U.S. patent application number 10/783209 was filed with the patent office on 2004-08-19 for link adaptation algorithm for packet based radio system.
This patent application is currently assigned to Nokia Mobile Phones Limited. Invention is credited to Gronberg, Petri.
Application Number | 20040160902 10/783209 |
Document ID | / |
Family ID | 23832768 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040160902 |
Kind Code |
A1 |
Gronberg, Petri |
August 19, 2004 |
Link adaptation algorithm for packet based radio system
Abstract
A method is disclosed for operating a channel coder, as is a
channel coder that operates in accordance with the method. The
method includes steps of (a) maintaining a first count (N_Number)
of transmitted packets and a second count (K_Number) of packets
that are erroneously decoded at a receiver; (b) periodically
performing a plurality of statistical tests using current values of
the first and second counts; and (c) based on a result of the
statistical tests, controlling the channel coder to either maintain
a current channel coding technique or to switch to another channel
coding technique. The step of controlling includes a further step
of resetting the first count and the second count.
Inventors: |
Gronberg, Petri; (Espoo,
FI) |
Correspondence
Address: |
HARRINGTON & SMITH, LLP
4 RESEARCH DRIVE
SHELTON
CT
06484-6212
US
|
Assignee: |
Nokia Mobile Phones Limited
|
Family ID: |
23832768 |
Appl. No.: |
10/783209 |
Filed: |
February 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10783209 |
Feb 20, 2004 |
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09461490 |
Dec 14, 1999 |
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6728259 |
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Current U.S.
Class: |
370/252 ;
370/242 |
Current CPC
Class: |
H04L 1/0009 20130101;
H04L 1/0019 20130101; H04L 1/0025 20130101 |
Class at
Publication: |
370/252 ;
370/242 |
International
Class: |
H04L 012/26 |
Claims
What is claimed is:
1. A method for operating a channel coder, comprising steps of:
maintaining a first count (N_Number) of transmitted packets and a
second count (K_Number) of packets that are erroneously decoded at
a receiver; periodically performing a plurality of statistical
tests using current values of the first and second counts; and
based on a result of said statistical tests, controlling said
channel coder to either maintain a current channel coding technique
or to switch to another channel coding technique.
2. A method as in claim 1, wherein said step of controlling is
comprised of a further step of resetting said first count and said
second count.
3. A method as in claim 1, wherein the step of periodically
performing a plurality of statistical tests is comprised of steps:
at a crossing point where a first channel coding algorithm (CS-1)
and a second channel coding algorithm (CS-2) provide a same net bit
rate, assuming as a first hypothesis that a packet error rate (PER)
is greater than a PER of CS-1, P1, if CS-1 is currently being used,
or assuming as the first hypothesis that the PER is less than a PER
of CS-2, P2, if CS-2 is currently being used; assuming as reference
case that N_Number of packets have been transmitted with a constant
PER equal to either P1 or P2, depending on the currently used
channel coding algorithm CS-1 or CS-2; determining a first
probability (P-value) using said first count and said second count
and the constant PER P1 or P2, depending on the currently used
channel coding algorithm CS-1 or CS-2; comparing P-value to a risk
level (RL) for determining whether the first hypothesis can be
rejected; and only if the first hypothesis is rejected, changing to
the other channel coding algorithm and resetting N_Number and
K_Number; assuming as a second hypothesis that PER is less than the
PER of CS-1, P1, if CS-1 is currently being used, or assuming as
the second hypothesis that PER is greater than the PER of CS-2, P2,
if CS-2 is currently being used; assuming the same reference case
that N_Number of packets have been transmitted with a constant PER
equal to either P1 or P2, depending on the currently used channel
coding algorithm CS-1 or CS-2; determining a second probability
(P-value) using said first count and said second count and the
constant PER P1 or P2, depending on the currently used channel
coding algorithm CS-1 or CS-2; comparing P-value to RL for
determining whether the second hypothesis can be rejected; and only
if the second hypothesis is rejected, resetting N_Number and
K_Number without changing to the other channel coding
algorithm.
4. A method as in claim 1, wherein the step of periodically
performing a plurality of statistical tests comprises steps of:
accessing at least one look-up table using the current values of
the first and second counts to retrieve a probability value
(P-value); and comparing the retrieved P-value to a threshold to
determine whether an assumed hypothesis should be accepted or
rejected.
5. A method for operating a channel coder to operate with a first
channel coding algorithm (CS-1) or a second channel coding
algorithm (CS-2), comprising steps of: maintaining a first count
(N_Number) of transmitted packets and a second count (K_Number) of
packets that are erroneously decoded at a receiver; periodically
performing a plurality of statistical tests in accordance with the
steps of, if a current channel coding is CS-1: determining if a
change should be made to CS-2 by assuming as a hypothesis that:
PER>P1; assuming as a reference case that N_Number of packets
have been transmitted with a constant PER value of P1; determining
a probability (P-value) in accordance with: 5 P - value = i = 0 K
Number ( N Number i ) P1 i ( 1 - P1 ) N Number - i if P-value is
less than a risk level (RL), rejecting the hypothesis with (1-RL)
confidence; if the hypothesis is rejected, changing to CS-2, and
resetting N_Number and K_Number, else if the hypothesis is
accepted, continuing to average channel readings; and then
confirming CS-1 by assuming as a hypothesis that: PER<P1;
assuming the same reference case; determining the probability
(P-value) in accordance with: 6 P - value = i = K Number N Number (
N Number i ) P1 i ( 1 - P1 ) N Number - i if P-value is less than
RL, rejecting the hypothesis with (1-RL) confidence; if the
hypothesis is rejected, resetting N_Number and K_Number, else if
the hypothesis is accepted, continuing to average channel readings;
else if the current channel coding is CS-2: determining if a change
should be made to CS-1 by assuming as a hypothesis that: PER<P2;
assuming the same reference case; determining the probability
(P-value) in accordance with: 7 P - value = i = K Number N Number (
N Number i ) P2 i ( 1 - P2 ) N Number - i if P-value is less than
RL, rejecting the hypothesis with (1-RL) confidence; if the
hypothesis is rejected, changing to CS-1, and resetting N_Number
and K_Number, else if the hypothesis is accepted, continuing to
average channel readings; and then confirming CS-2 by assuming as a
hypothesis that: PER>P2; assuming the same reference case;
determining the probability (P-value) in accordance with: 8 P -
value = i = 0 K Number ( N Number i ) P2 i ( 1 - P2 ) N Number - i
if P-value is less than RL, rejecting the hypothesis with (1-RL)
confidence; if the hypothesis is rejected, resetting N_Number and
K_Number, else if the hypothesis is accepted, continuing to average
channel readings.
6. A method as in claim 5, wherein the steps of determining the
P-value comprise an initial step of pre-computing P-values for a
range of values of N_Number and K_Number and P1 and P2 values;
storing the pre-computed values in at least one look-up table; and
accessing the look-up table with current values of N_Number and
K_Number to retrieve a corresponding P-value.
7. A method for operating a channel coder, comprising steps of:
while operating with a first channel coding technique, updating a
first count (N_Number) of transmitted packets and a second count
(K_Number) of packets that are erroneously decoded at a receiver;
and periodically performing a plurality of statistical tests using
current values of the first and second counts, wherein the step of
periodically performing the plurality of statistical tests is
comprised of sub-steps of, determining if a first hypothesis is
rejected, and if yes, switching to a second channel coding
technique, and resetting the first and second counts, before
continuing the step of averaging; while if the first hypothesis is
accepted, determining if a second hypothesis is rejected, and if
yes, resetting the first and second counts, before continuing the
step of averaging; while if the second hypothesis is also accepted,
continuing the step of averaging without first resetting the first
and second counts.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to digital radio data
communication systems and methods and, more particularly, to link
adaptation techniques for selecting an optimum channel coding for a
particular radio channel quality.
BACKGROUND OF THE INVENTION
[0002] In digital radio systems the information is typically
transmitted in data packets using a particular type of channel
coding. The goal of channel coding is to improve the transmission
quality when the transmitted signal encounters radio channel
disturbances. When a data packet is coded, some amount of redundant
information is added to the source data. A subsequent decoding
operation then makes use of the redundant information to detect
and/or correct bit errors that occurred during the
transmission.
[0003] When the amount of redundant information is increased the
error correction capabilities of the decoder can be improved.
However, the improvement in error correction capabilities comes at
the cost of a reduced net bit rate. As can be appreciated, it would
be advantageous to use a robust channel coding technique during
poor radio propagation conditions, and a channel coding technique
having a high net bit rate when the radio channel conditions are
good.
[0004] It is known in the art to employ link adaptation algorithms
in an attempt to select an optimum channel coding technique for a
given radio link. The selection of a particular channel coding
technique is based on link or channel quality estimates.
[0005] In a typical link adaptation algorithm the receiver measures
a carrier to interference ratio (C/I) or a raw Bit Error Rate
(BER), and then makes an estimate of the channel quality by
averaging the measurements over some period of time. Reference in
this regard can be had to a publication entitled "Bit Error Rate
Based Link Adaptation for GSM", J. Pons and J. Dunlop, Proceedings
of the 1998 9.sup.th IEEE International Symposium on Personal,
Indoor and Mobile Radio Communications", PIMRC, Part 3, pages
1530-1534.
[0006] In general, a link adaptation algorithm makes the decision
of whether to maintain or change a current channel coding technique
by comparing the estimated channel quality with one or more
threshold values. Some amount of hysteresis is typically used in
the comparison to avoid ping-pong effects (i.e., repetitive
switching between channel coding techniques when the estimated
channel quality is about equal to the switching threshold
value.)
[0007] If the particular link adaptation algorithm is run by the
receiver, then signalling is arranged so that the receiver can
command the transmitter to use the selected channel coding
technique. Otherwise, the signalling is arranged so that the
receiver sends the channel quality estimates to the transmitter,
which then executes the desired link adaptation algorithm.
[0008] A problem arises in these conventional approaches in that,
for some cases, an ability to make the channel quality estimation
in terms of the C/I or BER may be difficult, inaccurate or even
impossible. For example, the receiver may not have sufficient
processing power to perform the required measurements. In this case
a reduced complexity link adaptation algorithm can be used, such as
one that simply counts the numbers of successfully decoded and
unsuccessfully decoded packets. However, the packet counting
approach, while computationally less complex than other types of
channel quality estimation techniques, may result in a problematic
link adaptation algorithm. For example, in order to obtain an
accurate estimate of a packet error rate (PER) value a significant
number of packets must be received, thereby resulting in a slow
algorithm. As such, the link adaptation approach based on packet
counting will not be capable of rapidly responding to changes in
radio channel conditions.
OBJECTS AND ADVANTAGES OF THE INVENTION
[0009] It is a first object and advantage of this invention to
provide an improved link adaptation algorithm that overcomes the
foregoing and other problems.
[0010] It is a further object and advantage of this invention to
provide an improved link adaptation algorithm that uses a channel
estimation technique based on counting numbers of received and
unsuccessfully received packets, and that more quickly adapts to
changing channel conditions than conventional packet counting-based
techniques.
[0011] It is another object and advantage of this invention to
provide an improved link adaptation algorithm that uses a channel
estimation technique based on counting numbers of received and
unsuccessfully received packets, and that improves the speed of the
packet counting algorithm by employing statistical testing methods
to determine whether a current channel coding technique should be
changed.
SUMMARY OF THE INVENTION
[0012] The foregoing and other problems are overcome and the
objects of the invention are realized by methods and apparatus in
accordance with embodiments of this invention.
[0013] A method is disclosed for operating a channel coder, as is a
channel coder that operates in accordance with the method. The
method includes steps of (a) maintaining a first count (N_Number)
of transmitted packets and a second count (K_Number) of packets
that are erroneously decoded at a receiver; (b) periodically
performing a plurality of statistical tests using current values of
the first and second counts; and (c) based on a result of the
statistical tests, controlling the channel coder to either maintain
a current channel coding technique or to switch to another channel
coding technique. The step of controlling includes a further step
of resetting the first count and the second count.
[0014] In a presently preferred embodiment the step of periodically
performing a plurality of statistical tests includes steps of (b1),
at a crossing point where a first channel coding algorithm (CS-1)
and a second channel coding algorithm (CS-2) provide a same net bit
rate, assuming as a first hypothesis that a packet error rate (PER)
is greater than a PER of CS-1, P1, if CS-1 is currently being used,
or assuming as the first hypothesis that the PER is less than a PER
of CS-2, P2, if CS-2 is currently being used; (b2) assuming as
reference case that N_Number of packets have been transmitted with
a constant PER equal to either P1 or P2, depending on the currently
used channel coding algorithm CS-1 or CS-2; (b3) determining a
first probability (P-value) using the first count and the second
count and the constant PER P1 or P2, depending on the currently
used channel coding algorithm CS-1 or CS-2; (b4) comparing P-value
to a risk level (RL) for determining whether the first hypothesis
can be rejected; and (b5) only if the first hypothesis is rejected,
changing to the other channel coding algorithm and resetting
N_Number and K_Number.
[0015] The step of periodically performing a plurality of
statistical tests includes further steps of (b6) assuming as a
second hypothesis that PER is less than the PER of CS-1, P1, if
CS-1 is currently being used, or assuming as the second hypothesis
that the PER is greater than the PER of CS-2, P2, if CS-2 is
currently being used; (b7) assuming the same reference case as in
step (b2); (b8) determining a second probability (P-value) using
the first count and the second count and the constant PER P1 or P2,
depending on the currently used channel coding algorithm CS-1 or
CS-2; (b9) comparing P-value to RL for determining whether the
second hypothesis can be rejected; and (b10) only if the second
hypothesis is rejected, resetting N_Number and K_Number without
changing to the other channel coding algorithm.
[0016] In the presently preferred embodiment the step of
periodically performing a plurality of statistical tests includes
steps of accessing at least one look-up table using the current
values of the first and second counts to retrieve probability
values (P-values); and comparing the retrieved P-values to a
threshold to determine whether the assumed hypothesis should be
accepted or rejected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above set forth and other features of the invention are
made more apparent in the ensuing Detailed Description of the
Invention when read in conjunction with the attached Drawings,
wherein:
[0018] FIG. 1 is a conceptual block diagram of a packet data
communication system that operates in accordance with this
invention;
[0019] FIG. 2 is a graph of C/I (dB) versus time, and shows
CS-switching, in accordance with the presently preferred link
adaptation algorithm, when tested in a simulator where a mobile
station continuously transmitted data packets to a network under
varying C/I conditions; and
[0020] FIG. 3 is a logic flow diagram depicting a method in
accordance with the description found herein.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The presently preferred link adaptation algorithm is based
on statistical testing methods. In statistical testing a certain
hypothesis is made and then studied (tested), wherein a
determination is made of a probability (P-value) that a constructed
reference case would generate observed measures with the condition
of the hypothesis. Based on the obtained probability the hypothesis
is either accepted or rejected.
[0022] Consider a case that is pertinent to the teachings of this
invention, wherein two different channel coding algorithms or
schemes, CS-1 and CS-2, can be used. CS-1 is assumed to be more
robust than CS-2. As in most link adaptation techniques, one
determines beforehand the point where both CS-1 and CS-2 give the
same net bit rate (the crossing point of CS-1 and CS-2). This can
be accomplished either by link level simulations or by experimental
tests. Assume that at the crossing point between CS-1 and CS-2 the
packet error rate (PER) values for CS-1 and CS-2 are P1 and P2,
respectively. If CS-1 is used, and if the PER is less than P1, then
it would be advantageous to change to CS-2. If CS-2 is used, and if
the PER is larger than P2, then it would be advantageous to change
to CS-1. Since CS-1 is more robust that CS-2, P2 is larger than
P1.
[0023] In accordance with the teachings of this invention, during a
packet data transmission two counters are updated: N_Number gives a
total number of packets, and K_Number gives a number of erroneously
decoded packets that have been transmitted since the last link
adaptation decision.
[0024] After each transmitted packet, or alternatively at certain
predetermined intervals, two of the following four statistical
tests are performed (either 1 and 2, or 3 and 4).
[0025] 1. Current Channel Coding is CS-1; Change to CS-2?
[0026] Hypothesis: PER>P1
[0027] Reference case: N_Number of packets have been transmitted
with a constant PER value of P1. In this reference case the number
of erroneous packets follow a binomial distribution. 1 P - value =
i = 0 K Number ( N Number i ) P1 i ( 1 - P1 ) N Number - i
[0028] If P-value is less than a certain risk level (RL, a typical
value of which is about 5%), the hypothesis can be rejected with
(1-RL) confidence. This means that it is unlikely that the
reference case would yield the observed measures with the condition
of PER>P1.
[0029] The action to be taken in case the hypothesis is rejected is
to change to CS-2, and to reset the counters N_Number and
K_Number.
[0030] The action to be taken in case the hypothesis is accepted is
to continue averaging (no action).
[0031] Further in this regard, note that the ratio of K_Number
divided by N_Number estimates the experienced PER. The longer the
variables N_Number and K_Number are counted, the more accurate in a
statistical sense is the (average) estimate of the PER, assuming
that the radio channel conditions do not change substantially. When
the PER is sufficiently accurate, then the optimal channel coding
algorithm can be selected.
[0032] 2. Current Channel Coding is CS-1; Confirm CS-1?
[0033] Hypothesis: PER<P1
[0034] Reference case: N_Number of packets have been transmitted
with a constant PER value of P1. In this reference case the number
of erroneous packets follow a binomial distribution. 2 P - value =
i = K Number N Number ( N Number i ) P1 i ( 1 - P1 ) N Number -
i
[0035] If P-value is less than RL, a typical value of which is
about 5%, the hypothesis can be rejected with (1-RL) confidence.
This means that it is unlikely that the reference case would yield
the observed measures with the condition of PER<P1.
[0036] The action to be taken in case the hypothesis is rejected is
to reset the counters N_Number and K_Number (CS-1 is
confirmed).
[0037] The action to be taken in case the hypothesis is accepted is
to continue averaging (no action).
[0038] It should be noted that if the first hypothesis is rejected,
then the second hypothesis need not be tested. Note further that
the two P-values computed for the first hypothesis and for the
second hypothesis are nearly complementary to one another, and that
the sum of the two P-values is about unity (actually slightly
greater than unity). Therefore, if the first hypothesis is
rejected, the first P-value is less than RL (which is clearly less
than 0.5), and the second P-value will then clearly be larger than
0.5. As a result, it is known that the second hypothesis would have
been accepted and not rejected.
[0039] 3. Current Channel Coding is CS-2; Change to CS-1?
[0040] Hypothesis: PER<P2
[0041] Reference case: N_Number of packets have been transmitted
with a constant PER value of P2. In this reference case the number
of erroneous packets follow a binomial distribution. 3 P - value =
i = K Number N Number ( N Number i ) P2 i ( 1 - P2 ) N Number -
i
[0042] If P-value is less than RL, a typical value of which is
about 5%, the hypothesis can be rejected with (1-RL) confidence.
This means that it is unlikely that the reference case would yield
the observed measures with the condition of PER<P2.
[0043] The action to be taken in case the hypothesis is rejected is
to change to CS-1, and to reset the counters N_Number and
K_Number.
[0044] The action to be taken in case the hypothesis is accepted is
to continue averaging (no action).
[0045] 4. Current Channel Coding is CS-2; Confirm CS-2?
[0046] Hypothesis: PER>P2
[0047] Reference case: N_Number of packets have been transmitted
with a constant PER value of P2. In this reference case the number
of erroneous packets follow a binomial distribution. 4 P - value =
i = 0 K Number ( N Number i ) P2 i ( 1 - P2 ) N Number - i
[0048] If P-value is less than RL, a typical value of which is
about 5%, the hypothesis can be rejected with (1-RL) confidence.
This means that it is unlikely that the reference case would yield
the observed measures with the condition of PER>P1.
[0049] The action to be taken in case the hypothesis is rejected is
to reset the counters N_Number and K_Number (CS-2 is
confirmed).
[0050] The action to be taken in case the hypothesis is accepted is
to continue averaging (no action).
[0051] Having thus described preferred embodiments of the four
statistical tests, it should be noted that, in practice, the
P-values can be computed beforehand and stored in look-up tables
(with indices N_Number and K_Number). In this case the link
adaptation decisions can be performed by simply comparing the
predefined P-values with the given risk level RL.
[0052] It is desirable to restrict the size of the look-up tables
to a practical value. There are at least two different ways to
accomplish this.
[0053] In a first technique, since the binomial distribution
approaches a normal distribution when N_Number becomes large, the
P-values for large values of N_Number can be defined with a normal
distribution (using, for example, a separate look-up table.)
[0054] In a second technique, if K_Number increases beyond the
look-up table size, the counters N_Number and K_Number can be
reset. In this manner the number of samples (and thus the size of
the look-up tables) is limited, even if the link adaptation
algorithm does not make a decision for a long period of time.
[0055] Referring to FIG. 1, there is shown a conceptual block
diagram of a packet data communication system 10 that operates in
accordance with the statistical testing embodiments discussed
above. In the illustrated embodiment it is assumed that a packet
data receiver 12 contains first and second channel decoders (DS-1
and DS-2) that correspond to the first and second channel coders
(CS-1 and CS-2) of the packet data transmitter 14. The transmitter
14 includes a data source 16 that feeds packets to either CS-1 or
CS-2 through a logical switch S1. The state of S1 is controlled by
a CS controller 18 that receives a switching command input from the
receiver 12 via a receiver 20 and a wireless channel coding change
signalling link. The receiver 12 contains a packet data receiver 22
that feeds packets received from a communications channel to either
DS-1 or DS-2 via a logical switch S2. The state of S2 is controlled
by a DS controller 18 that receives a switching command input from
a comparator 26. The comparator 26 operates to compare a P-value
output from a P-value look-up table (LUT) 28 to RL. If P-value is
less than RL, when the statistical test hypothesis is PER>P1
when CS-1/DS-1 are active, or PER<P2 when CS-2/DS-2 are active,
then a channel coding/decoding scheme change is indicated by the
less-than output of comparator 26. This output signal is signalled
to the transmitter 14, via a signalling transmitter 27. This same
signal, also for the cases when the link adaptation algorithm
operates to confirm CS-1 or CS-2, is used to reset counters
N_Number 30, which counts the number of received packets, and
K_Number 32, which counts the number of erroneously decoded packets
from the active one of DS-1 or DS-2. The outputs of counter 30 and
32 are used as address inputs to index into the P-value LUT 28, as
was described above, so as to retrieve one of the pre-computed
P-values. A decoded packet output of the active one of DS-1 or DS-2
is provided to a data sink 34, where the received and decoded
packets are stored, displayed, or otherwise acted on in a desired
manner. The value of RL can be pre-set, or it may be varied during
operation.
[0056] In other embodiments of this invention some of the
components of the receiver 12, such as the P-value LUT 28 and
comparator 26, or just the comparator 26, can be moved to the
transmitter 14, and the signalling modified accordingly.
[0057] Referring to FIG. 2, the foregoing link adaptation algorithm
was tested in a simulator where a mobile station was continuously
transmitting data packets to a network under varying C/I
conditions. In this simulation the link adaptation algorithm was
run by the network side, and a message was sent to the mobile
station whenever the channel coding (CS-1 or CS-2) was changed (see
the bottom two traces). This was found to introduce a delay of
about 100 milliseconds for switching. In FIG. 2 the mean bit rate
was equal to 5.25 kbps, while the mean acknowledgement (ack) rate
was 3.89 l/s.
[0058] The use of the link adaptation algorithm described above is
applicable in various digital radio systems, such as the General
Packet Radio Service (GPRS) and Enhanced-GPRS systems, where
different channel codings (two or more) can be used. The use of the
link adaptation algorithm is especially applicable if the channel
quality cannot be measured accurately in terms of C/I or the raw
BER.
[0059] Furthermore, the link adaptation algorithm described above
can be used alone, or it may be used as a part of a larger link
adaptation algorithm which also employs one or more channel quality
estimates (for instance, PER and C/I) to make the required channel
coding decisions.
[0060] In general, the use of the link adaptation algorithm
described above may be restricted if one of the threshold values
(P1) is zero or about zero. In this case the PER measurement may
not yield the required information, or the convergence could be
unacceptably slow.
[0061] Based on the foregoing description, and referring now to
FIG. 3, it can be appreciated that a method has been disclosed for
operating a channel coder, as is a channel coder that operates in
accordance with the method. The method includes steps of: Step (A),
updating a first count (N_Number) of transmitted packets and a
second count (K_Number) of packets that are erroneously decoded at
a receiver; and Step (B), periodically performing a plurality of
statistical tests using current values of the first and second
counts. The Step (B) includes a first sub-step (B1) of determining
if the first hypothesis is rejected, if yes, performing a second
sub-step (B2) of switching to the other channel coding scheme or
algorithm, and a sub-step (B3) of resetting the first and second
counts, before continuing the averaging step (A). If the result of
the first sub-step (B1) determines that the first hypothesis is
accepted, control instead passes to sub-step (B4) where a
determination is made if the second hypothesis is rejected. If yes,
control passes to sub-step (B3) for resetting the first and second
counts, before continuing the averaging step (A) . If the result of
the sub-step (B4) determines that the second hypothesis is also
accepted, control instead passes to Step A to continue updating the
counts, without first resetting the counts at sub-step (B3).
[0062] The invention has been described in the context of a
presently preferred embodiments thereof, however the teachings of
this invention are not intended to be limited in scope to only
these disclosed embodiments. As but one example, while the
invention has been described in the context of maintaining a
running count of transmitted packets (N_Number) and packets that
are erroneously decoded at a receiver (K_Number), it is within the
scope of this invention to instead count packets that are
successfully decoded at the receiver, and to then derive the value
of K_Number by subtracting the number of successfully received
packets from N_Number. Alternatively, one could count packets that
are successfully decoded at the receiver as well as packets that
are unsuccessfully decoded at the receiver, and to then add these
two counts to derive N_Number.
[0063] Also, the teachings of this invention can be used with a
number of suitable channel coding algorithms, such as convolutional
channel coding algorithms.
[0064] Also, if not performed after each packet, a suitable
interval for performing the algorithm (and assuming that the
processing load is low) is preferably made short, such as after
every two packets. Note should be taken of the fact that with the
given parameters P1, P2 and RL, it is possible to compute
beforehand those N_Number and K_Number pairs with which a
particular hypothesis can be rejected. Based. on the obtained
N_Numbers it may then be possible to determine a suitable testing
interval.
[0065] Furthermore, it is within the scope of the teaching of this
invention to adapt the testing interval to the channel conditions,
although in this event it may be desirable to employ an additional
channel quality estimate over and above the results of the testing
described above.
[0066] Thus, while the invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that changes in form and
details may be made therein without departing from the scope and
spirit of the invention.
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