U.S. patent application number 17/699826 was filed with the patent office on 2022-07-07 for turbo hsdpa system.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Anand Ganesh Dabak, Eko Nugroho Onggosanusi, Aris Papasakellariou, Timothy Mark Schmidl.
Application Number | 20220216961 17/699826 |
Document ID | / |
Family ID | |
Filed Date | 2022-07-07 |
United States Patent
Application |
20220216961 |
Kind Code |
A1 |
Schmidl; Timothy Mark ; et
al. |
July 7, 2022 |
TURBO HSDPA SYSTEM
Abstract
A method of power saving for a wireless transceiver (FIGS. 1 and
2) is disclosed. The transceiver has an active power mode (504) and
a reduced power mode (510). The transceiver is operated in the
reduced power mode (510) and monitors transmissions from a remote
wireless transmitter while in the reduced power mode. The
transceiver identifies a transmission from the remote wireless
transmitter by a transceiver identity included in the transmission
(FIG. 6, UE identification). The transceiver transitions to the
active power mode (512) in response to identifying the
transmission.
Inventors: |
Schmidl; Timothy Mark;
(Dallas, TX) ; Onggosanusi; Eko Nugroho; (Allen,
TX) ; Dabak; Anand Ganesh; (Plano, TX) ;
Papasakellariou; Aris; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Appl. No.: |
17/699826 |
Filed: |
March 21, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14463422 |
Aug 19, 2014 |
11283563 |
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17699826 |
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11360654 |
Feb 22, 2006 |
8811273 |
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14463422 |
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60733333 |
Nov 3, 2005 |
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60655590 |
Feb 22, 2005 |
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International
Class: |
H04L 5/00 20060101
H04L005/00; H04B 1/16 20060101 H04B001/16; H04W 52/02 20060101
H04W052/02 |
Claims
1. A method of power saving in a transceiver during a time
interval, the time interval having a plurality of signals,
comprising the steps of: receiving a first signal of the plurality
of signals in an active power mode; determining if there are other
signals of the plurality of signals for the transceiver in response
to the first signal; operating the transceiver in the active power
mode when there are other signals of the plurality of signals for
the transceiver; and operating the transceiver in a reduced power
mode when there are no other signals of the plurality of signals
for the transceiver.
2. A method as in claim 1, wherein the first signal is transmitted
from a remote transmitter in a shared control channel.
3. A method as in claim 1, wherein the plurality of signals
comprises at least three orthogonal frequency division multiplex
(OFDM) symbols, and wherein the first signal is included in one of
a first and second OFDM symbols in time.
4. A method as in claim 3, wherein the first signal comprises an
identity of the transceiver.
5. A method of transmitting symbols, comprising the steps of:
forming a plurality of symbols in a packet; forming pilot and
control signals in a first symbol of the plurality of symbols;
excluding pilot signals from at least another symbol of the
plurality of symbols; and transmitting the packet.
6. A method as in claim 5, comprising the step of forming pilot and
control signals in a second symbol of the plurality of symbols,
wherein the second symbol is adjacent in time to the first
symbol.
7. A method as in claim 5, wherein the step of transmitting
comprises transmitting the packet during a transmit time interval
(TTI).
8. A method as in claim 5, wherein each symbol of the plurality of
symbols is an orthogonal frequency division multiplex (OFDM)
symbol.
9. A method as in claim 5, wherein a transmit power for the pilot
signals is greater than a transmit power for the control
signals.
10. A method of transmitting an orthogonal frequency division
multiplex (OFDM) signal, comprising the steps of: transmitting on a
plurality of control channels during a transmit time interval; and
transmitting a counter during the transmit time interval to
indicate a number of the plurality of control channels in the
transmit time interval.
11. A method as in claim 10, wherein each control channel
corresponds to a respective user in a wireless cell.
12. A method as in claim 10, wherein the counter value specifies a
number of the plurality of control channels with a specific coding
and modulation scheme.
13. A method of transmitting an orthogonal frequency division
multiplex (OFDM) signal during a transmit time interval (TTI),
comprising the steps of: transmitting a plurality of control
channels during a transmit time interval, each control channel
corresponding to a respective user; and transmitting a counter
associated with each respective control channel to indicate a size
of said each respective control channel of the plurality of control
channels.
14. A method as in claim 13, wherein the size of said each
respective control channel is variable.
15. A method of transmitting a broadcast orthogonal frequency
division multiplex (OFDM) signal, comprising the steps of:
determining a plurality of broadcast channels; transmitting on a
set of broadcast channels within the plurality of broadcast
channels during a transmit time interval (TTI); and transmitting a
broadcast channel bitmap to indicate the set of broadcast channels
are active during the transmit time interval.
16. A method as in claim 15, wherein a number of the set of
broadcast channels is less than a number of the plurality of
broadcast channels.
17. A method as in claim 15, wherein broadcast channels of the
plurality of broadcast channels other than the set of broadcast
channels are inactive during the transmit time interval.
18. A method for power saving during a communications session in
which packet transmission is scheduled at predetermined time
intervals, comprising the steps of: operating a transceiver having
an active power mode and a reduced power mode; operating the
transceiver in the active power mode at the predetermined time
intervals of the communications session; and operating the
transceiver in the reduced power mode during remaining time
intervals of the communications session.
19. A method as in claim 18, wherein the transceiver sends a remote
wireless transmitter an acknowledge (ACK) signal from the active
power mode.
20. A method as in claim 18, wherein the transceiver returns to the
reduced power mode at a first time after receiving a most recent
transmission from the remote wireless transmitter.
21. A method as in claim 20, wherein the transceiver has a second
reduced power mode, comprising the step of operating in the second
reduced power mode at an end of the communication session.
22. A method as in claim 18, wherein the transceiver determines the
predetermined time intervals in response to information in a shared
control channel.
23. A method as in claim 18, wherein the transceiver determines the
predetermined time intervals in response to information in a common
control channel.
24. A method of transmitting a control channel, comprising the
steps of: transmitting a first part of the control channel that is
encoded; and transmitting a second part of the control channel that
is encoded differently than the first part.
25. A method as in claim 24, wherein the control channel is an
orthogonal frequency division multiplex (OFDM) control channel.
26. A method as in claim 24, wherein the first part is a common
part comprising user equipment (UE) identities, and wherein the
second part is a UE dedicated part.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/463,422 filed Aug. 19, 2014, which is a
continuation of U.S. patent application Ser. No. 11/360,654 filed
Feb. 22, 2006 (now U.S. Pat. No. 8,811,273 issued on Aug. 19,
2014), which claims the benefit of U.S. Provisional Application No.
60/655,590 (TI-60022PS), filed Feb. 22, 2005, and of U.S.
Provisional Application No. 60/733,333 (TI-60022PS1), filed Nov. 3,
2005, all of which are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] The present embodiments relate to wireless communications
systems and, more particularly, to the Long Term Evolution of
High-Speed Downlink Packet Access (HSDPA) for a wireless
communication system.
[0003] Wireless communications are prevalent in business, personal,
and other applications, and as a result the technology for such
communications continues to advance in various areas. One such
advancement includes the use of spread spectrum communications,
including that of code division multiple access (CDMA) which
includes wideband code division multiple access (WCDMA) cellular
communications. In CDMA communications, user equipment (UE) (e.g.,
a hand held cellular phone, personal digital assistant, or other)
communicates with a base station, where typically the base station
corresponds to a "cell." CDMA communications are by way of
transmitting symbols from a transmitter to a receiver, and the
symbols are modulated using a spreading code which consists of a
series of binary pulses. The code runs at a higher rate than the
symbol rate and determines the actual transmission bandwidth. In
the current industry, each piece of CDMA signal transmitted
according to this code is said to be a "chip," where each chip
corresponds to an element in the CDMA code. Thus, the chip
frequency defines the rate of the CDMA code. WCDMA includes
alternative methods of data transfer, one being frequency division
duplex (FDD) and another being time division duplex (TDD, where the
uplink and downlink channels are asymmetric for FDD and symmetric
for TDD. Another wireless standard involves time division multiple
access (TDMA) apparatus, which also communicate symbols and are
used by way of example in cellular systems. TDMA communications are
transmitted as a group of packets in a time period, where the time
period is divided into time slots so that multiple receivers may
each access meaningful information during a different part of that
time period. In other words, in a group of TDMA receivers, each
receiver is designated a time slot in the time period, and that
time slot repeats for each group of successive packets transmitted
to the receiver. Accordingly, each receiver is able to identify the
information intended for it by synchronizing to the group of
packets and then deciphering the time slot corresponding to the
given receiver. Given the preceding, CDMA transmissions are
receiver-distinguished in response to codes, while TDMA
transmissions are receiver-distinguished in response to time
slots.
[0004] Since CDMA and TDMA communications are along wireless media,
then the travel of those communications can be affected in many
ways, and generally these effects are referred to as the channel
effect on the communication. For example, consider a transmitter
with a single antenna transmitting to a receiver with a single
antenna. The transmitted signal is likely reflected by objects such
as the ground, mountains, buildings, and other things that it
contacts. In addition, there may be other signals that interfere
with the transmitted signal. Thus, when the transmitted
communication arrives at the receiver, it has been affected by the
channel effect. Consequently, the originally-transmitted data is
more difficult to decipher due to the added channel effect. Various
approaches have been developed in an effort to reduce or remove the
channel effect from the received signal so that the
originally-transmitted data is properly recognized. In other words,
these approaches endeavor to improve signal-to-interference+noise
ratio (SINR), thereby improving other data accuracy measures (e.g.,
bit error rate (BER), frame error rate (FER), and symbol error rate
(SER)).
[0005] One approach to improve SINR is referred to in the art as
antenna diversity, which refers to using multiple antennas at the
transmitter, receiver, or both. For example, in the prior art, a
multiple-antenna transmitter is used to transmit the same data on
each antenna where the data is manipulated in some manner
differently for each antenna. One example of such an approach is
space-time transmit diversity ("STTD"). In STTD, a first antenna
transmits a block of two input symbols over a corresponding two
symbol intervals in a first order while at the same time a second
antenna transmits, by way of example, the complex conjugates of the
same block of two symbols and wherein those conjugates are output
in a reversed order relative to how they are transmitted by the
first antenna and the second symbol is a negative value relative to
its value as an input.
[0006] Another approach to improve SINR combines antenna diversity
with the need for higher data rate. Specifically, a multiple-input
multiple-output (MIMO) system with transmit diversity has been
devised, where each transmit antenna transmits a distinct and
respective data stream. In other words, in a MIMO system, each
transmit antenna transmits symbols that are independent from the
symbols transmitted by any other transmit antennas for the
transmitter and, thus, there is no redundancy either along a single
or with respect to multiple of the transmit antennas. The advantage
of a MIMO scheme using distinct and non-redundant streams is that
it can achieve higher data rates as compared to a transmit
diversity system.
[0007] Communication system performance demands in user equipment,
however, are often dictated by web access. Applications such as
news, stock quotes, video, and music require substantially higher
performance in downlink transmission than in uplink transmission.
Thus, MIMO system performance may be further improved for
High-Speed Downlink Packet Access (HSDPA) by Orthogonal Frequency
Division Multiplex (OFDM) transmission. With OFDM, multiple symbols
are transmitted on multiple carriers that are spaced apart to
provide orthogonality. An OFDM modulator typically takes data
symbols into a serial-to-parallel converter, and the output of the
serial-to-parallel converter is considered as frequency domain data
symbols. The frequency domain tones at either edge of the band may
be set to zero and are called guard tones. These guard tones allow
the OFDM signal to fit into an appropriate spectral mask. Some of
the frequency domain tones are set to values which will be known at
the receiver, and these tones are termed pilot tones or symbols.
These pilot symbols can be useful for channel estimation at the
receiver. An inverse fast Fourier transform (IFFT) converts the
frequency domain data symbols into a time domain waveform. The IFFT
structure allows the frequency tones to be orthogonal. A cyclic
prefix is formed by copying the tail samples from the time domain
waveform and appending them to the front of the waveform. The time
domain waveform with cyclic prefix is termed an OFDM symbol, and
this OFDM symbol may be upconverted to an RF frequency and
transmitted. An OFDM receiver may recover the timing and carrier
frequency and then process the received samples through a fast
Fourier transform (FFT). The cyclic prefix may be discarded and
after the FFT, frequency domain information is recovered. The pilot
symbols may be recovered to aid in channel estimation so that the
data sent on the frequency tones can be recovered. A
parallel-to-serial converter is applied, and the data is sent to
the channel decoder. Just as with HSDPA, OFDM communications may be
performed in an FDD mode or in a TDD mode.
[0008] While the preceding approaches provide steady improvements
in wireless communications, the present inventors recognize that
still further improvements may be made, including by addressing
some of the drawbacks of the prior art. Examples of these
improvements addressed by embodiments of the present invention
include improved frequency diversity to reduce inter-cell
interference, improved power control, and improved control
information. Indeed, to address some of these issues, the present
inventors described in co-pending U.S. patent application Ser. No.
10/230,003 (docket: TI-33494), filed Aug. 28, 2002, entitled, "MIMO
HYBRID-ARQ USING BASIS HOPPING", and hereby incorporated herein by
reference. In this referenced application, multiple independent
streams of data are adaptively transmitted with a variable basis
selected to improve signal quality. Further, a receiver is provided
that decodes the transmitted signals including the multipaths
therein. While this improvement therefore provides various benefits
as discussed in the referenced application, the inventors also
recognize still additional benefits that may be achieved with such
systems. Accordingly, the preferred embodiments described below are
directed toward these benefits as well as improving upon the prior
art.
BRIEF SUMMARY OF THE INVENTION
[0009] In a first preferred embodiment, a transceiver saves power
during a transmit time interval. The transmit time interval
includes a plurality of OFDM symbols transmitted sequentially in
time. The transceiver receives a first OFDM symbol in the transmit
time interval in an active power mode. The transceiver determines
if there are other OFDM symbols from the plurality of OFDM symbols
for the transceiver in response to the control and pilot channels
within the first OFDM symbol. The transceiver operates in the
active power mode for the remainder of the transmit time interval
if there are other OFDM symbols for the transceiver. The
transceiver operates in a reduced power mode for a remainder of the
transmit time interval if there are no other OFDM symbols for the
transceiver.
[0010] In a second preferred embodiment, the transmitter forms a
plurality of symbols in a packet with pilot and control signals in
a first symbol of the plurality of symbols. Pilot signals are
excluded from at least another symbol of the plurality of symbols.
The packet is then transmitted to remote user equipment (UE).
[0011] According to a third preferred embodiment, the transmitter
transmits a plurality of orthogonal frequency division multiplex
(OFDM) control channels during a transmit time interval. The
control channels may have different structures as defined by their
size and corresponding modulation and coding scheme. The
transmitter also transmits a counter during the transmit time
interval to indicate a number of control channels for each
structure in the transmit time interval.
[0012] According to a fourth preferred embodiment, the transmitter
transmits a plurality of orthogonal frequency division multiplex
(OFDM) control channels during a transmit time interval. The
transmitter also transmits a counter to indicate a data block size
associated with each control channel during the transmit time
interval.
[0013] In a fifth preferred embodiment, the transmitter transmits a
broadcast orthogonal frequency division multiplex (OFDM) signal
over a plurality of broadcast channels during a transmit time
interval. The transmitter also transmits a broadcast channel bitmap
to indicate which channels are active.
[0014] According to a sixth preferred embodiment, a transceiver
operates in an active power mode and in a reduced power mode during
a communications session. The transceiver transitions to the active
power mode only at predefined time intervals of the communications
session. The transceiver operates at the reduced power mode for the
remainder of the communications session. This may be useful and
applicable for a service such as voice over internet protocol
(VoIP) in which there may be periodic communication of small
packets, and the control overhead can be reduced by scheduling the
transmission intervals in advance. Moreover, the UE needs to
monitor transmissions only at predetermined time intervals thereby
conserving power for the remainder of the communications session by
reverting to the reduced power mode.
[0015] Other devices, systems, and methods are also disclosed and
claimed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] FIG. 1 is a block diagram of a transmitter that may employ
embodiments of the present invention;
[0017] FIG. 2 is a block diagram of a receiver that may employ
embodiments of the present invention;
[0018] FIG. 3 illustrates multiplexed frequency allocation units of
the transmitter of FIG. 1;
[0019] FIG. 4 illustrates organization of pilot, data, and control
signals of an OFDM symbol of FIG. 3;
[0020] FIG. 5 is a state diagram of power control modes of the
present invention;
[0021] FIG. 6 illustrates the structure of an OFDM shared control
channel (SCCH) according to the present invention; and
[0022] FIG. 7 illustrates the structure of an OFDM
broadcast/multicast (BCMCS) shared control channel (SCCH).
DETAILED DESCRIPTION OF THE INVENTION
[0023] The preferred embodiments of the present invention provide
interference reduction and power savings for a wireless
communication system. The wireless communication system preferably
provides for the Long Term Evolution of High-Speed Downlink Packet
Access (HSDPA) and multiple-input multiple-output (MIMO) as will be
explained in detail. A simplified block diagram of a wireless
transmitter of the present invention for such a system is shown in
FIG. 1. The wireless transmitter receives a data stream at input
100 from a baseband processor (not shown). This data stream may
include pilot signals, control signals, and data signals for
synchronization and control of remote wireless user equipment (UE).
The data is encoded, interleaved, and modulated by circuit 102 and
applied to the multiple antenna processing circuit 104. The
multiple antenna processing circuit 104 can provide for spatial
multiplexing or transmit diversity and performs other functions as
will be described in detail. Per antenna rate control (PARC) may be
performed by having multiple blocks 102 (not shown) in order to
have different modulation and/or coding on each antenna stream.
Transmit diversity may include open loop or closed loop modes or a
combination of open and closed loop modes. Open loop modes may
include STTD, which was described earlier. Closed loop modes may
include transmit adaptive array (TxAA), which is a form of
beamforming. In addition, double STTD or TxAA may be used with four
antenna transmission when a trade-off between diversity gain and
spatial multiplexing is desired. The output of multiple antenna
processing circuit 104 is then applied to the OFDM modulation
circuits 106 and transmitted by transmit antennas 108. Preferred
embodiments of the present invention may include one, two, four, or
more transmit antennas 108. Thus, OFDM modulation circuits 106
receive multiple inputs and produce multiple outputs.
[0024] Referring to FIG. 2, there is a simplified block diagram of
a wireless receiver of the present invention. Inventive features of
the transmitter of FIG. 1 are included in the receiver for
compatibility. Antennas 200 receive signals from a remote
transmitter as in FIG. 1. In a preferred embodiment, there are 1,
two, four, or more antennas 200. Signals from antennas 200 are
applied to OFDM demodulator circuit 202. The output of OFDM
demodulator circuit 202 is applied to circuit 208 to extract pilot
signals that are used to synchronize the receiver with the remote
transmitter. These pilot signals may have a power boost relative to
data signals. The extracted pilot signals are applied to circuit
210 to compute the effective channel between the receiver and
remote transmitter. The outputs of OFDM demodulator circuit 202 are
applied to the multi-antenna processing circuit 204 and corrected
by the effective channel estimate from circuit 210. Different types
of multi-antenna processing can be used such as linear, decision
feedback, or maximum likelihood. These signals are subsequently
converted to a serial data stream as will be explained with
reference to FIG. 3. The serial data stream is then demodulated
and, decoded in circuit 206, and applied to a baseband processor.
An optional feedback loop 212 from circuit 206 to circuit 204
allows a decision feedback operation which can improve the
estimation of data bits.
[0025] Referring now to FIG. 3, there is a diagram showing the
exemplary structure of an HSDPA packet produced by multi-antenna
processing circuit 104 of FIG. 1. For the purpose of illustration,
there are five separate packets in the diagram of FIG. 3. In this
exemplary embodiment each packet includes three OFDM symbols shown
in columns. However, the packet may comprise a different number of
OFDM symbols. The first OFDM symbol includes a shared control
channel (SCCH) and common pilot channel multiplexed with data. For
example, the first packet includes OFDM symbols 300, 302, and 304.
The second packet includes OFDM symbols 306, 308, and 310. Each
group of three OFDM symbols is transmitted in a respective transmit
time interval (TTI). For the purpose of illustration, each TTI has
duration of 0.5 milliseconds. Each OFDM symbol includes eight
sub-bands. These sub-bands provide frequency diversity within each
OFDM symbol of the wireless communication system. According to the
present invention the order of these sub-bands in the first OFDM
symbol, for example symbol 300, is randomly selected. The order of
sub-bands in each remaining OFDM symbol is obtained by a cyclic
shift of the order of the first OFDM symbol. For example, sub-bands
of OFDM symbol 302 are shifted five positions so that the position
of sub-band 8 in OFDM symbol 302 corresponds to the position of
sub-band 3 in OFDM symbol 300. Sub-bands of OFDM symbol 304 are
shifted another five positions so that the position of sub-band 8
in OFDM symbol 304 corresponds to the position of sub-band 6 in
OFDM symbol 300. Added frequency diversity of this sub-band packet
structure advantageously reduces inter-cell interference by
averaging the interference over different sub-bands. This increases
the SINR within the cell and is particularly improves communication
at high Doppler rates.
[0026] Recall from the discussion of FIG. 3 that the first OFDM
symbol of each packet includes a shared control channel (SCCH) and
common pilot channel multiplexed with data. By way of example, the
diagram of FIG. 4 illustrates individual tones or discrete
frequencies that modulate the sub-bands for the first OFDM symbol
in each packet for the case of two transmit antennas. Substantially
all pilot signals and control signals are included in the first
OFDM symbol of each packet. Alternatively, for a four antenna
system, a similar structure may be necessary for the first two OFDM
symbols of each packet. Preferably at least one or more subsequent
OFDM symbols in the packet would be reserved for data signals not
including pilot signals or control signals. For example, pilot
signals 400-406 in the first OFDM symbol 300 (FIG. 3) are
transmitted from a first antenna. Pilot signals 410-416 in the
first OFDM symbol 300 are transmitted from a second antenna. This
organization of pilot and control signals advantageously promotes
rapid synchronization of user equipment (UE) in a cell with a base
station. Each UE may monitor control signals and determine whether
a particular packet includes any data for that UE. When a
particular UE determines that the packet does not include relevant
data, the UE may enter a low power mode of operation for the
remainder of the transmit time interval (TTI). For example, with
the packet structure of FIG. 3, each UE would monitor a first OFDM
symbol 300 in a first packet. Each UE in the cell that found its UE
identity in the control information would continue to monitor the
remaining OFDM symbols 302 and 304 to process relevant data.
However, any UE that did not detect its UE identity in the control
information would enter a low power state for the remaining TTI.
Thus, significant power is conserved by each UE in the cell when no
relevant data is included in packets.
[0027] Because there are a limited number of tones available in the
first OFDM symbol, the shared control channel may be split into two
parts. In one embodiment, the UE identities may be transmitted as
part of the shared control channel in a common part and transmitted
in the first OFDM symbol. The UE dedicated scheduling information
may be transmitted in a dedicated part of the shared control
channel and transmitted in the first and second OFDM symbols or,
alternatively, throughout the TTI. UE dedicated scheduling
information may contain information related to the Hybrid-ARQ
process, the modulation and coding scheme, the transport format, or
other features. This split of the SCCH into common and dedicated
parts allows the UE to save power. The common and dedicated parts
of the SCCH preferably have different code rates. The UE may
monitor the first OFDM symbol. If the UE identity is not contained
in the first OFDM symbol, the UE does not need to process the rest
of the OFDM symbols in the TTI. With reference to FIG. 3, for
example, the UE identities may be contained in the control channel
transmitted in the first OFDM symbol 300, while the remainder of
the shared control channel may be transmitted in OFDM symbols 300
and/or 302.
[0028] The foregoing discussion with regard to FIGS. 3 and 4 is by
way of example only. For example, power saving advantages of the
present invention will be even greater for more OFDM symbols in
each TTI. A longer TTI would permit each UE to enter a reduced
power mode for greater periods of time, thereby conserving even
more power when a packet contained no relevant data. However,
additional pilot signals may be necessary for any UE that does
receive relevant data during the TTI. These additional pilot
signals may be included in at least another OFDM symbol within the
longer TTI so that circuits 208 and 210 (FIG. 2) may update the
channel estimate.
[0029] Given the above, FIG. 5 illustrates three operational modes
of a typical UE in the cell. Active mode 504 is a normal
operational mode in which the UE transmits and receives data. When
the UE does not receive a transmission for a first predetermined
time after a most recent transmission from the base station, it
transitions to a power saving mode 510 as shown by path 508. If the
UE still does not receive a transmission for a second predetermined
time after a most recent transmission from the base station, it
transitions to a sleep mode 500 as shown by path 514. The sleep
mode 500 produces an even greater power savings than the power
saving mode 510. However, the UE must then receive a page from the
base station to power up and return to the active mode 504 along
path 502. Alternatively, if the UE receives a valid transmission
over the SCCH while in the power saving mode 510 before elapse of
the second predetermined time, it returns to active mode 504 along
path 512. Furthermore, from active mode 504, the UE may also
receive a sleep instruction and move directly to sleep mode 500 as
illustrated by path 506. In this manner, each EU in the cell
conserves significant power but remains responsive to subsequent
packet transmissions.
[0030] In an alternative embodiment of FIG. 5, the UE transitions
from active mode 504 to power saving mode 510 as shown by path 508
for a predetermined time after it receives a transmission. This
predetermined time is preferably an integral number of transmit
time intervals. After this predetermined time, the UE transitions
back to the active mode 504 along path 512. This embodiment of the
present invention advantageously reduces control signal overhead
between the base station and the UE and maintains the power saving
features of the previous embodiment.
[0031] In an embodiment of the present invention, the base station
transmits a counter during each TTI to indicate a number of shared
control channels (SCCH) in the TTI. There is generally one SCCH for
each UE. The UE depends on a UE identification field in the OFDM
SCCH for identification. The counter may have several values. Each
value is associated with a particular shared control channel size.
For example, a first counter value of two may indicate two shared
control channels of a first size. A second counter value of three
may indicate three shared control channels of a second size. In
another embodiment of the present invention the base station
transmits a power control counter during each TTI to indicate a
number of power control bits in the TTI.
[0032] In another embodiment of the present invention, the base
station transmits a block size designator during each TTI. The
block size designator advantageously provides flexible block sizes
to accommodate a variable number of shared control channels and
other control information in each TTI.
[0033] Turning now to FIG. 6, there is a diagram of the OFDM SCCH
structure illustrating features of the present invention. The
diagram identifies each particular control feature of the SCCH in
the left column. Corresponding control bits associated with each
control feature are given in the right column. For example,
multiple power control bits are transmitted during each TTI on the
OFDM transmit power control channel (TPCCH). A modulation scheme is
transmitted in 7 bits during the TTI. The modulation scheme
preferably identifies the modulation format and antenna grouping.
For example, the modulation formats may include quadrature phase
shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM),
or 64-quadrature amplitude modulation (64-QAM). The selected
modulation format would typically depend on signal quality and
desired data rate. Moreover, the modulation format may be different
for each antenna and each UE. The block size identifier designates
the variable block size within the TTI. The Hybrid-ARQ field
identifies the automatic repeat request (ARQ) format to each UE. In
response to a transmission from the base station, the UE will
acknowledge (ACK) or not acknowledge (NACK) receipt of the
transmission. The UE identification field identifies the SCCH
corresponding to a specific UE as previously discussed.
[0034] Referring now to FIG. 7, there is a diagram of a
broadcast/multicast (BCMCS) SCCH structure illustrating features of
the present invention. As with FIG. 6, the diagram identifies each
particular control feature of the SCCH in the left column.
Corresponding control bits associated with each control feature are
given in the right column. However, the broadcast channels are
generally only monitored by the UE much as one might watch
television. Thus, several control features such as Hybrid-ARQ,
Redundancy, New-data indicator, and UE identification are
unnecessary. Furthermore, no power control bits are transmitted in
the BCMCS slots and each BCMCS transmit time interval (TTI) is
preferably 1.0 millisecond. According to the present invention, the
base station transmits a bitmap in each TTI to indicate which BCMCS
data streams are active. For example, if the BCMCS accommodates a
maximum of 12 data streams, a 12-bit bit map is transmitted during
each TTI. A value of 0 indicates a data stream is inactive, and a
value of 1 indicates the data stream is active. Thus, the UE may
check the bitmap to determine which data stream to monitor. This
advantageously eliminates a need to monitor all data streams of the
BCMCS. Moreover, the UE may also identify which BCMCS shared
control channels (SCCH) to ignore. This is because the shared
control channels are transmitted sequentially and correspond to the
order of the bitmap.
[0035] Still further, while numerous examples have thus been
provided, one skilled in the art should recognize that various
modifications, substitutions, or alterations may be made to to the
described embodiments while still falling with the inventive scope
as defined by the following claims.
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