U.S. patent application number 13/186221 was filed with the patent office on 2011-12-22 for method and apparatus for adaptive carrier allocation and power control in multi-carrier communication systems.
This patent application is currently assigned to Adaptix, Inc.. Invention is credited to Palaniappan Meiyappan.
Application Number | 20110312367 13/186221 |
Document ID | / |
Family ID | 32311647 |
Filed Date | 2011-12-22 |
United States Patent
Application |
20110312367 |
Kind Code |
A1 |
Meiyappan; Palaniappan |
December 22, 2011 |
METHOD AND APPARATUS FOR ADAPTIVE CARRIER ALLOCATION AND POWER
CONTROL IN MULTI-CARRIER COMMUNICATION SYSTEMS
Abstract
An apparatus and process for allocating carriers in a
multi-carrier system is described. In one embodiment, the process
comprises determining a location of a subscriber with respect to a
base station, selecting carriers from a band of carriers to
allocate to the subscriber according to the location of the
subscriber with respect to the base station, and allocating
selected carriers to the subscriber.
Inventors: |
Meiyappan; Palaniappan;
(Bellevue, WA) |
Assignee: |
Adaptix, Inc.
Carrollton
TX
|
Family ID: |
32311647 |
Appl. No.: |
13/186221 |
Filed: |
July 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10534200 |
Jan 18, 2006 |
8005479 |
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PCT/US2002/036030 |
Nov 7, 2002 |
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13186221 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04L 27/2608 20130101;
H04L 5/006 20130101; H04W 72/06 20130101; H04W 52/24 20130101; H04W
52/42 20130101; H04W 52/146 20130101; H04W 52/248 20130101; H04W
52/283 20130101; H04W 36/16 20130101; H04W 52/16 20130101; H04L
5/0037 20130101; H04L 5/0007 20130101; H04W 52/52 20130101; H04L
5/0044 20130101; H04W 52/367 20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04W 52/04 20090101
H04W052/04 |
Claims
1. A method for wireless communication power control, said method
comprising: receiving, at a subscriber unit, a power control
command, said power control command based, at least in part, upon a
determination of a transmit power requirement for said subscriber
unit; adjusting, at said subscriber unit, transmit power of said
subscriber unit in response to receiving said power control
command; and transmitting data to a base station according to said
adjustment.
2. The method of claim 1 further comprising: transmitting, from
said subscriber unit, an intent to transmit signal to said base
station; and wherein said receiving is in response to transmitting
said intent to transmit signal.
3. The method of claim 1 wherein said determination of said
transmit power requirement for said subscriber unit is based, at
least in part, upon a calculation of path loss associated with said
subscriber unit.
4. The method of claim 1 wherein said adjusting transmit power of
said subscriber unit comprises adjusting transmit power of said
subscriber unit to keep the power of signals received at said base
station from said subscriber unit at a desired level.
5. The method of claim 1 further comprising receiving, at said
subscriber unit, an updated power control command, said updated
power control command based, at least in part, upon a determination
of an updated transmit power requirement for said subscriber unit;
re-adjusting, at said subscriber unit, transmit power of said
subscriber unit in response to receiving said updated power control
command; and transmitting data to said base station according to
said re-adjustment; wherein data transmitted according to said
re-adjustment is transmitted at a different power than data
transmitted according to said adjustment.
6. The method of claim 5 wherein said determination of an updated
transmit power requirement for said subscriber unit is based, at
least in part, upon an updated calculation of path loss associated
with said subscriber unit.
7. The method of claim 1 wherein said receiving said power control
command comprises: receiving, at said subscriber unit, a command
from said base station to use a normal or extended power control
range.
8. The method of claim 7 wherein said command to use a normal or
extended power control range is based, at least in part, upon a
priority assigned to said subscriber unit.
9. The method of claim 1 wherein said adjusting transmit power of
said subscriber unit comprises adjusting transmit power according
to transmit power data stored in a look up table stored at said
subscriber unit, said transmit power data associated with a code
received from said base station.
10. The method of claim 9 wherein said subscriber unit uses said
code as in index into said look up table to adjust said transmit
power.
11. A subscriber unit comprising: a receiver for receiving a power
control command, said power control command based, at least in
part, upon a determination of a transmit power requirement for said
subscriber unit; a power control unit for adjusting, at said
subscriber unit, transmit power of said subscriber unit in response
to receiving said power control command; and a transmitter for
transmitting data to a base station according to said
adjustment.
12. The subscriber unit of claim 11 further comprising: wherein
said transmitter further transmits an intent to transmit signal to
said base station; and wherein said receiving is in response to
transmitting said intent to transmit signal.
13. The subscriber unit of claim 11 wherein said determination of
said transmit power requirement for said subscriber unit is based,
at least in part, upon a calculation of path loss associated with
said subscriber unit.
14. The subscriber unit of claim 11 wherein said adjusting transmit
power of said subscriber unit comprises adjusting transmit power of
said subscriber unit to keep the power of signals received at said
base station from said subscriber unit at a desired level.
15. The subscriber unit of claim 11 wherein said receiver further
receives an updated power control command, said updated power
control command based, at least in part, upon a determination of an
updated transmit power requirement for said subscriber unit; said
power control unit re-adjusts transmit power of said subscriber
unit in response to receiving said updated power control command;
and said transmitter further transmitting data to said base station
according to said re-adjustment; wherein data transmitted according
to said re-adjustment is transmitted at a different power than data
transmitted according to said adjustment.
16. The subscriber unit of claim 15 wherein said determination of
an updated transmit power requirement for said subscriber unit is
based, at least in part, upon an updated calculation of path loss
associated with said subscriber unit.
17. The subscriber unit of claim 11 wherein said receiving said
power control command comprises: receiving, at said subscriber
unit, a command from said base station to use a normal or extended
power control range.
18. The subscriber unit of claim 17 wherein said command to use a
normal or extended power control range is based, at least in part,
upon a priority assigned to said subscriber unit.
19. The subscriber unit of claim 11 wherein said adjusting transmit
power of said subscriber unit comprises adjusting transmit power
according to transmit power data stored in a look up table stored
at said subscriber unit, said transmit power data associated with a
code received from said base station.
20. The subscriber unit of claim 19 wherein said subscriber unit
uses said code as in index into said look up table to adjust said
transmit power.
21. A computer readable medium having instructions stored thereon,
wherein execution of said instructions directs a subscriber unit
to: receive a power control command, said power control command
based, at least in part, upon a determination of a transmit power
requirement for said subscriber unit; adjust transmit power of said
subscriber unit in response to receiving said power control
command; and transmit data to a base station according to said
adjustment.
22. The computer readable medium of claim 21 wherein execution of
said instructions directs a subscriber unit to: transmit an intent
to transmit signal to said base station; and wherein said receiving
is in response to transmitting said intent to transmit signal.
23. The computer readable medium of claim 21 wherein said
determination of said transmit power requirement for said
subscriber unit is based, at least in part, upon a calculation of
path loss associated with said subscriber unit.
24. The computer readable medium of claim 21 wherein said adjusting
transmit power of said subscriber unit comprises adjusting transmit
power of said subscriber unit to keep the power of signals received
at said base station from said subscriber unit at a desired
level.
25. The computer readable medium of claim 21 wherein execution of
said instructions directs a subscriber unit to: receive an updated
power control command, said updated power control command based, at
least in part, upon a determination of an updated transmit power
requirement for said subscriber unit re-adjust transmit power of
said subscriber unit in response to receiving said updated power
control command; and transmit data to said base station according
to said re-adjustment; wherein data transmitted according to said
re-adjustment is transmitted at a different power than data
transmitted according to said adjustment.
26. The computer readable medium of claim 25 wherein said
determination of an updated transmit power requirement for said
subscriber unit is based, at least in part, upon an updated
calculation of path loss associated with said subscriber unit.
27. The computer readable medium of claim 21 wherein said receiving
said power control command comprises: receiving, at said subscriber
unit, a command from said base station to use a normal or extended
power control range.
28. The computer readable medium of claim 27 wherein said command
to use a normal or extended power control range is based, at least
in part, upon a priority assigned to said subscriber unit.
29. The computer readable medium of claim 21 wherein said adjusting
transmit power of said subscriber unit comprises adjusting transmit
power according to transmit power data stored in a look up table
stored at said subscriber unit, said transmit power data associated
with a code received from said base station.
30. The computer readable medium of claim 29 wherein said
subscriber unit uses said code as in index into said look up table
to adjust said transmit power.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/534,200, filed May 6, 2005 and entitled
"METHOD AND APPARATUS FOR ADAPTIVE CARRIER ALLOCATION AND POWER
CONTROL IN MULTI-CARRIER COMMUNICATION SYSTEMS," which is a U.S.
National Stage under 35 USC 371, and claims priority to Application
No. PCT/US2002/036030 filed Nov. 7, 2002, designating the United
States, which claims priority to U.S. Pat. No. 6,751,444 issued on
Jun. 15, 2004, the disclosures of which are incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to the field of multi-carrier
communication systems; more particularly, the present invention
relates to allocating carriers and performing power control in a
multi-carrier system.
BACKGROUND OF THE INVENTION
[0003] With high-speed wireless services increasingly in demand,
there is a need for more throughput per bandwidth to accommodate
more subscribers with higher data rates while retaining a
guaranteed quality of service (QoS). In point-to-point
communications, the achievable data rate between a transmitter and
a receiver is constrained by the available bandwidth, propagation
channel conditions, as well as the noise-plus-interference levels
at the receiver. For wireless networks where a base-station
communicates with multiple subscribers, the network capacity also
depends on the way the spectral resource is partitioned and the
channel conditions and noise-plus-interference levels of all
subscribers. In current state-of-the-art, multiple-access
protocols, e.g., time-division multiple access (TDMA),
frequency-division multiple-access (FDMA), code-division
multiple-access (CDMA), are used to distribute the available
spectrum among subscribers according to subscribers' data rate
requirements. Other critical limiting factors, such as the channel
fading conditions, interference levels, and QoS requirements, are
ignored in general.
[0004] Recently, there is an increasing interest in orthogonal
frequency-division multiplexing (OFDM) based frequency division
multiple access (OFDMA) wireless networks. One of the biggest
advantages of an OFDM modem is the ability to allocate power and
rate optimally among narrowband sub-carriers. OFDMA allows for
multi-access capability to serve increasing number of subscribers.
In OFDMA, one or a cluster OFDM sub-carriers defines a "traffic
channel", and different subscribers access to the base-station
simultaneously by using different traffic channels.
[0005] Existing approaches for wireless traffic channel assignment
are subscriber-initiated and single-subscriber (point-to-point) in
nature. Since the total throughput of a multiple-access network
depends on the channel fading profiles, noise-plus-interference
levels, and in the case of spatially separately transceivers, the
spatial channel characteristics, of all active subscribers,
distributed or subscriber-based channel loading approaches as
fundamentally sub-optimum. Furthermore, subscriber-initiated
loading algorithms are problematic when multiple transceivers are
employed as the base-station, since the
signal-to-noise-plus-interference ratio (SINR) measured based on an
omni-directional sounding signal does not reveal the actual quality
of a particular traffic channel with spatial processing gain. In
other words, a "bad" traffic channel measured at the subscriber
based on the omni-directional sounding signal may very well be a
"good" channel with proper spatial beamforming from the
base-station. For these two reasons, innovative information
exchange mechanisms and channel assignment and loading protocols
that account for the (spatial) channel conditions of all accessing
subscribers, as well as their QoS requirements, are highly
desirable. Such "spatial-channel-and-QoS-aware" allocation schemes
can considerably increase the spectral efficiency and hence data
throughput in a given bandwidth. Thus, distributed approaches,
i.e., subscriber-initiated assignment are thus fundamentally
sub-optimum.
[0006] Linear Modulation Techniques, such as Quadrature phase shift
keying (QPSK), Quadrature Amplitude Modulation (QAM) and
multi-carrier configurations provide good spectral efficiency,
however the modulated RF signal resulting from these methods have a
fluctuating envelope. This puts stringent and conflicting
requirements on the power amplifier (PA) used for transmitting
communications. A fluctuating envelope of the modulating signal
requires highly linear power amplification. But in order to achieve
higher efficiency and improve uplink budget, power amplifiers have
to operate close to compression and deliver maximum possible power.
As a result, there is a trade off for power versus amount of
nonlinear amplification a system can handle.
[0007] Furthermore, non-linearity in the PA generates
intermodulation distortion (IMD) products. Most of the IMD products
appear as interference to adjacent channels. This power is referred
to Adjacent Channel Leakage Power Ratio (ACPR or ACLR) in wireless
standards.
[0008] The ACPR is important to the FCC and wireless standards
because of the co-existence with other users of the spectrum
operating in adjacent and alternate channels. In band or channel
distortion affects the performance of the licensee's own spectrum,
which, in turn, affects the transmitter signal-to-noise ratio (SNR)
of other users in the same system.
[0009] RF link budget in a wireless communication system refers to
balancing the available transmit power, antenna gain, propagation
loss and determining maximum allowable distance at which received
power meets a minimum detectable signal threshold. Several
parameters influence the RF link budget. Two main factors,
transmitter RF power available from the PA and receiver
sensitivity, are under circuit designer's control. Base station
design has relatively more degree of freedom than the Customer
Equipment (CE). This results in the RF link budget being imbalanced
in the uplink. This limitation is hard to overcome given the cost,
size and battery life requirements of CE.
SUMMARY OF THE INVENTION
[0010] An apparatus and process for allocating carriers in a
multi-carrier system is described. In one embodiment, the process
comprises determining a location of a subscriber with respect to a
base station, selecting carriers from a band of multiple carriers
to allocate to the subscriber according to the location of the
subscriber with respect to the base station, allocating selected
carriers to the subscriber, and indicating to the subscriber
whether or not to adjust transmit power above its normal transmit
power range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the invention, which, however, should not
be taken to limit the invention to the specific embodiments, but
are for explanation and understanding only.
[0012] FIG. 1A illustrates a multi-carrier system;
[0013] FIG. 1B illustrates spectral re-growth in a multi-carrier
system;
[0014] FIG. 1C illustrates power amplifier operating regions;
[0015] FIG. 2 is a flow diagram of one embodiment of a process for
allocating carriers in a multi-carrier system;
[0016] FIG. 3 is a flow diagram of one embodiment of a process for
a base station to allocate carriers in a multi-carrier system;
[0017] FIG. 4 is a flow diagram of one embodiment of a process by
which a subscriber unit is allocated carriers in a multi-carrier
system;
[0018] FIG. 5 illustrates an exemplary system having a base station
and a subscriber unit;
[0019] FIG. 6 illustrates a system having a base station and
multiple subscribers grouping based on constant path loss
contours;
[0020] FIG. 7 illustrates an exemplary WCDMA modulation terminal
power output for a 45 dBc ACLR;
[0021] FIG. 8 illustrates an exemplary WCDMA modulation terminal
power output for a 33 dBc ACLR as defined by the 3GPP standard;
[0022] FIG. 9 illustrates an OFDM selective tone modulation
terminal power output;
[0023] FIG. 10 illustrates NPR due to operating a Customer
Equipment (CE) at an increased power level;
[0024] FIG. 11 is a block diagram of one embodiment of a customer
equipment transmitter; and
[0025] FIG. 12 is a block diagram of one embodiment of a base
transmitter.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0026] A carrier allocation technique for use in multi-carrier
systems is described. The carrier allocation technique selects
carriers, or subcarriers, of a band to allocate to a subscriber or
Customer Equipment (CE) for their use. In one embodiment, the
allocation is performed such that carriers closer to or at the
center of the band are allocated to subscriber units and CEs
further away from a base station and carriers closer to the edge of
the band are allocated to those CEs and subscriber units closer to
the base station.
[0027] In one embodiment, the technique described herein increases
the transmitter radio frequency (RF) power available from a power
amplifier (PA) of the CPE, CE, terminal, subscriber unit, portable
device, or mobile by exploiting the multi-carrier nature of
multiple carrier systems, such as, for example, an orthogonal
frequency-division multiple access (OFDM) system. This technique
may double or even quadruple the PA output power, resulting in
balancing RF link design in a two-way communication system. In one
embodiment, this technique may be employed to control a PA device
to operate at a higher power and simultaneously meet the Adjacent
Channel Leakage Power (ACPR) emission requirements associated with
a standard (to which the system is adhering). This may occur when a
subscriber unit's power control drives up the transmit power when
farther away from the base station after being allocated carriers
at or near the center of the band being allocated. Thus, the
technique described herein allows the transmit power to be driven
up or down based on the position of the subscriber. In one
embodiment, the selective carrier method described herein results
in 3 to 6 dB increased power, which can considerably improve RF
link budget.
[0028] Such a method of allocation can be used in a wireless system
employing fixed, portable, mobile subscribers or a mixture of these
types of subscribers. Note that the term "subscriber," "customer
equipment" and "subscriber unit" will be used interchangeably.
[0029] In the following description, numerous details are set forth
to provide a thorough understanding of the present invention. It
will be apparent, however, to one skilled in the art, that the
present invention may be practiced without these specific details.
In other instances, well-known structures and devices are shown in
block diagram form, rather than in detail, in order to avoid
obscuring the present invention.
[0030] Some portions of the detailed descriptions that follow are
presented in terms of algorithms and symbolic representations of
operations on data bits within a computer memory. These algorithmic
descriptions and representations are the means used by those
skilled in the data processing arts to most effectively convey the
substance of their work to others skilled in the art. An algorithm
is here, and generally, conceived to be a self-consistent sequence
of steps leading to a desired result. The steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0031] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise as apparent from
the following discussion, it is appreciated that throughout the
description, discussions utilizing terms such as "processing" or
"computing" or "calculating" or "determining" or "displaying" or
the like, refer to the action and processes of a computer system,
or similar electronic computing device, that manipulates and
transforms data represented as physical (electronic) quantities
within the computer system's registers and memories into other data
similarly represented as physical quantities within the computer
system memories or registers or other such information storage,
transmission or display devices.
[0032] The present invention also relates to apparatus for
performing the operations herein. This apparatus may be specially
constructed for the required purposes, or it may comprise a general
purpose computer selectively activated or reconfigured by a
computer program stored in the computer. Such a computer program
may be stored in a computer readable storage medium, such as, but
is not limited to, any type of disk including floppy disks, optical
disks, CD-ROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or
optical cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus.
[0033] The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus.
Various general purpose systems may be used with programs in
accordance with the teachings herein, or it may prove convenient to
construct more specialized apparatus to perform the required method
steps. The required structure for a variety of these systems will
appear from the description below. In addition, the present
invention is not described with reference to any particular
programming language. It will be appreciated that a variety of
programming languages may be used to implement the teachings of the
invention as described herein.
[0034] A machine-readable medium includes any mechanism for storing
or transmitting information in a form readable by a machine (e.g.,
a computer). For example, a machine-readable medium includes read
only memory ("ROM"); random access memory ("RAM"); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.);
etc.
[0035] Selective Carrier Allocation
[0036] The selective carrier allocation technique disclosed is
applicable to multi-carrier systems. Example of these include
Orthogonal Frequency Division Multiple Access (OFDMA),
multi-carrier CDMA, etc. As an example, the selective carrier
allocation will be described below with reference to an OFDM
system.
[0037] In an OFDM system, OFDMA is used for uplink communications
to share the spectrum with co-users of the same sector. In other
words, the subscriber or CE uses only a portion of the available
carriers (or multi-tones) for any given transmission. The base
station allocates these carriers to subscribers in a methodical way
to avoid interfering, to the extent possibly, with other users in
the same sector. The decision to select a set of carriers can be
based on several criteria such as, for example, but not limited to,
fading, signal-to-noise ratio (SNR) and interference.
[0038] FIG. 1A illustrates the spectrum of one embodiment of a
multi-carrier system such as OFDM. In such a system, there are a
number of modulated carriers (n) occupying a certain bandwidth. For
a 3GPP system, this bandwidth is 3.84 MHZ. Non-linearities within
the PA mixes or modulates these tones with each other to generate
intermodulation distortion (IMD) products. A dominant element of
these IMDs is due to third order (2f.times.f) and fifth order
(3f.times.2f) mixing. The IMD generated by a wide band multiple
tone signal causes the spectrum to spread energy (or spill) beyond
the allocated 3.84 MHz bandwidth. This is commonly referred as
spectral re-growth. FIG. 1B depicts the spectral re-growth
phenomena.
[0039] Spectral re-growth due to third order mixing falls in the
upper and lower adjacent channels, whereas the fifth order mixing
product falls on the upper and lower alternate channels. Other
higher order products are usually weaker and can be ignored for
most practical applications.
[0040] As mentioned above, non-linearities in the PA are rich in
third order products and are of most concern. These products are
seen in the adjacent channels as ACLR power. The fifth and higher
order products are spread out further from the main channel and
their effect is not a determinant factor.
[0041] In a multi-carrier wireless system using `N` tones, the
subscriber unit or CE uses only a limited number of tones, such as
`X` tones where X is a much smaller number compared to N. A CE or
subscriber unit using a cluster of X tones will occupy (X/N) of the
total channel bandwidth. As depicted in FIG. 1B, spectral re-growth
due to third and fifth order products is stronger and is very
important. These determine the adjacent and alternate channel
coupled powers.
[0042] If clusters around the center of the allocated channel are
chosen for transmission, then it is possible for the main IMD
products to fall within the channel bandwidth. As a consequence,
these carriers can withstand higher level of non-linear
amplification and can be used to transmit at increased power levels
compared to other carriers. The CEs/subscriber units closer to the
base station operate at lower power than the CEs/subscriber units
farther away. FIG. 1C depicts the linear operation and IMD products
generated as a function of operating power.
[0043] CEs/subscriber units farther away from the base encounter
larger path loss and they need to operate at a higher power.
Operating at higher power produces a higher level of IMD products
and causes spectral growth. These CEs/subscriber units can be
allocated the clusters around the center of the operating channel,
thereby reducing, and potentially minimizing, the spill over to
adjacent channels while simultaneously achieving higher transmit
power.
[0044] FIG. 2 illustrates one embodiment of a process for
allocating carriers in a multi-carrier system. The process is
performed by processing logic that may comprise hardware (e.g.,
circuitry, dedicated logic, etc.), software (such as is run on a
general purpose computer system or a dedicated machine), or a
combination of both.
[0045] Referring to FIG. 2, the process begins with processing
logic of a base station comparing interference to adjacent channels
(e.g., adjacent channel leakage power) with the output power of a
subscriber unit in a multi-carrier system as a function of distance
of the subscriber unit from the base station (processing block
201). Then the processing logic of the base station selectively
allocates one or more carriers to the subscriber unit based on
results of the comparison (processing block 202). In one
embodiment, one or more subscribers closer to the base station are
allocated carriers closer to the band edges of the operating
channel and one or more subscribers farther from the base station
are allocated carriers around the center of the operating channel.
Referring to FIG. 1B, the CE occupies main channel bandwidth of
[(X/N)*3.84]Mhz for uplink transmission. Third order IMD products
generated by this channel will occupy [(X/N)*3.84]Mhz on the upper
and lower sides of the main channel. Similarly, fifth order IMD
products will occupy another [(X/N)*3.84]Mhz on either side of the
third order products. Thus, twice the main channel bandwidth on
each side of the main channel will be occupied by significant
components of IMD. Therefore, the clusters falling within
{1/2[3.84-(4*main channel bandwidth)]} from the center of the band
can benefit due to this carrier allocation method.
[0046] As a result of this allocation, dominant undesired spectral
re-growths can be restricted to lie within the wireless system's
occupied channel and avoid interference to adjacent channels.
Furthermore, the PA of a subscriber unit can be operated closer to
1 dB compression point and deliver higher power than the
conventional usage. Operation near compression point also improves
the PA efficiency.
[0047] In one embodiment, the carriers being allocated are
orthogonal frequency-division multiple access (OFDMA) carriers. The
OFDMA carriers may be allocated in clusters. In another embodiment,
each carrier may be a spreading code and the multi-carrier system
comprises a multi-carrier code-division multiple-access (MC-CDMA)
system.
[0048] In one embodiment, the multi-carrier system is a wireless
communication system. Alternatively, the multi-carrier system is a
cable system.
[0049] FIG. 3 illustrates one embodiment of a process performed by
a base station for allocating carriers of a band in a multi-carrier
system. The process is performed by processing logic that may
comprise hardware (e.g., circuitry, dedicated logic, etc.),
software (such as is run on a general purpose computer system or a
dedicated machine), or a combination of both.
[0050] Referring to FIG. 3, the process begins with processing
logic receiving a communication indicating that a subscriber
intends to transmit (processing block 301). In one embodiment, the
communication is a random access intention to transmit sent by the
subscriber and is received by a base.
[0051] In response to receiving the communication, processing logic
of the base calculates the transmit power requirements for the
subscriber unit and determines whether the subscriber is near or
far (processing block 302). In one embodiment, the processing logic
calculates the time delay and path loss associated with the
subscriber and uses this information to calculate the transmit
power requirements. Note that transmit power is based on the path
loss, and the time delay provides additional information on the
distance of the customer equipment. In one embodiment, processing
logic uses additional factors such as, for example, SINR, in
calculating the transmit power requirements
[0052] Based on the transmit power requirements calculated and the
determination of whether the subscriber unit is near or far,
processing logic allocates carriers to the subscriber (processing
block 303). In one embodiment, each carrier is identified by a tone
number or a group of carriers are identified by a cluster number in
a multi-carrier system. The base instructs the customer equipment
to use a particular set of carriers identified by their number. In
one embodiment, the processing logic in the base station allocates
carriers near the center of the band (it is to allocate) to
subscriber units far away from the base station and carriers near
the edges of the band to subscriber units closer to the base
station. The processing logic may attempt to allocate more carriers
closer the edges of band in order to save carriers for currently
non-present subscriber units that will enter the coverage area of
the base station in the future or present subscriber units that
will move from a location close to the base station to one farther
away from the base station.
[0053] In one embodiment, in order to allocate carriers to
subscribers, processing logic in the base station assigns a
priority code to each subscriber unit based on the location of the
subscriber unit in relation to the base station (e.g., whether the
subscriber unit is far away from or near to the base station). A
priority code is assigned based on the transmit power requirement,
which, in turn, is based on the path loss. The location of the CE
determines the path loss. In general, the farther away the CE from
the base, the path loss is more, but not always. For example, there
could be a nearby CE (to the base) but behind a tall building or
hill, causing an RF shadow. In such a case, this CE will have large
path loss. In one embodiment, the subscriber farthest from the base
station is allocated priority code #1, followed by the next
farthest subscriber with priority code #2, and so on.
[0054] Processing logic in the base station may also send a command
to a subscriber unit to cause the subscriber unit to use either a
normal or extended power control range of "z dB" above the normal
range depending on priority and carrier allocation (processing
block 304). In other words, the base station sends commands to the
subscriber to indicate whether to raise or lower its transmit
power. This is closed loop power control to tune the transmit power
of the subscriber.
[0055] In one embodiment, processing logic in the base station also
adjusts power control setting for the subscriber in a closed loop
power control setting and continuously monitors received power from
subscribers (processing block 305). For example, if the channel
characteristics change, the path loss changes and the base has to
update the transmit power of the CE.
[0056] FIG. 4 illustrates one embodiment of a process performed by
a subscriber unit in a multi-carrier system. The process is
performed by processing logic that may comprise hardware (e.g.,
circuitry, dedicated logic, etc.), software (such as is run on a
general purpose computer system or a dedicated machine), or a
combination of both.
[0057] Referring to FIG. 4, processing logic in the subscriber unit
sends a communication to a base station to indicate that it intends
to transmit (processing block 401). In one embodiment, the
processing logic sends a random access intention to transmit.
[0058] Processing logic in the subscriber unit receives an
indication of an allocation of carriers based on the location of
the subscriber unit with respect to a base station (processing
block 402). In one embodiment, the indication comes from the base
station on the control channel.
[0059] In one embodiment, processing logic in the subscriber unit
also receives a command from the base station to use either a
normal or extended power control range (processing block 403). In
one embodiment, whether the base station indicates to the
subscriber unit to use the normal or extended power control range
is based on assigned priority and carrier allocation. These command
indicate to the subscriber unit that it is to drive up or reduce
its transmit power, and whether it is one or the other depends on
the position of the subscriber relative to the base station.
[0060] FIG. 5 is a block diagram of one embodiment of a typical
system. Referring to FIG. 5, a base 510 is shown communicably
coupled to a subscriber unit 520. Base station 510 includes a power
control unit 511 coupled to a carrier allocator 512. Carrier
allocator 512 allocates carriers of a band to subscriber units,
such as subscriber unit 520, in the system, and power control unit
511. In one embodiment, carrier allocator 512 includes a priority
code look up table (LUT) 513. At a given instant, the farthest
subscriber(s) may not be active in the system. Therefore, the
embodiment described here uses predetermined threshold limits in
the LUT to determine the carrier allocation and power control.
[0061] In one embodiment, carrier allocator 512 decides the
spectral priority based on the information gathered from the access
requests sent by subscriber units. Carrier allocator 512 assigns
priorities to each subscriber based on location with respect to
base station 510 and then allocates carriers to each subscriber.
Carrier allocator 512 allocates carriers at or near the center of
the band to the subscribers farthest away from base station and
allocates carriers closer to or at the edge of the band to
subscribers closest to base station 510. In one embodiment, carrier
allocator 512 attempts to allocate sub-carriers at the edges of the
band to the nearest subscribers and make room for potential
subscribers located farther away from base station 510.
[0062] In one embodiment, carrier allocator 512 classifies
subscribers into priority groups rather than assigning them
individual priorities. In a cell-based system, carrier allocator
512 identifies subscribers near the center of the sector form one
group and have a certain priority code. If constant path loss
contours are imagined, subscribers falling between certain path
losses or between these contours form a group and are assigned a
certain priority.
[0063] Carrier allocator 512 also continuously monitors the
allocation of the carriers used by various subscribers in the
system and dynamically reallocates the carriers to subscribers. For
example, in a mobile system, both the mobile unit(s) and base
station continuously monitor the path loss and may perform
reallocation and adaptive power control to extend the range. If the
subscriber has moved closer to the base station, then carrier
allocator 512 changes the priority codes and deallocates the
sub-carriers near the center for other potential subscribers.
Similarly, when a subscriber moves away from base station 510, then
carrier allocator changes the priority codes and allocates the
sub-carriers near the center of the band depending on
availability.
[0064] The priority determined by sub-carrier allocator 512 is
communicated to subscriber unit 520 by power control unit 511. In
one embodiment, sub-carrier allocator 512 transmits information
about the specific carriers available for the subscriber, the
priority code on these carriers, and the power control range
(normal or extended). This communication indicates to the
subscribers to use a certain power control range based on their
priority and carrier allocation. Power control unit 511 indicates
to subscriber unit 520 the transmit power level it is to use. In
one embodiment, power control unit 511 indicates to subscriber unit
520 to extend power control range if subscriber unit 520 is
allocated carriers at center of the spectrum. That is, power
control unit 511 sends out power control commands to the
subscribers in order for the received power at base station 510 to
be at the desired level. Thus, power control unit 511 is
responsible for closed loop power control.
[0065] Subscriber unit 520 includes a power control unit 521. Power
control unit 521 controls the transmit power of subscriber unit
520. That is, power control unit 521 adjusts the transmit power
from subscriber unit 520 to keep the received power at base station
510 at a predetermined level desired by base station 510. Thus,
power control unit 521 is responsible for closed loop power
control.
[0066] In one embodiment, power control unit 521 processes power
control commands received from the base station and determines the
allocated power control range for subscriber unit 520. In one
embodiment, power control unit 521 includes a normal power control
range (i to j) and an extended power control range (m to n) and
power control unit 521 tells subscriber unit 520 to extend the
power control range if the subscriber is allocated sub-carriers at
the center of the spectrum. In one embodiment, the power control
unit signals the gain control circuit of the transmitter of the
subscriber unit to extend the power control range. In one
embodiment, subscriber unit 520 is responsive to a code received
from the base station which indicates the power control range to
use. Subscriber unit 520 may include a look up table (LUT) that
stores power control ranges and/or transmit powers associated with
each code received from the base station, and uses the code as an
index into the LUT to determine what power control range and/or
transmit power is being requested.
[0067] The system maintains its ACLR, however by allocating
carriers near or at the center of the band, the subscriber gets an
increase of power (e.g., 3-6 db). That is, in a system with
subscribers typically transmitting at 17 dBm with a 3 kilometer
range, a subscriber allocated carriers at the center may be able to
transmit 18 or 19 dBm, thereby allowing it to extend its range
potentially to 4 km.
[0068] FIG. 11 is a block diagram of one embodiment of a customer
equipment transmitter. Referring to FIG. 11, an upconverter 1101
mixes a signal to be transmitted with a signal from a local
oscillator 1102 to create an upconverted signal. The upconverted
signal is filtered by filter 1103. The filtered signal output from
filter 1103 are input to a variable gain amplifier 1104, which
amplifies the filtered signal. The amplified signal output from
variable gain amplifier 1104 is mixed with a signal from a local
oscillator 1106 using upconverter 1105. The upconverted signal
output from upconverter 1105 is filtered by filter 1107 and input
to variable gain amplifier 1108.
[0069] Variable gain amplifier 1108 amplifies the signal output
from filter 1107 based on a control signal. Variable gain amplifier
1108 and the control signal is controlled by DSP engine 1109 which
executes a power control algorithm 1121 with the use of priority
code and power control range look-up table (LUT) 1122. Both the
power control algorithm 1121 and priority code and power control
range LUT 1122 are stored in external memory. In addition, memory
1120 is also coupled to DSP engine 1109. In one embodiment, when
power is turned off power control algorithm 1121 and LUT 1122 are
stored in external memory 1120. DSP engine 1109 is also coupled to
external memory 1120 so that it can download code to the internal
memory of DSP engine 1109. The output of DSP engine 1109 is control
signal that is input to FPGA/ASIC 1111, which buffers the output
data from DSP engine 1109 and formats it so that the data is
readable by digital-to-analog (D/A) converter 1110. The output of
ASIC 1111 is coupled to an input of D/A converter 1110 which
converts the control signal from digital-to-analog. The analog
signal is input to variable gain amplifier 1108 to control the gain
that is applied to output of filter 1107.
[0070] The amplified signal output from output variable gain
amplifier 1108 is input to a power amplifier 1130. The output of
power amplifier 1130 is coupled to a duplexer or transmit switch
1131. The output duplexer/TR switch 1131 is coupled to antenna 1140
for transmission therefrom.
[0071] FIG. 12 is a block diagram of one embodiment of a base
transmitter. Referring to FIG. 12, DSP engine 1209 performs power
control and subcarrier allocation using power control algorithm
1221 in conjunction with a priority code and power control range
look-up table 1222 (stored in memory), and subcarrier allocator
1240, respectively. In addition, memory 1220 is also coupled to DSP
engine 1209. The output of DSP engine 1209 is power control
information that is embedded into a transmit message as control
bits. The transmit message is input to FPGA/ASIC 1211, which
buffers the output data from DSP engine 1209 and formats it so that
the data is readable by D/A converter 1210. The output of ASIC 1211
is input to modem and D/A converter 1210 which modulates the signal
and converts the signal from digital to analog. The analog signal
is input to upconverter 1201.
[0072] Upconverter 1201 mixes the signal from converter 1210 with a
signal from a local oscillator 1202 to create an upconverted
signal. The upconverted signal is filtered to filter 1203. The
filter signals output to a variable gain amplifier 1204 which
amplifies the signal. The amplified signal is output from variable
gain amplifier 1204 and mix with a signal from a local oscillator
1206 using upconverter 1205. The upconverted signal output from
upconverter 1205 is filtered by 1207.
[0073] Variable gain amplifier 1208 amplifies the signal output
from filter 1207. The amplified signal output from variable gain
amplifier 1208 is input to a power amplifier 1230. The output of
power amplifier 1230 is coupled to a duplexer or transmit switch
1231. The output duplexer/TR switch 1231 is coupled to antenna 1240
for transmission therefrom.
[0074] An Exemplary System
[0075] FIG. 6 illustrates an exemplary system having a base
station, with its coverage area, and multiple subscribers. The
coverage range of the base station is divided into distance groups
1 to 4. Although not limited as such, there are 5 subscribers A, B,
C, D and E sending random access intention to transmit. These
subscribers are located physically as depicted in FIG. 6.
[0076] The spectrum has been divided into sub groups numbered 1, 2,
3 and 4. Grouping is based on path loss in this case. Table 1
summarizes the group attributes and transmit power requirements of
each subscriber unit.
TABLE-US-00001 TABLE 1 Grouping and Power Control Table Spec-
Terminal tral Spec- Group Path Transmit Pri- trum Num- loss power
ority Allo- ber in dB in dBm Code cation Power Control Range 1
>-100 <-13 4 Center +3 Normal -40 dBm to +17 dBm 2 -101 -12 3
Center +2 Normal -40 dBm to -115 to +2 to +17 dBm 3 -116 +3 2
Center +1 Normal -40 dBm to -130 to +17 to +17 dBm 4 -131 +18 1
Center Ex- -40 dBm to -136 to +23 tended to +23 dBm
[0077] The allocation process to allocate carriers to subscriber A
is as follows. First, subscriber A sends a random access intention
to transmit to the base station. Second, the base station receives
the request and calculates time delay and path loss for subscriber
A. Next, based on results of the calculation of the time delay and
the path loss for subscriber A and Table 1, the base station
determines that subscriber A belongs to distance group-4. The base
station also determines that subscriber A needs to transmit with
spectral priority code-1. Then the base station commands to use an
extended power control range and allocates carriers in the center
of the spectrum. Thereafter, the base station and subscriber A
adjust power control settings in a closed loop power control mode
and continuously monitor. In the case of the base station, the base
station continuously monitors the signals received from subscribers
(and calculates the time delay and path loss).
[0078] It should be noted that subscribers may or may not be
allocated carriers that are closer to the edge or to the center of
the band in comparison to a subscriber that is adjacent to them.
For example, in the case of FIG. 6, in one allocation, subscriber E
could be allocated carriers closest to the edges of a band,
followed by carriers allocated to subscriber D being the next
closest, followed by carriers allocated to subscriber C, and so on,
until subscriber A, which would be allocated carriers closest to
the center of the band (in comparison to subscribers B-E). However,
during other allocations, one or more subscribers may be allocated
carriers closer to the edge of the band or closer to the center of
the band than carriers allocated to a subscriber who is closer to
or further from the base station, respectively. For example, in
FIG. 6, it is possible that subscriber D is allocated carriers
closer to the edge of the band than those allocated to subscriber
E.
[0079] Comparison with a Prior Art System
[0080] FIG. 7 is a spectral plot for ACLR of 45 dBc for a system
having a hardware platform designed for a 1800 MHZ TDD wireless
communication system. The 45 dBc amount is selected because if a
system is designed to coexist with ANSI-95, ACLR of 45 dBc has to
be met, and ACLR for a PCS CDMA system is defined in ANSI-95 to be
45 dBc in a RBW of 30 KHz. In order to meet the ACLR of 45 dB, the
output power capability of the terminal is about +17 dBm.
[0081] FIG. 9 shows the capability of terminal operating with the
use of the carrier allocation described herein is +23 dBm for ACLR
of 33 dBc. One of the evolving standards, 3 GPP, defines the ACLR
to be 33 dBc for CEs.
[0082] Note that operating the PA of a subscriber closer to
compression for more power results in in-band distortion. However,
employing the methodology of the present invention does not degrade
the system performance. This fact may be shown through the use of
an example as given below.
[0083] Power control algorithms ensure that power received at the
base station from all CEs or subscribers arrive at the same level.
This means that the signal peak to average ratio received at the
base is near zero. It is assumed in this example that a cluster of
carriers is allocated at the center of the channel to the farthest
user and this user meets the transmit signal quality and SNR
requirements for the base receiver to demodulate. If the minimum
detectable signal at the receiver is -92 dBm for an SNR of 10 dB,
then the receive noise floor is set at -102 dBm. If the farthest CE
operates at a TX SNR of 12 dB or better and power control algorithm
sets the system such that this signal from the CE arrives at -92
dBm to the base, then the IMD products generated by this CE are
buried in the RX noise floor. All the other channels see only the
receive noise floor. The receiver thermal noise floor is inherent
to all communication system. Hence, the overall performance of the
system has not been degraded.
[0084] In order to increase, and potentially maximize, the output
power available to the farthest terminal, a cluster at the center
of the channel can be allocated. This way the IMD products and
spectral re-growth generated by the farthest user does not cause
spill over to the adjacent channel.
[0085] FIG. 9 shows that the terminal is capable of transmitting at
output power level of +25 dBm while maintaining ACLR of 45 dBc.
This is an improvement of nearly 8 dB compared to situation
described above in FIG. 7. As mentioned above, the PA efficiency is
better when it operates closer to its saturated power. Thus, it
improves the battery life at no cost to hardware implementation.
Resulting inter modulation products for the in band channel are
measured to be 14 dB. This distortion product power level is lower
than the receiver SNR requirement of 12 dB requirement for the up
link in other systems.
[0086] In band Noise Power Ratio (NPR) typically characterizes
distortion for multi-carrier system. FIG. 10 is a measurement of
NPR when the CE is operated at a power level of +23 dBm. NPR is
about 22 dB, thereby indicating the distortion levels will be
buried well below the thermal noise floor of the base station
receiver.
[0087] Table 2 below summarizes the performance improvements
achieved the selective carrier allocation method described
herein.
TABLE-US-00002 TABLE 2 Performance Comparison ACPR - Channel Power
ACPR conventional Selective carrier (dBm) NPR (dB) way allocation
method 14 32 >45 >45 17 32 45 >45 20 28 39 >45 23 22 33
>45 24 18 -- >45 25 12 -- >45 26 9 -- 45
CONCLUSION
[0088] A carrier allocation method and apparatus are described
which potentially maximizes the subscriber unit or customer
equipment CE transmitter power. In one embodiment, improvements
from 3 dB to 6 dB can be achieved using the methodology described
herein to allocate OFDM tones to subscriber units or CEs.
[0089] Whereas many alterations and modifications of the present
invention will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that any particular embodiment shown and described
by way of illustration is in no way intended to be considered
limiting. Therefore, references to details of various embodiments
are not intended to limit the scope of the claims which in
themselves recite only those features regarded as essential to the
invention.
* * * * *