Note: Descriptions are shown in the official language in which they were submitted.
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ADAPTIVE PILOT/TRAFFIC CHANNEL POWER CONTROL FOR 3GPP
WCDMA
FIELD OF THE INVENTION
This invention relates to the field of wireless digital communications, and
more
particularly to gain factors.
BACKGROUND OF THE INVENTION
Wireless communications facilitates the delivery of information between the
transmitter and the receiver without a physical wired connection. Such
advantage
translates to the freedom of mobility for the users and to the savings of
wiring nuisance
for the users. However, spectrum has become scarce resource as the usage of
wireless
communications for various applications becomes more popular. Therefore the
efficiency of using spectrum presents challenges for the wireless industry. In
order to
maximize efficient spectrum utilization, various multiple access methods have
been
proposed to achieve the goal.
First generation cellular communications systems, Advanced Mobile Phone
Services (AMPS) employed the Frequency Division Multiple Access (FDMA) method
and provided voice communication services in the early days. Second generation
cellular communications systems improved the spectrum efficiency by uSlllg
more digital
processing of signals and employed Time Division Multiple Access (TDMA) method
in
GSM and IS-136 systems and Code Division Multiple Access (CDMA) method in IS-
95
systems. While second generation systems typically provide two to five times
voice
capacity over the first generation systems, data capabilities of second-
generation systems
are very limited.
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Recent rapid commercial development of Internet and multimedia applications
has created a strong demand for wireless cellular systems capable of providing
sufficient
bandwidth. In addition, further improvement of voice capacity in spectrum
efficiency is
in great demand as the spectrum allocated for service is very limited. This
scarcity
results in high licensing fees for the available spectrum.
Therefore there is a strong need to improve the system capacity and spectrum
efficiency for wireless communication systems.
SUMMARY OF THE INVENTION
The present invention is a method and system to determine the gain factors for
the uplinlc and downlink Dedicated Physical Control Channel (DPCC) and
Dedicated
Physical Data Channel (DPDC).
BRIEF DESCRIPTION OF THE DRAWINGS
A snore complete understanding of the present invention may be obtained from
consideration of the following description in conjunction with the drawing in
which Fig.
1 is a functional block diagram.
DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
The present invention is equally well suited for both uplink of WCDMA as well
as other similar systems like CDMA2000. One feature of the present invention
is a
method and system to determine the gain factors for the uplinlc and downlink
DPDCH
and DPCCH. This method and system is equally well suited for Physical Random
Access Channel (PRACH) message part.
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The uplinlc Dedicated Physical Control Channel (DPCCH) and Dedicated
Physical Data Channel (DPDCH) are transmitted on different codes. The gain
factors [3~
and [3d are important to 3GPP WCDMA system performance like capacity.
The initial uplink DPCCH transmit power is set by higher layers. Subsequently
the uplinlc transmit power control procedure simultaneously controls the power
of a
DPCCH and its corresponding DPDCHs (if present). The relative transmit power
offset
between DPCCH and DPDCHs is determined by the network and is computed using
the
gain factors signaled to the User Equipment (UE) using higher layer signaling.
There are two ways of controlling the gain factors of the DPCCH code and the
DPDCH codes for different Transport Format Combinations (TFCs) in normal (non-
compressed) frames:
- ~3~ and ~3d are signalled for the TFC, or
- ,(3~ and /3~ is computed for the TFC, based on the signalled settings for a
reference
TFC.
Combinations of the two above methods may be used to associate ~~ and /.3d
values to all
TFCs in the TFCS. The gain factors may vary on radio frame basis (1 radio
frame = 10
ms) depending on the current TFC used. Further, the setting of gain factors is
independent of the inner loop power control.
The operation of the inner power control loop, adjusts the power of the DPCCH
and DPDCHs by the same amount, provided there are no changes in gain factors.
Additional adjustments to the power of the DPCCH associated with the use of
compressed mode. Any change in the uplink DPCCH transmit power shall take
place
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immediately before the start of the pilot field on the DPCCH. The change in
DPCCH
power with respect to its previous value is derived by the User Equipment and
is denoted
bY ~DPCCH (in dB). The previous value of DPCCH power shall be that used in the
previous slot, except in the event of an interruption in transmission due to
the use of
S compressed mode, when the previous value shall be that used in the last slot
before the
transmission gap.
During the operation of the uplinlc power control procedure the User Equipment
transmit power shall not exceed a maximum allowed value which is the lower out
of the
maximum output power of the terminal power class and a value which may be set
by
higher layer signaling. Uplinlc power control shall be performed while the
User
Equipment transmit power is below the maximum allowed output power. If the
User
Equipment transmit power is below the required minimum output power [as
defined in
TS 25.101] and the derived value of dDPCCH is less than zero, the User
Equipment may
reduce the magnitude of ~DPCCH.
1S The User Equipment shall scale the total transmit power of the DPCCH and
DPDCH(s), such that the DPCCH output power follows the changes required by the
power control procedure with power adjustments of dDPCCH dB, unless this would
result
in a User Equipment transmit power above the maximum allowed power. In this
case
the User Equipment shall scale the total transmit power so that it is equal to
the
maximum allowed power.
The gain factors during compressed frames are based on the nominal power
relation defined in normal frames.
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When the gain factors /.3~ and did are signaled by higher layers for a certain
TFC,
the signaled values are used directly for weighting of DPCCH and DPDCH(s). The
variable A~, called the nominal power relation is then computed as:
A~ _ ~'' Equation 1.
'.
5 Typically each TFC has a unique data rate connected with a unique pair of
gain
factors for the DPCCH and DPDCH. The change of gain factors for DPCCH and
DPDCH are performed to keep constant the transmitted bit energy Eb (before
coding) on
the DPDCH, independent of the data rate. The DPCCH power is kept constant to
avoid
affecting the transmit power control (TPC). If the power ratio between DPDCH
and
DPCCH goes wrong, the TPC loop operating based on DPCCH will degrade the
WCDMA system performance.
The present invention provides a method and system to determine the gain
factors
for the uplink DPDCH and DPCCH.
rr~(1'~-1~ 1 1 1 '~~i~~l'13,3./1~~. '~y-t~~_1
~~.. ~1,~1~ ~ r~ ~1-., ' 1 _ l~ h i .1.. '~ ,i... (i ~ ~li'~~'~~a/f~;.~~ 1 _
P~ y-r~"
_1
' Equation 2.
In Equation 2, m represents number of paths, P represents reference power
ratio, Ro
represents cutoff rate, ro represents coding rate, B" represents the noise
bandwidth, and,
Rb represents information bit rate. A lcey concept of the present invention is
to link up
the nominal power relation in Equation 1 with both system and radio channel
parameters
through the closed form relationship given by Equation 2.
Referring to the functional diagram in Fig. 1 there can be seen an
illustration of
the use of the present invention in the form of a functional block diagram to
set up the
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normalized reference power ratio. By using an example the working principle
behind the
present invention can be better illustrated. In Step 102 we use the
corresponding
reference power ratio for voice (Most times the system parameters are
optimized for
voice performance and for a WCDMA system the initial focus is voice
applications) as
the initial value of Po. When the system is required to serve a new data rate,
say
r=3841:bps, we need to figure out what the new nominal power relation in
Equation 1.
The method illustrated in Fig. I is used to obtain the new A1. This new A~ can
be used by
the system to set up the signaled gain factors for the reference TFC. The
settings can be
sent through higher layers for a certain TFC. What really matters is the
relative settings
of one data rate to another initial data rate such as a voice channel. The
relative settings
play an important role in "calibrating" the system settings. If there is a
system error in
Equation 2, this scaling can reduce the error such that the relative settings
can more
accurately describe the functional relationship between one DPDCH data channel
and
another DPDCH data channel.
I S In step 102 an initial value is given to Ao. The data rate in step 104 is
given. In
step 106 the necessary system and radio channel parameters necessary for
Equation 2 are
given. The reference power ratio P~=P is solved using Equation 2 in step 108.
The
normalized reference power ratio is determined in step 110. Steps 104 through
110 are
dynamically repeated for new data rate.
In the present invention, the dynamic nature of the radio channel is directly
related to the dynamic nature of the DPDCH data channel. Therefore the present
invention responds quickly to the radio channel of the air interface while the
mobile
terminal is moving around. No simple scheme in power settings can be accurate
without
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dynamic response to the real-time radio channel being experienced by the DPDCH
data
channel and the DPCCH channel. Thus this scheme can be regarded as the
adaptive
scheme for the system to set up the resources to make certain that the WCDMA
system
works at an optimal state.
The significance of this method is the speed of the quick convergence.
Although
it may not be so accurate for some working conditions, the method is Fig. 1
dynamically
adjust the nominal power relation quickly. Thus the system is always working
at the
quasi-optimal system settings. One result of the net advantages of this method
is that the
system resource or system power is not wasted and thus the interference is
minimized.
These two interacting factors both lead to higher system throughput or system
capacity.
In view of the foregoing description, numerous modifications and alternative
embodiments of the invention will be apparent to those skilled in the art. The
present
invention is equally well suited for both uplink of WCDMA and similar systems
like
CDMA2000. One feature of the present invention is a method and system to
determine
the gain factors for the uplink and downlink DPDCH and DPCCH. This method and
system is equally well suited for Physical Random Access Channel (PRACH)
message
part. Accordingly, this description is to be construed as illustrative only
and is for the
purpose of teaching those skilled in the art the best mode of carrying out the
invention.
Details of the structure may be varied substantially without departing from
the spirit of
the invention, and the exclusive use of all modifications, which come within
the scope of
the appended claim, is reserved.
