U.S. patent application number 14/840457 was filed with the patent office on 2017-03-02 for apparatus and method for transmitting and receiving wireless signals subject to a spectral mask.
This patent application is currently assigned to HUAWEI TECHNOLOGIES CO., LTD.. The applicant listed for this patent is AHIKAM AHARONY, WEIKUN HOU, CHUANDONG LI, MAHDI ZAMANI, ZHUHONG ZHANG. Invention is credited to AHIKAM AHARONY, WEIKUN HOU, CHUANDONG LI, MAHDI ZAMANI, ZHUHONG ZHANG.
Application Number | 20170063408 14/840457 |
Document ID | / |
Family ID | 58096137 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170063408 |
Kind Code |
A1 |
ZAMANI; MAHDI ; et
al. |
March 2, 2017 |
APPARATUS AND METHOD FOR TRANSMITTING AND RECEIVING WIRELESS
SIGNALS SUBJECT TO A SPECTRAL MASK
Abstract
Provided is an apparatus and method for transmitting and
receiving wireless signals. A transmitting apparatus has a signal
processor and a transmitter. The signal processor is configured to
generate a signal having a middle channel and at least one side
channel. The transmitter is configured to wirelessly transmit the
signal subject to a spectral mask that has shoulder regions.
According to an embodiment of the invention, the signal processor
generates the signal such that each side channel is positioned in
one of the shoulder regions of the spectral mask. In this manner,
bandwidth from the shoulder regions can be utilized by one or more
side channels. Also provided is a receiving apparatus having a
receiver configured to wirelessly receive the signal, and a signal
processor configured to process the signal.
Inventors: |
ZAMANI; MAHDI; (OTTAWA,
CA) ; AHARONY; AHIKAM; (OTTAWA, CA) ; ZHANG;
ZHUHONG; (OTTAWA, CA) ; LI; CHUANDONG;
(OTTAWA, CA) ; HOU; WEIKUN; (OTTAWA, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZAMANI; MAHDI
AHARONY; AHIKAM
ZHANG; ZHUHONG
LI; CHUANDONG
HOU; WEIKUN |
OTTAWA
OTTAWA
OTTAWA
OTTAWA
OTTAWA |
|
CA
CA
CA
CA
CA |
|
|
Assignee: |
HUAWEI TECHNOLOGIES CO.,
LTD.
Shenzhen
CN
|
Family ID: |
58096137 |
Appl. No.: |
14/840457 |
Filed: |
August 31, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 1/40 20130101; H04L
27/0014 20130101; H04L 27/32 20130101 |
International
Class: |
H04B 1/10 20060101
H04B001/10; H04L 27/26 20060101 H04L027/26; H04L 27/00 20060101
H04L027/00; H04L 5/00 20060101 H04L005/00 |
Claims
1. A method comprising: generating a signal comprising a middle
channel and a side channel such that the side channel is positioned
in a shoulder region of a spectral mask; and wirelessly
transmitting the signal subject to the spectral mask; wherein the
signal as transmitted is a microwave or millimeter wave signal;
varying at least one of a power and an Adaptive Coding and
Modulation (ACM) of the middle channel based on a received feedback
signal.
2. (canceled)
3. (canceled)
4. A method comprising: generating a signal comprising a middle
channel and a side channel such that the side channel is positioned
in a shoulder region of a spectral mask; and wirelessly
transmitting the signal subject to the spectral mask; wherein the
signal as transmitted is a microwave or millimeter wave signal;
wherein generating the signal comprises: splitting a single
received data stream into a plurality of data streams including a
first data stream and a second data stream; generating a first
spectrum for the middle channel based on the first data stream;
generating a second spectrum for the side channel based on the
second data stream; and generating the signal by stitching the
first spectrum and the second spectrum together.
5. The method of claim 4, wherein: generating the first spectrum
comprises performing bit loading of bits of the first data stream
for the middle channel; and generating the second spectrum
comprises performing bit loading of bits of the second data stream
for the side channel.
6. The method of claim 5, wherein the middle channel and the side
channel have synchronous timing.
7. (canceled)
8. The method of claim 1, further comprising: varying an Adaptive
Coding and Modulation (ACM) of the side channel based on a received
feedback signal.
9. The method of claim 1, wherein the side channel is a first side
channel, the shoulder region is a first shoulder region of the
spectral mask, and the method further comprises: selectively
enabling or disabling a second side channel in a second shoulder
region of the spectral mask.
10. The method of claim 9, comprising: selectively enabling or
disabling the second side channel based on a received feedback
signal.
11. An apparatus comprising: a signal processor configured to
generate a signal comprising a middle channel and a side channel
such that the side channel is positioned in a shoulder region of a
spectral mask; and a transmitter configured to wirelessly transmit
the signal subject to the spectral mask; wherein the transmitter is
configured to wirelessly transmit the signal as a microwave or
millimeter wave signal; the side channel is a first side channel,
and the shoulder region is a first shoulder region of the spectral
mask; and the signal processor is configured to selectively enable
or disable a second side channel in a second shoulder region of the
spectral mask.
12. (canceled)
13. The apparatus of claim 11, wherein the signal processor
comprises: a first pulse shaper for generating a first spectrum for
the middle channel based on a first data stream; a second pulse
shaper for generating a second spectrum for the side channel based
on a second data stream; and a spectrum stitcher for generating the
signal by stitching the first spectrum and the second spectrum
together.
14. The apparatus of claim 11, wherein: the signal processor is
configured to vary at least one of a power and an Adaptive Coding
and Modulation (ACM) of the middle channel based on a received
feedback signal.
15. The apparatus of claim 11, wherein: the signal processor is
configured to vary an Adaptive Coding and Modulation (ACM) of the
side channel based on a received feedback signal.
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. An apparatus comprising: a receiver configured to wirelessly
receive a signal subject to a spectral mask, the signal comprising
a middle channel and a side channel that is positioned in a
shoulder region of the spectral mask; and a signal processor
configured to process the signal to separate a first spectrum for
the middle channel and a second spectrum for the side channel,
process the first spectrum to recover a first data stream, and
process the second spectrum to recover a second data stream;
wherein the receiver is configured to receive the signal as a
microwave signal or a millimeter wave signal; the signal processor
comprises an Inter-Channel Interference (ICI) equalizer for
interference cancellation for the side channel based on a result of
processing the middle channel.
25. (canceled)
26. (canceled)
27. The method of claim 1, wherein the shoulder region of the
spectral mask is used by the side channel to increase throughput
for the signal compared to not using the side channel.
28. The method of claim 11, wherein the shoulder region of the
spectral mask is used by the side channel to increase throughput
for the signal compared to not using the side channel.
29. The method of claim 1, wherein the signal is a single carrier
signal.
30. The method of claim 11, wherein the signal is a single carrier
signal.
Description
FIELD OF THE INVENTION
[0001] This application relates to wireless communication, and more
particularly to transmitting and receiving wireless signals that
are subject to a spectral mask.
BACKGROUND
[0002] Networks that provide wireless access may include wireless
backhaul connectivity between network nodes, for example using
microwave signals. The microwave signals are transmitted with
enough power to achieve an acceptable Signal to Noise Ratio (SNR).
The required power level depends on channel conditions. For
instance, during favorable channel conditions, the microwave
signals may be transmitted with relatively low power. Conversely,
in poor channel conditions, the microwave signals may need to be
transmitted with relatively high power.
[0003] However, transmitting the microwave signals with too much
power can result in interference between adjacent channels. As
such, the microwave signals are subject to a spectral mask, which
defines a maximum allowed transmit power over a range of
frequencies as a function of frequency. The spectral mask is
generally intended to reduce interference between adjacent channels
by limiting transmission power. Spectral masks have been defined by
various standardization bodies such as the International
Telecommunication Union (ITU), the Federal Communications
Commission (FCC), the Electronic Communications Committee (ECC),
the European Conference of Postal and Telecommunications
Administrations (CEPT), the European Telecommunications Standards
Institute (ETSI) and other standardization bodies.
[0004] When microwave signals are transmitted with relatively low
power, the microwave signals can be transmitted with wider
bandwidth while still complying with the spectral mask. There is a
desire to achieve improved spectral efficiency in these wider
bandwidth transmissions.
SUMMARY
[0005] The invention provides apparatuses and methods for
transmitting and receiving wireless signals that are subject to a
spectral mask, such as microwave or millimeter wave signals.
[0006] A transmitting apparatus provided by an embodiment of the
invention has a signal processor and a transmitter. The signal
processor is configured to generate a signal having a middle
channel and at least one side channel. The transmitter is
configured to wirelessly transmit the signal subject to a spectral
mask that has shoulder regions. According to an embodiment of the
invention, the signal processor generates the signal such that each
side channel is positioned in one of the shoulder regions of the
spectral mask. In this manner, bandwidth from the shoulder regions
can be utilized by one or more side channels. Also, the middle
channel may have a higher power level than the side channels
thereby allowing a higher ACM and greater spectral efficiency for
the middle channel.
[0007] A receiving apparatus provided by an embodiment of the
invention has a receiver and a signal processor. The receiver is
configured to wirelessly receive a signal subject to a spectral
mask that has shoulder regions. The signal has a middle channel and
at least one side channel. According to an embodiment of the
invention, each side channel is positioned in one of the shoulder
regions of the spectral mask. In this manner, bandwidth from the
shoulder regions can be utilized by one or more side channels.
Also, the middle channel may have a higher power level than the
side channels thereby allowing a higher ACM and greater spectral
efficiency for the middle channel. The signal processor is
configured to process the signal to separate a first spectrum for
the middle channel and a second spectrum for each side channel,
process the first spectrum to recover a first data stream, and
process each second spectrum to recover a second data stream.
[0008] Other aspects and features of the present invention will
become apparent, to those ordinarily skilled in the art, upon
review of the following description of the various embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Embodiments will now be described by way of example with
reference to the attached drawings in which:
[0010] FIG. 1 is a schematic diagram depicting an example spectral
mask;
[0011] FIG. 2 is a schematic diagram depicting a signal having a
middle channel and side channels subject to the spectral mask of
FIG. 1, in accordance with an embodiment of the invention;
[0012] FIG. 3 is a block diagram of a wireless communication
system, in accordance with an embodiment of the invention;
[0013] FIGS. 4A through 4D are schematic diagrams depicting other
example spectral masks;
[0014] FIG. 5 is a block diagram of an example signal processor of
a transmitting apparatus, in accordance with an embodiment of the
invention;
[0015] FIG. 6 is a signaling diagram showing example symbol streams
that may be generated by the signal processor of FIG. 5;
[0016] FIG. 7 is a block diagram of an example signal processor of
a receiving apparatus, in accordance with an embodiment of the
invention;
[0017] FIG. 8 is a block diagram of an example Inter-Channel
Interference (ICI) equalizer that may be implemented in the signal
processor of FIG. 7;
[0018] FIG. 9 is a block diagram of an example modem, in accordance
with an embodiment of the invention;
[0019] FIG. 10 is a block diagram of an example signal processor of
a transmitting apparatus, in accordance with an embodiment of the
invention;
[0020] FIG. 11 is a block diagram of an example signal processor of
a receiving apparatus, in accordance with an embodiment of the
invention;
[0021] FIG. 12 is a flow chart of an example method for
transmitting wireless signals, in accordance with an embodiment of
the invention;
[0022] FIG. 13 is a flow chart of an example method for receiving
wireless signals, in accordance with an embodiment of the
invention;
[0023] FIG. 14 is a graph showing an example power spectral density
for a three-channel signal, in accordance with an embodiment of the
invention; and
[0024] FIGS. 15 and 16 are graphs showing example data-rates that
may be achieved as power level of a middle channel is adjusted.
DETAILED DESCRIPTION OF EMBODIMENTS
[0025] It should be understood at the outset that although
illustrative implementations of one or more embodiments of the
present invention are provided below, the disclosed systems and/or
methods may be implemented using any number of techniques. The
invention should in no way be limited to the illustrative
implementations, drawings, and techniques illustrated below,
including the designs and implementations illustrated and described
herein, but may be modified within the scope of the appended claims
along with their full scope of equivalents.
Introduction
[0026] The original purpose of the shoulder regions of the
conventional spectral mask was to accommodate some degree of
distortion to a channel without affecting neighboring channels. To
illustrate this point, reference is made to FIG. 1, which is a
schematic diagram depicting an example spectral mask 100 with
shoulder regions 106, 107 for accommodating distortions of a
channel 101 at a high power level. In particular, as shown in FIG.
1, portions 102, 103 of the channel 101 extend outward due to
non-linear distortions. However, because the spectral mask 100 has
shoulder regions 106, 107, the channel 101 does not extend outside
of the spectral mask 100. The shoulder regions 106, 107 define a
cap on the amount of out of band (relative to middle channel)
interference that is deemed acceptable or tolerable within a given
system.
[0027] The amount of distortion is generally greater when the
channel 101 is transmitted at a higher power level. If the power
level is decreased as shown by arrow 104, for example, due to
improving channel conditions in which the high power is not needed,
then a resulting power spectral density 105 does not have
significant distortions extending outward such as the portions 102,
103 as shown. More generally, as the power level of the channel 101
is decreased, the magnitude of the portions 102, 103 will also
decrease. If the channel conditions improve to a point where the
middle channel can be transmitted with very low power, then the out
of band interference may be negligible.
[0028] Embodiments of the invention utilize the shoulder regions of
a spectral mask to transmit or receive one or more side channels by
making use of available bandwidth in the frequency range
corresponding to the shoulder regions. To illustrate this point,
reference is made to FIG. 2, which is a schematic diagram depicting
a signal having a middle channel 201 and side channels 202, 203
subject to the spectral mask 100 of FIG. 1. The middle channel 201
and the two side channels 202, 203 are both shown with power and
frequency characteristics that satisfy the spectral mask 100. By
positioning each side channel 202, 203 in the shoulder regions 106,
107 of the spectral mask 100, available bandwidth from the shoulder
regions 106, 107 can be utilized. Thus, the combination of the
middle channel 201 and the two side channels 202, 203 can better
utilize the bandwidth available within the spectral mask 100.
[0029] In some implementations, using the shoulder regions 106, 107
for the side channels 202, 203 may improve throughput by up to 50%
compared to not using the side channels 202, 203 at all. In
particular, if the middle channel 201 has bandwidth B, and each
side channel 202, 203 has bandwidth B/4, then the total bandwidth
may be 1.5B, which is an improvement of 50%. However, actual
improvement in throughput will depend on spectral efficiency, which
in turn will depend on channel conditions. For example, if the
middle channel 201 must be transmitted with high power due to poor
channel conditions, then the middle channel 201 might cause ICI for
the side channels 202, 203 due to non-linear distortions as
previously discussed for FIG. 1, and such ICI may limit an ACM for
the side channels 202, 203 thereby limiting throughput. Specific
possible results are presented below with reference to FIGS.
14-16.
[0030] Although embodiments of the invention focus on
implementations in which signals have a middle channel and two side
channels as shown, for example, in FIG. 2, it is to be understood
that other implementations are possible in which a different number
of side channels may be present. For example, in an alternative
implementation, there may be four side channels (e.g. two side
channels on each side of the middle channel). In another
implementation, there may be a single side channel (i.e. a side
channel on one side of the middle channel and no side channel on
the other side of the middle channel). Other implementations are
possible.
Apparatus for Transmitting and Receiving Wireless Signals
[0031] Referring now to FIG. 3, shown is a schematic diagram of a
wireless system 300 having a transmitting apparatus 310 and a
receiving apparatus 320, in accordance with an embodiment of the
invention. The transmitting apparatus 310 has a signal processor
311, a transmitter 312, a feedback receiver 313, and may have other
components that are not specifically shown. The signal processor
311, the transmitter 312, and the feedback receiver 313 may be
co-located, or installed in different locations. The receiving
apparatus 320 has a receiver 321, a signal processor 322, a
feedback transmitter 323, and may have other components that are
not specifically shown. The receiver 321, the signal processor 322,
and the feedback transmitter 323 may be co-located, or installed in
different locations.
[0032] Operation of the wireless system 300 will now be described.
The transmitting apparatus 310 generates a transmitter-side signal
S containing data to be transmitted over an air link 301 to the
receiving apparatus 320. The data may, for example, be a data
stream provided by a processor (not shown). The signal processor
311 of the transmitting apparatus 310 is configured to process the
transmitter-side signal S to generate a processed transmitter-side
signal S. The processed signal S' has a middle channel and at least
one side channel. An example of such processing is described later
with reference to FIG. 5. The transmitter 312 is configured to
transmit the processed signal S as a wireless signal S'.sub.W,
which includes the middle channel and each side channel subject to
a spectral mask. An example spectrum for the wireless signal
S'.sub.W is depicted in FIG. 2, which depicts the spectral mask
100, the center channel 201 and the side channels 202, 203. The
wireless signal S'.sub.W travels over the air link 301 to the
receiving apparatus 320.
[0033] A receiver-side wireless signal S.sup.W is wirelessly
received by the receiving apparatus 320. The receiver 321 of the
receiving apparatus 320 recovers receiver-side signal S' from the
wireless signal S.sup.W. The signal processor 322 of the receiving
apparatus 320 processes the recovered signal S' in a manner that is
complementary to the signal processor 311 of the transmitting
apparatus 310 such that the signal processor 322 of the receiving
apparatus 320 may recover the signal S.
[0034] The wireless signal S'.sub.W as transmitted is subject to a
spectral mask having shoulder regions. Practically, this means that
the transmitting apparatus 310 is responsible for ensuring that the
power of the transmitted signal at a given frequency does not
exceed the amount specified by the spectral mask. In some
embodiments, the signal processor 311 of the transmitting apparatus
310 generates the processed signal S' so that the processed signal
S' complies with the spectral mask. Thus, when the transmitter 312
transmits the wireless signal S'.sub.W based on the processed
signal S', the wireless signal S'.sub.W complies with the spectral
mask. More generally, the signal processor 311 generates the
processed signal S' such that the wireless signal S'.sub.W that is
transmitted complies with the spectral mask.
[0035] In some embodiments, the signal processor 311 of the
transmitting apparatus 310 is configured to selectively enable or
disable one or more side channels, for example, based on channel
conditions. For example, for implementations in which signals have
a middle channel and two side channels as shown in FIG. 2, each
side channel may be selectively enabled or disabled based on
channel conditions. If channel conditions are favorable for both
side channels, then both side channels are used. Channel conditions
may be favorable when there is a low amount of interference from
other transmissions in neighboring channels. However, if channel
conditions are not favorable for the first side channel, then the
first side channel can be disabled. The second side channel, which
may have favorable channel conditions, may be enabled
notwithstanding the first side channel being disabled. In
alternative implementations, both side channels are enabled at the
same time.
[0036] The spectral mask 100 shown in FIGS. 1 and 2 is only an
example and other spectral masks of varying shapes and sizes are
possible. To illustrate this point, reference is made to FIGS. 4A
through 4D, which are schematic diagrams depicting other example
spectral masks. Each schematic diagram shows half of a spectral
mask beginning at the center frequency f.sub.0. It is to be
understood that each spectral mask is symmetrical about the center
frequency f.sub.0.
[0037] FIG. 4A shows a spectral mask 410 having a middle region 411
and a shoulder region 412. The middle region 411 is bounded by a
power level k.sub.1 in the frequency range of f.sub.0 to f.sub.3.
The shoulder region 412 is bounded by a power level ranging from
k.sub.3 to a minimum value in the frequency range of f.sub.3 to
f.sub.5.
[0038] FIG. 4B shows a spectral mask 420 having a middle region 421
and a shoulder region 422. The middle region 421 is bounded by a
power level k.sub.1 in the frequency range of f.sub.0 to f.sub.1, a
power level ranging from k.sub.1 to k.sub.2 in the frequency range
of f.sub.1 to f.sub.2, and a power level ranging from k.sub.2 to
k.sub.3 in the frequency range of f.sub.2 to f.sub.3. The shoulder
region 422 is bounded by a power level ranging from k.sub.3 to
k.sub.4 in the frequency range of f.sub.3 to f.sub.4, and a power
level ranging from k.sub.4 to a minimum value in the frequency
range of f.sub.4 to f.sub.5.
[0039] FIG. 4C shows a spectral mask 430 having a middle region 431
and a shoulder region 432. The middle region 431 is bounded by a
power level k.sub.1 in the frequency range of f.sub.0 to f.sub.2,
and a power level ranging from k.sub.1 to k.sub.3 in the frequency
range of f.sub.2 to f.sub.3. The shoulder region 432 is bounded by
a power level k.sub.3 in the frequency range of f.sub.3 to f.sub.4,
a power level ranging from k.sub.3 to k.sub.5 in the frequency
range of f.sub.4 to f.sub.5, and a power level k.sub.5 in the
frequency range of f.sub.5 to f.sub.6.
[0040] FIG. 4D shows a spectral mask 440 having a middle region 441
and a shoulder region 442. The middle region 441 is bounded by a
power level k.sub.1 in the frequency range of f.sub.0 to f.sub.2,
and a power level ranging from k.sub.1 to k.sub.3 in the frequency
range of f.sub.2 to f.sub.3. The shoulder region 442 is bounded by
a power level ranging from k.sub.3 to k.sub.5 in the frequency
range of f.sub.3 to f.sub.5, and a power level k.sub.5 in the
frequency range of f.sub.5 to f.sub.6. In some implementations,
f.sub.6 is equal to 2.5 times the channel spacing.
[0041] In the foregoing examples with reference to FIGS. 4A through
4D, it is to be understood that the subscripts for the power levels
and the frequencies are used merely to distinguish the power levels
and the frequencies from one another within the same spectral mask.
While the same subscripts may be used in different spectral masks,
this does not imply that the power levels and the frequencies of
the different spectral masks must be the same. For example, f.sub.3
in FIG. 4A is not necessarily the same as f.sub.3 in FIG. 4B even
though the same subscript is used. Also, the subscripts do not
imply any specific magnitude in relation to one another.
[0042] FIGS. 4A through 4D demonstrate that there is a wide range
of possible shapes and sizes for spectral masks. However, the shape
and size of the spectral mask is normally constant in a given
wireless communication system. In some implementations, the number
of channels and/or modulation order of the channels can be adjusted
within the confines of the shape and size of the spectral mask.
Based on the shape and size of the spectral mask, each channel may
have a power level and baud-rate designed for spectral
efficiency.
[0043] Having regard to FIGS. 4A through 4D, a boundary between the
middle region and the shoulder region occurs approximately at a
frequency at which the spectral mask exhibits positive concavity
(i.e. a positive change of slope). In FIGS. 4A through 4D, this
frequency is at f.sub.3. The positive concavity forms the shoulder
regions.
[0044] However, it is to be understood that the boundary between
the middle region and the shoulder region does not necessarily need
to be exactly where the spectral mask exhibits positive concavity.
For example, with reference to FIG. 4B, the shoulder region 422
could alternatively be considered to start somewhere between the
frequencies f.sub.4 and f.sub.5. Furthermore, some spectral masks
may have more than one point with positive concavity. In such
cases, the shoulder region may start at one of the points with
positive concavity or at some other point.
[0045] In general, the precise boundaries of a shoulder region of a
spectral mask may depend on the particular shape of the spectral
mask, but the precise boundaries are normally related to a
frequency at which a spectral mask exhibits positive concavity.
Embodiments of the invention allow side channels to be positioned
in the shoulder regions. In this manner, bandwidth from the
shoulder regions can be utilized by one or more side channels. The
middle channel may have a higher power level than the side channels
thereby allowing a higher ACM and greater spectral efficiency for
the middle channel.
[0046] It is to be understood that the side channels do not have to
be completely positioned in the shoulder regions. In general, a
substantial portion of the side channels is positioned in the
shoulder regions. Thus, for example, 80% of a side channel may be
positioned in a shoulder region while 20% of the side channel is in
the middle region.
[0047] Referring back to FIG. 3, the air link 301 may attenuate the
wireless signal S'.sub.W, especially if there is precipitation such
as rain. Also, there may be interference from other transmissions.
Thus, the wireless signal S.sup.W that reaches the receiving
apparatus 320 will not be exactly identical to the wireless signal
S'.sub.W that has been transmitted. In general, the air link 301 is
not perfect, and such imperfections can limit the ACM for the
middle channel and each side channel.
[0048] In some implementations, based on channel conditions, the
signal processor 311 of the transmitting apparatus 310 adjusts
throughput of the wireless signal S'.sub.W by adjusting the power
and/or the ACM of the middle channel. Furthermore, the signal
processor 311 of the transmitting apparatus 310 selects an ACM of
each side channel. In some implementations, the power level of the
side channels is maintained at a constant value to fit in the
shoulder regions of the spectral mask. However, in alternative
implementations, the power level of the side channels can also be
set based on channel conditions, to the extent that the side
channels still comply with the spectral mask.
[0049] As mentioned above, the power level of the middle channel
may have a significant impact on the ACM that can be achievable for
each side channel, as the middle channel may cause interference to
the shoulder regions of the spectral mask resulting in ICI for any
side channels that are present, particularly when the middle
channel is transmitted with a high power. As such, in some
implementations, the power level on the middle channel is reduced
as much as it can be, while still achieving a best possible
throughput on the middle channel. For example, there may be a
maximum throughput that is defined by the available set of ACMs
that can be used in the system. So long as that ACM is used, the
best possible throughput can be achieved. By reducing the power on
the center channel while maintaining the maximum throughput, a side
benefit is that the interference with the shoulder portions is
reduced, and the ACM used for the side channels can be increased,
which can increase overall throughput. If the channel conditions
permit the same modulation constellation to be transmitted on the
middle channel but with very low power, then the out of band
interference may be negligible.
[0050] Referring back to FIG. 3, the wireless system 300 implements
feedback over a feedback link 302. The feedback link 302 might, for
example, be an existing channel of an air link from the receiving
apparatus 320 to the transmitting apparatus 310. The feedback link
302 uses a small portion of the air link for adaptive system
mechanisms such as ACM. In other implementations, the feedback link
102 is a wired link. The signal processor 322 of the receiving
apparatus 320 is configured to determine signal quality, and the
feedback transmitter 323 of the receiving apparatus 320 is
configured to send feedback based on the signal quality. The
feedback is received by the feedback receiver 313 of the
transmitting apparatus 310. The signal processor 311 is configured
to, based on the feedback, adjust throughput of the wireless signal
S'.sub.W as described earlier, typically by adjusting or varying
the ACM and/or the power of the middle channel, and/or by varying
the ACM of the side channels. Additionally, or alternatively, the
feedback is used to selectively enable or disable each side
channel.
[0051] In some implementations, the feedback includes an indication
of the signal quality for the middle channel and each side channel.
This may include three distinct indications of signal quality
(i.e., one indication per channel). For each channel, the
indication may, for example, include an SNR. However, other
indications of signal quality are possible and are within the scope
of the invention.
[0052] Based on the per-channel feedback, the power and/or ACM of
the corresponding channel may be adjusted. In particular, if
channel conditions for the middle channel are good, the throughput
of the middle channel can be increased if not already at the
maximum. If already at the maximum, then the transmit power for the
middle channel can be reduced. In some implementations, this may be
repeated such that a minimum transmission power that still yields
the maximum throughput may be used. The ACM used on each side
channel is adjusted based on feedback for the side channel.
Typically, as the power level on the middle channel is reduced, the
resulting improvement in channel conditions for the side channel
will allow the ACM to be adjusted to a more aggressive value.
[0053] In some implementations, for a given ACM, the power level on
the middle channel is set to a minimum amount that still allows
that ACM, and for each side channel, the signal processor 311 of
the transmitting apparatus 310 sets the ACM to achieve a high
throughput for the side channel. In some implementations, the
signal processor 311 of the transmitting apparatus 310 selects the
ACM that allows for a greatest achievable error-free throughput for
the side channels, given the current channel conditions. This ACM
for the middle channel may result in lower throughput for the
middle channel than would be possible with a more aggressive ACM,
although the resulting gains from the side channels may make up for
the loss in throughput by the middle channel. A goal is to maximize
overall spectral efficiency based on the feedback, and this might
not always be achieved by using the most aggressive ACM for the
middle channel.
[0054] In some implementations, as mentioned above, the side
channels have constant power. This ensures that the side channels
fit in the shoulder regions of the spectral mask. However, in
alternative implementations, the signal processor 311 of the
transmitting apparatus 310 sets the power level of the side
channels based on the feedback. The extent to which the power level
of the side channels can be manipulated may be based on the shape
and size of the spectral mask. A spectral mask with relatively
large shoulder regions may allow some freedom to manipulate the
power level of the side channels.
[0055] In some implementations, the feedback includes an indication
to enable or disable a side channel. The indication may be an
explicit indication (e.g. a command to enable or disable a side
channel), or an implicit indication (e.g. an indication of signal
quality from which it can be inferred that a side channel should be
disabled). A side channel may be disabled, for example, if channel
conditions are too poor to support the side channel.
[0056] In some embodiments, there is no feedback from the receiving
apparatus 320 to the transmitting apparatus 310. In some
embodiments, the transmitting apparatus 310 sets power levels and
the ACM for the middle and side channels such that robust
communication is expected to be possible under a wide variety of
channel conditions including poor conditions due to precipitation.
However, this approach may not take full advantage of greater
throughput that would be possible during favorable channel
conditions. In other implementations, the transmitting apparatus
310 checks the weather or the weather forecast from time to time,
and varies the power levels and the ACM for the middle and side
channels accordingly.
[0057] In some implementations, the transmitting apparatus 310 and
the receiving apparatus 320 have similar or even identical
configurations. In particular, the receiving apparatus 320 may also
have components for processing and transmitting data, and the
transmitting apparatus 310 may also have components for receiving
and processing data. Thus, the receiving apparatus 320 may be
capable of transmitting data, and the transmitting apparatus 310
may be capable of receiving the data. In other words, data
communication may be supported in both directions.
[0058] In some implementations, the wireless system 300 uses
microwave communication between the transmitting apparatus 310 and
the receiving apparatus 320. A microwave signal might, for example,
have a frequency of 38 GHz, which is a frequency that may also be
described as a millimeter wave because its wavelength is less than
one centimeter. Thus, according to some implementations, the
wireless system 300 can be said to use microwave communication or
millimeter wave communication. The wireless system 300 might, for
example, be part of a back-haul network. In specific
implementations, the transmitting apparatus 310 and the receiving
apparatus 320 include back-haul microwave modems. However, other
forms of wireless communication are possible and are within the
scope of the invention. For example, in other implementations, the
wireless system 300 uses any single carrier, high spectral
efficiency communication technique, for example Digital Video
Broadcasting--2.sup.nd Generation (DVB-S2) as defined by the
European Telecommunications Standards Institute in EN 302 307 (i.e.
satellites communication).
[0059] There are many possibilities for the signal processor 311 of
the transmitting apparatus 310 and the signal processor 322 of the
receiving apparatus 320. In some implementations, the signal
processors 311, 322 are Digital Signal Processors (DSPs). In
alternative implementations, the signal processors 311, 322 are
analog signal processors. More generally, the signal processors
311, 322 can be any appropriately configured processors for
processing signals as described herein. While shown as a single
element, each of the signal processors 311, 322 may be implemented
as a combination of multiple components. Example signal processor
implementations are described below with reference to FIGS.
5-10.
Example Signal Processor Implementations
[0060] Referring now to FIG. 5, shown is block diagram of an
example signal processor 500 of a transmitting apparatus, in
accordance with an embodiment of the invention. The signal
processor 500 of FIG. 5 is an example embodiment of the signal
processor 311 of FIG. 3 and might, for example, be implemented in a
DSP. It is to be understood that the signal processor 500 is shown
with very specific components in a very specific arrangement for
illustrative purposes only. Other configurations are possible and
are within the scope of the invention.
[0061] Information bits after a Forward Error Correction (FEC)
encoder (not shown) are split in three branches with a
Serial-to-Parallel (S2P) module (not shown). The three branches
include a left branch for a left channel, a middle branch for a
middle channel, and a right branch for a right channel. The middle
channel generated by the middle branch normally has more bandwidth
than each side channel, and may also be more spectrally efficient
than each side channel. Therefore, the middle branch normally has a
higher data-rate than the side branches.
[0062] Next, the information bits are mapped to their corresponding
constellations by symbol mappers 511, 512, 513. The mapping of the
bits to the constellations is also referred to as bit-loading. The
symbol mappers 511, 512, 513 include a left symbol mapper 511 for
the left branch, a middle symbol mapper 512 for the middle branch,
and a right symbol mapper 513 for the right branch. In some
implementations, the middle symbol mapper 512 uses 2048QAM (i.e. 11
bits per symbol) while the left symbol mapper 511 and the right
symbol mapper 513 use 16QAM (i.e. 4 bits per symbol). However,
other constellations are possible.
[0063] In some implementations, the ACMs for the middle channel and
the side channels are adapted based on channel conditions. For each
channel, this will determine the size of the constellation, and
number of bits per symbol (determined by constellation size and
coding rate). When channel conditions are favorable for a given
channel, more bits can be used per symbol, which results in greater
throughput. Conversely, when channel conditions are poor, fewer
bits can be used per symbol, which results in lower throughput.
[0064] The modulation order for the side channels is determined by
a power ratio of actual transmit power at a middle of the spectral
mask and actual transmit power at a side of the spectral mask. For
example, if the difference is 20 dB, then the modulation order for
the side channel can be set to 64QAM or some lower order
modulation. 64QAM is achievable with SNR of 19 dB with an FEC rate
of 7/8. As a rule of thumb, in a pure Additive White Gaussian Noise
(AWGN) channel, if the power difference of the signal at the middle
of the spectral mask and the signal at the side of the spectral
mask is P in dB, then the spectral efficiency difference between
the main channel and the side channel is approximately
P/log(2).
[0065] After the symbol mapping, the symbols are processed and
shaped by pulse shapers 521, 522, 523. The pulse shapers 521, 522,
523 include a left pulse shaper 521 that generates a spectrum for
the left branch, a middle pulse shaper 522 that generates a
spectrum for the middle branch, and a right pulse shaper 523 that
generates a spectrum for the right branch. In some implementations,
the pulse shapers 521, 522, 523 also perform pre-compensation in
order to compensate for any non-linear distortion created by power
amplification.
[0066] Next, a spectrum stitcher 531 generates a signal having the
three channels side-by-side as shown in FIG. 2 for example. This
involves stitching together the spectrum for the left channel, the
spectrum for the middle channel, and the spectrum for the right
channel. Spectrum stitching can be implemented in a frequency
domain with an Inverse Fast Fourier Transform (IFFT) of catenation
of a Fast Fourier Transform (FFT) of the channel signals, or in a
time domain using a Numerically Controlled Oscillator (NCO) by
multiplying the side channel signals by
e.sup..+-.j2.pi.f.sup.c.sup.t, where .+-.f.sub.c is the center
frequency for the side channels. This multiplication is performed
in baseband with the center frequency f.sub.c being zero, and then
the resulting signals can be upconverted. It is also possible to
generate the signals directly in RF, in which case the center
frequency f.sub.c of a side channel is an offset from the center
frequency f.sub.0 of the middle channel. The value for the center
frequency f.sub.c could be as low as the average of baud-rate of
the middle channel and the side channel. For example, if main
channel has baud-rate of f.sub.b1 and the side channel has
baud-rate of f.sub.b2, then f.sub.c=(f.sub.b1+f.sub.b2)/2.
[0067] In some implementations, the middle channel and the side
channels all have synchronous timing with a common clock. To
illustrate this point, reference is made to FIG. 6, which is a
signalling diagram showing example symbol streams that may be
generated by the symbol mappers 511, 512, 513 of the signal
processor 500 of FIG. 5. The symbol streams include a left symbol
stream 601 (with symbols L.sub.1, L.sub.2, . . . ) for the left
channel, a middle symbol stream 602 (with symbols M.sub.1, M.sub.2,
. . . ) for the middle channel, and a right symbol stream 603 (with
symbols R.sub.1, . . . ) for the right channel.
[0068] The symbol rate of the middle symbol stream 602 is four
times the symbol rate of the left symbol stream 601 and the right
symbol stream 603 in this example. The middle channel may use
different power and a higher-order constellation than the side
channels. Regardless, the middle symbol stream 602 and the side
symbol streams 601, 603 share alignment with a common clock. In
particular, each symbol for the side symbol streams 601, 603 is
aligned with a corresponding set of four symbols of the middle
symbol stream 602. Other symbol rates are possible.
[0069] Although the middle symbol stream 602 and the side symbol
streams 601, 603 share alignment with a common clock, the middle
symbol stream 602 and the side symbol streams 601, 603 do not have
to be transmitted at the same time. For example, the side symbol
streams 601, 603 can be transmitted later than the middle symbol
stream 602. In the illustrated example, the side symbol streams
601, 603 are shown to be shifted in time relative to the middle
symbol stream 602.
[0070] If the middle channel and the side channels all have
synchronous timing with a common clock, then on the receiver side
some processing such as clock recovery can be performed for one of
the channels such as the middle channel, and then applied across
all channels. However, in some implementations, additional
processing may be performed for the side channels due to ICI on the
side channels from the middle channel. As mentioned above with
reference to FIG. 1, there may be ICI on the side channels from the
main channel, especially if the power level of the main channel is
high. Such processing on the receiver side will be described in
further detail below with reference to FIG. 7.
[0071] Referring now to FIG. 7, shown is a schematic diagram of an
example signal processor 700 of a receiving apparatus having ICI
equalization, in accordance with an embodiment of the invention.
The signal processor 700 of FIG. 7 is an example embodiment of the
signal processor 322 of FIG. 3 and might, for example, be
implemented in a DSP. It is to be understood that the signal
processor 700 is shown with very specific components in a very
specific arrangement for illustrative purposes only. Other
configurations are possible and are within the scope of the
invention.
[0072] The signal processor 700 receives an input signal having a
middle channel and at least one side channel. The channels are
sliced by a spectrum slicer 710. In particular, the spectrum slicer
710 separates a spectrum for the left channel, a spectrum for the
middle channel, and a spectrum for the right channel. Spectrum
slicing can be implemented in either a frequency domain or a time
domain. Each channel is processed in parallel as described
below.
[0073] In some implementations, some processing such as clock
recovery, channel estimation, and carrier phase recovery can be
performed for one of the channels such as the middle channel, and
then applied across all channels. This may simplify the design and
reduce power consumption. In this particular example, a clock &
frame recovery block 720 and a channel estimator 730 process the
middle channel, and results of that processing are applied to the
side channels. The clock & frame recovery block 720 might, for
example, perform a PLL-based carrier recovery.
[0074] Next, each channel is processed by a respective equalizer
741, 742, 743. The complexity of the equalizers 741, 742, 743 may
depend on expected maximum baud-rates of the channels. In
particular, the equalizer 742 for the middle channel may have
greater complexity than the equalizers 741, 743 for the side
channels, particularity if the side channels have lower baud-rate
than the middle channel. The greater complexity of the equalizer
742 for the middle channel enables the equalizer 742 to process the
greater baud-rate.
[0075] Next, the center channel is processed by phase recovery
block 752, and the results of that processing are applied across
all channels. In particular, phase correction of the side channels
is performed by phase correctors 751, 753 based on the results from
the phase recovery block 752. Phase correction of the middle
channel is performed by phase corrector 762.
[0076] The power level of the side channels is relatively small, so
they do not normally produce significant interference on
neighboring channels or on the middle channel. However, as
mentioned above, the power level of the middle channel can cause
ICI on the side channels, especially when the power level of the
middle channel is very high. In some implementations, this ICI can
be mitigated by ICI equalizers 761, 763. The ICI equalizers 761,
763 might, for example, be symbol-rate equalizers. The ICI
equalizers 761, 763 perform interference cancellation to compensate
interference in each side channel from the middle channel. In some
implementations, the ICI equalizers 761, 763 use a result of the
processing of the middle channel, for example the output from the
phase recovery 752, when performing the interference cancellation
for the side channels.
[0077] Finally, the signal processor 700 has decoders 771, 772, 773
for the main and side channels. The decoders 771, 772, 773 might,
for example, be FEC decoders. In alternative implementations, if no
FEC encoding was performed by the transmitting apparatus, then
there is no FEC decoding performed by the signal processor 700. The
decoders 771, 772, 773 have outputs for outputting recovered data
from the main and side channels. In some implementations, the
signal processor 700 combines the recovered data from the main and
side channels into one signal.
[0078] In some implementations, the signal processor 700 implements
three independent parallel processors for three channels. This may
be preferred from a reduced complexity point of view. However, in
other implementations, the signal processor 700 instead implements
a joint processing scheme that is more general, but with a possible
cost of added complexity.
[0079] Referring now to FIG. 8, shown is a schematic diagram of an
example ICI equalizer 800 that may be implemented in the signal
processor of FIG. 7 for the ICI equalizer 761 and/or the ICI
equalizer 763. The ICI equalizer 800 is a Multiple Input Single
Output (MISO) 2.times.1 multi-tap equalizer, which has a first
finite impulse response (FIR) transversal filter 801 for a side
channel, and a second FIR transversal filter 802 for a main channel
that has been shifted by a frequency shifter 803 for successive
interference cancellation. The output of the second FIR transversal
filter 802 is added to the output of the first FIR transversal
filter 801 by adder 804 in order to compensate for the ICI by the
main channel.
[0080] As the tap coefficients are calculated based on the received
signal in the main and side channels, according to Adaptive
Transmission Power Control (ATPC), the ICI equalizer 800 will be
updated correspondingly and mitigate the ICI. Because the ICI has
both linear and non-linear parts, the linear part will be corrected
by the ICI equalizer 800 over the side channels. However, the
non-linear part may still be present. For a center frequency of the
side channels of .+-.f.sub.c where
f.sub.c.gtoreq.(f.sub.b1+f.sub.b2)/2, the non-linear part is
typically negligible. However, if the non-linear part is not
negligible, then a non-linear Volterra equalizer can be used to
mitigate the non-linear part with the cost of added complexity.
Alternatively, the non-linear Volterra equalizer can be omitted if
the non-linear part and its negative impact on SNR can be
tolerated.
[0081] Referring now to FIG. 9, shown is a block diagram of an
example modem 900 having a transmitting apparatus 910 and a
receiving apparatus 920, in accordance with an embodiment of the
invention. The transmitting apparatus 910 and the receiving
apparatus 920 of FIG. 9 are example embodiments of the signal
processor 311 and the signal processor 322 of FIG. 9 and may, for
example, be implemented in a DSP. It is to be understood that the
modem 900 is shown with very specific components in a very specific
arrangement for illustrative purposes only. Other configurations
are possible and are within the scope of the invention.
[0082] The transmitting apparatus 910 includes components for
generating a signal for transmission. The transmitting apparatus
910 has a Root Raised Cosine (RRC) filter 911 for pulse shaping for
the left channel, an RRC filter 912 for pulse shaping for the right
channel, and an RRC filter 913 for pulse shaping for the middle
channel. The left channel is shifted in frequency and amplified by
a Frequency Shift & Gain block 914, and the right channel is
shifted in frequency and amplified by a Frequency Shift & Gain
block 915. A spectrum stitcher 916 combines the side channels and
the middle channel. This involves stitching together a spectrum for
the left channel, a spectrum for the middle channel, and a spectrum
for the right channel. The combined signal is subjected to
interpolation sampling by a sampler 917 prior to transmission by a
transmitter (not shown).
[0083] In some implementations, the baud-rates for the middle
channel and the side channels are 49.5 MHz and 12.375 MHz (i.e.
49.5 MHz/4), respectively. However, other baud-rates are possible.
In some implementations, the gap between the middle channel and
each side channel is 4 MHz, and the gain by blocks 914 and 915 is
-20 dB. Therefore, the middle frequency for the side channels is
.+-.34.9375 MHz. In this example, it is desired to have SNRs of the
middle and side channels at 49 dB and 23 dB, respectively.
[0084] The receiving apparatus 920 includes components for
processing a received signal. The receiving apparatus 920 has an
Anti-Aliasing Filter (AAF) 921 for restricting bandwidth of the
signal to a band of interest. The restricted signal is then
subjected to interpolation sampling by a sampler 922. The sampler
922 performs sampling to separate a spectrum for the left channel,
a spectrum for the middle channel, and a spectrum for the right
channel. The spectra for the three channels are then processed by
three parallel paths. The middle channel is subjected to an
Adaptive Gain Controller (AGC) 923 to adjust power level, and an
RRC filter 924 for pulse shaping of an output signal. The right
channel is shifted in frequency and amplified by a Frequency Shift
& Gain block 928, which is complementary to the frequency shift
and amplification performed by Frequency Shift & Gain block
914, and then subjected to an RRC filter 929 for pulse shaping of
an output signal. The left channel is likewise shifted in frequency
and amplified by a Frequency Shift & Gain block 930, which is
complementary to the frequency shift and amplification performed by
Frequency Shift & Gain block 915, and then subjected to an RRC
filter 931 for pulse shaping of an output signal.
[0085] In the illustrated example, the sampler 922 performs
sampling based on feedback from the processing of the middle
channel. In particular, the output of the RRC filter 924 for the
middle channel is fed back through a Timing Error Detector (TED)
925, a low pass filter (LPF) 926 and an NCO 927, which creates a
synchronous (i.e. clocked) signal with correct timing for the
sampler 922. The TED 925 might, for example, implement a Gardner
method or any other appropriate method for detecting error in
timing. The Gardner method might, for example, recover the clock in
a two-fold sampling rate (i.e. two samples per symbol or T/2
sampling space).
[0086] In the illustrated example, the side channels do not have a
separate circuit for clock synchronization. Instead, they use the
same output as the middle channel's clock with division by a ratio
of the symbol rate of the main channel to the symbol rate of the
side channels. In this case, the side channels use the same output
as the middle channel's clock with division by four, because the
symbol rate of the main channel is four times that of the side
channels as similarly described with reference to FIG. 6. A Minimum
Mean Square Error (MMSE) time domain adaptive equalizer (not shown)
can provide 49 dB SNR for the middle channel, but may provide only
15 dB SNR for the side channels due to high ICI from the middle
channel over to the side channels. In the example above, it is
desired to have 23 dB SNR for the side channels, which is greater
than the 15 dB that may be available due to the high ICI from the
middle channel. To address this, a second stage equalizer as an
MISO 2.times.1 multi-tap ICIC may be implemented for side channels
to reach 23 dB SNR. An example ICI equalizer has been described
above with reference to FIG. 8.
[0087] In some implementations, if there is a larger gap between
the middle channel and the side channels, then there might be no
need for an ICI equalizer. In some implementations, there may be
separate synchronization circuits for each channel instead of using
the middle channel circuitry for all three channels. In that case,
there might be no need for an ICI equalizer.
[0088] Referring now to FIG. 10, shown is block diagram of an
example signal processor 940 of a transmitting apparatus, in
accordance with an embodiment of the invention. The signal
processor 940 of FIG. 10 is an example embodiment of the signal
processor 311 of FIG. 3 and might, for example, be implemented in a
DSP. It is to be understood that the signal processor 940 is shown
with very specific components in a very specific arrangement for
illustrative purposes only. Other configurations are possible and
are within the scope of the invention.
[0089] The signal processor 940 receives inputs 957 including a
clock signal and data to be transmitted. The data may be formed as
data symbols and encoded using an FEC encoder 941. The FEC encoder
941 generates three parallel paths for the middle and side
channels. A mapper 943 maps the data into QAM symbols for the
middle channel, a framer 946 assembles the QAM symbols into a data
frame, and an RRC filter 949 performs pulse shaping and may reduce
ICI between adjacent symbols. The side channels are likewise
processed with mappers 942, 944, framers 945, 947, and RRC filters
948, 950.
[0090] Next, a spectrum stitcher 951 generates a signal having the
three channels side-by-side as similarly shown in FIG. 2 for
example. This involves stitching together a spectrum for the left
channel, a spectrum for the middle channel, and a spectrum for the
right channel. Spectrum stitching can be implemented in a frequency
domain or in a time domain as previously described. The signal
having the three channels is then passed through a sampler 952 for
interpolation sampling and then through a Digital Pre-Distortion
(DPD) processor 953 for digital pre-distortion processing. This
processing may compensate for non-linear distortion created by
power amplification. Next, a compensator 954 performs compensation,
which may allow for adjustment of any imbalance between channels.
Next, a modulator 955 performs modulation to generate a modulated
signal. Finally, a DAC 956 converts the modulated signal to an
output 958 for transmission by a transmitter (not shown).
[0091] Referring now to FIG. 11, shown is a block diagram of a
signal processor 970 of a receiving apparatus, in accordance with
an embodiment of the invention. The signal processor 970 of FIG. 11
is an example embodiment of the signal processor 321 of FIG. 3 and
might, for example, be implemented in a DSP. It is to be understood
that the signal processor 970 is shown with very specific
components in a very specific arrangement for illustrative purposes
only. Other configurations are possible and are within the scope of
the invention.
[0092] The signal processor 970 receives an input signal 989. The
input signal 989 is converted from an analog signal to a digital
signal by an ADC 971. The digital signal is processed by a
demodulator 972 in order to demodulate the signal. This
demodulation is complementary to the modulation performed by the
modulator 955 shown in FIG. 10. Based on such demodulation,
feedback is provided through a first AGC 973 to adjust power level
of the conversion by the ADC 971. The demodulated signal is
processed by an Adaptive Feed Forward (AFF) filter 974. The AFF
filter 974 performs equalization and corrects frequency with a
fixed frequency offset.
[0093] Next, an NCO 975 creates a synchronous (i.e. clocked) signal
from the output of the AFF filter 974. The timing of the signal is
controlled with feedback. The second AGC 976 adjusts the gain of
the synchronous signal, and then to an RRC filter 977 for pulse
shaping of the middle channel. The RRC filter 977 provides feedback
to the second AGC 976 in order to adjust gain of the second AGC
976. A TED 986 and a loop filter 987 provide feedback for the
timing of the synchronous signal generated by the NCO 975. The TED
986 might, for example, implement a Gardner method or any other
appropriate method for detecting error in timing. Equalization and
carrier recovery (EQL/CR) are performed on the output of the RRC
filter 977 at block 978. Next, the recovered signal is demapped by
a de-mapper 979.
[0094] The output of the second AGC 976 is also provided to RRC
filters 983, 980 for pulse shaping of the side channels.
Equalization and carrier recovery are performed on the output of
the RRC filters 983, 980 at blocks 984, 981. Next, the recovered
signals are demapped by de-mappers 985, 982.
[0095] The recovered signals for the middle channel and the side
channels are combined and subjected to FEC decoding by an FEC
decoder 988 to produce an output 990, which is a combination of the
recovered signals. In alternative implementations, if no FEC
encoding was performed by the transmitting apparatus, then there is
no FEC decoding performed by the signal processor 970.
Methods for Transmitting and Receiving Wireless Signals
[0096] Referring now to FIG. 12, shown is a flow chart of an
example method for transmitting wireless signals, in accordance
with an embodiment of the invention. This method may be implemented
by a transmitting apparatus such as the transmitting apparatus 310
shown in FIG. 3 for example.
[0097] At steps 1201 through 1203, the transmitting apparatus
generates a signal that will be transmitted subject to a spectral
mask. In particular, at step 1201 the transmitting apparatus
generates a first spectrum for a middle channel based on a first
data stream, and at step 1202 the transmitting apparatus generates
a second spectrum for a side channel based on a second data stream.
In some implementations, the first data stream and the second data
stream have been split from one data stream containing data to be
transmitted as previously described. In other implementations, the
first data stream and the second data stream originate as
independent data streams to be transmitted. In some
implementations, the transmitting apparatus performs bit loading of
bits when generating the first spectrum and the second spectrum as
previously described. Next, at step 1203, the transmitting
apparatus stitches the first spectrum and the second spectrum
together, thereby generating a signal having both the middle
channel and the side channel.
[0098] In some implementations, steps 1201 and 1202 are executed
concurrently in parallel as shown in FIG. 12. However, in other
implementations, steps 1201 and 1202 are executed one after
another. The transmitting apparatus may also generate additional
spectra for any additional side channels. If any additional spectra
have been generated for any additional side channels, then these
additional spectra are also stitched with the first spectrum and
the second spectrum when generating the signal. In some
implementations, all channels have synchronous timing.
[0099] Steps 1201 through 1203 are executed such that the resulting
spectrum of the signal generated at step 1203 complies with the
spectral mask. In accordance with an embodiment of the invention,
the signal is generated such that each side channel of the signal
is positioned in one of the shoulder regions of the spectral mask.
An example of such positioning is shown in FIG. 2 for a given
spectral mask in the case of two side channels for illustrative
purposes. In this manner, bandwidth from the shoulder regions can
be utilized by one or more side channels.
[0100] At step 1204, the transmitting apparatus wirelessly
transmits the signal, for example as a microwave or millimeter wave
signal. The wireless signal is sent over an air link to a receiving
apparatus.
[0101] In some implementations, as in the illustrated example, the
transmitting apparatus receives feedback from the receiving
apparatus. There are many possibilities for this feedback. In some
implementations, the feedback includes an indication of the signal
quality for the middle channel and each side channel. In some
implementations, the feedback includes an indication to enable or
disable a side channel. Further details of the feedback have been
provided above and are not repeated here.
[0102] If at step 1205 the transmitting apparatus receives
feedback, then at step 1206 the transmitting apparatus adjusts
throughput of the transmission based on the feedback. For instance,
the transmitting apparatus may vary a power and/or an ACM of the
middle channel, and/or vary an ACM of the side channels.
Additionally, or alternatively, the transmitting apparatus may
disable or enable a side channel. Further details of how throughput
can be adjusted have been provided above and are not repeated
here.
[0103] If at step 1207 the transmission is complete, then the
method concludes. However, if at step 1207 the transmission is not
complete because there is more data to send, then the method loops
back to step 1201. Steps 1201 through 1204 are repeated until the
transmission is complete. Step 1206 is repeated when and if
feedback is received at step 1205.
[0104] In alternative implementations, the transmitting apparatus
may perform the transmission without any feedback as previously
described. For such alternative implementations, there may not be
any adjustment of throughput at step 1206.
[0105] Referring now to FIG. 13, shown is a flow chart of an
example method for receiving wireless signals, in accordance with
an embodiment of the invention. This method may be implemented by a
receiving apparatus such as the receiving apparatus 320 shown in
FIG. 3 for example.
[0106] At step 1301, the receiving apparatus wirelessly receives a
signal subject to a spectral mask that has shoulder regions. The
signal as received might be a microwave signal or a millimeter wave
signal for example. The signal includes a middle channel and at
least one side channel. In accordance with an embodiment of the
invention, each side channel is positioned in one of the shoulder
regions of the spectral mask. An example of such positioning is
shown in FIG. 2 for a given spectral mask in the case of two side
channels for illustrative purposes. In this manner, bandwidth from
the shoulder regions can be utilized by one or more side
channels.
[0107] At steps 1302 through 1304, the receiving apparatus
processes the signal for signal recovery. In particular, at step
1302 the receiving apparatus separates, from the received signal, a
first spectrum for the middle channel. For each side channel, the
receiving apparatus also separates a second spectrum for the side
channel. At step 1303, the receiving apparatus processes the first
spectrum to recover a first data stream. At step 1304, the
receiving apparatus processes the second spectrum to recover a
second data stream.
[0108] In some implementations, steps 1303 and 1304 are executed
concurrently in parallel as shown in FIG. 13. However, in other
implementations, steps 1303 and 1304 are executed one after
another. The receiving apparatus may also process additional
spectra for any additional side channels. If any additional spectra
for any additional side channels have been separated at step 1302,
then these additional spectra are also processed to recover
additional data streams. In some implementations, the receiving
apparatus combines, into one data stream, all of the data streams
recovered from the middle and side channels as previously
described. In other implementations, the receiving apparatus leaves
the data streams recovered from the middle and side channels as
separate data streams.
[0109] In some implementations, the receiving apparatus processes
the middle channel and applies at least one result of that
processing for decision feedback correction of each side channel as
previously described. This may reduce complexity of the receiving
apparatus. In some implementations, the receiving apparatus
performs interference cancellation for each side channel based on a
result of processing the middle channel as previously described.
Further details of how the signal may be processed have been
provided above and are not repeated here.
[0110] In some implementations, as in step 1305, the receiving
apparatus determines whether to send feedback to the transmitting
apparatus. The receiving apparatus might, for example, send
feedback only when there has been a measured change to signal
quality. Alternatively, the receiving apparatus might send feedback
on a periodic basis regardless of whether there has been any
measured change to signal quality.
[0111] If at step 1305 the receiving apparatus determines that
feedback is to be sent, then at step 1306 the receiving apparatus
sends feedback. The feedback may be used by the transmitting
apparatus to adjust throughput of the wireless signal as previously
described. Further details of the feedback have been provided above
and are not repeated here.
[0112] In alternative implementations, the receiving apparatus does
not provide any feedback.
[0113] If at step 1307 the reception is complete, then the method
concludes. However, if at step 1307 the transmission is not
complete because there is more data to receive, then the method
loops back to step 1301. Steps 1301 through 1305 are repeated until
the reception is complete. Step 1306 is repeated when and if
feedback is to be sent as determined by step 1305.
Example Implementations
[0114] Examples of possible implementations of the present
invention are described in this section. It is to be understood
that these implementations are very specific and are provided for
illustrative purposes only.
[0115] Referring now to FIG. 14, shown is a graph showing an
example power spectral density for a three-channel signal, in
accordance with an embodiment of the invention. This graph shows a
middle channel 1401 and side channels 1402, 1403 when the side
channels 1402, 1403 have each been subjected to ICI equalization to
compensate for ICI on the side channels 1402, 1403 from the middle
channel 1401. Use of ICI equalization might, for example, improve a
minimum square error on the side channels by 8 dB.
[0116] As previously mentioned, the data-rate that can be achieved
may depend on several factors including the power level of the
middle channel 1401. While ICI equalization can help to compensate
for ICI on the side channels 1402, 1403 from the middle channel
1401, the data-rate that can be achieved may be greater when the
power level of the middle channel 1401 is reduced. Examples of this
will be described below with reference to FIGS. 15 and 16.
[0117] Referring now to FIG. 15, shown is a graph showing example
data-rates that may be achieved as power level of a middle channel
is adjusted. In this example, the middle channel and each side
channel are subject to the spectral mask of FIG. 4C with the
parameters listed in Table 1 below.
TABLE-US-00001 TABLE 1 Parameters for spectral mask of FIG. 4C
Parameter k.sub.1 f.sub.2 k.sub.3 f.sub.3 f.sub.4 k.sub.5 f.sub.5
Value 2 dB 12.8 -23 dB 16.4 25 MHz -45 dB 45 MHz MHz MHz
[0118] This spectral mask is a standard class 1, 2 and 3 mask used
for 28 MHz channelization transmission. RRC filters with a
roll-off-factor of 0.2 are used for pulse shaping for all signals.
To transmit a single-carrier signal with full-power, the maximum
achievable baud-rate is 27 Mbaud. So the maximum data-rate using
2048QAM (11 bits/symbol) is 27 Mbaud.times.11 bits/symbol=297
Mb/s.
[0119] When three channels are used, the middle channel will be the
same as a single-carrier with 27 Mbaud. Each side channel can have
a baud-rate of 11.3 Mbaud, and their center frequency is .+-.22.05
MHz. The side channels have the same pulse shape as the middle
channel with a roll-off-factor of 0.2. Because the minimum SNR for
2048QAM is around 36 dB, and k.sub.3 is -24 dB, the side channels
have SNR of 14 dB, which makes it possible to transmit 16QAM (4
bits/symbol). The total achievable data-rate is 11.3 Mbaud.times.4
bits/symbol.times.2 side channels+297 Mb/s=387.4 Mb/s, which is
more than 30% increase in data-rate compared with using only the
middle channel as a single-carrier.
[0120] In the case of 6 dB back-off power, the modulation order can
increase to 64QAM (6 bits/symbol) because of a 6 dB improvement in
channel conditions. The baud-rates do not need to be changed. Thus,
a data-rate of 11.3 Mbaud.times.6 bits/symbol.times.2 side
channels+297 Mb/s=432.6 Mb/s may be achieved. The maximum data-rate
for other back-off values is summarized in Table 2 below and
plotted in FIG. 15.
TABLE-US-00002 TABLE 2 Example data-rate for spectral mask of FIG.
4C Side Channel Back-Off Power Modulation Data-Rate 0 dB 16QAM
387.4 Mb/s 6 dB 64QAM 432.6 Mb/s 12 dB 256QAM 477.8 Mb/s 18 dB
1024QAM 523 Mb/s 24 dB 2048QAM 545.6 Mb/s
[0121] The data-rate can be increased while maintaining the
baud-rates. Some systems that change baud-rates may need to be
restarted upon a change to the baud-rate. By avoiding changes to
the baud-rates, the present system may be "hitless" in the sense
that it avoids such restarts.
[0122] Referring now to FIG. 16, shown is a graph showing example
data-rates that may be achieved as power level of a middle channel
is adjusted. In this example, the middle channel and each side
channel is subject to the spectral mask of FIG. 4D is used with the
parameters listed in Table 2 below.
TABLE-US-00003 TABLE 2 Parameters for spectral mask of FIG. 4D
Parameter k.sub.1 f.sub.2 k.sub.3 f.sub.3 f.sub.5 k.sub.5 Value 2
dB 12.8 MHz -27 dB 17 MHz 56 MHz -55 dB
[0123] This spectral mask is a standard class 4L mask used for 28
MHz channelization transmission. RRC filters with a roll-off-factor
of 0.2 are used for pulse shaping for all signals. To transmit a
single-carrier signal with full-power, the maximum achievable
baud-rate is 27 Mbaud. So the maximum data-rate using 2048QAM (11
bits/symbol) is 27 Mbaud.times.11 bits/symbol=297 Mb/s.
[0124] When three channels are used, the middle channel will be the
same as a single-carrier with 27 Mbaud. Each side channel can have
a baud-rate of 7.5 Mb/s, and their center frequency is .+-.21.25
MHz. The side channels have the same pulse shape as the middle
channel with a roll-off-factor of 0.2. Because the minimum SNR for
2048QAM is around 36 dB, and the side channels are 29 dB lower, the
side channels have SNR of 7 dB, which makes it possible to transmit
4QAM (2 bits/symbol). The total achievable data-rate is 7.5
Mbaud.times.2 bits/symbol.times.2 side channels+297 Mb/s=327 Mb/s,
which is about 10% increase in data-rate compared with using only
the middle channel as a single-carrier.
[0125] The interference between the side channels and the middle
channel is limited, and the overall overlap is less than 0.4 MHz.
This makes the ICI negligible, and as a result, there might be no
need for ICI equalization without any performance loss.
[0126] In the case of 6 dB back-off power, the modulation order can
increase to 16QAM (4 bits/symbol) because of a 6 dB improvement in
channel conditions. The baud-rates do not need to be changed. Thus,
a data-rate of 7.5 Mbaud.times.4 bits/symbol.times.2 side
channels+297 Mb/s=357 Mb/s may be achieved. The maximum data-rate
for other back-off values is summarized in Table 4 below and
plotted in FIG. 16.
TABLE-US-00004 TABLE 4 Example data-rate for spectral mask of FIG.
4D Side Channel Back-off power Modulation Data-Rate 0 dB 4QAM 327
Mb/s 6 dB 16QAM 357 Mb/s 12 dB 64QAM 387 Mb/s 18 dB 256QAM 417 Mb/s
24 dB 1024QAM 447 Mb/s
[0127] Numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practised otherwise than as
specifically described herein.
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