U.S. patent application number 11/418984 was filed with the patent office on 2006-09-14 for common packet channel assignment method and apparatus.
Invention is credited to Mika Raitola, Antti Toskala.
Application Number | 20060203753 11/418984 |
Document ID | / |
Family ID | 22678791 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060203753 |
Kind Code |
A1 |
Toskala; Antti ; et
al. |
September 14, 2006 |
Common packet channel assignment method and apparatus
Abstract
A method and device for initiating uplink data packet
communication from a mobile device to a base station on a common
packet channel is disclosed. The communication is initiated when
the mobile device reads broadcast status of common packet channels,
after which the mobile device sends an access preamble to the base
station that is acknowledged by the base station, and then the
mobile device sends a collision preamble which the base station
answers with a matching collision response. If the base station's
response to the collision preamble also includes a channel
allocation message, then the base station begins uplink data packet
communication on an allocated channel provided that the allocated
channel previously had free broadcast status. However, if the base
station's response to the collision preamble includes a channel
allocation message designating channel(s) not previously having
free broadcast status, then the mobile device's access attempt is
aborted.
Inventors: |
Toskala; Antti; (Helsinki,
FI) ; Raitola; Mika; (Masala, FI) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &ADOLPHSON, LLP
BRADFORD GREEN, BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Family ID: |
22678791 |
Appl. No.: |
11/418984 |
Filed: |
May 4, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09790485 |
Feb 22, 2001 |
7079507 |
|
|
11418984 |
May 4, 2006 |
|
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60184899 |
Feb 25, 2000 |
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Current U.S.
Class: |
370/278 ;
370/329 |
Current CPC
Class: |
H04W 72/02 20130101;
H04W 88/08 20130101; H04W 74/0858 20130101; H04L 1/1607 20130101;
H04W 72/04 20130101; H04W 48/08 20130101; H04W 48/16 20130101; H04W
72/042 20130101; H04W 24/00 20130101; H04W 76/10 20180201 |
Class at
Publication: |
370/278 ;
370/329 |
International
Class: |
H04B 7/005 20060101
H04B007/005; H04Q 7/00 20060101 H04Q007/00 |
Claims
1. A method for a mobile terminal to initiate communication with a
base station by making an access attempt, this access attempt being
made in the context of a wireless telecommunications network, and
the method comprising the steps of: finding (200) at least one
available uplink channel by monitoring a channel status message
that is broadcast by the base station, sending (202) at least one
identification signal to the base station, including collision
detection information so that the base station will not confuse the
mobile terminal with other mobile terminals, receiving (204) a
channel allocation and a collision response signal from the base
station; proceeding (212) to transmit communication data to the
base station on an allocated common packet channel, if the
allocated common packet channel was indicated as available by the
channel status message, and also provided that the collision
response signal and the collision detection information are
indicative of matching signatures, and aborting (210) the access
attempt if the channel allocation did not allocate a channel which
had previously been indicated as available by the channel status
message.
2. A mobile terminal (102), capable of initiating communication
with a base transceiver station (114) in a wireless
telecommunication network, the mobile terminal comprising: a
channel status reader (310), responsive to user input and to a
broadcast status signal (314), for providing a free channel
information signal (316) indicative of at least one common packet
channel that is available according to the base station transceiver
(114); a channel requester (319), responsive to the free channel
information signal (316), for providing an access preamble signal
(335) indicative of at least one chosen common packet channel that
is chosen from the at least one common packet channel; a channel
allocation verifier (318), responsive to the free channel
information signal (316), and also responsive to a channel
allocation signal (320) having a magnitude indicative of at least
one channel allocated by the transceiver station (114), for
providing a verification signal (322) having a magnitude indicative
of whether an allocated channel was previously indicated as
available by the channel status reader (310); a data packet emitter
(324), responsive to the verification signal (322), for providing a
data signal (326) containing power control preamble information
followed by data to be communicated over a particular common packet
channel; and a transmit and receive device (308), responsive to the
access preamble signal (335) and to the data signal (326) by
transmitting information contained therein, and for providing the
broadcast status signal (314) and the channel allocation signal
(320) after receiving information contained therein.
3. The mobile terminal of claim 2, wherein the transmit and receive
device (308) is for transmitting and receiving information to and
from a base transceiver station (114), in a wireless communication
network (104) which utilizes wideband code division multiple
access.
4. The mobile terminal of claim 2, wherein the channel allocation
verifier (318) is also for providing an allocation defect signal
(328) signifying that attempted access is aborted if the allocated
channel was not previously indicated to be available.
5. The mobile terminal of claim 2, wherein the channel allocation
verifier (318) is also for providing an allocation defect signal
(328) signifying that attempted access is aborted if an allocated
channel was previously indicated to be available but the allocated
channel has a different data rate capability from a data rate
indicated by the access preamble signal (335).
6. The mobile terminal of claim 2, wherein the access preamble
signal (335) utilizes scrambling and spreading codes and timings,
and is transmitted with increasing power level.
7. The mobile terminal of claim 2, wherein the particular common
packet channel is the allocated channel.
8. The mobile terminal of claim 2, wherein: the channel requester
(319) is also responsive to an acknowledgement signal (340)
indicative of the base transceiver station (114) having received
the access preamble signal (335), and is for subsequently providing
a collision preamble signal (346) having a randomly selected
detection magnitude to differentiate from other mobile terminals,
and is also for providing a collision monitor signal (348) which
activates monitoring for a collision response from the base
transceiver station (114); the channel allocation verifier (318) is
also responsive to the collision monitor signal (348) and to a
collision response signal (350), and is also for providing a
collision detection defect signal (352) signifying that attempted
access is aborted if the collision response signal (350) indicated
a non-matching collision detection; the channel status reader (310)
is also responsive to the collision detection defect signal (352)
by starting a new access attempt; and the transmit and receive
device (308) is also responsive to the collision preamble signal
(346) by transmitting information contained therein, and is also
for providing the collision response signal (350) and the
acknowledgment signal (340) after receiving information contained
therein.
9. The mobile terminal of claim 8, wherein the non-matching
collision detection includes a signature that does not match a
signature indicated by the collision preamble signal (346).
10. The mobile terminal of claim 8, wherein the channel status
reader (310) starts a new access attempt in response to the
allocation defect signal (328) or in response to the collision
detection defect signal (352).
11. The mobile terminal of claim 8, wherein the particular common
packet channel is included in the at least one chosen common packet
channel, if the collision response signal (350) is provided to the
channel allocation verifier (318) without the channel allocation
signal (320).
12. The mobile terminal of claim 8, wherein the channel requester
(319) comprises: a free channel selector (330), responsive to the
free channel information signal (316), for providing a selected
channel signal (332) indicative of the at least one chosen common
packet channel; an access initiation module (334), responsive to
the selected channel signal (332), for providing the access
preamble signal (335) and for providing an acknowledgement monitor
signal (336) indicating that an acknowledgment should be expected
from the base transceiver station (114); an access acknowledgement
monitor (338), responsive to the acknowledgement monitor signal
(336) and to the acknowledgment signal (340), for providing an
acknowledgment receipt signal (342) indicating receipt of
acknowledgment; and a collision prevention module (344), responsive
to the acknowledgment receipt signal (342), for providing the
collision preamble signal (346), and for providing the collision
monitor signal (348).
13. A base transceiver station (114) capable of allowing a mobile
terminal (102) to initiate communication with the base transceiver
station (114) in a wireless telecommunication network, the base
transceiver station (114) comprising: a signal processor (475), for
providing a broadcast status signal (414) in order to broadcast
information about availability of channels usable for uplink packet
access; and a transmitting and receiving device (408), responsive
to all signals provided from the signal processor (475) by
transmitting information contained therein over an air interface,
and for providing all signals that are provided to the signal
processor (475) after receiving information contained therein over
the air interface, wherein the signal processor (475) is responsive
to an access preamble signal (435) indicative of an attempt by a
mobile device to access a common packet channel previously
indicated to be available, for providing an acknowledgement signal
(440) acknowledging receipt of the access preamble signal (435);
wherein the signal processor (475) is responsive to a collision
preamble signal (446) which differentiates the mobile terminal's
access attempt from simultaneous access attempts by different user
equipment, for providing a collision response signal (450) having a
signature; wherein the signal processor (475) also is for providing
a channel allocation signal (420) responsive to the collision
preamble signal (446), in order to allocate at least one common
packet channel for communication with the mobile terminal (102)
while giving priority allocation to common packet channels that
have been available a longer time than is necessary to initiate
communication.
14. The base transceiver station of claim 13, wherein the channel
allocation signal (420) allocates channels in such order that
channels that have been available longer are assigned for packet
data transmission before other channels are assigned.
15. The base transceiver station of claim 13, wherein each access
by a mobile terminal is accomplished during an access phase that
has an expected access duration, and wherein the channel allocation
signal (420) assigns channels in such order that channels allocated
first are channels that have been free more time than the expected
access duration.
16. A method of initiating transmission of data from a mobile
terminal (102) to a base transceiver station (114), comprising the
steps of: (a) reading (504) common packet channel status
information broadcast by the base transceiver station, and
continuing to read the status information until at least one free
common packet channel is identified, (b) providing (520) an access
preamble to the base transceiver station, using any free common
packet channel offering a desired data rate, the access preamble
being indicative of at least one chosen common packet channel that
is chosen from the at least one free common packet channel, (c)
detecting (528) an acknowledgement of the access preamble signal
from the base transceiver station, sent from the base transceiver
station to the mobile terminal in an acquisition indication
channel, (d) sending (540) a collision preamble signal to the base
transceiver station in order to differentiate the mobile terminal's
access attempt from simultaneous access attempts by different user
equipment, (e) receiving (546) a collision response from the
network in reply to the collision preamble signal, and (f) sending
(580) a power control preamble and then the data to the base
transceiver station on an allocated channel, if the collision
response from the network was accompanied or preceded by a channel
allocation pointing to the allocated channel, the allocated channel
coincides with the at least one free common packet channel
previously broadcast by the base transceiver station, and the
collision response has a signature matching a signature of the
collision preamble signal.
17. The method of claim 16, wherein the steps are repeated if the
collision response from the network was accompanied by a channel
allocation not pointing to a channel coinciding with the at least
one free common packet channel previously broadcast by the base
transceiver station.
18. The method of claim 16, wherein the steps are repeated if the
collision response from the network has a different signature from
a signature of the collision preamble signal.
19. The method of claim 16, wherein the access preamble signal
utilizes scrambling and spreading codes and timings, and is
transmitted with increasing power level.
20. The method of claim 16, wherein an access attempt is aborted if
the allocated channel has a data rate that is different from data
rate(s) of the at least one chosen common packet channel, in which
case the steps are repeated.
21. The method of claim 16, wherein the channel allocation
allocates channels in such order that channels that have been
available longer are assigned for packet data transmission before
other channels are assigned.
22. The method of claim 16, wherein each access by a mobile
terminal is accomplished during an access phase that has an
expected access duration, and wherein the channel allocation
assigns channels in such order that channels allocated first are
channels that have been free more time than the expected access
duration.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] A method and apparatus for transmitting data from user
equipment (UE) to a radio network subsystem within a mobile
telephone system, and in particular for selecting the common packet
channel (CPCH) to be used for the data transmission, within a
universal mobile telephone system (UMTS).
BACKGROUND ART
[0002] One of the major problems in mobile telephone systems with
packet data transmission in the uplink is how to divide the access
resources to different users when the need for resources varies
between users at a given point in time.
[0003] In current systems, each user is reserved a certain amount
of capacity and base station hardware resources during a
circuit-switched call for as long as communication capability is
needed. However, when using circuit-switched transmission of packet
data in this way wherein data to be transmitted is typically very
bursty in nature, it is a waste of radio capacity and physical
hardware resources to keep a single user's connection reserved all
the time according to the greatest possible momentary data
transmission need. Thus, packet-switched transmission of packet
data is preferable, but having the connection totally disconnected
between data transmissions can mean a lengthy process with a lot of
signaling via the Random Access Channel (RACH) every time there is
data to be transmitted.
[0004] In systems based on the code division multiple access (CDMA)
method, different users use different uplink scrambling codes. When
initiating transmission in a CDMA system, a big concern is how to
ensure that the access takes place fast without a lot of signaling
via RACH. Also, for longer packets, a major concern is how to take
care of power-control to avoid the near-far problem typical of the
non-orthogonal coding used in CDMA technology, in order to ensure
that user equipment near to a radio network subsystem or base
station will not exchange signals at unnecessarily high power
compared to different user equipment farther away.
[0005] In the current types of systems, the uplink services have
not been packet based, or they have been implemented with a circuit
switched connection. Also, for some of the services like short
message service (SMS), the data amount has been very small. In
future systems, the applications are expected to have a larger
range, from database applications, to email and internet browsing,
to any other TCP/IP traffic, and consequently the current types of
systems are not acceptable.
[0006] In the downlink, the power control problem is not that
severe and, in existing CDMA systems like IS-95A, a downlink power
control is not provided at all. In the downlink direction, a
greater emphasis is put on sharing the physical resources
efficiently, as has been done for example with a downlink shared
channel in wideband CDMA (i.e. WCDMA also known as UMTS).
[0007] In the UMTS system, the concept of an Uplink Common Packet
Channel (Uplink CPCH) has been proposed to solve the uplink access
problem. CPCH also has significant advantages for data
transmission. However, Uplink CPCH suffers from a reliability
problem. Using Uplink CPCH, the proposed channel allocation
procedures may lead to two or more user equipments transmitting
their data on the same CPCH channel and thus causing excessive
interference. Access to a CPCH channel takes time, and thus a
channel selected by a first UE may be reserved by a second UE
before the first UE completes the access process. In other words,
user channel selection (UCS) proceeds by the user selecting and
accessing a free CPCH channel according to the description of free
channels sent to the UE over a broadcast channel (BCH); however,
the delay in the access method and in the BCH transmission may
cause UE to access a channel which is already reserved.
[0008] Another attempted solution to the uplink access problem has
been to use versatile channel assignment (VCAM), where the channel
is assigned, after access preambles are exchanged, by way of an
acquisition indication channel (AICH). The problem with this
related art technique is that AICH typically has an error rate in
the range of one percent (1%). VCAM, however, requires reliable
signaling, and therefore the high AICH error rate often will cause
two UEs to transmit into the same CPCH. The UEs consequently would
follow a single power-control stream, often causing severe noise
levels at the receiver.
[0009] The basic CPCH structure discussed here is based on 3.sup.rd
Generation Partnership Project (3GPP) specifications available to
the public. 3G TS 25.211 "Physical channels and mapping of
transport channels onto physical channels (FDD)" (Version 3.1.1,
December 1999) describes the characteristics of transport channels
and physical channels in the frequency division duplex (FDD) mode
of UMTS terrestrial radio access (UTRA). 3G TS 25.212 "Multiplexing
and channel coding (FDD)" (Version 3.1.1, December 1999) describes
the characteristics of multiplexing and channel coding in the FDD
mode of UTRA. 3G TS 25.213 "Spreading and Modulation (FDD)"
(Version 3.1.1, December 1999) describes spreading and modulation
in the FDD mode of UTRA. 3G TS 25.214 "Physical Layer Procedures
(FDD)" (Version 3.1.1, December 1999) specifies and establishes the
characteristics of the physical layer procedures in the FDD mode of
UTRA. Further, the 3GPP TSG RAN WG1 submission 3GPP R1-00-0175
describes the basic monitoring channel structure (this document is
dated Jan. 18-21, 2000).
[0010] Submission 3GPP R1-00-0175 is a useful example to understand
the background of the present invention, and especially section
5.3.3.8 of that submission, which describes a CPCH status
indication channel (CSICH). Likewise, 3G TS 25.214 contains a
relevant section 6.2 entitled "CPCH Access Procedures." That
section 6.2 lists relevant physical layer parameters; the 18-step
access procedure described in section 6.2 is improved by the
present invention in order to address the prior art problems
discussed above.
DISCLOSURE OF THE INVENTION
[0011] It is an object of the invention to solve reliability
problems of the uplink CPCH by developing a method and apparatus
for improved reliability of the channel allocation within a WCDMA
system. This invention combines and improves aspects of existing
related art access methods, including UCS and VCAM, in a way which
substantially eliminates problems posed by those related art access
methods.
[0012] The present method is for allocating the channel over which
packet data is transmitted from a user equipment to a radio network
subsystem, or to a base station within a radio network subsystem.
The user equipment (UE) apparatus of the present invention is
adapted to carry out that method.
[0013] According to this invention, the radio network subsystem may
have already informed the user equipment (UE) of one or more
possible uplink CPCH channels to be used for packet data
transmission if those channels are free. The radio network
subsystem may also have already informed the user equipment (UE) of
the respective data bit rates, codes, and/or other parameters
corresponding to the possible uplink CPCH channels. A primary
purpose of the present invention is to efficiently determine which
uplink CPCH channel the UE should use to communicate data packets
to the radio network subsystem.
[0014] A preferred embodiment of the method can be summarized as
follows. The UE, upon having the need to transmit data, monitors
CPCH status broadcast information transmitted over a special
channel called a CPCH status indication channel (CSICH). This CPCH
information is broadcast over the CSICH from a base transceiver
station (BTS also denoted Node B), informing the UE which
channel(s) are free for a particular data rate or rates. The UE
then selects, from the free channels, at least one channel which
provides at least one of the desired data rates. Then the UE
initiates an access procedure, using scrambling and spreading codes
and timings, to transmit at least one access preamble according to
the parameters of the selected channel(s). Upon receiving
acknowledgement from the base station BTS on the corresponding
downlink acquisition indication channel (AICH), the UE sends a
collision detection preamble which is used to differentiate between
simultaneous access attempts by different user equipment that may
have been in the access procedure simultaneously on the same
physical channel. The UE waits after sending the collision
detection preamble until the radio network subsystem responds (via
the BTS) with a correct collision detection preamble matching the
access preamble sent by the user equipment; the BTS may
additionally respond with a channel allocation message to indicate
which CPCH channel(s) the UE should use for the data transmission,
among the channel(s) previously indicated to be free over the
CSICH. Channel allocation messages are sent from the BTS to the UE
using the acquisition indication channel (AICH).
[0015] If the channel allocation message from the BTS to the UE
only indicates a channel or channels not among the channels
previously indicated to be free over the CSICH (i.e. no allocated
channel is valid), then the access attempt is aborted.
Alternatively, if no channel allocation message is sent from the
BTS, then data transmission may proceed using one of the channels
previously indicated to be free over the CSICH. In certain
embodiments of this invention, a radio network subsystem is adapted
to use for the channel allocation message values based on the
previous status monitoring history, by estimating the time between
user equipment status broadcast decoding and the channel allocation
phase in the access procedure.
[0016] According to the method of the present invention, a channel
allocation message from the BTS has a limited set of valid values
which must be included within the free channels previously
specified by the status broadcast transmission. In other words, a
UE will transmit data over an allocated channel only if that
channel was previously among the free channels specified over the
CSICH when the UE initiated access. In the case where the BTS sends
a channel allocation message, and the channel allocation message
points to a previously busy channel, the access attempt is aborted
and returned to status monitoring. In the case where there is no
channel allocation message forthcoming from the BTS, then the UE
may begin transmission using one of the free channels previously
specified by the status broadcast transmission. This invention also
relates to user equipment (UE) apparatus capable of preparing to
transmit data packets according to the method just summarized.
[0017] This invention is substantially based on restricting the
valid channel allocation message values based on the information
previously given by the status broadcast transmission. The method
and apparatus of the invention provide several advantages. Problems
with data transmission reliability are solved for all users in the
system, by minimizing the probability for two users to follow a
single power control stream and thus create excessive interference.
Also, for a single user, reliability problems of the channel
allocation message decoding are solved, thereby improving the
probability of a successful packet transmission attempt. This
invention thereby enables efficient use of radio capacity.
Moreover, in the present claimed invention, the effects of delay in
channel selection are minimized via the claimed channel assignment
method. The channel assignment errors are minimized by increasing
the probability that free channels will be assigned. The invention
is backward compatible with the related art UE channel selection
(UCS) in the sense that the invention can be adapted as a
supplement to UCS.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows an example of a telecommunications network
environment in which the present invention operates.
[0019] FIG. 2 shows a simple flow chart of the access procedure
according to an embodiment of the present invention.
[0020] FIG. 3 shows a mobile terminal according to the present
invention.
[0021] FIG. 4 shows a base transceiver station according to the
present invention.
[0022] FIG. 5 shows a flow chart of the access procedure according
to an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] This invention can be used in the UMTS terrestrial radio
access (UTRA) systems based on the 3GPP specifications where it is
desired to use the uplink common packet channel (CPCH) for uplink
packet data transmission. Further information on UTRA is available
in the previously mentioned 3GPP technical specification documents.
The invention is not, however, restricted to UTRA, but rather can
be used in any radio communication system within the spirit and
scope of this invention.
[0024] This invention occurs in the context of a larger wireless
telecommunications system, as exemplified by FIG. 1 which shows the
structure of a wireless system according to UMTS (which is
synonymous with WCDMA or wideband code division multiple access).
As can be seen in FIG. 1, the UMTS architecture consists of user
equipment 102 (UE which is herein synonymous with "mobile device"
or "mobile terminal"), a UMTS Terrestrial Radio Access Network 104
(UTRAN), and a Core Network 126 (CN). The air interface between the
UTRAN and the UE is called Uu, and the interface between the UTRAN
and the Core Network is called Iu. The UTRAN consists of a set of
Radio Network Subsystems 128 (RNS), each of which has geographic
coverage of a number of cells 110 (C). The interface between the
subsystems is called Iur. Each Radio Network Subsystem 128 (RNS)
includes a Radio Network Controller 112 (RNC) and at least one Node
B 114, each Node B having geographic coverage of at least one cell
110 (a Node B is often referred to as a base transceiver station
(BTS) or simply a base station). As can be seen from FIG. 1, the
interface between an RNC 112 and a Node B 114 is called Iub, and
the Iub is hard-wired rather than being an air interface. For any
Node B 114 there is only one RNC 112. A Node B 114 is responsible
for radio transmission and reception to and from the UE 102 (Node B
antennas can typically be seen atop tall towers or preferably at
less conspicuous locations). The RNC 112 has overall control of the
logical resources of each Node B 114 within the RNS 128, and the
RNC 112 may also be responsible for handover decisions which entail
switching a call from one cell to another or between radio channels
in the same cell.
[0025] The service area of Node B is referred to here as a cell.
There can be many CPCHs in a cell, and UE must select one to be
accessed.
[0026] FIG. 2 illustrates a simple embodiment of the present
method, according to which a mobile terminal can initiate
communication with a base station, the access attempt being made in
the context of a wireless telecommunications network. A first step
is finding 200 at least one available uplink channel by monitoring
a channel status message that is broadcast by the base station. The
next step is sending 202 at least one identification signal to the
base station, including collision detection information in the form
of a randomly selected signature, so that the base station will not
confuse the mobile terminal with other mobile terminals. Then, the
base station receives 204 a channel allocation and a collision
response signal from the base station, the collision response
signal being indicative of a signature that can be compared to the
randomly selected signature previously sent to the base station.
The base station proceeds 212 to transmit communication data to the
base station on an allocated common packet channel, if the
allocated common packet channel was indicated as available by the
channel status message, and also provided that the collision
response signal indicates a signature matching the randomly
selected signature indicated by the identification signal. The
access attempt is aborted 210 if the channel allocation did not
allocate a channel which had previously been indicated as available
by the channel status message.
[0027] FIG. 3 shows a mobile terminal according to an embodiment of
the best mode of the present invention, designed to implement the
method illustrated by FIG. 2. A transmit and receive device 308 is
shown with various named signals entering and exiting the transmit
and receive device 308. Those named signals represent the signaling
that may occur in the access phase between UE 102 and Node B 114.
It should be noted that this depiction is an approximation that may
be varied with different kinds of core networks and RNS deployment
scenarios.
[0028] During the transmission of data, the UE is power-controlled
by the RNS, which is an essential requirement in a CDMA system. The
UE typically transmits the data with channel coding and uses
interleaving over one or more radio frames to achieve time
diversity. The transmission in the uplink is done with I/Q
multiplexing having a separate Dedicated Physical Control Channel
(DPCCH) and Dedicated Physical Data Channel (DPDCH) sent together
as a dual channel compressed QPSK signal. In the downlink
direction, the DPCCH and DPDCH are time multiplexed.
[0029] The access procedure may occur in an UTRA frequency division
duplex (FDD) system. The initial access phase for normal random
access operation, for example with registration or location updated
or with the CPCH access, has been specified to use a ramping
process as indicated by an access preamble signal on a line 335 in
FIG. 3. A UE starts at a certain power level based on the UE
measurements of the signal strength and of the parameters read from
the broadcast channel. The access with preambles is expected to be
continued with increasing power level for the 1 ms preamble
transmission until the preamble transmission is acknowledged by the
base station/RNS or until the transmission needs to be stopped due
to excessively high power level or due to the excessive number of
preambles transmitted.
[0030] With the CPCH procedure, the UE first has been through the
random access procedure and has exchanged the necessary parameters
on UE capability with the network and has been given permission to
access the CPCH channels with a certain data rate or a set of data
rates. When the need arises for user equipment to initiate the
transmission, the UE needs first to read the status information of
the CPCH channels from the CSICH, as indicated by a broadcast
status signal on a line 314 in FIG. 3. As mentioned, the related
art submission 3GPP R1-00-0175 has a section 5.3.3.8 describing the
CSICH. Depending upon whether channel allocation (i.e. channel
assignment) is used in the system, the UE may have a different
approach. With the channel assignment active, UE is expecting to
get a channel allocation message during the access procedure, as
indicated by a channel allocation signal on a line 320 of FIG. 3;
however, in the other case, UE considers accessing only a single
CPCH channel and either gets that particular channel or not during
the access procedure. In both cases, UE starts the access procedure
with an access preamble signal on a line 335 whereby the preambles
are sent, typically with increasing power between consecutive
preambles.
[0031] The UE 102 observes, after each access preamble, whether the
proper acknowledgement arrives in the corresponding acquisition
indication channel (AICH) via an acknowledgment signal on a line
340, which is used by the network to indicate that an access
preamble has been received. Upon reception of the AICH preamble
corresponding to the physical channel used for the access, the UE
sends a collision detection (CD) preamble as indicated by a
collision preamble signal on a line 346, which is chosen randomly
among possible preambles in order to differentiate user equipment
and thus avoid collisions in the access procedure. The user
equipment waits for the network to respond with the same CD
preamble as shown by a collision response signal on a line 350.
[0032] In case no channel allocation accompanies the collision
response signal on the line 350, then the user equipment starts the
transmission at this point as represented by a data signal on a
line 326. The transmission may be started with a power control
preamble which is a version of the DPCCH frame, for example, with
the length of 8 slots, or the data channel may start directly with
both DPCCH and DPDCH transmission.
[0033] In case a channel allocation signal on the line 320 does
accompany the collision response signal on the line 350 (recall
that channel allocation may also be denoted as channel assignment),
the channel allocation signal on the line 320 points the UE to one
of the CPCH channels in the system. The basic method of channel
allocation (CA) allows any of the CPCH channels to be chosen and to
be used for transmission based on the CA preamble contained in the
channel allocation signal on the line 320.
[0034] The use of a CA preamble has problems of reliability. The
typical error rate is one percent, which means that one out of one
hundred access attempts results in the user equipment starting to
transmit on an incorrect channel. Because this incorrect channel
may already be used by other user equipment, there may be a serious
collision when the new user equipment tries to follow the power
control intended for another UE.
[0035] Thus, in the present invention, the CA preamble error
sensitivity is reduced by linking the valid CA combinations to the
information provided on the CPCH status indication channel (CSICH).
In other words, the values given by the channel allocation signal
on the line 320 are linked to the previous broadcast values given
by the broadcast status signal on the line 314. If the CSICH
information is taken into account when considering the validity of
the decoded CA message, the possibility of two users being active
on a single code is reduced to a fraction of the probability when
basing the decisions on the CA preamble only. A UE 102 will reject
any channel pointed out by the CA preamble that was indicated by
CSICH to be busy before starting the ramping phase (i.e. before the
access preamble signal on the line 335).
[0036] The performance improvement of the present invention is due
to the fact that, in order to jump on an already busy channel, both
the broadcast status signal on the line 314 and the channel
allocation signal on the line 320 would need to be decoded
incorrectly. Those two signals have some time separation due to the
delay in the access procedure, and the decoding events therefore
have some independence of the channel state variations. Using this
procedure, the error probability in an example case of one percent
error rate for both is normally reduced to 0.01 percent error
probability or less, which is much easier for the network to
tolerate.
[0037] Referring again to FIG. 3, an apparatus according to the
best mode of the present invention is depicted. This mobile
terminal 102 is capable of initiating communication with a base
transceiver station 114 in a wireless telecommunication network.
The mobile terminal includes a channel status reader 310, which is
responsive to user input and to the broadcast status signal on the
line 314. The channel status reader 310 will begin operating when a
user has a need for data to be communicated to the network. The
channel status reader 310 is for providing a free channel
information signal on the line 316 indicative of at least one
common packet channel that is available according to the base
station transceiver 114.
[0038] A channel requester 319 is responsive to the free channel
information signal on the line 316, and is for providing the access
preamble signal on the line 335 having a magnitude indicative of at
least one chosen common packet channel that is chosen from the at
least one common packet channel that is available according to the
base station transceiver 114. A channel allocation verifier 318 is
responsive to the free channel information signal on the line 316,
and is also responsive to a channel allocation signal on the line
320 having a magnitude indicative of at least one channel allocated
by the base transceiver station 114. The channel allocation
verifier 318 is for providing a verification signal on a line 322
having a magnitude indicative of whether an allocated channel was
previously indicated as available by the channel status reader 310.
A data packet emitter 324 is responsive to the verification signal
on the line 322, and is for providing the data signal on the line
326 containing power control preamble information followed by data
to be communicated over a particular common packet channel (this
particular channel may be the allocated channel). As discussed
above, the transmit and receive device 308 is responsive to the
access preamble signal on the line 335 and to the data signal on
the line 326 for transmitting (over an air interface) information
contained in those two signals, and is for providing the broadcast
status signal on the line 314 and the channel allocation signal on
the line 320 after receiving them over the air interface from the
base station 114. In this embodiment, the transmit and receive
device 308 is for transmitting and receiving information to and
from a base transceiver station 114 in a wireless communication
network 104 which utilizes wideband code division multiple
access.
[0039] The channel allocation verifier 318 may also provide an
allocation defect signal on a line 328 signifying that attempted
access is aborted, if the allocated channel was not previously
indicated to be available by the broadcast status signal on the
line 314. The channel allocation verifier 318 may also provide an
allocation defect signal on a line 328 signifying that attempted
access is aborted if an allocated channel was previously indicated
to be available but the allocated channel has a different data rate
capability from a data rate indicated by the access preamble signal
on the line 335. In either case, the access attempt can be
aborted.
[0040] According to a further embodiment of the best mode of the
present invention, the access preamble signal on the line 335
utilizes scrambling and spreading codes and timings, and is
transmitted with increasing power level. The channel requester 319
is also responsive to an acknowledgement signal on a line 340
indicative of the base transceiver station 114 having received the
access preamble signal on the line 335, and is for subsequently
providing a collision preamble signal on a line 346 having a
randomly selected detection magnitude to differentiate from other
mobile terminals. The channel requester 319 is also for providing a
collision monitor signal on a line 348 which activates monitoring
for a collision response from the base transceiver station 114. The
channel allocation verifier 318 is also responsive to the collision
monitor signal on the line 348 and to a collision response signal
on a line 350, and is furthermore for providing a collision
detection defect signal on a line 352 signifying that attempted
access is aborted if the collision response signal on the line 350
indicated a non-matching collision detection, which may mean that
the collision response signal on the line 350 includes a signature
that does not match a signature indicated by the collision preamble
signal on the line 346. The channel status reader 310 is also
responsive to the collision detection defect signal on the line 352
by starting a new access attempt. Of course, the transmit and
receive device 308 is also responsive to the collision preamble
signal on the line 346 by transmitting information contained
therein, and is also for providing the collision response signal on
the line 350 and the acknowledgment signal on the line 340 after
receiving information contained therein.
[0041] According to a further embodiment of the best mode of the
present invention, the channel status reader 310 starts a new
access attempt in response to the allocation defect signal on the
line 328 or in response to the collision detection defect signal on
the line 352. In other words, instead of being content with
failure, the philosophy of this embodiment is to keep trying again,
at least within upper limits. If the collision response signal on
the line 350 is provided to the channel allocation verifier 318
without the channel allocation signal on the line 320, then the
particular common packet channel used for the data signal 326 is
included in the at least one chosen common packet channel indicated
by the access preamble signal on the line 335.
[0042] Thusfar, the internal structure of the channel requester 319
has not been detailed. However, a further embodiment of the best
mode of the present invention does offer details about various
parts of the channel requester 319. A free channel selector 330 is
responsive to the free channel information signal on the line 316,
and is for providing a selected channel signal on a line 332
indicative of the at least one chosen common packet channel that
will be described in the access preamble signal on the line 335. An
access initiation module 334 is responsive to the selected channel
signal on the line 332, and is for providing the access preamble
signal on the line 335 as well as an acknowledgement monitor signal
on a line 336 indicating that an acknowledgment should be expected
from the base transceiver station 114. An access acknowledgement
monitor 338 is responsive to the acknowledgement monitor signal on
the line 336 and to the acknowledgment signal on the line 340, and
is for providing an acknowledgment receipt signal on a line 342
indicating receipt of acknowledgment. Also, the channel requester
319 includes, in this embodiment, a collision prevention module 344
which is responsive to the acknowledgment receipt signal on the
line 342, and which is for providing the collision preamble signal
on the line 346, and is for also providing the collision monitor
signal on the line 348.
[0043] In one preferred embodiment of the best mode of the present
invention, the Node B does not try to immediately allocate a
channel that has been released (i.e. that could be allocated),
because UE 102 may nevertheless encounter information on such a
channel during the access process, the channel having been open
only temporarily. The most efficient solution is for the Node B to
use the CA message to point out channels that have been free longer
than the expected duration of the ramping phase in the access
procedure.
[0044] Referring now to FIG. 4, a very simplified diagram of the
base transceiver station 114 is shown, according to an embodiment
of the best mode of the present invention. The signals shown
between the signal processor 475 and the transmitting and receiving
device 408 closely correspond to the labeled signals in the mobile
terminal 102 of FIG. 3.
[0045] This base transceiver station 114 is capable of allowing a
mobile terminal 102 to initiate communication with the base
transceiver station 114 in a wireless telecommunication network.
The base transceiver station 114 includes a signal processor 475
for providing a broadcast status signal 414 in order to broadcast
information about availability of channels usable for uplink packet
access, and also includes a transmitting and receiving device 408
which is responsive to all signals provided from the signal
processor 475 by transmitting information contained therein over an
air interface (i.e. every signal from the signal processor to the
transmitting and receiving device is transmitted over the air).
Likewise, the transmitting and receiving device 408 is also for
providing all signals that are provided to the signal processor
475, after receiving information contained therein over the air
interface.
[0046] Furthermore, the signal processor 475 is responsive to an
access preamble signal on a line 435 indicative of an attempt by a
mobile device to access a common packet channel previously
indicated to be available, and the signal processor 475 is for
providing an acknowledgement signal on a line 440 acknowledging
receipt of the access preamble signal on the line 435. Also in this
embodiment of the best mode of the present invention, the signal
processor 475 is responsive to a collision preamble signal on a
line 446 which differentiates the mobile terminal's access attempt
from simultaneous access attempts by different user equipment, and
the signal processor 475 is also for providing a collision response
signal on a line 450, indicative of a signature. Moreover, the
signal processor 475 is for providing a channel allocation signal
on the line 420 responsive to the collision preamble signal on the
line 446, in order to allocate at least one common packet channel
for communication with the mobile terminal 102 while (as mentioned
above) giving priority allocation to common packet channels that
have been available a longer time than is necessary to initiate
communication. Similarly, it is preferred in this embodiment that
the channel allocation signal on the line 420 allocates channels in
such order that channels that have been available longer are
assigned for packet data transmission before other channels are
assigned. Likewise, one of the preferred embodiments of the present
invention requires that each access by a mobile terminal is
accomplished during an access phase that has an expected access
duration, and wherein the channel allocation signal on the line 420
assigns channels in such order that channels allocated first are
channels that have been free more time than the expected access
duration.
[0047] The free common packet channel ultimately used by the UE 102
can have a variety of data bit rate capabilities. In an embodiment
of the best mode, the actual data bit rate is decided only based on
the channel allocation (CA) preamble decoding. This embodiment, in
which the actual data bit rate differs from the data bit rate
capability, can be used for implementing system load control.
[0048] A UE can operate according to the present invention even if
other UEs cannot. In other words, some UEs can support the method
described in this invention while other UEs support, for example,
pure user channel selection (UCS). In this type of hybrid
situation, the UEs supporting the invention will be able to access
all CPCH channels, whereas UEs supporting pure UCS will only be
able to access those CPCH channels reserved for them. The
information about which CPCH channels are reserved for which UEs
can be sent along with other cell configuration data over the
broadcast channel (BCH), and can also be sent over the CPCH status
indication channel (CSICH).
[0049] Referring now to FIG. 5, we have a flow chart of the method
corresponding to an embodiment of the best mode of the present
invention. Some of the illustrated steps are more important than
others in describing the invention. The service negotiation 500
with the network gives a user permission to use given data rate(s)
with the uplink CPCH channel for packet data. Typically, there will
be an interval of waiting 502 before there is packet data to
transmit 503. It is then necessary to read 504 common packet
channel status information broadcast by the base transceiver
station, and to continue reading the status information until at
least one free common packet channel is identified 508. The next
step in this embodiment is to provide 520 an access preamble to the
base transceiver station, using any free common packet channel
offering a desired data rate, the access preamble being indicative
of at least one chosen common packet channel that is chosen from
the at least one free common packet channel. Providing the access
preamble leads to detection 528 of an acknowledgement by the base
transceiver station of the access preamble signal, the
acknowledgment having been sent from the base transceiver station
to the mobile terminal in an acquisition indication channel. Next
is sending 540 a collision preamble signal to the base transceiver
station in order to differentiate the mobile terminal's access
attempt from simultaneous access attempts by different user
equipment. Subsequently, the mobile terminal receives 546 a
collision response from the network in reply to the collision
preamble signal. Finally, the mobile terminal sends 580 a power
control preamble and then the data to the base transceiver station
on an allocated channel, if the collision response from the network
was accompanied or preceded by a channel allocation pointing to the
allocated channel, the allocated channel coincides with the at
least one free common packet channel previously broadcast by the
base transceiver station 560, and the collision response has a
signature matching a signature of the collision preamble signal
548.
[0050] If the collision response from the network was accompanied
by a channel allocation not pointing to a channel coinciding with
the at least one free common packet channel previously broadcast by
the base transceiver station, then the steps of the method can
simply be repeated. The same is true if the collision response from
the network has a different signature from a signature of the
collision preamble signal.
[0051] The access preamble may utilize scrambling and spreading
codes and timings, and be transmitted with increasing power level
until a response from the base transceiver station 114 arrives. An
access attempt may be aborted if the allocated channel has a data
rate that is different from data rate(s) of the at least one chosen
common packet channel, in which case the steps may be repeated.
[0052] Again, a preferred embodiment of this method entails
allocating channels in such order that channels that have been
available longer are assigned for packet data transmission before
other channels are assigned. Each access by a mobile terminal is
accomplished during an access phase that has an expected access
duration, and the channel allocation may assign channels in such
order that channels allocated first are channels that have been
free more time than the expected access duration.
[0053] For implementing the invention, the preferred means is by
software. In order to do so, it would be necessary to make changes
for the protocol and transmission control software for the user
equipment, as well as for the Node B or radio network controller CA
control software.
[0054] Even though the invention has been explained in the above
with reference to examples in accordance with the accompanying
drawing, it is obvious that the invention is not restricted to them
but can be modified in many ways by those skilled in the art within
the scope of the inventive idea disclosed in the attached claims.
Although this invention has been shown and described with respect
to best mode embodiments thereof, it should be understood by those
skilled in the art that the foregoing and various other changes,
omissions and additions in the form and detail thereof may be made
therein without departing from the spirit and scope of the
invention.
[0055] It is to be understood that all of the present Figures, and
the accompanying narrative discussions of the best mode
embodiments, do not purport to be rigorous treatments of the
methods and devices under consideration. For example, FIG. 3 only
shows certain blocks of a mobile terminal, and omits many other
blocks for the sake of clarity and relevance, as will be evident to
a person skilled in the art. Such a person will also understand
that the blocks in the Figures, and their interactions, may be
rearranged and supplemented within the scope of the present
invention, and will understand that those blocks do not necessarily
represent discrete hardware components; rather, those blocks can be
implemented by combinations of hardware and software in a variety
of different combinations and permutations. Likewise, the signals
between blocks represent general cause-and-effect relationships
that do not exclude intermediate interactions of various types, as
will be clear to those skilled in the art.
* * * * *