U.S. patent application number 13/397388 was filed with the patent office on 2012-06-07 for transmit emission control in a wireless transceiver.
This patent application is currently assigned to WI-LAN Inc.. Invention is credited to Todd R. Sutton.
Application Number | 20120140802 13/397388 |
Document ID | / |
Family ID | 41257017 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120140802 |
Kind Code |
A1 |
Sutton; Todd R. |
June 7, 2012 |
TRANSMIT EMISSION CONTROL IN A WIRELESS TRANSCEIVER
Abstract
Methods and apparatus for control of uplink resource allocation
and undesirable transmit emissions from a wireless transceiver in a
frequency division duplex (FDD) or hybrid frequency division duplex
(H-FDD) wireless system. The bandwidths spanned by the receive band
and the transmit band may be symmetric or asymmetric. Additionally,
each of the receive band or the transmit band may be contiguous or
may be an aggregate of multiple discontinuous frequency bands. The
wireless transceiver can control undesirable transmit emissions
from occurring in a predetermined frequency band by using an offset
LO frequency and restricting transmit signals to frequencies away
from the predetermined frequency band. Alternatively, in an
asymmetric FDD system where a receive band is larger than a
transmit band, the transceiver can limit transmit signal allocation
to the transmit band. The transceiver can further limit out of band
transmit emissions using an offset LO frequency.
Inventors: |
Sutton; Todd R.; (Delmar,
CA) |
Assignee: |
WI-LAN Inc.
Ottawa
CA
|
Family ID: |
41257017 |
Appl. No.: |
13/397388 |
Filed: |
February 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12114701 |
May 2, 2008 |
8125974 |
|
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13397388 |
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Current U.S.
Class: |
375/219 |
Current CPC
Class: |
H04L 5/0066 20130101;
H04W 4/20 20130101 |
Class at
Publication: |
375/219 |
International
Class: |
H04B 1/38 20060101
H04B001/38 |
Claims
1. A method of transmit emission control in a wireless transceiver,
the method comprising: receiving a downlink Orthogonal Frequency
Division Multiplex (OFDM) symbol in a downlink frequency band; and
determining an uplink allocation in an uplink OFDM symbol of an
uplink frequency band wherein the uplink frequency band is distinct
from the downlink frequency band and wherein the uplink OFDM symbol
includes a number of uplink subcarriers distinct from a number of
downlink subcarriers in the downlink OFDM symbol.
2. The method of claim 1, further comprising: remapping the uplink
allocation to a remapped allocation in a reduced uplink frequency
band that is narrower than the uplink frequency band; generating
the uplink OFDM symbol based on the remapped allocation; and
transmitting the uplink OFDM symbol.
3. A wireless apparatus with transmit emission control, the
apparatus comprising: a receiver configured to receive wireless
downlink signals in a downlink frequency band, the wireless signals
including a virtual uplink resource allocation; a channel index
remapper coupled to the receiver and configured to remap the
virtual uplink resource allocation to an uplink resource
allocation; a signal mapper configured to map uplink information to
a plurality of uplink subcarriers based on the uplink resource
allocation; and a transmitter configured to transmit the plurality
of uplink subcarriers in an uplink frequency band distinct from the
downlink frequency band.
4. The apparatus of claim 3, further comprising a filter configured
to filter a signal mapper output based on a bandwidth of the uplink
resource allocation, and couple a filtered uplink signal to the
transmitter.
5. The apparatus of claim 4, wherein the filter comprises a
programmable digital filter.
6. The apparatus of claim 4, wherein the filter comprises an analog
variable filter.
7. The apparatus of claim 4, further comprising a bandwidth
controller configured to vary a bandwidth of the filter based on
the uplink resource allocation.
8. The apparatus of claim 3, wherein the receiver is configured to
receive the wireless downlink signals during a downlink subframe
that is time division duplexed with an uplink subframe during which
the transmitter transmits the plurality of uplink subcarriers.
9. The apparatus of claim 3, wherein the receiver is configured to
receive the wireless downlink signals in a plurality of OFDM
symbols having a downlink subcarrier spacing that is substantially
the same as an uplink subcarrier spacing.
10. The apparatus of claim 9, wherein a number of downlink
subcarriers is the same as a number of subcarriers in a virtual
uplink bandwidth.
11. The apparatus of claim 9, wherein a number of downlink
subcarriers is the greater than a number of subcarriers in the
uplink frequency band.
12. The apparatus of claim 4, further comprising a local oscillator
(LO) and wherein the channel index remapper is configured to
program a LO frequency at a frequency offset from a nominal LO
frequency for a virtual uplink band, and remapping the virtual
uplink resource allocation based on the frequency offset.
13. A wireless apparatus with transmit emission control, the
apparatus comprising: a receiver configured to receive in a
downlink frequency band a plurality of downlink Orthogonal
Frequency Division Multiplex (OFDM) symbols including a virtual
uplink resource allocation; and a transmitter configured to
transmit a plurality of uplink OFDM symbols based on the virtual
uplink resource allocation and in an uplink frequency band distinct
from the downlink frequency band, wherein the uplink frequency band
has a second bandwidth distinct from a first bandwidth of the
downlink frequency band.
14. The apparatus of claim 13, wherein the second bandwidth is
narrower than the first bandwidth.
15. The apparatus of claim 13, wherein a downlink subcarrier
spacing is substantially identical to a virtual uplink subcarrier
spacing.
16. The apparatus of claim 13, wherein the receiver receives the
OFDM symbols in a downlink subframe that is time division duplexed
with an uplink subframe during which the transmitter is configured
to transmit.
17. The apparatus of claim 13, further comprising a channel index
remapper coupled to the receiver and configured to remap the
virtual uplink resource allocation to an uplink resource allocation
in the uplink frequency band.
18. The apparatus of claim 17, wherein the channel index remapper
remaps the virtual uplink resource allocation based in part on a
difference in a number of subcarriers in a virtual uplink frequency
band and a number of subcarriers in the uplink frequency band.
19. The apparatus of claim 13, further comprising: a local
oscillator (LO) common to the receiver and the transmitter; and a
LO controller configured to control a frequency of the LO based on
a time division duplexed transmit and receive timing.
20. The apparatus of claim 19, wherein the LO controller is further
configured to control a frequency of the LO based on a state of a
reduced emissions mode.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/114,701, filed May 2, 2008, now issued as U.S. Pat. No.
8,125,974 on Feb. 28, 2012, which is incorporated by reference as
if fully set forth.
FIELD OF INVENTION
[0002] The invention concerns methods, apparatus, and systems for
control and reduction of out of band transmit emissions from a
wireless transceiver operating in a wireless communication
system.
BACKGROUND
[0003] Wireless communication systems employ various techniques for
supporting two-way communications. For example, a wireless
communications system may support Time Division Duplex (TDD)
communications, where the same operating frequency band is time
multiplexed to support two-way communications. A wireless
communication system may support Frequency Division Duplex (FDD)
communications, where distinct frequency bands are used for the
distinct directions of the duplex communications.
[0004] A system designer may take several factors into account when
deciding on the manner in which duplex communications is to be
supported. In some systems, the manner of duplexing communications
is set forth in a standard or specification.
[0005] However, the duplexing configuration set forth in a standard
may pose design issues for optimizing communications within a given
frequency spectrum. For example, a wireless communication standard
may specify FDD operation in symmetric transmit and receive bands.
However, the actual frequency spectrum that is licensed by a
government entity may consist of two bands that may have different
bandwidths. The distinct bandwidths of the licensed bands make it
difficult to support the symmetric FDD operation specified in the
standard.
[0006] Additionally, one or more of the licensed bands may border a
band that is licensed to support some other type of communications.
There may be severe emissions constraints placed on transmitters
operating adjacent the band supporting other types of
communications. The emissions constraints may require a system
designer to implement a large guard band adjacent the other band
supporting other types of communications. In such situations,
symmetric FDD uplink and downlink bands may be licensed to a system
provider, but the effective usable bands may be asymmetric if the
large guard band is implemented in one of the licensed bands but
not another. Alternatively, the system capacity may be
unnecessarily limited if both the licensed uplink and downlink
bands implement the guard band, but only one of the uplink or
downlink bands is adjacent the band supporting other types of
communications.
[0007] A system designer may select from any one of several
duplexing implementations, but is constrained by spectrum
allocation, operating standards, and adjacent band emissions
constraints. The combination of design and operational constraints
may make it difficult to optimize system capacity across operating
bands.
SUMMARY
[0008] Methods and apparatus for control of undesirable transmit
emissions from a wireless transceiver are described herein. A
wireless transceiver can be configured to operate in multiple
frequency bands using frequency division duplex or hybrid frequency
division duplex, where a first operating band is designated for
receive signals and a second operating band is designated for
transmit signals. The bandwidths spanned by the first band and the
second band may be symmetric or asymmetric. Additionally, each of
the first band or the second band may be contiguous or may be an
aggregate of multiple discontinuous frequency bands.
[0009] The wireless transceiver can control undesirable transmit
emissions from occurring in a predetermined frequency band by using
an offset LO frequency and restricting transmit signals to
frequencies away from the predetermined frequency band.
Alternatively, in an asymmetric FDD system where a receive band is
larger than a transmit band, the transceiver can limit transmit
signal allocation to the transmit band. The transceiver can further
limit out of band transmit emissions using an offset LO
frequency.
[0010] Aspects of the invention include a method of transmit
emission control in a wireless transceiver. The method includes
receiving wireless downlink signals in a downlink frequency band,
determining a virtual uplink resource allocation within a virtual
uplink frequency band that is distinct from the downlink frequency
band and that has substantially a same bandwidth as the downlink
frequency band, remapping the virtual uplink resource allocation to
an uplink resource allocation in an uplink frequency band that is
narrower than the virtual uplink frequency band, and transmitting
an uplink signal on the uplink resource allocation.
[0011] Aspects of the invention include a method of transmit
emission control in a wireless transceiver. The method includes
receiving wireless downlink signals in a downlink frequency band,
where the downlink frequency band is distinct from an uplink
frequency band, determining an uplink resource allocation based on
a control message received in the downlink frequency band, the
uplink resource allocation restricted to a portion of the uplink
frequency band, remapping the uplink resource allocation based on a
frequency offset that is based in part on a difference between the
uplink bandwidth and the portion of the uplink frequency band over
which the uplink resource allocation is restricted, and
transmitting an uplink signal over the uplink bandwidth
allocation.
[0012] Aspects of the invention include a method of transmit
emission control in a wireless transceiver. The method includes
receiving wireless downlink signals in a downlink frequency band
having a first set of subcarriers, determining an uplink resource
allocation within an uplink frequency band that is distinct from
the downlink frequency band, and wherein the uplink frequency band
has a second set of subcarriers distinct from the first set of
subcarriers, and wherein the uplink frequency band has a second
bandwidth distinct from a first bandwidth of the downlink frequency
band, and transmitting an uplink signal in the uplink resource
allocation.
[0013] Aspects of the invention include a method of transmit
emission control in a wireless transceiver. The method includes
receiving a downlink Orthogonal Frequency Division Multiplex (OFDM)
symbol in a downlink frequency band, and determining an uplink
allocation in an uplink OFDM symbol of an uplink frequency band
where the uplink frequency band is distinct from the downlink
frequency band and where the uplink OFDM symbol includes a number
of uplink subcarriers distinct from a number of downlink
subcarriers in the downlink OFDM symbol.
[0014] Aspects of the invention include a wireless apparatus with
transmit emission control. The apparatus includes a receiver
configured to receive wireless downlink signals in a downlink
frequency band, the wireless signals including a virtual uplink
resource allocation, a channel index remapper coupled to the
receiver and configured to remap the virtual uplink resource
allocation to an uplink resource allocation, a signal mapper
configured to map uplink information to a plurality of uplink
subcarriers based on the uplink resource allocation, and a
transmitter configured to transmit the plurality of uplink
subcarriers in an uplink frequency band distinct from the downlink
frequency band.
[0015] Aspects of the invention include a wireless apparatus with
transmit emission control. The apparatus includes a receiver
configured to receive in a downlink frequency band a plurality of
downlink Orthogonal Frequency Division Multiplex (OFDM) symbols
including a virtual uplink resource allocation, and a transmitter
configured to transmit a plurality of uplink OFDM symbols based on
the virtual uplink resource allocation and in an uplink frequency
band distinct from the downlink frequency band, wherein the uplink
frequency band has a second bandwidth distinct from a first
bandwidth of the downlink frequency band.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The features, objects, and advantages of embodiments of the
disclosure will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings, in
which like elements bear like reference numerals.
[0017] FIG. 1 is a simplified functional block diagram of an
embodiment of a wireless communication system in a mixed signal
environment.
[0018] FIGS. 2A-2E are simplified spectrum diagrams.
[0019] FIGS. 3A-3C are simplified functional block diagrams of
embodiments of transceivers.
[0020] FIG. 4 is a simplified functional block diagram of an
embodiment of a transceiver.
[0021] FIG. 5 is a simplified functional block diagram of an
embodiment of a mode controller.
[0022] FIGS. 6A-6B are simplified spectrum diagrams for a FDD
system.
[0023] FIG. 7 is a simplified flowchart of a method of asymmetric
FDD operation.
[0024] FIG. 8 is a simplified functional block diagram of a method
of emission control in a FDD wireless device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Methods and apparatus for operating an asymmetric Frequency
Division Duplex (FDD) or Hybrid Frequency Division Duplex (H-FDD)
communication system are described herein. Additionally, methods
and apparatus for controlling transmit emissions in a symmetric or
asymmetric FDD or H-FDD communication system are described
herein.
[0026] As described herein, an H-FDD system is one in which
distinct downlink and uplink frequency bands are utilized as in a
FDD system. However, in an H-FDD system, the downlink and uplink
communications are also Time Division Multiplexed (TDM). In the
H-FDD system, a wireless communication device transmits and
receives frames in an uplink band that is distinct from a downlink
band, where a frame includes a downlink subframe and an uplink
subframe.
[0027] Although the descriptions provided herein are generally
presented in the context of an FDD system, the methods and
apparatus are applicable to an H-FDD system.
[0028] A wireless system operating in two distinct frequency bands
may designate a first frequency band as a downlink frequency band
and a second frequency band as an uplink frequency band. A
communications standard may specify symmetric downlink and uplink
frequency bands or may permit asymmetric downlink and uplink
frequency bands. Additionally, one of the downlink or uplink
frequency bands may be adjacent to a constrained emissions band.
The constraints imposed by the constrained emissions band may
greatly affect the ability of a wireless communication system to
utilize the entire downlink or uplink band.
[0029] The wireless communication system may communicate a greater
amount of information in one of the communication directions. For
example, a wireless communication system may support broadcast
channels in the downlink direction, where a broadcast channel is
not directed to any one destination device, but may be accessed
from any valid device in a broadcast region. A device receiving a
broadcast channel from a base station may have little to send in
uplink communications or may even be limited in the ability to send
uplink communications.
[0030] In a symmetric FDD system, the downlink capacity may be the
same as the uplink capacity, but the asymmetric nature of the
information communicated on the downlink and uplink may result in
the uplink band being lightly loaded, while the downlink band is
heavily loaded or otherwise operating near capacity. Typically, the
system specification in accordance with certain communication
standards, such as IEEE 802.16, may not support asymmetric downlink
and uplink bands.
[0031] However, the wireless communication system may be configured
to support a symmetric FDD standard while operating in an
asymmetric band allocation as described herein. An FDD wireless
communication system may operate with asymmetric downlink and
uplink bands. As an example, the downlink band may be wider than
the uplink band.
[0032] A wireless communication device may be configured to support
virtual symmetric FDD operating bands in one embodiment. In such an
embodiment, the wireless communication device supports a virtual
band that is substantially symmetric with the wider of the two FDD
bands. In the example described above, the wireless communication
device supports a virtual uplink band that is substantially
symmetric with the downlink band.
[0033] The wireless device can receive resource allocation in the
virtual uplink band and can remap the resource allocation to the
actual uplink band. The actual uplink band can be narrower than the
virtual uplink band, and the wireless device can remap the resource
allocation based on the difference in bandwidths. The wireless
device can then transmit the signal in the actual uplink band
effectively supporting the virtual resource allocation.
[0034] A resource allocator may be constrained to allocate
resources in the virtual uplink band that are supported in the
actual uplink band. That is, the resource allocator may be
constrained to not allocate any resources in the virtual uplink
band that are outside of the actual uplink band.
[0035] If the uplink band is positioned in the frequency spectrum
adjacent a constrained emissions band, regardless of symmetric or
asymmetric downlink and uplink bands, the wireless communication
device may offset its Local Oscillator (LO) in a direction away
from the constrained emissions band. The wireless communication
device may remap its resource allocations to reflect the LO offset.
The wireless communication device may reduce its emissions in the
constrained emissions band by utilizing a filter that is narrower
than would be acceptable in the absence of the LO offset.
[0036] The resource allocator may be constrained to allocate uplink
resources outside of a guard band that is positioned adjacent to
the constrained emissions band. The guard band may be a virtual
guard band, as the wireless communication device could receive
resource allocations in the virtual guard band and could support
communications in the virtual guard band in the absence of the
emissions restrictions imposed by operating adjacent to the
constrained emissions band.
[0037] The methods and apparatus for operating an asymmetric FDD,
an asymmetric H-FDD or an H-FDD system and controlling transmit
emissions are described herein in the context of an Orthogonal
Frequency Division Multiplex (OFDM) transceiver. The transceiver
can be configured, for example, to operate in accordance with a
predetermined wireless communication standard, such as IEEE
802.16e, Air Interface For Fixed Broadband Wireless Access Systems.
For example, the transceiver can be configured to operate in
accordance with the Wireless Metropolitan Area Network, Orthogonal
Frequency Division Multiple Access physical layer (WirelessMAN
OFDMA PHY) defined in the standard.
[0038] The methods and apparatus described herein are not limited
to application in an IEEE 802.16-complied transceiver, nor are the
methods and apparatus limited to application in an OFDM system. The
wireless communication system and implementations set forth herein
are provided as illustrative examples and are not to be construed
as limitations on the application of the methods and apparatus
described herein.
[0039] FIG. 1 is a simplified functional block diagram of an
embodiment of a wireless communication system 100 in a mixed signal
environment. The wireless communication system 100 operates in the
presence of another wireless communication system 102 operating in
a frequency spectrum in which emissions of the wireless
communication system 100 are constrained or otherwise limited. In
one embodiment, the operating band of the wireless communication
system 100 is adjacent the operating band of the wireless system
102, and the coverage areas, 112-1, 112-2, and 122, supported by
the respective systems at least partially overlap.
[0040] The wireless communication system 100 includes a first base
station 110-1 supporting a first corresponding service or coverage
area 112-1. The first base station 110-1 can be coupled to a
network 114, such as a wired network, and can be configured to
allow wireless communication with devices (not shown) in
communication with the network 114.
[0041] The first base station 110-1 can communicate with wireless
devices within its coverage area 112-1. For example, the first base
station 110-1 can wirelessly communicate with a first subscriber
station 130a and a second subscriber station 130b within the first
coverage area 112-1. In another example, the first subscriber
station 130a can communicate with a remote device (not shown) via
the first base station 110-1. In another example, the first
subscriber station 130a can communicate with the second subscriber
station 130b via the first base station 110-1.
[0042] The first base station 110-1 can be one of a plurality of
base stations that are part of the same wireless communication
system 100. The base station 110-1 can be in communication with one
or more other base stations, for example a second base station
110-2, either through a direct communication link or via an
intermediary network. The base stations 110-1 and 110-2
alternatively can be referred to as an access point or node.
[0043] The first base station 110-1 can be configured to support an
omni-directional coverage area or a sectored coverage area. For
example, the first base station 110-1 can support a sectored
coverage area 112-1 having three substantially equal sectors. The
first base station 110-1 treats each sector as effectively a
distinct coverage area. The number of sectors in the coverage area
112-1 is not a limitation on the operation of the methods and
apparatus described herein.
[0044] A second base station 110-2 supports a corresponding second
service or coverage area 112-2. The second base station 110-2 can
be configured to be substantially similar to the first base station
110-1.
[0045] In one embodiment, each of the base stations, e.g. 110-1 and
110-2, may support two types of access to multicast and broadcast
services. The two types of access may be termed single-BS access
and multi-BS access. In single BS access, a single base station,
e.g. 110-1, implements multicast and broadcast transport
connections. In multi-BS access, multiple base stations, e.g. 110-1
and 110-2 transmit time synchronized copies of the data.
[0046] An embodiment of multi-BS access described herein is
referred to as macro diversity. In this embodiment, each base
station, e.g. 110-1 and 110-2, is associated with a macro diversity
zone. Each base station, e.g. 110-1 and 110-2, associated with the
same macro diversity zone transmits identical multicast and
broadcast streams. The macro diversity zone can be identified using
a macro diversity identifier that is contained in the broadcast
streams. Because the broadcast and multicast streams may not be
directed to any particular subscriber station, e.g. 130a or 130b, a
single connection identifier (CID) can be used to identify the
aggregate broadcast stream.
[0047] Different CIDs may be used in different geographical regions
for the same broadcast streams. A multicast and broadcast zone
identifier can be used to indicate a region through which a
particular CID for a broadcast stream is valid. A subscriber
station, e.g. 130a, in an idle mode does not have to reconfigure
itself to receive the broadcast stream when it moves from the first
coverage area 112-1 to a second coverage area 112-2 in the same
macro diversity zone. However, if the subscriber station, e.g.
130a, moves, for example, into a different geographic region
supported by a different macro diversity zone having a different
macro diversity zone identifier, the subscriber station, e.g. 130a,
needs to re-establish reception of the new broadcast stream,
including upper layer stream parsing, so as to continue receiving
the desired broadcast service.
[0048] Macro diversity can enhance the reception, at the subscriber
station, of the broadcast stream. The base stations 110-1 and 110-2
associated with in the same macro diversity zone are synchronized.
In such case, each base station in the same macro diversity zone
transmits the same broadcast streams, using the same transmission
mechanism (symbol, subchannel, modulation, and etc.) at the same
time.
[0049] Synchronizing the broadcast streams across multiple base
stations 110-1 and 110-2 enables a subscriber station, e.g. 130a,
to receive the broadcast transmission from multiple base stations,
and thereby improves the reliability of reception.
[0050] The subscriber station 130a tuned to a macro diversity
broadcast stream need not be registered to any base station, e.g.
110-1. The lack of a registration requirement can allow for a
receive only mode of operation when a subscriber station, e.g.
130a, is out of range and cannot "close" the uplink, or in the case
where the subscriber station, e.g. 130a, has no transmitting
capabilities.
[0051] Although only two subscriber stations 130a and 130b are
shown in the wireless communication system 100, the system can be
configured to support virtually any number of subscriber stations.
The subscriber stations 130a and 130b can be mobile stations or
stationary stations. The subscriber stations 130a and 130b
alternatively can be referred to, for example, as mobile stations,
mobile units, or wireless terminals.
[0052] A mobile station can be, for example, a wireless handheld
device, a vehicle mounted portable device, or a relocatable
portable device. A mobile subscriber station can take the form of,
for example, a handheld computer, a notebook computer, a wireless
telephone, or some other type of mobile device.
[0053] In one example, the wireless communication system 100 is
configured for OFDM communications substantially in accordance with
a standard system specification, such as IEEE 802.16e or some other
wireless standard. The wireless communication system 100 can
support the methods and apparatus for reducing transmit emissions
described herein as an extension to the system standard or fully
compliant with the system standard.
[0054] Each base station, e.g. 110-1, is configured to transmit
data packets to the subscriber stations 130a and 130b organized in
frames using one or more slots. The term "downlink" is used to
refer to the direction of communication from the base station 110-1
to a subscriber station, e.g. 130a. Each slot can include a
predetermined number of OFDMA subcarriers, Orthogonal Frequency
Division Multiplex (OFDM) symbols, or a combination of subcarriers
and symbols.
[0055] Each base station 110-1 or 110-2 can supervise and control
the communications within its respective coverage area 112-1 or
112-2. Each active subscriber station, for example 130a, registers
with the base station, e.g. 110-1 upon entry into the coverage area
112-1. The subscriber station 130a can notify the base station
110-1 of its presence upon entry into the coverage area 112-1, and
the base station 110-1 can interrogate the subscriber station 130a
to determine the capabilities of the subscriber station 130a.
[0056] In a packet based wireless communication system 100, it may
be advantageous for the system to allocate resources as needed,
rather than maintaining an active channel assignment for each
subscriber station 130a or 130b having an established communication
session with the base station 110-1 or 110-2. The base stations
110-1 and 110-2 can allocate resources to the subscriber station
130a on an as needed basis. For example, in an OFDMA system, the
base station 110-1 or 110-2 can allocate time and frequency
resources to each subscriber station, e.g. 130a, when the
subscriber station 130a has information to send to the base station
110-1 or 110-2.
[0057] The communication link from the subscriber station 130a to
the base station 110-1 or 110-2 is typically referred to as the
"uplink." The base station, e.g. 110-1, can allocate uplink
resources to the subscriber station 130a to avoid collisions that
may occur if the subscriber stations 130a or 130b are allowed
random access to the resources. The base station 110-1 can allocate
the uplink resources in units of symbols and OFDMA subcarriers.
[0058] The wireless communication system 100 can also have the
ability to modify or otherwise dynamically select other parameters
related to the downlink and uplink communication links. For
example, the base stations 110-1 and 110-2 can determine a
modulation type and encoding rate from a plurality of modulation
types and encoding rates. The base stations 110-1 and 110-2 can be
configured to select from a predetermined number of modulation
types that can include Quadrature Phase Shift Keying (QPSK) and
various dimensions of Quadrature Amplitude Modulation (QAM), such
as 16-QAM and 64-QAM.
[0059] Each modulation type can have a limited number of available
encoding rates. For example, QPSK modulation can be associated with
rate 1/2 or rate 3/4 encoding, 16-QAM can be associated with rate
1/2 or rate 3/4 encoding, and 64-QAM can be associated with rate
1/2, rate 2/3, or rate 3/4 encoding. Thus, in this example, the
base station 110 can select a modulation type-encoding rate pair
from seven possible different types.
[0060] The base stations 110-1 and 110-2 can communicate the
modulation type-encoder rate pair to a subscriber station 130a or
130b in an overhead message. In one embodiment, the overhead
message can be a broadcast message that includes resource
allocation information. For example, the overhead message can
include the timing, modulation type-encoder rate pair, and slot
information allocated to each of the subscriber stations 130a and
130b in the current frame or one or more subsequent frames. The
base stations 110-1 and 110-2 can associate particular information
with a subscriber station identifier to allow the receiving
subscriber stations 130a and 130b to determine which resources are
allocated to them.
[0061] The base stations 110-1 and 110-2 can transmit the overhead
message using a predetermined modulation type and encoder rate,
such that the subscriber stations 130a and 130b know, a priori, how
to process the overhead message. For example, the base stations
110-1 and 110-2 can transmit the overhead messages using the lowest
data rate, that is, QPSK at rate 1/2.
[0062] In one embodiment, the base stations 110-1 and 110-2 are
configured to allocate uplink resources to the subscriber station
130a in accordance with the IEEE802.16 standard for OFDMA physical
layer communications. The base stations 110-1 and 110-2 send an
Uplink-Map (UL-MAP) in each frame, where a frame of information
spans a predetermined time.
[0063] In one embodiment, each frame time division multiplexes a
predetermined downlink time portion (downlink subframe) and a
predetermined uplink portion (uplink subframe) in a time division
duplex (TDD) fashion. In other embodiments, the uplink and downlink
time portions may occur during at least partially overlapping time
assignments, but may be separated in frequency in a frequency
division duplex (FDD) fashion. In another embodiment, termed H-FDD,
the uplink and downlink frequency bands are distinct, as in FDD,
and the uplink and downlink transmission times occur in exclusive
times.
[0064] In a TDD system, the base stations, e.g., 110-1 or 110-2,
and subscriber stations, e.g., 130a and 130b, alternate between
transmitting and receiving over the same operating frequencies. The
downlink and uplink periods are typically mutually exclusive to
minimize collisions and interference. In an FDD system, the base
stations 110-1 or 110-2 and subscriber stations 130a and 130b
transmit and receive signals over distinct uplink and downlink
operating frequencies. Uplink transmissions may occur concurrent
with downlink transmissions. In an H-FDD system, the base stations
110-1 or 110-2 and subscriber stations 130a and 130b alternate
between transmitting and receiving over the distinct uplink and
downlink operating frequencies.
[0065] Where the wireless communication system 100 is configured to
operate in accordance with the IEEE802.16 WirelessMAN OFDMA PHY,
the complete set of OFDMA subcarriers span substantially the entire
operating frequency band. The uplink resources assigned to a
particular subscriber station, e.g. 130a, may span substantially
the entire uplink frequency band or only a portion of the uplink
frequency band. As will be described in more detail below, the base
stations 110-1 and 110-2 can be configured to operate in a
predetermined mode in which the base stations 110-1 and 110-2
allocate uplink resources to subscriber stations 130a and 130b in
predetermined portions of the operating frequency band,
corresponding to a predetermined subset of OFDMA subcarriers.
Selective allocation of uplink resources, and in particular uplink
frequencies, permits limiting uplink allocations to a portion of an
actual uplink band that overlaps a virtual uplink band. Similarly,
selective allocation of uplink resources can substantially
contribute to the reduction of out of band emissions.
[0066] The wireless communication system 100 can operate in the
presence of a wireless system 102 supporting a corresponding
coverage area 122 that at least partially overlaps the coverage
areas 112-1 and 112-2 supported by the base stations 110-1 and
110-2. The wireless system 102 can operate over an operating
frequency band that is substantially adjacent the operating
frequency band of the wireless communication system 100. The
wireless system 102 may operate in a licensed or otherwise
regulated operating frequency band. The regulations or standards
applicable to the wireless system 102 may constrain the level of
emissions from sources outside the operating frequency band of the
wireless system 102. The regulations relating to operating in a
given spectrum may limit the level of permissible out of band
emissions.
[0067] Thus, the level of out of band emissions permitted of the
wireless communication system 100 may be constrained by the
regulations regarding allowable emissions in the adjacent operating
frequency band of the wireless system 102. The wireless
communication system 100 may be constrained to a permissible level
of out of band emissions for both the downlink and the uplink. The
out of band emission constraints can be the same for the downlink
and the uplink or can be different.
[0068] The base stations 110-1 and 110-2 and the subscriber
stations 130a and 130b may have differing abilities to comply with
an out of band emission constraint. The size and resources
available to the base stations 110-1 and 110-2 may allow for more
solutions than are available to a subscriber station, e.g. 130a,
that can be a mobile terminal. Thus, the solutions for satisfying a
particular out of band emission constraint may be different in the
base station, e.g. 110, and the subscriber stations 130a and 130b,
even if the downlink and uplink constraints are the same.
[0069] Each of the subscriber stations 130a and 130b is aware of
its respective downlink and uplink frequency bands. Furthermore,
each of the subscriber stations 130a and 130b is aware that it is
operating in a symmetric or asymmetric FDD or H-FDD system. In
systems that utilize symmetric uplink and downlink bands or in
systems that permit asymmetric operation, the subscriber stations
130a and 130b may receive uplink resource allocations directly from
the serving base station, e.g. 110-1. However, in systems that have
asymmetric uplink and downlink bands, but in which the operating
specification only supports uplink resource allocation in symmetric
uplink and downlink bands, the subscriber stations 130a and 130b
can implement virtual uplink bands that are substantially symmetric
with the downlink bands. The subscriber stations 130a and 130b can
receive uplink resource allocations indexed to the virtual uplink
band and can remap the resource allocation to a resource allocation
indexed to an actual uplink band. The base stations 110-1 and 110-2
can be configured to limit the uplink resource allocations to those
frequencies that occur in the actual uplink band.
[0070] In one embodiment, each of the subscriber stations 130a and
130b can determine its respective operating frequency band. The
subscriber stations 130a and 130b can also determine the base
station, e.g. 110-1, and corresponding coverage area 112-1 or
sector in which they are operating. Each subscriber station 130a
and 130b can individually determine whether to institute emission
reduction techniques based on the operating frequency, base station
110-1, and corresponding coverage area 112-1 or sector of a
coverage area.
[0071] For example, the first subscriber station 130a may determine
that it is operating within a frequency band within the sector of a
coverage area 112-1 of a base station 110-1. The first subscriber
station 130a may institute transmit emission reduction based on a
portion or a combination of this information. The first subscriber
station 130a may selectively institute enhanced transmit emission
reduction, because some or all of the emission reduction techniques
may result in reduced uplink bandwidth.
[0072] Similarly, the second subscriber station 130b may determine,
based on the operating frequency, sector of coverage area 112-1,
and base station 110-1, that it does not need to initiate enhanced
transmit emission reduction techniques. The second subscriber
station 130b can continue to operate using default transmit
emissions and the default emission reduction techniques.
[0073] The first subscriber station 130a limits its uplink
bandwidth in the enhanced emission reduction state. The base
stations 110-1 and 110-2 operate in a mode that restricts the
uplink bandwidth and associated uplink resources that can be
allocated to a subscriber station. The base stations 110-1 and
110-2 can be predetermined or otherwise controlled to limit the
amount of uplink bandwidth and corresponding portion of the uplink
operating band allocated to subscriber stations in the emission
reduction state. In embodiments where the base stations 110-1 and
110-2 do not control uplink resource allocation, the subscriber
station 130a may be configured to limit its uplink bandwidth and
portion of uplink operating band.
[0074] For example, the base stations 110-1 and 110-2 operating as
an IEEE 802.16 base station can be configured to operate the uplink
in an Adaptive Modulation and Coding (AMC) mode. In AMC mode, the
base stations 110-1 and 110-2 control an adjacent subcarrier
permutation scheme, where adjacent subcarriers are used to form
subchannels.
[0075] With the AMC permutation scheme, adjacent subcarriers are
assigned to a subchannel and the pilot and data subcarriers are
assigned fixed positions in the frequency domain within an OFDMA
symbol. The AMC permutation can be the same for both uplink and
downlink. When AMC permutation is used in a downlink or an uplink
subframe, the base stations 110-1 and 110-2 indicate the switch to
the AMC permutation zone by using a zone switch Information Element
(IE).
[0076] In one embodiment of an AMC permutation scheme, a set of
nine contiguous subcarriers within an OFDMA symbol is referred to
as a "bin." In each bin there is 1 pilot subcarrier and 8 data
subcarriers. A bin is a basic allocation unit both in downlink and
uplink to form an AMC subchannel.
[0077] An AMC subchannel consists of 6 contiguous bins, that may
span over multiple OFDMA symbols. An AMC subchannel of type N*M,
where N*M=6, refers to an AMC subchannel with N bins by M symbols.
The 802.16e OFDMA PHY defines 3 AMC subchannel types, i.e., 1*6,
2*3, and 3*2. All AMC subchannels in an AMC zone have the same type
of N*M, which is specified in a Zone Switch Information Element.
Depending on the AMC subchannel type (i.e., N*M), an AMC slot can
be 1 subchannel by 2, or 3, or 6 OFDMA symbols.
[0078] The AMC subcarrier allocation parameters are summarized in
Table 1.
TABLE-US-00001 TABLE 1 AMC Subcarrier Allocation Parameters
Parameters Values FFT size 128 512 1024 2048 Number of Guard 19 79
159 319 subcarriers Number of pilot 12 48 96 192 subcarriers Number
of data 96 384 768 1536 subcarriers Number of bins 12 48 96 192
Number of 12 48 96 192 subchannels of type 1 * 6 (i.e., over 6
symbols) Number of 6 24 48 96 subchannels of type 2 * 3 (i.e., over
3 symbols) Number of 4 16 32 64 subchannels of type 3 * 2 (i.e.,
over 2 symbols)
[0079] The base stations 110-1 or 110-2 operating in AMC mode can
be configured to limit the number and placement of bins that can be
allocated to the first subscriber station 130a. Thus, the base
station, e.g., 110-1 or 110-2, limits the available uplink
bandwidth and the subcarriers that may be allocated within that
bandwidth. The downlink bandwidth, from the base stations 110-1 and
110-2 to the first subscriber station 130a, need not be limited and
can span the entire downlink band. The downlink and uplink
bandwidths are not required to be symmetrical. If the base stations
110-1 and 110-2 operate with substantially full operating bandwidth
in the downlink and limited bandwidth in the uplink bandwidth, the
system is asymmetric.
[0080] The first subscriber station 130a can limit the baseband
bandwidth to a bandwidth that is sufficient to pass the reduced
uplink signal. The first subscriber station 130a can vary the
bandwidth dynamically, based on the uplink resource allocation
received from the base station or a maximum allocatable uplink
bandwidth in reduced emission mode. Because the uplink bandwidth is
less than the full operating bandwidth in reduced emission mode,
the first subscriber station 130a can be configured to set the
baseband bandwidth to less than the full operational bandwidth that
is available when not operating in reduced emissions mode.
[0081] The first subscriber station 130a can also be configured to
offset the uplink frequency translation in order to offset a center
frequency relative to the band edge nearest the emissions band of
interest. Thus, if the emissions band of interest is in a band
above the transmit band, the first subscriber station 130a can
offset the center frequency of the uplink signal down in frequency
and away from the emission band of interest. Alternatively, if the
emissions band of interest is below the transmit band, the first
subscriber station 130a can offset the center frequency of the
transmit signal up in frequency and away from the emission band of
interest.
[0082] The magnitude of the frequency offset is largely determined
by the allocated uplink bandwidth. Again, the first subscriber
station 130a can determine the magnitude of the frequency offset
dynamically based on the uplink allocation. Alternatively, the
first subscriber station 130a can determine the magnitude of the
frequency offset based on the maximum allocatable uplink bandwidth
in reduced emission mode. The magnitude of the frequency offset is
limited by the width of the transmit band. The magnitude of the
frequency offset should not exceed the offset that places the edge
of the uplink signal at the band edge.
[0083] The first subscriber station 130a can further limit the
magnitude of the frequency offset based on the uplink resources
allocated to it by the base station 110. The base station e.g.
110-1, may allocate particular OFDMA subcarriers, positioned at
particular frequencies in the uplink band. The first subscriber
station 130a may limit the magnitude of the frequency offset to an
offset that allows the first subscriber station 130a to perform
subcarrier remapping.
[0084] In subcarrier remapping, the first subscriber station 130a
remaps the uplink subcarrier indices allocated to it by the base
station 110 in order to compensate for the frequency offset
introduced local to the subscriber station. By utilizing subcarrier
remapping, the frequencies of the subcarriers allocated to the
first subscriber station 130a remain consistent with the indexing
scheme used by the base stations 110-1 and 110-2, even though the
first subscriber station 130a has shifted the center frequency of
the uplink signal. With subcarrier remapping, the base station has
no knowledge of various techniques utilized by the first subscriber
station 130a in supporting asymmetric FDD operation or in reducing
the transmit emissions. Therefore, the base stations 110-1 and
110-2 need not perform any additional signal processing, which may
require an extension to the system standard, in order to
communicate with a subscriber station operating in asymmetric FDD
bands or operating in reduced emissions mode.
[0085] FIG. 2A is a simplified spectrum diagram 200 illustrating an
embodiment of a transmit emission mask 202. The horizontal axis
denotes frequency, in terms of MHz, and the vertical axis denotes
power density, in terms of dBm/Hz. The spectrum diagram 200
illustrates permissible power densities in two distinct Wireless
Communication Services (WCS) operating bands, 210 and 220, that are
adjacent to a Digital Audio Radio Service (DARS) band 230.
[0086] The first and second WCS bands, 210 and 220, span the
frequencies from 2305-2320 MHz and 2345-2360 MHz, respectively. In
the United States, the first and second WCS bands 210 and 220
include four distinct frequency blocks, designated A-D. The A and B
frequency blocks are each paired frequency blocks, while the C and
D frequency blocks are unpaired. The A frequency block includes a
lower frequency portion 212 and an upper frequency portion 222. The
lower frequency portion of the A block 212 spans 2305-2310 MHz,
while the upper frequency portion of the A block 222 spans
2350-2355 MHz.
[0087] The B frequency block includes a lower frequency portion 214
and an upper frequency portion 224. The lower frequency portion of
the B block 214 spans 2310-2315 MHz and the upper frequency portion
of the B block 224 spans 2355-2360 MHz.
[0088] The C frequency block 216 includes 2315-2320 MHz and the D
frequency block 226 includes 2345-2350 MHz. The C frequency block
216 may be licensed separately from the D frequency block 226.
[0089] Because the A frequency blocks 212 and 222 as well as the B
frequency blocks 214 and 224 are symmetric about the DARS band 230,
licensing one or both of the A and B blocks results in symmetric
upper and lower bands. Similarly, if both the C band 216 and the D
band 226 are licensed, then symmetric upper and lower bands can be
maintained.
[0090] However, if only one of the C band 216 or D band 226 is
licensed in conjunction with the A and B blocks, then the upper and
lower frequency bands are asymmetric. For example, if the A and B
blocks are licensed with only the C block 216, the upper band has a
bandwidth of 10 MHz while the lower band has a bandwidth of 15 MHz.
Similarly, if the A and B blocks are licensed with only the D block
216, the upper band has a bandwidth of 15 MHz while the lower band
has a bandwidth of 10 MHz.
[0091] As an example, the upper band portion can correspond to a
downlink frequency band and the lower band portion can correspond
to an uplink frequency band in an FDD or H-FDD system. In
embodiments where the upper and lower bands are asymmetric, the
downlink band may be the band having the greater bandwidth and the
uplink band may be the band having the narrower bandwidth. The
uplink and downlink band designations are described as continuous
and separated by the DARS band 230. However, such a limitation is
not a requirement, and the uplink or downlink bands need not be
contiguous. Where non-contiguous bands are supported, the system
may implement asymmetric FDD or asymmetric H-FDD even when one or
both of the paired A or B blocks are licensed or if all A, B, C,
and D blocks are licensed.
[0092] In the situation where the upper and lower frequency blocks
are symmetric or where the operating specification permits
asymmetric FDD operation, a subscriber station need not configure a
virtual band and need not perform resource allocation remapping.
However, if the upper and lower frequency blocks are asymmetric,
and the operating specification does not support asymmetric FDD
operation, the subscriber station may implement a virtual band
combined with resource allocation remapping.
[0093] The transmit mask 202 is overlaid the frequency bands. As
can be seen, the upper band edge of the first WCS band 210 in the C
block 216 and the lower end of the second WCS band 220 in the D
block 226 are adjacent to the DARS band 230. The level of signal
rejection required at the WCS band edges of interest are nearly 70
dB. The C block 216 in the first WCS band 210 and the D block 226
in the second WCS band 220 are immediately adjacent the DARS band
230 and experience the greatest constraints on out of band
emissions due to the proximity to the DARS band 230. The emissions
requirement in the band 240 below the first WCS band 210 and in the
band 250 above the second WCS band 220 are not as onerous as the
emissions constraints in the DARS band 230.
[0094] Thus, subscriber stations transmitting in the A or B blocks
may not need to institute a reduced emissions mode, while
subscriber stations operating in the C or D blocks, 216 and 226
respectively, may be configured to support the reduced emissions
mode. Subscriber stations transmitting in the C block 216 of the
first WCS band 210 seek to limit out of band emissions above the
upper edge of the band, while subscriber stations operating in the
D block 226 of the second WCS band 220 seek to limit the out of
band emissions below the lower edge of the band.
[0095] Thus, the modes of operation may depend on the number and
position of the blocks licensed for use by a communication system.
The differing combinations of possibilities include symmetric or
asymmetric FDD bands with no reduced emission control and symmetric
or asymmetric FDD bands with reduced emission control.
[0096] For asymmetric FDD bands there is also the possibility of
asymmetric FDD band support in the system specification or the lack
of asymmetric FDD support in the system specification. Where
asymmetric FDD bands are supported in the system specification and
the system supports OFDM communications, the system specification
may permit an equal number of uplink and downlink subcarriers or a
distinct number of uplink and downlink subcarriers.
[0097] FIGS. 2B-2E are simplified spectrum diagrams of examples of
possible band allocations. FIG. 2B illustrates a simplified
spectrum diagram in which the A, B, C, and D bands are licensed.
The licensed spectrum in the first WCS band 210 has the same 15 MHz
bandwidth as the licensed spectrum in the second WCS band 220. A
wireless system can configure, for example, the first WCS band 210
as a downlink band and the second WCS band 220 as the uplink band.
The subscriber station can position its local oscillator (LO)
frequencies in substantially the center of each band. Thus, the
downlink LO 250 can be positioned at substantially the center of
the downlink band and the uplink LO 240 can be positioned at
substantially the center of the uplink band. The wireless system
can support symmetric FDD or H-FDD communications because the
downlink and uplink frequency bands have the same bandwidth.
[0098] FIG. 2C is a simplified spectrum diagram in which only the
A, B, and C bands are licensed. The wireless communication system
can configure, for example, the wider band for downlink
communications and can configure the narrower band for uplink
communications. In the spectrum of FIG. 2C, the lower A and B
bands, 212 and 214, along with the C band 216 can be configured to
support downlink communications, while the upper A and B bands, 222
and 224, can be configured to support uplink communications. The
wireless system can support asymmetric FDD or H-FDD communications
because the downlink and uplink frequency bands have different
bandwidths.
[0099] The subscriber station can be configured to position the
downlink LO 250 in substantially the center of the downlink band.
The subscriber station can configure an uplink LO 240 at
substantially a center of the actual uplink band 244. However, the
uplink resources allocated to the subscriber station may be
referenced to a virtual bandwidth 245. The virtual band 245
represents the spectrum that would have been available for uplink
communications had the D band 226 also been licensed. The virtual
band 245 has a bandwidth that is the same as the downlink
bandwidth.
[0100] The use of the virtual band 245 permits a wireless
communication system to support asymmetric FDD or H-FDD even where
the communication standard does not expressly support asymmetric
uplink and downlink frequency bands. The ability to support
asymmetric FDD bands may be advantageous in wireless communication
systems that span a geographic region where symmetric bands are
licensed for part of the geographic region and asymmetric bands are
licensed for other parts of the geographic region. In the example
illustrated in FIG. 2C, the upper WCS band includes the upper A and
B bands, 222 and 224, as well as the D band 226. The D band 226 may
be licensed for portions of the geographic regions in the wireless
communication system but may not be licensed for other portions of
the geographic regions in the wireless communication system.
[0101] The system can rely on the virtual bands to support
asymmetric FDD communications to minimize the expense and effort of
designing and configuring specialized base station equipment, which
may not conform to an operating standard, in the geographic regions
not having symmetric uplink and downlink bands. By utilizing a
virtual band, typically configured as a virtual uplink frequency
band, a base station always appears to operate over symmetric
uplink and downlink bands. The allocation of uplink resources can
be constrained through techniques that are provided for in the
operating standard. For example, an 802.16 base station may
restrict its uplink resource allocations based on AMC zones in
order to eliminate the possibility of the base station allocating
resources within a virtual band but outside of an actual band.
[0102] The base station can allocate uplink resources to the
subscriber station relative to the virtual band 245 and the
subscriber station can remap the resource allocations to the actual
uplink frequency band 244. For example, a wireless communication
system may support 1024 subcarriers in each of symmetric downlink
and uplink frequency bands. The subcarriers may be identified by an
index ranging from 0 through 1023, with the subcarrier having an
index of 0 being the lowest frequency subcarrier in the band. The
base station may allocate uplink resources to the subscriber
station by communicating to the subscriber station the indices of
the allocated subcarriers and times for which the subcarriers are
allocated.
[0103] The base station utilizes a subcarrier indexing that is
relative to the virtual band 245. The subcarrier indexing in the
base station resource allocation may be the same or different from
the subcarrier indexing implemented within the subscriber station
depending on the placement of the subscriber station uplink LO
240.
[0104] The subscriber station may determine a nominal LO 241 which
represents the LO frequency used by the subscriber station if
supporting the virtual band 245. The subscriber station may then
compare the frequencies of the nominal LO 241 against the uplink LO
240 to determine if the subcarrier indices in the resource
allocation need to be remapped. If the frequency of the nominal LO
241 is the same as the frequency of the uplink LO 240, the
subscriber station does not need to perform any subcarrier
remapping, and the subcarrier indexing used by the base station is
identical to the subcarrier indexing used by the subscriber station
in the actual uplink frequency band 244.
[0105] However, it may be advantageous for the subcarrier to have a
different frequency for the uplink LO 240 than the nominal LO 241
frequency. If the subscriber station positions the uplink LO 240 at
substantially the center of the actual uplink frequency band 244,
the subscriber station may use narrower baseband and RF filters
than if the nominal LO 241 frequency is used. Using a narrower
baseband filter, RF filter, or combination thereof enables the
subscriber station to further reduce out of band transmit
emissions.
[0106] In the example shown in FIG. 2C, the subscriber station can
implement an uplink LO 240 at substantially the center of the
uplink frequency band 244. The subscriber station can remap the
subcarrier indices in the resource allocations from the base
station to the subcarrier indexing in the subscriber station. The
subcarrier indexing can be remapped, for example, based on the
frequency difference between the nominal LO 241 and the uplink LO
240 and the subcarrier spacing.
[0107] FIG. 2D is a simplified spectrum diagram in which only the A
and D bands are licensed. The A band is licensed as a pair of
bands, Au and A.sub.L, 222 and 212 respectively. The wireless
communication system can implement downlink communications in the D
band 226 and upper A band 222. The wireless communication system
can implement uplink communications over the lower A band 212.
[0108] The subscriber station can implement a downlink LO 250
substantially at the center of the combination of the Au and D
bands, 222 and 226. The base station can allocate uplink resources
to the subscriber station indexed to a virtual band 245 and a
nominal LO 241 in the center of the virtual band 245. The
subscriber station can position the actual uplink LO 240 at
substantially the center of the uplink band 244, here the lower A
band 212. The subscriber station can remap the uplink resource
allocations to compensate for the difference in the frequencies of
the uplink LO 240 and nominal LO 241.
[0109] FIG. 2E is a simplified spectrum diagram in which only the B
and C bands are licensed. The B band is licensed as a pair of
bands, Bu and B.sub.L, 224 and 214 respectively. The wireless
communication system can implement downlink communications in the C
band 216 and lower B band 214. The wireless communication system
can implement uplink communications over the upper B band 224.
[0110] The subscriber station can implement a downlink LO 250
substantially at the center of the combination of the B.sub.L and C
bands, 214 and 216. The base station can allocate uplink resources
to the subscriber station indexed to a virtual band 245 and a
nominal LO 241 in the center of the virtual band 245. The
subscriber station can position the actual uplink LO 240 at
substantially the center of the uplink band 244, here the upper B
band 224. The subscriber station can remap the uplink resource
allocations to compensate for the difference in the frequencies of
the uplink LO 240 and nominal LO 241.
[0111] FIGS. 3A through 3C are simplified functional block diagrams
of embodiments of transceivers 300, 302, and 304 configured to
support FDD operation. The first transceiver embodiment 300 can be
configured to support H-FDD operation, while the second and third
transceiver embodiments 302 and 304 can be configured to support
full duplex FDD as well as H-FDD operations. Each of the
transceiver embodiments 300, 302, and 304 can be, for example, a
transceiver in a subscriber station of the system of FIG. 1
configured to operate in the spectrum of FIG. 2.
[0112] Each transceiver embodiment 300, 302, and 304 includes an
antenna 306 coupled to receive and transmit front end modules, 320
and 322 respectively, that are coupled to a baseband processor 340.
In one embodiment, compared with the first transceiver 300, the
second transceiver 302 additionally includes a mixer 334 and Local
Oscillator (LO) 336 to introduce the transmit/receive frequency
offset.
[0113] As shown in FIG. 3A, the first transceiver 300 includes an
antenna 306 through which the uplink and downlink signals are
communicated. The antenna 306 couples the downlink signals to a
transmit/receive (T/R) switch 310. The T/R switch 310 operates to
couple the downlink signals to the receiver portion of the
transceiver 300 during a downlink subframe and operates to couple
uplink signals from the transmitter portion of the transceiver 300
during an uplink subframe.
[0114] During the downlink portion or subframe, the T/R switch 310
couples the downlink signals to a receive RF front end 320. The
receive RF front end 320 can be configured, for example, to
amplify, frequency convert a desired signal to a baseband signal,
and filter the signal. The baseband signal is coupled to a receive
input of a baseband processor 340.
[0115] The receive input of the baseband processor 340 couples the
received baseband signal to an Analog to Digital Converter (ADC)
352 that converts the analog signal to a digital representation.
The output of the ADC 352 can be coupled to a transformation
module, such as Fast Fourier Transform (FFT) engine 354 that
operates to convert the received time domain samples of an OFDM
symbol to a corresponding frequency domain representation. The
sample period and integration time of the FFT engine 354 can be
configured, for example, based upon the downlink frequency
bandwidth, symbol rate, subcarrier spacing, as well as the number
of subcarriers distributed across the downlink band, or some other
parameter or combination of parameters.
[0116] The output of the FFT engine 354 can be coupled to a
channelizer 356 that can be configured to extract the subcarriers
from those symbols that are allocated to the particular transceiver
300. The output of the channelizer 356 can be coupled to a
destination module 358. The destination module 358 represents an
internal destination or output port to which received data may be
routed.
[0117] The uplink path is complementary to the downlink signal
path. A source module 362 of the base band processor 340, which may
represent an internal data source or an input port, generates or
otherwise couples uplink data to the baseband processor 340. The
source 362 couples the uplink data to an uplink channelizer 364
that operates to couple the uplink data to appropriate uplink
resources that are allocated to support the uplink
transmission.
[0118] The output of the uplink channelizer 364 is coupled to an
IFFT engine 366 that operates to transform the received frequency
domain subcarriers to a corresponding time domain OFDM symbol. The
uplink IFFT engine 366 may support the same bandwidth and number of
subcarriers as supported by the downlink FFT engine 356.
Alternatively, the uplink and downlink may support distinct numbers
and spacing of subcarriers. For example, the uplink and downlink
bandwidth may be substantially the same, but the uplink IFFT engine
366 may implement a 2048-point IFFT, while the downlink FFT engine
354 may implement a 1024-point FFT. In another example, the FFT
engine 354 and IFFT engine 366 may both implement the same size
transform, but the uplink bandwidth may be distinct from the
downlink bandwidth, resulting in distinct uplink and downlink
subcarrier spacing.
[0119] In asymmetric FDD configurations supported by a
corresponding system specification, the uplink FFT engine 366 may
support a number of subcarriers that span an uplink bandwidth that
is distinct from the downlink bandwidth that may comprise a
distinct number of subcarriers. Typically, in asymmetric FDD
configurations that emulate a symmetric FDD configuration, the
number of subcarriers and bandwidth of a virtual uplink bandwidth
can be equal to the number of subcarriers and bandwidth of the
downlink bandwidth, while the number of subcarriers in the actual
uplink band can be a subset of the number of downlink subcarriers.
However, the subcarrier frequency spacing in the uplink can be the
same as the subcarrier frequency spacing in the downlink.
[0120] The output of the uplink FFT engine 366 is coupled to a
Digital to Analog Converter (DAC) 368 that converts the digital
signal to an analog representation. The analog baseband signal is
coupled to a transmit front end 322, where the signal is frequency
translated to the desired frequency in the uplink band. The output
of the transmit front end 322 is coupled to the T/R switch 310 that
operates to couple the uplink signal to the antenna 306 during the
uplink subframe.
[0121] An LO 330 is coupled to a switch 332 or demultiplexer that
selectively couples the LO 330 to one of the receive front end 322
or transmit front end 322 so as to be synchronized to the state of
the T/R switch 310. The frequency of the LO 330 can be retuned to
reflect the different downlink and uplink bands. Additionally, the
frequency of the LO 330 can be tuned to reflect an LO offset
frequency that can be based on a guard band offset used to reduce
transmit emissions, a virtual uplink band offset, or a combination
of the two.
[0122] One embodiment of the second transceiver 302 is configured
similar to the above-descried embodiment of first transceiver 300.
As seen in FIG. 3B, the second transceiver additionally includes a
mixer 334 that couples the output of the baseband processor 340 to
the transmit front end 322. The mixer 334 is driven by an offset LO
336. The inclusion of the offset LO 336 permits full duplex
operation. The frequency of the offset LO 336 can be based on a
guard band offset used to reduce transmit emissions, a virtual
uplink band offset, or a combination of the two.
[0123] In the second transceiver 302, as shown in FIG. 3B, the LO
330 can operate to drive the receive front end 320 and transmit
front end 322 concurrently. A duplexer 312 is configured to
concurrently couple the antenna 304 to the receive front end 320
and the transmit front end 322. The duplexer 312 operates to
isolate the receive front end 320 from the transmit front end 322
to permit concurrent operation.
[0124] The third transceiver 304 embodiment is configured similar
to the second transceiver 302 embodiment. The third transceiver 304
permits full duplex operation by implementing independent downlink
LO 330 and uplink LO 332 instead of utilizing an offset LO. The
interface to the duplexer 312 and baseband processor 340 are
otherwise the same as in the first and second transceiver
embodiments, 300 and 302, respectively.
[0125] FIG. 4 is a simplified function block diagram of an
embodiment of a transceiver 400. The transceiver 400 can be
configured to emulate symmetric FDD bands when supporting
asymmetric FDD bands. The transceiver 400 can also be configured or
selectively controlled to operate in a reduced emission mode.
[0126] The transceiver 400 can be implemented in the wireless
communication system of FIG. 1, and more specifically, in a base
station or one or more subscriber stations illustrated in FIG. 1.
The transceiver 400 described below is described in the context of
a subscriber station operating in an IEEE802.16-complied wireless
communication system, but the described techniques for emulating
symmetric FDD operation and reducing out of band emissions are not
limited to application in a subscriber station nor are they limited
to application in an IEEE802.16-complied wireless communication
system.
[0127] The transceiver 400 includes a transmitter portion 401 and a
receiver 480 coupled to an antenna 470. In an embodiment, the
transmitter portion 401 and the receiver 480 operate in a Frequency
Division Duplex (FDD) manner, in which the transmitter portion 401
and the receiver 480 use distinct frequency bands. Or in an
alternative embodiment, the transmitter portion 401 and the
receiver 480 operate in a Hybrid-FDD (H-FDD) manner, in which the
transmitter portion 401 and the receiver 480 use distinct frequency
bands and a transmit period occurs in a time period distinct from a
receive period.
[0128] Although FIG. 4 depicts each data stream in transceiver 400
with a single communication path, some of the communication paths
may represent complex data, and a signal path for complex data may
be implemented using a plurality of communication paths. For
example, a complex communication path can include a first
communication line to communicate the real part or in-phase
component of the complex data and a second complex communication
line to communicate the imaginary part or quadrature component of
the complex data. Similarly, in a polar representation of complex
data, a first communication line can be used to communicate a
magnitude of the complex data and a second communication line can
be used to communicate a corresponding phase of the complex
data.
[0129] The transmitter portion 401 includes a data source 402 that
is configured to generate or receive data or information that is to
be transmitted to a destination at or via a base station. The data
source 402 can generate data internal to a subscriber station such
as internal performance metrics. Alternatively, the data source 402
can be configured to accept data or other information from a an
external source, via an input port or some other data
interface.
[0130] In the embodiment of FIG. 4, the data output from the data
source 402 is a stream of data in digital format. The data source
402 can be configured to receive or otherwise generate the digital
data format. In embodiments where the data source 402 receives one
or more analog signals, the data source 402 can include an Analog
to Digital Converter (ADC) (not shown) to convert the signals to a
digital format.
[0131] The output of the data source 402 is coupled to an encoder
404 that can be configured to encode the uplink data according to a
specified encoding rate and type. For example, a base station can
allocate uplink resources to the transceiver 400 and can specify a
type of encoding and corresponding encoding rate from a set of
encoding rates and types. In other embodiments, the encoder 404 is
configured to perform a predetermined encoding function.
[0132] The encoder 404 can be configured to perform, for example,
block interleaving, block coding, convolutional coding, turbo
coding, and the like, or some combination of coding types.
Additionally, for each coding type, the encoder 404 may have the
ability to encode the data at any one of a plurality of encoding
rates.
[0133] The output of the encoder 404 is coupled to a modulator 406
that can be configured to modulate the encoded data according to
one of a plurality of modulation types. As described above, the
base station can specify a modulation type in addition to
specifying the encoding rate. The modulation type can be selected
from the list including QPSK, QAM, 16-QAM, 64-QAM, and the like, or
some other modulation type. In other embodiments, the modulator 406
is configured to modulate the encoded data according to a fixed
modulation type.
[0134] The output of the modulator 406 is coupled to a serial to
parallel converter 410. In one embodiment, the serial to parallel
converter 410 can be controlled to generate a number of parallel
paths determined partially by the number of available subcarriers
of an OFDM system that can be used to carry information.
[0135] The output of the serial to parallel converter 410 is
coupled to a signal mapper 412. The signal mapper 412 is configured
to selectively map the parallel signals to the subcarriers
allocated to the transceiver 400 by the base station. The signal
mapper 412 can be configured to map the parallel signals or data to
any one of a plurality of subcarrier sets. For example, the
transceiver 400 can be selectively controlled to support generation
of an OFDM symbol having up to 128, 512, 1024, 2048, or some other
selectable number of subcarriers.
[0136] The transceiver 400 receives the dimension of the
subcarriers in a control message and can configure the signal
mapper 412 to map the data to the subcarriers allocated by the base
station. The signal mapper 412 can be configured to determine the
subcarrier mapping based on various factors such as control
signals, messages, or levels provided by a mode controller 490. In
some embodiments, the functions of the encoder 404, serial to
parallel converter 410, and signal mapper 412 can be combined in
the signal mapper 412, and a distinct encoder 404 and serial to
parallel converter 410 can be omitted.
[0137] The signal mapper 412 can also include a DC null module 413
or otherwise be configured to null a particular subcarrier within
the OFDM symbol. The position of the subcarrier corresponding to
the DC subcarrier can be determined, based in part on one or more
control signals, and can depend at least in part on a subcarrier
remapping that occurs as a result of a frequency offset introduced
into a LO frequency. The DC null module 413 can be configured, for
example, to null, omit, or otherwise attenuate any symbols, bits,
or sample values that would otherwise map to or modulate a DC
subcarrier.
[0138] The DC null module 413 may operate to null or otherwise
disable a subcarrier in the virtual band index that maps to the DC
subcarrier in the uplink frequency band. The effect of this DC null
operation may be that some uplink information is deleted and not
transmitted in the uplink resource allocation. However, because the
encoder 404 may implement forward error correction and block
interleaving, the information omitted from the uplink transmission
may be successfully recovered at the destination despite its
removal by the DC null module 413.
[0139] The DC null module 413 is illustrated as implemented within
the signal mapper 412. However, other embodiments can introduce the
DC null module 413 within some other position in the signal path.
For example, the DC null module 413 may be implemented within a
subsequent DFT (Discrete Fourier Transform) transform module 414,
in an RF signal path, in some other signal processing module, or in
a combination of signal processing modules.
[0140] The output of the signal mapper 412 is coupled to the
transform module 414. The transform module 414 can be configured to
generate an OFDM symbol based on the parallel inputs. The transform
module 414 can be configured, for example, to perform a Discrete
Fourier Transform (DFT), Fast Fourier Transform (FFT), Inverse Fast
Fourier Transform (IFFT) and the like, or some other transform
configured to generate the desired symbol.
[0141] The output of the transform module 414 is coupled to a
parallel to serial converter 416 that is configured to generate a
serial data stream from the parallel output of the transform module
414. The serial signal stream from the parallel to serial converter
416 is coupled to a windowing module 420 that is configured to
perform windowing or filtering of the serial signal stream. The
windowing module 420 can implement a window response that is
controllable. In one embodiment, the windowing module 420 can be
configured as a digital filter having a programmable bandwidth and
response. The output of the windowing module is coupled to a
digital filter 422, whose bandwidth may be programmable. The
bandwidth of the digital filter can be dynamically scaled based on
the transmit data bandwidth or spatial bandwidth. For example, the
digital filter 422 can be configured as a low pass filter, and the
bandwidth of the filter may be determined based on the transmit
data bandwidth or the uplink subcarrier allocation.
[0142] The output of the digital filter 422 is coupled to a Digital
to Analog Converter (DAC) 430. The DAC 430 converts the digital
signal stream to an analog signal stream. The analog output from
the DAC 430 is coupled to a variable gain amplifier (VGA) 432. The
gain of the VGA 432 can be controlled by the mode controller 490
that can include a portion that operates on a feedback power
control signal.
[0143] The output of the VGA 432 is coupled to a variable filter
440. The bandwidth of the variable filter 440 is controlled by the
mode controller 490, and is controlled to reduce transmit emissions
when the transceiver 400 operates in reduced emissions mode. The
variable filter 440 is typically implemented as a low pass filter
that operates on a baseband signal output from the VGA 432.
However, the actual configuration of the variable filter 440 can be
based on the spectrum of the signal from the VGA 432. In some
embodiments, the variable filter 440 can be implemented as a band
pass filter (BPF) or complex LPF or complex BPF.
[0144] The filtered output from the variable filter 440 is coupled
to an optional intermediate frequency conversion stage. The
optional intermediate frequency conversion stage includes a
frequency converter, shown as a first mixer 450 in the embodiment
of FIG. 4. The frequency converter is not limited to a mixer 450,
but can be some other type of frequency converter, such as a
multiplier, upsampler, modulator, and the like, or some other
manner of frequency conversion.
[0145] In the embodiment shown in FIG. 4, the output of the
variable filter 440 is coupled to an Intermediate Frequency (IF)
port of the first mixer 450. A signal from a controllable Local
Oscillator (LO) 452 drives a LO port of the first mixer 450. The
signal is frequency converted to an Intermediate Frequency (IF)
band or a Radio Frequency (RF) band. The mixer 450 can be
configured to generate a Single Side Band (SSB) version of the
input signal. The mixer 450 can be configured to output an upper
side band or a lower side band signal.
[0146] In an alternative embodiment, the first mixer 450 is
configured to directly modulate a complex signal from the variable
filter 440 onto the output signal from the LO 452. The resulted
output from the first mixer 450 is a frequency converted version of
the complex signal with a center frequency approximately equal to
the frequency of the LO 452. In such an embodiment, the first mixer
450 can include an in-phase mixer configured to frequency convert
an in-phase (I) signal component and a quadrature mixer configured
to frequency convert a quadrature (Q) signal component. The output
of the in-phase and quadrature mixers are combined, for example
using a signal summer.
[0147] The first mixer 450 can also include a splitter configured
to split or otherwise divide the LO signal into two signals. The
first mixer 450 can include a phase shifter to phase shift a first
of the LO signals by substantially 90 degrees relative to the
second of the LO signal. The first and second LO signals are
coupled to the LO input of the in-phase and quadrature mixers,
respectively.
[0148] The phases of the LO signals and the phases of the complex
signal components may correspond or may be complementary. That is,
the quadrature signal component may be upconverted using either the
quadrature LO signal or the in-phase LO signal. The in-phase signal
component is then upconverted with the LO signal that is not used
for the quadrature signal component.
[0149] The mode controller 490 controls the frequency of the LO
452. As will be discussed in further detail below, the frequency of
the LO 452 can be offset from a default frequency based on whether
the transceiver 400 emulates symmetric FDD operation or whether the
transceiver 400 is configured to operate in the reduced emissions
mode.
[0150] The upconverted signal from the mixer 450 is coupled to a
power amplifier 460 that is configured to amplify the transmit
signal to the desired output power. The power amplifier 460 can be
configured with a fixed gain or with a variable gain. The output of
the power amplifier 460 is coupled to a second mixer 464 that
operates to frequency translate the signal to the desired output
frequency.
[0151] An RF LO 468 used to drive the second mixer 464 to upconvert
the uplink signals. The RF LO 468 can be, for example, a fixed
frequency LO or a variable frequency LO. The output of the second
mixer 464 is coupled to an RF filter 462 that operates to minimize
undesired products that may be generated by the second mixer 464 or
power amplifier 460. The bandwidth of the RF filter 462 can be
fixed or can be variable.
[0152] In one embodiment, the bandwidth of the RF filter 462 is
fixed to a bandwidth that is less than a bandwidth of a transmit
operating band. For example, the bandwidth of the RF filter 462 can
be fixed to approximately 1/4, 1/3, 1/2, 2/3, 3/4 or some other
fraction of the bandwidth of the uplink frequency band. In another
embodiment, the bandwidth of the RF filter 462 is controlled by the
mode controller 490. The filtered output is coupled to the antenna
470 for transmission to a base station or other destination.
[0153] In an alternative embodiment, the intermediate frequency
conversion stage can be omitted, and the output from the variable
filter 440 is coupled to the input of the power amplifier 460. The
output of the power amplifier 460 is coupled to the second mixer
464 that operates in conjunction with the RF LO 468 to frequency
translate the signal to the desired output frequency. When the
intermediate frequency conversion stage is omitted, the second
mixer 464 in conjunction with the RF LO 468 operate to direct
convert the uplink signal to the desired operating frequency. The
position of the power amplifier 460 and second mixer 464 may also
be reversed to minimize losses from the power amplifier 460 to the
antenna 470.
[0154] In yet another embodiment, the intermediate frequency
conversion stage operates to direct convert the uplink signals to
the uplink operating frequency. In this embodiment, the second
mixer 464 and RF LO 468 may be omitted.
[0155] The downlink signals from the antenna 470 are coupled to the
receiver 480. The receiver 480 uses a downlink LO 482 to frequency
convert the received signals to baseband signals. The received
signals, and in particular, received mode control signals can be
coupled to the mode controller 490 to control the LO frequencies
and filter bandwidths, as necessary.
[0156] The transceiver 400 can be configured with a fixed uplink
frequency band and associated bandwidth or a dynamically allocated
uplink frequency band and associated bandwidth. In a system
supporting a dynamically allocated uplink, the transceiver 400 can
receive the uplink resource allocation in a predetermined downlink
packet, message, block or channel. For example, a transceiver 400
operating in an IEEE802.16e wireless system receives uplink
resource allocation in an Uplink-Map transmitted in a downlink
frame or during a downlink subframe portion of a frame.
[0157] In some embodiments, the transceiver 400 is configured to
continually emulate symmetric FDD operation and is configured to
operate in a reduced emission mode. In other embodiments, the
transceiver 400 can selectively transition FDD emulation, reduced
emission mode, or some combination of the two.
[0158] In a default operating mode or condition in which the
transceiver 400 is not configured for reduced transmit emissions,
the transceiver 400 can be allocated uplink resources spanning
substantially the entire actual uplink band.
[0159] In one embodiment, the transceiver 400 can selectively
control a transition into symmetric FDD emulation mode. The
transceiver 400 can transition modes or operating states based in
part on information received in the downlink. For example, the
transceiver 400 can transition to the symmetric FDD emulation mode
based on a transition to a base station coverage region that
includes asymmetric uplink and downlink bands, but requires
symmetric FDD operation. The transceiver 400 may receive such
indication, for example, in a registration message or a handoff
message.
[0160] In another embodiment, the transceiver 400 can selectively
control a transition into a reduced emissions mode. The transceiver
400 can transition modes or operating states based in part on
information received in the downlink. For example, the transceiver
400 can transition to the reduced emissions mode based on an
indication from the base station. Alternatively, the transceiver
400 can transition to the reduced emission mode based on a desired
operating frequency band. For example, the transceiver 400 can
operate in a reduced emissions mode any time when the uplink
frequency band is either the C block or D block WCS bands. In other
embodiments, the transceiver 400 can transition to the reduced
emissions mode based on some other parameter or combination of
parameters.
[0161] In one embodiment, the base station allocating uplink
resources operates in a predetermined state where the transceiver
400 is operating FDD emulation or in the reduced emissions mode. In
one embodiment, an IEEE802.16e OFDMA PHY base station allocating
uplink resources operates in AMC mode.
[0162] For symmetric FDD emulation mode, the base station restricts
the uplink resource allocations to those portions of the virtual
uplink band that correspond to an actual uplink band. For reduced
emissions mode, the base station restricts the uplink bandwidth to
a portion of the available uplink bandwidth.
[0163] The base station can limit or otherwise restrict the uplink
bandwidth by restricting which of the subcarriers to allocate to
subscriber stations for uplink transmissions. The number and
placement of the subcarriers can vary based on a variety of
factors, including the portion of the virtual uplink band occupied
by the actual uplink band, the location of the emissions band of
interest and the total number of allocatable subcarriers.
[0164] The base station can limit the uplink bandwidth to a
fraction of the total available operating bandwidth. For example,
the base station can limit the uplink bandwidth to approximately
3/4, 2/3, 1/2, 1/3, or 1/4 of the full operating bandwidth. In
other embodiments, the base station can limit the uplink bandwidth
to some other fraction of the virtual bandwidth or operating
bandwidth.
[0165] In reduced emissions mode, the base station can restrict the
usable uplink band to the portion of the operating band furthest
from the emission band of interest. Thus, where the emissions band
of interest is higher or greater than the operating band, such as
the case of the DARS band in relation to the WCS C block, the base
station may limit the uplink band to the portion of the operating
band at the lower end of the C block. Conversely, where the
emissions band of interest is lower than the operating band, such
as the case of the DARS band in relation to the WCS D block, the
base station may limit the uplink band to the portion of the
operating band at the higher end of the D block. Of course, the
base station is not limited to any particular offset of the uplink
band, and the offset can be fixed or programmable.
[0166] The transceiver 400 receives uplink resource allocations in
the same manner regardless of whether the transceiver 400 is
operating in symmetric FDD emulation mode, in reduced emissions
mode, in a combination of symmetric FDD emulation and reduced
emissions modes, or in a default, standard mode. For example, the
receiver 480 receives a UL-MAP in the downlink frame or downlink
subframe that allocates uplink resources to the transceiver 400
regardless of operating modes.
[0167] However, the transceiver 400 processes the uplink signals
differently when in symmetric FDD emulation mode, in reduced
emissions mode, or in a combination of symmetric FDD and reduced
emissions modes. The transceiver 400 can perform a number of
functions, either alone or in combination, based on the operating
mode or combination of operating modes. For example, the mode
controller 490 controls the bandwidth of the variable filter 440 to
a reduced bandwidth in reduced emissions mode. The mode controller
490 also controls the offset of the frequency of the LO 482 from
the frequency used in the standard mode based on whether symmetric
FDD emulation mode is active and/or whether reduced emissions mode
is active. The mode controller 490 can also control the remapping
of the subcarriers to maintain the position of the allocated
subcarriers. The mode controller 490 can perform a first remapping
based on the symmetric FDD emulation mode and can perform a second
remapping based on a reduced emissions mode. The mode controller
490 can be configured to apply the first and second remapping
independently or in combination, depending on the mode of the
transceiver 400.
[0168] FIG. 5 is a simplified functional block diagram of an
embodiment of a mode controller 490 for a transceiver. The mode
controller 490 can be implemented in the transceiver embodiment of
FIG. 4 to control the signal bandwidth, LO frequency offset, and
subcarrier remapping to support one or both of symmetric FDD
emulation or reduced emissions mode.
[0169] The mode controller 490 includes a processor 510 coupled to
memory 512 or some other processor readable storage media. The
processor 510 can operate in conjunction with one or more
instructions and data stored in the memory 512 to configure the
portions of the mode controller 490 that control each parameter
varied when transitioning or operating a transceiver in reduced
emissions mode.
[0170] The processor 510 is coupled to a plurality of control
modules, each of which is configured to control one parameter that
is varied during the transition or operation of the transceiver in
reduced emissions mode. The processor 510 is coupled to an LO
controller 520, a bandwidth controller 530, and a channel index
remapper 540. Although each of the modules is depicted as a
distinct module, other embodiments may integrate some or all of the
functions of one or more of the modules in another module. Other
embodiments may eliminate some of the control modules.
[0171] The processor 510 is configured to receive the uplink
resource allocation from a receiver (not shown). The processor 510
can determine from the uplink resource allocation or from some
other information, whether to transition to one or both of a
symmetric FDD emulation mode, a reduced emissions mode, or a
combination thereof. In some embodiments, the transceiver may
always operate in one or both of the symmetric FDD emulation mode
and reduced emissions mode, in which the processor 510 need not
determine a transition to one or both modes. The processor 510
configures the various control modules to provide uplink signals
over the allocated uplink resources.
[0172] The LO controller 520 is configured to offset the LO
frequency relative to an operating frequency in the absence of
symmetric FDD operation or reduced emissions mode. To support
symmetric FDD emulation mode, the LO controller 520 can be
configured to control the LO frequency based on a difference
between a bandwidth of a virtual uplink band and an actual uplink
band. To support reduced emissions mode, the LO controller 520
operates the LO based on a frequency offset of a center frequency
of transmit signal relative to an uplink band center frequency.
[0173] The LO controller 520 can be, for example, a frequency
synthesizer that controls an output frequency of a Voltage
Controlled Oscillator (VCO). The LO controller 520 can receive from
the processor 510 information or a control signal indicative of a
desired frequency and can control the output frequency of a LO
based on the information or control signal. In other embodiments,
the LO controller 520 can be a Numerically Controlled Oscillator
(NCO) or clock generator for an NCO, and the output signal or clock
rate can be varied by the processor to control the output frequency
of a LO. The LO controller 520 can have other implementations in
other embodiments, depending on the manner in which the LO signal
is generated.
[0174] The direction of the frequency offset is determined at least
in part on the position of the actual uplink band relative to the
virtual uplink band and the position of the emissions band of
interest relative to the uplink band. The LO controller 520 can be
configured to offset the frequency of the LO by the difference
between the center frequencies of the virtual uplink band and the
actual uplink band. In reduced emissions mode, the LO controller
520 operates to offset the LO frequency, and thus a center
frequency of the transmit signal, in a direction that positions the
transmit signal further away from the emission band of interest.
The position of the emission band of interest may be known by the
processor 510 by accessing relevant information in the memory 512.
In other embodiments, the location of the emissions band of
interest may be received in a control message from the
receiver.
[0175] The magnitude of the frequency offset introduced by the LO
controller 520 can be fixed or dynamically determined for each of
the symmetric FDD emulation mode or reduced emissions mode. The
magnitude of the LO offset for the symmetric FDD emulation mode is
the magnitude of the difference between the center frequencies of
the virtual uplink band and the actual uplink band.
[0176] The magnitude of the LO offset for the reduced emissions
mode can be predetermined to be a frequency offset that places the
edge of the transmit signal having the maximum allocatable
bandwidth at the edge of the operating band. The transmit signal
can have a bandwidth that is less than the full operational
bandwidth, for example, one-half of the available bandwidth.
[0177] In the situation where the magnitude of the frequency offset
introduced by the LO controller 520 is dynamic and selectable, the
magnitude can be determined based in part on the uplink resource
allocation. In one embodiment, the LO controller 520 can be
configured to maximize the magnitude of the frequency offset. In
such an embodiment, the LO controller 520 controls the magnitude of
the offset to place the edge of the transmit signal at the edge of
the operating band. The LO controller 520 increases the magnitude
of the frequency offset as the bandwidth allocated for transmit
signals decreases. Conversely, the LO controller 520 decreases the
magnitude of the frequency offset as the bandwidth allocated for
the transmit signal increases. The LO controller 520 can be
configured to implement the frequency offset in fixed increments,
and each increment can correspond to an OFDM subcarrier
spacing.
[0178] The bandwidth controller 530 can reduce the bandwidth of the
transmit signal relative to a standard or default bandwidth when
the transceiver operates in reduced emissions mode. The bandwidth
controller 530 can reduce the bandwidth of a baseband filter, IF
filter, RF filter, or some combination thereof.
[0179] The bandwidth controller 530 can vary the component values
of an analog filter, the tap values or tap lengths of a digital
filter, or perform some other parameter control that is related to
bandwidth control. In one embodiment, the bandwidth controller 530
is configured to vary the values of one or more varactors in an
analog filter.
[0180] The bandwidth controller 530 can reduce the bandwidth of a
filter by a fixed amount or a variable amount. For example, the
bandwidth controller 530 can reduce the bandwidth of a baseband low
pass filter to a bandwidth that is based on a maximum transmit
bandwidth in the reduced emissions mode. For example, where the
transmit signal in reduced emissions mode is a maximum of one-half
the operational band, the bandwidth controller 530 can be
configured to reduce the passband of a baseband low pass filter to
approximately one-half the operational bandwidth.
[0181] In a situation where the bandwidth is controlled dynamically
in the reduced emissions mode, the bandwidth controller 530 can be
configured to reduce the bandwidth of a baseband low pass filter to
the bandwidth of the signal allocated by the base station in the
uplink resource allocation messages. In such an embodiment, the
bandwidth controller 530 can adjust the bandwidth at a rate that
coincides with the rate of the uplink resource allocations, such as
every frame.
[0182] The bandwidth controller 530 reduces the signal bandwidth in
the reduced emissions mode to a bandwidth that is less than the
signal bandwidth needed to pass a transmit signal occupying
substantially the full operating band. Thus, the transmit signal
bandwidth in the reduced emissions mode is typically less than the
bandwidth of a transceiver operating in a standard non-reduced
emissions mode.
[0183] The reduced bandwidth results in reduced out of band
emissions. For example, a reduced bandwidth in an analog baseband
filter following the DAC reduces the undesired products output by
the DAC including out of band DAC noise. In another example, a
reduced RF bandwidth in an analog RF output filter can reduce the
level of out of band emissions, and particularly, the level of any
out of band higher order distortion products generated in the final
power amplifier stage.
[0184] The channel index remapper 540 operates to remap the indices
of the allocated uplink subcarriers to compensate for the LO
frequency offset. By remapping the indices of the allocated
subcarriers, the transmitter can maintain the position of the
allocated subcarriers in the presence of LO offset.
[0185] For example, the base station can allocate uplink
subcarriers by referencing an index that identifies the subcarrier
in a particular OFDM symbol format. The channel index remapper 540
can receive the indices of the allocated subcarriers from the
processor 510 and can remap the subcarrier indices to compensate
for the LO offset. The channel index remapper 540 supplies the
remapped channel indices to a signal mapper used in the DFT portion
of the transmitter, and the signal mapper need not have any
knowledge of the remapping operation. This remapping function is
described in more detail below with respect to FIGS. 6A-B.
[0186] The various symmetric FDD emulation techniques and emission
reduction techniques, particularly the LO offset, do not affect the
ability of the transceiver to maintain full compliance with an
operating standard, such as the IEEE802.16e Wireless MAN OFDMA PHY
operating standard, when operating in the symmetric FDD emulation
mode, the reduced emissions mode, or a combination thereof. The
base station need not have any knowledge of the symmetric FDD
emulation mode or the emission reduction techniques implemented by
the transceiver in the subscriber station. Instead, the base
station need only operate in a predetermined operating mode, such
as AMC in IEEE802.16e OFDMA PHY.
[0187] FIG. 6A is a simplified spectrum diagram 600 illustrating a
symmetric FDD emulation mode. The spectrum diagram 600 can
represent, for example, a symmetric FDD emulation implemented by
the transceiver of FIG. 4 operating in the spectrum shown in FIG.
2.
[0188] The spectrum diagram 600 illustrates a downlink frequency
band 610 and an actual uplink frequency band 630 that has a
bandwidth that is distinct from the bandwidth of the downlink
frequency band 610. In the spectrum diagram 600 embodiment of FIG.
6, the actual uplink frequency band 630 is narrower than the
downlink frequency band 610.
[0189] The downlink frequency band 610 has a center frequency 614
that can be, for example, the frequency of a LO used to frequency
convert the signals in the downlink frequency band 610 to baseband.
The downlink frequency band 610 is also capable of supporting, for
example, N OFDM subcarriers at a subcarrier spacing 612 of
F.sub.sc.
[0190] A virtual uplink frequency band 620 is depicted in relation
to the actual uplink frequency band 630. The virtual uplink
frequency band 620 has a bandwidth that is substantially the same
as the bandwidth of the downlink frequency band 610. The similarity
in the bandwidths is such that the virtual uplink frequency band
620 can be considered symmetric to the downlink frequency band 610.
The virtual uplink frequency band has a center frequency 624, which
can correspond to the frequency of a LO used to upconvert baseband
signals to the virtual uplink frequency band.
[0191] The virtual uplink frequency band 620, being symmetric with
the downlink frequency band 610, is capable of supporting N OFDM
subcarriers with a subcarrier spacing 622 of F.sub.sc. Thus, the
number of OFDM subcarriers capable of being supported in the
virtual uplink band 630 is the same as the number of subcarriers
that can be supported in the downlink frequency band 610, when the
subcarrier spacing 622 in the virtual uplink frequency band is the
same as the subcarrier spacing 612 in the downlink frequency band
610.
[0192] The actual uplink frequency band 630 has a center frequency
634 that can be, for example, a LO frequency used to upconvert
baseband signals to the actual uplink frequency band. The actual
uplink frequency band 630 can support fewer than N subcarriers with
a subcarrier spacing 622 of F.sub.sc. The difference in the
vertical scale of the actual uplink frequency band 630 and the
virtual uplink frequency band 620 is for purposes of illustration,
and is not intended to reflect any amplitude differences between
the two bands.
[0193] The transceiver receives an uplink resource allocation
indexed relative to the virtual uplink band 630. The transceiver
remaps the indices of the uplink resource allocation to the indices
of the subcarriers in the actual uplink band 630. After remapping,
the frequencies of the OFDM subcarriers in the resource allocations
remain the same. The remapping only affects the subcarrier indices
to reflect the center frequency offset 640 between the actual
uplink band 630 and the virtual uplink band 620.
[0194] As an example, the virtual uplink band 620 supports N
subcarriers centered about a center frequency 624. The left most
(lowest frequency) subcarrier in the virtual uplink band 620 can be
assigned an index value of zero. Each successive subcarrier is then
numbered relative to the prior subcarrier, such that the subcarrier
indices range from 0-(N-1).
[0195] The actual uplink band 630 is narrower than the virtual
uplink band 630, but retains the subcarrier indices as if the
actual uplink band 630 supported the same number of subcarriers as
supported by the virtual uplink band 630. Thus, the subcarrier
indices of the actual uplink band 630 would coincide with the
indices of the subcarriers of the virtual uplink band 620 if the
center frequencies 634 and 634, respectively, coincided.
[0196] Thus, it can be seen that the subcarrier indices in the
actual uplink band 630 typically do not start at zero, but instead
start at an index that can be determined based on the difference
between the bandwidths of the actual uplink band 630 from the
virtual uplink band 620. The index of a subcarrier in the virtual
uplink band 630 can be remapped to an index in the actual uplink
band 620, for example, by adding K/2, where K represents the
difference between the number of subcarriers supported in the
virtual uplink band, N, and the number of subcarriers supported in
the actual uplink band, M.
[0197] As an example, the virtual uplink band may correspond to the
lower A block and B block bands in combination with the C block
band of the WCS band illustrated in FIG. 2. The actual uplink band
may correspond to only the lower A block and B block bands. There
is a difference of approximately 5 MHz between the virtual uplink
band and the actual uplink band. The resource allocation in the
virtual uplink band can be remapped to a resource allocation in the
actual uplink band by adding the subcarrier index corresponding to
the number of subcarriers that appear in a bandwidth of 2.5 MHz to
the subcarrier index in the virtual uplink band.
[0198] FIG. 6B illustrates a simplified spectrum diagram 602 for
the LO offset and index remapping for reduced emissions mode. The
LO offset and index remapping can be performed, for example, using
the transceiver of FIG. 4 operating in the wireless communication
system of FIG. 1.
[0199] The downlink frequency band is identical to that illustrated
in FIG. 6A. The downlink frequency band 610 has a center frequency
614 that can be, for example, the frequency of a LO used to
frequency convert the signals in the downlink frequency band 610 to
baseband. The downlink frequency band 610 is also capable of
supporting N OFDM subcarriers at a subcarrier spacing 612 of
F.sub.sc.
[0200] The uplink frequency band 650 having an associated center
frequency 654 is illustrated as positioned in the spectrum adjacent
to a constrained emissions band 690. In order to reduce the uplink
emissions that fall within the constrained emissions band 690, the
transceiver offsets the LO to a LO 664 corresponding to, for
example, a center frequency of a reduced uplink band 660. The
reduced uplink band 660 corresponds to a portion of the uplink
frequency band 650.
[0201] The transceiver offsets the reduced uplink band 660 away
from the constrained emissions band 690 by a guard band 670. The
bandwidth of the guard band 670 corresponds approximately to the
magnitude of the LO offset 680.
[0202] The transceiver receives uplink resource allocation having
subcarriers indexed to uplink frequency band 650 and remaps the
subcarrier indices to the indexing relative to the reduced uplink
band 660. Using the same subcarrier indexing discussed above in
relation to symmetric FDD emulation, the subcarriers indexed to the
uplink frequency band 650 can be remapped to the indexing used in
the reduced uplink band 660 by adding a value equal to
approximately (N-M)/2, where N represents the number of subcarriers
supported in the uplink frequency band 650 and M represents the
number of subcarriers supported in the reduced uplink band 660.
[0203] The index remapping for reduced emissions mode can be
performed before or after index remapping performed for symmetric
FDD emulation. In the instance where both symmetric FDD emulation
and reduced emissions are performed, the index remapping can be
performed first for one mode and then remapped from the first
remapped index to a second remapped index to accommodate the second
mode.
[0204] FIG. 7 is a simplified flowchart of an embodiment of a
method 700 of asymmetric FDD operation with symmetric FDD
emulation. The method 700 can be performed, for example, by the
transceiver of FIGS. 3A-3B or FIG. 4.
[0205] The method 700 begins at block 710 where the transceiver
receives downlink signals in a downlink band. The transceiver
proceeds to block 720 and determines an uplink resource allocation
from the downlink signals. The uplink resource allocation
corresponds to a virtual uplink resource allocation in an
asymmetric FDD system, where the transceiver is configured to
perform symmetric FDD emulation.
[0206] The uplink resource allocation may be limited to that
portion of the virtual uplink band that overlaps the actual uplink
band. The uplink resource allocation may be limited, for example,
by utilizing an AMC zone.
[0207] The transceiver proceeds to block 730 and remaps the
subcarrier indices corresponding to the virtual uplink band to
subcarrier indices in an actual uplink band. The transceiver has
knowledge of the virtual uplink band and knowledge of the actual
uplink band in which the uplink signal will be transmitted. The
transceiver can remap the subcarrier indices based in part on the
difference in the number of subcarriers supported in the virtual
uplink band relative to the number of subcarriers supported in the
actual uplink band. The transceiver can also remap the subcarrier
indices based on the offset in center frequency of the virtual
uplink band relative to the center frequency of the actual uplink
band.
[0208] In embodiments in which the transceiver also remaps
subcarriers to control uplink emissions, the transceiver may remap
the subcarriers from an initial remapping performed during a
reduced emissions mode of operation.
[0209] The transceiver proceeds to block 740 and can optionally
control the LO frequency for the uplink signals. In a transceiver
that supports H-FDD, the transceiver may use the same LO for the
downlink processing and uplink processing, and the transceiver may
reconfigure the LO frequency to when transitioning between downlink
and uplink operations.
[0210] The transceiver proceeds to block 750 and generates the
uplink OFDM symbols based on the remapped subcarrier indices. A
symbol index, corresponding to the timing of the OFDM symbol, may
not change because the uplink time allocation does not change due
to the virtual uplink resource allocation.
[0211] The transceiver proceeds to block 760 and transmits the
symbols generated using the remapped subcarrier indices on the
actual uplink band. From the perspective of the base station that
allocates the uplink resources, the uplink resources utilized by
the transceiver correspond to those allocated. The remapping of
subcarrier indices is not detected by the base station.
[0212] The transceiver proceeds to block 770 and returns to the
receiver settings. It should be noted that in a full duplex FDD
system, the transceiver may concurrently receive and transmit
signals, and thus the process of reconfiguring the transceiver for
receive operation may be omitted.
[0213] FIG. 8 is a simplified functional block diagram of a method
800 of emission control in a FDD wireless device. The method 800
can be performed, for example, by the transceiver of FIGS. 3A-3B or
FIG. 4. The method 800 can be performed exclusive of any symmetric
FDD emulation or may be performed in addition to symmetric FDD
emulation.
[0214] The method begins at block 810 where the transceiver
receives downlink signals in a downlink band. The transceiver
proceeds to block 820 and determines an uplink resource allocation
from the downlink signals. The uplink resource allocation
corresponds to an uplink resource allocation in a reduced bandwidth
portion of the uplink band. The uplink resource allocation may be
limited to a reduced portion of the uplink band, for example, by
utilizing an AMC zone.
[0215] The transceiver proceeds to block 830 and remaps the
subcarrier indices of the full uplink band to subcarrier indices in
the reduced uplink band. The transceiver has knowledge of the
uplink band and knowledge of the reduced uplink band in which the
uplink signal will be transmitted.
[0216] The transceiver can remap the subcarrier indices based in
part on the difference in the number of subcarriers supported in
the uplink band relative to the number of subcarriers supported in
the reduced uplink band. The transceiver can also remap the
subcarrier indices based on the offset in LO or center frequency of
the uplink band relative to the LO or center frequency of the
reduced uplink band.
[0217] In embodiments in which the transceiver also remaps
subcarriers for symmetric FDD emulation, the transceiver may remap
the subcarriers from an initial remapping performed during a
symmetric FDD emulation mode of operation.
[0218] The transceiver proceeds to block 840 and can optionally
control the LO frequency for the uplink signals. In a transceiver
that supports H-FDD, the transceiver may use the same LO for the
downlink processing and uplink processing, and the transceiver may
reconfigure the LO frequency to when transitioning between downlink
and uplink operations.
[0219] The transceiver proceeds to block 850 and generates the
uplink OFDM symbols based on the remapped subcarrier indices.
[0220] The transceiver proceeds to block 860 and transmits the
symbols generated using the remapped subcarrier indices on the
reduced uplink band. From the perspective of the base station that
allocates the uplink resources, the uplink resources utilized by
the transceiver correspond to those allocated subcarriers. The
remapping of subcarrier indices is not detected by the base
station.
[0221] The transceiver proceeds to block 870 and returns to the
receiver settings. It should be noted that in a full duplex FDD
system, the transceiver may concurrently receive and transmit
signals, and thus the process of reconfiguring the transceiver for
receive operation may be omitted.
[0222] Methods and apparatus of symmetric FDD emulation and reduced
uplink emissions control and reduction are described herein. A
transceiver may emulate symmetric FDD operation to support
asymmetric FDD in a system that specifies symmetric FDD
operation.
[0223] The transceiver receives uplink resource allocation that
correspond to a virtual uplink band. The transceiver remaps the
resource allocation to reflect the subcarrier indices used in a
actual uplink band. Typically, only subcarrier indices are
remapped, as time indices corresponding to symbol times are not
affected by the symmetric FDD emulation.
[0224] The transceiver may also operate in a reduced or controlled
emissions mode by receiving uplink resource allocations, remapping
the uplink resource allocation to a reduced uplink band. Generating
symbols in the reduced uplink band using the remapped resources,
and filtering the uplink signal to reflect a reduced uplink band
that may be implemented by offsetting the LO used to frequency
convert the symbols in the reduced uplink band.
[0225] The symmetric FDD emulation can support FDD as well as H-FDD
systems, and can be used exclusive of, or in conjunction with,
reduced uplink emissions mode.
[0226] As used herein, the term coupled or connected is used to
mean an indirect coupling as well as a direct coupling or
connection. Where two or more blocks, modules, devices, or
apparatus are coupled, there may be one or more intervening blocks
between the two coupled blocks.
[0227] The steps of a method, process, or algorithm described in
connection with the embodiments disclosed herein may be embodied
directly in hardware, in a software module executed by a processor,
or in a combination of the two. The various steps or acts in a
method or process may be performed in the order shown, or may be
performed in another order. Additionally, one or more process or
method steps may be omitted or one or more process or method steps
may be added to the methods and processes. An additional step,
block, or action may be added in the beginning, end, or intervening
existing elements of the methods and processes.
[0228] The above description of the disclosed embodiments is
provided to enable any person of ordinary skill in the art to make
or use the disclosure. Various modifications to these embodiments
will be readily apparent to those of ordinary skill in the art, and
the generic principles defined herein may be applied to other
embodiments without departing from the scope of the disclosure.
* * * * *