U.S. patent application number 13/018755 was filed with the patent office on 2011-05-26 for random access burst transmission scheme.
This patent application is currently assigned to Sony Deutschland GmbH. Invention is credited to Stefan KORNPROBST.
Application Number | 20110122850 13/018755 |
Document ID | / |
Family ID | 8237736 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110122850 |
Kind Code |
A1 |
KORNPROBST; Stefan |
May 26, 2011 |
RANDOM ACCESS BURST TRANSMISSION SCHEME
Abstract
An apparatus for transmitting and receiving signals in a
wireless telecommunication system and to a method for transmitting
random access bursts in such an apparatus. The apparatus includes a
transmitter for transmitting random access bursts, a receiver for
receiving acknowledgement information confirming a successful
transmission of a random access burst, a decision unit for deciding
if acknowledgement information has been received, and a control
unit for randomly choosing a time point for an attempt to
retransmit said random access burst from an interval if no
acknowledgement information has been received after a random access
burst had been transmitted.
Inventors: |
KORNPROBST; Stefan;
(Stuttgart, DE) |
Assignee: |
Sony Deutschland GmbH
Koeln
DE
|
Family ID: |
8237736 |
Appl. No.: |
13/018755 |
Filed: |
February 1, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11862102 |
Sep 26, 2007 |
7899404 |
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13018755 |
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|
09521394 |
Mar 8, 2000 |
7359705 |
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11862102 |
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Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H04W 72/10 20130101;
H04W 28/04 20130101; H04W 74/0875 20130101; H04W 74/085 20130101;
H04L 1/188 20130101; H04W 74/08 20130101 |
Class at
Publication: |
370/336 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 1999 |
EP |
99-104-766.3 |
Claims
1. An apparatus for transmitting and receiving signals in a
wireless telecommunication system, the apparatus comprising: a
transmitter configured to transmit a random access burst; a
receiver configured to receive acknowledgement information
confirming a successful transmission of said random access burst; a
decision unit configured to decide if acknowledgement information
has been received; and a controller configured to randomly choose a
timepoint for an attempt to retransmit said random access burst
from an interval if no acknowledgement information has been
received after said random access burst has been transmitted,
wherein the controller is configured to set a length of said
interval depending on a number of unsuccessful attempts to transmit
said random access burst.
2. The apparatus of claim 1, wherein said interval length is set
longer when the number of unsuccessful attempts increases.
3. The apparatus of claim 2, wherein said interval length depends
exponentially on the number of unsuccessful attempts.
4. The apparatus of claim 1, wherein the controller is configured
to randomly choose said timepoint for a retransmission attempt
after a predetermined offset time has elapsed.
5. The apparatus of claim 1, wherein said controller is configured
to choose a timepoint for a retransmission attempt if it is
determined that the number of unsuccessful attempts is lower than a
predetermined maximum number of unsuccessful attempts.
6. The apparatus of claim 1, wherein said interval length is set
depending on a priority class of the random access burst.
7. The apparatus of claim 6, wherein said interval length is set
shorter for higher priority classes.
8. The apparatus of claim 1, wherein said interval is represented
by a series of numbers representing time slots in the wireless
telecommunication system.
9. A method for transmitting random access bursts in an apparatus
for transmitting and receiving signals in a wireless
telecommunication system, the method comprising: transmitting a
random access burst; deciding if acknowledgement information
confirming a successful transmission of said random access burst
has been received; and randomly choosing a timepoint for an attempt
to retransmit said random access burst from an interval if no
acknowledgement information has been received, wherein a length of
said interval is set depending on a number of unsuccessful attempts
to transmit said random access burst.
10. The method of claim 9, wherein said interval length is set
longer when the number of unsuccessful attempts increases.
11. The method of claim 10, wherein said interval length depends
exponentially on the number of unsuccessful attempts.
12. The method of claim 9, wherein said timepoint for a
retransmission attempt is randomly chosen after a predetermined
offset time has elapsed.
13. The method of claim 9, wherein said timepoint for a
retransmission attempt is only chosen if it is determined that the
number of unsuccessful attempts is lower than a predetermined
maximum number of unsuccessful attempts.
14. The method of claim 9, wherein said interval length is set
depending on a priority class of the random access burst.
15. The method of claim 14, wherein said interval is set shorter
for higher priority classes.
16. The method of claim 9, wherein said interval is represented by
a series of numbers representing time slots in the wireless
telecommunication system.
17. An apparatus for transmitting and receiving signals in a
wireless telecommunication system, the apparatus comprising:
transmitting means for transmitting a random access burst;
receiving means for receiving acknowledgement information
confirming a successful transmission of said random access burst;
decision means for deciding if acknowledgement information has been
received; and control means for randomly choosing a timepoint for
an attempt to retransmit said random access burst from an interval
if no acknowledgement information has been received after said
random access burst has been transmitted, wherein the control means
sets a length of said interval depending on a number of
unsuccessful attempts to transmit said random access burst.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and is based upon and
claims the benefit of priority under 35 U.S.C. .sctn.120 from U.S.
application Ser. No. 11/862,102, filed on Sep. 26, 2007 which is a
continuation of U.S. application Ser. No. 09/521,394, filed Mar. 8,
2000, and claims the benefit of priority from prior European Patent
Application No. 99 104 766.3, filed Mar. 10, 1999 the entire
contents of each of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for
transmitting and receiving signals in a wireless telecommunication
system and a method for transmitting random access bursts in such
an apparatus. Particularly, the present invention relates to a
backoff scheme for the transmission of random access bursts in a
mobile station of a wireless telecommunication system.
[0004] 2. Description of the Related Art
[0005] In wireless telecommunication systems, as for example the
GSM system, the mobile station uses the random access channel
(RACH) to send random access bursts to acquire services from the
network. If for example a mobile station of a mobile cellular
system needs a data channel to transmit user data, it sends a
random access burst over the random access channel to the selected
base station. The base station receiving a random access burst
sends an acknowledgement or a confirmation message to the mobile
station to indicate, that the transmission of the random access
burst from the mobile station to the base station has been
successful. The confirmation information might be the access grant
information sent by a base station to indicate that the requested
service is granted. After a successfully transmitted random access
burst, the base station allocates the respective requested service,
for example a user data channel, to the mobile station.
[0006] The transmission of a random access burst from a mobile
station to a base station is contention based and collisions can
occur. If for example several mobile stations within one cell of
the telecommunication system simultaneously send random access
bursts, collisions can occur and the random access bursts can not
be correctly received and confirmed by the base station. Having
sent a random access burst to a base station, the mobile station
checks if an acknowledgement information from the base station has
been received. If an acknowledgement information has not been
received after a predetermined time period, the mobile station
decides that the transmission attempt of the random access burst
has not been successful. After such a failed random access burst
transmission attempt, a backoff mechanism determines, when a new
transmission of the random access burst shall take place. The same
is true after a retransmission of a random access burst and not
only for the first transmission attempt.
[0007] Different kinds of backoff mechanisms are known in the prior
art. For example, in a so-called bayesian backoff scheme, the
network side, i.e. the base station, estimates, if the random
access channel has been occupied or not, if collisions occurred or
if a random access burst has been successfully transmitted.
Estimation information about the result of this estimation is sent
to the mobile stations, so that the mobile stations can set their
backoff mechanisms depending on the estimation information. Another
known possibility is a detection of the collisions of competing
random access bursts at the user equipment side. The known systems
require much downlink resources, since the base station has to
regularly transmit estimation information to the mobile stations or
are very complex because collision detection is needed.
[0008] The U.S. Pat. No. 5,544,196 discloses an apparatus and a
method for reducing message collision between mobile stations
simultaneously accessing the base station in a wireless
telecommunication system. Hereby, a mobile station inserts a random
delay between successive random access burst transmissions if it
does not receive an acknowledgement after a predetermined time
period. The random delay is set by randomly choosing a time point
from a predetermined time interval. Thus, the time interval, from
which a new time point for a retransmission of a random access
burst is chosen, is fixedly preset. This relatively simple backoff
mechanism is also used in the GSM system. Particularly in cases, in
which the random access channel is very occupied and a lot of
collisions occur, this known system is very ineffective, since a
lot of random access burst transmission attempts are performed with
a very low probability of a successful transmission.
SUMMARY OF THE INVENTION
[0009] The object of the present invention is therefore to provide
an apparatus for transmitting and receiving signals in a wireless
telecommunication system and a method for transmitting random
access bursts in an apparatus for transmitting and receiving
signals in a wireless telecommunication system, which provide a
more effective backoff scheme for the transmission of the random
access bursts.
[0010] This object is achieved by an apparatus for transmitting and
receiving signals in a wireless telecommunication system with
transmitting means for transmitting random access bursts, receiving
means for receiving acknowledgement information confirming a
successful transmission of a random access burst, decision means
for deciding if acknowledgement information has been received, and
control means for randomly choosing a time point for an attempt to
retransmit said random access burst from an interval if no
acknowledgement information has been received after a random access
burst had been transmitted, characterized in that said control
means sets the length of said interval depending on the number of
unsuccessful attempts to transmit a random access burst.
[0011] The above object is further achieved by a method for
transmitting random access bursts in an apparatus for transmitting
and receiving signals in a wireless telecommunication system
including the steps of transmitting a random access burst,
deciding, if an acknowledgement information confirming a successful
transmission of said random access burst has been received, and
randomly choosing a time point for an attempt to retransmit said
random access burst from an interval if no acknowledgement
information has been received, characterised by setting the length
of said interval depending on the number of unsuccessful attempts
to transmit a random access burst.
SUMMARY OF THE INVENTION
[0012] The present invention thus provides a backoff scheme for
retransmission of random access burst, which is very effective,
flexible and does not require a high complexity. Particularly, the
present invention does not require a system to detect or estimate
collisions of random access bursts at the network side but enables
at the same time a flexible adaptation of the backoff scheme to the
current random access channel situation. By setting the length of
the interval, from which the time point for the retransmission is
randomly chosen, depending on the number of previous unsuccessful
attempts, the number of unsuccessful attempts until a successful
transmission of a random access burst can be reduced. Thereby, the
performance is enhanced and the system stability is improved. At
the same time a high and effective throughput of random access
bursts on a random access channel can be achieved. Although the
present invention can advantageously be applied in mobile stations
of a wireless telecommunication system, it might also be
advantageous for terminals of other systems.
[0013] Advantageously, the interval length is set longer when the
number of unsuccessful attempts increases. Hereby, in situations of
heavy traffic on the random access channel and a large number of
collisions, the time point for a retransmission is postponed and
the probability for a successful retransmission is significantly
increased. Hereby, the interval length is advantageously depending
exponentially on the number of unsuccessful attempts.
[0014] Advantageously, the control means randomly chooses the time
point for a retransmission attempt after a predetermined offset
time has elapsed. After transmission or retransmission of a random
access burst it is determined only after said predetermined offset
time has passed if an acknowledgement information, e. g. from a
selected base station, has been received.
[0015] Further, the control means can only choose a time point for
a retransmission attempt if it is determined that the number of
unsuccessful attempts is lower than a predetermined maximum number
of unsuccessful attempts. By setting a maximum number of attempts
it can be avoided that an infinite number of attempts is performed.
Since according to the present invention the length of the interval
depends on the number of unsuccessful attempts, the probability is
reduced, that the maximum number of retransmissions is reached.
[0016] The concept of the present invention is further advantageous
in that it allows to allocate different priorities for the service
requests transmitted with the random access bursts. Hereby, the
interval length can be set depending on different priority classes
of the random access bursts. Advantageously, the interval length is
thereby set shorter for higher priority classes. This allows to
provide a very small mean time until a successful transmission of a
random access burst for high priority service requests, whereby
random access bursts of lower priority classes consequently have a
higher mean time until a successful transmission.
[0017] Further advantageously, the interval is represented by a
series of numbers representing time slots in the wireless
telecommunication system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the following description, the present invention is
explained in more detail on the basis of a preferred embodiment
relating to the enclosed drawings, in which
[0019] FIG. 1 shows a flow chart for explaining the back-off method
of the present invention, and
[0020] FIG. 2 shows a bloc diagram of a terminal of a wireless
telecommunication system incorporating a back-off mechanism
structure according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] FIG. 1 shows a flow chart of a method for transmitting
random access bursts in a terminal of a wireless telecommunication
system according to the present invention. In step S1, a first
transmission of a random access burst generated in the terminal is
sent. If, e. g., a mobile station of the wireless telecommunication
system needs a channel to transmit user data, a service request in
form of a random access burst is transmitted to the selected base
station. In case that the base station successfully receives the
random access burst, it generates and transmits an acknowledgement
information back to the mobile station. The acknowledgement
information can e. g. be an access grant information or the like.
In case that the mobile station successfully receives the
acknowledgement information, it decides in a step S2, that the
first transmission of the random access burst has been successful.
Consequently, no retransmission attempts are necessary and the
procedure is terminated in a step S3. A base station can transmit
together with or integrated in the acknowledgement information
further information on the allocation of the requested service, e.
g. on the channel to be used for the transmission of user data.
[0022] After the transmission of a first random access burst in
step S1, the apparatus, e. g. the mobile station, decides, if an
acknowledgement information had been received or not. In case that
an acknowledgement information has not been received after a
predetermined offset time period has elapsed, the decision is
negative and an unsuccessful transmission is assumed. In case an
acknowledgement information is received within said predetermined
offset time period, the decision is positive and a successful
transmission is assumed.
[0023] In case that the decision in step S2 is negative, the
procedure goes to step S4, in which the number of unsuccessful
attempts is accumulated. In the next step S5 it is determined, if
the number of unsuccessful attempts has reached a predetermined
maximum number of attempts. If this is the case, the procedure is
terminated in step S6. In case that the accumulated number of
unsuccessful attempts has not yet received the predetermined
maximum number of attempts, the procedure goes to step S7. In step
S7, a new time interval is set, from which a new time point for the
next transmission of the random access burst is chosen in step S8.
Hereby, the new time interval set in step S7 is calculated on the
basis of the accumulated number of unsuccessful previous attempts.
The time interval is thereby set by calculating a number of time
slots depending on the accumulated number of unsuccessful attempts.
The time interval is thus represented by a series of numbers {1, 2,
. . . , MW+S.times.B.sup.PO+NF}, whereby each number represents a
number of time slots as the basic unit. The time slots are thereby
the basic time slots of the respective wireless telecommunication
system. The factor MW is the minimum length of the time interval,
the factor S is a scaling factor, the factor B is a base factor,
the factor PO is a power offset factor and the factor NF is the
number of failures. The number of failures is hereby the
accumulated number of unsuccessful attempts calculated in step S4.
All factors are non-negative integers, whereby the factor NF varies
from attempt to attempt. The other factors can either be preset or
varied more slowly on the basis of other system parameters.
[0024] In step S8, a new time point for the next transmission or
the retransmission of the random access burst is randomly chosen
from the time interval set in step S7. Hereby, the new time point
is randomly drawn on the basis of the uniform probability
distribution. As can be seen from the above formula, the time
between transmissions is increased with an increasing number of
unsuccessful attempts or failures. Particularly due to the
exponential dependency, the time interval from which the new time
point is randomly chosen is strongly extended so that the
probability of future unsuccessful attempts, e. g. due to
collisions, is significantly reduced. Thus, the overall system
stability is strongly enhanced.
[0025] The factor MW which determines the minimum width of the time
interval can e. g. be set to ten time slots, so that a certain
minimum time interval is assured. The factors S, B and PO can be
used to support different priority classes for the random access
bursts. Thereby, these factors are preset so that the time interval
is shorter for higher priority classes. If, e. g. four different
priority classes for four different classes of service requirements
and consequently random access bursts are assumed, the factors can
have different values for the different priority classes. Hereby,
it is sufficient to vary e. g. only the scaling factor S for the
different priority classes. For the highest priority class, the
factors could be set as follows: S=1, B=2, PO=0. For the second
priority class, the following values could be used: S=4, B=2, PO=0.
For the third priority class, the factors could be set as follows:
S=8, B=2, PO=0. For the fourth and lowest priority class, the
factors could be set as follows: S=12, B=2 and PO=0. Simulations
have shown, that it is sufficient and thus recommendable to vary
only the factor S so that the calculation scheme is simplified.
[0026] After step S8, a retransmission of the random access burst
is performed at the randomly chosen time point. Thereby, the time
interval set in step S7 determines the number of time slots
starting from the end of the predetermined offset time, after which
it is determined in step S2, if an acknowledgement information had
been received or not. The absolute time point for a retransmission
of a random access burst is thus given by the predetermined offset
time plus the time point chosen in step S8. As can be seen from the
above example, only the scaling factor S is advantageously varied
for different priority classes. The base parameter B and the power
offset parameter PO remain unchanged, whereby these parameters can
also be changed to adapt the backup mechanism to slowly varying
system conditions.
[0027] In FIG. 2, a bloc diagram of an apparatus for transmitting
and receiving signals in a wireless telecommunication system
according to the present invention is shown. The shown apparatus 1
can e. g. be a mobile station of a cellular mobile system and is
adapted to perform the steps shown in and explained in relation to
FIG. 1. Thereby, the bloc diagram of FIG. 2 only shows the elements
which are important in relation to the present invention. Other
elements which are necessary to operate the shown apparatus 1 in a
corresponding telecommunication system, like modulators,
demodulators, interleavers, microphone, loudspeaker and so forth
are not shown for the sake of clarity.
[0028] The apparatus 1 comprises an antenna 2 for receiving and
transmitting signals in the wireless telecommunication system. The
antenna 2 is connected to a transmitting means 3 and a receiving
means 4. The transmitting means 3 serves for transmitting signals
and can e. g. comprise a corresponding high frequency portion. The
receiving means 4 serves for receiving signals and comprises a
corresponding high frequency portion for downconverting the
received high frequency signals to the base band. The receiving
means 4 is connected to a decision means 5. The transmitting means
3 is connected to a random access channel generation means 7, in
which random access bursts are generated. Both the random access
generation means 7 and the decision means 5 are connected to a
control means in form of a central processing unit 6.
[0029] In case that a service request or the like has to be made
from the apparatus 1 to another apparatus of the telecommunication
system, the central processing unit 6 gives a corresponding signal
to the random access generation means 7 to generate the necessary
random access burst. The random access burst is then transmitted by
the transmitting means 3. The decision means 5 checks if a
corresponding acknowledgement information has been received within
a predetermined offset time period by the receiving means 4. The
central processing unit 6 therefore informs the decision means 5 on
the time point of a transmission of a random access burst by the
transmitting means 3 so that the decision means 5 is able to
compare the actual time given by a timing generator with the
predetermined offset time period starting from the time point of
the transmission of a random access burst. In case that an
acknowledgement information is received by the receiving means 4
within the predetermined offset time period, no retransmission of a
random access burst is necessary. In case that no acknowledgement
information has been received after the predetermined offset time
has elapsed, the control means 6 randomly chooses a time point for
an attempt to retransmit a random access burst from a time
interval. The time interval is thereby set by the control means 6
depending on the number of previous unsuccessful attempts to
transmit the random access burst. The control means 6 thereby sets
the time point for the next attempt like described in relation to
steps S7 and S8 of FIG. 1.
[0030] Therefore, the present invention provides a backoff scheme
for transmitting random access bursts in a telecommunication
apparatus with a very good performance and with a very high
stability as compared to known systems. Particularly, the
throughput is still considerably high even for high loads, e. g. in
regions of congestion. Further, no backoff specific resources on
the downlink channel are required and the detection of collisions
on the network side is not necessary.
* * * * *