Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR CONTROLLING
TRANSMISSION GATED COMMUNICATION SYSTEM
This is a divisional of Application Serial No. 2,378,838, filed July 18,
2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communications. More particularly,
the present invention relates to a novel and improved method and apparatus for
transmitting variable rate data in a wireless communication system.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation
techniques is one of several techniques for facilitating communications in
which a
large number of system users are present. Other multiple access communication
system techniques, such as time division multiple access (TDMA) and frequency
division multiple access (FDMA) are known in the art. However, the spread
spectrum modulation techniques of CDMA have significant advantages over these
modulation techniques for multiple access communication systems. The use of
CDMA techniques in a multiple access communication system is disclosed in U.S.
Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS
COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL
REPEATERS", assigned to the assignee of the present invention. The use of
CDMA techniques in a multiple access communication system is further disclosed
in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR
GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE
SYSTEM", assigned to the assignee of the present invention.
CDMA by its inherent nature of being a wideband signal offers a
form of frequency diversity by spreading the signal energy over a wide
bandwidth.
Therefore, frequency selective fading affects only a small part of the CDMA
signal
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bandwidth. Space or path diversity is obtained by providing multiple signal
paths
through simultaneous links from a mobile user through two or more cell-sites.
Furthermore, path diversity may be obtained by exploiting the multipath
environment through spread spectrum processing by allowing a signal arriving
with different propagation delays to be received and processed separately.
Examples of path diversity are illustrated in U.S. Patent No. 5,101,501
entitled
"METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN
COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM", and U.S.
Patent No. 5,109,390 entitled "DIVERSITY PECEIVER IN A CDMA CELLULAR
TELEPHONE SYSTEM", both assigned to the assignee of the present invention.
A method for transmission of speech in digital communication
systems that offers particular advantages in increasing capacity while
maintaining
high quality of perceived speech is by the use of variable rate speech
encoding.
The method and apparatus of a particularly useful variable rate speech encoder
is
described in detail in U.S. Patent No. 5,414,796, entitled "VARIABLE RATE
VOCODER", assigned to the assignee of the present invention.
The use of a variable rate of speech encoder provides for data
frames of maximum speech data capacity when the speech encoder is providing
speech data at a maximum rate. When the variable rate speech encoder is
providing speech data at a less than maximum rate, there is excess capacity in
the transmission frames. A method for transmitting additional data in
transmission
frames of a fixed predetermined size, wherein the source of the data for the
data
frames is providing the data at a variable rate, is described in detail in
U.S. Patent
No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING
OF DATA FOR TRANSMISSON', assigned to the assignee of the present
invention. In the above mentioned patent application a method and apparatus is
disclosed for combining data of differing types from different sources in a
data
frame for transmission.
In frames containing less data than a predetermined capacity, power
consumption may be lessened by transmission gating a transmission amplifier
such that only parts of the frame containing data are transmitted.
Furthermore,
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message collisions in a communication system may be reduced if the data is
placed into frames in accordance with a predetermined pseudorandom process.
A method and apparatus for gating the transmission and for positioning the
data in
the frames is disclosed in U.S. Patent No. 5,659,569, entitled "DATA BURST
RANDOMIZER", assigned to the assignee of the present invention.
A useful method of power control of a mobile in a communication
system is to monitor the power of the received signal from the wireless
communication device at a base station. In response to the monitored power
level, the base station transmits power control bits to the wireless
communication
device at regular intervals. A method and apparatus for controlling
transmission
power in this fashion is disclosed in U.S. Patent No. 5,056,109, entitled
"METHOD
AND APPARATUS FOR CONTROLLING TRANSMISSION POWER INA CDMA
CELLULAR MOBILE TELEPHONE SYSTEM", assigned to the assignee of the
present invention.
In a communication system that provides data using a QPSK
modulation format, very useful information can be obtained by taking the cross
product of the I and Q components of the QPSK signal. By knowing the relative
phases of the two components, one can determine roughly the velocity of the
wireless communication device in relation to the base station. A description
of a
circuit for determining the cross product of the I and Q components in a QPSK
modulation communication system is disclosed in U.S. Patent No. 5,506,865,
entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", assigned to the assignee
of the present invention.
There has been an increasing demand for wireless communications
systems to be able to transmit digital information at high rates. One method
for
sending high rate digital data from a wireless communication device to a
central
base station is to allow the wireless communication device to send the data
using
spread spectrum techniques of CDMA. One method that is proposed is to allow
the wireless communication device to transmit its information using a small
set of
orthogonal channels. Such a method is described in detail in co-pending U.S.
Patent Application Serial No. 08/886,604, entitled "HIGH DATA RATE CDMA
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WIRELESS COMMUNICATION SYSTEM", assigned to the assignee of the
present invention.
In the just-mentioned application, a system is disclosed in which a
pilot signal is transmitted on the reverse link (the link from the wireless
communication device to the base station) to enable coherent demodulation of
the
reverse link signal at the base station. Using the pilot signal data,
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coherent processing can be performed at the base station by determining and
removing the phase offset of the reverse link signal. Also, the pilot data can
be used to optimally weigh multipath signals received with different time
delays before being combined in a rake receiver. Once the phase offset is
removed, and the multipath signals properly weighted, the multipath
signals can be combined to decrease the power at which the reverse link
signal must be received for proper processing. This decrease in the required
receive power allows greater transmission rates to be processed successfully,
or conversely, the interference between a set of reverse link signals to be
decreased.
While some additional transmit power is necessary for the
transmission of the pilot signal, in the context of higher transmission rates
the ratio of pilot signal power to the total reverse link signal power is
substantially lower than that associated with lower data rate digital voice
data transmission cellular systems. Thus, within a high data rate CDMA
system, the Eb/No gains achieved by the use of a coherent reverse link
outweigh the additional power necessary to transmit pilot data from each
wireless communication device.
However, when the data rate is relatively low, a continuously-
transmitted pilot signal on the reverse link contains more energy relative to
the data signal. At these low rates, the benefits of coherent demodulation
and reduced interference provided by a continuously-transmitted reverse
link pilot signal may be outweighed by the decrease in talk time and system
capacity in some applications.
SUMMARY OF THE INVENTION
The present invention ds a novel and improved method and system
for communicating a frame of information according to a discontinuous
transmit format. In particular, the present invention describes a method of
transmitting eighth rate speech or data frames employing transmit gating and
energy scaling which simultaneously reduces the battery usage of a variable
rate wireless communication device, increases the capacity of the reverse link
and provides reliable communication of the eighth rate frames. In the
present invention, four methods are presented for transmitting an eighth rate
data frame in which half of the frame is gated out and the remaining data is
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transmitted at nominal transmission energy to accomplish the aforementioned
goals.
According to one aspect of the present invention, there is provided in
a base station, a method for controlling the transmission energy of forward
link
5 signals comprising the steps of: receiving a potentially gated reverse link
signal
including forward link power control bits; determining whether said power
control
bits have been gated out; and adjusting forward link transmission energy in
accordance with said forward link power control bits only when said
determination
as to whether said forward link power control bits have been gated out
indicates
that said power control bits have not been gated out.
According to another aspect of the present invention, there is
provided: a base station for controlling the transmission energy of forward
link
signals comprising: means for receiving a potentially gated reverse link
signal
including forward link power control bits; means for determining whether said
power control bits have been gated out; and means for adjusting forward link
transmission energy in accordance with said forward link power control bits
only
when said determination as to whether said forward link power control bits
have
been gated out indicates that said power control bits have not been gated out.
According to another aspect of the present invention, there is
provided a computer program product comprising a computer readable memory
storing computer executable instructions thereon that when executed by a
computer perform a method for controlling the transmission energy of forward
link
signals, the method comprising: receiving a potentially gated reverse link
signal
including forward link power control bits; determining whether said power
control
bits have been gated out; and adjusting forward link transmission energy in
accordance with said forward link power control bits only when said
determination
as to whether said forward link power control bits have been gated out
indicates
that said power control bits have not been gated out.
According to another aspect of the invention, there is provided a
3o digital processor for controlling the transmission energy of forward link
signals
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comprising: a. a memory device; and b. a processor configured to: receive a
potentially gated reverse link signal including forward link power control
bits;
determine whether said power control bits have been gated out; and adjust
forward link transmission energy in accordance with said forward link power
control bits only when said determination as to whether said forward link
power
control bits have been gated out indicates that said power control bits have
not
been gated out.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of the present invention will
become more apparent from the detailed description set forth below when taken
in
conjunction with the drawings in which like reference characters identify
correspondingly throughout and wherein:
FIG. 1 is a functional block diagram of an exemplary embodiment of
the transmission system of the present invention embodied in wireless
communication device 50;
FIG. 2 is a functional block diagram of an exemplary embodiment of
modulator 26 of FIG. 1;
FIGS. 3A-3G illustrate the energy used to transmit the variable rate
frames t for four different data rates and including four alternative
embodiments for
transmitting an eighth rate frame;
FIG. 4 is a functional block diagram of selected portions of a base
station 400 in accordance with the present invention;
FIG. 5 is an expanded functional block diagram of an exemplary
single demodulation chain of demodulator 404 of FIG. 4; and
FIG. 6 is a block diagram illustrating the forward link power control
mechanism of the present invention.
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5b
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. I illustrates a functional block diagram of an exemplary
embodiment of the transmission system of the present invention embodied in
wireless communication device 50. It will be understood by one skilled in the
art
that the methods described herein could be applied to transmission from a
central
base station (not shown) as well. It will also be understood that various of
the
functional blocks shown in FIG. 1 may not be present in other embodiments of
the
present invention. The functional block diagram of FIG. 1 corresponds to an
embodiment that is useful for operation according to the TIA/EIA Standard IS-
95C,
also referred to as IS-2000. Other embodiments of the present invention are
useful for other standards including Wideband CDMA (WCDMA) standards as
proposed by the standards bodies ETSI and ARIB. It will be understood by one
skilled in
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the art that owing to the extensive similarity between the reverse link
modulation in the WCDMA standards and the reverse link modulation in
the IS-95C standard, extension of the present invention to the WCDMA
standards is easily accomplished.
In the exemplary embodiment of FIG. 1, the wireless communication
device transmits a plurality of distinct channels of information which are
distinguished from one another by short orthogonal spreading sequences as
described in the aforementioned U.S. Patent Application Serial No.
08/886,604. Five separate code channels are transmitted by the wireless
communication device: 1) a first supplemental data channel 38, 2) a time
multiplexed channel of pilot and power control symbols 40, 3) a dedicated
control channel 42, 4) a second supplemental data channel 44 and 5) a
fundamental channel 46. The first supplemental data channel 38 and
second supplemental data channel 44 carry digital data which exceeds the
capacity of the fundamental channel 46 such as facsimile, multimedia
applications, video, electronic mail messages or other forms of digital data.
The multiplexed channel of pilot and power control symbols 40 carries
pilots symbols to allow for coherent demodulation of the data channels by
the base station and power control bits to control the energy of
transmissions of the base station or base stations in communication with
wireless communication device 50. Control channel 42 carries control
information to the base station such as modes of operation of wireless
communication device 50, capabilities of wireless communication device 50
and other necessary signaling information. Fundamental channel 46 is the
channel used to carry primary information from the wireless
communication device to the base station. In the case of speech
transmissions, the fundamental channel 46 carries the speech data.
Supplemental data channels 38 and 44 are encoded and processed for
transmission by means not shown and provided to modulator 26. Power
control bits are provided to repetition generator 22 which provides
repetition of the power control bits before providing the bits to multiplexer
(MUX) 24. In multiplexer 24 the redundant power control bits are time
multiplexed with pilot symbols and provided on line 40 to modulator 26.
Message generator 12 generates necessary control information
messages and provides the control message to CRC and tail bit generator 14.
CRC and tail bit generator 14 appends a set of cyclic redundancy check bits
which are parity bits used to check the accuracy of the decoding at the base
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station and appends a predetermined set of tail bits to the control message to
clear the memory of the decoder at the base station receiver subsystem. The
message is then provided to encoder 16 which provide forward error
correction coding upon the control message. The encoded symbols are
provided to repetition generator 20 which repeats the encoded symbols to
provide additional time diversity in the transmission. Following repetition
generator certain symbols are punctured according to some predetermined
puncturing pattern by puncturing element (PUNC) 19 to provide a
predetermined number of symbols within the frame. The symbols are then
provided to interleaver 18 which reorders the symbols in accordance with a
predetermined interleaving format. The interleaved symbols are provided
on line 42 to modulator 26.
Variable rate data source 1 generates variable rate data. In the
exemplary embodiment, variable rate data source 1 is a variable rate speech
encoder such as described in aforementioned U.S. Patent No. 5,414,796.
Variable rate speech encoders are popular in wireless communications
because their use increases the battery life of wireless communication
devices and increases system capacity with minimal impact on perceived
speech quality. The Telecommunications Industry Association has codified
the most popular variable rate speech encoders in such standards as Interim
Standard IS-96 and Interim Standard IS-733. These variable rate speech
encoders encode the speech signal at four possible rates referred to as full
rate, half rate, quarter rate or eighth rate according to the level of voice
activity. The rate indicates the number of bits used to encode a frame of
speech and varies on a frame by frame basis. Full rate uses a predetermined
maximum number of bits to encode the frame, half rate uses half the
predetermined maximum number of bits to encode the frame, quarter rate
uses one quarter the predetermined maximum number of bits to encode the
frame and eighth rate uses one eighth the predetermined maximum
number of bits to encode the frame.
Variable rate date source 1 provides the encoded speech frame to CRC
and tail bit generator 2. CRC and tail bit generator 2 appends a set of cyclic
redundancy check bits which are parity bits used to check the accuracy of the
decoding at the base station and appends a predetermined set of tail bits to
the control message in order to clear the memory of the decoder at the base
station. The frame is then provided to encoder 4, which provides forward
error correction coding on the speech frame. The encoded symbols are
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provided to repetition generator 8 which provides repetition of the encoded
symbol. Following repetition generator certain symbols are punctured by
puncturing element 9 according to a predetermined puncturing pattern to
provide a predetermined number of symbols within the frame. The symbols
are then provided to interleaver 6 which reorders the symbols in accordance
with a predetermined interleaving format. The interleaved symbols are
provided on line 46 to modulator 26.
In the exemplary embodiment, modulator 26 modulates the data
channels in accordance with a code division multiple access modulation
format and provides the modulated information to transmitter (TMTR) 28,
which amplifies and filters the signal and provides the signal through
duplexer 30 for transmission through antenna 32.
In the exemplary embodiment, variable rate data source 1 sends a
signal indicative to the rate of the encoded frame to control processor 36. In
response to the rate indication, control processor 36 provides control signals
to transmitter 28 indicating the energy of the transmissions.
In IS-95 and cdma2000 systems, a 20 ms frame is divided into sixteen
sets of equal numbers of symbols, referred to as power control groups. The
reference to power control is based on the fact that for each power control
group, the base station receiving the frame issues a power control command
in response to a determination of the sufficiency of the received reverse link
signal at the base station.
FIG. 3A-3C illustrate the transmission energy versus time (in power
control groups) for the three transmission rates- full, half, and quarter. In
addition, FIGS. 3D-3G illustrate four separate alternative embodiments for
the transmission at eighth rate frames in which half of the time no energy is
transmitted. Because there is much redundancy introduced into the frames
that are of less than full rate, the energy at which the symbols are
transmitted may be reduced in approximate proportion to amount of
additional redundancy in the frame.
In FIG. 3A, for full rate frame 300, each power control group PCo
through PC15 are transmitted at energy E. For the sake, of simplicity the
frames are illustrated as being transmitted at an equal energy for the
duration of the frame. One skilled in the art will understand the energy will
vary over the frame and that what is represented in FIGS-3A-3G can be
thought of as the baseline energy at which the frames would be transmitted
absent external effects. In the exemplary embodiment, remote station 50
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responds to closed loop power control commands from the base station and
from internally generated open loop power control commands based on the
received forward link signal. The responses to the power control algorithms
will causes the transmission energy to vary over the duration of a frame.
In FIG. 3B, for half rate frame 302, the energy is equal to half the
predetermined maximum level, or E/2. This is represented in FIG. 3B.
The interleaver structure is such that it distributes the repeated symbols
over the frame in such a way to attain maximum time diversity.
In FIG. 3C for quarter-rate transmission 304, the frame is transmitted
at approximately one-quarter of the predetermined maximum level, or E/4.
In the exemplary embodiment, during the transmission of full rate,
half rate and quarter rate frames, the pilot signal is continuously
transmitted. However, in FIGS. 3D-3G transmitter 28 gates the transmission
of half of the frame. In the preferred embodiment, during the periods in
which the traffic channel transmissions are gated off, the pilot channel is
also gated off to reduce battery consumption and increase reverse link
capacity. In each of the embodiments, the frames are transmitted at a 50%
duty cycle in which half of the time the energy of the transmission is gated
off. During the period in which the frame is transmitted, the energy is
scaled to approximately the energy at which a quarter rate frame = is
transmitted E/4. However, the inventors have through extensive
simulation, determined the preferred average or baseline energy at which
the eighth rate frames should be transmitted for each of the alternative
embodiments for transmitting eighth rate frames. These energies have been
computed to maximize battery savings and reverse link capacity while
maintaining the level of reliability of transmission.
In the first embodiment, illustrated in FIG. 3D, the frame is
transmitted such that it is gated off at alternating 1.25 ms. intervals. Thus,
transmitter 28 is initially gated off for the first 1.25ms. The second power
control group (PCG1) is transmitted then with energy El during the second
1.25 ms. The third power control group (PCG2) is gated off. In this
embodiment, all the odd PCGs (1, 3, 5, 7, 9, 11, 13, 15) are transmitted while
all the even PCGs (0, 2, 4, 6, 8, 10,12, 14) are gated off. The puncturing
structure discards half of the repeated symbols and provides approximately
four versions of each transmitted symbol. In the preferred first
embodiment, the symbols are transmitted at an average or baseline energy
of 0.385E In the preferred embodiment, the gating of transmitter 28 is
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performed such that the last portions of the frame are not gated off. This is
preferred because it allows for meaningful closed power control commands
to be sent by the receiving base station to assist in reliable transmission of
the subsequent frame.
5 In the second embodiment, which is the preferred embodiment of the
present invention, illustrated in FIG. 3E, the frame is transmitted such that
it is gated off at alternating 2.5 ms. intervals. The transmission method
illustrated in FIG. 3E represents the preferred embodiment, because it results
in optimum battery savings and reverse link capacity. During the first 2.5
10 ms. interval (PCGO and PCG1) transmitter 28 is gated off. Then, transmitter
28 is gated on for next 2.5 ms (PCG2 and PCG3) and so on. I this embodiment
PCGs 2, 3, 6, 7,10,11,14,15 are gated on, while PCGs 0, 1, 4, 5, 8, 9, 12, 13
are
gated off. The puncturing structure is such that it discards exactly half of
the
repeated symbols during gate off in this embodiment. In the preferred
second embodiment, the symbols are transmitted at an average or baseline
energy of 0.32E.
In the third embodiment, illustrated in FIG. 3F, the frame is
transmitted such that it is gated off at alternating 5.0 ms. intervals. During
the first 5.0 ms. interval (PCGO-PCG3), transmitter 28 is gated off. Then, in
the next 5.0 ms interval PCGs 4, 5, 6, 7 are transmitted and so on. In this
embodiment PCGs 4, 5, 6, 7, 12, 13, 14, 15 are transmitted, while PCGs 0, 1,
2,
3, 8, 9, 10, 11 are gated off. The puncturing structure is such that it
discards
exactly half of the repeated symbols during gate off in this embodiment. In
the preferred third embodiment, the symbols are transmitted at an average
or baseline energy of 0.32E.
In the fourth embodiment, illustrated in FIG. 3G, the frame is
transmitted such that it is gated off during the first 10 ms. In the next 10ms
interval PCGs 8 through 15 are transmitted. In this embodiment PCGs 8, 9,
10, 11, 12, 13, 14, 15 are transmitted, while PCGs 0, 1, 2, 3, 4, 5, 6, 7 are
gated
off. The interleaver structure is such that it discards exactly half of the
repeated symbols during gate off in this embodiment. In the preferred
second embodiment, the symbols are transmitted at an average or baseline
energy of 0.335E.
FIG. 2 illustrates a functional block diagram of an exemplary
embodiment of modulator 26 of FIG. 1. The first supplemental data channel
data is provided on line 38 to spreading element 52 which covers the
supplemental channel data in accordance with a predetermined spreading
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sequence. In the exemplary embodiment, spreading element 52 spreads the
supplemental channel data with a short Walsh sequence (++--). The spread
data is provided to relative gain element 54 which adjusts the gain of the
spread supplemental channel data relative to the energy of the pilot and
power control symbols. The gain adjusted supplemental channel data is
provided to a first summing input of summer 56. The pilot and power
control multiplexed symbols are provided on line 40 to a second summing
input of summing element 56.
Control channel data is provided on line 42 to spreading element 58
which covers the supplemental channel data in accordance with a
predetermined spreading sequence. In the exemplary embodiment,
spreading element 58 spreads the supplemental channel data with a short
Walsh sequence The spread data is provided to relative
gain element 60 which adjusts the gain of the spread control channel data
relative to the energy of the pilot and power control symbols. The gain
adjusted control data is provided to a third summing input of summer 56.
Summing element 56 sums the gain adjusted control data symbols,
the gain adjusted supplemental channel symbols and the time multiplexed
pilot and power control symbols and provides the sum to a first input of
multiplier 72 and a first input of multiplier 78.
The second supplemental channel is provided on line 44 to spreading
element 62 which covers the supplemental channel data in accordance with
a predetermined spreading sequence. In the exemplary embodiment,
spreading element 62 spreads the supplemental channel data with a short
Walsh sequence (++--). The spread data is provided to relative gain element
64 which adjusts the gain of the spread supplemental channel data. The
gain adjusted supplemental channel data is provided to a first summing
input of summer 66.
The fundamental channel data is provided on line 46 to spreading
element 68 which covers the fundamental channel data in accordance with
a predetermined spreading sequence. In the exemplary embodiment,
spreading element 68 spreads the fundamental channel data with a short
Walsh sequence (++++----++++---). The spread data is provided to relative
gain element 70 which adjusts the gain of the spread fundamental channel
data. The gain adjusted fundamental channel data is provided to a second
summing input of summer 66.
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Summing element 66 sums the gain adjusted second supplemental
channel data symbols and the fundamental channel data symbols and
provides the sum to a first input of multiplier 74 and a first input of
multiplier 76.
In the exemplary embodiment, a pseudonoise spreading using two
different short PN sequences (PNI and PNQ) is used to spread the data. In the
exemplary embodiment the short PN sequences, PNI and PNQ, are
multiplied by a long PN code to provide additional privacy. The generation
of pseudonoise sequences is well known in the art and is described in detail
in aforementioned U.S. Patent No. 5,103,459. A long PN sequence is
provided to a first input of multipliers 80 and 82. The short PN sequence
PNI is provided to a second input of multiplier 80- and the short PN
sequence PNQ is provided to a second input of multiplier 82.
The resulting PN sequence from multiplier 80 is provided to
respective second inputs of multipliers 72 and 74. The resulting PN
sequence from multiplier 82 is provided to respective second inputs of
multipliers 76 and 78. The product sequence from multiplier 72 is provided
to the summing input of subtractor 84. The product sequence from
multiplier 74 is provided to a first summing input of summer 86. The
product sequence from multiplier 76 is provided to the subtracting input of
subtractor 84. The product sequence from multiplier 78 is provided to a
second summing input of summer 86.
The difference sequence from subtractor 84 is provided to baseband
filter 88. Baseband filter 88 performs necessary filtering on the difference
sequence and provides the filtered sequence to gain element 92. Gain
element 92 adjusts the gain of the signal and provides the gain adjusted
signal to upconverter 96. Upconverter 96 upconverts the gain adjusted
signal in accordance with a QPSK modulation format and provides the
unconverted signal to a first input of summer 100.
The sum sequence from summer 86 is provided to baseband filter 90.
Baseband filter 90 performs necessary filtering on difference sequence and
provides the filtered sequence to gain element 94. Gain element 94 adjusts
the gain of the signal and provides the gain adjusted signal to upconverter
98. Upconverter 98 upconverts the gain adjusted signal in accordance with a
QPSK modulation format and provides the upconverted signal to a second
input of summer 100. Summer 100 sums the two QPSK modulated signals
and provides the result to transmitter 28.
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Turning now to FIG. 4, a functional block diagram of selected portions
of a base station 400 in accordance with the present invention. Reverse link
RF signals from the wireless communication device 50 (FIG. 1) are received
by receiver (RCVR) 402, which downconverts the received reverse link RF
signals to an baseband frequency. In the exemplary embodiment, receiver
402 down converts the received signal in accordance with a QPSK
demodulation format. The baseband signal is then demodulated by
demodulator 404. Demodulator 404 is further described with reference to
FIG. 5 below.
The demodulated signal is provided to accumulator 405.
Accumulator 405 sums the symbol energies of the redundantly transmitted
power control groups of symbols. The accumulated symbols energies are
provided to de-interleaver 406 which reorders the symbols in accordance
with a predetermined de-interleaving format. The reordered symbols are
provided to decoder 408 which decodes the symbols to provide an estimate
of the transmitted frame. The estimate of the transmitted frame is then
provided to CRC check 410 which determines the accuracy of the frame
estimate based on the CRC bits included in the transmitted frame.
In the exemplary embodiment, base station 400 performs a blind
decoding on the reverse link signal. Blind decoding describes a method of
decoding variable rate data in which the receiver does not know a priori the
rate of the transmission. In the exemplary embodiment, base station 400
accumulates, deinterleaves and decodes the data in accordance with each
possible rate hypothesis. The frame selected as the best estimate is based on
quality metrics such as the symbol error rate, the CRC check and the
Yamamoto metric.
An estimate of the frame for each rate hypothesis is provided to
control processor 414 and a set of quality metrics for each of the decoded
estimates is also provided. Quality metrics that may include the symbol
error rate, the Yamamoto metric and the CRC check. Control processor
selectively provides one of the decoded frames to the remote station user or
declares a frame erasure.
Turning now to FIG. 5, an expanded functional block diagram of an
exemplary single demodulation chain of demodulator 404 is shown. In the
preferred embodiment, demodulator 404 has one demodulation chain for
each information channel. The exemplary demodulator 404 of FIG. 5
performs complex demodulation on signals modulated by the exemplary
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modulator 26 of FIG. 1. As previously described, receiver (RCVR) 402
downconverts the received reverse link RF signals to a baseband frequency,
producing I and Q baseband signals. Despreaders 502 and 504 respectively
despread the I and Q baseband signals using the long code from FIG. 1.
Baseband filters (BBF) 506 and 508 respectively filter the I and Q baseband
signals.
Despreaders 510 and 512 respectively despread the I and Q signals
using the PN1 sequence of FIG. 2. Similarly, despreaders 514 and 516
respectively despread the Q and I signals using the PNQ sequence of FIG. 2.
The outputs of despreaders 510 and 512 are combined in combiner 518. The
output of despreader 516 is subtracted from the output of despreader 512 in
combiner 520.
The respective outputs of combiners 518 and 520 are then Walsh-
uncovered in Walsh-uncoverers 522 and 524 with the Walsh code that was
used to cover the particular channel of interest in FIG. 2. The respective
outputs of the Walsh-uncoverers 522 and 524 are then summed over one
Walsh symbol by accumulators 530 and 532.
The respective outputs of combiners 518 and 520 are also summed
over one Walsh symbol by accumulators 526 and 528. The respective
outputs of accumulators 526 and 528 are then applied to pilot filters 534 and
536. Pilot filters 534 and 536 generate an estimation of the channel
conditions by determining the estimated gain and phase of the pilot signal
data 40 (see FIG. 1). The output of pilot filter 534 is then complex
multiplied
by the respective outputs of accumulators 530 and 532 in complex
multipliers 538 and 540. Similarly, the output of pilot filter 536 is complex
multiplied by the respective outputs of accumulators 530 and 532 in complex
multipliers 542 and 544. The output of complex multiplier 542 is then
summed with the output of complex multiplier 538 in combiner 546. The
output of complex multiplier 544 is subtracted from the output of complex
multiplier 540 in combiner 548. Finally, the outputs of combiners 546 and
548 are combined in combiner 550 to produce the demodulated signal of
interest 405.
A second aspect of the present invention is directed toward controlling
forward link transmission energy in the face of potentially gated reverse link
transmissions. Forward link performance is effected when the reverse link is
in gated mode of operation. Forward link power control bit is punctured into
reverse link pilot based on which the base station increases or decreases
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transmission power. Therefore when the reverse link is gated off 50% of the
time, the actual forward link power control command is sent at 400 Hz
instead of 800 Hz. However, base station does not know a priori whether the
mobile station is gated off. So in normal operation it will increase the power
5 during the interval when mobile station is gated off. By simulation it has
been found that there is a performance degradation of about 1 dB if the base
station is ignorant of mobile station's transmission mode than if the base
station knew that the mobile station is in gated mode and react to forward
link power control command that are sent in the reverse link pilot (400Hz).
10 Therefore, there should be a method by which the base station can detect
mobile station's transmission mode (gated/non gated).
One method of doing this is by defining a forward link power control
bit erasure decision region. That is, when the dot product magnitude
(summed over all combining fingers) is less than a threshold, decide erasure
15 and keep forward power unchanged. In this way, the base station will react
effectively to 400Hz forward link power control sent over the reverse link
pilot in the gated mode.
As described above, in the exemplary embodiment, the forward
power control symbols are multiplexed into the pilot symbol stream. The
demodulated pilot and power control symbols are provided to
demultiplexer 412, which separates out the power control bit energies and
provides the power control bit energies to control processor 414.
Control processor 414 also receives the power control bit energies for
other fingers of the reverse link signal provided from remote station 50.
From the summed energies from the different demodulated fingers, control
processor 414 generates commands for controlling the transmission energy
of the forward link signal and provides those commands to transmitter
(TMTR) 420. In the present invention control processor 414 detects when
the reverse link frame has gated out the power control bits by comparing the
summed energies of those bits to a threshold and if the summed energy is
less than a threshold amount inhibiting closed loop power control response.
Forward link traffic data for transmission to remote station 50 is
provided to processing element 416 which formats the data and encodes and
interleaves the resultant frame of data. The processed frame of data is
provided to modulator 418. Modulator 418 modulates the data for
transmission on the forward link. In the exemplary embodiment, the
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forward link signal is modulated in accordance with a CDMA modulation
format and in particular with a cdma2000 or IS-2000 modulation format.
The modulated signal is provided to transmitter 420, which
upconverts, amplifies and filters the signal for transmission. The energy at
which the signal is transmitted is determined in accordance with the control
signal from control processor 414.
FIG. 6 illustrates the operation performed by control processor 414.
The uncovered pilot and power control symbols from summers 526 and 528
of FIG. 5 are provided to demultiplexers 600 and 602 which separate out the
multiplexed power control symbol energies. The power control bit symbol
energies from all of the fingers being demodulated are summed in finger
combiner 604. The summed energy is provided to comparator 606 which
compares the summed energy to a predetermined threshold and outputs a
signal indicative of the comparison.
If the energy of the power control bits is below the threshold value,
then power control processor 608 determines that the forward link power
control bit has been gated out and inhibits adjustment of the forward link
transmission energy. If the energy of the power control bits is above the
threshold value, then power control processor 608 determines that the
forward link power control bit has not been gated out and adjusts the
forward link transmission energy in accordance with the estimated value of
the received power control bit.
The previous description of the preferred embodiments is provided
to enable any person skilled in the art to make or use the present invention.
The various modifications to these embodiments will be readily apparent to
those skilled in the art, and the generic principles defined herein may be
applied to other embodiments without the use of the inventive faculty.
Thus, the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope consistent
with the principles and novel features disclosed herein.
WE CLAIM:
