs (“Radio Network Controllers”) Each RNC
12
is linked to one or more base stations
13
by means of a so-called Iub interface. The base stations
13
, distributed over the territory covered by the network, are capable of communicating by radio with the mobile terminals
14
,
14
a
,
14
b
called UE (“User Equipment”). The base stations can be grouped together to form nodes called “node B”. Certain RNCs
12
may furthermore communicate with one another by means of a so-called Iur interface. The RNCs and the base stations form an access network called UTRAN (“UMTS Terrestrial Radio Access Network”).
The UTRAN comprises elements of layers
1
and
2
of the OSI model with a view to providing the links required on the radio interface (called Uu), and a stage
15
A for controlling the radio resources (RRC, “Radio Resource Control”) belonging to layer
3
, as described in the technical specification 3G TS 25.301, “Radio Interface Protocol”, version 3.4.0, published in March 2000 by the 3GPP (3
rd
Generation Partnership Project). Seen from the higher layers, the UTRAN acts simply as a relay between the UE and the CN.
FIG. 2
shows the RRC stages
15
A,
15
B and the stages of the lower layers which belong to the UTRAN and to UE. On each side, layer
2
is subdivided into a radio link control (RLC) stage
16
A,
16
B and a medium access control (MAC) stage
17
A,
17
B. Layer
1
comprises a coding and multiplexing stage
18
A,
18
B. A radio stage
19
A,
19
B caters for the transmission of the radio signals from trains of symbols provided by the stage
18
A,
18
B, and the reception of the signals in the other direction.
There are various ways of adapting the architecture of protocols according to
FIG. 2
to the hardware architecture of the UTRAN according to
FIG. 1
, and in general various organizations can be adopted depending on the types of channels (see section 11.2 of the technical specification 3G TS 25.401, “UTRAN Overall Description”, version 3.1.0, published in January 2000 by the 3GPP). The RRC, RLC and MAC stages are located in the RNC
12
. Layer
1
is located for example in node B. A part of this layer may however be located in the RNC
12
.
When several RNCs are involved in a communication with UE, there is generally a so-called serving RNC called SRNC where the modules pertaining to layer
2
(RLC and MAC) are located, and at least one drift RNC called DRNC to which is linked a base station with which the UE is in a radio link. Appropriate protocols cater for the exchanges between these RNCs over the Iur interface, for example ATM (“Asynchronous Transfer Mode”) and AAL2 (“ATM Adaptation Layer No. 2”). These same protocols can also be employed over the Iub interface for the exchanges between a node B and its RNC.
Layers
1
and
2
are each controlled by the RRC sublayer, whose characteristics are described in the technical specification 3G TS 25.331, “RRC Protocol Specification”, version 3.1.0, published in October 1999 by the 3GPP. The RRC stage
15
A,
15
B supervises the radio interface. Moreover, it processes streams to be transmitted to the remote station according to a “control plan”, as opposed to the “user plan” which corresponds to the processing of the user data arising from layer
3
.
The RLC sublayer is described in the technical specification 3G TS 25.322, “RLC Protocol Specification”, version 3.2.0, published in March 2000 by the 3GPP. In the transmit direction, the RLC stage
16
A,
16
B receives, according to the respective logical channels, data streams consisting of service data units (RLC-SDU) arising from layer
3
. An RLC module of the stage
16
A,
16
B is associated with each logical channel so as in particular to perform a segmentation of the RLC-SDU units of the stream into protocol data units (RLC-PDU) addressed to the MAC sublayer and comprising an optional RLC header. In the receive direction, an RLC module conversely performs a reassembling of the RLC-SDU units of the logical channel from the data units received from the MAC sublayer.
The RLC stage
16
A,
16
B can have several modes of operation as a function in particular of the type of logical channel. Subsequently in the present description, consideration will be given to the transparent mode of the RLC sublayer, which is suitable for a logical channel relating to a communication in circuit mode. In this transparent mode, the RLC module performs the segmentation and reassembling operations when they are necessary, and it does not introduce any header into the RLC-PDU units.
The MAC sublayer is described in the technical specification 3G TS 25.321, “MAC Protocol Specification”, version 3.3.0, published in March 2000 by the 3GPP. It transposes one or more logical channels onto one or more transport channels TrCH. In the transmit direction, the MAC stage
17
A,
17
B can multiplex one or more logical channels in one and the same transport channel. On such a transport channel, the MAC stage
17
A,
17
B delivers successive transport blocks TrBk each consisting of an optional MAC header and an RLC-PDU unit arising from an associated logical channel.
For each TrCH, the RRC sublayer provides the MAC sublayer with a set of transport formats (TFS, “Transport Format Set”). A transport format comprises a transmission time interval (TTI) equal to 10, 20, 40 or 80 ms, a transport block size, a transport block set size and parameters defining the protection scheme to be applied in the TrCH by layer
1
for detecting and correcting transmission errors. Depending on the current bit rate on the logical channel or channels associated with the TrCH, the MAC stage
17
A,
17
B selects a transport format from the TFS assigned by the RRC sublayer, and it delivers in each TTI a set of transport blocks complying with the selected format, whilst indicating this format to layer
1
.
Layer
1
can multiplex several TrCHs on a given physical channel. In this case, the RRC sublayer assigns a set of combinations of transport formats (TFCS, “Transport Format Combination Set”) to the physical channel, and the MAC sublayer dynamically selects a combination of transport formats from this TFCS set, thereby defining the transport formats to be used in the various multiplexed TrCHs.
UMTS uses the spread spectrum CDMA technique, that is to say the symbols transmitted are multiplied by spreading codes consisting of samples called “chips” whose rate (3.84 Mchip/s in the case of UMTS) is greater than that of the symbols transmitted. The spreading codes distinguish various physical channels (PhCH) which are superimposed on the same transmission resource consisting of a carrier frequency. The auto- and cross-correlation properties of the spreading codes enable the receiver to separate the PhCHs and to extract the symbols intended therefor. For UMTS in FDD mode (“Frequency Division Duplex”) on the downlink, a scrambling code is allocated to each base station, and various physical channels used by this base station are distinguished by mutually orthogonal channel codes (channelization codes). The base station can also use several mutually orthogonal scrambling codes. On the uplink, the base station uses the scrambling code to separate the transmitting UEs, and possibly the channel code to separate the physical channels arising from one and the same UE. For each PhCH, the overall spreading code is the product of the
Fauconnier Denis
Mousset Claire
Ferguson Keith
Nortel Networks Limited
Piper Rudnick LLP
Trost William
LandOfFree
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